We examined the effects of nitrogen addition (0, 30, 60, and 90 kg N·hm-2·a-1) to soil microbial biomass, enzyme activities, and nutrient contents of the Pinus massoniana-Quercus variabilis mixed plantations in the Three Gorges Reservoir Area, with the aim to provide a theoretical basis for predicting soil carbon dynamics under the background of continuously increasing atmospheric nitrogen deposition in this area. The results showed that nitrogen addition at all levels led to a significant increase of the contents of organic carbon, total nitrogen, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) in the forest soil, while a decrease of soil pH-value, and no significant effect on the total phosphorus content. Nitrogen addition increased the activities of β-1-4 glucosidase (BG), cellobiose hydrolase (CB), acid phosphatase (AP), N-acetylglucosaminosidase (NAG) and peroxidase (POD), while inhibited that of polyphenol oxidase (PPO). There was a significant seasonal variation in soil oxidase activities, in which the peroxidase activity was higher in May and August, and the polyphenol oxidase activity was the highest in August. Soil enzyme activities were significantly correlated with soil moisture and the contents of soil nutrients, MBC, MBN, and MBP. The variation of soil enzyme activities was caused by the comprehensive effects of multiple factors. The redundancy analysis (RDA) showed that the contents of total soil nitrogen and MBC were the main environmental factors driving soil enzyme activities. The continuous increase of atmosphere nitrogen deposition would lead to soil acidification and promote the turnover of soil organic carbon and nutrient cycling in the Pinus massoniana-Quercus variabilis mixed plantations of the study area.
选择三峡库区的马尾松-栓皮栎混交林,分析不同浓度氮添加(0、30、60、90 kg N·hm-2 ·a-1)对土壤微生物生物量、酶活性和养分含量的影响,为在大气氮沉降持续增加的背景下预测该地区森林土壤碳动态提供科学依据。结果表明: 各氮添加处理下土壤有机碳、全氮和微生物生物量碳、氮、磷均显著提高,土壤pH值下降,全磷含量无显著变化。氮添加提高了各季节土壤中β-1-4葡萄糖苷酶、纤维二糖水解酶、酸性磷酸酶、N-乙酰氨基葡萄糖苷酶和过氧化物酶的活性,但抑制了多酚氧化酶的活性。土壤氧化酶活性存在显著的季节差异,其中过氧化物酶活性在5月、8月较高,多酚氧化酶活性在8月最高。土壤酶活性与土壤含水量、养分含量及微生物生物量碳、氮、磷存在显著的相关性,酶活性变化是多因子综合作用的结果。冗余分析表明,全氮和微生物生物量碳是驱动土壤酶活性的主要环境因子。氮沉降的持续增加会导致土壤酸化,同时也促进了当地马尾松-栓皮栎混交林土壤有机碳的周转和养分循环。.
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