Effects of urban, atmosphericallyderived organic C on soil: A review

Urban areas generate about 77%, worldwide, of the carbon (C) based compounds that are annually released to the atmosphere, whether in the form of gases (e.g., 71% of CO2, 60% of CO) or fine aromatic C solids (70%), all of which may pose environmental risks, from biological cell to global levels (e.g., air quality, scattering light). Those C-rich atmospheric particles, referred to as “particulate matter and black carbon” (PM-BC), as opposed to aquatic origin “particulate organic carbon” (POC), are present as finer than 2.5 µm and produced during incomplete combustion processes such as in vehicle emissions, domestic heating and biomass burning. However, while the post combustion C gases remain for a while in the aerial environment, PM-BC undergoes a relatively brief cycle of emission-dispersion-transformation-deposition. Globally, these account for about 47 Tg C y-1 from wet deposition of PM-BC, and 400 Tg C y-1 from deposition of dissolved organic carbon (DOC) in rainfall, which generally disturbs the global C cycle, and specifically those of urban centers and surrounding areas, permanently shifting the C budget of the soil, and altering its chemistry, which is important because the soil is considered, by far, as the main C sink in terrestrial ecosystems. However, once the deposited C begins interacting with soil components, its negative effects are not necessarily measurable in the soil environment. On the contrary, soils in which PM-BC is deposited may produce a negative bioenergy that subsequently shifts the biogeochemical C reactions towards those materials that are composed of more stable organic molecules, thereby increasing the recalcitrant C pool, and likely contributing to other soil organic C (SOC) stabilization mechanisms that increase C sequestration in soil. In addition, PM-BC plays an important role as a strong sorbent for common urban pollutants (e.g., trace elements and persistent organic pollutants). Therefore, the focus of this review is to synthesize the previously published reports of the effects of PM-BC on the physico-chemical mechanisms of long term C storage in soils

Comparative Study between Silvopastoral and Agroforest Systems on Soil Quality in a Disturbed Native Forest of South-Central Chile

Agroforestry systems (AFSs) have gained recognition as a land use strategy to address food security and climate change. They involve intentionally cultivating trees alongside crops and/or animals. AFSs cover approximately 5% of the global forest area and promote sustainable soil conservation, including soil organic carbon (C) sequestration (CSEQ). In some areas of Chile, AFSs are used to preserve the ecological value of native forests. This study evaluates the effects of two AFSs, namely, an agroforest for fodder production (AGROFRST) and Silvopastoral (SPS), within a degraded native forest (Nothofagus obliqua sp.). The evaluation focuses on their impact on CSEQ capacity and soil quality (SQ), using soil quality indexes (SQIs) derived from 30 soil quality indicators (SINDs) related to physical, chemical, and microbiological properties at two depths (0–5 and 5–20 cm). The results for the total depth analyzed (0–20 cm) indicate an average CSEQ of 6.88 and 4.83 Mg C yr−1 and a global SQI of 37.8% and 31.0% for AGROFRST and SPS, respectively. Among the thirteen SINDs that demonstrated significant differences (p +, Ca2+, S, ECEC, and AlSAT), three differed between AGROFRST and SPS (BD, NH4+, NO3−), while SOC, K+, and Mg2+ varied across all conditions (e.g., combinations of systems and depths), and β-GLU and NMIN differed in a single condition. However, almost all 30 SINDs analyzed showed higher values at the 0–5 cm depth, indicating the positive effects of soil organic matter (SOM)/SOC additions. Significant interactions (Pearson’s correlation) revealed that SOC correlated with most SINDs (e.g., N, NH4+, P+, K+, Ca2+, Mg2+, S, ECEC, NMIN). These findings suggest that both AGROFRST and SPS systems have similar capabilities in restoring the ecological value of native Nothofagus forests while providing conditions for productive and complementary use. This sustainable option offers opportunities for cattle production alongside ecological restoration efforts and provides a possible strategy to generate public policies related to the ecosystem services of agroforestry systems

CHLSOC : the Chilean Soil Organic Carbon database, a multi-institutional collaborative effort [Data Paper]

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 x 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 a