Jv. Colpaert et Kk. Vantichelen, DECOMPOSITION, NITROGEN AND PHOSPHORUS MINERALIZATION FROM BEECH LEAF-LITTER COLONIZED BY ECTOMYCORRHIZAL OR LITTER-DECOMPOSING BASIDIOMYCETES, New phytologist, 134(1), 1996, pp. 123-132
The decomposition and the nitrogen and phosphorus mineralization of fr
esh beech (Fagus sylvatica L.) leaf litter are described. Leaves were
buried for up to 6 months in plant containers in which Scots pine (Pin
us sylvestris L.) seedlings were cultivated at a low rate of nutrient
addition. The saprotrophic abilities of three ectomycorrhizal fungi, T
helephora terrestris Ehrh.: Fr., Suillus bovinus (L.: Fr.) O. Kuntze a
nd Paxillus involutus (Batsch: Fr) Fr., were compared with the degrada
tion caused by the litter-decomposing basidiomycete, Lepista nuda (Bul
l.: Fr.) Cooke. Uninoculated leaves were included as controls. The inv
estigation was performed at two different pH values since substrate pH
is supposed to have an effect on the activities of extracellular enzy
mes of ectomycorrhizal fungi. The enzyme expression might also be larg
ely 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 colonize
d by mycorrhizal fungi showed no net release of nitrogen; on the contr
ary, a small accumulation of N in the litter was observed. It therefor
e seems likely that the ectomycorrhizal fungi studied do not have the
ability to decompose efficiently the lignocellulose matrix of the rela
tively recalcitrant beech leaf litter. The degradation of this matrix
seems to be essential for the fungi to gain access to the leaf nitroge
n pool of fresh beech litter. A direct release of nitrogen from organi
c 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 limit
ing factor in the cultivation system, and could therefore accumulate i
n the leaf litter colonized by the ectomycorrhizal mycelium.