LTM01 Herbarium and grassland sites leaf trait measurements at Konza Prairie

Using herbarium specimens spanning 133 years and field-collected measurements, we assessed intraspecific trait (leaf structure and stomata) variability from grass species in the Great Plains of North America. We focused on two widespread, closely-related grasses from tribe Paniceae: Dichanthelium oligosanthes subsp. scribnerianum (C3) and Panicum virgatum (C4). Thirty-one specimens per taxon were sampled from local herbaria from the years 1887 – 2013 to assess trait responses across time to changes in atmospheric [CO2] and growing season precipitation and temperature. In 2021 and 2022, the species were measured from eight grasslands sites to explore how traits vary spatially across natural continental precipitation and temperature gradients.

For temporal trends, we predicted Δ13C would decrease in D. oligosanthes and exhibit no change in P. virgatum. Dichanthelium oligosanthes is a C3 species, which we predict will respond to increased [CO2] concentrations by increasing its WUE to either conserve water while maintaining the same rates of photosynthesis or increase photosynthesis and maintain the same rates of water loss, thus decreasing Δ13C. We did not expect Δ13C of P. virgatum to respond over time because discrimination in C4 species is minimally affected by [CO2]. We also predicted both grasses will increase tissue C:N ratios and decrease stomatal density and stomatal lengths on both sides of the leaves in response to increased [CO2] over time. Lastly, we hypothesized %N and δ15N would decrease for both taxa. Because both taxa are widely distributed across North America and are known to exhibit variation in leaf morphology, we expected specific leaf area (SLA) to be greater in areas with warmer temperatures but not be correlated with differences in precipitation. We expect leaf dry matter content (LDMC) to increase with greater precipitation and decrease with higher temperatures.