Catalogue Search | MBRL
Search Results Heading
Explore the vast range of titles available.
MBRLSearchResults
-
DisciplineDiscipline
-
Is Peer ReviewedIs Peer Reviewed
-
Item TypeItem Type
-
SubjectSubject
-
YearFrom:-To:
-
More FiltersMore FiltersSourceLanguage
Done
Filters
Reset
269
result(s) for
"M. T. Tyree"
Sort by:
Moving beyond the cambium necrosis hypothesis of post‐fire tree mortality: cavitation and deformation of xylem in forest fires
by
Tyree, M. T
,
Michaletz, S. T
,
Johnson, E. A
in
Addition polymerization
,
Air conductivity
,
Air injection
2012
• It is widely assumed that post‐fire tree mortality results from necrosis of phloem and vascular cambium in stems, despite strong evidence that reduced xylem conductivity also plays an important role. • In this study, experiments with Populus balsamifera were used to demonstrate two mechanisms by which heat reduces the hydraulic conductivity of xylem: air seed cavitation and conduit wall deformation. Heat effects on air seed cavitation were quantified using air injection experiments that isolate potential temperature‐dependent changes in sap surface tension and pit membrane pore diameters. Heat effects on conduit wall structure were demonstrated using air conductivity measurements and light microscopy. • Heating increased vulnerability to cavitation because sap surface tension varies inversely with temperature. Heating did not affect cavitation via changes in pit membrane pore diameters, but did cause significant reductions in xylem air conductivity that were associated with deformation of conduit walls (probably resulting from thermal softening of viscoelastic cell wall polymers). • Additional work is required to understand the relative roles of cavitation and deformation in the reduction of xylem conductivity, and how reduced xylem conductivity in roots, stems, and branches correlates and interacts with foliage and root necroses to cause tree mortality. Future research should also examine how heat necrosis of ray parenchyma cells affects refilling of embolisms that occur during and after the fire event.
Journal Article
Low root reserve accumulation during drought may lead to winter mortality in poplar seedlings
by
S. M. Landhäusser
,
M. T. Tyree
,
David A. Galvez
in
Accumulation
,
Carbohydrate Metabolism
,
carbon and hydraulic stress
2013
Climate models suggest that more frequent drought events of greater severity and length, associated with climate change, can be expected in the coming decades. Although drought-induced tree mortality has been recognized as an important factor modulating forest demography at the global scale, the mechanisms underlying drought-induced tree mortality remain contentious.
Above- and below-ground growth, gas exchange, water relations and carbon reserve accumulation dynamics at the organ and whole-plant scale were quantified in Populus tremuloides and P. balsamifera seedlings in response to severe drought. Seedlings were maintained in drought conditions over one growing and one dormant winter season.
Our experiment presents a detailed description of the effect of severe drought on growth and physiological variables, leading to seedling mortality after an extended period of drought and dormancy. After re-watering following the dormant period, drought-exposed seedlings did not re-flush, showing that the root system had died off.
The results of this study suggest a complex series of physiological feedbacks between the measured variables in both Populus species. Further, they reveal that reduced reserve accumulation in the root system during drought decreases the conversion of starch to soluble sugars in roots, which may contribute to the root death of drought-exposed seedlings during the dormant season by compromising the frost tolerance of the root system.
Journal Article
Xylem Cavitation in the Leaf of Prunus laurocerasus and Its Impact on Leaf Hydraulics
by
Salleo, Sebastiano
,
Nardini, Andrea
,
Tyree, Melvin T.
