外源碳输入对中亚热带森林深层土壤碳矿化和微生物决策群落的影响

在陆地生态系统中,深层土壤是重要的有机碳库.外源碳输入可改变土壤有机碳(SOC)矿化速率(激发效应),进而影响土壤碳排放.然而深层土壤对外源碳输入的响应程度和方向如何还不清楚,引起激发效应的机理尚不明确.本文利用¹³C标记葡萄糖添加试验,分析亚热带森林不同层次SOC矿化的激发作用,并通过微生物决策群落(r-K策略者)的相对变化来探讨激发效应的机理.结果表明: 深层土壤矿化速率显著低于表层土壤,添加标记葡萄糖后能增加所有层次土壤原有SOC的矿化(正激发效应),但是深层土壤的激发效应强度(156%)显著高于表层土壤(45%).葡萄糖添加显著降低了各层次土壤微生物的最大比生长速率,表明r策略者相对比例下降而K策略者相对比例增加.推测SOC矿化的正激发效应主要由K策略者的相对比例变化引起.此外,葡萄糖添加后可溶性有机碳和可溶性氮的比值在深层土壤中(76.03)显著高于表层土壤(13.00),暗示深层土壤存在更为强烈的氮限制作用.深层土壤微生物为获取氮源,可能会加剧对原有SOC的矿化,进而产生更强烈的激发效应.深层土壤SOC矿化受碳源和氮源的限制,更容易受外源碳输入的影响,对未来气候变化也更敏感.

Effects of labile carbon addition on organic carbon mineralization and microbial growth strategies in subtropical forest soils.

Deep soil is a major organic carbon pool in terrestrial ecosystems. Labile carbon inputs can stimulate soil organic carbon (SOC) mineralization, causing priming effect, which in turn affects soil carbon emission. However, the mechanism of the priming effect in deep soil is still unclear. Therefore, to know how deep soil responds to labile carbon addition is essential for better understanding of deep soil carbon dynamics. In this study, we incubated three profiled soils (0-10 cm, 10-30 cm, 30-60 cm) from a subtropical forest with ¹³C-labeled glucose addition to analyze the priming effects and their relationship with the shift of microbial communities (r-K strategies). The results showed that glucose addition increased SOC mineralization in all soil layers, causing positive priming effects. But glucose addition significantly decreased the specific growth rates of microorgani-sms for all soils, indicating a relative decrease of r-strategists and a relative increase of K-strategists in the microbial community. Thus, we inferred that the positive priming effect was possibly attributed to the increased contribution of K-strategists. The priming effect in deep soil (156%) was significantly higher than that in surface soil (45%). Meanwhile, the ratio of dissolved organic carbon (DOC) and dissolved nitrogen (DN) after glucose addition was significantly higher in deep soil (76.03) than that in surface soil (13.00). These results suggested that there existed a stronger nitrogen limitation in deep soil. The microorganisms in deep soil tended to decompose recalcitrant SOC to acquire nitrogen, which then caused a greater priming effect. Overall, deep soil was more vulne-rable to labile carbon addition due to its carbon and nitrogen limitations, and hence was likely more sensitive to climate change in the future.