Table Of ContentBELOWGROUND RESPONSES TO RISING ATMOSPHERIC CO2
Developments in Plant and Soil Sciences
VOLUME 60
The titles published in this series are listed at the end of this volume.
Belowground Responses to Rising Atmospheric CO
2:
Implications for Plants, Soil Biota,
and Ecosystem Processes
Proceedings of a workshop held at the University of Michigan Biological Station,
Pellston, Michigan, USA, May 29-June 2, 1993
Edited by
P. S. CURTIS, E. G. O'NEILL, J. A. TEERI, D. R. ZAK and K. S. PREGITZER
Reprinted from Plant and Soil, Volume 165, No.1 (1994)
Springer-Science+Business Media, B.V.
A C.I.P. Catalogue record for this book is available from
the Library of Congress.
ISBN 978-90-481-4415-0 ISBN 978-94-017-0851-7 (eBook)
DOI 10.1007/978-94-017-0851-7
Printed on acid-free papers
All Rights Reserved
© 1995 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1995
No part of the material protected by this copyright notice
may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying,
recording, or by any information storage and retrieval
system, without written permission from the copyright
owner.
Contents
Preface VII
1. Belowground responses to rising atmospheric C02: Implications for plants, soil biota and
ecosystem processes. Executive summary
P.S. Curtis, E.G. O'Neill, I.A. Teeri, D.R Zak, K.S. Pregitzer
ROOT BIOLOGY
2. Issues and perspectives for investigating root responses to elevated atmospheric carbon dioxide
R.I. Norby 9
3. Root response to C02 enrichment and nitrogen supply in loblolly pine
A. Larigauderie, I.F. Reynolds, B.R. Strain 21
4. Free-air C02 enrichment of cotton: Vertical and lateral root distribution patterns
S.A. Prior, H.H. Rogers, G.B. Runion, G.R. Hendrey 33
5. Above- and belowground response of Populus grandidentata to elevated atmospheric C02 and
soil N availability
P.S. Curtis, D.R. Zak, K.S. Pregitzer, I.A. Teeri 45
SOIL BIOTA
6. Responses of soil biota to elevated atmospheric carbon dioxide
E.G. O'Neill 55
7. Soil microbial response in tall grass prairie to elevated CO2
C.W. Rice, F.O. Garcia, e.O. Hampton, C.E. Owensby 67
8. The response of mycorrhizal colonization to elevated C02 and climate change in Pascopyrum
smithii and Bouteloua gracilis
C.A. Monz, H.W. Hunt, F.B. Reeves, E.T. Elliott 75
9. Effect of elevated C02 on mycorrhizal colonization of loblolly pine (Pinus taeda L.) seedlings
I.D. Lewis, RB. Thomas, B.R Strain 81
10. Evaluation of the use of a model rhizodeposition technique to separate root and microbial
respiration in soil
J. Swinnen 89
VI Contents
ECOSYSTEM PROCESSES
11. Biomass production in a nitrogen-fertilized, tallgrass prairie ecosystem exposed to ambient and
elevated levels of C02
C.E. Owensby, L.M. Auen, P.I. Coyne 105
12. Effects of elevated C02 and nitrogen fertilization pretreatments on decomposition on tallgrass
prairie leaf litter
P.R. Kemp, D.G. Waldecker, C.E. Owensby, J.P. Reynolds, R.A Virginia 115
13. Soil pC02, soil respiration, and root activity in C02-fumigated and nitrogen-fertilized ponderosa
pine
D. Johnson, D. Geisinger, R. Walker, J. Newman, J. Vose, K. Elliot, T. Ball 129
14. Enhanced root system C-sink activity, water relations and aspects of nutrient acquisition in
mycotrophic Routeloua gracilis subjected to C02 enrichment
J.A Morgan, W.G. Knight, L.M. Dudley, H.W. Hunt 139
MODELLING
15. Modelling the below ground response of plants and soil biota to edaphic and climatic change -
What can we expect to gain?
S.D. Wullschleger, J.P. Lynch, G.M. Berntson 149
16. Carbon cost of root systems: An architectural approach
K.L. Nielsen, J.P. Lynch, AG. Jablokow, P.S. Curtis 161
Preface
There is an increasing recognition that interdisciplinary studies are required to improve scientific understanding
of the many complex environmental problems on earth. These studies will require an expansion in
communication and collaboration among researchers in numerous, and often previously disconnected, disciplines.
