Growth and yield response of common buckwheat (Fagopyrum esculentum Moench) to waterlogging at different vegetative stages

ABSTRACT

This study identified timing (1st, 3rd, or 5th leaf stage) and duration (1, 3, 6, or 10 days) of waterlogging treatment during the vegetative stage that had the most severe effect on yield and elucidated yield determining process. Yield was reduced the most by the waterlogging treatments at the 3rd leaf stage. Among stages, yield was significantly depressed, when the treatment duration was longer than 6 days. Seed weight of the 1st branches declined more under waterlogging treatments than did that of main stem and 2nd branches, accounting for approximately 55% of total seed weight in all treatments. On the other hand, the decline in node and branch numbers was more pronounced for 2nd branches than 1st branches at the ripening stage. The development of the 2nd branches during ripening did not contribute much to increase sink capacity. Development of the main stem and the 1st branches was almost complete until the full flowering stage and shoot dry weight did not increase from the full flowering stage to the ripening stage. Shoot dry weight at the full flowering stage was determined by both leaf number and net assimilation rate (NAR). Flower cluster number at that stage was significantly correlated with total seed weight. These results showed that the critical timing was at the 3rd leaf stage and the critical duration was longer than 6 days and indicated that maintenance of leaf number and NAR and development of flowers on the 1st branches until the full flowering stage would ensure the yield.

Abbreviations: NAR - net assimilation rate, SLA - specific leaf area, g_s - stomatal conductance.     

Growth Responses of Drought Resistant Rice Cultivars to Soil Compaction under Irrigated and Succeeding Non-irrigated Conditions during the Vegetative Stage

Abstract

We investigated whether drought resistant rice cultivars exhibit higher dry-matter production under wet and dry compacted soil conditions in the vegetative stage and determined the dominant factors governing resistance to soil compaction. Three rice cultivars, a drought-sensitive Nipponbare, and drought-resistant Senshou and Dular, were grown in pots at four soil bulk densities (SBD) ranging from 1300 to 1600 dry soil kg m^?3. Root and shoot dry matter productions was slightly smaller in Nipponbare over the 29 days after sowing under irrigated conditions than in the other cultivars at all SBDs. Senshou and Dular also maintained a higher dry matter production, both in relative and absolute values, than Nipponbare under the condition of withheld irrigation from days 29 — 39 after sowing. The higher stomatal conductance and leaf water potential of these two cultivars were supported by a larger root system which was mostly accompanied by lower top-root ratios in the irrigated and compacted soils. The higher plant growth rate under the non-irrigated condition might have been a result of both the higher water absorption rate and water use efficiency, which in turn were supported by the larger root biomass. We conclude that the ability of rice to rapidly develop a root system in the early vegetative phase under compacted soils facilitates plant production under subsequent soil desiccated conditions.     

外源硅对NaCl胁迫下小麦幼苗生长及光合特性的影响

为探讨外源硅对小麦幼苗耐盐性的调节作用,以抗盐小麦品种德抗961和非抗盐小麦品种泰山9818为材料,通过水培试验,研究了外源硅对NaCl胁迫下小麦幼苗生长、叶绿素含量和光合特性的影响。结果表明,在100mmol·L-1 NaCl胁迫下,随着外源硅浓度(0~3.0mmol·L-1)的增加,德抗961和泰山9818的株高、次生根数量、茎叶干重、根干重不断增加,叶片叶绿素、叶绿素a和叶绿素b含量先降后升,净光合速率及气孔导度逐渐升高,细胞间隙CO2浓度逐渐下降,气孔限制值先升后降。说明适量施硅可显著提高小麦抗盐性。     

Studies on Mechanisms of Dehydration Postponement in Cassava Leaves under Short-term Soil Water Deficits

