COS 50-10
Variation in plant growth rates across broad climate gradients: Toward a general metabolic scaling model linking climate, functional traits, and growth rate
Climate is thought to drive variation in plant growth rates via direct effects on the kinetics of photosynthesis and respiration. However, recent studies have shown that plant growth rates converge across climate gradients to a common scaling relationship with plant functional traits and plant biomass, suggesting that climatic variation in growth rates does not reflect a direct kinetic control of climate but instead an indirect control via constraints on maximum plant size and growing season length. We evaluated these hypotheses by: (1) extending metabolic scaling theory to include hypothesized relationships between climate variables (temperature, precipitation, evapotranspiration, and growing season length) and key plant functional traits (net carbon assimilation rates, specific leaf area, carbon use efficiency, tree carbon mass fraction, and leaf mass allocation) to predict mass growth rates of individual plants, and (2) assessing these relationships for 1580 woody plant species using functional trait and allometry data compiled from the literature with climate and stem diameter growth data collected from over 15,000 individual trees at 35 sites spanning broad gradients in latitude and elevation.
Results/Conclusions
Our results show that comparing normalized rates of biomass growth per individual plant reveals a remarkable overlap across sites. Almost none of the variation in plant growth rates was explained by climate variables; instead, most of the variation was explained by variation in plant functional traits and total plant biomass. These results suggest that woody plants across broad climate gradients converge to a similar normalized growth rates as a result of directional shifts in functional traits across climate gradients. This extension of metabolic scaling theory suggests that climatic variation in growth rates reflects not a direct kinetic control of growth physiology, but instead an indirect control on maximum plant size and/or growing season length.