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<p>Arbuscular mycorrhizal fungi (AMF) are important partners in plant nutrition, as they increase the range to scavenge for nutrients and can access resources otherwise occlude for plants. Under water shortage, when mobility of nutrients in soil is limited, AMF are especially important to acquire resources and can modulate plant drought resistance. Strategies of plants to cope with water and nutrient restrictions are shaped by the intensity of aridity. To investigate the effect of aridity on plant-AMF associations regarding drought resistance and plant nutrient acquisition, a <sup>13</sup>CO<sub>2</sub> pulse labeling was conducted across an aridity gradient. In a semiarid shrubland (66 mm a<sup>-1</sup>), a Mediterranean woodland (367 mm a<sup>-1</sup>), and a humid temperate forest (1500 mm a<sup>-1</sup>), root and soil samples were taken from 0-10 cm and 20-30 cm soil depth before labeling and at 1 day, 3 days, and 14 days after labeling. Carbon (C), nitrogen (N), and phosphorus (P) stocks as well as AMF root colonization, extraradical AMF biomass (phospho- and neutral lipid fatty acids (PLFA and NLFA) 16:1w5c), specific root length (SRL), and root tissue density (RTD) were measured. Plant C investment into AMF and roots was determined by the <sup>13</sup>C incorporation in 16:1w5c (PLFA and NLFA) and root tissue, respectively. Soil C:N:P stoichiometry indicated a N and P limitation under humid conditions and a P limitation in the topsoil under Mediterranean conditions. N stocks were highest in the Mediterranean woodland. A strong correlation of the AMF storage compound NLFA 16:1w5c to C:P ratio under semiarid conditions pointed to a P limitation of AMF, likely resulting from low P mobility in dry and alkaline soils. With increasing aridity, the AMF abundance in root (and soil) decreased from 45% to 20% root area. <sup>13</sup>C incorporation in PLFA 16:1w5c was similar across sites, while relative AMF abundance in topsoil (PLFA 16:1w5c:SOC) was slightly higher under semiarid and humid than under Mediterranean conditions, pointing to the importance of AMF for plant nutrition under nutrient limitation. Additionally, PLFA 16:1w5c contents in soil were higher with lower P availability in each site, underlining the role of AMF to supply P for plants under P deficiency. Under humid conditions (with strong N and P limitation) and semiarid conditions (with strong water limitation), root AMF colonization increased with lower N availability, displaying the role of AMF for plant N nutrition under nutrient and/or water shortage. Under humid and Mediterranean conditions, SRL decreased (0.5 and 0.3 times, respectively) and RTD increased (1.9 and 1.7 times, respectively) with depth, indicating a drought tolerance strategy of plants to sustain water shortage. Under semiarid conditions, SRL increased with depth (2.3 times), while RTD was consistently high, suggesting an increasing proportion of long-living fine roots with depth as scavenging agents for water. These relations point to a drought avoidance strategy of plants as adaptation to long-term water limitation. Under strong nutrient limitation, as under humid and semiarid conditions, AMF are crucial to sustain plant nutrition and to enhance plant resistance to water shortage.</p>

. One of the critical aspects in modelling soil organic carbon (SOC) predictions is the lack of access to soil information which is usually concentrated in regions of high agricultural interest. In Chile, most soil and SOC data to date is highly concentrated in 25 % of the territory that has intensive agricultural or forestry use. Vast areas beyond those forms of land use have few or no soil data available. Here, we present a new database of SOC for the country, which is the result of an unprecedented national effort under the frame of the Global Soil Partnership that help to build the largest database on SOC to date in Chile named “CHLSOC" comprising 13,612 data points. This dataset is the product of the compilation from numerous sources including unpublished and difficult to access data, allowing to fill numerous spatial gaps where no SOC estimates were publicly available before. The values of SOC compiled in CHLSOC range from 6×10−5 to 83.3 percent, reflecting the variety of ecosystems that exists in Chile. Profiting from the richness of geochemical, topographic and climatic variability in Chile, the dataset has the potential to inform and test models trying to predict SOC stocks and dynamics at larger spatial scales. Dataset available at https://www.doi.org/10.17605/OSF.IO/NMYS3 (Pfeiffer et al., 2019b).

