Instantaneous Transpiration Efficiency Research Articles

The slope of assimilation rate against stomatal conductance should not be used as a measure of water use efficiency or stomatal control over assimilation

Quantifying water use efficiency, and the impact of stomata on CO2 uptake are pivotal in physiology and efforts to improve crop yields. Although tempting, relying on regression slopes from assimilation-stomatal conductance plots to estimate water use efficiency or stomatal control over assimilation is erroneous. Through numerical simulations, I substantiate this assertion. I propose the term ‘instantaneous transpiration efficiency’ for the assimilation-to-transpiration ratio to avoid confusion with ‘intrinsic water use efficiency’ which refers to the assimilation-to-stomatal conductance ratio, and recommend to compute both metrics for each gas exchange data point.

Effect of vapour pressure deficit on gas exchange of field-grown cotton

BackgroundPlants respond to changes in vapour pressure deficit (VPD) between the leaf and the atmosphere through changes in stomatal response, which can consequently affect transpiration, photosynthesis, and leaf-level water use efficiencies. With projected warmer air temperatures, changes in rainfall distribution and altered VPD in future climates, it is important to understand the potential effect of VPD on leaf-level physiology of field-grown crops. The aim of this study was to assess the impact of altered VPD on leaf-level physiology of field-grown cotton to improve the current understanding of the plant-by-environment interaction, thereby contributing to validation and improvement of physiological and yield response models. Different VPD environments in the field were generated by planting cotton on three dates within the sowing window (early-season (S1) = 5th October 2011; mid-season (S2) = 9th November 2011; and late-season (S3) = 30th November 2011). VPD was also modified by altering crop irrigations.ResultsVPDL accounted for the largest proportion of the explained variation in both stomatal conductance (32%∼39%) and photosynthetic (16%∼29%) responses of cotton. Generally, smaller percentages of variation were attributed to other main factors such as the individual plant (Plant), and accumulated temperature stress hours (ASH; a measure of plant water status over time) and interactive factors, including leaf vapour pressure deficit (VPDL) × Plant and Plant × ASH; however, a proportion of variation was unexplained. In addition, the Asat/E (instantaneous transpiration efficiency, ITE) model developed based on cotton grown in the glasshouse was applied to cotton grown in the field. We found that the modelled Asat/E and field-measured Asat/E were very similar, suggesting that the mechanistic basis for ITE was similar in both environments.ConclusionsThis study highlights the importance of accounting for VPD in climate change research, given that stomata are highly responsive to changes in VPD. This experiment provides a basis for physiology and production models, particularly in terms of cotton response to projected climatic environments.

An Insight Into the Effect of Organic Amendments on the Transpiration Efficiency of Wheat Plant in a Sodic Duplex Soil.

Transpiration efficiency, the shoot biomass produced per unit of transpired water, is generally considered to be a constant property for a given crop in a given environment. To determine whether deep-banded organic amendments affect the transpiration efficiency (TE) of wheat plants and to provide a possible explanation for any changes in the TE, two-column experiments were carried out under controlled environment conditions. A Sodosol soil with physically constrained subsoils and a well-structured Vertosol were subjected to treatments including a control, fertilizer nutrients alone, and fertilizer-enriched organic amendments. The addition of fertilizer-enriched organic amendments in Sodosol consistently increased the canopy TE compared to the control and inorganic fertilizer treatments. The instantaneous TE, at the leaf level, was also increased by the organic-based amendments due to greater reductions in stomatal conductance and transpiration rates during periods of moderate water-deficit stress and the subsequent recovery from this stress. Shoot nitrogen (N) status could not explain the increases in TE following the addition of organic amendments relative to inorganic amendments. The increases in canopy TE were directly associated with increases in the absolute abundance of indigenous Bacillus (R2 = 0.92, p <0), a well-known genus comprising many strains of plant beneficial rhizobacteria, in subsoil below the amendment band. In contrast, there were no differences in the canopy TE and instantaneous leaf TE between the organic and fertilizer amendments in the Vertosol with a well-structured subsoil. The positive effect of organic amendments on TE in the Sodosol should be attributed to their direct or indirect effect on improving the physical structure or biological properties of the subsoil.

Genotypic variation of the interactive effects of elevated temperature and CO2 on leaf gas exchange and early growth of sugarcane.

