Effects of vegetation type on microbial biomass carbon and nitrogen in subalpine mountain forest soils

The effect of intercropping leguminous green manure on theanine accumulation in the tea plant: A metagenomic analysis

Intercropping is a widely recognised technique that contributes to agricultural sustainability. While intercropping leguminous green manure offers advantages for soil health and tea plants growth, the impact on the accumulation of theanine and soil nitrogen cycle are largely unknown. The levels of theanine, epigallocatechin gallate and soluble sugar in tea leaves increased by 52.87% and 40.98%, 22.80% and 6.17%, 22.22% and 29.04% in intercropping with soybean-Chinese milk vetch rotation and soybean alone, respectively. Additionally, intercropping significantly increased soil amino acidnitrogen content, enhanced extracellular enzyme activities, particularly β-glucosidase and N-acetyl-glucosaminidase, as well as soil multifunctionality. Metagenomics analysis revealed that intercropping positively influenced the relative abundances of several potentially beneficial microorganisms, including Burkholderia, Mycolicibacterium and Paraburkholderia. Intercropping resulted in lower expression levels of nitrification genes, reducing soil mineral nitrogen loss and N2 O emissions. The expression of nrfA/H significantly increased in intercropping with soybean-Chinese milk vetch rotation. Structural equation model analysis demonstrated that the accumulation of theanine in tea leaves was directly influenced by the number of intercropping leguminous green manure species, soil ammonium nitrogen and amino acid nitrogen. In summary, the intercropping strategy, particularly intercropping with soybean-Chinese milk vetch rotation, could be a novel way for theanine accumulation.

Agroforestry systems in the mid-hills of the north-western Himalaya: A sustainable pathway to improved soil health and climate resilience

Identifying the new tree crop combinations plays an important function in transforming the low input agriculture into land units with high economic returns, increasing carbon (C) sink and nutrients storage capacity, and acting as a panacea to achieve Sustainability Development Goals (SDGs). The present study aims to evaluate various tree-crop combinations for (i) biomass production, (ii) carbon accumulation, and (iii) soil nutrient enrichment of traditional and commercially evolved eight agroforestry systems (AFSs), including agri-silvi-horticulture system, agri-silviculture system, silvi-pasture, fruit tree, fodder tree, bamboo, melia and poplar based AFSs with sole cropping system in the mid-hill zone of the north-western Himalaya. The results demonstrated that poplar based AFS accumulated a higher amount of biomass (130.87 Mg ha-1) and carbon (65.44 Mg ha-1) closely followed by melia-based AFS. The C stored in leaf litter was higher (0.66 Mg ha-1) in poplar-based AFS, however, soil C stock was maximum (114.69 Mg ha-1) under bamboo-based AFS. Overall, the Melia based AFS exhibited a higher rate of carbon dioxide mitigation (19.30 Mg ha-1 yr-1) and C-sequestration (5.26 Mg ha-1 yr-1) than other studied AFSs. Moreover, soil macro-nutrients (available N, P, K, S and Ca) were maximum under bamboo-based AFS, on the other hand, the fruit-based AFS had the higher concentrations of micro-nutrients i.e., Cu (3.05), Fe (31.10 mg g-1) and Mn (17.31 mg g-1). The soil microbial counts were higher in poplar-based AFS, whereas, the soil quality index improved significantly under bamboo based and fruit tree based AFSs. Hence, it can be concluded that the experimentally evolved AFSs represent an effective approach for boosting C-sequestration, soil fertility, regenerating the soil and sustainability of hill agriculture in the north-western Himalayas over traditional AFSs and sole cropping.

