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There is great interest in understanding the factors that drive soil microbial activity and community composition in upland grassland ecosystems. We investigated the role of vertical gradients of chemical properties and various soluble C and N pools on soil microbial community structure by using a combination of chemical and biochemical methods coupled with PCR-denaturing gradient gel electrophoresis (DGGE) community fingerprinting and phospholipid fatty acid (PLFA) profiling. Soil samples were collected at increasing depth from a temperate upland grassland. Soil organic matter-related pools (total organic C and total Kjeldahl N) and functionally related active pools (microbial biomass C and N, K2SO4-extractable C and N, extractable organic N) markedly decreased with soil depth and were positively related to each other. The microbial community deep in the soil profile appeared neither C- nor N-limited. Conversely, DGGE community fingerprinting of bacteria, α-Proteobacteria, β-Proteobacteria and Actinobacteria revealed that each soil horizon was conducive to the dominance of particular ribotypes thus confirming links between soluble nutrients gradients and community structure. Soil microbial biomass C assessed by PLFA content decreased with soil depth less steeply than when estimated by the chloroform fumigation-extraction method. This suggests that chloroform fumigation efficiency in lysing microbial cells varied with soil depth with the varying amount and distribution of total and soluble C. The PLFA biomarker for fungal biomass markedly decreased throughout the three upper horizons, whereas that for arbuscular mycorrhizae strongly decreased in the deeper AB horizon only. Taken together with the increase across soil profile of total saturated-to-total monounsaturated fatty acids ratio, the PLFA data suggest that a compositional shift from fungal to bacterial dominance has taken place throughout the grassland layers.

Fire-induced soil heating deeply affects soil organic C pools and their dynamics. The objective of this study was to investigate, in a soil covered with different forest tree species (Eucalyptus camaldulensis, E. occidentalis, Pinus halepensis, and Cupressus sempervirens), the effect of controlled heating on C pools and C mineralization dynamics. Soil samples were heated under controlled condition in laboratory (160 and 380°C) and then wetted with distilled or sea water to simulate the extinction of wildfires. Soil organic C pools react to heating in different way depending on forest tree species. Total organic C was almost halved following the heating of soils at 380°C. Soil covered with Pinus halepensis showed the greater decrease in organic C. Heating increased the amount of the labile C pool, promoted a direct emission of CO2 from soil during the combustion phase and an indirect emission by increasing the substrates readily available for microbial respiration. Sea water applied after heating has generally reduced CO2 emission.

The super high density (SHD) model is a new olive growing system characterized by earlier and higher yields, fully mechanized harvesting and reduced orchard management costs. Until recently all commercial SHD orchards were planted primarily with three varieties: ‘Arbequina’, ‘Arbosana’ and ‘Koroneiki’. To increase variety diversity, broaden available olive oil chemical and organoleptic profiles, and olive oils for marketing, minor local varieties should be evaluated for adaptability to the SHD system. This study compares multiple Sicilian native genotypes to the three current cultivars ‘Arbequina’, ‘Arbosana’ and ‘Koroneiki’. The cumulative fruit and oil production, trunk-cross section area, canopy volume, alternate bearing behavior and oil quality were evaluated in a SHD system. Among the standard cultivars ‘Koroneiki’ had significantly higher and ‘Arbequina’ average productivity respectively compared to earlier reports and was chosen as the reference for evaluating the performance of the Sicilian genotypes. Many of the genotypes investigated had olive and oil yields equal to or higher than ‘Arbequina’; ‘Abunara’ and ‘ADE’ had very high productivity. ‘Abunara’ produced a medium-high quality oil. The ‘KALAT’ selection had high productivity and low vigor, and therefore high productive efficiency. However, the oil polyphenols were low. The ‘Cerasuola’ and ‘Piricuddara’ cultivars had good productivity and a very high quality oils. These results confirm the need to evaluate and preserve local genetic resources as a strategy for improving SHD olive management and increasing olive cultivar and oil diversity.

We investigated the effects of land levelling followed by deep tillage, thus inducing a drastic dismantlement of soil profile, on both soil functioning and quality by monitoring various bioindicators (microbial biomass and community structure, basal respiration, enzyme activities) expressed on either whole soil and TOC mass units, respectively. As expected, in disturbed soils all measured properties had much higher coefficients of variation (CVs), regardless of either whole soil or TOC mass basis, due to the induced spatial variability. The amount of total organic C in the first cubic meter of soil profile was of one order of magnitude greater in undisturbed soils compared to disturbed ones. Soil bioindicators monitored on whole soil mass basis appeared greatly worsened while unchanged or even improved under TOC mass basis. This was essentially due to a couple of reasons: (1) soil bioindicators are constitutively dependent on soil TOC content; (2) soil spatial rearrangement may have made some organic C available to microbial biomass, otherwise unreachable when allocated throughout the undisturbed soil profile. Concluding, our work highlighted the need of expressing soil biondicators on soil mass basis when the response of the whole agrosystem to soil deep spatial rearrangement has to be assessed, while on TOC mass basis if the soil biological features are the major concerns.

