Below‐ground responses of silver birch trees exposed to elevated CO₂ and O₃ levels during three growing seasons

Abstract

Field-growing silver birch (Betula pendula Roth) clones (clone 4 and 80) were exposed to elevated CO 2 and O 3 in open-top chambers for three consecutive growing seasons (1999)(2000)(2001). At the beginning of the OTC experiment, all trees were 7 years old. We studied the single and interaction effects of CO 2 and O 3 on silver birch below-ground carbon pools (i.e. effects on fine roots and mycorrhizas, soil microbial communities and sporocarp production) and also assessed whether there are any clonal differences in these belowground CO 2 and O 3 responses. The total mycorrhizal infection level of both clones was stimulated by elevated CO 2 alone and elevated O 3 alone, but not when elevated CO 2 was used in fumigation in combination with elevated O 3 . In both clones, elevated CO 2 affected negatively light brown/orange mycorrhizas, while its effect on other mycorrhizal morphotypes was negligible. Elevated O 3 , instead, clearly decreased the proportions of black and liver-brown mycorrhizas and increased that of light brown/ orange mycorrhizas. Elevated O 3 had a tendency to decrease standing fine root mass and sporocarp production as well, both of these O 3 effects mainly manifesting in clone 4 trees. CO 2 and O 3 treatment effects on soil microbial community composition (PLFA, 2-and 3-OH-FA profiles) were negligible, but quantitative PLFA data showed that in 2001 the PLFA fungi : bacteria-ratio of clone 80 trees was marginally increased because of elevated CO 2 treatments. This study shows that O 3 effects were most clearly visible at the mycorrhizal root level and that some clonal differences in CO 2 and O 3 responses were observable in the below-ground carbon pools. In conclusion, the present data suggests that CO 2 effects were minor, whereas increasing tropospheric O 3 levels can be an important stress factor in northern birch forests, as they might alter mycorrhizal morphotype assemblages, mycorrhizal infection rates and sporocarp production.

Impact of Elevated O3 on Soil Microbial Community Function Under Wheat Crop

“…Soil respiration decreased beneath the trembling aspen (Coleman et al 1996), Pinus taeda L. seedlings (Edwards 1991), and wheat and soybean (Islam et al 2000) after being exposed to O 3 treatments. In contrast, soil respiration increased under O 3 stress in the experiment with silver birch (Betula pendula Roth) (Kasurinen et al 2005). These inconsistent results make it difficult to assess the impact of elevated O 3 concentration on C cycle processes that critically influence plant growth as well as climate change (Andersen and Rygiewicz 1995).…”

Structure and function of rhizosphere and non-rhizosphere soil microbial community respond differently to elevated ozone in field-planted wheat

“…However, in ponderosa pine (Pinus ponderosa), the total fungal and bacterial biomasses increased at low O 3 levels, and the total microbial biomass decreased at high O 3 levels, compared to the biomasses under the control treatment (Scagel and Andersen, 1997). O 3 has also been reported as having only slight effects on soil biomass in field-grown silver birch exposed to eO 3 in OTCs for 3 years (Kasurinen et al, 2005). O 3 may shift microbial structure without altering total microbial biomass, as has previously been found under eCO 2 (Phillips et al, 2002).…”

Shifts of functional gene representation in wheat rhizosphere microbial communities under elevated ozone

“…For example, a significant discrimination of sole-carbon source utilization patterns was observed for the wheat rhizosphere soil but not for the bulk soil, and the functional diversity of the rhizosphere microbial communities was reduced under eO 3 (Chen et al, 2009). Also, a few studies at the Aspen FACE site (Larson et al, 2002;Phillips et al, 2002;Chung et al, 2006;Holmes et al, 2006;Zak et al, 2007) and with open-top chambers (Kasurinen et al, 2005) or mesocosms (Kanerva et al, 2008) indicated that eO 3 altered the functional diversity, structure and/or metabolic potential of soil microbial communities. In this study, our results did not fully support the above hypothesis that eO 3 would alter the overall functional diversity and structure of rhizosphere microbial communities.…”

“…In recent years, most studies on the effect of eO 3 on rhizosphere microbial communities were largely based on open-top chambers, and the results mainly focused on the changes of microbial biomass and structure by phospholipid fatty acid analysis, denaturing gradient gel electrophoresis methods (Kasurinen et al, 2005;Chung et al, 2006;Kanerva et al, 2008), and/or singlestrand conformation polymorphism method (Dohrmann and Tebbe, 2005). Those studies indicated that eO 3 had little or significant effects on soil microbial communities with different plants/ecosystems.…”