Phosphorus supply affects seedling growth of mycorrhizal but not cluster-root forming jarrah-forest species

Rachel J Standish,Matthew I Daws,Richard J Hobbs,John M Koch,Jane Speijers,Tim K Morald,Mark Tibbett

doi:10.1007/s11104-021-05268-2

Abstract

AimsFertiliser is often used to kick-start ecological restoration despite growing evidence of the potentially negative impacts on plant diversity. Jarrah (Eucalyptus marginata) forest species growing on nutrient (especially phosphorus) impoverished soils in southwestern Australia have a suite of adaptations for phosphorus (P) acquisition, including the formation of cluster roots, and associations with mycorrhizal fungi. Here we investigated how escalating P supply, along with a stoichiometric adjustment of nitrogen (N) supply, impacted the growth and nutrition of a wide range of jarrah forest seedlings.MethodsIn a pot experiment, we measured seedling biomass and nutritional responses of 12 jarrah forest species to a gradient of P supply in relation to N supply, and for the mycorrhizal species, inoculation with arbuscular mycorrhizal fungi.ResultsThree cluster-root forming species did not respond to increasing P, probably because they were reliant on seed P. Generally, mycorrhizal species showed a positive biomass response to increasing P when N was available. Mycorrhizas benefited seedling growth at low P (9 mg P added per kg of jarrah forest soil) when N was also available, and were parasitic to seedling growth at high P (243 mg P/ kg soil) without additional N.ConclusionsThese results highlight importance of P and N supply in determining the nature of the symbiosis between plants and mycorrhizal fungi. Since P supply has the potential to reduce plant growth, for a range of species, our results suggest careful consideration of fertiliser amounts for ecological restoration of ecosystems adapted to nutrient poor soils.

Highlights

Ecological restoration is required to meet global biodiversity conservation goals (United Nations Sustainable Development Goals 2015)
For arbuscular mycorrhizal (AM)-inoculated seedlings, the percentage length of fine roots colonised by Rhizophagus irregularis varied among species: Xanthorrhoea gracilis 0–1%, Eucalyptus marginata 0–6%, Acacia celastrifolia 0–37%, Acacia pulchella 0–47%, Allocasuarina fraseri 0–48%, Bossiaea ornata 0–51%, Bossiaea pulchella 0–51%, Bossiaea aquifolium 0–68%, Phyllanthus calycinus 0–90%
Percentage AM colonisation varied widely within and among P/N treatment combinations for all species except X. gracilis (i.e., AM colonisation was consistently low), and except for percentage AM colonisation at the highest P supply which was consistently low for all species except P. calycinus (Fig. 1)

Summary

Introduction

Ecological restoration is required to meet global biodiversity conservation goals (United Nations Sustainable Development Goals 2015). Ecosystems degraded by human activity pose a significant challenge for ecological restoration especially where degraded soils impact establishment of native vegetation (Bradshaw 1997). The application of fertiliser is considered necessary, to replace nutrients lost in vegetation and soils, and best practice, to kickstart restoration of native plants and ecosystems after surface mining in Brazil, Canada, and Australia (Bizuti et al 2020; Pinno et al 2012; Tibbett 2010). Smits et al 2008; Wassen et al 2005) These latter findings suggest caution in the use of fertilisers for mine restoration

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Discussion

Conclusion