Xylem acoustic emissions and water relations of Calluna vulgaris L. at two climatological regions of Britain

The acoustic emission rate (as a result of xylem cavitation), stem water content, stomatal conductance, and leaf water potential of heather (Calluna vulgaris L. Hull) were compared over a period of 18 months at two contrasting sites in Britain. The sites were Thursely Common in south-east England, and Flanders Moss in central Scotland (average rainfall of 600 mm per year and 1500 mm per year, respectively). In the first year of study (1992) the natural difference between the sites was amplified by a severe drought affecting south-east England. The relative water content of the xylem (RWC) did not differ between the sites, and did not fluctuate seasonally, despite the drought at Thursely. Acoustic emissions were detected at both sites, but the incidence was low. The same range of foliage water potential and stomatal conductance was found at both sites. The leaf area to sapwood area ratio at the dry site was half that at the wet site, and it is suggested that this adjustment of the transpiring area relative to the water conducting area facilitates the close physiological state of the plants at the two sites. The possible occurrence of aerial refilling and freezing induced xylem cavitation is also discussed.     

Interrelationships between water use and growth traits in biomass-producing willows

Abstract Water use, drought response and growth were examined under controlled conditions in four interbreeding willow species from different geographical origins (two clones of Salix viminalis L., one clone of S. viminalis × S. schwerenii E. Wolf and one clone of S. purpurea L.). The levels of soil water depletion that plants could sustain without wilting varied markedly between the clones. The level of drought resistance expressed this way was positively related to resistance to xylem cavitation, negatively related to the maximum stomatal conductance, and positively related to early stomatal closure. The rate of stomatal closure, however, was negatively related to the resistance to xylem cavitation. Prior to drought, there were no significant differences between leaf-specific hydraulic conductances of the clones when whole plants were considered. However, there were differences if the roots and shoots were considered separately. Drought resistance was negatively related to maximum growth yields. This is probably because resources were diverted away from leaf production to the production of denser wood (wood density was positively related to cavitation resistance), and, for one clone, to the growth of a larger root system. In addition, because the level of drought resistance was negatively related to the maximum stomatal conductance, growth may have been adversely affected as a result of reduced photosynthesis. Given its high water extraction ability, one of the clones started to wilt sooner than expected, although only lateral shoots were affected. This appeared to indicate a strategy of sacrificing expendable shoots.     

Leaf age and salinity influence water relations of pepper leaves

Plant growth is reduced under saline conditions even when turgor in mature leaves is maintained by osmotic adjustment. The objective of this study was to determine if young leaves from salt-affected plants were also osmotically adjusted. Pepper plants (Capsicum annuum L. cv. California Wonder) were grown in several levels of solution osmotic potential and various components of the plants' water relations were measured to determine if young, rapidly growing leaves could accumulate solutes rapidly enough to maintain turgor for normal cell enlargement. Psychrometric measurements indicated that osmotic adjustment is similar for both young and mature leaves although osmotic potential is slightly lower for young leaves. Total water potential is also lower for young leaves, particularly at dawn for the saline treatments. The result is reduced turgor under saline conditions at dawn for young but not mature leaves. This reduced turgor at dawn, and presumably low night value, is possibly a cause of reduced growth under saline conditions. No differences in leaf turgor occur at midday. Porometer measurements indicated that young leaves at a given salinity level have a higher stomatal conductance than mature leaves, regardless of the time of day. The result of stomatal closure is a linear reduction of transpiration.     

Rootstock control of scion response to water stress in grapevine

Rootstocks play a major role in grapevine tolerance to water stress by controlling and adjusting the water supply to shoot transpiration demand. This study aimed to characterize the influence of rootstock genotypes in the adaptive response of scions to water limiting conditions. The effect of rootstock genotype (140Ru and SO4) was observed in the different availability of water provided to the scions (Cabernet Sauvignon, Grenache, Merlot, Syrah), while scions influenced stomatal control of water transpiration. Implication on the cell-to-cell component of plant water transport in both rootstock and scion impacted on embolisms formation in roots and on hydraulics of leaves. The main conclusion of the present study was that rootstock and scion genotypes are able to confer to the plant traits of drought adaptability influencing respectively the capacity of water extraction from the soil and the sensitivity of the stomatal control.     

