毛竹叶凋落物分解对林冠和林下氮添加的差异化响应OACHSSCD

Alterations in litter decomposition under atmospheric nitrogen(N)deposition serves as a key driver of changes in material cycling and energy flow in forest ecosystems.However,traditional research methods predominantly simulate N deposition via understory N addition,overlooking the critical role of the forest canopy in intercepting and transforming deposited N.This methodological limitation may lead to inaccurate assessments of the actual ecological effects of atmospheric N deposition.Therefore,a comparative analysis of canopy versus understory N addition on leaf litter decomposition in Moso bamboo(Phyllostachys edulis)forests is essential for accurately assessing decomposition dynamics under N deposition.This study was conducted in a Moso bamboo forest ecosystem at the Anji Moso Bamboo Ecosystem Research Station of Zhejiang A&F University,in Anji County,Zhejiang Province.At this site,we employed four experimental treatments:canopy nitrogen addition(spraying NH4NO3 solution,50 kg N hm-2 a-1),canopy control(spraying water),understory nitrogen addition,and understory control.The primary objective was to investigate and compare the effects of these distinct N addition approaches(canopy vs.understory)on the decomposition of Moso bamboo leaf litter.To elucidate the underlying mechanisms governing these effects,we systematically measured concomitant changes in litter chemical composition,key soil chemical properties,and the activities of soil extracellular enzymes throughout the decomposition period.The results demonstrated that canopy N addition significantly promoted litter decomposition,increasing the decomposition rate constant kvalue(0.81±0.03)a-1 by 14.1％compared to the canopy control.Conversely,understory N addition significantly inhibited decomposition k value(0.61±0.03)a-1,decreasing the rate by 15.3％relative to the understory control.Canopy N addition significantly reduced cellulose and lignin contents in the decomposing litter,whereas understory N addition increased both.Canopy N addition did not induce significant alterations in soil pH or total inorganic nitrogen(TIN)content,whereas understory N addition significantly reduced soil pH and increased TIN content.Multivariate regression models revealed that under canopy N addition,changes in peroxidase(PER)and β-1,4-xylosidase(BX)activities and TIN content were positively correlated with litter mass loss rate,whereas lignin content were negatively correlated.Under understory N addition,the changes in soil pH and cellobiohydrolase(CBH)activity were positively correlated with mass loss rate,while the changes in TIN and cellulose contents exhibited negative correlations.In conclusion,this study indicated that the responses of Moso bamboo leaf litter decomposition to canopy and understory N addition differed significantly.Traditional understory N addition experiments may have led to a misestimation of the true impacts of atmospheric N deposition on Moso bamboo forest ecosystems.