Variation In Relative Growth Rate Research Articles

Growth and acclimation dynamics in reintroduced Erioderma pedicellatum (Hue) P.M.Jørg., a critically endangered cyanolichen in boreal rainforest

This study focuses on the critically endangered Erioderma pedicellatum, a sexually reproducing cyanolichen. The species’ decline is primarily attributed to habitat loss and extinction debts. The aim is to understand the possibilities of reintroduction via transplantation on Picea abies (L.) H.Karst. and gain insights into the species' growth response to environmental gradients in its boreal rainforest habitat. The source population of E. pedicellatum found on open, sun-exposed spruce branches within a waterfall spray zone, underwent a significant environmental shift when transplanted to the rainforest. The shift induced shade acclimation, which was marked by an increased maximal photosystem II efficiency (FV/FM), reduced thallus thickness and reduced apparent electron transport rate (ETRapp). However, stochastic fragmentation impacted 57 % of thalli, causing significant losses, particularly in sections with numerous apothecia, suggesting a trade-off between growth and reproduction. Unfragmented thalli with positive relative growth rate (RGR) exhibited increased growth correlated with base cation availability (high soil and bark pH) and light availability. Thalli that were already shade-adapted at the start (low ETRapp at high light) displayed the fastest growth in the rainforest. The best subset regression model of unfragmented thalli accounted for 72.8 % of the variation in RGR. The reintroduction of E. pedicellatum into the boreal rainforest is possible, but challenging, given that well-lit spruce branches with high base cation availability in humid canopy layers are rare.

Plant functional traits shape growth rate for xerophytic shrubs.

Trade-offs exist for xerophytic shrubs between functional traits, involving in water loss and assimilate accumulation, can contribute to its survival and growth rate regulation in arid environments. However, growth analysis based on plant functional traits has been focused on the study of herbs and woody species. It is still unclear how the functional traits of xerophytic shrubs regulate their growth rate. In this study, we selectedeight xerophytic shrubs as samples to analyze the regulation process of the functional traits of shrubs on growth rate. Plants were cultivated for three years, and three harvests (every one year) were carried out. Factors explaining between-species differences in relative growth rate (RGR) varied, depending on whether different ages were considered. The results showed that RGR was positively correlated with net assimilation rate, but there was a significant negative correlation with leaf area ration (LAR), specific leaf area (SLA), and leaf biomass ratio in the age 1. However, in the age 2, RGR showed a significant positive correlation with the morphological traits (i.e., leaf area ration and specific leaf area), but not with physiological traits (i.e., net assimilation rate) and leaf biomass allocation. Our results suggested that the fluctuation of environmental factors affects the regulation path of the plant functional traits on RGR of xerophytic shrubs. However, the analysis of causality model showed that no matter in which age, net assimilation rate and leaf area ration principally drive the variation in RGR among xerophytic shrubs.

High-throughput, image-based phenotyping reveals nutrient-dependent growth facilitation in a grass-legume mixture.

This study used high throughput, image-based phenotyping (HTP) to distinguish growth patterns, detect facilitation and interpret variations to nutrient uptake in a model mixed-pasture system in response to factorial low and high nitrogen (N) and phosphorus (P) application. HTP has not previously been used to examine pasture species in mixture. We used red-green-blue (RGB) imaging to obtain smoothed projected shoot area (sPSA) to predict absolute growth (AG) up to 70 days after planting (sPSA, DAP 70), to identify variation in relative growth rates (RGR, DAP 35-70) and detect overyielding (an increase in yield in mixture compared with monoculture, indicating facilitation) in a grass-legume model pasture. Finally, using principal components analysis we interpreted between species changes to HTP-derived temporal growth dynamics and nutrient uptake in mixtures and monocultures. Overyielding was detected in all treatments and was driven by both grass and legume. Our data supported expectations of more rapid grass growth and augmented nutrient uptake in the presence of a legume. Legumes grew more slowly in mixture and where growth became more reliant on soil P. Relative growth rate in grass was strongly associated with shoot N concentration, whereas legume RGR was not strongly associated with shoot nutrients. High throughput, image-based phenotyping was a useful tool to quantify growth trait variation between contrasting species and to this end is highly useful in understanding nutrient-yield relationships in mixed pasture cultivations.

