Decrease In Relative Growth Rate Research Articles

In vitro selection of salt tolerant cell lines in Solanum tuberosum L.

Cell lines able to grow on media containing 50, 100, 150 or 200 mM NaCl were established from potato callus cultures by direct recurrent selection or gradual selection. In callus subjected to direct selection only small clusters of cells survived on medium with 150 or 200 mM NaCl, whereas on 100 mM small cell portions appear necrotic. When cell lines were obtained by successive subcultures on media with increased concentrations of NaCl, salt-tolerant calli were more compact and developed a greenish colour free from necrotic areas. The response of calli lines grown on media with NaCl was compared to control line. The NaCl-tolerant calli showed a decrease in relative growth rate and water content, with higher reductions in the 150 mM tolerant callus. Lipid peroxidation was increased in 50 mM and 100 mM NaCl-tolerant calli, while in 150 mM tolerant callus remained similar to 100 mM values. There was a significant increase in ascorbic acid content in 100 mM and 150 mM NaCl-tolerant calli as compared to the 50 mM, that was two-fold the value found in the control. Also, the contents of soluble and insoluble proteins increased in salt-tolerant lines. SDS-PAGE of soluble proteins showed the synthesis of specific polypeptides in the presence of NaCl in culture medium and the synthesis of a new polypeptide.

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

Root respiratory characteristics associated with plant adaptation to high soil temperature for geothermal and turf-type Agrostis species

Respiration is a major avenue of carbohydrates loss. The objective of the present study was to examine root respiratory characteristics associated with root tolerance to high soil temperature for two Agrostis species: thermal Agrostis scabra, a species adapted to high-temperature soils in geothermal areas in Yellowstone National Park, and two cultivars ('L-93' and 'Penncross') of a cool-season turfgrass species, A. stolonifera (creeping bentgrass), that differ in their heat sensitivity. Roots of thermal A. scabra and both creeping bentgrass cultivars were exposed to high (37 degrees C) or low soil temperature (20 degrees C). Total root respiration rate and specific respiratory costs for maintenance and ion uptake increased with increasing soil temperatures in both species. The increases in root respiratory rate and costs for maintenance and ion uptake were less pronounced for A. scabra than for both creeping bentgrass cultivars (e.g. respiration rate increased by 50% for A. scabra upon exposure to high temperature for 28 d, as compared with 99% and 107% in 'L-93' and 'Penncross', respectively). Roots of A. scabra exhibited higher tolerance to high soil temperature than creeping bentgrass, as manifested by smaller decreases in relative growth rate, cell membrane stability, maximum root length, and nitrate uptake under high soil temperature. The results suggest that acclimation of respiratory carbon metabolism plays an important role in root survival of Agrostis species under high soil temperatures, particularly for the thermal grass adaptation to chronically high soil temperatures. The ability of roots to tolerate high soil temperatures could be related to the capacity to control respiratory rates and increase respiratory efficiency by lowering maintenance and ion uptake costs.

Effects of salinity on germination, seedling growth and physiology of three salt-secreting mangrove species