Abstract

Cassava (Manihot esculenta Crantz) can produce a high crop yield even in an environment with irregular rains. This is mainly attributed to its abilities to maintain leaf area under drought conditions and rapidly regrow after rain. In this study, we investigated the mechanism of leaf maintenance under water deficits through measurement of photosynthetic rate and water potential changes in leaves. The cassava plants were grown in pots and exposed to water deficits, and the diurnal changes in water potentials, rates of photosynthesis and transpiration and stomatal conductance were measured. The relationship between leaf water potential (ψW) and photosynthetic rate with decreasing soil water, and osmotic adjustment were also investigated. With respect to water supply in leaves, the movement of water in plants was measured using stem heat balance. Under water deficits, photosynthesis occurred only in the early morning. The water loss was reduced by stomatal closure in the mid-day. This was attributed to the complete closure of the stornata during the decrease in ψW to a range between –1.0 and –1.4 MPa. Furthermore, the firm stomatal closure is caused by the consistency of osmotic potential under decreases in soil water, i.e., to a lack of osmotic adjustment. Water stored in the pith parenchyma of stem flowed into leaves in the morning. From these results, we conclude that cassava can consistently maintain an adequate water level in leaves via water storage and the sensitivity of stornata to water deficits, thereby avoiding leaf dehydration.     

Effects of Low Root Temperature on Dry Matter Production and Root Water Uptake in Rice Plants

Abstract

Chilling is a major constraint in rice production in cool climates. In rice (Oryza sativa L.) plants, both the air temperature and the water (soil) temperature affect various growth processes independently, and low root zone temperature (thus, root temperature) can inhibit rice growth and yield. In this study, we investigated the effect of low root temperature on rice growth in relation to dry matter production and root water uptake. Plants were grown in hydroponic solutions at two temperatures, one equivalent to air temperature and the other 14ºC for 15 d starting 11 d after germination. Low temperature of the solution (low root temperature) inhibited dry matter production of rice plants by decreasing leaf area rather than photosynthetic rate. The response of leaf area was affected by changes in plant water status, that is relative water content (RWC) of stem was decreased by low root temperature resulting in reduced leaf area. The decrease in RWC caused by low root temperature was related to that in root hydraulic conductance (K_r). The responses of transpiration (E) and K_r to the low root temperature depended more on root surface area than on changes in hydraulic conductance per unit root surface area (Lp_r). These results suggest that dry matter production under the low root temperature condition is controlled mainly by quantitative growth parameters such as leaf area and root surface area.     

Morpho-Physiological Response of Oryza glaberrima to Gradual Soil Drying

Soil drought occurrence during dry season has been the main constraint, besides prolonged flooding during rainy season, in increasing cropping intensity and rice productivity in tropical riparian wetland. Use of drought tolerant rice genotype might be a suitable option for overcoming such problem. This study focused on the effects of gradual soil drying during early vegetative growth stage on morphological and physiological traits of five Oryza glaberrima genotypes, namely RAM12, RAM14, RAM59, RAM97 and RAM101, and two Oryza sativa subsp japonica genotypes, i.e. Koshihikari and Minamihatamochi. The plants were subjected to 6 d of gradual soil drying condition from 15 days after transplanting (DAT) to 20 DAT, and were allowed to recover until 22 DAT. Gradual soil drying reduced plant growth as indicated by dry mass accumulation. Drought reduced stomatal conductance and increased leaf rolling score of all the genotypes. All the genotypes showed comparable response on stomatal conductance, but O. glaberrima genotypes performed higher in leaf rolling recovery. Meanwhile, O. sativa genotypes decreased total leaf area and specific leaf area, but increased specific leaf weight in order to avoid further damages due to drought stress. Drought tolerance mechanisms in RAM101, RAM12, RAM59 and RAM14 were associated with leaf morpho-physiological responses, root traits and dry biomass accumulation.     

Simulating Organ Growth in Wheat Based on the Organ–Weight Fraction Concept

Abstract

Quantifying dry matter partitioning into individual organs of plants is a key component for simulating crop growth and yield formation. This study was undertaken to develop a dynamic module of biomass partitioning over the entire duration of growth in wheat. The partitioning fraction of shoot or root was defined as the fraction of its dry weight in plant biomass, and partitioning fraction of green leaf, stem or ear as the fraction of its dry weight in shoot mass of wheat. The functional relationships of the partitioning fraction with physiological development time for the entire growth period were established, in which harvest index (HI) regulated partitioning fraction of ear to shoot biomass as a genetic parameter. The dry weight of individual organ was the product of the respective partitioning fraction and plant weight or shoot weight. Test of the model with the field experiment data sets involving different sowing dates, plant densities and nitrogen fertilization strategies indicated a good agreement between the predicted and observed values.     

