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• 1. [Article] Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in foliar water transport

  The definitive version of this article is available at www.newphytologist.com.

  Citation × Citation Citation Abstract Copy Title: Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in foliar water transport Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B. The definitive version of this article is available at www.newphytologist.com. Title: Height-related trends in leaf xylem anatomy and shoot hydraulic characteristics in a tall conifer: safety versus efficiency in foliar water transport Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B. The definitive version of this article is available at www.newphytologist.com. Close

• 2. [Article] Coordination of leaf structure and gas exchange along a height gradient in a tall conifer

  The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Wl) near the tops of tall trees, which can influence ...

  Citation × Citation Citation Abstract Copy Title: Coordination of leaf structure and gas exchange along a height gradient in a tall conifer Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Johnson, D. M. The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Wl) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mm 2 m 1, 0.20 mm m 1, 5.9 · 10 3 mm m 1 and 0.012 mm2 m 1, respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 · 10 2 mm m 1 and 0.74 lm m 1, respectively. Mesophyll conductance (gm) and CO2 assimilation in ambient [CO2] (Aamb) decreased by 1.1 mmol m 2 s 1 per m and 0.082 lmol m 2 s 1 per m increase in height, respectively. Mean reductions in gm and Aamb of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in Aamb was associated with gm and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar d13C values with height (0.042& m 1) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior. Title: Coordination of leaf structure and gas exchange along a height gradient in a tall conifer Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Johnson, D. M. The gravitational component of water potential and frictional resistance during transpiration lead to substantial reductions in leaf water potential (Wl) near the tops of tall trees, which can influence both leaf growth and physiology. We examined the relationships between morphological features and gas exchange in foliage collected near the tops of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees of different height classes ranging from 5 to 55 m. This sampling allowed us to investigate the effects of tree height on leaf structural characteristics in the absence of potentially confounding factors such as irradiance, temperature, relative humidity and branch length. The use of cut foliage for measurement of intrinsic gas-exchange characteristics allowed identification of height-related trends without the immediate influences of path length and gravity. Stomatal density, needle length, needle width and needle area declined with increasing tree height by 0.70 mm 2 m 1, 0.20 mm m 1, 5.9 · 10 3 mm m 1 and 0.012 mm2 m 1, respectively. Needle thickness and mesophyll thickness increased with tree height by 4.8 · 10 2 mm m 1 and 0.74 lm m 1, respectively. Mesophyll conductance (gm) and CO2 assimilation in ambient [CO2] (Aamb) decreased by 1.1 mmol m 2 s 1 per m and 0.082 lmol m 2 s 1 per m increase in height, respectively. Mean reductions in gm and Aamb of foliage from 5 to 55 m were 47% and 42%, respectively. The observed trend in Aamb was associated with gm and several leaf anatomic characteristics that are likely to be determined by the prevailing vertical tension gradient during foliar development. A linear increase in foliar d13C values with height (0.042& m 1) implied that relative stomatal and mesophyll limitations of photosynthesis in intact shoots increased with height. These data suggest that increasing height leads to both fixed structural constraints on leaf gas exchange and dynamic constraints related to prevailing stomatal behavior. Close

• 3. [Article] Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance

  1. The xylem pressure inducing 50% loss of hydraulic conductivity due to embolism (P50) is widely used for comparisons of xylem vulnerability among species and across aridity gradients. However, despite ...

