Defining the metabolic strategies used by wheat to tolerate and recover from drought events will be important for ensuring yield stability in the future, but studies addressing this critical research topic are limited. To this end, the current study quantified the physiological, biochemical, and agronomic responses of a drought tolerant and drought sensitive cultivar to periods of water deficit and recovery. Drought stress caused a reversible decline in leaf water relations, membrane stability, and photosynthetic activity, leading to increased reactive oxygen species (ROS) generation, lipid peroxidation and membrane injury. Plants exhibited osmotic adjustment through the accumulation of soluble sugars, proline, and free amino acids and increased enzymatic and non-enzymatic antioxidant activities. After re-watering, leaf water potential, membrane stability, photosynthetic processes, ROS generation, anti-oxidative activities, lipid peroxidation, and osmotic potential completely recovered for moderately stressed plants and did not fully recover in severely stressed plants. Higher photosynthetic rates during drought and rapid recovery after re-watering produced less-pronounced yield declines in the tolerant cultivar than the sensitive cultivar. These results suggested that the plant’s ability to maintain functions during drought and to rapidly recover after re-watering during vegetative periods are important for determining final productivity in wheat.

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Low radiation reduces wheat grain yield in tree‐crop intercropping systems in the major wheat planting area of China. Here, two winter wheat (Triticum aestivum L) cultivars, Yangmai 158 (shading tolerant) and Yangmai 11 (shading sensitive), were shaded from jointing to maturity to evaluate the impact of low radiation on crop growth, photosynthesis and yield. Grain yield losses and leaf area index (LAI) reduction were less than the reduction in solar radiation under both shading treatment in both cultivars. Compared with the control (S0), grain yield only reduced 6.4 % and 9.9 % under 22 % shading treatment (S1), while 16.2 % and 25.8 % under 33 % shading (S2) in Yangmai 158 and Yangmai 11 respectively. The reduction in LAI was 6.0 % and 9.2 % (S1), and 18.2 % and 22.2 % (S2) in Yangmai 158 and Yangmai 11 respectively. However, decline in canopy apparent photosynthetic rate (CAP) was 15.0–22.9 % (S1) and 29.5–49.6 % (S2), which was consistent with the reduction in radiation. The reduction in LAI was partially compensated by increases in the fraction of the top and bottom leaf area to the total leaf area, which facilitated to intercept more solar radiation by the canopy. The decrease in photosynthetic rate (Pn) of flag leaf was partially compensated by the increase in Pn of the third leaf from the top. In addition, an inconsistency between the low Pn and the high Chl content in flag leaf was observed at 30 DAA. This could be explained that more excitation energy was dispersed via the non‐photochemical approaches in the photosystem II (PSII) of flag leaf after long‐term shading.

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instantaneous results and has been demonstrated as an effective tool to schedule N fertilization for rice (Oryza Nondestructive monitoring and diagnosis of plant N status is necsativa L.) on an as-needed basis (Turner and Jund, 1991; essary for precision N management. The present study was conducted to determine if canopy reflectance could be used to evaluate leaf Peng et al., 1993). However, there are two factors that N status in rice (Oryza sativa L.). Ground-based canopy spectral limit the use of SPAD meters for N fertilization. First, reflectance and N concentration and accumulation in leaves were a within-field reference (usually an adequately fertilized measured over the entire rice growing season under various treatments area or strip within the field) is required to accurately of N fertilization, irrigation, and plant population. Analyses were quantify N deficiencies. Second, the SPAD meter colmade on the relationships of seasonal canopy spectral reflectance, lects point measurements from a single leaf on a single ratio indices, and normalized difference indices to leaf N concentration plant. Consequently, many leaves from a number of plants and N accumulation in rice under different N treatments. The results must be sampled to obtain a representative average showed that at each sampling date, leaf N concentration was negatively value for a particular sampling date and to adequately asrelated to the reflectance at the green band (560 nm) while positively sess the spatial variability. In contrast, remote sensing related to ratio index, with the best correlation at jointing. However, the relationships between leaf N accumulation and reflectance at of canopy reflectance has the capability to sample a plant green band and ratio index were consistent across the whole growth population or community rather than individual plants period. The ratio of near infrared (NIR) to green (R 810 /R 560 ) was esand to rapidly assess the spatial variability of a crop field. pecially linearly related to total leaf N accumulation, independent of The possibility of predicting crop N status using can-N level and growth stage. Tests of the linear regression model with opy reflectance spectra has been examined for major agrodifferent field experiment data sets involving different plant densities, nomic crops (Thomas and Oerther, 1972; Shibayama N fertilization, and irrigation treatments exhibited good agreement and Akiyama, 1986; Fernandez et al., 1994; Blackmer between the predicted and observed values, with an estimation accuet al.racy of 96.69%, root mean square error of 0.7072, and relative error Shen et al., 2001). For a crop canopy, reflectance is low of Ϫ0.0052. These results indicate that the ratio index of NIR to green near the 480-and 680-nm region due to the strong ab-(R 810 /R 560 ) should be useful for nondestructive monitoring of N status in rice plants.