氮添加下典型草原凋落物质量和土壤酶活性对凋落物分解速率的影响

doi:10.11686/cyxb2019417

摘要/Abstract

摘要： 近年来,全球大气N沉降量持续增加,影响了陆地生态系统碳循环的关键过程,而凋落物分解是碳循环的关键过程之一。本研究在内蒙古温带典型草原设置了不同水平的N添加试验,通过测定不同分解时期凋落物的分解速率、质量指标和土壤酶活性,探讨N添加对凋落物分解的影响。结果表明:凋落物累积干重损失率主要发生在生长季时期,占整个研究阶段的91.3%,且N添加处理显著增加了生长季的干重损失率,而降低了非生长季的干重损失率。第一年生长季,N添加通过提高β-葡萄糖苷酶活性,降低纤维素、单宁含量从而促进了凋落物分解。第一年非生长季,低N处理促进了脲酶活性,降低木质素/N,促进分解,高N抑制了多酚氧化酶的活性,进而降低了木质素的分解速率。第二年生长季,高N处理促进了亮氨酸氨肽酶活性,提高N/P,利于凋落物分解。整个分解过程中,N添加降低了凋落物单宁和纤维素含量,而木质素含量则呈现增加趋势。养分释放特征表现为C的连续释放,P的释放-固定趋势。此外,凋落物中Ca、Mn、N的含量随分解时间增高,表现出富集现象。因此,N添加通过改变凋落物质量和土壤酶活性而对凋落物分解过程产生影响,且不同时期主导因子不同。研究结果为不同水平N沉降对草原碳循环关键过程提供了理论依据。

关键词: 草地生态系统, 氮添加, 凋落物分解, 凋落物质量, 土壤胞外酶

Abstract: Global atmospheric nitrogen (N) deposition has increased in recent years, affecting key processes of the carbon (C) cycle in terrestrial ecosystems. Litter decomposition is one of the key processes in the carbon cycle. We conducted a litter bag experiment at N addition rates ranging from 0 to 25 g·m^-2·yr^-1 in the typical temperate grasslands of Inner Mongolia. The effects of N addition on decomposition of litter samples were investigated by measuring the decomposition rate, quality index and soil enzyme activity of litter in different stages of decomposition. Our results showed that dry weight loss of litter mainly occurs in the growing season, which accounts for 91.3% of the total mass loss. N addition increased the rate of dry weight loss in the growing season, while decreasing the rate of dry weight loss in the non-growing season. N addition promoted litter decomposition by increasing the activity of β-glucosidase and reducing the content of cellulose and tannin in the first growing season. In the first non-growing season, low-N treatments enhanced urease activity, decreased lignin:N ratio, and accelerated decomposition, while high-N treatments inhibited the activity of polyphenol oxidase, thereby reducing the decomposition rate of lignin. High-N treatment promoted leucine aminopeptidase activity, improved N:P ratio, and facilitated the decomposition of litter in the second growing season. During the whole decomposition process, N addition reduced the content of tannin and cellulose, while showing a trend toward increased lignin content. This result may indicate that during decomposition, litter C showed a release pattern while phosphorus showed an immobilization-release pattern. In addition, the contents of calcium, manganese and N in litter increased with the progression of decomposition, showing an enrichment phenomenon. Our results indicate that the quality of litter samples and soil enzyme activity were the main factors influencing litter decomposition, and the dominant factors differ at different stages of the decomposition process. These results will provide a theoretical basis for understanding of the key processes of the grassland carbon cycle under different levels of N deposition in the future.

Key words: grassland ecosystem, N addition, litter decomposition, litter quality, soil enzyme

岳可欣, 龚吉蕊, 于上媛, 宝音陶格涛, 杨波, 王彪, 朱趁趁, 张子荷, 矢佳昱. 氮添加下典型草原凋落物质量和土壤酶活性对凋落物分解速率的影响[J]. 草业学报, 2020, 29(6): 71-82.

YUE Ke-xin, GONG Ji-rui, YU Shang-yuan, BAOYIN Taogetao, YANG Bo, WANG Biao, ZHU Chen-chen, ZHANG Zi-he, SHI Jia-yu. Effects of litter quality and soil enzyme activity on litter decomposition rate in typical grassland subject to nitrogen addition[J]. Acta Prataculturae Sinica, 2020, 29(6): 71-82.

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