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半干旱区不同围封年限对草地土壤和微生物碳氮含量的影响
张强1, 邓军2, 毛瑾1, 朵莹1, 程杰3, 郭梁4,5
1.西北农林科技大学 草业与草原学院, 陕西 杨凌 712100;2.宁夏云雾山国家级 自然保护区管理局, 宁夏 固原 756000;3.国家林业和草原局西北调查规划设计院, 陕西 西安 710048;4.西北农林科技大学 水土保持研究所, 陕西 杨凌 712100;5.中国科学院 水利部 水土保持研究所, 陕西 杨凌 712100
摘要:
[目的] 探究半干旱区草地根际土壤碳氮及土壤微生物量碳氮对不同封禁年限响应特征,为半干旱草地生态系统物质循环研究以及生态系统养分限制判定等提供依据,并为确定合理围封年限提供科学参考。[方法] 以宁夏回族自治区固原市云雾山国家级自然保护区半干旱草原为研究对象,应用生态化学计量学方法对比分析放牧地与围封10,25,35 a样地根际土壤有机碳、全氮、硝态氮、铵态氮和土壤微生物量碳氮含量及其化学计量特征变化过程与规律。[结果] 围封显著增加了土壤碳氮含量,其最大值出现在封育25 a样地,随后下降。围封10,25 a和35 a样地土壤有机碳含量分别是放牧样地的1.37,1.83倍和1.38倍;总氮含量分别是放牧样地1.34,1.52倍和1.24倍。但土壤C:N随围封年限增加基本保持稳定,其值与土壤有机碳含量存在极显著相关,而与土壤总氮无明显相关性。与放牧样地相比,围封样地铵态氮含量随封育年限无明显变化,硝态氮含量和硝态氮:铵态氮比值则普遍下降,在围封25 a时最低。围封增加了土壤微生物量碳氮含量,围封10,25,35 a样地土壤微生物量碳含量较放牧地分别提高了20.5%,45.7%和15.1%;微生物量氮含量分别提高了24.7%,60.5%和40.9%。而微生物量C:N则随围封年限延长而下降,微生物量碳占土壤有机碳百分比对围封年限无响应。围封10,25 a样地与放牧地相比,微生物量氮占土壤总氮百分比和化学计量不平衡性(即土壤C:N与微生物量C:N比值)均无显著差异,但其值却在围封35 a样地显著增加。[结论] 围封措施能够显著提高半干旱退化草地土壤碳、氮养分,促进土壤微生物活动,有利于退化草地恢复,但封育时间过长则可能产生负效应,封育25 a是草地长期封育措施中一个较为合理的围封年限。
关键词:  围封年限  半干旱草地  土壤碳氮含量  微生物量  生态化学计量
DOI:10.13961/j.cnki.stbctb.2021.01.005
分类号:S812.2;S157.9
基金项目:国家重点研发计划项目“北方农牧交错带草地退化机理及生态修复技术集成示范”(2016YFC0500700);国家自然科学基金项目(41701606);西北农林科技大学青年英才培育计划(2452020009)
Impacts of Different Enclosure Ages on Soil and Microbial Carbon and Nitrogen Contents in Semi-arid Grasslands
Zhang Qiang1, Deng Jun2, Mao Jin1, Duo Ying1, Cheng Jie3, Guo Liang4,5
1.College of Grassland Agriculture, Northwest A&F University, Yangling, Shaanxi 712100, China;2.Administration Bureau of Ningxia Yunwushan National Nature Reserve, Guyuan, Ningxia 75600, China;3.Northwest Surveying Planning and Designing Institute of National Forestry and Grassland Administration, Xi'an, Shaanxi 710048, China;4.Institute of Soil and Water Conservation, Northwest A&F University, Yangling, Shaanxi 712100, China;5.Institute of Soil and Water Conservation, Chinese Academy of Science and Ministry of Water Resource, Yangling, Shaanxi 712100, China
Abstract:
[Objective] The response characteristics of carbon and nitrogen in rhizosphere soil of semiarid grasslands and soil microbial biomass to different years of grazing exclusion were studied to provide basic information for the study of the material cycle of semi-arid grassland ecosystems and the determination of ecosystem nutrient limits, and to determine reasonable grazing exclusion periods.[Methods] Taking the typical semi-arid grassland of Yunwushan National Nature Reserve in Guyuan City, Ningxia Hui Autonomous Region, as the research object, the ecological stoichiometric method was used to compare and analyze the variation process and rule of rhizosphere soil organic carbon, total nitrogen, nitrate nitrogen, ammonium nitrogen, and soil microbial biomass carbon and nitrogen content, as well as the stoichiometric characteristics of the grazing land and the sampled land enclosed for 10, 25, and 35 years.[Results] Enclosure treatment significantly increased the soil carbon and nitrogen content. The maximum values appeared in the plot enclosed for 25 years, after which the values declined. The soil organic carbon contents of the plots enclosed for 10, 25, and 35 years were 1.37, 1.83 times and 1.38 times of that of the grazing plot, and the total nitrogen contents were 1.34, 1.52, and 1.24 times of that of the grazing land, respectively. However, soil C:N remained stable with the increase in enclosure years. It was significantly correlated with soil organic carbon content but had no evident correlation with soil total nitrogen. Compared with that of the grazing plot, the ammonium nitrogen content of enclosed plots did not change significantly with the enclosure years, but the nitrate nitrogen content and the nitrate:ammonium nitrogen ratio generally decreased, with the lowest values at 25-year grazing exclusion. Enclosure significantly increased the soil microbial biomass carbon and nitrogen content. The soil microbial biomass carbon contents of the sample plots enclosed for 10, 25, and 35-years increased by 20.5%, 45.7%, and 15.1% compared with grazing land, while the microbial biomass nitrogen contents increased 24.7%, 60.5%, and 40.9%, respectively. The microbial biomass C:N value decreased with the extension of the enclosure period. The percentage of microbial biomass carbon in soil organic carbon did not respond to the enclosure period. Compared with grazing land, 10-year and 25-year grazing exclusion had no significant difference in the percentage of microbial biomass nitrogen in total soil nitrogen and the stoichiometric imbalance (i.e., the ratio of soil C:N to microbial biomass C:N), but the value significantly increased in 35-year grazing exclusion.[Conclusion] Enclosure measures can significantly improve soil carbon and nitrogen nutrients in semi-arid degraded grasslands, promote soil microbial activities, and facilitate the restoration of degraded grassland. However, a too long enclosure treatment may have a negative effect. Twenty-five years of enclosure is a reasonable enclosure period in long-term enclosure measures of degraded grasslands.
Key words:  enclosure years  semiarid grassland  soil carbon and nitrogen  microbial biomass  ecological stoichiometry