Decrease In Stomatal Conductance Research Articles

Influence of the Ocean and Greenhouse Gases on Severe Drought Likelihood in the Central United States in 2012

Abstract The impacts of sea surface temperature (SST) anomalies and anthropogenic greenhouse gases on the likelihood of extreme drought occurring in the central United States in the year 2012 were investigated using large-ensemble simulations from a global atmospheric climate model. Two sets of experiments were conducted. In the first, the simulated hydroclimate of 2012 was compared to a baseline period (1986–2014) to investigate the impact of SSTs. In the second, the hydroclimate in a world with 2012-level anthropogenic forcing was compared to five “counterfactual” versions of a 2012 world under preindustrial forcing. SST anomalies in 2012 increased the simulated likelihood of an extreme summer precipitation deficit (e.g., the deficit with a 2% exceedance probability) by a factor of 5. The likelihood of an extreme summer soil moisture deficit increased by a similar amount, due in great part to a large spring soil moisture deficit carrying over into summer. An anthropogenic impact on precipitation was detectable in the simulations, doubling the likelihood of what would have been a rainfall deficit with a 2% exceedance probability under preindustrial-level forcings. Despite this reduction in rainfall, summer soil moisture during extreme drought was essentially unaffected by anthropogenic forcing because of 1) evapotranspiration declining roughly one-to-one with a decrease in precipitation due to severe water supply constraint and despite higher evaporative demand and 2) a decrease in stomatal conductance, and therefore a decrease in potential transpiration, with higher atmospheric CO2 concentrations.

Recently-released genotypes of naked oat (Avena nuda L.) out-yield early releases under water-limited conditions by greater reproductive allocation and desiccation tolerance

Naked oat (Avena nuda L.) is becoming increasingly popular because of its high nutritive value and increased yields. As naked oat is grown in marginal environments, one of the limitations to yield is drought stress. In this study conducted in the field and a rainout shelter, the yield, water relations, and physiological and biochemical responses to drought of six genotypes, three released since 2008 (recently-released, RR) and three genotypes released at least 60 years earlier (early-released, ER) were compared. The grain yield, harvest index (HI) and water use efficiency for grain were higher in the RR than ER genotypes under rainfed and irrigated conditions in the field and under drought and well-watered conditions in the rainout shelter. Aboveground biomass and HI had significant direct effects on grain yield, while leaf dry weight was negatively associated with grain yield in the rainout shelter. During a progressive soil drying experiment, the threshold soil water content (SWC) when stomatal conductance and photosynthesis began to decrease was lower in the RR [48–52% field capacity (FC)] than ER (54–58% FC) genotypes, but whole plant transpiration began to decrease when the leaf water potential and relative water content began to decrease at a threshold SWC of 31–44% FC in both the RR and ER genotypes. The beginning of the decrease in stomatal conductance and photosynthesis was associated with the increase in leaf abscisic acid concentration, but higher osmolyte accumulation, greater osmotic adjustment and less lipid peroxidation in the RR genotypes than the ER genotypes occurred at low SWC (below 30% FC) and are associated with greater desiccation tolerance in the RR genotypes. We conclude that the higher yields in the RR genotypes of naked oat are associated with selection for higher reproductive allocation and desiccation tolerance. The role of stomatal closure and osmotic adjustment on adaptation to drought are discussed.

Responses to atmospheric CO2 concentrations in crop simulation models: a review of current simple and semicomplex representations and options for model development.

Elevated atmospheric CO2 concentrations ([CO2 ]) cause direct changes in crop physiological processes (e.g. photosynthesis and stomatal conductance). To represent these CO2 responses, commonly used crop simulation models have been amended, using simple and semicomplex representations of the processes involved. Yet, there is no standard approach to and often poor documentation of these developments. This study used a bottom-up approach (starting with the APSIM framework as case study) to evaluate modelled responses in a consortium of commonly used crop models and illuminate whether variation in responses reflects true uncertainty in our understanding compared to arbitrary choices of model developers. Diversity in simulated CO2 responses and limited validation were common among models, both within the APSIM framework and more generally. Whereas production responses show some consistency up to moderately high [CO2 ] (around 700ppm), transpiration and stomatal responses vary more widely in nature and magnitude (e.g. a decrease in stomatal conductance varying between 35% and 90% among models was found for [CO2 ] doubling to 700ppm). Most notably, nitrogen responses were found to be included in few crop models despite being commonly observed and critical for the simulation of photosynthetic acclimation, crop nutritional quality and carbon allocation. We suggest harmonization and consideration of more mechanistic concepts in particular subroutines, for example, for the simulation of N dynamics, as a way to improve our predictive understanding of CO2 responses and capture secondary processes. Intercomparison studies could assist in this aim, provided that they go beyond simple output comparison and explicitly identify the representations and assumptions that are causal for intermodel differences. Additionally, validation and proper documentation of the representation of CO2 responses within models should be prioritized.

