Increased diversity of arbuscular mycorrhizal fungi in a long-term field experiment via application of organic amendments to a semiarid degraded soil

Abstract

In this study, we tested whether communities of arbuscular mycorrhizal (AM) fungi associated with roots of plant species forming vegetative cover as well as some soil parameters (amounts of phosphatase and glomalin-related soil protein, microbial biomass C and N concentrations, amount of P available, and aggregate stability) were affected by different amounts (control, 6.5 kg m(-2), 13.0 kg m(-2), 19.5 kg m(-2), and 26.0 kg m(-2)) of an urban refuse (UR) 19 years after its application to a highly eroded, semiarid soil. The AM fungal small-subunit (SSU) rRNA genes were subjected to PCR, cloning, single-stranded conformation polymorphism analysis, sequencing, and phylogenetic analyses. One hundred sixteen SSU rRNA sequences were analyzed, and nine AM fungal types belonging to Glomus groups A and B were identified: three of them were present in all the plots that had received UR, and six appeared to be specific to certain amendment doses. The community of AM fungi was more diverse after the application of the different amounts of UR. The values of all the soil parameters analyzed increased proportionally with the dose of amendment applied. In conclusion, the application of organic wastes enhanced soil microbial activities and aggregation, and the AM fungal diversity increased, particularly when a moderate dose of UR (13.0 kg m(-2)) was applied.

FIG. 1.

Proportional distribution of the total number of clones detected for each fungal type according to SSCP patterns in the roots of plant cover in the five plots analyzed (plot 0, control; plot 1, 6.5 kg m⁻² USR added; plot 2, 13.0 kg m⁻² USR added; plot 3, 19.5 kg m⁻² USR added; plot 4, 26.0 kg m⁻² USR added). The richness of AM fungal types is indicated at the tops of the respective bars.

FIG. 2.

NJ phylogenetic tree showing AM fungal sequences isolated from roots of cover plants in the five plots analyzed and reference sequences from GenBank. Numbers above branches indicate the bootstrap values (above 70%, 100 replicates) of the NJ analysis; numbers below branches indicate the bootstrap values of the maximum parsimony analysis. Sequences obtained in the present study are shown in boldface type. They are labeled with the clone identity number, the number of plots from which they were obtained (plot 0 [P0], plot 1, plot 2, plot 3, and plot 4), and the database accession number in parentheses (e.g., EMBL accession number FM876927). Identical sequences are grouped and are represented by letters, followed by the numbers of clones having that particular sequence. See the supplemental material for a detailed description of these clones' identifiers. The brackets show the delimitation of the fungal types found in this study. Group identifiers (for example, Glo unk1) are AM fungal sequence types found in our study. Paraglomus occultum and Paraglomus brasilianum were used as outgroups. Unc, uncultured.

FIG. 3.

Sampling-effort curves for the AM fungal community representing the observed (Obs.) and the estimated (Est.) richnesses for the whole sampling (A) and for each UR dose (B). The sample order was randomized by 100 replications in EstimateS, version 8.0 (9).

FIG. 4.

CA of the AM fungal communities found in the roots of plant cover for the five different plots. The eigenvalues of the first and second axes in the two-dimensional ordination diagrams are as follows: dimension 1, 0.50; dimension 2, 0.40. Circles represent the respective plots, and the triangles represent the fungal types. Ovals with dashed, dotted-dashed, dotted, full, and small dashed lines represent the distributions of diversity of AM fungal populations in plot 0 (P0), plot 1, plot 2, plot 3, and plot 4, respectively.