Photosynthetic responses of switchgrass to light and CO2 under different precipitation treatments

Authors: KIEFFER, CHRISTINA - Tennessee State University; KAUR, NAVNEET - Department Of Energy; LI, JIANWEI - Tennessee State University; MATAMALA, ROSE - Argonne National Laboratory; FAY, PHILIP - Retired ARS Employee; HUI, DAFENG - Tennessee State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Switchgrass is a prominent bioenergy crop with robust resilience to environmental stresses such as drought. However, our knowledge regarding how changing precipitation affects switchgrass photosynthesis and its responses to light and CO2 remains limited. These responses are crucial traits contributing to stress tolerance and biomass production. Measurements of photosynthesis-light response curves and photosynthesis-CO2 response curves in established stands of “Alamo” switchgrass undergoing experimental drought and irrigation treatments in central Tennessee revealed that changes in precipitation up to 50% below or 50% above the reference level caused significant, though small, effects on photosynthetic responses to light and CO2. Photosynthetic traits including maximum photosynthesis rates, light and CO2 uptake efficiencies, and light and CO2 compensation points, which help indicate the capacity of switchgrass to take up atmospheric CO2 in photosynthesis, all changed little in response to changing precipitation. These findings indicate that “Alamo” switchgrass photosynthetic capacity tolerated large increases or decreases in precipitation, and this stability in photosynthetic capacity may contribute to biomass feedstock production in central Tennessee.

Technical Abstract: Switchgrass is a prominent bioenergy crop with robust resilience to environmental stresses. However, our knowledge regarding how precipitations change affect switchgrass photosynthesis and its responses to light and CO2 remains limited. To address this knowledge gap, we conducted a field precipitation experiment at the Tennessee State University Agricultural Research and Education Center, Nashville, TN with five different precipitation treatments, including -50%, -33%, 0%, +33%, and +50% of ambient precipitation. To determine the responses of leaf photosynthesis to CO2 concentration and light, we measured leaf net photosynthesis of switchgrass under different CO2 concentrations and light levels over the growing season of 2020 and 2021 for each of the five precipitation treatments. We first evaluated four light and CO2 response models (i.e., rectangular hyperbola model, nonrectangular hyperbola model, exponential model, and the modified rectangular hyperbola model) using the measurements in the ambient precipitation treatment. Based on fitting criteria, we selected the nonrectangular hyperbola model as the optimal model and applied it to all precipitation treatments, and estimated model parameters. The results showed overall, the model fit all field measurements well for the light and CO2 response curves. Precipitation change did not influence the maximum net photosynthetic rate (Pmax) but influenced other model parameters including quantum yield (a), convexity ('), dark respiration (Rd), light compensation point (Lcp), and saturated light point (Lsp). Specifically, the mean Pmax of five precipitation treatments was 17.6 µmol CO2 m-2s-1, and the ambient treatment tended to have higher Pmax. The +33% treatment had the highest a, and ambient treatment had lower ' and Lcp, higher Rd, and relatively lower Lsp. Furthermore, precipitation significantly influenced all model parameters of CO2 response. The ambient treatment had the highest Pmax, largest a, and lowest ', Rd, and CO2 compensation point Lcp. Overall, this study improved our understanding of how switchgrass leaf photosynthesis responds to diverse environmental factors, providing valuable insights for accurately modeling switchgrass ecophysiology and productivity.