Decrease In Specific Leaf Area Research Articles

Morphological and Physiological Changes of Hydroponic Lettuce Grown in Varying Potassium Concentrations and an Adaptive Lighting Control System

We investigated the growth dynamics of hydroponic lettuce (Lactuca sativa) driven by the influence that potassium (K+) has on crop growth. This study aimed to determine whether increased K+ concentrations under different daily light integrals (DLIs) in a hydroponic system will boost growth of greenhouse lettuce. This study was conducted within a controlled glass greenhouse environment with varying DLIs achieved by integrating an adaptive lighting control system over a 16-hour photoperiod. We used three K+ treatments of 200, 400, or 600 mg⋅L−1 K+ and six DLI lighting treatments of 11.1, 12.9, 14.6, 15.9, 16.9, and 17 mol⋅m−2⋅d−1. We found that increasing K+ did not increase shoot dry weight, leaf area, or specific leaf area with increasing DLIs. Although K+ and DLI had an interacting effect on the root dry weight fraction, leaf chlorophyll content, and quantum yield of photosystem II, the K+ treatments did not increase or decrease with increasing DLIs. The influencing factor was DLI, which led to increases in shoot dry weight and leaf area, whereas a decrease in specific leaf area was observed with increasing DLIs. Ultimately, adding supplemental concentrations of K+ did not enhance lettuce growth, nor did these effects show any increase with increasing DLIs.

Leaf trait variation in grassland plant species in response to soil phosphorus

AbstractQuestionsIncreased soil phosphorus (P) availability in fertilized grasslands can drive both community degradation and delayed community recovery upon agricultural abandonment. Beyond describing grassland community patterns along gradients in P availability, it remains unclear how individual species with different strategies respond to increasing phosphorus. Here we studied intraspecific variability of leaf functional traits in response to soil phosphorus, for species with contrasting resource‐use strategies.MethodsWe set up a pot experiment with communities containing four species, assembled from a pool of 20 mesotrophic grassland species growing along a soil P gradient. Species selection included various growth forms (grasses vs forbs) and resource‐use strategies (acquisitive vs conservative resource use). We measured three variables characterizing the (a)biotic environmental context: bioavailable soil P concentration, total community biomass as a proxy for the intensity of competition, and the proportional biomass of a species in the community as a proxy for its competitive dominance. We investigated the effect of this environmental context on the expression of two leaf traits, specific leaf area (SLA) and leaf dry matter content (LDMC).ResultsWe found an acquisitive trait expression within species (increase in SLA and decrease in LDMC) in response to increased soil P supply and a conservative trait expression (decrease in SLA and increase in LDMC) in response to an increase in total community biomass. Importantly, the trait responses to the environmental context were generally consistent for species representing very different resource‐use strategies and growth forms.ConclusionsSpecies responded with a shift from an acquisitive to a conservative trait expression in response to limited resources; i.e., driven by a decrease in soil phosphorus concentration or an increase in total community biomass. Unexpectedly, the intraspecific variability in response to the changing environmental conditions was not clearly mediated by the species’ strategy. These findings show that plant ecological strategies are probably not the main driver for intraspecific trait variability in an experimental grassland community.

Changes in morphological traits associated with waterlogging, salinity and saline waterlogging in Festuca arundinacea.

Rising incidences of waterlogging and salinity, particularly in extensive livestock farming areas, pose increasing challenges to plant growth. This study investigated the morphological growth responses and tolerance of 39 Festuca arundinacea accessions to these stresses, with tolerance quantified by the relative growth rate under stress versus control conditions. Notably, more productive accessions under normal conditions also showed greater stress tolerance. Waterlogging was generally well-tolerated (89-113% of control relative growth rate), without significantly altering growth morphological components as increases in specific leaf area were offset by reductions in leaf weight ratio, maintaining stable leaf area ratios. Conversely, salinity and combined saline waterlogging significantly reduced relative growth rate (56-94% of control), with a substantial variation among accessions. A decrease in specific leaf area, suggestive of thicker leaves, correlated with higher tolerance to salinity and saline waterlogging (r =0.63). In summary, F. arundinacea displays diverse tolerance to these stresses, warranting further study into the adaptive mechanisms. Specific leaf area emerges as a potential selection marker for breeding programs targeting saline and waterlogging tolerance.

Increased wood biomass growth is associated with lower wood density in Quercus petraea (Matt.) Liebl. saplings growing under elevated CO2.

Atmospheric carbon dioxide (CO2) has increased substantially since the industrial revolution began, and physiological responses to elevated atmospheric CO2 concentrations reportedly alter the biometry and wood structure of trees. Additionally, soil nutrient availability may play an important role in regulating these responses. Therefore, in this study, we grew 288 two-year-old saplings of sessile oak (Quercus petraea (Matt.) Liebl.) in lamellar glass domes for three years to evaluate the effects of CO2 concentrations and nutrient supply on above- and belowground biomass, wood density, and wood structure. Elevated CO2 increased above- and belowground biomass by 44.3% and 46.9%, respectively. However, under elevated CO2 treatment, sapling wood density was markedly lower (approximately 1.7%), and notably wider growth rings—and larger, more efficient conduits leading to increased hydraulic conductance—were observed. Moreover, despite the vessels being larger in saplings under elevated CO2, the vessels were significantly fewer (p = 0.023). No direct effects of nutrient supply were observed on biomass growth, wood density, or wood structure, except for a notable decrease in specific leaf area. These results suggest that, although fewer and larger conduits may render the xylem more vulnerable to embolism formation under drought conditions, the high growth rate in sessile oak saplings under elevated CO2 is supported by an efficient vascular system and may increase biomass production in this tree species. Nevertheless, the decreased mechanical strength, indicated by low density and xylem vulnerability to drought, may lead to earlier mortality, offsetting the positive effects of elevated CO2 levels in the future.

Plant Factories Are Heating Up: Hunting for the Best Combination of Light Intensity, Air Temperature and Root-Zone Temperature in Lettuce Production.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

Specific leaf area is modulated by nitrogen via changes in primary metabolism and parenchymal thickness in pepper.

Nitrogen promotes changes in SLA through metabolism and anatomical traits in Capsicum plants. Specific leaf area (SLA) is a key trait influencing light interception and light use efficiency that often impacts plant growth and production. SLA is a key trait explaining growth variations of plant species under different environments. Both light and nitrogen (N) supply are important determinants of SLA. To better understand the effect of irradiance level and N on SLA in Capsicum chinense, we evaluated primary metabolites and morphological traits of two commercial cultivars (Biquinho and Habanero) in response to changes in both parameters. Both genotypes showed increased SLA with shading, and a decrease in SLA in response to increased N supply, however, with Habanero showing a stable SLA in the range of N deficiency to sufficient N doses. Correlation analyses indicated that decreased SLA in response to higher N supply was mediated by altered amino acids, protein, and starch levels, influencing leaf density. Moreover, in the range of moderate N deficiency to N sufficiency, both genotypes exhibited differences in SLA response, with Biquinho and Habanero displaying alterations on palisade and spongy parenchyma, respectively. Altogether, the results suggest that SLA responses to N supply are modulated by the balance between certain metabolites content and genotype-dependent changes in the parenchyma cells influencing leaf thickness and density.

Increasing temperature and decreasing specific leaf area amplify centipede predation impact on Collembola

Collembola is an abundant group of soil organisms playing a major role on litter decomposition process and nutrient cycling in forest ecosystems. Habitat structure strongly influences Collembola assemblages as plant litter physical characteristics and quantity provide structural niches and determine the outcome of their interactions with predators. Collembola are also extremely sensitive to environmental conditions such as soil temperature that control their demographic parameters and activity. In this context, increasing temperature with the ongoing climate change can have strong impact on Collembola assemblages and their responses to predation either directly by altering their behaviour or indirectly by altering their habitat structure. We therefore examined how the increase of temperature combined to the decrease of specific leaf area (SLA, a major functional plant trait) of the European common oak (Quercus robur L.) and the presence of a centipede predator (Chilopoda: Lithobiidae) will affect the abundance of Folsomia candida (Collembola: Isotomidae) in a 5-week microcosm experiment. Increasing temperature, decreasing SLA and presence of centipede altered F. candida abundance. We observed a significant temperature × predation interaction suggesting differential effects of increasing temperature on F. candida abundance with and without predator. We also observed a significant SLA × predation interaction highlighting that lower SLA decreases F. candida abundance only in predator presence. Finally, our findings evidenced that increasing temperature and decreasing SLA amplify the negative effect of centipede predation on F. candida abundance, suggesting that both direct and indirect effects of climate change would conjointly strengthen the top-down control of predators on preys.

How does Cariniana estrellensis respond to different irradiance levels?

Based on reports that variables related to photosynthesis (net assimilatory ratio and chloroplast pigments) are more plastic than the morphological and biochemical variables in a climax tropical species, Cariniana estrellensis, under contrasting irradiance, we hypothesised that plasticity of gas exchange variables is higher in relation to growth, biochemical and anatomical variables. Plants that were 14 months old were subjected to 200 up to 2000 µmol m−2 s−1 of photo synthetically active radiation (PAR) for 140 days. Growth increased up to 1400 µmol m−2 s−1 PAR and then decreased at 2000 µmol m−2 s−1 PAR (full sunlight). This was related to the rate of photosynthesis (A) which showed the same tendency as photosystem II performance index (PIABS). The greater thickness of the secondary xylem at 1400 µmol m−2 s−1 PAR indicated a higher water conductance capacity. The decrease in specific leaf area, elongation of mesophyll cells, and increase in stomatal density observed at higher irradiances were associated with higher leaf fructose and sucrose concentrations. We concluded that the better growth in partial shade was due to higher photosynthetic capacity. On the other hand, photosynthesis was inhibited equally in full sun and deep shade. The high adjustment capacity of C. estrellensis to wide amplitudes of irradiance was provided by greater plasticity of gas exchange variables in relation to growth, anatomical, and biochemical variables.

Response of contrasting root genotypes of castor (Ricinus communis L.) to water stress

Two contrasting genotypes for root biomass i.e. RG-111 with good root, RG-1520 with poor root were studied for root, shoot growth till 90 DAS in root structures and also in field for seed yield by imposing water stress (30-90 DAS) during late rabi (2011-12). The reduction in root length was less due to stress. But root volume, dry weight and shoot growth reduced with stress and the per cent reduction was less in poorer root genotype (RG-1520) compared to good root genotype (RG-111). With drought stress in field, the growth before relieving stress, seed yield of different order branches and total seed yield reduced significantly in both genotypes. RG-1520 showed adaptation to survive drought stress in root structure and in field by increasing chlorophyll content (SCMR), less reduction in relative water content (RWC), decrease in specific leaf area (SLA) and increase in bloomcontent as that of good root genotype RG-111. But, seed yield reduction was more in poor root genotype (RG-1520) and also recorded high drought susceptibility index (DSI) as its photo assimilates were spent for its survival in stress and assimilate translocation was less for seed growth. Hence good root is important for crop survival, growth and seed yield especially in drought conditions.

Plasticity of bud phenology and photosynthetic capacity in hybrid poplar plantations along a latitudinal gradient in northeastern Canada

Intensively managed plantations are being established in a wide range of environmental conditions to satisfy the high demand for wood products and reduce the exploitation pressure on natural forests. In this study, we investigated the plasticity of four hybrid poplar (Populus spp.) clones established in 2005 along a latitudinal gradient in northwestern Quebec, Canada. The effect of latitudinal gradient on maximum rates of electron transfer (Jmax) and carboxylation (Vcmax), dark respiration (Rd), spring and fall bud phenology, net photosynthesis (Pn), specific leaf area (SLA), per mass nitrogen leaf concentration (Nm) were assessed in order to evaluate if clonal plasticity would result in increased overall productivity.Growth season duration between the southernmost to the northernmost sites ranged 21–32 days, and was positively correlated to stem volume and negatively correlated to bud burst and bud set duration. Growth increment (stem volume) along the latitudinal gradient ranged 100–184% between the least and most productive clone. Clone 747215 had the most stable but the slowest growth. Leaf net photosynthesis decreased or did not change northwards except for the most productive clone for which it increased slightly likely due to a significant decrease in SLA. Maximum rates of carboxylation and photosynthesis electron transfer (Vcmax and Jmax) decreased northwards for three of the four clones, suggesting that photosynthesis of trees did not acclimate to lower temperatures from south to north. Plasticity of photosynthetic variables, measured with trait plasticity index was usually greater than that of SLA and Nm.

Functional leaf traits of understory species: strategies to different disturbance severities.

The specific leaf area (SLA) has been related to environmental disturbances, showing a positive correlation between the disturbances intensities and SLA in a plant community. These studies, however, assessed the responses of plant community as a whole, neglecting species attributes, such as the position in the vertical stratum of forests. Considering the importance of SLA to understand forest ecological processes, this study aimed to determine the influence of the disturbance regime on the SLA of understory species, considering that, unlike for communities as a whole, an increase in the disturbance intensity implies a decrease in SLA of understory species. This study was conducted in nine understories of seasonal forests in Brazil. The most abundant species were selected and their SLA were evaluated. The variability of SLA among populations in different forests was analyzed by Student's t-tests. The SLA of the understories (SLAU) was also compared by an adaptation of the Community-weighted mean index. The comparison of species SLA showed significant differences among the populations of understories under different disturbance regime, showing a decrease in SLA with an increase in the disturbance intensity. Similar results were found for the SLA of understories communities (SLAU), corroborating our hypothesis. The correlation between a reduction in species SLA and in SLA of understory with an increase in disturbance intensity, contradicted the trend observed in the literature for the community as a whole. This study highlights the importance of the evaluation of SLA in understories, as an indicator of the successional stage of communities.

Vliv vodního stresu na vybrané fyziologické charakteristiky rajčat

This work presents the results of a field experiment with tomato cv. Proton grown under water stress conditions and under well irrigated conditions. At the same time, the effects of Pentakeep supporting agent (consisting of aminolevulinic acid) was studied. The following characteristics of plant phy­sio­lo­gy were studied – specific leaf area (SLA), leaf water content (LWC) and leaf proline concentration.The obtained results show a significant decrease in SLA during plant vegetation (from 190 to 165 cm−2 . g−1). A decrease was also found under water stress treatment (163 cm−2 . g−1), in contrast to the well watered control (184 cm−2 . g). LWC values ranged from 81 to 87 % in both seasons. A significantly important decrease of LWC was found in the stressed variant. Pentakeep application did not affect either SLA or LWC characteristics.The level of proline in tomato leaves varied from 0.6 to 1.5 μmol . g−1. The highly significant effect of water conditions resulted in the increase of proline content under water stress treatment. Although Pentakeep increased the proline content by 9 %, its effect was not of significant importance. The proline content was also influenced by the date of sampling.The results indicate that physiological characteristics, such as SLA, LWC and proline content, are good indicators of water stress in tomato, proline content being a particularly reliable parameter corresponding to the actual water stress of plants.

A functional trait approach to fen restoration analysis

AbstractQuestionsEcological restoration has traditionally been evaluated with analyses focused on species identities and abundances. These analyses provide no ecological explanation to why certain species change in abundance. One solution may be a functional trait analysis. We asked whether shifts in functional traits could explain vegetation changes in fens restored through tree cutting and rewetting, and how the functional traits in the restored sites compare to those of the reference site?LocationThree former rich fens in east‐central Sweden.MethodsTree cutting and rewetting were applied in a factorial design, and species and abundance data were recorded for 8 yrs. Abundance data and trait data of canopy height, specific leaf area (SLA) and diaspore mass were used to calculate functional richness (FRic), functional divergence (FDiv), functional dispersion (FDis) and community‐weighted mean (CWM) of functional traits. Data were analysed in a linear mixed effect model for vascular plants and bryophytes jointly, and for vascular plants separately. Results of restoration treatments were compared to data from a reference site.ResultsAmong vascular plants, tree cutting caused a decrease in SLA, as shade‐sensitive species increased. In accordance with the change in SLA, FDis increased. In the joint analysis, tree cutting led to increased FDis, FDiv and FRic, indicating reduced filtering caused by the removal of the shading canopy, which allowed shade‐sensitive species to establish. The comparison to the reference site shows that even after 8 yrs, the restoration treatments have higher trait diversity than the reference site, indicating that the restoration sites have a too relaxed trait filter compared to conditions in an undisturbed fen. Our interpretation is that this is primarily caused by insufficient rewetting (and increased nutrient availability) that allow species of both natural and degraded fen conditions to co‐exist, and which failed to suppress the regrowth of trees.ConclusionsAnalysis of functional diversity improves our understanding of the ecological mechanisms affecting restoration results, and allows comparison among regions and communities with different species composition.

Developing and testing new halophyte crops: A case study of salt tolerance of two species of the Brassicaceae, Diplotaxis tenuifolia and Cochlearia officinalis

Diplotaxis tenuifolia (L.) and Cochlearia officinalis (L.) were presumed to be salt tolerant with potential as vegetable halophyte crops. The response to increasing salinity was analysed by means of the relative growth rate (RGR) and its components and mineral composition. No growth reductions occurred up to 100mM NaCl for D. tenuifolia, whereas C. officinalis showed a 37% decrease in total dry weight at this concentration of NaCl, corresponding to a 9% decrease in RGR. The RGR at higher salinity levels (≥200mM NaCl) showed reductions around 20% for both species, largely due to changes of leaf morphology (decrease in specific leaf area, increase in leaf succulence) rather than toxic leaf Na+ concentrations. In comparison to seven other species of the Brassicaceae, including salt sensitive and highly salt tolerant species, both D. tenuifolia and C. officinalis showed an intermediate response to increasing salinity. Both species were able to survive the highest salinity treatment (300mM NaCl for D. tenuifolia and 400mM NaCl for C. officinalis) and can be classified as salt tolerant with potential as vegetable crops for saline agriculture. Since D. tenuifolia is already in use as an agricultural crop, little constraints are foreseen for its introduction as a saline crop. Before C. officinalis can be used as a saline crop, agricultural practices and marketing still have to be addressed. A hands-on tool is provided for this process, which combines science, agronomy, the social system, and the business sector.

Germination and Seedling Responses of Subalpine Plants to Different Soil Substrates

In this study we explored the regeneration niche of 18 alpine plant species by testing the germination responses and seedling growth to soil mixtures made with gypsum, ophiolite, and quartzite, and a control soil. We analyzed different phases of germination: time of radicle emergence, germination duration, and germination percentage, and thereafter seedling performance measured using seedling biomasses. Species were grouped as acidophilous, basophilous and neutrophilous according to their Ellenberg indicator values. Seeds were germinated on each soil mixture in a greenhouse, and then seedlings were selected and transplanted outdoors to grow for one season at 2,050 m a.s.l. The time of radicle emergence, length of germination, final germination percentage, seedling biomass and specific leaf area (SLA) varied according to the soil mixtures depending on the pH group. There were some consistencies between the Ellenberg groups, which were built for adult plant species, and the way these seedlings responded to a particular soil mixture. For instance, the group of species predominantly occurring in basic soils during their adult life (basophilous) had the highest germination percentage and the shortest emergence time on the soil mixture composed of gypsum, but a low germination percentage and the smallest seedling biomass on the other two soil mixtures. In addition, the decrease in SLA for seedlings of the basophilous group when they were cultivated on acidic soil (especially quartzite) seems to indicate a weaker functioning of the plants. Our results highlight, first, the significance of the regeneration niche in the establishment of plants in a given soil environment, especially by emphasizing the links between germination and soil chemistry, and secondly, the consideration that different germination phases add more information about the plant community assemblage with respect to the soil environment.

