Environmental and Experimental Botany 43 2000 171 – 180
Effects of ozone on the production and utilization of assimilates in Plantago major
Youbin Zheng
1
, Tom Lyons , Jeremy Barnes
Air Pollution Laboratory, Department of Agricultural and En6ironmental Science, Ridley Building, The Uni6ersity, Newcastle Upon Tyne NE
1 7
RU, UK Received 14 August 1999; received in revised form 26 October 1999; accepted 28 October 1999
Abstract
The impact of ozone O
3
on the production and utilization of photoassimilates was examined in Plantago major population ‘Valsain’. Plants were exposed in controlled environment chambers to either charcoalPurafil
®
-filtered air CFA or CFA plus O
3
15 nmol mol
− 1
O
3
overnight rising to a maximum of 75 nmol mol
− 1
between 12:00 and 16:00 h. Measurements of leaf gas exchange and non-structural carbohydrate content were made on the youngest
fully expanded leaf after 28 and 42 days of O
3
exposure. Destructive harvests were made after 28 and 91 days. Impacts of O
3
on reproductive structures were assessed at the final harvest. Daily carbon budgets constructed for the youngest fully expanded leaf revealed that at the younger growth stage after 28 days exposure, net CO
2
assimilation rate as well as the amount and relative proportion of newly fixed carbon exported in the light were reduced in
O
3
-treated plants. As a result, non-structural carbohydrates mainly starch accumulated in source leaves during the day. ‘Costs’ associated with dark respiration were increased in O
3
-treated plants after 28 days fumigation. The effects of the pollutant on plant growth were consistent with shifts in leaf carbon metabolism; relative growth rate R
between 0 and 28 days fumigation was decreased by O
3
, but the pollutant caused a stimulation in R over the subsequent 63 days of the experiment. Despite this compensatory growth response, plants exhibited a reduction in
biomass and a decrease in the number of seeds produced per plant following exposure to environmentally relevant O
3
concentrations. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Assimilates; Growth rate; Ozone; Photosynthesis; Plant age; Respiration; Yield www.elsevier.comlocateenvexpbot
1. Introduction
Ozone O
3
is the most damaging air pollutant to which plants are exposed Chameides et al.,
1994. Current levels of the pollutant are high
Corresponding author. Tel.: + 44-191-222-6589; fax: + 44-191-222-5229.
E-mail address
:
t.m.lyonsncl.ac.uk T. Lyons
1
National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki, Japan.
S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 9 8 - 8 4 7 2 9 9 0 0 0 5 6 - 8
enough to cause significant decreases in the growth and yield of sensitive genotypes in many
parts of the world Heck et al., 1983; Wahid et al., 1995; Fuhrer et al., 1997. Numerous factors are
considered to underlie the decline in productivity induced by O
3
, including reduced photosynthetic capacity Darrall, 1989; Heath, 1994; Pell et al.,
1994, enhanced rates of maintenance respiration Amthor, 1988, and increased retention of fixed
carbon in source leaves Balaguer et al., 1995.
Plant responses to the pollutant vary both within and between species, and may be influ-
enced by the stage of growth andor leaf develop- ment Cooley and Manning, 1987; Fuhrer et al.,
1997; Danielsson et al., 1999. In addition, the impacts of O
3
are profoundly influenced by sev- eral other environmental factors Wolfenden and
Mansfield, 1991; Barnes et al., 1996; Barnes and Wellburn, 1998. Previous work on Plantago ma-
jor has demonstrated that geographically discrete populations exhibit wide variation in O
3
sensitiv- ity Reiling and Davison, 1992a; Lyons et al.,
1997; exposure of sensitive populations to envi- ronmentally relevant concentrations of the pollu-
tant causing decreases in the rate of net CO
2
assimilation Reiling and Davison, 1994, 1995; Whitfield et al., 1996, plant growth Reiling and
Davison, 1992a,b; Pearson et al., 1996; Lyons et al., 1997 and reproductive performance Reiling
and Davison, 1992b; Whitfield et al., 1996; Lyons and Barnes, 1998. However, O
3
-sensitive popula- tions may become more resistant to the pollutant
as plants age Reiling and Davison, 1992b; Lyons and Barnes, 1998, a phenomenon that has also
been documented in other species Blum and Heck, 1980; Walmsley et al., 1980; Lee et al.,
1988; Held et al., 1991; Kasana, 1991; Younglove et al., 1994.
The present study was undertaken to test the hypothesis that plant responses to O
3
are influ- enced by developmental age. An O
3
-sensitive pop- ulation of P. major ‘Valsain’; Lyons and Barnes,
1998; Lyons et al., 1999a was employed to exam- ine the effects of the pollutant on photosynthesis
and assimilate utilization by individual leaves at contrasting stages of plant growth.
2. Materials and methods
