736 Nguyen Tan Chung (Biochemical).cdr BIOCHEMICAL CHARACTERISTICS OF FLUVISOL THIONIC LINKED TO LAND USE TYPES IN SOUHTERN VIETNAM NGUYEN TAN CHUNG , SY DANH CHUNG and HOANG VAN THOI1* 2 2 1Department of Biotechnology, Nong Lam University, Ho Chi Minh City 70000, Viet Nam 2 Department of Centre for Fruit Tree Research, Southerm Institute of Fruit Tree Reseach, My Tho 203, Viet Nam 3 Department of Forest Ecology and Environment, Forest Science Institute of South Viet Nam, Ho Chi Minh City 70000, Viet Nam Received 10 December 2016/Accepted 25 May 2017 ABSTRACT Thionic Fluvisols soil in Southern Vietnam is like typical acid sulfate soil in the tropics and is severely polluted due to human activities. Salinity intrusion and industrial wastewater contamination are the main cause of environmental degradation in soil ecosystem. This research was aimed to determine a link between biochemical soil properties and land use types to provide suitable solutions for afforestation and soil restoration. Soil sampling was conducted in five different land use types at four soil layers (O, AB, Bj and Cp). The five land use types were sugarcane crop; Melaleuca plantation; 2-year Acacia plantation; 5-year Acacia plantation; and control (grass-covered land). The results showed that soil in those five land use types were very acidic (pH ≤ 4) having poor-nutrient condition with range of orthophosphate content of 378 - 640 mg/kg, N-NH of 586 - 999 mg/kg and N-NO of 830 - 1,112 mg/kg. 4 3 Concentration of toxic ions was very high with large variation among land use types and soil depths i.e. 1,799 – 12,403 2- 3+mg SO /kg; 22 - 1,645 mg exchangeable Fe/kg and 34 - 88 mg Al /kg soil. The lowest concentration of exchangeable 4 3+ 2-Fe and SO ions were found in sugarcane and Melaleuca plantations, respectively. Twenty-three sulfur-oxidizing 4 bacteria and two iron-oxidizing bacteria were identified. All these bacteria were initially identified as Thiobacillus sp. Sugarcane and Melaleuca plantations exhibited the most diverse Thiobacillus species which linked to reduction of 2-exchangeable Fe and SO concentrations in these two land use types. This study indicated that Thiobacillus sp. could 4 grow well in the Thionic Fluvisols. It is proposed that Melaleuca and sugarcane species could reduce iron and sulfur contents in Thionic Fluvisols in the tropics. Keywords: Acacia, acid sulfate soil, Melaleuca; sugarcane, Thionic Fluvisols, Thiobacillus sp. INTRODUCTION Thionic Fluvisols are acid sulfate soils 2- containing high SO content, having very low pH 4 (3 - 4) and containing high concentration of 3+ 3+ 2- exchangeable Al and Fe . High content of SO 4 accumulating in the soil mainly originates from an oxidation of potential minerals containing sulfur to form sulfuric acid (H SO ) (Sokolova & 2 4 Alekseeva 2008). While acid sulfate soil derives from sulfides oxidation containing minerals such as organic matter, sulfate, iron and aluminum, it could be formed in brackish water soil or other highly potential sulfate soil areas with a participation of microorganisms (Dao & Hoang 2005). Potential acid sulfate soil is a large source of heavy metal which causes pollution when being exposed to oxygen due to natural phenomena or artificial drainage, oxidizing pyrite to create H SO and thus, decrease soil pH 2 4 (Breemen 1993; Nguyen et al. 2004). Generally, iron and aluminum are often considered as toxic elements in the soils and greatly affect plant growth and development because excess of these elements can be toxic to plants (Nguyen et al. 2004; Dao & Hoang 2005). Concentrations of 2+ 3+ 3+ exchangeable Fe (Fe and Fe ) and Al exceeding 500 and 135 mg/kg, respectively, are toxic to rice (Le et al. 2000). When soil pH is less than 4.5, macro-nutrient ions (N, K, Ca, Mg, P) have relatively low concentration in acid soils. In contrast, Al and Fe are normally abundant in the soil with low pH (Brady & Well 2002). The more *Corresponding author: ntchung@hcmuaf.edu.vn BIOTROPIA 4 3 7 246 261 Vol. 2 No. , 201 : - DOI: 10.11598/btb.201 .2 . .7 4 3 736 246 acidic the soil is, the higher concentrations of these two ions are. According to Dao and Hoang (2005), 2+ 3+ 2- concentrations of Fe , Al and SO ions in acid 4 sulfate soil are much higher than concentrations that can be tolerated by plant. Sulfur and sulfate are two main compounds involved in the formation process of acidic soil. Total sulfur in two layers of Jarosite (Bj) and Pyrite (Cp) is an index to distinguish between an acid sulfate soil and other soil types. Major forms of sulfur in the 2- 2-acid soil are FeS, FeS , H S, SO , and SO . 2 2 3 4 2-Concentration of SO ions greatly varies among 4 2-different types of acidic soils. SO ions are toxic 4 to plants and are obstacles for land reclamation. In Southern Vietnam, total sulfur in the acidic soil ranges from 1 - 4% and can reach 5 - 6% when the acidic soil experiences a long-term flood (Dao & Hoang 2005). Metabolism and transformation of sulfur forms are complex with participation of sulfur-reducing bacteria in anaerobic conditions ( .Lamers et al. 2012; Pester et al. 2012) A total area of potential acid sulfate soil in Southern Vietnam was 2,415,727 ha (in 2005) (Ho et al. 2010). This area had active acidic soil area of 279,946 ha in 2005, which increased to 1,078,169 ha in 2011 (Pham 2011). Concentrations of et al. Fe and S ions increased while concentrations of K , Al , Total Organic Carbon (TOC), N and P + 3+ tended to decrease between year of 1975 and 2005 (Ho 2010). Kyuma (1976) and Le ( 2003) et al. showed that TOC content in the acidic soil located in the Mekong Delta was pretty high, ranging from 1.0 to 4.8% for soil having high concentration of sulfur ions and ranging from 3.2 to 5.2% for soil having low concentration of sulfur ions. Due to high content of TOC, the acidic soil also contains high concentration of Total Nitrogen (TN) (0.15 - 0.25%). However, concentration of Total Phosphorus (TP) (0.01 - 0.05%) and Total Potassium (TK) (0.03 - 0.09%) were very low in the acidic soil. 3+ 3+ 2-Contents of Al , Fe , SO and other 4 nutrients in