Plant growth strategies of Thymus vulgaris L. in response to population density

Thymus vulgaris L., known as common thyme, is a perennial subshrub native to the Mediterranean region. The use of the extracts and herb of thyme plants as antibacterial, antioxidant, natural food preservative and in cosmetic industry has increased the economic importance of this medicinal crop worldwide. Agricultural practices have an influence on growth and yield of thyme plants. Therefore, an experiment was undertaken to determine the effects of three intra-row spacing (15, 30 and 45 cm) and four harvesting times (vegetative, beginning of blooming, full blooming and fruit set) on plant growth and herbage biomass of thyme in 2007 in the research farm of Shoubak University College in the southern part of Jordan. The experiment was a split plot in randomized complete block design with four replicates. Apart from the experiment in 2007, measurements taken on the 15th of November in 2008 were treated as an independent experiment irrespective of harvesting stage. The effects of spacing were not significant for all the parameters measured in 2007. Intra-row spacing in 2008 had significant effects ( P < 0.05) on plant height, canopy diameter, herbage fresh and dry weight and number of leaves on long shoots. Its effect on dry weight of shoots, fresh and dry weight of long shoots, number of long shoots, root depth, leaf area and specific leaf area was very significant ( P < 0.01). Results of this study indicated that thyme plants grown using 15 cm planting space and harvested at the fruit set stage in 2007 had the highest fresh and dry weight of shoots. The highest dry weight of shoots, herbage fresh and dry weight was also obtained in 2008 in 15 cm spacing. Closer spacing resulted in significantly taller plants that exhibited higher shoot:root ratio and, therefore, plants grown using 15 cm intra-row spacing had a better use of light and accumulated more biomass compared to plants in wider spacing. The differentiation between long shoots and short shoots throughout plant development in 2007 suggests a specialization in carbon gain along different times in the growing season. Swings observed for shoot:root ratio, leaf area and specific leaf area were related to thyme growth. The decrease in specific leaf area between vegetative and full bloom stage indicated that leaves became thicker as part of an adaptive mechanism to the surrounding environment. Information obtained from growth parameters, leaf area and specific leaf area in particular, could be related to essential oil production in leaves of thyme plants.

Apoplastic antioxidative system responses to ozone stress in strawberry leaves

Cell wall polysaccharides, pectin composition, as well as apoplastic superoxide dismutase and peroxidase activities were investigated in strawberry (Fragaria x ananassa) cultivars (cvs) Korona and Elsanta differing in their ozone sensitivity. Plants were exposed to 140-170 microg m(-3) ozone either short-term for 7 days or long-term for 2 months in order to investigate whether differences in ozone sensitivity were due to differences in the apoplastic antioxidative systems. Cell wall polysaccharides were increased after 7 days and 2 months of ozone stress. While water-soluble pectins, low methoxy pectinates and NaOH-soluble pectinates were elevated after 7 days, their contents were unaffected (water-soluble pectins) or lower (low methoxy pectinates, NaOH-soluble pectinates) after 2 months. In cv. Elsanta, ozone treatment resulted in a significant reduction of superoxide dismutase activity after 7 days and 2 months, while it remained similar in cv. Korona. After 7 days, peroxidase activity was significantly higher in ozone-exposed leaves of cv. Korona, whereas after 2 months it was similar to or higher than in controls. Superoxide dismutase in cv. Korona detoxified ozone and its products in the apoplast, and the resulting elevated levels of H(2)O(2) were balanced within 7 days by an increase in peroxidase activity. Long-term peroxidase activity may not play a comparably significant role in ozone defence, but the increase in cell wall polysaccharides and cell wall thickness measured after 2 months, resulting in a decrease in specific leaf area, reflected structural modifications that limited activities of reactive oxygen species efficiently. In contrast, the reduction of superoxide dismutase activity in cv. Elsanta indicated a less efficient apoplastic radical scavenging system, at least during the first 7 days of ozone stress, which was accompanied by membrane leakage and contributed to accelerated leaf senescence. Long-term, the reduction of intercellular air space volume in leaves contributed to ozone tolerance of cv. Elsanta as in cv. Korona.

