The rich and poor: plant phosphorus and photosynthesis follow soil fertility

Abstract

Phosphorus (P) is a key nutrient for plant metabolism such as photosynthesis, understanding nutrient limitations to the processes underlying ecosystem productivity is a key focus for advancing our understanding of C cycling in present-day environmental conditions. As a result of these limitations, plants from low P-available ecosystems like those predominant on sandy and sandstone-derived substrates across Australia, maximise their photosynthetic efficiency in response to low soil P availability. Concurrent with nutrient-depleted soils, Australian landscapes are also subject to low rainfall and frequent fire events. This thesis investigates the effect of fire and aridity on how plants use P for photosynthesis. For Chapter 2, how changes in leaf chemistry and water relations impacted the photosynthesis of regrowing vegetation post-fire were investigated across a burn chronosequence at North Head in Sydney, Australia. The approach for Chapter 3 involved an assessment of the interactions among soil P, leaf P, and photosynthesis for a subset of native species from low, moderately low, and high P soils. To help generalise across different climate conditions, the sites occur across a rainfall gradient in south-eastern Australia.

In terms of post-fire regrowth (Chapter 2), I found a transient release from stomatal and nutrient limitations that supported post-fire regrowth in coastal heath scrub vegetation. Regrowing species capitalised on increased soil nutrients, which was arguably of greater consequence to photosynthesis than enhanced stomatal conductance. For Chapter 3, plants from low soil P sites were found to be significantly more efficient at using their leaf P for photosynthesis than plants on richer, volcanically-derived soils. Contrary to my hypothesis, a higher Pi fraction did not significantly correlate with photosynthesis or PPUE, nor did aridity. The results highlight the importance of the biochemical stimulation of soils by fire for the regrowth of plants atop highly weathered and nutrient-depleted soils. Moreover, the research shows the strength of low-P soils on the PPUE of Australian plants. Finally, the results from this research are discussed leading to some recommendations for future research directions.

Date of Thesis submission	2022
Original language	English
Awarding Institution	Western Sydney University
Supervisor	David Ellsworth (Supervisor), Kristine Crous (Supervisor) & Catriona Macdonald (Supervisor)