Water relations in almond trees under moderate water deficits

The responses of almond trees 'Guara' to different levels of water deficits were investigated. Three irrigation treatments as well as a rainfed treatment were applied in the field to 5-year-old trees during the summer of 2013. Plant water status was monitored by measurement of stem water potential at midday (Ψx), leaf gas-exchange was measured with a photosynthesis analyzer (IRGA) and stomatal conductance with a steady-state leaf porometer. Ψx of well-watered trees was near -0.9 MPa and always higher than -1.0 MPa. In the case of trees irrigated with amounts of water below full crop requirements, Ψx decreased down to -1.5 MPa, and simultaneously, a gradual decrease in stomatal conductance was observed. The close correlation between stomatal conductance (gs) and CO2 assimilation (A) pointed toward the stomatal limitation of CO2 assimilation in almond. Then although the stomatal closure will reduce photosynthesis, the fact that that closure occurs gradually as stress progresses will permit some rate of CO2 assimilation by the plant. The value of -1.0 MPa could be considered a reference threshold in full irrigation programming to ensure maximum stomatal conductance of 'Guara' almond trees. That high value showed the sensibility of this cultivar to water stress.

Water availability effect on gas exchanges and on phenology of ‘Cabula’ orange

As a continental country, Brazil has very diverse climate and growing conditions, which can be adverse to citrus growing in certain regions hindering regular fruit production. To know more about the effects of water stress on gas exchanges and phenological characteristics of orange tree cultivar 'Cabula', an experiment was conducted in a greenhouse where these parameters were analyzed by managing applied water. Three treatments were applied, and irrigation was based on suppling water to maintain 100, 50 and 25% of the soil water storage capacity. All technical features were assessed within 210 days, and a completely randomized design was used. The results were analyzed by means of variance analysis and compared by Tukey test at 5% probability. Starting at 100 days of drought, it was found that many of the gas exchange parameters were affected, observing reductions in photosynthesis (A) and transpiration (E), which followed the decrease in stomatal conductance (gs). Reductions were also observed in tree height and stem diameter of plants under stress. The production of flowers and fruits was also significantly (P<0.05) affected by the reduction in water availability. In general, it was observed that photosynthetic rate, growth parameters and producing flowers and fruits were higher in treatment “without stress”, suggesting that these require irrigation under farming field conditions above 50% of field capacity to keep production at satisfactory levels.

