Microsoft Word - 11380 NSB Bulu 2023.03.16.docx Received: 15 Nov 2022. Received in revised form: 01 Jan 2023. Accepted: 01 Mar 2023. Published online: 16 MAr 2023. From Volume 13, Issue 1, 2021, Notulae Scientia Biologicae journal uses article numbers in place of the traditional method of continuous pagination through the volume. The journal will continue to appear quarterly, as before, with four annual numbers. SHSTSHSTSHSTSHST Horticulture and ForestryHorticulture and ForestryHorticulture and ForestryHorticulture and Forestry Society of TransylvaniaSociety of TransylvaniaSociety of TransylvaniaSociety of Transylvania Bulu YI et al. (2023) Notulae Scientia BiologicaeNotulae Scientia BiologicaeNotulae Scientia BiologicaeNotulae Scientia Biologicae Volume 15, Issue 1, Article number 11380 DOI:10.15835/nsb15111380 Research ArticleResearch ArticleResearch ArticleResearch Article.... NSBNSBNSBNSB Notulae Scientia Notulae Scientia Notulae Scientia Notulae Scientia BiologicaeBiologicaeBiologicaeBiologicae Soil seed bank studies of Soil seed bank studies of Soil seed bank studies of Soil seed bank studies of TithoniaTithoniaTithoniaTithonia rotundifoliarotundifoliarotundifoliarotundifolia invaded fallow land and invaded fallow land and invaded fallow land and invaded fallow land and competitive association with competitive association with competitive association with competitive association with Chromolaena odorataChromolaena odorataChromolaena odorataChromolaena odorata Yetunde I. BULU*, Rilwan O. AHMED, Opefoluwa D. FADAYOMI, Otitoloju KEKERE Adekunle Ajasin University, Department of Plant Science and Biotechnology, Akungba-Akoko, Nigeria; yetunde.bulu@aaua.edu.ng (corresponding author); optimalrilwan@gmail.com; opeoluwafadayomi@yahoo.com; otito.kekere@aaua.edu.ng AbstractAbstractAbstractAbstract In Nigeria, Chromolaena odorata (L.) R. M. King and H. Rob and Tithonia rotundifolia (Mill.) S. F. Blake, are exotic invasive weeds, but a gradual decrease in the population of C. odorata with the rapid invasion of T. rotundifolia is now observed. Therefore, this study investigated the adaptive features of each weed in competition, with a further determination of seedling recruitment from the soil seed bank of plots invaded by T. rotundifolia. Field sampling was carried out in 10 plots: T. rotundifolia invaded plots and low or uninvaded plots in co-existing with other plants using 10 m x 10 m quadrats. The readily germinable seed species composition and the Sorensen index of similarity between the seed bank and their above ground vegetation were determined. Competition Series Experiment was also conducted for the two plants. Mariscus alternifolius (227) and Oldenlandia corymbosa (358) were the most abundant species in the seed bank while T. rotundifolia recruited 25 individuals. Low similarity index existed between the seed bank and the standing vegetation of the invaded and uninvaded plots. T. rotundifolia had improved growth in heteroculture with C. odorata over when in monoculture. However, a reduction in growth of C. odorata occurred when in competitive association with T. rotundifolia compared to when in monoculture. T. rotundifolia had competitive advantage over C. odorata. Keywords:Keywords:Keywords:Keywords: invasive plant species; seedling recruitment; soil seed bank IntroductionIntroductionIntroductionIntroduction In recent times, a lot of attention has been given to the harmful effect of invasive alien plant species on the functioning of ecosystems (Zhang et al., 2019). Among the mechanisms enhancing successful naturalization and invasion of a new environment by alien plant species, escape from their natural enemies (competitors, herbivores and pathogens) and ability to allocate resources to traits that promote greater competitive advantage, such as size and fecundity, are viewed as characters conveying advantage on them (Joshi and Vrieling, 2005). Aside the formation of a mono-specific stand, the ability to establish a reserve of seeds in the soil seed bank in their new environment can contribute significantly to their successful naturalization and invasion potential (Gioria et al., 2021). Giving the function of the soil seed bank as source of propagules, genetic diversity