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1.
Water and Nutrient Dynamics in Surface Roots and Soils are not Modified by Short-term Flooding of Phreatophytic Plants in a Hyperarid Desert 总被引:3,自引:0,他引:3
Fanjiang Zeng Timothy M. Bleby Peter A. Landman Mark A. Adams Stefan K. Arndt 《Plant and Soil》2006,279(1-2):129-139
Little is known of the mechanisms employed by woody plants to acquire key resources such as water and nutrients in hyperarid
environments. For phreatophytic plants, deep roots are necessary to access the water table, but given that most nutrients
in many desert ecosystems are stored in the upper soil layers, viable shallow roots may be equally necessary for nutrient
uptake. We sought to better understand the interaction between water and nutrient uptake from soil horizons differing in the
relative abundance of these resources. To this end, we monitored plant water and nutrient status before and after applying
flood irrigation to four phreatophytic perennial plant species in the remote hyperarid Taklamakan desert in western China.
Sap flow in the roots of five plants of the perennial desert species Alhagi sparsifolia Shap., Karelina caspica (Pall.) Less., Calligonum caput medusea Schrenk, and Eleagnus angustifolia Hill. was monitored using the heat ratio method (HRM). Additionally we measured predawn and midday water potential, foliar
nitrate reductase activity (NRA), xylem sap nutrient concentration and the concentration of total solutes in the leaves before,
12 and 96 h after flooding to investigate possible short-term physiological effects on water and nutrient status. Rates of
sap flow measured during the day and at night in the absence of transpiration did not change after flooding. Moderately high
rates of sap flow (HRM heat pulse velocity, 5–25 cm h−1) detected during the day in soils that had a near zero water content at the surface indicated that all species had contact
to groundwater. There was no evidence from sap flow data that plants had utilised flood water to increase maximum rates of
transpiration under similar climatic conditions, and there was no evidence of a process to improve the efficiency of water
or nutrient uptake, such as hydraulic redistribution (i.e. the passive movement of water from moist soil to very dry soil
via roots). Measurements of plant water status, xylem sap nutrient status, foliar NRA and the concentration of osmotically
active substances were also unaffected by flood irrigation. Our results clearly show that groundwater acts as the major source
of water and nutrients for these plants. The inability of plants to utilise abundant surface soil–water or newly available
nutrients following irrigation was attributed to the absence of fine roots in the topsoil layer. 相似文献
2.
Using stable hydrogen and oxygen isotopes to study water movement in soil-plant-atmosphere continuum at Poyang Lake wetland,China 总被引:2,自引:0,他引:2
Xiang Zhang Yang Xiao Hui Wan Zhimin Deng Guoyan Pan Jun Xia 《Wetlands Ecology and Management》2017,25(2):221-234
Water movement in the soil-plant-atmosphere continuum (SPAC) has a significant effect on the biogeochemical process in wetlands. This study investigated the water movement in the SPAC in Poyang Lake wetland, which is a protected area with an important ecological function within the Yangtze River basin, under different water-level conditions by analyzing the responses of river, groundwater, soil and plants to precipitation using stable hydrogen and oxygen isotopes. The results show that the stable hydrogen and oxygen isotopic compositions (δ18O and δD) of soil water decrease with increasing depth due to the near surface evaporation. During the dry season the water-level in Poyang Lake is low, when it rains the influencing depth of precipitation and evaporation on soil water isotopic signatures was 20 cm below the ground surface. The rain water infiltrates into the soil, recharges groundwater and flows to the river. When the water-level in Poyang Lake is low, the Xiu River is recharged by the groundwater, which recharges the soil water by capillary rise. During the flood season, the water-level is high and the water in Poyang Lake reaches or covers the meadows, recharges the groundwater and soil water. In the meantime, the water in Poyang Lake can be recharged by rain water when it rains. During the dry season when it doesn’t rain, plants mainly use groundwater, but soil water is preferred and plants don’t use rainwater directly when it rains. When the lake water-level is extremely low, the plants in Poyang Lake wetland may suffer from water stress, which is harmful for plant growth. 相似文献
3.