Propagules of three salt-secreting mangrove species, i.e. Acanthus ilicifolius L., Aegiceras corniculatum Blanco. and Avicennia marina (Forsk) Vierh., were germinated at salinities of 0, 5, 15, 25 and 35 parts per thousand (ppt). Their tolerance to salt stress was compared in terms of some parameters on germination, growth and physiology. Root initiations of Ae. corniculatum and Av. marina, two viviparous species, were about 3 and 6 d, respectively, not significantly affected by salinity, but those of Ac. ilicifolius, a non-viviparous species, were significantly delayed about 4 d at salinities over 25 ppt. Final seedling establishment percentages of Av. marina were 100% at all salinity treatments, while salinities over 25 ppt significantly reduced the values of Ae. corniculatum (28%) and Ac. ilicifolius (38%). As salinities increased from 0 to 35 ppt, decrease in relative growth rate (RGR) of Av. marina was only 5%, less than those of Ae. corniculatum (56%) and Ac. ilicifolius (70%). For each species, salt secretion from leaves increased with increases in salinity and the increases in salt secretion with every salinity increase of 10 ppt were about 0.9, 0.6 and 0.2 g m −2 d −1 for Av. marina, Ae. corniculatum and Ac. ilicifolius, respectively. When seedlings were cultured in fresh water, leaf tissue water of each species had salt concentrations around 2%, much higher than the environmental salinity (0 ppt). Under saline conditions from 5 to 35 ppt, salt concentrations in leaf tissue water of Av. marina maintained steady (4.3–5.0%), while the corresponding values increased from 2.4 to 4.5% in Ae. corniculatum and from 2.3 to 5.3% in Ac. ilicifolius. Evaporation and transpiration (evapo-transpiration) rates of these three species were similar under fresh water condition, but under saline conditions (5–35 ppt), Av. marina had significantly higher rates than Ac. ilicifolius and Ae. corniculatum. At salinities of 5–35 ppt, variations of evapo-transpiration were different between species with an order of Av. marina < Ae. corniculatum < Ac. ilicifolius. All of the parameters indicated that salt tolerance of the three salt-secreting mangrove species was in the descending order of Av. marina > Ae. corniculatum > Ac. ilicifolius.

Modulation of relative growth rate and its components by water stress in Mediterranean species with different growth forms

Effects of water availability on seedling growth were analysed in eight Mediterranean species naturally occurring in the Balearic Islands. Seedlings were grown outdoors during summer under two irrigation treatments: field capacity and 35% of field capacity. The relative growth rate (RGR) strongly depended on the growth form, from highest values in herbs to lowest in woody perennials. The main component associated with interspecific variation in RGR was the specific leaf area (SLA), and a quantitative grouping of the different growth forms appeared along the regression line between both parameters. The slow-growing species, i.e. woody perennial shrubs, had the lowest SLA and the fast-growing perennial herbs, the highest, while woody semi-deciduous shrubs appeared intermediate. Decreases in RGR due to water stress were analysed in terms of the relative contribution of the leaf mass ratio (LMR), SLA and the net assimilation rate (NAR). Pooling all species, the decrease in RGR caused by water deficit was mainly explained by decreases in SLA. However, this general pattern was strongly dependent of growth form. Thus, in the woody perennial plants, the decrease in RGR was accompanied by a three-fold decrease in NAR which, however, increased in perennial herbs. SLA increased with decreasing water supply in woody perennial plants, and decreased in woody semi-deciduous shrubs and perennial herbs. Finally, decreases in LMR partly explained decreases in RGR in perennial herbs and woody perennial shrubs. This different response of the different growth forms may reflect differences in seedling adaptation and surviving strategies to drought periods.

Duração do período de descanso e crescimento do dossel de Panicum maximum cv. Mombaça sob lotação intermitente

