Most natural and semi-natural communities are limited by major
nutrients such as nitrogen (N) or phosphorus
(P), but most experiments on the effects of ozone on wild plants have used
nutrient-rich composts or soil. In order
to investigate interactions between ozone and low nutrient supply, two
artificially selected lines (ozone-resistant
and ozone-sensitive) of two populations Plantago major ssp. major
L. were grown on a sandy loam, with (HN) and
without (LN) addition of fertilizer. The soil was from a semi-natural grassland
that has never been fertilized.
Plants were exposed to either charcoal/Purafil®-filtered air (CF=<5
nl O3 l−1) or 70 nl O3 l−1
7 h d−1
from the seedling stage to seed production.
Poor growth (c. 25% of that in HN) of the low-nutrient plants,
and leaf concentrations of N and P showed that
the LN plants were severely nutrient-limited. In addition to affecting
the total dry mass of the plants, the nutrient
supply altered seed production, reproductive effort (number of seeds per
total mass) and root-to-shoot allocation.
Exposure to ozone had significant effects on physiology, growth, and seed
production that varied with population,
selection line, time, and plant development. There also were significant
interactions between ozone effects and
nutrient regime. In the Lullington Heath population, ozone reduced plant
dry weight at 4 wk only in the LN
treatment, and in the sensitive line of the Bush population, seed production
was reduced by ozone only in LN.
Therefore, contrary to what was expected, in the present experiment, plants
given the LN treatment were often
more sensitive to ozone than those grown under the high-nutrient regime.
This increase in sensitivity was despite
the fact that the LN treatment reduced stomatal conductance and ozone flux.
It is concluded that there are
potentially important interactions between ozone and low nutrient supply
that need further investigation, particularly under field conditions.