Deciphering Interactions between Phosphorus Status and Toxic Metal Exposure in Plants and Rhizospheres to Improve Crops Reared on Acid Soil.

Acid soils are characterized by deficiencies in essential nutrient elements, oftentimes phosphorus (P), along with toxicities of metal elements, such as aluminum (Al), manganese (Mn), and cadmium (Cd), each of which significantly limits crop production. In recent years, impressive progress has been made in revealing mechanisms underlying tolerance to high concentrations of Al, Mn, and Cd. Phosphorus is an essential nutrient element that can alleviate exposure to potentially toxic levels of Al, Mn, and Cd. In this review, recent advances in elucidating the genes responsible for the uptake, translocation, and redistribution of Al, Mn, and Cd in plants are first summarized, as are descriptions of the mechanisms conferring resistance to these toxicities. Then, literature highlights information on interactions of P nutrition with Al, Mn, and Cd toxicities, particularly possible mechanisms driving P alleviation of these toxicities, along with potential applications for crop improvement on acid soils. The roles of plant phosphate (Pi) signaling and associated gene regulatory networks relevant for coping with Al, Mn, and Cd toxicities, are also discussed. To develop varieties adapted to acid soils, future work needs to further decipher involved signaling pathways and key regulatory elements, including roles fulfilled by intracellular Pi signaling. The development of new strategies for remediation of acid soils should integrate the mechanisms of these interactions between limiting factors in acid soils.

Phosphorus status and adsorption characteristics of perennial vegetable-cultivated soils in South China.

Phosphorus (P) is an essential element for crop production and a key source of nonpoint pollution in agroecosystems. In this study, we sought to analyze P levels and the factors affecting soil P availability, via P adsorption, in a typical field system that is characterized by the year-round cultivation of vegetables. A total of 190 sites were sampled from vegetable fields in Guangdong Province, South China. Within the research area, average concentrations of 124.49 mg P kg-1 and 1.55 g P kg-1 were recorded for available P (AP) and total P (TP), respectively, which are 8.53- and 1.78-fold higher, respectively, than the corresponding values recorded in 1980. The determined P adsorption maximum (Qm) averaged at 488.38 mg kg-1, which represents a reduction of 16% compared to the values obtained four decades ago. Accumulations of both TP and AP were found to be negatively correlated with the soil's maximum adsorption buffering capacity (MBC), although no significant correlations with the soil binding energies (k) and Qm, were seen. However, soil pH was found to be significantly correlated with k and Qm. Furthermore, both free Mn oxides (Mnd) and silt concentrations in the soil were found to contribute to explaining the variations in Qm. Collectively, the findings of this study provide evidence to indicate that there has been an excessive accumulation of P in the perennial vegetable fields of Guangdong Province over the past four decades, which may have had negative effects on the P supply potential of the soil by reducing the maximum adsorption buffering capacity.

Long-term nutrient inputs shift soil microbial functional profiles of phosphorus cycling in diverse agroecosystems.

Microorganisms play an important role in soil phosphorus (P) cycling and regulation of P availability in agroecosystems. However, the responses of the functional and ecological traits of P-transformation microorganisms to long-term nutrient inputs are largely unknown. This study used metagenomics to investigate changes in the relative abundance of microbial P-transformation genes at four long-term experimental sites that received various inputs of N and P nutrients (up to 39 years). Long-term P input increased microbial P immobilization by decreasing the relative abundance of the P-starvation response gene (phoR) and increasing that of the low-affinity inorganic phosphate transporter gene (pit). This contrasts with previous findings that low-P conditions facilitate P immobilization in culturable microorganisms in short-term studies. In comparison, long-term nitrogen (N) input significantly decreased soil pH, and consequently decreased the relative abundances of total microbial P-solubilizing genes and the abundances of Actinobacteria, Gammaproteobacteria, and Alphaproteobacteria containing genes coding for alkaline phosphatase, and weakened the connection of relevant key genes. This challenges the concept that microbial P-solubilization capacity is mainly regulated by N:P stoichiometry. It is concluded that long-term N inputs decreased microbial P-solubilizing and mineralizing capacity while P inputs favored microbial immobilization via altering the microbial functional profiles, providing a novel insight into the regulation of P cycling in sustainable agroecosystems from a microbial perspective.