O crescimento do dossel do capim-Mombaça foi analisado sob lotação intermitente com três períodos de descanso (PD), tratamentos definidos em função do tempo necessário para a expansão de 2,5; 3,5 e 4,5 novas folhas por perfilho e período de pastejo de seis dias. A área experimental foi dividida em cinco ou seis piquetes por tratamento. Utilizaram-se cinco novilhos mestiços (holandês x zebu) por tratamento, como animais de prova, além de outros, como animais de equilíbrio, que foram adicionados, quando necessário, para garantir índice de área foliar (IAF) residual de 2,0, ao final do 6(0) dia de cada período de pastejo. O estudo constou de duas fases de crescimento: 1) após roçada de uniformização, no início da estação de pastejo e 2) após alguns ciclos de pastejo, sob efeito dos três PDs. Os piquetes receberam adubação em cobertura de N, P2O5 e K2O, na dose de 50; 12,5 e 50 kg/ha, no início dos crescimentos 1 e 2. A intervalo médio de seis dias, durante 45 dias, estimaram-se a intercepção da radiação fotossinteticamente ativa (RFA), o IAF e a massa seca de forragem verde (MSFV). Aos dados de MSFV e de área foliar foram ajustados polinômios de segundo grau em função da idade, a partir dos quais foram estimados os valores instantâneos de biomassa e IAF e, a partir destes, as taxas de crescimento relativo (TCR) e de assimilação líquida (TAL) e a razão de área foliar (RAF), para cada idade. A intercepção da RFA pelo dossel evoluiu assintoticamente, alcançando valores máximos entre 95 e 98%, enquanto os valores de IAF e MSFV experimentaram incrementos ainda na faixa de estabilidade da intercepção da RFA. Os valores de TCR, TAL e RAF exibiram evolução assintótica decrescente. A grande proporção de colmo do dossel, ao final do PD mais longo, favoreceu a TCR e a TAL.

PHYSIOLOGICAL EFFECTS INDUCED BY COPPER EXCESS IN PEACH ROOTSTOCK MRS 2/5 AND GF 677 GROWTH IN VITRO

In this work the physiological effect of copper excess on the peach rootstock MrS 2/5 and GF 677 was studied by means of an in vitro system. Two different copper treatments (10 and 100 µM CuSO4) for each rootstock were carried out and compared to a control containing 0.1 µM of CuSO4. Relative growth rate and copper concentration inside rootstock tissues were measured after 21 days from the beginning of the treatments and used to compare the genotypes’ reaction to copper excess. The GF 677 in vitro plantlets did not show any significant decrease in relative growth rate, while it increased in MrS 2/5 plantlets exposed to 100 µM CuSO4. In both rootstocks, the copper concentration in plantlet tissues increased when CuSO4 changed from 0.1 to 10 and 100 µM.

Light and growth rate effects on crop and weed responses to nitrogen

The nitrogen (N) response of competing plants may be affected by photosynthetically active radiation (PAR) availability and maximum potential growth rate, which determine N requirements. The responses of two crop (corn and soybean) and six weed species (common lambsquarters, common waterhemp, giant foxtail, velvetleaf, wild mustard, and woolly cupgrass) in low and high (150 and 450 μmol m−2s−1) PAR levels to daily fertilization with either low or high (0.2 or 7.5 mM) NH4NO3levels were studied. Leaf area of all species responded positively to N by 8 d after emergence (DAE) when grown in high PAR; in low PAR, most species did not respond until 11 DAE. Dry weight and leaf area of all species at 18 DAE were greater with high than with low N. These responses to high N were also greater in high than in low PAR for all species. Dry weights with high N were up to 100% greater in low PAR and up to 700% greater in high PAR than dry weights with low N. These responses suggest that low PAR reduced the benefit of N to the plants. The regression of relative growth rate (RGR) with high N to RGR with low N had a slope that was less than unity (β = 0.79), indicating that species with a higher RGR with high N experienced greater decreases in RGR with low N. Similarly, the sensitivity (change in RGR) of plants grown with high and low N was positively related to RGR with high N. RGR differences among crop and weed species may be related to differences in N requirement that could be exploited for weed management. RGR and seed size were negatively correlated, which may explain previous observations that small-seeded weeds were more sensitive to environmental stress.

Interactive Effects of Salinity and Ozone Pollution on Photosynthesis, Stomatal Conductance, Growth, and Assimilate Partitioning of Wheat (Triticum aestivum L.)

