On the spatial variation of soil rhizospheric and heterotrophic respiration in a winter wheat stand

Field-scale soil respiration reveals a tremendous variability in space. In order to quantify the spatial variability originating from the heterotrophic and the rhizospheric contribution to total soil respiration, the root exclusion method was applied. At 61 locations within a 50 m × 50 m plot in a winter wheat stand, 7 cm-collars and 50 cm-collars were inserted prior to the root growth to simultaneously measure total respiration and heterotrophic respiration. The rhizospheric component was determined as the difference between the flux measurements of total and heterotrophic respiration. During the vegetation period 2009, in total 18 repeated measurements, including soil temperature and moisture, were carried out.The highest spatial variability in terms of standard deviation up to 2.9 mol CO2 m−2 s−1 was detected for the rhizospheric respiration during the period of massive plant growth. Compared to the heterotrophic contribution the coefficient of variation in space was constantly higher for the rhizospheric contribution. Variogram analyses revealed an almost completely random spatial distribution of heterotrophic respira- tion, whereas the rhizospheric respiration showed a clear spatial autocorrelation. The spatial pattern of total respiration mainly resembles the pattern of the rhizospheric component and is characterized by an average spatial correlation length of 18 m.The results indicate that the sampling design for chamber-based measurements of soil respiration in agro-ecosystems should account for the high spatial variability during plant growth and collars should be separated by a distance larger than the spatial correlation range to ensure uncorrelated samples and thus unbiased representative flux estimates