HR: 14:40h
AN: B13B-05    [Abstracts]
TI: Crown-To-Rhizosphere Carbon Transfer In A Temperate Mixed Forest
AU: * Siegwolf, R T
EM: rolf.siegwolf@psi.ch
AF: Paul Scherrer Institut, OLFA / 109, Villigen, 5232 Switzerland
AU: Steinmann, K
EM: katharina.steinmann@wsl.ch
AF: University of Basel, Botanical Institute Schoenbeinstrasse 6, Basel, 4056 Switzerland
AU: Saurer, M
EM: matthias.saurer@psi.ch
AF: Paul Scherrer Institut, OLFA / 109, Villigen, 5232 Switzerland
AU: Koerner, C
EM: Ch.Koerner@unibas.ch
AF: University of Basel, Botanical Institute Schoenbeinstrasse 6, Basel, 4056 Switzerland
AB: Flux measurements across a range of (managed) European forests showed that ecosystem respiration amounts up to 80 percent of gross primary production (Janssens et al. 2001), the rest is in large sequestered into biomass. According to Malhi et al. (1999) soil respiration accounts for 60-70 percent of total forest ecosystem respiration. A considerable part is released as CO2 via belowground plant component (autotrophic) and soil micro-organism (heterotrophic) respiration. Recent studies on the autotrophic and heterotrophic respiratory fluxes indicate that the proportion of the autotrophic respiration was most likely underestimated (Hoegberg et al, 2001). Furthermore, highly diverging lengths of time have been estimated between the synthesis of carbohydrates and their availability in the rhizosphere. The goal of the presented study was to i) estimate the transport time for new photosynthates from the leaves to the rhizosphere, ii) determine the spatial distribution of these products, and iii) detect a seasonal course in the autotrophic and heterotrophic respiration of freshly formed assimilates. This study was carried out in a temperate mixed forest (The Swiss Canopy Crane Project in Hofstetten near Basel, Switzerland, cf. Pepin and Koerner 2002, Koerner et al, 2005), exposed to an elevated mean CO2 concentration of 530 ppm. The added CO2 originated from fossil fuel combustion and was depleted in 13C, thus serving as an ideal tracer. Based on the isotopic signature of the soil CO2 it was shown that freshly assimilated carbohydrates were transferred to the rhizosphere within ca. 5 days. The spatial variability was considerable and could mostly be explained with the varying tree population, whereas, the broad-leafed area revealed a more negative d13C value than the conifers. A distinct seasonal course in soil ?13C of the CO2 concentration indicated a seasonal variation in the crown-to-rhizosphere carbon transfer Steinmann et al (2004). Hoegberg P, et al. (2001) Large-scale forest girdling shows that current photosynthesis drives soil respiration. Nature, 411 (6839): 789-792. Pepin, S and Koerner C (2002). Web-FACE: a new canopy free-air CO2 enrichment system for tall trees in mature forests. Oecologia 133(1): 1-9. Janssens IA et al (2001) Productivity overshadows temperature in determining soil and ecosystem respiration across European forests. Global Change Biol 7:269-278 Malhi Y, Baldocchi DD, Jarvis PG (1999) The carbon balance of tropical, temperate and boreal forests. Plant Cell Environ 22:715-740 Koerner C, Asshoff R., Bignucolo O, Haettenschwiler S., Keel SG., Pela'ez-Riedl S., Pepin S, Siegwolf RTW., Zotz G. (2005). Carbon Flux and Growth in Mature Deciduous Forest Trees Exposed to Elevated CO2. Science, Vol. 309/Nr. 5739, pp. 1360-1362. Steinmann K., Siegwolf RTW, Saurer M., Koerner C. (2004) Carbon fluxes to the soil in a mature temperate forest assessed by 13C isotope tracing. Oecologia 141: 489-501
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
SC: Biogeosciences [B]
MN: Fall Meeting 2005