Solanum habrochaites introgression line grafted as rootstock in cultivated tomato maintains growth and improves yield under cold and drought stresses

Grafting tomato (Solanum lycopersicum L.) onto introgression lines (ILs) derived from S. habrochaites with introgression of a quantitative trait locus (QTL), stm9, for shoot turgor maintainer located on chromosome 9 has been suggested for improving yield under abiotic stresses. However, the physiological and agronomic responses of grafts with IL rootstocks to low root-zone temperature (RZT) and drought stresses are not yet clearly understood. Therefore, recurrent parent (RP) grafted onto IL and donor (D) rootstocks, and self-grafted IL and RP were examined at different combinations of optimal (20°–26°C RZT and well-watered) and suboptimal (10°C RZT and well-watered, and 20°–26°C RZT and cyclic drought) temperatures. Graft combinations were compared with self-grafted controls for dry weights, stomatal conductance (g_s), leaf parameters, osmotic adjustment, and stress tolerance index. The RP grafted onto IL rootstocks regulated g_s efficiently, retained the green trait, and produced higher biomass than the self-grafted RP. The IL rootstocks improved tolerance of the scion to drought and low RZT. Potential of IL rootstocks for improving tomato production under stressed conditions is discussed.     

Characterization of the morphological and physiological traits of rice cultivars with adaptation to unflooded condition during early vegetative growth

This study aimed to characterize the physiological and morphological traits that are associated with adaptation to unflooded soil conditions in rice. Four indica rice cultivars (Puluik Arang, Badari Dhan, Shwe Nang Gyi, and Ratul), which were previously identified as highly or less adaptable to unflooded soil conditions, were grown under flooded and unflooded (soil water potential; －0.10 MPa) soil conditions. Water uptake was measured every day for three weeks, and then the leaf water potential, the stomatal conductance, the dry matter weight, shoot and root morphological traits were measured. Puluik Arang and Badari Dhan exhibited greater leaf area expansion and higher maintenance of root development under the unflooded condition than that by other cultivars. The leaf water potential and stomatal conductance of fully expanded highest leaf in Puluik Arang and Badari Dhan were not affected by unflooded soil regime. Leaf area and root morphological traits were significantly correlated with water uptake regardless of soil moisture regimes. These results suggested that Puluik Arang and Badari Dhan exhibited great water uptake capacity through physiological and morphological adaptation of shoot and root traits to unflooded condition, resulting in great biomass productivity under the condition.     

小麦苗期抗旱相关形态指标的灰色关联度分析

为了系统研究小麦苗期形态指标与抗旱性的关系并筛选有效的抗旱性指标,使用PEG-6000模拟干旱胁迫,采用灰色关联度分析法分析了28份小麦品种苗期干旱胁迫下的苗高、最长根长、根数、地上部鲜重、地上部干重、根鲜重、根干重、叶片数、根冠比等9个形态指标与抗旱系数的关联程度,并以所得加权抗旱系数对各品种进行聚类分析.结果显示,各形态指标与抗旱系数的关联度依次为:叶片数(0.817)>苗高(0.766)>地上部干重(0.746)>地上部鲜重(0.729)>根数(0.699)>根干重(0.688)>根鲜重(0.681)>根冠比(0.645)>最长根长(0.399).研究还表明,9个形态指标可分为叶片相关因子、地上部生物量因子和根部生物量因子三大类,地上部生物量因子的关联度大于根部生物量因子;不能只通过差异显著度检验来判断某一指标是否可以用作抗旱性鉴定;聚类结果能较好地反映各小麦品种的地域分布.因此,进行小麦品种苗期抗旱性鉴定时,应加强对地上部形态指标的选择和鉴定,以提高选择效率.     

Change in Hydraulic Resistance and Shoot Morphology of Napiergrass (Pennisetum purpureum Schumach.) under Shaded Condition

Abstract

Acclimation to light condition is associated with change in water transport system in napiergrass. In this study, the effects of shading on shoot hydraulic resistance and morphology of napiergrass (Pennisetum purpureum Schumach.) were investigated. In the plants under shading (to 30% of full sunlight) for 30 days (S plants), total hydraulic resistance of a shoot (Rshoot) increased from that of full sunlight (control). In the plants grown under shade condition for 24 d followed by full sunlight conditions for 6 d (SF), the Rshoot value was intermediate between that of control and S plants. A similar response to shading was found in total hydraulic resistance of a stem (R_stem), which accounted for more than 60% of Rshoot, but the total hydraulic resistance of the leaves was not significantly affected by shading. Leaf length, leaf area and stem length were larger, but the stem cross-sectional area (SA) was smaller in S and SF plants than in the control plants. SF plants showed similar leaf length, leaf area and stem length to those in S plants, but the SA in SF plants was slightly larger. Normalization of R_stem by SA and stem length decreased the difference among the treatments, indicating the increase of Rshoot and R_stem under shading resulted from the decrease of SA and the increase of stem length.     

