New seed morphological features in Moehringia L. (Caryophyllaceae) and their taxonomic and ecological significance

Abstract

Relative growth rate (RGR) is a fundamental trait for comparative plant ecology but cannot be measured in situ, leading to problems in interpreting vegetation function. However, the components of RGR (net assimilation rate (NAR), leaf area ratio (LAR), leaf weight ratio (LWR), and specific leaf area (SLA)) can be calculated for wild plants from morphological measurements (leaf area, leaf dry mass, whole plant dry mass), which potentially reflect RGR. Seeds of 19 species from Italian prealpine calcareous grasslands were collected and seedlings were cultivated under controlled conditions. RGR, NAR, LAR, LWR and SLA were analysed. The results demonstrated that RGR was positively correlated with SLA and LAR (p < 0.01). Furthermore, LAR was positively correlated with LWR and negatively with NAR (p < 0.05). Monocotyledons showed significantly higher LAR, LWR and NAR than dicotyledons, as the latter allocated a greater proportion of biomass to stems, but RGR and SLA showed no such phylogenetic constraint. Therefore SLA is the most reliable indicator of RGR in ecological and functional surveys of prealpine calcareous grasslands, and has the additional advantage that it can be measured from leaf material alone. Lower mean RGR and SLA for calcareous grassland species suggests that this vegetation is less likely to recover from the effects of disturbance than meadows and dry meadows.     

Responses of photosynthesis,leaf conductance and growth to different salinities in three coastal dune plants

The effects of soil-water salinity on growth and photosynthesis of three coastal dune plants were examined by salt-treatment in order to clarify the causal relationship between salinity and plant distribution in a dune habitat. Plants were cultivated hydroponically at three salinity levels: 0, 10 and 100 mM NaCl. With the 100 mM salt treatment,Calystegia soldanella (C₃ species) had the highest relative growth rate (RGR) (0.085 g g⁻¹ d⁻¹), followed byCarex kobomugi (C₃) (0.066), andIschaemum anthephoroides (C₄) (0.060). This order coincides with the distribution pattern of the three species on coastal dunes;Calystegia soldanella is generally distributed in more seaward areas whereasI. anthephoroides occurs further inland. The order of RGR was determined exclusively by leaf area ratio (LAR) among the three species. Due to its C₄ pathway,I. anthephoroides had higher net photosynthetic rate (Pn) and net assimilation rate (NAR) than the two C₃ plants at all NaCl concentrations, despite its low RGR. This apparent discrepancy is explainable by differences of LAR among the three species; LAR ofI. anthephoroides was lowest, and about half that ofCalystegia soldanella. These results suggest that LAR is one of the main determinants of salt tolerance based on RGR, whereas Pn or NAR may not be significant. This article is dedicated to Professor Hideo Iwaki, University of Tsukuba, in appreciation of the sincere encouragement he has given to the authors.     

The effects of NaCl and CaCl2 on photosynthesis and growth of alfalfa plants

The effects of 0, 30, 60, and 90 mM NaCl, and 0 and 5 mM CaCl2 on certain parameters of photosynthesis and growth in alfalfa (Medicago sativa L. cv. Ghara yonjeh) plants were studied. The increasing NaCl concentration in the Hoagland nutrient solution decreased the contents of chlorophylls and the net photosynthetic rate, and increased the rate of respiration (RD) and CO2 compensation concentration in the leaves of treated plants. The contents of carotenoids (Car) were not significantly affected. The addition of 5 mM CaCl2 enhanced the RD and increased the Car contents in treated leaves. With the NaCl concentration in the culture medium increasing, the dry matter production in both root and shoot decreased, as well as the relative growth rate (RGR), net assimilation rate (NAR), and leaf area ratio (LAR). The addition of CaCl2 caused a partial elimination of the NaCl effects on the root and shoot, RGR and NAR, and it decreased the LAR.     