This 2-year study aimed to verify whether the continuous application of no tillage (NT) for over 20 years, in comparison with conventional tillage (CT), affects nitrous oxide (NO) and ammonia (NH) emissions from a Vertisol and, if so, whether such an effect varies with crop sequence (continuous wheat, WW and wheat after faba bean, FW). To shed light on the mechanisms involved in determining N-gas emissions, soil bulk density, water filled pore space (WFPS), some carbon (C) and nitrogen (N) pools, denitrifying enzyme activity (DEA), and nitrous oxide reductase gene abundance (nosZ gene) were also assessed at 0–15 and 15–30 cm soil depth. Tillage system had no significant effect on total NH emissions. On average, total NO emissions were higher under NT (2.45 kg NO-N ha) than CT (1.72 kg NO-N ha), being the differences between the two tillage systems greater in FW than WW. The higher NO emissions in NT treatments were ascribed to the increased bulk density, WFPS, and extractable organic C under NT compared to CT, all factors that generally promote the production of NO. Moreover, compared to CT, NT enhanced the potential DEA (114 vs 16 μg N kg h) and nosZ gene abundance (116 vs 69 copy number mg dry soil) in the topsoil. Finally, NT compared to CT led to an average annual increase in C stock of 0.70 Mg C ha year. Though NT can increase the amount os soil organic matter so storing CO into soil, some criticisms related to the increase of NO emission arise, thereby suggesting the need for defining management strategies to mitigate such a negative effect., We thank Beatriz Moreno (CSIC-EEZ) and Vincenzo Cannella(Università degli Studi di Palermo) for technical advice and support.This work was funded by the Italian Ministry for Education, University and Research (MIUR) to Fondazione Angelo e Salvatore Lima Mancuso (Università degli Studi di Palermo)–PON/01_01145 Project–ISCOCEM

Understanding relationships between environmental changes and soil microbial respiration is critical for predicting changes in soil organic carbon (SOC) fluxes and content. The maritime Antarctic is experiencing one of the fastest rates of warming in the world and is therefore a key location to examine the effect of temperature on SOC mineralization by the respiration of soil micro-organisms. However, depletion of the labile substrates at higher temperatures relative to the total SOC and greater temperature sensitivity of recalcitrant components of the SOC confound simple interpretations of the effects of warming. We have addressed these issues by testing the hypothesis that respiration by heterotrophic soil micro-organisms is not down-regulated with increasing temperature by comparing the increase in biomass-specific respiration rate with temperature to the increase in respiration rate per unit SOC. We used five soils from the maritime Antarctic ranging in latitude and SOC content and measured the soil respiratory responses to temperatures ranging from 2 to 50 °C in laboratory incubations lasting up to 31 days. In all cases, soil respiration increased with temperature up to 50 °C, even though this exceeds the temperatures normally be experienced, indicating that the community contained sufficient physiological diversity to be able to respire over large temperature ranges. Both the biomass-specific respiration rate and the overall rate of SOC mineralization increased with temperature, which we interpret as respiration by soil micro-organisms not down-regulating relative to temperature.

Fire may cause significant alterations in soil properties. Post-fire soil dynamics can vary depending, among other factors, on rainfall patterns. However, little is known regarding variations in response to post-fire drought. This is relevant in arid and semiarid areas with poor soils, like much of the western Mediterranean. Furthermore, climate change projections in such areas anticipate reduced precipitation and longer annual drought periods, together with an increase in fire severity and frequency. This research evaluates the effects of experimental drought after fire on soil dynamics of a Cistus-Erica shrubland (Central Spain). A replicated (n = 4) field experiment was conducted in which the total rainfall and its patterns were manipulated by means of a rain-out shelters and irrigation system. The treatments were: environmental control (natural rainfall), historical control (average rainfall, 2. months drought), moderate drought (25% reduction of historical control, 5. months drought) and severe drought (45% reduction, 7. months drought). After one growing season under these rainfall treatments, the plots were burned. One set of unburned plots under natural rainfall served as an additional control. Soils were collected seasonally. Fire increased soil P and N availability. Post-fire drought treatments reduced available soil P but increased N concentration (mainly nitrate). Fire reduced available K irrespective of drought treatments. Fire reduced enzyme activities and carbon mineralization rate, a reduction that was higher in post-fire drought-treated soils. Fire decreased soil microbial biomass and the proportion of fungi, while that of actinomycetes increased. Post-fire drought decreased soil total microbial biomass and fungi, with bacteria becoming more abundant. Our results support that increasing drought after fire could compromise the resilience of Mediterranean ecosystems to fire.

The variations in species composition and assemblage of unmanaged simple-intensive green roofs in Hannover, Germany, were investigated over a thirty year period, in order to assess the persistence of the initial seed mixture and to evaluate floristic changes. The roofs were greened in 1985 with soil-based turf rolls sown with a mixture of five grasses (Festuca rubra, Festuca ovina, Agrostis capillaris, Lolium perenne and Poa pratensis). Three sets of 120 phytosociological releves, sampled in 1987, 1999 and 2014, have been compared to assess: (1) nestedness vs spatial turnover, (2) functional diversity and (3) the importance of vegetation dynamics on green roof performance and design. Results demonstrated that from 1987 to 1999 the species diversity increased and the species turnover prevailed over nestedness, due to the progressive niche occupation by new species. In contrast, from 1999 to 2014 species diversity remained steady, suggesting that nestedness prevailed over species turnover. The main driver of the observed functional changes was a shift towards relatively more thermoxeric conditions. In terms of plant life strategies, the competitive species sown on the roof gradually gave way to stress-tolerant and ruderal species, along with a progressive increase in species with shortdistance seed dispersal strategies. It is concluded that: (a) to create resilient green roofs, spontaneous colonisation should be accepted and considered as a design factor; and (b) regional plant communities could serve as a model for seed recruitment and installations.