Gustavo Curaqueo

TILLAGE EFFECT ON SOIL ORGANIC MATTER, MYCORRHIZAL HYPHAE AND AGGREGATES IN A MEDITERRANEAN AGROECOSYSTEM

Arbuscular mycorrhizal fungi (AMF) and their product glomalin (GRSP) play a decisive role in the soil aggregation, affecting the carbon (C) dynamics in agroecosystems. Tillage affects the AMF activity and GRSP content, influencing the stability and the soil C forms as well. The aim of this study was to compare the effect of no tillage (NT) and conventional tillage (CT) on: i) arbuscular mycorrhizal hyphal length and GRSP content; ii) the nature of soil organic matter by means of physical fractionation (free particulate organic matter (fPOM); occluded particulate organic matter (oPOM) and mineral-associated soil organic matter (Mineral)), as well as chemical fractionation (fulvic acid, humic acid and humin), and iii) the relationships between AMF parameters, soil carbon and water stable aggregates (WSA) in a Mollisol of Central Chile managed for 6 years under NT and CT using a wheat-corn rotation. Higher values in the AMF hyphal length, GRSP and WSA in NT compared with CT were observed. Significant relationships were found between GRSP and WSA (r = 0.66, p < 0.01) and total mycelium and GRSP (r = 0.58, p< 0.05). The total carbon increased 44% under NT compared with CT. The chemical fractionation showed percentage greater than 95% for humim in both treatments. Physical fractionation indicates that the higher part of the SOC (89.4 - 95.1%) was associated with the mineral fraction.

Effect of Compost Application on Some Properties of a Volcanic Soil from Central South Chile

Soil compost application is a common soil management practice used by small farmers of Central-South Chile that produces positive effects on soil properties and also promotes presence and activity of arbuscular mycorrhizal fungi (AMF). This fungi form symbiosis with plant roots improving plant nutrition, as well as producing glomalin, a glycoprotein that has been associated with soil aggregation stability. Therefore, the aim of this study was to evaluate, in an Ultisol from Central-South Chile, the effect of different doses of compost on some soil characteristics at the end of the third year of a crop sequence including wheat (Triticum aestivum L.), bean (Phaseolus vulgaris L.), and grassland (Lolium multiflorum Lam. associated with Trifolium repens L.). Studied soil characteristics included chemical (pH, available-P, organic C), biological (C and N biomass, AMF spore number, root colonization percentage, mycelium length, and glomalin content), as well as physical parameters (water holding capacity [WHC], and water stable aggregates [WSA]). Results showed that, in general, compost application increased soil

ARBUSCULAR MYCORRHIZAE IN AGRICULTURAL AND FOREST ECOSYSTEMS IN CHILE

Arbuscular mycorrhizal (AM) association plays a key role in the sustainability of terrestrial plant ecosystems, in particular those presenting limitations for the establishment and subsequent growth of plants. In Chile, more than 50% of arable soils are originated from volcanic ashes, showing in general several constraints to crop production, such as low pH, high exchangeable aluminum content and low levels of available P. Under these conditions, the management of AM fungal propagules using adequate cultural management practices emerges as a successful alternative in order to maximize the positive effects of AM symbiosis on plant growth in these types of soil. This review presents the results of several years of research about the effect of different agronomic and forest management practices on the density and functionality of the native fungal populations in volcanic soils from Southern Chile, and their subsequent effect on the improvement of soil characteristics. These investigations have contributed to a better understanding of the role played by AM symbiosis in such soils and provide guidance on the most appropriate alternatives to increase its presence and functionality.

Influence of Aluminum on the Growth and Organic Acid Exudation in Alfalfa Cultivars Grown in Nutrient Solution

ABSTRACT A study was conducted to evaluate the effects of aluminum (Al) in nutrient solutions on the dry weight (DW) yield, Al and phosphorus (P) contents, and organic acid exudation in alfalfa (Medicago sativa L.). Four alfalfa cultivars (‘Robust’, ‘Sceptre’, ‘Aquarius’, and ‘California-55’) were grown in nutrient solution at pH 4.5 and 6.0, with (50 and 100 μM) and without Al. The results revealed that Al caused a significant reduction in DW, especially in pH 4.5 treatment. Organic acid exudation was affected by pH and Al treatments. Citrate and succinate exudation increased with the high Al treatment at pH 4.5. However, no relationship between pH and carboxylate exudation was observed at pH 6.0. Accumulation of P and Al in roots suggests the existence of an exclusion mechanism for Al in alfalfa. Selection of cultivars with enhanced organic exudation capacity in response to Al might be useful for alfalfa production in moderately acidic soils.

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 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.