Do oxalic acid exudates from mycorrhizal fungi influence the uptake of phosphorus by primary producers in the karst critical zone of south west China?

Abstract

Karst landscapes cover 12% of Earth’s continental land area and are often characterised by their nutrient-poor soils. The karst critical zone of south west China, home to 35 million people, is being intensively farmed, despite its highly-degraded and nutrient-limited soils. Phosphorus, a key nutrient for plant growth, is thought to be a limiting nutrient in karst soils as a result of negligible concentrations found in limestone bedrock and the influence of anthropogenic farming practices. This research sought to understand if organic acid exudates from mycorrhizal fungi, found in >80% of plants, altered the uptake of phosphorus by primary producers in karst soils. To answer this, a sequence of plant-based experiments were conducted using soils collected from Chenqi subcatchment, Guizhou Province. Oxalic acid treatments were added to soils to simulate the action of organic acids exuded by mycorrhizal fungi, to identify if non-labile phosphorus was being broken down into labile species. SEM EDS analysis of soil from Chenqi was used to identify the phosphorus species present in the soil, to better our understanding of the phosphorus cycle in karst environments. The results indicate that soils in Chenqi subcatchment are severely limited with respect to phosphorus, and that this impacts detrimentally upon the overall health and growth of plants. Statistical analysis suggests that oxalic acid does not significantly increase the concentration of phosphorus taken up by plants in karst soils. This research is part of the NERC-NSFC-Newton funded SPECTRA project, investigating soil processes and ecological services in the karst critical zone of south west China, an international project involving research institutions in the UK and China. The results of this research will be collated with other SPECTRA project findings, to be used in improving understanding and management of the response, resilience and recovery of the south west China karst.

Date of Award	1 Oct 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Penny J Johnes (Supervisor) & Heather L Buss (Supervisor)