Effects of combined ozone and nitrogen deposition on the in situ properties of eleven key plant species of a subalpine pasture

Abstract

Tropospheric O(3) and deposition of reactive N threaten the composition and function of natural and semi-natural vegetation even in remote regions. However, little is known about effects of these pollutants individually or in combination on plant species in alpine habitats. We analyzed 11 frequent plant species of a subalpine Geo-Montani-Nardetum pasture exposed at 2,000 m a.s.l. in the Swiss Alps during 3 years using a factorial free-air exposure system with three concentrations of O(3) and five rates of N application. The aim was to detect subtle effects on leaf chlorophyll and N concentrations, leaf weight, specific leaf area (SLA), and delta(18)O and delta(13)C as proxies for gas exchange. We expected that the species' responsiveness to O(3) and N would be related to their functional traits and that N-induced changes in these traits would modify the species' response to O(3) via increased growth and higher leaf conductance (g (s)). Most species reacted to N supply with the accumulation of N and chlorophyll, but with no change in SLA, g (s), and growth, except Carex sempervirens which showed increased water use efficiency and leaf weight. Elevated O(3) reduced g ( s ) in most species, but this was not related to a reduction in leaf weight, which was recorded in half of the species. Contrary to our expectation, the magnitude of the response to both O(3) and N was not related to species-specific traits such as SLA or g (s). No pronounced O(3) x N interactions were observed. In conclusion, since for most species neither N nor gas exchange limited growth, their short-term response to O(3) and N and to their combination was small. O(3) x N interactive effects are expected to be more pronounced in habitats where species are more responsive to N due to favorable growth conditions in terms of nutrient availability and temperature.

The importance of considering origin in effects of nitrogen deposition on plant performance and competitive ability

“…vulgaris plants from all accessions responded positively to N addition in terms of a greater biomass production and increased chlorophyll and leaf N concentration, which is consistent with numerous N addition and fertilization experiments (e.g Van den Berg et al 2005;Bassin et al 2009;Bubier et al 2011)…”

Drivers of spatial variability in urban plant and soil isotopic composition in the Los Angeles basin

“…Elevated atmospheric O 3 has been reported to affect plant δ 13 C by altering plant gas exchange and carbon isotope discrimination (Gessler et al 2009;Inclán et al 2011;Jäggi and Fuhrer 2007) directly through oxidant damage to guard cells and mesophyll membrane that decreases stomatal control (Torsethaugen et al 1999) or indirectly through changes in photosynthetic enzymes (such as Rubisco) and internal CO 2 concentrations (Ci) (Andersen 2003;Zheng et al 2002). Under elevated O 3 concentrations, plant δ 13 C may be enriched (Jäggi and Fuhrer 2007) or unchanged (Bassin et al 2009;Gessler et al 2009;Jäggi and Fuhrer 2007) depending on species and the complex effects of O 3 on gas exchange as well as local microclimate.. These mechanisms are possible in our study; however, since all of the pollution variables are correlated with each other, and also with CO 2 concentrations, the causal mechanisms underlying the observed relationships are not known.…”

Spatial heterogeneity confounded ozone-exposure experiment in semi-natural grassland

“…However, results from physiological investigations point to the possibility of subtle ozone effects, which over much longer time scales may lead to changes at the community level. The observed changes include changes in carbon and oxygen stable isotopic signatures that indicate effects of ozone on the water economy of some species (Jäggi and Fuhrer 2007;Bassin et al 2009), or accelerated leaf senescence (Bassin et al 2007b).…”