Changes In Relative Growth Rate Research Articles

Growth and reproduction of the alpine grasshopper Miramella alpina feeding on CO2-enriched dwarf shrubs at treeline

The consequences for plant-insect interactions of atmospheric changes in alpine ecosystems are not well understood. Here, we tested the effects of elevated CO(2) on leaf quality in two dwarf shrub species (Vaccinium myrtillus and V. uliginosum) and the response of the alpine grasshopper (Miramella alpina) feeding on these plants in a field experiment at the alpine treeline (2,180 m a.s.l.) in Davos, Switzerland. Relative growth rates (RGR) of M. alpina nymphs were lower when they were feeding on V. myrtillus compared to V. uliginosum, and were affected by elevated CO(2) depending on plant species and nymph developmental stage. Changes in RGR correlated with CO(2)-induced changes in leaf water, nitrogen, and starch concentrations. Elevated CO(2) resulted in reduced female adult weight irrespective of plant species, and prolonged development time on V. uliginosum only, but there were no significant differences in nymphal mortality. Newly molted adults of M. alpina produced lighter eggs and less secretion (serving as egg protection) under elevated CO(2). When grasshoppers had a choice among four different plant species grown either under ambient or elevated CO(2), V. myrtillus and V. uliginosum consumption increased under elevated CO(2) in females while it decreased in males compared to ambient CO(2)-grown leaves. Our findings suggest that rising atmospheric CO(2) distinctly affects leaf chemistry in two important dwarf shrub species at the alpine treeline, leading to changes in feeding behavior, growth, and reproduction of the most important insect herbivore in this system. Changes in plant-grasshopper interactions might have significant long-term impacts on herbivore pressure, community dynamics and ecosystem stability in the alpine treeline ecotone.

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.

Early plant growth: identifying the end point of the seedling phase.

• Despite the importance of seedling establishment in plant biology, there is no consensus on what constitutes a 'seedling'. Here we examined aspects of early plant development that could be used to mark the transition from the seedling to the postseedling phase. • Using a hypogeal species (pea, Pisum sativum) and an epigeal species (sunflower, Helianthus annuus), we investigated whether the utilization of cotyledon-stored mineral nutrients coincides with any changes in relative growth rate (RGR). We also examined how the timing of cotyledon removal at different points during early development affected subsequent growth. • For both species, the timing of RGRmax , the exhaustion of cotyledon reserves, and the attainment of independence from cotyledons all roughly coincided (though exhaustion of seed reserves was not observed in the epigeal species because the cotyledons absorbed external nutrients). • We conclude that because the point of attainment of RGRmax is a distinctly identifiable event, it is a more reliable marker for defining the end of the seedling stage than either the exhaustion of mineral reserves, or the cessation of dependence on cotyledon reserves.

Rapid change in relative growth rate between the vegetative and reproductive stage of the life cycle in Plantago coronopus.

• A growth experiment with seedlings from Plantago coronopus, originating from small (0.13mg) and large (0.20mg) seeds, was conducted under optimum nutrient conditions to gain insight into the physiological processes associated with the vegetative and generative phase of plant growth. • The relative growth rate (RGR) during the vegetative stage was 300mgg-1 d-1 and dropped at the initiation of flowering buds to 60mgg-1 d-1 , a fivefold reduction, while remaining exponential. Investment in reproductive structures had prevalence over vegetative structures during the generative phase of the life cycle. The RGR of reproductive structures was 105mgg-1 d-1 . • The initiation of flowering was stage-dependent. After the formation of about 14 leaves, plants started to form flowering buds, independent of weight or leaf size. The shoot:root ratio stayed the same during both the vegetative and generative stages. The change from a two-compartment system (shoot and root) to a three-compartment system (shoot, root and reproductive structures) did not change the balance or functional equilibrium between root and shoot. • Seed size effects lasted until the end of the experiment and were reflected in all morphological measurements.

Improvement in growth and salt resistance of lemon (Citrus limon) trees by an interstock-induced mechanism.