Effects of light availability on leaf attributes and seedling growth of four tree species in tropical dry forest

BackgroundIn tropical dry forests, variation in understory light availability due to season and canopy tree density could be a governing factor in establishment and growth of tree seedlings. Species with varying life history traits are expected to respond differentially to such heterogeneity. We investigated the response of seedlings of four tree species in a tropical day forest in relation to spatiotemporal variability of light. We attempt to explore the role of leaf attributes in explaining intra- and inter-specific variations in relative growth rate. Four study sites, each with three contrasting canopy conditions, were selected along a soil moisture gradient. Seedlings of four tree species (viz., Acacia catechu, Bridelia retusa, Lagerstroemia parviflora, and Shorea robusta), varying in life history traits, were monitored for seasonal variations in growth traits across canopy condition and sites for 2 years.ResultsWe observed a larger variation in leaf attributes for pioneer species. A. catechu showed highest mean values for leaf dry matter content, leaf nitrogen concentration, leaf phosphorus concentration, net stomatal conductance, net photosynthetic rate, and relative growth rate in high light conditions. S. robusta and B. retusa demonstrated highest mean values for all the leaf attributes (except leaf dry matter content) in low light conditions. However, intermediate values for leaf attributes were observed in L. parviflora which preferred moderate light conditions.ConclusionsSeasonal variations in light availability at the forest floor appear to play an important role in the establishment and growth of tree seedlings in seasonal dry forests. Leaf attributes can be used to explain intra- and inter-specific variation in response to light availability. Leaf attributes in combinations can be used to predict relative growth rate of tree species in tropical dry environment, which apart from soil moisture is also determined by light availability due to seasonal changes and canopy tree density.

Intraspecific trait variation and neighborhood competition drive community dynamics in an old-growth spruce forest in northwest China

Identifying the factors driving the growth and mortality of trees is important for understanding the mechanisms of forest dynamics. Here, we studied the growth and survival of trees ≥10 cm diameter at breast height (DBH) in a 15-ha temperate coniferous old growth forest plot in northwest China. We examined the relative importance of abiotic (i.e., soil nutrient and topographic) and biotic variables (i.e., tree size, competition intensity, and wood density of each individual) on the growth and mortality Picea schrenkiana, the dominant species in this forest. We found a high mortality rate and a low recruitment rate for P. schrenkiana over a period of six years. The total abundance and basal area of this species decreased, respectively. Overall, nearly 10% of P. schrenkiana individuals died. Our models of mortality had relatively low explanatory power (3% for all trees and 5% for trees <30 cm DBH), while growth models had moderate explanatory power. The growth of P. schrenkiana trees more strongly correlated with biotic factors (i.e., competition and trait) than abiotic factors (i.e., soil nutrients and topography). Overall, DBH, neighborhood crowding index (NCI), wood density (WD), and convexity explained 26% of the variation in the relative growth rate (RGR) of P. schrenkiana trees. The majority of this variation was explained by DBH alone. For trees with DBH <30 cm, DBH, NCI, WD, convexity, and slope) explained 29% of variation in RGR. In contrast, models of the absolute growth rate (AGR) of all P. schrenkiana trees only explained 3% of variation. For trees <30 cm DBH, NCI, WD, and slope explained 21% variation in AGR and the main part was explained by intraspecific variation in WD. Ultimately, our results highlight the importance of intraspecific variation in traits and competition when exploring demographic process in low-density and species-poor forests.