One example of this need is the research required to understand the potential responses of terrestrial ecosystems
to rising levels of atmospheric CO2, Many investigators now realize that the responses of soil biota and soil
processes will be important in determining the nature of terrestrial ecosystem responses to elevated atmospheric
CO2, This realization has resulted in new collaborations and the development of multidisciplinary research teams
with a greater range of expertise than has been the case in the past. This type of organizational framework is
defining the shape of much of the current research on the potential ecological impacts of elevated atmospheric
CO2,
We convened a workshop with the goal of increasing the integration of aboveground and belowground
perspectives in elevated CO research. Scientists representing a broad range of disciplines met to discuss our
2
current underst.mding of belowground responses to elevated atmospheric CO and to consider the implications
2
for plants, soil biota and ecosystem processes.
The workshop was held 29 May - 2 June, 1993, at the University of Michigan Biological Station at Douglas
Lake, Michigan, USA. Participants presented results of original research which are reported in the contributions
to this volume. We also divided into four working groups to consider the broader workshop objectives. The
findings of the working groups are presented in the Executive Summary. We would like to thank the editors
of Plant and Soil and Kluwer Academic Publishers for facilitating the timely appearance of this volume. We
also are most grateful to the organizations listed herein that provided financial support for the workshop.
Peter S. Curtis
Elizabeth G. O'Neill
James A. Teeri
Workshop Organizing Committee
Plant and Soil 165: 1-6, 1994.
© 1994 Kluwer Academic Publishers.
Belowground responses to rising atmospheric CO Implications for plants,
2:
soil biota and ecosystem processes
Executive summary
Peter S. Curtis 1, Elizabeth G. Q'Neill2, James A. Teeri3, Donald R. Zak:4 and Kurt S. Pregitze~
I Department of Plant Biology, The Ohio State University, Columbus, OH 432 J 0, USA, 2 Environmental Sciences
Division, Oak Ridge National Laboratory, P.o. Box 2008, Oak Ridge, TN 37831-6034, USA, 3Biological Station,
University ofM ichigan, Pellston, M149769, USA, 4 School of Natural Resources and Environment, University of
Michigan, Ann Arbor, MJ 48109, USA and 5 School of Forestry, Michigan Technological University, Houghton, M1
49931, USA
Introduction belowground systems from a hierarchical perspec
tive (sensu O'Neill et aI., 1986); i.e., to determine
As atmospheric C02 concentrations increase there how below ground proce~ses and organisms might con
almost certainly will be alterations in the flux of C strain ecosystem response to CO2 enrichment. This,
from plants to the soil. It is likely that such alterations of course, would require that below ground effects be
will be accompanied by changes in the allocation of considered in the context of negative and positive feed
C to organic structures and to soil processes. These backs, and the significance of these feedbacks or con
changes have the potential for further altering the struc straints to terrestrial ecosystems. Presented here is a
ture and function of terrestrial ecosystems. While there summary of key areas of uncertainty and an evaluation
has been increasing recognition of the importance of of research methodologies from each working group,
soil-mediated responses to global climate change, the followed by a statement of research priorities across
nature and magnitude of these responses are not well groups.
understood.
In an effort to expand our understanding of below
ground responses to rising atmospheric CO2, a work Root biology
shop ·.vas organized that resulted in the contributions
that are contained in this volume. The primary objec The extent to which the belowground represents a
tives of the workshop were to: significant constraint to ecosystem response to CO2
1) Assess the present level of understanding of below enrichment ultimately depends upon the allocation of
ground responses to elevated atmospheric CO2 and C to coarse or fine roots, i.e., to storage vs. resource
identify key areas where fundamental knowledge capture functions. Allocation to coarse roots should
was lacking; have little short-term effect on belowground function,
2) Evaluate existing and proposed methods for inves and would tend to buffer responses of ecosystems
tigating belowground responses to rising CO2; and to rising CO2. On the other hand, allocation to fine
3) Identify high priority research topics aimed at roots could have an immediate and significant effect
improving our understanding of below ground on belowground structure and function and extend to
responses to elevated C02 and the consequences the ecosystem level through changes in soil organic
for whole ecosystems. matter (SOM), effects on microbial communities and
Recognizing the wide range of processes and bio biomineralization, and eventual effects on plant com
ta spanned by considering "belowground responses", munity composition.