Interstocks can reduce toxic ion accumulations in leaves of budded citrus trees, but the mechanism is not understood. We grew sour orange (Citrus aurantium L.; SO) seedlings, budded trees of 'Salustiano' orange (Citrus sinensis L. Osbeck; SAO) on SO, 'Verna' lemon (Citrus limon L. Burm. f; VL/SO) and interstock trees (VL/SAO/SO) in pots of sand watered with nutrient solution containing 5 (control) or 50 mM NaCl (saline treatment) for 12 weeks. Plants were harvested in six successive harvests and time trends in relative growth rate (RGR) and its components were estimated by fitting a Richards function regression to the harvest data. The VL/SAO/SO trees in saline conditions had higher mean RGR than VL/SO trees in control conditions. Increases in both net assimilation rate on a leaf mass basis (NARw) and leaf mass fraction (LMF) contributed equally to a twofold increase in RGR of VL/SAO/SO trees in saline conditions. In control conditions, the increase in RGR caused by the interstock had growth response coefficients of GRC(NARw) = 0.20 and GRC(LMF) = 0.80. Structural modifications-specific leaf area, leaf area ratio and LMF-had a slight influence on the salt-induced changes in RGR, whereas NARw had a large influence. Salinity decreased root mass fraction (RMF) and increased stem mass fraction (SMF). In contrast, the interstock decreased SMF and increased LMF and RMF. The VL/SAO/SO trees had the highest RMF and proportionally higher Cl- and Na+ allocations in roots than the other plant types. In saline conditions, reductions in leaf ion transport rate and dilution of imported ions by foliar growth nearly halved ion accumulations in leaves of VL/SAO/SO trees.

RESPONSES OF AN INSECT FOLIVORE AND ITS PARASITOIDS TO MULTIYEAR EXPERIMENTAL DEFOLIATION OF ASPEN

Foliage quality may decline in deciduous trees following defoliation, thus affecting the insect generation responsible for the herbivory (rapid induced resistance, RIR), or future generations (delayed induced resistance, DIR). During outbreaks, trees often suffer partial or complete defoliation for two or more successive years, yet most studies have examined induced resistance following only one season of defoliation, which may not reveal its full impact on herbivores. In a field experiment, 40 trees from each of two clones of trembling aspen, Populus tremuloides, were severely defoliated for one, three, and four years in succession by experimentally manipulating densities of an outbreak folivore, the forest tent caterpillar, Malacosoma disstria. Treatments were applied such that the individual and combined effects of RIR and DIR on the fitness of the forest tent caterpillar could be assessed independently. In field assays, defoliation treatments did not affect larval development time and only marginally affected survival. However, fecundity in both clones was significantly reduced by a single season of defoliation concurrent with the bioassay (effects of RIR), by three consecutive years of defoliation prior to the year of the bioassay (effects of DIR), and by four consecutive years of defoliation (combined effects of RIR and DIR). There were no differences among the three defoliation treatments, indicating that the effects of DIR and RIR combined were not greater than each acting alone. Reductions in fecundity were less than half those observed during natural outbreaks, suggesting that other factors also must contribute to declining fecundity during the collapse of outbreaks. Short-term laboratory bioassays indicated that defoliation effects observed in long-term field assays were not due to changes in relative growth rate (RGR) of second instars or final-instar males, which were unaffected, possibly because of increased relative consumption rates (RCR). Defoliation treatments decreased RGR of final-instar females in laboratory bioassays, despite elevated RCR. Both defoliation treatment and aspen clone influenced parasitism by tachinid flies that detect hosts through volatiles released from leaves damaged by caterpillars. Parasitism was highest on trees defoliated concurrently with the larval bioassay. However, there were no differences between trees defoliated prior to the bioassay and control trees, indicating that effects on parasitism were not due to defoliation-induced changes in host quality per se. Thus, there were no additive interactions between DIR and parasitism that would amplify delayed density-dependent effects on population dynamics. Spatial responses of these tachinids to host density or to current defoliation rather than the defoliation history of the trees may enhance the stabilizing effect of RIR on population dynamics. Conversely, differences in parasitism among clones could contribute to spatial variation in tent caterpillar population density. Neither defoliation effect on host quality nor parasitism was sufficient to slow reproductive rates to levels observed in declining outbreaks in nature, suggesting that single-factor explanations for tent caterpillar population dynamics are unlikely.

