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1.
In a field trial involving four tepary lines (Phaseolus acutifolius A. Gray), NE#8A and NE#19 produced higher grain yield than NE#5 and NE#7 under both well watered and drought conditions. However, NE#8A is considered more resistant than NE#19 in terms of drought sensitivity index. Greenhouse investigations on intact plants indicated no differences among the four lines in leaf and stem dry mass, and leaf area. Root depth did not strictly differentiate lower‐yielding from higher‐yielding lines. In contrast to lower‐yielding lines, however, plants of higher‐yielding ones allocated greater dry matter (DM) in roots in response to imposed water stress. Distinctly, NE#19 had the greatest root : shoot (R : S) while NE#8A characterized by high net photosynthesis. Both NE#8A and NE#19 showed reduced leaf area : root dry mass ratio, stomata conductance and transpiration rate. Consequently, these two lines showed no significant changes in leaf relative water content while photosynthetic water‐use‐efficiency increased in response to water stress. Calli derived from leaf and root tissues of higher‐yielding lines exhibited low initial osmotic potential (ψs). These calli did not show alterations in ψs, DM% and relative growth rate (RGR) when subjected to water stress. Although leaf‐ and root‐derived calli of lower‐yielding lines exhibited osmotic adjustment, they suffered water stress in terms of elevated DM and reduced RGR. Overall, results suggest that dehydration‐avoidance mechanisms conditioned by increased root mass and stomata resistance accompanied with low initial cellular ψs sustained high grain yield of tepary under limited water supply.  相似文献   

2.
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3.
A field trial conducted on the melon cultivar Huanghemi irrigated with saline water was carried out in Minqin County in the 2‐year period, 2007 and 2008. In three irrigation treatments, different saline water concentrations were applied, that is 0.8 g l?1 (Control C), 2 g l?1 (Treatment S1) and 5 g l?1 (Treatment S2), reproducing the natural groundwater concentration in the county. The electrical conductivity of the saline water was as follows: 1.00, 2.66 and 7.03 dS m?1, respectively. The aims of the study were (i) to monitor water consumption and water potential, (ii) assess, during the whole crop cycle, some growth parameters and their relations for estimating the morpho‐functional plant response irrigated with saline water and (iii) determine the ion concentration in different plant tissues to evaluate which mechanism the plant activates in the presence of high salt concentrations. Under salinity stress, the plants sustained the concentration of Ca, Mg and K, but at a level not sufficient to limit the Na adsorption. Therefore, the melon yield decreased and it was determined by a displacement of the ratio K/Na and by a lower (total potential MPa). Consequently with increasing salinity, a significant reduction was observed in: water consumption (ET c, mm), leaf area duration (LAD, m2 d), on shoot dry weight aboveground (W , g plant?1), on specific leaf area (SLA, cm2 g?1) and on leaf area ratio (LAR, cm2 g?1). In treatment S2, in addition to these changes which mainly affected the plant morphology with effects on the biomass produced, a moderate reduction was also observed in net assimilation rate (NAR, g m?2 d?1), water use efficiency (WUE), a significant reduction in the energy conversion efficiency (ECE, %) and, in short, in a reduction in the relative growth rate (RGR, g g?1 d?1).  相似文献   

4.
An accurate estimation of stomatal resistance (rS) also under drought stress conditions is of pivotal importance for any process‐based prediction of transpiration and the energy budget of real crop canopies and quantification of drought stress. A new model for rS was developed and parameterized for winter wheat using data from field experiments accounting for the influences of net radiation (RNet), air temperature (TAir) and vapour pressure deficit of the atmosphere (VPD) interacting with an average water potential in the rooted soil (ψRootedSoil). rS is simulated with a limiting factor approach as maximum of the metabolic (related to photosynthesis) and hydraulic (related to drought stress) acting influences assuming that, if drought stress occurs, it will dominate stomatal control: rS = max(rS(TAir), rS(RNet), rS(VPD, ψRootedSoil)). This transitional approach is suited to reproduce measured daily time courses of rS with a varying accuracy for the single measurement dates but performed satisfactorily for the whole data set (r2 = 0.63, RMSE = 59 s m?1, EF = 0.60). This new semi‐empiric approach calculates rS directly from external environmental conditions. Therefore, it can be easily implemented in existing model frameworks as link between operational crop growth models that use the concept of radiation use efficiency instead of mechanistic photosynthesis modelling and soil–vegetation–atmosphere transport models.  相似文献   

