Summary And Future Work

White-rot basidiomycetes that formed litter mats significantly increased rates of mass loss during the first 3 months of decomposition in field experiments in a Puerto Rican tropical wet forest. Litter mats generally decreased in density with increasing elevation and decreasing slope. The decrease in mat density with increasing elevation was correlated with reduced litter fall rates at high elevation, but more studies are needed to confirm this relationship. While abundance of white-rot litter decomposers is expected to decrease with increasing litter nutrient concentrations, this aspect has not been explored in tropical forests.

Litter mats tended to move upslope on steep inclines, probably because they grew into the litter that accumulated on their upslope side, but downslope on more gentle gradients associated with overland flows in valleys. The mobile basidiomycete mats in tropical montane forests are thus less likely to leave distinctive signatures in soils, such as the patchwork of mull and mor soils observed in Finland in association with decomposer basidiomycete mats (Hintikka, 1970). Studies of the abundance of litter mats formed by decomposer basidiomycetes are needed from tropical forests with less topographic relief and from non-insular areas in order to determine their general importance in the tropics.

Nitrogen additions had a significant negative effect on litter mat size and leaf trapping rates in high-elevation forest that had limited nitrogen cycling, but little or no effect on basidiomycete mats in a lower elevation forest where nitrogen in litter fall was more abundant. This raises the possibility of partial resilience among decomposer basidiomycetes to nitrogen loading. Studies of ligninolytic enzyme production in response to nitrogen addition are needed to explore this possibility. As nutrient cycling in lowland tropical forests is more often limited by phosphorus than nitrogen, and decomposer basidiomycetes play a key role in recycling of phosphorus in the litter layer (Lodge, 1993,1996), negative effects of nitrogen from air pollutants on decomposer basidiomycetes could significantly slow leaf decomposition in tropical forests.

Basidiomycetes that formed litter mats and subcanopy nets were tested for moisture preferences. The fungi tested indicated differential responses to shading and associated moisture. M. crinis-equi (a subcanopy species) produced most attachments, and has potential for reclamation of steep eroding slopes. Further applied studies are needed to develop protocols for using litter-binding bas-idiomycetes in reclamation of road cuts and landslides, and to determine their effectiveness.

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