Iron distribution in three central Amazon tree species from whitewater-inundation areas (várzea) subjected to different iron regimes

Trees inhabiting central Amazon floodplain forests are subjected to an annual flood-pulse lasting up to 10 months, leading to both oxygen shortage and accumulation of high levels of reduced iron. To understand the mechanisms underlying the adaptation to these conditions, cuttings from three tree species typical of varzea inundation forests (Salix martiana, Tabernaemontana juruana, and Laetia corymbulosa), were cultivated either aerobically or anaerobically under different iron regimes in greenhouse experiments. Although all species are considered to be non-deciduous, Laetia corymbulosa lost and formed new leaves continuously during the experimental period. Although relative growth rates (RGRs) of all species declined in response to hypoxic conditions, no marked changes in RGRs were apparent among different iron concentrations in the growth medium, ranging from 50 to 500 µM, supplied in ferrous form as FeSO4. Whereas roots exhibited color changes due to the formation of iron precipitates, no visual symptoms of iron toxicity were observed in the leaves. Iron concentration increased in all organs of all species with increasing iron concentrations in the medium, except for leaves of S. martiana and T. juruana, suggesting an effective restriction of iron influx into the leaf symplast. Although the leaf iron concentration was at the upper limit of the critical range at high external iron levels, it is suggested that internal active transport rather than intracellular detoxification mechanisms contribute to the tolerance to supra-optimal iron levels. Anatomical traits such as suberization of peripheral cell walls and the formation of aerenchyma appear to be of minor importance for Fe tolerance.

Size Distribution, Growth and Inter-year Variation in Sex Expression of Bischofia javanica, an Invasive Tree

Flowering activity and sex expression of Bischofia javanica Blume were investigated for 3 years. B. javanica is an invasive dioecious tree of subtropical forests on the Bonin Islands in the western Pacific of Japan. The sex ratio showed a significant male bias (1.25-2.33). Smaller trees were significantly male biased, whereas larger trees showed no significant difference in sex expression, suggesting that males tend to be more precocious in sexual reproduction. We found evidence for sex changes in B. javanica; these have not been reported previously. Most of the 1,653 census trees remained non-flowering (58.1 %); 3.7 % of them showed sex changes, and the percentage of trees repeatedly flowering as males and females was 10.5 and 3.4 %, respectively. Sex changes were observed in both directions but a larger percentage of male trees became female. Flowering frequency and sex expression were significantly related to tree size (i.e. diameter at breast height). Over the 3 years, trees that were consistent females were the largest; inconsistent trees (switching sex between years) were intermediate in size, whereas consistent males were the smallest. There were no significant differences in relative growth rate (RGR) among trees of different sex or flowering frequencies. These results suggest that the maintenance of female reproduction is not related to changes in RGR of diameter but to flowering frequency or the reversal to the male form, dependent upon the internal resource status of individual trees.

Bryophyte community structure in a boreal poor fen II: interspecific competition among five mosses

A possible competitive hierarchy among five boreal bryophytes (Sphagnum angustifolium, Sphagnum fuscum, Sphagnum magellanicum, Ptilium crista-castrensis, and Pleurozium schreberi) was examined in a 2-year transplant experiment conducted in two habitats of a poor fen in northern Alberta, Canada, using a sixth moss (Aulacomnium palustre) as a phytometer. Change in relative growth rate in length and weight of A. palustre, measured as competitive effect, indicated the existence of a hierarchy in this peatland wherein the feather mosses are subordinates to the Sphagnum mosses. Relative competitive performance, which was calculated relative to the growth of the phytometer in monoculture, indicated that S. magellanicum exhibited the greatest competitive effect. Sphagnum magellanicum may be a strong competitor and partially inhibit S. fuscum from occupying its full fundamental niche. The competitive ability of S. fuscum and S. angustifolium in this peatland is low relative to that of the other study species. The feather mosses did not demonstrate competitive effect and may have facilitated growth of the phytometer.Key words: bryophyte, competition, feather moss, peatland, phytometer, Sphagnum.

Interspecies variation in nitrogen uptake kinetic responses of temperate forest species to elevated CO2: potential causes and consequences

