| Climate change is truly a global issue, which has got unprecedented concern and awareness across the international community. The climate warming and changing precipitation pattern, as two remarkable features of climate change, exert a strong effect on terrestrial ecosystem carbon cycle and carbon sequestration. Hence, understanding the feedback of soil carbon in forest ecosystems to climate change is necessary when we assess the role of soil carbon in sink-source transition. Quantifying the response magnitudeof soil respiration to climate warming and precipitation pattern change will be helpful in evaluating soil carbon balance and budget. In this study, a field experiment based ona randomized complete block design was conducted with soil warming (W) and throughfall exclusion (TE)(the factorial combinations of soil warming with throughfall exclusion) in a temperate oak (Quercus aliena var. acuteserrata) forest in centre China. Combined with plot trenching, we examined how soil warming and throughfall exclusion influence the soil respirations from different components and corresponding temperature sensitivities. Phospholipid fatty acids (PLFAs) analysis was used to characterize soil microbial community, and its response to soil warming and throughfall exclusion was furtheranalyzed. The main results are as follows:(1) Soil temperature and moisture at5cm were significantly altered by simulated soil warming and throughfall exclusion. Soil warming through infrared heaters significantly increased soil temperature by1.43-1.93℃, with higher increment in daily mean maximum soil temperature compared to mean minimum temperature. Besides, diurnal soil temperature increased greater than that in night. Enhancement of soil temperature resultedfrom experimental warming in early spring was higher than those in other seasons. Soil moisture was significantly decreased by5.7-9.5v/v under soil warming and throughfall exclusion treatments, with the maximum reduction in June. Therefore, increased tempe rature and decreased precipitation can be imitated through infrared heater and throughfall exclusion.(2) Soil warming and throughfall exclusion significantly increase total soil respirations. Significant interactive effects relative to main ones of soil warming and throughfallexclusion were found on soil respirations. Soil warming significantly elevated soil respirations by35.3%in ambient precipitation plots, with23.1%and44.3%increments inungrowing and growing season, respectively. However, soil respirations were not significantly affected (+14.2%,-0.65%) by soil warming in both growing and ungrowing season under throughfall exclusion. Throughfall exclusion significantly increased soil respirations by20.5%under ambient temperature, with significant increases (31.6%) in growingseason. The finding from the data of continuous19months indicated that soil warming and throughfall exclusion can stimulate soil respirations in growing season. Besides, soil warming also increased soil respirations in ungrowing season. Increases of soil respiration by treatments are mainly resulted from the elevated soil microbial biomass carbon and soil organic carbon. The study indicates that regional climate warming and precipitation reduction may promote the emission potencial of soil carbon and act as a positive feedback to cliamte change.(3) There were significant differences in the response patterns of soil heterotrophicrespiration (RH) and autotrophic respiration (RR) to soil warming and throughfall exclusion. RHwas signficantly affected by the main effect of soil warming. RHwas significantly elevated by27.8%during the whole period, and signficantly increased by28.2%and27.4%in growing and ungrowing season, respectively. The enhancement of RHwaspositively correlated with soil microbial carbon and nitrogen. Throughfall exclusion decreased RHby2.8%in ambient temperature, without significant difference in both growing and ungrowing season. However, RHwas stimulated by16.9%under througfall exclusion with warming, with higher increases in growing season (22.6%) than that in ungr owing season(9.3%). The results implied that RHis more sensitive to soil temperature than soil water availability changes.Warming significantly interacted with the throughfall exclusion in terms of their effects on RR.Soil warming enhanced RRby20.1%and73.2%under ambient preciptation in ungrowing and growing season,respectively, but reduced it by28.6%and2.0%under precipitation exclusion treatment in ungrowing and growing season. RRwas increased by23.7%and89.2%by throughfall exclusion in ungrowing and growing season under ambient temperature, respectively. Increases of RRinduced by warming and decreased precipitation were positively correlated to fine root biomass. Our experiment indicatesthat increases of soil respirations under througfall exclusion treatment were mainly induced by the enhancement of autotrophic respiration, while that under soil warming wasresulted from both RHand RR.(4) There were significant differences in the response of temperature sensitivity (Q10) for soil respirations and different components to soil warming and throughfall exclusion. Q10of soil total respirations was significantly influenced by the main effect of warming and its interaction with throughfall exclusion. Throughfall exclusion significantly increased Q10of RS(2.73) in ambient temperature, but had no significant effects on it(2.64) under warming treatment. Q10of RSunder warming treatment in ambient precipitation was significantly higher than that under ambient temperature (2.22). Both soil warming and throughfall exclusion had no significant effects on Q10of RH. Q10of RRwassignificantly elevated by soil warming and throughfall exclusion and their interaction(3.77,3.52and3.69). RRhad a significantly greater Q10than those of RSand RHunder all treatments. Moreover, Q10of all respiration components increases with elevated soil temperature,which implies that Q10of soil respiration may increase under global warming.(5) Response of soil microbial community to soil warming and precipitation varieswith trench treatment. Interactive effects of soil warming, throughfall exclusion and tre nch significantly influenced microbial PLFA relative to main effects of single environmental factor. In untrenched plots, single factor of soil warming and throughfall exclusionsignificantly elevated microbial total PLFA, bacterial PLFA, fungal PLFA, and gram-negative bacterial PLFA by53.7-72.6%. However, both warming and decreased precipitation had no effects on microbial PLFA in trenched plots. These findings indicate that thesensitivity of microbial PLFA to climate change in untrenched plots was greater than that in trenched plots. Besides, trench treatment resulted in significant reduction in microbial PLFA under throughfall exclusion. In terms of microbial community structure, however, combination of soil warming and throughfall exclusion significantly decreased bacterial and gram-positive bactierial relative abundance in untrenched plots, which may beexplained by the dependence of bacterial on soil water availability. In trenched plots,soil warming significantly increased gram-positive bacterial abundance under ambient precipitation, while combination of soil warming and throughfall exclusion reduced abundance of gram-negative bacterial, but increase abundance of actinomycosis. |
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