Global coordination in plant physiological and rooting strategies in response to water stress

However, it is still poorly understood how these strategies vary in relation to climate and land cover types and how they could coordinate globally. Based on daily microwave vegetation optical depth (VOD) from AMSR-E and AMSR2 over 2002-2011, we estimate two proxies for stress regulation: (a) an effective plant rooting depth (Zr*) and (b) the effective plant hydraulic conductance (Kplant*) to delineate two strategies: deep rooting and strong physiological regulation.

We find that plants with deeper Zr* (e.g., evergreen/deciduous broadleaf forest) are mostly distributed in warm or wet regions, and maintain a relatively steady nighttime VOD because of access to deeper water. Taller plants exhibit greater drop in daytime VOD due to their greater physiological vulnerability. While physiological regulation appears to be the dominant water stress regulation strategy at Northern high latitudes where open shrubland and (woody) savannas are distributed, this physiological regulation is coupled with deep rooting in forest and (woody) savanna areas in the tropics, Eastern US, and Southeastern China.