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

Abstract

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 (Reco) and its components, the autotrophic (Ra) and heterotrophic respiration (Rh) which vary tremendously in time and space. This study presents a method to separate Reco into Ra [as the sum of Ra (shoot) and Ra (root)] and Rh in order to detect temporal and small‐scale spatial dynamics within their relative contribution to overall Reco. Thus, predominant environmental drivers and underlying mechanisms can be revealed. Reco was derived during nighttime by automatic chamber CO2 flux measurements on plant covered plots. Rh was derived from CO2 efflux measurements, which were performed in parallel to Reco measurements on a fallow plot using CO2 sampling tubes in 10 cm soil depth. Ra (root) was calculated as the difference between sampling tube CO2 efflux measurements on a plant covered plot and Rh. Ra (shoot) was calculated as Reco – Ra (root) – Rh. 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. Reco 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 Ra and Rh were in general smaller compared to the independently measured Reco, contributing in average 58% and 42% to Reco. However, both varied strongly regarding their environmental drivers and particular contribution throughout the study period, following the seasonal development of soil temperature and moisture (Rh) as well as crop development (Ra). Thus, our results consistently revealed temporal dynamics regarding the relative contribution of Ra (root) and Ra (shoot) to Ra, as well as of Ra and Rh to Reco. Based on the observed results, implications for partitioning of Reco in croplands are given.

A multi‐layer, closed‐loop system for continuous measurement of soil CO2 concentration

“…The gas probes are equipped with diffusion-based membranes (ACCUREL tubes), which were previously tested for gas permeation efficiency and diffusion coefficients (Gut et al, 1998;DeSutter et al, 2006), and for the absence of isotopic fractionation (Parent et al, 2013). These tubes have been applied in a series of investigations at different sites, including grassland (Flechard et al, 2007;Wolf et al, 2011), forests (Ekblad and Hö gberg, 2001;Goffin et al, 2014), and arable land (Hoffmann et al, 2018). In multiple investigations, spatial variability was accounted for by burying tubes ranging from 1.5 m (Gut et al, 1998;Flechard et al, 2007) to 8 m length (DeSutter et al, 2008;Hoffmann et al, 2018) in order to integrate over an extended soil volume.…”

“…These tubes have been applied in a series of investigations at different sites, including grassland (Flechard et al, 2007;Wolf et al, 2011), forests (Ekblad and Hö gberg, 2001;Goffin et al, 2014), and arable land (Hoffmann et al, 2018). In multiple investigations, spatial variability was accounted for by burying tubes ranging from 1.5 m (Gut et al, 1998;Flechard et al, 2007) to 8 m length (DeSutter et al, 2008;Hoffmann et al, 2018) in order to integrate over an extended soil volume. However, in this study we preferred to install soil gas probes with 30 cm diffusible length in order to minimize any disturbance of the soil structure and root systems caused by any installation procedure, which is important especially for forest soils.…”

A Method for Estimating Annual Cumulative Soil/Ecosystem Respiration and CH4 Flux from Sporadic Data Collected Using the Chamber Method

“…In recent years, this limitation has been largely overcome by the introduction of computer-controlled automatic sampling systems [11,12]. However, the automatic equipment is usually expensive to install, although increasingly more studies have started to use this new efficient system [13][14][15][16][17]. Thus, for the archived data now available, the observation frequency is often less than once a month, determined according to the practicability of accessing the site, and usually in the daytime.…”

How to best address spatial and temporal variability of soil‐derived nitrous oxide and methane emissions

“…A better understanding of the ecosystem functioning requires the inclusion of the whole soil–plant–atmosphere system ( Maier et al, , this issue), as well as partitioning ecosystem respiration into autotrophic and heterotrophic respiration ( Hoffmann et al, , this issue).…”