The Effect Of Inputs Of Plant Residues On Productivity Of Streams In The Alpine Forest

Plant residues from land and riparian zone play a key role in the cycle of nutrient and energy flow of fresh water ecosystem.Due to the low nutrient levels and primary productivity,especially in the low level of streams,this kind of allochthonous organic matter is the necessary source of carbon and nutrient for aquatic life.However,the existing researches about effect of inputs of allochthonous organic matter to productivity of plankton community are rare.As alpine forest at western Sichuan are an important conservation of water,forest debris plays an essential role in energy flow in ecosystem.Therefore,the study about the influence of inputs of plant residues of alpine forest on net productivity of plankton community in stream ecosystem is significantly meaningful for understanding material circulation,energy flow,communication across ecosystems and protection of water conservation.With the study area locating at alpine forest of the upper reaches of Minjiang River,this experiment adopted 3 groups of control experiments under four treatments,such as without inputs of plant residues,with inputs of non-woody residues,inputs of woody residues,with inputs of non-woody and woody residues.During the growing season,we studied the influence of inputs of alpine forest plant residues on structure of phytoplankton community and net productivity of plankton community in headwater streams through monitoring the inputs of non-woody residues,content of organic carbon and nutrient of plant residues,structure of phytoplankton community and environment factors of headwater streams,with determination of productivity by using black and white bottle method..The results are showed as follows:?1?Bacillariophyta and Cyanophyta were the main algae in the alpine headwater streams in the upper reaches of Minjiang River and Bacillariophyta had absolute advantages and Melosira,Fragilaria and Eunotia Her were dominant algae in the stream ecosystem during the growing season.The factors of phytoplankton community structure,were significantly affected by inputs of plant residues,groups,time and their interaction and it showed similar trends in different groups and different treatments.The mean values of factors of phytoplankton community structure were showed as with inputs of woody residues>with inputs of non-woody residues.The removal of inputs of plant residues could improve number of species,density and biomass of phytoplankton in streams.The structure of phytoplankton community was also related to inputs of non-woody residues,chemical indicators of plant residues and environmental factors of streams.?2?The net productivity of plankton community in different treatments and groups varied from-0.44gO₂·?m³·d?^-11 to 0.95 gO₂·?m³·d?^-1.The inputs of plant residues,groups,time and their interaction had significant impact on net productivity of plankton community in streams.During the growing season,the inputs of plant residues could increase the net productivity of plankton in streams,and the net productivity of plankton community was significantly correlated with the input of non-woody residues and C/N of plant residues inputs.The trends of net productivity of plankton community in streams with different treatments and groups were similar,and the values of net productivity of plankton community were approximately summarized as with inputs of non-woody residues>with inputs of non-woody and woody residues>with inputs of woody residues>without inputs of plant residues.?3?The effect of environmental factors on net productivity of plankton community in alpine headwater streams was different under different treatment.With inputs of plant residues,the net productivity of plankton community could also be affected by structure of phytoplankton community in varying degrees.To summary,the community structure of phytoplankton was not only related to input of forest plant residues,but also influenced by environmental factors of streams.This is of great significance for understanding the mechanism of structure of phytoplankton community in alpine forest.In addition,inputs of plant residues from alpine forest significantly increased the net productivity of plankton community and net productivity of plankton community also related to factors of environment and phytoplankton community structure.This provides basic data for understanding the effect of allochthonous organic matter inputs on productivity of headwater streams.In conclusion,this study explored the effect of inputs of plant residues on structure of phytoplankton community and net productivity of plankton community in alpine headwater streams through a controlled experiments.It also summarized dynamic variation rule and the differences of the structure of phytoplankton community and net productivity of plankton community under different treatment as with inputs of non-woody residues,with inputs of non-woody and woody residues,with inputs of woody residues,without inputs of plant residues during the growing season.These results provides basic data for the in-depth understanding of the effects of allochthonous organic matter on the ecosystem of forest streams,and it is of great significance to the understanding of the material circulation and energy flow of the freshwater ecosystem.