Global Variation in the Fraction of Leaf Nitrogen Allocated to Photosynthesis
Understanding how much nitrogen is allocated to RuBisCO (fLNR) is critical to our understanding of plant nitrogen use strategy and the estimation of global photosynthesis. We find global fLNR is 18.2 ± 6.2%, with its variation largely driven by leaf thickness and phosphorus, while soil and climate have substantial regional influences.
Our study provides a data-driven map of fLNR and Vcmax25 to constrain a key source of uncertainty in global carbon model parameterization. We identify the key biotic and abiotic controls on the variation in fLNR, and provide insight on the nitrogen use strategy of global vegetation.
Plants invest a considerable amount of leaf nitrogen in the photosynthetic enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO), forming a strong coupling of nitrogen and photosynthetic capacity. Variability in the nitrogen-photosynthesis relationship indicates different nitrogen use strategies of plants (i.e., the fraction nitrogen allocated to RuBisCO; fLNR), however, the reason for this remains unclear as widely different nitrogen use strategies are adopted in photosynthesis models. Here, we use a comprehensive database of in situ observations, a remote sensing product of leaf chlorophyll and ancillary climate and soil data, to examine the global distribution in fLNR using a random forest model. We find global fLNR is 18.2 ± 6.2%, with its variation largely driven by negative dependence on leaf mass per area and positive dependence on leaf phosphorus. Some climate and soil factors (i.e., light, atmospheric dryness, soil pH, and sand) have considerable positive influences on fLNR regionally. This study provides insight into the nitrogen-photosynthesis relationship of plants globally and an improved understanding of the global distribution of photosynthetic potential.