5.
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6.
Quinoa (Chenopodium quinoa Willd.) is a promising crop for food security in dry areas. Studies have been conducted to define nitrogen (N) fertilization levels and to understand the responses of quinoa to drought, but little is known about the response of this crop to N fertilization under drought stress. The aim of this study was to investigate whether N fertilization could improve quinoa yield and physiology under limited water. A greenhouse experiment was carried out with quinoa grown at four N fertilization levels (0, 0.2, 0.4 and 0.6 g N pot?1) and two watering treatments (progressive drought and full irrigation; 10 and 98 % of pot water holding capacity, respectively). Results of this experiment showed that N may confer a certain degree of drought tolerance to quinoa as seed quality and yield of N‐fertilized plants were not affected by drought stress. Responses such as faster stomatal closure, reduced leaf water potential, higher leaf abscisic acid (ABA) concentration and particularly an improved N remobilization in N‐fertilized plants may have played a role in sustaining seed yield in the drought‐stressed treatment. These results under controlled conditions serve as a basis to elucidate drought tolerance mechanisms activated with N fertilization and to define the use of N in management practices under semi‐arid environments.  相似文献   

7.
Worldwide rice productivity is being threatened by increased endeavours of drought stress. Among the visible symptoms of drought stress, hampered water relations and disrupted cellular membrane functions are the most important. Exogenous use of polyamines (PAs), salicylic acid (SA), brassinosteroids (BRs), glycinebetaine (GB) and nitrous oxide (NO) can induce abiotic stresses tolerance in many crops. In this time course study, we appraised the comparative role of all these substances to improve the drought tolerance in rice (Oryza sativa L.) cultivar Super‐Basmati. Plants were subjected to drought stress at four leaf stage (4 weeks after emergence) by maintaining soil moisture at 50 % of field capacity. Pre‐optimized concentrations of GB (150 mg l?1), SA (100 mg l?1), NO (100 μmol l?1 sodium nitroprusside as NO donor), BR (0.01 μm 24‐epibrassinolide) and spermine (Spm; 10 μm ) were foliar sprayed at five‐leaf stage (5 weeks after emergence). There were two controls both receiving no foliar spray, viz. well watered (CK1) and drought stressed (CK2). There was substantial reduction in allometric response of rice, gas exchange and water relation attributes by drought stress. While drought stress enhanced the H2O2, malondialdehyde (MDA) and relative membrane permeability, foliar spray of all the chemicals improved growth possibly because of the improved carbon assimilation, enhanced synthesis of metabolites and maintenance of tissue water status. Simultaneous reduction in H2O2 and MDA production was also noted in the plants treated with these substances. Drought tolerance was sturdily associated with the greater tissue water potential, increased synthesis of metabolites and enhanced capacity of antioxidant system. Of all the chemicals, foliar spray with Spm was the most effective followed by BR.  相似文献   

8.
Canopy temperature has been recognised as an indicator of crop water status and may thus be a useful secondary trait in selecting for yield under dry conditions. The aim of this study was to test the suitability of canopy temperature depression (CTD = Tair ? Tcanopy) in a temperate climate with winter rye, by means of three infrared (IR) temperature measuring devices. In the years 2011 and 2012, 16 winter rye genotypes were examined under drought stress conditions in a rainout shelter and under well‐watered conditions. In each year, the CTD was determined several times during the growth period using two IR thermometers and an IR camera. By means of CTD, it was possible to detect drought stress and to differentiate between water regimes. The three measurement devices showed comparable results, despite greatly different costs. Under drought‐stress conditions, a significant positive correlation between grain yield and CTD was found on most measurement dates in 2011 and on some dates in 2012. When the CTD was pooled across water regimes, a significant positive correlation between grain yield and CTD was obtained on every measurement date. However, as genotypic differences for CTD were non‐existent, the correlations are less meaningful. The missing genotypic differences for CTD were rather caused by the limited genetic variability of the genotypes used in this study, than by climatic conditions. Due to this limitation, we were not able to make a concluding statement about the CTD in a temperature climate, although the results are quite promising and indicate that the CTD can potentially be used in a temperate climate.  相似文献   

