313 Turkis.vp Acta Bot. Croat. 69 (2), 275–290, 2010 CODEN: ABCRA 25 ISSN 0365–0588 Foliar resorption and chlorophyll content in leaves of Cistus creticus L. (Cistaceae) along an elevational gradient in Turkey SEVDA TURKIS, TUGBA OZBUCAK* Department of Biology, Faculty of Arts and Sciences, Ordu University, 52750 Ordu, Turkey Foliar nitrogen and phosphorus dynamics, leaf resorption efficiency, proficiency, chang- ing of chlorophyll a/b proportions in leaves of Cistus creticus L. (Cistaceae) along an elevational gradient (sea level-30 m, middle-670 m, high-880 m) were investigated. Sta- tistically significant differences were found in foliar nitrogen and phosphosrus content in terms of growth periods, while no significant differences were found according to eleva- tions. Nitrogen and phosphorus resorption efficiency and proficiency values were high as compared to the other evergreen species. Cistus creticus effectively used nitrogen and phosphorus. No statistically significant differences were found among elevations in terms of specific leaf area. However, statistically significant differences were found in terms of growth periods. There were significant differences in chlorophyll a/b proportion accord- ing to both growth periods and elevations. Besides, the chlorophyll a/b proportion in- creased along senescence period. Key Words: Leaf, nitrogen, phosphorus, resorption, chlorophyll, Cistus creticus, eleva- tion Introduction The Cistaceae family includes 8 genera with 175 species distributed in the temperate zone of the northern hemisphere, especially in Mediterranean climates. Five Cistus L. spe- cies are found in Turkey (DAVIS 1965). Cystus creticus is an evergreen shrub and distributed all along the coastal belt of the Turkish Mediterranean phytogeographical region, as well as in some enclaves along the Black Sea coast. These species adorn habitats with their purple flowers from late March till June, extending from sea level up to an altitude of 1000 m (DAVIS 1965, BASLAR et al. 2001). The leaves of these species exude a fragrant, sticky gum called ladanum used in perfumery and folk medicine (BAYTOP 1994). C. creticus is one of the pio- neer plants of secondary succession and it succeeds pine after fire. Therefore, sites where ladanum communities are distributed are evidence of the existence of pine forest communi- ties before a fire in the environs (TURKMEN and DUZENLI 2005). ACTA BOT. CROAT. 69 (2), 2010 275 * Corresponding author, e-mail: tsiozbucak@hotmail.com Concentrations of nutrients in mature leaves can indicate the nutritional status of a plant. For this reason, foliar analysis is a classic tool for diagnosing nutrient efficiencies and has long been applied to forests (MAYOR and RODA 1992). But leaf nutrient concentra- tions vary with species, age of the tissue, climate, soil and other factors (SCHLESINGER 1997, TEKLAY 2004). Forest trees, shrubs and herbs retranslocate sizeable proportions of the nu- trient content of leaves before leaf abscission (MAYOR and RODA 1992). One of the most im- portant methods to measure of nutrient use efficiency in plants is to determine foliar resorp- tion, the process of nutrient translocation from the leaves into storage tissues during senescence (KILLINGBECK 1988, LUKEN 1988). In particular, seasonal changes in leaf nutri- ents occur in response to resorption or retranslocation before senescence (CHAPIN 1980). The rate of nutrient resorption from senescing leaves may also vary with the availability of nutrients for resorption. The duration of retention of leaf nutrients in a plant is largely a function of leaf resorption (ESCUDERO et al. 1992). Especially, N and P are largely with- drawn from senescing leaves before abscission, and used for new growth or stored in vege- tative tissue until the next growing season (VAN HEERWAARDEN et al. 2003). This process plays an important role in nutrient conversation (CHAPIN 1980). Obviously, species and seasonal pattern of nutrients strongly influence nutrient resorption (TEKLAY 2004, AERTS 1996, CHAPIN and KEDROWSKI 1983, KILLINGBECK 1996). It has been reported that