首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Many authors have attempted to explain the adaptive response of tropical plants to drought based on studies of water relations at the leaf level. Little attention has been given to the role of the xylem system in the control of plant water requirements. To evaluate this role, we studied the hydraulic architecture and water relations parameters of two tropical canopy trees with contrasting leaf phenologies: deciduous Pseudobombax septenatum (Jacq.) Dug and evergreen Ochroma pyramidale (Cav. ex lamb) Urban, both in the family Bombacaceae. The hydraulic architecture parameters studied include hydraulic conductivity, specific conductivity, leaf specific conductivity, and Huber value. Water relations parameters include leaf water potential, stem and leaf water storage capacitance, transpiration, stomatal conductance, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Compared to temperate trees, both species showed a pattern of highly vulnerable stems (50% loss of conductivity due to embolism at water potentials less than 1 MPa) with high leaf specific conductivities. The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma (e.g., 9.08 and 11.4 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively), were 3.4 and 2.3 times higher, respectively, than those of the deciduous species, Pseudobombax (e.g., 2.64 and 5.15 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively). A runaway embolism model was used to test the ability of Ochroma and Pseudobombax stems to maintain elevated transpiration rates during the higher evaporative demand of the dry season. The percent loss of leaf area predicted by the runaway embolism model for stems of Pseudobombax ranged from 5 to 30%, not enough to explain the deciduous phenology of this tree species without analysis of root resistance or leaf and petiole vulnerability to embolism.  相似文献   

2.
Hydraulic traits were studied for six Nothofagus species from South America (Argentina and Chile), and for three of these species two populations were studied. The main goal was to determine if properties of the water conductive pathway in stems and leaves are functionally coordinated and to assess if leaves are more vulnerable to cavitation than stems, consistent with the theory of hydraulic segmentation along the vascular system of trees in ecosystems subject to seasonal drought. Vulnerability to cavitation, hydraulic conductivity of stems and leaves, leaf water potential, wood density and leaf water relations were examined. Large variations in vulnerability to cavitation of stems and leaves were observed across populations and species, but leaves were consistently more vulnerable than stems. Water potential at 50% loss of maximum hydraulic efficiency (P(50)) ranged from -0.94 to -2.44 MPa in leaves and from -2.6 to -5.3 MPa in stems across species and populations. Populations in the driest sites had sapwood and leaves more vulnerable to cavitation than those grown in the wettest sites. Stronger diurnal down-regulation in leaf hydraulic conductance compared with stem hydraulic conductivity apparently has the function to slow down potential water loss in stems and protect stem hydraulics from cavitation. Species-specific differences in wood density and leaf hydraulic conductance (K(Leaf)) were observed. Both traits were functionally related: species with higher wood density had lower K(Leaf). Other stem and leaf hydraulic traits were functionally coordinated, resulting in Nothofagus species with an efficient delivery of water to the leaves. The integrity of the more expensive woody portion of the water transport pathway can thus be maintained at the expense of the replaceable portion (leaves) of the stem-leaf continuum under prolonged drought. Compensatory adjustments between hydraulic traits may help to decrease the rate of embolism formation in the trees more vulnerable to cavitation.  相似文献   

3.
Tsuda M  Tyree MT 《Tree physiology》1997,17(6):351-357
Hydraulic properties were studied in Acer saccharinum L., a riparian species that also grows well on a dry soil when transplanted. Hydraulic resistances were measured by two independent techniques: a new high-pressure flowmeter (HPFM) method and a conventional evaporative flux (EF) method. Vulnerability to cavitation was also investigated on petioles, stems and roots using a hydraulic conductivity technique. Vulnerability segmentation was found, i.e., roots, stems and petioles had different vulnerabilities to xylem dysfunction. Petioles were most vulnerable with 50% loss of hydraulic conductivity at -0.5 MPa, roots were least vulnerable (50% loss at -2.2 MPa) and stems were intermediate in vulnerability. The HPFM and the EF methods gave comparable results, except that the EF method gave a significantly higher value for resistance across petioles plus leaves. Native embolism was high enough to explain the discrepancy in resistance across petioles plus leaves between the HPFM and the EF methods, indicating that the HPFM estimates the minimum (potential) hydraulic resistance of plants. Whole-plant hydraulic resistance of A. saccharinum was low compared to resistances of other temperate species. The hydraulic characteristics of A. saccharinum were consistent with adaptation to its typical environment: low whole-plant resistance assures high transpiration rates in the presence of sufficient water, and vulnerability segmentation provides the ability to survive during droughts through shedding of expendable organs.  相似文献   

