Great Basin Naturalist


This study compared the abilities of two cool-season bunchgrasses to extract moisture from a drying soil and compared photosynthetic and stomatal responses of the two species as soil moisture supplies were depleted. When grown in 49-L pots in a greenhouse, Leymus cinereus extracted more water from the soil and maintained higher gas exchange rates to lower absolute amounts of soil water than did Agropyron desertorum. The soil water content at the lower limit of extraction was 10.3% for L. cinereus and 13.3% for A. desertorum. When soil moisture was expressed as extractable soil water, there was little difference between the species in pattern of water use. Both species maintained high stomatal conductances (gw) and photosynthetic rates (A) until extractable soil moisture was reduced to about 15%. For field-grown plants under severe water stress, A was higher in L. cinereus than in A. desertorum at comparable leaf water potentials. The relationship between A and gw was similar for the two species; higher A in L. cinereus was a consequence of higher gw. Thus, higher A in L. cinereus is achieved through some sacrifice of water-use efficiency.