Temporal Variability of CO2 and N2O Flux Spatial Patterns at a Mowed and a Grazed Grassland

Abstract

Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO 2 and N 2 O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N 2 O flux, soil water content, and soil temperature during a four-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80×60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N 2 O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40-50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N 2 O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p<0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO 2 and N 2 O fluxes.

Predicting nitrous oxide emissions after the application of solid manure to grassland in the United Kingdom

“…Previous work has shown, however, that the sampling time of day was generally representative of the daily flux (De Klein & Harvey, 2015). Factors such as these may contribute to a lower accuracy in the model's prediction of N 2 O emissions (Alsina, Fanton-Borges, & Smart, 2013;Butterbach-Bahl et al, 2013;Fóti et al, 2018;Wei et al, 2018). reported lower goodnessof-fit statistical values (R 2 = .36 and NSE = 0.35 during the calibration period; R 2 = .02 and NSE = −0.07 during the validation period) in temperate grassland regions of North America compared with the current findings.…”

Two potential equilibrium states in long-term soil respiration activity of dry grasslands are maintained by local topographic features

“…The grassland may potentially turn into a source of carbon in drought years 50 with the annual Net Ecosystem carbon Exchange (NEE) ranging from -212.6 (sink, 2004) to + 91.2 (source, 2009) g C m −2 for the previous 15 years 51,52 . Soil respiration (R s , µmol CO 2 m −2 s −1 ) was measured by means of closed chamber systems (Licor 6,400, LiCor, Inc. Lincoln, NE, USA and EGM-4 PPSystems, Amesbury, USA) at 78 sampling locations (arranged as a 80 × 60 m grid 18 ) in each measurement campaign. Target CO 2 concentration was set by placing the soil chamber on its side on the ground to monitor the CO 2 concentration over the surface.…”

“…In our study we conducted a long-term (7-year-long) spatial investigation in a piece of semi-natural grazed grassland in Hungary. The finely undulating (no more than 1.5 m elevation differences within the study site) surface in our study site is formed through the combined effects of wind, water erosion and drought, resulting in uneven soil nutrient (soil organic carbon, SOC) and water distributions together with different above-ground biomass covers between crests and depressions 18 . We measured R s , T s and SWC along 15 measuring campaigns in 80 × 60 m grids and SOC in 6 of these occasions.…”

“…Digital elevation models (DEM) are frequently used not only in landform classification [27][28][29][30][31] or soil mapping 32 but in ecological studies 18,33 as well. Detailed spatial analysis of DEM help to capture relevant information about the terrain surface elements, which can have important ecological effects.…”

“…Our current research question formulated on the basis of spatial samplings (15 occasions) was how soil respiration activity of the grasslands would respond to a range of environmental constraints in terms of resistance and resilience in the longterm, and whether the terrain features were responsible for differences in response stability. We hypothesized on the basis of our previous work 18 that lower micro-elevation levels (surface depressions), rather than the crests, could be responsible for more stable R s activities in general through the effect of more persistent water availability even under drought.…”