降雨隔离和温度增加对杉木幼林土壤可溶性碳氮的影响

土壤可溶性碳氮在森林土壤碳循环和养分循环中起到重要作用,因其对气候变化高度敏感且可被微生物直接利用.本研究通过在2年生杉木人工林内设置隔离50%降雨处理(P)、增温5 ℃+隔离50%降雨处理(WP),利用张力测渗计野外原位收集土壤溶液,研究降雨和温度变化对不同深度土壤可溶性碳氮浓度的影响.结果表明: 降雨和温度变化没有改变土壤可溶性有机碳(DOC)浓度的季节变化,土壤溶液DOC浓度在10月最高.降雨和温度变化增加了不同土层土壤溶液DOC浓度,60 cm处增加量最大,与对照相比,P和WP处理土壤溶液DOC浓度的增加幅度分别为30.4%～88.7%和32.8%～137.6%,10 月的差异值最大,对照土壤溶液DOC浓度随土壤深度增加而降低,但降雨和温度变化后各土层间土壤溶液DOC浓度没有显著差异.WP处理土壤溶液NO₃^--N浓度大幅增加,增加幅度为221.1%～931.0%.在未来全球变化背景下,亚热带地区降雨减少将增加土壤通透性和细根向深层土壤的生长,促进土壤微生物活性和有机质分解,可能增加本地区土壤有机碳氮淋溶流失,而温度增高将加剧碳氮流失风险.

Effects of precipitation exclusion and warming on soil soluble carbon and nitrogen in a young Cunninghamia lanceolata plantation

Soil soluble carbon and nitrogen play important roles in soil carbon and nutrient cycles and are highly sensitive to climate change, as they can be directly used by microorganisms. We used Tension Lysimeter to collect soil solution in 50% precipitation exclusion (P) and warming (5 ℃) plus 50% precipitation exclusion (WP) treatments in a 2 year-old Cunninghamia lanceolata plantation in subtropics, to examine the effects of precipitation and temperature on soil soluble carbon and nitrogen concentrations in soil profile. Results showed that neither P treatment nor WP treatment changed seasonal dynamics of soil dissolved organic carbon (DOC) concentration, with maximum value at October among all treatments. DOC concentration was increased in both P and WP treatments in the whole soil profile, especially in 60 cm soil depth. Compared with the control, DOC concentration was increased by 30.4%-88.7% and 32.8%-137.6% in P and WP treatments, respectively, with the most obvious difference being found in October. DOC concentration was decreased with the increases of soil depth in the control, but no significant difference among different soil layers were found in P and WP treatments. NO₃^--N concentration was increased by 221.1%-931.0% in WP treatment. Therefore, precipitation reduction might increase losses of C and N from soil solution in subtropical forest, due to improvement of soil permeability by the increases of fine roots grown into deep soil, which might stimulate soil microorganism activities and soil organic matter decomposition. Furthermore, warming would exacerbate the risk of C and N losses.