刺槐林凋落物输入量变化对土壤有机碳的影响

Effects of litter input changes on soil organic carbon in Robinia pseudoacacia forest

【目的】分析刺槐林凋落物输入量变化对土壤有机碳含量的影响,以探明其调控机制,为预测全球变化背景下土壤碳动态提供科学依据。【方法】2018年3月-2019年3月,在黄土高原中部,选择林龄15年的典型人工刺槐林开展野外试验,设置对照(地上凋落物输入量无变化)、地上凋落物完全去除和加倍3个处理,采集0~10和10~20 cm土层的土壤样品,测定不同处理的土壤温度、含水量、有机碳、易氧化有机碳、顽固性有机碳、微生物生物量碳含量以及土壤呼吸速率,并用结构方程模型对土壤有机碳与土壤呼吸速率、微生物生物量碳之间的关系进行了分析。【结果】在0~10 cm土层,与对照相比,地上凋落物去除处理土壤温度在2018年6,9和12月份均显著增加,而在2019年3月份无显著差异;地上凋落物加倍处理土壤温度在整个试验期间与对照相比均无显著差异。在2018年6月和9月,土壤含水量在3个凋落物处理间均无显著差异;而在2018年12月,与对照相比,凋落物去除处理0~10 cm土层土壤含水量显著降低了24.44%,而地上凋落物加倍处理无显著变化;在2019年3月,3个凋落物处理土壤含水量差异显著。2019年3月,在0~20 cm土层,与对照相比,凋落物加倍处理中土壤有机碳、易氧化有机碳、顽固性有机碳含量均无显著变化,而地上凋落物去除处理的土壤有机碳、易氧化有机碳、顽固性有机碳含量均明显增加且总体差异达显著水平。在0~10 cm土层,与对照相比,地上凋落物加倍处理仅在2018年6月显著降低了土壤微生物生物量碳含量;凋落物去除处理土壤微生物生物量碳含量在2018年6月显著降低了71.96%,而在2018年9月和12月分别显著增加了101.59%和120.27%。对照和地上凋落物加倍、去除处理的土壤呼吸速率分别为1.41,1.84和1.32μmol/(m^(2)·s)。结构方程模型表明,土壤呼吸速率和土壤微生物生物量碳含量能解释土壤有机碳41%的方差变异,且土壤有机碳与土壤微生物生物量碳呈显著正相关关系,而与土壤呼吸速率呈极显著负相关关系。【结论】在黄土丘陵区,短期去除凋落物有利于土壤有机碳的积累,而凋落物加倍处理则对其无显著影响,这可能与微生物的碳储存过程及土壤呼吸的碳释放过程有关。

【Objective】The effect of Robinia pseudoacacia litter input amount on soil organic carbon content was analyzed to provide basis for predicting soil carbon dynamics under the background of global change.【Method】During March 2018-March 2019,a typical artificial Robinia pseudoacacia forest at the age of 15 years in the middle of Loess Hilly Region was selected to carry out field experiments.Three groups of control(CK),aboveground litter removal(NL)and double aboveground litter(DL)were established and soil quarterly samples were collected at two soil layers(0-10 and 10-20 cm).Soil temperature(ST),soil water content(SWC),soil organic carbon(SOC),labile organic carbon(LOC),recalcitrant organic carbon(ROC),microbial biomass carbon content(MBC)and soil respiration rate(SR)were determined,and the relationships between SOC,MBC and SR were analyzed by structural equation model.【Result】In the 0-10 cm soil layer,compared with CK,ST of NL increased significantly in June,September and December 2018,but there was no significant difference in March 2019.There was no significant difference in ST between DL and CK during the whole test period.In June and September 2018,there was no significant difference in SWC among the three treatments.In December 2018,SWC of 0-10 cm layer was significantly reduced by 24.44%in NL compared with CK,but there was no significant change in DL.In March 2019,in the 0-20 cm soil layer,contents of SOC,ROC and LOC in DL had no significant changes compared with CK,while those in NL increased significantly.Compared with CK,MBC in DL was significantly reduced only in June 2018,MBC in NL was significantly reduced in June 2018 by 71.96%,while it increased in September and December 2018 by 101.59%and 120.27%in comparison to CK.SR were 1.41,1.84 and 1.32μmol/(m^(2)·s)in CK,DL and NL,respectively.The structural equation model showed that SR and MBC could explain 41%variance of SOC.SOC was positively correlated with MBC and negatively correlated with SR.【Conclusion】In Loess Hilly Region,short-term litter removal is beneficial to the accumulation of SOC,while litter doubling treatment has no significant effect,which may be related to carbon storage of microorganisms and carbon release process of soil respiration.