不同强度净风频繁吹袭对樟子松(Pinus sylvestris var.mongolica)幼苗光合蒸腾特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 不同强度净风频繁吹袭对樟子松(Pinus sylvestris var.mongolica)幼苗光合蒸腾特征的影响 DOI: 10.5846/stxb201510142070 作者: 作者单位: 中国科学院寒区旱区环境与工程研究所,中国科学院寒区旱区环境与工程研究所,鲁东大学生命科学学院,中国科学院寒区旱区环境与工程研究所,中国科学院寒区旱区环境与工程研究所,中国科学院寒区旱区环境与工程研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（31270752，30972422） Effects of wind frequency on the rates of photosynthesis and transpiration in Pinus sylvestris var. mongolica seedlings Author: Affiliation: Cold and Arid Regions Environment and Engineering Institute,CAS,Lanzhou,Cold and Arid Regions Environment and Engineering Institute,CAS,Lanzhou,,Cold and Arid Regions Environment and Engineering Institute,CAS,Lanzhou,Cold and Arid Regions Environment and Engineering Institute,CAS,Lanzhou,Cold and Arid Regions Environment and Engineering Institute,CAS,Lanzhou 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:为了解不同强度净风频繁吹袭对樟子松幼苗光合蒸腾特性的影响，2013年春季在内蒙古科尔沁沙地研究了0（对照）、6、9、12、15、18 m/s等6个风速处理（分别相当于0、4、5、6、7、8级风）4次吹袭下樟子松幼苗光合速率、蒸腾速率、水分利用效率等指标的变化。结果表明，净风频繁吹袭没有改变樟子松幼苗的光合速率和蒸腾速率的日变化规律，但可使其光合蒸腾的“午休”时间加长、“休眠”程度加深；随着风吹强度的增加，其日均光合能力和蒸腾速率显著降低，其中18 m/s处理较对照分别下降27.6%和22.3%；随着风吹强度增加，气孔导度、胞间CO2浓度均先下降后回升，除18 m/s处理胞间CO2浓度显著高于CK外，其他处理均显著低于CK；随着风吹强度增加，水分利用效率和光能利用效率均先增加后下降，其中除18 m/s处理的水分利用效率显著低于CK，6 m/s处理的光能利用效率高于CK外，其他处理的水分利用效率均高于CK，光能利用效率均低于CK；日均光合蒸腾速率的下降主要源于气孔导度的降低，而水分利用效率和光能利用效率的变化均受制于光合速率和蒸腾速率的变化。 Abstract:To understand the effects of frequent gusts of wind on the rates of photosynthesis and transpiration in Pinus sylvestris var. mongolica seedlings, a field wind-blowing experiment using a wind speed gradient of 0 (CK), 6, 9, 12, 15, and 18 m/s and four episodes of wind blowing was conducted in the spring of 2013 in the Horqin Sand Land of Inner Mongolia. The results showed that:1) Frequent wind blowing did not change the diurnal variation in the rates of photosynthesis and transpiration in seedlings, but resulted in in an extension of midday depression and a higher degree of dormancy in photosynthesis and transpiration. 2) Increasing the wind strength led to a significant decrease in the average daily rates of photosynthesis and transpiration, with a decrease of 27.6% and 22.3% in the 18 m/s-treated seedlings compared to the CK, respectively. With an increase in wind strength, stomatal conductance and intercellular CO2 concentrations first increased and then decreased, and were significant lower in all treatment groups as compared with the CK group, with the exception of intercellular CO2 concentration, which was higher in the 18 m/s group. 3) Increasing the wind-sand flow strength led to a significant increase in water-use efficiency, except for a significant decrease in the 18 m/s treatment group as compared with the CK group. In addition, the efficiency of sunlight energy use tended to decrease except for a significant increase in the 6 m/s-treatment group as compared with the CK group. 4) Decreases in the average daily rates of photosynthesis and transpiration resulted from a decrease in stomatal conductance, and changes in water-use efficiency and sunlight energy-use efficiency resulted from changes in the rates of photosynthesis and transpiration. 参考文献 相似文献 引证文献

北京山区侧柏水分利用策略

PDF HTML阅读 XML下载 导出引用 引用提醒 北京山区侧柏水分利用策略 DOI: 10.5846/stxb201605261017 作者: 作者单位: 北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室,北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室,北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室,北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室,北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室,北京林业大学水土保持学院 教育部水土保持与荒漠化防治重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（41430747）；青年科学基金项目（41401013） Water use strategy of Platycladus orientalis in Beijing mountainous area Author: Affiliation: Beijing Forestry University,Beijing Forestry 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:侧柏是北京山区分布范围较广的典型针叶树种，揭示其在不同土壤水分条件下的水分利用策略具有重要意义。通过测定分析生长季内侧柏枝条水、土壤水和地下水的δD和δ18O值，并利用多元混合模型（Iso-source软件）计算侧柏对土壤水或地下水的利用比例，再结合叶片水势（ψ）、气孔导度（Gs）、光合速率（Ps）和蒸腾速率（Tr）等生理生态因子同步观测，了解侧柏在生长季内的水分来源及生理生态适应。结果表明：侧柏的水分利用策略随季节波动，其在不同季节对不同土层水分的利用比例存在差异。在旱季，侧柏对表层0-20cm土壤水的平均利用率介于27.6-31.3%，对深层80-100cm土壤水和地下水的利用率分别介于27.0-33.7%和22.0-28.9%之间；进入雨季，侧柏对表层0-20cm土壤水利用比例增大，介于47.2-60.9%，对深层80-100cm土壤水和地下水的利用比例减小，分别介于10.5-16.2%和15.2-19.8%。旱季的侧柏水分亏缺更为严重，其叶片水势峰值比雨季低44.5%；旱季中的侧柏气孔导度在上午10：00达到峰值，但比雨季峰值低51.67%，其光合速率和蒸腾速率峰值也相应的下降了22.3%和37.0%。侧柏能通过降低气孔导度减少水分损失来获得较高的碳同化速率，维持较高的水分利用效率来适应干旱生境，表现出较强的适应能力。 Abstract:In order to understand water source of the dominant tree species Platycladus orientalis and its eco-physiological adaptation during growing season in Beijing mountainous area, the Platycladus orientalis of water use strategy under different soil moisture conditions during growing season was studied. We employed the Iso-source software and measured the δD and δ18O in branches of trees, soil and groundwater to clarify their water source during growing season, and analysis combined with eco-physiological factors,such as leaf water potential (ψ), stomatal conductance (GS) and water use efficiency (WUE). Results show that Platycladus orientalis water use strategy with seasonal fluctuations, the in different seasons of different depths of soil moisture utilization ratio are different. In the dry season, Platycladus orientalis absorbed water in 0-20cm soil layer, the average utilization rate between 27.6-31.3%, at the same time, it utilization of 80-100 cm deep soil water and groundwater are in the range of 27.0%-33.7% and 22.0%-28.9% respectively. In the rainy season, the ratio of Platycladus orientalis absorbed 0-20cm soil water increased range of 47.2%-60.9%, the ratio of absorbed water in 80-100 cm deep soil layer and groundwater is decreased, range of 10.5%-16.2% and 15.2%-19.8% respectively. In dry season, the drought and water shortage of Platycladus orientalis is more serious, leaf water potential 44.5% less than in the rainy season; the peak of Platycladus orientalis stomatal conductance appeared at 10:00 am in the dry season, but 51.67% less than in rainy season, the photosynthetic rate and transpiration rate of peak also corresponding fell 22.3% and 37.0% respectively. Platycladus orientalis can reduce stomatal conductance decrease water loss to obtain higher carbon assimilation rate and maintain higher water use efficiency to adapt the arid condition, showed high adaptability to arid condition. 参考文献 相似文献 引证文献