Plants of an Egyptian cultivar of wheat (Triticum aestivum L. cv. Giza 63) were exposed in open-top chambers (OTCs) for 8 h d−1 for up to 75 d to a factorial combination of two levels of salinity (0 and 50 mM NaCl) and two levels of O3 (filtered air and 50 mm3 m−3). Exposure to 50 mm3 m−3 O3 significantly decreased stomatal conductance (g s), net photosynthetic rate (P N), and chlorophyll (Chl) content by 20, 25, and 21 %, respectively. This reduction resulted in a change in assimilate allocation in favour of shoot growth leading to a decrease in root to shoot ratio and eventually to a decrease in relative growth rate (RGR) of both root and shoot. There was a very large reduction in yield parameters, especially in the number of ears/plant and 1 000-grain mass. Soil salinity significantly reduced P N and g s by 17 and 15 %, respectively, while Chl content was increased by 17 %. Root growth was decreased leading to an increase in root/shoot ratio. Yield parameters were decreased due to salt stress. There was antagonistic interaction between salinity (50 mM NaCl) and O3 (50 mm3 m−3) showing that salinity effectively protects against the adverse effects of O3 by increasing g s during O3 fumigation.

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

TEMPERATURE EFFECTS ON PHOTOSYNTHESIS, GROWTH RESPIRATION, AND MAINTENANCE RESPIRATION OF MARIGOLD

Effect of Magnesium Deficiency on Pepper Growth Parameters: Implications for Determination of Magnesium‐Critical Value

In order to improve determinations of nutrient critical levels using growth response curves, a detailed study of magnesium (Mg) deficiency on pepper (Capsicum annuum L.) biomass allocation was performed. For each growth parameter, data were fitted using the modified Mitscherlich's model and Mg‐critical level was calculated. Under Mg‐deficiency, pepper plants showed a decrease in their relative growth rate (RGR), total dry weight (DW), stem and root mass fractions (SMF and RMF), total leaf area, specific leaf area (SLA), and unit leaf rate (ULR), whereas leaf mass fraction (LMF) and shoot to root ratio increased. Growth response coefficient (GRC) analysis indicated that the decrease in RGR was mainly due to a decrease in ULR. When the interval time between two harvests was ≥10 days, determination of Mg‐critical level (x c ) using the modified Mitscherlich's model showed that the best growth parameter for early detection of Mg‐deficiency in pepper plants was total DW (x c ≈ 0.21%), whereas other parameters underestimated Mg‐critical level.

Quantitative traits associated with adaptation of three barley (Hordeum vulgare L) cultivars to suboptimal iron supply

Iron stress responses were examined for 3 barley cultivars (Hordeum vulgare L. cvs. Steptoe, Morex and Dicktoo) grown at 5 iron levels (pFe 16.5, 17, 17.5, 18, 19) in chelator-buffered hydroponic solutions. Among the 3 cultivars, Steptoe produced the highest biomass and maintained the highest leaf chlorophyll content at each incremental decrease in Fe supply, followed by Dicktoo and Morex. All 3 cultivars responded to Fe limitation by early release of phytosiderophore prior to onset of Fe-deficiency chlorosis sp., but differed in the length of time prior to maximum phytosiderophore release. With Steptoe, near maximum release [42 μmol g−1 root (2 h)−1] occurred at day 6 for plants grown at pFe 18, and the plants maintained the same relative growth rate as Fe-sufficient plants (pFe 16.5) until day 15. In contrast, maximum rates of phytosiderophore release in Dicktoo and Morex peaked higher at 67 and 56 μmol g−1 root (2 hr)−1, but not until day 12 and day 18, respectively. By day 10, both Dicktoo and Morex were chlorotic and had a ∼50% decrease in relative growth rate. Under moderate Fe stress, all 3 cultivars decreased their shoot:root ratios by 25–30%, but differed with respect to specific root length and numbers of root tips per unit root length. The results suggest that differences in plant adaptation to Fe limitation cannot always be attributed to differences in quantities of phytosiderophore release, but also reflect several additive responses including timing of phytosiderophore release, root morphological adaptations and efficiency in Fe metabolism at low tissue Fe concentrations.

Effects of shading and removal of plant parts on growth of Trema micrantha seedlings.

