Journal list menu

Volume 72, Issue 2 p. 453-461
Forest, Range & Wildland Soils

The Influence of Soil Fertility on Rhizosphere Effects in Northern Hardwood Forest Soils

Richard P. Phillips

Corresponding Author

Richard P. Phillips

Department of Natural Resources, Cornell Univ., Ithaca, NY, 14853

Corresponding author ([email protected]).Search for more papers by this author
Timothy J. Fahey

Timothy J. Fahey

Department of Natural Resources, Cornell Univ., Ithaca, NY, 14853

Search for more papers by this author
First published: 01 March 2008
Citations: 57

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Abstract

Enhanced levels of microbial biomass and activity in the rhizosphere arise from labile C released from roots but the factors that mediate such “rhizosphere effects” are poorly understood. We hypothesized that the magnitude of rhizosphere effects would be reduced by increases in soil fertility, consistent with plant C allocation theory, which predicts decreased C flux to roots in fertile soils. Replicate plots of sugar maple (Acer saccharum Marshall) and northern red oak (Quercus rubra L.) at the Turkey Hill Plantations, New York, and yellow birch (Betula allenghaniensis Britton) at the Hubbard Brook Experimental Forest, New Hampshire, were fertilized from 2001 to 2003. In fall of 2003, rhizosphere and bulk soils were sampled from the organic horizon of control and fertilized plots and analyzed for microbial biomass and nutrient transformation rates. In general, fertilization reduced microbial biomass and activity in plots of all three species, and the magnitude of such effects was generally greater in rhizosphere than in bulk soil. In red oak soils, fertilization reduced rhizosphere effects on microbial biomass, net N mineralization rates, and phosphatase enzyme activity (P = 0.026, 0.091, and 0.061, respectively). In contrast, fertilization only reduced rhizosphere effects on microbial biomass in sugar maple soils (P = 0.019). In yellow birch soils, fertilization decreased rhizosphere effects on microbial biomass (P = 0.015). These results suggest that soil fertility may mediate the degree to which roots affect microbial activity in forest soils, possibly due to fertilizer-induced shifts in belowground C supply.