https://www.notulaebiologicae.ro/index.php/nsb/index Bulu YI et al. (2023). Not Sci Biol 15(1):11380 2 and a mechanism of safeguarding against reproductive failure and unfavorable environmental conditions (Larson and Funk, 2016; Gioria et al., 2021), early seed sets and their storage in the seed bank may give an alien invasive plant a hedge over the native plants. In response to invasion from an alien species, the seed bank may likewise serve a protective role to the native plants by preventing their extinction by functioning as source of seed storage and recruitments for species absent from the aboveground vegetation during the process of revegetation of the invaded community. So far, the effect of invasive plant species on plant communities and biodiversity has only been viewed by investigating changes in the above ground species richness with little information on the impact or significance of the seed bank. Therefore, investigating the changes occurring in the seed bank of exotic invasive species and native species in invaded communities is essential to predict the recruitment potential of these species from the seed bank and in understanding the roles of the seed bank in invasion success. Chromolaena odorata (L.) R. M. King and H. Rob. and Tithonia rotundifolia (Mill.) S. F. Blake are invasive alien weeds from Mexico that are widely distributed in the south-western part of Nigeria. C. odorata is a perennial herb that grows up to 2.5 m tall in open areas. It is hairy and glandular with leaves that are opposite, triangular to elliptical with serrated edges. The white to pale pink tubular flowers are in panicles of 10 to 35 flowers that form at the ends of branches. T. rotundifolia on the other hand is an erect annual herb with yellow or orange red blooms that contains between 8 and l0 ray florets and between 65 and 90 disk florets in its capitulum (Adebowale and Olorode, 2005; Olorode et al., 2011). C. odorata was reportedly introduced into the country from Sri Lanka in 1937 and has currently reached an alarming population (Uyi et al., 2013; Uyi and Igbinosa, 2013). On the other hand, T. rotundifolia is gaining increasing attention because of the formation of dense mono-specific stand and an ability to outcompete native vegetation (Adebowale and Olorode, 2005). The successful establishment and invasion of T. rotundifolia and C. odorata in new environment have been attributed to their fast growth rates, early maturity and large seed sets relative to native plant species. Currently, T. rotundifolia is prominently observed in the country with a consequent gradual decrease in the population of C. odorata especially in the south western part of the country where it once dominated (Adebowale and Olorode, 2005). In this study, we hypothesized that T. rotundifolia outcompete C. odorata and form a large and persistent seed bank which will enhance its establishment and invasiveness in any new environment. This study therefore investigated the relative reciprocal performance of the two invasive species viz T. rotundifolia and C. odorata on each other. The study also examined the characteristics of the seed bank of T. rotundifolia invaded and uninvaded plots. Materials and MethodsMaterials and MethodsMaterials and MethodsMaterials and Methods Vegetation analysis and soil seed bank determination Soil seed bank studies were carried out at the screenhouse of the Department of Plant Science and Biotechnology (PSB), Adekunle Ajasin University (AAUA), Nigeria. A recognisance study was first embarked upon in the Northern part of Ondo State, South Western Nigeria, to identify areas of vegetation cover with high population of T. rotundifolia in co-existence with C. odorata and other plant species. Consequently, a field survey was embarked upon in fallow land vegetation along Akure-Akungba expressway in Ondo State, Nigeria (07°16ʼ34.0ʼN; 005°17ʼ48.9E to 07°27ʼ11.6ʼN; 005°43ʼ47.0E). Sampling points were systematically placed at every 5 km distance along the expressway from Akungba-Akoko (07°16ʼ34.0ʼN; 005°17ʼ48.9E) to Akure (07°27ʼ11.6ʼN; 005°43ʼ47.0E) between July and December, 2020. At each point, two sampling plots were selected in fallow land vegetation in the area; one dominated by T. rotundifolia (invaded