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

Abstract. Soil respiration (R_s), the sum of respiration by soil organisms (R_h) and roots (R_a), is known to be highly variable in both, space and time. There is less information available about the behaviour of R_h and R_a 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 R_s and a 50 cm soil collar to exclude roots and to measure R_h only. R_a was assumed to equal R_s−R_h. 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 R_s was 69% and thus higher than the autotrophic contribution. Seasonal changes of soil temperature and especially water content explained well the temporal variability of R_s (r²=0.74) and R_a (r²=0.80). Spatial variability of R_a was on average much higher (CV=88%) than the spatial variability of R_h (CV=30%). However, R_h was mainly randomly distributed in space, whereas R_a showed spatial autocorrelation. Spatial correlation and cross-variograms showed a significant spatial dependence of R_s on R_a. 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.