南亚热带森林土壤微生物量碳对氮沉降的响应

Effects of elevated nitrogen deposition on soil microbial biomass carbon in the main subtropical forests of southern China

研究了鼎湖山自然保护区3种森林生态系统土壤微生物量碳对氮沉降增加的响应。选取南亚热带代表性森林类型马尾松林、混交林和季风常绿阔叶林(季风林)建立野外模拟氮沉降试验样地。2003年7月开始每月进行氮处理。这些处理分别为对照、低氮处理、中氮处理和高氮处理,即0、50、100 kg N hm-2a-1和150 kg N hm-2a-1。在2004年11月和2006年6月用氯仿熏蒸浸提法分别测定土壤微生物量碳和土壤可浸提有机碳。土壤微生物量碳和可浸提有机碳含量均表现为2006年6月高于2004年11月;季风林高于马尾松林和混交林。随着氮沉降增加季风林土壤微生物量碳减少,但可浸提有机碳含量则增加,且此趋势在高氮处理下表现明显。然而,氮沉降增加对马尾松林和混交林土壤微生物量碳和可浸提有机碳含量的影响不显著。以上结果表明,氮沉降增加可能提高季风林土壤有机碳的固持能力。

Effects of elevated nitrogen deposition on soil microbial biomass carbon （C） and extractable dissolved organic carbon （DOC） in three forest types of southern China were studied in November 2004 and June 2006. Plots were established in pine forest （ PF）, pine and broad-leaf mixed forest （MF） and monsoon evergreen broad-leaf forest （MEBF） in Dinghushan Biosphere Reserve. Nitrogen treatments included Control（no N addition）, Low-N（50kg N hm^-2a^-1）, Medium-N（ 100kg N hm^-2a^-1） and High-N （150kg N hm^-2a^-1 ）. Microbial biomass C and extractable DOC were determined using the chloroform fumigation-extraction method. Results indicated that microbial biomass C and extractable DOC were higher in June 2006 than in November 2004, and were higher in MEBF than in PF or MF. Responses of soil microbial biomass C and extractable DOC to N deposition varied depending on forest type and the N treatment level. In PF or MF forests, no significant effects of N addition were found on soil microbial biomass C and extractable DOC. In MEBF forest, however, soil microbial biomass C generally decreased with increasing N addition, and high N addition significantly reduced soil microbial biomass C. The response of soil extractable DOC to N addition in MEBF showed the opposite trends to soil microbial biomass C. These results suggest that N deposition may increase the accumulation of soil organic carbon in MEBF in the study region.