Characterization of peach tree crown by using high-resolution images from an unmanned aerial vehicle

In orchards, measuring crown characteristics is essential for monitoring the dynamics of tree growth and optimizing farm management. However, it lacks a rapid and reliable method of extracting the features of trees with an irregular crown shape such as trained peach trees. Here, we propose an efficient method of segmenting the individual trees and measuring the crown width and crown projection area (CPA) of peach trees with time-series information, based on gathered images. The images of peach trees were collected by unmanned aerial vehicles in an orchard in Okayama, Japan, and then the digital surface model was generated by using a Structure from Motion (SfM) and Multi-View Stereo (MVS) based software. After individual trees were identified through the use of an adaptive threshold and marker-controlled watershed segmentation in the digital surface model, the crown widths and CPA were calculated, and the accuracy was evaluated against manual delineation and field measurement, respectively. Taking manual delineation of 12 trees as reference, the root-mean-square errors of the proposed method were 0.08 m (R2 = 0.99) and 0.15 m (R2 = 0.93) for the two orthogonal crown widths, and 3.87 m2 for CPA (R2 = 0.89), while those taking field measurement of 44 trees as reference were 0.47 m (R2 = 0.91), 0.51 m (R2 = 0.74), and 4.96 m2 (R2 = 0.88). The change of growth rate of CPA showed that the peach trees grew faster from May to July than from July to September, with a wide variation in relative growth rates among trees. Not only can this method save labour by replacing field measurement, but also it can allow farmers to monitor the growth of orchard trees dynamically.

Leaf traits explaining the growth of tree species planted in a Central Amazonian disturbed area

Tree species selected for planting should exhibit both high survival and fast growth. The growth of a tree or forest plantation is affected by the resource supply (light, water and nutrients), the fraction of resources acquired and resource use efficiency. Leaf traits related to the last two processes have the potential to explain the growth rates. In this study, we evaluated 24 leaf traits (morphological and physiological) at the individual level to investigate whether simple leaf traits can be used to predict the variation in relative growth rates of eight native tree species in a mixed plantation in disturbed areas in Central Amazonia 15 months after planting. Tachigali vulgaris and Trattinnickia rhoifolia exhibited the highest growth rates in both height and diameter, which were approximately three and two times higher than those of Bombacopsis macrocalyx, respectively. Species exhibited different establishment strategies as indicated by the functional leaf trait performance. Tachigali vulgaris, Ochroma pyramidale, Trattinnickia rhoifolia and Ceiba pentandra are efficient resource use species, have high light-saturated photosynthetic rates and are tolerant to high irradiance stress. Endlicheria anomala exhibited the worst performance based on functional traits, with the lowest light-saturated photosynthetic rate (Amax) and maximum quantum yield of photosystem II (FV/FM). Of all traits analyzed, 12 leaf traits were correlated with the relative growth rate (RGR). Leaf traits related to resource acquisition, such as individual leaf area, chlorophyll content, leaf water potential and leaf nutrient concentration, were not good predictors of growth. Only stomatal conductance (gs) was related to the RGR. Leaf traits related to photosynthetic use efficiency (carbon use efficiency and photosynthetic nitrogen and phosphorus use efficiency) explained, on average, 20% and 30% of tree growth in height and diameter, respectively. Resource use efficiency traits were better predictors of growth than the individual physiological traits gs and Amax, which explained, on average, 12% and 19% of the growth in height and diameter, respectively. Photosynthetic efficiency-related traits are good predictors of tree growth, and species with high efficiency – such as T. vulgaris, O. pyramidale, T. rhoifolia and C. pentandra – can achieve high growth in Amazonian disturbed areas. The identification of species with better performance during initial establishment can improve the design of mixture plantations in disturbed areas. Additionally, the selection of traits most correlated with growth performance can be more informative for reforestation monitoring; consequently, previous silvicultural interventions can be adopted prior to the reduction in both growth and survival rates.