Increased atmospheric CO2 and consequent increases in temperature are two prominent features of climate change, a major challenge to crops. Here, our objectives were to determine: (1) the responses of sugarcane during the first 90 days of elevated CO2 (ECO2 ) and elevated temperature (ETem), both individually and together, and (2) the genotypic variation of these responses. Eight varieties were grown both in open-top chambers in a factorial combination of ambient/ECO2 concentrations (344-351/777-779 ppm) and ambient/ETem (34.9-35.6/36.6-38.4°C) and in open fields. Significant treatment × variety interaction effects were observed on leaf net photosynthetic rate (An ), stomatal conductance (gs ), transpiration rate (El ), and instantaneous transpiration efficiency (TE ). In most varieties, ECO2 alone did not affect An, but the combination of ECO2 and ETem decreased An . ECO2 decreased gs and El while increasing TE in all varieties. These effects were amplified when ETem was combined with ECO2 . ETem alone had variable effects on An and gs depending on variety, while it increased El and did not affect TE in a majority of varieties. Germination, tillering and stem diameter were not affected by treatments and did not show varietal variation. Leaf water potential, chlorophyll (spad), leaf area, and aboveground dry weight per plant showed varietal variations but were not affected by treatments. The variable responses to ETem and the significant genotypic variation to ECO2 and elevated temperature (ETem) observed in this work, both individually and together, demonstrate a considerable scope to breed sugarcane varieties for a future high-CO2 and warmer climate.

Characterizing the Efficacy of a Film-Forming Antitranspirant on Raspberry Foliar and Fruit Transpiration.

The film-forming antitranspirant, di-1-p-menthene, is able to reduce transpiration in a number of crops, potentially resulting in water savings and improved productivity. The success of the response is, however, dependent on genotype and environmental factors. We aimed to assess the efficacy of this natural terpene polymer on red raspberry (Rubus idaeus, L.) cv. Tulameen leaf water-use efficiency across a 25–40 °C temperature range under controlled conditions. The film reduced transpiration (E) and was most effective when applied to the lower leaf surface. Leaf net assimilation (A) and stomatal conductance (g) were also curtailed after the application of di-1-p-menthene, and as a consequence intrinsic transpiration efficiency (A/g) and instantaneous transpiration efficiency (ratio of net carbon fixation to water loss, A/E) did not improve. At 40 °C, gas exchange of both treated and untreated leaves was minimal due to stomatal closure. The antitranspirant was effective at reducing water loss from berries, but only at the immature stages when transpiration rates were naturally high. Further studies are required to determine if the antitranspirant, di-1-p-menthene, will offer protection against dehydration across a range of temperatures and if productivity and berry composition will benefit.

Elevated Atmospheric CO2 Increases Root Exudation of Carbon in Wetlands: Results from the First Free-Air CO2 Enrichment Facility (FACE) in a Marshland

Experiments employing free-air CO2 enrichment (FACE) facilities have indicated that elevated atmospheric carbon dioxide (eCO2) stimulates growth in diverse terrestrial ecosystems. Studies of the effects of eCO2 on wetland plants have indicated a similar response, but these studies were mostly performed in growth chambers. We conducted a 2-year FACE experiment [CO2 ≈ 582 µmol mol−1] in a marsh in Spain to test whether the common reed (Phragmites australis) responds to carbon enrichment, as previously reported in other macrophytes. More specifically, we tested the effect of eCO2 on P. australis growth, photosynthesis, transpiration, and biomass, its effect on modifying plant and soil ratios of carbon, nitrogen, and phosphorus, and whether the strong environmental variability of this wetland modulates these responses. Our findings show that effects of eCO2 in this wetland environment are more complex than previously believed, probably due to hydrological effects. The effects of eCO2 on reed plants were cumulative and manifested at the end of the growing season as increased 38–44% instantaneous transpiration efficiency (ratio of net photosynthesis to transpiration), which was dependent on plant age. However, this increase did not result in a significant increase in biomass, because of excessive root exudation of carbon. These observations contrast with previous observations of wetland plants to increased atmospheric CO2 in growth chambers and shed new light on the role of wetland plants as a carbon sink in the face of global climate change. The combined effects of water stress, eCO2, and soil carbon processes must be considered when assessing the function of wetlands as a carbon sink under global change scenarios.