Mechanisms Driving the Distribution and Activity of Mineralization and Nitrification in the Reservoir Riparian Zone

The riparian zone ecosystems have greater energy flow and elemental cycling than adjacent terrestrial and aquatic ecosystems. Mineralization and nitrification are important initiating processes in the nitrogen cycle, but their distribution and activity under different environmental conditions in the riparian zone and the driving mechanisms are still not clear. We investigated the effects of environmental and microbial factors on mineralization and nitrification activities by analyzing the community of alkaline (apr) and neutral (npr) metallopeptidase, ammonia-oxidizing archaea (AOA), and bacteria (AOB) in soils and sediments under different land-use types in the riparian zone of Miyun Reservoir, as well as measuring potential nitrogen mineralization and ammonia oxidation rates (AOR). The results showed that the mineralization and nitrification activities of soils were greater than those of sediments. AOA and AOB dominate the ammonia oxidation activity of soil and sediment, respectively. NH4+ content was a key factor influencing the ecological niche differentiation between AOA and AOB. The high carbon and nitrogen content of the woodland significantly increased mineralization and nitrification activity. Microbial communities were significantly clustered in the woodland. The land-use type, not the flooding condition, determined the distribution of microbial community structure. The diversity of npr was significantly correlated with potential N mineralization rates, while the transcript abundance of AOA was significantly correlated with ammonia oxidation rates. Our study suggests that environmental changes regulate the distribution and activity of mineralization and nitrification processes in the reservoir riparian zone by affecting the transcript abundance, diversity and community structure of the microbial functional genes.

Characterization of Rhizosphere Microbial Communities for Disease Incidence and Optimized Concentration of Difenoconazole Fungicide for Controlling of Wheat Dwarf Bunt

Rhizosphere soil microorganisms have great agricultural importance. To explore the relationship between rhizosphere microorganisms and the disease incidence, and to optimize the concentration of difenoconazole fungicide for the control of wheat dwarf bunt, caused by Tilletia controversa Kühn, the rhizosphere microorganisms were characterized based on sequencing methods. We found that the disease incidence correlated with the relative abundance of some microbial communities, such as Acidobacteria, Nocardioides, Roseiflexaceae, Pyrinomonadaceae, and Gemmatimonadaceae. Actinobacteria showed significant differences in the infected soils when compared to the control soils, and the relative abundance of Acidobacteria, Pyrinomonadaceae, Gemmatimonadaceae, and Saccharimonadales populations was distinctly higher in the T. controversa-inoculated group than in the control group. The members of Dehalococcoidia, Nitrosomonadaceae, and Thermomicrobiales were found only in T. controversa-inoculated soils, and these taxa may have potential effects against the pathogen and contribute to disease control of wheat dwarf bunt. In addition, for T. controversa-infected plants, the soil treated with difenoconazole showed a high relative abundance of Proteobacteria, Actinobacteria, Ascomycota, Basidiomycota, Mortierellomycota, and Olpidiomycota based on the heatmap analysis and ANOVA. Our findings suggest that the optimized concentration of fungicide (5% recommended difenoconazole) exhibits better control efficiency and constant diversity in the rhizosphere soil.

The interactions between tree-herb layer diversity and soil properties in the oriental beech (Fagus orientalis Lipsky) stands in Hyrcanian forest

This study investigated the interactions between tree-herb layer diversity and some physico-chemical and eco-physiological characteristics of soil in natural oriental beech stand in western Guilan, Iran. The data were collected from nine research sites (50 m × 50 m) which were described as a gradient from pure oriental beech (Fagus orientalis Lipsky) stands to mixed stands with up to nine deciduous tree species (n = 27) in Hyrcanian forest. Herbaceous plants were sampled within ten 1 m × 1 m sub-plots in two plots of 400 m² which were installed randomly in each research site. Composite soil samples were taken at five positions in each research site. We found that the increase in tree diversity in mature oriental beech stands brought about an increase in microbial biomass carbon, soil carbon content, and the ratio of microbial biomass carbon to the organic carbon (C_mic/C_org). Increased soil organic carbon raised microbial biomass carbon through creating suitable environment for microorganisms. The findings also indicated that the ratio of microbial biomass carbon to the organic carbon (C_mic/C_org) increased as a quantitative indicator of soil carbon dynamics that finally benefits soil fertility of mixed oriental beech stands compared to pure oriental beech stands. The results showed that humus layer and litter thickness were negatively correlated with tree layer richness. Generally, it can be stated that maintaining a mixture of tree layer species in natural oriental beech stands results in an increase in richness and diversity values of herb plants as well as carbon content and microbial biomass carbon of soil.