DEPLETION OF SOIL-MOISTURE BY 2 COLD-DESERT BUNCHGRASSES AND EFFECTS ON PHOTOSYNTHETIC PERFORMANCE

This study compared the abilities of to cool-season bunchgrasses to ex tract moisture from a drying soil and compared photosynthetic and stom atal responses of the to species as soil moisture supplies were deplet ed. When grown in 49-L pots in a greenhouse, Leymus cine-errs extracte d more water from the soil and maintained higher gas exchange rates to lower absolute amounts of soil water than did Agropyron desertorum. T he soil water content at the lower limit of extraction was 10.3% for L . cillereus and 13.3% for A. desertorum. When soil moisture was expres sed as extractable soil water, there was little difference between the species in pattern of water use. Bath species maintained high stomata l conductances (g(w)) and photosynthetic rates (hi until extractable s oil moisture was reduced to about 15%. For field-grown plants under se vere water stress, A was higher in L. cinereus than in A. desertorum a t comparable leaf water potentials. The relationship between A and g(w ) was similar for the two species; the higher A in L. cinereus was a c onsequence of higher g(w). Thus, higher A in L. cinereus is achieved t hrough some sacrifice of water-use efficiency.