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

Szilvia Fóti,Levente Kardos,Zoltán Nagy,Krisztina Pintér,Bernadett Gecse,János Balogh,Marianna Papp,Péter Koncz,Dávid Mónok

doi:10.1038/s41598-020-71292-4

Szilvia Fóti, Levente Kardos + Show 7 more

Open Access

https://doi.org/10.1038/s41598-020-71292-4

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Abstract

Soil respiration of grasslands is spatio-temporally variable reflecting the changing biological activities of the soil. In our study we analysed how the long-term soil respiration activities of dry grasslands would perform in terms of resistance and resilience. We also investigated how terrain features are responsible for response stability. We conducted a 7-year-long spatial study in a Hungarian dry grassland, measuring soil respiration (Rs), soil temperature (Ts) and soil water content (SWC) along 15 measuring campaigns in 80 × 60 m grids and soil organic carbon content in 6 of the occasions. Two proxy variables were introduced to grasp the overall Rs activity, as well as its temporal stability: average rankRs, the temporal average Rs rank of a measuring position from the campaigns revealed the persistent spatial pattern of Rs, while rangeRs, the range of ranks of the positions from the campaigns described the amplitude of the Rs response in time, referring to the response stability in terms of resistance or resilience. We formulated a hypothetic concept of a two-state equilibrium to describe the performance of the long-term Rs activity: Rs activity with smaller rangeRs, that is both the lower elevation positions with larger rankRs (“state I”) and the higher elevation positions with smaller rankRs (“state II”) correspond to an equilibrium state with several terrain attributes being responsible for the equilibrium responses. Majority of the measuring positions was belonging to none of these equilibrium states. These positions showed higher rangeRs for medium rankRs, suggesting resilience (not resistance) as a major strategy for this ecosystem.

Highlights

Soil respiration of grasslands is spatio-temporally variable reflecting the changing biological activities of the soil
We investigated the potential direct effects of the different terrain attributes (local mean elevation, standard deviation of elevation (SD), topographic position index (TPI), slope (Sl), Easterness and Northness (East, North)) on the spatial distributions of our proxy variables by using the terrain attributes originating from differently smoothed Digital elevation models (DEM) rasters
DEM1 was the original, 0.2 m resolution model, while DEMs 2–6 were progressively smoothed by a factor of two resulting in different resolution DEM rasters (DEM2: 0.4 m, DEM3: 0.8 m, DEM4: 1.6 m, DEM5: 3.2 m, DEM6: 6.4 m, respectively), and DEM7 met the resolution of the field measuring campaigns (10 m)

Summary

Introduction

Soil respiration of grasslands is spatio-temporally variable reflecting the changing biological activities of the soil. Two proxy variables were introduced to grasp the overall R s activity, as well as its temporal stability: average rankRs, the temporal average Rs rank of a measuring position from the campaigns revealed the persistent spatial pattern of R s, while rangeRs, the range of ranks of the positions from the campaigns described the amplitude of the R s response in time, referring to the response stability in terms of resistance or resilience. R s and its main abiotic drivers, Ts and SWC, show substantial horizontal heterogeneity at different spatial s cales[4,9,10,11,12,13], which is made even more complex by the interaction of the explanatory variables (e.g., cooling effect of soil moisture[4,11,14]) These point to the relevance of spatial studies with temporal replicates[14]. An equilibrium system would respond with different amplitude and response time than a perturbed system[20,22], whether in nutrient cycling or in community d ynamics[26]

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