Plant Stomatal Conductance Research Articles

Photosynthetic gas-exchange and PSII photochemical acclimation to drought in a native and non-native xerophytic species (Artemisia ordosica and Salix psammophila)

The mechanisms of plant photosynthetic acclimation to drought remains incomplete. We examined the photosynthetic performance through plant photosystem-fluorescence response to a long-lasting, anomalous summer drought (i.e., lasting for 61 days, with soil water content <0.1 m3·m−3) and subsequent post-drought recovery of a native and a non-native desert shrub species (Artemisia ordosica and Salix psammophila, respectively) growing in northwest China. Key indicators to the examination are derived estimates of plant stomatal conductance (gs), transpiration (Tr), water use efficiency (WUE), maximum and actual photochemical efficiency (Fv/Fm and ФPSII), non-photochemical quenching (NPQ), and leaf photosynthesis (PN) from simultaneous, continuous in situ measurements of gas exchange and chlorophyll fluorescence. Chlorophyll fluorescence-associated indicator “Fv/Fm” for both species was down regulated in response to deficits in soil water content (SWC), with differential SWC thresholds of 0.07 and 0.08 m3 m−3 for A. ordosica and S. psammophila, respectively. The results revealed that both species acclimate to summer drought by a stomatal-regulation mechanism of reducing gs and WUE and by a PSII NPQ mechanism of dissipating the excessive light energy, indicative of a water-conservation strategy in the acclimation to drought. In comparison with the non-native species, the native species generally had greater photosynthetic performance under water-deficit conditions demonstrating higher transpiration, net CO2 assimilation, and greater PSII photochemical efficiency. Lower WUE and greater drought resistance and resilience, combined with minor changes in PSII photochemical efficiency are consistent with a well-defined water-conservation response by A. ordosica. The results support the hypothesis that native desert-shrub species can potentially outperform non-native shrub species, due to stronger resistance and faster overall recovery from long-lasting drought. Therefore, with increased drought severity and duration anticipated with future climate change, the native shrub species is suggested to be used in desertification control and ecological restoration for sustainable ecosystem management.

Increasing stomatal conductance in response to rising atmospheric CO2.

Background and Aims Studies have indicated that plant stomatal conductance (g(s)) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. ...

Increasing stomatal conductance in response to rising atmospheric CO2.

Studies have indicated that plant stomatal conductance (gs) decreases in response to elevated atmospheric CO2, a phenomenon of significance for the global hydrological cycle. However, gs increases across certain CO2 ranges have been predicted by optimization models. The aim of this work was to demonstrate that under certain environmental conditions, gs can increase in response to elevated CO2. Using (1) an extensive, up-to-date synthesis of gs responses in free air CO2 enrichment (FACE)experiments, (2) in situ measurements across four biomes showing dynamic gs responses to a CO2 rise of ~50 ppm (characterizing the change in this greenhouse gas over the past three decades) and (3) a photosynthesis-stomatal conductance model, it is demonstrated that gs can in some cases increase in response to increasing atmospheric CO2. Field observations are corroborated by an extensive synthesis of gs responses in FACE experiments showing that 11.8 % of gs responses under experimentally elevated CO2 are positive. They are further supported by a strong data-model fit (r2 = 0.607) using a stomatal optimization model applied to the field gs dataset. A parameter space identified in the Farquhar-Ball-Berry photosynthesis-stomatal conductance model confirms field observations of increasing gs under elevated CO2 in hot dry conditions. Contrary to the general assumption, positive gs responses to elevated CO2, although relatively rare, are a feature of woody taxa adapted to warm, low-humidity conditions, and this response is also demonstrated in global simulations using the Community Land Model (CLM4). The results contradict the over-simplistic notion that global vegetation always responds with decreasing gs to elevated CO2, a finding that has important implications for predicting future vegetation feedbacks on the hydrological cycle at the regional level.

