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Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability. Rice is the most Al-resistant species among small grain cereal crops and prefers NH4 + as its major inorganic nitrogen source. This study investigates the effects of NH4 + and NO3 − on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH4 + preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH4 + and NO3 − supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH4 +-preferring than Yangdao6. NH4 + alleviated Al toxicity in two cultivars compared with NO3 −. Both NH4 +-Al supply and pretreatment with NH4 + reduced Al accumulation in roots and root tips compared with NO3 −. NH4 + decreased but NO3 − increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO3 − concentration enhanced Al accumulation in root tips but increasing the NH4 + concentration had the opposite effect. These results show NH4 + alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO3 −, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH4 +, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated with the preferred utilization of NH4 + is suggested. [ABSTRACT FROM AUTHOR]

Background and Aims: Suitable N source supply is critical to improve plant growth and N uptake, but the importance of nitrate (NO3−) for rice (Oryza sativa L.) and microbiota is often neglected in acidic paddy soils where ammonium (NH4+) is dominant. This study aimed to explore the differential effects of NH4+ and NO3− on rice growth, fertilizer nitrogen recovery efficiency (FNRE), and rhizosphere bacterial community in acid soil. Methods: Two rice varieties, Kasalath (Al-sensitive indica) and Koshihikari (Al-tolerant japonica), were exposed to different N sources with or without lime in an acid soil. Results: Liming and NO3− application solely improved the growth and FNRE of the Al-sensitive rice, namely, by increasing soil pH and alleviating Al toxicity. Compared with liming and rice variety, N source had a more pronounced influence on rhizobacterial community composition. Of the two sources, NO3− had a stronger effect on the rhizobacterial community than NH4+. Remarkably, rice plants fed with NH4+ specifically recruited Desulfosporosinus and Desulfitobacterium associated with ferric NH4+ oxidation in the rhizosphere, whereas those exposed to NO3− recruited Alicyclobacillus with NO3−-reducing iron oxidation ability. Three keystone taxa were identified in a rhizobacterial co-occurrence network analysis: Alicyclobacillus, which was positively associated with rice growth and FNRE, and Acidobacteriales and WPS-2, both with negative associations. Conclusion: Compared with NH4+, NO3− enhances the growth and FNRE of Al-sensitive rice and exerts dominant effects on the rhizobacterial community, which indicates the importance of NO3− for rice and has instructive implications for N management in acid soil. [ABSTRACT FROM AUTHOR]

Aims: Silicon (Si) as a beneficial element can improve nutrient imbalance, but the molecular mechanism for this effect is poorly understood. The objective of this study is to examine the mechanism underlying Si-induced decrease of phosphorus (P) uptake in rice (Oryza sativa) at adequate/high P supply.Method: A rice mutant (lsi1) defective in Si uptake and its wild type (cv. Oochikara) were used. The P uptake was compared in the presence and absence of Si and the expression of Pi transporter genes was quantified.Results: Si addition in the nutrient solution significantly decreased shoot P concentration and uptake in the WT, but not in lsi1 mutant at two P levels, adequate (90 μM) and high (210 μM). Neither the root-to-shoot translocation of P nor the P distribution in different organs was altered by Si in both WT and lsi1. Heterogeneous expression of Lsi1 in Xenopus oocyte did not show transport activity for Pi. The expression of Pi transporter genes (OsPT1, 2 and 8) in the roots was hardly affected by Si in both WT and lsi1, but that of OsPT6 was down-regulated by Si in the WT roots, but not in the lsi1 roots. Furthermore, a split root experiment showed that Si accumulated in the shoots suppressed the expression of OsPT6. In rice grown in paddy field, lsi1 showed higher P concentration in the straw, husk and brown rice than the WT.Conclusion: Si decreased P uptake through down-regulating the expression of P transporter gene, OsPT6 in rice and Si accumulated in the shoot is required for this down-regulation. [ABSTRACT FROM AUTHOR]