东北地区4种林分土壤呼吸及温、湿度敏感性对氮添加的短期响应

全球变化中氮沉降日益严重,已对森林生态系统的各个过程产生了重要影响。因此,通过研究氮添加对森林生态系统土壤碳输出的影响,对分析全球变化背景下土壤碳吸存具有重要意义。对黑龙江省帽儿山实验林场白桦(Betula platyphylla)次生林,以及水曲柳(Fraxinus mandschurica)、红松(Pinus koraiensis)、长白落叶松(Larix olgensis)人工林通过2年氮添加(对照(0 kg N hm~(-2) a~(-1)),低氮(50 kg N hm~(-2) a~(-1)),中氮(100 kg N hm~(-2) a~(-1))和高氮(150 kg N hm~(-2) a~(-1)))试验,测定根生物量密度、土壤微生物量碳浓度、土壤呼吸速率及温、湿度敏感性等指标,旨在探讨森林生态系统土壤呼吸对氮添加的短期响应。结果表明:(1)低氮处理对白桦和水曲柳林土壤呼吸速率影响不显著,但显著提高了红松和长白落叶松林土壤呼吸速率;水曲柳林分中高氮处理土壤呼吸速率显著降低于低氮和中氮处理,而其他林分高氮处理土壤呼吸速率仅显著低于低氮处理。(2)氮添加处理下,4种林分中林分土壤呼吸速率与根生物量密度呈极显著正相关,Pearson相关系数为0.81。(3)低氮处理下5 cm和10 cm处土壤呼吸温度敏感性系数Q_(10)值较CK处理分别提高了2.65%和3.12%,高氮处理较CK处理分别降低了6.29%和5.46%。但氮添加处理对土壤呼吸和土壤湿度间的相关性无影响。综上所述,阔叶林与针叶林土壤呼吸速率对氮添加的响应存在差异。根生物量密度是影响不同林分土壤呼吸对短期氮添加响应的主要因素,同时氮添加处理显著改变了土壤温度敏感性系数。

Short-term responses of soil respiration, temperature and humidity sensitivity to nitrogen addition in four forests of Northeast China

Nitrogen (N) deposition has been increasingly severe in global change, which had an important impact on various processes of forest ecosystems. Evaluating the effects of N addition on the output of soil carbon (C) in forest ecosystems was important for estimating the soil C sequestration to global change. A two-year N addition experiment was conducted with four different N addition levels, including the control (CK, 0 kg N hm^-2 a^-1), low N addition (LN, 50 kg N hm^-2 a^-1), medium N addition (MN, 100 kg N hm^-2 a^-1) and high N addition (HN, 150 kg N hm^-2 a^-1) levels, in four forests with different tree species compositions (i.e., Betula platyphylla, Fraxinus mandschurica, Pinus koraiensis, and Larix olgensis) in Maoershan Experimental Station of Heilongjiang Province. Root biomass density, soil microbial biomass C concentration, soil respiration rate, temperature and humidity sensitivity were measured to evaluate the responses of the soil respiration to N addition. (1) The soil respiration rate in P. koraiensis and L. olgensis stands increased significantly under LN treatment, while that were not affected in B. platyphylla and F. mandschurica stands. Compared with LN and MN treatments, the soil respiration rate under HN treatment were decreased significantly in F. mandschurica stand. The soil respiration rate under HN treatment was significantly lower than that of LN treatment in other stands. (2) The soil respiration rate was significantly positive correlation with root biomass density under N addition treatments. The Pearson''s correlation coefficient was 0.81. (3) Compared with the CK treatment, the soil temperature sensitivity coefficients (Q10) in the depth of 5 cm and 10 cm were increased by 2.65% and 3.12% under LN treatment, but that were decreased by 6.29% and 5.46% under HN treatment, respectively. But the soil respiration was not significantly correlated with the soil humidity after N addition. Thus the responses of the soil respiration of broad-leaved and coniferous forests were different after N addition. The root biomass density was the main factor affecting the responses of the soil respiration in different forests after short-term N addition. The soil temperature sensitivity coefficient was changed significantly by N addition treatments.