9.
To study the effects of early drought priming at 5th‐leaf stage on grain yield and nitrogen‐use efficiency in wheat (Triticum aestivum L.) under post‐anthesis drought and heat stress, wheat plants were first exposed to moderate drought stress (drought priming; that is, the leaf water potential reached ca. ?0.9 MP a) at the 5th‐leaf stage for 11 days, and leaf water relations and gas exchange rates, grain yield and yield components, and agronomic nitrogen‐use efficiency (ANUE ) of the primed and non‐primed plants under post‐anthesis drought and heat stress were investigated. Compared with the non‐primed plants, the drought‐primed plants possessed higher leaf water potential and chlorophyll content, and consequently a higher photosynthetic rate during post‐anthesis drought and heat stress. Drought priming also resulted in higher grain yield and ANUE in wheat under post‐anthesis drought and heat stress. Drought priming at vegetative stage improves carbon assimilation and ANUE under post‐anthesis drought and heat stress and their combination in wheat, which might be used as a field management tool to enhance stress tolerance of wheat crops to multiple abiotic stresses in a future drier and warmer climate.  相似文献   

10.
以新棉33B为试验材料,在防雨棚中设置严重干旱、中度干旱和正常供水3个处理(土壤水分分别为田间持水量的35%～45%、45%～65%、65%～85%),利用14CO2同位素示踪技术研究了水分胁迫对棉花不同层次主茎叶光合同化物运转分配的影响.结果表明:干旱胁迫使叶片光合产物合成受阻,降低了叶片14C的同化量.并且随着干旱...  相似文献   

11.
With increasingly erratic rainfall patterns particularly in drought‐prone production systems, the capacity of plants to recover productively from drought spells becomes an important feature for yield stability in rainfed agriculture. Consequently, effects of water management at the stem elongation stage on partitioning and remobilization of dry matter, alteration in photosynthesis and water‐use efficiency (WUE), and yield components of wheat plants were studied in a glasshouse pot experiment. The plants were subjected to three soil moisture regimes: well watered during all phenological stages (WW), drought affected during stem elongation and post‐anthesis stages (DD) and drought affected during stem elongation and rewatered at post‐anthesis stage (DW). Total dry weight substantially decreased by both drought treatments. However, DD plants allocated relatively higher assimilates to roots whereas DW plants remobilized them to the grains. Drought applications resulted in a decrease of grain yield and thousand grain weight while reduction was more pronounced in DD treatment. Relative contribution of post‐anthesis photosynthesis to dry matter formation in grain was higher in WW treatment (72.6 %) than DD (68.5 %) and DW (68.2 %) treatments. Photosynthetic rate, gas exchange and transpiration decreased whereas leaf (photosynthetic) and plant level WUE increased with drought applications. However, all these parameters were rapidly and completely reversed by rewatering. Our findings showed that partitioning of dry weight to grain increases with rewatering of wheat plants subjected to drought during stem elongation phase, but the relative contributions of remobilization of stem reserves and post‐anthesis photosynthesis to grain did not change. Moreover, rewatering of plants at booting stage after a drought period lead to full recovery in photosynthesis and WUE, and a significant although partial recovery of yield components, such as grain yield, TGW and harvest index.  相似文献   

