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Wheat straw burial has great potential to sustain rice production under alternate wetting and drying (AWD) irrigation. A field experiment was conducted with three wheat straw burial treatments, including without straw burial (NSB), with light straw burial of 300 kg/hm2 (LSB) and dense straw burial of 800 kg/hm2 (DSB), as well as three AWD regimes: alternate wetting/moderate drying (AWMD), alternate wetting/severe drying (AWSD) and alternate wetting/critical drying (AWCD). The rice growth and grain quality were higher in LSB and NSB than those in NSB under the same AWD regime. The AWMD × DSB treatment resulted in the highest yield, brown rice rate, milled rice rate, amylose content and protein content. Conversely, the AWCD × NSB treatment led to the lowest yield, brown rice rate, milled rice rate, amylose content and protein content. The active absorption area and nitrate reductase activity of roots were higher in the AWMD × DSB treatment than those in the AWCD × NSB treatment, as the former increased organic carbon and nitrogen contents in the rhizosphere, whereas the latter reduced their availability. Total soluble protein content and glutamine synthetase activity were greater in the AWMD × DSB treatment than those in the AWCD × NSB treatment. The activities of superoxide dismutase and catalase were higher in the AWMD × DSB treatment compared with the AWCD × NSB treatment, leading to the amelioration of oxidative cell injury, as shown by a lower malonaldehyde level. This study suggested that farmers should implement AWMD irrigation after leaving the straw residues in the field, followed by deep tillage to improve soil quality and mitigate the drought stress cycles of AWD. This approach can improve rice growth and grain quality and alleviate the problems of disposal of straw residues and water scarcity for sustainable rice production.

In recent years, a new water-saving controlled irrigation technique aiming at more heavy rains in the South of China is proposed. It can reduce irrigation cost and make full use of rainfall, but may lead to alternative stress of drought-waterlogging-drought for rice. It is unclear about the root changes affected by the alternative stress. Therefore, in this study, a pot experiment was carried out to determine the effects of alternative stress of drought and waterlogging at tillering stage on rice root anatomical structure. The differences of root aerenchyma, column, the root epidermal cell development and root epidermal thickness in rice underwaterlogging stress treatments and the conventional irrigation were analyzed. The rice experienced three phases of drought stress (heavy drought A1 and light drought A2) and heavy waterlogging stress (15 cm water layer, B). The results indicated that A1 and A2 promoted development of root aerenchyma earlier than conventional irrigation (C) at stage I of drought stress; The thickness of the outer layer of roots in A1 and A2 treatments were higher than C treatment. A1 at stage I had a significant impact on root anatomical structure of flooding stress at stage II of drought converted to heavy waterlogging (AiB, heavy waterlogging for 5 d at stage II), of which the diameter, total area of tube and the column area increased by 43.3%, 52.8%, 76.5%, respectively, compared to conventional irrigation at stage II (CC); And the number of catheter, catheter area and in the column area of A2B treatment (heavy waterlogging for 5 d at stage II) was lower than that of CC treatment. However, the rice root formed a small amount of aerenchyma under the condition of flooding stress at stage II (CB, heavy waterlogging for 5 d at stage II). Effects of heavy drought and light drought stress at stage III (A1BA1 and A2BA2) after flooding stress on rice root anatomical structure were similar to the effects of drought stress at stage I. AiBAi formed more gas cavity, and there was still much residual cortex parenchyma cells in cortex; A2BA2 also formed more regular gas cavity. The number of catheter, catheter diameter, vessel area, and the column area of roots in AiBAi treatment increased by 30.30%, 0.74%, 30.24%, and 52.84% compared with CCC treatment (conventional irrigation at stage III). The number of catheter and columns area of A2BA2 treatment increased compared with CCC treatment, and the catheter number and total area and column area of CBC treatment increased by 30.30%, 5.37% and 14.31%, respectively. Cortical cells of A2BA2 treatment were developed well with thick wall, and cortical cells of CBC treatment were also developed well but partial disordered. Therefore, short-term drought stress could improve the development of root aerenchyma, but could not decrease the waterlogging tolerance of rice. The anatomical changes might express post-effect of drought stress on rice root growth and a certain degree of drought and waterlogging stress played a positive role in improving the ability of late rice. The research could provide a valuble information for water-harvesting and controlled irrigation technology. [ABSTRACT FROM AUTHOR]

Natural abundance of the stable isotope (δ 13 C and δ 15 N) in plants is widely used to indicate water use efficiency (WUE). However, soil water and texture properties may affect this relationship, which remains largely elusive. Therefore, the purpose of this study was to evaluate δ 13 C as affected by different combinations of alternate wetting and drying irrigation (AWD) with varied soil clay contents in different organs and whole plant and assess the feasibility of using δ 13 C and δ 15 N as a physiological indicator of whole-plant water use efficiency (WUE whole-plant ). Three AWD regimes, I 100 (30 mm flooded when soil reached 100% saturation), I 90 (30 mm flooded when reached 90% saturation) and I 70 (30 mm flooded when reached 70% saturation) and three soil clay contents, 40% (S 40 ), 50% (S 50 ), and 60% (S 60 ), were included. Observed variations in WUE whole-plant did not conform to theoretical expectations of the organs δ 13 C (δ 13 C organs ) of plant biomass based on pooled data from all treatments. However, a positive relationship between δ 13 C leaf and WUE ET (dry biomass/evapotranspiration) was observed under I 90 regime, whereas there were no significant relationships between δ 13 C organs and WUE ET under I 100 or I 70 regimes. Under I 100 , weak relationships between δ 13 C organs and WUE ET could be explained by (i) variation in C allocation patterns under different clay content, and (ii) relatively higher rate of panicle water loss, which was independent of stomatal regulation and photosynthesis. Under I 70 , weak relationships between δ 13 C organs and WUE ET could be ascribed to (i) bigger cracks induced by water-limited irrigation regime and high clay content soil, and (ii) damage caused by severe drought. In addition, a negative relationship was observed between WUE whole-plant and shoot δ 15 N (δ 15 N shoot ) across the three irrigation treatments, indicating that WUE whole-plant is tightly associated with N metabolism and N isotope discrimination in rice. Therefore, δ 13 C should be used cautiously as an indicator of rice WUE whole-plant at different AWD regimes with high clay content, whereas δ 15 N could be considered an effective indicator of WUE whole-plant ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wang, Liu, Wang, Agathokleous, Hamoud, Qiu, Hong, Tian, Shaghaleh and Guo.)