Interactive effect of nitrogen and long-term moderate water stress on water relations in tomato (Lycopersicon esculentum Mill.) plants

The influence of three levels of N fertlization on the water relations of t omato plants (Lycopersicon esculentum Mill., cv. Royesta) grown on a sandy soil and subjected to long-term moderate water stress was established. In e ach treatment a volume representing 80% (stressed) or 100% (well-watered) o f the water evapotranspired the day preceding supply of Hoagland's solution (NO treatment), Hoagland's solution plus 60 mmol/L NO3- (N1 treatment) or Hoagland's solution plus 110 mmol/L NO3- (N2 treatment). The WFft/W-D ratio increased in stressed NO and N2 plants, although no significant difference s were observed between the values at either time considered. However, for the N1 dose a significant increase was observed in well-watered plants and no increase in stressed plants. The greatest decrease in LWP was observed i n water-stressed N1 plants, while the LWP value of well-watered plants rema ined constant throughout the experiment. The smaller decrease in LOPtlp tha n LOPft values in both stressed N1 and N2 plants suggests a mechanism of os motic adjustment or an increase in cell wall elasticity. However, the signi ficant increase in RWCtlp (3.5%) and cell wall rigidity (130% increase in E ) and the drop in LOPtlp (16%) indicate that there was a true osmotic adjus tment of 0.10 MPa in stressed N1 plants.