Field water relations of a wet-tropical forest tree species,Pentaclethra macroloba (Mimosaceae)

Summary The water relations of Pentaclethra macroloba (Willd.) Kuntze, a dominant, shade-tolerant, tree species in the Atlantic lowlands of Costa Rica, were examined within the forest canopy. Pressure-volume curves and diurnal courses of stomatal conductance and leaf water potential were measured in order to assess differences in water relations between understory, mid-canopy and canopy leaves. Leaves in the canopy had the smallest pinnules but the largest stomatal frequencies and stomatal conductances of the three forest levels. Osmotic potentials at full turgidity decreased with height in the forest; in the canopy and midcanopy they were reduced relative to those in the understory just enough to balance the gravitational component of water potential. Consequently, maximum turgor pressures were similar for leaves from all three canopy levels. Bulk tissue elastic modulus increased with height in the canopy. Leaf water potentials were lowest in the canopy and highest in the understory, even when the gravitational component was added to mid-canopy and canopy values. As a result, minimum turgor pressures were also lowest in the canopy compared to those at lesser heights, and approached zero in full sunlight on clear days.Osmotic potentials at each canopy level were similar for both wet and dry season samples dates suggesting that seasonal osmotic adjustment does not occur. Despite lowered predawn water potentials during the dry season, turgor was maintained in the understory by reduced stomatal conductances.     

The effect of nitrogen on plant water relations in tea (Camellia sinensis)

An experiment was carried out to study the effect of nitrogen deficiency on the water relations of tea (Camellia sinensis). The plants were grown in sand and nitrogen deficiency induced by witholding the supply of nitrogen. Nitrogen deficiency increased stomatal resistance and reduced transpiration. The capacity of the stomata to open fully in the morning was not impaired by nitrogen deficiency. Leaf water potential and probably root resistance were not affected by nitrogen deficiency. The sensitivity of transpiration and stomatal resistance to sand water stress was increased by nitrogen deficiency.     

Water relations and stomatal characteristics of Mediterranean plants with different growth forms and leaf habits: responses to water stress and recovery

The aim of this study was to extent the range of knowledge about water relations and stomatal responses to water stress to ten Mediterranean plants with different growth forms and leaf habits. Plants were subjected to different levels of water stress and a treatment of recovery. Stomatal attributes (stomatal density, StoD), stomatal conductance (g _s), stomatal responsiveness to water stress (SR), leaf water relations (pre-dawn and midday leaf water potential and relative water content), soil to leaf apparent hydraulic conductance (K _L) and bulk modulus of elasticity (ε) were determined. The observed wide range of water relations and stomatal characteristics was found to be partially depended on the growth form. Maximum g _s was related to StoD and the stomatal area index (SAI), while g _s evolution after water stress and recovery was highly correlated with K _L. Relationships between SR to water deficit and other morphological leaf traits, such as StoD, LMA or ε, provided no general correlations when including all species. It is concluded that a high variability is present among Mediterranean plants reflecting a continuum of leaf water relations and stomatal behaviour in response to water stress.     

Seasonal patterns of gas exchange,water relations and growth of it Roupala montana,an evergreen savanna species

Roupala montana is an evergreen species widespread in the seasonal savannas of the central plains of Brazil. I examined the degree of coupling of photosynthetic gas-exchange characteristics, water relations and growth responses of R. montana with regard to seasonal changes in soil water availability. Despite a rainless period of over three months soil water potential at 60 cm depth reached values of only about -1.0 MPa, while pre-dawn leaf water potential (^l) reached about -0.4 MPa by the end of the three-month drought. Thus, R. montana had access to deep soil water in the dry period, but pre-dawn ^l did not reach the high wet season values of -0.2 MPa. Most of the shoot growth was concluded in the onset of the rainy season. Although some individual branches might have shown some extension thereafter, most of them remained inactive during the rest of the rainy season and the subsequent dry season. New leaf production was also restricted to the first part of the wet period. R. montana remained evergreen in the dry season, but there was a 27% decrease in the number of leaves and herbivory removed about 16% of the leaf area still present in the plant. CO₂-exchange rates of these leaves reached only ca. 55% of the maximum rainy season values of 14 µmol m^-2 s^-1. Thus, the estimated potential daily carbon gain was about 34% of the maximum by the end of the dry period. These values will be even lower, if we considered the decrease in photosynthetic rates that occurred around midday. These reductions in photosynthetic rates as a result of partial stomatal closure were measured both in the wet and dry season and they were related to increases in the evaporative demand of the atmosphere. In conclusion, the combined effect of herbivory, leaf loss and reductions in photosynthetic rates limited plant productivity in the dry season.     

