Edaphic Legacy of Phosphorus Fertiliser in the Restoration of the Biodiverse Kwongan Ecosystem in Ultra-Low Phosphorus Soils
Oliveira, V. H. De, M. P. Dobrowolski, S. Duddigan and M. Tibbett. 2024.
Abstract
The kwongan ecosystem is a biodiversity hotspot on the coastal sandplain of southwest Western Australia harbouring rare and endemic plant species adapted to nutrient impoverished soils, particularly low phosphorus (P). In some kwongan regions surface strip-mining has drastically disturbed these ecosystems, requiring restoration by soil profile reconstruction and re-establishment of the native vegetation. Post-mining restoration aims to reinstate the ecosystem function and biodiversity, often involving fertilisation to promote plant growth. We examined monitoring data from post-mining soils of restored kwongan vegetation (n = 127), categorised by age groups (10, 20, 30 and 40-year-old sites) or by fertilisation management. 32 soil variables were compared to the surrounding native soils (n = 135) by multivariate and univariate statistical approaches to determine whether different restoration ages and fertilisation regimes had long-term impacts on soil physicochemical characteristics. Overall, restored soils differed from native, with substantially lower carbon (by 41%) and nitrogen (by 15%). The 10-year-old sites have higher sodicity and much lower porosity levels, while 40-year-old sites differed by nearly ten times higher Total P. While recent non-fertilised soils have similar P concentrations to the reference sites, the high legacy P found in older restored soils clearly resulted from single superphosphate fertilisation, greatly decreasing N:P stoichiometric ratios. Thus, after decades, restored soils are still impacted by both mining activities and fertilisation practices. These changes will likely alter microbial and plant communities, impairing restoration trajectories towards the native kwongan vegetation, particularly for P-sensitive species. Despite benefits of P-fertilisation (e.g. improved plant cover), the low carbon stocks and N:P ratios indicate a divergent ecosystem from the native state. Such changes in ecosystem stoichiometry may affect plant species competitiveness, and alter the composition of other trophic levels. Adjusting future restoration practices to reduce P fertilisation is promising, but addressing long-term stoichiometric shifts and soil compaction remains crucial.
Key Words
C:N ratio, Ecological restoration, PRS probes, rehabilitation, soil compaction, superphosphate fertiliser
