氮沉降对中国森林土壤CO_2通量的影响

Effects of Nitrogen Deposition on CO_2 Fluxes of Forest Soils in China

氮沉降可能改变森林土壤CO_2通量,已有研究结果对氮沉降作用的方向和强度上具有很大的不确定性。通过整合已有模拟氮沉降的野外监测数据,评估了氮沉降对中国森林土壤CO_2通量的影响。结果表明,氮沉降平均降低了中国土壤CO_2通量的8.7%,且这种影响对次生林和人工林影响较大,而对原始林影响较小。同时,氮沉降对土壤CO_2通量的影响对阔叶林、针叶林和针阔混交林均无显著影响,但显著降低了竹林土壤CO_2通量的36%。施加>100 kg N·hm^(-2)·a^(-1)时才会对森林土壤CO_2通量造成显著降低,且施加硝酸铵的降低大于尿素。氮沉降的这种影响主要是由于过多的氮抑制了土壤微生物活性造成的。

Nitrogen （N） deposition could change CO2 efflux in forest soils, but current experimental resuits showed a high uncertainty in the direction and magnitude of the effect of N deposition. By combining the in situ monitoring results of N deposition experiments that were conducted in China, the effects of N deposition were assessed on CO2 efflux in forest soils at national scale. The results showed that N deposition significantly declined 8.7% of the CO2 efflux in forest soils in China,and this influence was greater for secondary forests and plantations than that for for primary forests. Moreover, N deposition had no significant effects on soil CO2 efflux in broad-leaved, needle and mixed forests, but significantly decreased the CO2 efflux in bamboo soils by 36%. However, this influence was significant only when the dose of N fertilization was more than 100 kg N·hm^-1·a^-1,and the effect of ammonium nitrate was greater than urea. The decline in CO2 efflux in forest soils was due to the decrease of soil microbial activity induced by fertilized N.