Nitrogen deposition and ectomycorrhizas

Abstract

As a result of increasing anthropogenic nitrogen deposition, N availability in many forest ecosystems, which are normally N-limited, has been enhanced. We discuss the impacts of this increased N availability on the ectomycorrhizal (ECM) symbiosis which is generally regarded as an adaptation to nutrient limited conditions. Nitrogen deposition can influence fruit-body formation by ECM fungi, the production and distribution of the extraradical mycelium in the soil and the formation of ectomycorrhizas.Available data from long-term N deposition studies indicate that the most prominent effects might be discernible above-ground (i.e. on the formation of fruit bodies). ' Generalist ' species, forming a symbiosis with a wide range of tree species, seem to be less affected by increased N availability than ' specialist ' species, especially those living in symbiosis with conifers. However, the importance of below-ground investigations to determine the impacts of N deposition on the ECM symbiosis must not be underestimated. Culture experiments show an optimum N concentration for the formation of extraradical mycelium and mycorrhizas. Often, negative effects only become visible at comparatively high N concentrations, but the use of a few easily cultivated species of ECM fungi, which are adapted to higher N concentrations, undermines our ability to generalize.So far, N deposition experiments in the field have only shown minor changes in the below-ground mycorrhizal population, as estimated from the investigation of mycorrhizal root tips. However, effects on the ECM mycelium, which is the main fungal component in terms of nutrient uptake, cannot be excluded and need further consideration.Because the photoassimilate supply from the plant to the fungal partner is crucial for the maintenance of the ECM symbiosis, we discuss the possible physiological implications of increasing N inputs on the allocation of C to the fungus. Together with ultrastructural changes, physiological effects might precede obvious visible changes and might therefore be useful early indicators of negative impacts of increasing N inputs on the ECM symbiosis.

Long-term dynamics of aboveground fungal communities in a subalpine Norway spruce forest under elevated nitrogen input

“…Soil base saturation, pH and organic matter content are among the most important factors governing the distribution of macrofungi (Agerer et al 1998;Erland and Taylor 2002;Wallenda and Kottke 1998;Kernaghan 2005). Whereas organic matter content did not differ between the two treatments, the soil pH and base saturation were significantly reduced in the N plot in the course of our experiment (Table 1).…”

“…The critical loads for N in Swiss forests are within the range of 8-20 kg N ha -1 year -1 (Waldner et al 2007). Bobbink et al (1992) cited in Wallenda and Kottke (1998) suggested critical loads of 15-20 kg N ha -1 year -1 for changes in sporocarp production of ectomycorrhizal fungi. This means that the atmospheric N input in our site at least reaches or probably exceeds critical loads affecting forest ecosystems in general and ectomycorrhizal sporocarps in particular.…”

“…inputs in forest ecosystems have been shown to reduce ectomycorrhizal mycelium growth in the soil (Arnebrant 1994;Nilsson and Wallander 2003) and to decrease the species diversity and sporocarp production of ectomycorrhizal species, whereas saprobic species are much less affected (Ritter and Tölle 1978;Arnolds 1991;Wiklund et al 1995;Wallenda and Kottke 1998;Lilleskov et al 2001;Peter et al 2001a;Trudell and Edmonds 2004). The diverse ways of C acquisition of ectomycorrhizal and saprobic fungi might explain the different reactions of the two communities to N input.…”

Ectomycorrhizal fungal taxa differing in response to nitrogen deposition also differ in pure culture organic nitrogen use and natural abundance of nitrogen isotopes

“…There is evidence that high inorganic N additions can lead to changes in EMF community structure (Wallenda & Kottke, 1998;Lilleskov et al , 2001Lilleskov et al , , 2002Peter et al , 2001). We characterized the dominant EMF taxa over an N deposition gradient in Alaska and found that with increasing N availability most taxa declined both in sporocarp production and in abundance on root tips, and that the dominant taxa changed (Lilleskov et al , 2001(Lilleskov et al , , 2002.…”

The application of potato starch effluent causes a reduction in the photosynthetic efficiency and growth of Scots pine (Pinus sylvestris L.)

“…Some ectomycorrhizal symbiotic fungi inhibit pathogens (Rudawska 1990), probably due to metabolites produced by symbiotic fungi and synthesized in roots (Oleksyn 1998). Symbionts seem to be sensitive to the high amount of N applied (Wallenda and Kottke 1998). Some other research point out the negative influence of fertilization, negative effect of high fertilization is the decrease tree resistance to insects (Glynn and Herms 2001).…”