these objectives were addressed separately by four Significant changes in C fluxes into SOM could
working groups (Appendix I), covering: 1) Root biol occur with increases in atmospheric CO2 concentra
ogy, 2) Soil biota, 3) Ecosystem processes, and 4) tions. Questions of concern include coarse and fine
Modeling. Working groups were asked to consider root production, fine root longevity and tissue chem-
2
istry, the magnitude and role of exudation, and the through increased aboveground production and litter
contribution of mycorrhizae to these processes. fall. The magnitude of changes in quality or quantity
Increased C allocation to fine roots may increase of C input with rising C02 will determine whether
the total viable rhizosphere and bulk soil microbial soil biota in turn represent a significant constraint to
biomass, or induce shifts in microbial and mycorrhizal ecosystem functioning in a changing climate.
community structure (see below). Such shifts have the We do not know if present constraints exerted by
potential to alter patterns of biomineralization and soil soil biota will increase in importance as atmospheric
formation, change nutrient pool sizes, and affect the CO2 rises. Soil organisms vary in their sensitivity to
formation of SOM. We have very little information on changes in C input and in their impact on ecosystem
root-rhizosphere interactions at elevated CO2. processes. We need to identify which biotic groups reg
Finally, differential responses among plant species ulate these processes, assess the importance of species
in the dynamics of C allocation belowground with diversity and functional redundancy in regulation, and
rising C02 may lead to changes in plant communi determine the scales over which soil processes operate.
ty composition and hence to fundamental changes in Soil biota may be affected by rising CO at the
2
ecosystem-level processes. Indeed, changes in species organism, population or community levels. Although
composition due to CO2 effects on plant-plant interac all soil biota may ultimately feel the impact of chang
tions should have a greater impact on processes such ing C inputs to soil, several organisms were identi
as SOM formation and nutrient cycling than will C02- fied as critical to understanding soil system responses.
induced changes in plant tissue chemistry. Traditional Mycorrhizae are of key interest due to their impor
ly, emphasis has been placed on root physiological tance in linking roots to soil communities, their role in
responses when assessing the impact of plant-plant establishing and maintaining soil structure, and their
interactions on community composition. The degree dependence on plant-derived C. Future experiments
to which root morphology determines competitive out should avoid studies without normal levels of mycor
comes among plants is equally important and not well rhizal infection. Responses of organisms involved in
understood. The architecture of root systems, vertical nutrient transformations also deserve high priority.
and horizontal distribution of roots, and the plastic Finally, plant pathogens merit attention because of
ity of these features may constrain the potential for their potential to alter ecosystem structure and impact
adjustment and the ability of plants to more efficiently human society. For soil biota in general we may see
exploit soil resources. differential interspecific or even intraspecific respons
Methodologically, improved quantification of fine es to increased C input and consequent changes in
root turnover, the source of much of the C flowing to below ground community structure and process rates.
soil microbes, is essential. Wider application of non If environmental pressures force ecosystem migration,
destructive, repetitive video sampling using minirhi we need to know whether migration rates of soil organ
zotron and related technologies was recommended. isms and communities will prove to be a critical con
Measurement of fine root dynamics in a multi-species straint to plant movement.
setting remains problematic. Molecular methods and Detecting responses of soil communities and
new radio- and/or stable-isotope tracer methods must assessing the impact of those responses on the ecosys
be developed to better quantify the nature, amounts, tem are particularly difficult because the stressor (ele
and ultimate fate of compounds exuded by roots under vated CO2) is several levels removed from the com
field conditions. We are also lacking reliable meth munity of interest. Thus, the most important concep
ods for quantifying mycorrhizae and measuring their tual problems with regard to soil biota relate to scale
function in soil. and heterogeneity. Soil processes operate on a multi
tude of temporal and spatial scales; we must identify
the scales over which each soil process is important.
Soil biota There is a primary need to determine if, and to what
degree, changes in C input will influence the soil biota
Ecosystem processes that are mediated by soil bio in both the short term (transient) and the longer term
ta (e.g., biomineralization) are constrained by energy (years to decades). We must also learn to deal with
(C) input to the soil. This input is likely to increase the almost insurmountable degree of heterogeneity that
as C02 concentrations in the atmosphere rise, either exists in most soil systems. The latter will require con
through increased root production or exudation, or tinued development of statistical techniques designed
