Carbon Dioxide Assimilation Rate Research Articles

English

Rust (Uromyces appendiculatus) is a major foliar disease that reduces yield and pod quality in beans. The field trial of French beans was established at Jomo Kenyatta University of Agriculture and Technology (JKUAT). Single plant extracts and combinations of Boscia angustifolia, Zanthoxylum chalybeum and Melea volkensii were used to evaluate their effect on U. appendiculatus in the field. During the growing period, beans were infected with rust from natural inoculum at the field. Physiological responses such as carbon dioxide assimilation, transpiration (E), stomatal conductance (gs), and photosynthetic rate (Pn) of French beans treatments were examined after extracts of three antifungal plants were sprayed. B. angustifolia - Z. chalybeum combination and single plant treatment M. volkensii had positive effects on enhancing the rate of photosynthesis in bean plants. The high regressions between stomatal conductance and rate of transpiration in the treatments indicated that stomatal conductance and rate of transpiration were interdependent and it was interpreted to mean that stomatal conductance enhanced rate of transpiration at different times of the day. These plant extracts however caused an increase in the rate of transpiration of the bean plants, which resulted in loss of water. Results reveal bioactive potential of the flora from M. volkensii and a combination of B. angustifolia and Z. chalybeum to produce metabolites with potential applications as botanical pesticides.   Key words: Antifungal, beans, physiological responses, rust.

Comparison of the Vegetative Growth, Eco-Physiological Characteristics and Mineral Nutrient Content of Basil Plants in Different Irrigation Ratios of Hydroponic:Aquaponic Solutions

Aquaponics is the combined culture of fish and plants in recirculating systems. This experiment was conducted to evaluate the production of basil out of the aquaponic system by irrigation of the plants with different ratios of hydroponic and aquaponic solutions. Basil seedlings were irrigated three times day−1 with 200 mL aquaponic-aquaponic-aquaponic (AAA), aquaponic-hydroponic-aquaponic (AHA), hydroponic-aquaponic-hydroponic (HAH), and hydroponic-hydroponic-hydroponic (HHH) solutions, respectively. Fresh and dry mass of shoots and roots of basil decreased at AAA treatment significantly. The plants were slightly less green at AHA treatments, and a visible chlorosis appeared in the leaves of AAA-treated plants. This chlorosis resulted lower net carbon dioxide (CO2) assimilation rate, transpiration rate, and stomatal conductance in AAA treatment. Iron (Fe), manganese (Mn), and potassium (K) concentrations in leaves decreased and zinc (Zn) concentration increased in higher ratios of aquaponic:hydroponic solution. Lower Fe, Mn, and K concentrations in aquaponic solution may be a main part of the reason for growth reduction.

Corn Growth Response to Elevated CO<sub>2</sub> Varies with the Amount of Nitrogen Applied

Corn, with C4 photosynthetic metabolism, often has no photosynthetic or yield response to elevated carbon dioxide concentrations. In C3 species, the yield stimulation at elevated carbon dioxide concentrations often decreases with nitrogen limitation. I tested whether such a nitrogen interaction occurred in corn, by growing sweet corn in field plots in open top chambers at ambient and elevated (ambient + 180 mmol·mol-1) carbon dioxide concentrations for four seasons, with six nitrogen application rates, ranging from half to twice the locally recommended rate. At the recommended rate of nitrogen application, no carbon dioxide effect on production occurred. However, both ear and leaf plus stem biomass were lower for the elevated carbon dioxide treatment than for the ambient treatment at less than the recommended rate of nitrogen application, and higher at the highest rates of nitrogen application. There were no significant responses of mid-day leaf gas exchange rates to nitrogen application rate for either carbon dioxide treatment, and elevated carbon dioxide did not significantly increase leaf carbon dioxide assimilation rates at any nitrogen level. Leaf area index during vegetative growth increased more with nitrogen application rate at elevated than at ambient carbon dioxide. It is concluded that elevated carbon dioxide increased the responsiveness of corn growth to nitrogen application by increasing the response of leaf area to nitrogen application rate, and that elevated carbon dioxide increased the amount of nitrogen required to achieve maximum yields.