Plant physiological changes along an encroachment gradient: an assessment of US Mid-Atlantic serpentine barrens

Serpentine barrens of the Mid-Atlantic United States are globally rare, grass-dominated ecosystems thought to exclude C₃ species and characterized by unique soil composition. However, like many grassland ecosystems globally, these sites are presently facing encroachment by surrounding forest. In this ecosystem, the tendril climbing vine, Smilax rotundifolia, forms dense thickets around barrens that typically precede forest encroachment. While numerous factors speculatively initiate and promote encroachment in these systems, few studies have examined photosynthetic responses of serpentine grasses to changes in resource availability initiated by encroachers or physiological ability of encroaching S. rotundifolia to colonize high-light barren environments. We sought to understand both environmental and physiological dynamics of encroachment along an irradiance gradient in these systems. At three serpentine barren sites in southeastern Pennsylvania, physiological responses of the native grasses Sorghastrum nutans and Schizachyrium scoparium to increased shading by S. rotundifolia were examined. Additionally, the physiological performance of S. rotundifolia in the forest understory was compared to that in sunlit barrens environments. Light-saturated photosynthesis (Aₛₐₜ), stomatal conductance (gₛ), instantaneous transpiration efficiency (ITE), maximum efficiency of photosystem II (Fᵥ/Fₘ), midday leaf water potential (ψₗₑₐf) and specific leaf area (SLA) were measured for all species over the course of the 2014 growing season. Two-way analyses of variance were used to assess changes in these parameters across growing environments, as well as seasonally for each species. Multiple regression analyses were also performed to investigate the influence of vapor pressure deficit (D) and leaf temperature (Tₗₑₐf) on Aₛₐₜ and ITE. Light-saturated photosynthesis was significantly greater in S. rotundifolia growing in sun than in the shade (P < 0.001) and early in the season (P = 0.012). Sun S. rotundifolia had up to 27% greater Aₛₐₜ than shaded plants. Even with reduced ψₗₑₐf in the barrens, S. rotundifolia maintained high gₛ though Aₛₐₜ was limited by high D later in the growing season. These data are in agreement with recent research suggesting that plants are not subject to water limitation in Mid-Atlantic barrens. Unexpectedly, shaded grasses at the encroachment interface did not exhibit any significant reduction in Aₛₐₜ. Declines in grass photosynthesis do not likely occur until S. rotundifolia rhizomes transition into monotypic thickets, completely excluding grasses. Encroachment by S. rotundifolia appears to be primarily facilitated by its ability to capitalize on light resources early on in the summer growing season, when environmental conditions are less stressful.

Responses of transpiration and transpiration efficiency of almond trees to moderate water deficits

The majority of world almond acreage is grown under rainfed conditions but most of the production is obtained under irrigation. Increased water scarcity is reducing water availability for irrigation thus the need to characterize the responses of almond to water deficits. Several works have defined well the stomatal closure in almond leaves under water deficits, but the behavior at the canopy level is not well understood. A field experiment was conducted in an almond (cv. Guara) orchard in Córdoba (Spain) under four different levels of irrigation supply to investigate the responses of almond tree transpiration (T) and transpiration efficiency (TE) to water stress. Stem water potential (Ψx), whole tree transpiration (T) and leaf gas-exchange were periodically measured throughout the 2013 growing season. Tree T decreased linearly as midday Ψx decreased below a threshold value of about −1.1MPa, and declined to about 50% of the Control value when midday Ψx reached −1.6MPa. The quick decline in T in response to the lowering of ψx suggests a high sensitivity of almond T to water deficits. The instantaneous transpiration efficiency (TE) of almond leaves was unaffected by water and varied essentially with vapor pressure deficits. On a daily scale, the leaf TE of stressed trees followed the same pattern as in the non-stressed trees. Then, contrary to the behavior observed in olive and citrus, there were no instantaneous or daily TE increments in almond trees in response to water deficits.

Elevated CO2 concentrations alleviate the inhibitory effect of drought on physiology and growth of cassava plants

