Paula Aguilera

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.

Effect of dairy manure rate and the stabilization time of amended soils on atrazine degradation

The application rate of liquid cow manure (LCM) in the field and the stabilization time of amended soils before application of pre-plant herbicides are factors that determine their efficiency. This study includes evaluation of residual atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) in soil and amended soils with equivalent rate of 100,000; 200,000; and 300,000 L ha(-1) of LCM and the effect of pre-incubation time of amended soils on atrazine degradation. The study was carried out under controlled conditions using an Andisol with previous historical application of atrazine. The respiratory activity and fluorescein diacetate (FDA) studies indicated that the time necessary for stabilization of amended soils is over 20-30 d. During the measurement of respiratory and FDA activity, no significant differences were observed when atrazine was applied. The half-life of atrazine ranged from 5 to 8d and the relative distribution of degradation products seem to be affected by the application of LCM. The pre-incubation time of amended soil and LCM dose would not affect atrazine degradation rate, when the soil has a history of herbicide application. However, repeated applications of LCM in a long period of time could change the soil pH and increase the content of dissolved organic carbon (DOC) which could further contribute to a faster degradation of atrazine. Both effects would reduce the effectiveness of atrazine in weed control.

Diversity of Arbuscular Mycorrhizal Fungi in Acidic Soils and Their Contribution to Aluminum Phytotoxicity Alleviation

Acidic conditions limit crop production on 40 % of the world’s soils. These soils are characterized by a pH between 4.5 and 5.5, low phosphorus (P) availability, high contents of aluminum (Al) and manganese (Mn), and low soil basic cations. Edaphic conditions of acidic soils limit plant growth, mainly due to Al3+ phytotoxicity, which reduces water and nutrient acquisition from soils and severely limits root growth of sensitive species. However, the association of symbiotic arbuscular mycorrhizal (AM) fungi with plant roots often modifies plant response to acid soil factors through enhanced P acquisition and reduced Al exposure. Several management practices are implemented to mitigate the negative effects of acidic soils on plant growth, among which are lime application, P fertilization, and the use of Al-tolerant plants. In this regard, the inoculation with AM fungi appears as another management alternative, because of the well-documented AM contribution to plants growing in acidic soils. Several reports have demonstrated that AM fungal structures and glomalin-related soil protein (GRSP) protect plants against stress produced by high levels of Al. However, there is broad functional diversity among AM fungal genera or species in their capacity to confer Al-resistance to host plants in acidic soils. Therefore, the aim of this review is to summarize AM fungal diversity present in acidic soils as well as relate their presence with the potential to alleviate Al phytotoxicity.

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.

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.

Think globally, research locally: emerging opportunities for mycorrhizal research in South America

More than20 years agoDavidReadhighlighted the ideal relationship between dominant vegetation and plant mycorrhizal types; he divided the world into major biomes and hypothesized that mycorrhizal symbioses modulate biome dynamics through soilnutrient processes (Read, 1991). This idea has been accepted and further developed theoretically in the northern hemisphere (Read & Perez-Moreno, 2003), but conversely, no clear further development has beenmade in the southern hemisphere, and in particular in South America, despite its contrasting patterns of mycorrhizal association with forests dominated by arbuscular mycorrhizal (AM) gymnosperms and angiosperms, or ectomycorrhizal (ECM) Nothofagus spp. (Fontenla et al., 1998; Palfner, 2001). These South American mycorrhizal patterns, linked to its unique geology, climate and biogeographic history (McGlone et al., 2016; Goymer, 2017), have already provided interesting insights into mycorrhizal research, such as the discovery of new mycorrhizal associations (Bidartondo et al., 2002), or regional differences in the distribution ofmycorrhizal fungi (Tedersoo et al., 2014; Davison et al., 2015). In the last decade, the development of molecular and macroecological approaches has boosted mycorrhizal research globally (Chagnon et al., 2016), which is allowing comparisons to be made among northern and southern hemisphere patterns. However, global initiatives have been initiated in the northern hemisphere, and might lack the integration of local southern perspectives into the global context. As a consequence, the sampling effort among northern and southern regions is far from balanced (Fig. 1), further highlighting the need for more mycorrhizal research in understudied regions, such as South America (Goymer, 2017). The first international mycorrhizal meeting in South America, ‘Mycorrhizal symbiosis in the southern cone of South America’, took place in Valdivia, Chile, 6–9March 2017, and has been a key step towards this goal (Fig. 2). The meeting gathered 70 South American and Europeanmycorrhizal researchers from eight countries (Argentina, Brazil, Chile, Estonia, Germany, Spain, United Kingdom and Uruguay) and 26 institutions, including universities, research centers, companies, foundations and public entities (https:// mycorrhyzal.wordpress.com/). The topics addressed in the meeting fit broadly under two themes: ecology of mycorrhizas and mycorrhizal applications, representing timely research directions both in the region and globally.

