Sebastián Meier

Glomalin-related soil protein in a Mediterranean ecosystem affected by a copper smelter and its contribution to Cu and Zn sequestration.

The amount of glomalin-related soil protein (GRSP), a glycoprotein produced by arbuscular mycorrhizal fungi (AMF), its contribution to the sequestering of Cu and Zn in the soil, and the microsite variation of other soil traits (pH, water-stable aggregates--[WSA], soil organic carbon--[SOC]) was studied in a semi-arid Mediterranean ecosystem near a copper smelter and affected by deposit of metal-rich particles since 1964. Rhizospheric (R) and non-rhizospheric (NR) soil of four representative plants (Argemone subfusiformis, Baccharis linearis, Oenothera affinis and Polypogon viridis) was analyzed. The results showed a strong variability in GRSP (6.6-36.8 mg g(-1)), Cu content (62-831 mg kg(-1) for the total Cu and 5.8-326 mg kg(-1) for the available Cu) and pH (4.2-5.5) in the different plant and rhizospheric zones analyzed. A strong relationship between the GRSP with the soil Cu and Zn contents was found (r=0.89 and 0.76 for Cu and Zn respectively, p<0.001). The GRSP-bound Cu ranged from 3.76 to 89.0 mg g(-1) soil and represents 1.44-27.5% of the total Cu content in soil. Moreover, the WSA reached 89% in P. viridis R. For this plant, the C contained in GRSP represented up to 89% of SOC, and this coincided with the most extreme conditions of soil degradation within the ecosystem (the highest content of heavy metals and low pH values). This study provides evidence on the role of the GRSP in Cu and Zn sequestration and suggests a highly efficient mechanism of AMF to mitigate stress leading to stabilization of soils highly polluted by mining activities.

Phytoremediation of Metal-Polluted Soils by Arbuscular Mycorrhizal Fungi

Human activities generate wastes, some of which contain large amounts of heavy metals/metalloids that could enter natural ecosystems and alter the activities and functioning of soil micro- and macroorganisms. Microorganisms can adapt/resist to metal stress, and some of them are able to promote the plants establishment and therefore the phytoremediation process. In this context, the use of arbuscular mycorrhizal fungi (AMF), and their role in phytoremediation, has emerged as a new and interesting choice. In addition to AMFs well-known contribution to plant nutrient acquisition and growth, these fungi develop diverse mechanisms that encourage plants to grow in soils with high toxic metals concentrations. The authors are concerned about the AMF metal tolerance mechanisms and its role in the promotion of in phytoremediation processes.

Maturity indices in co-composting of chicken manure and sawdust with biochar

Several maturity indices were evaluated for in-vessel co-composting of chicken manure and pine sawdust with three different biochars. All the seven mixtures (piles) contained chicken manure and sawdust. Six of these piles contained biochar; each biochar was added at two rates, 5% and 10% wet weight. The maturity of composts was assessed by C/N, dissolved organic carbon (DOC), seed germination, NO3(-)-N/NH4(+)-N, and the Solvita test. The C/N values of finished composts were from 31.5 to 35.7, which were much higher than the optimum value of 21 for matured compost. Nevertheless, the rest of the parameters indicated that the composts were matured. The C/N values were high because of the high amount of recalcitrant carbon present in the feedstocks: biochar and sawdust. Biochar treated piles showed higher respiration as well as decomposition of DOC indicating higher microbial activity. Use of biochar in composting may reduce NH3 emission and nitrate leaching.

Influence of copper on root exudate patterns in some metallophytes and agricultural plants.

