Publications

Forest Wildfires in Chile: Effects on Soil Degradation and Damage Mitigation

The 2022-2023 Chilean summer showed increased temperatures and similar burned area, compared to the 2016-2017 season, where more than 500,000 hectares were compromised, mainly in the rural areas. After a brief review, it is revealed that the effects of forest fires on soil and hydrological properties are barely debated in Chile. Here, we showed a climatological analysis where temperature records in the 2016-2017 season were unusual, as well as another unexpected increase in the summer of 2022-2023, resulting in high-severity fires known as ‘mega-fires’ or “storm-fires”. Mega-fires affect forest plantations and native forests mainly from 33º S (Maule Region) to 39º S (Los Ríos Region) and they are expected to become frequent due to climate change, moving from the north to the south. We present an overview of the influence of wildfires on soil components in the most affected areas (inland, Coastal, and Andes ranges), their hydrological impacts, and potential erosion risk due to high winter precipitation. We propose several management practices that could help to prevent or mitigate these events, including pre-and post-fire interventions, such as afforestation and seeding, selective logging, mulching, erosion barriers, soil preparation, and dam monitoring. We argue that any effective plan in fire-prone and affected areas should include a combination of actions taken at the hillslope scale at integral ecosystem management, whose effectiveness should be monitored and verified regionally at the watershed scale.

A Long Time Since Fire: Land-use legacy controls microbial functional recovery in volcanic Andisols under Nothofagus forests and Pinus radiata plantations

Contribution of the Fenton reaction and ligninolytic enzymes to soil organic matter mineralisation under anoxic conditions

Mechanisms of carbon dioxide (CO2) release from soil in the absence of oxygen were studied considering the Fenton process, which encompasses the reaction of H2O2 with Fe(II) yielding a hydroxyl radical (OH), in combination with manganese peroxidase (MnP) and lignin peroxidase (LiP). This study aimed to explain the high rate of soil organic matter (SOM) mineralisation and CO2 release from humid temperate rainforest soils under oxygen-limited conditions. The investigated mechanisms challenge the traditional view that SOM mineralisation in rainforest is slow due to anaerobic (micro)environments under high precipitation and explain intensive CO2 release even under oxygen limitation. We hypothesised that the Fenton reaction (FR) greatly contributes to the CO2 released from SOM mineralised under anaerobic conditions especially in the presence of ligninolytic enzymes. We used a novel technique that combines labelled H2 18O2 and Fe(II) to induce the FR and measured CO18O, Fe(II) solubilisation, and peroxide consumption in a closed gas circulation system for 6 h. Maximal CO2 amount was released when the FR was induced in combination with LiP addition. The CO2 efflux with LiP was 10-fold that of abiotic FR reactions without enzymes, or in soils amended with MnP. This was consistent with i) the contribution of 18O from peroxide to CO2 release, ii) peroxide consumption, and iii) Fe(II) solubilisation by FR. The amount of consumed peroxide was closely correlated with the CO18O derived from soil without enzyme addition or with LiP addition. Concluding, abiotic Fenton Reaction coupled with oxidative enzymes, such as LiP, are crucial for SOM oxidation under anaerobic conditions, e.g. in temperate rainforest soils.

Nitrogen Gain and Loss Along an Ecosystem Sequence: From Semi-desert to Rainforest