Green roof Petunia, Ageratum, and Mentha responses to water stress, seaweeds, and trinexapac-ethyl treatments

The availability of sufficient irrigation water and the development of drought-tolerant species are challenging factors in the design and maintenance of green roofs in modern cities. Green roof plants of Petunia hybrid Headliner® Red Star, Ageratum hybrid Artist® blue, and Mentha spicata L. grown in a simulated green roof pot system under controlled greenhouse conditions. The plants were watered every 2 or 6 days (2DWI/6DWI) for 8 weeks accompanied by either a 6-day treatment of seaweed extracts of Ascophyllum nodosum as a soil drench or foliar spray, or two concentrations of trinexapac-ethyl (TE) biweekly sprays. Following treatments, leaf number, leaf area, dry weights, plant height, stomatal conductanse, photosynthetic and transpiration rates and leaf water potential and relative water content were determined in two seasons during 2016 and 2017. The prolonged irrigation intervals reduced plant growth as revealed by morphological and physiological parameters. The application of SWE as drench treatment improved Petunia and Ageratum plant vegetative growth, stomatal conductance, photosynthetic and transpiration rates and leaf water potential and relative water content during prolonged irrigation intervals. TE increased the vegetative growth as well as the physiological performance of Ageratum plants. However, neither SWE nor TE treatments improved the performance of Mentha plants under prolonged irrigation intervals. It was suggested that improved photosynthetic rates were stimulated by enhanced stomatal conductance leading to improved leaf water potential as well as increased relative water content during prolonged irrigation conditions.

How do leaf and ecosystem measures of water-use efficiency compare?

The terrestrial carbon and water cycles are intimately linked: the carbon cycle is driven by photosynthesis, while the water balance is dominated by transpiration, and both fluxes are controlled by plant stomatal conductance. The ratio between these fluxes, the plant water-use efficiency (WUE), is a useful indicator of vegetation function. WUE can be estimated using several techniques, including leaf gas exchange, stable isotope discrimination, and eddy covariance. Here we compare global compilations of data for each of these three techniques. We show that patterns of variation in WUE across plant functional types (PFTs) are not consistent among the three datasets. Key discrepancies include the following: leaf-scale data indicate differences between needleleaf and broadleaf forests, but ecosystem-scale data do not; leaf-scale data indicate differences between C3 and C4 species, whereas at ecosystem scale there is a difference between C3 and C4 crops but not grasslands; and isotope-based estimates of WUE are higher than estimates based on gas exchange for most PFTs. Our study quantifies the uncertainty associated with different methods of measuring WUE, indicates potential for bias when using WUE measures to parameterize or validate models, and indicates key research directions needed to reconcile alternative measures of WUE.

Seedling Regeneration in the Alpine Treeline Ecotone: Comparison of Wood Microsites and Adjacent Soil Substrates

Although climate warming is generally expected to facilitate upward advance of forests, conifer seedling regeneration and survival may be hindered by low substrate moisture, high radiation, and both low and high snow accumulation. To better understand substrate-related factors promoting regeneration in the alpine treeline ecotone, this study compared 2 substrates supporting conifer seedlings: rotten downed wood and adjacent soil. Study locations, each with 3 levels of incoming radiation, were randomly selected at forest line–alpine meadow borders in Pacific Northwest wilderness areas extending along an east–west precipitation gradient. Associations among substrate type, seedling density, radiation, site moisture, site temperature, plant water potential, and plant stomatal conductance were assessed. Wood microsites, flush with the ground and supporting Abies spp conifer seedlings, extended up to 20 m into alpine meadows from the forest line. Although wood microsites thawed later in the spring and froze earlier in the fall, they had warmer summer temperatures, greater volumetric water content, and more growing degree hours, and seedlings growing on wood had higher water potentials than seedlings growing on adjacent soil. At drier eastern sites, there was a positive relationship between seedling density and volumetric water content. Further, there was a positive relationship between seedling stomatal conductance and volumetric water content. Our study indicates that in the Pacific Northwest. and likely elsewhere, seedlings benefit from wood microsites, which provide greater water content. Given predictions of increased summer drought in some locations globally, wood microsites at forest line–alpine meadows and forest line–grasslands borders may become increasingly important for successful conifer regeneration.