plot) and another with low population of T. rotundifolia in co-existence with C. odorata and other plant species (uninvaded plot). A total of ten plots were identified with six designated as invaded plots (plots 1, 2, 3 4, 5 and 10) and four uninvaded plots (plots 6, 7, 8 and 9). In each sampling plot, a three 10 m x 10 m quadrat was laid out randomly Bulu YI et al. (2023). Not Sci Biol 15(1):11380 3 for determination of floristic composition with identification of plants to species level. Species whose identities were in doubt were collected and taken to the Department of PSB Herbarium for proper identification. Three replicate soil samples were also collected each at depths of 0-15 cm and 15-30 cm, taken to the Laboratory of the Department of PSB and air-dried. The soils were filled into perforated plastic pots and the direct germination method of Thompson and Grime (1979) was used to assess the readily germinable seed species composition. The relative abundance of plant species or families on the standing vegetation and seed bank was estimated as the percentage each species or families contributed to the total number of individuals present. The Sorensen Index of Similarity between the above ground vegetation and their seed bank was estimated according to Chao et al. (2005). Plant competition experiment Uniform seedlings (relatively equal size) of C. odorata and T. rotundifolia were collected from an open field around the sampling area with known history of clearing four weeks prior to the commencement of the experiment. The seedlings were transplanted into perforated polythene pots (30 cm by 25 cm) filled with top soil collected from the experimental field of the Department of PSB which was a nutrient-rich sandy-loam soil according to Kekere et al. (2020). Each pot replicated five times, contained a total of 6 seedlings in monoculture or heteroculture in a competition series experiment viz: T1 = 6 C. odorata: 0 T. rotundifolia; T2 = 5 C. odorata: 1 T. rotundifolia; T3 = 4 C. odorata: 2 T. rotundifolia; T4 = 3 C. odorata: 3 T. rotundifolia; T5 = 2 C. odorata: 4 T. rotundifolia; T6 = 1 C. odorata: 5 T. rotundifolia; and T7 = 0 C. odorata: 6 T. rotundifolia. The pots were arranged in a completely randomized experimental design in the screen house of the Department of PSB. The experiment lasted for 12 weeks. Plant stem girth was measured with vernier calliper at the 2 cm point from the base of the stem while a meter rule was used to measure the height from the soil surface to the apical bud. Plant leaves were counted and the leaf area determined with the Leaf Area Meter (LI-COR 300 model). At 12 weeks after planting, the plants were carefully uprooted and the primary roots counted with their lengths measured. The shoot lateral branches were also counted. Fresh and dry mass of plant parts were measured and the moisture content calculated as ����� ��� � ��� ��� � ����� ��� � �100 while the relative growth rate was accounted for according to Hoffmann and Poorter (2002) with the formula: �� ����� �� �� � where w1 and w2 are the means of the natural logarithm of transformed plant weight. All data obtained were subjected to one-way ANOVA. Statistical means were separated with New Duncan Multiple Range test at 95% level of significance using the Statistical Package for Social Sciences (SPSS software, version 24.0). ResultsResultsResultsResults Species composition of the standing vegetation Forty-four plant species belonging to 15 families were identified in the ten plots of the standing vegetation. The plant habits as shown in Table 1, comprised 26 herbs (59.10%), 10 shrubs (22.70%), 7 grasses (15.90%) and 1 climber (2.30%). On the invaded plots, plants belonged to six families (Figure 1) contributed plant species to the above ground vegetation with the Poaceae having the highest number of individuals (33.33%). Each of the Fabaceae, Amaranthaceae and Euphorbiaceae families had a relative abundance (RA) of 16.67%. Other families had a RA of 8.33% and below. Similarly, fourteen families were enumerated on the uninvaded plots. However, the Fabaceae family had the highest RA (21.86%) followed by the Poaceae and Asteraceae with 12.50% each. Meanwhile, the relative abundance of the