Carbon Allocation into Different Fine-Root Classes of Young Abies alba Trees Is Affected More by Phenology than by Simulated Browsing

Abies alba (European silver fir) was used to investigate possible effects of simulated browsing on C allocation belowground by 13CO2 pulse-labelling at spring, summer or autumn, and by harvesting the trees at the same time point of the labelling or at a later season for biomass and for 13C-allocation into the fine-root system. Before budburst in spring, the leader shoots and 50% of all lateral shoots of half of the investigated 5-year old Abies alba saplings were clipped to simulate browsing. At harvest, different fine-root classes were separated, and starch as an important storage compartment was analysed for concentrations. The phenology had a strong effect on the allocation of the 13C-label from shoots to roots. In spring, shoots did not supply the fine-roots with high amounts of the 13C-label, because the fine-roots contained less than 1% of the applied 13C. In summer and autumn, however, shoots allocated relatively high amounts of the 13C-label to the fine roots. The incorporation of the 13C-label as structural C or as starch into the roots is strongly dependent on the root type and the root diameter. In newly formed fine roots, 3–5% of the applied 13C was incorporated, whereas 1–3% in the ≤0.5 mm root class and 1–1.5% in the >0.5–1.0 mm root class were recorded. Highest 13C-enrichment in the starch was recorded in the newly formed fine roots in autumn. The clipping treatment had a significant positive effect on the amount of allocated 13C-label to the fine roots after the spring labelling, with high relative 13C-contents observed in the ≤0.5 mm and the >0.5–1.0 mm fine-root classes of clipped trees. No effects of the clipping were observed after summer and autumn labelling in the 13C-allocation patterns. Overall, our data imply that the season of C assimilation and, thus, the phenology of trees is the main determinant of the C allocation from shoots to roots and is clearly more important than browsing.ISSN:1932-620

Carbon Allocation into Different Fine-Root Classes of Young <i>Abies alba</i> Trees Is Affected More by Phenology than by Simulated Browsing

<div><p><i>Abies alba</i> (European silver fir) was used to investigate possible effects of simulated browsing on C allocation belowground by ¹³CO₂ pulse-labelling at spring, summer or autumn, and by harvesting the trees at the same time point of the labelling or at a later season for biomass and for ¹³C-allocation into the fine-root system. Before budburst in spring, the leader shoots and 50% of all lateral shoots of half of the investigated 5-year old <i>Abies alba</i> saplings were clipped to simulate browsing. At harvest, different fine-root classes were separated, and starch as an important storage compartment was analysed for concentrations. The phenology had a strong effect on the allocation of the ¹³C-label from shoots to roots. In spring, shoots did not supply the fine-roots with high amounts of the ¹³C-label, because the fine-roots contained less than 1% of the applied ¹³C. In summer and autumn, however, shoots allocated relatively high amounts of the ¹³C-label to the fine roots. The incorporation of the ¹³C-label as structural C or as starch into the roots is strongly dependent on the root type and the root diameter. In newly formed fine roots, 3–5% of the applied ¹³C was incorporated, whereas 1–3% in the ≤0.5 mm root class and 1–1.5% in the >0.5–1.0 mm root class were recorded. Highest ¹³C-enrichment in the starch was recorded in the newly formed fine roots in autumn. The clipping treatment had a significant positive effect on the amount of allocated ¹³C-label to the fine roots after the spring labelling, with high relative ¹³C-contents observed in the ≤0.5 mm and the >0.5–1.0 mm fine-root classes of clipped trees. No effects of the clipping were observed after summer and autumn labelling in the ¹³C-allocation patterns. Overall, our data imply that the season of C assimilation and, thus, the phenology of trees is the main determinant of the C allocation from shoots to roots and is clearly more important than browsing.</p></div

Results of two-way ANOVA of the effect of the clipping treatment (C) and the harvesting seasons (H) (spring, summer, autumn) on the starch concentration and on the relative ¹³C content of the starch of two fine-root classes.

<p>Significant effects (<i>P</i><0.05) are given in bold. (-: data not available).</p

Results of two-way ANOVA testing the effect of the clipping treatment (C) and the harvesting seasons (H) (spring, summer, autumn) on relative ¹³C contents (%) of three fine-root classes.

<p>Significant effects (<i>P</i><0.05) are given in bold. (-: data not available).</p

Results of two-way ANOVA testing the effect of the clipping treatment (C) and the harvesting seasons (H) (spring, summer, autumn, spring+1 yr) on total biomass and root/shoot ratio as well as on the percentage of the various tree components.

<p>Significant effects (<i>P</i><0.05) are given in bold.</p

Number of harvested and ¹³CO₂ pulse-labelled trees during the seasons in two years for two clipping treatments and three ¹³CO₂ labelling seasons.

<p>Treatments are 'Control' = unclipped trees, and 'Clipped' = clipped trees.</p

Results of two-way ANOVA testing the effect of the clipping treatment (C) and the various fine-root classes (R; new roots, size classes ≤0.5 mm, >0.5–1.0 mm, >1.0–1.5 mm, and >1.5–2.0 mm) on fine-root biomass at various harvesting seasons.

<p>Significant effects (<i>P</i><0.05) are given in bold (autumn data were tested with non-parametric tests due to non-normal distribution).</p