acid sulfate soil greatly vary among soil layers and seasons (Le et al. 2000; Le 2003). Soil in the Mekong Delta had average organic layer depths (O) of 20 - 23 cm, transitional layer (AB) of 23 - 46 cm, Jarosite layer (Bj) or sulfur forms producing layer of 47 - 88 cm and Pyrite layer (Bp) greater than 89 cm (Duong et al. 2010). Total Organic Carbon (TOC) and Total Nitrogen (TN) in layer O of acidic soil are 5.47% and 0.26%, respectively (Ngo 2010). Other studies in Southern Vietnam conducted by Nguyen et al. (2011) showed that soil pH, TOC and TN in topsoil layer (O) were respectively 3.38 - 3.75; 2.24 - 4.04%; and 0.15 - 0.27%. Concentrations of 3+ 3+ 2-Al , Fe and SO ions not only varied due to 4 seasonal changes, but also depended on depths of soil layers (Do & Nguyen 1999; Tran et al. 2011). Tran et al. (2011) showed concentrations of exchangeable Fe ions were seasonally fluctuated in layer O, which could reach a peak of 11,780 mg/kg at the beginning of the rainy season, but dramatically decreased to 521 mg/kg at the end of 3+the rainy season while Al concentration greatly varied among soil layers, fluctuated from 0 to 749 mg/kg in soil layer A and 104 to 1,109 mg/kg soil in soil layer Cp. Other study measuring 2+ 3+ 2-concentrations of Fe , Al and SO in layer Bj 4 of different acid sulfate soils in Southern Vietnam 2- showed that SO concentration was less than 4 0.15%, 0.11 - 0.25%, and 0.27 - 0.74% for acidic soils having less, medium and high activity of 2+ 3+ sulfur forms; while Fe and Al concentrations ranged from 29 - 166 mg/kg and 73 - 111 mg/kg, respectively (Ngo 2002). Vegetation density and composition reflect soil biological property and fertility depending on soil location, type and depth (Dang 2009). At et al. soil depth of 0 - 22 cm, microbial density could reach 232 x 10 CFU/g, however, vegetation 5 density was much lower at soil depth higher than 55 cm (Araragi & Tangcham 1979). Hitomo & Naoto (2005) identified four species of Thiomonas genus that could reduce sulfur from paddy rice in Sado Island of Japan, including T. cuprina, T. intermedia, T. perometabolis T. thermosulfate. and These microorganisms could transform the concentration of Thiosulfate ions from 1.51 to 1.60 mM from initial Thiosulfate concentration of 1.61 mM used for the cultural media (Hitomo & Naoto 2005). Gram negative Thiobacillus isolated from paddy soil in India is highly capable of reducing sulfur forms (Rajagopal & Sridar 2007). Results of other study conducted in acid sulfate soil in Binh Chanh District of Ho Chi Minh City showed that a total number of sulfur- reducing microbes at soil depths of 0 - 20 and 20 - 40 cm ranged from 1.6 x 10 to 8.9 x 10 CFU/g 5 5 soil (Nguyen & Phan 1992). The study also identified sp. which mainly Thiobacillus contributed to oxidize sulfate ions and pointed out that the presence of sp. Thiobacillus 247 Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. BIOTROPIA Vol. 24 No. 3, 2017 248 therefore, threatens biodiversity of the ecosystem leading to the decrease in crop production. It is important to use every possible effort to rehabilitate and restore degraded acid sulfate soil quality based on soil biochemical characteristics. Biological approach is among efforts to restore the degraded acid sulfate soil. This study was aimed to determine biochemical characteristics of acid sulfate soil in relation to different vegetation types grown on the soil and to select appropriate crops to renovate degraded acid sulfate soil. MATERIALS AND METHODS Several steps were conducted to achieve the research objectives i.e. 1. measuring nutrients concentrations (C, N, P, K) and toxins (exchangeable Fe , Al , SO ) of acid sulfate soil 3+ 3+ 2- 4 in Southern Vietnam; 2. isolating and identifying microorganisms that are capable of reducing sulfur and iron; and 3. evaluating potential relationship between biochemical characteristics and land use types. Study Site This study was conducted on five different land use types located in Binh Chanh protected forest, Binh Chanh District of Ho Chi Minh City. This location represented Thionic Fluvisols soil (acid sulfate soil) having high concentration of 2-So . This area was highly polluted due to 4 anthropogenic activities and industrial wastewater. The study site was surrounded by a canal system to water several species of plants growing in the area. Land Use Types Five land use types were selected for conducting sample collections i.e. sugarcane plantation, 2-year plantation, 5-year Acacia Acacia plantation, 10-year plantation and Melaleuca grass-covered land (as control; the grass was dominated by sp. and sp.)Eleocharis Cyprus . Statistical Analysis This study was designed using Completely Randomized Design with six replications for each treatment. The treatments were the five land use depended on land use types and cultivation time of crops. In order to improve acidic status of sulfate soil, some researchers planted different species on sulfate soil (Le 1999; Wathinee 2015; et al. et al. Kogawara 2006). Watanabe (1997) et al. et al. conducted trials on adaptability of Melaleuca cajuputi Melastona marabathricum and on acid sulfate soil in Thailand and observed that these species grew well. was capable of Melaleuca cajuputi accumulating high aluminum concentration in its root system, while Melastona marabathricum accumulated Al in its foliage. Satoshi (2006) et al. showed that in a greenhouse condition having lack of oxygen and acidic pH of 5.8, M. cajuputi grew better than . Le (1999) E. camaldulensis et al. and Thai (2009) planted and Melaleuca leucadendra Melaleuca cajuputi on acid soil located in the Mekong Delta and observed that Melaleuca leucadendra Melaleuca cajuputi and could adapt to the Mekong Delta region with survival rate greater than 75%. Pham and Pham (2009) and Pham and Vu (2014) planted sp. and sp. on Eucalyptus Melaleuca seasonally inundated soil in the Mekong Delta and observed that ,Eucalyptus camaldulensis Eucalyptus tereticormis Melaleuca leucadendra Melaleuca viridiflora , , and could grow very well on the Melaleuca cajuputi acid