Effect of Photoperiod on Vegetative Growth in Two Natural Populations of Dactylis glomerata L.

The growth of two natural populations of cocksfoot from contrastingclimatic regions (Norway and Portugal) was studied at four temperaturesand two photoperiods. Serial harvests were taken and quadraticcurves were fitted to log dry weight and leaf area for eachreplicate in order to calculate growth attributes at a constantplant weight for all treatments. Interactions of population,temperature, and photoperiod on relative growth-rate (RGR) werefound, with the greatest population differences at 5 and 30°C in an 8-h photoperiod. Leaf-area ratio (LAR) played alarger part than net assimilation rate (NAR) in determiningthe differential population responses in RGR to daylength, andthese differences in LAR were primarily the result of differentpatterns of dry-matter distribution within the plant.     

Net assimilation rate and relative nitrogen assimilation rate in relation to the dry matter production of alfalfa cultivars

Summary Twelve alfalfa cultivars inoculated with an indigenous strain (RM9) ofRhizobium meliloti, were compared for their seedling morphological characters, and growth characters, including net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR) and relative nitrogen assimilation rate (R_N). Highly significant differences were obtained between cultivars for most characters.Simple correlation showed that NAR influenced RGR (r=0.91) more than leaf area ratio (LAR) (r=–0.44), and that most characters measured were highly correlated with seedling dry weight. Factor analysis showed that NAR, RGR and R_N contributed 25% of the total variation in the dependence structure. The grouping indicated that the higher the NAR and R_N the greater was the RGR. Path-coefficient analysis showed that NAR had more important direct and indirect effects than R_N in dry matter accumulation. The relationship implied that selection for plants with high NAR, or high efficiency in converting light energy to dry matter production could contribute greater N₂ fixation in alfalfa.     

The Interrelated Effects of Stage of Development and Seasonal Changes in Light and Temperature on the Components of Growth in Zea mays

Seeds of Orla 266, a double cross hybrid of Zea mays, were sownin pots in the open 3, 6, and 9 weeks before the individualplants were sampled at consecutive weekly intervals from theend of August. On each occasion the weights of the whole plantand its parts plus leaf area were recorded, and the proceduresof growth analysis applied to the data. Between the youngest and oldest plants over all occasions thegreatest reductions with age were for the rate of leaf expansionand the ratio of leaf area to leaf weight. The net assimilationrate (NAR) and the leaf weight ratio (LWR) were depressed leastwhile the relative growth-rate (RGR) and leaf area ratio (LAR)occupied an intermediate position. The age effects were mostpronounced for RGR, NAR and the ratio of leaf area to leaf weightat the beginning of the experiment, whereas for LAR and LWRthe divergencies were largest at the end. On the basis of the recorded changes in solar radiation andtemperature and prior studies of the interacting effects oflight and temperature on the vegetative growth of Zea it waspossible to predict for the several growth components the patternsof change which should be expected. For the youngest and intermediatepopulations there was close agreement between the expected andobserved values for RGR, NAR, and LAR and it was concluded thatthe time courses were primarily dependent on environmental factors.On the other hand, for the oldest plants from the third intervalonwards the observed values for NAR and less so for RGR werematerially above expectation. It was noted that this divergencecoincided with the rapid extension of the shoot which was confinedto the oldest plants. It is advanced that the higher NAR isassociated with the vertical separation of the leaves.     

Potassium requirements for growth and its related processes determined by plant analysis in wheat

Summary Potassium requirements for growth—dry matter (DM) and leaf area (LA) and related processes — relative leaf growth rate (RLGR), relative growth rate (RGR), net assimilation rate (NAR) and crop growth rate (CGR) were determined by plant analysis during the entogeny of wheat. Wheat (Triticum aestivum cv. HD 2329) plants were supplied with different amounts of K from deficient to adequate through nutrient solution. Samples were taken at specific stages for K determinations. The DM and LA were recorded at 45d, 75d and 105d. The growth related processes RGR, NAR and CGR were estimated between 30–45d, 45–75d and 75–105d. In case of RLGR the observations were carried out between 15–30d, 30–45d and 45–75d. These physiological processes and grain yield were correlated with K concentration in whole plant at 30 and 45d and top two leaves at 75 and 105d. The results indicated that k status in plants influences growth mostly through leaf area formation which inturn influences successively RLGR, RGR and CGR and finally grain yield. For vegetative growth the optimum concentration required in plants was always lower than the optimum for grain production.     

