Publications

Relationship between extractable Al and organic C in volcanic soils of Chile

In previous studies, Al extracted by acid ammonium acetate (Ala) or Na-pyrophosphate (Alp), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Ala is a comparable method (as much as CuCl2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0–53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Ala, Alp, oxalate (Alo, Sio and Feo), cold NaOH (Aln) and un-buffered salts, CuCl2 (AlCu), LaCl3 (AlLa) and KCl (Alk). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Ala had a good correspondence with Alp (R 2 =0.76) in the top soil with Ala/Alp ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R2 >0.62). Acid ammonium acetate was as effective as AlCu to determine the Al–OM in allophanic soils. It is cheaper than AlCu and Alp and 0.5 h shaking is required compared to 2 h of AlCu and 16 h of Alp. The efficiency of the extraction was: Aln ≥Alo >Alp >AlCu ≥Ala >AlLa >Alk. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R 2 =0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R 2 >0.60) the largest proportion of variation of soil OC across studied soils.

High winter diversity of arbuscular mycorrhizal fungal communities in shallow and deep grassland soils

The identity and diversity of the arbuscular mycorrhizal fungal (AMF) symbionts have a large impact on ecosystem functioning and stability, indicating the need to assess their distribution in terrestrial environments. Four temperate grassland sites of low to medium fertility located on a common soil were sampled in winter and summer at two different depths (0–40 cm, 40–80 cm) using a spatially intensive experimental sampling design. Arbuscular mycorrhizal fungal community composition was determined via the amplification of AMF rRNA gene fragments present in fine roots combined with terminal-restriction fragment length polymorphism (T-RFLP) and sequencing analyses. For one out of three endonucleases applied, a site × depth interaction on T-RF richness (S) and Shannon's diversity index (H′) was observed, indicating differences between sites in the upper soil layer and depth effects on S and H′ for the extensively managed, low fertility site. The S and H' of the AMF taxa present in fine plant roots were marginally lower in winter than in summer (−14% and −16% for S and H′, respectively). Evenness E did not vary as a function of site, season or depth. The AMF community profiles, as determined by nonmetric multidimensional scaling, differed between sites and seasons, but not among soil depths. The intersite AMF community variations were attributed to niche differentiation based on soil phosphorus availability and pH. Seasonal shifts could not be related to variations in root densities or physico-chemical soil properties measured in this study, suggesting climate and plant regulation as major processes responsible for the variations between winter and summer AMF communities. It is concluded that diverse winter AMF communities are present in temperate grassland soils, and that plant roots colonizing subsoils harbour similar and equally diverse AMF assemblages than those present in topsoil layers.

Mineral-associated carbon persistence arises from steady-state dynamics, not saturation

Climate and root proximity as dominant drivers of enzyme activity and C and N isotopic signature in soil

No abstract is provided for this article.

Manganese-Oxidizing Antarctic Bacteria (Mn-Oxb) Release Reactive Oxygen Species (ROS) as Secondary Mn(II) Oxidation Mechanisms to Avoid Toxicity

Manganese (Mn) oxidation is performed through oxidative Mn-oxidizing bacteria (MnOxb) as the main bio-weathering mechanism for Mn(III/IV) deposits during soil formation. However, with an increase in temperature, the respiration rate also increases, producing Reactive Oxygen Species (ROS) as by-products, which are harmful to microbial cells. We hypothesize that bacterial ROS oxidize Mn(II) to Mn(III/IV) as a secondary non-enzymatic temperature-dependent mechanism for cell protection. Fourteen MnOxb were isolated from Antarctic soils under the global warming effect, and peroxidase (PO) activity, ROS, and Mn(III/IV) production were evaluated for 120 h of incubation at 4 °C, 15 °C, and 30 °C. ROS contributions to Mn oxidation were evaluated in Arthrobacter oxydans under antioxidant (Trolox) and ROS-stimulated (menadione) conditions. The Mn(III/IV) concentration increased with temperature and positively correlated with ROS production. ROS scavenging with Trolox depleted the Mn oxidation, and ROS-stimulant increased the Mn precipitation in A. oxydans. Increasing the Mn(II) concentration caused a reduction in the membrane potential and bacterial viability, which resulted in Mn precipitation on the bacteria surface. In conclusion, bacterial ROS production serves as a complementary non-enzymatic temperature-dependent mechanism for Mn(II) oxidation as a response in warming environments.

