Al-induced cell rigidity is one of the symptoms of Al toxicity, but the mechanism by which plants tolerate this toxicity is still unclear. In this study, we found that overexpression of OsPIN2, an auxin transporter gene, could alleviate Al-induced cell rigidity in rice root apices. A freeze-thawing experiment showed that the Al-treated roots of wild-type (WT) plants had more damage in the epidermal and outer cortex cells than that found in lines overexpressing OsPIN2 (OXs), and the freeze-disrupt coefficient was 2-fold higher in the former than in the latter. Furthermore, Al could induce aberrations of the cell wall-plasma membrane interface, which was more prominent in the epidermal cells of the elongation zone of the WT. Overexpressed OsPIN2 reduced Al-induced formation of reactive oxygen species and weakened Al-induced lipid peroxidation and lignification in roots. Compared with WT, a 16.6-32.6% lower Al-triggered hemicellulose 1 accumulation was observed in root apices of OXs, and 17.4-20.5% less Al accumulated in the cell wall of OXs. Furthermore, overexpression of OsPIN2 ameliorated the Al inhibitory effect on basipetal auxin transport and increased Al-induced IAA and proton release. Taken together, our results suggest that by decreasing the binding of Al to the cell wall and Al-targeted oxidative cellular damage, OXs lines show less Al-induced damage. By modulating PIN2-based auxin transport, IAA efflux, and cell wall acidification, lines overexpressing OsPIN2 alleviate Al-induced cell rigidity in the rice root apex.

The use of inorganic nitrogen (N) fertilizers has increased drastically to meet the food requirements of the world's growing population. However, the excessive use of chemical nitrogen fertilizer has caused a series of soil and environmental problems, such as soil hardening, lower nitrogen use efficiency (NUE), nitrate pollution of water sources, nitrous oxide emissions, etc. In this review, we aimed to elaborate and discuss the role of engineered biochar in inducing the stability of water-stable macroaggregates, improving inorganic N transformation, and utilization efficiency to address the current uncertainties of nitrogen loss and maintaining soil and water quality. Firstly, we elucidated the characteristics of engineered biochar in improving biochar quality to work as a multifunctional player in the ecosystem and promote resource utilization, soil conservation, and ecosystem preservation. Secondly, we discussed how the engineered biochar modulates the stability of water-stable macroaggregates and soil inorganic nitrogen transformation to enhance plant response under various toxic or deficient nitrogen conditions in the soil. Thirdly, the role of engineered biochar in biological nitrogen fixation, mediating nirK, nirS, and nosZ genes to promote the conversion of N₂O to N₂, and decreasing denitrification and N₂O emission was reviewed. Altogether, we suggest that engineered biochar amendment to soil can regulate soil water-stable macroaggregates, reduce N input, improve nitrogen metabolism, and finally, NUE and crop growth. To the best of our knowledge, this is the first time to evaluate the combined interactions of "engineered biochar × soil × NUE × crop growth,” providing advantages over the increasing N and water utilization and crop productivity separately with the aim of enhancing the stability of water-stable macroaggregates and NUE together on a sustainable basis. Graphical abstract

Seaweed extracts (SEs) have been widely used as biostimulants in crop management due to their growth-promoting and stress-resistant effects. To date, there are few reports of the effect of SEs on sucrose content and cane yield. Here, we conducted field experiments for three consecutive growth seasons (2017∼2019) in two areas (Suixi and Wengyuan) of China, to investigate the yield and sugar content of sugarcane in response to SE treatment at different growth stages. The results showed that spraying SEs once at seedling (S), early elongation (E), and early mature (M) stages, respectively, once at S and E stages, respectively, or once at the S stage increased the cane yield by 9.23, 9.01, and 3.33%, respectively, implying that SEs application at the early elongation stage played a vital role in promoting sugarcane growth. Photosynthetic parameters and nutrient efficiency analysis showed that spraying SEs at S and E stages enhanced the net photosynthetic rate, transpiration rate, and water use efficiency, and increased N, P, or K utilization efficiency, compared with those of the control. Notably, cane yield increasing rate of SEs in 2017 and 2018 were higher than those in 2019 in Wengyuan but lower than those in 2019 in Suixi. Interestingly, the total rainfall and monthly average rainfall in 2017 and 2018 were lower than those in 2019 in Wengyuan but higher than those in 2019 in Suixi. The results suggested that the yield increasing rate of SEs on sugarcane was better in less rainfall years. The sucrose content of sugarcane showed no difference between spraying SEs at the M stage alone or at the three growth stages but was higher than those of SE treatments at S and/or E stages. Enzyme activity analysis showed that spraying SEs at the M stage increased the activity of sucrose phosphate synthase activity by 9.14% in leaves and 15.16% in stems, and decreased soluble acid invertase activity in stems by 16.52%, which contributed to the sucrose increase of 5.00%. The above results suggested that SEs could increase cane yield and promote sucrose accumulation in sugarcane. The yield increasing effect was more obvious under conditions of drought stress.