sulfate soil. 3+ Melaleuca sp. can fix Al ions into its root system through symbiosis activities of soil microorganisms associated with the root which can release organic acids to neutralize Al ions 3+ (Tran 2012). This capability of sp. leads Melaleuca to the role of sp. in reclamation of Melaleuca sulfate-affected soil in the Mekong Delta. In addition to highly adaptable sp. in Melaleuca the Mekong delta (Nakabayashi 2001; et al. Duong 2005), there are many native plant et al. species grow on acid sulfate soil in the Mekong Delta (Dang 2009; Pham 2014). Nine et al. et al. species dominating sulfate soils are Melaleuca cajeputi, Polygonum tomentosum, Nypa fruticans, Eleocharis dulcis, Nymphaea pubescens, Sonneratia caseolaris, Melastoma , Cryptocoryne ciliata sp. and Annona glabra. There are several indigenous species adapting to seasonally flooded sulfate soil such as , Calophyllum inophyllum Thespesia populnea and (Dang 2009; Pham Gluta velutina et al. et al. 2014). Environmental quality of acid sulfate soil in Southern Vietnam is seriously degraded and 249 types i.e. sugarcane plantation, 2-year Acacia plantation, 5-year plantation, 10-year Acacia Melaleuca plantation and grass-covered land (as control; the grass was dominated by sp. Eleocharis and sp.). ANOVA of this experimental Cyprus design including the Tukey's test for determining the significant differences were computed using Minitab 17 software at < 0.05. Sigmaplot 12 p software was used to develop charts. Soil Samples Collection Six different soil sampling points were randomly selected in each land use type to collect soil samples and to determine soil profiles. Soil samples were collected from four soil layers i.e. O (organic layer), AB (transitional layer between A and Bj), Bj (Jarosite layer) and Cp (Pyrite layer) (Duong et al. 2010). Soil samples were air-dried for two weeks, then were sieved using 2-mm mesh size sieve. Soil samples were analyzed at the Soil Laboratory of Forest Science Institute of South Vietnam. Macronutrient elements and toxins were analyzed from soil samples (TCVN 1995). Different batches of soil samples for isolating and identifying microbes capable of transforming or oxidizing iron and sulfur were also collected from O and AB soil layers of the same soil sampling points in each land use type (Araragi & Tangcham 1979; Nguyen & Phan 1992). Figure 1 Study sites in the Mekong delta, Vietnam Table 1 Analytical methods used to measure soil nutrients and toxins Criteria Analytical method pH Soil: DDI water = 1 : 5 Total Nitrogen (TN) Kjeldahl method Total Phosphorus (TP) Dry-ashed and 6N HCl Total Potassium (TK) Dry-ashed and 6N HCl Total Organic Carbon (TOC) Walkley – Black NH4 + Soil: 2M KCl = 1 : 10 NO3 - Soil: 2M KCl = 1 : 10 Orthophosphate Mehlich 3 Al3+ Mehlich 3 SO4 2- Turbidimetric method Fe3+ Mehlich 3 Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. 250 BIOTROPIA Vol. 24 No. 3, 2017 for ingAnalytical methods applied measur + - macronutrients (C, N, P, K, Nh , NO , 4 3 Orthophosphate) and toxic ions (Exchangeable 3+ 3+ 2- Fe , Al , SO ) re presented in Table 1.4 a Isolation and Identification of Sulfur- oxidizing Microbes Isolation of sulfur-oxidizing microbes was carried out based on methods described by Rajagopal and Sridar (2007), using the Starkey and Thiosulfate culture media. These culture media had initial pH of 8.0. The total number of sulfur- reducing microbes was determined using method described by TCVN (2005) and computed using Equation 1 developed by TCVN (2005): where: A = numbers of bacteria cells in 1 g soil (colony forming units or CFU/g) N = total colony count n = number of disks having colony growth at i each dilution V = amount of sample solution in each disk f = dilution concentration in each diski In order to screen microbes capable of sulfur oxidation and/or transformation, the isolated microbes were continually cultured in Thiosulfate media supplemented by three different concentrations of Na S O i.e. 5, 10 and 15 g/L 2 2 3 culture media. Once screened, these microbes were tested for their biochemical characteristics such as Catalase, Voges-Proskauer Indole, Citrat, Gram, and (VP), nutritional types using methods described by Nguyen et al. (1978) and Nguyen (2005a; 2005b). The biochemical characteristics test were carried out prior to classifying and identifying these microbes. Total numbers of microbes where determined afterward. Isolation and Identification of Fe-oxidizing Microbes Iron-oxidizing microbes were isolated using culture media containing . This 2+1% of Fe ion method was described by . Suparna et al. (2014) Total number of Fe-reducing microbes was determined using methods described by TCVN (2005) and computed using Equation 1. The isolated microbes were continually cultured in 2+ culture media 3% and 6% of Fe containing ion. These media were used t iron-toleranto screen microbes capable of iron as well as microbes oxidation. lassification and dentification of the C i s microbes were based on creened carried out growth probability test in culture media having four levels of pH i.e. . Biochemical 3, 5, 7, 9 characteristics test was also carried out prior to classifying and identifying the microbes. The biochemical characteristics test included Catalase, G m ram, obilization ability of colonies and assimilation Total ability of organic carbon. numbers of microbes where determined afterward. RESULTS AND DISCUSSION Soil pH Soil pH is an important indicator as it relates directly to crops development, microbial activity and biochemical reactions occurring in soils. The study results showed that soil pH of the five land use types were less than 4.0 (Table 2). Soil pH differed among land use types within each soil layer of O, AB and Bj (Table 2). Although sugarcane plantation and grass-covered land (control) had higher pH than the 2-year Acacia plantation, 5-year Acacia plantation and Melaleuca plantation, the pH difference was not significant. Table 2 Soil pH of five land use types within each soil layer Soil layer Sugarcane plantation 2-year Acacia plantation 5-year Acacia plantation