Temporal patterns of carbon flow from grassland vegetation to soil microorganisms measured using 13C-labelling and signature fatty acids

Johanna Birgander,Pål Axel Olsson

doi:10.1007/s11104-021-04854-8

Abstract

PurposeWe investigated how the C flow from plants to microorganisms varies throughout the year in a temperate grassland. Additionally, we investigated how the C flow relates to saprotrophic activity and vegetation changes.MethodsIn situ stable isotope pulse labelling (13CO2) was employed to estimate the flow of recently plant-derived C to soil microorganisms by using signature fatty acids. Bacterial and fungal growth was estimated using radio-labelling in laboratory incubations.ResultsThe C flow from plants to arbuscular mycorrhizal (AM) fungi peaked during the warmer parts of the year, but saprotrophic microorganisms showed little temporal variation in C flow. Also saprotrophic fungi received considerable amounts of C from plants throughout the year. Bacterial and fungal growth showed temporal variation with a growth peak in August for both. This suggests a shift in the C source from mainly rhizosphere C in colder parts of the year, to older C-sources in warmer parts of the year (August).ConclusionWe conclude that AM fungi, saprotrophic fungi and bacteria differ in the amount of recently-fixed C they receive from plants throughout the year. Hence, temporal patterns need to be considered to understand ecosystem functioning. The studied plant community included winter annuals, which potentially maintain a high C flow to saprotrophic fungi during the cold season.

Highlights

IntroductionSeasonality in temperature and light affects plants, microorganisms and their interactions
In temperate ecosystems, seasonality in temperature and light affects plants, microorganisms and their interactions
Plants can still photosynthesise during the cold season, and photosynthesis has been measured at temperatures as low as 0 °C (Larsen et al 2007)

Summary

Introduction

Seasonality in temperature and light affects plants, microorganisms and their interactions. Both plants and microorganisms can be active during the winter season, despite low temperatures (Brooks et al 1997). Photosynthetic activity is low during the winter because of low temperature, and because of reduced light availability and soil moisture (Flanagan and Johnson 2005). Plants can still photosynthesise during the cold season, and photosynthesis has been measured at temperatures as low as 0 °C (Larsen et al 2007). Carbon (C) assimilation (Lekberg et al 2013) and nitrogen (N) uptake (Andresen and Michelsen 2005; Groffman et al 2001) in plants have been shown to occur in temperate ecosystems during the cold season. Soil respiration can be substantial in winter climate, often under a snow cover (Brooks et al 1997; Alm et al 1999; Larsen et al 2007)

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Conclusion