Decomposition nitrogen and phosphorus

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New Phytol. (19%), 134, 123-132 Decomposition, nitrogen and phosphorus mineralization from beech leaf litter colonized by ectomycorrhizal or litter- decomposing basidiomycetes BY JAN V. COLPAERTi* AND K A T I A K. VAN TICHELEN^ ^Laboratory of Developmental Biology, Institute of Botany, Katholieke Universiteit Leuven, K. Mercierlaan, 92, B-3001 Leuven, Belgium ^Laboratory of Plant Ecology, Institute of Botany, Katholieke Universiteit Leuven, K. Mercierlaan, 92, B-3001 Leuven, Belgium (Received 12 October 1995; accepted 12 March 1996) S U M M A R Y T h e 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. T h e 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. T h e investigation was performed at two different p H values since substrate p H 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. T h e 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. T h e 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. Key words: Basidiomycetes, ectomycorrhiza, litter decomposition, leaf litter mineralization, nutrient cycling. understood, as many studies on this topic have been INTRODUCTION made under fairly artificial conditions. Very httle The ectomycorrhizal mycehum of many basidio- work has been done w.th intact mycorrbizal systems mvcetes which colonize the organic bonzons of colonizing organic substrates that occur in forest forest soils is thought to be tnvolved tn direct ecosystems (Bending & Read. 1995). The importance mobilization of nutrients from organic substrates of the saprotrophic abihties o the ectomycorrhizal (Abuzinadah, Fmlay & Read, 1986; Read, 1991). fungi for a particular host and for nutrient cycling m There ts clear evidence that mycorrhizal fung. can forest ecosystems ,s still unclear. Comparisons artd produce enzymes which m.ght allow them to derive .nteract,on studies with true sapro roph.c fung a e Lmeral nutrknts and carbon from organic resources .nd.spensable as they will allo^w us to °btain a be r (Dtghton 1991). However, Dighton (1991) con- understanding of the decomposition and m.nerahz- cludes that the whole st^bject is far from completely ation processes m forest '^'^^A'f ^ " f . In forests both nitrogen (Iv) and phosphorus (f) , accumulate in a wide array of organic compounds * To whom correspondence should be addressed. 124 y. V. Colpaert and K. K. Van Tichelen and the availability of these elements is inherently linked to the turnover of organic N and P compounds which can have very long half-lives (Attiwill & Adams, 1993). Free inorganic N and P can hardly be detected, because of their fast turnover in the soil. Competition for uptake of ammonium between the different soil-inhabiting organisms is high, non- mycorrhizal roots being poor competitors (Smith & Smith, 1990). In temperate forests, saprotrophic and mycor- rhizal basidiomycetes colonize intensively the F- litter layers of the mor and moder humus (Hering, 1982). Vegetation growing on these soils produces a litter that is not especially palatable to soil animals since it contains a lot of phenolic compounds. It is also poor in N which, in addition, is not readily accessible as it is retained within refractory com- pounds such as protein-polyphenol complexes. Leaf litter falling on the soil surface is normally already colonized by microfungi, which originally become established as biotrophs or necrotrophs. Once the easily degradable carbohydrates from the fresh leaf litter have been metabolized by the microfungi, saprotrophic bas...

Tagi:
  • decomposition
  • nitrogen
  • phosphorus

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