Limits...
Patterns in hydraulic architecture from roots to branches in six tropical tree species from cacao agroforestry and their relation to wood density and stem growth.

Kotowska MM, Hertel D, Rajab YA, Barus H, Schuldt B - Front Plant Sci (2015)

Bottom Line: Our results confirmed a hump-shaped vessel size distribution in nearly all species.Drought-adapted species showed divergent patterns of hydraulic conductivity, vessel density, and relative vessel lumen area between root, stem and branch wood compared to wet forest species.Our study results suggest that future research on conceptual trade-offs of tree hydraulic architecture should consider biogeographical patterns underlining the importance of anatomical adaptation mechanisms to environment.

View Article: PubMed Central - PubMed

Affiliation: Plant Ecology and Ecosystems Research, Albrecht von Haller Institute for Plant Sciences, University of Göttingen, Göttingen Germany.

ABSTRACT
For decades it has been assumed that the largest vessels are generally found in roots and that vessel size and corresponding sapwood area-specific hydraulic conductivity are acropetally decreasing toward the distal twigs. However, recent studies from the perhumid tropics revealed a hump-shaped vessel size distribution. Worldwide tropical perhumid forests are extensively replaced by agroforestry systems often using introduced species of various biogeographical and climatic origins. Nonetheless, it is unknown so far what kind of hydraulic architectural patterns are developed in those agroforestry tree species and which impact this exerts regarding important tree functional traits, such as stem growth, hydraulic efficiency and wood density (WD). We investigated wood anatomical and hydraulic properties of the root, stem and branch wood in Theobroma cacao and five common shade tree species in agroforestry systems on Sulawesi (Indonesia); three of these were strictly perhumid tree species, and the other three tree species are tolerating seasonal drought. The overall goal of our study was to relate these properties to stem growth and other tree functional traits such as foliar nitrogen content and sapwood to leaf area ratio. Our results confirmed a hump-shaped vessel size distribution in nearly all species. Drought-adapted species showed divergent patterns of hydraulic conductivity, vessel density, and relative vessel lumen area between root, stem and branch wood compared to wet forest species. Confirming findings from natural old-growth forests in the same region, WD showed no relationship to specific conductivity. Overall, aboveground growth performance was better predicted by specific hydraulic conductivity than by foliar traits and WD. Our study results suggest that future research on conceptual trade-offs of tree hydraulic architecture should consider biogeographical patterns underlining the importance of anatomical adaptation mechanisms to environment.

No MeSH data available.


Mean vessel diameter in relation to vessel density in tree organs (roots, stems, and branches) along the flow path for the six tree species.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4379754&req=5

Figure 4: Mean vessel diameter in relation to vessel density in tree organs (roots, stems, and branches) along the flow path for the six tree species.

Mentions: We found considerable variation in wood anatomical and derived hydraulic traits along the flow path from root, to stem and branch wood for all six species. Exemplary pictures for this variation from three of the species are given in Figure 3. In four of the six species average vessel diameter (d) was significantly largest in the stem and not in the root wood; in the remaining two species d was comparable between root and stem wood (Figure 2). Along the flow path smallest vessels were always observed in the branch wood of all species with the exception of D. zibethinus (Figure 2). The same pattern was observed for the hydraulically weighted vessel diameter (dh) for branch wood, while the differences in dh between root and stem wood were only significant in T. cacao and D. zibethinus. In general, several wood anatomical and derived hydraulic traits allowed a grouping between the three perhumid tree species originating from strictly wet tropical environments, and the three seasonal tree species reported to tolerate moderate droughts. As mentioned above, dh was not significantly higher in stem than in root wood for the three seasonal tree species, and VD was comparable between root and branch wood and did not differ significantly. On the other hand, highest vessel densities were observed in the branch wood of all perhumid tree species, although differences were only significant in two of the three species. However, when comparing the two groups (perhumid vs. seasonal) significant differences were found (‘lme’; p < 0.001). In general, VD varied considerably between the organs and species as well and was found to decrease in the order branch – root – stem across all six species (Figure 2). Variation in VD numbers was lowest (factor < 2) in the root xylem and highest (factor > 10) in the stem xylem. VD decreased exponentially with increasing vessels diameter; we therefore concentrate on changes in d along the flow path in the following (Figure 4).