individuals growing in less fertile sites may use nutrients more efficiently than those growing in more fertile sites. However, some stress factors such as low soil moisture may reduce resorption, especially of nitrogen. Several studies examining foliar nutrient resorption among temperate deciduous stands support these hypotheses for N and P (BOERNER 1984, ESCUDERO et al. 1992, MINOLETTI and BOERNER 1994). The nutri- ents resorbed from the trees during senescence are directly available for further plant growth, which makes a species less dependent on current nutrient uptake. Nutrients which are not resorbed, however, will be circulated through litterfall in the longer term. All of this has important implications for element cycling at the ecosystem level (AERTS and CHAPIN 2000, MARTÍÁEZ-SÁNCHEZ 2005). Resorption can be expressed in two ways: as resorption efficiency and resorption profi- ciency. Resorption efficiency is most accurately calculated for any nutrient as area-specific mass in green leaves minus area-specific mass in senesced leaves divided by area-specific mass in green leaves, and the quantity multiplied by 100. A new measure of resorption was introduced by KILLINGBECK (1996) as resorption proficency. Proficiency is simply the amount of a nutrient that remains in fully senesced leaves (KILLINGBECK 2004). From a bio- logical perspective, an important advantage of measuring resorption as proficiency rather than efficiency is that proficiency is a more unequivocal measure of the degree to which se- lection has acted to minimize nutrient loss in ephemeral leaves (KILLINGBECK 2004). The chlorophylls (Chl a and Chl b) are the most important photosynthetic pigments, and thus virtually essential for the oxygenic conversion of light energy to the stored chemi- cal energy that powers the biosphere. From an applied perspective, leaf pigmentation is im- portant to both land managers and ecophysiologists (RICHARDSON et al. 2002, LIN et al. 2005). The amount of solar radiation absorbed by a leaf is largely a function of the concen- trations of leaf photosynthetic pigments and, therefore, low concentrations of chlorophyll can directly limit photosynthetic potential and hence primary production (CURRAN et al. 1990, FILELLA et al. 1995) Much of the leaf nitrogen is incorporated in chlorophyll, so 276 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. quantifying chlorophyll content gives an indirect measure of nutrient status (FILELLA et al. 1995, MORAN et al. 2000). Pigmentation can be directly related to stress physiology, as con- centrations of chlorophylls generally decrease under stress and during senescence (PENU- ELAS and FILELLA 1998). The relative concentrations of pigments are known to change with abiotic factors such as light, so quantifying these proportions can provide important infor- mation about relationship between plants and their environment. The seasonal changes of leaf ecophysiological and ecomorphological characters depend on both internal and exter- nal factors. Particularly, seasonal changes are informative for evergreens, because the leaf character of a plant changes according to age of plant, growth of leaf and vegetative repro- ductive phases (NUNEZ-OLIVERA et al. 1996). The present study addresses three main objectives : (1) the seasonal variation of N and P contents, efficiency and proficiency, and (2) to find whether N and P resorption efficiency and proficiency is changed along an elevational gradient or not, (3) determining chl a/b in leaves of the evergreen C. creticus L. along an elevational gradient. Material and methods Study area This study was conducted in natural Cystus creticus populations at Samsun (41°17’ N; 36°20’ E) and Amasya (40° 39’ N; 35°51’ E) counties in 2004–2006. Samsun and Amasya are situated on the north, Black Sea region of Turkey (A6 square based on the grid system of Davis) (Fig.1). Mean annual temperature and precipitation in Samsun (30 m a.s.l. 670 m a.s.l.) and Amasya (880 m) are 12.16 °C, 65.7 mm and 13.37 °C, 450.3 mm, respectively ACTA BOT. CROAT. 