Photosynthesis of winter wheat effectively reflected multiple physiological responses under short-term drought-rewatering conditions.

BACKGROUND: Based on the interrelationship among photosynthesis (Pn), water consumption and drought resistance physiology under water changes, this study aimed to explore whether easily measured Pn could be used to reflect the physiological state of winter wheat and soil moisture. The study was a greenhouse pot experiment, with three growth periods and four gradients of moisture. RESULTS: The instantaneous water use efficiency of wheat improved significantly under short-term regulated deficit irrigation conditions. The photosynthetic parameters could effectively reflect the level of soil moisture (receiver operating characteristic curve analysis, area under the curve = 0.683-0.988). There was a significant correlation between Pn and yield under drought and rewatering (P < 0.05). The water consumption of winter wheat was significantly reduced by 15.5% to 47.6% (P < 0.05) during drought owing to the reduction of stomatal conductance and transpiration rate (Tr). There was a significant linear relationship between Tr and daily water consumption (R2 > 0.745, P< 0.05). There was a significant quadratic linear relationship (R2 > 0.600, P < 0.05) between Pn and the drought resistance indicators. The protective effect of drought resistance physiology on Pn was more significant during drought than during rewatering. Among the four physiological indicators of drought resistance, the relationship between peroxidase activity and Pn was relatively close (grey relational analysis, GRO = 1). CONCLUSIONS: The photosynthetic parameters during conditions of short-term water changes could effectively reflect the status of soil moisture, water consumption, yield and drought resistance. A focus on Pn and the rational use of related relationships are conducive to the selection of drought-resistant varieties and developing refined agricultural management. © 2021 Society of Chemical Industry.

Propagation of meteorological to hydrological drought for different climate regions in China.

Drought can lead to considerable agricultural, ecological, and societal damage. Improving our understanding of the propagation relationship between meteorological and hydrological drought is necessary to lessen drought impacts. The different drought responses and underlying mechanisms among different climate types are not yet sufficiently understood. By applying the standardized precipitation index and standardized runoff index, we investigated the propagation relationship between meteorological and hydrological drought. Because of short-term response between meteorological and hydrological droughts, the propagation time was considered among time scales of 1-12 months. Wavelet analysis was employed to examine the two types of drought from 1902 to 2014. Our results showed that arid environments had a weaker propagation relationship than moist environments. There was a stronger relationship between the two types of drought in summer and autumn than in spring and winter. The climate was not the only factor impacting drought propagation; land (cover and topographic feature) may also impact propagation time and intensity from meteorological to hydrological drought. This study analyzed and highlighted that the most susceptible regions in China and global scale, respectively. The most susceptible regions were tropical and subtropical Chinese southern zones in China and equatorial and warm temperate climate zones in global; however, arid climate zones showed little interaction between the two kinds of drought. Other factors that impact drought propagation, such as land cover, landforms, and human activity, should be considered in future research.

Spatial and temporal effects of drought on Chinese vegetation under different coverage levels.

Land surface vegetation dynamics are strongly affected by drought. Thus, understanding the responses of vegetation to drought can inform measures to increase biome stability. In this study, the normalized difference vegetation index (NDVI) and the Palmer drought severity index (PDSI) were utilized to investigate the relationship between vegetation activity and drought across different drought regions and ecological community types from 1982 to 2015. Our results showed that the highest correlation between monthly NDVI and PDSI at different timescales (1-36 months) indicated the degree of drought impact on vegetation. There were diverse responses of vegetation to drought according to the drought features and climatic environment. The northern grassland, cropland, and desert ecosystems were strongly impacted by drought. These vegetation ecosystems had a low sensitivity to drought in southern China. Drought had the strongest impact on grassland in summer, which is the high frequency drought season. The most susceptible ecosystem types to drought were those with homogenous vegetation, especially under long-term drought conditions (such as the Inner Mongolia Plateau dominated by grassland). Under global warming, drought with high-temperature characteristics is expected to become more frequent and severe. Such drought could threaten the survival of plateau grassland, arid plain grassland, and rain-fed cropland, as high temperatures accelerate evaporation, leading to water deficit. However, moist forests showed little threat under normal drought. We suggest that future research should focus on vegetation activity in northern and southwestern China, where the vegetation shows the greatest sensitivity to drought.

[Effects of Water Deficit on Greenhouse Gas Emission in Wheat Field in Different Periods].

Field experiments and static chamber-gas chromatography analysis were conducted in 2016-2017 to study the effects of deficit irrigation on CO2, N2O, and CH4 emissions from soils of winter wheat fields and to optimize irrigation management measures in the Guanzhong Plain of China. Three irrigation levels (full irrigation, 100%; medium water deficit, 80%; and severe water deficit, 60%) were set during the three important growth periods of winter wheat (overwintering, jointing to heading, and heading to filling periods), with 6 distinct treatments (CK, T1, T2, T3, T4, T5, in which CK treatment is full irrigation, and others are water deficit treatments). The dynamic characteristics of the emission fluxes of the three greenhouse gases were described. Crop yield, long-term net global warming potential (net GWPL), and seasonal net global warming potential (net GWPS) were used to comprehensively evaluate the influence of water deficit levels during different growth periods of wheat on economic and ecological issues in the Guanzhong Plain. The results showed that the CO2 and N2O emission fluxes increased, with the highest values for CK treatment. The CH4 absorption fluxes decreased rapidly with increased irrigation, there was even indication of CH4 emissions during high irrigation treatment. Compared to CK treatment, T1, T2, T3, T4, and T5 CO2 emissions decreased significantly by 13.32%, 25.98%, 5.55%, 15.47%, and 17.52% (P<0.05); and N2O emissions decreased by 12.20%, 18.00%, 5.63%, 11.54%, and 13.53%(P<0.05), respectively. The total CH4 absorption significantly increased by 46.47%, 75.78%, 19.47%, 53.40%, and 62.33%(P<0.05), respectively. Net GWPL for T1, T2, T3, T4, and T5 treatments were significantly reduced by 10.07%, 12.77%, 6.50%, 6.81%, and 11.53% (P<0.05), respectively, in comparison with CK treatment. In addition to T3 treatment, net GWPS of T1, T2, T4, and T5 treatments decreased significantly by 13.21%, 37.65%, 24.60%, and 19.86% (P<0.05), respectively, compared with CK. Wheat yield at T1, T2, T3, T4, and T5 treatments reduced significantly by 12.56%, 32.53%, 2.25%, 20.93%, and 18.14% compared with CK treatment (P<0.05). Even though wheat yield under T3 treatment was reduced by 2.25% compared with CK treatment, there was no significant difference (P>0.05). In addition, there were highly significant (P<0.01) positive partial correlations between CO2, N2O, and CH4 emission fluxes and soil WFPS. Therefore, deficient irrigation can significantly reduce greenhouse gas emissions in wheat fields, but there are varying degrees of reduction. Considering both economic and ecological effects of water deficit in different growth periods, T3 treatment is the most conducive to keep the balance between production yield, water conservation, and emission reduction of winter wheat crops in the Guanzhong Plain.