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Hydraulic Architecture (hydraulic + architecture)
Selected AbstractsOntogenetically stable hydraulic design in woody plantsFUNCTIONAL ECOLOGY, Issue 2 2006J. S. WEITZ Summary 1An important component of plant water transport is the design of the vascular network, including the size and shape of water-conducting elements or xylem conduits. 2For over 100 years, foresters and plant physiologists have recognized that these conduits are consistently smaller near branch tips compared with major branches and the main stem. Empirical data, however, have rarely been assembled to assess the whole-plant hydraulic architecture of woody plants as they age and grow. 3In this paper, we analyse vessels of Fraxinus americana (White Ash) within a single tree. Vessels are measured from cross-sections that span 12 m in height and 18 years' growth. 4We show that vessel radii are determined by distance from the top of the tree, as well as by stem size, independently of tree height or age. 5The qualitative form for the scaling of vessel radii agrees remarkably well with simple power laws, suggesting the existence of an ontogenetically stable hydraulic design that scales in the same manner as a tree grows in height and diameter. 6We discuss the implications of the present findings for optimal theories of hydraulic design. [source] Hydraulic differentiation of Ponderosa pine populations along a climate gradient is not associated with ecotypic divergenceFUNCTIONAL ECOLOGY, Issue 4 2002H. Maherali Summary 1.,Pinus ponderosa occurs in a range of contrasting environments in the western USA. Xeric populations typically have lower leaf : sapwood area ratio (AL/AS) and higher whole-tree leaf specific hydraulic conductance (KL) than mesic populations. These climate-driven shifts in hydraulic architecture are considered adaptive because they maintain minimum leaf water potential above levels that cause xylem cavitation. 2.,Using a common garden study, we examined whether differences in biomass allocation and hydraulic architecture between P. ponderosa populations originating from isolated outcrops in the Great Basin desert and Sierran montane environments were caused by ecotypic differentiation or phenotypic plasticity. To determine if populations were genetically differentiated and if phenotypic and genetic differentiation coincided, we also characterized the genetic structure of these populations using DNA microsatellites. 3.,Phenotypic differentiation in growth, biomass allocation and hydraulic architecture was variable among populations in the common garden. There were no systematic differences between desert and montane climate groups that were consistent with adaptive expectations. Drought had no effect on the root : shoot and needle : stem ratio, but reduced seedling biomass accumulation, leaf area ratio, AL/AS and KL. Stem hydraulic conductance (KH) was strongly size-dependent, and was lower in droughted plants, primarily because of lower growth. 4.,Although microsatellites were able to detect significant non-zero (P < 0·001) levels of differentiation between populations, these differences were small and were not correlated with geographic separation or climate group. Estimates of genetic differentiation among populations were low (<5%), and almost all the genetic variation (>95%) resided within populations, suggesting that gene flow was the dominant factor shaping genetic structure. 5.,These results indicate that biomass allocation and hydraulic differences between desert and montane populations are not the result of ecotypic differentiation. Significant drought effects on leaf : sapwood allocation and KL suggest that phenotypic differentiation between desert and montane climates could be the result of phenotypic plasticity. [source] The hydraulic architecture of Juniperus communis L. ssp. communis: shrubs and trees comparedPLANT CELL & ENVIRONMENT, Issue 11 2008BARBARA BEIKIRCHER ABSTRACT Juniperus communis ssp. communis can grow like a shrub or it can develop a tree-like habit. In this study, the hydraulic architecture of these contrasting growth forms was compared. We analysed the hydraulic efficiency (leaf-specific conductivity, kl; specific conductivity, ks; Huber value, HV) and the vulnerability to cavitation (the water potential corresponding to a 50% loss of conductivity, ,50), as well as anatomical parameters [mean tracheid diameter, d; mean hydraulic diameter, dh; cell wall reinforcement (t/b)h2] of shrub shoots, tree stems and tree branches. Shrub shoots were similar to tree branches (especially to lower branches) in growth form and conductivity (kl = 1.93 ± 0.11 m2 s,1 MPa,1 10,7, ks = 5.71 ± 0.19 m2 s,1 MPa,1 10,4), but were similar to tree stems in their vulnerability to cavitation (,50 = ,5.81 ± 0.08 MPa). Tree stems showed extraordinarily high kl and ks values, and HV increased from the base up. Stem xylem was more vulnerable to cavitation than branch xylem, where ,50 increased from lower (,50 = ,6.44 ± 0.19 MPa) to upper branches (,50 = ,5.98 ± 0.13 MPa). Conduit diameters were correlated with kl and ks. Data indicate that differences in hydraulic architecture correspond to changes in growth form. In some aspects, the xylem hydraulics of tree-like Juniperus communis differs from that of other coniferous tree species. [source] Effects of hydraulic architecture and spatial variation in light on mean stomatal conductance of tree branches and crownsPLANT CELL & ENVIRONMENT, Issue 4 2007B. E. EWERS ABSTRACT In a Pinus taeda L. (loblolly pine) plantation, we investigated whether the response to vapour pressure deficit (D) of canopy average stomatal conductance (GS) calculated from sap flux measured in upper and lower branches and main stems follows a hydraulically modelled response based on homeostasis of minimum leaf water potential (,L). We tested our approach over a twofold range of leaf area index (L; 2,4 m2 m,2) created by irrigation, fertilization, and a combination of irrigation and fertilization relative to untreated control. We found that GS scaled well from leaf-level porometery [porometry-based stomatal conductance (gs)] to branch-estimated and main stem-estimated GS. The scaling from branch- to main stem-estimated GS required using a 45 min moving average window to extract the diurnal signal from the large high-frequency variation, and utilized a light attenuation model to weigh the contribution of upper and lower branch-estimated GS. Our analysis further indicated that, regardless of L, lower branch-estimated GS represented most of the main stem-estimated GS in this stand. We quantified the variability in both upper and lower branch-estimated GS by calculating the SD of the residuals from a moving average smoothed diurnal. A light model, which incorporated penumbral effects on vertical distribution of direct light, was employed to estimate the variability in light intensity at each canopy level in order to explain the increasing SD of both upper and lower branch-estimated GS with light. The results from the light model showed that the upper limit of the variability in individual branch-estimated GS could be attributed to incoming light, but not the variation below that upper limit. A porous medium model of water flow in trees produced a pattern of variation below the upper limit that was consistent with the observed variability in branch-estimated GS. Our results indicated that stems acted to buffer leaf- and branch-level variation and might transmit a less-variable water potential signal to the roots. [source] | ||||||||||