69 (2), 2010 277 FOLIAR RESORPTION AND CHLOROPHYLL CONTENT OF CISTUS CRETICUS L. Fig. 1. The map of study area. 1 – Kurupelit (30 m), 2 – Kavak (670 m), 3 – Yenice (880 m). (Tab. 1). A western Mediterranean type precipitation regime is present in Samsun. A west- ern Black Sea region 2nd type oceanic precipitation regime is seen in Amasya (AKMAN 1990). Cistus creticus occurs on loamy and strongly alkaline soils (Tab. 1). Sampling Plant samples were collected from along an elevational gradient from 30 to 880 m. Five (25 m ´ 25 m) plots were chosen in homogeneous places at altitudes of 30 m a.s.l., 670 m a.s.l. and 880 m a.s.l. in homogeneous places. In each plot, at least five individuals were randomly selected and flagged. Individuals were selected ³2.5 m from the stems of neigh- boring canopy trees to avoid potential microsite variation (BOERNER and KOSLOWSKY 1989) Leaf samples from throughout the midcrown per individual were taken to avoid effects of crown position of the canopy and subcanopy species and consisted of leaves with no evi- dence of insect attack. Chemical analyses Leaf samples were dried at 60 °C until constant weight, ground, and sieved and digested in a mixture of nitric and perchloric acids with the exception of samples for nitrogen (N) analysis. Nitrogen was determined by the micro Kjeldahl method with a Kjeltec Auto 1030 Analyser (Tecator, Sweden) after the samples were digested in concentrated H2SO4 with a selenium catalyst. Phosphorus (P) was determined with the stannous chloride method with the use of a Jenway spectrophotometer (ALLEN et al. 1986). Concentrations of chlorophyll a and b were determined according to standard methods (ODABAS 1981). Leaf samples were scanned and leaf area was calculated with the use of a SPSS 10.0 for Windows (ANONYMOUS 1999). Specific leaf area (SLA) was calculated according to (CORNELISSEN et al. 1997, KUTBAY 2001): SLA = S LA (cm2) / S LDW (mg) N contents = S LDW (mg) ´ crude N concentration/ SLA = mg cm–2 P contents = S LDW (mg) ´ crude P concentration/ SLA = mg dm–2 LA – Leaf area (cm2) LDW – Leaf dry weight (mg) 278 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. Tab. 1. General characters of the study areas. (See Fig.1) Locality Mean annual temperature (°C) Mean annual precipitation (mm) Soil Texture pH Composition of the study area Samsun 12.16 65.70 Loamy 8.35 Pinus pinea dominates, Quercus ilex, Cistus salviifolius. Amasya 13.37 45.03 Loamy 8.20 Pinus pinea dominates, Cistus salviifolius. ACTA BOT. CROAT. 69 (2), 2010 279 FOLIAR RESORPTION AND CHLOROPHYLL CONTENT OF CISTUS CRETICUS L. Fig. 2. Concentration of N and P (µg cm–2), percentage of N resorption efficiency (NRE), P resorp- tion efficiency (PRE), N resorption proficiency (NRP) and P resorption proficiency (PRP). Seasonal N concentrations (a), N concentrations along the elevational gradient (b), seasonal P concentrations (c), P concentrations along the elevational gradient (d), NRE (%) along the elevational gradient (e), PRE (%) along the elevational gradient (f), NRP concentration along the evational gradient, PRP concentration along the evational gradient (g) (Standard errors are indicated. Means followed by the same letter are not significantly different at the 0.05 level using Tukey’s HSD test). Resorption efficiency was calculated as the percentage of N, P and recovered from senescing leaves (ORGEAS et al. 2002, REJMANKOVA 2005): [(Nutrient in live leaves – Nutrient in senescent leaves)/ Nutrient in live leaves] ´ 100 Statistical analyses One and two-way analysis of variance (ANOVA) tests and multivariate General Linear Models procedure were carried out with the use of the programme SPSS 10.0. The depend- ent and independent variables were foliar nutrient concentrations and foliar resorption and, growth period and localities, respectively. Tukey’s HSD test was used to rank means fol- lowing analysis of variance with the use of SPSS 10.0. Pearson correlation coefficients were also calculated with SPSS 10.0 version (ANONYMOUS 1999). Results Nitrogen and phosphorus dynamics and specific leaf area Nitrogen and phosphorus concentrations of C. creticus changed according to months and altitudes (Figs. 2a, 2b, 2c, 2d). There were statistically significant differences in terms of N and Specific Leaf Area (SLA) (P<0.01) but there were no significant differences in P concentration (Tabs. 2, 3). The highest N concentration was observed in August (55.5 mg cm–2). In the beginning of senescence (September), the N concentration of leaves de- creased (25.3 mg cm–2). The highest P concentration was observed in August (0.49 mg cm–2) while the lowest P concentration was found in June and November (0.21 mg/cm–2, 0.25 g cm–2) while the flower were in bloom (Figs. 2a, 2b, 2c, 2d). 