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.     

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.     

Relative growth rate and biomass allocation in ten woody species with different leaf longevity using phylogenetic independent contrasts (PICs)

In this study, we compare the relative growth rate (RGR) and biomass allocation of 10 woody species (5 deciduous and 5 evergreen) from the Mediterranean region using phylogenetic independent contrasts (PICs) to test if these two functional groups differ in these traits. In general, the results were similar when using PICs or without taking into account phylogenetic relations. Deciduous species had a higher RGR than evergreen species, due to the higher net assimilation rate (NAR). Deciduous species had a higher specific leaf area (SLA) but a lower leaf mass ratio (LMR), resulting in a similar LAR for deciduous and evergreen species (LAR = SLA x LMR). In some cases, the use of PICs revealed patterns that would not have appeared if phylogeny had been overlooked. For example, there was no significant correlation between RGR and final dry mass (after 4 months of growth) but PICs revealed that there was a positive relation between these two variables in all deciduous-evergreen pairs. In general, RGR decreased with time and this temporal variation was due primarily to NAR variations (r = 0.79, p < 0.01), and also to variations in LAR (r = 0.69, p < 0.05). Considering the phylogeny, the only variable constantly different for all deciduous-evergreen pairs was SLA. This result, and the fact that SLA was the best correlated variable with RGR (r = 0.81, p < 0.01), reinforce the value of SLA as a variable closely associated to growth and to the functional groups (deciduous vs. evergreen).     

Modelling the relative growth rate as a function of plant nitrogen concentration

The relationship between the relative growth rate (RGR) and the nitrogen concentration of the whole plant (PNC) was analyzed by using experimentally determined relations (1) between the PNC and the fraction of dry matter (LWR) and nitrogen in leaves, (2) between the specific leaf area (SLA) and the leaf nitrogen concentration (LNC) and (3) between the net assimilation rate (NAR) and the LNC on an area basis. A strong dependence of RGR on nitrogen concentration resulted from the increase in NAR, LWR and SLA with increasing PNC. A curvilinear relationship between RGR and PNC gave an optimum curve for nitrogen productivity against PNC.     

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.     

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.     

Applicability and limitations of optimal biomass allocation models: a test of two species from fertile and infertile habitats

BACKGROUND AND AIMS: The practical applicability of optimal biomass allocation models is not clear. Plants may have constraints in the plasticity of their root : leaf ratio that prevent them from regulating their root : leaf ratio in the optimal manner predicted by the models. The aim of this study was to examine the applicability and limitations of optimal biomass allocation models and to test the assumption that regulation of the root : leaf ratio enables maximization of the relative growth rate (RGR). METHODS: Polygonum cuspidatum from an infertile habitat and Chenopodium album from a fertile habitat were grown under a range of nitrogen availabilities. The biomass allocation, leaf nitrogen concentration (LNC), RGR, net assimilation rate (NAR), and leaf area ratio (LAR) of each species were compared with optimal values determined using an optimal biomass allocation model. KEY RESULTS: The root : leaf ratio of C. album was smaller than the optimal ratio in the low-nitrogen treatment, while it was almost optimal in the high-nitrogen treatment. In contrast, the root : leaf ratio of P. cuspidatum was close to the optimum under both high- and low-nitrogen conditions. Owing to the optimal regulation of the root : leaf ratio, C. album in the high-nitrogen treatment and P. cuspidatum in both treatments had LNC and RGR (with its two components, NAR and LAR) close to their optima. However, in the low-nitrogen treatment, the suboptimal root : leaf ratio of C. album led to a smaller LNC than the optimum, which in turn resulted in a smaller NAR than the optimum and RGR than the theoretical maximum RGR. CONCLUSIONS: The applicability of optimal biomass allocation models is fairly high, although constraints in the plasticity of biomass allocation could prevent optimal regulation of the root : leaf ratio in some species. The assumption that regulation of the root : leaf ratio enables maximization of RGR was supported.     

Close relationship between leaf life span and seedling relative growth rate in temperate hardwood species

The life span of resource-acquiring organs (leaves, shoots, fine roots) is closely associated with species successional position and environmental resource availability. We examined to what extent leaf life span is related to inter- and intraspecific variation in seedling relative growth rate (RGR). We examined relationships between relative growth rate in mass (RGR_M) or height (RGR_H) and leaf life span, together with classical RGR_M components [net assimilation rate (NAR), specific leaf area (SLA), leaf weight ratio (LWR), and leaf area ratio (LAR)] for seedlings of five hardwood species of different successional position across a wide range of environmental resource availability, including the presence or absence of leaf litter in shaded forest understory, small canopy gaps, and large canopy gaps. Both SLA and LAR were negatively correlated with RGR_M along the environmental gradient for all species. However, positive correlations were observed among species within microsites, indicating that these two components cannot consistently explain the variation in RGR_M. Both NAR and LWR affect interspecific, but not intraspecific, variation in RGR_M. Leaf life span was negatively correlated with either RGR_M or RGR_H in both inter- and intraspecific comparisons. Species with short-lived, physiologically active leaves have high growth rates, particularly in resource-rich environments. Consequently, leaf life span is a good predictor of seedling RGR. Leaf life span affects plant performance and has a strong and consistent effect on tree seedling growth, even among contrasting environments.     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.     

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.     

