Climate regulation of autumn phenology and its impact on carbon cycle

Abstract:

Autumn phenology is important to the global carbon and water cycles and its regulating factors is expected to change under global warming. Here we use two case studies to show how a combination of observations from satellite, eddy covariance (EC) flux tower and simulations from Earth system models (ESMs) can help us better understand the ecosystem carbon dynamics in late growing season. In the first study, we explored the environmental limitation of late season photosynthesis at a global scale. We found contrasting spatial patterns of water and temperature limitation, the threshold to separate these regions are determined by mean annual temperature and pre-season soil moisture. Considering the global warming predicted by ESMs, water limited area is projected to increase and cause stronger variations to the late season photosynthesis. In the second study, we used an analytical framework and quantified the light limitation at northern high latitude for both spring and autumn. Combined with EC data, we show that regions with stronger/weaker light limitation will release/fix more carbon with autumn warming. This result reconciles the contradictory reports on the autumn warming effects on ecosystem carbon uptake by previous studies.