The Effects Of Abiotic Stress On Growth And Plant-plant Interaction Between Three Sphagnum Species

Being one group of special bryophytes, Sphagnum usually is the dominant plant and major carbon manufacturer in peatlands. It plays an important role in global carbon cycle. Global change made an important impact on Sphagnum growth and plant-plant interaction. There are many studies on alpine areas, arid environment, salt marshes mires, temperate grassland and other environment stress areas, finding that the target with neighbor is better than targets without neighboring plants. There were few studies with bryophytes, especially the report with peatland bryophytes so far.In this study, I chose three Sphagnum species including one hollow specie S. fallax and two hummock species S. capillifolium and S. palustre as materials. Mono-culture and mix-culture communities were built in natural density to study the effects of drought, flooding and shading stresses on growth and plant-plant interaction between Sphagnum species. The main results and conclusions are as follows:(1) Water is one of the most important factors to impact the growth of Sphagnum. Drought stress depressed the growth of three species more than effects of neighbors, resulting in a decline of height, biomass and branch shoots. The hollow specie S. fallax was depressed by neighbors under drought. hummock specie S. capillifolium was seldom affected by neighbors.(2) Interspecies interaction were more significant under flooding stress. S. fallax was able to adept to flooding stress, and benefited from neighbors or no effects. The growth of S. palustre was depressed not only by flooding stress but also by neighbors. S. capillifolium was depressed by flooding stress. S. fallax depressed the height, biomass and branch shoots of the two hummock species significantly. Even S. capillifolium depressed the growth of S. palustre.(3) The height of the three sphagna had most significant response on shade, having feeble effect on biomass. Open-mire hummock was more sensitive than the other two species from hollow and forest edge. And the two species competed with S. palustre. S. fallax was the strongest competitor under shade, depressing the biomass and branch shoots of its neighbors. Competing for light between species made the capacity of S. capillifolium declined.(4) The coverage horizontal expansion were significantly different in different mixture conmunities and treatments. S. palustre mix-cultured with S. capillifolium, under shade, were mainly affected by shade, S. palustre coverage increased at the expense of the coverage expansion of S. capillifolium. under shade stress, Sphagna were mainly affected by neighbors, the coverage S. capillifolium expanded at the expense of the coverage of S. palustre. The shade resulted in a loose growth of Sphagnum. (5) In this study, water and shading stress only significantly reduced C concentration of mono-cultural S. capillifolium. In mix-cultured, the neighborhood increased C concentration of S. capillifolium under all stress. Under the control treatment, the C concentration was depressed by neighbors. There were significant interaction between neighborhood and all the stress treatments, indicating that the neighbors promote C input under stress in peatlands.(6) N concentration increased along water and shade level. N concentration of Sphagnum capitulum in mix-cultured were mainly affected by stress, not by neighbors.(7) The C/N is decreasing along the water increasing which is opposite to the N concentration. Flooding and deep shade depressed the C/N. The C/N under shallow shade is higher than deep shade, indicating that shading by modest vascular plant was benefit to carbon accumulation. When flooding, shade and drought stress occurs, the C/N of S. fallax mix-cultured with S. capillifolium changed along two opposite directions.(8) In this study, positive interaction was showed when other Sphagnum species as neighbor of S. fallax, with a interspecific interaction (+,-) and no mutulism and commensalism was found. Most plant-plant interactions are competition (-,0) . Hence, this study did not support Stress Gradient Hypothesis (SGH), namely plant-plant interaction did not change from competition to positive interaction along stress gradients. Sphagnum-Sphagnum interaction is related to ability of competition response and tolerant ability of stress in Sphagnum.