Cucurbitaceae, Portulacaceae, Euphorbiaceae and others ranged between 3.13% and 9.38%. Bulu YI et al. (2023). Not Sci Biol 15(1):11380 4 Table 1Table 1Table 1Table 1. Plant species composition on the standing vegetation of the study plots S/N Species Family Habit 1 2 3 4 5 6 7 8 9 10 1 Aeschynomene indica Fabaceae Shrub - - - - + + - - - - 2 Amaranthus viridis Amaranthaceae Herb - - - + - - - - - - 3 Andropogon tectorum Poaceae Grass - + - - - + - - - - 4 Argeratum conyzoides Asteraceae Herb - - - - - - + - - - 5 Blumea aurita Asteraceae Herb - - - + - - + - - - 6 Brachiaria jubata Poaceae Grass - + - - - - - - - - 7 Calopogonium spp Fabaceae Herb + + - - + + - - - + 8 Celosia argentea Amaranthaceae Herb - - - + - - - - - - 9 Centrosema pubescens Fabaceae Herb - - + - - + - + - - 10 Chamaecrista rotundifolia Fabaceae Shrub - - - - - - + - - - 11 Chromolaena odorata Asteraceae Shrub - - - - - - - + - - 12 Digitaria gayana Poaceae Grass - - - - - + - - - - 13 Cissus quadragullaris Vitaceae Climber - - - - - - - + - + 14 Corchorus spp Malvaceae Herb + - - - - - - - - - 15 Desimodium spp Fabaceae Shrub - - - - - + - - - - 16 Eleutheranthera ruderalis Asteraceae Herb - - + - - - - - - - 17 Euphorbia alta Euphorbiaceae Herb - - - - - - - - + - 18 Euphorbia heterophylla Euphorbiaceae Herb - - + - + - - - - - 19 Euphorbia hirta Euphorbiaceae Herb - - - + - - - - - - 20 Fleurya aestuans Urticaceae Herb - - + - - - - - - - 21 Gomphrena celosioides Amaranthaceae Herb - - - - - - + - + - 22 Indigofera indica Fabaceae Shrub - - - - - - - + - - 23 Luffa cylindrical Cucurbitaceae Herb - - - - - - - - + - 24 Mariscus alterniphorus Cyperaceae Herb - - + - - - - - - + 25 Melanthera scanden Asteraceae Herb - - + - - - - - - - 26 Mimosa invisa Fabaceae Shrub - - - - + - - + + - 27 Mitracapous villosus Rubiaceaea Herb - - - - - - - - - + 28 Oldenlandia corymbosa Rubiaceae Herb - - - - - - + - - + 29 Panicum maximum Poaceae Grass + + - - + - - + - + 30 Paspalum scrobiculatum Poaceae Grass - - - - - - - - - + 31 Peperomia pellucida Piperaceae Herb - - + + - - - - - - 32 Phyallathus amarus Euphorbiaceae Herb + + - - - - - - - - 33 Physalis angulata Solanaceae Herb + - - - - - - - - - 34 Physalis micrantha Solanaceae Herb - - - - - - - - + - 35 Pupalia lappacea Amaranthaceae Herb - - - - - - - - + - 36 Rhynchelytrum repens Poaceae Grass + - - - - - - - - - 37 Richadia brasilensis Rubiaceae Herb + - - - - - - - - - 38 Senna hirsute Fabaceae Shrub - - - - - - - - + - 39 Sida acuta Malvaceae Shrub + - - - - - + - - - 40 Spermacoce latifolia Rubiaceae Herb - - - - - - + - - + 41 Sporobolus pyramidalis Poaceae Grass - - - - - + - - - - 42 Talinum trangularae Portulacaceae Herb - - - + - - - - - - 43 Tithonia rotundifolia Asteraceae Shrub + + + + + - - - - + 44 Urena lobata Malvaceae Shrub - - - - - - - - + + Key + = Present; - = Absent Plant species composition of soil seed bank Seedling emergence from the soil seed bank at 0 - 15 cm and 15 – 30 cm depths are shown in Figures 2 and 4. At 0-15 cm depth, there were 20 herbs, 10 grasses and 4 shrubs constituting 58.4% herbs, 29.4% grasses Bulu YI et al. (2023). Not Sci Biol 15(1):11380 5 and 11.8% shrubs respectively. The plants belonged to 14 families each on invaded and uninvaded plots with Poaceae having the highest RA of 15% and 30% on invaded and uninvaded plots respectively. Other families ranged between 10% and 5% for invaded plots, and 10% and 3.33 for uninvaded plots. The plant species composition from the soil seed bank at 15-30 cm depth is shown in Figure 3. A total of 29 species composing of 18 herbs, 8 grasses and 3 shrubs were found, constituting 62.07%, 27.59% and 10.54% respectively. Each of the invaded and uninvaded plots had plant species found in 13 families. Poaceae had the highest RA of 28% on uninvaded plots and 35% on invaded plots. On the uninvaded plots, other families had 4-12% RA while 4-10% was recorded on the invaded plots. Figure 1.Figure 1.Figure 1.Figure 1. Families of plant species in the standing vegetation of the studied plots Figure 2.Figure 2.Figure 2.Figure 2. Families of plant species recruited from the seed bank at 0-15 cm depth Seedling recruitment from the soil seed bank Figure 4 shows the relative abundance of seedling recruited from the soil seed bank from the invaded and uninvaded plots at 0-15 cm and 15-30 cm depths. On the uninvaded plots, soils collected at 0-15 cm and 15-30 cm depths had the highest number of seedling recruits from seed bank at plot 7 (43.63 and 34.12 respectively) and lowest at plot 8 (3.73 and 2.56 respectively). On the invaded plots, seedling recruitment from the seed bank peaked at plot 3 (10.58 and 16. 