Physiological comparisons of switchgrass cultivars differing in transpiration efficiency

Production of forage species like switchgrass (Panicum virgatum L.) is often relegated to areas with minimal inputs of water and fertilizer, therefore, selection should be based on efficient use of these resources. This study examined genotypic variation in switchgrass transpiration efficiency (TE), defined as the weight of dry matter per unit of water transpired, under conditions of water and N stress. Since reports show TE to be correlated with specific leaf weight (SLW) and leaf ash, these easily measured traits were assessed for their potential as predictors of switchgass TE. In one greenhouse experiment with nine cultivars and two outdoor experiments with two cultivars, plants were grown in closed containers in a soil-peat mix or solution culture and subjected to water or N deficit. Cultivars differed in TE; however, TE did not differ between water stressed and well-watered conditions. With decreasing N in solution, TE also decreased. Cultivars differed in their values of TE when grown in nutrient solutions containing 10.0 and 1.0 mM N, but not at 0.3 mM N. Transpiration efficiency was positively correlated with SLW in each experiment and across all experiments (r = 0.85), Correlation between TE and leaf ash was inconsistent, with a negative relationship in the water stress experiment and a positive relationship in the N experiment. The results show differences in TE among switchgrass cultivars and show that SLW is consistently predictive of TE.