Temporal and spatial patterns of fungal diversity along an elevational gradient in an arid ecosystem with implications to ecosystem functioning.

摘要

To evaluate the linkage between fungal taxonomic and functional diversity, and litter decomposition, the decomposition of Agave lechuguilla leaves was followed over a 2 year period along a Chihuahuan Desert watershed. Lechuguilla leaves were air-dried, weighed, tagged, and placed out in 5 vegetation zones along the watershed in Jun97. Vegetation zones included a lowland scrub, creosotebush bajada, sotol grassland, oak forest, and an oak-pine forest. The 5 zones also differed in moisture inputs, soil nitrogen concentration, and mean annual temperature. Every 6 months, 10 tagged leaves per zone were collected until Jun99.; Decomposition was measured as mass loss. Changes in soluble carbon, holocellulose, and lignin fractions during decomposition were also measured. Taxonomic diversity was obtained by plating leaf particles on a general medium (MEA+) and a xerophilic and xerotolerant medium (DG18). To determine fungal functional diversity, a novel method was developed called the FungiLog approach.; Mass loss from decomposing lechuguilla leaves over 2 years ranged from 38.5% in the oak forest to 24.5% in all the other vegetation zones. Mass loss was positively correlated with litter moisture content along the watershed gradient. The soluble carbon fraction of the litter decreased from 39.1% to less than 1% of the initial mass in all vegetation zones after 24 months in the field. The soluble carbon fraction represents readily decomposed carbon sources for decomposers as well as readily leached compounds. There was a perceived increase in the holocellulose fraction over the 24 month period most likely due to an increase in fungal biomass. The lignin fraction decreased from an initial 5.8% to a final 0.3%.; The oak-forest fungi had the greatest functional diversity. The two low elevation zones had the lowest functional diversity. Mass loss was correlated with substrate richness, diversity, and evenness, as well as CO₂ evolution. Spatial and temporal patterns in temperature and water available are the major regulating factors controlling decomposition rates along this watershed in the Chihuahuan Desert. Fungal functional diversity was found to be a better predictor of decomposition rates than taxonomic diversity across this landscape irrespective of vegetation type.