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1.
Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees 总被引:1,自引:0,他引:1
M. Fernanda Ortuño Yelitza García-Orellana Wenceslao Conejero M. Carmen Ruiz-Sánchez Juan José Alarcón Arturo Torrecillas 《Trees - Structure and Function》2006,20(1):1-8
The sensitivity of continuous (on a whole-day basis) and discretely (at midday) measured indicators of the plant water status
in adult lemon trees in response to a cycle of water deprivation and recovery, and the feasibility of obtaining baselines
for tree water status indicators was investigated in 30-year-old Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Control plants (T0) were irrigated daily above their crop water requirements in order to obtain non-limiting
soil water conditions, while T1 plants were subjected to water stress by withholding irrigation for 50 days, after which time
irrigation was restored and plant recovery was studied for 16 days. In T0 plants the water relations and the plant symptoms
confirmed that they had not suffered waterlogging. In contrast, T1 plants showed a substantial degree of water stress, which
developed very slowly. Maximum daily trunk shrinkage (MDS) increased in response to water stress during the first 15 days
of the experiment, but when the stem water potential (Ψstem) fell below −1.8 MPa, the MDS signal intensity decreased. However, Ψstem and sap flow (SF) signal intensities progressively increased during the water stress period. The results showed that MDS
is a very suitable plant-based indicator for precise irrigation scheduling in adult lemon trees. Reference or baseline relationships
for MDS, Ψstem, and SF measurements as a function of several parameters related to the evaporative demand of the atmosphere were obtained.
This fact open up the possibility of considering a plant-based indicator measurement at a given time relative to the expected
value under non-limiting water conditions, which can be calculated from the reference relationships. 相似文献
2.
Comparison of continuously recorded plant-based water stress indicators for young lemon trees 总被引:2,自引:0,他引:2
Continuously recorded plant-based water stress indicators (sap flow and parameters derived from trunk diameter fluctuations)
were compared in potted young lemon trees (Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock submitted to deficit irrigation. Daily maximum (MXTD) and minimum (MNTD) trunk diameters and daily trunk diameter
shrinkage (MDS) were directly influenced by the water supply to the trees from the soil. The continuously recorded plant-based
water stress indicators presented different degrees of sensitivity when used to estimate the water status of the plants. Sap
flow (SF) and MDS were more immediate and sensitive than MXTD and MNTD. However, the higher signal intensity: noise for SF
and the fact that its signal intensities remained clearly above unity during the stress period, indicating that the soil water
was depleted, point to the greater reliability of this indicator. Also, the possibility of developing further baseline relationships
between SF and air vapour pressure deficit in fully irrigated trees in field conditions increases the feasibility of using
this parameter in automatic irrigation systems. 相似文献
3.
Almond plants (Amygdalus communis L.) of the Garrigues variety were grown in the field drip irrigated and rainfed. Leaf water potential (Ψ) and leaf conductance
(g1) were determined throughout one growing season. Pre-dawn measurement for Ψ in the irrigated treatment was consistent through
the growing season, whereas in the rainfed treatment it decreased gradually. Ψ values at midday (Ψ minimum) was closely dependent
on atmospheric evaporative demand, and their recovery was quicker in the wet treatment than in the dry. The g1 values were higher in the wet than dry treatments, decreasing in both cases by leaf ageing. Maximum values for g1 were reached when evaporative demand was highest in the day. The relationship between Ψ and g1 revealed a decrease in the hysteresis throughout the growing season, being most marked in the dry treatment. The results
highlight the close dependence of Ψ and g1 on evaporative demand, leaf ageing and irrigtion treatment during the growing season. 相似文献
4.
