The chelating effect of citric acid, oxalic acid, amino acids and Pseudomonas fluorescens bacteria on phytoremediation of Cu, Zn, and Cr from soil using Suaeda vera.

Phytoextraction is a green technique for the removal of soil contaminants by plants uptake with the subsequent elimination of the generated biomass. The halophytic plant Suaeda vera Forssk. ex J.F.Gmel. is an native Mediterranean species able to tolerate and accumulate salts and heavy metals in their tissues. The objective of this study was to explore the potential use of S. vera for soil metal phytoextraction and to assess the impact of different chelating agents such as natural organic acids (oxalic acid [OA], citric acid [CA]), amino acids (AA) and Pseudomonas fluorescens bacteria (PFB) on the metal uptake and translocation. After 12 months, the highest accumulation of Cu was observed in the root/stem of PFB plots (17.62/8.19 mg/kg), in the root/stem of CA plots for Zn (31.16/23.52 mg/kg) and in the root of OA plots for Cr (10.53 mg/kg). The highest accumulation of metals occurred in the roots (27.33-50.76 mg/kg). Zn was the metal that accumulated at the highest rates in most cases. The phytoextraction percentages were higher for Cu and Zn (∼2%) with respect to Cr (∼1%). The percentages of metal removal from soil indicate the need to monitor soil properties, to recognize the influence of each treatment and to increase the concentration of bioavailable metals by the use of agricultural management practices aimed at promoting plant growth.

Greenhouse gas emissions and soil organic matter dynamics in woody crop orchards with different irrigation regimes.

Water scarcity in arid, semiarid and dry regions is a limiting factor for the development of sustainable agriculture. As a consequence, the adoption of new strategies such as regulated deficit irrigation (RDI) to reduce water and energy consumption will be essential. Decreases in irrigation water content may also have positive effects on soil C cycle. Thus, an experiment was setup in three woody crop orchards during two years, with the objective of assessing if RDI can reduce soil CO2 and N2O emissions, modify soil inorganic C and organic C quality and stability and affect soil aggregation. Soil CO2 and N2O emissions were measured every two weeks while soil samplings were carried out every three months. Results indicated that decreases in soil moisture by RDI implementation were related to significant decreases in CO2 emissions in all crops. RDI contributed to an average decrease, compared with full irrigation, of 1088-1664 g CO2 m-2 in the experimental period. Furthermore, CO2 emission was negatively correlated with inorganic C, suggesting the protective effect of soil carbonates towards organic matter. RDI also contributed to significantly decrease soil N2O emissions. However, N2O emission patterns did not directly follow soil moisture patterns and were constant in the experimental period. RDI contributed to an average decrease, compared with full irrigation, of 90-409 mg N2O m-2. No physicochemical property was significantly affected by irrigation regime. Although microbial biomass was not significantly affected by RDI, ß-glucosidase activity was significantly higher under full irrigation during the warm seasons, with significant positive correlation with CO2 emissions. This seems to suggest that a significant fraction of CO2 emitted from soil derives from organic matter degradation, which is limited with low water content. So, RDI could contribute to promote soil C sequestration by reduced greenhouse gas emissions, with no negative effects on soil structure at short-term.

Bioaugmentaton in Technosols created in abandoned pyritic tailings can contribute to enhance soil C sequestration and plant colonization.

Creation of Technosols in combination with phytostabilization may be a sustainable strategy to minimize the environmental and human health hazards derived from mine tailings. Bioaugmentation can facilitate plant establishment and growth for efficient phytostabilization. In order to assess if bioaugmentation can increase soil quality and fertility, decrease metal(loid) mobility and accelerate plant colonization, a one-year field experiment was designed with creation of Technosols in two tailings ponds with different pH (acidic (AT) and neutral (NT)), with addition of marble waste (MaW) and two organic materials (pig manure (PM) and sewage sludge (SS), without or with inoculation of effective microorganisms (EM) at three rates. Results showed that MaW was the main factor responsible for maintaining pH ~7 in AT and ~8 in NT, decreasing salinity, and decreasing the soluble fraction of metals (70-99%). The soluble fraction of As decreased ~45% in AT, related to increases in pH up to neutrality, while increased ~90% in NT with PM due to pH>8 and higher content of organic compounds. The addition of PM and SS significantly increased soil organic C (SOC), nutrient contents and microbial biomass and activity in both tailings, being PM more effective. However, a positive priming effect was observed in NT with SS addition likely due to higher C/N ratio and lack of nutrients. There was a significant effect of EM rate on inorganic C, SOC, N, K and microbial biomass and activity, with higher values as rate increased. Vegetation richness and density directly increased with increasing EM rate. Multivariate analyses showed that the most important properties contributing to increase richness and plant density were microbial biomass and N. Thus, bioaugmentation contributed to soil C sequestration (as organic and inorganic C) and soil fertility, related to high soil microbial biomass and activity, which facilitated an effective colonization of vegetation.