Forest Soil Bacteria: Diversity, Involvement in Ecosystem Processes, and Response to Global Change

Abstract

The ecology of forest soils is an important field of research due to the role of forests as carbon sinks. Consequently, a significant amount of information has been accumulated concerning their ecology, especially for temperate and boreal forests. Although most studies have focused on fungi, forest soil bacteria also play important roles in this environment. In forest soils, bacteria inhabit multiple habitats with specific properties, including bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are shaped by nutrient availability and biotic interactions. Bacteria contribute to a range of essential soil processes involved in the cycling of carbon, nitrogen, and phosphorus. They take part in the decomposition of dead plant biomass and are highly important for the decomposition of dead fungal mycelia. In rhizospheres of forest trees, bacteria interact with plant roots and mycorrhizal fungi as commensalists or mycorrhiza helpers. Bacteria also mediate multiple critical steps in the nitrogen cycle, including N fixation. Bacterial communities in forest soils respond to the effects of global change, such as climate warming, increased levels of carbon dioxide, or anthropogenic nitrogen deposition. This response, however, often reflects the specificities of each studied forest ecosystem, and it is still impossible to fully incorporate bacteria into predictive models. The understanding of bacterial ecology in forest soils has advanced dramatically in recent years, but it is still incomplete. The exact extent of the contribution of bacteria to forest ecosystem processes will be recognized only in the future, when the activities of all soil community members are studied simultaneously.

Keywords: bacteria; decomposition; ecosystem processes; forest ecology; global change; litter; nutrient cycling; soil.

FIG 1

Distribution of temperate and boreal forests in the Northern Hemisphere. Natural areas of deciduous and mixed temperate forest (light green) and evergreen coniferous forest (dark green) are shown in green, and natural areas occupied by boreal forests are shown in blue. The regions in which microbial communities inhabiting soil have been studied are shown as dots. The bottom images show forest ecosystems dominated by Quercus, Pinus, Fagus, and Picea trees.

FIG 2

Drivers of bacterial community composition in forest soils and features of bacterial ecology in the rhizosphere, litter/deadwood, and soil compartments of the forest floor.

FIG 3

Schematic view of the coupled biogeochemical cycles of carbon, nitrogen, and phosphorus in forest ecosystems. Colored arrows show the transfer of elements (C in orange, N in green, and P in blue) between ecosystem compartments. Ecological processes with the active involvement of bacteria are highlighted in bold.