春季不同时期低温对小麦光合特性和粒重形成的影响

为探讨春季低温导致小麦粒重下降的生理机制,以春性品种扬麦16和半冬性品种徐麦30为材料,分别于倒二叶出生期、孕穗期和开花期对小麦进行人工气候室低温处理,研究不同时期低温对小麦光合生理特性、干物质积累和转运及强、弱势粒粒重形成的影响。结果表明,不同时期低温对叶片SPAD值的影响均表现为低温处理开始至结束后3 d持续下降,结束后6～9 d逐渐回升,两品种在低温处理结束当天和处理后3 d均以孕穗期低温处理下SPAD值降幅最大。不同时期低温处理显著降低叶片净光合速率和气孔导度,并影响花前干物质转运和花后干物质积累。与孕穗期、开花期低温处理相比,倒二叶出生期低温处理显著降低小麦花前干物质转运量,但提高花后干物质积累及其对籽粒产量的贡献率,千粒重降幅最小,扬麦16和徐麦30分别仅为4.49%和4.20%。不同时期低温处理下小麦强势粒粒重的降幅均小于弱势粒,倒二叶出生期低温处理下弱势粒粒重降幅显著低于孕穗期和开花期低温处理。相关性分析表明,低温胁迫下小麦平均千粒重和强势粒粒重相关性不显著(r=0.319,P>0.05),但与弱势粒粒重显著相关(r=0.691,P<0.05)。综上,春季低温胁迫主要通过影响小麦开花前后的光合作用和同化物向籽粒的转运,限制弱势粒的灌浆充实,最终导致粒重下降。     

Effects of Soil Temperature on Growth and Root Function in Rice

Abstract

The objective of this study was to clarify the effects of soil temperature in the stage from late tillering to panicle initiation (SI) and during the grain-filling stage (SII) on grain setting, dry matter production, photosynthesis, non-structural carbohydrate (NSC), xylem exudation and abscisic acid (ABA) levels in rice (Oryza sativa L. cv. Koshihikari). Rice plants were exposed to four different soil temperatures during SI or SII: 17.5, 25, 31.5 and 36.5°C (ST18, ST25, ST32 and ST37, respectively). The yield, yield components, grain filling and quality in SI were negatively influenced by high soil temperature of 37°C. On the other hand, there was no significant difference in those characters among temperature treatments in SII. The root/shoot ratio was smallest in the ST37 plants in both SI and SII, mainly due to their lighter root weight. At 7 days after initiation of treatment (DAT) in both SI and SII, the photosynthetic and xylem exudation rate tended to increase slightly as soil temperature increased up to 32°C. At 21 DAT, however, the photosynthetic rate was lowest in ST37, with concurrent decrease of diffusion conductance and SPAD value. In addition, decrease of NSC concentration in stem and xylem exudation rate, and increase of ABA level in leaves and xylem exudate were observed in ST37 plants at 21 DAT. These results suggested that high soil temperature before heading especially influenced yield, grain quality and plant growth. Possible mechanisms of the effect of soil temperature are discussed.     

Root Development,Water Uptake,and Shoot Dry Matter Production under Water Deficit Conditions in Two CSSLs of Rice: Functional Roles of Root Plasticity

Abstract

Root traits that can contribute to drought resistance have not been clearly indentified. We examined the role of root system development in enhancing water uptake and contribution to dry matter production by using the root box-pinboard method, with which quantitative assessment of root system development and the water uptake of root are possible. Chromosome segment substitution lines CSSL45 and CSSL50, and the recurrent parent Nipponbare were grown under continuously waterlogged conditions (control), and various intensities of water deficit in root boxes. There was no significant difference among the genotypes in shoot growth and root development, while CSSL45 and CSSL50 showed greater shoot dry weight than Nipponbare under water deficit conditions. This was due to their abilities to promote root system development as compared with Nipponbare, which facilitated greater water extraction than Nipponbare, especially under the mild water deficit condition of 20–25% w/w soil moisture contents. Furthermore, the increased root length density did not exceed the estimated critical value for water uptake, which indicates that plastic root system development was functionally effective and efficient for the enhancement of water uptake under mild water deficit conditions.     