Effects of artificial shading and removal of plant parts on growth of Trema micrantha (L.) Blume (Ulmaceae) seedlings were studied. Seedlings were grown in pots in a greenhouse in 45, 30, 10.6, 4.8 and 1.8% of full sunlight. Shading for 60 days had no effect on survival, but it influenced all growth parameters measured. Total biomass decreased with decreasing irradiance, reflecting reductions in dry mass of leaves, stems and roots. In response to shading, allocation of biomass to leaves increased, while allocation of biomass to roots decreased. Specific leaf area, leaf area ratio and leaf mass ratio increased with decreasing irradiance. Decreases in relative growth rate were caused by reductions in net assimilation rate rather than leaf area ratio. Photosynthetic efficiency, as determined by the Fv/Fm ratio (Fv = variable fluorescence, Fm = maximal fluorescence), was unaffected by the shading treatments. Partial removal of leaves, stem or roots did not affect seedling survival. Seedlings responded to removal of plant parts by compensatory growth. Topophysis was observed when the apex was removed: the lateral buds developed only as new plagiotropic lateral shoots; consequently, the decapitated plant ceased height growth and was unable to compete with its neighbors for light.

Influence of Seed Size on Seedling Growth of Albizia procera Under Different Soil Water Levels

Albizia procera Benth. is an early successional leguminous tree species that occurs naturally in dry tropical forests in India. The growth response of seedlings of A. procera from seeds of different sizes was studied under four soil water levels. Seeds were surface sterilized, germinated and grown in a glasshouse for 3 weeks under optimal water supply, and were subsequently maintained at four soil water levels for 4 months. Soil matric potentials for 1,<$>{\ extstyle\\raise1.3pt{1\\over 2}}<$>,<$>{\ extstyle\\raise1.3pt{1\\over 3}}<$>and<$>{\ extstyle\\raise1.3pt{1\\over 4}}<$>water holding capacity (WHC) were −0.01, −0.1, −0.61 and −1.20MPa, respectively. Plant height, stem diameter and leaf area were measured fortnightly. Seedlings were harvested at the end of the experiment. Biomass, relative growth rate (RGR), stem weight ratio (SWR), root:shoot ratio (R:S ratio) and net assimilation rate (NAR) were determined. Seedlings from large seeds had a higher biomass and leaf area and were more tolerant of long-term extreme water stress compared to those from small seeds which were more tolerant of moderate levels of water stress. Seedlings from small seeds did not survive beyond 75d at<$>{\ extstyle\\raise1.3pt{1\\over 4}}<$>WHC. Increase in the R:S ratio along with a decrease in SWR reflected a shift in biomass allocation from above- to below-ground parts as soil water level decreased. SLA declined sharply with increasing water stress, which in turn led to a decrease in RGR. NAR increased with water stress. The study revealed the ability of the species to acclimate to a wide range of moisture stress by morphogenetic (increased R:S ratio and decreased SWR) and physiological (increased NAR) plastic responses.

Plasticity in relative growth rate and its components following a change in irradiance

ABSTRACTA total of 244 plants from two species, Lythrum salicaria and Epilobium glandulosum, were grown individually in hydroponic sand culture from seed for 36 d. Until day 27 all plants experienced an irradiance of 550 μmol m−2 s−1 PFD and on day 27 half of the plants were subjected to a neutral shade treatment in which irradiance was reduced to 100 μmol m−2 s−1 photon fluy density (PFD). Measures of relative growth rate, net assimilation rate, specific leaf area, biomass partitioning to leaves, roots, structural tissues (i.e. stems, petioles and inflorescences) and tissue density were obtained from intensive harvests three or four times per day. The shade treatment caused an immediate decrease in relative growth rate and net assimilation rate. Within hours the specific leaf area of the shaded plants increased and leaf tissue density decreased, thus partially offsetting the decrease in relative growth rate. Biomass partitioning was not affected.

