Background/Question/Methods Although root respiration represents a large percentage of a grassland’s total C budget and is a major source of grassland soil respiration, little is known about the extent that allocation to root respiration and the relative contribution of root respiration to soil respiration may vary seasonally and across a landscape. The objective of this study was to measure monthly changes in root respiration and its relative contribution to soil respiration in five grassland communities that varied in elevation, topographic position, edaphic properties, and plant productivity in Yellowstone National Park.

Results/Conclusions

Overall, mass-specific root respiration was weakly correlated with soil temperature and moisture. However, dryer sites experienced greater seasonal variation in mass-specific root respiration (µmol CO₂ g^-1 s^-1) and ecosystem root respiration (µmol CO₂ m^-2 s^-1) rates than wetter sites, where no seasonal differences were observed. All sites exhibited seasonal peaks in root respiration when primary plant production peaked. When root respiration rates were corrected for soil pore space CO₂ concentrations at the two  grassland sites where it was possible, root respiration contributed proportionately the greatest percentage (75-100%) to soil respiration during the first month of the growing season and thereafter dropped to 15-38%. These results indicated that dryer sites showed greater seasonal variation in carbon allocation to root respiration compared to wetter sites. However, relative contributions of root respiration to soil respiration on two grassland sites experiencing different moisture conditions responded the same. Data suggest how seasonal variation and topographic position play roles in determining root respiration and its relative contribution to soil respiration.