Effects Of Environmental Heterogeneity On The Growth Of Plants

Environmental heterogeneity plays an essential role in the dynamics of plant population and communities and both the heterogeneity in natural habitats (i.e., nutrient, water and light) and plant interactions (i.e., distribution pattern, occupation and fragmentation of spatial resource) contribute to the changing traits of plant individual, population and community. Numerous studies have tested the effects of heterogeneity in nutrient, water and light on the performance of plant, but few have tested the effects of heterogeneity in plant distribution pattern on the plant performance. In this thesis, greenhouse and garden experiments were conducted to test (1) how the patchy distributions of competitors affect the performance of plant individual,(2) how long-term heterogeneous nutrient supply and plant distribution pattern within population affect the performance of clonal plant population and (3) how soil particle heterogeneity affects the yield and structure of experimental community.We conducted a greenhouse experiment to examine how patchy distributions of competitors affect the growth of a rhizomatous wetland plant Bolboschoenus planiculmis and whether such effects depend on the density of the competitors. We grew one ramet of B. planiculmis in the center of each of the experimental boxes without competitors (Schoenoplectus triqueter), with a homogeneous distribution of the competitors of low or high density, and with a patchy distribution of the competitors of low or high density. The presence of competitors markedly decreased the growth (biomass, number of ramets, number of tubers and rhizome length) of the B. planiculmis clones. When the density of the competitors was low, the growth of B. planiculmis did not differ significantly between the competitor patches and competitor-free patches. However, when the density of the competitors was high, the growth of B. planiculmis was significantly higher in the competitor-free patches than in the competitor patches. Therefore, B. planiculmis can respond to patchy distributions of competitors by placing more ramets in competition-free patches when the density of competitors is high, but cannot do so when the density of competitors is low.We conducted a garden experiment to examine how long-term (2years) nutrient heterogeneity and plant distribution within population affect the clonal plant population. We planted Carex neutocarpa (phalanx) and B. planiculmis (guerilla) in monoculture or mixture (i.e., uniform distribution and cluster distribution) pattern in a wood experimental box with homogeneous or heterogeneous nutrient supply. Long-term heterogeneity in nutrient supply did not affect the performance of clonal plant population and the species within population. However, the distribution pattern of population may greatly affect the growth of plants by changing the intra-and interspecific competition. More field experiments should be conducted to test whether the heterogeneity and population distribution pattern in natural habitats affect the growth of plants.We conducted a greenhouse experiment to examine how soil particle heterogeneity and species richness affect the yield and structure of experimental community. We sowed seeds of4-species or8-species in three heterogeneous treatments consisting of64,16or4patches of small (1.5mm) and large particles (3.0mm), one homogeneous treatment with an even mixture of small and large particles. Biomass was significantly greater in the community with high species richness than that with low species richness. However, soil heterogeneity did not affect the yield and structure of the experimental community. The effects of the soil particle heterogeneity on the performance of the community may greatly depend on the special traits (e.g. clonality) and dominant species within community.