Water relations and gas exchange in olive trees under regulated deficit irrigation and partial rootzone drying 总被引:2,自引:1,他引:1
J. E. Fernández A. Díaz-Espejo J. M. Infante P. Durán M. J. Palomo V. Chamorro I. F. Girón L. Villagarcía 《Plant and Soil》2006,284(1-2):273-291
It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However,
experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared
to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation
or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as
compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature
‘Manzanilla‘ olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ETc) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every
3 weeks in 2004. Measurements of stem water potential (Ψstem), stomatal conductance (g
s) and net CO2 assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ETc (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD
and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We
found small and random differences in Ψstem, g
s and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance
decreased in PRD trees as compared to Control trees, but a similar decrease in g
s was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also
showed no evidence of g
s being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation
treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in
either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches
of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted
in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and
that there is no need to alternate irrigation for achieving this effect.
Section Editor: R. E. Munns 相似文献
5.
We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity
higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψw) and leaf osmotic potential (Ψs) decreased. Leaf Ψw was at least −0.32 MPa lower than the Ψw of solution. Na+ and K+ ions explained about 78 % of decrease in Ψs. K+ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely,
Na+ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P
N) and stomatal conductance (g
s) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO2 concentration (C
i) followed the same trend. The P
N as a function of C
i showed that both the initial linear slope and upper plateau of the P
N
vs. C
i curve were markedly affected by high salinity (40 and 55 ‰). 相似文献
6.
Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach
Tom De Swaef Carmen D. Mellisho Annelies Baert Veerle De Schepper Arturo Torrecillas Wenceslao Conejero Kathy Steppe 《Trees - Structure and Function》2014,28(6):1607-1622
Key message
The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators.Abstract
Stem diameter (D stem) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D stem derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages. 相似文献7.
Water status and gas exchange of beech (Fagus sylvatica L.) and sessile oak [Quercus petraea (Mattuschka) Liebl.] were studied in a mixed stand in the Montejo de la Sierra forest (central Iberian Peninsula), one of
the southernmost locations of both species in Europe. Gas exchange and water potential were measured in leaves at different
canopy levels over several days in two growing seasons. The daily variation pattern was established with the measurements
of three selected dates per year, representative of the soil moisture content situations in early, mid- and late summer. A
similar daily time course of leaf water potential was found for the two species. Nevertheless, beech showed a most noticeable
decrease of water potential at midmorning and maintained lower leaf water potential than oak in the early afternoon. In 1994
the sessile oak saplings showed higher values of predawn water potential (Ψpd) than beech at the end of summer, when soil moisture content was lowest (20 cm depth). Beech showed a significantly lower
net assimilation rate (A) than sessile oak for leaves under the same PPFD. Maximum net photosynthesis values (A
max) for beech and sessile oak on sunny leaves were 10.1±0.4 μmol m–2 s–1 and 17.8±1.7 μmol m–2 s–1 respectively, and those for water vapour stomatal conductance (g
wv) were 265±31 mmol m–2 s–1 and 438±74 mmol m–2 s–1. Differences in A and g
wv between the two species were maintained throughout the day on all measurement dates. No clear relationship was found between
water status of saplings and stomata performance; there was only a negative correlation between Ψpd and g
wvmid in beech. Nevertheless, a significant response to the air vapour pressure gradient between leaf and air was translated into
stomata closure on an hourly basis, more intensively in beech.
Received: 4 March 1999 / Accepted: 21 December 1999 相似文献
8.
In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (P
N) and stomatal conductance (g
s) of attached leaves decreased as leaf water potential (Ψw) declined from −0.3 to −2.9 MPa. Although g
s decreased over the whole range of Ψw, nearly constant values in the intercellular CO2 concentrations (C
i) were observed as Ψw decreased to −1.8 MPa, but C
i increased as Ψw decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased
with water deficit, whereas non-photochemical quenching (qNP) increased progressively. A highly significant negative relationship between qNP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content
suggesting metabolic impairment. At a photon flux density of 550 μmol m−2 s−1, the allocation of electrons from photosystem (PS) 2 to O2 reduction was increased by 51 %, while the allocation to CO2 assimilation was diminished by 32 %, as Ψw declined from −0.3 to −2.9 MPa. A significant linear relationship between mean P
N and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear
when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas qP declined only at very severe stress and the excess photon energy was dissipated by increasing qNP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation
of PS2 and supported the protective role of qNP against photoinhibition in sunflower. 相似文献
9.