Soils control biogeochemical shifts resulting from the conversion of native forest to pine plantations

Conversion from native temperate deciduous Nothofagus spp. forests to exotic Pinus spp. plantations in South-Central Chile, can substantially alter soil carbon (C) and nutrient cycling. We assessed the biogeochemical shifts resulting from this forest conversion by monitoring carbon and nutrient dynamics at 10 paired adult native forest and plantation sites across contrasting soil types (5 sites), including litterfall, LAI, fine root biomass, and soil CO₂ efflux, over a period of three years. In addition, we quantified aboveground tree biomass and total C, N, and P stocks in trees and soils. C inputs were significantly higher in native systems than in plantations (5.17 ± 1.19 vs. 3.19 ± 0.99 Mg C ha⁻¹ year⁻¹, respectively). Native forests also exhibited higher total C losses through soil CO₂ efflux (-3.19 ± 1.68 Mg C ha⁻¹ year⁻¹) than pine plantations (-2.54 ± 1.52 Mg C ha⁻¹ year⁻¹), yet maintained a more favorable balance between inputs and losses, largely due to differences in the dominant C input pathways. Native forests showed greater fine-root production and deeper, denser rooting systems, whereas plantations were characterized by higher litterfall and faster decomposition rates, potentially accelerating carbon mineralization. Across soil types, native forests exhibited significantly higher aboveground biomass than adjacent plantations. Although aboveground carbon stocks tended to be higher in native forests, these differences were not statistically significant when all soil types were considered together. Nevertheless, native forests consistently allocated a greater proportion of carbon belowground, whereas plantations concentrated carbon inputs in aboveground compartments. Native forests also maintained larger soil and aboveground biomass N and P stocks than plantations. Responses varied systematically among soil types, with residual crystalline soils and older volcanic deposits showing higher carbon losses relative to inputs than younger volcanic ash-derived soils. Overall, our results demonstrate that soil parent material modulates post-conversion carbon fluxes and the distribution of ecosystem C, N, and P stocks, highlighting the importance of soil–vegetation interactions when evaluating carbon benefits and long-term sustainability of forest management strategies. • Plantations showed faster litter decomposition and carbon turnover than natural forests. • Fine-root production was consistently higher in native forests. • Soil parent material constrained the balance between carbon inputs and losses. • Soil type modulated post-conversion carbon fluxes and nutrient stocks.

Mathematical–Statistical Problem that Has a Significant Implication on Estimation of Interval-Specific Rates of Soil-Forming Processes

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

Gradient Studies Reveal the True Drivers of Extreme Life in the Atacama Desert

Studies of hyper‐arid sites contribute to our understanding on how life adapted to extreme conditions. They are often used to further deduce implications for extraterrestrial biology by the so‐called analogue site‐approach. The Atacama Desert, Chile, is one of the most prominent analogue sites despite its neighboring productive ecosystems due to its hyper‐aridity and geochemical features resembling Martian environments. We hypothesize that many drivers of extremophile life in analogue sites are only mistakenly attributed to aridity alone, thus obscuring a clear view of the far more complex process interactions originating in nearby earthly ecosystems. To test this, we investigated 54 soil profiles up to 60 cm of soil depth along of four transects in the Atacama Desert, either running parallel (S‐N) or perpendicular (W‐E) to the Andes. Our objective was to reveal the processes controlling the formation of soil organic carbon (SOC) as the most reliable proxy for microbial life in order to understand the boundary conditions of life in extreme habitats. Further, we aimed at identifying analogue sites as uncompromised as possible by external influences of for example, vegetated or marine ecosystems. We found a mixture of influences driving habitable conditions on gradients perpendicular to the Andes, for example, fog and precipitation scavenging caused by altitudinal variations and differing proximity to the Pacific Ocean, while transects parallel to the Andes were much less biased by external factors. Our results show that studies on life under extreme conditions should clarify the explanatory strength of the investigated factors by a gradient study approach.