Due to the rise in anthropogenic greenhouse gas concentrations, the earth's climate is expected to change, with precipitation being reduced in some areas resulting in growth-limiting drought and, as a consequence, reduced plant productivity. We investigated the physiological and growth responses of cassava (Manihot esculenta Crantz) to approximate present-day ambient (390μLL−1) and elevated (750μLL−1) atmospheric CO2 concentrations under well-watered and water deficit conditions, aiming at understanding how cassava would face those problems. Water deficits led to reductions in the Leaf Elongation Rate of plants grown at ambient as well as CO2-enriched concentrations. However, plants grown at 750μLL−1 of CO2 maintained leaf growth two days longer than plants grown at 390μLL−1. Three Days After Withholding Water (DAWW), photosynthesis and stomatal conductance were reduced in plants grown under ambient CO2, while in plants under an elevated CO2 concentration, these physiological functions remained similar to that of control plants grown under good water availability. Five DAWW plants grown with 750μLL−1 continued to have enhanced gas exchange compared with plants grown under 390μLL−1. Under drought stress, the instantaneous transpiration efficiency was always greatest for plants grown under elevated CO2. The positive response of elevated CO2 levels on total dry mass was 61% in the water-stressed plants and only 20% for the plants grown under good water availability. Stomatal limitation was an important factor reducing CO2 assimilation in cassava growing under drought conditions.

Elevated CO&lt;sub&gt;2&lt;/sub&gt; increased photosynthesis and yield without decreasing stomatal conductance in broomcorn millet

Broomcorn millet (Panicum miliaceum L.) is one of the important C4 crops in the semiarid regions of northern China. It is a close relative of biofuel crop switchgrass. Yet, there is no information on how these crops might respond to a climate change in China. In order to gain insight into such a response, we studied the effect of elevated CO2 concentration (EC) on broomcorn millet. The changes in leaf photosynthesis, chlorophyll fluorescence, morphological parameters, biomass and yield in response to EC [i.e., + 200 µmol(CO2) mol−1] over two years were determined at the open-top chamber (OTC) experimental facility in north China. EC increased net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, instantaneous transpiration efficiency, effective quantum yield of PSII photochemistry, and photochemical quenching coefficient of fully expanded flag leaves. Maximal quantum yield of PSII photochemistry declined under EC in 2013, but was not affected in 2014. EC significantly decreased intrinsic efficiency of PSII in 2013, but increased in 2014. Leaf nonphotochemical quenching decreased under EC both in 2013 and 2014. EC significantly enhanced the aboveground biomass and yield by average of 31.4 and 25.5% in both years, respectively. The increased yield of broomcorn millet under EC occurred due to the enhanced number of grains per plant. We concluded that photosynthesis of broomcorn millets was improved through increased stomatal conductance in leaves under EC, which led to an increase in height, stem diameter, aboveground biomass, and yield. This study extends our understanding of the response of this ancient C4 crop to elevated CO2 concentration.

Photosynthesis of Chinese cabbage and radish in response to rising leaf temperature during spring

Photosynthesis in leaves, exposed to temperature change, was measured during spring to provide information for modeling of cropping systems for Chinese cabbage (Brassica campestris subsp. napus var. pekinensis) and radish (Raphanus sativus) in Jeju Island. The net photosynthetic rates (A) of Chinese cabbage and radish were depressed at temperatures above approximately 25°C (corresponding to the optimum temperature for photosynthesis), due in part to high rates of respiration above 25 or 30°C. Chinese cabbage was more sensitive to high temperature than radish. Above 25°C, stomatal conductance (g s) declined steeply with a sharp increase in the vapor pressure deficit (VPD) and transpiration rate (E), suggesting that stomatal closure could not be associated with transpiration rate, particularly in Chinese cabbage. Dramatic declines in water use efficiency (WUE), instantaneous transpiration efficiency (ITE), and carboxylation efficiency (CE) above 30°C indicated that the plants could be severely affected negatively by high temperatures above 30°C. However, compared to Chinese cabbage, radish had high light use efficiency and potential to assimilate CO2, judged by their high quantum yield (φ) and maximum photosynthetic rate (A max). Radish utilized high levels of photosynthetic photon flux and strongly acclimated to the light environment, considering their high light saturation point (Q sat) and low light compensation point (Q comp). These results suggested that rising temperature might substantially alter water availability of plants by itself and/or through effects on the rate of water loss from leaves of Chinese cabbage and radish under diurnal and/or seasonal fluctuations of temperature, and/or global temperature change. To maintain the high productivity and quality of these crop species, it may be necessary to harvest them until early June, when the daily maximum temperature is below 25°C in Jeju Island.

Near-optimal response of instantaneous transpiration efficiency to vapour pressure deficit, temperature and [CO2] in cotton (Gossypium hirsutum L.)