Plants and microorganisms, besides the climate, drive nitrogen (N) cycling in ecosystems. Our objective was to investigate N losses and N acquisition strategies along a unique ecosystem-sequence (ecosequence) ranging from arid shrubland through Mediterranean woodland to temperate rainforest. These ecosystems differ in mean annual precipitation, mean annual temperate, and vegetation cover, but developed on similar granitoid soil parent material, were addressed using a combination of molecular biology and soil biogeochemical tools. Soil N and carbon (C) contents, δ 15 N signatures, activities of N acquiring extracellular enzymes as well as the abundance of soil bacteria and fungi, and diazotrophs in bulk topsoil and rhizosphere were determined. Relative fungal abundance in the rhizosphere was higher under woodland and forest than under shrubland. This indicates toward plants' higher C investment into fungi in the Mediterranean and temperate rainforest sites than in the arid site. Fungi are likely to decompose lignified forest litter for efficient recycling of litter-derived N and further nutrients. Rhizosphere—a hotspot for the N fixation—was enriched in diazotrophs (factor 8 to 16 in comparison to bulk topsoil) emphasizing the general importance of root/microbe association in N cycle. These results show that the temperate rainforest is an N acquiring ecosystem, whereas N in the arid shrubland is strongly recycled. Simultaneously, the strongest 15 N enrichment with decreasing N content with depth was detected in the Mediterranean woodland, indicating that N mineralization and loss is highest (and likely the fastest) in the woodland across the continental transect. Higher relative aminopeptidase activities in the woodland than in the forest enabled a fast N mineralization. Relative aminopeptidase activities were highest in the arid shrubland. The highest absolute chitinase activities were observed in the forest. This likely demonstrates that (a) plants and microorganisms in the arid shrubland invest largely into mobilization and reutilization of organically bound N by exoenzymes, and (b) that the ecosystem N nutrition shifts from a peptide-based N in the arid shrubland to a peptide- and chitin-based N nutrition in the temperate rainforest, where the high N demand is complemented by intensive N fixation in the rhizosphere.

Soil Redox Controls CO2, CH4 and N2O Efflux from White-Rot Fungi in Temperate Forest Ecosystems

Microaerophilic white-rot fungi (WRF) are impacted by oxygen depletion because of fluctuating redox occurrence in southern temperate forest soils of Chile (1500–5000 mm year−1). How these conditions influence WRF survival has been scarcely examined. We explored the contributions of WRF to greenhouse gas (GHG) emissions of N2O and CH4 and soil organic C oxidation (CO2) in five sterilized and inoculated forest soils derived from various parent materials and climates. The soil was incubated for 20 days following (i) oxic, (ii) anoxic, and (iii) fluctuating redox conditions. Fungi contributed to 45% of the total GHG under redox fluctuating conditions, including the contribution of bacteria, while the opposite (26%) was valid for oxic treatment. On average, the highest gas emission (62%) was N2O for WRF under redox treatment, followed by anoxic (22%) and oxic (16%) treatments, while CO2 and CH4 emissions followed oxic > redox > anoxic. These data suggest that indigenous microbial WRF communities are well adapted to fluctuating redox milieu with a significant release of GHG emissions in humid temperate forests of the southern cone.

Wildfire Effects on Organic Matter Stability in Forest Tundra Soils

Highlights• Soil organic matter (SOM) includes pools of various thermal stability• Thermal stability of soil organic matter reflects to its microbial decomposition• Fire rises thermal stability of SOM reducing labile and increasing persistent pools• Increase in SOM thermal stability after fire reduced its microbial decomposition

Effects of snow cover on CO 2 production and microbial composition in a thin topsoil layer

<p>Temperate rain forest soils (>8000 mm yr -1 ) of south of Chile in the East Andes range are<br>intensively affected by increasing freezing and thawing cycles (FTC) due to increasing<br>climate variability in the last 20 years. Most of these volcanic forests soils are unpolluted<br>(pristine) and receive seasonal snow-cover. In spite of pollutant free precipitations, the<br>snow cover in these ecosystems contains aerosols, nutrients and microorganisms from<br>circumpolar south west winds. These inputs and FTC generate specific conditions at the<br>shallow layer at the soil surface for soil microbiology and biochemistry. The objectives of<br>the study were to compare (micro)biological and chemical properties of topsoil and snow<br>cover in an pristine forest and after clear-cut. The organic matter mineralization was<br>monitored in a microcosm experiment to explore the effects of FTC and snow melting on<br>redox potential and other topsoil parameters. FTC for soil+snow released more CO 2 in<br>closed forest (81.9 mg CO 2 kg -1 ) than that after clear-cut (20.5 mg CO 2 kg -1 ). Soil texture<br>and soil organic matter accumulation played a crucial role for organic matter mineralization<br>and CO 2 fluxes. Gradually increase of temperature after freezing reveled that loamy soils<br>with certain amount of available C maintain active microbial population that response very<br>fast to temperature change. Sandy soils with very low C content showed the opposite<br>results – very slow response of microbial community and CO 2 fluxes. In conclusion,<br>microbial community structure and functions have distinct transition from snow to the soil<br>in temperate snow-covered forest ecosystem. FTC showed that different microbial groups</p><p>are responsible for organic matter mineralization in soil under forest and clear-cut, because<br>the pH and redox potential are influenced by snow melting.</p>

