Publications

<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>

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.

The effects of cultivation in hillside (> 30% slope) on soil C and N stocks after forest clearance and subsequent cultivation in new re-growth forest sites not always induce rapid soil organic matter (SOM) loss in subtropical areas. In the present study we evaluated the sensitivity to SOM changes of material floatable in water (Fw), coarse sand (> 250 µm), fine sand (50-250 µm), silt (2-50 µm) and clay (0-2 µm) fractions by the impact of cultivation of Mexican Ferrasols. This research also determined the relative degree of C and N saturation in the silt and clay size particles. The soil physical fractions were obtained after ultrasonic vibration and sedimentation. Soil organic matter stock (0-20 cm depth) in cultivated sites ranged from 54 to 146 Mg C ha-1 and from 3.9 to 7.1 Mg N ha-1 and in the forest soil 46-94 Mg C ha-1 and 3.7-5.1 Mg N ha-1. The relative distribution of C and N was lower in the coarse sand and highest in the silt fraction; the latter paralleled the changes of whole soil C and N. Coarse sand was the most sensitive fraction responding to cultivation, thus representing a diagnostic pool to assess the SOM shifts under cultivation. Half of our studied soil showed a low degree of C and N saturation in the silt and clay fraction indicating potential for accumulation of C and N, while the other half were well above the saturation limit.

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.

Forest wildfire and stubble burning practices in agriculture contribute to the formation of black carbon (BC), a continuum of pyrogenic carbon ranging from slightly charred degradable biomass to highly condensed refractory soot. We examined the BC contribution to Andisol after a wildfire in a pristine Araucaria-Nothofagus spp. temperate rain forest and after 17years of stubble burning on an agricultural soil. We tested the hypothesis that the severity of stubble burning and forest fire affects the quantity and composition of soil organic matter (SOM) and that fire-derived aromatic BC is the main contributor to stabilised SOM in fire-affected soil. BC contribution was analysed as the aromatic fraction of the acid dichromate oxidation residue (CORECarom). The results indicated that the BC content of agricultural soil was unaffected by the stubble burning, whereas in the forest soil, it increased with fire severity from 0.5% at an unburned site to up to 7% in the topsoil severely affected by wildfire. For both ecosystems, the total C stock correlated positively with pyrophosphate extractable Al, whereas a poor or inconsistent relationship was found with BC. We conclude that aromatic BC plays a minor role in C stabilisation in these fire-affected soils due to losses most likely following transport. Aliphatic compounds were less affected by the dichromate oxidation treatment relative to the aromatic compounds than any other functional groups, emphasising the importance of alkyl C for soil C sequestration by virtue of chemical recalcitrance.

Mathematical–statistical problem on estimation of soil-forming processes. This paper raises a mathematical–statistical problem that finally can

Understanding nitrogen (N) retention mechanisms in pristine humid temperate rainforest soils is critical for effective ecosystem management and nutrient conservation. The potential abiotic transformation of nitrite (NO2−) into organic N forms in the absence of microbial activity in these ecosystems remains largely unexplored, despite its role in mitigating N leaching. This study focuses on the abiotic incorporation of nitrite (NO2−) into dissolved organic nitrogen (DON) under anoxic conditions, a mechanistic step not directly evaluated in previous research, which employed 15N-labelled nitrate (NO3−). To address this gap, we used 15N-labelled NO2− at 5 and 15 mg L−1 in a lab incubation study under anoxic conditions to trace the contribution of abiotic nitrite transformation to organic N formation in organic matter-rich soils from temperate rainforests developed on both volcanic and non-volcanic parent materials. The added 15N declined rapidly after 15 min by 52% and 60% in both soil solutions, while it started to form labelled DON, increasing by 11% and 34%, after five days of incubation, with the highest accumulation at 15 mg L−1 of 15N-NO2−. These results show that up to 77% of the added 15N-NO2− can be abiotically incorporated into the DON of unpolluted old-growth temperate rainforest, whether developed on volcanic or non-volcanic soils. Nitrogen input has a stronger effect than soil parent material from which the soils originate. This reveals the natural resilience of unpolluted temperate rainforests to N loss, with implications for long-term ecosystem stability and nutrient cycling.

Recent studies with Andisols show that the carbon (C) stabilization capacity evolves with soil age relative to the evolution of the mineral phase. However,

Nitrogen (N) mineralization in soil depends on carbon (C) input of plant materials, site environmental conditions, and soil texture. Empirical correlates of N mineralization can be difficult to interpret, however, because of interactions among these factors. A multiple regression model relating N mineralization to C input rates, litter quality, and soil texture in Chilean temperate rain forest soils was developed. Nitrogen mineralization rates ranged from 3.0 to 5.7 mg kg−1 soil d−1 depending on C input rate and soil texture but were not influenced by litter quality. We compared C storage of both forest and long‐term‐cropped soils with the protective capacity (i.e., the expected maximum C pool associated with the clay and silt fractions). Soil organic C associated with the fine fraction of forest soils was significantly greater than the calculated protective capacity, with clay‐rich soils averaging 141% more C than this limit and coarser soils having 56% more than predicted. In contrast, C content of cropped soils was well below the calculated protective capacity, averaging ∼32–60% less than this limit, showing the potential of these soils for sequestering C. The results were consistent with the finding that N mineralization was positively correlated with the amount of free organic matter associated with the sand‐size fraction in forest soils. The study illustrates that (i) the capacity of soils to preserve soil organic C in clay‐ and silt‐sized particles was greater than that of agricultural soils and (ii) in highly saturated soils, the N mineralization is a function of the quantity of organic‐matter input, which in turn accumulates as free organic C in the sand‐size fraction.