Hydraulic conductance and water potential gradients in squash leaves showing mycorrhiza-induced increases in stomatal conductance

Stomatal conductance (g _s) and transpiration rates vary widely across plant species. Leaf hydraulic conductance (k _leaf) tends to change with g _s, to maintain hydraulic homeostasis and prevent wide and potentially harmful fluctuations in transpiration-induced water potential gradients across the leaf (ΔΨ _leaf). Because arbuscular mycorrhizal (AM) symbiosis often increases g _s in the plant host, we tested whether the symbiosis affects leaf hydraulic homeostasis. Specifically, we tested whether k _leaf changes with g _s to maintain ΔΨ _leaf or whether ΔΨ _leaf differs when g _s differs in AM and non-AM plants. Colonization of squash plants with Glomus intraradices resulted in increased g _s relative to non-AM controls, by an average of 27% under amply watered, unstressed conditions. Stomatal conductance was similar in AM and non-AM plants with exposure to NaCl stress. Across all AM and NaCl treatments, k _leaf did change in synchrony with g _s (positive correlation of g _s and k _leaf), corroborating leaf tendency toward hydraulic homeostasis under varying rates of transpirational water loss. However, k _leaf did not increase in AM plants to compensate for the higher g _s of unstressed AM plants relative to non-AM plants. Consequently, ΔΨ _leaf did tend to be higher in AM leaves. A trend toward slightly higher ΔΨ _leaf has been observed recently in more highly evolved plant taxa having higher productivity. Higher ΔΨ _leaf in leaves of mycorrhizal plants would therefore be consistent with the higher rates of gas exchange that often accompany mycorrhizal symbiosis and that are presumed to be necessary to supply the carbon needs of the fungal symbiont.     

北美枫香的离体培养和植株再生

1植物名称北美枫香(Liquidambar styraciflua L.). 2材料类别幼嫩枝条. 3培养条件(1)腋芽诱导培养基:MS 6-BA 0.2mg·L-1(单位下同);(2)不定芽增殖培养基:MS 6-BA 0.2,0.5,1.0,2.0 NAA 0.2;(3)壮苗培养基:MS 6-BA 0.2 NAA 0.02;(4)生根培养基:1/2MS IBA 0.2 NAA 0.2.以上培养基pH为5.7～5.8,加入3%蔗糖和0.48%琼脂.培养温度为25℃,光照时间为12 h·d-1,光照度为2 000 1x.     

Photosynthesis and leaf morphology ofLiquidambar styraciflua L. under variable urban radiant-energy conditions

Diminished sunlight, characteristic of urban canyons, has been suggested as being potentially limiting to plant growth. This study investigated the response of sweetgum (Liquidambar styraciflua L.) to variable irradiance in a range of urban locations. Diurnal photosynthesis was measured in situ on mature trees, comparing an open site at an urban park with an urban canyon that received 4 h of midday sun in midsummer. Photosynthesis for trees growing in the canyon was lower both during shaded and sunlit periods compared with trees at the park. Photosynthesis of detached shoots in a growth chamber was greater in canyon than park foliage at low irradiance, indicating possible photosynthetic shade acclimation analogous to tree species growing in the forest understorey. Shoot and trunk growth and morphological characteristics were measured onL. styraciflua growing along boulevards at 15 additional urban sites and related to seasonal interception of solar radiation. Angular elevation and orientation of buildings and trees that defined the horizon topography at each site were used in modeling the potential irradiance of global shortwave radiation. Seasonal irradiance among sites ranged from 21% in the urban core to nearly 95% in outlying residential districts of that potentially received under an unobstructed horizon. Shade acclimation was confirmed by differences in leaf morphology, as foliage became flatter, thinner, and more horizontally oriented at sites with lower irradiance. Photosynthetic and morphological acclimation to shade did not compensate for lower available radiant energy as both shoot and trunk growth decreased at sites of lower irradiance. Unlike the forest understorey, the static light environment of urban canyons may subject shade-intolerant species such asL. styraciflua to chronic, low-radiant-energy stress.     

