Phosphorus speciation and release from different plant litters on a River Murray (Australia) floodplain

Purpose Phosphorus (P) is a key nutrient controlling primary productivity and eutrophication of floodplain-river ecosystems. The aim of this study was to investigate the P speciation and release during rewetting of litter from the dominant plant communities (river red gum; black box; lignum; chenopods; and grassland) on the Pike floodplain (6,700 ha) of Australia's largest river system, the River Murray. Average litter loads varied from 1.8 t ha(-1) (chenopods) to 12.9 t ha(-1) (river red gums). Methods Phosphorus concentration (via digestion) and speciation (using P-31 NMR spectroscopy) of litters were assessed and dynamics of P release was investigated in 5-day rewetting experiments. Results Grassland litter had the highest total P (2.23 mg g(-1)) and orthophosphate (1.50 mg g(-1)) concentrations, and released the most orthophosphate (0.38 mg g(-1)) on rewetting. However, due to the higher elevation of grasslands, P mobilisation would only be significant in large flood events. River red gum litter produced the largest amount of litter and this had moderate total P (0.4-0.6 mg g(-1)) comprised mostly of orthophosphate. River red gums occupy lower elevations so P release would occur more regularly. Black box litter had higher monoester-P concentrations and released lower amounts of P, and then absorbed P, following rewetting. Aged leaf litters had lower total P concentration and release during rewetting than fresh litter. The amount of total P in litter released as soluble P upon rewetting was variable (1-38 %). Conclusion These results can inform the future management of P mobilisation and associated risks or benefits on regulated floodplains and rivers.

Automated summary

This study aimed to investigate the phosphorus speciation and release in litter from different plant communities on the Pike floodplain of Australia's River Murray. Results showed that grassland litter had the highest total P and orthophosphate concentrations, while river red gum litter had moderate total P primarily composed of orthophosphate.