Elsevier

Applied Soil Ecology

Volume 63, January 2013, Pages 120-126
Applied Soil Ecology

Moisture effects on microbial communities in boreal forest floors are stand-dependent

https://doi.org/10.1016/j.apsoil.2012.09.006Get rights and content

Abstract

Landscape level factors such as overstory canopy composition can have a profound effect on the ecology of microbial communities in boreal forest floors. However, factors influencing community composition at the microsite scale are still poorly described and understood. Here we explored moisture effects on microbial communities in forest floor derived from undisturbed trembling aspen and white spruce stands, two of the dominant trees in the boreal forest of western Canada. Forest floor samples were incubated in a laboratory experiment for a period of one month under a moisture regime ranging from moist to dry (field capacity, 60% of field capacity and wilting point). As in previous studies we found that the origin of the forest floor material had a strong effect on the microbial community. Additionally, we found that moisture manipulation did not alter the microbial communities of the white spruce forest floor. On the other hand, the moisture had a profound effect on the aspen forest floor, and resulted in structurally and functionally distinct microbial communities. This different response to moisture could be linked to the adaptation of microbial groups to the physical environment inherent to the aspen and spruce forest floors and provides an avenue to further work into microbial mediated biogeochemical processes in the boreal forest.

Highlights

► Microbial response to moisture manipulation was related to forest type. ► Moisture manipulation altered aspen microbial communities but not spruce. ► Response to moisture was linked to forest floor physical properties.

Introduction

The organic horizons, or forest floors, of forest soils are often much thinner than the underlying mineral soil horizons. Nevertheless, forest floors are at the forefront of a multitude of biogeochemical cycles and interactions between the biotic and abiotic components of forest ecosystems. Landscape scale factors including forest stand composition (Grayston and Prescott, 2005) along with human (Bååth et al., 1995) and natural disturbances such as fire (D’Ascoli et al., 2005) all play a role in determining the structure and function of the microbial community in the forest floors. Likewise, the community structure of forest floor microbes is the primary driver behind biogenic greenhouse gas release (Schimel and Gulledge, 1998) and nitrogen mineralization (Fraterrigo et al., 2006).

Larger scale factors such as stand composition can have quantifiable effects on forest floor chemical and physical properties (Vesterdal and Raulund-Rasmussen, 1998). However, describing large scale factors alone does not sufficiently capture the micro-environmental gradients present in forest floors. For example, physical attributes such as bulk density dictate the quantity and availability of moisture within the forest floor. Microbial communities exhibit adaptive resilience to wet-dry cycles when such conditions are present in situ (Frier et al., 2003, Griffiths et al., 2003, Lundquist et al., 1999). Conversely, moisture fluctuations can alter soil microbial community structure (Drenovsky et al., 2004), particularly for microbial communities from stable moisture environments (Frier et al., 2003).

The boreal landscape of Northern Alberta is predominantly composed of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.) stands. Research in the area has consistently shown that aspen and spruce forest floors have structurally and functionally distinct microbial communities (Hannam et al., 2006, Swallow et al., 2009). Aspen and spruce communities are able to retain their distinctiveness over time even when reciprocally transplanted into the other forest floor environment (Hannam et al., 2007). Past work in this region (Hannam et al., 2006, Hannam et al., 2007) has attributed microbial community differences to chemical properties such as pH. However, other factors influencing community composition have been less studied; in particular, aspen and spruce forest floors provide different physical habitats for microorganisms as aspen forest floors can have higher bulk density but be thinner than spruce forest floors (Redding et al., 2005).

In this study we investigated how the forest floor microbial communities under either aspen or spruce responded when exposed to different physical microenvironments generated by a gradient of soil moisture. Microbial community structural diversity was characterized using phospholipid fatty acid (PLFA) analysis which has successfully been used to fingerprint soil microorganisms across a broad range of ecosystems and is often times more sensitive at detecting community changes than other physiological and molecular methods (Ramsey et al., 2006). We described the functional diversity of the microbial communities using the MicroResp™ system developed by Campbell et al. (2003). This system utilizes the whole soil approach of the original multi-SIR developed by Degens and Harris (1997), but increases the speed and efficiency at which samples can be processed and has been shown to be more sensitive to changes of community function than other physiological based methods (Campbell et al., 2003).

