Informing models through empirical relationships between foliar phosphorus, nitrogen and photosynthesis across diverse woody species in tropical forests of Panama

Abstract

SummaryOur objective was to analyze and summarize data describing photosynthetic parameters and foliar nutrient concentrations from tropical forests in Panama to inform model representation of phosphorus (P) limitation of tropical forest productivity.Gas exchange and nutrient content data were collected from 144 observations of upper canopy leaves from at least 65 species at two forest sites in Panama, differing in species composition, rainfall and soil fertility. Photosynthetic parameters were derived from analysis of assimilation rate vs internal CO 2 concentration curves (A/C i ), and relationships with foliar nitrogen (N) and P content were developed.The relationships between area-based photosynthetic parameters and nutrients were of similar strength for N and P and robust across diverse species and site conditions. The strongest relationship expressed maximum electron transport rate (J max ) as a multivariate function of both N and P, and this relationship was improved with the inclusion of independent data on wood density.Models that estimate photosynthesis from foliar N would be improved only modestly by including additional data on foliar P, but doing so may increase the capability of models to predict future conditions in P-limited tropical forests, especially when combined with data on edaphic conditions and other environmental drivers.

The impact of alternative trait‐scaling hypotheses for the maximum photosynthetic carboxylation rate (Vcmax) on global gross primary production

“…), which is not consistent with our data‐driven estimate (Environ_PFT). N limitation hypothesis predictions of tropical V cmax,25 were consistent with the literature, often reported in the range 20–80 μmol m −2 s −1 (Domingues et al ., , ; Vårhammar et al ., ; Norby et al ., ), but were not consistent with values reported for the high Arctic, in the range 60–160 μmol m −2 s −1 (A. Rogers et al ., unpublished).…”

In situ temperature response of photosynthesis of 42 tree and liana species in the canopy of two Panamanian lowland tropical forests with contrasting rainfall regimes

“…() found, for tropical montane trees, that T Opt of J Max was lower than that of V cMax . However, although leaf nitrogen content and V cMax are significantly lower at PNSL, J Max is not (Norby et al ., ). As a result, species at PNSL are more likely to be limited by carboxylation capacity – and its temperature dynamics – than by electron transport.…”

“…Even under similar environmental conditions in the canopy, physiological parameters that play a role in shaping the temperature response of photosynthesis differ enormously among co‐occurring ‘slow’ and ‘fast’ species. Species differ systematically in maximum stomatal conductance (Reich et al ., ), stomatal responsiveness to drought (Huc et al ., ), respiratory capacity (Slot et al ., ), photosynthetic biochemistry as determined from CO 2 –response curves (Norby et al ., ) and the temperature optima of Rubisco carboxylation and photosynthetic electron transport rates (Vårhammar et al ., ). These systematic differences could lead to higher T Opt in ‘fast’ than in ‘slow’ species, consistent with the observations in seedlings (Slot et al ., ).…”

“…These systematic differences could lead to higher T Opt in ‘fast’ than in ‘slow’ species, consistent with the observations in seedlings (Slot et al ., ). For example, photosynthesis at high temperature is commonly limited by electron transport (Wise et al ., ; Sage & Kubien, ): ‘fast’ species have higher electron transport capacity than slow species (Norby et al ., ), which may enable the maintenance of higher photosynthesis rates at high temperature than in ‘slow’ species. Among tropical montane trees, ‘fast’ species also have higher T Opt of electron transport (Vårhammar et al ., ), which may further favor their performance at high temperature.…”

A representation of the phosphorus cycle for ORCHIDEE (revision 4520)

“…2). While the link between leaf nitrogen concentration and the carboxylation efficiency of photosynthesis (V cmax ) is well established (Kattge et al, 2009), the role of leaf phosphorus concentration in photosynthesis is less clear as nitrogen and phosphorus concentrations usually co-vary (Reich et al, 2009;Kattge et al, 2009;Domingues et al, 2010;Bahar et al, 2016;Norby et al, 2016).…”