Plant water relations and the effects of elevated CO2: a review and suggestions for future research

Increased ambient carbon dioxide (CO₂) has been found to ameliorate water stress in the majority of species studied. The results of many studies indicate that lower evaporative flux density is associated with high CO₂-induced stomatal closure. As a result of decreases in evaporative flux density and increases in net photosynthesis, also found to occur in high CO₂ environments, plants have often been shown to maintain higher water use efficiencies when grown at high CO₂ than when grown in normal, ambient air. Plants grown at high CO₂ have also been found to maintain higher total water potentials, to increase biomass production, have larger root-to-shoot ratios, and to be generally more drought resistant (through avoidance mechanisms) than those grown at ambient CO₂ levels. High CO₂-induced changes in plant structure (i.e., vessel or tracheid anatomy, leaf specific conductivity) may be associated with changes in vulnerability to xylem cavitation or in environmental conditions in which runaway embolism is likely to occur. Further study is needed to resolve these important issues. Methodology and other CO₂ effects on plant water relations are discussed.Abbreviations A net photosynthesis - C_a ambient [CO₂] - C_i internal [CO₂] - E evaporative flux density - g₁ leaf conductance - g_s stomatal conductance - LSC leaf specific conductivity - IRGA infrared gas analyzer - LAI leaf area index - PAR photosynthetically active radiation - total plant water potential - _soil soil water potential - _s solute potential - _pt turgor pressure potential - _px xylem pressure potential - RH relative humidity - R : S root to shoot ratio - RWC relative water content - SLA specific leaf area - SLW specific leaf weight - SPAC soil-plant-atmosphere-continuum - SWC soil water content - VPD vapor pressure deficit - WUE water use efficiency     

Wood anatomy constrains stomatal responses to atmospheric vapor pressure deficit in irrigated, urban trees

Plant transpiration is strongly constrained by hydraulic architecture, which determines the critical threshold for cavitation. Because species vary greatly in vulnerability to cavitation, hydraulic limits to transpiration and stomatal conductance have not generally been incorporated into ecological and climate models. We measured sap flow, leaf transpiration, and vulnerability to cavitation of a variety of tree species in a well-irrigated but semi-arid urban environment in order to evaluate the generality of stomatal responses to high atmospheric vapor pressure deficit (D). We found evidence of broad patterns of stomatal responses to humidity based on systematic differences in vulnerability to cavitation. Ring-porous taxa consistently had vulnerable xylem and showed strong regulation of transpiration in response to D, while diffuse-porous taxa were less vulnerable and transpiration increased nearly linearly with D. These results correspond well to patterns in the distribution of the taxa, such as the prevalence of diffuse-porous species in riparian ecosystems, and also provide a means of representing maximum transpiration rates at varying D in broad categories of trees.     

Effects of plant size and water relations on gas exchange and growth of the desert shrub Larrea tridentata

Larrea tridentata is a xerophytic evergreen shrub, dominant in the arid regions of the southwestern United States. We examined relationships between gasexchange characteristics, plant and soil water relations, and growth responses of large versus small shrubs of L. tridentata over the course of a summer growing season in the Chihuahuan Desert of southern New Mexico, USA. The soil wetting front did not reach 0.6 m, and soils at depths of 0.6 and 0.9 m remained dry throughout the summer, suggesting that L. tridentata extracts water largely from soil near the surface. Surface soil layers (<0.3 m) were drier under large plants, but predawn xylem water potentials were similar for both plant sizes suggesting some access to deeper soil moisture reserves by large plants. Stem elongation rates were about 40% less in large, reproductively active shrubs than in small, reproductively inactive shrubs. Maximal net photosynthetic rates (P_max) occurred in early summer (21.3 mol m^-2 s^-1), when pre-dawn xylem water potential (XWP) reached ca. -1 MPa. Although both shrub sizes exhibited similar responses to environmental factors, small shrubs recovered faster from short-term drought, when pre-dawn XWP reached about -4.5 MPa and P_max decreased to only ca. 20% of unstressed levels. Gas exchange measurements yielded a strong relationship between stomatal conductance and photosynthesis, and the relationship between leaf-to-air vapor pressure deficit and stomatal conductance was found to be influenced by pre-dawn XWP. Our results indicate that stomatal responses to water stress and vapor pressure deficit are important in determining rates of carbon gain and water loss in L. tridentata.     

Seasonal variations on water relations ofAmygdalus communis L. under drip irrigated and non irrigated conditions

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.     

