Biol Fertil Soils (2007) 44:259–268 DOI 10.1007/s00374-007-0198-6
ORIGINAL PAPER
Responses of microbial biomass and respiration of soil to topography, burning, and nitrogen fertilization in a temperate steppe Weixing Liu & Wenhua Xu & Yi Han & Changhui Wang & Shiqiang Wan
Received: 14 January 2007 / Revised: 2 April 2007 / Accepted: 4 April 2007 / Published online: 27 April 2007 # Springer-Verlag 2007
Abstract Temporal dynamics of microbial biomass and respiration of soil and their responses to topography, burning, N fertilization, and their interactions were determined in a temperate steppe in northern China. Soil microbial indices showed strong temporal variability over the growing season. Soil microbial biomass C (MBC) and N (MBN) were 14.8 and 11.5% greater in the lower than upper slope, respectively. However, the percentage of organic C present as MBC and the percentage of total N present as MBN were 16.9 and 26.2% higher in the upper than lower slope, respectively. Neither microbial respiration (MR) nor metabolic quotient (qCO2) was affected by topography. Both MBC and MBN were increased by burning, on average, by 29.8 and 14.2% over the growing season, and MR and qCO2 tended to reduce depending on the sampling date, especially in August. Burning stimulated the percentage of organic C present as MBC and the percentage of total N present as MBN in the upper slope, but did not change these two parameters in the lower slope. No effects of N fertilization on soil microbial indices were observed in the first growing season after the treatment. Further research is needed to study the long-term relationships between changes in soil microbial diversity and activity and plant community in response to burning and N fertilization. W. Liu : W. Xu : Y. Han : C. Wang : S. Wan (*) Laboratory of Quantitative Vegetation Ecology, Institute of Botany, The Chinese Academy of Sciences, Xiangshan, Beijing 100093, China e-mail:
[email protected] W. Liu : W. Xu : Y. Han Graduate University of the Chinese Academy of Science, Yuquanlu, Beijing 100049, People’s Republic of China
Keywords Burning . Microbial biomass . N fertilization . Metabolic quotient . Temperate steppe . Topography
Introduction Soil microorganisms play an important role in regulating the litter and organic matter decomposition, nutrient release, and soil nutrient availability (Garcia and Rice 1994; O’Lear et al. 1996), consequently affecting plant nutrient uptake, growth, and productivity (Bardgett et al. 1999a; Janna et al. 2005). Temperature, moisture, soil physical and chemical properties, and substrate quality can all affect soil microbial activities (Sinsabaugh et al. 1991; Hu et al. 2001). With their high turnover rate, soil microbes are sensitive to changes in the above environmental factors. Better understanding of soil microbial dynamics in natural systems would help to explain the responses of plant communities to natural and anthropogenic perturbations. Topography has been documented to influence soil microclimate, species composition, community structure, and ecosystem function in the tallgrass prairie (Abrams and Hulbert 1987; Hartnett et al. 1996) and shortgrass steppe (Burke et al. 1999) in North America. For example, the lower slope has a different vegetation structure, with more grasses, higher rates of C and N mineralization than the upper slope in the shortgrass steppe (Hook and Burke 2000). Differences in soil temperature and moisture as well as physical and chemical properties could have contributed to the spatial variability of plant community and patterns (Bartha et al. 1995). Due to the differences in the above biotic and abiotic factors that regulate microbial activities, it is expected that, on one hand, topography may have profound impacts on soil microbial activities. On the other hand, topographical position may also influence the
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Biol Fertil Soils (2007) 44:259–268
responses of soil microbes to natural and anthropogenic disturbance (fire, for example). Fire as a natural or anthropogenic disturbance can profoundly influence terrestrial ecosystem structure and function (Knapp et al. 1998; Wan et al. 2001). Removal of aboveground biomass and litter caused by fire can affect light penetration, energy balance, and evapotranspiration, subsequently leading to changes in soil microclimate (i.e., temperature and moisture; Schaffers 2002; Mullen et al. 2006). In addition, a meta-analysis showed that fire can increase soil N availability across various terrestrial ecosystems (Wan et al. 2001). Alterations of the above factors could lead to changes in plant growth, species composition, and net primary productivity after burning (Andrew 2003). However, our understanding of the possible impact of burning on composition and activity of soil microflora and whether and how responses of soil microbes contribute to the changes in plant community is limited. Nitrogen fertilization may affect microbial activities directly by enhancing soil N availability, and/or indirectly via altering plant species composition, growth, and belowground C input (Bardgett et al. 1999a; Ostertag and Verville 2002). The effects of topography, burning, and N fertilization on plant growth, community structure, and ecosystem productivity have well been studied, especially in North American grasslands (Garcia and Rice 1994; Turner et al. 1997). However, it is not clear yet whether these factors interactively or additively influence composition and activity of soil microflora when they are taken into consideration together. The semiarid temperate steppe in northern China is part of the typical vegetation across the Eurasian continent and is predicted to be sensitive to climate change (Christensen and Christensen 2004). The temperate steppe experienced severe degradation over large areas due to overgrazing since the middle of the 20th century. The Chinese government put great effort to restore the temperate steppe
Table 1 Soil physiochemical properties and plant biomass and coverage in the upper and lower slopes
Soil organic C (g kg−1) Soil total N (g kg−1) Soil pH Bulk density (g cm−3) Sand (%) Silt (%) Clay (%) Peak aboveground biomass (g m−2) Total plant cover (%)
Upper slope
Lower slope
7.77±0.23b 0.70±0.03b 6.32±0.04a 1.42±0.003a 86.64±0.11a 4.59±0.03b 8.77±0.03b 198±9.8b 29.5±1.10b
9.43±0.73a 0.90±0.04a 6.10±0.07b 1.29±0.003b 83.86±0.08b 6.38±0.04a 9.76±0.05a 255±12.8a 36.6±1.91a
n = 6 for soil organic C, total N, soil pH, soil texture, peak aboveground biomass, and total plant cover; n=3 for soil bulk density. Different letters are statistically different (P
