Interspecific Plant Interactions Reflected in Soil Bacterial Community Structure and Nitrogen Cycling in Primary Succession

Abstract

Past research demonstrating the importance plant-microbe interactions as drivers of ecosystem succession has focused on how plants condition soil microbial communities, impacting subsequent plant performance and plant community assembly. These studies, however, largely treat microbial communities as a black box. In this study, we sought to examine how emblematic shifts from early successional Alnus viridus ssp. sinuata (Sitka alder) to late successional Picea sitchensis (Sitka spruce) in primary succession may be reflected in specific belowground changes in bacterial community structure and nitrogen cycling related to the interaction of these two plants. We examined early successional alder-conditioned soils in a glacial forefield to delineate how alders alter the soil microbial community with increasing dominance. Further, we assessed the impact of late-successional spruce plants on these early successional alder-conditioned microbiomes and related nitrogen cycling through a leachate addition microcosm experiment. We show how increasingly abundant alder select for particular bacterial taxa. Additionally, we found that spruce leachate significantly alters the composition of these microbial communities in large part by driving declines in taxa that are enriched by alder, including bacterial symbionts. We found these effects to be spruce specific, beyond a general leachate effect. Our work also demonstrates a unique influence of spruce on ammonium availability. Such insights bolster theory relating the importance of plant-microbe interactions with late-successional plants and interspecific plant interactions more generally.

Keywords: bacterial community; glacier forefield; nitrogen cycling; plant microbiome; plant–microbe interactions; plant–plant interactions; primary succession; soil.

FIGURE 1

Map of Mendenhall Glacier and forefield, sampling locations, and extent of glacial cover at various years. Darkest blue color is the existing glacier, medium blue is the glacial lake, and light blue is exposed ground. Soil collection sites for increasing alder dominance are marked.

FIGURE 2

Principal Coordinates Analysis (PCoA) based on phylogenetic dissimilarity of microbial communities associated with end of experimental leachate addition microcosms. Green = control, Red = alder leachate, and Blue = Spruce leachate.

FIGURE 3

Relative change in microbial taxa at genus level with alder and spruce leachate addition in comparison with controls for major taxa [bars represent standard error; asterisk indicates significant differences (P < 0.05)].