Tasa relativa de crecimiento en plántulas de dos poblaciones de Magnolia pugana (Magnoliaceae) en distintos niveles de luz y fertilidad del suelo

Relative growth rate in Magnolia pugana (Magnoliaceae) seedlings from two populations at different light levels and soil fertility. The study of ecophysiology of endangered species is key to the success of conservation and ecological restoration programs. The objective of this work was to know the effect of light, soil fertility and seed origin on the growth of Magnolia pugana seedlings. The relative growth rate (RGR) and its components (Net Assimilation Rate: NAR and Leaf Area Ratio: LAR), as well as the root-shoot ratio (R/S) were estimated. Seedlings were obtained from seeds collected in two localities in Zapopan, Jalisco, Mexico, the first is a wild population in San Nicolás (SN) and the second is a plantation located in the gardens of the Centro Universitario de Ciencias Biológicas y Agropecuarias (CUCBA). The experiment was conducted under greenhouse conditions. In September 2015, 96 seedlings of approximately three months old were subjected to the following treatments in a factorial experiment (2x2x2): light level (high = 1 120 μmol m-2 s-1 and low = 136.3 μmol m-2 s-1), seedling origin (SN and CUCBA) and soil fertility (high fertility = SN soil, low fertility = CUCBA soil) with 12 replicates for each combination of factors and levels. Growth was estimated in two harvests: the first harvest after 30 days of starting the experiment and the second at 60 days. Light and soil fertility levels, as well as seedling origin influenced growth through physiological and morphological adjustments. In general, Magnolia pugana showed higher RGR and NAR in high light, while LAR decreased. Soil fertility and seedling origin did not affect RGR or its components. However, these were affected by the light level, seedlings from SN grew more in high light. Stem height varied due to soil fertility and seedling origin, in low fertility soil (CUCBA) the seedlings of SN were 35 % higher than those of CUCBA. Low fertility soil under high light caused greater investment in seedling root biomass. The physiological component (NAR) was the major determinant of intraspecific variation in RGR. SN seedlings showed greater phenotypic plasticity due to coming from a wild population, which possibly has higher genetic variation than the cultivated population from CUCBA. The results suggest that Magnolia pugana is a species capable of adapting to diverse environments due to its phenotypic plasticity in response to different light and soil fertility levels. Rev. Biol. Trop. 66(2): 622-633. Epub 2018 June 01.

Meta-analyses of oil yield in Cuphea PSR23

Oil content and composition of Cuphea seed are of special economic value as raw materials for industrial and food applications. The inherent unpredictability in determining and predicting Cuphea’s oil yield is attributed, in part, to the indeterminate growth habit and the persistence of the domestication syndrome of this semi-domesticated potential oilseed crop. Meta-analysis using multivariate statistical modeling, computer simulations, and custom profiling was carried out on a database collated from several studies carried out in growth chamber, greenhouse and field experiments. Meta-analyses identified the importance of, and quantified direct and indirect relationships and tradeoffs between and within functional traits classified within five interrelated plant modules. Several multivariate statistical analyses procedures were employed in predicting oil content and oil yield, as performance measures of Cuphea at the plant and population levels of integration. The most parsimonious partial least squares regression model identified plant-, capsule-, and seed-based traits that can be used in reconstructing the best configuration needed for high agronomic performance at the individual plant and population levels. Variance-based structural equation modeling suggested that the variation in relative growth rate was strongly linked to differences in specific leaf area and leaf mass ratio; both traits expressed large positive direct and indirect effects on oil yield, but not oil content. Results of custom profiling suggested that seed yield, oil% and oil yield can be optimized by trait adjustments within the phenotypic and metabolic modules. Adjustments to thousand-seed weight and protein content would influence seed yield, oil yield and oil%, in a decreasing order. Improvements in eco-physiological traits, nutrient ratios and structural traits would lead to a slightly higher oil% and eventually higher oil yield.

Which plant trait explains the variations in relative growth rate and its response to elevated carbon dioxide concentration among Arabidopsis thaliana ecotypes derived from a variety of habitats?