WILD RELATIVES AS A SOURCE FOR SUB-OPTIMAL TEMPERATURE TOLERANCE IN TOMATO

Greenhouse tomato cultivation often requires a high energy input to maintain set-point temperatures. If set-point temperatures could be lowered by a few degrees this would reduce energy consumption significantly. However, this can only be applied when new, more energy-efficient cultivars are developed, i.e. cultivars that can be cultivated at sub-optimal temperatures without loss of production or quality. As variation for temperature response within the current elite tomato cultivars is limited, it is important to look for other sources of variation. One option are wild relatives which originate from South America, where they grow at altitudes up to 3300 m. In this study we examined the effects of temperature (12?24°C) on growth of young vegetative tomato plants of the cultivar `Moneymaker? and two wild relatives (L. hirsutum LA 1777 and L. pennellii LA 716). The aim was to elucidate the physiological and morphological parameters which underlie interspecific differences in growth response to sub-optimal temperatures. During a 28-day period five destructive measurements were carried out in which total dry weight, including root weight, leaf area and leaf dry weight were measured in order to calculate growth parameters. Even though `Moneymaker? had a higher relative growth rate (RGR) over a large temperature range (16?24°C), RGR of `Moneymaker? was severely reduced below 20°C, while RGRs of L. hirsutum and L. pennellii were only decreased below 16°C. At 12°C RGR of `Moneymaker? was reduced by 41% compared to 20°C, while in L. pennellii and L. hirsutum this decrease was only 27 and 18%, respectively. This decrease in RGR in `Moneymaker? was mainly a result of a decreased leaf area ratio (LAR), caused by a 35% decrease in specific leaf area (SLA). In contrast, the decrease in RGR in L. pennellii and L. hirsutum was a result of a decreased net assimilation rate (NAR) of 24 and 14%, respectively. This study illustrates that wild tomato species provide possibilities for the breeding of more energy-efficient tomato greenhouse cultivars

Effects of nitrogen supply on photosynthetic and anatomical changes in current-year needles of Pinus koraiensis seedlings grown under two irradiances

We investigated the responses of photon-saturated photosynthesis rate (P sat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant increase of N content in needles under both irradiances, the increase of P sat tended to be suppressed only in shade (S). The significant increase of P sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll (Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of full irradiance), which would result in a small increase of P sat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle. Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through improvement of the allocation of N in both irradiances.

Can CO2 enrichment modify the effect of water and high light stress on biomass allocation and relative growth rate of cork oak seedlings?

To test whether the impact of an enriched-CO2 environment on the growth and biomass allocation of first-season Quercus suber L. seedlings can modify the drought response under shade or sun conditions, seedlings were grown in pots at two CO2 concentrations × two watering regimes × two irradiances. Compared to CO2, light and water treatment had greater effects on all morphological traits measured (height, stem diameter, number of leaves, leaf area, biomass fractions). Cork oak showed particularly large increases in biomass in response to elevated CO2 under low-watered (W−) and high-illuminated conditions (L+). Allocation shifted from shoot to root under increasing irradiance (L+), but was not affected by CO2. Changes in allocation related to water limitation were only modest, and changed over time. Relative growth rate (RGR) and net assimilation rate (NAR) were significantly greatest in the L+/W+ treatment for both CO2 concentrations. Changes in RGR were mainly due to NAR. Growth responses to increased light, water or CO2 were strongest with light, medium with water availability and smallest for CO2, in terms of RGR. The rise in NAR for light and water treatments was counterbalanced by a decrease in SLA (specific leaf area) and LMF (leaf mass fraction). Results suggest that elevated CO2 caused cork oak seedlings to improve their performance in dry and high light environments to a greater extent than in well-irrigated and low light ones, thus ameliorating the effects of soil water stress and high light loads on growth.