4.
Hydraulic properties of xylem in seven species of conifer were studied during late winter and early spring 1991. Vulnerability to cavitation and air embolism was investigated using hydraulic conductivity and acoustic techniques. Embolisms were induced in branches excised from mature trees by air-drying them in the laboratory. Both techniques gave comparable results indicating that they both assess the same phenomenon. Within a tree, vulnerability was related to the permeability of the xylem, the largest stems tended to cavitate before the smallest ones when water deficits developed in a branch. Interspecific comparisons showed large differences in the xylem water potential needed to induce significant embolism, values ranged from -2.5 MPa in Pinus sylvestris to -4 MPa in Cedrus atlantica, but these differences did not correlate with differences in the xylem permeability of the species. The vulnerability of a species to air embolism was found to be consistent with its ecophysiological behavior in the presence of water stress, drought-tolerant species being less vulnerable than drought-avoiding species.  相似文献   

5.
Ladjal M  Huc R  Ducrey M 《Tree physiology》2005,25(9):1109-1117
We studied hydraulic traits of young plants of the Mediterranean cedar species Cedrus atlantica (Endl.) G. Manetti ex Carrière (Luberon, France), C. brevifolia (Hook. f.) Henry (Cyprus), C. libani A. Rich (Hadeth El Jebbe, Lebanon) and C. libani (Armut Alani, Turkey). With an optimum water supply, no major differences were observed among species or provenances in either stem hydraulic conductivity (Ks) or leaf specific conductivity (Kl) measured on the main shoot. A moderate soil drought applied for 10 weeks induced marked acclimation through a reduction in Ks, particularly in the Lebanese provenance of C. libani, and a decrease in tracheid lumen size in all species. Cedrus atlantica, which had the smallest tracheids, was the species most vulnerable to embolism: a 50% loss in hydraulic conductivity (PsiPLC50) occurred at a water potential of -4.4 MPa in the well-watered treatment, and at -6.0 MPa in the moderate drought treatment. In the other species, PsiPLC50 was unaffected by moderate soil drought, and only declined sharply at water potentials between -6.4 and -7.5 MPa in both irrigation treatments. During severe drought, Ks of twigs and stomatal conductance (g(s)) were measured simultaneously as leaf water potential declined. For all species, lower vulnerability to embolism based on loss of Ks was recorded on current-year twigs. The threshold for stomatal closure (10% of maximum g(s)) was reached at a predawn water potential (Psi(pd)) of -2.5 MPa in C. atlantica (Luberon) and at -3.1 MPa in C. libani (Lebanon), whereas the other provenance and species had intermediate Psi(pd) values. Cedrus brevifolia, with a Psi(pd) (-3.0 MPa) close to that of C. libani (Lebanon), had the highest stomatal conductance of the study species. The importance of a margin of safety between water potential causing stomatal closure and that causing xylem embolism induction is discussed.  相似文献   

6.
Ecotypic variations in leaf conductance, soil-to-leaf hydraulic conductance, components of tissue water potential, hydraulic architecture parameters and xylem embolism were examined in greenhouse-grown two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings from six origins representing the geographic range of the species in Italy. Cortical resin composition of the seedlings was also determined. Measurements were made on well-watered seedlings and on seedlings subjected to recurring severe drought. Drought-stressed seedlings had lower mean leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than well-watered seedlings. They also exhibited more negative osmotic potentials, higher relative water deficit at incipient plasmolysis, but a similar maximum modulus of elasticity. Drought-stressed seedlings showed a higher degree of xylem embolism, a lower Huber value, lower leaf specific conductivity and lower specific conductivity than well-watered seedlings. Drought-stressed seedlings of provenances from more xeric habitats (Tremiti, Porto Pino and Mottola) had greater leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than drought-stressed seedlings of provenances from more mesic habitats (Imperia, Otricoli and Vico del Gargano). They also showed higher osmotic adjustment and a lower degree of xylem embolism. Among provenances, there were no significant differences in hydraulic architecture parameters in response to the drought treatment; however, Tremiti and Porto Pino seedlings displayed smaller drought-induced reductions in specific conductivity and leaf specific conductivity, respectively, than seedlings from other provenances. These differences suggest that seedlings from xeric provenances, especially Tremiti, have greater resistance to desiccation than seedlings from mesic provenances. No clear association was found between terpene variability and the other traits investigated, although terpene composition was related to the geographical distribution of the provenances. We conclude that the drought-tolerance responses of Tremiti make it a more suitable provenance than the others for establishment on sites prone to severe soil water deficits.  相似文献   

