Water stress effects on biomass production and partitioning In processing tomatoes

Abstract

Experiments were conducted at the University of California, Davis field station. Soils were deep silty loam with high water storage capacity. water stress effects on vegetative and reproductive growth, canopy light conversion efficiency and single leaf photosynthesis of tomato, cultivar U.C. 82B were investigated under different irrigation regimes. Irrigation treatments were: well irrigated (I) and non-irrigated (NI). Treatment NI received no more irrigation after the sixth leaf stage and thus depended largely on water stored in the soil. There was little or no difference in leaf water potential between I and NI through most of the season. Single leaf photosynthetic rate also showed little response to irrigation treatments. However, withholding irrigation caused marked depression on canopy expansion. Non-irrigated plots had much smaller canopies and the resulting incomplete ground cover greatly reduced biomass accumulation. A linear relationship was found between cummulative intercepted radiation and biomass accumulation. The slope of this line is an expression of canopy photosynthetic efficiency. water stress reduced this parameter but this effect was much less than the reduction of canopy expansion suggesting that water stress depressed biomass accumulation largely through its effects in inhibiting canopy growth rather than canopy photosynthetic efficiency. Generally water stress depressed vegetative growth but enhanced or had no effect on reproductive growth. Water stressed plants had higher fruit set on early flower trusses. They al so had higher coeff icient of biomas s partitioning into fruits through most of the season but the duration of biomass accumulation into fruits was reduced. Prevention of fruit development by continuous flower removal failed to stimulate canopy growth in water stressed plants suggesting that the preferential partitioning of biomass into fruits may not be explained by simple competition for assimilates. Due to depression of canopy expansion, water stressed plants may be limited by vegetative sinks and this could ultimately lead to photosynthetic inhibition. Removal of all fruits depressed photosynthesis presumably through sink limitation and the mechanism involved was apparently similar to that reported for water stress limitation on photosynthesis. It is thus suggested that effect of water stress on photosynthesis could be operating through sink limitation.