凋落叶分解是控制森林湿地物质循环的重要生态过程,是全球C、N等元素循环的重要一部分.以美国南卡罗来纳州10种典型植物的凋落叶为研究对象,通过2a的分解实验测定分解阶段凋落叶的生物量残留率、分解速率常数k和C、N残留百分比,探讨初始凋落叶化学性质对分解速率常数k的影响.结果表明:(1)十种凋落叶生物量在两年内降解至初始的14.5％-66.2％,种间差异可达4倍以上;分解速率常数k在0.26-1.64 a-1之间,针叶分解速率＜阔叶分解速率;(2)分解速率常数k与初始凋落叶酸溶性组分(AS)极显著正相关(P＜ 0.001),与初始C含量、酸不溶组分(AIF)和AIF/N比均显著负相关(P＜0.05);(3)凋落叶C残留百分比持续下降至10.2％-66.1％,而N残留百分比因物种与分解阶段不同呈现不同变化规律.结果表明,森林湿地中凋落叶初始C组分差异是其分解速率的种间极大差异的主要原因,评估森林湿地的C、N循环应充分考虑种间差异.%Forested wetland is a critical transition zone between terrestrial and aquatic ecosystems.The zone is characterized by high productivity and an active biogeochemical cycle,and it likely exhibits carbon (C) and nitrogen (N) turnover rates that are different from those of non-flooding upland forests.Furthermore,leaf litter decomposition is a vital ecological process that controls C and N cycling in forested wetlands.However,because most litter decomposition studies have focused on non-flooding forests,less is known about the C and N dynamics during litter decomposition in mixed forested wetlands.In the present study,a two-year litter decomposition experiment was performed in a representative freshwater forested wetland in Georgetown,South Carolina,USA for the leaf litters of 10 local plant species:Nyssa aquatica,Acer rubrum,Asimina triloba,Celtis occidentalis,Fraxinus pennsylvanica,Liquidambar styraciflua,Pinus palustris,Platanus occidentalis,Taxodium distichum,and Ulmus americana.The C and N contents of the initial and decomposed litter samples were measured,and the initial litter samples were also measured for their chemical composition,including extractives,acid soluble,acid insoluble,and ash fractions.Percentages of remaining biomass,C,and N and the decomposition rate constant (k) were also calculated and linked to the initial mass and C and N contents,as well as to each litter's initial chemical composition.The results showed that after two years of decomposition,the percentage of remaining biomass varied largely across species and accounted for from 14.5％ to 66.2％ of the initial biomass (up to 4-times difference across species).Meanwhile,k ranged from 0.26 a-1 for P.palustris to 1.64 a-1 for A.triloba and was greater for broadleaf litter than coniferous litter.In addition,k was also positively correlated with initial acid soluble fraction (AS) of the litter and negatively correlated with initial C content,acid insoluble fraction (AIF),and AIF/N,which indicated that the initial chemistry of litter was a key factor in determining decomposition rate.Similarly,the remaining C content gradually decreased to 10.2％-66.1％ of the initial C content,with the greatest loss in A.triloba and the lowest in P.palustris.In contrast,the N content was either immobilized or mineralized during the decomposition process,depending on plant species and decomposition stage.For example,the N content of N.aquatica,P.occidentalis,and P.palustris was immobilized during early decomposition and was released at later stages.However,N was consistently immobilized in the litter samples of U.americana and A.rubrum and was consistently released from the litter samples of A.triloba,C.occidentalis,F.pennsylvanica,L.styraciflua,and T.distichum.Thus,the present study demonstrated that,similar to the litter decomposition of non-flooding forests,initial litter chemistry could explain the large variation observed in the decomposition rates of different plant species at individual sites.In addition,there are also large differences in the C and N dynamics during the decomposition of litter from plant species.Accordingly,our study highlights the importance of fully considering inter-species differences when evaluating the C and N cycling of forested wetlands.
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