Interactive effects of ozone and soil volume on Plantago major

Abstract

SUMMARYPlantago major L. ssp. major usually grows on trampled paths, tracks and gateways, and its root system is often restricted by compaction or by a limited volume of soil. In this heterogeneous environment, individuals close to each other will experience variable degrees of root restriction. As some populations of P. major have been demonstrated to be sensitive to ozone, the aim of this study was to investigate the effect of root restriction on the response of P. major to ozone.It was hypothesized that root restriction should reduce the effects of ozone. If this is true it would have implications for evolution of ozone resistance. A single population of P. major was grown in controlledenvironment chambers and exposed to either charcoal/Purafil-filtered air or to ozone (70 nl O3 1"^^ for 7 h d"~^). Plants were grown in pots of four different volumes: 0-175 1; 0-365 1; 2-280 1; and 5-830 1. Four harvests were performed, at 21, 37, 51 and 91 d from germination. At the final harvest, the total nitrogen content of leaf tissue was analysed and compared with that of plants collected from the field. Stomatal conductance {g^ and net carbon assimilation {A) rate were also recorded during development.Plants grown in the smallest pots exhibited severely impaired growth, lower ^^ and lower A than non-restricted plants. Root growth w-as less impaired than shoot growth. However, only plants in the smallest pots resembled those found in the field, which implies that realistic assessment of ozone effects on this species should involve a degree of root restriction. Appearance and leaf nitrogen content of leaves suggested that root restriction may have caused nitrogen deficiency. Contrary to the initial hypothesis, exposure to ozone reduced the grow-th of plants in all sizes of pot. Stomatal conductance was consistently lower in plants exposed to O3, but there w'as no effect of ozone on A.

The effects of nutrient limitation on the response of Plantago major to ozone

“…Similarly, in both populations, the effects of ozone on stomatal conductance were greater in the low-nutrient treatment. A reduction in g s is a commonly reported effect of ozone on P. major and is likely to be independent of the effect on photosynthetic capacity (Reiling & Davison, 1995 ;Pearson et al, 1996 ;Whitfield et al, 1996). Stomatal conductance was reduced in low-nutrient plants and was further reduced with exposure to ozone.…”

“…Thus, any reduction in leaf photosynthetic rates as a result of ozone exposure might be expected be inconsequential (Weinstein & Yanai, 1994). However, in previous work on Plantago major (Whitfield, Davison & Ashenden, 1996), we reported that seed production of plants in which the roots were severely restricted was further depleted by ozone.…”

“…Previous work has shown that 0n3-l pots produce plants that are about the same size as those found in the field. If larger pots are used, plants grow much larger than in nature (Whitfield et al, 1996). Analysis of the soil-nutrient content determined the following concentrations of nutrients in the soil : 73n3 µg N g −" of soil (9n3 NH % -N and 64 NO $ -NjNO # -N) ; 13n0 µg P g −" of soil ; 64n0 µg K g −" of soil ; 30n0 µg Na g −" of soil ; 430n0 µg Ca g −" of soil ; 30n4 µg Mg g −" of soil.…”

Plant–plant interactions and soil moisture might be important in determining ozone impacts on grasslands

“…Before more insight into the mechanisms can be obtained, no quantitative conclusions should be drawn with respect to ozone effects in the open field. The difficulty in extrapolating beyond the conditions of the experiment is further complicated because of possible interactions of the ozone effects with the amount of fertilizer applied, with the use of containers, or with the chamber climate (Whitfield et al, 1996(Whitfield et al, , 1998Nussbaum & Fuhrer, 2000). However, even if the effects observed here are modulated by these additional factors, it seems reasonable to assume that in qualitative terms they play an important role in real ecosystems.…”

Patterns of molecular genetic variation in Plantago major and P. intermedia in relation to ozone resistance

“…The study also demonstrates that some wild species may be able to adapt to higher ground-level O $ concentrations, and this may be reflected in changes in genetic composition. It has been reported that fitness of O $ -sensitive genotypes in the wild is possibly lower due to the production of less seed (Whitfield et al, 1996 ;Lyons & Barnes, 1998) and\or due to lower competitive ability, especially in the early phases of life (Berrang et al, 1988).…”