SummaryDespite the recognition that the capacity to acquire N is critical in plant response to CO2 enrichment, there is little information on how elevated CO2 affects root N uptake kinetics. The few available data indicate a highly variable pattern of response to elevated CO2, but it is presently unclear if the observed inconsistencies are caused by differences in experimental protocols or by true species differences. Furthermore, if there are interspecific variations in N uptake responses to elevated CO2, it is not clear whether these are associated with different functional groups. Accordingly, we examined intact root‐system NH4+ and NO3– uptake kinetic responses to elevated CO2 in seedlings of six temperate forest tree species, representing (i) fast‐ vs. slow‐growers and (ii) broad‐leaves vs. conifers, that were cultured and assayed in otherwise similar conditions. In general, the species tested had a higher uptake capacity (Vmax) for NH4+ than for NO3–. Species substantially differed in their NO3– and NH4+ uptake capacities, but the interspecific differences were markedly greater for NO3– than NH4+ uptake. Elevated CO2 had a species‐dependent effect on root uptake capacity for NH4+ ranging from an increase of 215% in Acer negundo L. to a decrease of about 40% in Quercus macrocarpa Michx. In contrast, NO3– uptake capacity responded little to CO2 in all the species except A. negundo in which it was significantly down‐regulated at elevated CO2. Across species, the capacity for NH4+ uptake was positively correlated with the relative growth rate (RGR) of species; however, the CO2 effect on NH4+ uptake capacity could not be explained by changes in RGR. The observed variation in NH4+ uptake response to elevated CO2 was also inconsistent with life‐form differences. Other possible mechanisms that may explain why elevated CO2 elicits a species‐specific response in root N uptake kinetics are discussed. Despite the fact that the exact mechanism(s) for such interspecific variation remains unresolved, these differences may have a significant implication for competitive interactions and community responses to elevated CO2 environment. We suggest that differential species responses in nutrient uptake capacity could be one potential mechanism for the CO2‐induced shifts in net primary productivity and species composition that have been observed in experimental communities exposed to elevated levels of CO2.

The importance of temperature differences, directly after anthesis, in determining growth and cellular development of Malus fruits

SummaryThe growth temperature of fruit on Mahis domestica trees of two cultivars (‘Queen Cox’ and ‘Golden Delicious’) was altered during an eight-week period shortly after anthesis. This was achieved by moving potted trees in a reciprocal transfer experiment within two temperature controlled glasshouse compartments. The trees were initially grown at either 15°C or 20°C. After about three weeks, half the trees at each temperature were moved to the other temperature compartment. Throughout the growing season fruit size was measured non-destructively on selected fruit. Measurements of fruit size were used to determined temperature-induced changes in relative growth rate. Measurements were also made of cortical cell size to determine if fruit cell number had increased. Complementary measurements, at harvest time, were made of total fruit weight, number of fruit and mean fruit size per tree and seasonal tree growth. The results of this work show that the fruit setting potential of ‘Queen Cox’ and ‘Golden Delicious’ was severely reduced at the higher temperature. Fruit set was highest for ambient temperature treatment, but this treatment had a significantly reduced mean fruit size at harvest. The largest fruit were obtained from ‘Golden Delicious’ trees initially growing at 20°C. However, fruit set was the lowest on these trees. Measurements of fruit growth showed that treatment differences in ‘Golden Delicious’ fruit size at harvest were unlikely to be explained by initial differences in fruit number per tree. Despite higher temperatures producing larger fruit, measurements of cortical cell size showed that increasing the temperature induced larger cells not more cells per apple.

A comparative study of embryonic development of Japanese quailselected for different patterns of postnatal growth

Patterns of early embryonic development have traditionally been viewed as invariant within vertebrate taxa. It has been argued that the specific differences which are found arise during the later stages of development. These differences may be a result of allometry, heterochrony or changes in relative growth rates. To test whether early embryonic development is indeed invariant, or whether selection of adult characteristics can alter embryonic growth, we compared embryonic development in birds selected for different patterns of postnatal growth. Using quail lines selected for high and low body mass, we compared somite formation, and muscle and feather development. We obtained data that showed changes in the rate of myotome formation in the brachial somites which contribute to muscle formation in the limbs and thorax. We think these observations are connected with intraspecific changes in adult morphology, ie., breast muscle size. Our findings suggest that selection for late ontogenetic/adult stages affects early embryonic development.