The instantaneous transpiration efficiency (ITE, the ratio of photosynthesis rate to transpiration) is an important variable for crops, because it ultimately affects dry mass production per unit of plant water lost to the atmosphere. The theory that stomata optimize carbon uptake per unit water used predicts that ITE should be proportional to the atmospheric [CO2] (Ca), approximately inversely proportional to the square root of the leaf-to-air vapour pressure deficit (Ds), and weakly dependent on leaf temperature (Tleaf). We measured the response of ITE to a range in Ds at constant air temperature (Tair), for two cultivars (DP16 and Sicot 71BRF) of cotton (Gossypium hirsutum L.) grown in two Ca (400 and 640μll−1) and two Tair (28 and 32°C) treatments. To interpret responses of ITE to these variables, we used a model based on the assumption that stomata are regulated to optimize carbon uptake per unit water used. The measured ITE response to Ds was very close to that predicted by the model, but ITE was overpredicted at low Ds. We found that one model adequately fit all Tair and Ca treatments, and found no significant differences in the single parameter of the model with Ca, Tair, or cultivar. As predicted, ITE increased in proportion to Ca (a 51–64% increase in ITE compared to a 60% increase in Ca). Photosynthesis rate was 16–22% higher in the elevated Tair treatment, which led to a corresponding increase in transpiration rate at a given Ds, again as predicted. The results show that, in cotton, a straightforward framework based on optimal stomatal theory successfully predicted responses of ITE to Ds, Tair, and Ca. These findings greatly simplify modelling of an important component of crop water-use efficiency in response to climate change.

Effects of elevated atmospheric [CO2] on instantaneous transpiration efficiency at leaf and canopy scales in Eucalyptus saligna

AbstractRising atmospheric concentrations of CO2 (Ca) can reduce stomatal conductance and transpiration rate in trees, but the magnitude of this effect varies considerably among experiments. The theory of optimal stomatal behaviour predicts that the ratio of photosynthesis to transpiration (instantaneous transpiration efficiency, ITE) should increase in proportion to Ca. We hypothesized that plants regulate stomatal conductance optimally in response to rising Ca. We tested this hypothesis with data from young Eucalyptus saligna Sm. trees grown in 12 climate‐controlled whole‐tree chambers for 2 years at ambient and elevated Ca. Elevated Ca was ambient + 240 ppm, 60% higher than ambient Ca. Leaf‐scale gas exchange was measured throughout the second year of the study and leaf‐scale ITE increased by 60% under elevated Ca, as predicted. Values of leaf‐scale ITE depended strongly on vapour pressure deficit (D) in both CO2 treatments. Whole‐canopy CO2 and H2O fluxes were also monitored continuously for each chamber throughout the second year. There were small differences in D between Ca treatments, which had important effects on values of canopy‐scale ITE. However, when Ca treatments were compared at the same D, canopy‐scale ITE was consistently increased by 60%, again as predicted. Importantly, leaf and canopy‐scale ITE were not significantly different, indicating that ITE was not scale‐dependent. Observed changes in transpiration rate could be explained on the basis that ITE increased in proportion to Ca. The effect of elevated Ca on photosynthesis increased with rising D. At high D, Ca had a large effect on photosynthesis and a small effect on transpiration rate. At low D, in contrast, there was a small effect of Ca on photosynthesis, but a much larger effect on transpiration rate. If shown to be a general response, the proportionality of ITE with Ca will allow us to predict the effects of Ca on transpiration rate.

Varietal Variation in Stomatal Conductance, Transpiration and Photosynthesis of Commercial Sugarcane Varieties Under Two Contrasting Water Regimes

The study was conducted to evaluate some physiological characters of commercial sugarcane varieties under different growing conditions in Sri Lanka. A field experiment was conducted at the Sugarcane Research Institute, Uda Walawe (6°21'N latitude, 80°48'E longitude and 76 m altitude) using eight sugarcane ( Saccharum hybrid L.) varieties grown under irrigated and rainfed conditions in a split plot de-sign. Stomatal conductance ( g s ), instantaneous transpiration rate ( E 1 ) and photosynthetic rate per unit leaf area ( P n ) were measured. Canopy stomatal conductance ( g c ), instantaneous canopy transpiration rate ( E c ) and transpiration efficiency ( P n / E 1 ) was calculated. The behaviour of g s in many respects to the moisture availability and growing stage was similar to the responses seen in P n . Water deficit significantly reduced g s , E 1 and P n . Recovery of g s and P n from water stress with rainfall was quite rapid under rainfed conditions. The varieties Co775, SL8306, SL7103 and SL88116 which had higher P n and P n / E 1 , and lower g s , E 1 , g c and E c showed comparatively superior physiological performances under rainfed conditions. Water conservation through lowering stomatal conductance, both at the individual leaf and canopy level, and higher photosynthetic rate were identified as some physiological mechanisms responsible for drought tolerance of sugarcane. Key words: Sugarcane; Stomatal conductance; Transpiration; Photosynthesis; Water regimes DOI: 10.4038/tare.v12i2.2798 Tropical Agricultural Research & Extension 12(2): 2009 pp.97-102