  Citation × Citation Citation Abstract Copy Title: Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Johnson, D. M., McCulloh, K. A. 1. The xylem pressure inducing 50% loss of hydraulic conductivity due to embolism (P50) is widely used for comparisons of xylem vulnerability among species and across aridity gradients. However, despite its utility as an index of resistance to catastrophic xylem failure under extreme drought, P5o may have no special physiological relevance in the context of stomatal regulation of daily minimum xylem pressure and avoidance of hydraulic failure under non-extreme conditions. Moreover, few studies of hydraulic architecture have accounted for the buffering influence of tissue hydraulic capacitance on daily fluctuations in xylem pressure in intact plants. 2. We used data from 104 coniferous and angiosperm species representing a range of woody growth forms and habitat types to evaluate trends in three alternative xylem hydraulic safety margins based on features of their stem xylem vulnerability curves and regulation of daily minimum stem water potential (Ystem min) under non-extreme conditions: (i)Ystem min - P50, (ii) Y stem min - Pe, the difference between Ystem min and the threshold xylem pressure at which loss of conductivity begins to increase rapidly (Pe) and (iii) Pe - P50 an estimate of the steepness of the vulnerability curve between Pe and P50. Additionally, we assessed relationships between xylem capacitance, species-specific set-points for daily minimum stem water potential and hydraulic safety margins in a subset of species for which relevant data were available. 3. The three types of hydraulic safety margin defined increased with decreasing species-specific set-points for Y stem min, suggesting a diminishing role of stem capacitance in slowing fluctuations in xylem pressure as Ystem min became more negative. The trends in hydraulic safety were similar among coniferous and angiosperm species native to diverse habitat types. 4. Our results suggest that here is a continuum of relative reliance on different mechanisms that confer hydraulic safety under dynamic conditions. Species with low capacitance and denser wood experience greater daily maximum xylem tension and appear to rely primarily on xylem structural features to avoid embolism, whereas in species with high capacitance and low wood density avoidance of embolism appears to be achieved primarily via reliance on transient release of stored water to constrain transpiration-induced fluctuations in xylem tension. Title: Xylem hydraulic safety margins in woody plants: coordination of stomatal control of xylem tension with hydraulic capacitance Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Johnson, D. M., McCulloh, K. A. 1. The xylem pressure inducing 50% loss of hydraulic conductivity due to embolism (P50) is widely used for comparisons of xylem vulnerability among species and across aridity gradients. However, despite its utility as an index of resistance to catastrophic xylem failure under extreme drought, P5o may have no special physiological relevance in the context of stomatal regulation of daily minimum xylem pressure and avoidance of hydraulic failure under non-extreme conditions. Moreover, few studies of hydraulic architecture have accounted for the buffering influence of tissue hydraulic capacitance on daily fluctuations in xylem pressure in intact plants. 2. We used data from 104 coniferous and angiosperm species representing a range of woody growth forms and habitat types to evaluate trends in three alternative xylem hydraulic safety margins based on features of their stem xylem vulnerability curves and regulation of daily minimum stem water potential (Ystem min) under non-extreme conditions: (i)Ystem min - P50, (ii) Y stem min - Pe, the difference between Ystem min and the threshold xylem pressure at which loss of conductivity begins to increase rapidly (Pe) and (iii) Pe - P50 an estimate of the steepness of the vulnerability curve between Pe and P50. Additionally, we assessed relationships between xylem capacitance, species-specific set-points for daily minimum stem water potential and hydraulic safety margins in a subset of species for which relevant data were available. 3. The three types of hydraulic safety margin defined increased with decreasing species-specific set-points for Y stem min, suggesting a diminishing role of stem capacitance in slowing fluctuations in xylem pressure as Ystem min became more negative. The trends in hydraulic safety were similar among coniferous and angiosperm species native to diverse habitat types. 4. Our results suggest that here is a continuum of relative reliance on different mechanisms that confer hydraulic safety under dynamic conditions. Species with low capacitance and denser wood experience greater daily maximum xylem tension and appear to rely primarily on xylem structural features to avoid embolism, whereas in species with high capacitance and low wood density avoidance of embolism appears to be achieved primarily via reliance on transient release of stored water to constrain transpiration-induced fluctuations in xylem tension. Close

• 4. [Article] Safety factors for xylem failure by implosion and air-seeding within roots, trunks and branches of young and old conifer trees

  The cohesion-tension theory of water transport states that hydrogen bonds hold water molecules together and that they are pulled through the xylem under tension. This tension could cause transport failure ...