Elevated atmospheric carbon dioxide (CO2) concentration ([CO2]) enhances plant growth, but this enhancement varies considerably. It is still uncertain which plant traits are quantitatively related to the variation in plant growth. To identify the traits responsible, we developed a growth analysis model that included primary parameters associated with morphology, nitrogen (N) use, and leaf and root activities. We analysed the vegetative growth of 44 ecotypes of Arabidopsis thaliana L. grown at ambient and elevated [CO2] (800μmolmol(-1)). The 44 ecotypes were selected such that they were derived from various altitudes and latitudes. Relative growth rate (RGR; growth rate per unit plant mass) and its response to [CO2] varied by 1.5- and 1.7-fold among ecotypes, respectively. The variation in RGR at both [CO2]s was mainly explained by the variation in leaf N productivity (LNP; growth rate per leaf N),which was strongly related to photosynthetic N use efficiency (PNUE). The variation in the response of RGR to [CO2] was also explained by the variation in the response of LNP to [CO2]. Genomic analyses indicated that there was no phylogenetic constraint on inter-ecotype variation in the CO2 response of RGR or LNP. We conclude that the significant variation in plant growth and its response to [CO2] among ecotypes reflects the variation in N use for photosynthesis among ecotypes, and that the response of PNUE to CO2 is an important target for predicting and/or breeding plants that have high growth rates at elevated [CO2].

Interactions among cluster-root investment, leaf phosphorus concentration, and relative growth rate in two Lupinus species.

Cluster-root (CR) formation is a desirable trait to improve phosphorus (P) acquisition as global P resources are dwindling. CRs in some lupine species are suppressed at higher P status. Whether increased growth rate enhances CR formation due to a "dilution" of leaf P concentration is unknown. We investigated interactive effects of leaf P status and relative growth rate (RGR) on CR formation in two Lupinus species, which differ in their CR biomass investment. Variation in RGR was imposed by varying day length. Lupinus albus and L. pilosus were grown hydroponically with KH2PO4 at a day length of 6, 10, or 14 h. We used a slightly higher P supply at longer day lengths to avoid a decline in leaf P concentration, which would induce CRs. Cluster-root percentage, leaf P concentrations, and RGR were determined at 22, 38, and 52 d after sowing. Lupinus species grown at similar root P availability, but with a faster growth rate, as dependent on day length, showed a greater CR percentage. Because our aim to achieve exactly the same leaf P concentrations at different day lengths was only partially achieved, we carried out a multiple regression analysis. This analysis showed the CR percentage was strongly and negatively correlated with plant P status and only marginally and positively correlated with RGR. The two Lupinus species invariably formed fewer cluster roots at higher leaf P status, irrespective of RGR. Differences in RGR or leaf P concentration cannot explain the species-specific variation in cluster-root investment.

Carbon acquisition strategies uncoupled from predictions derived from species life-cycle

We compare carbon use strategies of congeneric annual (P. gracilis and P. angustifolia) and perennial (P. mendocina and P. pinetorum) Physaria (Brassicaceae), to evaluate the relevance of eco-physiological traits as determinants of differences in growth and to add information on the current debate on the agro-ecological suitability of perennial species for grain production in low resource ecosystems. Because of differences in growth and in seed-output previously found within this genus, we hypothesized that C acquisition strategies would not be fully coupled with predictions derived from a species life-cycle. Further, we expected to find different suites of traits related to C-acquisition among perennial species of Physaria. We found species with high (P. gracilis and P. pinetorum) and low (P. mendocina and P. angustifolia) relative growth rate (RGR) and biomass. The variation in RGR was linked to differences in specific leaf area (SLA) and allocation to leaves (leaf mass ratio, LMR) and roots (root mass ratio, RMR), but not to the species life-cycle. Physaria gracilis had high allocation to leaf area (leaf area ratio, LAR), LMR, high SLA, and low RMR and carbohydrates reserves. The slow-growth strategy found in P. mendocina was linked to low LAR, low SLA and large below-ground allocation. The other species showed intermediate strategies between these two. The sets of traits present in P. gracilis and in P. mendocina are extremes in the C acquisition–conservation trade-off, and may allow them to cope with low resource environments in different ways. SLA, LMR and RMR were the main determinants of RGR, while total non-structural carbohydrates (TNC) and leaf longevity were linked to the life-cycle. Taken together these characters define the intermediate growth strategies of P. angustifolia and P. pinetorum. These intermediate strategies were not dependent on the species life cycle and support the hypothesis of uncoupled relationships between growth, C acquisition strategies and life-cycle.

Survival and growth of seven tree species from three stocktypes planted in created wetlands in Loudoun County, Virginia

Successful establishment and growth of trees in created wetlands is an important factor in efforts to compensate for forested wetland losses. Proper selection of seedlings to be planted in a replacement wetland, including tree species and stocktype, is essential to the ecological and economic viability of a wetland afforestation project. In this study seven commonly-planted forested wetland tree species and three stocktypes were planted in three created wetlands in the Piedmont region of Virginia. Quercus bicolor in 1-gallon container stocktype had the highest survival rate (96.2±2.13% SE) and Quercus phellos planted as tubeling stocktype had the lowest survival rate (18.8±3.33% SE). High survival rate occurred in 1-gallon stocktypes overall and may be related to larger initial seedling height and root collar diameter. Both tree species and stocktype explained a significant amount of variation in relative growth rates (RGR) of height (H), root collar diameter (RCD), and canopy diameter (CD), with the exception of RCDRGR for stocktype. Salix nigra and Betula nigra were good performers overall, and exhibited moderate survival and growth rates across stocktypes. These survival and growth results should be considered when tree species and stocktypes are selected for seasonally flooded or saturated sites.

Cluster-root formation and carboxylate release in three Lupinus species as dependent on phosphorus supply, internal phosphorus concentration and relative growth rate

Some Lupinus species produce cluster roots in response to low plant phosphorus (P) status. The cause of variation in cluster-root formation among cluster-root-forming Lupinus species is unknown. The aim of this study was to investigate if cluster-root formation is, in part, dependent on different relative growth rates (RGRs) among Lupinus species when they show similar shoot P status. Three cluster-root-forming Lupinus species, L. albus, L. pilosus and L. atlanticus, were grown in washed river sand at 0, 7·5, 15 or 40 mg P kg(-1) dry sand. Plants were harvested at 34, 42 or 62 d after sowing, and fresh and dry weight of leaves, stems, cluster roots and non-cluster roots of different ages were measured. The percentage of cluster roots, tissue P concentrations, root exudates and plant RGR were determined. Phosphorus treatments had major effects on cluster-root allocation, with a significant but incomplete suppression in L. albus and L. pilosus when P supply exceeded 15 mg P kg(-1) sand. Complete suppression was found in L. atlanticus at the highest P supply; this species never invested more than 20 % of its root weight in cluster roots. For L. pilosus and L. atlanticus, cluster-root formation was decreased at high internal P concentration, irrespective of RGR. For L. albus, there was a trend in the same direction, but this was not significant. Cluster-root formation in all three Lupinus species was suppressed at high leaf P concentration, irrespective of RGR. Variation in cluster-root formation among the three species cannot be explained by species-specific variation in RGR or leaf P concentration.

Growth and secondary compound investments in the epiphytic lichensLobaria pulmonariaandHypogymnia occidentalistransplanted along an altitudinal gradient in British Columbia

We investigated altitudinal variation (550–1650 m) in relative growth rates (RGR) and carbon-based secondary compounds (CBSC) in the cephalolichen Lobaria pulmonaria (L.) Hoffm. and the chlorolichen Hypogymnia occidentalis L. H. Pike transplanted for 14 months in a U-shaped valley in inland southern British Columbia. Prior to transplantation, half of the thalli were treated with phosphorus (P) to examine effects of P on carbon allocation. Growth in L. pulmonaria was substantially higher in the toe-slope position, corresponding to much higher bark pH. Sixty-four percent of the variation in RGR was accounted for by positive pH effects and adverse effects of direct light exposure in the best subset multiple regression model. For H. occidentalis, 57% of the variation in RGR was accounted for by positive and negative effects of indirect and direct light, respectively. Neither altitude nor P had a noticeable effect on RGR, the former possibly reflecting a trade-off between orographic precipitation and inversion-boosted nocturnal dew in valley bottom localities. Neither was there any correlation between altitude and CBSCs, although treatment with P did significantly trigger secondary metabolism in L. pulmonaria, but not in H. occidentalis. No significant intraspecific relationship between growth and CBSC investments was noted.

Prolonging the hydration and active metabolism from light periods into nights substantially enhances lichen growth

This study investigates how hydration during light and dark periods influences growth in two epiphytic old forest lichens, the green algal Lobariapulmonaria and the cyanobacterial L.scrobiculata. The lichens were cultivated in growth chambers for 14days (200μmolm(-1)s(-2); 12h photoperiod) at four temperature regimes (25/20°C, 21/16°C, 13/8°C, and 6/1°C; day/night temperatures) and two hydration regimes (12hday-time hydration; 12hday-time+12h night-time hydration). Growth was highly dynamic, showing that short-term growth experiments in growth cabinets have a high, but largely unexplored potential in functional lichen studies. The highest measured growth rates were not far from the maximal dry matter gain estimated from published net photosynthetic CO2 uptake data. For the entire data set, photobiont type, temperature, hydration regime and specific thallus mass accounted for 46.6% of the variation in relative growth rate (RGR). Both species showed substantially higher relative growth rates based on both biomass (RGR) and thallus area (RTAGR) when they were hydrated day and night compared to hydration in light only. Chronic photoinhibition was substantial in thalli hydrated only during the day time and kept at the highest and lowest temperature regimes, resulting in exponential increases in RGR with increasing maximal PSII efficiency (F v/F m) in both species. However, the depression in F v/F m was stronger for the cyanolichen than for the cephalolichen at extreme temperatures. The growth-stimulating effect of night-time hydration suggests that nocturnal metabolic activity improves recovery of photoinhibition and/or enhances the conversion rate of photosynthates into thallus extension.

Toward an understanding of disequilibrium dihedral angles in mafic rocks

The median dihedral angle at clinopyroxene‐plagioclase‐plagioclase junctions in mafic rocks, Θcpp, is generally lower than equilibrium (109° ± 2°). Observation of a wide range of mafic bodies demonstrates that previous work on systematic variations of Θcpp is incorrect in several important respects. First, the spatial distribution of plagioclase compositional zoning demonstrates that the final geometry of three‐grain junctions, and hence Θcpp, is formed during solidification (the igneous process): sub‐solidus textural modification in most dolerites and gabbros, previously thought to be the dominant control on Θcpp, is insignificant. Θcpp is governed by mass transport constraints, the inhibiting effects of small pore size on crystallization, and variation in relative growth rates of pyroxene and plagioclase. During rapid cooling, pyroxene preferentially fills wider pores while the narrower pores remain melt‐filled, resulting in an initial value of Θcpp of 78°, rather than 60° which would be expected if all melt‐filled pores were filled with pyroxene. Lower cooling rates create a higher initial Θcpp due to changes in relative growth rates of the two minerals at the nascent three‐grain junction. Low Θcpp (associated with cuspate clinopyroxene grains at triple junctions) can also be diagnostic of infiltration of previously melt‐free rocks by late‐stage evolved liquids (the metasomatic process). Modification of Θcpp by sub‐solidus textural equilibration (the metamorphic process) is only important for fine‐grained mafic rocks such as chilled margins and intraplutonic chill zones. In coarse‐grained gabbros from shallow crustal intrusions the metamorphic process occurs only in the centers of oikocrysts, associated with rounding of chadacrysts.

Reproducibility of trace element profiles in a specimen of the deep-water bamboo coral Keratoisis sp.

