Competition increasingly dominates the responsiveness of juvenile beech and spruce to elevated CO₂ and/or O₃ concentrations throughout two subsequent growing seasons

Abstract

Saplings of Fagus sylvatica and Picea abies were grown in mono-and mixed cultures in a 2-year phytotron study under all four combinations of ambient and elevated ozone (O 3 ) and carbon dioxide (CO 2 ) concentrations. The hypotheses tested were (1) that the competitiveness of beech rather than spruce is negatively affected by the exposure to enhanced O 3 concentrations, (2) spruce benefits from the increase of resource availability (elevated CO 2 ) in the mixed culture and (3) that the responsiveness of plants to CO 2 and O 3 depends on the type of competition (i.e. intra vs. interspecific).Beech displayed a competitive disadvantage when growing in mixture with spruce: after two growing seasons under interspecific competition, beech showed significant reductions in leaf gas exchange, biomass development and crown volume as compared with beech plants growing in monoculture. In competition with spruce, beech appeared to be nitrogen (N)-limited, whereas spruce tended to benefit in terms of its plant N status.The responsiveness of the juvenile trees to the atmospheric treatments differed between species and was dominated by the type of competition: spruce growth benefited from elevated CO 2 concentrations, while beech growth suffered from the enhanced O 3 regime. In general, interspecific competition enhanced these atmospheric treatment effects, supporting our hypotheses. Significant differences in root : shoot biomass ratio between the type of competition under both elevated O 3 and CO 2 were not caused by readjustments of biomass partitioning, but were dependent on tree size.Our study stresses that competition is an important factor driving plant development, and suggests that the knowledge about responses of plants to elevated CO 2 and/or O 3 , acquired from plants growing in monoculture, may not be transferred to plants grown under interspecific competition as typically found in the field.

Density-dependent responses of Picea purpurea seedlings for plant growth and resource allocation under elevated temperature

“…However, the success of an individual plant generally depends on the ability to acquire resources from external pools (Kozovits et al 2005a). To ensure this, plant must allocate these resources into leaves and fine roots, which in turn are involved in the process of resource acquisition.…”

Competition Alters Responses of Juvenile Woody Plants and Grasses to Nitrogen Addition in Brazilian Savanna (Cerrado)

“…Our results also suggest that the responsiveness of plants to N deposition, as observed for other atmospheric nutrients or pollutants (Kozovits et al 2005) depends in part on the type of competition (intra-or interspecific) occurring, and that this needs to be take into account in models of vegetation dynamics in response to nutrient deposition.…”

Plant-Mediated Ecosystem Effects of Tropospheric Ozone

“…Phytotron studies to test O 3 effects on the competition between Fagus sylvatica and Picea abies revealed that the responses to O 3 strongly depended on the type of competition: although the response to O 3 of P. abies was not significantly affected by either intra-or interspecific competition, the competitive ability of this species was scarcely affected by O 3 as indicated by an enhanced aboveground growth of the competing F. sylvatica plants (Grams et al 2002;Kozovits et al 2005). Under conditions of interspecific competition, P. abies was found to be superior in nitrogen acquisition whereas F. sylvatica in turn appeared to be nitrogen-limited (Grams and Matyssek 2010;Kozovits et al 2005). Effects on nutrient efficiency indicate that processes of stress defence due to O 3 exposure trigger a nutrient demand at the expense of above-ground competition (Rodenkirchen et al 2009).…”