Rolf Bordiert 《Trees - Structure and Function》1994,8(3):115-125
Summary Bud break, shoot growth and flowering of trees involve cell expansion, known to be inhibited by moderate water deficits. In apparent contradiction to physiological theory, many trees flower or exchange leaves during the 6 month-long, severe dry season in the tropical dry forest of Guanacaste, Costa Rica. To explore this paradox, changes in tree water status during the dry season were monitored in numerous trees. Water potential of stem tissues (stem) was obtained by a modification of the pressure chamber technique, in which xylem tension was released by cutting defoliated branch samples at both ends. During the early dry season twigs bearing old, senescent leaves generally had a low leaf water potential (leaf), while stem varied with water availability. At dry sites, stem was very low in hardwood trees (<–4 MPa), but near saturation (>–0.2 MPa) in lightwood trees storing water with osmotic potentials between –0.8 and –2.1 MPa. At moist sites trees bearing old leaves rehydrated during drought; their stem increased from low values (<–3 MPa) to near saturation, resulting in differences of 3–4 MPa between stem and leaf. Indirect evidence indicates that rehydration resulted from osmotic adjustment of stem tissues and improved water availability due to extension of roots into moist subsoil layers. In confirmation of physiological theory, elimination of xylem tension by leaf shedding and establishment of a high solute content and high stem were prerequisites for flowering and bud break during drought. 相似文献
10.
Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables 总被引:7,自引:0,他引:7
M. S. Mielke M. A. Oliva N.F. de Barros R. M. Penchel C. A. Martinez S. da Fonseca A.C. de Almeida 《Trees - Structure and Function》2000,14(5):263-270
In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt
plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (Ψpd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (Θ) and microclimatic variables
were also recorded. Most of the rainfall during the experimental period occurred from October to December 1995 and from March
to April 1996, causing a significant variation in Θ and Ψpd. A high positive correlation (r
2=0.92) was observed between Ψpd and Θ measured at 0.3 m depth from the soil surface. During conditions of high soil water availability, the maximum values
of stomatal conductance for water vapor (g
s) and net photosynthetic rate (A) were over 0.4 mol m–2 s–2 and l5 μmol m–2 s–1, respectively. The results showed that Ψpd and leaf gas exchange of the examined trees were susceptible to changes in the water content of the upper soil layers, where
the major concentration of active roots occur. Multiple linear regression analysis indicated that photosynthetic active radiation
(Q), vapor pressure deficit (VPD), atmospheric CO2 molar fraction (C
a), and Ψpd were the most important factors controlling g
s whereas Q and VPD were the main microclimatic variables controlling A.
Received: 5 November 1998 / Accepted: 10 November 1999 相似文献
11.
Meinzer FC Woodruff DR Domec JC Goldstein G Campanello PI Gatti MG Villalobos-Vega R 《Oecologia》2008,156(1):31-41
Stomatal regulation of transpiration constrains leaf water potential (ΨL) within species-specific ranges that presumably avoid excessive tension and embolism in the stem xylem upstream. However,
the hydraulic resistance of leaves can be highly variable over short time scales, uncoupling tension in the xylem of leaves
from that in the stems to which they are attached. We evaluated a suite of leaf and stem functional traits governing water
relations in individuals of 11 lowland tropical forest tree species to determine the manner in which the traits were coordinated
with stem xylem vulnerability to embolism. Stomatal regulation of ΨL was associated with minimum values of water potential in branches (Ψbr) whose functional significance was similar across species. Minimum values of Ψbr coincided with the bulk sapwood tissue osmotic potential at zero turgor derived from pressure–volume curves and with the
transition from a linear to exponential increase in xylem embolism with increasing sapwood water deficits. Branch xylem pressure
corresponding to 50% loss of hydraulic conductivity (P
50) declined linearly with daily minimum Ψbr in a manner that caused the difference between Ψbr and P
50 to increase from 0.4 MPa in the species with the least negative Ψbr to 1.2 MPa in the species with the most negative Ψbr. Both branch P
50 and minimum Ψbr increased linearly with sapwood capacitance (C) such that the difference between Ψbr and P
50, an estimate of the safety margin for avoiding runaway embolism, decreased with increasing sapwood C. The results implied a trade-off between maximizing water transport and minimizing the risk of xylem embolism, suggesting
a prominent role for the buffering effect of C in preserving the integrity of xylem water transport. At the whole-tree level, discharge and recharge of internal C appeared to generate variations in apparent leaf-specific conductance to which stomata respond dynamically. 相似文献
12.
