Dynamic C and N stocks – key factors controlling the C gas exchange of maize in a heterogenous peatland

Abstract

Abstract. Drainage and cultivation of fen peatlands creates complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater-level (GWL). To date, it remains unclear if such sites are sources or sinks for greenhouse gases like CO2 and CH4, especially if used for cropland. As individual control factors like GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL – defined as dynamic C and N stocks – play a key role in the regulation of plant- and microbially mediated C gas fluxes of these soils. To test this assumption, the present study analysed the C gas exchange (gross primary production – GPP, ecosystem respiration – Reco, net ecosystem exchange – NEE, CH4) of maize using manual chambers for four years. The study sites were located near Paulinenaue, Germany. Here we selected three soils, which represent the full gradient in pedogenesis, GWL and SOC stocks (0–1 m) of the fen peatland: (a) Haplic Arenosol (AR; 8 kg C m−2); (b) Mollic Gleysol (GL; 38 kg C m−2); and (c) Hemic Histosol (HS; 87 kg C m−2). Daily GWL data was used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks. Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m−2 a−1 at AR to −305 ± 123 g C m−2 a−1 at GL and −127 ± 212 g C m−2 a−1 at HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP:Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and transformation processes in the plant-soil system, which promote CO2 input via GPP more than CO2 emission via Reco. The process-oriented approach of dynamic C and N stocks is a promising, potentially generalizable method for system-oriented investigations of the C gas exchange of groundwater-influenced soils and could be expanded to other nutrients and soil characteristics. However, in order to assess the climate impact of arable sites on drained peatlands, it is always necessary to consider the entire range of groundwater-influenced mineral and organic soils and their respective areal extent within the soil landscape.

High emissions of greenhouse gases from grasslands on peat and other organic soils

“…The concept of dynamic aerated soil C and N stocks was developed in the underlying project and first tested for arable sites in one of the study areas (Pohl et al ., ). It integrates soil organic matter, soil C:N ratio, and bulk density with the daily water table dynamics.…”

Net ecosystem fluxes and composition of biogenic volatile organic compounds over a maize field–interaction of meteorology and phenological stages

“…Data noise that originated from either turbulence or pressure fluctuation caused by chamber deployment or from increasing saturation and canopy microclimate effects was excluded by the application of a death‐band of 5% to each measurement (Davidson et al ., ; Kutzbach et al ., ; Langensiepen et al ., ). Multiple data subsets based on a variable moving window with a minimum length of 4 min were generated for each measurement (Hoffmann et al ., ) and linearly fitted (ordinary least squares; Leiber‐Sauheitl et al ., ; Leifeld et al ., ; Pohl et al ., ) to calculate the concentration change with time. Resulting multiple NEE fluxes per measurement (based on the moving window data subsets per measurement) were subsequently scrutinized by the following threshold criteria: (i) range of within‐chamber air temperature less than ±1.5 K (R eco and NEE fluxes) and deviation of photosynthetic active radiation (PAR) less than ±20% of the average; (ii) significant regression slope ( P ≤ 0.1); and (iii) nonsignificant tests ( P > 0.1) for normality (Lillifor′s adaption of the Kolmogorov–Smirnov test), homoscedasticity (Breusch‐Pagan test) and linearity of CO 2 concentration data.…”

Peatland Governance: The Problem of Depicting in Sustainability Governance, Regulatory Law, and Economic Instruments

“…This refers in particular to the already mentioned factors, including peat thickness, water availability, and nutrient content (respectively danger of eutrophication). However, peat soils themselves also differ considerably in terms of their pedogenesis and geogenesis, and these differences, in turn, have a considerable influence on possible sustainable use, renaturation, the C balance, water storage and conductivity, GHG release and much more [78]. In addition, the gyttjas, which lie below to many peat soils, are still poorly researched.…”

“…First, the results suggest that the dynamic C stocks and the subordinate gyttjas have a strong influence on the GHG fluxes and the C balance of the individual peatlands. However, research focusing on the latter aspects is still widely missing (see, e.g., [78,79]).…”