Mycorrhizas and nutrient cycling in ecosystems – a journey towards relevance?

Abstract

SummaryProgress towards understanding the extent to which mycorrhizal fungi are involved in the mobilization of nitrogen (N) and phosphorus (P) from natural substrates is reviewed here. While mycorrhiza research has emphasized the role of the symbiosis in facilitation of capture of these nutrients in ionic form, attention has shifted since the mid-1980s to analysing the mycorrhizal fungal abilities to release N and P from the detrital materials of microbial faunal and plant origins, which are the primary sources of these elements in terrestrial ecosystems. Ericoid, and some ectomycorrhizal fungi have the potential to be directly involved in attack both on structural polymers, which may render nutrients inaccessible, and in mobilization of N and P from the organic polymers in which they are sequestered. The advantages to the plant of achieving intervention in the microbial mobilization-immobilization cycles are stressed. While the new approaches may initially lack the precision achieved in studies of readily characterized ionic forms of N and P, they do provide insights of greater ecological relevance. The results support the hypothesis that selection has favoured ericoid and ectomycorrhizal systems with well developed saprotrophic capabilities in those ecosystems characterized by retention of N and P as organic complexes in the soil. The need for further investigation of the abilities of arbuscular mycorrhizal fungi to intervene in nutrient mobilization processes is stressed.

Large and variable genome size unrelated to serpentine adaptation but supportive of cryptic sexuality in Cenococcum geophilum

“…Although the important role that fungi play in ecosystem diversity and functioning is under active research (e.g., Read and Perez-Moreno 2003), until recently, there has been relatively scarce information on genome structure and size for non-model fungal species despite its relevance for comparative biodiversity research (Gregory et al 2007). Nevertheless, a growing body of evidence indicates large variation in genome size in the fungal kingdom.…”

Recent advances in population genetics of ectomycorrhizal mushroomsRussulaspp.

“…Globally, a large percentage of terrestrial plants form this type of plant–fungal mutualism. Therefore, in natural ecology systems, ectomycorrhizal symbiosis is one of the most ubiquitous phenomena that play important roles in accelerating nutrient and mineral cycling and in maintaining ecosystem stability (Read and Perez-Moreno 2003; Smith and Read 2008). …”

Enzyme secretion by ECM fungi and exploitation of mineral nutrients from soil organic matter

“…The saprotrophic potential of ECMs may reflect the fact that the ectomycorrhizal symbiosis has evolved several times independently from presumably saprotrophic groups within basidio-and ascomycetes (Bruns and Shefferson 2004;Hibbett and Matheny 2009). ECM evolution has even been related to nutrient-poor conditions with nutrients patchily distributed and often protected from mineralization by surrounding organic material (Lambers et al 2009;Read and Perez-Moreno 2003).…”