Vegetation and soil respiration: Correlations and controls

Soil respiration rates vary significantly among major plant biomes, suggest ing that vegetation type influences the rate of soil respiration. However, correlations among climatic factors, vegetation distributions, and soil res piration rates make cause-effect arguments difficult. Vegetation may affect soil respiration by influencing soil microclimate and structure, the quant ity of detritus supplied to the soil, the quality of that detritus, and the overall rate of root respiration. At the global scale, soil respiration ra tes correlate positively with litterfall rates in forests, as previously re ported, and with aboveground net primary productivity in grasslands, provid ing evidence of the importance of detritus supply. To determine the directi on and magnitude of the effect of vegetation type on soil respiration, we c ollated data from published studies where soil respiration rates were measu red simultaneously in two or more plant communities. We found no predictabl e differences in soil respiration between cropped and vegetation-free soils , between forested and cropped soils, or between grassland and cropped soil s, possibly due to the diversity of crops and cropping systems included. Fa ctors such as temperature, moisture availability, and substrate properties that simultaneously influence the production and consumption of organic mat ter are more important in controlling the overall rate of soil respiration than is vegetation type in most cases. However, coniferous forests had simi lar to 10% lower rates of soil respiration than did adjacent broad-leaved f orests growing on the same soil type, and grasslands had, on average, simil ar to 20% higher soil respiration rates than did comparable forest stands, demonstrating that vegetation type does in some cases significantly affect rates of soil respiration.