Low Transpiration Efficiency Research Articles

Crop Performance Indexes Applied to Legume Used as Summer Cover Crops under Water Deficit Conditions

Summer legume cover crops (CC) such as Crotalaria juncea, Crotalaria spectabilis, Crotalaria ochroleuca, and Cajanus cajan could offer diverse advantages for the environment and productive cropping systems. A low transpiration efficiency (TE) of CC can induce soil water content to levels that present a challenge for the subsequent crop. In a 75-day growth chamber experiment, using the natural abundance of 13C, 18O, and 15N we evaluated the TE and BNF under two soil water conditions. Our results showed that the four species tested are good candidates for their use as CC because they showed good results in terms of productivity parameters, TE, and BFN. Cajanus cajan had the highest TE, a high shoot dry matter production, and accumulated more N from BFN in the shoot than C. spectabilis, C. juncea, and C. ochroleuca. ∆18O increased under moderate water deficit and showed an inversely proportional relationship with the amount of transpired water, supporting the use of this isotopic indicator as a proxy for transpiration and stomatal conductance. For the isotopic parameters no interaction between the factors water regimen and species were found. We propose the mass ratio of nitrogen fixed by the volume of transpired water and the isotopic discrimination of 13C as useful indicators of drought fixing legumes tolerance.

Effect of simulated warming on leaf functional traits of urban greening plants

BackgroundResponse and adaptation strategies of plants to the environment have always been the core issues in ecological research. So far, relatively little study exists on its functional traits responses to warming, especially in an urban environment. This information is the key to help understand plant responses and trade-off strategy to urban warming.ResultsWe chose the common greening trees of mature age in Beijing (Fraxinus pennsylvanica, Koelreuteria paniculata, and Sophora japonica) as the research subjects, and used infrared heaters to simulate warming for three gradients of natural temperature (CK), moderate warming (T1) and severe warming (T2). Results showed that:(1) Leaf dry matter content (LDMC), chlorophyll content (CHL), leaf tissue density (LTD), and stomatal density (SD) all increased with temperature warming. Specific leaf area (SLA), stomatal size (SS), and stomatal aperture (SA) decreased with simulated warming. (2) SLA was extremely significantly negatively correlated with CHL, LDMC, LTD and SD (P < 0.01), and was extremely significantly positively correlated with SS (P < 0.01). SA was extremely negatively correlated with SD (P < 0.01), and was extremely significantly positively correlated with SS (P < 0.01). There was a significant positive correlation between LDMC and LTD (P < 0.01). This showed that urban greening trees adapted to the environment by coordinating adjustment among leaf functional traits. (3) Under the T1 treatment, the R2 and slope among the leaf traits were higher than CK, and the significance was also enhanced. The correlation between leaf traits was strengthened in this warming environment. Conversely, it will weaken the correlation between leaf traits under the T2 treatment.ConclusionOur study demonstrated that there was a strong trade-off between leaf functional traits in the urban warming environment. Plants in the warming environment have adopted relatively consistent trade-offs and adaptation strategies. Moderate warming was more conducive to strengthening their trade-off potential. It is further verified that the global leaf economics spectrum also exists in urban ecosystems, which is generally tend to a quick-investment return type with the characteristics of thick leaves, strong photosynthetic capacity, low transpiration efficiency and long life in urban environments.

Genetic variation for leaf carbon isotope discrimination and its association with transpiration efficiency in canola (Brassica napus).

Drought is a major constraint to canola production around the world. There is potential for improving crop performance in dry environments by selecting for transpiration efficiency (TE). In this work we investigated TE by studying its genetic association with carbon isotope discrimination (Δ) and other traits, e.g. specific leaf weight (SLW) and leaf chlorophyll content (SPAD). Among the 106 canola genotypes - including open-pollinated, hybrid, inbred types and cytoplasmic variants - tested in the field and glasshouse there was significant genotypic variation for TE, Δ, plant total dry weight, SLW and SPAD. Strong negative correlations were observed between TE and Δ (-0.52 to -0.76). Negative correlations between Δ and SLW or SPAD (-0.43 to -0.78) and smaller but significant positive correlations between TE and SLW or SPAD (0.23 to 0.30) suggested that photosynthetic capacity was, in part, underpinning the variation in TE. A cytoplasmic contribution to genetic variation in TE or Δ in canola was also observed with Triazine tolerant types having low TE and high Δ. This study showed that Δ has great potential for selecting canola germplasm with improved TE.