97) and plot 5 (8.29 and 16.97) for soils collected at 0-15 and 15- 30 cm depths respectively. 0 5 10 15 20 25 30 35 R e la ti v e a b u n d a n c e Family Invaded Uninvaded 0 5 10 15 20 25 30 R e la ti v e a b u n d a n c e Family Invaded Uninvaded Bulu YI et al. (2023). Not Sci Biol 15(1):11380 6 Figure 3.Figure 3.Figure 3.Figure 3. Families of plant species recruited from the seed bank at 15-30 cm depth At both the invaded and uninvaded plots, Mariscus alternifolius and Oldenlandia corymbosa were the most abundant species in the seed bank. The number of seedlings recruited from the soil seed bank from the invaded and uninvaded plots include O. corymbosa (73 and 513 seedlings), M. alternifolius (128 and 82), Eleusine indica (24 and 11), Panicum maximum (38 and 2), Mitracarpus villosus (33 and 31), Celosia leptostachya (80 and 3), and T. rotundifolia (13 and 12) respectively. Figure 4Figure 4Figure 4Figure 4. Relative abundance of species recruited from the soil seed bank Similarity in species composition (standing vegetation and seed banks) Table 2 shows the Sorensen Similarity Index between the soil seed bank at different depths (0-15 cm and 15-30 cm) on the invaded and uninvaded plots. High similarity index was recorded between 0-15 cm and 15-30 cm depths on the invaded plots at plot three (0.78), five (0.63) and ten (0.57) but there was no similarity in plot 1 as similarity index was 0.00. In addition, high similarity index ranging from 0.46 to 0.61 was recorded between 0-15 cm and 15-30 cm depths for plant species composition on the uninvaded plots. The similarity index in species composition between soil seed bank at both depths and the standing vegetation gave low values for both invaded and uninvaded plots. 0 5 10 15 20 25 30 35 40 R el at iv e ab u n d an ce R el at iv e ab u n d an ce R el at iv e ab u n d an ce R el at iv e ab u n d an ce Family Uninvaded invaded 0 5 10 15 20 25 30 35 40 45 50 1 2 3 4 5 6 7 8 9 10 Invaded uninvaded Invaded R el at iv e ab u n d ac e R el at iv e ab u n d ac e R el at iv e ab u n d ac e R el at iv e ab u n d ac e Plots 0-15 cm 15-30 cm Bulu YI et al. (2023). Not Sci Biol 15(1):11380 7 Table 2Table 2Table 2Table 2.... Similarity index in species composition at different soil depths and between standing vegetation Plot No Plot type Similarity index 0-15 cm and 15-30 cm soil depth Standing vegetation and 0-15 cm soil depth Standing vegetation and 15-30 cm soil depth 1 Invaded 0.00 0.29 0.00 2 Invaded 0.22 0.20 0.44 3 Invaded 0.78 0.17 0.00 4 Invaded 0.36 0.40 0.22 5 Invaded 0.63 0.00 0.00 6 Uninvaded 0.61 0.20 0.07 7 Uninvaded 0.54 0.37 0.37 8 Uninvaded 0.57 0.40 0.31 9 Uninvaded 0.46 0.14 0.00 10 Invaded 0.57 0.14 0.00 Growth parameters of C. odorata and T. rotundifolia under different levels of interspecific competition The height of C. odorata was significantly reduced by higher density of T. rotundifolia (Table 3). For example, the lowest value of 33.00 cm and 33.25 cm were recorded at ratios 1:5 and 2:4 C. odorata and T. rotundifolia respectively. C. odorata however had the highest height (40.08cm) when the mixture of the two plants was of equal number. Other growth parameters including stem girth (1.80 cm), number of leaves (16.58) and leaf area (33.04 cm) of C. odorata were highest when grown alone in pots than in competition with T. rotundifolia. The height of T. rotundifolia increased with increase ratio of C. odorata such that the highest height of 106.75 cm was recorded at T. rotundifolia and C. odorata density of ratio 1:5. Except for the number of leaves where the highest value of 26.42 was recorded at T. rotundifolia and C. odorata 3:3 ratio, all other parameters including the stem girth (3.80 cm) and the leaf area (220.28 cm2) were highest at 1:5 ratio. In the absence of T. rotundifolia, C. odorata had significantly higher number of roots than when T. rotundifolia was present (Table 4). A significant reduction in the number of roots was recorded in C. odorata with increased density of T. rotundifolia in the pots. A similar trend was recorded in the length of the roots of C. odorata where a significant high value of 15. 