Long-Term Effects of Natural Sunlight under Various Ultraviolet Radiation Conditions on Growth and Photosynthesis of Intertidal Ulva rigida (Chlorophyceae) Cultivated In Situ

Long-term effects of full-spectrum solar radiation, solar radiation without UVB, and solar radiation without total UV (UVA + UVB) radiation were studied in intertidal Ulva rigida C. Agardh (Chlorophyta). The experiment was carried out under natural conditions and at prevailing winter levels of UV radiation. Changes in relative growth rate, photosynthesis and pigment content were studied after 7 and 20 d of cultivation under the three solar radiation conditions. Relative growth rate was enhanced (50 %) in the absence of UVB radiation after one week, but no difference was found after 20 d. Pigment content (chlorophyll a, chlorophyll b and carotenoids) was significantly higher in the presence of UVB, suggesting an efficient protective-pigment mechanism. When UVB was removed, photosynthetic performance measured as oxygen exchange and fluorescence parameters exhibited higher values than under the other treatments after 7 d of incubation. When samples were cultivated under PAR alone, photosynthetic performance was always negatively affected compared to in the presence of UV radiation. On the whole, intertidal U. rigida exhibited a remarkable capacity to cope with fluctuating light conditions.

Morphometry and Sexual Maturity in the Spider Crab Maja Squinado (Decapoda: Majidae) in Galicia, Spain

Ontogenetic changes in the relative growth of males and females of the spider crab Maja squinado were analyzed and related to their reproductive (maturity) status in order to define criteria to assign individuals to each growth phase. The sampling was carried out in two different areas of southern Galician waters, northwestern Spain, in shallow water ( 20 m) with soft bottoms (adult habitat). A Principal Component Analysis (PCA) of morphometric variables and a nonhierarchic K-means cluster of PCA scores differentiated two morphometric groups defined as juvenile and adult phases. A significant change in allometry of cheliped size was detected in juvenile males with a break point at a 109-mm carapace length (CL). This point may indicate a change in the relative growth of juveniles, separating the immature and adolescent phases. Histological analysis of a subsample of males showed that sperm were present in most adolescent crabs, but not in immature crabs. Bivariate morphometric linear discriminant functions allow for the identification of juvenile and adult males (classified previously by K-means cluster) with over 99% correct classification using CL and the length or height of the right cheliped. Carapace length at the onset of sexual maturity was estimated to be 132.7 mm (50% of adult males), although in a broad range, 112-165 mm, the size of juveniles and adults overlap. The life history of male spider crabs shows 3 phases differentiated by the relative growth rate of chelipeds separated by two 2 critical molts: prepubertal molt (immature-adolescent) determines a slight increase in allometry, and pubertal or terminal molt (adolescent-adult) determines an increase in the relative size and allometry of chelipeds and the onset of functional maturity. Females showed only 2 phases separated by the terminal molt. Growth of chelipeds in females showed no changes in allometry and was similar to juvenile males. Juvenile females presented a smaller relative width and a higher allometry of the abdomen with regard to adult females. Unlike juvenile females with a flat abdomen, adult females with a domed abdomen have well-developed pleopods, gonads, and seminal receptacles. Carapace length at the onset of sexual maturity was estimated to be 130.4 mm (50% of adult females). The range of overlap of the size of juveniles and adults (114-143 mm) was smaller than in males. The spider crab Maja squinado (Herbst) inhabits the Northeast Atlantic from the British Isles to Guinea and the Mediterranean Sea (de Kergariou, 1984; Le Foll, 1993). It is subject to an intense fishery, especially in the waters along the coast of the English Channel and Galicia, northwestern Spain. As for other species of the Majidae, the postlarval life history of Maja squinado consists of two main phases, growth and reproduction, which are separated by a terminal molt (Vernet-Cornubert, 1958; Hartnoll, 1963, 1978; Conan and Comeau, 1986; Comeau and Conan, 1992; Meyer, 1993; Gonzalez-Gurriaran et al., 1995; Freire et al., in press). The first morphometric study done on this species (Teissier, 1935) distinguished three main developmental phases in males, separated by two critical molts. In males, the most obvious morphological change throughout growth is the development of the chelipeds. This led morphometric studies to be based primarily on changes in relative growth rates, or allometric levels, of different variables measuring the size of the chelipeds. Females undergo changes in morphology and in the allometry of the width of the abdomen. Later, these changes in external morphology were used in growth and maturity studies of other species of the Majidae (Vernet-Cornubert, 1958; Hartnoll, 1978; Conan and Comeau, 1986). In studies carried out on other majids, the different phases of the life history and critical molts were based on morphological, morphometric, physiological (gonad maturation), and behavioral criteria (Fig. 1). In males, the first postlarval phase, known as immature or juvenile, gives rise to a second phase, known as prepubertal, juvenile, or adolescent, after a prepubertal, pubertal, or juvenile molt.

