Distribution and diversity of Paraglomus spp. in tilled agricultural soils.

Understanding of the ecology of arbuscular mycorrhizal fungi comes primarily from the order Glomerales, and relatively little is known of the ecology of other orders including the Paraglomerales. We investigated the distribution of the Paraglomerales across the English agricultural landscape under different management systems. Soils were collected from 11 tilled agricultural sites. Presence of Paraglomerales was assessed using PCR amplification of 18S/ITS region ribosomal DNA isolated from trap plants, terminal restriction fragment length polymorphism and cloning. Paraglomus spp. were detected in all samples from one location and sporadically in six more, but not at the other locations. Distribution was not related to soil physiochemical characteristics, but the Paraglomaceae were significantly more common in soils under organic management. Cloning of samples from three sites produced sequences closely related to Paraglomus laccatum but only distantly related to Paraglomus brasilianum and Paraglomus occultum. Individual sites had between 10 and 27 separate terminal restriction fragments (T-RFs). The large number of T-RFs reflected a significant sequence diversity in the ITS region. Paraglomerales were, therefore, widely distributed across the agricultural landscape, though with patchy distribution and low diversity. More intensive agricultural management appeared to impact negatively on Paraglomus spp.

Contrasting arbuscular mycorrhizal communities colonizing different host plants show a similar response to a soil phosphorus concentration gradient.

High soil phosphorus (P) concentration is frequently shown to reduce root colonization by arbuscular mycorrhizal (AM) fungi, but the influence of P on the diversity of colonizing AM fungi is uncertain. We used terminal restriction fragment length polymorphism (T-RFLP) of 18S rDNA and cloning to assess diversity of AM fungi colonizing maize (Zea mays), soybean (Glycene max) and field violet (Viola arvensis) at three time points in one season along a P gradient of 10-280 mg l(-1) in the field. Percentage AM colonization changed between sampling time points but was not reduced by high soil P except in maize. There was no significant difference in AM diversity between sampling time points. Diversity was reduced at concentrations of P > 25 mg l(-1), particularly in maize and soybean. Both cloning and T-RFLP indicated differences between AM communities in the different host species. Host species was more important than soil P in determining the AM community, except at the highest P concentration. Our results show that the impact of soil P on the diversity of AM fungi colonizing plants was broadly similar, despite the fact that different plants contained different communities. However, subtle differences in the response of the AM community in each host were evident.