Effects of Trifluralin on Carp: Biochemical and Histological Evaluation

Acute and subacute toxicity of the herbicide trifluralin on fish was investigated in laboratory toxicity tests with carp. Median lethal concentrations were determined in acute tests. The 96-h LC50 value was 0.045 (0.036–0.051)mg/L. Fish were exposed to subacute concentrations of the herbicide (0.005, 0.01, and 0.02 mg/L trifluralin) in the 14-day toxicity tests and the effects on the relative growth rate, some biochemical parameters [alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanin aminotransferase (ALT) activities in serum, gills, liver, and kidney], gills, liver, and kidney structure were studied. A decrease in relative growth rate was found. An increase of functional enzyme activities in blood serum and the organs examined, particularly in the highest concentration of trifluralin indicated changes in the vital organs, was confirmed by histological analysis. The most severe changes (although mostly reversible) were found in the gills and kidney of the fish examined.

Compared Effects of Sudden and Progressive Impositions of Salt Stress in Three Durum Wheat (Triticum durum Desf.) Cultivars

The effect of sudden vs. progressive exposure to salt stress at the seedling stage was investigated in three durum wheat cultivars differing in their mean level of sale and drought resistance. Both procedures of stress imposition induced a decrease in relative growth rates, K concentrations and leaf osmotic potential values, as well as an increase in Na, proline and soluble sugar contents. Growth inhibition was largest in the drought-resistant cultivar Omrabi 5, suggesting that drought and salt-resistance are not necessarily linked in Triticum durum. Suddenly-applied NaCl often appeared more detrimental than progressive exposure. Quantitative differences between the effects of the two modes of stress imposition suggested the existence of a precocious adaptative mechanism in response to progressive exposure but varied according to the physiological parameter used to evaluate plant behaviour, the final dose of NaCl and the genotype. The most salt-resistant cultivar (Belikh) was the less influenced by the kinetics of stress application. The modification of the mineral nutrition- and osmotic adjustment-related parameters is discussed in relation to the specific physiological strategy of salinity resistance postulated in Triticum durum and in light of the contrasting evidence in the literature.

Sensitivity to and requirement for iron in Plantago species

The relative importance of some aspects of iron nutrition for the distribution of six Plantago species (P. maritima L., P. coronopus L., P. major ssp. major L., P. serpentina All., P. media L. and P. lanceolata L.) with different habitat requirements for soil pH and moisture was evaluated. Iron efficiency and Fe tolerance of hydroponically‐grown plants were assessed by determining the decrease in relative growth rates caused by suboptimal and supra‐optimal external Fe concentrations. Marked interspecific differences were observed in visual symptoms of Fe deficiency and Fe toxicity and in the external Fe concentrations leading to 50% inhibition of maximal relative growth rates (rgr50%). Whereas P. serpentina displayed a clear preference for low external Fe concentrations, growth rates of P. maritima and P. media were found to be increased at higher concentrations. Severe growth restriction at both low and high Fe concentrations was evident in P. lanceolata and P. major. A broad optimum was observed in P. coronopus exhibiting a low external Fe requirement and a high tolerance to supra‐optimal Fe concentrations. Iron efficiency and Fe tolerance differed in a way which was only partly correlated with the expected Fe availability at the natural habitat of the species, suggesting that Fe concentrations are of minor importance for their distribution, or that some of the mechanisms that render Fe oxides available for uptake in situ are masked in solution experiments.To gain insight into the impact of the physiological and morphological characteristics of the species on Fe efficiency, the effect of Fe status on shoot∶root ratio, relative root surface area, root Fe(III) reductase and proton extrusion capacity were investigated. Roots of all species showed increased Fe chelate reduction activity upon growth at suboptimal Fe concentrations; marked differences were observed with respect to the kinetic parameters of the reductase. Maximal velocity of the reduction was positively correlated with relative growth rate and was not related to the Fe efficiency of the species. By contrast, Km corresponded to Fe efficiency ranking and can therefore be regarded as an important parameter for the uptake of Fe at low availability. Enhanced ability to acidify the rhizosphere was only observed in P. major. From the morphological characteristics investigated, root surface area appears to be the most important parameter in the uptake of Fe at suboptimal external concentrations.