Variation in the components of relative growth rate in 10 Acacia species from contrasting environments

In this study we assessed the inherent relative growth rate (RGR) under controlled environment conditions of 10 contrasting Acacia species from semi‐arid and mesic environments. For several of the species, compound pinnate leaves produced early in the seedling stage, were gradually replaced by phyllodes (expanded petioles that form simple lamina). Other species either did not form phyllodes, or only did so to a minor degree by the end of the study. Phyllode production was dominant in the four slow‐growing Acacia species from semi‐arid environments (A. aneura, A. colei, A. coriacea and A. tetragonophylla), with leaf production being exclusive or dominant in five (A. dealbata, A. implexa, A. mearnsii, A. melanoxylon and A. irrorata) of the six faster‐growing species from mesic environments. The exception was A. saligna which was fast growing but did produce phyllodes. From a carbon economy perspective, slow growth in the semi‐arid species was not associated with lower net assimilation rates or less plant mass allocated to foliage. Rather, the primary factor associated with their slow growth was a smaller foliage area per unit foliage mass. This was true for comparisons based on the mean over all harvests or at set plant masses. The production of phyllodes by the semi‐arid species substantially reduced foliage area per unit foliage mass, as this was lower for phyllodes than leaves in all species. To assess the impact that phyllode production had on ontogenetic changes in RGR, we modelled the situation where only leaves were formed. This analysis showed that changing from leaves to phyllodes substantially reduced the RGR. There was little difference in plant nitrogen concentration or the ratio of foliage nitrogen to plant nitrogen between the species. This resulted in foliage nitrogen productivity (dry mass gain per unit foliage nitrogen and time) being directly proportional to foliage area per unit foliage mass between species. We concluded that a smaller foliage area per unit foliage mass and phyllode production are the primary factors associated with lower RGR in contrasting Acacia species.

Responses to light changes in tropical deciduous woody seedlings with contrasting growth rates.

We evaluated the responses in growth, biomass allocation, photosynthesis and stomatal conductance, to changes in light in woody seedlings from the tropical deciduous forest in Mexico, which shows a highly seasonal rain pattern. We studied ten species, which differed by 30-fold in relative growth rate (RGR). We analyzed plant growth in two contrasting light levels during 52 days and two transfers: from high to low (HL) and from low to high (LH) light intensity, and the respective controls in high (HH) and low (LL) light for another 52 days. The photosynthetic capacity (A max) and stomatal conductance were measured at the day of the transfer between light conditions and at the end of the experiment. Species with high RGR showed the largest changes in RGR in response to contrasting light conditions (HH/LL ratio), and species with low RGR showed low responses. The fast-growing species were the most plastic, followed by species with intermediate growth rates, with the slow-growing species being the least plastic. Fast-growing species achieved higher maximum photosynthetic capacities (A max) and stomatal conductance and higher response to light than slow-growing species. Species with high RGR showed a low RGR HH/LH ratio, suggesting a large response of L plants when transfered to H. The RGR of the species were associated with species specific leaf area and with the response in the leaf area, net assimilation rate and leaf weight ratio, suggesting the importance of the leaf area produced and the leaf characteristics rather than root:shoot ratio in determining RGR. Considering that seed germination is expected at the beginning of the rainy period, seedlings of most of the species will experience high-light conditions during its early growth. There are large annual variations in the time required for canopy closure (35-75 days). The influence of these variations may have different effect on the species studied. Species with intermediate growth rate and intermediate response to light changes were less affected by light reduction than fast-growing species. The intermediate-RGR species Caesalpiniaeriostachys is the most abundant and widely distributed species, perhaps this could be in part due to its ability to acclimate to both light increases and decreases. The fast-growing species studied here can be found in open sites in the forest and in areas cleared for pasture growth. These fast-growing species eventually reach the canopy, although this may require several canopy openings during their lives, which implies juvenile shade tolerance. In the tropical deciduous forest juvenile pioneer trees also benefit from the temporary high light available caused by the dry period during the rainy season. The slow-growing species Celaenodendronmexicanum forms small patches of monospecific forest; the adult trees are not completely deciduous, and they retain their old leaves for a long time period before shedding. Thus seedlings of this species may receive lower levels of light, in agreement with its shade tolerance and its lower response to light increases.

