Defoliation Effects on Pasture Photosynthesis and Respiration

Skinner, R. Howard; Goslee, Sarah C.

doi:10.2135/cropsci2015.12.0733

Cited by 3 publications

(3 citation statements)

References 39 publications

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“…However, no complete reduction of GPP was estimated from EC measurements after a cutting and the time lag until the site showed a net daily CO 2 uptake again was mostly less than one week. This conforms to results of Skinner and Goslee () who found an average reduction in maximum GPP of 70% during the first week following defoliation by cutting in a 9‐year EC field experiment. Thus, photosynthesis proceeded on an attenuated level as observed with the EC measurements of this study.…”

Section: Discussionmentioning

confidence: 99%

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

Poyda

Reinsch

Skinner

et al. 2017

J. Plant Nutr. Soil Sci.

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Due to their high emission potential, the reporting of CO2 emissions from peatlands requires exact emission factors for different land use categories. Recently used emission factors are mainly based on CO2 flux measurements by chamber techniques or the micrometeorological eddy covariance (EC) method. However, evidence about the reliability and comparability of annual CO2 balances based on these methods is scarce. Therefore, manual chamber measurements of ecosystem respiration (RECO) and net ecosystem exchange (NEE) were conducted for two years (March 2012–April 2014) to model annual balances of two sites on fen soils with different land use intensity in northern Germany: an unutilized and rewetted grassland (UG) and an intensively utilized wet grassland (GW). Simultaneously, EC measurements of NEE were conducted on the sites. Two reasons for occasionally great deviations in NEE between the methods could be observed: (1) the accordance of both methods was most hampered during transition periods such as the beginning of the growing season and the onset of regrowth after a grassland defoliation due to different spatial scales of EC and chamber measurements and (2) RECO and gross primary production (GPP) partitioned from EC NEE measurements were systematically lower than those from the chamber‐based model, which could be a result of the EC energy balance gap. Differences were more pronounced for the managed site GW as a result of more frequent regrowth periods. It is concluded that the EC and chamber method can show comparable results for the CO2 exchange of grasslands on fen soils when the limitations of both methods are known and considered for the reporting of emission factors. These limitations are due to energy balance closure and potentially biased footprints for EC and a restricted representativeness especially during early stages of plant development for the chamber method.

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Section: Discussionmentioning

confidence: 99%

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

Poyda

Reinsch

Skinner

et al. 2017

J. Plant Nutr. Soil Sci.

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“…Plant senescence results in transfers of biomass C to litter and dead organic matter in the soil which undergo decomposition. Defoliation, through grazing and cutting, is a major disturbance to C cycling (Gastal and Lemaire, 2015;Skinner and Goslee, 2016). Grass cutting abruptly removes most of the aboveground C from the ecosystem, forcing the grass to rebuild the leaf area necessary for photosynthesis and growth.…”

Section: Introductionmentioning

confidence: 99%

The carbon budget of the managed grasslands of Great Britain – informed by earth observations

2022

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Abstract. Grasslands cover around two-thirds of the agricultural land area of Great Britain (GB) and are important reservoirs of organic carbon (C). Direct assessments of the C balance of grasslands require continuous monitoring of C pools and fluxes, which is only possible at a small number of experimental sites. By relying on our quantitative understanding of ecosystem C biogeochemistry we develop models of grassland C dynamics and use them to estimate grassland C balance at various scales. Model-based estimation of the C budget of individual fields and across large domains is made complex by the spatial and temporal variability in climate and soil conditions, as well as in livestock grazing, grass cutting and other management activities. In this context, earth observations (EOs) provide subfield-resolution proxy data on the state of grassland canopies, allowing us to infer information about vegetation management, to apply observational constraints to the simulated ecosystems and, thus, to mitigate the effects of model input data uncertainty. Here, we show the potential of model–data fusion (MDF) methods to provide robust analyses of C dynamics in managed grasslands across GB. We combine EO data and biogeochemical modelling by implementing a probabilistic MDF algorithm to (1) assimilate leaf area index (LAI) times series (Sentinel-2); (2) infer defoliation instances (grazing, cutting); and (3) simulate livestock grazing, grass cutting, and C allocation and C exchanges with the atmosphere. The algorithm uses the inferred information on grazing and cutting to drive the model's C removals-and-returns module, according to which ≈1/3 of C in grazed biomass returns to the soil as manure (other inputs of manure not considered) and C in cut grass is removed from the system (downstream C emissions not considered). Spatial information on soil C stocks is obtained from the SoilGrids dataset. The MDF algorithm was applied for 2017–2018 to generate probabilistic estimates of C pools and fluxes at 1855 fields sampled from across GB. The algorithm was able to effectively assimilate the Sentinel-2-based LAI time series (overlap = 80 %, RMSE = 1.1 m2 m−2, bias = 0.35 m2 m−2) and predict livestock densities per area that correspond with independent agricultural census-based data (r = 0.68, RMSE = 0.45 LU ha−1, bias = −0.06 LU ha−1). The mean total removed biomass across all simulated fields was 6 (±1.8) t DM ha−1 yr−1. The simulated grassland ecosystems were on average C sinks in 2017 and 2018; the net biome exchange (NBE) was -191±81 (2017) and -49±69 gC m−2 yr−1 (2018). Our results show that the 2018 European summer drought reduced the strength of C sinks in GB grasslands and led to a 9-fold increase in the number fields that were annual C sources (NBE > 0) in 2018 (18 % of fields) compared to 2017 (2 % of fields). The field-scale analysis showed that management in the form of timing, intensity and type of defoliation were key determinants of the C balance of managed grasslands, with cut fields acting as weaker C sinks compared to grazed fields. Nevertheless, extreme weather, such as prolonged droughts, can convert grassland C sinks to sources.