U. G. Hacke J. S. Sperry B. E. Ewers D. S. Ellsworth K. V. R. Schäfer R. Oren 《Oecologia》2000,124(4):495-505
We analyzed the hydraulic constraints imposed on water uptake from soils of different porosities in loblolly pine (Pinus taeda L.) by comparing genetically related and even-aged plantations growing in loam versus sand soil. Water use was evaluated
relative to the maximum transpiration rate (E
crit) allowed by the soil-leaf continuum. We expected that trees on both soils would approach E
crit during drought. Trees in sand, however, should face greater drought limitation because of steeply declining hydraulic conductivity
in sand at high soil water potential (Ψ
S). Transport considerations suggest that trees in sand should have higher root to leaf area ratios (A
R:A
L), less negative leaf xylem pressure (Ψ
L), and be more vulnerable to xylem cavitation than trees in loam. The A
R:A
L was greater in sand versus loam (9.8 vs 1.7, respectively). This adjustment maintained about 86% of the water extraction
potential for both soils. Trees in sand were more deeply rooted (>1.9 m) than in loam (95% of roots <0.2 m), allowing them
to shift water uptake to deeper layers during drought and avoid hydraulic failure. Midday Ψ
L was constant for days of high evaporative demand, but was less negative in sand (–1.6 MPa) versus loam (–2.1 MPa). Xylem
was more vulnerable to cavitation in sand versus loam trees. Roots in both soils were more vulnerable than stems, and experienced
the greatest predicted loss of conductivity during drought. Trees on both soils approached E
crit during drought, but at much higher Ψ
S in sand (<–0.4 MPa) than in loam (<–1.0 MPa). Results suggest considerable phenotypic plasticity in water use traits for P. taeda which are adaptive to differences in soil porosity.
Received: 28 December 1999 / Accepted: 31 March 2000 相似文献
13.
Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψπ) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized
to (Ψπ) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl2 or Na2SO4. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO3. The nutrient solutions were sampled for NO3 analysis each day immediately before renewing the solutions. The accumulative loss of NO3 from the solutions was considered to be uptake whereas NO3 reduction was the difference between uptake and seedling content. Lowering the (Ψπ) of the nutrient solutions resulted in decreased concentrations of NO3 in the plant, little or no effect (except at the lowest (Ψπ) level) on uptake, and increased nitrate reductase activity. Increased rates of NO3 reduction were in particular associated with the Cl concentration of the nutrient solution. 相似文献
14.
Potted 2-year-old lemon trees [Citrus limon (L.) Burm. fil, cv. Verna] grafted on sour orange (C. aurantium L.) rootstock were subjected to flooding for 3 d. Control plants were irrigated daily to field capacity. Continuously (sap
flow, trunk diameter fluctuations) and discretely (predawn and midday leaf water potential, leaf conductance) measured plant-based
water status indicators were compared. The sensitivity of the maximum daily trunk shrinkage signal intensity to flooding and
its behaviour during the recovery period demonstrated that this indicator is more feasible than the others for use in automatic
irrigation. The responses to flooding of continuously and discretely measured plant-based water status indicators were very
similar to those observed in response to drought stress indicating that it necessary to use soil water measurement automatic
sensors to detect the cause of the stress. The results underlined the robustness of the compensation heat-pulse technique
for estimating instantaneous and daily transpiration rates on flooding stress and recovery. 相似文献
15.
