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Understanding plant response and resilience to drought under a high CO2 environment will be crucial to ensure crop production in the future. Sorghum bicolor is a C4 plant that resists drought better than other crops, which could make it a good alternative to be grown under future climatic conditions. Here, we analyse the physiological response of sorghum under 350 ppm CO2 (aCO2) or 700 ppm CO2 (eCO2) with drought (D) or without drought (WW) for 9, 13 and 16 days; as well as its resilience under long (R1: 9D + 7R) or short (R2: 13D + 3R) recovery treatments. Sorghum showed elevated rates of gs under aCO2 and WW, which resulted in a significant decrease in Ψw, gs, E, ΦPSII, Fv’/Fm′ when exposed to drought. Consequently, A was greatly decreased. When re-watered, both re-watering treatments prioritized A recovery by restoring photosynthetic machinery under aCO2, whereas under eCO2 plants required little recovery since plant were hardly affected by drought. However, sorghum growth rate for aboveground organs did not reach control values, indicating a slower long-term recovery. Overall, these results provide information about the resilience of sorghum and its utility as a suitable candidate for the drought episodes of the future. This research was financially supported by grant GRUPO Gobierno Vasco-IT022-16. X. S. Martínez-Goñi is the recipient of a grant from Departamento de Universidades e Investigación del Gobierno Vasco (Spain). A. Robredo was the recipient of a grant from Departamento de Educación, Universidades e Investigación del Gobierno Vasco (Spain).

Main conclusion Growth was not strictly linked to photosynthesis performance under salinity conditions in quinoa. Other key traits, which were varieties-specific, rather than photosynthesis explained better growth performance. Abstract Phenotyping for salinity stress tolerance in quinoa is of great interest to select traits contributing to overall salinity tolerance and to understand the response mechanisms to salinity at a whole plant level. The objective of this work was to dissect the responses of specific traits and analyse relations between these traits to better understand growth response under salinity conditions in quinoa. Growth response to salinity was mostly related to differences in basal values of biomass, being reduced the most in plants with higher basal biomass. Regarding the relationship between growth and specific traits, in Puno variety, better photosynthetic performance was related to a better maintenance of growth. Nevertheless, in the rest of the varieties other traits rather than photosynthesis could better explain growth response. In this way, the development of succulence in F-16 and Collana varieties, also the osmotic adjustment but in smaller dimensions in Pasankalla, Marisma and S-15-15 helped to maintain better growth. Besides, smaller increases of Cl− could have caused a limited nitrate uptake reducing more growth in Vikinga. Ascorbate was considered a key trait as a noticeable fall of it was also related to higher reductions in growth in Titicaca. These results suggest that, due to the genetic variability of quinoa and the complexity of salinity tolerance, no unique and specific traits should be taken into consideration when using phenotyping for analysing salinity tolerance in quinoa.

Soybean (Glycine max L.) future response to elevated [CO] has been shown to differ when inoculated with B. japonicum strains isolated at ambient or elevated [CO]. Plants, inoculated with three Bradyrhizobium strains isolated at different [CO], were grown in chambers at current and elevated [CO] (400 vs. 700 ppm). Together with nodule and leaf metabolomic profile, characterization of nodule N-fixation and exchange between organs were tested through N-labeling analysis. Soybeans inoculated with SFJ14-36 strain (isolated at elevated [CO]) showed a strong metabolic imbalance, at nodule and leaf levels when grown at ambient [CO], probably due to an insufficient supply of N by nodules, as shown by N-labeling. In nodules, due to shortage of photoassimilate, C may be diverted to aspartic acid instead of malate in order to improve the efficiency of the C source sustaining N-fixation. In leaves, photorespiration and respiration were boosted at ambient [CO] in plants inoculated with this strain. Additionally, free phytol, antioxidants, and fatty acid content could be indicate induced senescence due to oxidative stress and lack of nitrogen. Therefore, plants inoculated with Bradyrhizobium strain isolated at elevated [CO] may have lost their capacity to form effective symbiosis at ambient [CO] and that was translated at whole plant level through metabolic impairment., This work was financially supported by the following grants: GRUPO Gobierno Vasco IT1022-16 and projects 32-2016-00043, 37-2017-00047, and 000049-IDA2019-38 from the Economic Development and Infrastructures Department of the Basque Country, Spain. DS was a recipient of a Ph.D. grant supported by the Public University of Navarra. AS-S was partially supported by a postdoctoral fellowship granted by the Education, and Linguistic Policy Department of the Basque Country, Spain and the Alabama Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, United States Department of Agriculture. Technical support by Azucena González, Phytotron Service, SGIker (UPV/EHU) is gratefully acknowledged.

The response of plant species to external factors depends partly on the interaction with the environment and with the other species that coexist in the same ecosystem. Several studies have investigated the main traits that determine the competitive capacity of plant species, and although the relevance of the traits is not clear, traits both from belowground and aboveground have been observed. In this paper, we grew Trifolium pratense and Agrostis capillaris in intra- and interspecific competition, analyzing the photosynthetic metabolism and nitrogen uptake, among other variables. The results indicated that T. pratense possesses better competition ability due to the higher competitive performance for soil resources compared to A. capillaris, explained by a higher root biomass and a higher nitrogen uptake rate in the former than in the latter. These traits permitted T. pratense to show higher photosynthetic rate than A. capillaris when both species were grown in mixture. Furthermore, the interspecific competition provoked A. capillaris to activate its antioxidant metabolism, through SOD activity, to detoxify the reactive oxygen species generated due to its lower capacity for using the photochemical energy absorbed. In this experiment, we conclude that the competitiveness seems to be more related with soil resources competition than with light competition, and that the photosynthetic rate decline in A. capillaris is more a secondary effect as a consequence of nitrogen limitation.

Climate change can have major consequences for grassland communities since the different species of the community utilize different mechanisms for adaptation to drought and elevated CO2 levels. In addition, contradictory data exist when the combined effects of elevated CO2 and drought are analyzed because the soil water content is not usually similar between CO2 concentrations. Thus, the objectives of this work have been to examine the effect of water stress on plant water relations in two grassland species (Trifolium pratense and Agrostis capillaris), analyzing the possible differences between the two species when soil water content is equal in all treatments, and to elucidate if development under elevated CO2 increases drought tolerance and if so, which are the underlying mechanisms. At ambient CO2, when soil volumetric water content was 15%, both species decreased their water potential in order to continue taking up water. Trifolium pratense performed osmotic adjustment, while Agrostis capillaris decreased the rigidity of its cell wall; moreover, both species increased the root to shoot ratio and decreased leaf area. However, these mechanisms were not sufficient to maintain cell turgor. Elevated CO2 partially mitigated the negative impact of drought on turgor potential in Trifolium pratense through a higher osmotic adjustment and root to shoot ratio and in Agrostis capillaris through a higher leaf relative water content caused by higher hydraulic conductance, but the impact of drought was not mitigated in either species by higher soil water conservation.

Both salt stress and high CO2 level, besides influencing secondary metabolism, can affect oxidative status of plants mainly acting in an opposite way with salinity provoking oxidative stress and elevated CO2 alleviating it. The aim of the present work was to study the changes in the composition of phenolic acids and flavonoids as well as in the antioxidant activity in two differently pigmented lettuce cvs (green or red leaf) when submitted to salinity (200 mM NaCl) or elevated CO2 (700 ppm) or to their combination in order to evaluate how a future global change can affect lettuce quality. Following treatments, the red cv. always maintained higher levels of antioxidant secondary metabolites as well as antioxidant activity, proving to be more responsive to altered environmental conditions than the green one. Overall, these results suggest that the application of moderate salinity or elevated CO2, alone or in combination, can induce the production of some phenolics that increase the health benefits of lettuce. In particular, moderate salinity was able to induce the synthesis of the flavonoids quercetin, quercetin-3-O-glucoside, quercetin-3-O-glucuronide and quercitrin. Phenolics-enrichment as well as a higher antioxidant capacity were also observed under high CO2 with the red lettuce accumulating cyanidin, free chlorogenic acid, conjugated caffeic and ferulic acid as well as quercetin, quercetin-3-O-glucoside, quercetin-3-O-glucuronide, luteolin-7-O-glucoside, rutin, quercitrin and kaempferol. When salinity was present in combination with elevated CO2, reduction in yield was prevented and a higher presence of phenolic compounds, in particular luteolin, was observed compared to salinity alone.

Anion-exchange FPLC has been used to resolve the isoforms of glutamine synthetase (GS, EC 6.3.1.2) from Zea mays mesophyll (MC) and bundle sheath cells (BSC). Two different isoforms were detected in both types of photosynthetic cells. The predominantly active isoform was GS1 (61%) in MC and GS2 (67%) in BSC. The relative contribution of GS1 and GS2 to the overall GS activity in BSC in maize here reported resembles the proportion described for most C3 plants. Differences among these isoforms in terms of their susceptibility to phosphinothricin (PPT), an analogue of glutamate and known inhibitor of GS, were found. The GS1 isoenzyme from MC was the most sensitive form, being inhibited by 50% at approximately 2.0 μM DL-PPT, whereas the GS2 from BSC presented the highest tolerance to the inhibitor (I50=30 μM). The transferase-to-semibiosynthetic activity ratio for the MC isoforms, which was higher than the ratio for the BSC isoforms, and the differences shown by the isoforms in susceptibility to PPT predict important differences in the biochemical properties and regulation of GS isoenzymes. In this regard, the cytoplasmic isoenzymes, and especially the one in MC, due to its relatively high contribution to mesophyll cell GS activity, could play a vital role in nitrogen metabolism in maize.

Over the past 10 years, it has been demonstrated in the literature that legume responses to elevated [CO2], whether positive, negative, or null, are in part dependent on the Rhizobium species and genotypes that establish symbiosis with the plant. However, all the strains used in these past experiments were isolated in field conditions at ambient [CO2]. We studied for first time the fitness response of soybean inoculated with a Rhizobium strain that has been previously isolated from nodules of plants grown at elevated [CO2] in field conditions at a FACE site. In experiments developed in controlled growth chambers, and in the field under ambient [CO2], the plants inoculated with the strain isolated at elevated [CO2] showed similar response as plants without inoculation. We hypothesize that deficient nodulation may be associated with a change in root exudates caused by the change in [CO2]. This study showed that the strains isolated in nodules at elevated [CO2] are not capable of properly nodulating soybean plants grown at ambient [CO2] and that the origin of strains do not ensure the performance of plants under the same conditions. However, more research is needed in order to understand how changes in environmental conditions can affect the symbiotic relationship and ultimately how we can improve plant fitness in a changeable world., A. Sanz-Sáez was the recipient of a post-doctoral fellowship granted by the Education, Linguistic Policy, and Education Department of the Basque Country, Spain. This research was financially supported by the following grant: GRUPO GobiernoVasco-IT1022-16.

Human activities enhance the atmospheric CO2 concentration and modify climatic patterns, which could change the growth and quality of plant materials, as well as their subsequent decomposition, thus altering stream ecosystem functioning. These effects could be modulated by interactions between plant species differing in biological traits and competitive capacity. We cultivated the forb Trifolium pratense and the grass Agrostis capillaris under different CO2 concentration (ambient or elevated), water availability (control or drought), and competition (monoculture or mixture). The material thus grown was conditioned in a stream for microbial colonization, and its subsequent decomposition was measured in laboratory microcosms. Elevated CO2 reduced the quality of T. pratense but not that of A. capillaris. Water shortage limited plant quality but did not interact with CO2 concentration. Interspecific competition only affected nitrogen concentration in A. capillaris. Elevated CO2 did not affect decomposition rate, and A. capillaris, the species richer in nutrients, decomposed more slowly. Our results showed that the decomposition rates of plant materials grown under elevated CO2 are difficult to predict due to species-specific responses and interactions with other factors.

The present study was focused on lettuce, a widely consumed leafy vegetable for the large number of healthy phenolic compounds. Two differently-pigmented lettuce cultivars, i.e. an acyanic-green leaf cv. and an anthocyanic-red one, were grown under high light intensity or elevated CO2 or both in order to evaluate how environmental conditions may affect the production of secondary phenolic metabolites and, thus, lettuce quality. Mild light stress imposed for a short time under ambient or elevated CO2 concentration increased phenolics compounds as well as antioxidant capacity in both lettuce cvs, indicating how the cultivation practice could enhance the health-promoting benefits of lettuce. The phenolic profile depended on pigmentation and the anthocyanic-red cv. always maintained a higher phenolic amount as well as antioxidant capacity than the acyanic-green one. In particular, quercetin, quercetin-3-O-glucuronide, kaempferol, quercitrin and rutin accumulated under high light or high CO2 in the anthocyanic-red cv., whereas cyanidin derivatives were responsive to mild light stress, both at ambient and elevated CO2. In both cvs total free and conjugated phenolic acids maintained higher values under all altered environmental conditions, whereas luteolin reached significant amounts when both stresses were administered together, indicating, in this last case, that the enzymatic regulation of the flavonoid synthesis could be differently affected, the synthesis of flavones being favored.

The interest of improving yield and quality of vegetables has increased in the recent years due to their benefits on human health. The aim of this study was to investigate if salt stress and elevated CO2 applied alone or in combination can improve the growth and nutritional quality of two differently pigmented (green and red) Lactuca sativa (L.) cultivars. Seedlings grown under ambient (400 ± 20 μmol mol−1) or elevated (700 ± 20 μmol mol−1) CO2 concentration for 35 days were subsequently supplied with 0 or 200 mM NaCl for 4 days. Then, biomass production, antioxidant capacity and minerals, nitrates, carbohydrates, proteins and hydrophilic and lipophilic antioxidant concentrations were measured. Red-pigmented lettuce showed higher nutritional quality than green-pigmented lettuce due to higher concentrations of Ca, P, Zn, and higher concentrations of lipophilic (Chl-a, Chl-b, and carotenoids) and hydrophilic (reduced ascorbate, total phenolics, and anthocyanins) antioxidants. Under elevated CO2, both lettuce cultivars increased the uptake of almost all minerals to adjust to the higher growth rates, reaching similar concentrations to the ones detected under ambient CO2; only Mg and Fe were reduced. Furthermore, the antioxidant capacity, Chl-b and glutathione concentration increased in both cultivars. Under salt stress, the N and K concentrations decreased in both cultivars, while Ca, Mg, and P concentrations were also reduced in the red cultivar, probably due to a blockage in the uptake of these nutrients. Both lipophilic and hydrophilic antioxidant compounds increased in order to defend against the oxidative stress caused by an imbalance in ATP and NADPH production and consumption. The magnitude of the response was dependent on the cultivar. When salt stress was imposed under elevated CO2, each cultivar responded differently. The red cultivar seemed to gain a greater advantage from elevated CO2 than the green cultivar because it better adjusted both mineral uptake and antioxidant metabolism. We conclude that elevated CO2 alone or in combination with short environmental salt stress permits us to increase the nutritional quality (increasing the concentration of some minerals and antioxidants) of lettuce without yield losses or even increasing production; however, the choice of the best growing conditions is dependent on the attributes we wish to improve.

This study presents changes in the nutraceutical quality and biomass production of two differently pigmented Lactuca sativa (L.) cultivars grown under various combinations of high light (700 μmol photons m−2 s−1) and elevated CO2 (700 μmol mol−1) conditions. In an ambient CO2 atmosphere, high light intensity increased biomass production in the green cultivar (Blonde of Paris Batavia) but not in the red cultivar (Oak Leaf). In both cultivars, high light intensity increased the concentration of soluble proteins and sugars. High light intensities also increased the levels of carotenoids, glutathione, total phenols and anthocyanins, which was most likely due to oxidative stress. Conversely, the levels of almost all minerals remained unchanged compared with the values detected for control light intensity and ambient CO2 conditions. When a high light intensity was applied at elevated CO2 conditions, the biomass production increased in both cultivars. The concentrations of minerals (except Fe and Mg), glutathione and ascorbate remained constant compared with the high light and ambient CO2 conditions, which indicated that these components and biomass accumulated at comparable rates. The decreases in the levels of Chl-a, carotenoids, total phenols and anthocyanins in response to elevated CO2 levels at high light conditions could indicate a relief of oxidative stress due to an improved balance between ATP and NADPH production and consumption at elevated CO2 levels. These results demonstrate that the biomass production and the nutritional quality of lettuce can be improved, but the response is cultivar-specific, and the choice of the best cultivation practice (using high light intensity alone or in combination with elevated CO2 levels) depends on the attributes that are targeted for improvement.

The present study was focused on lettuce, a widely consumed leafy vegetable for the large number of healthy phenolic compounds. Two differently-pigmented lettuce cultivars, i.e. an acyanic-green leaf cv. and an anthocyanic-red one, were grown under high light intensity or elevated CO

Climate change can have major consequences for grassland communities since the different species of the community utilize different mechanisms for adaptation to drought and elevated CO

Nitrogen (N) is an important regulator of photosynthetic carbon (C) flow in plants, and an adequate balance between N and C metabolism is needed for correct plant development. However, an excessive N supply can alter this balance and cause changes in specific organic compounds associated with primary and secondary metabolism, including plant growth regulators. In previous work, we observed that high nitrate supply (15 mM) to maize plants led to a decrease in leaf expansion and overall biomass production, when compared with low nitrate supply (5 mM). Thus, the aim of this work is to study how overdoses of nitrate can affect photosynthesis and plant development. The results show that high nitrate doses greatly increased amino acid production, which led to a decrease in the concentration of 2-oxoglutarate, the main source of C skeletons for N assimilation. The concentration of 1-aminocyclopropane-1-carboxylic acid (and possibly its product, ethylene) also rose in high nitrate plants, leading to a decrease in leaf expansion, reducing the demand for photoassimilates by the growing tissues and causing the accumulation of sugars in source leaves. This accumulation of sugars, together with the decrease in 2-oxoglutarate levels and the reduction in chlorophyll concentration, decreased plant photosynthetic rates. This work provides new insights into how high nitrate concentration alters the balance between C and N metabolism, reducing photosynthetic rates and disrupting whole plant development. These findings are particularly relevant since negative effects of nitrate in contexts other than root growth have rarely been studied.

The effects of elevated CO2 and drought on ecophysiological parameters in grassland species have been examined, but few studies have investigated the effect of competition on those parameters under climate change conditions. The objective of this study was to determine the effect of elevated CO2 and drought on the response of plant water relations, gas exchange, chlorophyll a fluorescence and aboveground biomass in four grassland species, as well as to assess whether the type of competition modulates that response. Elevated CO2 in well-watered conditions increased aboveground biomass by augmenting CO2 assimilation. Drought reduced biomass by reducing CO2 assimilation rate via stomatal limitation and, when drought was more severe, also non-stomatal limitation. When plants were grown under the combined conditions of elevated CO2 and drought, drought limitation observed under ambient CO2 was reduced, permitting higher CO2 assimilation and consequently reducing the observed decrease in aboveground biomass. The response to climate change was species-specific and dependent on the type of competition. Thus, the response to elevated CO2 in well-watered grasses was higher in monoculture than in mixture, while it was higher in mixture compared to monoculture for forbs. On the other hand, forbs were more affected than grasses by drought in monoculture, while in mixture the negative effect of drought was higher in grasses than in forbs, due to a lower capacity to acquire water and mineral nutrients. These differences in species-level growth responses to CO2 and drought may lead to changes in the composition and biodiversity of the grassland plant community in future climate conditions.

The objective of this study was to determine the response of barley's carbon isotope composition and other physiological parameters to the interaction of salt stress and elevated CO 2 levels, and the usefulness of carbon isotope discrimination (Δ 13 C) as indicative of the functional performance of barley ( Hordeum vulgare L.). Barley plants were grown under ambient (350 μmol mol −1 ) and elevated (700 μmol mol −1 ) CO 2 conditions and subjected to salt stress (0, 80, 160, and 240 mM NaCl) for 14 days. Elevated CO 2 levels increased biomass production, water use efficiency and the photosynthetic rate, although this parameter was partly acclimated to elevated CO 2 levels. Salt stress decreased this acclimation response because it enhanced the sink strength of the plant. Elevated CO 2 significantly decreased the 13 C isotopic composition (δ 13 C) in all plant organs; however, the ratio of δ 13 C between the root and the leaf was increased, indicating a higher allocation of δ 13 C to the below-ground parts. Conversely, salt stress increased plant δ 13 C, showing differences between plant organs. From the strong correlations between Δ 13 C and biomass production, the photosynthetic rate or water use efficiency both at ambient and elevated CO 2 , we concluded that Δ 13 C is a useful parameter for evaluating leaf and whole plant responses to salinity and can provide an integrated index of processes to understand the mechanisms underlying salt tolerance of barley both under current and future environmental CO 2 conditions.

The effects of elevated CO 2 on the content of several nutrients in plants have been well studied, but few studies have investigated plant nutrient dynamics under future environmental conditions, which are expected to include elevated CO 2 and elevated soil salt concentrations. This study investigated whether high salt and CO 2 conditions, singly or in combination, might affect nutrient dynamics, and the underlying mechanisms. We measured macro- and micronutrient uptake and translocation rates, nutrient content and concentrations in whole seedlings and in each plant organ. We estimated whole-plant nutrient use efficiencies in barley subjected to 0, 80, 160, or 240 mM NaCl and grown at either 350 (ambient) or 700 (elevated) μmol mol −1 CO 2 . Under non-saline conditions, plants grown at elevated CO 2 adjusted their root size and activity to change nutrient uptake and transport efficiency in response to the demand for a given nutrient. Under high saline conditions, salt stress reduced K, Ca, N, B, and S uptake rates and concentrations in tissues, which caused growth reduction. Nevertheless, barley had the ability to increase the selectivity of K over Na, and Ca over Na. Under combined conditions of salt stress and elevated CO 2 , barley seedlings were able to maintain higher uptake and translocation rates of almost all nutrients. This ability allowed the plants to adapt to higher demands under elevated CO 2 ; they could grow more rapidly by allocating more C to root growth and by increasing active nutrient uptake and translocation. Our results indicated that salinity generally increased nutrient use efficiency under both CO 2 conditions. However, we found no consistent evidence that nutrient use efficiency was affected by CO 2 concentration, either under non-saline or saline conditions.

As a consequence of the increasing importance of vegetables in the human diet, there is an interest in enhancing both the productivity and quality of vegetables. A number of factors, including plant genotype and environmental growing conditions, can impact the production and quality of vegetables. The objective of this study was to determine whether elevated CO2, salinity, or high light treatments assayed individually, or salinity or high light in combination with elevated CO2, increased biomass production and antioxidant capacity in two lettuce cultivars. Elevated CO2 and its combination with salinity or high light increased biomass production in both cultivars, while high light treatment alone increased production in green-leaf lettuce but not in red-leaf lettuce. On the other hand, elevated CO2 and its combination with salinity or high light increased the antioxidant capacity of both cultivars, while high light treatment alone increased the antioxidant capacity of red-leaf lettuce, but not of green-leaf lettuce.

The future environment will exhibit increases in soil salt concentrations and atmospheric CO2. In general, plant growth is inhibited by salt stress and stimulated by elevated CO2. This study investigated whether elevated CO2 could improve plant growth under salt stress and the mechanisms involved. We measured functional and morphological components of growth in barley (cv. Iranis) subjected to 0, 80, 160, or 240 mM NaCl and grown at either 350 (ambient) or 700 (elevated) μmol mol−1 CO2. Under nonsaline conditions, elevated CO2 stimulated growth by increasing the relative growth rate (RGR). Maximum CO2 stimulation was observed within the first 10 days of development, before the start of the salt treatment. Afterwards, salt stress caused reductions in biomass production and RGR by decreasing the photosynthetic rate and increasing the respiration rate; this resulted in a reduced net assimilation rate (functional component). In addition, salt stress caused nutritional imbalances, which reduced the leaf expansion capacity, and changed the root-to-shoot ratio. This resulted in reductions in the specific leaf area and leaf weight ratio (morphological components). However, the functional component became more relevant with increasing salt stress. Under elevated CO2 conditions, salt stress inhibited growth less than that observed at ambient CO2. This occurred because (1) more dry biomass was synthesized for a given leaf area due to higher photosynthetic rates, and (2) greater leaf area and root biomass were maintained for photosynthesis and water and mineral uptake, respectively.

Both salt stress and high carbon dioxide (CO2) levels can affect plant nitrogen (N) metabolism by acting in parallel, decreasing N metabolism; or acting in opposite directions, with salt stress decreasing N metabolism and elevated CO2 levels enhancing it. The objective of this work was to analyse the effect of salinity on N acquisition, distribution, and assimilation, the consequences of these effects on growth in barley (Hordeum vulgare L., cv. Iranis), and the possible effects on these processes provoked by elevated CO2 levels. Several steps of N metabolism were studied in H. vulgare plants exposed to 0, 80, 160, or 240 mM NaCl under ambient (350 μmol mol−1) or elevated (700 μmol mol−1) CO2. Salt stress reduced the N uptake (NUR) and translocation (NTR) rates and nitrate reductase (EC 1.7.1.1) activity, altering plant N isotope discrimination (Δ15N). Although salt stress increased glutamine synthetase (EC 6.3.1.2) activity, N and protein content, and photosynthetic nitrogen use efficiency decreased. The decrease in nitrate reductase activity was related to decreases in NUR and NTR, while Δ15N correlated with the NUR and with the nitrate reductase activity. Under mild salt stress, N metabolism was better maintained under elevated CO2 levels than under ambient CO2 levels, since NUR, NTR, photosynthetic nitrogen use efficiency, and nitrate reductase activity were less affected, yielding lower Δ15N and higher growth. In addition, growth was negatively correlated with Δ15N indicating that the Δ15N determination may allow the estimation of barley growth. As a consequence of all these results, barley plants subjected to elevated CO2 levels will likely overcome mild saline conditions because of their capacity to maintain efficiency in N metabolism.

Both salt stress and high CO

The future environment may be altered by high concentrations of salt in the soil and elevated [CO(2)] in the atmosphere. These have opposite effects on photosynthesis. Generally, salt stress inhibits photosynthesis by stomatal and non-stomatal mechanisms; in contrast, elevated [CO(2)] stimulates photosynthesis by increasing CO(2) availability in the Rubisco carboxylating site and by reducing photorespiration. However, few studies have focused on the interactive effects of these factors on photosynthesis. To elucidate this knowledge gap, we grew the barley plant, Hordeum vulgare (cv. Iranis), with and without salt stress at either ambient or elevated atmospheric [CO(2)] (350 or 700 μmol mol(-1) CO(2), respectively). We measured growth, several photosynthetic and fluorescence parameters, and carbohydrate content. Under saline conditions, the photosynthetic rate decreased, mostly because of stomatal limitations. Increasing salinity progressively increased metabolic (photochemical and biochemical) limitation; this included an increase in non-photochemical quenching and a reduction in the PSII quantum yield. When salinity was combined with elevated CO(2), the rate of CO(2) diffusion to the carboxylating site increased, despite lower stomatal and internal conductance. The greater CO(2) availability increased the electron sink capacity, which alleviated the salt-induced metabolic limitations on the photosynthetic rate. Consequently, elevated CO(2) partially mitigated the saline effects on photosynthesis by maintaining favorable biochemistry and photochemistry in barley leaves.

We evaluated the combined effects of elevated CO2 and water availability on photosynthesis in barley. Soil and plant water content decreased with water stress, but less under elevated CO2 concentration (EC) compared with ambient CO2 concentration (AC). During water stress, stomatal conductance, carboxylation rate, RuBP regeneration, and the rate of triose phosphate utilisation (TPU) were decreased but less when plants grew under EC. Drought treatments caused only a slight effect on maximum photochemical efficiency (variable to maximum fluorescence ratio, Fv/Fm), whereas the actual quantum yield (ΦPS2), maximum electron transport rate (Jmax) and photochemical quenching (qP) were decreased and the non photochemical quenching (NPQ) was enhanced. Under water deficit, the allocation of electrons to CO2 assimilation was diminished by 49 % at AC and by 26 % at EC while the allocation to O2 reduction was increased by 15 % at AC and by 12 % at EC.

With the changing climate, plants will be facing increasingly harsh environmental conditions marked by elevated salinity in the soils and elevated concentrations of CO 2 in the atmosphere. These two factors have opposite effects on water status in plants. Therefore, our objective was to determine the interaction between these two factors and to determine whether elevated [CO 2 ] might alleviate the adverse effects of salt stress on water status in two barley cultivars, Alpha and Iranis, by studying their relative water content and their water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency. Both cultivars maintained their water status under salt stress, increasing water use efficiency and conserving a high relative water content by (1) reducing water potential via passive dehydration and active osmotic adjustment and (2) decreasing transpiration through stomatal closure and reducing hydraulic conductance. Iranis showed a greater capacity to achieve osmotic adjustment than Alpha. Under the combined conditions of salt-stress and elevated [CO 2 ], both cultivars (1) achieved osmotic adjustment to a greater extent than at ambient [CO 2 ], likely due to elevated rates of photosynthesis, and (2) decreased passive dehydration by stomatal closure, thereby maintaining a greater turgor potential, relative water content, and water use efficiency. Therefore, we found an interaction between salt stress and elevated [CO 2 ] with regard to water status in plants and found that elevated [CO 2 ] is associated with improved water status of salt-stressed barley plants.

We analysed the impact of elevated CO2 on water relations, water use efficiency and photosynthetic gas exchange in barley (Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO2]. Elevated CO2 had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO2 concentrations. The values of relative water content, water potential and osmotic potential were higher under elevated CO2 during the entire drought period. The better water status of water-limited plants grown at elevated CO2 was the result of stomatal control rather than of osmotic adjustment. Despite the low stomatal conductance produced by elevated CO2, net photosynthesis was higher under elevated than ambient CO2 concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO2. The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO2, increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants. Thus, the metabolism of barley plants grown under elevated CO2 and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit.

Nitrous oxide (N 2 O) is involved in both ozone destruction and global warming. In agricultural soils it is produced by nitrification and denitrification mainly after fertilization. Nitrification inhibitors have been proposed as one of the management tools for the reduction of the potential hazards of fertilizer-derived N 2 O. Addition of nitrification inhibitors to fertilizers maintains soil N in ammonium form, thereby gaseous N losses by nitrification and denitrification are less likely to occur and there is increased N utilization by the sward. We present a study aimed to evaluate the effectiveness of the nitrification inhibitor dicyandiamide (DCD) and of the slurry additive Actilith F2 on N 2 O emissions following application of calcium ammonium nitrate or cattle slurry to a mixed clover/ryegrass sward in the Basque Country. The results indicate that large differences in N 2 O emission occur depending on fertilizer type and the presence or absence of a nitrification inhibitor. There is considerable scope for immediate reduction of emissions by applying DCD with calcium ammonium nitrate or cattle slurry. DCD, applied at 25 kg ha -1 , reduced the amount of N lost as N 2 O by 60% and 42% when applied with cattle slurry and calcium ammonium nitrate, respectively. Actilith F2 did not reduce N 2 O emissions and it produced a long lasting mineralization of previously immobilized added N.

This study is concerned with the effects of storage conditions, planting shock and water availability at planting sites on nitrogen assimilation in Pinus radiata. Seedlings were stored for 1, 8 or 15 days at 4 or 10 °C with or without soil around the roots and afterwards planted in well-irrigated or dry soils. Our analysis of protein content and the activities of glutamine synthetase (GS; EC 6.3.1.2) and glutamate dehydrogenase (GDH; EC 1.4.1.2) showed that, as storage duration increased, there was a gradual reduction in soluble protein content and an inhibition of GS, whereas GDH activity increased. Thus there appears to be a close relationship between desiccation and changes in nitrogen assimilation. These effects were more pronounced in bare-root seedlings than in seedlings with soil around the roots, indicating that the rooting-plug medium provides protection against desiccation. Seedlings were susceptible to planting shock even under well-watered conditions. Drought enhanced the severity of planting shock and both protein content (80%) and GS activity (75%) were drastically reduced when water was withheld, whereas GDH activity increased by more than 170%. Thus, the decline in needle relative water content (RWC) appeared closely related to a decrease in protein content and GS activity, and on the other hand, to an increase in GDH. There was a remarkable recovery of these parameters after rewatering, depending however, on stock quality at the moment of planting.

The capacity of radiata pine seedlings to overcome planting shock in wet and dry conditions and their dependence on previous history was analysed by studying post-planting resumption of gas exchange and photochemical reactions, and survival 2 months later. Even under well-irrigated soil conditions, seedlings showed the effects of stress: gas exchange was reduced, but a clear difference between soil-plugged (PR) seedlings and bare-root (BR) seedlings was observed. Drought enhanced the severity of photosynthesis deprivation. Photochemical reactions, analysed by chlorophyll a fluorescence parameters, were not affected by planting shock in conditions of available soil water, but altered dramatically when drought stress was raised, suggesting structural damage of photosynthetic machinery. Despite the dramatic sensitivity of radiata pine to water availability, rewatering produced remarkable recovery, indicating good photosynthetic components repair capacity, which depended, however, on stock quality at the moment of planting. The ability of radiata pine to cope with drought in terms of post-planting performance depended on both storage conditions and water availability at the planting site. These findings provide information for tree physiologists and foresters as to how the management of radiata pine seedlings before planting can affect post-planting performance potential under wet or dry environmental conditions.

International audience; We examined the post-planting effect of storage on the plant quality and initial survival potential of bare-root (BR) and soil-plugged root (PR) of radiata pine seedlings outplanted in wet and dry soils. Seedlings were subjected to planting shock even under well-watered conditions. Although the transpiration rate declined, indicating closure of stomata, water stress occurred as evidenced by the decline in relative water content (RWC) and in the leaf water potential. More than 80% of the PR seedlings and only 20% of BR seedlings transplanted in well-watered regimen survived. Regardless of storage conditions and duration, seedlings planted under water shortage with a RWC < 50% did not survive. According to these results, it is not advisable to store radiata pine seedlings for more than 1 week when planting is under drought conditions even if the seedlings have soil around roots (PR seedlings).; Effet des conditions de stockage sur l'état hydrique et l'établissement de plantules de Pinus radiata D. Don avec motte et à racines nues. L'étude a porté sur l'effet du stockage sur la qualité du plant et sur les potentialités de survie initiale de plantules de Pinus radiata D. Don à racine nue (BR) et avec motte (PR), replantées dans des sols humides et secs. Les plantules ont subi un stress de transplantation, même dans des conditions hydriques optimales. Malgré la diminution de la transpiration, signe d'une fermeture stomatique, un stress hydrique est intervenu, comme en témoigne la baisse tant du contenu hydrique relatif (RWC) que du potentiel hydrique. Plus de 80 % des plantules PR et uniquement 20 % des plantules BR ont survécu à leur transplantation dans des conditions hydriques optimales. Indépendamment des conditions de stockage et de la durée de celui-ci, les plantules mises en place sous déficit hydrique, avec un RWC inférieur à 50 %, n'ont pas survécu. Conformément à ces résultats, le stockage de plantules de Pinus radiata pour des périodes supérieures à une semaine est déconseillé lorsque la transplantation se fait sous déficit hydrique, même lorsqu'il s'agit de plantules avec motte (PR).

Post-storage gas exchange parameters like CO2 assimilation, stomatal conductance, transpiration, water use efficiency and intercellular CO2 concentrations, together with several chlorophyll a fluorescence parameters: F o, F v, F v/F m, F m/F o and F v/F o were examined in radiata pine (Pinus radiata D. Don) seedlings that were stored for 1, 8 or 15 days at 4° or 10°C with or without soil around the roots. Results were analysed in relation to post-storage water potential and electrolyte leakage in order to forecast their vitality (root growth potential) following cold storage, and post-planting survival potential under optimal conditions. During storage at 4° and 10°C, photosynthesis was reduced, being more pronounced in bare-root seedlings than in seedlings with soil around the roots. The depletion of CO2 assimilation seemed not to be solely a stomatal effect as effects on chloroplasts contributed to this photosynthetic inhibition. Thus, the fall in the ratios F v/F m, F v/F o and F m/F o indicated photochemical apparatus damage during storage. Photosynthetic rate was positively correlated with the root growth index and new root length showing that new root growth is dependent primarily on current photosynthesis. Pre-planting exposure of bare-root radiata pine seedlings to temperatures of 10°C for more than 24 h during transportation or storage is not recommended.

The photorespiration cycle plays an important role in avoiding carbon drainage from the Calvin cycle and in protecting plants from photoinhibition. The role of photorespiration is frequently underestimated in C(4) plants, since these are characterized by low photorespiration rates. The aim of this work was to study the relationship between CO(2) assimilation, PS II photochemistry and the xanthophyll cycle when the photorespiratory cycle is disrupted in Zea mays L. To this end, the photorespiration inhibitor phosphinothricin (PPT) was applied individually or together with the photorespiratory C(2) acids, glycolate and glyoxylate to maize leaves. Application of PPT alone led to the inhibition of CO(2) assimilation. Moreover, feeding with glycolate or glyoxylate enhanced the effect of PPT on CO(2) assimilation. Our results confirm that the avoidance of the accumulation of the photorespiratory metabolites glycolate, glyoxylate or phosphoglycolate, is of vital importance for coordinated functioning between the glycolate pathway and CO(2) assimilation. Relatively early changes in PS II photochemistry also took place when the photorespiratory cycle was interrupted. Thus, fluorescence photochemical quenching (qP) was slightly reduced (10%) due to the application of PPT together with glycolate or glyoxylate. A decrease in the efficiency of excitation-energy capture by open PS II reaction centres (F'v/F'm) and an increase in thermal energy dissipation (non-photochemical quenching, NPQ) were also measured. These observations are consistent with a limitation of activity of the Calvin cycle and a subsequent lower demand for reduction equivalents. The increase in NPQ is discussed on the basis of changes in the xanthophyll cycle in maize, which seem to provide a limited protective role to avoid photoinhibition when the glycolate pathway is blocked. We conclude that C(2) photorespiratory acids can act as physiological regulators between the photorespiratory pathway and the Calvin cycle in maize.

We have investigated the effect of storage conditions (duration: 1, 8 or 15 days; temperature: 4°C or 10°C) and root coverage [bare root (BR) or soil-plugged root (PR)] on the water status, electrolyte leakage and root growth potential (number of new roots and new root length) of radiata pine (Pinus radiata D. Don) seedlings. We have also examined the effects that storage causes on plant quality and initial survival potential and their usefulness for detecting physiological damage to seedlings. We observed a gradual decrease of seedling water status and an increase in electrolyte leakage, both in root and shoot, with duration of storage, the latter indicating damage to membranes. Both storage temperature and duration influenced the ability of radiata pine seedlings to initiate and elongate new roots. The effect was more pronounced in BR than in container seedlings, suggesting that the rooting-plug medium provides protection against desiccation. The close relationship (r=0.923, P

Summary In this work we investigated the sequential effects of simulated acid rain and drought on water relations of radiata pine ( Pinus radiata D. Don) seedlings. Whole seedlings were firstly subjected during 1 month to acid rain, pH 3.0, applied 5 times a week at 3 mm precipitation equivalent per day. Afterwards, drought treatment was applied by withholding water for 20 days and subsequent rewatering for 6 days to analyze the sequential effect of acid precipitation and drought. Water status parameters were determined before the initiation of acid rain treatment and within 3 weeks after the end of treatment. Acid rain treatment in well-watered plants did not affect either water potential or relative water content, whereas a marked effect on electrolyte leakage from the needles and on instantaneous transpiration was recorded. Drought treatment had great effects on leaf water potential (-2.5 MPa), RWC (50 % diminution), membrane permeability (340 % increase) and transpiration rate (25 % inhibition). Interactions involving acid precipitation and drought led to much greater impacts on all of the parameters analyzed. We conclude that although acid rain had slight, if any, direct effects on the water relations of well-watered radiata pine, it altered the drought tolerance of this tree species. Under conditions of soil-water deficit, plants exposed previously to acid rain are more sensitive to drought and desiccation.

Previous studies have indicated that the rate of photorespiration in C4 plants is low or negligible. In this study, wild-type and mutant leaves of the C4 plant Amaranthus edulis were treated with the glutamine synthetase inhibitor, phosphinothricin and the glycine decarboxylase inhibitor, aminoacetonitrile, at different concentrations of CO2. The time course of ammonia accumulation in leaves of the wild type was compared with a mutant lacking phosphoenolpyruvate carboxylase activity (EC 4.1.1.31), and with three different mutants that accumulated glycine. The increase in the concentration of ammonia in the leaves, stimulated by the treatments was used as a measurement of the rate of photorespiration in C4 plants. The application of glutamine and glycine maintained the rate of photorespiratory ammonia production for a longer period in the wild type, and increased the rate in a mutant lacking phosphoenolpyruvate carboxylase suggesting that there was a lack of amino donors in these plants. The calculated rate of photorespiration in Amaranthus edulis wild-type leaves when the supply of amino donors was enough to maintain the photorespiratory nitrogen flow, accounted for approximately 6% of the total net photosynthetic CO2 assimilation rate. In a mutant lacking phosphoenolpyruvate carboxylase, however, this rate increased to 48%, when glutamine was fed to the leaf, a value higher than that found in some C3 plants. In mutants of Amaranthus edulis that accumulated glycine, the rate of photorespiration was reduced to 3% of the total net CO2 assimilation rate. The rate of ammonia produced during photorespiration was 60% of the total produced by all metabolic reactions in the leaves. The data suggests that photorespiration is an active process in C4 plants, which can play an important role in photosynthetic metabolism in these plants.

Summary We have analyzed the comparative effect of nitrate and ammonium on the nitrogen-dependent induction of anaplerotic CO 2 fixation in detached leaves of N-limited barley plants. The supply of N, either in the form of NO 3 − or NH 4 + , provoked induction of phosphoenolpyruvate carboxylase activity (PEPCase), whereas the extractable pyruvate kinase, malate dehydrogenase and malic enzyme activities were not affected. The time course induction of PEPCase was dependent on the rate of ammonia assimilation and not on nitrate or ammonium uptake or accumulation. Treatment of N-deprived leaves with phosphinothricin (an inhibitor of glutamine synthetase activity) caused inhibition of ammonia assimilation, resulting in the reversion of ammonia-/nitrate-dependent enhancement of PEPCase. The results indicate that glutamine level controls phosphoenolpyruvate carboxylase activation in both nitrate and ammonium fed plants; consequently, if glutamine synthesis is inhibited, PEPCase activity is not enhanced. Determination of malate content showed that as PEPCase activity increased in response to increasing ammonia assimilation, there was a linear decline in the level of that metabolite. The highest rates of PEPCase enhancement in excised barley leaves when ammonia salt is the N source are in accordance with the highest rates of ammonia assimilation.

This review presents a detailed analysis of the papers published over the past 10 years addressing the response of several physiological parameters to the interaction between salinity and elevated CO2, which are both anticipated to affect more severely future environmental conditions. This review demonstrates that the response to this interaction is species and even cultivar specific and that the predicted higher biomass production at elevated CO2 is not a general trend. Most strategies to cope with salt stress involve active regulation of water potential and stomatal conductance, active regulation of photosynthetic metabolism as a whole, and active regulation of other salt-tolerance mechanisms. However, these salt-tolerance mechanisms are energetically expensive, and even if under elevated CO2 there is generally higher energy supply than under ambient CO2, biomass production will depend on the trade-off between the anabolic (photosynthesis) and catabolic (chloro-, photo-, and basal-respiration) rates, as well as the ability to control the stomatal conductance.

The objective of this study was to determine the response of nitrogen metabolism to drought and recovery upon rewatering in barley ( Hordeum vulgare L.) plants under ambient (350 μmol mol −1 ) and elevated (700 μmol mol −1 ) CO 2 conditions. Barley plants of the cv. Iranis were subjected to drought stress for 9, 13, or 16 days. The effects of drought under each CO 2 condition were analysed at the end of each drought period, and recovery was analysed 3 days after rewatering 13-day droughted plants. Soil and plant water status, protein content, maximum (NR max ) and actual (NR act ) nitrate reductase, glutamine synthetase (GS), and aminant (NADH-GDH) and deaminant (NAD-GDH) glutamate dehydrogenase activities were analysed. Elevated CO 2 concentration led to reduced water consumption, delayed onset of drought stress, and improved plant water status. Moreover, in irrigated plants, elevated CO 2 produced marked changes in plant nitrogen metabolism. Nitrate reduction and ammonia assimilation were higher at elevated than at ambient CO 2 , which in turn yielded higher protein content. Droughted plants showed changes in water status and in foliar nitrogen metabolism. Leaf water potential ( Ψ w ) and nitrogen assimilation rates decreased after the onset of water deprivation. NR act and NR max activity declined rapidly in response to drought. Similarly, drought decreased GS whereas NAD-GDH rose. Moreover, protein content fell dramatically in parallel with decreased leaf Ψ w . In contrast, elevated CO 2 reduced the water stress effect on both nitrate reduction and ammonia assimilation coincident with a less-steep decrease in Ψ w . On the other hand, Ψ w practically reached control levels after 3 days of rewatering. In parallel with the recovery of plant water status, nitrogen metabolism was also restored. Thus, both NR act and NR max activities were restored to about 75–90% of control levels when water supply was restored; the GS activity reached 80–90% of control values; and GDH activities and protein content were similar to those of control plants. The recovery was always faster and slightly higher in plants grown under elevated CO 2 conditions compared to those grown in ambient CO 2 , but midday Ψ w dropped to similar values under both CO 2 conditions. The results suggest that elevated CO 2 improves nitrogen metabolism in droughted plants by maintaining better water status and enhanced photosynthesis performance, allowing superior nitrate reduction and ammonia assimilation. Ultimately, elevated CO 2 mitigates many of the effects of drought on nitrogen metabolism and allows more rapid recovery following water stress.

Summary Maize plants fed with PPT (a glutamine synthetase inhibitor) accumulate ammonia. Approximately 50 % of the ammonia accumulated seems to come from the photorespiratory pathway, while the nonphotorespiratory ammonia is derived from nitrate reductase activity. The ammonia accumulated, however, is not sufficient to increase GDH activity. We also carried out a comparative study of the effect of PPT and AOA on photosynthesis. Both compounds inhibit the photorespiratory pathway, causing glycolate accumulation and diminishing photosynthesis.

Future environmental conditions will include elevated concentrations of salt in the soil and an elevated concentration of CO(2) in the atmosphere. Because these environmental changes will likely affect reactive oxygen species (ROS) formation and cellular antioxidant metabolism in opposite ways, we analyzed changes in cellular H(2)O(2) and non-enzymatic antioxidant metabolite [lipoic acid (LA), ascorbate (ASA), glutathione (GSH)] content induced by salt stress (0, 80, 160 or 240 mM NaCl) under ambient (350 micromol mol(-1)) or elevated (700 micromol mol(-1)) CO(2) concentrations in two barley cultivars (Hordeum vulgare L.) that differ in sensitivity to salinity (cv. Alpha is more sensitive than cv. Iranis). Under non-salinized conditions, elevated CO(2) increased LA content, while ASA and GSH content decreased. Under salinized conditions and ambient CO(2), ASA increased, while GSH and LA decreased. At 240 mM NaCl, H(2)O(2) increased in Alpha and decreased in Iranis. When salt stress was imposed at elevated CO(2), less oxidative stress and lower increases in ASA were detected, while LA was constitutively higher. The decrease in oxidative stress could have been because of less ROS formation or to a higher constitutive LA level, which might have improved regulation of ASA and GSH reductions. Iranis had a greater capacity to synthesize ASA de novo and had higher constitutive LA content than did Alpha. Therefore, we conclude that elevated CO(2) protects barley cultivars against oxidative damage. However, the magnitude of the positive effect is cultivar specific.

The aim of this work was to concentrate on the effect of the inhibitor on CO2 assimilation and other aspects of photosynthesis. The changes in quantum requirement and in the characteristics of chlorophyll fluorescence emission brought about by feeding phosphinothricin to primary leaves were reported. The methods employed provide indirect information on the redox state of the photosynthetic electron transport and on chloroplast energization

Future environmental conditions will include elevated concentrations of salt in the soils and elevated concentrations of CO 2 in the atmosphere. Soil salinization inhibits crop growth due to osmotic and ionic stress. However, plants possess salt tolerance mechanisms, such as osmotic and elastic adjustment, to maintain water status. These mechanisms, which enhance the uptake and accumulation of ions and the synthesis of compatible solutes, require substantial energy expenditure. Under elevated CO 2 , the carbon and energy supplies are usually higher, which could facilitate the energetically expensive salt tolerance mechanisms. To test this hypothesis, the factors involved in osmotic and elastic adjustments in two barley cultivars ( Hordeum vulgare cv. Alpha and cv. Iranis) grown under several salt concentrations and at ambient or elevated [CO 2 ] were evaluated. Under ambient [CO 2 ] and salt stress, both cultivars (1) decreased the volumetric elasticity modulus ( e ) of their cell walls, and (2) adjusted osmotically by accumulating ions (Na + and Cl − ) from the soil, confirming barley as an includer species. The contributions of sugars and other unidentified osmolytes also increased, while the contribution of organic acids decreased. Under elevated [CO 2 ] and salt stress, e decreased less and osmotic adjustment (OA) was greater than at ambient [CO 2 ]. In fact, the greater OA under elevated [CO 2 ] was positively correlated with the contributions of sugars and other unidentified compounds. These results indicate that barley is likely to be successful in more salinized soils due to its capacity for OA under elevated [CO 2 ].

Changes in antioxidant metabolism because of the effect of salinity stress (0, 80, 160 or 240 mM NaCl) on protective enzyme activities under ambient (350 micromol mol(-1)) and elevated (700 micromol mol(-1)) CO(2) concentrations were investigated in two barley cultivars (Hordeum vulgare L., cvs Alpha and Iranis). Electrolyte leakage, peroxidation, antioxidant enzyme activities [superoxide dismutase (SOD), EC 1.15.1.1; ascorbate peroxidase (APX), EC 1.11.1.11; catalase (CAT), EC 1.11.1.6; dehydroascorbate reductase (DHAR), EC 1.8.5.1; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; glutathione reductase (GR), EC 1.6.4.2] and their isoenzymatic profiles were determined. Under salinity and ambient CO(2), upregulation of antioxidant enzymes such as SOD, APX, CAT, DHAR and GR occurred. However, this upregulation was not enough to counteract all ROS formation as both ion leakage and lipid peroxidation came into play. The higher constitutive SOD and CAT activities together with a higher contribution of Cu,Zn-SOD 1 detected in Iranis might possibly contribute and make this cultivar more salt-tolerant than Alpha. Elevated CO(2) alone had no effect on the constitutive levels of antioxidant enzymes in Iranis, whereas in Alpha it induced an increase in SOD, CAT and MDHAR together with a decrease of DHAR and GR. Under combined conditions of elevated CO(2) and salinity the oxidative damage recorded was lower, above all in Alpha, together with a lower upregulation of the antioxidant system. So it can be concluded that elevated CO(2) mitigates the oxidative stress caused by salinity, involving lower ROS generation and a better maintenance of redox homeostasis as a consequence of higher assimilation rates and lower photorespiration, being the response dependent on the cultivar analysed.

Summary Differences in sensitivity to chlorsulfuron from 100 up to 1000-fold were observed between wheat and maize plants. Free amino acid content was analyzed in wheat and maize embryos and plants after 24 h and 10 days of chlorsulfuron treatment, respectively. Accumulation of free amino acids and increase in relative proportion of some of them were observed even when decreases in branched amino acid content could hardly be measured. Acetolactate synthase extracted from chlorsulfuron treated plants showed the same levels of extractable enzyme as from untreated plants. An effect of chlorsulfuron on acetolactate synthase in vivo could not be detected in wheat or maize at any time of plant treatment; this strongly suggests that the enzyme-inhibitor complex does not remain bound throughout the enzyme extraction procedure. Moreover, the extractable enzyme had the same properties as acetolactate synthase of untreated plants, showing that the enzyme in vivo is not irreversibly damaged by chlorsulfuron. This result is further supported by the growth recovery found in treated plants after removing the herbicide.

The Lower Decreases Of Pigment Content And Assimilation Rates And The Higher Rates Of Instantaneous Water Use Efficiency Observed In Plants Grown Under Salinity And Elevated Co2 Would Indicate A Better Photosynthetic CapaCity Than Their Counterparts At Ambient Co2.

Chlorsulfuron was preemergence applied in field trials at La Corufia, Spain, at rates from 5 to 30 g ai ha-1 (1987-88) and from 5 to 100 g ai ha71 (1988-89) for weed control in winter and spring wheat. Excellent control of broadleaf weeds was obtained in both; however, narrowleaf control at the last evaluation (heading) was poor. Chlorsulfuron at 30 g ha-1 did not cause a residual problem in 1987-88, with only 0.24 jig kg-1 of dry soil recovered after both a winter and spring wheat cropping season. However, chlorsulfuron persistence at the same rate was very high in the dry year 1988-89, with 0.43 jg kg71 and 0.53 jg kr1 recovered in winter and spring wheat, respectively. 'Cardeno' spring wheat showed no phytotoxic symptom at any rate of chlorsulfuron from 5 to 100 g ha71. Its yield and yield components (spikes m-2, grain number spike-1, grain weight) were greater with all chlorsulfuron rates, but not in 'Fiel' winter wheat for rates of 30 g ha71 or higher. Nomenclature: Chlorsulfuron, 2-chloro-N-(((4-methoxy- 6 - methyl - 1,3,5-triazin - 2 - yl)-amino)carbon- yl)benzenesulfonamide; wheat, Triticum aestivum L. Cardeno and Fiel. Additional index words. Bioassay, efficacy, tolerance.

Summary In a preliminary work we showed that when plants were sprayed with several doses of glufosinate, GS activity of the leaf was reduced by 50% after 48 h of application of 250 µM herbicide. Enzyme inhibition was accompained by a dramatic accumulation of ammonia. In this paper we analyze the time-course effect of phosphinothricin on nitrogen metabolism. Our results show that GS activity is the first process affected; more than 50% activity reduction is observed after 2 h of a 1,000 µM treatment, whereby ammonia values 400% higher than control were reached. NRase did not change until 24 h of assay, whereas protein content was reduced after 48 h. GDH activity was enhanced, but only 24 h after starting the treatment. These results indicate that the main target of PPT action is on GS activity, and other processes are long-term modified. GDH could, perhaps, reassimilate some of the ammonia produced but its activity is not able to completely prevent, the injury caused by phosphinothricin.