4.
When soil moisture is heterogeneous, sap flow from, and ABA status of, different parts of the root system impact on leaf xylem ABA concentration ([X-ABA]leaf). The robustness of a model for predicting [X-ABA]leaf was assessed. 'Two root-one shoot' grafted sunflower (Helianthus annuus L.) plants received either deficit irrigation (DI, each root system received the same irrigation volumes) or partial rootzone drying (PRD, only one root system was watered and the other dried the soil). Irrespective of whether relative sap flow was assessed using sap flow sensors in vivo or by pressurization of de-topped roots, each root system contributed similarly to total sap flow during DI, while sap flow from roots in drying soil declined linearly with soil water potential (Psisoil) during PRD. Although Psisoil of the irrigated pot determined the threshold Psisoil at which sap flow from roots in drying soil decreased, the slope of this decrease was independent of the wet pot Psisoil. Irrespective of whether sap was collected from the wet or dry root system of PRD plants, or a DI plant, root xylem ABA concentration increased as Psisoil declined. The model, which weighted ABA contributions of each root system according to the sap flow from each, almost perfectly explained [X-ABA] immediately above the graft union. That the model overestimated measured [X-ABA]leaf may result from changes in [X-ABA] along the transport pathway or an artefact of collecting xylem sap from detached leaves. The implications of declining sap flow through partially dry roots during PRD for the control of stomatal behaviour and irrigation scheduling are discussed. 相似文献
5.
Yang Liu Nadezhda Nadezhdina Nan Di Xu Ma Jinqiang Liu Songyan Zou Benye Xi Brent Clothier 《Plant physiology》2021,186(1):361
Maintaining the activity and function of the shallow root system of plants is essential for withstanding drought stress, but the associated mechanism is poorly understood. By investigating sap flow in 14 lateral roots (LRs) randomly selected from trees of a Chinese white poplar (Populus tomentosa) plantation receiving three levels of irrigation, an unknown root water transport mode of simultaneous daytime bi-directional water flow was discovered. This mode existed in five LRs confined to the surface soil without attached sinker roots. In the longer term, the bi-directional water flow was correlated with the soil water content. However, within the day, it was associated with transpiration. Our data demonstrated that bi-directional root sap flow occurred during the day, and was driven by evaporative demand, further suggesting the existence of circumferential water movement in the LR xylem. We named this phenomenon evaporation-driven hydraulic redistribution (EDHR). A soil-root water transport model was proposed to encapsulate this water movement mode. EDHR may be a crucial drought-tolerance mechanism that allows plants to maintain shallow root survival and activity by promoting root water recharge under extremely dry conditions. 相似文献
6.
Interference from xylem sap in an enzyme-linked immunosorbent assay for zeatin riboside 总被引:1,自引:0,他引:1
The extent of interference from xylem sap in an enzyme-linked immunosorbent assay was determined for a woody perennial [ Populus trichocarpa Torr. & Gray x P deltoides Bart, ex Marsh (Hybrid 1l–ll)] and a herbaceous annual ( Phasesolus vulgaris L. cv. Contender). Crude xylem sap collected from excised roots from both species interfered with the assay for zeatin riboside. Assays for zeatin riboside in xylem sap collected from Popidus overestimated endogenous levels, and added standards could not be accurately measured from a range of sap dilutions. When Phaseolus plants were grown under various nutrient regimens, interference in the assay was dependent on nutrient availability. Of xylem sap components (inorganic minerals, amino acids and sucrose) which may vary with environmental conditions or among species, only sucrose interfered at the concentrations tested. Since the pH of xylem sap varies it was necessary to buffer samples prior to analysis. Partial purification using anion exchange columns and Sep-Paks cffectively eliminated interference. These results demonstrate that estimates of plant growth regulators in xylem sap by the ELISA (enzyme-linked immunosorbant assay) method can be influenced by species and environmental conditions such as plant nutritional status. 相似文献
7.
