Influence of Temperature and Soil Moisture on Soil Respiration of a Degraded Steppe Community in the Xilin River Basin of Inner Mongolia

Abstract

Soil respiration is not only an indicator of belowground metabolic acti vity of roots and soil microbes, but also a necessary component of carbon cycle. Measurement of the CO 2 efflux from soil and the determination of the relation sh ip between soil respiration and environmental factors such as temperature and wa ter regime are of great importance in understanding the carbon cycling processes in terrestrial and aquatic ecosystems. To evaluate the role that the degraded s teppe ecosystems in the temperate China play in global carbon cycle and to dete rmine the factors that regulate soil respiration in these ecosystems, we conduct ed field experiment to examine the soil respiration rate by using the alkali abs orption technique in a degraded steppe community in the Xilin River Basin, Inner Mongolia. We also evaluated the influence of temperature and soil moisture on s oil respiration rate. The research site is located in the Baiyinxile Livestock F arm (43°55′ N, 116°19′ E, with an altitude of about 1 200 m). This region ha s a typical temperate and semi_arid climate. The topography is basically flat with mild relief and the soil is classified as chestnut. The original vegetation was Leymus chinensis steppe, and, due to over_grazing in the past decades, the v eget ation has degraded to some extent depending on habitat types and grazing intensi ty. More than 30 species of plants can be found in the region, among which Ach illea frigida, Cleistogenes squarrosa and Carex korshinskyi are the most dominant, followed by L. chinensis, Stipa grandis, Agropyron cristatum, Heter opappus altaicus and Kochia prostrata in terms of their importance value. In addition, Caragana microphylla is sparsely scattered. The maximum coverag e is about 40%. The seasonal pattern of CO 2 efflux was irregular, though the rate of CO 2 evo luti on was greater in summer than in other seasons. Significant relationships were f ound between CO 2 evolution rate, ambient air temperature and soil temperature (t he surface, 5 cm depth, 10 cm depth, 15 cm depth and 20 cm depth, respectively), which could be best described by exponential equations (R 2=0.407 0.571 4 , p=0.001 8 0.014 1). The influence of temperature was more conspicuous at lower temperature than at higher temperature conditions. This was consistent wit h the results reported by other researchers. Soil respiration rate was linearly correlated with soil gravimetric water content at 0 10 cm (R 2=0.422 5, p=0.011 9) and 10 20 cm (R 2=0.500 9, p=0.004 6), but more significa nt power functions could be obtained after removing the confounded effect by tem perature (0_10 cm: R 2=0.551 8, p=0.003 9; 10_20 cm: R 2=0.645 1, p=0.000 8). The relations hip between soil respiration rate (y) and the two variables of air temperatu re ( T a) and soil moisture at 10_20 cm soil depth (M 2) could be described by the following multiple regression equation: y=5 911.648×e 0.042 16 Ta ×M 2 0. 907 58 (R 2=0.858 4, p0.000 1). This equation has m u ch more predicative power than that using temperature and water as single indepe ndent variables. The mean soil respiration rate during the study period was 661.35 mg C·m -2 ·d -1 , and the calculated Q 10 values based on air temperature and soil temperature at surface, 5 cm, 10 cm, 15 cm and 20 cm depth were 1.63, 1.47, 1.52, 1.70, 1.90 a n d 1.97, respectively. Both Q 10 and soil respiration rate were lower a t our stud y site than at the original L. chinensis community studied by Li et al . (200 0) in the adjacent area, possibly due to the difference in water content in the two sites. Our results implied that drought in the growing season tended to have lower Q 10 values and lower soil respiration rate. We suggested that t he variations in soil respiration and Q 10 between degraded and undegra ded L. chinensis steppe ecosystems as affected by other environmental factor s need to be further studied.