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

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 (R(s)), soil temperature (T(s)) 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 R(s) activity, as well as its temporal stability: average rankR(s), the temporal average R(s) rank of a measuring position from the campaigns revealed the persistent spatial pattern of R(s), while rangeR(s), 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. We formulated a hypothetic concept of a two-state equilibrium to describe the performance of the long-term R(s) activity: R(s) activity with smaller rangeR(s), that is both the lower elevation positions with larger rankR(s) (“state I”) and the higher elevation positions with smaller rankR(s) (“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 rangeR(s) for medium rankR(s), suggesting resilience (not resistance) as a major strategy for this ecosystem.