Melaleuca plantation Grass-covered land (control) O 3.8ab 3.3b 3.5ab 3.2b 3.9a AB 3.6ab 2.9c 3.4bc 3.5ab 4.0a Bj 3.5abc 3.0c 3.2bc 3.6ab 4.0a Cp 3.3ns 3.3ns 3.3ns 3.8ns 3.7ns Note: Numbers within a row (soil layer) followed by the same letter did not differ significantly at p < 0.05 ns = non significantly different 251 Concentrations of N and P among Land Use Types Total Nitrogen (TN) is an important criteria used to evaluate soil fertility depending on the content of soil organic matter. Nitrogen in soil is produced by microbial decomposition of soil organic matter and is a result from fixation of nitrogen gas by rhizosphere in plant root system. Nitrogen mainly accumulated in topsoil layer (O layer) and AB layer for all land use types (Fig. 1). TN concentration in the topsoil layer was higher compared to those in deeper soil layers within each land use types. TN concentration ranged from 2.3 g/kg (in sugarcane plantation) to 5.2 g/kg (Melaleuca plantation) (Table 3). TN concentration in topsoil layer (O layer) was slightly different from that in AB layer, however, it was significantly different from TN concentration in Bj and Cp layers, with exception for Melaleuca plantation and grass-covered land (control). -Concentration of NO ranged from 830 - 1,112 3 +mg/kg soil, while concentration of NH ranged 4 from 586 - 999 mg/kg soil (Table 3). - +Concentrations of TN, NO , NH decreased 3 4 with increasing soil depth (Fig. 1). The topsoil layer of Melaleuca plantation always contained the -highest concentrations of TN (5.2 g/kg), NO 3 +(1,112 mg/kg) and NH (999 mg/kg soil) (Table 4 3). Sugarcane and 2-year Acacia plantations -showed the lowest concentrations of NO and 3 + NH (Table 3).4 Concentrations of total phosphorus (TP) and orthophosphate in topsoil layer (O layer) were low for all land use types (Table 3; Fig. 2). Range of TP and orthophosphate concentrations in topsoil layer (O layer) were 785 - 958 mg/kg and 378 - 640 mg/kg, respectively (Table 3; Fig. 2). Low concentration of orthophosphate might be due to partial binding of orthophosphate with Al and Fe to form Al-P and Fe-P complex 3+ 3+ (Bertsch 1996; Brady & Well 2002). Under acidic condition (pH < 4.0) the increase of Al and Fe 3+ 3+ concentrations resulted to a reduction of orthophosphate ions through Al-P and Fe-P complexation (Brady & Well 2002). TP concentrations in topsoil layer (O layer) were not significantly different among the five land use types. The highest orthophosphate concentration was observed in the topsoil layer (O layer) of the 5-year Acacia plantation (Table 3; Fig. 2). Table 3 Variations of N and P concentrations among land use types Criteria Soil layer Sugarcane crop 2-year Acacia plantation 5-year Acacia plantation Melaleuca plantation Grass-covered land (control) p value TN (g/kg) O 2.28b 2.37b 2.50b 5.18a 2.36b 0.002 AB 1.68ab 1.96a 2.14a 2.00a 0.98b 0.012 Bj 0.86b 1.12ab 1.19ab 1.84a 0.72b 0.003 Cp 0.82ns 1.98ns 0.96ns 1.12ns 0.50ns 0.091 NH4 + (mg/kg) O 611.7bc 585.7c 861.8ab 998.7a 775.2bc 0.001 AB 448.5b 441.2b 736.5a 467.3b 386.1b 0.003 Bj 133.8b 171.1b 504.6a 526.5a 266.6b < 0.001 Cp 106.6ns 136.9ns 219.0ns 152.0ns 227.8ns 0.078 NO3 - (mg/kg) O 830.0bc 625.1c 1070.1ab 1111.8a 991.4ab < 0.001 AB 656.1abc 586.1bc 898.4a 850.7ab 436.6c 0.001 Bj 263.4c 268.0c 599.9ab 706.5a 447.3b < 0.001 Cp 218.1b 218.1b 294.4ab 395.1a 216.2b 0.012 TP (mg/kg) O 784.6ns 800.6ns 957.9ns 871.7ns 810.9ns 0.118 AB 578.9bc 737.7abc 758.0ab 535.4c 939.8a < 0.001 Bj 553.2bc 687.2b 671.3b 457.9c 905.1a < 0.001 Cp 603.9b 628.6b 591.1b 519.3b 855.7a 0.004 PO4 3- (mg/kg) O 493.7ab 462.4b 640.0a 395.5b 377.7b 0.001 AB 307.2b 417.3ab 461.0a 297.3b 303.0b 0.002 Bj 280.5ab 362.2a 349.8a 274.3ab 219.5b 0.013 Cp 337.3a 289.0ab 315.6a 249.3ab 156.5b 0.012 Note: Numbers within a row (soil layer) followed by the same letter did not differ significantly at p < 0.05 ns = non significantly different Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. 252 BIOTROPIA Vol. 24 No. 3, 2017 Variation of TOC and TK among Land Use Types TOC concentration within each land use type decreased with increasing soil depth (Table 4). In each of land use types, TOC concentration in the topsoil layer was higher than those in deeper layers. Within topsoil layer, the lowest TOC concentration (2.98%) was observed in sugarcane plantation, whereas the highest TOC concentration (5.29%) was observed in Melaleuca plantation. Differences of TOC concentration were significantly different (Table 4). TOC concentrations in all land use types observed in this study were slightly lower than the average TOC concentration observed in previous study conducted in the Mekong Delta i.e. 5.5% (Ngo 2010). The lowest TK concentration was observed in Melaleuca plantation ranging from 0.494 to 0.564%. Other land use types showed similar TK concentrations, ranging from 0.641 to 0.769%, which was higher than TK concentration in Melaleuca plantation. Differences in TK concentration, however, were not significant. TK concentrations showed in this study were within the results of previous study conducted in the Mekong Delta (Ngo 2002). Although five land use types did not show a significant difference of TK concentrations in their topsoil layer, they were significantly different among vegetation types within taking into account of each other lower layers (AB, Bj, Cp) (Table 4). Concentrations of TN, TP, TOC and TK were significantly lower in topsoil layer (O layer) than Figure 2 Concentrations of total and bioavailable N and P in five land use types 253 those in deeper soil layers (AB, Bj, Cp) within each land use type (Table 3 & 4). Bioavailability of Fe, Al and S Elements in Soil Concentration of exchangeable Fe ions was particularly very low topsoil layer of sugarcane plantation (20 mg/kg soil), 2-year Acacia plantation (48 mg/kg soil) and 5-year Acacia plantation (37 mg/kg soil). Concentration of exchangeable Fe ions was highly accumulated in Cp soil layer of all land use types ranging from 684 mg/kg (in sugarcane plantation) to 2,645 mg/kg ( in g rass-covered land) . The h ighest concentration of exchangeable Fe ions was observed in the AB, Bj and Cp soil layers of Melaleuca plantation.The lowest concentrations of ions were observed in the grass-3+ 2- Al and SO4 covered land (control) and Melaleuca plantation (Table 5). Concentration of ion in all soil layers of 2-SO4 Melaleuca plantation was not significantly different, ranging from 3 to 4 g/kg soil. The lowest concentration of was observed in 2-SO ion4 the soil layers of AB, Bj and Cp Melaleuca 2-plantation SO 4. The highest concentration of ion 2-year Acacia plantation was observed in the and 5-year Acacia plantation for all soil layers, ranging from .2 .4 / . The concentration 9 to 12 g kg differences within the same soil layer were not significant. 