Relationships between δ13C, δ18O and grain yield in bread wheat genotypes under favourable irrigated and rain-fed conditions

In previous investigations, carbon isotope composition (δ13C) has been used in C3 cereals to screen for genotypes with high transpiration efficiency and oxygen isotope composition (δ18O) has been shown to correlate with transpiration rate. We examined associations of δ13C of the grain and flag leaf and δ18O of the flag leaf with respect to grain yield in wheat cultivars in UK field conditions. Field experiments were carried out at University of Nottingham in 2009–10 and 2010–11 testing 17 wheat cultivars under fully irrigated and rain-fed conditions. Averaging across years grain yield was reduced by 1.69tha−1 (16.5%) in the rain-fed treatment (P<0.001). There was a negative linear relationship between grain yield and grain δ13C amongst cultivars, under both irrigated (R2=0.47, P<0.01) and rain-fed (R2=0.70, P<0.001) conditions. Grain δ13C was negatively correlated with flag-leaf stomatal conductance (r=−0.94, P<0.01) in a subset of six of the cultivars, indicating that higher transpiration efficiency was associated with lower stomatal conductance. The associations between grain yield and flag-leaf δ13C and flag-leaf δ18O amongst cultivars under irrigated and rain-fed conditions were not statistically significant. There was a positive linear relationship between flag-leaf δ18O and grain δ13C amongst cultivars under irrigated conditions (R2=0.38, P<0.01), indicating a trade-off between transpiration and transpiration efficiency (TE). Genetic variation in grain yield under rain-fed conditions was also associated with delayed onset of flag-leaf senescence (R2=0.35, P<0.05). The 17 wheat cultivars ranged in year of release (YoR) from 1964 to 2009 and grain yield increased linearly under irrigated conditions by 60.4kgha−1yr−1 (0.72%yr−1) and under rain-fed conditions by 47.5kgha−1yr−1 (0.66% yr−1) over the 45year period and grain δ13C composition decreased by 0.0255 and 0.0304‰ yr−1, respectively, indicating genetic gains in wheat yield potential in the UK seem likely to have been achieved through a lower TE, higher water uptake and lesser limitation of stomatal conductance.

Variation in drought-tolerance components and their interrelationships in the core collection of foxtail millet (Setaria italica) germplasm

Foxtail millet (Setaria italica (L.) P.Beauv.) is an ancient cereal cultivated worldwide in arid and marginal lands. It is an ideal crop for the changing climate, with high photosynthetic efficiency. A trait-based selection for drought tolerance is sought for yield stability. The present work had segregated the drought yield as total water use (T), transpiration efficiency (TE) and harvest index (HI) and assessed the importance of these components and their association with drought tolerance. The core collection of foxtail millet germplasm (n = 155) was evaluated in mini-lysimeters under both terminal drought stress (DS) and well-watered (WW) environments. The contribution of T to grain yield under drought was minor but the contribution of TE was positive and of HI negative. Crop duration, T and TE positively influenced, and HI negatively influenced, shoot biomass production. Under drought, the core germplasm accessions varied in shoot biomass, grain yield, HI and T by &gt;3-fold and in TE by 2-fold. Categorisation of the germplasm for TE had differentiated groups of accessions as high TE (n = 17) and low TE (n = 22). Among the three races of foxtail millet, indica was strong for T and TE, and maxima and moharia for HI, with useful exceptions.

