Interannual variability of soil microbial biomass and respiration in responses to topography, annual burning and N addition in a semiarid temperate steppe Weixing Liu a , Wenhua Xu a , Jianping Hong b , Shiqiang Wan a,c, ⁎ a State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing 100093, China b College of Resources and Environment, Shanxi Agriculture University, Taigu, Shanxi, 030801, China c Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng, Henan 475004, China abstract article info Article history: Received 7 November 2009 Received in revised form 30 April 2010 Accepted 6 May 2010 Keywords: Carbon Fire Hillslope Microorganisms Nitrogen Precipitation Soil microorganisms are sensitive to changes in environmental factors and play critical roles in the responses of terrestrial ecosystems to natural or anthropogenic perturbations. This study was conducted to examine interannual variability of soil microbial biomass and respiration in response to topography, annual burning and N addition in a semiarid temperate steppe in northern China. Averaged across the 3 years from 2005 to 2007, soil microbial biomass carbon (MBC), nitrogen (MBN) and respiration (MR) were 31.6, 36.7, and 16.2% greater in the lower than upper slope, respectively. The topographic difference was larger in the drier year, leading to stronger temporal variability of MBC, MBN, and MR in the upper than lower slope. Annual burning stimulated MBC and MBN, on average, by 23.3 and 14.4%, but it suppressed MR. Both the positive responses of soil microbial biomass and the negative responses of MR to burning declined over time. Nitrogen addition reduced MBC and MBN by 17.1 and 8.3% respectively, and the negative effects increased with year. N addition also amplified temporal variability of MBC, MBN and MR. Across the 48 plots, soil microbial biomass and respiration showed positive dependence upon soil moisture and dissolved organic carbon (C). In addition, coefficient variations (CVs) of microbial biomass and respiration were also positively correlated with CVs of soil moisture and aboveground biomass (AGB), suggesting water and plant regulation on the interannual variability of soil microorganisms in response to environmental disturbances in the semiarid temperate steppe. Amplified temporal variability of soil microorganisms under drought, fire and N addition indicates reduced stability of soil microbial community with consequent influences on ecosystem function under environmental change. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In terrestrial ecosystems, soil microorganisms play an important role in regulating many ecological processes such as litter decompo- sition, soil nutrient turnover and consequently plant growth and primary productivity (Wardle et al., 2004). Because of their rapid turnover rates relative to other ecosystem components (i.e., plants and animals), soil microorganisms are highly sensitive to environ- mental perturbation. Therefore, temporal changes in soil microorgan- isms under interannual climate (temperature and precipitation) fluctuations can profoundly impact ecosystem structure and func- tioning (Briggs and Knapp, 1995; Potila and Sarjala, 2004). However, little information is available on interannual dynamics of soil microbes and their responses to environmental perturbation. Spatial heterogeneity is an intrinsic characteristic in terrestrial ecosystems (Schimel et al., 1985; Turner et al., 1997; Burke et al., 1999; Sariyildiz et al., 2005). At the local scale, upper slopes generally have lower water availability than lower slopes, resulting in stronger water limitation to ecosystem processes and components including soil microbes (Liu et al., 2007). In arid and semiarid grassland regions, water is a predominant limiting factor (Zhang et al., 2008a; Liu et al., 2009). Given the stronger water limitation in the upper than lower slope, soil microorganisms in the upper slope are expected to be more sensitive to changes in precipitation and water availability. Therefore, we hypothesize that soil microorganisms in the upper slope experience stronger temporal variability than those in the lower slope under interannual precipitation fluctuations. Unlike spatial discrepancy that forms at long-term scales, natural or anthropogenic fire can exert transient and strong influence on soil microorganisms (Hossain et al., 1995; Andersson et al., 2004; Waldrop and Harden, 2008). Burning has been reported to have positive effects on soil microbial biomass and activity in North American tallgrass prairie and African savanna through altering solar energy at the soil surface and soil moisture (Singh et al., 1991; Garcia and Rice, 1994; Geoderma 158 (2010) 259–267 ⁎ Corresponding author. State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing 100093, China. Tel.: +86 10 6283 6512; fax: +86 10 8259 6134. E-mail address: swan@ibcas.ac.cn (S. Wan). 0016-7061/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2010.05.004 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma