Our knowledge of the rhizosphere bacterial communities in deep soils and the role of Eucalyptus and Acacia on the structure of these communities remains very limited. In this study, we targeted the bacterial community along a depth profile (0 to 800 cm) and compared community structure in monospecific or mixed plantations of Acacia mangium and Eucalyptus grandis. We applied quantitative PCR (qPCR) and sequence the V6 region of the 16S rRNA gene to characterize composition of bacterial communities. We identified a decrease in bacterial abundance with soil depth, and differences in community patterns between monospecific and mixed cultivations. Sequence analysis indicated a prevalent effect of soil depth on bacterial communities in the mixed plant cultivation system, and a remarkable differentiation of bacterial communities in areas solely cultivated with Eucalyptus. The groups most influenced by soil depth were Proteobacteria and Acidobacteria (more frequent in samples between 0 and 300 cm). The predominant bacterial groups differentially displayed in the monospecific stands of Eucalyptus were Firmicutes and Proteobacteria. Our results suggest that the addition of an N2-fixing tree in a monospecific cultivation system modulates bacterial community composition even at a great depth. We conclude that co-cultivation systems may represent a key strategy to improve soil resources and to establish more sustainable cultivation of Eucalyptus in Brazil.

Intercropping forest plantations of Eucalyptus with nitrogen-fixing trees can increase soil N inputs and stimulate soil organic matter (OM) cycling. However, microbial indicators and their correlation in specific fractions of soil OM are unclear in the tropical sandy soils. Here, we examined the microbial indicators associated with C and N in the soil resulting from pure and intercropped Eucalyptus grandis and Acacia mangium plantations. We hypothesized that introduction of A. mangium in a Eucalyptus plantation promotes changes in microbial indicators and increases C and N concentrations on labile fractions of the soil OM, when compared to pure eucalyptus plantations. We determined the microbial and enzymatic activity, and the potential for C degradation by the soil microbial community. Additionally, we evaluated soil OM fractions and litter parameters. Soil (0–20 cm) and litter samples were collected at 27 and 39 months after planting from the following treatments: pure E. grandis (E) and A. mangium (A) plantations, pure E. grandis plantations with N fertilizer (E+N) and an E. grandis, and A. mangium intercropped plantations (E+A). The results showed that intercropped plantations (E+A) increase 3, 45, and 70% microbial biomass C as compared to A, E+N, and E, at 27 months after planting. The metabolic quotient (qCO2) showed a tendency toward stressful values in pure E. grandis plantations and a strong correlation with dehydrogenase activity. A and E+A treatments also exhibited the highest organic fractions (OF) and C and N contents. A canonical redundancy analysis revealed positive correlations between microbial indicators of soil and litter attributes, and a strong effect of C and N variables in differentiating A and E+A from E and E+N treatments. The results suggested that a significant role of A. mangium enhance the dynamics of soil microbial indicators which help in the accumulation of C and N in soil OF in intercropped E. grandis plantations. Our results are mostly relevant to plantations in sandy soil areas with low levels of OM, suggesting and efficient method for improving nutrient availability in the soil and optimizing eucalyptus growth and development.

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Sustainable agronomic practices are tried all over the world to promote safe and ecofriendly crop production. Therefore, in the present study, the effect of seed endophytic bacteria and its consortium on soil biochemical property and yield of chickpea (Cicer arietinum L.) under field and pot conditions are investigated. Both the experimental results proved a significant increase in total soil organic carbon (OC), electric conductivity (EC), organic matter (OM), and soil nutrients like available N, P, and K content and important soil enzymes like dehydrogenase (DHA), beta glucosidase, alkaline phosphate, urease, and microbial population in soil was observed under the Enterobacter hormaechei BHUJPCS-15 (T 1 ), Enterobacter cloacae BHUJPCS-21 (T 2 ), and combined T 3 (consortium of T 1 and T 2 ) treatments. Similarly, a significant increase in the grain yield (27-45% and 57-73%) in microbial treatment was found in pot and field experiments, respectively, than in control. In addition, whereas the higher plant biomass (14-38% and 42-78%) was recorded in treated plant over the control plant. Similarly, the plant photosynthetic pigments (Chl a, b, total Chl) were increased in microbial treated plant than the control untreated chickpea plant. Consortium of endophytes were recorded effective result for enhancing plant growth attributes, productivity, and soil health. The consortium can be further used as biofertilizers for sustainable chickpea production. Our present study highlights the significance of sustainable agronomic practices for improving the soil quality and agricultural yield while reducing adverse impacts of chemicals by the use of seed endophytic microbes and its consortium.chickpea, microbial consortium, plant growth promoting microbes (PGPM), seed endophytes, soil health and fertility | INTRODUCTIONRecently, the main problem around the world agriculture is the loss of soil quality and fertility. Due to loss of organic matter (OM) and decomposition of different chemicals into the agricultural soil, productivity of agricultural crops reduces. Currently, other major problems are random industrialization, urbanization, and cutting of natural forest. In addition, the poor agro-waste management practices increase the greenhouse gas emissions, random chemical use leads to loss of soil quality and fertility along with the loss of soil biodiversity (Abhilash et al., 2016). Furthermore, the overgrowth of population around the world requires more quality food in limited fertile soils.

There are lack of studies regarding the effects of microbial diversity on specific soil functions, such as pesticides degradation. This study evaluated the role of bacterial community diversity and biochar on chlorothalonil (CTN) degradation, using ‘dilution to extinction’ approach, PCR-DGGE/16S rRNA gene technique, and radiorespirometry (14C-CTN). Biochar and microbial community dilution affected structure of the microbial community. In spite of that, CTN mineralization was slow, but dissipation was very fast (D50 < 1.0 d) due to immediate chemical degradation and formation of non-extractable (bound) residues. However, any depletion on soil microbial diversity strongly affected CTN mineralization, suggesting that this function is related to less abundant but specific microbial groups (CTN degraders) or to soil microbial diversity. The extent of these effects will strongly depend on the compound nature (recalcitrance) and soil matrix/substrate (bioavailability). It can be corroborated by the fact that biochar affected CTN sorption, its bioavailability, and subsequently its mineralization rate in the NS. These data indicate a strong relationship between soil microbial diversity and pesticide degradation, which is an acting form to mitigate xenobiotics accumulation in the environment.

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