in
Agronomy. Soil science and plant productions
,
Biological and medical sciences
,
Cavitation flow
2001
This paper reports how water stress correlates with changes in hydraulic conductivity of stems, leaf midrib, and whole leaves of Prunus laurocerasus. Water stress caused cavitation-induced dysfunction in vessels of P. laurocerasus. Cavitation was detected acoustically by counts of ultrasonic acoustic emissions and by the loss of hydraulic conductivity measured by a vacuum chamber method. Stems and midribs were approximately equally vulnerable to cavitations. Although midribs suffered a 70% loss of hydraulic conductance at leaf water potentials of -1.5 MPa, there was less than a 10% loss of hydraulic conductance in whole leaves. Cutting and sealing the midrib 20 mm from the leaf base caused only a 30% loss of conduction of the whole leaf. A high-pressure flow meter was used to measure conductance of whole leaves and as the leaf was progressively cut back from tip to base. These data were fitted to a model of hydraulic conductance of leaves that explained the above results, i.e. redundancy in hydraulic pathways whereby water can flow around embolized regions in the leaf, makes whole leaves relatively insensitive to significant changes in conductance of the midrib. The onset of cavitation events in P. laurocerasus leaves correlated with the onset of stomatal closure as found recently in studies of other species in our laboratory.
Journal Article
Plant hydraulic conductance measured by the high pressure flow meter in crop plants
by
Tsuda, Makoto
,
Tyree, Melvin T.
in
Agronomy. Soil science and plant productions
,
Biological and medical sciences
,
Biomechanical Phenomena
2000
A new high pressure flow meter (HPFM) method for measuring plant hydraulic conductances (K) was investigated to examine whether its results are comparable to those from a conventional evaporative flux (EF) method in crops. Hydraulic conductance (K) was measured by the two methods under quasi‐steady‐state conditions in six crops grown in pots: soybean (Glycine max L. Merr. cv. Tsurunoko daizu), sunflower (Helianthus annuus L. cv. Russian mammoth), kidney bean (Phaseolus vulgaris L. cv. Tsurunashi morocco), tomato (Lycopersicon esculentum Mill. cv. Sekai‐ichi), green pepper (Capsicum annuum L. cv. shishitou), and eggplant (Solanum melongena L. cv. Seiguro chunaga nasu). There was a 1 : 1 agreement between K values measured by the two methods for K values of whole plant, root and stem, and leaf under quasi‐steady‐state conditions. Leaf water potential (Ψleaf) and evaporative flux density (E) in sunflower was curvilinear, indicating whole plant K estimated by the EF method increased with increase of E. Predicted Ψleaf(=E divided by whole plant K measured by the HPFM method) agreed with measured Ψleaf. Diurnal changes were also found in K measured by the HPFM confirming that K changed in response to temperature and E. The HPFM revealed that variable conductance was located in all organs: roots, stems, petioles, and leaves. These observations indicated that the HPFM is valid for crops as well as for trees (as previously established by Tsuda and Tyree) and has advantages over the EF method because of the speed and ease of the HPFM method.
Journal Article
Impact of Simulated Herbivory on Water Relations of Aspen (Populus tremuloides) Seedlings: The Role of New Tissue in the Hydraulic Conductivity Recovery Cycle
by
Tyree, M. T.
,
Gálvez, David A.
in
Animal and plant ecology
,
Animal, plant and microbial ecology
,
Autoecology
2009
Physiological mechanisms behind plant–herbivore interactions are commonly approached as input–output systems where the role of plant physiology is viewed as a black box. Studies evaluating impacts of defoliation on plant physiology have mostly focused on changes in photosynthesis while the overall impact on plant water relations is largely unknown. Stem hydraulic conductivity$(k_h )$, stem specific conductivity$(k_s )$, percent loss of hydraulic conductivity (PLC), CO₂ assimilation (A) and stomatal conductance$(g_s )$were measured on well-irrigated 1-month-old Populus tremuloides (Michx.) defoliated and control seedlings until complete refoliation. PLC values of defoliated seedlings gradually increased during the refoliation process despite them being kept well irrigated.$k_s $of defoliated seedlings gradually decreased during refoliation. PLC and$k_s $values of control seedlings remained constant during refoliation.$k_s $of new stems, leaf specific conductivity and A of leaves grown from new stems in defoliated and control seedlings were not significantly different, but$g_s $was higher in defoliated than in control seedlings. The gradual increase of PLC and decrease of$k_s $values in old stems after defoliation was unexpected under well-irrigated conditions, but appeared to have little impact on new stems formed after defoliation. The gradual loss of conductivity measured during the refoliation process under well-irrigated conditions suggests that young seedlings of P. tremuloides may be more susceptible to cavitation after herbivore damage under drought conditions.
Journal Article
Branch sacrifice : cavitation-associated drought adaptation of riparian cottonwoods
by
COOMBS, K
,
ROOD, S. B
,
PATINO, S
in
Agronomy. Soil science and plant productions
,
Biological and medical sciences
,
Economic plant physiology
2000
In their native riparian zones (floodplains), Populus deltoides (prairie cottonwood) and P. fremontii (Fremont cottonwood) commonly experience substantial branch die-back. These trees occur in semi-arid areas of North America and unexpectedly given the dry regions, they are exceptionally vulnerable to xylem cavitation, drought-induced air embolism of xylem vessels. We propose that the vulnerability to cavitation and branch die-back are physiologically linked; drought-induced cavitation underlies branch die-back that reduces transpirational demand enabling the remaining shoot to maintain a favorable water balance. This proposal follows field observation along various western North American rivers as precocious branch senescence, the yellowing and death of leaves on particular branches during mid- to late summer, was common for P. deltoides and P. fremontii during hot and dry periods of low stream-flow. Branches displaying precocious senescence were subsequently dead the following year. The proposed association between cavitation, precocious senescence and branch die-back is also supported by experiments involving external pressurization of branches to about 2.5 MPa with a branch collar or through an adjacent cut-branch. The treatments induced xylem cavitation and increased leaf diffusive resistance (stomatal closure) that was followed by leaf senescence and branch death of P. deltoides. P. trichocarpa (black cottonwood) appeared to be less affected by the pressurization treatment and this species as well P. angustifolia (narrowleaf cottonwood) and P. balsamifera (balsam poplar) seldom display the patchy summer branch senescence typical of P. deltoides and P. fremontii. 'Branch sacrifice' describes this cavitation-associated senescence and branch die-back that may provide a drought adaptation for the prairie and Fremont cottonwoods.[PUBLICATION ABSTRACT]
Journal Article
Growth Dynamics of Root and Shoot Hydraulic Conductance in Seedlings of Five Neotropical Tree Species: Scaling to Show Possible Adaptation to Differing Light Regimes
by
Velez, Virginia
,
Dalling, J. W.
,
Tyree, Melvin T.
in
Animal and plant ecology
,
Animal, plant and microbial ecology
,
Architecture
1998
The dynamics of growth (shoot and root dry weights, surface areas, hydraulic conductances, and root length) were measured in seedlings of five neotropical tree species aged 4-16 months. The species studied included two light-demanding pioneers (Miconia argentea and Apeiba membranacea) and three shade-tolerant young- or old-forest species (Pouteria reticulata, Gustavia superba, and Trichilia tuberculata). Growth analysis revealed that shoot and root dry weights and hydraulic conductances and leaf area all increased exponentially with time. Alternative methods of scaling measured parameters to reveal differences that might explain adaptations to microsites are discussed. Scaling root conductance to root surface area or root length revealed a few species differences but nothing that correlated with adaptation to light regimes. Scaling of root surface area or root length to root dry weight revealed that pioneers produced significantly more root area and length per gram dry weight investment than shade-tolerant species. Scaling of root and shoot hydraulic conductances to leaf area and scaling of root conductance to root dry weight and shoot conductance to shoot dry weight also revealed that pioneers were significantly more conductive to water than shade-tolerant species. The advantages of scaling hydraulic parameters to leaf surface area are discussed in terms of the Ohm's law analogue of water flow in plants.
Journal Article
Changes in root hydraulic conductance (KR) of Olea oleaster seedlings following drought stress and irrigation
by
LO GULLO, MARIA A.
,
TYREE, MELVIN T.
,
SALLEO, SEBASTIANO
in
Agronomy. Soil science and plant productions
,
Biological and medical sciences
,
Dehydration
1998
Quasi-steady-state measurements of root hydraulic conductance
(KR) of Olea oleaster Hoffmgg. et Link potted
seedlings were performed using a pressure chamber with the aim of:
(a) measuring the impact of different water-stress levels on a
KR;
(b) measuring the kinetics of KR recovery
several days after soil rewetting; (c) relating changes
in KR to changes in root anatomy and morphology.
Increasing water-stress was applied in terms of ratio of leaf
water potential (ΨL) measured at midday to that at
zero turgor (ΨTLP), i.e. ΨL/ΨTLP=0·5,
1·0, 1·2, 1·6; KR was
measured initially and at 24, 48, 72, 96 h after irrigation. Values of KR in seedlings stressed to
ΨL/ΨTLP=1·2 increased for
48 h after irrigation from 0·23 to
0·97×10−5 kg s−1 m−2
MPa−1 i.e. from 16% to 66% of that measured in
unstressed seedlings. A marked shift of
the x-axis intercept of the straight line relating flow to
pressure (zero flow at non-zero pressure) was recorded
initially after irrigation and persisted up to 48 h. Recovery
of KR occurred within 24 h after irrigation in seedlings
at ΨL/ΨTLP=0·5 and
48 h later in those at ΨL/ΨTLP=1·0. Severe drought stress (ΨL/ΨTLP=1·6)
caused anatomical changes to roots which formed a two-layered
exodermis with thicker suberized walls and a three- to four-layered
endodermis with completely suberized
tangential walls. Recovery of KR in these roots
required resumed growth of root tips and emergence of new lateral roots.
Journal Article
Do Woody Plants Operate near the Point of Catastrophic Xylem Dysfunction Caused by Dynamic Water Stress?: Answers from a Model
by
Sperry, John S.
,
Tyree, Melvin T.
in
Biological and medical sciences
,
Branches
,
Cavitation flow
1988
We discuss the relationship between the dynamically changing tension gradients required to move water rapidly through the xylem conduits of plants and the proportion of conduits lost through embolism as a result of water tension. We consider the implications of this relationship to the water relations of trees. We have compiled quantitative data on the water relations, hydraulic architecture and vulnerability of embolism of four widely different species: Rhizophora mangle, Cassipourea elliptica, Acer saccharum, and Thuja occidentalis. Using these data, we modeled the dynamics of water flow and xylem blockage for these species. The model is specifically focused on the conditions required to generate 'runaway embolism,' whereby the blockage of xylem conduits through embolism leads to reduced hydraulic conductance causing increased tension in the remaining vessels and generating more tension in a vicious circle. The model predicted that all species operate near the point of catastrophic xylem failure due to dynamic water stress. The model supports Zimmermann's plant segmentation hypothesis. Zimmermann suggested that plants are designed hydraulically to sacrifice highly vulnerable minor branches and thus improve the water balance of remaining parts. The model results are discussed in terms of the morphology, hydraulic architecture, eco-physiology, and evolution of woody plants.
Journal Article
Hydraulic architecture of Acer saccharum and A. rubrum: comparison of branches to whole trees and the contribution of leaves to hydraulic resistance
by
Yang, Shudong
,
Tyree, Melvin T.
in
Acer
,
Agronomy. Soil science and plant productions
,
Biological and medical sciences
1994
Hydraulic resistance to water flow was measured in the xylem and leaves of above-ground portions of Acer saccharum and Acer rubrum for trees with trunk diameters (D) ranging from 0.02 to 0.2 m. Resistance (area basis) to water flow in leaves and petioles was 24 and 13 × 10 MPa m2s kg−1 for A. saccharum and A. rubrum, respectively. Leaf area of whole trees was proportional to D1.52. Absolute xylem resistance (MPa s kg−1 was proportional to D−1.54. So xylem resistance (area basis) was proportional to D0.2, which was not significantly different from a zero dependence (D0) for D≪0.2 m. On a leaf area basis, the resistance to water flow in the whole shoots was found to be approximately 50% in leaves and petioles, 35% in crown xylem, and 15% In trunk xylem for D≪0.2 m.
Journal Article