Spatial and seasonal variability of heterotrophic and autotrophic soil respiration in a winter wheat stand

Soil respiration (Rs), the sum of respiration by soil organisms (Rh) and roots (Ra), is known to be highly variable in both, space and time. There is less information available about the behaviour of Rh and Ra in time and particularly in space. The objective of this study was to quantify the contribution of each component to the temporal and spatial variability of soil respiration in a winter wheat stand. We measured soil respiration from March to July 2009 by closed-dynamic chambers for 61 sampling points in a 50×50 m plot in a winter wheat stand close to Jülich, Germany. Each sampling point was equipped with a 7 cm soil collar to measure total Rs and a 50 cm soil collar to exclude roots and to measure Rh only. Ra was assumed to equal Rs−Rh. Simultaneously, soil temperature and soil water content were measured in 6 cm depth. Biweekly the temporal development of the leaf area index was measured. On average, the heterotrophic contribution to Rs was 69% and thus higher than the autotrophic contribution. Seasonal changes of soil temperature and especially water content explained well the temporal variability of Rs (r2=0.74) and Ra (r2=0.80). Spatial variability of Ra was on average much higher (CV=88%) than the spatial variability of Rh (CV=30%). However, Rh was mainly randomly distributed in space, whereas Ra showed spatial autocorrelation. Spatial correlation and cross-variograms showed a significant spatial dependence of Rs on Ra. From our results we concluded that spatial variability of soil respiration in a winter wheat stand represented mainly the spatial variability of the autotrophic component.