Abstract
AbstractThis study reports the annual carbon balance of a drained riparian fen under two‐cut or three‐cut managements of festulolium and tall fescue. CO2 fluxes measured with closed chambers were partitioned into gross primary production (GPP) and ecosystem respiration (ER) for modelling according to environmental factors (light and temperature) and canopy reflectance (ratio vegetation index, RVI). Methodological assessments were made of (i) GPP models with or without temperature functions (Ft) to adjust GPP constraints imposed by low temperature (<10 °C) and (ii) ER models with RVI or GPP parameters as biomass proxies. The sensitivity of the models was also tested on partial datasets including only alternate measurement campaigns and on datasets only from the crop growing period. Use of Ft in GPP models effectively corrected GPP overestimation in cold periods, and this approach was used throughout. Annual fluxes obtained with ER models including RVI or GPP parameters were similar, and also annual GPP and ER fluxes obtained with full and partial datasets were similar. Annual CO2 fluxes and biomass yield were not significantly different in the crop/management combinations although the individual collars (n = 12) showed some variations in GPP (−1818 to −2409 g CO2‐C m−2), ER (1071 to 1738 g CO2‐C m−2), net ecosystem exchange (NEE, −669 to −949 g CO2‐C m−2) and biomass yield (556 to 1044 g CO2‐C m−2). Net ecosystem carbon balance (NECB), as the sum of NEE and biomass carbon export, was only slightly negative to positive in all crop/management combinations. NECBs, interpreted as emission factors, tended to favour the least biomass producing systems as the best management options in relation to climate saving carbon balances. Yet, considering the down‐stream advantages of biomass for fossil fuel replacement, yield‐scaled carbon fluxes are suggested to be given additional considerations for comparison of management options in terms of atmospheric impact.
Highlights
Cultivation of natural peatlands is initiated by drainage, which exposes the peat to aerobic conditions leading to continuous mineralization and CO2 emissions (Maljanen et al, 2010; Tiemeyer et al, 2016)
The climate impact of these inputs may be offset by down-stream greenhouse gas (GHG) savings in terms of replacement of fossil fuels by bioenergy derived from the perennial crops (Shurpali et al, 2010)
The Groundwater table (GWT) generally fluctuated at 10–40 cm below the soil surface during the growing period, but was closer to the surface (0–16 cm) in the non-growing period (Fig. 4e) which is normal at the study site
Summary
Cultivation of natural peatlands is initiated by drainage, which exposes the peat to aerobic conditions leading to continuous mineralization and CO2 emissions (Maljanen et al, 2010; Tiemeyer et al, 2016). Festulolium is a hybrid or a hybrid derivative between any species of fescue (Festuca) and ryegrass (Lolium) designed for their combined complementary characteristics (Ghesquiere et al, 2010; Østrem et al, 2013). These grasses are known for quick establishment, aggressive growth and weed suppression, regrowth capacity, winter survival and high yield. Spring growth of festulolium in particular is earlier than, e.g., perennial ryegrass, and festulolium can be harvested earlier (Helgadottir et al, 2014) Both festulolium and tall fescue are native to northern Europe and have large genetic variation which is a useful basis for breeding of cultivars with desired characteristics (Ghesquiere et al, 2010)
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