A hydroponic experiment was carried out to determine the root exudation patterns in two Cu-metallophytes (Oenothera picensis and Imperata condensata) and two agricultural plants (Lupinus albus and Helianthus annuus). Plants were grown in nutrient solution at increasing Cu doses (0, 0.125, 0.25, 0.5, 1 and 2mgCuL(-1)), and plant growth, root elongation, Cu accumulation and root exudates were measured. All plants showed a decrease of over 60% in root elongation at the highest Cu supply level, being O. picensis the most sensitive specie and showing the highest shoot and root Cu concentrations (116 and 2657μgCug(-1), respectively), which were six fold higher than the other species. Differences in root exudation patterns of low molecular weight organic acids were found, with extremely high amounts of succinic acid exuded by O. picensis (1049μmolg(-1)h(-1)), and citric acid by I. condensata (164μmolg(-1)h(-1)). In metallophytes, the organic acid exudation was increased even with no root elongation, meanwhile agricultural plants exuded citric acid at constant levels. Exudation of phenolic compounds was highly species-dependent, with catechin mainly exuded by I. condensata, (2.62μmolg(-1)h(-1)) cinnamic acid by O. picensis (5.08μmolg(-1)h(-1)) and coumaric acid exclusively exuded by H. annuus (13.6μmolg(-1)h(-1)) at high Cu levels. These results indicated that differences in root exudation patterns among metallophytes and agricultural plants could affect their Cu tolerance. Particularly, the higher exudation rate showed by I. condensata can be an effective exclusion mechanism to tolerate high Cu concentrations, supporting its use in Cu phytostabilization programs.

Use of biochar on two volcanic soils: effects on soil properties and barley yield

The use of biochar in agricultural soils appears to be promising because it is known to improve soil properties and increase crop production. However, few studies have been conducted with biochar on volcanic soils. Two field experiments were conducted simultaneously to evaluate the effect of oat hull biochar (OBC) on various physical-chemical properties of two volcanic soils, an ‘Inceptisol’ and an ‘Ultisol’, and to evaluate the resulting effects on the yields of barley (Hordeum vulgare) grown on these soils. The OBC doses applied to field microplots were equivalent to 0, 5, 10 and 20 Mg ha -1 . The results showed that pH, total exchangeable bases, and electrical conductivity increased at the highest dose of OBC in both soils. Glomalin-related soil protein (GRSP) was significantly high in the Ultisol at a rate of 20 Mg OBC ha -1 . Water-stable aggregates (WSA) and mean weight diameter (MWD) were enhanced at the highest doses of OBC in both soils. However, water-holding capacity (WHC) only increased in the Ultisol when amended with OBC at rates of 10 and 20 Mg ha -1 . Barley yield (grain weight m -2 ) significantly increased at the highest OBC dose by 31.3% and 21.9% for crops grown on the Inceptisol and Ultisol, respectively. Significant relationships were observed between WHC and glomalin fractions (r = 0.81, p < 0.01 for easily extractable-GRSP and r = 0.62, p < 0.01 for Total-GRSP) as well as between organic C and WSA and both glomalin fractions. According to this study, biochar may be used effectively to improve the quality of these two volcanic soils and promote sustainable grain production.

Arbuscular Mycorrhizal Fungi Improve Tolerance of Agricultural Plants to Cope Abiotic Stress Conditions

Abiotic stresses have strong impact on agriculture, decreasing the stability of agroecosystems worldwide, due mainly to water and nutrient limitations and the presence of toxic elements. Several studies have demonstrated that soil microorganisms can improve plant growth, even more when plants are under stressful conditions, being probably the most important are the arbuscular mycorrhizal fungi (AMF). This kind of fungi forms symbiosis with approximately 80% of plant species, including the majority of agricultural plants, and is present in all terrestrial ecosystems. Via its extraradical mycelium, the AMF can improve the absorption of water and nutrients of their host plants under stress conditions, as well as contribute to cope with the presence of toxic elements such as phytotoxic aluminum and other toxic metal(loid)s, increasing plant growth and crop production. Moreover, several studies have determined that AMF strains isolated from agroecosystems affected by different abiotic limiting conditions enhance the growth of plants than those isolated from soils without such limiting condition. In this chapter we describe the main ways by which AMF contribute to the plant tolerance to cope the abovementioned abiotic stresses. Moreover, the physiological, biochemical, and molecular bases that explain the responses mediated by AMF in host plants are covered. Finally, biotechnological prospects of AMF present under stress conditions and their potential use as bio-inoculants are presented.