Reviewing the carbon cycle dynamics and carbon sequestration potential of Cyperus papyrus L. wetlands in tropical Africa

Tropical papyrus wetlands have the ability to assimilate and sequester significant amounts of carbon. However, the spatial extent, productivity and carbon sink strength associated with papyrus wetlands remains poorly characterised. The objective of this study was to collate information from peer-reviewed publications and relevant government and NGO reports to better understand carbon dynamics within papyrus dominated wetlands, and to assess the processes that regulate the magnitude of the carbon sink. Papyrus wetlands were shown to exhibit high rates of photosynthetic carbon dioxide (CO2) assimilation of up to 40 μmol CO2 m−2 s−1 where the incident photosynthetic photon flux density was ≥1,000 μmol m−2 s−1, high rates of net primary production ranging between 14 and 52 g DM m−2 d−1 and represent a significant carbon sink where up to 88 t C ha−1 is stored in the aboveground and belowground components of the papyrus vegetation. Under flooded conditions significant detrital and peat deposits accumulate in excess of 1 m in depth, representing an additional carbon store in the order of 640 t C ha−1. This study also highlighted the lack of empirical data on emissions of other radiatively important trace gases such as methane and nitrous oxide and also the vulnerability of these carbon sinks to both future changes in climate, in particular periods of hydrological drawdown, and anthropogenic land use change where the papyrus vegetation is removed in favour of subsistence agricultural cropping systems.

In Vivo Packaging of Triacylglycerols Enhances Arabidopsis Leaf Biomass and Energy Density

Our dependency on reduced carbon for energy has led to a rapid increase in the search for sustainable alternatives and a call to focus on energy densification and increasing biomass yields. In this study, we generated a uniquely stabilized plant structural protein (cysteine [Cys]-oleosin) that encapsulates triacylglycerol (TAG). When coexpressed with diacylglycerol O-acyltransferase (DGAT1) in Arabidopsis (Arabidopsis thaliana), we observed a 24% increase in the carbon dioxide (CO2) assimilation rate per unit of leaf area and a 50% increase in leaf biomass as well as approximately 2-, 3-, and 5-fold increases in the fatty acid content of the mature leaves, senescing leaves, and roots, respectively. We propose that the coexpression led to the formation of enduring lipid droplets that prevented the futile cycle of TAG biosynthesis/lipolysis and instead created a sustained demand for de novo lipid biosynthesis, which in turn elevated CO2 recycling in the chloroplast. Fatty acid profile analysis indicated that the formation of TAG involved acyl cycling in Arabidopsis leaves and roots. We also demonstrate that the combination of Cys-oleosin and DGAT1 resulted in the highest accumulation of fatty acids in the model single-cell eukaryote, Saccharomyces cerevisiae. Our results support the notion that the prevention of lipolysis is vital to enabling TAG accumulation in vegetative tissues and confirm the earlier speculation that elevating fatty acid biosynthesis in the leaf would lead to an increase in CO2 assimilation. The Cys-oleosins have applications in biofuels, animal feed, and human nutrition as well as in providing a tool for investigating fatty acid biosynthesis and catabolism.

Reduction of Oxalate Levels in Tomato Fruit and Consequent Metabolic Remodeling Following Overexpression of a Fungal Oxalate Decarboxylase

The plant metabolite oxalic acid is increasingly recognized as a food toxin with negative effects on human nutrition. Decarboxylative degradation of oxalic acid is catalyzed, in a substrate-specific reaction, by oxalate decarboxylase (OXDC), forming formic acid and carbon dioxide. Attempts to date to reduce oxalic acid levels and to understand the biological significance of OXDC in crop plants have met with little success. To investigate the role of OXDC and the metabolic consequences of oxalate down-regulation in a heterotrophic, oxalic acid-accumulating fruit, we generated transgenic tomato (Solanum lycopersicum) plants expressing an OXDC (FvOXDC) from the fungus Flammulina velutipes specifically in the fruit. These E8.2-OXDC fruit showed up to a 90% reduction in oxalate content, which correlated with concomitant increases in calcium, iron, and citrate. Expression of OXDC affected neither carbon dioxide assimilation rates nor resulted in any detectable morphological differences in the transgenic plants. Comparative proteomic analysis suggested that metabolic remodeling was associated with the decrease in oxalate content in transgenic fruit. Examination of the E8.2-OXDC fruit proteome revealed that OXDC-responsive proteins involved in metabolism and stress responses represented the most substantially up- and down-regulated categories, respectively, in the transgenic fruit, compared with those of wild-type plants. Collectively, our study provides insights into OXDC-regulated metabolic networks and may provide a widely applicable strategy for enhancing crop nutritional value.

Expression of the minor isoform pea ferredoxin in tobacco alters photosynthetic electron partitioning and enhances cyclic electron flow.

Ferredoxins (Fds) are ferrosulfoproteins that function as low-potential electron carriers in plants. The Fd family is composed of several isoforms that share high sequence homology but differ in functional characteristics. In leaves, at least two isoforms conduct linear and cyclic photosynthetic electron transport around photosystem I, and mounting evidence suggests the existence of at least partial division of duties between these isoforms. To evaluate the contribution of different kinds of Fds to the control of electron fluxes along the photosynthetic electron transport chain, we overexpressed a minor pea (Pisum sativum) Fd isoform (PsFd1) in tobacco (Nicotiana tabacum) plants. The transplastomic OeFd1 plants exhibited variegated leaves and retarded growth and developmental rates. Photosynthetic studies of these plants indicated a reduction in carbon dioxide assimilation rates, photosystem II photochemistry, and linear electron flow. However, the plants showed an increase in nonphotochemical quenching, better control of excitation pressure at photosystem II, and no evidence of photoinhibition, implying a better dynamic regulation to remove excess energy from the photosynthetic electron transport chain. Finally, analysis of P700 redox status during illumination confirmed that the minor pea Fd isoform promotes enhanced cyclic flow around photosystem I. The two novel features of this work are: (1) that Fd levels achieved in transplastomic plants promote an alternative electron partitioning even under greenhouse light growth conditions, a situation that is exacerbated at higher light intensity measurements; and (2) that an alternative, minor Fd isoform has been overexpressed in plants, giving new evidence of labor division among Fd isoforms.

O2-enhanced induction of photosynthesis in rice leaves: the Mehler-ascorbate peroxidase (MAP) pathway drives cyclic electron flow within PSII and cyclic electron flow around PSI

Lowering the oxygen (O2) partial pressure from 21 kPa to 1 kPa delayed the light-dependent increase of the net carbon dioxide (CO2) assimilation rate in rice (Oryza sativa L. cv. Notohikari) leaves. Researching the underlying molecular mechanisms that act before the start of photosynthesis, we established the following facts. First, O2 at 21 kPa enhanced the quantum yield of PSII [Y(II)] and PSI [Y(I)]. More than 90% of Y(II) and Y(I) were not accounted for by O2-dependent electron flow in the Mehler-ascorbate peroxidase (MAP) pathway. Both yields increased further with the start of photosynthesis. Second, O2 enhanced photochemical quenching of chlorophyll (Chl) fluorescence (qL). qL also increased further with the rate of photosynthesis. Third, O2 enhanced the photo-oxidation of P700. Fourth, O2 suppressed the reduction of P700. Fifth, O2 enhanced non-photochemical quenching of Chl fluorescence (NPQ). These results showed that the MAP pathway triggered cyclic electron flow within PSII (CEF-II) and cyclic electron flow around PSI (CEF-I) by inducing ΔpH across thylakoid membranes and oxidizing the plastoquinone pool, before photosynthesis started. We propose that the photosynthetic electron transport system is controlled by the MAP pathway, which would explain the O2-dependent enhancement of the induction of photosynthesis.

WATER STRESS AND NITROGEN MANAGEMENT EFFECTS ON GAS EXCHANGE, WATER RELATIONS, AND WATER USE EFFICIENCY IN WHEAT

A field experiment was conducted over two years to evaluate the gas exchange, water relations, and water use efficiency (WUE) of wheat under different water stress and nitrogen management practices at Crop Physiology Research Area, University of Agriculture, Faisalabad, Pakistan. Four irrigation regimes and four nitrogen levels, i.e., 0, 50, 100, and 150 kg N ha−1 were applied in this study. The photosynthetic gas exchange parameters [net carbon dioxide (CO2) assimilation rate, transpiration rate and stomatal conductance] are remarkably improved by water application and nitrogen (N) nutrition. Plants grown under four irrigation treatments as compared with those grown under one irrigation treatment average stomatal conductance increased from 0.15 to 0.46 μ mol m−2s−1mol during 2002–2003 and 0.18 to 0.33 μ mol m−2s−1mol during the year 2003–2004 and photosynthetic rate from 9.33 to 13.03 μmol CO2 m−2 s−1 and 3.99 to 7.75 μmol CO2 m−2 s−1 during the year 2002–2003 and 2003–2004, respectively. The exposure of plants to water and nitrogen stress lead to noticeable decrease in leaf water potential, osmotic potential and relative water content. Relative water content (RWC) of stressed plants dropped from 98 to 75% with the decrease in number of irrigation and nitrogen nutrition. The higher leaf water potential, and relative water contents were associated with higher photosynthetic rate. Water use efficiency (WUE) reduced with increasing number of irrigations and increased with increasing applied nitrogen at all irrigation levels.

CHARACTERIZATION OF THE PHYSIOLOGICAL RESPONSE OF THE HIGHLY-TOLERANT TOMATO CV. ‘PONCHO NEGRO’ TO SALINITY AND EXCESS BORON

The variety of tomato (Solanum lycopersicum) called ‘Poncho Negro’ by farmers represents an important source of genetic resources of agricultural interest, because it has managed to thrive at levels of salinity and excess B that other varieties of the same species find impossible. This work was conducted under controlled growth conditions in a greenhouse, evaluating and obtaining plant material that served for physiological, chemical, and biochemical determinations. Stress conditions were supplied by irrigation, using different concentrations of sodium chloride (NaCl; 75 and 150 mM) and excess boron (B; 5 and 20 mg L−1). The rate of net carbon dioxide (CO2) assimilation, the quantum efficiency of photosynthesis and the relative water content (RWC) were measured. In addition, B, sodium (Na+), potassium (K+), and calcium (Ca2+), soluble sugars, and proline were quantified. The results suggest that ‘Poncho Negro’ accumulated Na+ mainly in the roots, partly limiting its entry into the aerial parts. In addition, it should be noted that the interaction of B and salinity reduced the movement of Na+ to the leaves. The ability of cv. ‘Poncho Negro’ to minimize leaf Na+ accumulation, accumulate more leaf B than control plants, and maintain its K+ level, when grown with an excess of B, possibly allowed the observed increase in the rate of photosynthesis. In addition, these tomato plants used proline and soluble sugars as osmo-regulators under high-B and saline conditions. Under all stress conditions studied, this variety of tomato was able to regulate its water content, with RWC values of approximately 86%.

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

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

Flooding tolerance of Calophyllum brasiliense Camb. (Clusiaceae): morphological, physiological and growth responses

Calophyllum brasiliense Camb. (Clusiaceae) is a tree of swampy areas of the coastal “Restinga” in southeastern Brazil (a coastal sand-plain scrub and forest formation). To elucidate possible adaptive strategies that enable this species to occupy areas subjected to seasonal or perennial waterlogging, growth characters such as shoot height, biomass production, leaf expansion, new leaf development, stem diameter, carbon dioxide assimilation rate, stomatal conductance, chlorophyll concentration and fluorescence were studied in controls and plants flooded for up to 150 days. Although flooded plants kept incorporating carbon all through the experiment, their assimilation rate and growth rate were lower than control, non-flooded plants. Injuries such as leaf senescence and abscision were not observed but some flooded plants showed signs of leaf chlorosis. In view of its capacity to maintain carbon assimilation and growth during the treatment, C. brasiliense can be classified as flood-tolerant tree. Flooding induced hypertrophy of lenticels, increased stem diameter and development of adventitious roots. These characteristics of C. brasiliense are most probably responsible for its survival and success in naturally seasonally flooded areas, inhospitable environments for most tree species. Reduction in total chlorophyll concentration was probably the main cause of reduced carbon dioxide assimilation rate. Based on the results we recommend C. brasiliense for rehabilitation of native vegetation in flood-prone areas.

Anaerobic sulfur oxidation in the absence of nitrate dominates microbial chemoautotrophy beneath the pelagic chemocline of  the eastern Gotland Basin, Baltic Sea

Oxic-anoxic interfaces harbor significant numbers and activity of chemolithoautotrophic microorganisms, known to oxidize reduced sulfur or nitrogen species. However, measurements of in situ distribution of bulk carbon dioxide (CO(2)) assimilation rates and active autotrophic microorganisms have challenged the common concept that aerobic and denitrifying sulfur oxidizers are the predominant autotrophs in pelagic oxic-anoxic interfaces. Here, we provide a comparative investigation of nutrient, sulfur, and manganese chemistry, microbial biomass distribution, as well as CO(2) fixation at the pelagic redoxcline of the eastern Gotland Basin, Baltic Sea. Opposing gradients of oxygen, nitrate, and sulfide approached the detection limits at the chemocline at 204 m water depth. No overlap of oxygen or nitrate with sulfide was observed, whereas particulate manganese was detected down to 220 m. More than 70% of the bulk dark CO(2) assimilation, totaling 9.3 mmol C m(-2) day(-1), was found in the absence of oxygen, nitrite, and nitrate and could not be stimulated by their addition. Maximum fixation rates of up to 1.1 mumol C L(-1) day(-1) were surprisingly susceptible to altered redox potential or sulfide concentration. These results suggest that novel redox-sensitive pathways of microbial sulfide oxidation could account for a significant fraction of chemolithoautotrophic growth beneath pelagic chemoclines. A mechanism of coupled activity of sulfur-oxidizing and sulfur-reducing microorganisms is proposed.

Physiological responses of red mangroves to the climate in the Florida Everglades

This manuscript reports the findings of physiological studies of red mangrove (Rhizophora mangle L.) conducted from June to August 2001 and from May to June 2003 in the Florida Everglades. In situ physiological measurements were made using environmentally controlled gas exchange systems. The field investigations were carried out to define how regional climate constrains mangrove physiology and ecosystem carbon assimilation. In addition, maximum carboxylation and photosynthetic active radiation (PAR) limited carbon assimilation capacities were investigated during the summer season to evaluate whether ecophysiological models developed for mesophyte plant species can be applied to mangroves. Under summertime conditions in the Florida Everglades, maximum foliar carbon dioxide (CO2) assimilation rates reached 18 μmol CO2 m−2 s−1. Peak molar stomatal conductance to water vapor (H2O) diffusion reached 300 mmol H2O m−2 s−1. Maximum carboxylation and PAR‐limited carbon assimilation rates at the foliage temperature of 30°C attained 76.1 ± 23.4 μmol CO2 m−2 s−1 and 128.1 ± 32.9 μmol (e−) m−2 s−1, respectively. Environmental stressors such as the presence of hypersaline conditions and high solar irradiance loading (>500 W m−2 or >1000 μmoles of photons m−2 s−1 of PAR) imposed sharp reductions in carbon assimilation rates and suppressed stomatal conductance. On the basis of both field observations and model analyses, it is also concluded that existing ecophysiological models need to be modified to consider the influences of hypersaline and high radiational loadings on the physiological responses of red mangroves.

