Soil and microbial C:N:P stoichiometries play vital roles in regulating P transformation in agricultural ecosystems:A review

Stoichiometry plays a crucial role in biogeochemical cycles and can modulate soil nutrient availability and functions. In agricultural ecosystems,phosphorus(P) fertilizers(organic or chemical) are often applied to achieve high crop yields. However, P is readily fixed by soil particles, leading to low P use efficiency. Therefore, understanding the role of carbon:nitrogen:P stoichiometries of soil and microorganisms in soil P transformation is of great significance for P management in agriculture. This paper provides a comprehensive review of the recent research on stoichiometry effect on soil P transformation in agricultural ecosystems. Soil microorganisms play an important role in the transformation of soil non-labile inorganic P to microbial biomass P by regulating microbial biomass stoichiometry. They also mobilize soil unavailable organic P into available P by changing ecoenzyme stoichiometry. Organic materials, such as manure and straw, play an important role in promoting the transformation of insoluble P into available P as well. Additionally, periphytic biofilms can reduce P loss from rice field ecosystems. Agricultural stoichiometries are different from those of natural ecosystems and thereby should receive more attention due to the influences of anthropogenic factors. Therefore, it is necessary to conduct further stoichiometry research on the soil biochemical mechanisms underlying P transformation in agricultural ecosystems. In conclusion, understanding stoichiometry impact on soil P transformation is crucial for P management in agricultural ecosystems.

Strategies for improving fertilizer phosphorus use efficiency in Chinese cropping systems

A four-year project,entitled"The mechanisms of fraction transformation and high use efficiency of P fertilizer in Chinese cropping systems"commenced in 2017.The project was established to answer three key questions and looked at 17 cropping systems on ten soils.First,we asked what are the dynamics of transformation,fixation and mobilization of P fertilizers in soil-cropping systems?Second,what are the mechanisms of soil-cropmicrobe interactions by which P fertilizer can be efficiently used?Third,how to manipulate the processes of P use in cropping systems?The targets of this project are(1)to explore the mechanisms of P fixation,the pathways of loss of P availability and the threshold of migration of fertilizer P in the field;(2)to uncover mechanisms by which soil legacy P is mobilized through root physiological and morphological processes and through arbuscular mycorrhizal fungi and P-solubilizing bacteria in rhizosphere and hyphosphere;(3)to estimate the biological potential of crops for high efficiency P absorption and use;(4)to innovate new approaches for improving the efficiency of P fertilizers.The outcomes will provide theoretical support for setting standards for limitation of P fertilizer application rate in the main cropping zones of China.

Loss of two families of SPX domain-containing proteins required for vacuolar polyphosphate accumulation coincides with the transition to phosphate storage in green plants

Phosphorus is an essential nutrient for plants.It is stored as inorganic phosphate(Pi)in the vacuoles of land plants but as inorganic polyphosphate(polyP)in chlorophyte algae.Although it is recognized that the SPX-Major Facilitator Superfamily(MFS)and VPE proteins are responsible for Pi influx and efflux,respectively,across the tonoplast in land plants,the mechanisms that underlie polyP homeostasis and the transition of phosphorus storage forms during the evolution of green plants remain unclear.In this study,we showed that CrPTCI,encoding a protein with both SPX and SLC(permease solute carrier 13)domains for Pi transport,and CrVTC4,encoding a protein with both SPX and vacuolar transporter chaperone(VTC)domains for polyP synthesis,are required for vacuolar polyP accumulation in the chlorophyte Chlamydomonas rein-hardtii.Phylogenetic analysis showed that the SPX-SLC,SPX-VTC,and SPX-MFS proteins were present in the common ancestor of green plants(Viridiplantae).The SPX-SLC and SPX-VTC proteins are conserved among species that store phosphorus as vacuolar polyP and absent from genomes of plants that store phosphorus as vacuolar Pi.By contrast,SPX-MFS genes are present in the genomes of streptophytes that store phosphorus as Pi in the vacuoles.These results suggest that loss of SPX-SLC and SPX-VTC genes and functional conservation of SPX-MFS proteins during the evolution of streptophytes accompanied the change from ancestral polyP storage to Pi storage.