280 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. Tab. 2. The comparison of the monthly changes in N, P, specific leaf area (SLA) and leaf mass area (LMA) in C.creticus by using one-way ANOVA. Parameter Sum of Square df Mean square F Sig. N Between Groups 8100.518 8 1012.565 8.307 0.000** Within Groups 18648.795 153 121.888 Total 26749.313 161 P Between Groups 0.756 8 9.448E-02 1.784 0.084 NS Within Groups 8.103 153 5.296E-02 Total 8.858 161 SLA Between Groups 0.747 8 9.338E-02 6.961 0.01** Within Groups 0.966 72 1.342E-02 Total 1.713 80 LMA Between Groups 59.338 8 7.417 6.535 0.01** Within Groups 81.725 72 1.135 Total 141.063 80 *P< 0.05 **P< 0.01 NS: Not Significant Nitrogen and phosphorus concentrations of C. creticus changed with respect to study period and along the elevation gradient. N concentration was higher in July (28 mg cm–2) and at 670 m (44 mg cm–2) (Figs. 2a, 2b). The lowest N concentration was found in September (25.3 mg cm–2) and at 30 m (38 mg cm–2). The highest P concentration (37.5 mg cm–2) was determined at 880 m, while the lowest P concentration (34 mg cm–2) was found at 670 m (Figs. 2c, 2d). In the present study, it was found that mature leaf nutrients was higher than in senescent leaf. There were significant differences during the study period (p<0.01**), whereas there were no significant differences along the elevational gradient (Tabs. 2. 4). ACTA BOT. CROAT. 69 (2), 2010 281 FOLIAR RESORPTION AND CHLOROPHYLL CONTENT OF CISTUS CRETICUS L. Tab. 3. The comparison of the monthly changes in N, P and specific leaf area (SLA) in C.creticus by using Tukey’s HSD test. Months N P SLA March 4.76bc 0.20 ab 0.34 bcd April 7.16bc 0.66 a 0.38 abc May 15.03bc 0.92 a 0.38 abc June1 6.78ab 0.18 ab 0.38 abc July 28.00a 0.24 ab 0.33 bcd August 15.93bc 0.14 ab 0.26 cd September 10.39 bc 0.26 ab 0.19 d October 9.80 bc 0.26 ab 0.44 ab November 3.94 c 0.22 ab 0.54 a F-value 8.307 1.784 6.961 Std. Error 0.368 0.767 0.546 *P< 0.05 **P< 0.01 Tab. 4. The comparison of the elevation gradient in N, P, specific leaf area (SLA) and leaf mass area (LMA) in C.creticus by using one-way ANOVA. Parameter Sum of Square df Mean square F Sig. N Between Groups 441.810 2 220.905 1.320 0.270NS Within Groups 26601.618 159 167.306 Total 27043.428 161 P Between Groups 0.318 1 0.318 5.661 0.020NS Within Groups 4.442 79 0.056 Total 4.760 80 SLA Between Groups 0.035 1 0.035 1.486 0.226NS Within Groups 1.844 79 0.023 Total 1.878 80 LMA Between Groups 0.502 1 0.502 0.282 0.597NS Within Groups 140.561 79 1.779 Total 141.063 80 *P< 0.05 **P< 0.01 NS: Not Significant Significant correlations were found among N, P and N/P (p<0.01**, p<0.05*) (Tab. 5). Strong positive correlations were reported between green-leaf N concentra- tion and N/P and N contents, respectively for C. creticus. However, significant differ- ences were found along the elevational gra- dient and during the growth period in respect to the N/P ratio. Negative correla- tions were found between green-leaf P con- centrations and the N/P ratio (Tab. 5). N/P ratios of C. creticus were > 16 at only at 30 m, but < 14 at 670 and 880 m, respectively. Except for March, June and July the N/P ra- tio was < 14 during the study period (Tab. 6). Nitrogen and phosphorus resorption efficiency and resorption proficiency The highest N resorption efficiency (85.60) was found at 30 m, while the low- est N resorption efficiency value (80.36) was found at 880 m (Fig. 2e). The highest and lowest N resorption proficiency (11.18, 4.85) were