12.
The cup plant (Silphium perfoliatum L.) is discussed as an alternative energy crop for biogas production in Germany due to its ecological benefits over continuously grown maize. Moreover, a certain drought tolerance is assumed because of its intensive root growth and the dew water collection by the leaf cups, formed by fused leaf pairs. Therefore, the aim of this study was to estimate evapotranspiration (ET ), water‐use efficiency (WUE ) and the relevance of the leaf cups for the cup plant's water balance in a 2‐year field experiment. Parallel investigations were conducted for the two reference crops maize (high WUE ) and lucerne‐grass (deep and intensive rooting) under rainfed and irrigated conditions. Root system performance was assessed by measuring water depletion at various soil depths. Transpiration‐use efficiency (TUE ) was estimated using a model approach. Averaged over the 2 years, drought‐related above‐ground dry matter reduction was higher for the cup plant (33 %) than for the maize (18 %) and lucerne‐grass (14 %). The WUE of the cup plant (33 kg ha?1 mm?1) was significantly lower than for maize (50 kg ha?1 mm?1). The cup plant had a lower water uptake capacity than lucerne‐grass. Cup plant dry matter yields as high as those of maize will only be attainable at sites that are well supplied with water, be it through a large soil water reserve, groundwater connection, high rainfall or supplemental irrigation.  相似文献   

13.
The long‐term effects of salt stress (11 dS m?1) and drought stress (35 % WHC) were investigated for two maize genotypes, focusing on the relation between metabolic changes around the time of pollination and the impact on yield determinants at maturity. The relatively salt‐resistant hybrid Pioneer 3906 and the relatively drought‐resistant hybrid Fabregas were compared. The experiments were conducted in large plastic containers in a vegetation hall in two consecutive years (2011 and 2012). Plant height and leaf area were significantly reduced under both stress conditions. The transpiration rate was only slightly reduced under drought stress; but under salt stress, a significant reduction occurred 40–53 days after sowing. As a significant increase in sucrose concentrations was observed in the salt‐treated maize kernels 2 days after pollination, the availability of assimilates was not limiting and the plants could afford to save water by reduced stomatal opening. Although under both stress conditions the soluble acid invertase activity was reduced 2 days after pollination, concomitantly, an increase in hexose concentrations was observed. Thus, in these experiments, the delivery of hexoses by acid invertase activity did not limit kernel development. Differences in grain yield at maturity between salt and drought stress were most likely caused by salt‐specific effects (Na+ toxicity), Fabregas being more affected than Pioneer 3906.  相似文献   

14.
In drought‐prone environments, sweet sorghum and sorghum‐sudangrass hybrids are considered worthy alternatives to maize for biogas production. The biomass productivity of the three crops was compared by growing them side‐by‐side in a rain‐out shelter under different levels of plant available soil water (PASW) during the growing periods of 2008 to 2010 at Braunschweig, Germany. All crops were established under high levels of soil water. Thereafter, the crops either remained at the wet level (60–80 % PASW) or were subjected to moderate (40–50 % PASW) and severe drought stress (15–25 % PASW). While the above‐ground dry weight (ADW) of sweet sorghum and maize was insignificantly different under well‐watered conditions, sweet sorghum under severe drought stress produced 27 % more ADW than maize. The ADW of sorghum‐sudangrass hybrids significantly lagged behind sweet sorghum at all levels of water supply. The three crops differed markedly in their susceptibility to water shortage. Severe drought stress reduced the ADW of maize by 51 %, but only by 37 % for sweet sorghum and 35 % for sorghum‐sudangrass hybrids. The post‐harvest root dry weight (RDW) in the 0–100 cm soil layer for maize, sweet sorghum and sorghum‐sudangrass hybrids averaged 4.4, 6.1 and 2.9 t ha?1 under wet and 1.9, 5.7 and 2.4 t ha?1 under severe drought stress. Under these most dry conditions, the sorghum crops had relatively higher RDW and root length density (RLD) in the deeper soil layers than maize. The subsoil RDW proportion (20–100 vs. 0–20 cm) for maize, sweet sorghum and sorghum‐sudangrass hybrids amounted to 6 %, 10 % and 20 %. The higher ADM of sweet sorghum compared with maize under dry conditions is most likely attributable to the deep root penetration and high proportion of roots in the subsoil, which confers the sorghum crop a high water uptake capacity.  相似文献   

15.
Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψleaf) and its components and stomatal conductance (gs) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (ECw) of 22 dS m?1. As water and salt stress developed and Ψleaf decreased, the leaf osmotic potential (Ψπ) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψleaf (with a steep drop at Ψleaf between ?0.8 and 1.2 MPa) and Ψπ (with a steep drop at Ψπ between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and gs. Leaf water potentials and gs were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψleaf and turgor pressure, Ψp, vs. gs) or linear (Ψleaf and Ψp vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψleaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψπ at full turgor. As soil was drying, the association between Ψleaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.  相似文献   