  Citation × Citation Citation Abstract Copy Title: Safety factors for xylem failure by implosion and air-seeding within roots, trunks and branches of young and old conifer trees Author: Meinzer, F. C., Lachenbruch, B., Warren, J. M., Domec, J.-C. The cohesion-tension theory of water transport states that hydrogen bonds hold water molecules together and that they are pulled through the xylem under tension. This tension could cause transport failure in at least two ways: collapse of the conduit walls (implosion), or rupture of the water column through air-seeding. The objective of this research was to elucidate the functional significance of variations in tracheid anatomical features, earlywood to latewood ratios and wood densities with position in young and old Douglas-fir and ponderosa pine trees in terms of their consequences for the safety factors for tracheid implosion and air-seeding. For both species, wood density increased linearly with percent latewood for root, trunk and branch samples. However, the relationships between anatomy and hydraulic function in trunks differed from those in roots and branches. In roots and branches increased hydraulic efficiency was achieved at the cost of increased vulnerability to air-seeding. Mature wood of trunks had earlywood with wide tracheids that optimized water transport and had a high percentage of latewood that optimized structural support. Juvenile wood had higher resistance to air-seeding and cell wall implosion. The two safety factors followed similar axial trends from roots to terminal branches and were similar for both species studied and between juvenile and mature wood. Title: Safety factors for xylem failure by implosion and air-seeding within roots, trunks and branches of young and old conifer trees Author: Meinzer, F. C., Lachenbruch, B., Warren, J. M., Domec, J.-C. The cohesion-tension theory of water transport states that hydrogen bonds hold water molecules together and that they are pulled through the xylem under tension. This tension could cause transport failure in at least two ways: collapse of the conduit walls (implosion), or rupture of the water column through air-seeding. The objective of this research was to elucidate the functional significance of variations in tracheid anatomical features, earlywood to latewood ratios and wood densities with position in young and old Douglas-fir and ponderosa pine trees in terms of their consequences for the safety factors for tracheid implosion and air-seeding. For both species, wood density increased linearly with percent latewood for root, trunk and branch samples. However, the relationships between anatomy and hydraulic function in trunks differed from those in roots and branches. In roots and branches increased hydraulic efficiency was achieved at the cost of increased vulnerability to air-seeding. Mature wood of trunks had earlywood with wide tracheids that optimized water transport and had a high percentage of latewood that optimized structural support. Juvenile wood had higher resistance to air-seeding and cell wall implosion. The two safety factors followed similar axial trends from roots to terminal branches and were similar for both species studied and between juvenile and mature wood. Close

• 5. [Article] Impacts of tree height on leaf hydraulic architecture and stomatal control in Douglas-fir

  This study investigated the mechanisms involved in the regulation of stomatal closure in Douglas-fir and evaluated the potential impact of compensatory adjustments in response to increasing tree height ...

  Citation × Citation Citation Abstract Copy Title: Impacts of tree height on leaf hydraulic architecture and stomatal control in Douglas-fir Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Warren, J. M., McCulloh, K. A. This study investigated the mechanisms involved in the regulation of stomatal closure in Douglas-fir and evaluated the potential impact of compensatory adjustments in response to increasing tree height upon these mechanisms. In the laboratory, we measured leaf hydraulic conductance (Kleaf) as leaf water potential (Yl) declined for comparison with in situ diurnal patterns of stomatal conductance (gs) and Yl in Douglas-fir across a height gradient, allowing us to infer linkages between diurnal changes in Kleaf and gs. A recently developed timed rehydration technique was used in conjunction with data from pressure–volume curves to develop hydraulic vulnerability curves for needles attached to small twigs. Laboratory-measured Kleaf declined with increasing leaf water stress and was substantially reduced at Yl values of -1.34, -1.45, -1.56 and -1.92 MPa for foliage sampled at mean heights of approximately 20, 35, 44 and 55 m, respectively. In situ gs measurements showed that stomatal closure was initiated at Yl values of -1.21, -1.36, -1.74 and -1.86 MPa along the height gradient, which was highly correlated with Yl values at loss of Kleaf. Cryogenic scanning electron microscopy (SEM) images showed that relative abundances of embolized tracheids in the central vein increased with increasing leaf water stress. Leaf embolism appeared to be coupled to changes in gs and might perform a vital function in stomatal regulation of plant water status and water transport in conifers. The observed trends in gs and Kleaf in response to changes in Yl along a height gradient suggest that the foliage at the tops of tall trees is capable of maintaining stomatal conductance at more negative Yl. This adaptation may allow taller trees to continue to photosynthesize during periods of greater water stress. Title: Impacts of tree height on leaf hydraulic architecture and stomatal control in Douglas-fir Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Warren, J. M., McCulloh, K. A. This study investigated the mechanisms involved in the regulation of stomatal closure in Douglas-fir and evaluated the potential impact of compensatory adjustments in response to increasing tree height upon these mechanisms. In the laboratory, we measured leaf hydraulic conductance (Kleaf) as leaf water potential (Yl) declined for comparison with in situ diurnal patterns of stomatal conductance (gs) and Yl in Douglas-fir across a height gradient, allowing us to infer linkages between diurnal changes in Kleaf and gs. A recently developed timed rehydration technique was used in conjunction with data from pressure–volume curves to develop hydraulic vulnerability curves for needles attached to small twigs. Laboratory-measured Kleaf declined with increasing leaf water stress and was substantially reduced at Yl values of -1.34, -1.45, -1.56 and -1.92 MPa for foliage sampled at mean heights of approximately 20, 35, 44 and 55 m, respectively. In situ gs measurements showed that stomatal closure was initiated at Yl values of -1.21, -1.36, -1.74 and -1.86 MPa along the height gradient, which was highly correlated with Yl values at loss of Kleaf. Cryogenic scanning electron microscopy (SEM) images showed that relative abundances of embolized tracheids in the central vein increased with increasing leaf water stress. Leaf embolism appeared to be coupled to changes in gs and might perform a vital function in stomatal regulation of plant water status and water transport in conifers. The observed trends in gs and Kleaf in response to changes in Yl along a height gradient suggest that the foliage at the tops of tall trees is capable of maintaining stomatal conductance at more negative Yl. This adaptation may allow taller trees to continue to photosynthesize during periods of greater water stress. Close

