Journal Article

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

Finzi, Adrien C., Drake, John E., Brzostek, Edward R., Greco, Alison

2013

Overview

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.

• Publisher: Springer-Verlag,Springer,Springer Netherlands,Springer Nature B.V
• Subject: Acer saccharum / Acer saccharum subsp. saccharum / Acid soils / Amino acids / Animal and plant ecology / Animal, plant and microbial ecology / Arbuscular mycorrhizas / Availability / Bioavailability / Biogeosciences / Biological activity / Biological and medical sciences / Carbon / chemistry / Chitinase / Decomposition / Earth and Environmental Science / Earth Sciences / Earth, ocean, space / Ecosystems / ectomycorrhizae / Ectomycorrhizas / Environmental Chemistry / Enzymatic activity / Enzyme activity / Enzymes / Exact sciences and technology / Extracellular enzymes / Extracellular matrix / Exudation / Fagus / Forest soils / forest trees / Forests / Fraxinus / Fundamental and applied biological sciences. Psychology / Fungi / Geochemistry / Life Sciences / Microbial activity / Microorganisms / Nitrogen / nutrient availability / Organic matter / Plant roots / Plant species / Primary production / primary productivity / Rhizosphere / Rhizosphere microorganisms / root exudates / Roots / Saccharides / Soil / Soil and rock geochemistry / Soil biochemistry / Soil chemistry / Soil ecology / Soil enzymes / Soil microorganisms / Soil organic matter / Soils / Surficial geology / Synecology / Temperate forests / Terrestrial ecosystems / Trees / vesicular arbuscular mycorrhizae