Soil Bacterial and Archaeal Communities and Their Potential to Perform N-Cycling Processes in Soils of Boreal Forests Growing on Well-Drained Peat

Abstract

Peatlands are unique wetland ecosystems that cover approximately 3% of the world’s land area and are mostly located in boreal and temperate regions. Around 15 Mha of these peatlands have been drained for forestry during the last century. This study investigated soil archaeal and bacterial community structure and abundance, as well as the abundance of marker genes of nitrogen transformation processes (nitrogen fixation, nitrification, denitrification, and dissimilatory nitrate reduction to ammonia) across distance gradients from drainage ditches in nine full-drained, middle-aged peatland forests dominated by Scots pine, Norway spruce, or Downy birch. The dominating tree species had a strong effect on the chemical properties (pH, N and C/N status) of initially similar Histosols and affected the bacterial and archaeal community structure and abundance of microbial groups involved in the soil nitrogen cycle. The pine forests were distinguished by having the lowest fine root biomass of trees, pH, and N content and the highest potential for N fixation. The distance from drainage ditches affected the spatial distribution of bacterial and archaeal communities (especially N-fixers, nitrifiers, and denitrifiers possessing nosZ clade II), but this effect was often dependent on the conditions created by the dominance of certain tree species. The composition of the nitrifying microbial community was dependent on the soil pH, and comammox bacteria contributed significantly to nitrate formation in the birch and spruce soils where the pH was higher than 4.6. The highest N2O emission was recorded from soils with higher bacterial and archaeal phylogenetic diversity such as birch forest soils. This study demonstrates that the long-term growth of forests dominated by birch, pine, and spruce on initially similar organic soil has resulted in tree-species-specific changes in the soil properties and the development of forest-type-specific soil prokaryotic communities with characteristic functional properties and relationships within microbial communities.

Morphological Variation in Absorptive Roots in Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) Forests Growing on Drained Peat Soils

“…In one of the spruce stands (S3), the most distant plot from the ditch was at 40 m, and plots at 5 m and 15 m were duplicated toward the next ditch at the same stand. A detailed description of the study sites and soil properties (Table 1) is available in a previously published paper by our team [9]. Briefly, all stands were classified as a drained Oxalis forest site type [36] and soils were classified as histosols [37].…”

“…Table 1. Geographical coordinates, and means ± standard errors of fine root biomass and soil characteristics of the four sampling plots per stand (B1-B3, birch stands; S1-S3, spruce stands) and of the three replicate stands per birch and spruce [9].…”

“…This is due to the enhanced aeration of the substrate and more rapid decomposition rate of organic matter, caused by lowered water table levels at distances near ditches [6,8]. Truu et al [9] showed that the distance from drainage ditches affected soil microbial communities; however, such an effect was dependent on the dominant tree species and the specific site conditions. Fine roots (diameter < 2 mm) are key peat-forming elements in peatland ecosystems [10] but are understudied in most trait-related research in peatland forest ecosystems.…”

“…is a late-successional conifer in boreal forests [35]. Recently, it has been shown that forests dominated by birch and spruce growing at initially similar drained histosols caused tree-species-specific changes in the soil chemical properties, including pH, nitrogen content (N), and C/N ratio, and affected the soil bacterial communities [9]. This study investigated the effect of distance from the ditch on the morphological variation in absorptive roots at drained histosols of forests dominated by Downy birch and Norway spruce.…”

Comparative Analyses of Phyllosphere Bacterial Communities and Metabolomes in Newly Developed Needles of Cunninghamia lanceolata (Lamb.) Hook. at Four Stages of Stand Growth

“…Host-plant-associated bacteria affect the growth, health, and nutrient absorption and cycling of the host plant, especially plant growth-promoting rhizobacteria (Chen et al, 2020 ; Swarnalakshmi et al, 2020 ). Previous studies of forest bacterial communities have focused on belowground processes, such as carbon sequestration, root activity, and litter decomposition (Prada-Salcedo et al, 2020 ; Truu et al, 2020 ; Yokobe et al, 2020 ). Little attention has been paid to the functions of foliar bacterial communities in forest ecosystems.…”