Leaf Transpiration Efficiency in Four Corn Cultivars Grown at Elevated Carbon Dioxide

ABSTRACTHigh leaf transpiration efficiency (TE) occurs in some cultivars of corn (Zea mays L.) and could be a useful trait to improve yield under water deficits. The CO2 concentration in the atmosphere continues to increase rapidly, and it is not certain that cultivar differences in leaf TE occurring at the current CO2 concentration would still occur at elevated CO2. Two cultivars of sweet corn with high leaf TE and two with low TE were grown for two seasons in plots with free‐air CO2 enrichment systems to determine whether elevated CO2 altered the ranking of the cultivars in leaf TE. Measurements were also made at ambient CO2 2 h and 5 d after termination of the CO2 application. The results indicated that growth at 1.4 times the current CO2 concentration resulted in one cultivar having about 25% higher leaf TE than the other three cultivars, which had similar values of TE. The changed ranking of one cultivar was a result of growth at elevated CO2 and not the elevated measurement concentration. Thus, in one cultivar, the high leaf TE trait was stable across growth CO2 conditions, but in another cultivar, the high TE trait was no longer evident when the plants were grown at elevated CO2. Screening of corn genotypes for high leaf TE at projected future CO2 concentrations may be more efficiently accomplished at those concentrations.

Can a wheat cultivar with high transpiration efficiency maintain its yield advantage over a near-isogenic cultivar under elevated CO2?

This study investigated whether yield advantages of the wheat cultivar ‘Drysdale’ (selected for high transpiration efficiency) over recurrent parent ‘Hartog’ (low transpiration efficiency) are maintained under future atmospheric CO2. Growth, yield and yield components at three developmental stages (stem elongation, anthesis, maturity) were evaluated at two CO2 concentrations (ambient, a[CO2], ∼390μmolmol−1 and elevated, e[CO2], ∼550μmolmol−1). Growth under e[CO2] stimulated yield and above ground biomass on average by ∼18%. ‘Hartog’ compared to ‘Drysdale’ had significantly greater crop growth rate (∼14%), above ground biomass (∼15%), leaf area index (∼25%) and tiller numbers (∼16%) during early development (stem elongation). ‘Hartog’, however, lost this initial growth advantage over ‘Drysdale’ until anthesis when ‘Drysdale’ had more green leaf mass (∼15%) and greater spike (∼8%) and tiller (∼11%) numbers, particularly when grown under e[CO2]. At maturity, this resulted in a yield advantage of ∼19% of ‘Drysdale’ over ‘Hartog’ when grown under e[CO2] but only of ∼2% under a[CO2]. We suggest that wheat cultivars selected for superior transpiration efficiency will remain successful in a high [CO2] world. Evidence from this study even indicates that such cultivars may confer future advantage in some environments where this is not evident under current [CO2].

The Effect of Solar Loading on Soil Temperatures and Developmental Variation in Greenhouse Studies

Water is the single most limiting factor of crop yield. A high throughput method of screening sorghum for transpiration efficiency (TE) might allow selection for plants able to maintain production in semiarid regions having few irrigation resources. A high throughput TE assay was characterized. We hypothesized that variation in solar radiation absorbed by containers could introduce soil temperature variation and influence measured TE. To test our hypothesis, two sorghum lines, Liang Tang Ai (High TE) and TX‐7078 (Low TE), were grown in either conventional black plastic or in insulated containers and TE determined as biomass/water transpired. Soil temperatures in the sealed conventional thermoplastic containers exceeded 50°C and plants developed more slowly than those grown in insulated containers. Liang Tang Ai showed 30% greater TE as compared to TX‐7078 when grown in insulated containers, but any potential TE differences were masked by supra‐optimal temperatures in the conventional black plastic containers. Our results showed that the effects of solar radiation loading can lead to high soil temperatures and must be considered when designing TE screening experiments or other physiological studies.

The effect of rice straw mulch on evapotranspiration, transpiration and soil evaporation of irrigated wheat in Punjab, India

