Role of roots and mycorrhizal mycelia in soil C and N cycling

Heljä-Sisko Helmisaari1
1 Department of Forest Sciences, University of Helsinki

Invited Talk 4 in Below ground turnover of C and nutrients in forest soils

14.07.2014, 10:45-11:15, H17

Forests are known to store a great amount of global carbon (C) both in vegetation and in soils. Soil organic matter (SOM) is mostly formed of litter inputs, aboveground inputs being relatively well known in relation to those from belowground. Quantification of the C flux to fine roots, mycorrhizas and mycelia and C input into soil in litter require estimating belowground biomasses and turnover rates. Progress has taken place in recent years to quantify these for species and sites. The rate of growth and turnover of fine roots and mycelia are affected by the availability of carbohydrates and nutrients, and by environmental factors such as soil temperature and moisture (e.g. Leppälammi-Kujansuu et al. 2013). Recent studies also suggest that fine root longevity may be related to mycorrhizal species colonising the root tips (Ostonen et al. 2011).

Several studies report that the share of belowground litter C input may be as large or larger than that from aboveground while the relative importance of litter of different origin and quality for SOM formation is still poorly known. Recent reports also highlight the importance of total fungal production, including sheaths and mycelia, which may be similar in magnitude to fine root production (Ouimette et al. 2013).

The quality of litter together with the environmental conditions in soil greatly affect SOM formation, soil C storage and turnover.  Several recent studies discuss how the differences in above- and belowground litter quality may affect the share of litter C being finally incorporated into SOM. Further, the decomposition rate of old C compounds which is intensively studied in relation to rising global temperature, may vary in relation to soil C origin. The C flux into SOM through roots and mycelia in exudates is still a large gap in our understanding of the terrestrial C cycle but easily available C through rhizosphere priming has been shown to be important for SOM decomposition (Lindén et al. 2014)

Soil organic matter also accumulates and is a source of important nutrients such as nitrogen (N) for plant uptake. Fine roots and mycelia are rich in N but the N input through them into soil is still poorly known as retranslocation process in roots has been difficult if not impossible to quantify. The transformation processes of N affecting the availability and uptake of the element may be closely related to the origin and quality of litter. Organic N has been shown to be important especially in northern and infertile ecosystems where amino acids dominate over ammonium and nitrate (Näsholm et al. 2012).

This presentation will concentrate on the recent research results for understanding the role of roots and mycorrhizal mycelia in soil C and N cycling. Drivers of fine root and mycelia C allocation and input to SOM as well as interactions between C allocation and nutrient uptake strategies will be reviewed and discussed.

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last modified 2014-06-19