Phytoremediation affects microbial development on a limestone quarry.

Phytoremediation was used to regenerate a limestone quarry area. Plant growth mixed medium added over the quarry surface, consisting of a mixture of pyrolusite byproducts, natural soil, sand, and rice husk. Three different plant species: pine, cypress, and broom were planted at 9 randomized plots in order to assess the effects of vegetation on the microbial development, which was measured for the following 3 years. Substrate samples were analyzed for organic carbon content (Corg), microbial biomass (Cmic), basal CO2 respiration activity (BR), alkaline phosphatase (ALP), and acid phosphatase activities at each plant specie and year. Furthermore, the ratio Cmic/Corg, the metabolic quotient (qCO2), and the C mineralization quotient (qM) were determined. The highest survival rates occurred for broom (93.52%), followed by cypress and pine (82.41%) at the final year, while the content of Cmic, BR, and ALP was increased significantly under plants (pine, cypress, and broom) compared with control. Cmic content and BR was plant dependent. Cypress sites had the highest values of Cmic (214.9 µgCg-1) and BR (112.8 µgCO2-Cg-1d-1) at the 3rd year. The plant root environment clearly enhances and regulates the microbial community, in correspondence to the species used. Below ground enhanced activity could fulfill the scope of phytoremediation strategies.

Both the arbuscular mycorrhizal fungus Gigaspora rosea and Frankia increase root system branching and reduce root hair frequency in Alnus glutinosa.

Alnus glutinosa is an important pioneer species that forms effective symbioses with Frankia and ecto and arbuscular mycorrhizal fungi (AMF). There is evidence that Frankia and AMF interact and the focus of this study was to investigate how interactions affected root system and root hair development. A. glutinosa seedlings were grown in pots in soil pre-inoculated with the AMF Gigaspora rosea. Seedlings were inoculated with Frankia either immediately on transfer to AMF-inoculated pots (day 0) on day 15 or on day 30 following AMF inoculation so the effect of timing of inoculation on interactions could be determined. Seedlings were harvested in batches at intervals of 10, 15, 20, 25 and 30 days after the commencement of each treatment. Both G. rosea and Frankia increased root branching and effects were greater when both were present. By contrast, both G. rosea and Frankia decreased root hair numbers markedly. Effects on root hair development were not a consequence of phosphorous, as P levels were not changed significantly in seedlings colonised by G. rosea or nodulated by Frankia. Effects are not due to differences in root system size but conceivably could offset some of the carbon costs incurred by the symbioses.

Short-term effects of thinning on soil CO2, N2O and CH4 fluxes in Mediterranean forest ecosystems.

In Mediterranean ecosystems an increasing demand for in situ trace gas exchange data is emerging to enhance the adaptation and mitigation strategies under forest degradation. Field-chamber green-house gas fluxes and site characteristics were analysed in two Mediterranean peri-urban pine forests showing degradation symptoms. We examined the effect of different thinning interventions on soil CO2, CH4 and N2O fluxes, addressing the relationships with the environmental variables and C and N contents along forest floor-soil layers. Soil temperature resulted as the main driving variable for CO2 efflux and CH4 uptake. Soil moisture content and organic matter availability affected CO2 emission patterns in the two sites. N2O fluxes showed a positive correlation with soil moisture under wetter climatic conditions only. GHG fluxes showed significant correlations with C and N content of both forest floor and mineral soil, especially in the deepest layers, suggesting that it should be considered, together with environmental variables when accounting GHG fluxes in degraded forests. Short-term effects of thinning on CO2 emissions were dependent on disturbance induced by logging operations and organic matter inputs. After thinning CH4 uptake increased significantly under selective treatment, independently from specific site-induced effects. N2O fluxes were characterized by low emissions in both sites and were not affected by treatments. Soil CO2 efflux was the largest component of global warming potential (GWP) from both sites (11,553 kg ha-1 y-1 on average). Although it has a large global warming potential, N2O contribution to GWP was about 131 kg CO2eq ha-1 y-1. The contribution of CH4-CO2 equivalent to total GWP showed a clear and significant CH4 sink behaviour under selective treatment (36 kg ha-1 y-1 on average). However, in the short-term both thinning approaches produced a weak effect on total GWP.