PHYSIOLOGICAL AND PHENOLOGICAL VEGETATIVE RESPONSES OF Campomanesia adamantium (Cambess) O. Berg (Myrtaceae) TO THE HYDRIC SEASONALITY OF RUPESTRIAN FIELDS

ABSTRACT The rupestrian fields have two well-defined seasons throughout the year, with rainfall rates that reflect the rainy and dry seasons. This distinction in water availability affects the morphology, physiology and chemistry of plants, among other characteristics. Thus, it is aimed at evaluating the leaf water status, vegetative phenology and photosynthetic behavior of Campomanesia adamantium from a rupestrian field during the dry and rainy season. The study was conducted in Serra do Cipó, Minas Gerais, Brazil. From November 2011 to November 2012 it was examined vegetative phenophases and development of six individuals. Water potential, stomatal conductance, quantum yield and concentration of pigments were evaluated from four leaves of 3rd node per individual (n = 4-5) in the dry and rainy seasons. C. adamantium is an evergreen type and presents mature leaves and sprouting throughout the year. This species showed strategies that reduce water loss during the dry season in rupestrian field, such as decrease in stomatal conductance throughout the day, also associated with a reduction in leaf water potential. However, low water availability did not affect the photosynthetic performance, which enables the construction of new leaves and renovation of the crown even in dry periods. Finally, little reduction in the values of Fv/Fm throughout the day and increase the values of ΔF/Fm' in warmer times, both in the dry season, reiterates the ability of C. adamantium to adjust their physiology to seasonal water deficit of the rupestrian field.

Grapevine RD22a constitutive expression in tobacco enhances stomatal adjustment and confers drought tolerance

Drought is one of the major constraints limiting crop production worldwide including grapevine. Investigations of drought tolerance genotypes by genetic engineering are an important goal in Vitis breeding program. Three dehydration-responsive RD22 genes (VviRD22) were identified in Vitis vinifera L. Here, we aim to evaluate the constitutive expression of VviRD22a effect on tobacco performance under low water availability conditions, namely under drought and under osmotic stress. In vitro, and under osmotic stress, transgenic seeds of tobacco showed an enhanced tolerance at the germination and seedling stages compared to the wild-type (WT). When drought was applied ex vitro by stopping irrigation during 9 days, transgenic lines exhibited an earlier decrease of stomatal conductance that was, interestingly, followed by an internal adjustment leading to a moderate decline of the photosynthetic rate. Additionally, differences between WT and transgenics under both control and stressed conditions were revealed at ultrastructural level through shape alteration within the transgenics. Additionally, the performances of the VviRD22a lines under drought were notably maintained in terms of biomass production (vegetative dry material) and water status (Relative water content and water retention ability). A significant distinctiveness between VviRD22a-expressing lines and WT under stress conditions but not under control conditions (principal component analyses) was found. Protection effect of VviRD22a constitutive expression towards drought involved root biomass, water status and stomatal adjustment traits. Overall, our data suggest that VviRD22a transgenic expression plays a positive role in drought tolerance improvement supporting it as an important candidate gene for molecular breeding of drought tolerant grapevines.

