Decomposition, nitrogen and phosphorus mineralization from beech leaf litter colonized by ectomycorrhizal or litter‐decomposing basidiomycetes

Abstract

S U M M A R YThe decomposition and the nitrogen and phosphorus mineralization of fresh beech (Fagus sylvatica L.) leaf litter are described. Leaves were buried for up to 6 months in plant containers m which Scots pine (Pxnus sylvestris L.) seedlings were cultivated at a low rate of nutrient addition. The saprotrophic abilities of three ectomycorrhizal fungi, Thelephora terrestris Ehrh.: Fr., Suillus bovinus (L.: Ft.) O. Kuntze and Paxillus involutus (Batsch: Fr) Ft., were compared with the degradation caused by the iittet-decomposing basidiomycete, Lepista nuda (Bull.: Ft.) Cooke. Uninoculated leaves were included as controls. The investigation was performed at two different pH values since substrate pH is supposed to have an effect on the activities of extracellular enzymes of ectomycorrhizal fungi. The enzyme expression might also be largely influenced by the substrate they colonised. The mycorrhizal fungi caused only a low decomposition rate of the litter compared with that of L. nuda, and nitrogen was released only by L nuda. Leaves colonized by mycorrhizal fungi showed no net release of nitrogen; on the contrary, a small accumulation of N in the litter was observed. It therefore seems likely that the ectomyccrrhizal fungi studied do not have the ability to decompose efficiently the ligDOcellulose matrix of the relatively recalcitrant beech Jeaf litter. The degradation of this matrix seems to be essential for the fungi to gain access to the leaf nitrogen pool of fresh beech litter A direct release of nitrogen from organic compounds by ectomycorrhizal fungi seems therefore to be confined to the older litter layers. The beech leaf litter contained an important fraction of easily mineralizable phosphorus. P was not a growth limiting factor m the cultivation system, and could therefore accumulate m the leaf litter colonized by the ectomycorrhizal mycelium.

A comparison of the extracellular enzyme activities of two ectomycorrhizal and a leaf‐saprotrophic basidiomycete colonizing beech leaf litter

“…Mycorrhizal mycelium exported 23 % of the total N contained in pine organic matter from a fermentation horizon (Bending & Read, 1995 a). In a preceding paper (Colpaert & Van Tichelen, 1996) we found no evidence for export of N from fresh beech leaf litter colonized by three different mycorrhizal fungi, whereas a whiterot litter decomposer was able to release up to 30% of the initial N retained in this litter. These observations suggest that ectomycorrhizal fungi can only mobilize N from organic compounds which become available or are produced during the later stages of the litter degradation.…”

“…Unlike L. nuda, very low decay rates were achieved by S. bovinus and T. terrestris in the beech leaf litter studied (Colpaert & Van Tichelen, 1996). It is not too surprising that the taxonomically related groups of the saprotrophic and mycorrhizal basidiomycetes still possess the same enzyme systems.…”

“…It is possible that the pH of the assay buffer had some effect, but it was also likely that the enzyme production decreased at the lower pH. Phosphate was not a growth-limiting nutrient in the culture system, it was easily available in sufficient quantities and it might even accumulate in mycorrhizal mycelium (Colpaert & Van Tichelen, 1996). At high levels of P availability, micro-organisms probably expend less energy in extracellular phos-phatase production to acquire P from organic sources (Sinsabaugh et al, 1993).…”

“…To ohtain a clean substrate the leaves were washed thoroughly with plenty of water. For more details see the preceding paper in which we also comment on the choice of the organic matter (Colpaert & Van Tichelen, 1996). Exactly 2-00 g of dried leaf material was put in nylon hags with a mesh size of 100 fim to exclude root growth in the litter.…”

The Exotic Legume Tree Species Acacia holosericea Alters Microbial Soil Functionalities and the Structure of the Arbuscular Mycorrhizal Community

“…Olsson et al (51) have found that the presence of ectomycorrhizal mycelia reduced bacterial activity in a sandy soil, whereas it has been previously demonstrated that ectomycorrhizal symbiosis had a selective pressure on bacterial communities by promoting the development of bacterial strains potentially beneficial to the symbiosis and to the plant (i.e., organic phosphate-solubilizing bacteria) (32). It is generally admitted that ectomycorrhizal fungi have a reduced ability to decompose complex organic compounds of carbon (9), but the impact of ectomycorrhizal symbiosis on soil microbiota could promote the process of decomposition of organic N and P compounds, leading to higher soil P and N contents. Changes in the catabolic response profiles also revealed this mycorrhizosphere effect (46).…”