Temporal changes in the spatial variability of soil respiration in a meadow steppe: The role of abiotic and biotic factors

How and why spatial patterns of soil respiration (SR) emerge and change or persist over time, and what makes spatial patterning of SR and environment variables interdependent or non-interdependent, is poorly understood. Our objectives were to quantify temporal changes in spatial patterns of SR for a grassland dominated by Leymus chinensis and to explore the underlying ecological mechanisms. We conducted simultaneous measurements of SR, along with a suite of other aboveground and belowground properties, for 75 sampling points in May, July (when SR was measured twice due to a distinct temporal fluctuation in soil water content and higher temperatures) and September. No spatial structure was detected for SR in May. The degree of spatial dependence of SR in September was lower than on 17 July and 23 July, while the autocorrelation range for SR in September (7.2 m) was higher than on 17 July (1.7 m) and 23 July (3.8 m). SR was explained by soil physicochemical properties (soil organic carbon content, organic carbon:total nitrogen ratio and soil pH) in May, and soil pH was the most influential factor at this time. On 17 July, SR was explained by the combination of soil water content, bulk density, aboveground biomass, soil fungal:bacterial biomass ratio and C acquiring enzyme activity. Soil temperature, bulk density, soil electrical conductivity and aboveground biomass explained 53% of the spatial variability in SR on 23 July. SR was mostly controlled by soil temperature (positively) in September. These results indicated that the spatial patterns of SR varied remarkably across the four observations and evolved temporally as a result of seasonal shifts in environmental conditions and vegetation. Biological factors (e.g. plant and microbial biomass) were important determinants of the spatial pattern of SR in July, when the strongest spatial heterogeneity was observed.