Section snippets

Sample collection and experimental design

Material for the laboratory incubations was collected during the summer of 2008 from representative aspen and white spruce sites located within the boreal mixedwood plains of northwestern Alberta near Fort McMurray, Alberta. The mature aspen site had an overstory of trembling aspen interspersed with the occasional white spruce in the understory, while the mature spruce site was dominated almost entirely by white spruce. Collection of the forest floor material occurred along a 10 m transect at 1 m

Moisture retention

The amount of moisture retained at a specific retention pressure was related to the origin of the litter material. On average, the gravimetric water content for the spruce material was 123% for field capacity (FC), 118% for 60%FC and 111% for the wilting point (WP). Overall, aspen material held less gravimetric moisture at FC (110%), 60%FC (94%) and WP (74%) than spruce. Variation between sample moisture content was low with the coefficient of variation for samples within each moisture

Drivers of microbial community diversity

The chemical environment of the litter generated by the dominant trees and understory plants has often been offered as the primary explanation for the influence that plant communities have on the structure of forest floor microbial communities (Priha et al., 2001). In this study, the origin of the plant litter was a strong determinant of the structure and function of the microbial community. The air-drying of the litter most likely had a strong effect upon the microbial communities.

Acknowledgments

The authors would like to thank the National Science and Engineering Research Council of Canada for its support through a Discovery Grant to SAQ.

References (48)

  • W.J. Landesman et al.

    Response of soil microbial communities and the production of plant-available nitrogen to a two-year rainfall manipulation in the New Jersey Pinelands

    Soil Biol. Biochem.

    (2010)
  • E.J. Lundquist et al.

    Rapid response of soil microbial communities from conventional, low input, and organic farming systems to a wet/dry cycle

    Soil Biol. Biochem.

    (1999)
  • P.W. Ramsey et al.

    Choice of methods for soil microbial community analysis: PLFA maximizes power compared to CLPP and PCR-based approaches

    Pedobiologia

    (2006)
  • L.S. Ruamps et al.

    Microbial biogeography at the soil pore scale

    Soil Biol. Biochem.

    (2011)
  • M. Swallow et al.

    Microbial community structure and function: the effect of silvicultural burning and topographic variability in northern Alberta

    Soil Biol. Biochem.

    (2009)
  • P.J.K. Uikman et al.

    15N-mineralization from bacteria by protozoa grazing at different soil moisture regimes

    Soil Biol. Biochem.

    (1991)
  • R. Vargas et al.

    Protozoan predation of bacterial cells in soil aggregates

    FEMS Microbiol. Lett.

    (1986)
  • S.T. Williams et al.

    Studies on the ecology of actinomycetes in soil. vi. The influence of moisture tension on growth and survival

    Soil Biol. Biochem.

    (1972)
  • S.M. Adl et al.

    Protists in soil ecology and forest nutrient cycling

    Can. J. Forest Res.

    (2006)
  • E.G. Bligh et al.

    A rapid method for the total lipid extraction and purification

    Can. J. Biochem. Physiol.

    (1959)
  • P.J. Brennan

    Chemotaxonomic use of lipids – an overview

  • C.D. Campbell et al.

    A rapid microtiter plate method to measure carbon dioxide evolved from carbon substrate amendments so as to determine the physiological profiles of soil microbial communities by using whole soil

    Appl. Environ. Microbiol.

    (2003)
  • R. D’Ascoli et al.

    Functional diversity of the microbial community in Mediterranean maquis soils as affected by fires

    Int. J. Wildland Fire

    (2005)
  • J.L. Devore

    Probability and Statistics for Engineering and the Sciences

    (2000)
  • Cited by (0)

    View full text