Genetic Variations in Dry Matter Production,Nitrogen Uptake,and Nitrogen Use Efficiency in the AA Genome Oryza Species Grown under Different Nitrogen Conditions

Abstract

To clarify the genotypic variation of nitrogen (N) response in the AA genome Oryza species, we investigated dry matter production, N uptake, N and water use efficiencies (NUE and WUE), bleeding sap rate (BR), and root morphological traits at vegetative stage in 6 cultivars and 4 strains of 6 species (O. sativa, O. glaberrima, O. barthii, O. nivara, O. meridionalis, and O. rufipogon) grown under standard N (SN) and low N (LN) conditions. Some wild Oryza strains and O. glaberrima showed high dry matter production under both N conditions. In most plants, total dry weight decreased and root dry weight increased under the LN condition, resulting in decreased top-root ratio. In japonica cultivars of O. sativa, however, these traits were unaffected by the N condition. There were no significant differences in WUE with plant species or N conditions. In all plants, however, NUE was higher in the LN than SN condition, and was conspicuously high in most wild Oryza species and O. glaberrima. Some of them showed increased capacity of nitrate-N (NO₃-N) uptake under the LN condition. In cultivars and strains with a high NUE, root dry weight, root surface area, and BR were also higher under the LN condition. These results suggest that a high NUE is associated with the development of a root system, increased BR, and probably increased capacity of NO₃-N uptake. This study revealed the presence of superior wild Oryza strains for growth under LN that may be a promising genetic resource for low N-input agriculture.     

Root plasticity under fluctuating soil moisture stress exhibited by backcross inbred line of a rice variety,Nipponbare carrying introgressed segments from KDML105 and detection of the associated QTLs

In rainfed lowland rice ecosystem, rice plants are often exposed to alternating recurrences of waterlogging and drought due to erratic rainfall. Such soil moisture fluctuation (SMF) which is completely different from simple or progressive drought could be stressful for plant growth, thereby causing reduction in yield. Root plasticity is one of the key traits that play important roles for plant adaptation under such conditions. This study aimed to evaluate root plasticity expression and its functional roles in dry matter production and yield under SMF using Nipponbare, KDML 105 and three backcross inbred lines (BILs) and to identify QTL(s) associated with root traits in response to SMF at two growth stages using Nipponbare/KDML105 F₂ plants. A BIL, G3-3 showed higher shoot dry matter production and yield than Nipponbare due to its greater ability to maintain stomatal conductance concomitant with greater root system development caused by promoted production of nodal and lateral roots under SMF. QTLs were identified for total nodal root length, total lateral root length, total root length, number of nodal roots, and branching index under SMF at vegetative and reproductive stages. The QTLs detected at vegetative and reproductive stages were different. We discuss here that relationship between root system of G3-3 and the detected QTLs. Therefore, G3-3 and the identified QTLs could be useful genetic materials in breeding program for improving the adaptation of rice plants in target rainfed lowland areas.     

The Occurrence of Delayed Stem Senescence in Relation to trans-Zeatin Riboside Level in the Xylem Exudate in Soybeans Grown under Excess-Wet and Drought Soil Conditions

Abstract

Delayed stem senescence (DSS) after pod maturation in soybean (Glycine max) lowers the quality of products in the mechanized harvest. The effects of drought and excess wet soil conditions on the occurrence of DSS were studied with special reference to remobilization of vegetative nitrogen and supply of cytokinin via xylem. Excess wet soil treatment was applied throughout the reproductive period to field-grown soybean in 2003 (Exp.1) and short-term drought stress treatment was applied during the reproductive period to pot-grown soybean plants in 2004 (Exp.2). The degree of DSS at pod maturing was evaluated by the DSS score from “1” for severe DSS to “5” for completely synchronous senescence of pods and vegetative parts. The DSS score in Exp.1 varied from 2.2 to 2.5 and that in Exp.2 from 2.8 to 3.7. Excess wet soil treatment in Exp.1 promoted the occurrence of DSS, while drought stress treatments during the periods of flowering to pod elongation, later seed-filling and seed maturing decreased it. The soybean plants that showed distinct DSS had lower ratios of seed number to vegetative dry weight at seed maturity and a lower rate of nitrogen remobilization from vegetative organs to seeds during the latter half of the reproductive period. The trans-zeatin riboside (t-ZR) level in xylem exudate tended to be higher in soybeans with severer DSS than in those normally matured in both experiments showing increased t-ZR concentration and/or higher exudation rate. These results suggest that DSS can be caused by a wet soil water condition, which lowers pod/seed number and increases vegetative organs mediated by the increased supply of cytokinin through xylem during seed-filling.     

