Gas exchange, water relations, and leaf traits were studied in the tuberous-root producing legumes ahipa (Pachyrhizus ahipa) and yambean (P. erosus) under different environmental conditions. Differences in leaf traits (hairiness, leaf area, areal leaf mass, stomatal density) and paraheliotropism were found between ahipa and yambean. Under sufficient water supply, the increase in air temperature and decrease in air humidity increased stomatal conductance (gs) and net photosynthetic rate (PN) in yambean but reduced them in ahipa. In a drying soil (14 d after irrigation), inter-specific variation in gas exchange was only observed in the early morning, and yambean showed a greater sensitivity to water restriction than ahipa. High gs at low humidity increased PN of P. erosus but resulted in lower water-use efficiency (WUE). However, long-term WUE, estimated by leaf carbon isotope discrimination, showed little variation between species. Daily-irrigated ahipa and yambean grown in the greenhouse did not show significant differences in gas exchange. However, leaf temperature was significantly greater in yambean than in ahipa while a steepper relationship between E and PN and gs was observed in ahipa.
Net photosynthetic (P^) and transpiration (£) rates and stomatal conductance (gj) were determined in cotton genotypes under drought during the growth cycle. A decrease in P^, E and gs was observed as soil water availability diminished. appeared dosely related to stomatal apertuře at low g^ levels. However, intercellular CO2 concentration was not so much affected by stomatal closure. An important inter- and intra-genotypic variation in g^ was found at the initial sampling dates. Inter-genotypic variation for increased with time, probably as a result of a higher capacity for water uptake in some genotypes.