Organic matter stabilization in two Andisols of contrasting age under temperate rain forest

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

Black carbon contribution in volcanic soils affected by wildfire or stubble burning

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.

Effect of wildfire on soil organic matter in an Andisol of a southern Chilean temperate rain forest

Old-growth forests of southern Chile represent an important reserve of temperate forests worldwide. The precipitation chemistry in Chile still reflects the time of pre-industrial conditions. Thus, the productivity of the ecosystem mainly depends on the internal cycling of soil organic matter (SOM). However, catastrophic events, such as wildfires can initiate important changes in the physical and biogeochemical properties of SOM and therefore on the ecosystem habitat. We studied Araucaria-Nothofagus forests in the Andean mountains of Chile (38° S, 71° W) three years after they were affected by a huge wildfire in February 2002. The aims of this investigation were: (1) to analyze the effect of fire on the quality of SOM at different soil depths and (2) the changes in carbon content of an incomplete combustion of vegetal material after wildfire, refractory to decomposition, referred to as black carbon (BC). We used a combination of C and N analyses and SOM fractionation. The chemical and elemental composition of the soil samples was studied by solid state C CPMAS NMR spectroscopy and BC determination. We found an increase in nitrification rates after fire, and a wider aromatic C to alkyl C ratio of the incorporated char, leading to an increase in BC quantity. Our results point out that wildfire induces changes in the chemical composition of the SOM. A clear relationship between isotopic SOM signature and C and N cycling processes could be established. This indicates that C and N and NMR techniques can be used as proxy to assess the fire impact on the SOM dynamics.

Effects of drying/rewetting on soil aggregate dynamics and implications for organic matter turnover

Drying and rewetting (D/W) of soil have significant impacts on soil organic matter (SOM) turnover. We hypothesised that frequent D/W cycles would release t

Fortalecimiento de la calidad y visibilidad internacional de la revista Journal of Soil Science and Plant Nutrition

No abstract is provided for this article.

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

CHLSOC: the Chilean Soil Organic Carbon database, a multi-institutional collaborative effort

. A critical aspect of predicting soil organic carbon (SOC) concentrations is the lack of available soil information; where information on soil characteristics is available, it is usually focused on regions of high agricultural interest. To date, in Chile, a large proportion of the SOC data have been collected in areas of intensive agricultural or forestry use; however, vast areas beyond these forms of land use have few or no soil data available. Here we present a new SOC database for the country, which is the result of an unprecedented national effort under the framework of the Global Soil Partnership. This partnership has helped build the largest database of SOC to date in Chile, named the Chilean Soil Organic Carbon database (CHLSOC), comprising 13 612 data points compiled from numerous sources, including unpublished and difficult-to-access data. The database will allow users to fill spatial gaps where no SOC estimates were publicly available previously. Presented values of SOC range from 6×10-5 % to 83.3 %, reflecting the variety of ecosystems that exist in Chile. The database has the potential to inform and test current models that predict SOC stocks and dynamics at larger spatial scales, thus enabling benefits from the richness of geochemical, topographic and climatic variability in Chile. The database is freely available to registered users at https://doi.org/10.17605/OSF.IO/NMYS3 (Pfeiffer et al., 2019b) under the Creative Commons Attribution 4.0 International Public License.

