Convergence of potential net ecosystem production among contrasting C3 grasslands

Previous synthesis studies concluded that net ecosystem production (NEP) differs among contrasting C3 grasslands. However, it has not yet been investigated whether differences in ecosystem traits, environment and management alter the intrinsic potential NEP (NEPPOT) and thereby explain some of the range in annual apparent NEP. We estimated NEPPOT for nine C3 grasslands under contrasting climate and management regimes using multi-year eddy-covariance data. NEPPOT converged within a narrow range suggesting no differences in the net CO2 uptake capacity across C3 grasslands. Our results indicate a unique feature of C3 grasslands compared to other terrestrial ecosystems and suggest a state of stability in NEP based on coupled production and respiration processes during non-limiting conditions. Consequently, the annual CO2 sink-source strength of C3 grasslands is primarily a function of seasonal and short-term environmental and management constraints, and therefore especially susceptible to changes in future climate patterns and associated adaptation of management practices.