Growth and Transpiration Responses of Elephantgrass and Energycane to Soil Drying

Abstract

ABSTRACTElephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.) are promising perennial bioenergy crops in the southeastern United States. Despite plentiful rainfall in this region, these perennial grasses have a long growing season and are subject to intermittent drying cycles frequently during summer and fall, yet there is little information on their response to intermittent drought stress. The objectives of this study were to investigate water relations of elephantgrass and energycane genotypes under optimal water inputs and in response to progressive soil drying. Three elephantgrass genotypes (‘UF‐1’, ‘Merkeron’, and ‘PI‐300086’) and three energycane genotypes (‘L79‐1002’, ‘US84‐1047’, and ‘875‐3’) were grown in a greenhouse. Under well‐watered conditions, elephantgrass and energycane exhibited similar daily and total water use, but energycane possessed greater average daily transpiration per unit leaf area (EAVE,leaf) and lower shoot transpiration efficiency (TEshoot) than elephantgrass. Consistent with EAVE, leaf, energycane demonstrated higher stomatal conductance than elephantgrass, but lower assimilation to transpiration ratio (A/T). Among all genotypes, UF‐1 elephantgrass exhibited relatively high A/T, shoot mass production, and TEshoot. In response to progressive soil drying, elephantgrass genotypes closed their stomata at a lower fraction of transpirable soil water and produced higher shoot mass during the drying cycle than energycane genotypes. The different plant water use patterns indicated a species difference in the sensitivity to mild drought stress and could be correlated with their stomatal density and size. The results from this study indicated that elephantgrass is more suited to the frequent mild drought stress between rainfall events common during summer in the southeastern United States.