Assessing the genetic relatedness of higher ozone sensitivity of modern wheat to its wild and cultivated progenitors/relatives

Modern wheat (Triticum aestivum L.) is one of the most ozone (O(3))-sensitive crops. However, little is known about its genetic background of O(3) sensitivity, which is fundamental for breeding O(3)-resistant cultivars. Wild and cultivated species of winter wheat including donors of the A, B and D genomes of T. aestivum were exposed to 100 ppb O(3) or charcoal-filtered air in open top chambers for 21 d. Responses to O(3) were assessed by visible O(3) injury, gas exchange, chlorophyll fluorescence, relative growth rate, and biomass accumulation. Ozone significantly decreased light-saturated net photosynthetic rate (-37%) and instantaneous transpiration efficiency (-42%), but increased stomatal conductance (+11%) and intercellular CO(2) concentration (+11%). Elevated O(3) depressed ground fluorescence (-8%), maximum fluorescence (-26%), variable fluorescence (-31%), and maximum photochemical efficiency (-7%). Ozone also decreased relative growth rate and the allometric coefficient, which finally reduced total biomass accumulation (-54%), but to a greater extent in roots (-77%) than in the shoot (-44%). Winter wheat exhibited significant interspecies variation in the impacts of elevated O(3) on photosynthesis and growth. Primitive cultivated wheat demonstrated the highest relative O(3) tolerance followed by modern wheat and wild wheat showed the lowest. Among the genome donors of modern wheat, Aegilops tauschii (DD) behaved as the most O(3)-sensitive followed by T. monococcum (AA) and Triticum turgidum ssp. durum (AABB) appeared to be the most O(3)-tolerant. It was concluded that the higher O(3) sensitivity of modern wheat was attributed to the increased O(3) sensitivity of Aegilops tauschii (DD), but not to Triticum turgidum ssp. durum (AABB) during speciation.

Stomatal density and gas exchange in six wheat cultivars

Stomatal density (SD) and stomatal index (SI) on the abaxial flag leaf epidermis, gas exchange of flag leaves and yield of six wheat ( Triticum aestivum L.) cultivars differing in drought resistance were studied in plant growth chamber. There were significant differences among cultivars in SD, SI, epidermal cell density (ED), photosynthetic rate (P n ), transpiration rate (E), instantaneous transpiration efficiency (ITE), shoot dry weight yield (Ys), grain yield (Yd) and whole growth season water use efficiency (WUE), but not in stomatal conductance (g s ). Wheat cultivars with moderate drought resistance had higher P n and Yd than cultivars with strong or weak drought resistance. SD was negatively correlated with ITE (r=−0.85) and WUE (r=−0.84), but not with P n , E and Yd. There were significant relationships between ED and Yd (r=−0.92), between SI and P n (r=0.84). These results revealed that breeding wheat cultivar only to raise drought resistance might cause yield decrease when water stress was not t...

The Effect of Elevated Atmospheric CO2 Concentration on Two Populus Clones Grown in a FACE System

SUMMARY Two poplar clones, hybrid Populus deltoides Bartr. Ex Marsh X Populus nigra L. (Populus xeuramericana), clone I-214, and Populus deltoides, clone Lux, were grown from hardwood cuttings for one growing season in either ambient (360 μmol mol−1) or elevated (560 μmol mol−1) [CO2] in FACE-systemrings at Rapolano Terme (Siena, Italy). Both clones I-214 and Lux exhibited a higher aboveground bio-mass, photosynthesis at light saturation and instantaneous transpiration efficiency (ITE) in CO2-enriched air. The elevated [CO2]-induced responses of clone I-214 included increased investment in branch and leaf biomass, and enhanced stem volume. The elevated [CO2]-induced responses of clone Lux included an increase in the number of branches (and foliage area). Indication of photosynthetic acclimation under elevated [CO2] was found during the early morning, but only in clone I-214. Stomatal conductance decreased under elevated [CO2] particularly in clone Lux. Clone differences in response to elevated [CO2] should be taken in account when planning future poplar plantations in forecast warmer and drier Mediterranean sites.