Soil evaporation (Es) is considered to be a non-productive component of evapotranspiration (ET). So, measures which moderate Es may influence the amount of water available for transpiration (T), the productive component of ET. Field experiments investigating the effects of rice straw mulch on components of the water balance of irrigated wheat were conducted during 2006–2007 and 2007–2008 in Punjab, India, on a clay loam soil. Daily Es was measured using mini-lysimeters, and total seasonal ET was estimated as the missing term in the water balance equation. Mulch lowered total Es over the crop growth season by 35 and 40 mm in relatively high and low rainfall years, respectively. Much of this “saved water” was partitioned into T, which increased by 30 and 37 mm in the high and low rainfall years, respectively. As a result, total ET was not affected by mulch in either year. In both years, there was a trend for higher biomass production and grain yield with mulch, but with significant differences only in 2006–2007. Transpiration efficiency (TE) with respect to grain yield was 18.8–19.1 kg ha−1 mm−1 in 2006–2007, and 14.6–16.4 kg ha−1 mm−1 in 2007–2008. While wheat grown in the presence of mulch tended to lower TE, this was only significant in 2007–2008. The results suggest that while mulching of well-irrigated wheat reduces Es, it does not “save” water because the crop compensates by increased T and reduced TE.

Leaf Transpiration Efficiency of Sweet Corn Varieties from Three Eras of Breeding

ABSTRACTWhen measured under midday field conditions, modern varieties of maize (Zea mays L.) often have substomatal carbon dioxide concentration (Ci) values in excess of those required to saturate the photosynthetic carbon dioxide assimilation rate (A). This results in lower leaf transpiration efficiency (TE), the ratio of photosynthesis to transpiration, than potentially achievable for a given rate of photosynthesis. In some other crops, breeding has indirectly resulted in a large increase in stomatal conductance (gs), which would decrease TE. I tested whether this occurred in sweet corn by comparing five open‐pollinated varieties released before 1903 with four standard hybrid varieties released in the mid‐1900s and four varieties released after 1990. Leaf gas exchange of each variety was measured under ambient midday field conditions on eight sunny days over two seasons in Beltsville, MD. Although there were significant differences among varieties in gs, A, Ci, and TE, no effect of era was significant for any variable except A. Of the four modern varieties tested, two had the highest gs and two had the lowest gs of any of the varieties compared, with high gs associated with low TE. These four varieties were further compared in a third year and were found to differ consistently in leaf TE but not in A. It is concluded that breeding over the last century has not increased gs or decreased leaf TE in sweet corn but that there is significant variation in TE among modern sweet corn varieties.

Relationships Between Transpiration Efficiency and Its Surrogate Traits in the rd29A:DREB1A Transgenic Lines of Groundnut

Transpiration efficiency (TE) contributes to crop performance under water-limited conditions, but is difficult to measure. Herein, we assess the relationships between TE and surrogate traits and how these interact with water regimes, using isogenic materials: five transgenic events of groundnut and their wild-type (WT) parent JL 24, among which large variation in TE was previously reported. These five events came from the insertion of transcription factor DREB1A from Arabidopsis thaliana, driven by stress responsive promoter rd29. The events were in T3 generation and had been selected from a preliminary trial for having a large range of variation in the time needed to deplete soil moisture upon exposure to soil drying. Two experiments were conducted, in each case with plants exposed to well-watered (WW) and water-stressed (WS) conditions. Significant correlations were found between TE and soil plant analysis development chlorophyll meter readings (SCMR), TE and specific leaf area (SLA), and SLA and SCMR in both experiments. Nevertheless, these significant relationships were confined to the drought stress (DS) treatment. No correlation between TE and Δ13C (carbon isotope discrimination) was found in the present study, regardless of the water regime, and in none of the two experiments. A significant negative correlation was established between TE and the fraction of transpirable soil water (FTSW) threshold values where transpiration declined upon soil drying, in both experiments. The mean vapour pressure deficit in the two different seasons (1.47 kPa and 0.73 kPa) did not affect the ranking of genotypes for TE. It is concluded that surrogates for TE, when used, need careful consideration of the drought stress status of plants at the time of measurement, and that differences in TE might be closely related to how plants respond to soil drying, with high TE genotypes maintaining gas exchange until the soil is dryer than low TE genotypes.