Anticipated impacts of climate change on 21st century Maumee River discharge and nutrient loads

Abstract Climate change holds great potential to affect the Lake Erie ecosystem by altering the timing and magnitude of precipitation driven river discharge and nutrient runoff in its highly agricultural watershed. Using the SWAT hydrologic model and an ensemble of global climate models, we predicted Maumee River (Ohio) discharge during the 21st century under two Intergovernmental Panel on Climate Change (IPCC) greenhouse gas emissions scenarios: RCP4.5 (mid-range, moderate reductions) and RCP8.5 (high, “business as usual”). Annual discharge was projected to increase under both scenarios, both in the near-century (RCP4.5 = 6.5%; RCP8.5 = 2.0%) and late-century (RCP4.5 = 9.2%; RCP8.5 = 15.9%), owing to increased precipitation and reduced plant stomatal conductance. Holding fertilizer application rates at baseline levels, we found that reduced winter surface runoff and increased plant phosphorus (P) uptake led to a respective decrease in annual total P (TP) runoff in the near-century (RCP4.5 = − 4.3%; RCP8.5 = − 6.6%) and by the late-century (RCP4.5 = − 14.6%; RCP8.5 = − 7.8%). Likewise, soluble reactive P (SRP) runoff was predicted to decrease under both scenarios in the near-century (RCP4.5 = − 0.5%; RCP8.5 = − 3.5%) and by the late-century (RCP4.5 = − 11.8%; RCP8.5 = − 8.6%). By contrast, when fertilizer application was modeled to increase at the same rate as plant P uptake, TP loading increased 4.0% (0.9%) in the near-century and 9.9% (24.6%) by the late-century and SRP loading increased 10.5% (6.1%) in the near-century and 26.7% (42.0%) by the late-century under RCP4.5 (RCP8.5). Our findings suggest that changes in agricultural practices (e.g., fertilization rates) will be key determinants of Maumee River discharge during the 21st century.

Parâmetros biométricos e fisiológicos de Heliconia bihai cultivada em região litorânea sob diferentes níveis de radiação solar

The aim of this work was evaluate the effect of different levels of light intensity on the physiology, vegetative and reproductive development of Heliconia bihai cv. Lobster Claw Two grown under coastal zone of Ceara State. Plants of this species were grown under full and 30%, 40% and 50% reduction sunlight intensity. It was evaluated the number of leaves and tillers per plant; amount of stalks; leaf area, water and carbohydrate content in the leaf next to the inflorescence arising and next to the inflorescence at harvest stage. Photosynthesis, transpiration and stomatal conductance of plants were measured for six consecutive months. Significant difference were attained for leaf area and water content in leaves close to the inflorescence at harvest stage, with lower values, and carbohydrate contents in leaves, with higher values in plants grown in full sun. The treatments with lower levels of solar radiation had higher amounts of stalks and higher vegetative growth, the reduction in vegetative growth of the plants under full sun was due to the lower photosynthetic rate and lower translocation of assimilates.

Salt tolerance of Beta macrocarpa is associated with efficient osmotic adjustment and increased apoplastic water content.

The chenopod Beta macrocarpa Guss (wild Swiss chard) is known for its salt tolerance, but the mechanisms involved are still debated. In order to elucidate the processes involved, we grew wild Swiss chard exposed to three salinity levels (0, 100 and 200mm NaCl) for 45days, and determined several physiological parameters at the end of this time. All plants survived despite reductions in growth, photosynthesis and stomatal conductance in plants exposed to salinity (100 and 200mm NaCl). As expected, the negative effects of salinity were more pronounced at 200mm than at 100mm NaCl: (i) leaf apoplastic water content was maintained or increased despite a significant reduction in leaf water potential, revealing the halophytic character of B.macrocarpa; (ii) osmotic adjustment occurred, which presumably enhanced the driving force for water extraction from soil, and avoided toxic build up of Na(+) and Cl(-) in the mesophyll apoplast of leaves. Osmotic adjustment mainly occurred through accumulation of inorganic ions and to a lesser extent soluble sugars; proline was not implicated in osmotic adjustment. Overall, two important mechanisms of salt tolerance in B.macrocarpa were identified: osmotic and apoplastic water adjustment.

Carbon dioxide level and form of soil nitrogen regulate assimilation of atmospheric ammonia in young trees.

The influence of carbon dioxide (CO2) and soil fertility on the physiological performance of plants has been extensively studied, but their combined effect is notoriously difficult to predict. Using Coffea arabica as a model tree species, we observed an additive effect on growth, by which aboveground productivity was highest under elevated CO2 and ammonium fertilization, while nitrate fertilization favored greater belowground biomass allocation regardless of CO2 concentration. A pulse of labelled gases (13CO2 and 15NH3) was administered to these trees as a means to determine the legacy effect of CO2 level and soil nitrogen form on foliar gas uptake and translocation. Surprisingly, trees with the largest aboveground biomass assimilated significantly less NH3 than the smaller trees. This was partly explained by declines in stomatal conductance in plants grown under elevated CO2. However, unlike the 13CO2 pulse, assimilation and transport of the 15NH3 pulse to shoots and roots varied as a function of interactions between stomatal conductance and direct plant response to the form of soil nitrogen, observed as differences in tissue nitrogen content and biomass allocation. Nitrogen form is therefore an intrinsic component of physiological responses to atmospheric change, including assimilation of gaseous nitrogen as influenced by plant growth history.