Particle Film Mechanisms of Action That Reduce the Effect of Environmental Stress in ‘Empire’ Apple

Heat stress is a limiting factor of plant productivity throughout the world and kaolin-based particle films (PF) have demonstrated that the reflective nature of the resulting plant surface can increase plant productivity primarily by reducing temperature in fruit, leaf, and canopy. The purpose of this study was to evaluate the environmental mechanisms and related physiological responses of ‘Empire’ apple (Malus ×domestica) gas exchange at the canopy level to PF treatments to identify those parameters key to plant response and increased plant productivity. Trees received either no treatment or season-long applications of a PF treatment and each treatment either received no supplemental irrigation or full replacement of evapotranspiration. Studies were begun in 1998 and continued to 2007. Fruit number and fruit weight were measured in all years. Whole canopy carbon dioxide assimilation rates (A) were measured in apple for a 4-year period to determine the relationship with incoming light and vapor pressure deficit (VPD) levels. The photosynthetic response to the irrigation and PF treatments varied between years as a result of environmental variation in VPD and photosynthetically active radiation (PAR) levels. There was a unique treatment response for PAR levels greater than 1600 μmol·m−2·s−1 in which the combination of PF and irrigation maintained midday A at maximum levels compared with other treatments although A was reduced by increasing VPD. This response indicated that although VPD limited A, the combination of PF and adequate water could maintain maximum A rates at full sun levels during the midday period and minimize the midday depression of A that is commonly observed and reduces the daily carbon accumulation. The increased carbon accumulation during the midday period was likely partitioned to the fruit. Increased fruit weight resulting from the PF treatment, compared with the control, was positively correlated with the growing season air temperature and VPD indicating that as the environment becomes hotter and/or drier, the magnitude of the PF response increased as a result of the reduced leaf and fruit temperature and the subsequent physiological effect. The PF treatments reduced radiation and heat load on exposed leaves enabling them to better regulate leaf temperature and improved the light distribution inside the canopy resulting in increased carbon gain at the whole plant scale. Fruit hue angle was reduced and red color improved by PF treatments in 5 of 10 years. The use of PF may be an effective substitute for evaporative cooling to reduce solar injury and to improve apple quality through increased fruit weight. The results indicate that benefits of PF treatments would occur in agroecosystems with large VPDs and high temperatures and that use of irrigation would further enhance the benefits at high PAR levels.

Microbial community of the water column of the Selenga River-Lake Baikal biogeochemical barrier

The microbial communities of the estuarine zone and the mixing zone of river and lake waters in the Selenga River estuary were studied using the fluorescence in situ hybridization (FISH) method. The microorganisms belonging to the phylogenetic group Gammaproteobacteria were found to predominate in the river estuary, constituting up to 17% of the total bacterial community. Among cultivable microorganisms, organotrophic bacteria were predominant (2040 CFU/ml) in this zone, which results in high rates of microbial production (6.0 microg C/(1 day). The microbial community structure changed with distance from the river estuary; representatives of the Alpha-, Beta-, and Gammaproteobacteria were present in equal proportions; psychrotolerant and oligotrophic bacteria were numerous. The rate of heterotrophic carbon dioxide assimilation decreased to 3.8 microg C/(1 day). At 5-7 km from the river estuary, where the hydrologic, physical, and chemical conditions are similar to those of lake waters, members of the Betaproteobacteria, which are typical of the open waters of Lake Baikal, are the major representatives of planktonic microorganisms.

Potato Maximum Yield as Affected by Crop Parameters and Climatic Factors in Brazil

There is currently a great deal of interest in estimating crop productivity as a function of climatic factors by means of different crop weather models. In this article, an agrometeorological model based on maximum carbon dioxide assimilation rates for C3 plants, fraction of photosynthetically active radiation, air temperature, photoperiod duration, and crop parameters is assessed as to its performance under tropical conditions. Crop parameters include leaf area, harvest index, dry matter content of potato tubers, and crop cycles to estimate potential potato yields. Productivity obtained with the cultivar Itararé, grown with adequate soil water supply conditions at four different sites in the state of São Paulo (Itararé, Piracicaba, Tatuí, and São Manuel), Brazil, was used to test the model. The results revealed excellent performance of the agrometeorological model proposed here with an underestimation of irrigated potato productivity of less than 10%.

Elevated growth temperatures reduce the carbon gain of black spruce [Picea mariana (Mill.) B.S.P.