Contribution of inoculation with arbuscular mycorrhizal fungi to the bioremediation of a copper contaminated soil using Oenothera picensis

The Bradford-reactive soil protein (BRSP) fraction includes glomalin, a glycoprotein produced by arbuscular mycorrhizal (AM) fungi that is able to bind some metals, such as copper (Cu), which could promote the bioremediation of Cu-polluted soils. This study aimed to analyze the Cu-binding capacity of BRSP in Oenothera picensis that was inoculated or not inoculated with AM fungi. O. picensis plants were established in a Cu contaminated sterilized soil and treated with the following: i) uninoculated (-M); ii) inoculated with native AM fungal propagules (+M); or iii) inoculated with a Claroideoglomus claroideum (CC) strain isolated from non-contaminated soil. In each case, five Cu levels were applied to the soil (basal level 497.3 mg Cu kg-1): 0 (T1); 75 (T2); 150 (T3); 225 (T4); and 300 mg Cu kg-1 (T5). A high BRSP accumulation in AM inoculated treatments, especially with CC, was observed. A higher Cu-bound-to-BRSP content was found with increasing Cu concentrations, representing up to 20-22% of the total Cu in the soil. Moreover, a higher root Cu concentration in +M was observed. These results suggest a high Cu binding capacity by BRSP, which is a relevant aspect to consider in the design of bioremediation programs together with the selection of endemic metallophytes and AM fungal strains, which are able to produce glomalin at high quantities.

Arbuscular mycorrhizal status of pioneer plants from the mouth of lake Budi, Araucanía Region, Chile

Abstract Arbuscular mycorrhizal fungi (AMF) have an important role on the ecosystem stability promoting water and nutrient acquisition by plants and allowing their growth under stress conditions including drought and salinity. This study aimed at describing the colonization of native AMF associated to pioneer plant species growing at the mouth of lake Budi, which receive seasonally marine water. For this, root samples and rhizosphere substrate of Polygonum maritimum, Carpobrotus chilensis, Ambrosia chamissonis, Ammophyla arenaria were collected and analyzed. Mycorrhizal root colonization, spore and hyphal density, and some soil chemical properties (pH, conductivity, organic matter -OM-, and microbial activity) were determined. Results showed that A. Arenaria presented the highest root colonization (53%), mycelium (10 m g-1) and AMF spores (300 spores in 100g of substrate) densities, which were highly correlated with an elevated OM content (1.64%; r=0.53, r=0.48 y r=0.87, respectively) and soil microbial activity (3.57 µg fluoresce in g-1 h-1; r=0.89 r=0.76 and r=0.53, respectively). On the other hand, a low AMF species richness was found in the rhizospheric soils of all four evaluated plants, finding a total of five AMF species. Nevertheless, one of these corresponds to a new specie (Corymbiglomus pacificum), which was associated to A. arenaria. Our results suggest an important role of AMF associated to pioneer plants in saline ecosystems, especially enhancing the establishment of A. arenaria and Amb. chamissonis, which could promote a further nurse effect that allow the establishment of other plant species. AM fungi could be considered as a biotechnological tool since they could be used for stabilization of coastal ecosystems, and in soils under saline or hydric limitations.

Copper immobilization by biochar and microbial community abundance in metal-contaminated soils

Biochar (BC) is gaining attention as a soil amendment that can remediate metal polluted soils. The simultaneous effects of BC on copper (Cu) mobility, microbial activities in soil using metallophytes have scarcely been addressed. The objective of this study was to evaluate the effects of biochar BCs on Cu immobilization and over soil microbial communities in a Cu-contaminated soil evaluated over a two-year trial. A Cu-contaminated soil (338mgkg-1) was incubated with chicken manure biochar (CMB) or oat hull biochar (OHB) at rates of 1 and 5% w/w. Metallophyte Oenothera picensis was grown over one season (six months). The above process was repeated for 3 more consecutive seasons using the same soils. The BCs increased the soil pH and decreased the Cu exchangeable fraction Cu by 5 and 10 times (for OHB and CMB, respectively) by increasing the Cu bound in organic matter and residual fractions, and its effects were consistent across all seasons evaluated. BCs provided favorable habitat for microorganisms that was evident in increased microbial activity. The DHA activity was increased in all BC treatments, reaching a maximum of 7 and 6 times higher than control soils in CMB and OHB. Similar results were observed in microbial respiration, which increased 53% in OHB and 61% in CMB with respect to control. The BCs produced changes in microbial communities in all seasons evaluated. The fungal and bacterial richness were increased by CMB and OHB treatments; however, no clear effects were observed in the microbial diversity estimators. The physiochemical and microbiological effects produced by BC result in an increase of plant biomass production, which was on average 3 times higher than control treatments. However, despite being a metallophyte, O. picensis did not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments.