The role of carbon in fungal nutrient uptake and transport

Abstract

T he arbuscular mycorrhizal (AM) symbiosis, which forms between plant hosts and ubiquitous soil fungi of the phylum Glomeromycota, plays a key role for the nutrient uptake of the majority of land plants, including many economically important crop species. AM fungi take up nutrients from the soil and exchange them for photosynthetically fixed carbon from the host. While our understanding of the exact mechanisms controlling carbon and nutrient exchange is still limited, we recently demonstrated that (i) carbon acts as an important trigger for fungal N uptake and transport, (ii) the fungus changes its strategy in response to an exogenous supply of carbon, and that (iii) both plants and fungi reciprocally reward resources to those partners providing more benefit. Here, we summarize recent research findings and discuss the implications of these results for fungal and plant control of resource exchange in the AM symbiosis.

Arbuscular mycorrhizal fungal communities associated with two dominant species differ in their responses to long‐term nitrogen addition in temperate grasslands

“…Future studies on the impacts of global change on grassland ecosystems should focus on the interactions between plant species and fungal communities. Nevertheless, our findings provide a compelling evidence to support the hypothesis that that the host plants are in control of AMF–plant symbiosis (Fellbaum, Mensah et al., ).…”

“…Moreover, 7-year N addition at a rate 40 kg ha −1 year −1 reduced AM fungal spore density, species richness and extraradical hyphal lengths in four functional groups (C 3 grasses, C 4 grasses, forbs and legumes) in North American tallgrass prairies (Antoninka, Reich, & Johnson, 2011). In contrast, the N addition had little effects on spore abundance in forbs and extraradical hyphal length in C 4 grasses and legumes in the tallgrass prairies of their photosynthetically fixed C to their associated AM fungi (Fellbaum, Mensah et al, 2012;Johnson, 2010;Smith & Read, 2008;Wright, Read, & Scholes, 1998). In this study, we found that N addition significantly reduced the photosynthetic rate and root/shoot ratio in A. frigida, while N addition had no impact on photosynthetic rates and root/shoot ratio in S. krylovii (Figures 5 and 7c).…”

“…Plant‐derived C drives AM fungal fitness because they are asexual obligate biotrophs that rely exclusively on C from the host plants to complete their life cycle. The host plants can transfer up to 20% of their photosynthetically fixed C to their associated AM fungi (Fellbaum, Mensah et al., ; Johnson, ; Smith & Read, ; Wright, Read, & Scholes, ). In this study, we found that N addition significantly reduced the photosynthetic rate and root/shoot ratio in A. frigida , while N addition had no impact on photosynthetic rates and root/shoot ratio in S. krylovii (Figures and c).…”

A phosphorus threshold for mycoheterotrophic plants in tropical forests

“…We speculate that this could indicate a phosphorus-dependent shift in the underlying exchange relationships between photosynthetic plants and their AM fungal partners. Although elucidation of the exact mechanism falls outside the scope of this study, we hypothesize that such a functional shift could be underpinned by a reduction in carbon allocation from photosynthetic plants to AM fungal partners at increasing concentrations of soil phosphorus [47], either inhibiting the release of chemical factors from the fungi that stimulate the germination of mycoheterotrophs [48], or causing the fungi to restrict carbon flow to mycoheterotrophs [49]. Alternatively, it could be that changes in AM fungal community dynamics (such as competition) at elevated soil phosphorus (indicated by changes in soil AM fungal community composition; figure 4) may affect mycoheterotroph abundance.…”

Kinetic Study on Flooded Soil Recovery Using Soil Containing Arbuscular Mycorrhizal Fungi

“…The increase in the P capacity of the plants can be attributed to the large increase in soil exploration area (more than one hundred times) due to mycorrhizal external mycelium production, its greater efficiency of nutrient absorption and higher affinity (lower Km) for P uptake from the soil solution. More recent work demonstrated that C also acts as a trigger for fungal N and K uptake and transport [11]. N in the soil had high mobility to move to plant roots through mass flow, therefore it had been suggested that the AMF played little role in N uptake.…”