Distribution of Soil Extracellular Enzymatic, Microbial, and Biological Functions in the C and N-Cycle Pathways Along a Forest Altitudinal Gradient.

The diverse chemical, biological, and microbial properties of litter and organic matter (OM) in forest soil along an altitudinal gradient are potentially important for nutrient cycling. In the present study, we sought to evaluate soil chemical, biological, microbial, and enzymatic characteristics at four altitude levels (0, 500, 1,000, and 1,500 m) in northern Iran to characterize nutrient cycling in forest soils. The results showed that carbon (C) and nitrogen (N) turnover changed with altitude along with microbial properties and enzyme activity. At the lowest altitude with mixed forest and no beech trees, the higher content of N in litter and soil, higher pH and microbial biomass nitrogen (MBN), and the greater activities of aminopeptidases affected soil N cycling. At elevations above 1,000 m, where beech is the dominant tree species, the higher activities of cellobiohydrolase, arylsulfatase, ß-xylosidase, ß-galactosidase, endoglucanase, endoxylanase, and manganese peroxidase (MnP) coincided with higher basal respiration (BR), substrate-induced respiration (SIR), and microbial biomass carbon (MBC) and thus favored conditions for microbial entropy and C turnover. The low N content and high C/N ratio at 500-m altitude were associated with the lowest microbial and enzyme activities. Our results support the view that the plain forest with mixed trees (without beech) had higher litter quality and soil fertility, while forest dominated by beech trees had the potential to store higher C and can potentially better mitigate global warming.

Composition of soil bacterial and fungal communities in relation to vegetation composition and soil characteristics along an altitudinal gradient.

The objective of the present study was to evaluate how altitudinal gradients shape the composition of soil bacterial and fungal communities, humus forms and soil properties across six altitude levels in Hyrcanian forests. Soil microbiomes were characterized by sequencing amplicons of selected molecular markers. Soil chemistry and plant mycorrhizal type were the two dominant factors explaining variations in bacterial and fungal diversity, respectively. The lowest altitude level had more favorable conditions for the formation of mull humus and exhibited higher N and Ca contents. These conditions were also associated with a higher proportion of Betaproteobacteria, Acidimicrobia, Acidobacteria and Nitrospirae. Low soil and forest floor quality as well as lower bacterial and fungal diversity characterized higher altitude levels, along with a high proportion of shared bacterial (Thermoleophilia, Actinobacteria and Bacilli) and fungal (Eurotiomycetes and Mortierellomycota) taxa. Beech-dominated sites showed moderate soil quality and high bacterial (Alphaproteobacteria, Acidobacteria, Planctomycetes and Bacteroidetes) and fungal (Basidiomycota) diversity. Particularly, the Basidiomycota were well represented in pure beech forests at an altitude of 1500 m. In fertile and nitrogen rich soils with neutral pH, soil quality decreased along the altitudinal gradient, indicating that microbial diversity and forest floor decomposition were likely constrained by climatic conditions.

Changes of soil carbon dioxide, methane, and nitrous oxide fluxes in relation to land use/cover management.

Conversions of land use/cover are associated with changes in soil properties and biogeochemical cycling, with implications for carbon (C), nitrogen (N), and trace gas fluxes. In an attempt to provide a comprehensive evaluation of the significance of different land uses (Alnus subcordata plantation, Taxodium distichum plantation, agriculture, and deforested areas) on soil features and on the dynamics of greenhouse gas (GHG) fluxes at local scale, this study was carried out in Mazandaran province, northern Iran. Sixteen samples per land use, from the top 10 cm of soil, were taken, from which bulk density, texture, water content, pH, organic C, total N, microbial biomass of C and N, and earthworm density/biomass were determined. In addition, the seasonal changes in the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were monitored over a year. Our results indicated that the different land uses were different in terms of soil properties and GHG fluxes. Even though the amount of the GHG varied widely during the year, the highest CO2 and CH4 fluxes (0.32 mg CO2 m(-2) day(-1) and 0.11 mg CH4 m(-2) day(-1), respectively) were recorded in the deforested areas. N2O flux was higher in Alnus plantation (0.18 mg N2O m(-2) day(-1)) and deforested areas (0.17 mg N2O m(-2) day(-1)) than at agriculture site (0.05 mg N2O m(-2) day(-1)) and Taxodium plantation (0.03 mg N2O m(-2) day(-1)). This study demonstrated strong impacts of land use change on soil-atmosphere trace gas exchanges and provides useful observational constraints for top-down and bottom-up biogeochemistry models.