Boy et al.: Gradient Studies Reveal the True Drivers of Extreme Life in the Atacama Desert.

The file contains supplementary data on correlation matrices, spatial visualizations of soil pH, clay content, electric conductivity, and soluble salts as well as tables for salt concentrations in different soil depths across four large-scale soil transects in the Atacama Desert, Chile, from the Earth Shape Project. The excel file provides the values for the measured properties. Corresponding author: Diana Boy (diana.boy@ifmb.uni-hannover.de)

GRAZING MANAGEMENT, AMMONIA AND NITROUS OXIDE EMISSIONS: A GENERAL VIEW

The grazing management of grassland has a direct effect on nitrogen (N) recycling. This is an important reason why management has become an alternative to improve the grassland production and quality, in turn to make it more suitable for the environment. However, the livestock system intensification induces changes in the natural dynamics of the N cycle, accelerating gas emmisions (e.g. ammonia, NH3 and nitrous oxide, N2O) and leaching losses from soil under grazing. When the amount of N in the environment increases, there is an impact on smog episodes, global warming, stratospheric ozone depletion, acid rain and eutrophication of fresh water. There are different techniques to evaluate the gases emitted from the soil. This klonowledge is useful to design the strategies to reduce the negative consequences of theses gases on the environment. In this review, the effect of grazing managements on N gas emissions from soils and the current techniques for N gas emission measurements in the field and laboratories conditions are discussed.

DYNAMIC BIOGEOCHEMICAL SHIFTS AFTER CONVERSION FROM NATURAL FORESTS TO EXOTIC PINE PLANTATIONS

Descomposición de hojarasca de Pinus radiata y tres especies arbóreas nativas

En el centro-sur de Chile, las ultimas decadas han sido testigo de una conversion masiva de bosques, matorrales y tierras agricolas a plantaciones de arboles exoticos. Aunque se ha estudiado la influencia de dichos cambios sobre el balance hidrico, los posibles efectos sobre otros procesos ecosistemicos han recibido poca atencion. En esta breve comunicacion se presentan datos de un estudio de la descomposicion de hojarasca de Pinus radiata y tres especies arboreas nativas, llevado a cabo con el fin de explorar los posibles efectos del reemplazo de bosque nativo por plantaciones exoticas sobre el ciclaje de nutrientes. Se incubaron muestras de las cuatro especies en dos ambientes distintos en sitios colindantes: bajo un bosque nativo secundario, y bajo un rodal de P. radiata. Se registro la perdida de peso seco despues de dos meses y seis meses. Las tasas diarias de descomposicion fueron mucho mayores durante los primeros dos meses de incubacion que durante los cuatro meses subsiguientes. En ambas fechas hubo diferencias significativas entre las especies y entre los sitios: todas las especies presentaron mayores tasas de descomposicion bajo P. radiata que bajo el bosque nativo. No hubo evidencia de interaccion entre sitio y especie. Despues de seis meses, el orden de perdida de peso seco fue Nothofagus obliqua > P. radiata > Peumus boldus > Cryptocarya alba. La variacion interespecifica en la tasa de descomposicion presento mas relacion con el area foliar especifica que con el contenido de nitrogeno en la hojarasca. Dado que la hojarasca de P. radiata se descompuso mas lentamente que la de la especie caducifolia N. obliqua, pero mas rapidamente que las especies esclerofilas, los efectos de la sustitucion o invasion sobre descomposicion dependerian de la composicion original del bosque nativo en cuestion