弱光胁迫下接种Glomus mosseae对玉米生长生理指标的影响

采用盆栽实验,以"云瑞47"为研究材料,Glomus mosseae(Gm)为接种菌剂,研究弱光和丛枝菌根真菌(AMF)对玉米生长生理的影响。结果表明,弱光作用下,玉米根系的AMF侵染率明显降低,叶片数、茎粗和总叶面积减少,植株地上部干重、地下部干重和总干重下降,株高增加,叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量上升,叶绿素a/b值降低,净光合速率减弱。弱光胁迫下接种Gm,能够增加玉米的叶片数、茎粗、株高和总叶面积,促进地上部干重、地下部干重和总干重的积累,提高叶片叶绿素a、叶绿素b、类胡萝卜素和总叶绿素含量,增强净光合速率。接种Gm真菌,能够缓解弱光对玉米生长产生的不良影响,促进植株生长。     

Effect of nitrogen application on the expression of drought-induced root plasticity of upland NERICA rice

ABSTRACT

This study evaluated the effect of three N fertilization levels 60 (low), 120 (medium), and 180 (high) kg N ha^?1 and soil moisture content gradients created by a line-source sprinkler on the expression of plasticity in lateral root branching and dry matter production (DMP) of upland new rice for Africa (NERICA) 1 and 4. There were no significant differences in DMP between NERICA 1 and 4 under well-watered, mild drought, and severe drought conditions regardless of N level. In contrast, under moderate drought (12–21% v/v of soil moisture content [SMC] in 2011 and 16–24% v/v of SMC in 2012), NERICA 1 had significantly higher shoot dry weight, total root length (TRL), lateral root length, and branching index than NERICA 4 at medium and high N; however, there was no significant difference between the two NERICAs in DMP at low N. TRL of NERICA 1 was significantly higher under moderate drought than well-watered conditions, but only with medium and high N. Regardless of N level, moderate drought did not enhance NERICA 4’s root system. Thus, NERICA 1’s root system exhibited plastic development, promoting lateral root branching at medium and high N. These morphological changes were associated with the greater DMP in NERICA 1 than NERICA 4 under moderate drought, whereas the lack of such plasticity at low N meant genotypic differences in DMP were obscured. Our findings implied that N application can improve upland NERICA productivity under moderate drought conditions, but differences in variety and field conditions may influence efficacy.     

Varietal Differences in Seedling Traits under the Low Dissolved Oxygen Level in Water-Seeded Rice

Abstract

A snap bean (Phaseolus vulgaris L.) cultivar Haibushi shows high productivity under high-temperature conditions. Together with intensive radiation, high temperature enhances transpiration and causes water deficit in plants even when they are irrigated enough. To characterize daily change in water balance of the heat-tolerant cultivar, we compared parameters of water balance, dry matter production and pod yield among cultivars. Four snap bean cultivars, Haibushi, Kurodane-Kinugasa, Oregon and Kentucky Wonder, were grown under optimal temperature (spring cropping) and high temperature (summer cropping) condition in the field. The daily water balance and gas exchange rate in the heat-tolerant cultivar Haibushi were compared with those in the heat-sensitive cultivar Kentucky Wonder, grown in 0.02 m² Wagner pots. In the summer cropping in the field, dry matter production, pod yield, stomatal conductance, photosynthetic rate and transpiration rate were higher in Haibushi and Kurodane-Kinugasa than in the other cultivars. In a glasshouse, the sap flow rate was lower than the transpiration rate in the morning when the transpiration rate rapidly increased in both Haibushi and Kentucky Wonder. In spite of the higher transpiration rate, Haibushi showed a higher sap flow rate and smaller cumulative water loss in the morning than Kentucky Wonder. We conclude that better growth of the heat-tolerant snap bean cultivar Haibushi under high temperature was due to higher photosynthetic rate resulting from higher stomatal conductance during the daytime, which had a higher water uptake rate.