Difference in leaf water use efficiency/photosynthetic nitrogen use efficiency of Bt-cotton and its conventional peer.

This study is to test the effects of Bt gene introduction on the foliar water/nitrogen use efficiency in cotton. We measured leaf stomatal conductance, photosynthetic rate, and transpiration rate under light saturation condition at different stages of a conventional cultivar (zhongmian no. 16) and its counterpart Bt cultivar (zhongmian no. 30) that were cultured on three levels of fertilization, based on which leaf instantaneous water use efficiency was derived. Leaf nitrogen concentration was measured to calculate leaf photosynthetic nitrogen use efficiency, and leaf δ13C was used to characterize long term water use efficiency. Bt cultivar was found to have lower stomatal conductance, net photosynthetic rates and transpiration rates, but higher instantaneous and long time water use efficiency. In addition, foliar nitrogen concentration was found to be higher but net photosynthetic rate was lower in the mature leaves of Bt cultivar, which led to lower photosynthetic nitrogen use efficiency. This might result from the significant decrease of photosynthetic rate due to the decrease of stomatal conductance. In conclusion, our findings show that the introduction of Bt gene should significantly increase foliar water use efficiency but decrease leaf nitrogen use efficiency in cotton under no selective pressure.

The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest.

From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO2 concentrations from 270 to 400mol mol-1 . The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of free-air CO2 enrichment (FACE) experiments. These experiments have found (i) an increase in internal CO2 partial pressure (ci ) alongside acclimation of photosynthetic capacity, (ii) variable decreases in stomatal conductance, and (iii) that increases in yield do not increase commensurate with CO2 concentrations. Our data set, which includes a 115-year-long selection of grasses collected in New Mexico since 1892, is consistent with an increased ci as a response to historical CO2 increase in the atmosphere, with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity Index (PDSI) for New Mexico indicates a moderate correlation with Δ13 C (r2 =0.32, P<0.01) before 1950, with no correlation (r2 =0.00, P=0.91) after 1950. These results indicate that increased ci may have conferred some drought resistance to these grasses through increased availability of CO2 in the event of reduced stomatal conductance in response to short-term water shortage. Comparison with C3 trees from arid environments (Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments (Bromus and Poa grasses in New Mexico) suggests differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO2 while wetter environments see increased ci . This study suggests that (i) the observed increases in ci in FACE experiments are consistent with historical CO2 increases and (ii) the CO2 increase influences plant sensitivity to water shortage, through either increased WUE or ci in arid and wet environments, respectively.

Acclimation of Betula alleghaniensis Britton to moderate soil water deficit: small morphological changes make for important consequences in crown display.

In the context of the predicted increasing frequency of summer droughts in the northeastern deciduous forest of North America due to climate change, we investigated the acclimation capacity of yellow birch, an economically important native tree species, to soil water deficit. We carried out an integrated examination of allocation of biomass, leaf physiology, branching pattern and in situ 3D crown display. Potted seedlings were subjected to moderate soil water deficit for four consecutive months during their second growing season. Individuals under soil water deficit showed a 40% decrease in biomass accumulation but no change in the relative allocation of biomass to the different plant compartments. Net CO2 assimilation rates at leaf level decreased under water deficit (~15%) but could not alone explain the total reduction in growth, excluding the carbon starvation hypothesis. The observed reduction in net CO2 assimilation rates was related to a decrease in stomatal conductance and chlorophyll content. STARzen (in situ silhouette to total leaf area ratio; a proxy for light interception efficiency) decreased under soil water deficit due to shifts in biomass allocation within the branch compartment from long upper axes to short bottom axes. Despite the fact that the understanding of the processes involved in growth reduction and branching pattern alteration will need more attention in future research, we conclude that under water deficit yellow birch at young stages will: (i) experience a substantial loss of growth and biomass; and (ii) acclimate through architectural plasticity rather than through changes in the relative allocation of root biomass to enhance its water management.

Genome-Wide Transcriptional Profile Analysis of Prunus persica in Response to Low Sink Demand after Fruit Removal.

