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Industrial activities have led to a gradual and global increase in soil aluminum (Al) and atmospheric CO 2 concentrations. Al bioavailability strongly depends on the soil pH, which in turn is affected by atmospheric CO 2 levels. In spite of the concurrent impact which Al and elevated CO 2 (eCO 2) could have on plants, their interaction and how it might affect the growth of economically important crop species has not been investigated. Here, we have investigated the combined impact of soil Al and eCO 2 exposure on key C3 (wheat, oat) and C4 (maize, sorghum) crops, at the physiological and biochemical level. Compared to C3 plants, C4 plants accumulated less Al by stimulating soil Al retention through exudation of root organic acids. Consequently, Al-exposed C4 plants maintained photosynthetic performance and anti-oxidative capacity. Exposure to eCO 2 reduced the stress responses of C3 and C4 crops to Al exposure. Elevated CO 2 decreased Al accumulation and oxidative damage in all cereals, and ameliorated C3 plant growth. This was reflected on the biochemical level, where eCO 2 inhibited ROS production and restored RuBisCo activity in C3 crops only. Overall, our data suggest that, compared to C3 crops, C4 cereals are more tolerant to soil Al exposure under current ambient CO 2 (aCO 2) levels whereas future eCO 2 levels might stimulate Al tolerance in C3 crops. [Display omitted] • Al differentially accumulated in C3 and C4. • Al differentially induced oxidative damage in C3 and C4. • eCO2 suppressed Al uptake and antagonized its phytotoxicity. • eCO2 inhibited ROS production and restored RuBisCo activity in C3 plants. • C4 plants appear more tolerant to soil Al exposure. [ABSTRACT FROM AUTHOR]

Despite the wide utilization of chitosan nanoparticles (CSNPs) as a promising approach for sustainable agriculture, their efficiency under elevated CO 2 (eCO 2), has not been evaluated. The interactive effects of CSNPs and eCO 2 were evaluated on the growth and C and N metabolism of soybean plants. Plants were treated with CSNPs and grown under ambient CO 2 (410 ppm, aCO 2) or eCO 2 (645 ppm). Regardless of CO 2 level, CSNPs improved the net photosynthetic rate. CSNPs aggravated the effect of eCO 2 treatment on the levels of non-structural carbohydrates (i.e., glucose, fructose, sucrose, and starch), especially in shoots, which was inconsistence with the upregulation of carbohydrates metabolizing enzymes. Being the most pivotal energetic and signaling organic compounds in higher plants, the synergistic action of CSNPs and eCO 2 on the accumulation of soluble sugars upregulated the N metabolism as indicated by induced activities of nitrate reductase, arginase, glutamate dehydrogenase, glutamine synthetase, and glutamine oxoglutarate aminotransferase which was manifested finally as increased shoot and root total nitrogen content as well as proline and aspartate in roots. At the hormonal level, the coexistence of eCO 2 with CSNPs further supports their positive impact on the contents of IAA and, to a lesser extent, GAs. The present data prove that the biofertilization capacity of CSNPs is even more potent under futuristic eCO 2 levels and could even further improve the growth and resilience of plants. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are beneficial for the plant growth under heavy metal stress. Such beneficial effect is improved by elevated CO 2 (eCO 2). However, the mechanisms by which eCO 2 improves AMF symbiotic associations under arsenite (AsIII) toxicity are hardly studied. Herein, we compared these regulatory mechanisms in species from two agronomical important plant families – grasses (wheat) and legumes (soybean). AsIII decreased plant growth (i.e., 53.75 and 60.29% of wheat and soybean, respectively) and photosynthesis. It also increased photorespiration and oxidative injury in both species, but soybean was more sensitive to oxidative stress as indicated by higher H 2 O 2 accumulation and oxidation of protein and lipid. eCO 2 significantly improved AMF colonization by increasing auxin levels, which induced high carotenoid cleavage dioxygenase (CCDs) activity, particularly in soybean roots. The improved sugar metabolism in plant shoots by co-application of eCO 2 and AsIII allocated more sugars to roots sequentially. Sugar accumulation in plant roots is further induced by AMF, resulting in more C skeletons to produce organic acids, which are effectively exudated into the soil to reduce AsIII uptake. Exposure to eCO 2 reduced oxidative damage and this mitigation was stronger in soybean. This could be attributed to a greater reduction in photorespiration as well as a stronger antioxidant and detoxification defence systems. The grass/legume-specificity was supported by principal component analysis, which revealed that soybean was more affected by AsIII stress and more responsive to AMF and eCO 2. This study provided a mechanistic understanding of the impact of AMF, eCO 2 and their interaction on As-stressed grass and legume plants, allowing better practical strategies to mitigate AsIII phytotoxicity. [Display omitted] • Soybean was more sensitive to As stress but more reponsive to AMF and eCO 2 impact. • High strigolactone biosynthesis by eCO 2 induced AMF colonization, mainly in soybean. • Increased photosynthesis by eCO 2 allocated more sugars to AMF roots of soybean and wheat. • eCO 2 increased soil retention resulting in less As accumulation in AMF treated plants. • eCO 2 strengthen AMF impact on decreasing ROS production and increasing their detoxification. [ABSTRACT FROM AUTHOR]