Resolving the multiple controls of biomass production efficiency in woody plants

Plants assimilate carbon through photosynthesis to support biomass production (BP), autotrophic respiration (Ra) and the synthesis of non-structural compounds. Biomass production efficiency (BPE), the fraction of assimilated carbon allocated to BP, is one key factor influencing ecosystems’ potential to store carbon. However there is no consensus on the controls of BPE, and even the sign of its response to growth temperature is unclear. By means of statistical hypothesis testing using the largest observational dataset to date on annual BPE (n = 514) from evergreen and deciduous woody plants, we confirm earlier findings that BPE declines with stand age and is greater in deciduous plants. However, we also show that BPE declines towards more organic, sandy, or alkaline soils; and responds differently to growing-season and winter temperatures – declining with both growing-season warmth and winter cold. Such a dual temperature response is consistent with additional carbon costs being incurred by the need for cold-hardening processes, and helps to resolve contradictory published reports of positive and negative effects of temperature on BPE. This study advances understanding of the global controls of BPE, and suggests a route towards the improved representation of plant growth in vegetation and land surface models.