Abstract
Many aspects concerning the role of arbuscular mycorrhizal (AM) fungi in plant nutrient uptake from organic sources remain unclear. Here, we investigated the contribution of AM symbiosis to N and P uptake by durum wheat after the addition of a high C:N biomass to a P-limited soil. Plants were grown in pots in the presence or absence of a multispecies AM inoculum, with (Org) or without (Ctr) the addition of 15N-labelled organic matter (OM). A further treatment, in which 15N was applied in mineral form (Ctr+N) in the same amount as that supplied in the Org treatment, was also included. Inoculation with AM had positive effects on plant growth in both control treatments (Ctr and Ctr+N), mainly linked to an increase in plant P uptake. The addition of OM, increasing the P available in the soil for the plants, resulted in a marked decrease in the contribution of AM symbiosis to plant growth and nutrient uptake, although the percentage of mycorrhization was higher in the Org treatment than in the controls. In addition, mycorrhization drastically reduced the recovery of 15N from the OM added to the soil whereas it slightly increased the N recovery from the mineral fertiliser. This suggests that plants and AM fungi probably exert a differential competition for different sources of N available in the soil. On the whole, our results provide a contribution to a better understanding of the conditions under which AM fungi can play an effective role in mitigating the negative effects of nutritional stresses in plants.
Highlights
The majority of terrestrial plant species, including many agricultural crops, can form mutualistic associations with arbuscular mycorrhizal (AM) fungi (Smith and Read 2008) belonging to the subphylum Glomeromycotina (Spatafora et al 2017)
The present paper reports data from a pot study in which wheat plants were grown in a substrate low in P, in the presence or absence of AM fungal inoculum, and with the addition or not of a high C:N organic material
Test conditions were intended to simulate a situation commonly encountered in Mediterranean cropping systems, where wheat is undoubtedly a key crop, soils are generally poor in P available to plants, and crop residues of cereals often represent the sole source of organic matter (OM) that is returned to the soil
Summary
The majority of terrestrial plant species, including many agricultural crops, can form mutualistic associations with arbuscular mycorrhizal (AM) fungi (Smith and Read 2008) belonging to the subphylum Glomeromycotina (Spatafora et al 2017). The potential benefits of AM symbiosis on plant growth and productivity are well known and include enhanced mineral nutrition and increased tolerance to both biotic and abiotic stresses (Pozo and Azcón-Aguilar 2007; Smith and Smith 2011a; Lenoir et al 2016). Mycorrhiza (2021) 31:441–454 of soil beyond the depletion zone in the rhizosphere), (ii) higher substrate affinity of P uptake into fungal hyphae than directly into plant roots (due to the presence in the extraradical mycelium of high-affinity P transporters that allow mycorrhizal plants to acquire orthophosphate from soil solution at lower concentrations than roots alone; Benedetto et al 2005), (iii) acidification of the mycorrhizosphere (that can increase the mobilisation of sparingly-soluble inorganic P compounds, this occurs typically in alkaline soils), and (iv) possible fungal hydrolysis of organic P, especially under mineral P deficiency (Sato et al 2015; Ezawa and Saito 2018; Andrino et al 2019). A number of studies have shown that AM fungi may regulate the expression of many plant N transporter genes (Duan et al 2015; Saia et al 2015), suggesting their active role in this process
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