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

Mohammad Bayranvand,Javad Gharechahi,Gholamreza Salehi Jouzani,Petr Baldrian,Moslem Akbarinia

doi:10.3389/fmicb.2021.660603

Abstract

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, β-xylosidase, β-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.

Highlights

In terrestrial ecosystems, forest soils, as the largest carbon (C) reservoir, play a pivotal role in C cycling (Nottingham et al, 2020) and can potentially affect nitrogen (N) dynamics (Ndossi et al, 2020)
The lowest soil C/N ratio was recorded at the 0-m altitude, and its content increased with altitude, in beech forests (Table 2)
Our findings indicate that N stock increases under plain mixed forest, which likely results from increased soil temperature (ST), tree diversity, litter N, microbial biomass nitrogen (MBN), pH, and leucine/alanine aminopeptidase enzymes

Summary

Introduction

Forest soils, as the largest carbon (C) reservoir, play a pivotal role in C cycling (Nottingham et al, 2020) and can potentially affect nitrogen (N) dynamics (Ndossi et al, 2020). Altitude has long been considered a potential driver of soil nutrient turnover through its influence on the biotic and abiotic components of forest ecosystems (Gebrewahid et al, 2018). Climatic conditions (i.e., decreased temperature and humidity) are heavily influenced by altitude, which in turn affects vegetation distribution/composition and alters the quality and quantity of litter/soil characteristics and C loss (Kotas et al, 2018; Quan et al, 2019). Recent studies have documented how changes in climatic conditions and forest canopy composition associated with altitude can affect the litter decomposition rate (Cardelli et al, 2019), soil microbial/enzyme activities (Feng et al, 2019; D’Alò et al, 2021), and nutrient storage in different ways (Bello et al, 2015)

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