间伐对马尾松人工林根际土壤氮含量及酶活性的影响

【目的】间伐是生产实践中常见的一种干扰,研究间伐对马尾松人工林根际土壤氮含量及相关酶活性的影响,为马尾松人工林的可持续经营提供科学参考。【方法】以南京市溧水区林场30年生马尾松人工林为研究对象,采用抖落法收集根际土,测定4种间伐强度(强度(65%)、中度(45%)、弱度(25%)、对照(未间伐))下根际土壤不同形态氮含量及氮循环相关酶活性,并分析其与土壤理化性质之间的关系。【结果】弱度间伐显著增加了根际土壤铵态氮含量,而强度间伐下则显著降低; 根际土壤全氮、硝态氮和可溶性有机氮含量在各间伐强度下均表现为:中度>对照>弱度>强度; 根际土壤微生物生物量氮和碱解氮均在弱度和中度间伐下显著升高。弱度和中度间伐显著降低根际土壤脲酶活性,而显著增加根际土壤亚硝酸酶活性; 间伐对根际土壤蛋白酶、硝酸还原酶和羟胺还原酶活性的影响不显著,表明脲酶和亚硝酸酶对间伐的响应更敏感,可作为土壤氮变化的指标。除硝酸还原酶活性以外,根际土壤中其余4种氮循环相关酶活性以及不同形态氮素含量均高于非根际土壤,表现出明显的正根际效应。此外,根际土壤不同形态氮素含量及相关酶活性与含水量、pH密切相关。【结论】间伐强度对根际土壤不同形态氮和酶活性有显著影响,总体来看,弱度和中度间伐能改变土壤含水量和酶活性,有利于土壤氮素的积累,可将其作为间伐强度的参考指标。

Effects of thinning on nitrogen contents and enzyme activities of rhizosphere soil in Pinus massoniana plantations

Abstract: 【Objective】The aim of this study was to investigate the effects of thinning intensity on soil nitrogen content and the soil nitrogen-cycle enzyme activities in the rhizosphere soil of Pinus massoniana plantations, which could provide reference data for the sustainable management of P. massoniana plantations.【Method】Soil samples were collected from the rhizosphere of P. massoniana plantations, which were thinned at different intensities(control(CK), 0%; light intensity thinning(LIT), 25%; moderate intensity thinning(MIT), 45%; and heavy intensity thinning(HIT), 65%), to study the effect of thinning on soil nitrogen, and to assess the associations among soil nitrogen, enzyme activities, and physicochemical properties.【Result】 Compared to that in CK, ammonium nitrogen content of rhizosphere soil was significantly increased in LIT, but was decreased in HIT. The total nitrogen, nitrate nitrogen, and dissolved organic nitrogen contents of rhizosphere soil were in the order of MIT>CK>LIT>HIT. Both microbial biomass nitrogen and alkali-hydrolyzable nitrogen contents of rhizosphere soil increased in LIT and MIT. LIT and MIT significantly decreased urease activity of rhizosphere soil, but increased the nitrite reductase activity. The effects of thinning on soil protease, nitrate reductase, and hydroxylamine reductase activities were not significant, indicating that urease and nitrite reductase are more sensitive to thinning, and may serve as indicators of soil nitrogen dynamics. In addition to nitrate reductase activity, the other four nitrogen-cycle enzyme activities and the nitrogen content of rhizosphere soil were higher than those of the bulk soil, indicating a positive rhizosphere effect. Moreover, soil nitrogen content and enzyme activities were closely correlated with the soil water content and pH.【Conclusion】Thinning had significant effects on soil nitrogen content by changing soil water content and enzyme activities. We recommend LIT and MIT as efficient management practices for improving the efficiency of soil nitrogen use in P. massoniana plantations.