Prunus persica fruits were removed from 1-year-old shoots to analysis photosynthesis, chlorophyll fluorescence and genes changes in leaves to low sink demand caused by fruit removal (−fruit) during the final stage of rapid fruit growth. A decline in net photosynthesis rate was observed, accompanied with a decrease in stomatal conductance. The intercellular CO2 concentrations and leaf temperature increased as compared with a normal fruit load (+fruit). Moreover, low sink demand significantly inhibited the donor side and the reaction center of photosystem II. 382 genes in leaf with an absolute fold change ≥1 change in expression level, representing 116 up- and 266 down-regulated genes except for unknown transcripts. Among these, 25 genes for photosynthesis were down-regulated, 69 stress and 19 redox related genes up-regulated under the low sink demand. These studies revealed high leaf temperature may result in a decline of net photosynthesis rate through down-regulation in photosynthetic related genes and up-regulation in redox and stress related genes, especially heat shock proteins genes. The complex changes in genes at the transcriptional level under low sink demand provided useful starting points for in-depth analyses of source-sink relationship in P. persica.

Does belowground interaction with Fagus sylvatica increase drought susceptibility of photosynthesis and stem growth in Picea abies?

Mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) frequently over-yield, when compared to respective monospecific stands. Over-yielding is attributed to enhanced resource uptake efficiency through niche complementarity alleviating species competition, for example through enhanced root stratification in mixture. Under severe and frequent summer drought, however, water limitation may become crucial in modifying the prevailing competitive interaction in mixed beech-spruce forests. We hypothesize, therefore, that under drought (H I) inter-specific interaction with beech reduces water accessibility for spruce more than intra-specific conditions, thus (H II) exacerbating drought susceptibility of spruce in terms of reduced photosynthesis and stem growth. Reactions at the organ (leaf, fine root), tree and stand scale were analysed in a mature forest with beech-spruce group mixture. Under inter-specific conditions spruce’s fine-root production and depth of water uptake (assessed via δ18O of xylem water) shifted to shallow, drought-prone soil horizons, in agreement with H I. Overall, lowered fine root production and ramification along with a reduction in long-distance explorative ectomycorrhizal types resulted in decreased soil exploitation in spruce when growing together with beech. Spruce’s drought sensitivity was exemplified by a distinct decrease in stomatal conductance, net CO2 uptake rate and stem growth during periods of water limitation. Notwithstanding, species interaction effects were absent in leaf gas exchange and stem diameter growth, during a six-week summer drought period in 2013 as well as in the extremely dry year of 2003, hence rejecting H II. Based on results from soil moisture measurements and water uptake depth, we interpret the conflicting findings for H I and H II to result from: (i) seasonal shifts between positive (during spring drought) and negative (during summer drought) effects of beech neighbourhood on soil water availability for spruce, possibly overriding each other in their effect on annual stem diameter growth and (ii) the group-wise mixture pattern, where spruce is exposed to competition with beech only along group edges, i.e. laterally only, so that the putatively adverse beech effect on water accessibility stays limited. Our results suggest, compared to single tree mixture, group-wise mixture of beech and spruce to be a favourable silvicultural option in the face of climate change.

Beneficial effects of potassium application in improving submergence tolerance of rice (Oryza sativa L.)

The rainfed lowland rice ecosystem is affected by not only water deficit but also excess water. Although the rice plant is well adapted to aquatic environments, it is unable to survive if it is completely submerged in water for an extended period. The impact of submergence on survival, chlorophyll, photosynthesis, post-recovery growth and anti-oxidant capacities in four rice cultivars namely IR 64, IR 64-Sub1, Swarna and Swarna-Sub1 having differential response to potassium application were examined. All the cultivars showed inhibition of photosynthesis, this was accompanied with decrease in stomatal conductance, chlorophyll and carbohydrate contents; the decrease was more pronounced in non-sub1 cultivars. The activity of anti-oxidants was found to be significantly high and lipid peroxidation was low in sub1 cultivars. Potassium application improved the survival mainly because of maintenance of carbohydrates, chlorophyll and contributing to less lodging and leaf senescence. Furthermore, K application resulted in inhibition of lipid peroxidation and increase in catalase and Peroxidase activities. Potassium at higher levels was more beneficial in terms of improving survival, photosynthesis and growth after recovery. The germplasm improvement is beneficial if provided with best management practices, modification in plant nutrition by K application enhance the survival, recovery and growth of rice during complete submergence.

