Responses of photosynthesis and carbohydrate‐partitioning to limitations in nitrogen and water availability in field‐grown sunflower^*

Abstract

Abstract. Sunflower plants (Helianthus annuus L., cv. CGL 208) were field‐grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient‐stress (N‐stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen‐limited. Water‐stress (H2O‐stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient‐stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen‐use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O‐stress treatments. In addition, N‐stress reduced photosynthetic water‐use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O‐stress. In addition, sunflower plants responded to H2O‐stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O‐stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field‐grown sunflower manages a trade‐off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.

Starch and soluble carbohydrates in leaves of water-stressed oak saplings

“…This result contrasted with the lack of drought effects on hexose in grapevine (Rodrigues et al, 1993), but was similar to the seven-to 14-fold increase in glucose concentration in sunflower leaves observed by Fredeen et al (1991). Despite a significant decrease in sucrose concentration, total soluble carbohydrates (sucrose + glucose + fructose) greatly increased in water-stressed plants (+76%).…”

“…5.3.1.9) and then into 6-phosphogluconate by glucose-6-P deshydrogenase (E.C. (Bensari et al, 1990;Fredeen et al, 1991;Quick et al, 1992) or remained at levels close to those of control plants in lupin or grapevine (Quick et al, 1992).…”

Growth, physiology, and nutrient retranslocation in nitrogen-15 fertilized Quercus rubra seedlings

“…We speculate that leaf N concentration was not the only factor contributing to the greater effects on growth responses between unfertilized and fertilized seedlings. Freeden et al [18] suggested that the photosynthetic process is down-regulated under conditions of N limitation. In our study, the observed decline in g s in unfertilized seedlings resulted in reduced CO 2 assimilation rates.…”

Impact of Saline Conditions and Nitrogen Fertilization on Citrus Production and Gas Exchanges

“…In citrus plants, Syvertsen, Smith e Boman (1993) observed that N concentration decreased as Cl -concentrations increased in the leaves; however, Lea-Cox and Syvertsen (1993) reported that foliar N application increased photosynthesis rate in citrus plants subjected to saline stress. Greater stomatal resistance was observed in plants cultivated under low N conditions, and the authors concluded that the decrease in photosynthesis was caused by the inhibition of the activity of the RuBP enzyme (Ribulose-1,5-bisphosphate carboxylase/oxygenase) (FREDEEN; GAMON;FIED, 1991).…”