Contrasting carbon allocation responses of juvenile European beech (Fagus sylvatica) and Norway spruce (Picea abies) to competition and ozone.

Allocation of recent photoassimilates of juvenile beech and spruce in response to twice-ambient ozone (2 × O(3)) and plant competition (i.e. intra vs. inter-specific) was examined in a phytotron study. To this end, we employed continuous (13)CO(2)/(12)CO(2) labeling during late summer and pursued tracer kinetics in CO(2) released from stems. In beech, allocation of recent photoassimilates to stems was significantly lowered under 2 × O(3) and increased in spruce when grown in mixed culture. As total tree biomass was not yet affected by the treatments, C allocation reflected incipient tree responses providing the mechanistic basis for biomass partitioning as observed in longer experiments. Compartmental modeling characterized functional properties of substrate pools supplying respiratory C demand. Respiration of spruce appeared to be exclusively supplied by recent photoassimilates. In beech, older C, putatively located in stem parenchyma cells, was a major source of respiratory substrate, reflecting the fundamental anatomical disparity between angiosperm beech and gymnosperm spruce.

Below-ground carbon allocation in mature beech and spruce trees following long-term, experimentally enhanced O3 exposure in Southern Germany.

Canopies of adult European beech (Fagus sylvatica) and Norway spruce (Picea abies) were labeled with CO(2) depleted in (13)C to evaluate carbon allocation belowground. One-half the trees were exposed to elevated O(3) for 6 yrs prior to and during the experiment. Soil-gas sampling wells were placed at 8 and 15 cm and soil CO(2) was sampled during labeling in mid-late August, 2006. In beech, delta(13)CO(2) at both depths decreased approximately 50 h after labeling, reflecting rapid translocation of fixed C to roots and release through respiration. In spruce, label was detected in fine-root tissue, but there was no evidence of label in delta(13)CO(2). The results show that C fixed in the canopy rapidly reaches respiratory pools in beech roots, and suggest that spruce may allocate very little of recently-fixed carbon into root respiration during late summer. A change in carbon allocation belowground due to long-term O(3) exposure was not observed.