En el centro-sur de Chile, las últimas décadas han sido testigo de una conversión masiva de bosques, matorrales y tierras agrícolas a plantaciones de árboles exóticos.Aunque se ha estudiado la influencia de dichos cambios sobre el balance hídrico, los posibles efectos sobre otros procesos ecosistémicos han recibido poca atención.En esta breve comunicación se presentan datos de un estudio de la descomposición de hojarasca de Pinus radiata y tres especies arbóreas nativas, llevado a cabo con el fin de explorar los posibles efectos del reemplazo de bosque nativo por plantaciones exóticas 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 registró la pérdida de peso seco después de dos meses y seis meses.Las tasas diarias de descomposición fueron mucho mayores durante los primeros dos meses de incubación 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 descomposición bajo P. radiata que bajo el bosque nativo.No hubo evidencia de interacción entre sitio y especie.Después de seis meses, el orden de pérdida de peso seco fue Nothofagus obliqua > P. radiata > Peumus boldus > Cryptocarya alba.La variación interespecífica en la

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Para analizar la dinámica del carbono orgánico de los suelos (COS) asociada a su cambio de uso, de vegetación y prácticas de manejo, es necesario desarrollar modelos para usarse en forma predictiva. Un enfoque de modelación es la distribución del COS presente en los complejos organominerales primarios (arcillas, limos y arenas) ligado a las fracciones físicas. Para la separación de las fracciones físicas se emplea la dispersión del suelo por ultrasonido, paso que requiere optimizar las energías de sonicación para lograr la completa dispersión del suelo. En este trabajo se discute el modelo COLPOS y su hipótesis, así como sus posibles extensiones que consideran las masas y los enriquecimientos de las fracciones físicas del suelo, adicionalmente al análisis de las relaciones entre esas fracciones. Para analizar los patrones asociados al modelo COLPOS y sus extensiones, se analizan resultados disponibles de fraccionamientos de suelos mexicanos realizados con ultrasonido, además de tres bases de datos de fraccionamientos similares publicados en la literatura. Éstos muestran que el modelo COLPOS puede ser parametrizado en función del tamaño y masa de las partículas del suelo; aunque para el caso de las masas algunos resultados son inconsistentes. Del análisis de los cocientes del carbono orgánico entre fracciones para dos cinéticas lineales diferentes (organomineral y organomineral más partícula) las relaciones muestran mayor dispersión que para el caso de solo considerar fracciones de una cinética.

Amorphous mineral-associated organic carbon (AMAOC) and organo-Al/Fe complexes (Cp) play crucial roles in soil carbon (C) sequestration in volcanic soils. This study investigated the effects of land use management and liming on the C sequestration capacity of a young allophanic Andisol and old halloysitic-kaolinitic volcanic Ultisol sampled at 0–10 and 10–20 cm depth. This study was designed to test two hypotheses: (1) management and liming affect the C sequestration capacity of Andisol by reducing Cp and increasing AMAOC to offset Cp losses, and (2) they do not significantly affect the carbon sequestration capacity of Ultisol because of its more crystalline mineral forms and reduced amount of Cp. This study was conducted using a selective dissolution technique and density fractionation with agricultural soils and forests as control soils. After 43 years of intensive management and liming, the soil organic carbon (SOC) content decreased by 32% in the topsoil compared to the original native forest soil (178 ± 2 g kg−1 soil), mainly in the particulate organic matter (POM) fraction, which decreased by 74% compared to the native forest soil (61 ± 9 g kg−1 soil). However, Cp decreased only by 40% compared to the forest soil (62 ± 1 g kg−1 soil) from pHKCl 4.8–5.0, and AMAOC increased in 17% in the topsoil and 64% in the subsoil, supporting the first hypothesis of this study. In the cultivated Ultisol, SOC decreased by 35% due to the POM fraction, and mineral-associated organic C (MAOC) decreased by 37% compared to the forest soil (38 ± 7 g kg−1 soil). These results partially support the second hypothesis because the crystalline clay minerals from which MAOC originated remained unchanged and were strongly correlated with SOC. The mass balance of both soils indicated that the stable C losses from native forest soils were < 14%. These results highlight the importance of different C sequestration mechanisms to compensate for SOC losses in the young allophanic Andisol and old volcanic Ultisol. Our findings imply that both mechanisms can be used to estimate the C sequestration capcity in similar soil types.