Exploring Andean High-Altitude Lake Extremophiles through Advanced Proteotyping

Quickly identifying and characterizing isolates from extreme environments is currently challenging while very important to explore the Earth′s biodiversity. As these isolates may, in principle, be distantly related to known species, techniques are needed to reliably identify the branch of life to which they belong. Proteotyping these environmental isolates by tandem mass spectrometry offers a rapid and cost-effective option for their identification using their peptide profiles. In this study, we document the first high-throughput proteotyping approach for environmental extremophilic and halophilic isolates. Microorganisms were isolated from samples originating from high-altitude Andean lakes (3700–4300 m a.s.l.) in the Chilean Altiplano, which represent environments on Earth that resemble conditions on other planets. A total of 66 microorganisms were cultivated and identified by proteotyping and 16S rRNA gene amplicon sequencing. Both the approaches revealed the same genus identification for all isolates except for three isolates possibly representing not yet taxonomically characterized organisms based on their peptidomes. Proteotyping was able to indicate the presence of two potentially new genera from the families of Paracoccaceae and Chromatiaceae/Alteromonadaceae, which have been overlooked by 16S rRNA amplicon sequencing approach only. The paper highlights that proteotyping has the potential to discover undescribed microorganisms from extreme environments.

Microbial response to warming and cellulose addition in a maritime Antarctic soil

Maritime Antarctic King George Island (South Shetland Islands) has experienced rapid warming in recent decades, but the impacts on soil organic matter (SOM) decomposition remain ambiguous. Most vegetation cover is dominated by bryophytes (mosses), whereas a few vascular plants, such as Deschampsia antarctica and Colobanthus quitensis grow interspersed. Therefore, SOM is mainly enriched with carbohydrates and C‐alkyl, provided by mosses, which lack lignin as a precursor for aromatic compounds and humus formation. However, there is no clear answer to how substrate and temperature increase changes in Antarctic microbial respiration. We determined in what way SOM mineralization changes with temperature and substrate addition by characterizing the temperature sensitivity (Q 10 ) of soil respiration in an open‐top chamber warming experiment. We hypothesized that: (a) cold‐tolerant microorganisms are well adapted to growing in maritime Antarctic soils (~ 0°C), so would not respond to low and moderate temperature increases because they undergo various metabolic mechanism adjustments until they experience increasing temperatures toward optimum growth (e.g., by enzyme production); and (b) cellulose, as a complex carbonaceous substrate of vegetated areas in Maritime Antarctic soils, activates microorganisms, increasing the Q 10 of soil organic carbon (SOC) mineralization. Soils (5–10 cm) were sampled after four consecutive years of experimental warming for SOC composition, microbial community structure, and C mineralization at 4, 12, and 20°C with and without cellulose addition. Functional group chemoheterotrophs, represented mainly by Proteobacteria, decomposed more refractory SOC (aromatic compounds), as indicated by nuclear magnetic resonance (NMR) spectroscopy, in ambient plots than in warming plots where plants were growing. The C‐CO 2 efflux from the incubation experiment remained stable below 12°C but sharply increased at 20°C. Q 10 varied between 0.4 and 4 and was reduced at 20°C, whereas cellulose addition increased Q 10 . In conclusion, as confirmed during field studies in a climate scenario, cold‐tolerant microorganisms in maritime Antarctic soils were slightly affected by increasing temperature (e.g., 4–12°C), with reduced temperature sensitivity, as summarized in a conceptual model.

Microbial mobilization of various P species depends on weathering history of soils

No abstract is provided for this article.