Assimilation,respiration and allocation of carbon inPlantago major as affected by atmospheric CO2 levels

The response ofPlantago major ssp,pleiosperma plants, grown on nutrient solution in a climate chamber, to a doubling of the ambient atmospheric CO₂ concentration was investigated. Total dry matter production was increased by 30% after 3 weeks of exposure, due to a transient stimulation of the relative growth rate (RGR) during the first 10 days. Thereafter RGR returned to the level of control plants. Photosynthesis, expressed per unit leaf area, was stimulated during the first two weeks of the experiment, thereafter it dropped and nearly reached the level of the control plants. Root respiration was not affected by increased atmospheric CO₂ levels, whereas shoot, dark respiration was stimulated throughout the experimental period. Dry matter allocation over leaves stems and roots was not affected by the CO₂ level. SLA was reduced by 10%, which can partly be explained by an increased dry matter content of the leaves. Both in the early and later stages of the experiment, shoot respiration accounted for a larger part of the carbon budget in plants grown at elevated atmospheric CO₂. Shifts in the total carbon budget were mainly due to the effects on shoot respiration. Leaf growth accounted for nearly 50% of the C budget at all stages of the experiment and in both treatments.Abbreviations LAR leaf area ratio - LWR leaf weight ratio - RGR relative growth rate - R/S root to shoot ratio - RWR root weight ratio - SLA specific leaf area - SWR stem weight ratio     

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.     

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.     

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.     

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.     

Differential salt tolerance of two Artemisia species growing in contrasting coastal habitats

To investigate factors determining the differences in their salt tolerance, growth and germination, experiments were conducted on two plant species belonging to genus Artemisia: Artemisia fukudo Makino, a biennial salt marsh plant and Artemisia stelleriana Bess, a perennial coastal hind dune plant. Growth experiments revealed that salinity (100 and 300 m m NaCl) inhibited the relative growth rate (RGR) in A. stelleriana significantly but not in A. fukudo. These specific differences in salt tolerance were mainly attributed to differential responses of net assimilation rate (NAR). That is, the reduction in RGR in A. stelleriana was mainly due to the reduction in NAR, whereas no significant reduction in NAR was observed in A. fukudo. The reduction in RGR in A. stelleriana in the salt treatment was also attributable to a reduced leaf area ratio (LAR). Specific leaf area (SLA) in the two species decreased in the 300 m m treatment. The decrease in SLA in A. fukudo was, however, compensated for partly by an increase in leaf weight ratio (LWR). Germination experiments also showed that A. fukudo has a higher salt tolerance than does A. stelleriana. These results are consistent with the differences in the salinity conditions between the native habitats of the two species.     

Interspecific correlates of plasticity in relative growth rate following a decrease in nitrogen availability

Background and Aims

Nitrogen availability varies greatly over short time scales. This requires that a well-adapted plant modify its phenotype by an appropriate amount and at a certain speed in order to maximize growth and fitness. To determine how plastic ontogenetic changes in each trait interact and whether or not these changes are likely to maximize growth, ontogenetic changes in relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA) and root weight ratio (RWR), before and after a decrease in nitrogen supply, were studied in 14 herbaceous species.

Methods

Forty-four plants of each species were grown in hydroponic culture under controlled conditions in a control treatment where the supply of nitrogen remained constant at 1 mm, and in a stress treatment where the nitrogen supply was abruptly decreased from 1 to 0·01 mm during the growth period.

Key Results and Conclusions

In the treatment series, and in comparison with the control, NAR and RGR decreased, RWR increased, and SLA did not change except for the timing of ontogenetic change. Species having greater increases in the maximum rate of change in RWR also had smaller reductions in RGR; plasticity in RWR is therefore adaptive. In contrast, species which showed a greater decrease in NAR showed stronger reductions in RGR; plasticity in NAR is therefore not adaptive. Plasticity in RGR was not related to plasticity in SLA. There were no significant relationships among the plasticities in NAR, RWR or SLA. Potentially fast-growing species experienced larger reductions in RGR following the nitrogen reduction. These results suggest that competitive responses to interspecific competition for nitrogen might be positively correlated with the plasticity in the maximum rate of change in RWR in response to a reduction in nitrogen supply.     

Contribution of root growth responses to leaf traits and relative growth rate of Populus alba under different water-table conditions

Water-table depth variations alter root growth response and may affect whole-plant growth in arid and semi-arid regions. We examined how root biomass allocation and root morphological traits affect the leaf physiological and morphological traits and whole-plant growth of Populus alba growing under different water tables. We exposed 1-year-old P. alba cuttings to contrasting soil–water conditions via water table changes in a greenhouse for 90 days. We examined relationships among net assimilation rate (NAR) and other growth components obtained from our published data for trees harvested every 30 days. Strongly negative correlations were found between RMR and root morphological traits. Root mass ratio had a strong negative relationship with LMR, and proportion of fine-root biomass per total root biomass was positively correlated with SLA and NAR. Both NAR and leaf area ratio were important determinants of variation in relative growth rate (RGR). Leaf mass ratio (LMR) and specific leaf area (SLA) were positively correlated with RGR; the correlation was stronger in the case of LMR. Along a water-table gradient, negative relationships between root growth responses are likely to indirectly influence RGR through changes in NAR, LMR, and SLA.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

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.