Temporal changes in nematode community structure in a desert ecosystem

The effects of soil conditions on soil nematode community were studied. Soil samples from the upper soil layer (0-10 cm) were collected monthly (except for two samplings in February 1999), under the canopies of the two halophytic shrubs: Artemisia monosperma and Retama raetam. Significant differences in soil environmental variables (soil moisture, organic matter, electrical conductivity, Ca²⁺, K⁺ and Na⁺) were observed between the canopies and the bare soil samples (p < 0.01) during the study period. The soil water content under shrubs and in bare soil was <1.0% from April to December 1998 then increased to 4.9% in January 1999. During the winter season (December 1998 to March 1999), the mean numbers of total free-living nematodes were found to be lower under A. monosperma than under R. raetam. Various ecological indices were used to assess and compare the response of nematode populations to the soil conditions. From October 1998 to February 1999, the mean values of Simpson's diversity index (SI), Shannon's index (H′) and Sigma maturity index (∑MI) were observed to be lower under A. monosperma than under R. raetam. The ratio of (fungivores + bacterivores) to plant parasites ((FF + BF)/PP), SI, H′ and ∑MI were found to be sensitive to moisture stress in a sandy desert ecosystem.