Effects of elevated root zone CO2 on xerophytic shrubs in re-vegetated sandy dunes at smaller spatial and temporal scales.

The below-ground CO2 concentration in some crusted soils or flooded fields is usually ten or hundred times larger than the normal levels. Recently, a large number of studies have focused on elevated CO2 in the atmosphere; however, only few have examined the influence of elevated root zone CO2 on plant growth and vegetation succession. In the present study, a closed-air CO2 enrichment (CACE) system was designed to simulate elevated CO2 concentrations in the root zones. The physio-ecological characteristics of two typical xerophytic shrubs C. korshinskii and A. ordosica in re-vegetated desert areas were investigated at different soil CO2 concentrations from March 2011 to October 2013. Results showed that plant growth, phenophase, photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency for the two xerophytic shrubs were all increased at first and then decreased with increasing soil CO2 concentrations, and the optimal soil CO2 concentration thresholds for C. korshinskii and A. ordosica were 0.554 and 0.317%, respectively. And A. ordosica was more tolerate to root zone CO2 variation when compared with C. korshinskii, possible reasons and vegetation succession were also discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-015-1091-7) contains supplementary material, which is available to authorized users.

Growth and physiological responses of isohydric and anisohydric poplars to drought.

Understanding how different plants prioritize carbon gain and drought vulnerability under a variable water supply is important for predicting which trees will maximize woody biomass production under different environmental conditions. Here, Populus balsamifera (BS, isohydric genotype), P. simonii (SI, previously uncharacterized stomatal behaviour), and their cross, P. balsamifera x simonii (BSxSI, anisohydric genotype) were studied to assess the physiological basis for biomass accumulation and water-use efficiency across a range of water availabilities. Under ample water, whole plant stomatal conductance (gs), transpiration (E), and growth rates were higher in anisohydric genotypes (SI and BSxSI) than in isohydric poplars (BS). Under drought, all genotypes regulated the leaf to stem water potential gradient via changes in gs, synchronizing leaf hydraulic conductance (Kleaf) and E: isohydric plants reduced Kleaf, gs, and E, whereas anisohydric genotypes maintained high Kleaf and E, which reduced both leaf and stem water potentials. Nevertheless, SI poplars reduced their plant hydraulic conductance (Kplant) during water stress and, unlike, BSxSI plants, recovered rapidly from drought. Low gs of the isohydric BS under drought reduced CO2 assimilation rates and biomass potential under moderate water stress. While anisohydric genotypes had the fastest growth under ample water and higher photosynthetic rates under increasing water stress, isohydric poplars had higher water-use efficiency. Overall, the results indicate three strategies for how closely related biomass species deal with water stress: survival-isohydric (BS), sensitive-anisohydric (BSxSI), and resilience-anisohydric (SI). Implications for woody biomass growth, water-use efficiency, and survival under variable environmental conditions are discussed.