Responses of Photosynthetic Rate and Stomatal Conductance to Water Stress in Soybean Leaves

Responses of photosynthetic rate and stomatal conductance to water stress as weI1 as the relationship between photosynthetic rate and stomatal conductance were investigated with soybean cultivars “Ludou No. 4” and “7605”. The former was a high yield cultivars widely used in Shandong province, and the latter was a small grain soybean line bred by Shandong Academy of Agricultural science. Soil water stress decreased leaf apparent photosynthetic rate and stomatal conductance of two soybean cultivars, and “Ludou No. 4” decreased more than “7605”. At the same value of water potential, photosynthetic rate and stomatal conductance of “7605” were higher than those of “Ludou No,4”,but the rate of stomatal closure for “7605” was higher than “Ludou No. 4”. Decreasing of stomatal conductance caused rising of leaf temperature of two soybean cultivars, and the rising of “7605” was more rapid than “Ludou No. 4”, but at the same treatment of water stress, leaf temperature of “Ludou No. 4” was higher than “7605”. Leaf water use efficiecy (WUE) of two soybean cultivars were decreased under water stress, and the rate of decreasing in “Ludou No.4” was more rapid than in “7605”. These results showed that “7605” was more resistant to water:stress than “Ludou No. 4”.     

In vitro adventitious shoot formation on mature-phase leaves and petioles of Liquidambar styraciflua L.

Adventitious shoots were induced to form on leaves and petiole segments of mature-phase Liquidambar styraciflua L. Shoot organogenesis occurred directly, without the formation of a distinct callus stage, and well-defined shoots were visible in 6–9 weeks. Prolific shoot production was supported by Woody Plant Medium supplemented with relatively high levels of benzyladenine (2.5 mg/l). Changes in benzyladenine concentration and the addition of 0.1 mg/l naphthaleneacetic acid to the medium altered the relative abundance of shoots on various parts of a leaf. Shoot formation occurred most frequently at or near breaks in major vasculature. Wounding of the leaves by slashing across the lamina and vasculature significantly increased the total number of shoots formed per explant and also altered the pattern of organogenesis. Differences in organogenic response were seen between the cultivars ‘Moraine’ and ‘Variegata’. Shoots derived from leaves were easily rooted and acclimated to greenhouse conditions. Three new variegation types arose in vitro as a result of adventitious shoot formation on ‘Variegata’ leaves.     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water relations of three cowpea cultivars (Vigna unguiculata,L.)

The effects of soil water stress imposed at different growth stages of three cowpea varieties, namely, Adzuki (an erect type), Ife Brown (semi erect) and New Era (a spreading type) on growth, floral abscission and yield were investigated in the greenhouse. Stomatal density, aperture and behaviour as influenced by soil water potential was also evaluated. Root system development, grain yield, soil water content and potentials were determined in a field experiment. Soil moisture stress significantly reduced the growth and yield (34–46%) of the three cowpea cultivars. Although grain yield reduction was highest (36.8%) when stress was imposed at flowering/podding stage for Ife Brown, the variety New Era showed no reduction in yield. Floral abortion which increased with a decrease in matric potential may also be linked with imperfect aeration conditions. The choice of these cultivars for intercropping purposes should take cognisance of depth of rooting, lateral root spread, and root density, which affect water extraction at different soil depths, leaf area index, stomatal density, aperture and behaviour to decreased soil water potential all of which differed widely amongst the cultivars.     

Comparative water relations of four Mediterranean oak species

The water relations and responses of two evergreen (Quercus ilex L. and Q. suber L.) and two deciduous (S. afares Pomel. and Q. faginea Will.) Quercus species were studied under experimental conditions. Two-year old seedlings grown in 30 l. pots were subjected to a drying period during which stomatal conductance, pre-dawn potential and minimum foliar potential were measured.The results shows that, for all species, the daily course of stomatal conductance agrees with the patterns proposed by Hinckley et al. (1978 & 1983). Concurrent with the species responses to short-term variation in water availability, it was found that pre-dawn leaf water potential controlled the maximum daily leaf conductance. There was a strong correlation between pre-dawn leaf potential and maximum daily conductance as described by the reciprocal function g_{srmax for}=(-0.47+2.61._p)^-1 the evergreen oaks and g_{srmax for}=(-1.94+7.39._p)^-1 for the deciduous species. These differences between the two groups may partialy explain their geograhic distributions, and suggest general questions concerning the mechanisms which optimize water-use efficiency in Mediterranean oak species.