Energy partitioning and its controls over a heterogeneous semi‐arid shrubland ecosystem in the Lake Naivasha Basin, Kenya

AbstractThis paper reports on the energy balance and partitioning analysed from 3‐year micrometeorological flux measurements of energy and water fluxes over a heterogeneous semi‐arid shrubland ecosystem in Lake Naivasha basin. The measurements enabled the characterization of the seasonal and interannual variability of the energy and water fluxes of the ecosystem covering two wet years (2012 and 2013) and one drought year (2014). On an annual scale, more than 60% of net radiation (Rn) was partitioned as latent (LE) and sensible (H) energy flux, with the latter being the larger consumer of Rn (~34%) and dominant for most months. The transition from H to LE dominance occurred from early noon to late afternoon in the wettest months of April and May. The residual energy balance closure term (C) accounted for between 25 and 40% of the Rn with the imbalance tending to be highest during periods of high insolation. Annual evapotranspiration was estimated at 873 mm, 632 mm and 537 mm for year 2012, 2013 and 2014 respectively. This accounted for at least 80% of the annual precipitation received for the respective years. Surface conductance (gs) scaled significantly with leaf expansion and Priestley–Taylor α coefficient, but was limited during periods of drought because of inadequate soil moisture suggesting that, change in LE was paralleled by changes in green leaf area index. Low values of decoupling coefficient (Ω) during these periods indicated that evapotranspiration was strongly controlled by gs and vapour pressure deficit (VPD). However, under non‐limiting moisture conditions evapotranspiration was decoupled from the atmosphere. This suggested that during the dry seasons and periods of prolonged drought, a lack of moisture in combination with high VPD leads to significant decreases in stomatal conductance that eventually limits partitioning of available energy into LE in the semi‐arid ecosystem part of the Lake Naivasha basin. However, during wet season these factors are non‐limiting and radiation is the dominant control of energy partitioning into LE in the ecosystem. The coupling and decoupling pattern provide insights towards formulating models that quantify evapotranspiration for ecosystems that experience seasonal shifts in controlling factors. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Role of leaf hydraulic conductance in the regulation of stomatal conductance in almond and olive in response to water stress

The decrease of stomatal conductance (gs) is one of the prime responses to water shortage and the main determinant of yield limitation in fruit trees. Understanding the mechanisms related to stomatal closure in response to imposed water stress is crucial for correct irrigation management. The loss of leaf hydraulic functioning is considered as one of the major factors triggering stomatal closure. Thus, we conducted an experiment to quantify the dehydration response of leaf hydraulic conductance (Kleaf) and its impact on gs in two Mediterranean fruit tree species, one deciduous (almond) and one evergreen (olive). Our hypothesis was that a higher Kleaf would be associated with a higher gs and that the reduction in Kleaf would predict the reduction in gs in both species. We measured Kleaf in olive and almond during a cycle of irrigation withholding. We also compared the results of two methods to measure Kleaf: dynamic rehydration kinetics and evaporative flux methods. In addition, determined gs, leaf water potential (Ψleaf), vein density, photosynthetic capacity and turgor loss point. Results showed that gs was higher in almond than in olive and so was Kleaf (Kmax = 4.70 and 3.42 mmol s(-1) MPa(-1) m(-2), in almond and olive, respectively) for Ψleaf > -1.2 MPa. At greater water stress levels than -1.2 MPa, however, Kleaf decreased exponentially, being similar for both species, while gs was still higher in almond than in olive. We conclude that although the Kleaf decrease with increasing water stress does not drive unequivocally the gs response to water stress, Kleaf is the variable most strongly related to the gs response to water stress, especially in olive. Other variables such as the increase in abscisic acid (ABA) may be playing an important role in gs regulation, although in our study the gs-ABA relationship did not show a clear pattern.

Temperature-induced water stress in high-latitude forests in response to natural and anthropogenic warming.