16.
王卫锋  杨晓青  张岁岐  山仑 《作物学报》2013,39(8):1462-1468
剪去小麦部分根系能瞬间打破其水分平衡,研究根系导水特性对剪根的响应有助于解释静水压对作物根系吸水的调节机制。通过对苗期小麦(Triticum aestivum)剪根与水分胁迫处理,用压力探针技术测定单根和细胞两种尺度上的根导水特性变化,以及根中TaPIP1;2和TaPIP2;5的转录调节变化。结果显示,剪根处理或水分胁迫处理使叶片蒸腾速率和气孔导度均显著低于对照,而单根导水率和细胞导水率均与对照无显著差异。剪根处理的叶片蒸腾速率、气孔导度、叶水势、单根导水率和细胞导水率均显著高于水分胁迫处理,而剪根且水分胁迫处理的各参数均显著低于其他处理。各处理的单根导水率与细胞导水率显著正相关。各处理根中TaPIP1;2和TaPIP2;5相对mRNA含量的变化规律与单根和细胞导水率的变化规律相似。剪根处理显著上调了TaPIP1;2和TaPIP2;5转录,水分胁迫处理显著下调了其转录,但TaPIP1;2和TaPIP2;5在剪根且水分胁迫处理中的转录水平最低。这些结果表明,小麦的根导水特性在单根尺度和细胞尺度上具有一致性;剪根短期内能够增加小麦幼苗的水分敏感性。推测TaPIP1;2和TaPIP2;5参与了静水压对小麦根导水特性的调节过程。  相似文献   

17.
Two chilling‐tolerant genotypes, that is, weedy rice WR03‐45 and cultivated rice Lijiangxintuanheigu and two chilling‐sensitive genotypes, that is, weedy rice WR03‐26 and cultivated rice Xiuzinuo were used in this study to investigate the effects of exogenous abscisic acid (ABA) on protection against chilling damage as well as on changes in physiological features. The results showed that under chilling stress the increased levels of superoxide radical (), hydrogen peroxide (H2O2) and malondialdehyde (MDA) in WR03‐45 and Lijiangxintuanheigu were lower than those in WR03‐26 and Xiuzinuo. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR)) and non‐enzymatic antioxidants (ascorbate acid (AsA) and reduced glutathione (GSH)) were enhanced in WR03‐45 and Lijiangxintuanheigu, whereas they were decreased significantly in WR03‐26 and Xiuzinuo. Application of exogenous ABA reduced the chilling damage in the four genotypes. The pre‐treatment with ABA decreased the levels of , H2O2 and MDA caused by chilling stress in the four genotypes through increasing the activities of SOD, CAT, APX, GR and the contents of AsA and GSH in the four genotypes under chilling stress. Moreover, pre‐treatment with Fluridone, the ABA biosynthesis inhibitor, prohibited the effects of ABA through enhancing the oxidative damages and suppressing the antioxidant defence systems under chilling stress. The results indicate the mechanism for rice with chilling tolerance is to enhance the capacity of antioxidant defence systems under chilling stress. Furthermore, ABA plays important roles in the tolerance of rice against chilling stress for it could induce the capacity of whole antioxidant defence systems including enzymatic and non‐enzymatic constitutions under chilling stress.  相似文献   