08 cm was obtained in the absence of T. rotundifolia. Significantly higher value of 14.75 was recorded for the number of roots of T. rotundifolia when it occurred in equal density with C. odorata than when it occurred alone. A significant increase in the length of roots of T. rotundifolia (29.25 cm) was recorded when C. odorata and T. rotundifolia occurred at a ratio of 5:1 but this decreased when T. rotundifolia density increased with a corresponding reduction in the density of C. odorata. Bulu YI et al. (2023). Not Sci Biol 15(1):11380 8 Table 3Table 3Table 3Table 3. Growth parameters of T. rotundifolia and C. odorata under different levels of interspecific competition Growth param. Plant species Plant mixture (ratio) 6CR:0TR 5CR:1TR 4CR:2TR 3CR:3TR 2CR:4TR 1CR:5TR 0CR:6TR Height (cm) CR 36.44±2.96d 35.05±2.74c 34.43±3.03b 40.08±2.88e 33.25±1.98a 33.00±2.38a 0.00 TR 0.00 106.75±15.32f 53.81±7.13d 68.83±9.22e 40.27±2.10a 49.36±8.62c 45.68±3.83b Stem girth CR 1.80±0.05d 1.63±0.05c 1.58±0.04b 1.64±0.15c 1.59±0.08b 1.48±0.09a 0.00 (cm) TR 0.00 3.80±0.20f 3.01±0.15e 2.87±0.15d 2.41±0.09b 2.30±0.09a 2.58±0.14c No of CR 16.58±0.85f 13.20±1.47d 11.06±0.77b 14.25±1.29e 12.00±0.20c 9.00±1.91a 0.00 leaves TR 0.00 21.75±3.12e 21.13±0.55d 26.42±12.21f 17.81±0.34c 16.60±4.87b 10.83±0.24a Leaf area CD 33.04±2.81e 23.79±1.88c 23.22±1.08c 27.52±17.56d 17.58±1.70b 16.39±1.71a 0.00 (cm2) TR 0.00 220.28±43.74f 92.70±18.42b 138.81±67.29e 98.63±6.12d 93.52±30.43c 58.43±5.98a Where CR= Chromolaena odorata, TR= Tithonia rotundifolia. Values are mean ± standard error for 5 replicates. Means with similar alphabets in superscript on the same row are not significantly different from each other at p≥0.05 (Duncan Multiple Range test). The root to shoot ratio (R:S) of C. odorata decreased with increasing density of T. rotundifolia (Table 4). R:S of C. odorata was highest (0.20) in the absence of T. rotundifolia (6:0). This value was however not significantly different from the R:S of C. odorata when the ratio of the density of the two plants were 5:1 and 4:2 but differed significantly when the densities of C. odorata to T. rotundifolia were 3:3 (0.13), 2:4 (0.14) and 1:5 (0.15). T. rotundifolia equally had high R:S (0.49) in the absence of C. odorata which differed significantly from all other combination levels of the two plants. At high density of C. odorata, the R:S of T. rotundifolia was significantly low; 5CR:1TR (0.21) and 4CR:2TR (0.19) compared to R:S obtained at 2CR:4TR (0.42). Table 4.Table 4.Table 4.Table 4. Root growth of C. odorata and T. rotundifolia under different levels of interspecific competition Plant mixture (ratio) Number of roots Root length (cm) Root: shoot ratio CR TR CR TR CR TR 6CR:0TR 9.33±1.02d 0.00 15.08±1.02d 0.00 0.20±0.11b 0.00 5CR:1TR 6.00±1.15c 11.90±0.55b 11.31±1.20c 29.25±2.80c 0.18±0.09b 0.21±0.09a 4CR:2TR 4.56±0.16a 11.00±1.08a 10.04±1.47b 23.13±2.73b 0.18±0.09b 0.19±0.08a 3CR:3TR 5.25±0.08b 14.75±0.55c 9.64±1.50b 22.15±1.69b 0.13±0.07a 0.25±0.09a 2CR:4TR 5.13±0.97b 11.56±1.16b 7.53±1.32a 18.93±2.09ab 0.14±0.08a 0.42±0.15bc 1CR:5TR 5.25±1.03b 11.90±0.55b 9.10±1.04b 15.49±0.63a 0.15±0.09a 0.38±0.08b 6TR:0CR 0.00 10.83±0.44a 0.00 16.23±1.51a 0.00 0.49±0.14c Key: CR= Chromolaena odorata, TR= Tithonia rotundifolia. Values are mean ± standard error for 5 replicates. Means with similar alphabets in superscript on the same column are not significantly different from each other at p≥0.05 (Duncan Multiple Range test). The total fresh mass (6.39 g) and dry mass (1.75 g) of C. odorata were significantly higher in the absence of T. rotundifolia (ratio of 6:0) than in its presence as shown in Table 5. The fresh and dry biomass of C. odorata was significantly reduced when grown with T. rotundifolia compared to its monoculture. In contrast, T. rotundifolia in mixed culture with C. odorata (5CR:1TR) had high fresh (117.16 g) and dry (28.20 g) biomass which were significantly higher than the fresh (18.94 g) and dry (4.81 g) biomass of T. rotundifolia grown in monoculture (0CR:6TR). Bulu YI et al. (2023). Not Sci Biol 15(1):11380 9 Table 5.Table 5.Table 5.Table 5. Fresh and dry mass, relative growth rate and moisture content of C. odorata and T. rotundifolia grown under interspecific competition Plant mixture (ratio) Total fresh mass (g) Total dry mass (g) Relative growth rate (mg/g) Moisture content (%) CR TR CR TR CR TR CR TR 6CR:0TR 6.39±1.12b 0.00 1.75±0.45b 0.00 0.024±0.002b 0.00 72.57±10.98a 0.00 5CR:1TR 3.46±0.13a 117.16±20.24b 0.83±0.09a 28.20±9.00a 0.017±0.001a 0.032±0.004b 76.15±11.01a 75.93±11.00a 4CR:2TR 3.50±0.11a 108.72±22.28b 0.92±0.08a 23.92±8.12a 0.017±0.001a 0.029±0.002b 73.02±10.88a 75.71±10.89a 3CR:3TR 3.78±0.14a 105.28±22.81b 0.97±0.10a 25.41±8.44a 0.018±0.001a 0.031±0.004b 74.94±10.89a 75.89±11.00a 2CR:4TR 4.00±0.19a 25.64±9.00a 0.89±0.06a 5.51±0.33b 0.019±0.001a 0.014±0.001a 77.75±10.99a 78.51±11.47a 1CR:5TR 3.92±0.15a 21.62±9.18a 1.01±0.41a 5.13±0.35b 0.018±0.001a 0.012±0.001a 74.50±9.35a 76.27±11.23a 6TR:0CR 0.00 18.94±8.09a 0.00 4.81±0.22b 0.00 0.010±0.001a 0.00 74.60±10.54a Key: CR= Chromolaena odorata, TR= Tithonia rotundifolia. Values are mean ± standard error for 5 replicates. Means with similar alphabets in superscript on the same column are not significantly different from each other at p≥0.05 (Duncan Multiple Range test) DiscussionDiscussionDiscussionDiscussion In the study, herbaceous plants, grasses and few shrubby species were found in the above ground vegetation of the invaded and uninvaded plots. The species richness of the above ground vegetation of the uninvaded plots were higher than those of the invaded plots across the plots covered in the study. The low richness of the weedy flora on the invaded plots can be explained by the fact that the vegetation cover in these plots consisted of monoculture stand of T. rotundifolia which provided vegetation cover with minimal open spaces for the survival of other plant species. In this situation, other weedy species could not have thrived. Many families contributed to the weedy species to the flora of the uninvaded plots. The prominent families in this study include the Fabaceae, Poaceae, Asteraceae, Rubiaceae, Amaranthaceae, Malvaceae, and Solanaceae in a diminishing order of importance. On the other hand, the invaded plots had a total of six families contributing to the weed flora with the Poaceae, Fabaceae and Euphorbiaceae listed as the major ones. The recruitment data from the seed bank indicated a considerably large number of families making contribution to the seed bank of the invaded plots. While 14 families contributed plant species at the 0-15cm depths, 13 families were recorded at the 15-30 cm depth. The dominant plant family on the standing vegetation i.e., the Poaceae also made the highest contribution of seedlings to this soil seed bank. The Poaceae also dominated the seed bank of the uninvaded plots. Similar observation was reported by De Andrade and Miranda (2014) that Poaceae (64%) are often the most abundant species in the soil seed bank following fire disturbance in savanna ecosystem. The absence of tree species in the standing vegetation of the plots could also account for their absence in the soil seed bank. The high density of herbaceous seeds in the seed bank may be related to species traits where an earlier study had reported that herbaceous seeds remain viable for a longer period of time in the soil than other seed types (Ghersa and Martinez-Ghersa, 2000; Wang et al., 2009). The result from this study shows that T. rotundifolia was either not found richly or totally absent in the seed bank of most of the invaded plots, though it was found in numerous populations in the standing vegetation. Its absence from the seed bank may be as a result of rapid seedling emergence from the soil which will likely promote its establishment and spread (invasion) in a new environment. This result has shown that formation of a large or persistent seed bank may not be essential for successful invasion in a new environment as pointed out by Gioria and Pyšek (2016). Contrarywise, many dominant plant species in the seed bank were absent in the above ground vegetation. Notable examples from