Effects of drought-flood abrupt alternation on phosphorus in summer maize farmland systems

Phosphorus (P) is well known as a vital nutrient required for plant growth and a critical factor often causing eutrophication in water bodies. However, few studies have focused on the effects of drought-flood abrupt alternation (DFAA), a new type of extreme climate event, on the transformation of P in farmland systems. In this study, we, therefore, focused on DFAA effects on available P (AP) in topsoil, soluble P (SP) and total P (TP) in surface runoff, as well as plant P contents and P uptake in summer maize farmland systems. Field control experiments (sheltered under a ventilated shed with an artificial rainfall device) were conducted to simulate two levels of DFAA (i.e., light drought-light flood and moderate drought-light flood) during parts of two summer maize growing seasons (i.e., seeding-jointing stage and tasseling-grain filling stage). Results showed that DFAA increased AP concentration in topsoil, which was probably induced by the accumulation of the phyla Proteobacteria and Actinobacteria under moderate drought and by an increase in phosphate-solubilizing bacteria (PSB), especially the genera Bacillus and Bradyrhizobium. In addition, broken soil aggregates and increasing soil porosity caused by DFAA could also cause an increase of AP in topsoil. Soluble P and TP in surface runoff showed a decreasing trend with moderate drought in DFAA. The higher AP increased the root P uptake, while P in stems and leaves could be transported to fruits under DFAA with moderate drought. The results could provide some references for the study of the effects and adaptation-strategies related to extreme climate events and their effects on P in farmland systems.