Km. Jacobson, MOISTURE AND SUBSTRATE STABILITY DETERMINE VA-MYCORRHIZAL FUNGAL COMMUNITY DISTRIBUTION AND STRUCTURE IN AN ARID GRASSLAND, Journal of arid environments, 35(1), 1997, pp. 59-75
The arid central dune held of the Namib Desert is characterized by a p
ronounced rainfall gradient across its west-east, 160 km breadth, and
a correlated increase in sand stability and grass community complexity
. In addition to these macro-gradients, micro-gradients of sand stabil
ity and available moisture across each dune slope result in stratified
grass communities on the dunes. The effects of abiotic factors and pl
ant associations on the community structure of VA-mycorrhizal fungi in
a naturally arid and unstable grassland could thus be investigated. M
ycorrhizal fungal communities associated with five grass species were
sampled at sites located across the gradients. Diversity and abundance
of spores, as well as percent mycorrhizal colonization of plant roots
, were used to characterize the fungal communities and their plant spe
cificity. Five Glomus species (Glomales) were associated with grasses
at all sites, but no plant specificity was observed. Rather, the funga
l communities varied in diversity and abundance both within a dune sit
e and across the dune field. Regression analyses showed that spore abu
ndance and colonization levels were significantly affected by abiotic
factors. Sand stability affected spore abundance and thus determined t
he limits of distribution of the fungal community in the dune grasslan
d. In contrast, colonization levels were primarily affected by moistur
e availability, and fungal growth and spore production following an is
olated rain event were closely associated with moisture availability.
A rapid and opportunistic growth response to moisture, production of r
esilient spores in response to declining moisture, and lack of plant s
ymbiont specificity are characteristics which allow mycorrhizal fungal
communities to function under hyperarid conditions. (C) 1997 Academic
Press Limited