AbstractWe explored the effect of high‐growth temperatures on a dominant North American boreal tree, black spruce [Picea mariana (Mill.) B.S.P.]. In 2004 and 2005, we grew black spruce at either 22 °C/16 °C day/night temperatures [low temperature (LT)] or 30°/24 °C [high temperature (HT)] and determined how temperature affected growth, leaf morphology, photosynthesis, respiration and thermotolerance. HT spruce were 20% shorter, 58% lighter, and had a 58% lower root : shoot ratio than LT trees. Mortality was negligible in the LT treatment, but up to 14% of HT seedlings died by the end of the growing season. HT seedlings had a higher photosynthetic temperature optimum, but net photosynthesis at growth temperatures was 19–35% lower in HT than LT trees. HT seedlings had both a lower apparent maximum ribulose‐1,5‐bisphosphate carboxylation capacity (Vcmax) and a lower apparent maximum electron transport rate (Jmax) than LT trees, indicating reduced allocation to photosynthetic components. Consistently, HT needles had 26% lower leaf nitrogen content than LT needles. At each measurement temperature, HT seedlings had 20–25% lower respiration rates than LT trees; however, this did not compensate for reduced photosynthetic rates at growth temperature, leading to a greater ratio of dark respiration to net carbon dioxide assimilation rate in HT trees. HT needles had 16% lower concentrations of soluble sugars than LT needles, but similar starch content. Growth at high temperatures increased the thermotolerance of black spruce. HT trees showed less PSII inhibition than LT seedlings and no increase in electrolyte leakage when briefly exposed to 40–57 °C. While trees that develop at high temperatures have enhanced tolerance for brief, extreme heat events, the reduction in root allocation indicates that seedlings will be more susceptible to episodic soil drying and less competitive for belowground resources in future climates of the boreal region.

Responses to temperature and shade in Abies alba seedlings from diverse provenances

Intraspecific variability in responses to temperature and shade was studied at Champenoux, north-eastern France, with seedlings from five Polish provenances of silver fir (Abies alba Mill.). Acclimation of photosynthesis to temperature was investigated in seedlings exposed to 10, 25 and 35°C in a climate chamber for 1 week. During two growth seasons, a population of seedlings was grown in the nursery under four different irradiance regimens: 100, 48, 18 and 8% of natural irradiance. Maximum carboxylation rate (V cmax), maximum light driven electron flow (J max) and maximum net carbon dioxide assimilation rate (A max) measured at 25°C increased with population altitude. One week of exposure to 35°C caused discoloration and massive needle shedding. After 2 years’ acclimation to different levels of irradiance, a significant interprovenance variability was evidenced in growth, total biomass, biomass allocation and photosynthetic performance. This study provided evidence for the existence of functional variation among the examined provenances.

Screening Pecan Cultivars for Drought Tolerance Using Physiological Parameters

Pecan is a riparian species distributed over an area of geographic and climatic variation; such a wide distribution produces exposure to varied environmental conditions, providing a potential for genetic adaptation within the cultivars. Genotypes can be screened in order to obtain more drought tolerant cultivars using indirect screening parameters (chlorophyll fluorescence, osmotic adjustment, and abscisic acid assay) based on physiological responses of plants to abiotic stress conditions. A study was established at Texas A&M University, College Station, using a mixture of fritted clay (Quick dry) and pure sand in 1:1 (by weight) ratio to study the effects of drought on pecan rootstocks. The experiment was set up with the three water potential levels as treatments (–0.033 MPa, –0.1 MPa, –0.3 MPa) in a randomized complete-block design with three blocks. Measurements will include leaf water relations (relative water content, leaf water potential, osmotic adjustments, etc.), gas exchange parameters [net carbon dioxide assimilation rate (A), transpiration rate (E), stomatal conductance (gs)], chlorophyll fluorescence measurements [minimum (Fo), maximum (Fm), and variable fluorescence (Fv), quantum efficiency], water use efficiency, and abscisic acid assay on roots. Statistical analysis systems (SAS) package will be used for analysis. PROC GLM of the SAS will be used for statistical analysis of study involving plant response to water potential levels.