Effects of plant physiological traits on photosynthetic capacity and parameters are scale-dependent

Background/Question/Methods

Leaf traits affect carbon assimilation rates by influencing components of the biochemical processes in photosynthesis. The impacts of leaf traits on biochemical parameters need to be investigated to obtain a mechanistic understanding of the observed relationship between carbon assimilation and leaf traits. In order to examine the effects of leaf traits on photosynthetic parameters, we conducted field experiments in a tall-grass prairie restoration project in Urbana, IL, USA. Photosynthetic CO₂ (A/Ci) and light (A/q) response curves, leaf nitrogen (N), chlorophyll (Chl) concentration, and specific leaf area (SLA) were measured monthly from June to October for 25 grassland perennial species in 2010 and 2011. For purposes of simplifying our analyses these species were assigned to five plant functional types (PFT): C3 grasses, C4 grasses, forbs, legumes and sedge. C3 Farquhar, von Caemmerer and Berry (FvCB) model (Farquhar et al. 1980) and simplified C4 intercellular transport (ICT) model (Collatz et al. 1992) were parameterized using a novel Hierarchical Bayesian approach.

Results/Conclusions

The results confirmed the positive sign of the overall effects of leaf N and SLA on photosynthetic capacity (photosynthetic rate at saturating light and ambient CO2, denoted as A_net) found in global plant trait analysis (Wright et al. 2004; Wright et al. 2005; Reich et al. 2007), but extended these analyses to address the scale-dependence of such results. Effects of leaf N, Chl, and SLA on A_net varied among species and changed through the growing season. SLA was not found to be as important as expected for predicting photosynthetic rates in species-specific fine scale studies. V_cmax was ~ 20 µmol m^-2 s^-1 for C4 species and ranged from 43.21 to 130.48 µmol m^-2 s^-1 for C3 species. The effects of leaf N on maximum Rubisco carboxylation capacity (V_cmax) and the effects of Chl on quantum efficiency were significant for most species. Effects of SLA on quantum efficiency were only significant for four species. V_cmax was positively related with species average A_net, J_max, quantum efficiency and respiration among C3 species. V_cmax and maximum electron transport rate (J_max) of legumes were generally high, which associates with high leaf N, Chl and SLA level.