模拟岩溶旱钙土壤基质中AM真菌对玉米幼苗光合生长的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 模拟岩溶旱钙土壤基质中AM真菌对玉米幼苗光合生长的影响 DOI: 10.5846/stxb201402190287 作者: 作者单位: 西南大学生命科学学院,西南大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金(31360106) Effect of AMF on the photosynthetic characteristics and growth of maize seedlings under the stress of drought, high calcium and their combination in Karst area Author: Affiliation: School of Life Science,Southwest University,School of Life Science,Southwest University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用盆栽试验,探讨了AM真菌在模拟岩溶区干旱、高钙及其双重胁迫的土壤基质中对玉米幼苗光合生长的影响。结果表明:玉米幼苗的菌根侵染率在不同处理下的大小顺序为对照 > 干旱 > 双重胁迫 > 高钙。无论接种与否,干旱、高钙及其双重胁迫均导致玉米幼苗生物量、净光合速率下降。未接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低3.2%、63.7%、76.0%,净光合速率较对照分别低33.4%、86.9%、98.8%;接种AM真菌条件下,玉米幼苗生物量在干旱、高钙及其双重胁迫下较对照分别低16.3%、78.4%、80.2%,净光合速率较对照分别低9.7%、92.8%、91.7%。与同种条件下的非菌根植株相比,干旱及双重胁迫下的菌根植株生物量、叶绿素含量、光合蒸腾速率、最大光化学效率,以及P吸收均呈上升趋势;高钙胁迫下的菌根植株叶绿素含量、最大光化学效率有所增加,但生物量、光合蒸腾速率以及N、P的吸收未体现菌根促进效应。AM真菌与干旱及双重胁迫的交互作用对玉米幼苗的净光合速率影响显著,与高钙交互作用对玉米幼苗净光合速率无显著影响。AM真菌能够通过促进玉米幼苗N、P吸收及叶绿素含量增加,光化学效率、气孔导度增大,从而提高玉米幼苗光合作用能力促进生长。实验结果对岩溶生态系统中合理利用菌根技术及制定合理的农业生产措施具有重要的理论和实践意义。 Abstract:Drought and high concentration of calcium are the main characters of the karst soils, and always show great heterogeneity in the karst ecosystems. In order to explore the effects of AMF on the photosynthetic and growth characters of maize (Zea mays L.) under various stresses, three treatments including drought, high concentration of calcium (high Ca), and their combination (double stress) were applied to potted maize seedlings. The results showed that the colonization rate of the AMF to maize seedlings was following the sequence of: control > drought > double stress > high Ca. Compared to the control group, the biomass, net photosynthetic rate (Pn) of the seedlings were decreased in the three treatments. Under non-inoculation conditions, the biomass of maize seedlings subjected to drought, high calcium and double stress were 3.2%, 63.7%, 76% lower than that of control respectively, while those of Pn were 33.4%, 86.9%, and 98.8%. In the same time, under inoculation conditions, compared with the control, the seedling's biomass in drought, high calcium and double stress were 16.3%, 78.4%, 80.2% lower, and net photosynthetic rate were 9.7%, 92.8%, and 91.7% lower. Additionally, compared to the seedlings without AMF, those vaccinated AMF showed significantly higher biomass, chlorophyll content, transpiration rate (Tr), maximum photochemical efficiency, and absorbed more phosphorus, when subjected to the drought and double stress. On the contrary, in the environment of high calcium, the AMF only enhanced the content of chlorophyll, maximum photochemical efficiency, while there was no increase in terms of plant biomass, Tr and the absorbing amount of nitrogen and phosphorus. Moreover, the interaction of AMF×drought and AMF×double stress had significant effects on the Pn of seedlings, while no significant effects of AMF×high Ca were found on the Pn. AM fungi can assist the plant to absorb more phosphorus, enhancing the contents of chlorophyll, improving the activity of light reaction center, increasing the plant stomatal conductance, so as to enhance photosynthesis ability to promote the growth of plant. This research can provide references for a reasonable utilization of AMF and increasing agricultural productivity in the karst ecosystem. 参考文献 相似文献 引证文献

Differential physiological and biochemical responses to drought in grapevines subjected to partial root drying and deficit irrigation

The effects of two different irrigation methodologies, partial root drying (PRD) and deficit irrigation (DI), on grapevines (Vitis vinifera L., cv. Mavrodafni) physiological and biochemical parameters were studied using split-rooted potted plants. Five irrigation treatments were applied: fully irrigated (FI) at both parts of the rootzone to soil capacity; deficit irrigated (DI50 and DI25) receiving 50% and 25% irrigation water of FI plants, respectively, to the entire rootzone and partial root drying (PRD50 and PRD25) receiving 50% and 25% irrigation water of FI plants, respectively, which was successively applied to one and the other part of the rootzone. Compared with DI50, PRD50 plants exhibited higher stomatal conductance and photosynthetic rate maintaining more favorable plant water status throughout the experimental period. On the contrary, no significant differences in physiological parameters between PRD25 and DI25 plants were observed, suggesting that irrigation amount could influence different irrigation methodologies effects on plant's performance. Leaf abscisic acid (ABA) concentration at the end of the drought period was significantly higher in DI compared to PRD plants while the opposite trend was evident concerning cytokinins (Cks) concentration. Irrespective the irrigation amount applied, stomatal conductance (gs) in DI plants exhibited the strongest correlation with leaf abscisic acid (ABA) concentration among the treatments but this relationship was significantly weakened when gs was regressed against ABA/CKs ratio. PRD plant's stomatal conductance was also strongly correlated with leaf abscisic acid (ABA) concentration but this relationship was markedly improved when ABA/CKs ratio was used. These results imply a more pronounced role of CKs in mediating stomatal responses in PRD plants. In contrast in DI grapevines ABA concentration seemed to dominate stomatal responses to drought.

