The interplay of direct and mycorrhizal pathways for plants to efficiently acquire phosphorus from soil

Highlights

	● Plants make potential trade-off between direct and mycorrhizal pathways based on C input and P gain.
	● AM fungi sense soil P heterogeneity and release exudates that select for organic P-mineralizing bacteria.
	● AM fungi and soil bacteria develop a C–P mutualistic exchange in organic P patches.

Abstract

To efficiently obtain P from soil, most terrestrial plants form symbiosis with arbuscular mycorrhizal (AM) fungi and thus have two P uptake pathways, i.e., the direct pathway (DP) via roots, particularly root hairs, and the mycorrhizal pathway (MP) via AM fungal hyphae. AM fungi form an extraradical hyphal network to expand their contact area with soil and release carbon-rich compounds, which provide a high-energy habitat for soil bacteria. The bacteria affected by AM fungi support P nutrition of AM fungi by secreting extracellular phosphatases. During the P acquisition process, both DP and MP function and require C fixed by plant photosynthesis to maintain P transport. Plants make trade-offs between DP and MP based on C inputs and P benefits. This review first systematically explores the potential trade-offs between plant C inputs and P gains of DP and MP as well as the factors that influence such trade-offs. Then the response of AM fungi to soil nutrient heterogeneity and the mechanisms by which AM fungi select bacteria to mineralize organic P and increase the P contribution of MP were analyzed. Future studies need to apply emerging methods and technologies to accurately quantify the contribution of DP and MP to plant P absorption under different conditions and provide the theoretical basis for optimizing sustainable agricultural production systems.

Graphical abstract

Keywords

Arbuscular mycorrhizal fungi / direct pathway / mycorrhizal pathway / trade-offs / organic phosphorus-mineralizing bacteria

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Acknowledgements

This research was funded by the National Key R&D Program of China (2022YFD1901304) and China Scholarship Council (202206350052).

Compliance with ethics guidelines

Shilong Duan, Yijie Huo, Yuxuan Tian, Wenhui Yan, Timothy S. George, Chengdong Huang, Gu Feng, and Lin Zhang declare that they have no conflicts of interest or financial conflicts to disclose. This article does not contain any studies with human or animal subjects performed by any of the authors.

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The Author(s) 2024. Published by Higher Education Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0)