3+ Concentration of Al ion was similar within the same soil layer among five land use types. Table 4 Variations of total organic carbon (TOC) and total potassium (TK) among land use types Soil layer Sugarcane crop 2-year Acacia plantation 5-year Acacia plantation Melaleuca plantation Grass-covered land (control) p value TOC (%) O 2.98b 3.08b 3.44b 5.29a 3.21b < 0.001 AB 2.38bc 2.96ab 3.66a 3.57ab 1.39c < 0.001 Bj 1.29b 1.88b 1.72b 3.08a 1.71b 0.001 Cp 1.83 ns 2.50 ns 2.06 ns 1.89 ns 2.22 ns 0.903 TK (%) O 0.662a 0.650a 0.641a 0.494b 0.660a 0.006 AB 0.691a 0.659a 0.652a 0.511b 0.751a < 0.001 Bj 0.769a 0.702a 0.696a 0.514b 0.696a < 0.001 Cp 0.694ab 0.675b 0.759a 0.564c 0.654b < 0.000 Note: Numbers within a row (soil layer) followed by the same letter did not differ significantly at p < 0.05 ns = non significantly different 3+ 3+ 2-Table 5 Variations of Al , Fe and SO concentrations among land use types4 Criteria Soil layer Sugarcane crop 2-year Acacia plantation 5-year Acacia plantation Melaleuca plantation Grass-covered land (control) p value Al3+ (mg/kg) O 37.9ns 49.7ns 38.8ns 40.7ns 34.3ns 0.101 AB 49.9ns 56.0ns 61.8ns 59.0ns 43.8ns 0.105 Bj 63.4ab 61.2ab 74.0a 52.8bc 37.5c 0.001 Cp 84.9a 63.2ab 68.5ab 70.8a 46.2b 0.003 Exchangeable Fe (mg/kg) O 22.4c 44.6c 38.7c 223.6b 455.4a < 0.001 AB 16.0c 51.0c 35.6c 1462.6a 958.0b < 0.001 Bj 62.1d 1052.8b 489.4c 1269.3ab 1365.4a < 0.001 Cp 684.6b 1721.0a 1692.4a 1612.5a 2144.9a < 0.001 SO4 2- (g/kg) O 1.80c 10.04a 7.65b 2.38c 3.86c < 0.001 AB 3.24b 9.57a 9.00a 3.33b 3.45b < 0.001 Bj 4.50b 12.62a 4.99b 2.70b 3.37b < 0.001 Cp 10.92a 10.93a 8.11b 3.94c 8.66ab < 0.001 Note: Numbers within a row (soil layer) followed by the same letter did not differ significantly at p < 0.05 ns = non significantly different Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. 254 BIOTROPIA Vol. 24 No. 3, 2017 3+ Concentration of Al ion increased with 3+increasing soil depth. Range of Al ion concentrations was 38 - 85 mg/kg for all soil layers among the five land use types. Concentrations of 3+ Al ion were significantly different between O soil layer and Cj soil layer within each land use type (Table 5; Fig. 3). Bioavailability of exchangeable Fe ions and Al ion fluctuated with soil pH differences. 3+ Grass-covered land having higher soil pH exhibited lower concentration of Al ion and 3+ higher concentration of exchangeable Fe ions (Dao & Hoang 2005). 3+ 2-Figure 3 Concentrations of soil exchangeable Fe ions, Al ion and SO ion among land use types4 255 Isolation of Sulfur- and Iron-oxidizing Microbes Soil samples taken from O and AB soil layers were used to isolate microbes capable of reducing sulfur and iron content in the soil. Total numbers of microbes where determined afterward. Total number of sulfur-oxidizing microbes varied from 0.75 x 10 to 172 x 10 CFU/g soil 5 5 (Table 6). Total numbers of sulfur-oxidizing microbes isolated from the O soil layer were not significantly different among the five land use types. Total numbers of sulfur-oxidizing microbes isolated from the AB soil layer were significantly different among the five land use types. The highest number of sulfur-oxidizing microbes was recorded in soil samples taken from the AB soil layer of the plantation (172 x 10 5Melaleuca CFU/g), followed by the -year plantation Acacia (134 x 10 CFU/g). These results indicated that 5 species richness and species density of sulfur- oxidizing microbes were quite high among the five land use types. Total number of iron-oxidizing microbes (range of 1.0 x 10 - 4.1 x 10 CFU/g for all land 4 4 use types) was much lower than those of sulfur- oxidizing microbes (Table 6). Italicized numbers within brackets in Table 6 indicated the numbers of sulfur- or iron-oxidizing microbial species isolated from soil samples. These microbes survived in the sulfur- or iron-enriched culture media. There were 23 different microbial species capable of growing well and metabolizing sulfur in sulfur-enriched culture media. Most of these microbial species were isolated from O layer. The highest numbers of sulfur-oxidizing microbes were found in the O layer of sugarcane plantation (8 species), followed by those found in the O layer of plantation (6 species). Other species Melaleuca were found in the O layer of 2-year Acacia plantation (3 species), in the O layer of 5-year Acacia plantation (3 species), in the AB layer of sugarcane plantation (1 species), in the AB layer of 5-year plantation (1 species) and in the Acacia AB layer of grass-covered land/control (1 species). In the Starky's sulfur-enriched culture media, colonies of these microbes had yellow, orange or dark pink color with smooth surface, which are similar to the results of studies conducted by and ) and Hitomo Naoto (2005 Rajagopal and Sridar (2007). Two microbia l spec ies capable of metabolizing iron in iron-enriched culture media were found in the AB layer of sugarcane plantation (1 species) and in the AB layer of 5- year plantation (1 species). Diameter of Acacia these iron-oxidizing microbes colonies ranged from 2 to 4 mm. The colonies grew closely to the surface of the culture media and had golden- white color. Identification of Sulfur-oxidizing Microbial Genera Ten of the 23 sulfur-oxidizing microbial species performed high capacity of sulfur oxidation and thus, reduced pH of the Starkey culture media and Thiosulfate from 8.0 to 5.0 (Table 