Ozone pollution effects on gas exchange, growth and biomass yield of salinity-treated winter wheat cultivars

A sand-culture experiment was conducted in four Open-Top-Chambers to assess the effects of O3 on salinity-treated winter wheat. Two winter wheat cultivars, salt-tolerant Dekang961 and salt-sensitive Lumai15, were grown under saline (100mM NaCl) and/or O3 (80±5nmolmol−1) conditions for 35days. Significant (P<0.05) O3-induced decreases were noted for both cultivars in terms of gas exchange, relative water content, growth and biomass yield in the no-salinity treatment. Significant (P<0.01) corresponding decreases were measured in Dekang961 but not in Lumai15 in the salinity treatment. Soluble sugar and proline contents significantly increased in both cultivars in combined salinity and O3 exposure. O3-induced down-regulation in the gradients of A-Ci and A-PPFD response curves were much larger in Dekang961 than in Lumai15 under saline conditions. Significant (P<0.05) interactions were noted in both salinity×cultivars and salinity×O3 stresses. The results clearly demonstrated that O3 injuries were closely correlated with plant stomatal conductance (gs); the salt-tolerant wheat cultivar might be damaged more severely than the salt-sensitive cultivar by O3 due to its higher gs in saline conditions.

The Impact of Seed Priming and Aging on Physiological Performance of Chickpea Under Different Irrigation Treatments

Abstract A sub-sample of chickpea (Cicer arietinum L. CV.ILC482) seeds was kept as control and two other subsamples were aged at 40 °C for 3 and 5 days. Consequently, three seed lots with different levels of vigor were provided. These seed lots were soaked in distilled water at 15°C for 12 and 18 hours and then dried back to initial moisture content at a room temperature of 20–22°C. Then seeds were sown in the field as split plot factorial based on RCB design. Hydro-priming improved leaf chlorophyll content index of plants from different seed lots. Hydro-priming also enhanced stomatal conductance of plants from all seed lots under all irrigation levels, but this advantage for plants from low vigor seed lots particularly under limited irrigations was higher than that for other treatments. Plants from high vigor seed lot under different irrigation treatments had higher relative water content, compared with those from low vigor seed lots. Hydro-priming improved relative water content, membrane stability and grain yield of chickpea plants from different seed lots under various irrigation treatments. It was concluded that hydro-priming to some extent can repair aged seeds and improve their performance under different irrigation treatments.

Pimenteira ornamental submetida a tratamentos com daminozide em vasos com fibra de côco ou areia

The demand for ornamental pepper as “potted plants” is growing. It is possible to produce these plants with growth regulators in substrates easily acquired and capable of providing high quality plants at low cost. The present study had the goal of evaluating the effect of applications of levels of the regulator daminozide on ornamental pepper grown in pots containing coconut fiber (FC) or sand as substrates. A completely randomized design was employed in a 2x5 factorial scheme consisting of two types of substrate (FC and sand) and five levels of daminozide (0, 2, 4, 6 and 8 g L-1) applied three times during the experiment, at 25, 40, and 55 days after sowing. The following variables were analyzed: plant height, stem diameter, number, width and length of fruits, dry matter of leaf, stem, fruits, and root, leaf area, relative chlorophyll index, net photosynthesis, reduced stomatal conductance, internal CO2 concentration, transpiration rate and temperature of leaves. Daminozide reduced plant height pepper on both substrates, and the coconut fiber provided greater vigor and development. With increasing concentrations of the regulator pepper plants had more thicker stems, lower height and leaf area, leaves with higher chlorophyll content, and presented reduction in the following variables: width and length of fruits, rates of transpiration, net photosynthesis, and stomatal conductance of plants.

How does a shelter of solar panels influence water flows in a soil–crop system?