7.
Adequate water transport is necessary to prevent stomatal closure and allow for photosynthesis. Dysfunction in the water transport pathway can result in stomatal closure, and can be deleterious to overall plant health and survival. Although much is known about small branch hydraulics, little is known about the coordination of leaf and stem hydraulic function. Additionally, the daily variations in leaf hydraulic conductance (K(leaf)), stomatal conductance and water potential (Ψ(L)) have only been measured for a few species. The objective of the current study was to characterize stem and leaf vulnerability to hydraulic dysfunction for three eastern U.S. tree species (Acer rubrum, Liriodendron tulipifera and Pinus virginiana) and to measure in situ daily patterns of K(leaf), leaf and stem Ψ, and stomatal conductance in the field. Sap flow measurements were made on two of the three species to compare patterns of whole-plant water use with changes in K(leaf) and stomatal conductance. Overall, stems were more resistant to hydraulic dysfunction than leaves. Stem P50 (Ψ resulting in 50% loss in conductivity) ranged from -3.0 to -4.2 MPa, whereas leaf P50 ranged from -0.8 to -1.7 MPa. Field Ψ(L) declined over the course of the day, but only P. virginiana experienced reductions in K(leaf) (nearly 100% loss). Stomatal conductance was greatest overall in P. virginiana, but peaked midmorning and then declined in all three species. Midday stem Ψ in all three species remained well above the threshold for embolism formation. The daily course of sap flux in P. virginiana was bell-shaped, whereas in A. rubrum sap flux peaked early in the morning and then declined over the remainder of the day. An analysis of our data and data for 39 other species suggest that there may be at least three distinct trajectories of relationships between maximum K(leaf) and the % K(leaf) at Ψ(min). In one group of species, a trade-off between maximum K(leaf) and % K(leaf) at Ψ(min) appeared to exist, but no trade-off was evident in the other two trajectories.  相似文献   

8.
Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.  相似文献   

9.
We examined the effects of drought on the water relations, osmotic adjustment and xylem vulnerability to embolism of olive (Olea europaea L.) varieties, 'Meski' and 'Chemlali'. Two-year-old self-rooted cuttings growing in sand-filled pots in a greenhouse were subjected to water stress by withholding water for 60 days. Water relations and gas exchange measurements showed that 'Chemlali' was more drought resistant than 'Meski' and had a greater capacity for osmotic adjustment through solute accumulation. However, when water stress was acute, the effect of osmoregulation on leaf cell turgor was largely counteracted by xylem cavitation. Cavitation vulnerability curves showed that both varieties were highly resistant to embolism formation. The xylem water potential inducing 50% loss of stem conductivity approached -7 MPa in 'Meski' and only slightly less in 'Chemlali'. Although the difference between varieties in susceptibility to xylem embolism was small, it appears to account in large part for the difference between them in the ability to tolerate severe drought.  相似文献   

10.
In this paper, ten woody plants grew on the campus of the Beijing Forestry University were selected for measuring hydraulic architecture parameters and water potential of one-year-old twigs. The results show that day and night change of water potential and hydraulic architecture parameters appear to be obviously convex trend. The relationship models between water potential and hydraulic conductivity, special conductivity and leaf special conductivity were respectively established, which were simulated by equations Y=axb and Y=ax2 bx c, through which the parameters physiological meanings were discussed. The results show also show that embolism vulnerability of ten tree species was Robinia pseudoacacia> Gleditsia sinensis> Acer truncatum> Prunus davidiana> Cornus alba> Platycladus orientalis> Cedrus deodara> Pinus bungeana> Pinus tabulaeformis> Jasminum nudiflorum, and that the water transport efficiency in xylem and embolism vulnerability of the species are ring-porous species> diffuse-porous species>non  相似文献   

11.
Despite considerable investigations of diurnal water use characteristics in different plant functional groups, the research on daily water use strategies of woody bamboo grasses remains lacking. We studied the daily water use and gas exchange of Sinarundinaria nitida (Mitford) Nakai, an abundant subtropical bamboo species in Southwest China. We found that the stem relative water content (RWC) and stem hydraulic conductivity (K(s)) of this bamboo species did not decrease significantly during the day, whereas the leaf RWC and leaf hydraulic conductance (K(leaf)) showed a distinct decrease at midday, compared with the predawn values. Diurnal loss of K(leaf) was coupled with a midday decline in stomatal conductance (g(s)) and CO(2) assimilation. The positive root pressures in the different habitats were of sufficient magnitude to refill the embolisms in leaves. We concluded that (i) the studied bamboo species does not use stem water storage for daily transpiration; (ii) diurnal down-regulation in K(leaf) and gs has the function to slow down potential water loss in stems and protect the stem hydraulic pathway from cavitation; (iii) since K(leaf) did not recover during late afternoon, refilling of embolism in bamboo leaves probably fully depends on nocturnal root pressure. The embolism refilling mechanism by root pressure could be helpful for the growth and persistence of this woody monocot species.  相似文献   

12.
We measured xylem pressure potentials, soil osmotic potentials, hydraulic conductivity and percent loss of conductivity (PLC) due to embolism, and made microscopic observations of perfused dye in the white mangrove tree, Laguncularia racemosa (L.) Gaertn. f., (1) to determine its vulnerability to air embolism compared with published results for the highly salt-tolerant red mangrove tree, Rhizophora mangle L., and (2) to identify possible relationships between air embolism, permanent blockage of vessels and stem diameter. Laguncularia racemosa was more vulnerable to embolism than reported for R. mangle, with 50 PLC at -3.4 MPa. Narrow stems (5-mm diameter) had higher PLC than larger stems (8.4- or 14-mm diameter) of the same plants. Basic fuchsin dye indicated that up to 89% of the vessels, especially in the narrow stems, had permanent blockage that could not be reversed by high pressure perfusion. Air embolism could lead to permanent vessel blockage and eventual stem mortality. Such vulnerability to embolism may restrict the growth of L. racemosa and limit its distribution to less salty areas of mangrove communities.  相似文献   

13.
We studied the effect of tree architecture on xylem anatomy in three Betula pendula Roth., three Picea abies (L.) H. Karst. and three Pinus sylvestris (L.) trees (mean age 35 years). First, the analysis of conduit anatomy in different tree parts showed that conduits tapered and their frequency increased from roots (≥ 2 mm) to stem, from stem to branches and further to leaf petioles in B. pendula. Conduit anatomy in lateral and main roots, as well as lateral and main branches, significantly differed from each other in all the studied species. The increase in conduit diameter and decrease in frequency from the pith to the bark were clear aboveground, but variable patterns were observed belowground. In the leaf petioles of B. pendula, conduit diameter increased and conduit frequency decreased with increasing individual leaf area. Second, the results concerning the scaling of conduit diameter were compared with the predictions of the general vascular scaling model (WBE model) and Murray's law. The scaling parameter values at the tree level corresponded with the predictions of the WBE model in all the studied trees except for one tree of both conifer species. However, the scaling parameter values changed from one tree compartment to another rather than remaining uniform inside a tree, as assumed by the WBE model. The assumptions of the WBE model of a constant conductivity ratio, constant tapering and an unchanged total number of conduits were not fulfilled. When the conductivity ratio and relative tapering were plotted together, the results aboveground corresponded quite well with Murray's law: the conductivity ratio increased when relative tapering decreased. Our results support the theory that trees adjust both their macro- and microstructure to maximize their water transport efficiency, but also to prevent embolism and ensure mechanical safety.  相似文献   

14.
In the Rocky Mountains, ponderosa pine (Pinus ponderosa (ssp.) ponderosa Dougl. ex P. Laws. & C. Laws) often co-occurs with Douglas-fir (Pseudotsuga menziesii var. glauca (Mayr) Franco). Despite previous reports showing higher shoot vulnerability to water-stress-induced cavitation in ponderosa pine, this species extends into drier habitats than Douglas-fir. We examined: (1) whether roots and shoots of ponderosa pine in riparian and slope habitats are more vulnerable to water-stress-induced cavitation than those of Douglas-fir; (2) whether species-specific differences in vulnerability translate into differences in specific conductivity in the field; and (3) whether the ability of ponderosa pine to extend into drier sites is a result of (a) greater plasticity in hydraulic properties or (b) functional or structural adjustments. Roots and shoots of ponderosa pine were significantly more vulnerable to water-stress-induced cavitation (overall mean cavitation pressure, Psi(50%) +/- SE = -3.11 +/- 0.32 MPa for shoots and -0.99 +/- 0.16 MPa for roots) than those of Douglas-fir (Psi(50%) +/- SE = -4.83 +/- 0.40 MPa for shoots and -2.12 +/- 0.35 MPa for roots). However, shoot specific conductivity did not differ between species in the field. For both species, roots were more vulnerable to cavitation than shoots. Overall, changes in vulnerability from riparian to slope habitats were small for both species. Greater declines in stomatal conductance as the summer proceeded, combined with higher allocation to sapwood and greater sapwood water storage, appeared to contribute to the ability of ponderosa pine to thrive in dry habitats despite relatively high vulnerability to water-stress-induced cavitation.  相似文献   

15.
Domec JC  Pruyn ML 《Tree physiology》2008,28(10):1493-1504
Effects of trunk girdling on seasonal patterns of xylem water status, water transport and woody tissue metabolic properties were investigated in ponderosa pine (Pinus ponderosa Dougl. ex P. Laws.) trees. At the onset of summer, there was a sharp decrease in stomatal conductance (g(s)) in girdled trees followed by a full recovery after the first major rainfall in September. Eliminating the root as a carbohydrate sink by girdling induced a rapid reversible reduction in g(s). Respiratory potential (a laboratory measure of tissue-level respiration) increased above the girdle (branches and upper trunk) and decreased below the girdle (lower trunk and roots) relative to control trees during the growing season, but the effect was reversed after the first major rainfall. The increase in branch respiratory potential induced by girdling suggests that the decrease in g(s) was caused by the accumulation of carbohydrates above the girdle, which is consistent with an observed increase in leaf mass per area in the girdled trees. Trunk girdling did not affect native xylem embolism or xylem conductivity. Both treated and control trunks experienced loss of xylem conductivity ranging from 10% in spring to 30% in summer. Girdling reduced xylem growth and sapwood to leaf area ratio, which in turn reduced branch leaf specific conductivity (LSC). The girdling-induced reductions in g(s) and transpiration were associated with a decrease in leaf hydraulic conductance. Two years after girdling, when root-to-shoot phloem continuity had been restored, girdled trees had a reduced density of new wood, which increased xylem conductivity and whole-tree LSC, but also vulnerability to embolism.  相似文献   

16.
In tropical moist forests, seasonal drought limits plant survival, productivity and diversity. Drought-tolerance mechanisms of tropical species should reflect the maximum seasonal water deficits experienced in a particular habitat. We investigated stem xylem vulnerability to cavitation in nine tropical species with different life histories and habitat associations. Stem xylem vulnerability was scored as the xylem water potential causing 50 and 75% loss of hydraulic conductivity (P50 and P75, respectively). Four shade-tolerant shrubs ranged from moderately resistant (P50=-1.9 MPa for Ouratea lucens Kunth. Engl.) to highly resistant to cavitation (P50=-4.1 MPa for Psychotria horizontalis Sw.), with shallow-rooted species being the most resistant. Among the tree species, those characteristic of waterlogged soils, Carapa guianensis Aubl., Prioria copaifera Griseb. and Ficus citrifolia Mill., were the most vulnerable to cavitation (P50=-0.8 to -1.6 MPa). The wet-season, deciduous tree, Cordia alliodora (Ruiz and Pav.) Oken., had resistant xylem (P50=-3.2 MPa), whereas the dry-season, deciduous tree, Bursera simaruba (L.) Sarg. was among the most vulnerable to cavitation (P50=-0.8 MPa) of the species studied. For eight out of the nine study species, previously reported minimum seasonal leaf water potentials measured in the field during periods of drought correlated with our P50 and P75 values. Rooting depth, deciduousness, soil type and growth habit might also contribute to desiccation tolerance. Our results support the functional dependence of drought tolerance on xylem resistance to cavitation.  相似文献   

17.
We evaluated the osmotic adjustment capacity of leaves and roots of young olive (Olea europaea L.) trees during a period of water deficit and subsequent rewatering. The trials were carried out in Basilicata (40 degrees 24' N, 16 degrees 48' E) on 2-year-old self-rooted olive plants (cv. 'Coratina'). Plants were subjected to one of four drought treatments. After 13 days of drought, plants reached mean predawn leaf water potentials of -0.45 +/- 0.015 MPa (control), -1.65 +/- 0.021 (low stress), -3.25 +/- 0.035 (medium stress) and -5.35 +/- 0.027 MPa (high stress). Total osmotic adjustment increased with increasing severity of drought stress. Trees in the high stress treatment showed total osmotic adjustments ranging between 2.4 MPa at 0500 h and 3.8 MPa at 1800 h on the last day of the drought period. Osmotic adjustment allowed the leaves to reach leaf water potentials of about -7.0 MPa. Active osmotic adjustment at predawn decreased during the rewatering period in both leaves and roots. Stomatal conductance and net photosynthetic rate declined with increasing drought stress. Osmotic adjustment in olive trees was associated with active and passive osmotic regulation of drought tolerance, providing an important mechanism for avoiding water loss.  相似文献   

