Ecophysiological traits in C₃ and C₄ grasses: a phylogenetically controlled screening experiment

Abstract

Summary• Experimental evidence demonstrates a higher efficiency of water and nitrogen use in C 4 compared with C 3 plants, which is hypothesized to drive differences in biomass allocation between C 3 and C 4 species. However, recent work shows that contrasts between C 3 and C 4 grasses may be misinterpreted without phylogenetic control.• Here, we compared leaf physiology and growth in multiple lineages of C 3 and C 4 grasses sampled from a monophyletic clade, and asked the following question: which ecophysiological traits differ consistently between photosynthetic types, and which vary among lineages?• C 4 species had lower stomatal conductance and water potential deficits, and higher water-use efficiency than C 3 species. Photosynthesis and nitrogen-use efficiency were also greater in C 4 species, varying markedly between clades. Contrary to previous studies, leaf nitrogen concentration was similar in C 4 and C 3 types. Canopy mass and area were greater, and root mass smaller, in the tribe Paniceae than in most other lineages. The size of this phylogenetic effect on biomass partitioning was greater in the C 4 NADP-me species than in species of other types.• Our results show that the phylogenetic diversity underlying C 4 photosynthesis is critical to understanding its functional consequences. Phylogenetic bias is therefore a crucial factor to be considered when comparing the ecophysiology of C 3 and C 4 species.

Plant nutrients do not covary with soil nutrients under changing climatic conditions

“…Nutrient concentrations were more strongly influenced by precipitation for most tissues in Stipa and Agropyron but were more associated with temperature for both tissues in Cleistogenes. This may be an underlying mechanism contributing to the differential response of biomass allocation to climate change between the C3 plants (Stipa and Agropyron) and the C4 plant (Cleistogenes) [Luo et al, 2013], reflecting the differences in fundamental biochemical pathways and processes between C3 and C4 plants [Taylor et al, 2010;Still et al, 2014].…”

Evolution of C 4 plants: a new hypothesis for an interaction of CO 2 and water relations mediated by plant hydraulics

“…The lower E and greater WUE of C 4 than C 3 plants was first recognized more than 40 years ago [60], although it is subject to ecological adaptation that can lead to significant interspecific variation and thus overlaps in the ranges of photosynthesis and transpiration for the two photosynthetic types [61]. However, recent work sampling multiple independent lineages of C 4 grasses from a range of different habitats showed that g s is significantly lower in each lineage of C 4 species than in closely related lineages of C 3 grasses [57,58]. The need for a lower g s to conserve water is especially strong when CO 2 levels fall and leaves tend to open stomata to maintain photosynthesis.…”

Partitioning the Components of Relative Growth Rate: How Important Is Plant Size Variation?

“…We illustrate the associated problems using a single data set (Taylor et al 2010) analyzed with both a classical analysis and an analysis in which RGR and its components are calculated at a common size.…”

“…At each harvest, the total leaf area (A L ), total leaf mass (M L ), and total plant mass (M P ) were measured (mass always refers to dry biomass). Using these data, we performed a species-specific functional growth analysis by fitting growth functions to the time trajectories of m P (Venus and Causton 1979;Hunt 1982;Rose et al 2009;Taylor et al 2010) and used these species-specific functions to estimate RGR at a common reference size for all species (Rose et al 2009). Armed with an estimate of rgr, we then need to estimate both a L and m L at the reference size in order to apply equation (2); this was achieved by establishing regressions between both leaf area and mass and total plant mass.…”