Biotic and abiotic factors controlling the spatial and temporal variation of soil respiration in an agricultural ecosystem

Based on the continuous observation of soil respiration and environmental factors in a maize ecosystem from late April to late September in 2005, the spatial and temporal variation of soil respiration and their controlling factors were analyzed. There was a significant spatial pattern for soil respiration at the plant scale and higher soil respiration rates tended to occur near the maize plant during the growing season. On one measurement moment, root biomass (B) in soil collars exerted significant influence on the spatial pattern of soil respiration under the relatively homogeneous environmental conditions. A linear relationship existed between soil respiration rate and root biomass SR = alpha B + beta. (1) At daily scale, the coefficient alpha and beta in Eq. (1) fluctuated because soil temperature (T) markedly reduced the intercept (beta) of the linear equation and significantly increased its slope (a). Based on this, we developed SR = ae(bT) B+ cT + d. (2) Eq. (2) indicated that increasing soil temperature ameliorated the positive relationship between soil respiration and root biomass in the daily variation of soil respiration. At seasonal scale, parameter a, b and c in Eq. (2) were affected mainly by soil moisture (W), soil temperature and net primary productivity (NPP), respectively. Thus, we developed SR = (aW + b)e(cT) B + (dNPP + e)T +f (3) to estimate soil respiration during the growing season. Eq. (3) demonstrated that soil temperature, soil moisture, root biomass and NPP combined affected soil respiration at season scale, and they accounted for 78% of the seasonal and spatial variation of soil respiration during the growing season. Eq. (3) not only took into account the influence of soil temperature and moisture, but also incorporated biotic factors as predictor variables, which would lead to an improvement in predictive capabilities of the model. Moreover, Eq. (3) could simulate instantaneous soil respiration rates from different sampling points and at different temporal scales, so it could explain not only the temporal variation of soil respiration, but also its spatial variation. Although this model might not be broadly applicable, the results suggested that there was significant spatial heterogeneity in soil respiration at the plant scale and root biomass dominated the small-scale spatial patterns of soil respiration. Thus, the models of soil respiration should not only take into account the influence of environmental factors, but also incorporate biotic factors in order to scale-up the chamber measurements of soil respiration to ecosystem level. (c) 2006 Elsevier Ltd. All rights reserved.