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 leaf water potential (Psi (1p)) and leaf water content (omega (1)) of creosote bush to 10 rainfall events in the Chihuahuan Desert were investigated. Infiltration of rainwater was manipulated by applying municipal biosolids. The responses of P-n and water relation parameters to rainfall ( > 10 mm) were mainly dependent upon drought severity: (1) following a moderate drought, P-n, g(s), Psi (1p) and omega (1) recovered to corresponding values of irrigated plants within 2 days after a 23-mm rainfall; (2) Psi (1p) and g(s) responded to a 15-mm rainfall within 2 days, following a 25-day drought, whereas responses of P-n and w, were delayed for several days; (3) responses of 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 control of water loss even though xylem embolism was reduced. Biosolids applied at high rates (3.4 and 9 kg m(-2)) decreased the soil water by 2 to 4 mm following rainfall events, and this in turn delayed and decreased the responses of P-n and water relation parameters to rainfall. P-n and g(s) were linearly related to omega (1) and exponentially related to Psi (1p). With the generally coincidental responses of P-n or g(s) and omega (1) to rainfall, We concluded that the responses of P-n and g(s) to rainfall were dependent on leaf rehydration which resulted from restored hydraulic conductance following drought.