PNNL

Abstract

Global greening hides different plant leaf strategies: increase maximal leaf area (LAImax) and extend length of growing season (LOS). Nevertheless, little is known about which strategy is the optimal choice that plants prefer to change under climate change. Here, we used multiple satellite-based datasets to explore the temporal changes in LAImax (??LAI?_max) and LOS (?LOS) over global deciduous broadleaved forests; and found a negative correlation nexus between ??LAI?_max and ?LOS. Notably, this negative nexus strongly depends on canopy height. Tall forests with pretty large amounts of green leaves, mostly clustered in southeastern USA, eastern Europe, and Japan, give prior to the strategy of extending LOS, accompanied by changes in leaf physics and chemistry, i.e., leaf chlorophyll content, leaf water content, and leaf albedo per leaf area. This strategy enables strong decrease in leaf light and water use and efficiencies. Conversely, short forests with insufficient green leaves, clustered in northeastern USA, central Europe and China, prefer to increase LAImax but do not change LOS much. This strategy leads to small shifts in leaf physics and chemistry and thus keeps much stable light and water use and efficiencies. Our findings are helpful for better understanding the casual relationships between changes of green leaves and growing seasons as well as their consequences for ecosystem functioning.