Variation in relative growth rate of 20 Aegilops species (Poaceae) in the field: The importance of net assimilation rate or specific leaf area depends on the time scale

Field experiments reporting the relative growth rate (RGR) patterns in plants are scarce. In this study, 22 herbaceous species (20 Aegilops species, Amblyopyrum muticum and Triticum aestivum) were grown under field conditions to assess their RGR, and to find out if the differences in RGR amongst species were explained by morphological or physiological traits. Plants were cultivated during two months, and five harvests (every 13–19 days) were carried out. Factors explaining between-species differences in RGR varied, depending on whether short (13–19 days) or longer periods (62 days) were considered. RGR for short periods (4 growth periods of 13–19 days each) showed a positive correlation with net assimilation rate (NAR), but there was no significant correlation with leaf area ratio (LAR) (with the exception of the first growth period). In contrast, when growth was investigated over two months, RGR was positively correlated with morphological traits (LAR, and specific leaf area, SLA), but not with physiological traits (NAR). A possible explanation for these contrasting results is that during short growth periods, NAR exhibited strong variations possibly caused by the variable field conditions, and, consequently NAR mainly determined RGR. In contrast, during a longer growth period (62 days) the importance of NAR was not apparent (there was no significant correlation between RGR and NAR), while allocation traits, such as LAR and SLA, became most relevant.     

A Further Analysis of Hybrid Vigour in Zea mays during the Vegetative Phase

Employing the procedures of growth analysis further pot experimentson hybrid vigour in Zea mysa have been conducted in a glasshouse.By serial sampling the changes in plant weight and leaf areahave been followed for six hybrids and their immediate parentsof either dent or flint type. Within 2–3 weeks from sowingthe relative growth-rate (RGR) of the hybrid was significantlygreater in four out of the six triplets and in the remainingtwo the rate for the hybrid exceeded that of one parent. Thesedifferences diminished with time but when observations ceasedat the end of 7 weeks the weight and area of the hybrid wasfrom 1.5 to 1.9 times greater than that of the larger parent.By this time too all but one of the hybrids but none of theparents were in flower. The two components of growth, the leaf-area ratio (LAR) andthe net assimilation rate (NAR) did not differentiate in a consistentmanner between the hybrid and the parents, because of the considerablevariation between emergence and flowering. All the hybrids atsome time up to 28 days had a significantly higher LAR thanthose of one or both parents. Similarly for NAR on no occasionup to 4 weeks did any parent exceed the level of the hybridbut for some hybrids and for some occasions the NAR was significantlyhigher than that of at least one of the parents. Later for bothparameters none of the differences within triplets were significant. A flint and a dent triplet were grown at constant air temperaturesof 10, 15, and 20 °C and illuminated for 14 h at 22 600lx and sampled during the vegetative phase. The results showedthat there were marked differences in the temperature responseswithin and between triplets. The flint hybrid grew faster thanits parents at 15 and 20 °C but not at 10 °C. In contrast,the superiority of the RGR of the dent hybrid was greatest at10 °C. These differences are largely reflected by changesin NAR rather than LAR. The higher NAR of the flint hybrid isfound at 15 and 20 °C, but the superiority of the dent hybridis most evident at 10 °C. The comparative performance within one triplet was examinedfor small and large grains. The patterns of change in the growthcomponents were not influenced by grain size. The interacting effects of genotype, stage of development, andtemperature level are discussed. It is concluded that in thefield the over-riding factor determining hybrid vigour is thehigher RGR in the postemergence phase and that the genetic variationover the six triplets is greater for NAR than LAR.     