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“…CC BY 4.0 License. disturbance for managed grassland C cycling (Gastal and Lemaire, 2015;Skinner and Goslee, 2016). Grass cutting abruptly removes most of the aboveground C from the ecosystem forcing the grass to rebuild the leaf area necessary for photosynthesis and growth.…”

Section: Introductionmentioning

confidence: 99%

The carbon budget of the managed grasslands of Great Britain constrained by earth observations

Myrgiotis

Smallman

Williams

2021

Preprint

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Abstract. Grasslands cover around two thirds of the land area of Great Britain (GB) and are important reservoirs of terrestrial biological carbon (C). Outside a few well-monitored sites the quantification of C dynamics in managed grasslands is made complex by the spatio-temporal variability of weather conditions combined with grazing and cutting patterns. Earth observation (EO) missions produce high-resolution frequently-retrieved proxy data on the state of grassland canopies but synergies between EO data and biogeochemical modelling to estimate grassland C dynamics are under-explored. Here, we show the potential of model-data fusion (MDF) to provide robust near-real time analyses of managed grasslands of GB (England, Wales andScotland). We combine EO data and process-based modelling to estimate grassland C balance and to examine the role of management. We implement a MDF algorithm to (1) infer grassland management from vegetation reduction data (Proba-V), (2) optimise model parameters by assimilating leaf area index (LAI) data (Sentinel-2) and (3) simulate livestock grazing, grass cutting, and C allocation and loss to the atmosphere. The MDF algorithm was applied for 2017 and 2018 at 1855 fields sampled from across GB. The algorithm was able to effectively assimilate the Sentinel-2 based LAI time series (overlap = 80 %, RMSE = 1 gCm−2, bias = 0.35 gCm−2) and predict livestock densities per area that correspond with independent census-based data (r = 0.68). The mean total removed biomass across all simulated fields was 6 (±1.8) tDM ha−1 y−1. The simulated grassland ecosystems were on average C sinks in 2017 and 2018; the GB-average net ecosystem exchange (NEE) and net biome exchange (NBE) for 2017 was −232 ± 94 and for 2018 was −120 ± 103 gCm−2 y−1. The 2018 summer drought reduced C sinks, with a 9-fold increase in the number fields that were C sources (NBE > 0) in 2018 compared to 2017. We conclude that management in the form of sward condition and the timing, intensity and type of defoliation are key determinants of the C balance of managed grasslands. Nevertheless, extreme weather, such as prolonged droughts, can convert grassland C sinks to sources.

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Defoliation Effects on Pasture Photosynthesis and Respiration

Cited by 3 publications

References 39 publications

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

The carbon budget of the managed grasslands of Great Britain – informed by earth observations

The carbon budget of the managed grasslands of Great Britain constrained by earth observations

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Defoliation Effects on Pasture Photosynthesis and Respiration

Cited by 3 publications

References 39 publications

Comparing chamber and eddy covariance based net ecosystem CO2 exchange of fen soils

Comparing chamber and eddy covariance based net ecosystem CO2 exchange of fen soils

The carbon budget of the managed grasslands of Great Britain – informed by earth observations

The carbon budget of the managed grasslands of Great Britain constrained by earth observations

Contact Info

Product

Resources

About

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils

Comparing chamber and eddy covariance based net ecosystem CO₂ exchange of fen soils