Growth and water use of the mangroves Rhizophora apiculata and R. stylosa in response to salinity and humidity under ambient and elevated concentrations of atmospheric CO2

ABSTRACTTwo mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m−3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO2 concentration (340 and 700 cm3 m−3). Under ambient [CO2], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO2] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO2] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt‐tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO2], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO2] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO2] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients.

Effects of Experimental Burial on Survival, Growth, and Resource Allocation of Three Species of Dune Plants

1 Changes in the survival, allocation of resources and growth rate of three dune plant species from Mono Lake, CA were studied in response to experimental burial. Dominant species, the shrubs, Sarcobatus vermiculatus and Chrysothamnus nauseosus, and the grass, Distichlis spicata, were used. 2 In both field and pot experiments, plants were buried at four different levels: no burial, partial burial, initial complete burial, and complete burial repeated every two weeks. 3 All species survived partial burial. S. vermiculatus and D. spicata were much more tolerant of repeated burial than was C. nauseosus. 4 As the severity of burial increased, all species shifted biomass from below-ground to above-ground components. Nitrogen allocation in S. vermiculatus and C. nauseosus shifted from roots to stems and leaves. 5 The only change in relative growth rate found in response to any of the burial treatments was a decline in that of S. vermiculatus in the field experiment. Relative growth rate of all species was more highly correlated with net assimilation rate than with leaf area ratio. 6 The outcomes of the two experiments were sometimes different, emphasizing the importance of confirming the results of pot experiments with field experiments before drawing ecological conclusions. 7 Desert dune plants survive burial in much the same manner as do coastal dune plants.

Regression Smoothers for Estimating Parameters of Growth Analyses

The objective of regression smoothers is to obtain predicted values of a dependent variable and its first derivative from empirical data without having to assume any particular functional relationship between the dependent and independent variables. An early variant of this type of analysis, specifically natural B-splines, was first applied to growth analyses by Parsons and Hunt in 1981 ( Annals of Botany 48: 341–352, 1981). The object of this paper is to describe and evaluate two recent advances in this area (cubic spline smoothers and loess smoothers) in the context of plant growth analysis and compare them to natural B-splines. The accuracies of these methods are evaluated using simulated data of a type that normally causes difficulties with other methods. A bootstrap procedure is described that improves the estimate of the optimal smoother parameter. It is shown that these smoothers can capture even subtle changes in relative growth rate. The method is then applied to growth data of Holcus lanatus.

Carbohydrate accumulation and utilization in soybean plants in response to altered phosphorus nutrition

We conducted a study to determine whether increased starch accumulation is the cause or the result of decreased growth in phosphorus‐deficient soybean plants (Glycine max [L.] Merr. cv. Ransom). Nitrate‐dependent plants were provided with nutrient solution containing either 0.05 or 1.00 mM phosphorus. On day 22 after transplanting the phosphorus concentration in solutions supplied to one‐half of the plants that had received 0.05 mM phosphorus was increased to 1.0 mM phosphorus and the phosphorus concentration in solutions supplied to plants that had received 1.0 mM phosphorus was decreased to 0.05 mM P. The other half of plants in each treatment remained at the same external phosphorus concentration to serve as phosphorus‐deficient or phosphorus‐sufficient controls. Onset of phosphorus deficiency decreased (1) photosynthetic capacity through negative effects on whole plant leaf area and photosynthetic rate per unit leaf area and (2) relative growth rate and leaf elongation rate. However, continuous increases in starch concentration in all organs during onset of phosphorus deficiency indicated that decreased nonstructural carbohydrate availability was not the primary cause of decreased growth. During onset of phosphorus deficiency, significant decreases in relative growth rate (3–8‐day interval) and in day and night leaf elongation rate (8 days) occurred before or at the same time as significant increases in stem, leaf and root starch concentrations. These results support the conclusion that disruption of metabolic functions associated with growth impaired utilization of available nonstructural carbohydrate in plants adjusting to phosphorus deficiency. After phosphorus‐deficient plants were transferred to the sufficient external phosphorus concentration, starch concentrations in leaves and stems decreased to those of phosphorus‐sufficient control plants within 3 days. These decreases in starch concentration in leaves and stems preceded measurable changes in relative growth rate (3–8‐day interval), day and night leaf elongation rate (8 days) or CO2 exchange rate (8 days). Therefore, when soybean plants recover from phosphorus deficiency, starch stored in leaves and stems is ready to be utilized in the synthesis of structural biomass during the time required for activation and/or development of additional photosynthetic capacity.