There and back again: Intraspecific plant physiological responses to multiple droughts and recovery in a perennial C4 grass

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Nathan Emery, Linnea Fraser, Ian Willick, Anne-Sophie Bohrer and Sunil K. Kenchanmane Raju, Plant Biology, Michigan State University, East Lansing, MI, Mauricio Tejera, Plant Research Laboratory, Michigan State University, East Lansing, MI

Background/Question/Methods
Plant species are increasingly experiencing water deficits due to our changing climate. Periodic drought results in differential outcomes for different plant populations based on local adaptation, genetics, and physiological plasticity. Panicum virgatum (switchgrass) is a native perennial C4 grass that grows across a wide swath of central and eastern North America and is a focal species for bioenergy crop research. Previous research has investigated drought tolerance of various switchgrass populations, but less is known about how these plants recover and persevere through multiple droughts. We asked how several drought-tolerant genotypes of switchgrass succumb to drought, recover, and respond to a subsequent drought. We selected three genotypes of switchgrass based on their differential drought tolerance (most tolerant, AP13; moderately tolerant, Kanlow; and least tolerant, Cave-in-rock). In a glasshouse, plants were subjected to drought, well-watered for recovery, and deprived of water a second time. We quantified water potential, leaf hydraulics, and gas exchange. Additionally, we measured stomatal characteristics pre-experiment and during recovery to identify any morphological legacies of drought.
Results/Conclusions
We found that each genotype responded differently to drought and recovery. While all three genotypes reduced assimilation rates and stomatal conductance during peak drought, two only had small reductions in water potential despite being on opposite ends of the drought tolerance spectrum (AP13 and Cave-in-rock). In contrast, the third genotype (Kanlow), had a much greater reduction in water potential as well as a fast physiological recovery after rewatering. AP13 and Cave-in-rock did not recover photosynthetic rates or water potential 36hrs after rewatering compared to Kanlow. Additionally, AP13 drought plants did not recover to control gas exchange rates even one month after recovery and fertilization. It is possible that AP13 experienced membrane injury during the initial recovery process, as treatment plants had higher tissue conductivity post-watering than during peak drought, contrary to reductions in conductivity for Kanlow and Cave-in-rock droughted plants. This suggests two strategies of managing drought between the populations: a conservative, yet imperturbable strategy employed by AP13 and Cave-in-rock, and a fast, responsive strategy employed by Kanlow. Our results highlight the importance of considering the complex strategies that plants employ for drought tolerance and recovery, and how intraspecific variation in drought response will affect plant productivity and persistence. This has important implications for conservation of locally adapted populations and for bioenergy production efforts to grow switchgrass in regions predicted to experience periodic water deficits.