川西南常绿阔叶林凋落物分解及养分释放对模拟氮沉降的响应

通过原位进行了对照(CK)、低氮(LN,50kgN.hm-2.a-1)、中氮(MN,100kgN.hm-2.a-1)和高氮(HN,150kgN.hm-2.a-1)处理,研究了川西南天然常绿阔叶林凋落物分解及养分释放对模拟N沉降的响应.结果表明:凋落物分解95%需要4.72～6.33年,分解率最高的为CK,最低的为HN.经过365d,各处理的分解率均低于CK,仅HN与CK间差异显著(P<0.05);C残留率均高于CK;N和K残留率均显著高于CK(P<0.05);P残留率均高于CK,仅LN与CK间差异显著(P<0.05).各处理凋落物的C/N升高3.9%～23.7%.凋落物分解过程中N元素的迁移模式为富集-释放,C、P和K元素则表现为直接释放.N沉降对凋落物中养分元素的释放及木质素和纤维素的降解均具有抑制作用.随着处理时间的延长,N沉降对川西南常绿阔叶林凋落物分解的影响从正效应转向负效应,且负效应随沉降浓度的增加而加强.

Responses of litter decomposition and nutrient release to simulated nitrogen deposition in an evergreen broad-leaved forest in southwestern Sichuan

An in situ experiment was conducted in an evergreen broad-leaved forest in southwestern Sichuan to study the responses of litter decomposition and nutrient release to simulated nitrogen deposition. Four treatments were installed, i.e., null level (CK), low nitrogen level (LN, 50 kg N x hm(-2) x a(-1)), moderate nitrogen level (MN, 100 kg N x hm(-2) x a(-1)) and high nitrogen level (HN, 150 kg N x hm(-2) x a(-1)). The results showed that it would take 4.72-6.33 years to decompose 95% of litter mass, with the highest decomposition rate in CK and the lowest one in HN. After 365 days, the litter decomposition rate in N-amended treatments was lower than that in CK, but significant difference was only observed between HN and CK (P < 0.05). The remained C was higher, and the remained N and K were significantly higher in N-amended treatments than in CK (P < 0.05). The remained P was also higher in N-amended treatments than in CK, but significant difference was only observed between LN and CK (P < 0.05). Compared with CK, all N-amended treatments had a 3.9%-23.7% increase of litter C/N ratio. During litter decomposition, element N featured a pattern of accumulation at early stage and release later, while C, P and K released all the time. Nitrogen deposition inhibited both the nutrient release from the litter and the decomposition of its lignin and cellulose. The effects of nitrogen deposition on litter decomposition in the forest changed from positive to negative as time passed, and the negative effect could be strengthened with the increase of deposited nitrogen concentration.