found at 670 and 30 m, respectively (Figs. 2g). However, the high- est P resorption efficiency (78) was found at 670 m while the lowest P resorption effi- ciency value (53.48) was found at 30 m (Figs. 2f). The highest and lowest P resorption pro- ficiency (1.95, 0.79) were found at 30 and 880 m, respectively (Fig. 2h). Chlorophyls (Chl a, Chl b, Chl a+ b, Chl a/ b) It was found that chlorophyll content of C. creticus changed both seasonally and along the elevational gradient (Tab. 7, Figs. 3a, b, c, d). In C. creticus, the highest chl a content was found in October (38 mg cm–2) and at 880 m (28 mg cm–2), while the lowest chl a con- tent was found in November (13 mg cm–2) and at 670 m (17 mg cm–2) (Figs. 3a, b). The highest chl b content of C. creticus was observed in June (70 mg cm–2) and at 880 m (9.7 mg cm–2) while the lowest chl b was found in August (17.5 mg cm–2) and at the 670 m (8.2 mg cm–2) (Figs. 3c, d). Chl a and chl b values exhibited significant changes seasonally and along the elevational gradient. chl a+ b content was higher in June (73 mg cm–2) and at 670 m (37 mg cm–2) (Figs. 3e, f), while the lowest chl a/b content was found in July (0.49 mg cm–2) and at 880 m (1.08 mg cm–2), respectively (Figs. 3g, h). Seasonal chl a, chl b, chl a+ b and chl a/b of C. creticus are compared in table 8 and 9, using one way anova and Tukey’s HSD. According to statistical analysis there were signifi- cant differences in terms of seasonal variation (p<0.01**, p<0.05*) but no significant dif- ferences along the elevational gradient (Tabs. 8, 9). 282 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. Tab. 5. Pearson correlations among N, P con- tent and N/P in C. creticus (**p<0.01; *p<0.05) N P N/P N 1.000 0.059 0.199* P 0.059 1.000 –0.289** N/P 0.199* –0.289** 1.000 Tab. 6. N/P ratio in C. creticus along the eleva- tional gradient N/P Locality 30m 18.89 >16 670m 13.65 <14 880m 10.07 <14 Months March 18.47 >16 April 13.72 <14 May 15.92<14 June 16.51 >16 July 20.34 >16 August 12.16 <14 September 9.73 <14 October 5.15 <14 November 2.87<14 Discussion It has been found that foliar nutrient contents of deciduous species in the early growing season are high. These values are stable from mid-growing season to the beginning of se- nescence, but low in the beginning of abscission. Similar results were reported for some ev- ergreen species. However, foliar nutrient concentrations for some evergreen species in- crease in the abscission phases (KUTBAY and KILINÇ 1994, HEVIA et al. 1999). In deciduous species the most mature phases of leaf are mid-summer (DIAZ and CABIDO 1997). However, in evergreen species fully-expanded leaves are found in the middle of spring but this phase may change according to climatic factors (HEVIA et al., 1999). There were notable seasonal ACTA BOT. CROAT. 69 (2), 2010 283 FOLIAR RESORPTION AND CHLOROPHYLL CONTENT OF CISTUS CRETICUS L. Tab. 7. The comparison of the monthly changes in Chl a, Chl b, Chl a+b, Chl a/b in C.creticus by us- ing one-way ANOVA. Parameter Sum of Square df Mean square F Sig. Chl a BetweenGroups 1478.563 5 295.713 10.528 0.000** Within Groups 1348.237 48 28.088 Total 2826.800 53 Chl b Between Groups 21111.373 5 4222.275 64.882 0.000** Within Groups 3123.641 48 65.076 Total 24235.015 53 Chl a+ b Between Groups 15462.828 5 3092.566 21.764 0.000** Within Groups 4262.787 30 142.093 Total 19725.615 35 Chl a/b Between Groups 13.720 5 2.744 6.029 0.001* Within Groups 13.653 30 0.455 Total 27.373 35 *P< 0.05 **P< 0.01 NS: Not Significant Tab. 8. The comparison of the monthly changes in Chl a, Chl b, Chl a+b, Chl a/b in C.creticus by us- ing Tukey’s HSD test. Months Chl a Chl b Chl a+b Chl a/b June 23.40 a 45.57 a 70.07 a 0.65 b July 23.53 a 55.00 a 62.26 a 0.47 b August 12.90 b 7.00 b 21.20 b 1.89 a September 11.16 b 4.63 b 21.49 b 2.15 a October 15.51 b 11.79 b 26.06 b 1.71 ab November 11.16 b 13.35 b 21.64 b 1.60 ab F-value 10.528 64.882 21.764 6.029 Std. Error 2.49 3.80 6.88 0.38 *P< 0.05 **P< 0.01 variations in N and P concentrations in C. creticus. The N and P dynamics of C. creticus are a bit different from similar species (i.e. Cistus laurifolius) and N concentration peaked in July, while P concentration peaked in August. In other words, a summer peak was observed in both N and P concentrations. Peak concentrations of N and P of similar species in Medi- terranean region were May and March for N and P, respectively, on an area basis and this may be due to differences in phenological patterns. However, the overall pattern for P con- centrations was quite similar to that of C. laurifolius (MILLA et al. 2004). Foliar N and P concentrations in the present study were low in the early growing season as compared to the mid-growing season. Although P concentrations declined, N concentrations increased in the senescence period (Figs. 2a, c). HOBBIE and GOUGH (2002) stated that species with short leaf lifespans (deciduous trees, sedges, and forbs) have higher foliar nutrient concentrations than evergreen species. How- ever, N and P resorption efficiency values in the present study were found to be higher than that of other evergreen species (Fig. 2e). A longer leaf life span is regarded as a mechanism for conserving nutrients since it reduces the loss of minerals during leaf abscission (LIMA et al. 2006). The greater the resorption efficiency, the more nitrogen is reused by the plant (CORTE et al. 2009). N resorption efficiency was higher at 30 m in C. creticus and decreased along the elevational gradient. However, P resorption efficiency was higher at 670 m. C. creticus in- dividuals effectively used nitrogen at low elevations, whilst phosphorus was effectively used at high elevations. It has been hypothesized that N and P resorption efficiency usually decreased as nutrient concentrations in green leaves increased (RATNAM et al. 2008). N and P resorption efficiency usually and green leaf N and P concentrations in C. creticus leaves supported that hypothesis. 284 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. Tab. 9. The comparison of the elevation gradient in Chl a, Chl b, Chl a+b, Chl a/b in C.creticus by using one-way ANOVA. Parameter Sum of Square df Mean square F Sig. Chl a BetweenGroups 398.7 5 199.3 4.187 0.201 NS Within Groups 2428.1 48 47.6 Total 2826.8 53 Chl b Between Groups 890.5 2 445.3 0.973 0.385 NS Within Groups 23344.5 51 457.7 Total 24235.0 53 Chl a+ b Between Groups 609.1 2 304.5 0.526 0.596 NS Within Groups 19116.5 33 579 Total 19725.6 35 Chl a/b Between Groups 0.2 2 0.1 0.137 0.873 NS Within Groups 27.1 33 0.8 Total 27.4 35 *P< 0.05 **P< 0.01 NS: Not Significant ACTA BOT. CROAT. 69 (2), 2010 285 FOLIAR RESORPTION AND CHLOROPHYLL CONTENT OF CISTUS CRETICUS L. Fig. 3. Pigment content (µg cm–2). Seasonal chlorophyll a content (a), along the evational gradient (b), seasonal chlorophyll b content (c), chlorophyll b content along the elevational gradient (d), seasonal chlorophyll a+b content (e), chlorophyll a+b content along the elevational gra- dient (f), seasonal chlorophyll a/b content, chlorophyll a/b content along the elevational gra- dient (Standard errors are indicated. Means followed by the same letter are not significantly different at the 0.05 level using Tukey’s HSD test). In some evergreen species, N resorption efficiency values were found to range from 25.7% – 75.1% (KILLINGBECK and COSTIGAN 1988, HEVIA et al. 1999, MEDIAVILLA and ESCUDERO 2003, ESCUDERO et al. 1992, KUTBAY et al. 2003, ÖZBUCAK et al. 2008). Woody evergreens show a higher resorption than deciduous species because mature evergreens have lower nutrient concentrations than deciduous leaves (KILLINGBECK 1996). In some de- ciduous species like Quercus suber, Populus nigra and Frangula alnus N resorption effi- ciency was found to be 47.9, 62.6 and 61.6, respectively (ESCUDERO et al. 1992). In the present study, N and P resorption efficiency values of evergreen C. creticus were found that are higher than those of other evergreen species (KILLINGBECK and COSTIGAN 1988, ESCUDERO et al. 1992). The N and P resorption processes are more efficient due to the higher N and P concentrations before senescence (MILLA et al. 2004). Low N and P concentrations were found in some deciduous species at