Liangju Zhao Lixin Wang Lucas A. Cernusak Xiaohong Liu Honglang Xiao Maoxian Zhou Shiqiang Zhang 《Plant, cell & environment》2016,39(8):1848-1857
Deuterium depletions between stem water and source water have been observed in coastal halophyte plants and in multiple species under greenhouse conditions. However, the location(s) of the isotope fractionation is not clear yet and it is uncertain whether deuterium fractionation appears in other natural environments. In this study, through two extensive field campaigns utilizing a common dryland riparian tree species Populus euphratica Oliv., we showed that no significant δ18O differences were found between water source and various plant components, in accord with previous studies. We also found that no deuterium fractionation occurred during P. euphratica water uptake by comparing the deuterium composition (δD) of groundwater and xylem sap. However, remarkable δD differences (up to 26.4‰) between xylem sap and twig water, root water and core water provided direct evidence that deuterium fractionation occurred between xylem sap and root or stem tissue water. This study indicates that deuterium fractionation could be a common phenomenon in drylands, which has important implications in plant water source identification, palaeoclimate reconstruction based on wood cellulose and evapotranspiration partitioning using δD of stem water. 相似文献
8.
The phytoremediation of trichloroethylene (TCE) from contaminated groundwater has been extensively studied using the hybrid poplar tree (Populus spp.). Several metabolites of TCE have been identified in the tissue of poplar including trichloroethanol (TCEOH) and dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). In addition to the use of hybrid poplar for the phytoremediation of TCE, it is important to screen native tree species that could be successful candidates for field use. This study involves a greenhouse-based comparison of four different native southeastern conifers to a hybrid poplar species for their potential to phytoremediate TCE through the analysis of various plant tissues for TCE and major TCE metabolites, as well as several growth parameters that are desirable for phytoremediation. Longleaf pine (Pinus palustris), Leyland cypress (X Cupressocyparis leylandii), two varieties of Loblolly pine (Pinus taeda), and hybrid poplar species H11-11 (Populus trichocarpa x deltoides) were examined for the concentration of TCE and its metabolites in their tissue following treatment with either a low (50 mg L?1) or high dose of TCE (150 mg L?1) for 2 mo. The amount of water taken up, change in height of the tree, TCE transpiration, and total fresh weight of various tissue types were also measured. All trees contained detectable levels of TCE in their root and stem tissue. TCEOH was found only in the tissue of longleaf pine, suggesting that TCE metabolism was occurring in this tree. TCAA was only detected in the leaves of hybrid poplar and piedmont loblolly pine. Conifers took up less water over the 2-mo treatment period than hybrid poplar and grew at a slower rate. However, phytoremediation field sites may benefit from the evergreen's ability to transpire water throughout the winter months. 相似文献
9.
Betula pendula (Silver birch) trees growing on two contaminated sites were evaluated to assess their capacity to phytoscreen and phytoremediate chlorinated aliphatic compounds and heavy metals. Both locations are industrially-contaminated properties in central Sweden. The first was the site of a trichloroethylene (TCE) spill in the 1980s while the second was polluted with heavy metals by burning industrial wastes. In both cases, sap and sapwood from Silver birch trees were collected and analyzed for either chlorinated aliphatic compounds or heavy metals. These results were compared to analyses of the surface soil, vadose zone pore air and groundwater. Silver birch demonstrated the potential to phytoscreen and possibly phytoremediate TCE and related compounds, but it did not demonstrate the ability to effectively phytoextract heavy metals when compared with hyperaccumulator plants. The capacity of Silver birch to phytoremediate TCE appears comparable to tree species that have been employed in field-scale TCE phytoremediation efforts, such as Populus spp. and Eucalyptus sideroxylon rosea. 相似文献
10.
