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Abstract

Great uncertainty exists in the global exchange of carbon between the atmosphere
and the terrestrial biosphere. An important source of this uncertainty
lies in the dependency of photosynthesis on the maximum rate of carboxylation
(Vcmax) and the maximum rate of electron transport (Jmax). Understanding and
making accurate prediction of C fluxes thus requires accurate characterization
of these rates and their relationship with plant nutrient status over large geographic
scales. Plant nutrient status is indicated by the traits: leaf nitrogen (N),
leaf phosphorus (P), and specific leaf area (SLA). Correlations between Vcmax
and Jmax and leaf nitrogen (N) are typically derived from local to global scales,
while correlations with leaf phosphorus (P) and specific leaf area (SLA) have
typically been derived at a local scale. Thus, there is no global-scale relationship
between Vcmax and Jmax and P or SLA limiting the ability of global-scale carbon
flux models do not account for P or SLA. We gathered published data from 24
studies to reveal global relationships of Vcmax and Jmax with leaf N, P, and SLA.
Vcmax was strongly related to leaf N, and increasing leaf P substantially
increased the sensitivity of Vcmax to leaf N. Jmax was strongly related to Vcmax,
and neither leaf N, P, or SLA had a substantial impact on the relationship.
Although more data are needed to expand the applicability of the relationship,
we show leaf P is a globally important determinant of photosynthetic rates. In a
model of photosynthesis, we showed that at high leaf N (3 gm
2), increasing
leaf P from 0.05 to 0.22 gm
2 nearly doubled assimilation rates. Finally, we
show that plants may employ a conservative strategy of Jmax to Vcmax coordination
that restricts photoinhibition when carboxylation is limiting at the expense
of maximizing photosynthetic rates when light is limiting.