BIOGEOQUIMICA EN BOSQUES TEMPLADOS DEL SUR DE CHILE

No abstract is provided for this article.

Divergent soil structure dependent functions responses to livestock intensification and peat extraction in Patagonian wetlands

Vegetation strategies for nitrogen and potassium acquisition along a climate and vegetation gradient: From semi-desert to temperate rainforest

Nutrient acquisition strategies of plants regulate water flow and mass transport within ecosystems, shaping earth surface processes. Understanding plant strategies under current conditions is important to assess and predict responses of natural ecosystems to future climate and environmental changes. Nitrogen (N) and potassium (K) (re-)utilization from topsoil and their acquisition from subsoil and saprolite were evaluated in a continental transect, encompassing three study sites – an arid shrubland, a mediterranean woodland, and a temperate rainforest – on similar granitoid parent material in the Chilean Coastal Cordillera. The short-term (<1 year) plant N and K acquisition was traced with 15N and the K analogs rubidium and cesium. To do so, the tracers were either injected into topsoil, subsoil, or saprolite, in the immediate vicinity of eight individual plants per study site and injection depth. The long-term (>decades) K uplift by plants was investigated by the vertical distribution of exchangeable K+ and Na+. Recoveries of 15N and K analogs by arid shrubland plants were similar from topsoil, subsoil, and saprolite. Mediterranean woodland shrubs recovered the tracers primarily from topsoil (i.e., 89 % of recovered 15N and 84 % of recovered K analogs). Forest plants recovered the tracers from topsoil (15N = 49 %, K analogs = 57 %) and partially from greater depth: 38 % of recovered 15N and 43 % of recovered K analogs were acquired from subsoil and saprolite, respectively. Low nutrient accessibility in the topsoil (e.g., because of frequent droughts) drives shrubland plants to expand their N and K uptake to deeper and moister soil and saprolite. Woodland and forest plants dominantly recycled nutrients from topsoil. In the forest, this strategy was complemented by short-term uplift of N and K from depth. The vertical distribution of exchangeable K indicated long-term uplift of K by roots in all three sites. This highlighted that long-term K uplift from depth complements the nutrient budget across the continental transect.

Carbon distribution in top‐ and subsoil horizons of two contrasting Andisols under pasture or forest

Volcanic ash soils display distinctive morphological, physical and chemical properties and they contain several times more organic matter than non‐volcanic soils. So far, there are few studies of soil organic matter (SOM) distribution in different chemically and physically protected carbon pools of soil horizons of volcanic soils. The aim of this study was to determine the SOM distribution (and its δ 13 C and δ 15 N composition) in different chemical and physical fractions at various depth horizons of two Andisols under pasture or rain forest in southern Chile. We used the amount of humus‐complexes (C p ) extracted with Na pyrophosphate as a measure of C stabilized by aluminum (Al p ) and iron (Fe p ) in combination with density fractionation to separate particulate organic matter as free (fPOM), occluded (oPOM) and organic matter associated with the mineral fraction (MF). The results showed that soil SOM stock (0–40 cm) in the pasture soil was 166 Mg C ha −1 (11.7 Mg N ha −1 ) and in the forest soil 100 Mg C ha −1 (4.1 Mg N ha −1 ). The SOM variation was explained largely by the differences in C p , Al p and Fe p . About 34% of total soil C was found as C p in both oPOM and MF in the topsoil, whereas 33–53% was found in the subsoil horizons. The oPOM fraction was more important in the forest soil and generally decreased in the subsoil where these fractions were enriched with δ 13 C and δ 15 N. Our results emphasize the importance of the humus complex and oPOM formation as the SOM stabilization mechanism in the forest Andisol, whereas under pasture organo‐mineral interaction, including the formation of humic‐metal complexes, is the most important stabilization mechanism. A conceptual model is lacking to demonstrate the major areas of uncertainty within known mechanisms and factors that explain the distribution of SOM through soil profiles in Andisols.