Fichot R Chamaillard S Depardieu C Le Thiec D Cochard H Barigah TS Brignolas F 《Journal of experimental botany》2011,62(6):2093-2106
Tests were carried out to determine whether variations in the hydraulic architecture of eight Populus deltoides×Populus nigra genotypes could be related to variations in leaf function and growth performance. Measurements were performed in a coppice plantation on 1-year-old shoots under optimal irrigation. Hydraulic architecture was characterized through estimates of hydraulic efficiency (the ratio of conducting sapwood area to leaf area, A(X):A(L); leaf- and xylem-specific hydraulic conductance of defoliated shoots, k(SL) and k(SS), respectively; apparent whole-plant leaf-specific hydraulic conductance, k(plant)) and xylem safety (water potential inducing 50% loss in hydraulic conductance). The eight genotypes spanned a significant range of k(SL) from 2.63 kg s(-1) m(-2) MPa(-1) to 4.18 kg s(-1) m(-2) MPa(-1), variations being mostly driven by k(SS) rather than A(X):A(L). There was a strong trade-off between hydraulic efficiency and xylem safety. Values of k(SL) correlated positively with k(plant), indicating that high-pressure flowmeter (HPFM) measurements of stem hydraulic efficiency accurately reflected whole-plant water transport efficiency of field-grown plants at maximum transpiration rate. No clear relationship could be found between hydraulic efficiency and either net CO(2) assimilation rates, water-use efficiency estimates (intrinsic water-use efficiency and carbon isotope discrimination against (13)C), or stomatal characteristics (stomatal density and stomatal pore area index). Estimates of hydraulic efficiency were negatively associated with relative growth rate. This unusual pattern, combined with the trade-off observed between hydraulic efficiency and xylem safety, provides the rationale for the positive link already reported between relative growth rate and xylem safety among the same eight P. deltoides×P. nigra genotypes. 相似文献
11.
Masaharu Kitano Kazuki Urayama Yoshinobu Sakata Yasutaka Sonoda Kenji Ebihara Yuki Sago Hisashi Yoshikoshi Takuya Araki Daisuke Yasutake Hiroyuki Cho Tetsuo Kobayashi 《Biologia》2009,64(3):474-477
Water deficit and salt accumulation in soil presents serious problems to crop production in semi-arid regions. These problems
depend on the active transpiration stream and the selective absorption of ions by crop roots. In this study, a large sized
soil column system was used to examine the dynamics of water and ion transport and salt accumulation in soil layers. Special
reference was placed on the effects of the active and selective absorption by roots of different crops (i.e., corn plants,
sunflower plants and no plants). The column system was equipped with on-line systems for the control of groundwater level.
Soil water content sensors enabled time-course evaluations of the volumetric water content and hence upward flux of the groundwater
in the soils at different depths. Furthermore, the distribution and accumulation of ions in soil layers, plant organs and
xylem sap were analyzed using ion chromatography. In this column experiment, diurnal and longer term changes in water movement
and ion accumulation in soil, affected by root absorption characteristics of plants, were evaluated quantitatively. The results
demonstrated that the column system was applicable for the quantitative analysis of the effects of root absorption by different
crops on water deficit and salinization in soils. 相似文献
12.
Evidence is increasing to suggest that a major activity of roots is to redistribute soil water. Roots in hydraulic contact with soil generally either absorb or lose water, depending on the direction of the gradient in water potential between root and soil. This leads to phenomena such as "hydraulic lift" where dry upper soil layers drive water transfer from deep moist layers to the shallow rhizosphere and, after rain or surface irrigation, an opposite, downward water transfer. These transport processes appear important in environments where rainfall is strongly seasonal (e.g. Mediterranean-type climates). Irrigation can also induce horizontal transfers of water between lateral roots. Compared with transpiration, the magnitudes, pathways, and resistances of these redistribution processes are poorly understood. Field evidence from semi-arid eucalyptus woodlands is presented to show: (i) water is rapidly exchanged among lateral roots following rain events, at rates much faster than previously described for other types of hydraulic redistribution using sap flow methods; (ii) large axial flows moving vertically up or down the stem are associated with the horizontal transfer of water between roots on opposite sides of the stem. It appears that considerable portions of the stem axis become involved in the redistribution of water between lateral roots because of partial sectoring of the xylem around the circumference of these trees. 相似文献
13.