The effect of nitrogen nutrition on growth and biomass partitioning of annual plants originating from habitats of different nitrogen availability

Summary The hypothesis was tested that faster growth of nitrophilic plants at high nitrogen (N) nutrition is counterbalanced by faster growth of non-nitrophilic plants at low N-nutrition. Ten annual plant species were used which originated from habitats of different N-availability. The species' preference for N was quantified by the N-number of Ellenberg (1979), a relative measure of nitrophily. The plants were cultivated in a growth cabinet at five levels of ammonium-nitrate supply. At low N-supply, the relative growth rate (RGR) was independent of nitrophily. At high N-supply, RGR tended to be higher in nitrophilic than in non-nitrophilic species. However, the response of RGR to N-supply was strongly and positively correlated with the nitrophily of species. Increasing N-supply enhanced partitioning to leaf weight per total biomass (LWR) and increased plant leaf area per total biomass (LAR). Specific leaf weight (SLW) and LWR were both higher in non-nitrophilic than in nitrophilic species at all levels of N-nutrition. NAR (growth per leaf area or net assimilation rate) increased with nitrophily only under conditions of high N-supply. RGR correlated positively with LAR, irrespective of N-nutrition. Under conditions of high N-supply RGR correlated with SLW negatively and with NAR positively.     

The Influences of Seasonal Changes in Solar Radiation and Air Temperature on the Growth in the Early Vegetative Phase of Zea mays

At weekly intervals from May to September over 2 years the growthof separate batches of Zea mays (Swiss hybrid Orla 266) wasrecorded for individual plants in pot experiments, togetherwith the corresponding weekly means of solar radiation and themean, maximum, and minimum diurnal air temperatures. To reducesampling errors the plants were ranked on the bases of initialgrain size and leaf number. To minimize differences in stageof development at the end of 21 days from sowing the size wasadjusted in 1965 by switching the pots in and out of a glasshouse:in 1966 the plants were kept for the first 11 days in a controlledenvironment and then hardened off in the open. Between 21 and28 days when the second sample was taken half the plants weresubjected to light shade (0.65–0.70 daylight). Multiple regression analysis showed that the relative growthrate of the whole plant (RGR), the rate of increase in leafarea (RLGR), and the net assimilation rate (NAR) were positivelydependent on both radiation and mean air temperature. In 1965there were negative effects of minimum temperature on RGR andNAR and a positive response of RLGR to leaf number. In 1966an increase in leaf number led to a higher RGR and LAR but depressedRLGR, while minimal temperature had no significant effects.In all these regressions the variation accounted for was high,ranging from 80 to 89 per cent. At the second sampling occasion the leaf-area ratio (LAR_f) wasinversely related to radiation, negatively dependent on daytemperature, but positively linked with night temperature. Theorder of the initial LAR exerted no influence. The RGRs of theshoot and the root were positively associated with both radiationand mean temperature. In 1965 there were small negative responsesof the shoot to both minimum temperature and leaf number andfor the root only leaf number. The variation accounted for wasleast for LAR_f (59–62 per cent) and intermediate for RGR_aand RGR_r (77–89 per cent). For RGR, NAR, and RLGR the calculated partial regression coefficientsfor mean temperature in 1965 were larger than those for radiationbut in 1966, apart from RLGR, they were equalled by radiation.The discrepancies between years can be ascribed to a highercorrelation coefficient between radiation and temperature in1965 (0.53) as against 1966 (0.33). The value of multiple regression analysis in the evaluationof the environment by carefully designed field experiments isemphasized in relation to other investigations of light andtemperature undertaken under controlled conditions.     