Bamboo corals (Order Gorgonacea, Family Isididae) are attractive prospects for deep-sea paleoceanographic reconstruction, capturing trace elements in their calcitic skeletons that may serve as environmental proxies with subdecadal resolution over multi-century timescales. We study the reproducibility and fidelity of trace-element profiles (Ba, Mg, Sr, Mn, U, Pb) in a 420-year-old specimen of the bamboo coral Keratoisis sp. from the SE USA. Using laser-ablation ICP-MS to obtain multiple replicate profiles, we use spectral techniques to distinguish noise and irreproducible variations from fully reproducible geochemical fluctuations that are candidates for environmental signals. By quantifying variability between profiles, we assess the fidelity with which the corals potentially record environmental information. Barium is the most reproducible element in the skeleton, with large fluctuations along different growth radii reproducing to within 4%. Both Mg and Sr have very uniform levels within the coral, but display low-amplitude irreproducible variations that might represent an internal biological process. In the case of Mg, which has been proposed as a paleotemperature proxy, this irreproducibility would represent an intrinsic uncertainty of ∼±0.1 to 0.4 °C. Both Mn and Pb contain some irreproducibility superimposed upon broad reproducible profiles that may be environmental signals. Some of the irreproducible Pb fluctuations correlate with cracks and dark bands in the sample suggesting detrital or surface contamination. Uranium displays large amplitude variations which are not reproducible along different radii. This suggests that uranium cannot be used for paleoenvironmental reconstruction, and may show signs of early diagenesis – a possibility that could complicate attempts to date young Keratoisis sp. samples by U-series geochemistry. The highly reproducible Ba signal allows precise alignment of profiles and thus we can show that growth rate along one radius can vary by a factor of two relative to growth along a different radius. There is no evidence that this large variation in relative growth rate affects either the Mg or Sr incorporation. In addition, geochemical anomalies in Ba and Mg indicate that the very central axis of the specimen may represent a different mode of growth. This study suggests that Keratoisis sp. corals are imperfect recorders of geochemical information, but do contain reproducible variations which are good candidates for environmental signals.

Why do genotypes of Picea glauca differ in their growth response to elevated CO2?

Meta-analyses reveal that fast-growing species have a greater growth response to elevated CO(2) than slow-growing species. It is unknown whether this is a direct response or whether inter-specific differences in growth are simply correlated with other physiological or morphological differences among species that affect the growth response to CO(2). Here we use intra-specific variation in Picea glauca to examine the mechanistic basis for this relationship. Relative growth rate (RGR) of 29 genotypes grown at ambient (370 µl l(-1)) or elevated (740 µl 1(-1)) CO(2) was measured. Physiological and morphological traits describing differences in allocation, canopy structure, stomatal function and photosynthesis were determined. Most variation in RGR (74%) was explained by traits associated with canopy structure. Although there was a strong correlation between RGR(740) and RGR(370), we found no evidence that genotypes that grew fast at ambient CO(2) had a greater relative growth response to CO(2). Given that the pattern found at the intra-specific level differed from that reported at the inter-specific level, our results suggest that RGR per se does not affect the growth response to CO(2). Rather, the CO(2) growth response is determined by traits that may or may not be correlated with RGR.

Long-term acclimation of mesophyll conductance, carbon isotope discrimination and growth in two contrasting Picea asperata populations exposed to drought and enhanced UV-B radiation for three years

Two Picea asperata Mast. populations originating from wet and dry climate regions of China were subjected to enhanced UV-B radiation, drought and their combination in a greenhouse for 3 years. Drought treatment caused a significant decrease in photosynthesis, mesophyll conductance ( g m), carbon isotope discrimination ( Δ) and growth characteristics when compared with well-watered treatment. In contrast to the great effects of drought stress, enhanced UV-B radiation showed some but not as substantial negative effects on these parameters. Little interaction effect between drought and UV-B radiation was detected, and the drought effect in combination with enhanced UV-B was not more pronounced than with no enhanced UV-B radiation. These results suggest that enhanced UV-B radiation does not aggravate the drought effect on P. asperata seedlings. The results also showed that the proportional role of the intercellular CO 2 ( C i) decreased, while the role of chloroplastic concentration ( C c) became increasingly important in explaining the high values of carbon isotope composition ( δ 13C), when the water stress progressed in time. In addition, multivariate causal models proposed that there is a direct causal relationship between specific leaf area (SLA) and g m, which is not mediated by leaf N. Besides, there are functional links between g m and photosynthetic capacity ( V cmax). On the other hand, the study showed that net assimilation rate (NAR) is the main driving force for changes in relative growth rate (RGR), especially in low-water environments, and the degree of acclimation of respiration in the light ( R L) is of central importance to the greater role played by NAR in determining variation in RGR.