Carbon flux to woody tissues in a beech/spruce forest during summer and in response to chronic O<sub>3</sub> exposure

Abstract

Abstract. The present study compares the dynamics in carbon (C) allocation of adult deciduous beech (Fagus sylvatica) and evergreen spruce (Picea abies) during summer and in response to seven-year-long exposure with twice-ambient ozone (O 3 ) concentrations (2 × O 3 ). Focus was on the respiratory turn-over and translocation of recent photosynthates at various positions along the stems, coarse roots and soils. The hypotheses tested were that (1) 2 × O 3 decreases the allocation of recent photosynthates to CO 2 efflux of stems and coarse roots of adult trees, and that (2) according to their different O 3 sensitivities this effect is stronger in beech than in spruce.Labeling of whole tree canopies was applied by releasing 13 C depleted CO 2 (δ 13 C of −46.9 ‰) using a free-air stable carbon isotope approach. Canopy air δ 13 C was reduced for about 2.5 weeks by ca. 8 ‰ in beech and 6 ‰ in spruce while the increase in CO 2 concentration was limited to about 110 µl l −1 and 80 µl l −1 , respectively. At the end of the labeling period, δ 13 C of stem CO 2 efflux and phloem sugars was reduced to a similar extend by ca. 3-4 ‰ (beech) and ca. 2-3 ‰ (spruce). The fraction of labeled C (f E,new ) in stem CO 2 efflux amounted to 0.3 to 0.4, indicating slow C turnover of the respiratory supply system in both species.Elevated O 3 slightly stimulated the allocation of recently fixed photosynthates to stem and coarse root respiration in spruce (rejection of hypothesis I for spruce), but resulted in a significant reduction in C flux in beech (acceptance of hypotheses I and II). The distinct decrease in C allocation to Correspondence to: T. E. E. Grams (grams@tum.de) beech stems indicates the potential of chronic O 3 stress to substantially mitigate the C sink strength of trees on the longterm scale.

Stable Isotopes in Tree Rings: Inferring Physiological, Climatic and Environmental Responses

“…At the whole tree level, elevated O 3 affects allocation processes of photoassimilates. In mature trees, longterm exposure to twice ambient O 3 concentrations significantly reduced allocation to stems (Ritter et al 2011), which is well in line with the often-found reduction of stem growth in natural environments with high O 3 exposure (Karnosky et al 2005). Below ground, O 3 impaired source-sink relations are believed to reduce belowground C allocation (reviewed by Andersen 2003, typically resulting in lower root/shoot biomass ratios.…”

Effects of Combined CO2 and O3 Exposures on Net CO2 Assimilation and Biomass Allocation in Seedlings of the Late-Successional Fagus Crenata

“…This suggests that F. crenata seedlings grown under the +CO 2 +O 3 allocated larger amounts of biomass to aboveground tissues than belowground tissues, resulting in higher S:R ratio and L:R ratio, and in lower RWR compared with other treatments (Table 3). Reduced C allocation into root has also been demonstrated in young [16,30,65] and mature trees of Fagus species under conditions of elevated O 3 [19]. However, in mature Fagus species, different responses to elevated O 3 were also observed, such as stimulation of root growth [66,67] and no changes in carbon allocation into belowground tissues [68].…”

“…Elevated CO 2 stimulates plant growth by enhancing photosynthetic carbon assimilation [10][11][12], although long-term exposure to elevated CO 2 results in photosynthetic down-regulation, especially under limiting nutrient conditions [13,14]. Elevated O 3 concentrations reduce net CO 2 assimilation (A) and accelerate leaf senescence [15,16], potentially resulting in substantial losses of the C-sink strengths in trees [9,[17][18][19][20].…”

“…Hence, O 3 exposure may alter the C metabolism and decrease C stocks for tree species, likely through changes in quantities or the compositions of nonstructural carbohydrates [24]. They may in turn alter C allocation in plants [19,25]. Increased O 3 concentrations have been shown to shift carbon allocation in favor of aboveground plant tissues, especially leaves, at the expense of root growth, presumably to allocate resources for detoxification and repair of damaged leaves [6,16,[26][27][28][29][30].…”

Preface "Stable Isotopes and Biogeochemical Cycles in Terrestrial Ecosystems''

“…Stress, e.g. induced by chronic ozone exposure, can reduce the allocation of recent photosynthates to stem and root respiration (Ritter et al, 2011;cf. also Brüggemann et al, 2011).…”