Leaf Transpiration Efficiency of Some Drought‐Resistant Maize Lines

Field measurements of leaf gas exchange in maize (Zea mays L.) often indicate stomatal conductances higher than required to provide substomatal carbon dioxide concentrations saturating to photosynthesis. Thus maize leaves often operate at lower transpiration efficiency (TE) than potentially achievable for species with C4 metabolism. I tested whether several maize lines described as drought resistant or drought tolerant operated with higher leaf TE than less drought‐adapted lines. Field measurements of leaf TE were conducted over two seasons for five reputedly drought‐resistant lines of maize and three locally grown lines not regarded as drought resistant. Midday photosynthesis, transpiration, stomatal conductance, and substomatal carbon dioxide concentration measurements were made under the ambient field conditions of air temperature and humidity in Beltsville, MD. Soil moisture was not limiting. Consistent and significant differences among the lines occurred for stomatal conductance, substomatal carbon dioxide concentration, and TE, but no significant differences among the lines occurred in photosynthesis. One drought‐tolerant line had higher TE than all others tested, and one of the local lines had the lowest TE, but the drought‐tolerant lines as a group did not have significantly higher TE. It is concluded that significant genotypic variation in leaf TE exists in maize, and that TE could be improved without reducing photosynthesis.

Assessment of transpiration efficiency in peanut (Arachis hypogaea L.) under drought using a lysimetric system

Transpiration efficiency (TE) is an important trait for drought tolerance in peanut (Arachis hypogaea L.). The variation in TE was assessed gravimetrically using a long time interval in nine peanut genotypes (Chico, ICGS 44, ICGV 00350, ICGV 86015, ICGV 86031, ICGV 91114, JL 24, TAG 24 and TMV 2) grown in lysimeters under well-watered or drought conditions. Transpiration was measured by regularly weighing the lysimeters, in which the soil surface was mulched with a 2-cm layer of polythene beads. TE in the nine genotypes used varied from 1.4 to 2.9 g kg(-1) under well-watered and 1.7 to 2.9 g kg(-1) under drought conditions, showing consistent variation in TE among genotypes. A higher TE was found in ICGV 86031 in both well-watered and drought conditions and lower TE was found in TAG-24 under both water regimes. Although total water extraction differed little across genotypes, the pattern of water extraction from the soil profile varied among genotypes. High water extraction within 24 days following stress imposition was negatively related to pod yield (r(2) = 0.36), and negatively related to water extraction during a subsequent period of 32 days (r(2) = 0.73). By contrast, the latter, i.e. water extraction during a period corresponding to grain filling (24 to 56 days after flowering) was positively related to pod yield (r(2) = 0.36). TE was positively correlated with pod weight (r(2) = 0.30) under drought condition. Our data show that under an intermittent drought regime, TE and water extraction from the soil profile during a period corresponding to pod filling were the most important components.

Genetic diversity of transpiration efficiency in sorghum

Sorghum is the fifth most important grain crop and is becoming increasingly important as a biofuel feedstock due to its superior tolerance to water-deficit stress. Sorghum is commonly grown under rain-fed conditions in the Southern Plains in the U.S.A. and other semi-arid regions in the world. Thus, its production is strongly affected by the availability of soil water during the growing season. Enhancing transpiration efficiency (TE), defined as biomass accumulation per unit water transpired, may be an effective approach to increasing sorghum yield in arid and semi-arid regions under no or limited irrigation. In this report, we surveyed 341 sorghum accessions for variation in TE. A selection of 25 lines was used to confirm the initial survey and these accessions were studied in a greenhouse experiment over 2 years. TE in these selected lines varied from year to year; however, similar rank was observed in both studies. Several accessions with consistent high or low TE were identified. TE based on biomass production was strongly correlated with increased biomass accumulation rather than with reduced water use. Gas-exchange analysis indicated that low internal CO 2 concentration and enhanced photosynthetic capacity may be a factor accounting for the high TE in some lines; other physiological processes also contribute to the TE based on integrated biomass. The result suggests that considerable genetic variation in TE exists in the sorghum germplasm collection and that TE is strongly influenced by environment. The sorghum lines with contrasting TE may serve as an important genetic resource for identification of physiological mechanisms regulating TE and for improvement of this trait in sorghum breeding.