To understand the mechanisms of salt tolerance in a halophyte, sea aster (Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM
NaCl stress. The contents of Na+ and Cl- were highest in NaCl-stressed leaves. Leaf osmotic potentials (Ψ
s) were decreased by both stress treatments, whereas leaf turgor pressure (Ψ
t) was maintained under NaCl stress. Decrease inΨ
s without any loss ofΨ
t accounted for osmotic adjustment using Na+ and Cl- accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water
stress than under NaCl stress. Additionally, maximum CO2 fixation rate and O2 evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration.
Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl
stress have dehydration tolerance due to maintenance of Ψ
t and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized
environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated
Na+ and Cl-, and that this plant has typical halophyte characteristics, but not drought tolerance.
Electronic Publication 相似文献
16.
D. O Otieno C. Kurz-Besson J. Liu M. W. T. Schmidt R. Vale-Lobo do T. S. David R. Siegwolf J. S. Pereira J. D. Tenhunen 《Plant and Soil》2006,283(1-2):119-135
Studies were conducted to examine changes in soil (Ψs) and plant water status during summer in a 16-year old Quercus suber plantation in southern Portugal. Continuous measurements were conducted between May 2003 and August 2004, while discontinuous
measurements were conducted on a monthly basis between May and September 2003 and repeated between March and September 2004.
Intensive measurements were conducted on five trees with mean height and DBH of 5.3 m and 11.6 cm, respectively, growing at
close proximity to each other. Weather conditions and soil water potential (Ψs) at the rhizosphere of each of the trees measured
at 0.3 and 1 m soil depth were continuously monitored. Predawn (Ψpd) and midday (Ψmd) leaf water potentials were determined
every month. Soil and plant samples were also collected in June and September from different locations within the study site
for δ18O isotope composition analysis. Pressure–volume (p–v) curves were constructed from plant shoots at different times during the vegetative period to determine osmotic potential
at full saturation (Π100), water potential at turgor loss point (Ψtlp), relative water content at turgor loss point (R*tlp) and bulk modulus of elasticity (ε). Significant P < 0.05 decline in Ψs occurred between May and September, the lowest value recorded being –2.0 MPa. Decline in soil moisture
affected tree water status, but decline in leaf water potential varied significantly (P < 0.05) among the trees. At the end of summer drought, lowest Ψpd measured was –1.7 MPa while the highest measured during
this time was –0.8 MPa. Differences among trees were attributed to differences in rooting depth, as shown by regression analysis
of 18O isotopes. Radial stem growth ceased when Ψs within the upper 0.3 m depth approached –1.5 MPa. The upper soil layers contributed
approximately 33% of the total tree water requirement, between spring and mid summer when drought was experienced by trees.
Deep soil layers however, supplied most of the water required during drought and no growth was recorded during this time.
Stressed trees increased solute concentration of their tissues by a Magnitude of 0.7 MPa while bulk tissue elastic modulus
increased by about 17 MPa. The study emphasizes the significance of roots as determinants of tree productivity and survival
in the Mediterranean ecosystems. 相似文献
17.
Arne Sellin 《Plant and Soil》1996,184(2):273-280
Variation in base water potential (Ψb, a daily maximum level of plant water potential, which is presumed to correspond to the condition of equilibrium between
the soil and plant water potentials) was examined in shoots of Norway spruce trees growing in well-drained and waterlogged
soils. The influence of soil water content, air temperature, and vapour pressure deficit of the atmosphere on Ψb was studied using the pressure chamber technique. Maximum daily water potentials were not always observable before dawn;
some were registered up to two hours later. This tendency being characteristic of trees growing under stress (shade, waterlogging)
conditions, increased with declining soil water availability. In trees growing in well-drained soil, Ψb depended asymptotically on the available soil water storage (R2=0.73), while the values were slightly influenced by vapour pressure deficit of the atmosphere as well. In trees growing in
waterlogged soil, Ψb was independent of the soil water storage, but sensitive to the vapour pressure deficit. 相似文献
18.