Hydraulic Lift in Cork Oak Trees in a Savannah-Type Mediterranean Ecosystem and its Contribution to the Local Water Balance 总被引:3,自引:1,他引:2
Cathy Kurz-Besson Dennis Otieno Raquel Lobo do Vale Rolf Siegwolf Markus Schmidt Alastair Herd Carla Nogueira Teresa Soares David Jorge Soares David John Tenhunen João Santos Pereira Manuela Chaves 《Plant and Soil》2006,282(1-2):361-378
The aim of this study was to identify the sources and depth of water uptake by 15-years old Quercus suber L. trees in southern Portugal under a Mediterranean climate, measuring δ18O and δD in the soil–plant-atmosphere continuum. Evidence for hydraulic lift was substantiated by the daily fluctuations observed
in Ψs at 0.4 and 1 m depth and supported by similar δ18O values found in tree xylem sap, soil water in the rhizosphere and groundwater. From 0.25 m down to a depth of 1 m, δD trends
differed according to vegetation type, showing a more depleted value in soil water collected under the evergreen trees (−47‰)
than under dead grasses (−35‰). The hypothesis of a fractionation process occurring in the soil due to diffusion of water
vapour in the dry soil is proposed to explain the more depleted soil δD signature observed under trees. Hydraulically lifted
water was estimated to account for 17–81% of the water used during the following day by tree transpiration at the peak of
the drought season, i.e., 0.1–14 L tree−1 day−1. Significant relationships found between xylem sap isotopic composition and leaf water potential in early September emphasized
the positive impact of the redistribution of groundwater in the rhizosphere on tree water status. 相似文献
14.
In Prince Edward Island, Canada, widespread intensive potato production has contributed to elevated nitrate concentrations in groundwater and streams, and eutrophic or anoxic conditions occur regularly in several estuarine systems. In this research, the stable isotopes of nitrogen and oxygen in nitrate in intertidal groundwater discharge and stream water were used, in conjunction with water quality and quantity data and land use information, to better understand the characteristics of nitrate delivered to two small estuaries with contrasting land use in their contributory catchments. Most of the water samples collected during the two-year study had isotopic signatures that fell in the range expected for nitrate derived from ammonium-based fertilizers (26.5 % of the samples) or in the overlapping range formed between ammonium-based fertilizers and nitrate derived from soil (64 % of the samples). Overall, isotopic signatures spanned over relatively narrow ranges, and correlations with other water quality parameters, or catchment characteristics, were weak. Nitrate in groundwater discharge and surface water in the Trout River catchment exhibited significantly different isotopic signatures only for the nitrogen isotope, while in the McIntyre Creek catchment groundwater discharge and surface water had similar isotopic signatures. When the isotopic results for the waters from the two catchments were compared, the surface waters were found to be similar, while the isotopic signatures of nitrate in groundwater were distinct only for the nitrogen isotope. Denitrification in the two study catchments was not evident based on the isotopic results for nitrate; however, in the case of the Trout River catchment, where a small freshwater pond exists, an average nitrate load reduction of 14 % was inferred based on a comparison of nitrate loads entering and leaving the pond. Overall, it appears that natural attenuation processes, occurring either in the streams or groundwater flow systems, do not significantly reduce nitrate loading to these estuaries. 相似文献
15.
Nadezhda Nadezhdina Maria Isabel Ferreira Rodolfo Silva Carlos Arruda Pacheco 《Plant and Soil》2008,305(1-2):105-119
Hydraulic redistribution (HR) is the phenomenon where plant roots transfer water between soil horizons of different water
potential. When dry soil is a stronger sink for water loss from the plant than transpiration, water absorbed by roots in wetter
soil horizons is transferred toward, and exuded into dry soil via flow reversals through the roots. Reverse flow is a good
marker of HR and can serve as a useful tool to study it over the long-term. Seasonal variation of water uptake of a Quercus suber tree was studied from late winter through autumn 2003 at Rio Frio near Lisbon, Portugal. Sap flow was measured in five small
shallow roots (diameter of 3–4 cm), 1 to 2 m from the tree trunk and in four azimuths and at different xylem depths at the
trunk base, using the heat field deformation method (HFD). The pattern of sap flow differed among lateral roots as soil dried
with constant positive flow in three roots and reverse flow in two other roots during the night when transpiration ceased.
