Combining a root exclusion technique with continuous chamber and porous tube measurements for a pin‐point separation of ecosystem respiration in croplands

To better assess ecosystem C budgets of croplands and understand their potential response to climate and management changes, detailed information on the mechanisms and environmental controls driving the individual C flux components are needed. This accounts in particular for the ecosystem respiration (R eco ) and its components, the autotrophic (R a ) and heterotrophic respiration (R h ) which vary tremendously in time and space. This study presents a method to separate R eco into R a [as the sum of R a (shoot) and R a (root) ] and R h in order to detect temporal and small‐scale spatial dynamics within their relative contribution to overall R eco . Thus, predominant environmental drivers and underlying mechanisms can be revealed. R eco was derived during nighttime by automatic chamber CO 2 flux measurements on plant covered plots. R h was derived from CO 2 efflux measurements, which were performed in parallel to R eco measurements on a fallow plot using CO 2 sampling tubes in 10 cm soil depth. R a (root) was calculated as the difference between sampling tube CO 2 efflux measurements on a plant covered plot and R h . R a (shoot) was calculated as R eco – R a (root) – R h . Measurements were carried out for winter wheat ( Triticum aestivum L.) during the crop season 2015 at an experimental plot located in the hummocky ground moraine landscape of NE Germany. R eco varied seasonally from < 1 to 9.5 g C m −2 d −1 , and was higher in adult (a) and reproductive (r) than juvenile (j) stands (g C m −2 d −1 : j = 1.2, a = 4.6, r = 5.3). Observed R a and R h were in general smaller compared to the independently measured R eco , contributing in average 58% and 42% to R eco . However, both varied strongly regarding their environmental drivers and particular contribution throughout the study period, following the seasonal development of soil temperature and moisture (R h ) as well as crop development (R a ). Thus, our results consistently revealed temporal dynamics regarding the relative contribution of R a (root) and R a (shoot) to R a , as well as of R a and R h to R eco . Based on the observed results, implications for partitioning of R eco in croplands are given.