Variation in transpiration efficiency and its related traits in a groundnut ( Arachis hypogaea L.) mapping population

Transpiration efficiency (TE) has been recognized as an important source of yield variation under drought stress in groundnut. Here the variation for TE is evaluated in a set of 318 recombinant inbred lines (RILs) of groundnut at F 8 generation, derived from a cross between a high TE (ICGV 86031) and a low TE (TAG 24) parent, and the value of specific leaf area (SLA), SPAD chlorophyll meter readings (SCMR) and carbon isotope discrimination (Δ 13C) as surrogates of TE are measured. Transpiration efficiency was measured gravimetrically in the 318 RILs and parents under progressive soil drying in a pot culture in two post-rainy seasons. Large and consistent variation for TE existed among the RILs across years. The overall distribution of TE among the RILs indicated that TE was governed by dominant and additive genes. Surrogates SLA and SCMR, were measured prior, during and after completion of the drought period, whereas Δ 13C was measured on the dried tissue after harvest. Transpiration efficiency was negatively associated with SLA after the completion of stress treatment ( r 2 = 0.15) and Δ 13C in leaves ( r 2 = 0.13) and positively associated with SCMR during stress ( r 2 = 0.17). These associations, all fairly weak, were significant only in 2004. None of these relationships was found in 2005. Although the heritability of SCMR during 2005 was relatively higher than that of TE, and although SCMR has previously been used to identify contrasting germplasm for TE, the stress-dependence of the relationship with TE, and the poor regression coefficients ( r 2) with that RIL population, do not confer that these surrogates are adequately robust enough in that population. Though more time consuming, a direct gravimetric evaluation for TE appeared to be more reliable.

Differential gene expression of wheat progeny with contrasting levels of transpiration efficiency

High water use efficiency or transpiration efficiency (TE) in wheat is a desirable physiological trait for increasing grain yield under water-limited environments. The identification of genes associated with this trait would facilitate the selection for genotypes with higher TE using molecular markers. We performed an expression profiling (microarray) analysis of approximately 16,000 unique wheat ESTs to identify genes that were differentially expressed between wheat progeny lines with contrasting TE levels from a cross between Quarrion (high TE) and Genaro 81 (low TE). We also conducted a second microarray analysis to identify genes responsive to drought stress in wheat leaves. Ninety-three genes that were differentially expressed between high and low TE progeny lines were identified. One fifth of these genes were markedly responsive to drought stress. Several potential growth-related regulatory genes, which were down-regulated by drought, were expressed at a higher level in the high TE lines than the low TE lines and are potentially associated with a biomass production component of the Quarrion-derived high TE trait. Eighteen of the TE differentially expressed genes were further analysed using quantitative RT-PCR on a separate set of plant samples from those used for microarray analysis. The expression levels of 11 of the 18 genes were positively correlated with the high TE trait, measured as carbon isotope discrimination (Delta(13)C). These data indicate that some of these TE differentially expressed genes are candidates for investigating processes that underlie the high TE trait or for use as expression quantitative trait loci (eQTLs) for TE.

Effect of drought on leaf gas exchange, carbon isotope discrimination, transpiration efficiency and productivity in field grown durum wheat genotypes

Under drought prone conditions, wheat productivity is strongly related to photosynthetic activity and transpiration efficiency. In the present study, photosynthesis related traits were assessed at anthesis under rainfed and irrigated conditions on five durum wheat ( Triticum durum Desf.) cultivars grown under Mediterranean conditions. Carbon isotope discrimination was also evaluated in flag leaf at anthesis (Δ L a) and grain at maturity (Δ G m). Under rainfed conditions, highly significant correlations were found between both Δ L a and Δ G m, and leaf CO 2 exchange rate (CER), stomatal conductance ( g s) and internal to ambient CO 2 concentration ratio ( C i/ C a). Δ G m was correlated negatively with transpiration efficiency (measured as CER/ g s) under rainfed conditions, and positively under irrigated conditions. Under both conditions, Δ G m was positively associated with grain yield. No significant correlation was observed between mesophyll conductance and CER. In contrast, the latter trait was positively related to g s under irrigated conditions suggesting that CER was driven by stomatal limitations. No correlation was found between Δ L a and grain yield. It is concluded that breeding for high Δ G m would lead, under Mediterranean drought conditions, to higher stomatal conductance, lower transpiration efficiency and higher grain yield.