Associating on the same land area an upper layer of solar panels together with a crop layer at the ground level has been shown to allow significant saving of land resource compared to separate energy and food productions (Marrou et al., 2013a). Indeed, crops can achieve high yield under the fluctuating shade of these agrivoltaic systems. Moreover, under dry Mediterranean climate, microclimate measurements at crop level below these panels suggest that these systems could contribute to alleviate climatic stress and to save water. On two experimental prototypes of these agrivoltaic systems, we combined two complementary approaches to assess the impact of the solar panels cover on crop water use. First we calculated the bulk actual evapotranspiration (AET) of irrigated lettuces and cucumbers grown in agrivoltaic systems and in the full sun, from field measurements using the water balance equation for a crop–soil system. Then, we proposed a conceptual framework to analyze AET modifications in the partial shade and assess the contribution of identified drivers to this change. This conceptual framework breaks AET into two components (plant transpiration and soil evaporation) and four drivers: climatic demand at canopy level (ET0), fraction of radiation intercepted by the vegetation, plant stomatal conductance, and soil surface hydraulic conductance. From specific field measurements, we assessed the contribution of each driver to the variations of evapotranspiration below the photovoltaic panels (PVP), in comparison with the full sun. Crop AET calculated with the first approach (water balance) was reduced in agrivoltaic systems by 10–30% when available light was equal to 50–70% of full sun radiation, with variations according to the weather season. The second approach showed that reduction of evapotranspiration was mainly driven by the reduction of the climatic demand below the solar panels and did not result systematically in an increase of the water use efficiency, depending on the genotypic plant sensibility of dry matter accumulation to shade. The conceptual framework suggest that water use efficiency in agrivoltaic systems could be increased by selecting crop species and varieties with a rapid soil covering, which contributes to increased light capture and to decreased soil evaporation, leaving more water for plant transpiration and thereby for biomass production.

Enhanced Nitrogen Uptake and Photosynthesis of Rice Grown with Deep and Permanent Irrigation Method: Possible Mechanism for Chalky Grain Reduction

Recently, the occurrence of chalky grain caused by high temperature stress at the ripening stage has been a global problem for rice. We previously showed that the deep and permanent irrigation method, which is the combination of the V-furrow direct seeding and deep-flood irrigation methods, reduced chalky grain occurrence. To study the possible physiological mechanisms for reduced chalky grain occurrence by the deep and permanent irrigation method, we conducted field experiments in 2008 and 2009 to examine the effects of the deep-flood treatment on plant nitrogen (N) content, stomatal conductance and photosynthetic rate especially at the ripening stage. Results showed that in the deep-flood treatment that maintained a 20 cm water depth, leaf N content was consistently and significantly higher than the control with only a 10 cm water depth. Except two measured days, the stomatal conductance under the deep-flood treatment was significantly higher than in the control. Furthermore, stomatal conductance and photosynthetic rate in the deep-flood treatment were always significantly higher than in the control in both years. Thus, the deep-flood treatment enhanced N uptake, and consequently photosynthetic activity, resulting in the reduction of chalky grain formation, as previously reported. Accordingly, the effects of deep- flood treatment on grain quality improvement in rice may possibly be attributed to the improvement in source activity.

The effect of irrigation frequency on growth, flowering and stomatal conductance of osteospermum 'Denebola' and New Guinea impatiens 'Timor' grown on ebb·and-flow benches

The response of osteospermum 'Denebola' and New Guinea impatiens 'Timor' grown on ebb-and-flow benches to different water potential of growing medium applied during whole growing period was investigated by measuring plant growth parameters and stomatal conductance (g&lt;sub&gt;S&lt;/sub&gt;). After cutting establishment, four different irrigation treatments based on soil water potential were applied to osteospermum: at -0,5 , -3,0 , -10,0 , -20 kPa. In the case of impatiens the last water treatment was omitted. Plants were evaluated when they reach one ofthe three growth stages: lateral shoots development, visible flower buds (osteospermum) or beginning of flowering (impatiens) and at flowering. All plants produced with a moderate water deficit (irrigation at -3 and -10 kPa) were more compact than plants irrigated at -0,5 kPa but their flowering were not affected. Strong decrease in pIant growth and flowering was observed when plants were irrigated at the lowest water potential (-20 kPa). However, for impatiens the highest irrigation frequency was also not favorable. As a result of water stress the decrease in stomatal conductance (g~) in both plants was observed. Osteospermum was more resistant to water stress than impatiens.