high elevations. However, it was found that N and P concentrations in evergreen species increased along an elevation gradient (HEVIA et al. 1999). Similar results were observed in the present study for the evergreen C. creticus (Figs. 2b, 2d). This may probably be due to the decrease of soil moisture along the elevational gradient (KUTBAY and OK 2003). Resorption proficiency is considered a more stable indicator of the plant capacity to re- use nutrients than resorption efficiency (KILLINGBECK 1996, LIMA et al. 2006). According to KILLINGBECK (1996) N and P resorption proficiencies are high when ey are below 50 g cm–2 and 3 g cm–2, respectively. Based on these threshold values N and P resorption proficien- cies are biochemically complete in C. creticus (Figs. 2 g, h). N/P ratios are more important than N and P concentrations in terms of mineral nutrition (GUSEWELL 2005). If N/P <14, N-limitation is present. However, if N/P>16, P-limitation is present (KOERSELMAN and MEULEMAN 1996). In present study, the N/P ratio of C. creticus was found to be below 14 at 30, 670 and 880 m, whilst the N/P ratio was found to be > 16 at 30 m (Tab. 6). As a result of this, P-limitation is present at low elevations, while the N-limi- tation is present at high elevations. N and P resorption efficiency in C. creticus were quite high as compared to the other evergreen species, whichmay probably be due to N- and P-limitation along the elevational gradient (Tab. 6). Chlorophyll a is located only in the reaction centres of the photosystems, while Chl b is located both in the reaction centres and the light harvesting complexes (LIN et al. 2005). A change in the Chl a/b ratio reflects an adaptation mechanism to balance the amount of light captured by the leaf and its utilization for photochemical processses (LIN et al. 2005). FILELLA and PEÒUELAS (1999) found that chlorophyll concentrations were not signifi- cantly changed along the elevational gradient. However, COVINGTON (1975) and RICHARD- SON and BERLYN (2002) found chlorophyll concentrations changed significantly along the elevational gradient, which the present study confirms. These results are further evidence of the usefulness of reflectance measures for the rapid and noninvasive detection of plant stress (RICHARDSON and BERLYN 2002). Chlorophyll a and b contents were curvilinear in style. Similar results were reported for the chlorophyll a and b contents in Phyllostachys pubescens (LIN et al. 2005). Chl a, b con- tent and Chl a+b content of mature leaves was higher in summer than in autumn with re- spect to leaf growth phases (P<0.01) (Figs. 3a, c, e). Chlorophyll a content was higher at 30 m and 880 m (Fig. 3b), while chlorophyll b was higher at 880 m (Fig. 3d). Chl a+b content 286 ACTA BOT. CROAT. 69 (2), 2010 TURKIS S., OZBUCAK T. was similar in all the elevations (Figs. 3e, f). Chl a/b ratio of mature leaves was higher in autumn than summer with respect to leaf growth phases (P<0.01) (Figs. 3g, h). In particu- lar, Chl b content declined more than that of Chl a (Figs. 3a, b, c, d). Similar results were found in some studies (LIN et al. 2005). SCHEUMAN et al. (1999) observed that the Chl a/b ratio of barley seedling increased during senescence from 2.9 at day 0 to 5 at day 8, and sug- gested that either degradation of Chl b was faster than that of Chl a or that Chl b was trans- formed into Chl a. GOSSAUER and ENGEL (1996) proposed that the conversion of Chl b to Chl a should precede chlorophyll degradation in higher plants. LIN et al. (2005) reported a chlorophyll content decrease but a Chl a/b ratio increase during leaf senescence. In the present study the Chl a/b ratio increased in August, September and October(Fig. 3g). Chlo- rophyll a and b contents were decreased after senescence due to vulnerability to winter stress and the chl a/b ratio was compatible to the shade acclimation hypothesis, which indi- cates the increasing shade characteristics of leaves (ZELIOU et al. 2009). The resorbed nitrogen may be used for the synthesis of chlorophyll a (JAIN and GADRE 2004). 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