Growth and ion accumulation of two rapid-cycling Brassica species differing in salt tolerance

The response of two rapid-cycling Brassica species differing in tolerance to seawater salinity was studied over a period of 24 days. In response to 8 dS m⁻¹ salinity, the two Brassica species showed clear differences in the changes in relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR). The RGR of B. napus was slightly reduced by salinity, wheareas the RGR of B. carinata was largely reduced in the early stages of salinization. LAR of B. napus was affected by salinity in the later stages of growth and significantly correlated with the reduction in RGR. On the other hand, the NAR of B. carinata was decreased by salinity, corresponding to the decrease of the RGR of B. carinata. The NAR of B. napus was not significantly affected by salinity according to analysis of covariance. The shoot concentrations of Na, Mg and Cl increased while the concentrations of K and Ca decreased sharply during the first 5 days of salinization; subsequently, all ion concentrations remained relatively constant. The concentrations of Na, K, Ca, Mg and Cl in the root were similarly affected by salinity. There were no significant differences of ion concentrations between species that could be related to the differences in salt tolerance. Thus, the differences in salt tolerance between species can not be related to differences in specific-ion effects, but may be related to some factor that reduces the NAR of B. carinata during the early stages of growth.     

Assimilation Rate and Growth of Lolium Populations in the Glasshouse in Contrasting Light Intensities

Using growth-analysis techniques, the variation in relativegrowth-rate (RGR) and its components, net assimilation rate(NAR), and leaf-area ratio (LAR), was examined in 18 populationsof L. perenne, six of L. multiflorum, and two hybrid cultivarsfrom contrasting climatic and agronomic origins, grown at lowand high light intensities in the glasshouse. Significant differences between populations were found for RGR,NAR, and LAR at both light intensities. At both intensitiesthe annual or biennial multiflorum group had a greater LAR anda lower specific leaf weight and chlorophyll content than theperennial perenne group. At the low intensity this was compensatedby a greater NAR in the perenne group, with no resultant differencein RGR. At the high intensity there was no difference betweenthe groups in NAR, and hence a greater RGR in the multiflorumgroup. Within the perenne and multiflorum groups, at both light intensities,the variation between populations in RGR was based on differencesin NAR rather than in LAR. There was no regular correlationof NAR with either specific leaf weight, or chlorophyll contentat either light intensity, though at low light intensity itwas significantly correlated with shoot-root ratio.     

The effect of a rosette-crown fly, Botanophila turcica, on growth,biomass allocation and reproduction of the thistle Carthamus lanatus

Plant growth and reproductive output of the winter annual invasive thistle, Carthamus lanatus was characterised in relation to plant size in three native populations in southern France. The effects of the rosette-crown feeding fly Botanophila turcica on these plant characteristics were assessed by comparing unattacked with naturally attacked plants at each site and by a field experiment. Indirect effects of B. turcica on plant seed production were also compared with direct seed loss caused by a guild of capitulum-feeding insects that incidentally attacked the marked plants at these sites. C. lanatus showed no size or weight requirement for flowering, but larger flowering plants produced less total receptacle surface and less seed production (female reproductive potential) in proportion to plant weight than smaller flowering plants. B. turcica did not select hosts on the basis of size or density. B. turcica reduced plant relative growth rate (RGR) in all situations, but attacked plants compensated fully at two of three sites as attack failed to halt rosette growth. Attacked plants suffered 12 % mortality, and 71 % lower seed production than unattacked plants at the site with the lowest RGR. This corresponded to 9 % lower seed production for the whole thistle population compared to 8.6–19.5 % direct seed loss to capitulum insects across all sites.     