Highly productive papyrus (Cyperus papyrus L.) wetlands dominate many permanently flooded areas of tropical East Africa; however, the cycling of carbon and water within
these ecosystems is poorly understood. The objective of this study was to utilise Eddy Covariance (EC) techniques to measure
the fluxes of carbon dioxide and water vapour between papyrus vegetation and the atmosphere in a wetland located near Jinja,
Uganda on the Northern shore of Lake Victoria. Peak, midday rates of photosynthetic CO2 net assimilation were approximately 40 μmol CO2 m−2 s−1, while night time losses through respiration ranged between 10 and 20 μmol CO2 m−2 s−1. Numerical integration of the flux data suggests that papyrus wetlands have the potential to sequester approximately 0.48 kg C m−2 y−1. The average daily water vapour flux from the papyrus vegetation through canopy evapotranspiration was approximately 4.75 kg
H2O m−2 d−1, which is approximately 25% higher than water loss through evaporation from open water. 相似文献
19.
S. Silim R. Nash D. Reynard B. White W. Schroeder 《Trees - Structure and Function》2009,23(5):959-969
The dynamic responses of stomatal conductance (g
s) net photosynthesis (A) and leaf water potential (Ψleaf) to a progressive drought were examined in nine poplar clones (Populus spp.) with contrasting drought tolerance from the Canadian Prairies, a region prone to frequent droughts. Plants were grown
in a greenhouse and either well-watered or drought preconditioned (5–6 cycles of drought) for 8 weeks. At the end of the last
cycle, plants were watered to saturation then progressively dried-down (−1.25 MPa Ψsoil) during which A, g
s and Ψleaf were measured. Drought tolerant Okanese reached the lowest combined Ψleaf while sensitive clones (Assiniboine and Imperial) had the highest (−1.6 vs. −1.1 MPa). Steady state g
s (measured under well watered conditions) was lower in tolerant (Okanese and Tristis SBC#1) than in sensitive clones. Preconditioning
reduced steady state g
s in all clones, lowered the threshold Ψleaf for stomatal closure and the minimum Ψleaf in most clones but did not affect the steady state A. Tolerant and some moderately tolerant clones maintained higher A at lower Ψleaf than the other clones. Stomatal closure was gradual in tolerant clones and in moderately tolerant Northwest but rapid in
the other clones. Stomata in the sensitive clones closed at the highest Ψleaf, Okanese closed at the lowest. The substantial range in gas exchange and Ψleaf responses observed here represented both drought tolerance and taxonomic (Aegiros or Tacamahaca sections) traits which could play a role in the survival and productivity in environments with limited water or during periods
of drought. 相似文献
20.
Water potential and sap flow rate in adult trees with moist and dry soil as used for the assessment of root system depth 总被引:4,自引:0,他引:4
Sap flow rate (Qw) and leaf water potential (Ψw.leaf) in adult specimens of birch (Betula) and oak (Quercus) were measured under contrasting soil moisture conditions (Ψw.sofl). With sufficient soil moisture Qw reached about 250 cm3h−1 calculated per unit tree-trunk segment as given by 1 cm length of its circumference. In soil water-stress conditions (when
Ψw.leaf = = −15 × 105Pa), birch stopped transpiration and wilted. Oak transpired even when Ψw.leaf fell below −20 × 105Pa. The relation between Qw and Ψw.leaf was always linear and with various Ψw.soil differed in the slopes of regression lines only. Hydraulic conductance (Kwcu) with nonlimiting moisture conditions reached about 6 × 10−9m3 10−5Pa−1s−1 and “conductivity” (“kwa”) when calculated per leaf area unit reached about 23 m 10−5Pa−1s−1. Kwcu and “kwa” were of about one half to nine times greater in birch than in oak. On the basis of relations between Ψw.soil at various depths, Ψw.leaf and Qw (resp. Kw) it is possible to assess the maximal rooting depth and the effective depth where the maximum of absorption of roots occurs.
It is to be seen that the root system macrostructure substantially participates in the drought avoidance of adult trees in
a forest stand. 相似文献