18.
Downward redistribution of soil water through plant roots has important consequences for water and nutrient balance of arid and semi-arid ecosystems. Nevertheless, information on the seasonal patterns and magnitudes of redistribution is lacking for all but a few plant species. We measured sap flow in the taproot and three main lateral roots of a 10-year-old Juglans major Torr. tree, on an ephemeral catchment in southeastern Arizona, to determine how patterns of redistribution respond to pulses of summer precipitation. Groundwater was beyond rooting depth and a hardpan prevented recharge of surface water to deep soil layers. Reverse flow (hydraulic descent) commenced in the taproot and deep lateral roots in early August after a series of moderate precipitation events, and abruptly ceased after all shallow roots were experimentally severed in mid-August. On some days, hydraulic descent continued in the deep lateral roots during periods of daytime transpiration, and the daily volume of hydraulic descent (deep lateral roots plus taproot) ranged from 10 to nearly 60% of daily transpiration. The persistent pattern of reverse flow demonstrates that, in some plants, water potential gradients from soil to leaf during transpiration are often smaller than those between soil layers within the rooting zone. Hydraulic descent may be an important component of the water balance of phreatophytic trees by facilitating root growth in deep soil layers and by transferring water away from shallow-rooted competitors.  相似文献   

19.
Roots from healthy and diseased mature ponderosa pine, Pinus ponderosa Laws., trees were excavated from a site near Burns, Oregon. The diseased trees were infected with black-stain root disease, Leptographium wageneri Kendrick, or annosus root disease, Heterobasidion annosum (Fr.) Bref., or both. Axial hydraulic conductivity of the roots was measured under a positive head pressure of 5 kPa, and the conducting area was stained with safranin dye to determine specific conductivity (k(s)). In diseased roots, only 8-12% of the cross-sectional xylem area conducted water. Resin-soaked xylem completely restricted water transport and accounted for 13-16% of the loss in conducting area. In roots with black-stain root disease, 17% of the loss in conducting area was associated with unstained xylem, possibly resulting from occlusions or embolisms. Based on the entire cross-sectional area of infected roots, the k(s) of roots infected with black-stain root disease was 4.6% of that for healthy roots, whereas the k(s) of roots infected with annosus root disease was 2.6% of that for healthy roots. Although these low values were partly the result of the presence of a large number of diseased roots (72%) with no conducting xylem, the k(s) of functional xylem of diseased roots was only 33% of that for healthy roots. The low k(s) values of functional xylem in diseased roots may be caused by fungus induced occlusions preceding cavitation and embolism of tracheids. The k(s) of disease-free roots from diseased trees was only 70% of that for healthy roots from healthy trees. The disease-free roots had the same mean tracheid diameter and tissue density as the healthy roots, suggesting that the lower k(s) in disease-free roots of diseased trees may also have been caused by partial xylary occlusions.  相似文献   

20.
The relationship between root elongation and root hydraulic conductivity was investigated in 1-year-old, overwintered black spruce (Picea mariana (Mill.) seedlings. Hydraulic conductivity was estimated by observing water flux through decapitated roots under positive pressure. Five hydraulic conductivity parameters were estimated: (1) water flux under a minimal pressure of 0.2 MPa (J(v, min)); (2) pressure at which a linear relationship between water flux and pressure began (P(min)); (3) slope of the linear water flux-pressure relationship (L(v)); (4) pressure at which the linear relationship between water flux and pressure ended (P(max)); and (5) maximum water flux (J(v, max)). Between day 1 and day 2 after thawing of the growing medium, there were significant increases in L(v) and J(v, max) but there was little, if any, root elongation. Root elongation averaged 5.4 cm seedling(-1) 5 days after thawing and 88.2 cm seedling(-1) 20 days after thawing. Root hydraulic conductivity increased with new root length initially. But between days 20 and 30, when new root length nearly doubled, P(min) was the only measure of hydraulic conductivity that increased significantly. There were significant correlations (P < 0.05) between white root length and both J(v, min) (r(2) = 0.90) and J(v, max) (r(2) = 0.91).  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号