7). pH 8.0 is the initial pH of the Starkey and Thiosulfate media. All of these ten microbial species was able to transform more than 50% of Na S O content in 2 2 3 culture media supplemented with 5 mg Na S O /L (Table 7).2 2 3 Table 6 Total numbers of sulfur- and iron-oxidizing microbes isolated from soil samples Soil layer Sugarcane plantation 2-year Acacia plantation 5-year Acacia plantation Melaleuca plantation Grass-covered land (control) Total sulfur-oxidizing microbes (CFU/g soil) O 11.8 x 105 (8) 16.8 x 105 (3) 3.9 x 105 (3) 0.75 x 105 (6) 2.1 x 105 (0) AB 31.3 x 105 (1) 134 x 105 (0) 12.5 x 105 (1) 172 x 105 (0) 11.4 x 105 (1) Total iron-oxidizing microbes (CFU/g soil) O 1.9 x 104 1.4 x 104 2.4 x 104 1.4 x 104 1.3 x 104 AB 1.7 x 104 (1) 1.5 x 104 4.1 x 104 (1) 1.0 x 104 1.1 x 104 Note: Italic numbers in the brackets are the twenty-three different species of sulfur-reducing microbes and two different species of iron- reducing microbes isolated from soil samples Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. BIOTROPIA Vol. 24 No. 3, 2017 256 G en er a is o la te d fr o m su lf ur – en ri ch ed cu lt ur e m ed ia p H in c ul tu re m ed ia af te r m ic ro b es is o la ti o n (o ri gi n al p H = 8 ) R ea ct io n s N ut ri ti o n al ty p e C o n ce n tr at io n o f N a 2 S 2 O 3 su p p le m en te d in to th e T h io su lf at e cu lt ur e m ed ia 5 g/ L 10 g /L 15 g /L St ar ke y T h io su lf at e C at al as e V P In do l C it ra t G ra m G C S- T r (% ) G C S- T r (% ) G C S- T r (% ) Su g- A -G en 1 5 8 p o s n eg n eg p o s n eg au to tr o p h ic + + 61 .1 - 0 - 0 Su g- A -G en 2 5 5 p o s n eg n eg p o s n eg h et er o tr o p h ic + + 52 .9 - 0 - 0 Su g- A -G en 3 4. 5 5 p o s n eg n eg p o s n eg h et er o tr o p h ic + + 53 .3 - 0 - 0 Su g- A -G en 4 4. 5 8 p o s n eg n eg p o s n eg au to tr o p h ic + + + 98 .0 + + + 93 .5 - 0 Su g- A -G en 5 5 8 p o s n eg n eg p o s n eg h et er o tr o p h ic + + 64 .5 - 0 - 0 Su g- A -G en 6 4. 5 5 p o s n eg n eg p o s n eg au to tr o p h ic + + 70 .6 - 0 - 0 M el -A -G en 7 5 5 p o s n eg n eg p o s n eg h et er o tr o p h ic + + + 84 .8 - 0 - 0 M el -A -G en 8 5 6 p o s n eg n eg p o s n eg h et er o tr o p h ic + + 73 .7 - 0 - 0 M el -A -G en 9 4. 5 8 p o s n eg n eg p o s n eg h et er o tr o p h ic + + + 97 .1 + 33 .3 - 0 G ra -A B -G en 10 4. 5 8 p o s n eg n eg p o s n eg au to tr o p h ic + + + 96 .1 + + + 95 .9 - 0 T ab le 7 R es ul ts o f b io ch em ic al a n al ys es o f th e te n s ul fu r- ox id iz in g m ic ro b es N o te : Su g- A -G en 1 = G en us 1 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; Su g- A -G en 2 = G en us 2 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; Su g- A -G en 3 = G en us 3 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; Su g- A -G en 4 = G en us 4 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; Su g- A -G en 5 = G en us 5 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; Su g- A -G en 6 = G en us 6 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; M el -A -G en 7 = G en us 7 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f M el al eu ca p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; M el -A -G en 8 = G en us 8 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f M el al eu ca p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; M el -A -G en 9 = G en us 9 o f T hi ob ac ill us s p. is o la te d fr o m t h e A la ye r o f M el al eu ca p la n ta ti o n h av in g h ig h ly t ra n sf o rm ed s ul fu r; G ra -A B -G en 10 = G en us 1 0 o f T hi ob ac ill us s p. is o la te d th e A B la ye r o f G ra ss -c ov er ed la n d/ co n tr o l h av in g h ig h ly t ra n sf o rm ed s ul fu r; p o s = p o si ti ve r ea ct io n ; n eg = n eg at iv e re ac ti o n ; G C = g ro w th c ap ac it y; S -T r ( % ) = p er ce n ta ge o f tr an sf o rm ed s ul fu r; - = n o g ro w th ; + = n o rm al g ro w th ; + + = g o o d gr ow th ; + + + = ve ry g o o d gr ow th 257 Three species were able to transform more than 96% of Na S O in Thiosulfate culture media 2 2 3 supplemented with 5 mg Na S O /L i.e. Sug-A-2 2 3 Gen4 Mel-A-Gen9 Gra-AB-Gen10, , and (Table 7). These three species were able to decrease pH of the Starkey media from 8.0 to 4.5, however, these species were not able to decrease pH of Thiosulfate media (Table 7). These three species were the only species survived and grew well in Thiosulfate culture media supplemented with 10 mg Na S O /L, however, they did not survive in 2 2 3 Thiosulfate culture media supplemented with 15 mg Na S O /L (Table 7). These three microbial 2 2 3 species were found in the O and AB layers of sugarcane plantation, plantation and Melaleuca grass-covered land/control, and thus, would be able to oxidize sulfur in the soil of these three land use types (Fig. 3). Results of biochemical testing for the ten sulfur-oxidizing microbial species are presented in Table 7. All of these species had negative reaction toward Gram, VP and Indol tests, however, they had positive reaction toward Catalase and Citrat tests. Nutritional test showed that the ten sulfur-oxidizing microbial species consisted of three autotrophic species from sugarcane plantation, three heterotrophic species from sugarcane plantation, one autotrophic species from grass-covered land/control and three heterotrophic species from Melaleuca plantation (Table 7). Autotrophic microbes are microbes that can synthesize inorganic carbon sources for their growth without the presence of organic carbon compounds. Heterotrophic microbes are microbes that can only grow well in media containing high organic carbon source and cannot grow without organic carbon compounds (Brady & Well 2002). Identification of these ten sulfur-oxidizing microbial species was conducted based on the results of biochemical characteristics analyses, results of studies conducted by Kantachote and Innuwat (2004) and handbook of bacterial identification written by Kelly and Harrison (1989). The identification indicated that the ten sulfur-oxidizing microbial species belong to genus .Thiobacillus Identification of Iron-oxidizing Microbial