Hydraulic architecture with high root-resistance fraction contributes to efficient carbon gain of plants in temperate habitats.

PREMISE: The hydraulic architecture in the leaves, stems and roots of plants constrains water transport and carbon gain through stomatal limitation to CO2 absorption. Because roots are the main bottleneck in water transport for a range of plant species, we assessed the ecophysiological mechanism and importance of a high fraction of root hydraulic resistance in woody and herbaceous species. METHODS: Biomass partitioning and hydraulic conductance of leaves, stems, and roots of Japanese knotweed (Fallopia japonica, a perennial herb) and Japanese zelkova (Zelkova serrata, a deciduous tall tree) were measured. Theoretical analyses were used to examine whether the measured hydraulic architecture and biomass partitioning maximized the plant photosynthetic rate (the product of leaf area and photosynthetic rate per leaf area). RESULTS: Root hydraulic resistance accounted for 83% and 68% of the total plant resistance for Japanese knotweed and Japanese zelkova, respectively. Comparisons of hydraulic and biomass partitioning revealed that high root-resistance fractions were attributable to low biomass partitioning to root organs rather than high mass-specific root conductance. The measured partitioning of hydraulic resistance closely corresponded to the predicted optimal partitioning, maximizing the plant photosynthetic rate for the two species. The high fraction of root resistance was predicted to be optimal with variations in air humidity and soil water potential. CONCLUSIONS: These results suggest that the hydraulic architecture of plants growing in mesic and fertile habitats not only results in high root resistance due to small biomass partitioning to root organs, but contributes to efficient carbon gain.

Short interval overnight laser scanning suggests sub-circadian periodicity of tree turgor.

A recent study by Zlinszky et al., 1 uses high-resolution terrestrial laser scanning to investigate the variability of overnight movement of leaves and branches in vascular plants. This study finds among others that the investigated plants show periodic movements of around one centimetre in amplitude and 2-6 hour periodicity. Sub-circadian process dynamics of plants were so far not in focus of research, but here we compare the findings with other published cases of short-term periodicity in leaf turgor, sap flow and especially trunk diameter. Several authors have noted overnight variations in these parameters within periods of several hours and in absence of environmental changes with similar dynamics. We revisit the unknown questions of short-term plant movement and make a suggestion for future research.

Short interval overnight laser scanning suggest sub-circadian periodicity of tree turgor.

A recent study by Zlinszky et al., 1 uses high-resolution terrestrial laser scanning to investigate the variability of overnight movement of leaves and branches in vascular plants. This study finds among others that the investigated plants show periodic movements of around one centimetre in amplitude and 2-6 hour periodicity. Sub-circadian process dynamics of plants were so far not in focus of research, but here we compare the findings with other published cases of short-term periodicity in leaf turgor, sap flow and especially trunk diameter. Several authors have noted overnight variations in these parameters within periods of several hours and in absence of environmental changes with similar dynamics. We revisit the unknown questions of short-term plant movement and make a suggestion for future research.