| Since the industrial revolution,human activities have produced and discharged a large amount of active nitrogen?N?into the atmosphere,resulting in a global N deposition problem.Over the past half-century,a large number of studies have been conducted around the world to explore the impact of N deposition increases on ecosystems.However,the study of long-term nitrogen deposition is relatively scarce,in order to further the effect of long-term N deposition increasing on the ecosystem process,based on the long term simulated nitrogen deposition test sample of the Pleioblastus amarus plantation in the rain-screen area of West China,by means of continuous N-adding?NH4NO3 N source?in the field,combined with the method of ecosystem stoichiometry measurement,The responses of different N-added gradients(CK,LN,MN and HN,0,50,150 and 300 kg N·hm-2·a-1,respectively)were studied with plant-litter-soil as a whole.The results showed that:?1?The concentration of N and P in bamboo leaves is significantly higher than that of bamboo,bamboo root and litter N and P,and the ratio of bamboo leaves C:N and C:P is the lowest,the N:P ratio is the highest,and the C concentration of each organ is no significant difference.LN treatment increased C concentration,C:N and C:P ratio,MN treatment reduced the root C concentration,HN treatment decreased the C concentration of bamboo leaves,increased the root C concentration;N deposition significantly decreased the concentration of N in bamboo leaves,significantly increased the concentration of root N and N:P ratio,and had no significant effect on bamboo shoots and leaf litter.?2?The pH value of rhizospheric and bulk soil of Pleioblastus amarus forest was significantly decreased by simulating N deposition,and bulk soil C concentration and C:N and C:P of the Pleioblastus amarus forest were also significantly reduced,but N deposition did not affect the concentration of C,N and P in rhizospheric soil and its ecosystem stoichiometry.?3?The microbial biomass in rhizospheric was higher than that of bulk microorganisms,the simulated N deposition significantly reduced the rhizospheric soil MBN and MBN:MBP in the Pleioblastus amarus plantation,significantly increased the rhizospheric and bulk soil MBC:MBN,the bulk soil MBP increased first and then decreased with N deposition,and the rhizospheric and bulk soil MBC:MBP and bulk soil MBN:MBP decreased first and then increased with the increase of N deposition.?4?The activity of rhizospheric enzymes was higher than that of bulk enzymes,the simulated N deposition significantly inhibited the activity of BG enzymes,rhizospheric and bulk soil?LAP+NAG?enzyme activities in the Pleioblastus amarus plantation,made the the ratio of?LAP+NAG?:AP in the Pleioblastus amarus plantation decreased significantly,and the ratio of BG:?LAP+NAG?,BG:AP,?LAP+NAG?:AP in rhizospheric soil decreased first and then increased with N addition.,but the activity of AP enzyme in rhizospheric increased first and then decreased with N addition.Combined with the above results,the effect of N deposition on bamboo leaves and bamboo roots is stronger than that of bamboo shoots and litters,and the plant has certain internal stability,in which the inner stability of bamboo shoots is stronger than that of bamboo leaves and bamboo roots.The effect of N deposition on the soil ecosystem stoichiometry is more obvious than that of the plants,and the microbial biomass and enzyme activity of rhizospheric soil is higher than that of bulk soil,and the response of soil to N deposition is very different between rhizospheric and bulk soil.The response of microbial biomass and enzyme activity to nitrogen deposition was significantly stronger than that in the rhizospheric,which indicated that the response of the rhizospheric to nitrogen deposition was more sensitive. |
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