Evolutionary history plays a key role driving patterns of trait variation across plant species. For scaling and modeling purposes, grass species are typically organized into C3 versus C4 plant functional types (PFTs). PFT groupings may obscure important functional differences among species. Rather, grouping grasses by evolutionary lineage may better represent grass functional diversity.
We measured 11 structural and physiological traits in situ from 75 grass species within the North American tallgrass prairie. We tested whether traits differed significantly among photosynthetic pathways or lineages (tribe) in annual and perennial grass species. We hypothesized that tribe would be the best predictor of traits, more so than photosynthetic pathway. We further hypothesized that there would be substantial variation of traits in species among the seven C4 lineages represented at our site.
Research location: Sampling occurred throughout the entirety of Konza Prairie Biological Station – there was no specific location for measuring all the species given that we measured naturally established individuals growing within their own viable habitat.
Sampling occurred throughout the entirety of the Konza Prairie Biological Station during the summer of 2020. A suite of plant traits was collected for each replicate in coordination with the initiation of flowering for each species. Traits measured include photosynthetic A-Ci response curves (to derive Vcmax, Jmax, and Vpmax (for C4 species)), leaf osmotic potential at full turgor (MPa), specific leaf area (SLA; cm2 g−1), leaf dry matter content (LDMC), leaf thickness (mm), maximum plant flowering and vegetative heights (cm), leaf C:N, and δ13C leaf composition. Vcmax is the maximum rate of carboxylation of Rubisco (μmol m−2s−1), Jmax is the maximum rate of electron transport (μmol electrons m−2s−1), and Vpmax is the maximum rate of carboxylation of PEPc (μmol m−2s−1).
Leaf gas exchange was measured with a LI-6400XT Portable Photosynthesis System (Li-COR, Inc., Lincoln, Nebraska, USA), osmotic potential was measured using a VAPRO® Vapor Pressure Osmometer (Model 5600; Logan, Utah, USA). Leaf C and N content and stable C isotopic composition were measured at the Stable Isotope Mass Spectrometry Laboratory at Kansas State University. Maximum flowering height and maximum vegetative height (cm) were measured from the ground to the highest point of the inflorescence or the uppermost leaf, respectively. Leaf area was measured in the field using Leafscan, a mobile app for measuring the surface area of individual leaves. Leaf wet mass was measured after leaf rehydration and leaf dry mass was measured after the leaf had been dried for at least 48 hours at 60 °C. Rehydration was performed by submerging the leaf in water for 24-72 hours. Leaf thickness was derived from (SLA * LDMC)-1 and multiplied by 10 to convert to mm.