对马尾松人工林凋落物进行了12个月的模拟氮沉降试验[对照CK,0 kg N/(hm2·a)]、低氮[(LN,50 kg N/(hm2·a)]、中氮[MN,100 kg N/(hm2·a)]和高氮[HN,150 kg N/(hm2·a)],研究了凋落物分解特征、土壤微生物活性及其对模拟氮沉降的响应。结果 表明:(1)随着氮浓度的增加,马尾松凋落物的分解系数呈先增加后降低趋势,MN处理下马尾松凋落物的分解系数达到最高,之后有所下降; 与对照相比,LN,MN,HN凋落物分解系数分别增加了15.36%,56.89%和12.97%;(2)模拟氮沉降促进了微生物量碳、氮、磷,相同月份微生物量碳、氮、磷均随着氮浓度的增加呈先增加后降低趋势,在MN处理下微生物量碳、氮、磷达到最大,HN处理下微生物量碳、氮、磷有所降低;(3)模拟氮沉降增加了大部分土壤酶的活性,HN处理下有所抑制,土壤中与碳(纤维素酶、纤维二糖水解酶、β-葡萄糖苷酶和β-木糖苷酶)、氮(硝酸还原酶)、磷(酸性磷酸酶和碱性磷酸酶)元素循环相关的酶均随着时间的增加呈增加趋势,相同月份在MN处理下达到最大,HN处理下有所降低。(4)不同氮处理下土壤微生物活度、微生物代谢熵、自养呼吸、异养呼吸、总呼吸变化趋势基本保持一致,随着时间的增加呈增加趋势,相同月份在MN处理下达到最大,HN处理下有所降低;(5)相关性分析表明纤维素酶、β-葡萄糖苷酶、β-木糖苷酶、硝酸还原酶与凋落物分解系数呈显著正相关(p<0.05),土壤微生物量碳、氮、微生物活度、微生物代谢熵和微生物总呼吸与凋落物分解系数呈显著正相关; PCA排序表明:土壤微生物呼吸和土壤微生物代谢熵很大程度上反映了其微生物特性,其中土壤碳循环酶、微生物活度、土壤微生物代谢熵对凋落物分解贡献最大。
This study was conducted in Pinus massoniana plantations to measure soil microbial activities and the effects of nitrogen deposition on litter decomposition. Nitrogen addition experiments were carried out within the forest in 2017. Four N addition treatments such as control, No N [CK, 0 kg N/(hm2·a)], low N [LN, 50 kg N/(hm2·a)], medium N [MN, 100 kg N/(hm2·a)] and High N [HN, 150 kg N/(hm2·a)] with three replicates were established in Pinus massoniana plantations. The results showed that:(1)simulated nitrogen deposition had a strong effect on litter decomposition and soil microbial activities in Pinus massoniana plantations; the litter decomposition coefficient increased at first and then decreased, and the largest litter decomposition coefficient was found in treatment of MN; the litter decomposition coefficients of treatments of LN, MN and HN increased by 15.36%, 56.89% and 12.97%, respectively, compared with CK;(2)simulated nitrogen deposition promoted soil microbial biomass carbon, nitrogen, phosphorus, which increased at first and then decreased, and the highest soil microbial biomass was observed in the treatment of MN;(3)simulated nitrogen deposition increased soil enzyme activity, soil enzyme activity was inhibited in the treatment of HN; the soil enzyme activity related to carbon, nitrogen, phosphorus increased at first and then decreased, and the highest soil enzyme activity was found in the treatment of MN;(4)soil microbial activity, microbial metabolic entropy, autotrophic respiration, heterotrophic respiration, total respiration showed the same change trend, which increased at first and then decreased, and the greatest values of these indicators were found in the treatment of MN;(5)correlation analysis indicated that there was a significant positive correlation between the decomposition coefficient of litter and the soil microbial biomass carbon, nitrogen, microbial activity, microbial metabolic entropy and total microbial respiration; soil microbial respiration and soil microbial metabolic entropy significantly reflected their microbial characteristics, among which soil carbon cycle enzyme, microbial activity and soil microbial metabolic entropy had the important contribution to the decomposition of litter.