• 6. [Article] Climate-related trends in sapwood biophysical properties in two conifers: avoidance of hydraulic dysfunction through coordinated adjustments in xylem efficiency, safety, and capacitance.

  The definitive version is available at www3.interscience.wiley.com.

  Citation × Citation Citation Abstract Copy Title: Climate-related trends in sapwood biophysical properties in two conifers: avoidance of hydraulic dysfunction through coordinated adjustments in xylem efficiency, safety, and capacitance. Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Barnard, D. M., Johnson, D. M., McCulloh, K. A. The definitive version is available at www3.interscience.wiley.com. Title: Climate-related trends in sapwood biophysical properties in two conifers: avoidance of hydraulic dysfunction through coordinated adjustments in xylem efficiency, safety, and capacitance. Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Barnard, D. M., Johnson, D. M., McCulloh, K. A. The definitive version is available at www3.interscience.wiley.com. Close

• 7. [Article] Maximum height in a conifer is associated with conflicting requirements for xylem design

  Copyright © 2008 National Academy of Sciences. All rights reserved. The copy here is the final accepted version before it was copyedited by the journal. The final version is available at http://www.pn...

  Citation × Citation Citation Abstract Copy Title: Maximum height in a conifer is associated with conflicting requirements for xylem design Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Warren, J. M., McCulloh, K. A., Domec, J.-C. Copyright © 2008 National Academy of Sciences. All rights reserved. The copy here is the final accepted version before it was copyedited by the journal. The final version is available at http://www.pnas.org/. Title: Maximum height in a conifer is associated with conflicting requirements for xylem design Author: Meinzer, F. C., Woodruff, D. R., Lachenbruch, B., Warren, J. M., McCulloh, K. A., Domec, J.-C. Copyright © 2008 National Academy of Sciences. All rights reserved. The copy here is the final accepted version before it was copyedited by the journal. The final version is available at http://www.pnas.org/. Close

• 8. [Article] Moving water well: comparing hydraulic efficiency in twigs and trunks of coniferous, ring-porous, and diffuse-porous saplings from temperate and tropical forests

  The definitive version of this article is available at www.newphytologist.com.

  Citation × Citation Citation Abstract Copy Title: Moving water well: comparing hydraulic efficiency in twigs and trunks of coniferous, ring-porous, and diffuse-porous saplings from temperate and tropical forests Author: Voelker, S., Lachenbruch, B., Reich, P. B., McCulloh, K. A., Sperry, J. S., Meinzer, F. C. The definitive version of this article is available at www.newphytologist.com. Title: Moving water well: comparing hydraulic efficiency in twigs and trunks of coniferous, ring-porous, and diffuse-porous saplings from temperate and tropical forests Author: Voelker, S., Lachenbruch, B., Reich, P. B., McCulloh, K. A., Sperry, J. S., Meinzer, F. C. The definitive version of this article is available at www.newphytologist.com. Close