Michigan State University Santa Barbara, Michigan, United States
Background/Question/Methods
Detecting plant physiological function remotely has great potential for assessing plants in applied and natural environments. While remotely distinguishing plant species is relatively well established, detecting intraspecific variation in plant function is less understood. In Panicum virgatum (switchgrass), a native perennial C4 grass that grows across central and eastern North America, there are multiple populations that are locally adapted to different climate conditions. Genetic profiles suggest that there are four major groups consisting of Eastern, Midwest, Texas, and the Gulf coast populations. As part of the Great Lakes Bioenergy Research Center at Michigan State University, we assessed the relationship between multispectral reflectance (normalized difference vegetation index, NDVI) and individual plant gas exchange using a LI-6800 for 150 plants for two years in a genome-wide association study. We asked how populations vary in physiological function and reflectance across a season. Additionally, we sought to establish predictive relationships between spectral reflectance and gas exchange in switchgrass.
Results/Conclusions
We found that while populations had similar gas exchange rates early in the season, Midwest and Eastern plants began senescing earlier than populations from southern regions. Interestingly, populations from Texas were almost indistinguishable from Midwest and Eastern plants when comparing greenness across the season (using NDVI). Gulf coast plants, on the contrary, maintained high photosynthetic activity and greenness values through September. This late season activity is likely reflective of their inability to acclimate to cold temperatures and reallocate resources into belowground tissues. There was a significant positive relationship between NDVI and gas exchange for all populations when the month of June was excluded from the analysis. In the early season, there was a large amount of variation in gas exchange rates despite consistent high greenness NDVI values. This is possibly an important disconnect between remotely sensed reflectance and plant physiological function. These results have important implications for assessments of plant physiological function across populations and for bioenergy production efforts to grow switchgrass populations outside of their locally adapted climates.