Photosynthesis and Water Use Efficiency in Twenty Tropical Tree Species of Differing Succession Status in a Brazilian Reforestation

Leaf gas exchange characteristics were measured in twenty woody species that differ in succession status ranging from pioneer species (PS) to late succession species (LS) in a Brazilian rain-reforestation ecosystem. Photon-saturated photosynthetic rate, calculated per either a leaf area (PNA) or a dry mass (PNM) basis, differed among species. PNA and PNM were highest in PS and lowest in LS. Variation among species was 3-fold (from 7 to 23 μmol m-2 s-1) for PNA, and 5-fold (from 50 to 275 μmol kg-2 s-1) for PNM. The highest PNA (23 μmol m-2 s-1) and PNM (275 μmol kg-2 s-1) values were recorded in PS Croton urucurana, while the lowest PNA (7 μmol m-2 s-1) and PNM (50 μmol kg-2 s-1) values were recorded in LS Aspidosperma cylindrocarpon. A considerable overlap was recorded between PS and LS in values of stomatal conductance (gs), transpiration rate (E), and leaf mass to area ratio (ALM). However, C. urucurana also showed highest gs and E. PNM was highly correlated with ALM in both PS and LS (r=-0.75 and -0.90, respectively). The high values of instantaneous transpiration efficiency (ITE) and intrinsic water use efficiency (WUEi) were also observed in the PS when compared with the LS.

Stomatal responses of Douglas‐fir seedlings to elevated carbon dioxide and temperature during the third and fourth years of exposure

AbstractTwo major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2] and temperature on seasonal patterns of stomatal conductance (gs), transpiration (E) and instantaneous transpiration efficiency (ITE) in Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers at either ambient CO2 (AC) or ambient + 180 µmol mol−1 CO2 (EC), and at ambient temperature (AT) or ambient + 3·5 °C (ET) in a full‐factorial design. Needle gas exchange at the target growth conditions was measured approximately monthly over 21 months. Across the study period and across temperature treatments, growth in elevated [CO2] decreased E by an average of 12% and increased ITE by an average of 46%. The absolute reduction of E associated with elevated [CO2] significantly increased with seasonal increases in the needle‐to‐air vapour pressure deficit (D). Across CO2 treatments, growth in elevated temperature increased E an average of 37%, and did not affect ITE. Combined, growth in elevated [CO2] and elevated temperature increased E an average of 19% compared with the ACAT treatment. The CO2 supply and growth temperature did not significantly affect stomatal sensitivity to D or the relationship between gs and net photosynthetic rates. This study suggests that elevated [CO2] may not completely ameliorate the effect of elevated temperature on E, and that climate change may substantially alter needle‐level water loss and water use efficiency of Douglas‐fir seedlings.

The Photosynthetic Response to Elevated CO&lt;sub&gt;2&lt;/sub&gt; in High Altitude Potato Species (Solanum curtilobum)

Plants of Solanum curtilobum (from high altitude) and Solanum tuberosum (from low altitude) were grown in open-top chambers in a greenhouse at either ambient (AC, 360 µmol mol-1) or ca. twice ambient (EC, 720 µmol mol-1) CO2 concentrations for 30 d. CO2 treatments started at the reproductive stage of the plants. There were similar patterns in the physiological response to CO2 enrichment in the two species. Stomatal conductance was reduced by 59 % in S. tuberosum and by 55 % in S. curtilobum, but such a reduction did not limit the net photosynthetic rate (PN), which was increased by approximately 56 % in S. curtilobum and 53 % in S. tuberosum. The transpiration rate was reduced by 16 % in both potato species while instantaneous transpiration efficiency increased by 80 % in S. tuberosum and 90 % in S. curtilobum. Plants grown under EC showed 36 and 66 % increment in total dry biomass, whereas yields (dry mass of tubers) were increased by 40 and 85 % in S. tuberosum and S. curtilobum, respectively. EC promoted productivity by increasing PN. Thus S. tuberosum, cultivated around the world at low altitudes, and S. curtilobum, endemic of the highland Andes, respond positively to EC during the tuberisation stage.