Long-term effects of irrigation with waste water on soil AM fungi diversity and microbial activities: the implications for agro-ecosystem resilience.

The effects of irrigation with treated urban wastewater (WW) on the arbuscular mycorrhizal fungi (AMF) diversity and soil microbial activities were assayed on a long-term basis in a semiarid orange-tree orchard. After 43 years, the soil irrigated with fresh water (FW) had higher AMF diversity than soils irrigated with WW. Microbial activities were significantly higher in the soils irrigated with WW than in those irrigated with FW. Therefore, as no negative effects were observed on crop vitality and productivity, it seems that the ecosystem resilience gave rise to the selection of AMF species better able to thrive in soils with higher microbial activity and, thus, to higher soil fertility

Bar plot showing the number of clones detected for each AM fungal sequence type in the soil irrigated with fresh water (FW) and treated wastewater (WW) 43 years after establishment.

<p>Bar plot showing the number of clones detected for each AM fungal sequence type in the soil irrigated with fresh water (FW) and treated wastewater (WW) 43 years after establishment.</p

Sampling effort curve for the AM fungal sequence types richness observed in this study.

<p>The sample order was randomized by 100 replications in EstimateS, version 8.0 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047680#pone.0047680-Colwell1" target="_blank">[32]</a>. Bars represent error standard (n = 5).</p

Pearson’s coefficients of correlation and significance level between the soil parameters measured, and the AMF community composition

<p>Pearson’s coefficients of correlation and significance level between the soil parameters measured, and the AMF community composition</p

The application of an organic amendment modifies the arbuscular mycorrhizal fungal communities colonizing native seedlings grown in a heavy-metal-polluted soil

A mesocosm experiment was conducted to investigate whether communities of arbuscular mycorrhizal (AM) fungi associated with roots of native (Piptatherum miliaceum, Retama sphaerocarpa, Psoralea bituminosa, Coronilla juncea, and Anthyllis cytisoides) and for comparison (Lolium perenne) seedlings in a heavy-metal-contaminated, semiarid soil were affected by the application of composted sugar beet waste. We also investigated whether there were relation between AMF diversity and metal concentration (Al, Cd, Cu, Fe, Mn, Pb and Zn) and total P in shoot as well as some soil parameters (total organic carbon and total N) when the SB waste was added to the soil. We analyzed a portion of approximately 795 base pairs of the small-subunit (SSU) rRNA gene by nested PCR, cloning, sequencing, and phylogenetic analyses. Twelve different AMF sequence types were distinguished: seven of these belonged to Glomus group A, one to Glomus group B, one to Diversispora, one to Archaeospora, and two to Paraglomus. The AM fungal populations colonizing roots in a heavy-metal-polluted soil were quite dependent on the host plant, the highest diversity values being obtained in authochtonous plants recognized as metallophytes, such as P. bituminosa, and in an allochtonous, invasive species (L. perenne). No significant correlation was found between AMF diversity and plant metal concentration and soil parameters. Excepting P. bituminosa, when sugar beet waste was added to soil, the populations of AM fungi in roots increased and the shoot metal concentrations decreased in all host plant species studied. Therefore, the addition of sugar beet waste can be considered a good strategy for the remediation and/or phytostabilization of mine tailing sites.MM Alguacil was supported by the Juan de la Cierva programme (Ministerio de Educación y Ciencia, Spain). This research was supported by “Plan Nacional I+D” Spain (Project number REF. AGL-2006-09453-CO2-01-FOR).Peer reviewe