In the complex network of ecosystems, plant growth is closely linked to nutrient acquisition, with phosphorus playing a critical role. Although phosphorus is abundant in soil, most of it exists in forms that are difficult for plants to utilize directly, making phosphorus one of the primary limiting nutrients for plant growth. As a result, through long-term evolution, plants have developed two primary pathways for phosphorus acquisition: the direct pathway (DP) and the mycorrhizal pathway (MP). The direct pathway involves plants absorbing available phosphorus from the soil through their root epidermal cells and root hairs. In contrast, the mycorrhizal pathway involves a symbiotic relationship between plants and arbuscular mycorrhizal (AM) fungi. The hyphae of AM fungi can extend into soil depths that plant roots cannot reach, absorbing phosphorus and transferring it to the plant host.
How do plants regulate these two pathways? Recently, a review article published by Professor Lin Zhang’s team at China Agricultural University pointed out that plants balance carbon expenditure with phosphorus acquisition efficiency. When soil phosphorus is scarce, plants increase investment in their root systems, allocating more carbon resources to the roots to search for limited phosphorus through the direct pathway. Conversely, when soil phosphorus is relatively abundant, plants reduce carbon allocation to the mycorrhizal symbiotic system. Additionally, different AM fungi vary in their ability to assist plants in phosphorus acquisition, and plants appear to recognize this, preferentially allocating more carbon resources to fungal partners that are more efficient at providing phosphorus.
In the mycorrhizal pathway, the synergistic role of rhizosphere bacteria is crucial. Due to the spatial heterogeneity of soil nutrients and the limited ability of AM fungi to decompose organic matter, phosphate-solubilizing rhizosphere bacteria become key metabolic supplements. AM fungi release hyphal exudates that specifically attract and alter the composition of rhizosphere bacterial communities. Among these, phosphate-solubilizing bacteria can secrete acid phosphatases to mineralize insoluble organic phosphorus in the soil into plant-available forms, complementing the function of AM fungi and jointly promoting plant phosphorus acquisition. The related research has been published in Frontiers of Agricultural Science and Engineering (DOI: 10.15302/J-FASE-2024589).
Although existing research has revealed the basic framework of plant phosphorus acquisition strategies, several key questions about the synergistic regulation of the “dual pathways” remain unanswered. First, how do plants precisely regulate the allocation of carbon resources between roots and the mycorrhizal symbiotic system? Second, what is the sequence and coordination mechanism of the direct and mycorrhizal pathways under different soil environments and growth stages? Moreover, the signaling and collaborative details between rhizosphere bacteria and AM fungi require further investigation. In the future, interdisciplinary approaches, such as quantum dot technology and high-throughput stable isotope probing, should be employed to systematically elucidate the molecular mechanisms and ecological processes of plant phosphorus acquisition.
DOI: 10.15302/J-FASE-2024589