Population of arbuscular mycorrhizal fungi in semi-arid environment of Jordan as influenced by biotic and abiotic factors

This study was conducted to evaluate the population of the arbuscular mycorrhizal fungi (AMF) in the semi-rid agro-ecosystem of North Jordan and to evaluate the effect of the biotic and abiotic factors on AMF population. Soil samples were collected from 12 locations where several soil samples were collected from each location. The collected soil samples were analysed for chemical and physical properties and spores were separated from the soil by the floating-adhesion technique and examined by the dissecting microscope. The AMF spores densities vary among locations and crops. The spore density was relatively low, with the highest observed under fruit trees and the lowest under a fallow system. Eight species were identified. Glomus mosseae was the most common species among samples, which was found in 85% of the soil samples collected. G. geosporum was found in 20%, while G. constrictum and G. clarum were found in 10% of the samples collected. G. caledomium was found in 8% of the samples. The lowest occurrence was observed for the G. monosporum and G. clariodum, Which were found in only 5% of samples collected. Twenty percent of the samples collected contained Acaulospora spp. The spore density was not clearly affected neither by the host plants nor by the location, which suggest the absence of location or plant specificity for the AMF observed in soils of North Jordan. This may suggest that other factors could have an effect on mycorrhizal distribution. Therefore, biotic factors may be relatively less important than abiotic factors for establishing population patterns. The spore density of AMF had a very weak correlation with the soil pH and electrical conductivity (EC), and no significant correlation with the percentages of soil clay and silt particles. The organic matter (OM) and CaCO3 percentages were significantly positively correlated with AMF spore density. On the other hand, the AMF spore density was negatively related to the soil phosphorus. In conclusion, the G. mosseae was the most common AMF species and no host plant or geographic location specificity was observed, suggesting the population of AMF species was affected mainly by abiotic factors and cropping patterns. (C) 2002 Elsevier Science Ltd.