Biogeochemistry

, Volume 115, Issue 1, pp 65–76

Root carbon inputs to the rhizosphere stimulate extracellular enzyme activity and increase nitrogen availability in temperate forest soils

Authors

    • Department of GeographyIndiana University
  • Alison Greco
    • Department of BiologyBoston University
  • John E. Drake
    • Department of BiologyBoston University
  • Adrien C. Finzi
    • Department of BiologyBoston University
Article

DOI: 10.1007/s10533-012-9818-9

Cite this article as:
Brzostek, E.R., Greco, A., Drake, J.E. et al. Biogeochemistry (2013) 115: 65. doi:10.1007/s10533-012-9818-9

Abstract

The exudation of carbon (C) by tree roots stimulates microbial activity and the production of extracellular enzymes in the rhizosphere. Here, we investigated whether the strength of rhizosphere processes differed between temperate forest trees that vary in soil organic matter (SOM) chemistry and associate with either ectomycorrhizal (ECM) or arbuscular mycorrhizal (AM) fungi. We measured rates of root exudation, microbial and extracellular enzyme activity, and nitrogen (N) availability in samples of rhizosphere and bulk soil influenced by four temperate forest tree species (i.e., to estimate a rhizosphere effect). Although not significantly different between species, root exudation ranged from 0.36 to 1.10 g C m−2 day−1, representing a small but important transfer of C to rhizosphere microbes. The magnitude of the rhizosphere effects could not be easily characterized by mycorrhizal associations or SOM chemistry. Ash had the lowest rhizosphere effects and beech had the highest rhizosphere effects, representing one AM and one ECM species, respectively. Hemlock and sugar maple had equivalent rhizosphere effects on enzyme activity. However, the form of N produced in the rhizosphere varied with mycorrhizal association. Enhanced enzyme activity primarily increased amino acid availability in ECM rhizospheres and increased inorganic N availability in AM rhizospheres. These results show that the exudation of C by roots can enhance extracellular enzyme activity and soil-N cycling. This work suggests that global changes that alter belowground C allocation have the potential to impact the form and amount of N to support primary production in ECM and AM stands.

Keywords

RhizosphereRoot exudationExtracellular enzymesOrganic N cyclingAmino acidsTemperate forestsMycorrhizal fungi

Supplementary material

10533_2012_9818_MOESM1_ESM.docx (24 kb)
Supplementary material 1 (DOCX 23 kb)
10533_2012_9818_MOESM2_ESM.tif (549 kb)
Supplementary material 2 (TIFF 549 kb)

Copyright information

© Springer Science+Business Media Dordrecht 2012