Microbial regulation of the soil carbon cycle: evidence from gene-enzyme relationships.

A lack of empirical evidence for the microbial regulation of ecosystem processes, including carbon (C) degradation, hinders our ability to develop a framework to directly incorporate the genetic composition of microbial communities in the enzyme-driven Earth system models. Herein we evaluated the linkage between microbial functional genes and extracellular enzyme activity in soil samples collected across three geographical regions of Australia. We found a strong relationship between different functional genes and their corresponding enzyme activities. This relationship was maintained after considering microbial community structure, total C and soil pH using structural equation modelling. Results showed that the variations in the activity of enzymes involved in C degradation were predicted by the functional gene abundance of the soil microbial community (R2>0.90 in all cases). Our findings provide a strong framework for improved predictions on soil C dynamics that could be achieved by adopting a gene-centric approach incorporating the abundance of functional genes into process models

Microbial legacies alter decomposition in response to simulated global change.

Terrestrial ecosystem models assume that microbial communities respond instantaneously, or are immediately resilient, to environmental change. Here we tested this assumption by quantifying the resilience of a leaf litter community to changes in precipitation or nitrogen availability. By manipulating composition within a global change experiment, we decoupled the legacies of abiotic parameters versus that of the microbial community itself. After one rainy season, more variation in fungal composition could be explained by the original microbial inoculum than the litterbag environment (18% versus 5.5% of total variation). This compositional legacy persisted for 3 years, when 6% of the variability in fungal composition was still explained by the microbial origin. In contrast, bacterial composition was generally more resilient than fungal composition. Microbial functioning (measured as decomposition rate) was not immediately resilient to the global change manipulations; decomposition depended on both the contemporary environment and rainfall the year prior. Finally, using metagenomic sequencing, we showed that changes in precipitation, but not nitrogen availability, altered the potential for bacterial carbohydrate degradation, suggesting why the functional consequences of the two experiments may have differed. Predictions of how terrestrial ecosystem processes respond to environmental change may thus be improved by considering the legacies of microbial communities

Response of arbuscular mycorrhizal mungbean plants to ambient air pollution

The experiments were conducted in open top chamber system installed at the University of the Punjab, Quaid-e-Azam Campus, Lahore, Pakistan. The mungbean ( Vigna radiata (L.) Wilczek var.M28) seeds were sown in earthen pots and were kept in filtered air, unfiltered air and ambient air. The ozone concentration was monitored daily during 1000hrs till 1600 h. The data for light intensity and relative humidity was also regularly collected. The sets of plants growing in FA chambers (without ozone and dust particles) responded well as regards growth and yields are concerned. Unfiltered air reduced the number of nodules, their biomass and nitroginase activity in mungbean plants. The present study documents that the species of mycorrhizal fungi sensitive to tropospheric ozone failed to reproduce in ambient air and unfiltered air chambers (without dust particles). Out of a total of 24 species, eighteen species belonged to the genus Glomus, two each to Sclerocystis, to Acaulospora and one each to Gigaspora and Scutellospora. The total number of species was variable during the growth phase. The total number of species reduced in soil of UFA chambers with the passage of time. Species richness reduced to almost half in UFA plants as compared to FA plants. Species of the Genus Glomus were highly abundant species at various harvests in all air treatments. Amongst most abundantly recovered Glomus species were G. fasciculatum, G. mosseae, G. aggregatum, G. caledonicum, G. deserticola, G. geosporum, and G. monosporum. The pattern of abundance kept on varying at various harvests for different air and mycorrhizal treatments. In the case of plants of UFA treatment, only two species of Glomus were abundant namely G. fasciculatum and G. geosporum. Species of Acaulospora and Gigaspora in particular and Scutellospora and Sclerocystis in general were sensitive to polluted air

Contrasting soil fungal communities in Mediterranean pine forests subjected to different wildfire frequencies

Mediterranean forest ecosystems are characterized by various vascular plant groups with their associated mycorrhizae and free living soil fungi with various ecological functions. Fire plays a major role in Mediterranean ecosystem dynamics and impacts both above- and below-ground community structure and functioning. However, studies on the effects induced by altered disturbance regimes (associated with recent land use and climate extremes) on fire ecology and especially on its below-ground impacts are few. The objectives of this study were to evaluate the effects of different wildfire regimes on soil fungal community structure using two different molecular methods. We investigated the long-term effects of wildfire on soil fungal communities associated with Pinus pinaster forests in central Portugal, by comparing the results of denaturing gradient gel electrophoresis (DGGE)-based profiling with those obtained with 454 pyrosequencing. Four forest stands with differing fire history and fire return interval, and vegetation cover (mature forest, early successional stage of pine regeneration, and forest converted to scrubland) were sampled 6 years after the last fire event. The pyrosequencing-based approach indicated ca. eight-fold higher numbers of taxa than DGGE. However, fungal community fingerprinting data obtained for the different study stands with DGGE were congruent with those obtained with pyrosequencing. Both short (7.6 years) and long (24 years) fire return intervals (indicated by the presence of ericaceous shrubs in the understorey) induced a decrease in the abundance ratio between basidiomycetes and ascomycetes and appeared to reduce the frequency of ectomycorrhizal fungal species and saprophytes. Wildfire significantly reduced the frequency of late stage successional taxa (e.g. Atheliaceae and Cantharellales) and known or putative saprophytes belonging to the Clavulinaceae and the Archaeorhizomycetaceae. Conversely, early successional fungal species belonging to the Thelephoraceae were favoured by both fire return intervals, while the abundance of Cortinarius and Hebeloma, which include several Cistus-specific species, increased with short wildfire return intervals. This last finding highlights the relationship between post-fire vegetation composition and cover (vegetation successional stage), and fungal symbionts. We hypothesise that these changes could, in the long term, exhaust the resilience of Mediterranean pine forest vegetation and associated soil fungal communities by preventing pine regeneration. © 2014, Mushroom Research Foundation