The Arctic is particularly sensitive to climate change, but the independent effects of increasing atmospheric CO2 concentration (pCO2 ) and temperature on high-latitude forests are poorly understood. Here, we present a new, annually resolved record of stable carbon isotope (δ(13) C) data determined from Larix cajanderi tree cores collected from far northeastern Siberia in order to investigate the physiological response of these trees to regional warming. The tree-ring record, which extends from 1912 through 1961 (50 years), targets early twentieth-century warming (ETCW), a natural warming event in the 1920s to 1940s that was limited to Northern hemisphere high latitudes. Our data show that net carbon isotope fractionation (Δ(13) C), decreased by 1.7‰ across the ETCW, which is consistent with increased water stress in response to climate warming and dryer soils. To investigate whether this signal is present across the northern boreal forest, we compiled published carbon isotope data from 14 high-latitude sites within Europe, Asia, and North America. The resulting dataset covered the entire twentieth century and spanned both natural ETCW and anthropogenic Late Twentieth-Century Warming (~0.7 °C per decade). After correcting for a ~1‰ increase in Δ(13) C in response to twentieth century pCO2 rise, a significant negative relationship (r = -0.53, P < 0.0001) between the average, annual Δ(13) C values and regional annual temperature anomalies is observed, suggesting a strong control of temperature on the Δ(13) C value of trees growing at high latitudes. We calculate a 17% increase in intrinsic water-use efficiency within these forests across the twentieth century, of which approximately half is attributed to a decrease in stomatal conductance in order to conserve water in response to drying conditions, with the other half being attributed to increasing pCO2 . We conclude that annual tree-ring records from northern high-latitude forests record the effects of climate warming and pCO2 rise across the twentieth century.

Effects of elevated CO&lt;inf&gt;2&lt;/inf&gt; concentration on root and needle anatomy and physiological functions in Pinus koraiensis seedlings

Aims The impacts of CO2 concentration on the anatomy and physiology of plant roots have rarely been studied. Here we studied the effects of elevated CO2 on anatomical and physiological traits of needles and root tips in Pinus koraiensis seedlings. Our objectives were: 1) to examine how the anatomy of needles and root tips change under doubled CO2 concentration treatment; and 2) to explore physiological responses of needles and root tips to the rising CO2 concentration; and 3) to reveal potential relationships of physiological trait changes between nee- dles and root tips. Methods Three-year-old seedlings of P. koraiensis were grown in CO2 chambers under doubled and ambient CO2 concentrations (350 and 700 µmol·mol -1 ). Physiological traits of needles were measured by the LI-6400 portable photosynthesis system during the experiment. After 5 months, needles and root tips were sampled to de- termine their anatomical characteristics. Theoretical hydraulic conductivity of needles and root tips were calcu- lated based on the Hagen-Poiseuille's Law. Important findings Elevated CO2 concentration had a significant influence on the anatomical characteristics of needles and root tips in P. koraiensis seedlings. Under doubled CO2 concentration, needles had a lower stomatal desnity, greater areas of leaf mesophyll, phloem and xylem. In comparision, root tips under doubled CO2 concentration had a larger diameter, a greater cortical thickness and a larger number of cortical cell layer. Physio- logical traits of needles and root tips also changed substantially under the elevated CO2 concentration, such as increases in needle photosynthetic rate and water use efficiency, xylem cavitation resistance of roots, as well as decreases in stomatal conductance, transpiration rate and root hydraulic conductivity. These results suggest that the anatomical structure and physiological function of leaf and root respond simultaneously to elevated CO2

Changes in growth, physiological parameters and the hormonal status of Myrtus communis L. plants irrigated with water with different chemical compositions

Myrtus communis, an important Mediterranean ornamental shrub, was used to study the effect of irrigation water with different chemical compositions in the plant response. A treatment with NaCl was used to establish the plant resistance to high salinity at long term. Plants were subjected to four irrigation treatments with drainage for three months: Control (0.8dSm−1); two treatments using reclaimed water (RWs): RW1 (2.0dSm−1) and RW2 (5.0dSm−1); and NaCl (10.0dSm−1). High levels of electric conductivity of RWs not affected plant growth, while NaCl decreased leaf dry weight. Coinciding with the accumulation of Na+ and Cl− in the roots, soil water potential decreased, which hinders the mobilization of water to the leaves, decreasing leaf water potential. The osmotic adjustment in the NaCl treatment was due to Na+ and Cl− ions, although the proline could contribute as an Osmo compatible solute, increasing the turgor plants. Also changes in cell walls rigidity minimize the negative effects on the water balance; however, a higher lipid peroxidation was observed in these plants. Stomatal closure was associated with a decrease in K+ and an increase in abscisic acid. NaCl produced an increase in salicylic acid and did not affect jasmonic acid contents at the end of the experiment. Similar behavior in soil and leaf water potentials, although less pronounced than in NaCl, was shown in RW2 plants. The abscisic acid increased in the RW2 with respect to the control and a decrease in stomatal conductance was observed at the end of the experiment. Plants irrigated with RW1 behaved similarly to the control.