火烧对黄土高原草地土壤氮素净矿化速率和净硝化速率的影响

Effects of burning on soil net nitrogen mineralization rate and net nitrification rate in a semi-arid grassland on the Loess Plateau

[目的]封育是半干旱地区退化草地植被恢复的有效措施。封育后植被恢复会形成大量的凋落物,从而引起自然或人为火烧。火烧改变了土壤微生物特性和养分动态。本文旨在探究火烧对黄土高原典型草地养分(特别是氮)循环的影响。[方法]以宁夏回族自治区云雾山国家级自然保护区封育34年的典型草地作为研究对象,分别采集新烧地、火烧后1年和火烧后2年的对照和火烧土壤样品(共计6个处理),比较分析土壤上层(0~5 cm)和下层(5~25 cm)总碳、总氮含量,无机态氮(铵态氮和硝态氮)含量,微生物生物量碳、氮含量,氮素净矿化速率和氮素净硝化速率等指标的变化。[结果]火烧处理仅显著影响了上层土壤的性质。火烧显著降低了新烧地上层土壤的总氮含量、微生物生物量碳和氮含量;同时,新烧地上层的铵态氮、硝态氮、无机态氮含量和土壤基础呼吸显著高于对照,而火烧后2年则显著低于对照;土壤氮素净矿化速率和净硝化速率均随火烧年限的增加而呈现出先升高后降低的变化趋势。[结论]火烧提高了短时期内黄土高原典型草地土壤的氮素可利用性和微生物活性,有利于新植物的生长。

[Objectives] Enclosure is an effective measure for vegetation restoration of degraded grasslands. However, enhanced litter accumulation and dead standing plant biomass are vulnerable to both natural and human-related fires, which alter soil microbial properties and nutrient dynamics. The purpose of this study was to explore the impact of burning on nutrient （particular nitrogen, N） cycling in a semi-arid grassland on the Loess Plateau. [Methods] We conducted a field experiment to examine the effects of burning on microbial properties and N cycling in a typical steppe at the Yunwu Mountains Nature Conserve, Ningxia Hui Autonomous Region, China. Soils were collected from three sites,which were burned at three different times （B0, new burning;B1, one year after burning;B2, two years after burning）. Three adjacent unburned stands were selected as their respective controls. Total soil carbon （TC） and nitrogen （ TN ） , extractable inorganic N [ TIN, i. e., the sum of ammonium （ NH4 ） and nitrate （ NO3^- ） ] , microbial biomass carbon （ MBC ） and nitrogen （ MBN）, net N mineralization rate （ Rmin ） and net nitrification rate （ Rni＇ ） were measured. [ Results ] Burning only significantly affected the measured properties in the topsoil. It reduced TN, MBC and MBN in B0 soil, but this effect disappeared in B1 and B2 soils. Also,it significantly increased NH4, NO3^- ,TIN and basal respiration in the B0 topsoil, but significantly reduced them in the B2 topsoil. Burning also tended to increase Rmin and Rnit in the B0 and B1 topsoil, but reduced them in the B2 soil. [ Conclusions ] Our results show that burning can increase soil available N and microbial activity in soil of the Loess Plateau over the short term, potentially benefiting the establishment and growth of new plants.