Effects of nitrogen nutrition and root medium water potential on growth, nitrogen uptake and osmotic adjustment of rice

Abstract

The effects of nitrogen (N) nutrition on growth, N uptake and leaf osmotic potential of rice plants (Oryza sativa L. ev. IR 36) during simulated water stress were determined. Twenty‐one‐day‐old seedlings in high (28.6 × 10 −4M) and low (7.14 × 10 4M) N levels were exposed to decreased nutrient solution water potentials by addition of polyethylene glycol 6000. The roots were separated from the solution by a semi‐permeable membrane. Nutrient solution water potential was −0.6 × 105 Pa and was lowered stepwise to −1 × 105, −2 × 105, −4 × 105 and −6 × 105 Pa at 2‐day intervals. Plant height, leaf area and shoot dry weight of high and low nitrogen plants were reduced by lower osmotic potentials of the root medium. Osmotic stress caused greater shoot growth reduction in high N than in low N plants. Stressed and unstressed plants in 7.14 × 104M N had more root dry matter than the corresponding plants in 28.6 × 104M N. Dawn leaf water potential of stressed plants was 1 × 105 to 5.5 × 105 Pa lower than nutrient solution water potential. Nitrogen‐deficient water‐stressed plants, however, maintained higher dawn leaf water potential than high nitrogen water‐stressed plants. It is suggested that this was due to higher root‐to‐shoot ratios of N deficient plants. The osmotic potentials of leaves at full turgor for control plants were about 1.3 × 105 Pa higher in 7.14 × 10−4M than in 28.6 × 10−4M N and osmotic adjustment of 2.6 × 105 and 4.3 × 105 Pa was obtained in low and high N plants, respectively. The nitrogen status of plants, therefore, affected the ability of the rice plant to adjust osmotically during water stress. Plant water stress decreased transpiration and total N content in shoots of both N treatments. Reduced shoot growth as a result of water stress caused the decrease in amount of water transpired. Transpiration and N uptake were significantly correlated. Our results show that nitrogen content is reduced in water‐stressed plants by the integrated effects of plant water stress per se on accumulation of dry matter and transpiring leaf area as well as the often cited changes in soil physical properties of a drying root medium.

Genotypic Variation in Nitrogen Uptake during Early Growth among Rice Cultivars under Different Soil Moisture Regimes

“…In rice, soil water deficit results in a reduction of transpiration of plants, thereby limiting N uptake (O'Toole and Baldia, 1982;O'Toole and Padilla, 1984;Yambao and O'Toole, 1984). Our results confirmed this relationship; the reduction of soil moisture resulted in the reduction of water uptake and N uptake (Fig.…”

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

“…Drought-conditioned wheat leaves are apparently capable of maintaining a high RWC by increasing 7r along with e (11). Higher 7r reported for well-watered low-N wheat leaves in this study (week 1, Table I) and for well-watered or predawn cotton leaves in other work (16,19) would suggest that low N nutrition may sometimes result in a similar response, although Yambao and O'Toole (29) reported greater 7r for high N rice leaves. In grasses, N nutrition has been shown to be negatively associated with TNC content of plant tissue (26,28).…”

“…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).…”

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

“…For short-term experiments, withholding water is the most common method, but, to simulate more realistic responses to drought, long-term water stress or cyclic water stress is needed (Pennypacker et al 1990). In addition, the development of water stress could be different in plants of different size, induced, e.g., by different nitrogen nutrition (Yambao et al 1984, Radin et al 1985. Therefore, it is necessary to carry out experiments where the plants grow in a moderate and progressive water stress; in addition, the different treatments assayed should have a comparable water-stress regime, to eliminate the uncertain effects of the treatments on the growth of the plants.…”