外源碳和氮输入对降水变化下土壤呼吸的短期影响

利用野外原位小区控制试验，模拟研究了降水变化下草地生态系统土壤呼吸对外源碳和氮输入的响应.在2014年，以内蒙古锡林河流域温带典型草原为研究对象，测定了增加降水处理（CK）、增加降水配施氮肥处理CN，2.5 g·（m²·a）^-1]、增加降水配施碳源处理CG，24 g·（m²·a）^-1]和增加降水配施氮肥和碳源处理CNG，2.5 g·（m²·a）^-1+24 g·（m²·a）^-1]下土壤呼吸的变化，并分析了土壤呼吸与土壤温度、土壤水分、土壤可溶性有机碳（DOC）、土壤微生物量碳（MBC）之间的关系.结果表明，在自然降水较多的第一次增加降水（FWE）阶段，CG处理和CNG处理168 h土壤CO₂累积通量显著增加，而CN处理168 h土壤CO₂累积通量无显著变化，并且CG处理和CNG处理土壤MBC含量显著高于CK处理和CN处理，同时，该阶段平均CO₂释放速率与土壤MBC含量正相关（P<0.05）.与FWE阶段相比，无自然降水的第二次增加降水（SWE）阶段各处理168 h土壤CO₂累积释放量显著降低，并且各处理MBC含量也显著降低（P<0.05），仅有土壤DOC含量显著增加（P<0.05），CG处理和CN处理168 h土壤CO₂累积通量显著降低（P<0.05）.两个降水阶段土壤呼吸速率与土壤温度或土壤体积含水量均有显著的正相关性（P<0.05）.因此，自然降水的分布对土壤水分的影响调控着外源氮和碳对半干旱草地生态系统土壤呼吸的作用效应.

Effects of Short-term Exogenous Nitrogen and Carbon Input on Soil Respiration Under Changing Precipitation Pattern

The responses of soil respiration to exogenous carbon (C) and nitrogen (N) inputs under changing precipitation patterns were explored via in-situ field experiments. In 2014, a typical temperate grassland on the Xilin River of Inner Mongolia was taken as the research site, and soil respiration was measured in the following treatments:addition of water alone (CK), addition of water + N fertilizerCN, 2.5 g·(m²·a)^-1], addition of water + labile CCG, 24 g·(m²·a)^-1], and addition of water + N fertilizer+ labile CCNG, 2.5 g·(m²·a)^-1+24 g·(m²·a) ^-1], and the correlations of soil respiration with soil temperature, soil moisture, soil dissolved organic C (DOC), and soil microbial biomass C (MBC) were analyzed. During the first water application event (FWE) with the frequency of natural precipitation, cumulative CO₂ efflux over 168 hours significantly increased in the CG and CNG treatments, whereas there was no such change in the CN treatment. In addition, soil MBC contents in the CG and CNG treatments were significantly higher than that in the CK and CN treatments, and the correlation of average soil respiration rate with soil MBC content among these treatments was positively significant (P<0.05). In contrast with during the FWE, cumulative CO₂ efflux over 168 hours and soil MBC content significantly decreased during the second water application event (SWE) with no natural precipitation (P<0.05), whereas soil DOC content significantly increased (P<0.05). The cumulative CO₂ efflux over 168 hours significantly decreases in the CN and CG treatments (P<0.05).During both the water application events, soil respiration rate had a positive relationship with soil temperature and soil volume water content (P<0.05). Therefore, it is proposed that the distribution of natural precipitation influences soil water content, which controls the effects of exogenous C and N on soil respiration in semiarid grassland ecosystems.