Rain modified the pattern of flow in these two roots by eliminating reverse flow and substantially increasing water uptake
for transpiration during the day. The increase in water uptake in three other roots following rain was not so substantial.
In addition, the flux in individual roots was correlated to different degrees with the flux at different radial depths and
azimuthal directions in trunk xylem. The flow in outer trunk xylem seemed to be mostly consistent with water movement from
surface soil horizons, whereas deep roots seemed to supply water to the whole cross-section of sapwood. When water flow substantially
decreased in shallow lateral roots and the outer stem xylem during drought, water flow in the inner sapwood was maintained,
presumably due to its direct connection to deep roots. Results also suggest the importance of the sap flow sensor placement,
in relation to sinker roots, as to whether lateral roots might be found to exhibit reverse flow during drought. This study
is consistent with the dimorphic rooting habit of Quercus suber trees in which deep roots access groundwater to supply superficial roots and the whole tree, when shallow soil layers were
dry. 相似文献
16.
F. TARDIEU N. KATERJI O. BETHENOD J. ZHANG W. J. DAVIES 《Plant, cell & environment》1991,14(1):121-126
Abstract. Stomatal conductance, leaf water potential, soil water potential and concentration of abscisic acid (ABA) in the xylem sap were measured on maize plants growing in the field, in two treatments with contrasting soil structures. Soil compaction affected the stomatal conductance, but this effect was no longer observed if the soil water potential was increased by irrigation. Differences in leaf water potential did not account for the differences in conductance between treatments. Conversely, the relationship between stomatal conductance and concentration of ABA in the xylem sap was consistent during the experiment. The proposed interpretation is that stomatal conductance was controlled by the root water potential via an ABA message. Control of the stomatal conductance by the leaf water potential or by an effect of mechanical stress on the roots is unlikely. 相似文献
17.
荒漠防护林典型树种液流特征及其对环境因子的响应 总被引:2,自引:0,他引:2
利用基于热补偿理论的SF300分体液流仪对干旱荒漠区人工防护林典型树种(俄罗斯杨、胡杨、榆树、沙枣)树干液流全天候监测,自动气象站同步记录相关环境因子变化。研究表明:①4种防护林树种茎干液流日变化除沙枣树外均存在明显昼夜节律,液流速度在同属种间差异较小,在不同属种间差异显著,俄罗斯杨的日平均液流速度可以达到沙枣的13.8倍,耗水量排序为俄罗斯杨胡杨榆树沙枣树。②水分充足条件下,增加实验地灌溉量使4种树木蒸腾受到抑制,液流流速降低,水分利用效率降低。③液流流速因所处树干径向位点不同而存在差异,俄罗斯杨、榆树、沙枣液流速度表现出由形成层到髓心的递减趋势,胡杨树干径向位点液流没有表现一定规律。④树干液流流速与环境因子进行相关分析,通过逐步回归分析建立了4个典型树种茎干液流速度与环境因子关系估算模型,分析认为4种树木的环境敏感性排序为俄罗斯杨榆树胡杨沙枣。 相似文献
18.
Xianchong Wan Simon M. Landhäusser Janusz J. Zwiazek Victor J. Lieffers 《Physiologia plantarum》2004,122(1):79-85
The mechanisms regulating stomatal response following exposure to low (5°C) soil temperature were investigated in aspen ( Populus tremuloides Michx.) seedlings. Low soil temperature reduced stomatal conductance within 4 h, but did not alter shoot xylem pressure potential within 24 h. The xylem sap composition was altered and its pH increased from 6.5 to 7.1 within the initial 4 h of the low temperature treatment. However, the increase in abscisic acid (ABA) concentration in xylem sap was observed later, after 8 h of treatment. These changes were accompanied by a reduction in the electrical conductivity and an increase in the osmotic potential of the xylem sap. The timing of physiological responses to low soil temperature suggests that the rapid pH change of the xylem sap and accompanying changes in ion concentration were the initial factors which triggered stomatal closure in low temperature-treated seedlings, and that the role of the more slowly accumulating ABA was likely to reinforce the stomatal closure. When leaf discs were exposed to xylem sap extracted from low soil temperature-treated plants, stomatal aperture was negatively correlated with ABA and positively correlated with K+ concentrations of the xylem sap. The stomatal opening in the leaf discs linearly increased in response to exogenous KCl concentrations when K+ concentrations were in the similar range to those detected in the xylem sap. The lowest concentration of exogenous ABA to induce stomatal closure was several-fold higher compared with the concentration present in the xylem sap. 相似文献
19.