Patterns in hydraulic architecture from roots to branches in six tropical tree species from cacao agroforestry and their relation to wood density and stem growth.

Kotowska MM, Hertel D, Rajab YA, Barus H, Schuldt B - Front Plant Sci (2015)

Mean vessel diameter in relation to vessel density in tree organs (roots, stems, and branches) along the flow path for the six tree species.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4379754&req=5

Figure 4: Mean vessel diameter in relation to vessel density in tree organs (roots, stems, and branches) along the flow path for the six tree species.
Mentions: We found considerable variation in wood anatomical and derived hydraulic traits along the flow path from root, to stem and branch wood for all six species. Exemplary pictures for this variation from three of the species are given in Figure 3. In four of the six species average vessel diameter (d) was significantly largest in the stem and not in the root wood; in the remaining two species d was comparable between root and stem wood (Figure 2). Along the flow path smallest vessels were always observed in the branch wood of all species with the exception of D. zibethinus (Figure 2). The same pattern was observed for the hydraulically weighted vessel diameter (dh) for branch wood, while the differences in dh between root and stem wood were only significant in T. cacao and D. zibethinus. In general, several wood anatomical and derived hydraulic traits allowed a grouping between the three perhumid tree species originating from strictly wet tropical environments, and the three seasonal tree species reported to tolerate moderate droughts. As mentioned above, dh was not significantly higher in stem than in root wood for the three seasonal tree species, and VD was comparable between root and branch wood and did not differ significantly. On the other hand, highest vessel densities were observed in the branch wood of all perhumid tree species, although differences were only significant in two of the three species. However, when comparing the two groups (perhumid vs. seasonal) significant differences were found (‘lme’; p < 0.001). In general, VD varied considerably between the organs and species as well and was found to decrease in the order branch – root – stem across all six species (Figure 2). Variation in VD numbers was lowest (factor < 2) in the root xylem and highest (factor > 10) in the stem xylem. VD decreased exponentially with increasing vessels diameter; we therefore concentrate on changes in d along the flow path in the following (Figure 4).

Bottom Line: Our results confirmed a hump-shaped vessel size distribution in nearly all species.Drought-adapted species showed divergent patterns of hydraulic conductivity, vessel density, and relative vessel lumen area between root, stem and branch wood compared to wet forest species.Our study results suggest that future research on conceptual trade-offs of tree hydraulic architecture should consider biogeographical patterns underlining the importance of anatomical adaptation mechanisms to environment.

View Article: PubMed Central - PubMed

Affiliation: Plant Ecology and Ecosystems Research, Albrecht von Haller Institute for Plant Sciences, University of Göttingen, Göttingen Germany.

ABSTRACT
For decades it has been assumed that the largest vessels are generally found in roots and that vessel size and corresponding sapwood area-specific hydraulic conductivity are acropetally decreasing toward the distal twigs. However, recent studies from the perhumid tropics revealed a hump-shaped vessel size distribution. Worldwide tropical perhumid forests are extensively replaced by agroforestry systems often using introduced species of various biogeographical and climatic origins. Nonetheless, it is unknown so far what kind of hydraulic architectural patterns are developed in those agroforestry tree species and which impact this exerts regarding important tree functional traits, such as stem growth, hydraulic efficiency and wood density (WD). We investigated wood anatomical and hydraulic properties of the root, stem and branch wood in Theobroma cacao and five common shade tree species in agroforestry systems on Sulawesi (Indonesia); three of these were strictly perhumid tree species, and the other three tree species are tolerating seasonal drought. The overall goal of our study was to relate these properties to stem growth and other tree functional traits such as foliar nitrogen content and sapwood to leaf area ratio. Our results confirmed a hump-shaped vessel size distribution in nearly all species. Drought-adapted species showed divergent patterns of hydraulic conductivity, vessel density, and relative vessel lumen area between root, stem and branch wood compared to wet forest species. Confirming findings from natural old-growth forests in the same region, WD showed no relationship to specific conductivity. Overall, aboveground growth performance was better predicted by specific hydraulic conductivity than by foliar traits and WD. Our study results suggest that future research on conceptual trade-offs of tree hydraulic architecture should consider biogeographical patterns underlining the importance of anatomical adaptation mechanisms to environment.

No MeSH data available.