18.
Drought stress may affect sucrose accumulation of sugar beet by restricting leaf development and storage root growth. The objective of this study was to identify changes occurring in the storage root of Beta beets in growth characteristics and ions and compatible solutes accumulation under drought with regard to sucrose accumulation. Two pot experiments were conducted: (1) sugar beet well supplied with water (100 % water capacity), under continuous moderate (50 %) and severe drought stress (30 %), (2) sugar beet and fodder beet well supplied with water (100 %) and under continuous severe drought stress (30 %). Under drought stress, the ratio of storage root to leaf dry matter of sugar beet decreased indicating a different partitioning of the assimilates. The sucrose concentration of the storage root was reduced. In the root, the number of cambium rings was only slightly affected, although drought stress was implemented already 6 weeks after sowing. In contrast, the distance between adjacent rings and the cell size was considerably restricted, which points to a reduced expansion of existing sink tissues. The daily rate of sucrose accumulation in the root showed a maximum between 16 and 20 weeks after sowing in well‐watered plants, but it was considerably reduced under drought stress. The concentration of compatible solutes (K, Na, amino acids, glycine betaine, glucose and fructose) decreased during growth, while it was enhanced because of drought. However, when sucrose concentration was added, a constant sum of all examined solutes was found throughout the vegetation period. It was similar in sugar beet and in fodder beet despite different concentrations of single solutes, and the total sum was not affected by water supply. A close negative relationship between the concentration of compatible solutes and sucrose occurred. It is therefore concluded that the accumulation of compatible solutes in the storage root of Beta beets under drought might be a physiological constraint limiting sucrose accumulation.  相似文献   

19.
The relationship between biomass production and N2 fixation under drought‐stress conditions in peanut genotypes with different levels of drought resistance is not well understood. The objective of this study was to determine the effect of drought on biomass production and N2 fixation by evaluating the relative values of these two traits under well watered and water‐stress conditions. Twelve peanut genotypes were tested under field conditions in the dry seasons of 2003/2004 and 2004/2005 in north‐east Thailand. A split‐plot design with four replications was used. Main‐plot treatments were three water regimes [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW], and sub‐plot treatments were 12 peanut lines. Data were recorded on biomass production and N2 fixation under well watered and water‐stress conditions. Genotypic variations in biomass production and N2 fixation were found at all water regimes. Biomass production and N2 fixation decreased with increasing levels of drought stress. Genotypes did not significantly differ in reductions for biomass production, but did differ for reductions in N2 fixation. High biomass production under both mild and severe drought‐stress conditions was due largely to high potential biomass production under well‐watered conditions and, to a lesser extent, the ability to maintain high biomass production under drought‐stress conditions. High N2 fixation under drought stress also was due largely to high N2 fixation under well‐watered conditions with significant but lower contributions from the ability to maintain high nitrogen fixation under drought stress. N2 fixation at FC was not correlated with the reduction in N2 fixation at 2/3 AW and 1/3 AW. Positive relationships between N2 fixed and biomass production of the tested peanut genotypes were found at both levels of drought stress, and the relationship was stronger the more severe the drought stress. These results suggested that the ability to maintain high N2 fixation under drought stress could aid peanut genotypes in maintaining high yield under water‐limited conditions.  相似文献   

20.
The rise of atmospheric CO2 concentration ([CO2]) affects stomatal conductance and thus transpiration and leaf temperature. We evaluated the effect of elevated [CO2] levels under different water supply on daily sap flow and canopy microclimate (air temperature (Tc) and vapour pressure deficit (VPD)) of maize. The crop was cultivated in circular field plots under ambient (AMB, 378 μmol mol?1) and elevated [CO2] (FACE, 550 μmol mol?1) using free‐air CO2 enrichment with sufficient water in 2007, while in 2008 a DRY semicircle received only half as much water as compared to the WET semicircle from mid of July. In 2007, sap flow was measured in WET simultaneously under AMB and FACE conditions and was significantly decreased by elevated [CO2]. In 2008, sap flow was measured in all four treatments but not simultaneously. Therefore, data were correlated with potential evaporation and the slopes were used to determine treatment effects. Drought reduced whole‐plant transpiration by 50 % and 37 % as compared to WET conditions under AMB and FACE, respectively. Moreover, CO2 enrichment did not affect sap flow under drought but decreased it under WET by 20 % averaged over both years. The saving of water in the period before the drought treatment resulted in a displacement of dry soil conditions under FACE as compared to AMB. Under WET, CO2 enrichment always increased Tc and VPD during the day. Under DRY, FACE plots were warmer and drier most of the time in August, but cooler and damper short after the start of drought in July and from the end of August onwards. Thus, the CO2 effect on transpiration under drought was variable and detectable rather easy by measuring canopy microclimate.  相似文献   

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