Relationships between Grain Yield, Flag Leaf Morphology, Carbon Isotope Discrimination and Ash Content in Irrigated Wheat

AbstractThe purpose of this study was to examine how differences in leaf angle, leaf rolling (LR) and glaucousness (GL) can modify yield components and leaf physiological traits in wheat. A set of 167 lines derived from a cross between two high‐yielding bread wheat cultivars differing for these traits was grown under flood irrigation and high evaporative demand in the north‐west of Mexico. Area, mass per unit area and chlorophyll content of the flag leaf were assessed. Carbon isotope discrimination (Δ) and ash content (ma) were also measured. A significant correlation was found between grain yield (GY) and both Δ and ma suggesting that, despite well‐watered conditions, leaf stomatal conductance was the main yield‐limiting factor. Leaf posture and LR did not significantly affect yield, Δ and ma. Higher grain weight was noted, however, in lines with droopy flag leaves. Erect leaves had higher mass per unit area. GL was associated with a significant increase in GY and grain weight. Glaucous lines also had higher Δ and ma, suggesting higher transpiration rate and lower transpiration efficiency. The study confirms that Δ and ma represent promising criteria for GY in wheat and provides evidence that GL can contribute to higher yield, even under irrigated conditions.

Stomatal and photosynthetic responses of olive (Olea europaea L.) leaves to water deficits

AbstractThe leaf gas exchange of mature olive trees (Olea europaea L.) was characterized over a wide range of water deficits in the field during 1998, in Cordoba, Spain. Leaf photosynthesis (A) and stomatal conductance (gl) responded diurnally and seasonally to variations in tree water status and evaporative demand. In the absence of water stress, A and gl were generally high during autumn and low in days of high vapour pressure deficits (VPD). Leaf A varied between 0 and 2 µmol m−2 s−1 under severe water deficits that lowered the stem water potential (Ψx) to −8·0 MPa, but recovered rapidly following rehydration. Transpiration efficiency (TE) was curvilinearly related to VPD and not influenced by water deficits except in cases of severe water stress, where low TE values were observed at Ψx below −4 MPa. Three models of leaf conductance were calibrated and validated with the experimental data; two were based on the model proposed by Leuning (L) and the other was derived from the widely used Jarvis (J) model. The L models performed better than the J model in two validation tests. The scatter of the predictions and the limited accuracy of all three models suggest that, in addition to the physiological and environmental variables considered, there are additional endogenous factors influencing the gl of olive leaves.

A Grant of Drought Avoidance and Efficient Water Use because of Dwarfing Genes Utilization.

稈(茎)長において異なる同質遺伝子系統, ソルガム2系統;Plainsman tall typeとPlainsman short type, ダイズ2系統;ヒュウガとヒュウガ矮性系統, 水稲2系統;銀坊主と短銀をポット栽培し, 正常系統と矮性系統の消費水量(CU)と乾物増加量(ΔW)および収量との関係を比較検討した.CUとΔWの間にはそれぞれ作物について直線関係が認められた.ΔW=0におけるCUは, ダイズ2系統を除いて, 蒸発量(Es)にほぼ等しかった.蒸散効率(ΔW/(CU-Es))は矮性遺伝子の有無によってほとんど影響されなかった.ΔWが大きくかつ蒸散効率(TE)の低かったヒュウガは, 供試作物中最も多量の水を消費した.またこれにはソルガム系統や水稲系統と異なり, 開花期以降ΔW=0におけるCUが蒸発量を上回る傾向を示したことも関係した.ソルガム2系統はダイズおよび水稲の2系統よりTEにおいて勝ったもののΔWが大きく, 結果的に水稲2系統と匹敵するCUを示した.これに対して矮性系統は, 供試した作物の全てで, 正常系統より常にCUが小さかった.加えて, 矮性系統は絶対収量において正常系統に劣るものの, 同一の蒸散量をより効率的に収量生産へと結びつけることが示された.このような矮性系統の特性は干害回避性と水利用の効率化という両面からも有用であろう.