Meta-analysis of heavy metal effects on soil enzyme activities

No abstract is provided for this article.

A simple model for estimating the contribution of nitrogen mineralization to the nitrogen supply of crops from a stabilized pool of soil organic matter and recent organic input

A simple model was developed to estimate the contribution of nitrogen (N) mineralization to the N supply of crops. In this model the soil organic matter is

From rock-eating to vegetarian ecosystems — plant phosphorus acquisition strategies along a Chilean precipitation gradient

<p>Besides nitrogen, phosphorus (P) is the major limiting nutrient of terrestrial primary productivity, with major P stocks being bound in soils. Stocks, speciation, and bioavailability of soil P differ among ecosystem types and with rock weathering status, which are both driven by climatic conditions. Microorganisms and plants have developed a range of strategies to mobilize P from organic and inorganic sources, e.g. expression of extracellular phosphatases and excretion of low-molecular-weight organic acids (LMWOA). However, the impact of precipitation, vegetation type, and soil P speciation on plant P acquisition strategies is not well understood, yet.</p><p>A semi-desert-to-humid-temperate-rainforest ecosystem sequence was investigated. Soil samples were taken from three sampling sites, all developed on granodiorite, comprising a precipitation gradient (66 mm a<sup>-1</sup> to 1469 mm a<sup>-1</sup>) along the Chilean Coastal Cordillera. Small-scale gradients (mm) from single roots to bulk soil in three depths were sampled to examine changes in P speciation, enabling the identification of local P depletion by plant roots and differences in P-speciation between rhizosphere and non-rhizosphere soil. Phosphorus speciation was examined by X-ray absorption near edge structure analysis. LMWOA as biotic weathering agents, and acid phosphatase kinetics as proxy for organic P recycling, were quantified. The aim was to disentangle the impact and functions of roots and associated microorganisms on driving agents of P-cycling.</p><p>Rhizosphere P speciation in soil changed considerably along the precipitation gradient from mainly primary P minerals in the semi-desert ecosystem to a dominance of organic P species in the humid-temperate rainforest. Contents of organically bound P were higher in root proximity compared to bulk soil in the humid-temperate rainforest soils (320 mg kg<sup>-1 </sup>and 70 mg kg<sup>-1</sup>, respectively) and in the topsoil of the Mediterranean woodland ecosystem (134 mg kg<sup>-1 </sup> and 62 mg kg<sup>-1</sup>, respectively).  In contrast, the rhizosphere soil was depleted in sesquioxide-adsorbed P in comparison to root-free bulk soil.</p><p>The content of LMWOA was correlated with inorganic P in soils of the semi-desert ecosystem, indicating intensive LMWOA exudation for biogenic P weathering of primary and secondary minerals. Under temperate rainforest LMWOA content, phosphatase activity, and microbial biomass carbon exhibited a negative correlation with secondary inorganic P forms but were positively linked to organic P species. We therefore conclude that P nutrition in this ecosystem relies less on weathering of P bearing minerals by LMWOA but is mainly based on organic P sources.</p><p>In terms of process understanding, these findings clearly show that LMWOA fundamentally change their role in the rhizosphere depending on the nutrient acquisition strategy of the respective ecosystem, which is affected by mean annual precipitation. While LMWOA facilitate biogenic weathering of P bearing minerals in the semi-desert, they mainly contribute to P recycling in the humid-temperate rainforest by preventing its precipitation and sorption. We conclude that P acquisition and cycling depends on the nutritional constrains of the given ecosystem: from biological weathering of inorganic P forms in the semi-desert driven by LMWOA and plant uptake to intensive P recycling from organic forms in the humid-temperate rainforest.</p>

Effects of the Signalling Principle on EFL Learning: A Study of Explicit Presentation of Frequent Grammar Mistakes Using an Adapted Functional Teaching Approach

No abstract is provided for this article.

Effect of aluminium on dissolved organic matter mineralization in an allophanic and kaolinitic temperate rain forest soil