Genera Results of biochemical testing for the two iron-oxidizing microbial species are presented in Table 8. Two iron-oxidizing microbial species were isolated from the five land use types. These two microbial species showed negative reaction toward Gram test, however, showed positive reaction toward Catalase test. These two iron-oxidizing microbial species were initially isolated in culture media containing 1% Fe . The two iron-oxidizing microbial species 2+ grew well in iron-enriched culture media having 3 and 6% Fe concentrations with culture media 2+ pH ≤ 5.0. These two microbial species showed negative reaction toward glucose, sucrose and maltose tests, indicating that these two microbial species were autotrophic. Identification based on biochemical characteristics analyses, results of studies conducted by Kantachote and Innuwat (2004) and handbook of bacterial identification written by Kelly and Harrison (1989) indicated that these two iron-oxidizing microbial species belong to genus .Thiobacillus Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. BIOTROPIA Vol. 24 No. 3, 2017 258 T ab le 8 R es ul ts o f b io ch em ic al a n al ys es o f tw o h ig h ly ir o n -o xi di zi n g p er fo rm ed m ic ro b es G en er a is o la te d f ro m ir o n -e n ri ch ed c ul tu re m ed ia R ea ct io n s A b ili ty t o c o lo n y p ro du ct io n A b ili ty t o co lo n y m o b ili za ti o n G ro w th w it h ir o n su p p le m en t h av in g co n ce n tr at io n o f G ro w th w it h s up p le m en t o f o rg an ic ca rb o n s o ur ce s G ro w th in c ul tu re m ed ia h av in g di ff er en t p H C at al as e G ra m 3% 6% G lu co se Su cr o se M al to se 3 5 7 9 Su g- A B -G en 1 p o s n eg - + + + - - - + + - - A ca -A B -G en 2 p o s n eg - + + + - - - + + - - N o te : Su g- A -G en 1 = G en us 1 o f T hi ob ac ill us s p. is o la te d fr o m th e A B la ye r o f S ug ar ca n e p la n ta ti o n h av in g h ig h ly tr an sf o rm ed ir o n ; A ca -A B -G en 2 = G en us 2 o f T hi ob ac ill us s p. i so la te d fr o m th e A B la ye r o f 5- ye ar A ca cia p la n ta ti o n h ig h ly tr an sf o rm ed ir o n ; p o s = p o si ti ve re ac ti o n ; n eg = n eg at iv e re ac ti o n ; + = n o rm al g ro w th ; - = n o g ro w th 259 CONCLUSIONS The five land use types had very acidic soil with soil pH of ≤ 4.0, low concentrations of phosphorus and potassium. Total organic carbon (TOC) in O layers in all five land use types was higher than that in deeper soil layers. Melaleuca plantation had the highest concentration of TOC in the O layer. Concentrations of exchangeable 3+ 3+ 2- Fe , Al , SO ions varied among the five land use 4 2-types. The lowest concentration of SO was 4 observed in the grass-covered land (control) and Melaleuca plantation. Ten sulfur-oxidizing microbial species were isolated from sugarcane plantation, Melaleuca plantation and grass-covered land/control and were identified as belong to genus . Thiobacillus Two iron-oxidizing microbial species were isolated from sugarcane plantation and 5-year Acacia plantation and were also identified as belong to genus .Thiobacillus It is proposed that there is a strong relationship between sp. and sugarcane plantation Thiobacillus which indicates that sp. isolated from Thiobacillus sugarcane plantation can oxidize sulfur and iron in the polluted acid sulfate soil. ACKNOWLEDGEMENTS The authors thank Ho Chi Minh People Committee's Department of Forestry and Forest Science Institute of South Vietnam for providing financial support for this study. REFERENCES Araragi M, Tangcham B. 1979. Effect of rice straw on the composition of volatile sod gas and microflora in the tropical paddy field. J Plant Nutr Soil Sci 25:283-95. Bertsch B. 1996. Aluminum: methods of soil analysis. Part 3- chemical methods. Madison (US): Soil Sci Soc of America Inc. p. 517-50. Brady NC, Well RR. 2002. The nature and properties of soils. New Jersey (US): Prentice Hall Inc. Breemen V. 1993. Environmental aspects of acid sulfate soils. In: Dent DL, van Mensvoorst MEF, editors. Proceeding of symposium on acid sulfate soils in Ho Chi Minh City, March 1992. Wageningen (NL): International Institute for Land Reclamation and Improvement. Publ 53. p. 391-402. Dang VS, Ngo TTT, Pham VN. 2009. Diversity of wetland ecosystems in Binh Chanh District, Ho Chi Minh City. Vietnam Wetland Association. Available from: https://vnwa.wordpress.com/2011/ 08/06/da- d % E 1 % B A % A 1 n g - t h % E 1 % B B % B 1 c - v%E1%BA%ADt-tren-h%E1%BB%87-sinh-thai- d % E 1 % B A % A 5 t - n g % E 1 % B A % A D p - n%C6%B0%E1%BB%9Bc-huy%E1%BB%87n- b i n h - c h a n h - t h a n h - p h % E 1 % B B % 9 1 - h%E1%BB%93-chi-minh/ Dao XH, Hoang TD. 2005. Utilization and reclamation of brackish water and acidic soils. Hanoi (VN): Vietnam Publishing House of Agriculture. Do DS, Nguyen NB. 1999. Evaluation of potential use of forest land in the Mekong Delta. Hanoi (VN): Vietnam Publishing House of Agriculture. p. 71-6. Duong VN, Le DK, Ito J, Ngo TB. 2005. Melaleuca plantation in acid soil in the Mekong Delta and its application and role in industry. SAPROF team for Japan Bank International Cooperation (JBIC). p 54- 60. Duong TN, Ngo NH, Le VP, Vo QM, Le QT. 2010. Some characteristics of acidic soil profile in the Mekong Delta. Vietnamese J Sci 14:243-9. Hitomo O, Naoto O. 2005. Isolation and identification of sulfur-oxidizing bacteria from the buried layer containing reduced sulfur compounds of a paddy field on Sado Island. Bulletin of the Faculty of Agriculture 58:55-61. Niigata (JP): Niigata University. Ho QD, Nguyen VD, Tran XC, Le TMH. 2010. Status of acid sulfate and mangrove soils in Mekong Delta after 30 years of utilization. Vietnamese J AgriSciTechnol 1(22):56-8. Kantachote D, Innuwat W. 2004. Isolation of sp Thiobacillus . for use in treatment of rubber sheet wastewater. Songklanakarin J Sci Technol 26:649-57. Kelly DP, Harrison AP. 1989. Genus of sp. In: Thiobacillus Staley GT, Penning N, Holt JG, editors. Bergey's manual of systematic bacteriology. Baltimore (US): Williams & Wilkinson Co. p. 1842-71. Kogawara S, Yamanoshita T, Norisada M, Masumori M, Kojima K. 2006. Photosynthesis and photo- assimilate transport during root hypoxia in M. cajuputi E. , a flood-tolerant species and in camaldulensis, a moderate flood-tolerant species. Tree Physiol 26:1413-23. Kyuma K. 1976. Paddy soils in the Mekong Delta of Vietnam. Discuss Pap 85. Center for Southeast Asian Studies. Kyoto (JP): Kyoto University. Lamers LPM, van Diggelen JMH, Op den Camp HJ, Visser EJ, Lucassen EC, Vile MA, ... Roelofs JG. 2012. Microbial Transformations of Nitrogen, Sulfur, and Iron Dictate Vegetation Composition in Wetlands: A Review. 