The Effects of N Nutrition on the Water Relations and Gas Exchange Characteristics of Wheat (Triticum aestivum L.)

Abstract

The purpose of this study was to characterize leaf photosynthetic and stomatal responses of wheat (Triticum aestivum L.) plants grown under two N-nutritional regimes. High-and low-N regimes were imposed on growth-chamber-grown plants by fertilizing with nutrient solutions containing 12 or I millimolar nitrogen, respectively. Gas-exchange measurements indicated not only greater photosynthetic capacity of high-N plants under well-watered conditions, but also a greater sensitivity of CO2 exchange rate and leaf conductance to CO2 and leaf water potential compared to low-N plants. Increased sensitivity of high-N plants was associated with greater tissue elasticity, lower values of leaf osmotic pressure and greater aboveground biomass. These N-nutritional-related changes resulted in greater desiccation (lowered relative water content) of high-N plants as leaf water potential fell, and were implicated as being important in causing greater sensitivity of high-N leaf gas exchange to reductions in water potential. Water use efficiency of leaves, calculated as CO2 exchange rate/transpiration, increased from 9.1 to 13 millimoles per mole and 7.9 to 9.1 millimoles per mole for high-and low-N plants as water became limiting. Stomatal oscillations were commonly observed in the low-N treatment at low leaf water potentials and ambient CO2 concentrations, but disappeared as CO2 was lowered and stomata opened. but was also more responsive to I, resulting in lower g as water became less available (24,27,30). Other work on cotton and tea has indicated an opposite response; decreased stomatal sensitivity to I associated with high N nutrition (15,17,19). Nitrogen nutrition was found to have little effect on stomatal response of Panicum maximum var trichoglume or rice (Oryza sativa L.) to changes in ' (10, 29).Stomatal closure resulting from water stress is apparently linked to ABA metabolism. The release and/or production of ABA in the mesophyll occurs in response to water stress in these cells (21). ABA then travels to the guard cells where its accumulation results in stomatal closure, and often, increased stomatal sensitization to C, (20)(21)(22). In the long run, water stress induced reductions in mesophyll photosynthetic capacity may affect stomatal conductance since reduced carbon compounds required for stomatal performance are synthesized in the mesophyll (7, 21).The purpose of the present study was to investigate further the effect of N nutrition on stomatal and photosynthetic response to I in wheat leaves in conjunction with investigations on N nutritional effects on internal plant water relations. Stomatal response to I will be assessed in terms of sensitivity of g to.and Ci. Effects of water stress on mesophyll photosynthetic capacity will be determined from C, response curves of CER. The objective of this analysis is to better understand the physiological nature of increased stomatal sensitivity of wheat gas exchange to water stress related to high N nutrition. MATERIALS AND METHODSPlant Material. Caryopses of 'Olaf...

Interactive Effects of N-, P- and K-Nutrition and Drought Stress on the Development of Maize Seedlings

“…The lower shoot DW with N, NP and NPK fertilization may be due to an increase in assimilate allocation to roots for maintaining root growth, for osmotic adjustment and for turgor maintenance [10,25,26]. Similar results were reported by other authors [21,47,48]. Therefore, higher root/shoot ratios could be exploited as a strategy for stress tolerance in crop plants.…”

Moderate water stress affects tomato leaf water relations in dependence on the nitrogen supply

“…The objective of this research was to assess the effects of nitrogen fertilisation, with three different doses, on the water relations of tomato plants exposed to drought with the same water deficit regardless the original size of the plants, in order to clearly separate, in accordance with Morgan (1986), the intrinsic effects of N-nutrition from those related to plant growth phenomena, and to assess comparable water-stress regimes.…”

Cell membrane stability and leaf water relations as affected by nitrogen nutrition under water stress in maize

“…Osmotic adjustment of 0.49 MPa (average in three cultivars) was evident at the highest N level in the water stress treatment. Morgan (1986) observed an osmotic adjustment of 0.29 MPa with higher N supply under water stress in wheat. Increase in osmotic adjustment with increasing N levels was largest in P-3358, smallest in G-4578, and intermediate in FFR-677, and this cultivar order was the same as that of the reduction in injury percentage in the PEG test under water stress conditions.…”

“…Plants were stressed by limited soil moisture at higher N levels. Decreases in leaf water potential with higher N levels and low soil moisture conditions have been observed in various crop plants (Radin and Parker 1979;Radin and Ackerson 1981;Morgan 1986). Radin et al (1982) observed decreases in the leaf water potential of about 0.4 MPa with higher N level in cotton.…”

“…Nitrogen deficiency sensitized cotton (Gossypium hirsutum L.) plants to water stress causing the effects of stress to occur at a higher water potential (Radin and Ackerson 1981). When the nitrogen level was high, wheat (Triticum aestivum L.) plants showed an increase in tissue elasticity, a decrease in leaf osmotic potential, and an increase in sensitivity of leaf conductance to water deficit (Morgan 1986).…”