the invaded plots are Oldenlandia corymbosa and Mariscus alternifolius. Although species composition in the above-ground and seed bank recruitments are often related such that the seed bank allows plant species that are lost from the vegetation to be re-established (Bakker et al., 1996), a low similarity was observed between the species composition of the seed bank and above- ground vegetation on the invaded and uninvaded plots in this study. Bulu YI et al. (2023). Not Sci Biol 15(1):11380 10 This study has also shown that the negative effect of competition was more pronounced on C. odorata compared to T. rotundifolia as evident in their growth parameters. A significant reduction in the above and below ground growth parameters of C. odorata was observed while the growth of T. rotundifolia was facilitated when in interspecific competition with C. odorata as against when in monoculture. The possession of higher growth by T. rotundifolia than C. odorata increased its chance of high productivity which may confer advantage on its invasive potential. The ability of T. rotundifolia to produce larger leaf surface area when in competition with C. odorata must have given it better photosynthetic ability for more rapid growth and better canopy layer to suppress growth of C. odorata. The improved root system of T. rotundifolia might have been responsible for better competition for water and nutrient absorption than C. odorata. Increased density of the two plants when in mixed culture caused significant reduction on the root/shoot ratio of one another compared to when grown separately in monoculture. The study reported increased in the biomass of T. rotundifolia when in mixed culture contrary to the reduced biomass of C. odorata. At monoculture stand of C. odorata, the growth was better than when in competition with T. rotundifolia. In the presence of high density of C. odorata, the growth T. rotundifolia was significantly improved over when in monoculture stands and/or reduce density of C. odorata. This must have accounted for the gradual decrease in the population of C. odorata with rapid invasion of T. rotundifolia currently being observed in fallow land areas previously occupied by the former. ConclusionsConclusionsConclusionsConclusions The presence of T. rotundifolia affected the richness and relative abundance of other plant species in the environment. The general paucity of weedy species contributing to the above flora on the invaded plots can be explained by the direct effect of T. rotundifolia mono clonal stand disrupting the ability of other weedy species to germinate therefore their dominance in the seed bank. It is likely that many plants will be driven to extinction if the invasion by T. rotundifolia continually persist since native species present in the soil seed bank are unable to germinate and maybe exposed to predation or decomposition in the soil. T. rotundifolia has some adaptations for competitive advantage over C. odorata and other plant species in the study area. This was through rapid seedling emergence after seed set; more rapid root growth for better water and nutrient uptake; and formation of canopy cover to suppress the growth of C. odorata. Authors’ ContributionsAuthors’ ContributionsAuthors’ ContributionsAuthors’ Contributions Conceptualization: YIB and OK; Funding acquisition: all authors; Data curation: ROA and ODF; Formal analysis: All authors; Writing - review and editing: YIB and OK. All authors read and approved the final manuscript. Ethical approvalEthical approvalEthical approvalEthical approval (for researches involving animals or humans) Not applicable. Bulu YI et al. (2023). Not Sci Biol 15(1):11380 11 AcknowledgementsAcknowledgementsAcknowledgementsAcknowledgements This research received no specific grant from any funding agency in the public, commercial, or not-for- profit sectors. Conflict of InterestsConflict of InterestsConflict of InterestsConflict of Interests The authors declare that there are no conflicts of interest related to this article. ReferencesReferencesReferencesReferences Adebowale A, Olorode O (2005). An overview of the invasive potential of Tithonia species (Asteraceae) in Nigeria. 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