3:156. doi:10.3389/ Front Microbiol fmicb.2012.00156. Biochemical characteristics of thionic fluvisol linked to land use types - Chung et al. BIOTROPIA Vol. 24 No. 3, 2017 260 Le HB. 2003. Based acid sulfate soil problems. Hanoi (VN): Vietnam National University's Publishing House. Le DK, Hoang C, Nguyen TN, Pinyopusa R. 1999. Genetic selection of spin the Mekong Delta. Melaleuca Proceedings of workshop on forest plantation techniques on acid sulfate soil in Mekong Delta. For Sci Inst of South Vietnam. p. 243-53. Le HB, Le TNH, Phan KP, Doan TY, Nguyen L. 2000. Environmental toxicology. Ho Chi Minh City (VN): HCMC National University's Publishing House. Nakabayashi K, Nguyen NT, Thomson J, Fujita K. 2001. Effect of embankment on growth and mineral uptake of under acid sulfate soil Melaleuca cajuputi condition. Soil Sci Plant Nutr 74(4):711-25. Ngo DQ. 2002. Restoration and development of wetland and forests in Vietnam. Hanoi (VN): Melaleuca Vietnam Publishing House of Agriculture. 88 p. Available from: http://lib.dntu.edu.vn:8080/ dspace/bitstream/DNTU_123456789/1591/1/kh oi%20phuc%20va%20phat%20trien%20rung%20 ngap%20man%20rung%20tram%20o%20viet%20 nam%201.pdf Ngo NH. 2010. Relationship between organic carbon and nitrogen in Mekong Delta's paddy soils. Vietnamese J Soil Sci 34:46-50. Nguyen NH. 2005a. Practicing of microorganism research. Hanoi (VN): Vietnam Publishing House of Labor. Nguyen TD. 2005b. Basis of biological microorganisms. Hanoi (VN): Vietnam Publishing House of Education. Nguyen KQ, Lam NP, Le XT, Phan TN, Ngo NH. 2011. Effects of NPK fertilizer on sugarcane crops growing in acid soils in Hau Giang Province. Vietnamese J Sci 19b 145-57. : Nguyen TTP, Phan L. 1992. Microbiological characteristics of acid sulfate soils: a case study in the Ho Chi Minh City environment. In: Dent DL, van Mensvoorst MEF, editors. Proceeding of symposium on acid sulfate soils in Ho Chi Minh City. Wageningen (NL): International Institute for Land Reclamation and Improvement, Publ 53. p. 237-40. Nguyen LD, Nguyen TH, Le DL, Pham TTC, Doan XM, Pham VT. 1978. Research methodologies of microorganism Hanoi (VN): Hanoi Publishing . House of Science and Technique. Nguyen HM, Tran TK, Astrom M, Huynh CT. 2004. Pollution of some toxic metals in canal water leached out from acid sulfate soils in the Mekong Delta. In: Hiroyasu S, editors. Proceeding of the Second International Symposium on Southeast Asian Water Environment on December 2004. Ha Noi (Vietnam). Southeast Asian Water Management 2. p. 99-106. Pester M, Knorr K-H, Friedrich MW, Wagner M, Loy A. 2012. Sulfate-Reducing Microorganisms in Wetlands – Fameless Actors in Carbon Cycling and Climate Change. Frontiers in Microbiology 3:72. DOI:10.3389/fmicb.2012.00072. Pham VN, Nguyen TN, Dang VS. 2014. Composition and distribution of wetland plant species in Duc Hue District, Long An Province. Vietnamese J Sci 58:50- 65. Pham TD, Pham NC. 2009. Techniques of Melaleuca planation on acid sulfate based plantation in Long An province. Vietnamese Academy of Forest Sciences. Available from: http://vafs.gov.vn/vn/ 2009/03/mot-so-nghien-cuu-ve-ky-thuat-trong- rung-tram-tren-dat-chua-phen-o-huyen-thanh- hoa-long-an/ Pham TV, Vo QM, Le QT, Tran TT. 2011. Soils of the Mekong Delta c lass if ied by WRB-FAO classification system. Vietnamese J Sci 18b: 10-7. Pham TD, Vu DH. 2014. Biomass of plantation in Melaleuca Long An. Vietnamese J For Sci 2 3318-23.: Rajagopal V, Sridar R. 2007. Isolation and characterization of sulfur oxidizing bacteria. J Cult Collect 5:73-7. Satoshi K, Takashi Y, Mariko N, Masaya M, Katsumi K. 2006. Photosynthesis and photoassimilate transport during root hypoxia in , a flood-Melaleuca cajuputi tolerant species, and in , a moderately E. camaldulensis flood-tolerant species. Tree Physiol 26:1453-67. Sokolova TA, Alekseeva SA. 2008. Adsorption of Sulfate Ions by Soils (A Review). EJSS 41(2):140–148 Suparna D, Ankita P, Arti M. 2014. Isolation of a novel iron oxidizing bacteria from the iron scraps of a steel industry. Adv Appl Sci Res 5(1):277-81. Thai TL. 2009. The research plan for improving productivity and quality of the indigenous Melaleuca species in way of hybridization with exotic species in the sulphate acid lands of seasonally fooded areas in the Mekong Delta. Vietnamese J Agric Rural Dev 3:153-61. Tran QB. 2012. Possibility of forest on soil and Melaleuca water improvement in flooded areas of Mekong Delta. Vietnamese J Agric Rural Dev 1:95-100. Tran NH, Dang DM, Nguyen MH. 2011. Chemical characteristics of peat soil in the surroundings area and in the core zone in U Minh Ha National Reserve of Ca Mau province. Vietnamese J Sci18b:83-91. Vietnam Standard and Quality Insitute. 1995. TCVN 5297:1995. Soil quality and soil sampling methods. Hanoi (VN): Vietnam Standard and Quality Insitute, Directorate for Standards, Metrology and Quality. Vietnam Standard and Quality Insitute. 2005. TCVN 4884:2005. Microorganisms in livestock food, methods in determination of total microbial number on cultural media, and technique on counting microbial colony. Hanoi (VN): Vietnam Standard and Quality Insitute, Directorate for Standards, Metrology and Quality. 261 Watanabe T, Osaki M, Tadano T. 1997. Response of plants adapted in low pH soils to aluminum. Plant Nutr for Sustainable Food Prod Environ 78:459-60. Wathinee S, Nuntawoot S, Waravooth S. 2015. Growth and aboveground biomass of Plantation in M. cajuputi Trat Province-Thailand. Thai J For 34:57-64. 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