Factors affecting arbuscular mycorrhizal fungi of Chilean temperate rainforests

While arbuscular mycorrhizal (AM) fungi in Chile have been widely documented in agro-ecosystems, there is a knowledge gap regarding AM fungal diversity in Chilean temperate rainforests. AM fungal communities of these forests are affected by several factors: the mountain systems of Chile (Coastal Range or Andes Mountains), the mycorrhizal dominance of the forest (either ectomycorrhizal -EMor AM), soil chemistry, and altitude. We tested the effects of mountain system, mycorrhizal dominance, soil chemistry, and altitude on AM fungal diversity. From 7,120 AM fungal spores recovered, we identified 14 species, that were found in 41 soil samples collected from 14 plots located in EM and AM forests of the Coastal Range and Andes Mountains of Southern Chile. Mountain system and mycorrhizal dominance affected AM fungal community composition, although neither fungal richness nor abundance were affected. Soil Olsen available P, Ca, Mg, and Na were the edaphic variables structuring AM fungal community composition. There was no relationship between altitude and AM fungal richness, however at high altitudes there was higher abundance. Finally, with this and other studies, a total of 59 AM fungal species, many of which were previously registered exclusively in agroecosystems, are registered on the Chilean AM fungal species list.

Arbuscular mycorrhizal assemblages along contrasting Andean forests of Southern Chile

Southern Chilean pristine temperate rainforests have been floristically stable during the Holocene, thus representing a pre-industrial baseline of forest ecology. Given this and its edaphic limitations, it is imperative to better understand these forests ecological patterns of mycorrhizal symbiosis. Therefore, here we compare the arbuscular mycorrhizal (AM) communities in three treeline Nothofagus pumilio contrasting plots of Chilean Andes (a volcano crater, pristine forest, and disturbed forest). The AM community assemblages were determined by morphological identification and spore counting, in three A horizon soil samples by plot. In the same nine soil samples, standard chemical analysis was performed. Eighteen AM species were described; Acaulospora was the most abundant genus. The forest plot had the highest AM species richness compared to the disturbed and crater plots. Interestingly, soils Olsen P (plant available phosphorus), pH, and Al+++ saturation similarly affected the AM assemblages. We suggest that some AM species could be specially adapted to extremely high Al saturation and extremely low plant available P conditions, as those experienced on Andean Nothofagus forests. These species may help initiate biological succession on highly disturbed ecosystems. We suggest that mycorrhizal fungi play a key role in seedling colonization of extreme environments such as the Andean treeline.

EFFECT OF LIQUID COW MANURE ON CHEMICAL AND BIOLOGICAL PROPERTIES IN AN ANDISOL

The aim of this work was to establish the effect of the dose of liquid cow manure (LCM) on some chemical properties and biological activity in an Andisol. This study was carried out under laboratory conditions using an Andisol and LCM from a dairy farm located in the South of Chile. The dose of LCM were the equivalent to 0 (S0), 100 (S100), 200, (S200) and 300 (S300) thousand L ha -1 . This amount is equivalent to regular agronomic LCM applications. The chemical characterization indicated that the LCM addition modified all the tested Andisol chemical properties. These begin to return to the initial conditions from 10 days on, with the exception of EC, K and DOC. The C- CO2 evolution indicated that LCM incorporation at increasing dose enhanced the respiratory activity. Enzyme activity was greater in the amended soils than in S0. The results of this study indicated that the period of time necessary for the LCM amended soils returning to a similar behavior to S0 is more than 10 days, with a strong correlation between the chemical properties of the amended soils and their biological activity, mainly C-CO2 evolution.