Responses of photosynthesis and water relations to rainfall in the desert shrub creosote bush (Larrea tridentata) as influenced by municipal biosolids

Responses of photosynthesis (P-n), stomatal conductance (g(s)), pre-dawn le af water potential (Psi (1p)) and leaf water content (omega (1)) of creosot e bush to 10 rainfall events in the Chihuahuan Desert were investigated. In filtration of rainwater was manipulated by applying municipal biosolids. Th e responses of P-n and water relation parameters to rainfall ( > 10 mm) wer e mainly dependent upon drought severity: (1) following a moderate drought, P-n, g(s), Psi (1p) and omega (1) recovered to corresponding values of irr igated plants within 2 days after a 23-mm rainfall; (2) Psi (1p) and g(s) r esponded to a 15-mm rainfall within 2 days, following a 25-day drought, whe reas responses of P-n and w, were delayed for several days; (3) responses o f P-n, g(s), Psi (1p) and omega (1) to a 14.7-mm rainfall were all delayed for several weeks following a 110-day drought, but the delay was longer in P-n, g(s) and omega (1) than in Psi (1p). Creosote bush responded to small rainfall events (approximately 6 to 8 mm) with an increase in Psi (1p), but without noticeable changes in g(s) and P-n, suggesting a strong stomatal c ontrol of water loss even though xylem embolism was reduced. Biosolids appl ied at high rates (3.4 and 9 kg m(-2)) decreased the soil water by 2 to 4 m m following rainfall events, and this in turn delayed and decreased the res ponses of P-n and water relation parameters to rainfall. P-n and g(s) were linearly related to omega (1) and exponentially related t o Psi (1p). With the generally coincidental responses of P-n or g(s) and om ega (1) to rainfall, We concluded that the responses of P-n and g(s) to rai nfall were dependent on leaf rehydration which resulted from restored hydra ulic conductance following drought.