Organic enrichment of sediments reduces arbuscular mycorrhizal fungi in oligotrophic lake plants

TY - JOUR

T1 - Organic enrichment of sediments reduces arbuscular mycorrhizal fungi in oligotrophic lake plants

AU - Møller, Claus Lindskov

AU - Kjøller, Rasmus

AU - Jensen, Kaj Sand

PY - 2013/4

Y1 - 2013/4

N2 - 1.Arbuscular mycorrhizal fungi (AMF) commonly colonise isoetid species inhabiting oxygenated sediments in oligotrophic lakes but are usually absent in other submerged plants. We hypothesised that organic enrichment of oligotrophic lake sediments reduces AMF colonisation and hyphal growth because of sediment O2 depletion and low carbon supply from stressed host plants. 2.We added organic matter to sediments inhabited by isoetids and measured pore-water chemistry (dissolved O2, inorganic carbon, Fe2+ and), colonisation intensity of roots and hyphal density after 135days of exposure. 3.Addition of organic matter reduced AMF colonisation of roots of both Lobelia dortmanna and Littorella uniflora, and high additions stressed the plants. Even small additions of organic matter almost stopped AMF colonisation of initially un-colonised L.uniflora, though without reducing plant growth. Mean hyphal density in sediments was high (6 and 15mcm-3) and comparable with that in terrestrial soils (2-40mcm-3). Hyphal density was low in the upper 1cm of isoetid sediments, high in the main root zone between 1 and 8cm and positively related to root density. Hyphal surface area exceeded root surface area by 1.7-3.2 times. 4.We conclude that AMF efficiently colonise isoetids in oligotrophic sediments and form extensive hyphal networks. Small additions of organic matter to sediments induce sediment anoxia and reduce AMF colonisation of roots but cause no apparent plant stress. High organic addition induces night-time anoxia in both the sediment and the plant tissue. Tissue anoxia reduces root growth and AMF colonisation, probably because of restricted translocation of nutrient ions and organic solutes between roots and leaves. Isoetids should rely on AMF for P uptake on nutrient-poor mineral sediments but are capable of growing without AMF on organic sediments.

AB - 1.Arbuscular mycorrhizal fungi (AMF) commonly colonise isoetid species inhabiting oxygenated sediments in oligotrophic lakes but are usually absent in other submerged plants. We hypothesised that organic enrichment of oligotrophic lake sediments reduces AMF colonisation and hyphal growth because of sediment O2 depletion and low carbon supply from stressed host plants. 2.We added organic matter to sediments inhabited by isoetids and measured pore-water chemistry (dissolved O2, inorganic carbon, Fe2+ and), colonisation intensity of roots and hyphal density after 135days of exposure. 3.Addition of organic matter reduced AMF colonisation of roots of both Lobelia dortmanna and Littorella uniflora, and high additions stressed the plants. Even small additions of organic matter almost stopped AMF colonisation of initially un-colonised L.uniflora, though without reducing plant growth. Mean hyphal density in sediments was high (6 and 15mcm-3) and comparable with that in terrestrial soils (2-40mcm-3). Hyphal density was low in the upper 1cm of isoetid sediments, high in the main root zone between 1 and 8cm and positively related to root density. Hyphal surface area exceeded root surface area by 1.7-3.2 times. 4.We conclude that AMF efficiently colonise isoetids in oligotrophic sediments and form extensive hyphal networks. Small additions of organic matter to sediments induce sediment anoxia and reduce AMF colonisation of roots but cause no apparent plant stress. High organic addition induces night-time anoxia in both the sediment and the plant tissue. Tissue anoxia reduces root growth and AMF colonisation, probably because of restricted translocation of nutrient ions and organic solutes between roots and leaves. Isoetids should rely on AMF for P uptake on nutrient-poor mineral sediments but are capable of growing without AMF on organic sediments.

U2 - 10.1111/fwb.12083

DO - 10.1111/fwb.12083

M3 - Journal article

SN - 0046-5070

VL - 58

SP - 769

EP - 779

JO - Freshwater Biology

JF - Freshwater Biology

IS - 4

ER -