模拟氮沉降对森林土壤可溶性有机碳的影响

Effects of Nitrogen Deposition on Soluble Organic Carbon: A Simulation Study in Subtropical Forest Soils

以亚热带森林生态系统为研究对象，于2009--2012年原位模拟氮沉降（对照，CK，0kg·hm^-2·a^-1、低氮LN，30kg·hm^-2·a^-1和高氮HN，100kg·hm^-2·a^-1），分析亚热带阔叶林（罗浮栲、浙江桂）和针叶林（杉木）森林土壤中可溶性有机碳变化，以探究土壤不同层次、不同植被类型和凋落物是否去除条件下土壤可溶性碳对氮沉降的响应．结果表明：针叶林土壤不同层次可溶性有机碳的差异较大，表层0～15cm在HN水平下最高；而15～30cm和30～40cm在LN水平下最高，HN水平下15—30cm可溶性有机碳含量显著降低；而阔叶林（罗浮栲、浙江桂）15—30cm和30—40cm土壤可溶性有机碳随施氮水平有小幅度的升高．通过模拟氮沉降前后表层土壤（0～15cm）可溶性有机碳含量的比较，发现针叶林和阔叶林对氮沉降的响应存在差异，氮沉降后瞬时效应显示，杉木林土壤可溶性有机碳含量随氮水平而降低，但阔叶林并没有降低，甚至有增加趋势，尤其是在罗浮栲林．土壤自身碳含量的差异也是影响其响应氮沉降的重要因素；且模拟氮沉降后瞬时的效果在一定程度上影响最终的长期结果，而凋落物去除处理的效果短时间还无法观察到．

In 2009--2012 in situ simulation nitrogen deposition experiments （control, CK, 0 kg · hm^-2 . a^- 1, low nitrogen LN, 30 kg · hm^-2 · a^- 1 and high nitrogen HN, 100 kg · hm^-2 · a- 1） were conducted to study effects of nitrogen deposition on soil soluble organic carbon for broad-leaved forest （ Cinnamomum chekiangense and Castanopsis fabri） and coniferous forest （ Cunninghamia lanceo- lata ） in subtropical areas with different soil depth, different vegetation and litter removed or not. The results showed that soluble organic carbon at different soil depth for coniferous forest was largely differ- ences with highest at HN for 0 - 15 cm soil depth. However, soil soluble organic carbon has the high- est level for 15 -30 cm and 30 -40 cm at LN and it was decreased significantly for 15 -30 cm at HN. Different from coniferous forest （Cunninghamia lanceolata）, soil soluble organic carbon for broadleaved forest （Cinnamomum chekiangense and Castanopsisfabri） in 15 -30 cm and 30 -40 cm depth increased in small amplitude with nitrogen deposition. With comparing the soluble organic carbon after nitrogen application to that prior to fertilization for 0 - 15 cm soil, it was found that the response of broad-leaved forest and coniferous forest to nitrogen deposition was different. Nitrogen deposition reduced soil soluble organic carbon content for coniferous forest, but not reduced the content for broad- leaved forest; even increase their content, especially in the broad-leaved forest （Castanopsis fabri）. These showed that the difference of soil carbon content in different forest soils is also an important fac- tor affecting the response of soil soluble organic carbon to nitrogen deposition. The response of soil sol- uble organic carbon to nitrogen application time and again at short-term to some extent affect the final long-term results. However, the effects of litter removed could not be observed at a short-term.