间伐和林下植被剔除对毛竹林土壤氮矿化速率及其温度敏感性的影响

选择中亚热带毛竹人工林为研究对象,利用野外原位和室内培养相结合的方法,探讨不同间伐强度(25%间伐、50%间伐)和林下植被剔除对土壤氮矿化速率及其温度敏感性的影响。结果表明,25%间伐显著增加土壤氨化速率(P0.01),但降低硝化速率(P0.01);50%间伐显著增加土壤硝化速率(P0.01),而林下植被剔除显著降低土壤硝化速率(P0.01)。相关分析的结果表明,土壤氨化速率与有机碳(SOC)、全氮(TN)及全磷(TP)含量呈显著负相关关系;硝化速率与SOC、含水量(SWC)呈显著正相关关系,与铵态氮(NH~+_4-N)含量呈显著负相关关系。随着温度的升高,不同处理下的氨化速率均显著增加(P0.01),而硝化速率显著降低(P0.01)。25%间伐显著降低土壤净氮矿化和氨化过程的Q_(10)值,对硝化过程的Q_(10)值影响不显著;50%间伐对氨化和硝化过程的Q_(10)值影响均不显著;林下植被剔除对氨化过程的Q_(10)值影响不显著,但显著增加硝化过程的Q_(10)值。不同处理下的土壤氮矿化过程的Q_(10)值介于1.17—1.36之间。25%间伐和林下植被保留有利于毛竹林土壤氮素的供给。

Effects of thinning and understory removal on soil nitrogen mineralization rate and temperature-sensitivity in a moso-bamboo plantation

Nitrogen (N) is an essential element for plant growth, and only inorganic N can be directly absorbed by plants. Thus N mineralization and its temperature sensitivity are of significance to the biogeochemical cycle and ecosystem function. In the present study, field experiments in combination with thermostatic cultivation were conducted to investigate the effects of thinning intensities[25%thinning (25%Th) and 50%thinning (50%Th)] and understory removal (UR) on soil N mineralization and its temperature sensitivity in Moso plantation. The results showed that 25%Th significantly increased the soil N ammonification rate (P < 0.01), but it decreased the nitrification rate (P < 0.01). By contrast, 50%Th and UR had significant effects on the nitrification rate, but not on the ammonification rate. Specifically, 50%Th remarkably increased the nitrification rate (P < 0.01), whereas UR decreased the nitrification rate (P < 0.01). Correlation analysis showed that there were negative correlations between the ammonification rate and soil organic carbon content (SOC), total nitrogen content and total phosphorus content; the soil nitrification rate showed positive correlations with SOC and soil water content, but negative correlation with ammonium nitrogen (NH₄⁺-N) content. Q₁₀ was used to indicate the correlation between temperature and N mineralization. 25%Th decreased the Q₁₀ of net N mineralization and ammonification, while UR increased that of nitrification. In general, Q₁₀ under different treatments were 1.17 and 1.36. In conclusion, 25%Th and understory conservation are beneficial to soil N supply in Moso plantation.