Effects of sodium, potassium and calcium on salt-stressed barley. I. Growth analysis

Barley ( Hordeum vulgare L. cv. CM 72) was grown for a 28-day period and stressed with treatments of 125 mol m⁻³ NaCl or KC1 with low Ca²⁺ (0.4 mol m⁻³ Ca²⁺) or high Ca²⁺ (10 mol m⁻³ Ca²⁺). Plants were harvested periodically so that relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) could be calculated using the functional approach to plant growth analysis. Relative growth rate declined with time for all treatments, including controls. Salinity inhibited RGR relative to control values by day 10. High Ca²⁺ improved the growth of salt-stressed plants in both NaCl-salinity and KCl-salinity. KC1 proved more toxic than NaCl, especially for KCI-salinity plants with low Ca²⁺, which died by day 28. Net assimilation rate, but not LAR, was highly correlated with RGR for all treatments. This indicates that the photosynthetic-assimilatory machinery was limiting RGR and not the leaf area of the plant.     

Modelling seedling growth rates of 18 temperate arable weed species as a function of the environment and plant traits

BACKGROUND AND AIMS: The early growth rate of seedlings in the exponential phase is an important eco- physiological trait in crop/weed competition models based on assessments of relative weed green area. An understanding of the role of various plant traits in determining early growth rate may also be useful for identifying contrasting weed strategies for establishment before canopy closure. METHODS: The response of seedling relative growth rate (RGR) to the environment was measured in outdoor sand beds in the autumn and the spring for 18 temperate annual weed species and two crops. Seedling growth was modelled using thermal time and effective day-degrees (combining the effect of temperature and radiation). The contribution of various plant traits in determining variability in RGR was investigated using regression analysis. KEY RESULTS: The effective day-degree model was more effective for describing early weed growth than thermal time. Variability in RGR measured in the autumn was largely determined by differences between the species in net assimilation rate (NAR), whereas in the spring leaf area ratio (LAR) played a larger part. There were differences between the broadleaf and grass species in the relative contribution of NAR and LAR to RGR in both seasons. RGR in the spring was negatively correlated with initial seedling size. CONCLUSIONS: The parameters derived in this study can be used to calibrate empirical models of crop yield loss based on relative weed green area to different growing seasons and assessment dates. The grass weeds, which tended to have large seeds, had a higher investment in roots in the seedling stage, potentially making them more competitive later in the season when resources become limiting.     

Waterlogging injury in sorghum seedlings and their kinetin effected rapid recovery

Short term waterlogging affected the growth of sorghum seedlings as indicated by a high mortality rate of the seedlings and a decrease in the shoot and root biomass, net assimilation rate (NAR), leaf area ratio (LAR), relative growth rate (RGR), total photosynthetic area and rate of photosynthesis. Plant resistance to the stress was exhibited by decreased stomatal index (SI), rate of transpiration and rate of respiration. When the stressed plants were exposed to normal conditions, the recovery of the seedlings was rapid and was enhanced by foliar application of kinetin at 5 mgl^-1.     

Growth Responses of Two Solanum Species to Contrasting Temperatures and Irradiance Levels: Relations to Photosynthesis, Dark Respiration and Chlorophyll Fluorescence

Potato production in the tropical lowlands during the rainyseason is constrained by high temperature and low irradiance.This study examined the effect of these two variables on drymatter production and allocation, using plant growth, leaf anatomy,gas exchange and chlorophyll fluorescence measurements. Plantsof two clones, Solanum goniocalyx cv. Garhuash Huayro (GH) andDTO-33, a heat tolerant clone of S. tuberosum x S. phureja,were grown in growth chambers at 33/25 °C or 20/10 °Cday/night temperature. At each temperature, plants were grownin either 12 h high irradiance (430–450 µmol m^–2s^–1 PAR) or 12 h low irradiance (250–280 µmolm^–2 s^–1) both with a 6–h photoperiod extensionof 6 µmol m^–2 s^–1. Plants were harvested after10 d (initial harvest) and after 20 d (final harvest). By theend of the study DTO-33 had produced more dry matter and hadtuberized, whereas GH had a greater leaf area ratio (LAR) andspecific leaf area (SLA). The highest relative growth rate (RGR)was at low temperature and low irradiance, possibly due to acombination of thin leaves with a large surface area. At thehigh temperature, low irradiance had the opposite effect, producingthe lowest net assimilation rate (NAR) and lowest RGR. Bothtuber number and weight were markedly reduced by high temperature.Low irradiance, in combination with high temperature, producedvirtually no tubers. Stomatal density, which was greater onGH than in DTO-33, was increased at high temperature. When measuredat 30 °C both clones, especially DTO-33, showed heat-adaptationin terms of ability to maintain a high rate of net photosynthesisat 30 °C. Plants grown at high irr-adiance and low temperaturehad the lowest net photosynthetic rate at 30 °C. Concurrentmeasurements of chlorophyll fluorescence indicated that onlythe initial (O) fluorescence parameter was affected. The dataconfirm the field observation that reduction in potato growthat high temperature can be aggravated by lower irradiance. Thisreduction is associated with a reduced leaf area and NAR. Growth analysis, heat adaptation, light     

