Leaf Gas Exchange and Fluorescence of Two Winter Wheat Varieties in Response to Drought Stress and Nitrogen Supply

Abstract

Water and nitrogen supply are the two primary factors limiting productivity of wheat (Triticum aestivum L.). In our study, two winter wheat varieties, Xinong 979 and large-spike wheat, were evaluated for their physiological responses to different levels of nitrogen and water status during their seedling stage grown in a phytotron. Our results indicated that drought stress greatly reduced the net photosynthetic rate (Pn), transpiration rate (E), and stomatal conductance (Gs), but with a greater increase in instantaneous water use efficiency (WUE). At the meantime, the nitrogen (N) supply improved photosynthetic efficiency under water deficit. Parameters inferred from chlorophyll a measurements, i.e., photochemical quenching coefficient (qP), the maximum photochemical efficiency (Fv/Fm), the quantum yield of photosystemII(ΦPSII), and the apparent photosynthetic electron transport rate (ETR) decreased under water stress at all nitrogen levels and declined in N-deficient plants. The root–shoot ratio (R/S) increased slightly with water stress at a low N level; the smallest root–shoot ratio was found at a high N level and moderate drought stress treatment. These results suggest that an appropriate nitrogen supply may be necessary to enhance drought resistance in wheat by improving photosynthetic efficiency and relieving photoinhibition under drought stress. However, an excessive N supply had no effect on drought resistance, which even showed an adverse effect on plant growth. Comparing the two cultivars, Xinong 979 has a stronger drought resistance compared with large-spike wheat under N deficiency.

Efficient Physiological and Nutrient Use Efficiency Responses of Maize Leaves to Drought Stress under Different Field Nitrogen Conditions

“…After 10-15 days of no water supply, the maize leaves at 120, 180, 240, and 260 kg N ha −1 treatment rates gradually began to curl from 10:00 a.m. to 5:00 p.m. daily, and the leaves were unfurled for the rest time of the day (Figure 2a). Several studies have shown that N deficiency exacerbated the sensitivity of stomata to drought [15,26]; however, we did not observe the leaf curling in the absence of N treatments, which was found under higher N treatment rates. This might be the case, as the application of N fertilizers increased plant water transpiration ( Figure 5), causing the plants treated with higher N treatment rates to enter the drought state earlier, which masked the increased resistance to drought stress with additional N treatments for the maize.…”

“…Since nitrogen (N) is a vital component required for the synthesis of chlorophyll and photosynthetic enzymes in plants, which directly and indirectly impact the photosynthesis of crops, its presence or absence can determine the overall yields of crops [14]. Drought stress strongly affects growth and N metabolism, while the application of N can contribute to drought resistance to a certain extent in many plants [15]. Under water deficits, N supplies can be conducive toward the enhancement of the drought resistance of crops by protecting photosynthetic apparatus, activating antioxidant defense systems and improving osmoregulation [16].…”

Effect of terminal drought on yield and some physiological traits of winter wheat

“…In contrast, WUEi slightly (not significant) or WUE significantly (during morning measurement period) increased under terminal drought (Figure 2i, 2j, 2k and 2l), due to faster decrease in gs and E compared to A. Similar increase in WUE and WUEi under drought stress were reported for wheat seedlings (WANG et al, 2016). The flag leaf is the major source of assimilates for grain-filling (LARBI, 2004), therefore stay-green strategy which combines delaying senescence, maintaining leaf chlorophyll content, sustaining transpiration, and photosynthetic rate (VADEZ et al, 2011) represents one of the key factors that contributes to embodiment of yield potential under terminal drought stress.…”

Physiological Responses of Physalis angulata Plants to Water Deficit

“…The CO 2 assimilation rate decreased by 41.06% when compared to plants growth with 100% and 20% of field capacity (Figure 3a). The effects of reducing water availability on the photosynthetic rate were reported in several studies (Rahmati et al, 2015;X. Wang, L. Wang, & Shangguan, 2016;Pazzagli, Weiner, & Liu, 2016).…”