滇中高原川滇高山栎凋落叶、枝分解过程对模拟氮沉降的响应

The litter decomposition of fallen leaves and branches from sub-alpine Quercus aquifolioides of central Yunnan Plateau under simulated nitrogen deposition

【目的】氮(N)沉降增加通过影响凋落物分解过程中碳(C)、氮(N)元素的有效性,进而影响生物地球化学循环中的碳和养分平衡。通过研究模拟N沉降下川滇高山栎(Quercus aquifolioides)凋落物分解速率及养分含量变化特征,为川滇高山栎森林生态系统的有效管理提供参考。【方法】以滇中新平县磨盘山川滇高山栎林为研究对象,以尿素(有效成分CH_(4)N_(2)O)为氮源,采用尼龙袋法进行N沉降处理以及凋落物原位分解试验,4个N沉降水平为:对照[CK,0 g/(m^(2)·a)]、低氮[LN,10 g/(m^(2)·a)]、中氮[MN,20 g/(m^(2)·a)]和高氮[HN,25 g/(m^(2)·a)],每月施氮1次,持续12个月后测定凋落叶及枝质量残留,及其木质素、纤维素和C、N、P、K含量变化。【结果】(1)分解1 a后,各N沉降处理凋落叶(0.84%~3.87%)、枝(1.67%~3.30%)质量残留率均显著增加(P<0.05),说明随时间延长,凋落物分解被抑制,且抑制强度与施氮水平成正比;(2)凋落叶、枝分解系数变化范围分别为0.271~0.368和0.167~0.218 kg/(kg·a),凋落枝C/N(69.02)和木质素氮比(54.65)高于凋落叶的值(52.09和44.42),叶分解速率快于枝;(3)凋落物化学组成会影响凋落物质量残留率,表现为凋落物质量残留率与凋落叶和枝的N、P含量呈极显著负相关,与C、纤维素含量,C/N、C/P、木质素氮比、纤维素氮比等比值呈极显著正相关。【结论】(1)N沉降抑制了凋落物的分解,且随施氮水平的增加,抑制作用明显增强;(2)初始养分含量会影响凋落物的养分固持和释放,其中,N含量、C/N、木质素氮比是凋落物分解过程中的重要影响因子。

【Objective】Increased nitrogen(N)deposition affects carbon(C)and N availability by affecting the litter decomposition process,after which it affects the C-nutrient balance of the biogeochemical cycle.In this study,the nylon mesh bag method was used to study the decomposition rate and nutrient content changes of Quercus aquifolioides litter under simulated N deposition,providing a reference for an effective Q.aquifolioides forest ecosystem management.【Method】The in situ litter decomposition test was carried out in the Q.aquifolioides forest of Mopanshan in Xinping County,central Yunnan Province.Four N levels were applied using the nylon mesh bag method,with urea(CH_(4)N_(2)O)as the N source for in situ decomposition of litter and N deposition treatment.The four N deposition levels were:control[CK,0 g/(m^(2)·a)],low N[LN,10 g/(m^(2)·a)],medium N[MN,20 g/(m^(2)·a)]and high N[HN,25 g/(m^(2)·a)].Leaf litter and twig mass remaining,lignin,cellulose,and C,N,P and K contents were then measured.【Result】①After one year of decomposition,the N deposition treatment significantly increased the mass remaining rate(P<0.05)of leaf litter(0.84%-3.87%)and twig(1.67%-3.30%).The litter decomposition was inhibited,and the inhibition intensity was proportional to N content application.②Variation coefficients of leaf and twig litter decomposition were 0.271-0.368 and 0.167-0.218 kg/(kg·a),respectively.The lhe C/N(69.02)and lignin/N(54.65)of twig litter were significantly higher compared with leaf litter(52.09 and 44.42,respectively).Leaf decomposition rate was faster compared with that of twig.③The chemical composition of the litter affected its mass remaining rate,which was negatively correlated with N and P contents of leaf and twig litters,and positively correlated with C,cellulose,C/N,C/P,lignin/N and cellulose/N.【Conclusion】The N deposition inhibits litter decomposition,and this effect is significantly enhanced by increased nutrient content.Initial nutrient content effects nutrient retention and litter release processes,among which N level,C/N and lignin/N are important influencing factors.