Precipitation pulse use by an invasive woody legume: the role of soil texture and pulse size 总被引:9,自引:0,他引:9
Plant metabolic activity in arid and semi-arid environments is largely tied to episodic precipitation events or “pulses”.
The ability of plants to take up and utilize rain pulses during the growing season in these water-limited ecosystems is determined
in part by pulse timing, intensity and amount, and by hydrological properties of the soil that translate precipitation into
plant-available soil moisture. We assessed the sensitivity of an invasive woody plant, velvet mesquite (Prosopis velutina Woot.), to large (35 mm) and small (10 mm) isotopically labeled irrigation pulses on two contrasting soil textures (sandy-loam
vs. loamy-clay) in semi-desert grassland in southeastern Arizona, USA. Predawn leaf water potential (Ψpd), the isotopic abundance of deuterium in stem water (δD), the abundance of 13C in soluble leaf sugar (δ13C), and percent volumetric soil water content (θv) were measured prior to irrigation and repeatedly for 2 weeks following irrigation. Plant water potential and the percent
of pulse water present in the stem xylem indicated that although mesquite trees on both coarse- and fine-textured soils quickly
responded to the large irrigation pulse, the magnitude and duration of this response substantially differed between soil textures.
After reaching a maximum 4 days after the irrigation, the fraction of pulse water in stem xylem decreased more rapidly on
the loamy-clay soil than the sandy-loam soil. Similarly, on both soil textures mesquite significantly responded to the 10-mm
pulse. However, the magnitude of this response was substantially greater for mesquite on the sandy-loam soil compared to loamy-clay
soil. The relationship between Ψpd and δ13C of leaf-soluble carbohydrates over the pulse period did not differ between plants at the two sites, indicating that differences
in photosynthetic response of mesquite trees to the moisture pulses was a function of soil water availability within the rooting
zone rather than differences in plant biochemical or physiological constraints. Patterns of resource acquisition by mesquite
during the dynamic wetting–drying cycle following rainfall pulses is controlled by a complex interaction between pulse size
and soil hydraulic properties. A better understanding of how this interaction affects plant water availability and photosynthetic
response is needed to predict how grassland structure and function will respond to climate change. 相似文献
20.
Marion Zapater Christian Hossann Nathalie Br��da Claude Br��chet Damien Bonal Andr�� Granier 《Trees - Structure and Function》2011,25(5):885-894
Hydraulic lift (HL) by tree roots in a young, broad-leaved, mixed temperate European forest was investigated during the 2008
growing season by injecting 18O-enriched soil water at a depth of 75–90 cm under drought conditions experimentally imposed in a rain-exclusion system. Based
on sap flow, leaf water potential, 2-D root distribution measurements, soil isotope profiles, and xylem water isotope composition,
water acquisition and use by two tree species, beech (Fagus sylvatica) and oak (Quercus petraea) was compared. We showed that, unlike oak, beech experienced a marked decrease in sap flow and predawn leaf water potential
with increasing soil drought. This behaviour was logical considering the shallower root system in beech than in oak. Six days
after 18O-labelling, we observed isotopic enrichment in the shallower soil layers. Since the intermediate soil layers did not display
any enrichment, our results clearly pointed to hydraulic lift by tree roots. The superficial enrichment that was observed
in the vicinity of oak trunks and the increase in the isotopic signature of xylem sap in the oak trees but not in the beech
trees confirmed the predominant role of oak in the hydraulic lift at our site. Even though facilitation for water acquisition
among species was not observed here, our results suggest a potential positive contribution of species like oak toward maintaining
species diversity in mixed forest ecosystems submitted to severe drought events. 相似文献