Carbon flows into and out of the soil are important processes that contribute to controlling the global climate. The relationship between soil organisms and the climate is interdependent since the organisms that contribute to carbon and greenhouse gas fluxes are simultaneously affected by climate change and soil management. Temperature, soil moisture, pH, nutrient level, redox potential and organic matter quality are key elements affecting the microorganisms involved in organic carbon flows in the soil. Climate, topography (slope and position in the landscape), soil texture, soil mineralogy and land-use regulate those key elements and, thus, the C fluxes in the pedosphere. Soil microbes can increase carbon influx and storage by promoting plant growth, mycorrhizal establishment, and particle aggregation. Conversely, microorganisms contribute to carbon efflux from the soil via methanogenesis, rhizospheric activity, and organic carbon mineralization. Nevertheless, strategies and management practices could be used to balance out carbon emissions to the atmosphere. For example, carbon influx and storage in the soil can be stimulated by plant growth promoting microorganisms, greater plant diversity via crop rotation and cover crops, cultivating mycotrophic plants, avoiding or reducing the use of fungicides and adopting organic farming, no-tillage crop systems and conservative soil management strategies. Therefore, this review aimed to shed light on how soil microorganisms can contribute to increase C influxes to the soil, and its significance for climate change. Then, we also seek to gather the practical actions proposed in the scientific literature to improve carbon sequestration and storage in the soil. In summary, the review provides a comprehensive basis on soil microorganisms as key to carbon fluxes and helpers to lessen climate change by increasing carbon fixation and storage in agroecosystems via stimulation or application of beneficial microorganisms.

Arbuscular mycorrhizal fungi (AMF) play an important role in plant community productivity and structure, and so studying the factors that affect the diversity and structure of this fungal community is important for understanding their ecology in tropical forests. We investigated AMF spore communities and root colonization under three forest phytophysiognomies (Restinga Forest, REF; Lowland Ombrophilous Dense Forest, LLF; and Montane Ombrophilous Dense Forest, MTF). Spore abundance was lowest in LLF and highest in REF, with no statistical differences relative to MTF. Spore diversity indices and root colonization rates were not statistically different among the phytophysiognomies. However, principal components analysis revealed that AMF community structure differed according to forest phytophysiognomy. Hierarchical partitioning analysis indicated that most of the AMF community variables were better explained by phytophysiognomy than by chemical and physical attributes of the soil. In addition to the plant community, clay content, pH, Boron, P, S and CEC best explained some of the AMF community variables. Thus, we conclude that while several factors determine AMF community structure in the Atlantic Forest, phytophysiognomy is the most significant.

Processed organic agricultural byproducts such as liquid organic fertilizer (LOF) are promising alternatives that can improve crop productivity while reducing mineral fertilizer use and improving sustainability. The effects on beneficial soil organisms, such as arbuscular mycorrhizal (AM) fungi and phosphate solubilizing microorganisms (PSM), caused by LOF spraying on shoots is poorly understood. Therefore, we evaluated how AM colonization and soil PSM are affected by LOF spraying on common beans (Phaseolus vulgaris L.) grown in a greenhouse. The LOF was obtained by anaerobically fermenting a mixture of fresh water, cattle manure, bovine milk, sugarcane molasses and mineral salts. LOF was applied twice on the plant shoots. Fresh and dry mass of root and shoot, P content, P accumulation in the shoots and AMF spore counts in the soil were not LOF dose dependent. However, we found that a 5% LOF application stimulated AM colonization and led to dose-dependence for calcium and aluminium phosphate solubilizing bacteria and fungi. These results show that LOF sprayed on shoots causes responses on soil communities. We therefore endorse the use of LOF in low input agriculture.