Effects of nitrogen supply on the anatomy and chemical composition of leaves of four grass species belonging to the genus Poa, as determined by image‐processing analysis and pyrolysis–mass spectrometry

ABSTRACTPrevious experiments have shown that the anatomy and chemical composition of leaves of inherently fast‐ and slow‐growing grass species, grown at non‐limiting nitrogen supply, differ systematically. The present experiment was carried out to investigate whether these differences persist when the plants are grown at an intermediate or a very low nitrogen supply. To this end, the inherently fast‐growing Poa annua L. and Poa trivialis L., and the inherently slow‐growing Poa compressa L. and Poa pratensis (L.) Schreb. were grown hydroponically at three levels of nitrate supply: at optimum (RGRmax) and at relative addition rates of 100 and 50 mmol N (mol N)−1 d−1 (RAR100 and RAR50), respectively.As expected, at the lowest N supply, the potentially fast‐growing species grew at the same rate as the inherently slow‐growing ones. Similarly, the differences in leaf area ratio (LAR, leaf area:total dry mass), specific leaf area (SLA, leaf arear:leaf dry mass) and leaf mass ratio (LMR, leaf dry mass:total dry mass) disappeared. Under optimal conditions, the fast‐growing species differed from the slow‐growing ones in that they had a higher N concentration. There were no significant differences in C concentration. With decreasing N supply, the total N concentration decreased and the differences between the species disappeared. The total C concentration increased for the fast‐growing species and decreased for the slow‐growing ones, i.e. the small, but insignificant, difference in C concentration between the species at RGRmax increased with decreasing N supply.The chemical composition of the leaves at low N supply, analysed in more detail by pyrolysis–mass spectrometry, showed an increase in the relative amounts of guaiacyl lignin, cellulose and hemicellulose, whereas those of syringyl lignin and protein decreased.The anatomy and morphology of the leaves of the four grass species differing in RGRmax were analysed by image‐processing analysis. The proportion of the total volume occupied by mesophyll plus intercellular spaces and epidermis did not correlate with the amount of leaf mass per unit leaf area (specific leaf mass, SLM) at different N supply. The higher SLM at low N supply was caused partly by a high proportion of non‐veinal sclerenchymatic cells per cross‐section and partly by the smaller volume of epidermal cells.We conclude that the decrease in relative growth rate (and increase in SLM) at decreasing N supply is partly due to chemical and anatomical changes. The differences between the fast‐ and slow‐growing grass species at an optimum nutrient supply diminished when plants were growing at a limiting nitrogen supply.

Growth of Cucumber Fruit as Affected by the Addition of NaCl to Nutrient Solution.

Effects of adding NaCl to a nutrient solution of cucumber (Cucumis sativus L. cv. Asomidori) plants at 10 leaves stage on the fruit growth were studied in solution culture. Nondestructive growth analyses of individual fruits until marketable size (20 cm long) were repeated for 3 to 4 weeks after the treatment.NaCl had marked effects on the relative growth rate (RGR) based on volume depending on NaCl concentration and the growing season. Thirty mM NaCl had little effect on fruit RGR, whereas 100 mM NaCl caused necrosis. In the spring experiments, 50 mM and 60 mM NaCl caused a decrease in RGR with high variablility among fruits. In the autumn experiments, 60 mM NaCl did not decrease RGR when fruit temperature was not controlled, but it did when fruits were kept at 20°C or 30°C. Sixty mM NaCl is suggested to be the threshold for normal fruit growth, at which other environmental factors seem to interact with the treatment.