Growth of bean and tomato plants as affected by root absorbed growth substances and atmospheric carbon dioxide

Summary Bean and tomato plants were grown in solution culture root media containing pre-determined concentrations of gibberellin A₃ (GA), 1-naphthaleneacetic acid (NAA), N⁶-benzyladenine (BA), (2-chloroethyl)trimethylammonium chloride (CCC), and at atmospheric levels of 300 and 1000 ppm of CO₂. Net assimilation rates (NAR), relative growth rates (RGR), leaf area ratios (LAR), root to top dry weight ratios (R/T) and changes in dry weight, size, and form of each organ were recorded.Gibberellin had no effect on RGR of either plant species but increased the NAR of tomatoes at 1000 ppm CO₂. Total dry weight was only slightly affected by GA but root growth and R/T were markedly depressed. CCC had no effect on NAR, but decreased RCR and LAR. Root growth of beans and R/T in both plants were promoted by CCC. NAR and RGR were strongly inhibited by BA and NAA. Inhibition of stem and leaf growth by CCC and NAA was greater than that for roots; thus, R/T ratios were increased. Root branching was promoted by NAA.High (1000 ppm), compared to the low (300 ppm), atmospheric levels of CO₂ generally promoted root growth and produced an increase in the R/T, both in the absence and presence of chemical treatment. The multiplicity of effects of the rootabsorbed chemical growth substances and CO₂ on growth and photosynthesis is discussed.Journal article No 3883 of the Michigan Agricultural Experiment Station.NATO Fellow, University of Pisa, Italy.     

Interspecific Variation in RGR and the Underlying Traits among 24 Grass Species Grown in Full Daylight

Abstract: A growth analysis was conducted with 24 central European grass species in full daylight to test whether traits underlying interspecific variation in relative growth rate (RGR) are the same in full daylight as they are at lower light, and whether this depends on the ecological characteristics of the studied species, i.e., their requirements with respect to nutrient and light availability.
In contrast to studies with herbaceous species at lower light, net assimilation rate (NAR) contributed more than leaf area ratio (LAR) or specific leaf area (SLA) to interspecific variation in RGR. This was associated with a larger interspecific variation in NAR than found in experiments with lower light. Without the two most shade-tolerant species, however, the contribution of LAR and its components to interspecific variation in RGR was similar or even higher than that of NAR.
Leaf dry matter content correlated negatively with RGR and was the only component of LAR contributing in a similar manner to variation in LAR and RGR. There was a positive correlation between NAR and biomass allocation to roots, which may be a result of nutrient-limited growth. RGR correlated negatively with biomass allocation to leaves. Leaf thickness did not correlate with RGR, as the positive effect of thin leaves was counterbalanced by their lower NAR.
Low inherent RGR was associated with species from nutrient-poor or shady habitats. Different components constrained growth for these two groups of species, those from nutrient-poor habitats having high leaf dry matter content, while those from shady habitats had thin leaves with low NAR.