Variation In Plant Size Research Articles

Arabidopsis response to copper is mediated by density and root exudates: Evidence that plant density and toxic soils can shape plant communities.

Plants grown at high densities show increased tolerance to heavy metals for reasons that are not clear. A potential explanation is the release of citrate by plant roots, which binds metals and prevents uptake. Thus, pooled exudates at high plant densities might increase tolerance. We tested this exclusion facilitation hypothesis using mutants of Arabidopsis thaliana defective in citrate exudation. Wild type Arabidopsis and two allelic mutants for the Ferric Reductase Defective 3 (FRD3) gene were grown at four densities and watered with copper sulfate at four concentrations. Plants were harvested before bolting and dried. Shoot biomass was measured, and shoot material and soil were digested in nitric acid. Copper contents were determined by atomic absorption. In the highest-copper treatment, density-dependent reduction in toxicity was observed in the wild type but not in FRD3 mutants. For both mutants, copper concentrations per gram biomass were up to seven times higher than for wild type plants, depending on density and copper treatment. In all genotypes, total copper accumulation was greater at higher plant densities. Plant size variation increased with density and copper treatment because of heterogeneous distribution of copper throughout the soil. These results support the hypothesis that citrate exudation is responsible for density-dependent reductions in toxicity of metals. Density-dependent copper uptake and growth in contaminated soils underscores the importance of density in ecotoxicological testing. In soils with a heterogeneous distribution of contaminants, competition for nontoxic soil regions may drive size hierarchies and determine competitive outcomes.

Genetic Diversity Analysis of Five Different Species of Riccia

Five species of the Riccia genus have been investigated by Rapid Amplified Polymorphic DNA (RAPD) analysis. The species is explained and demonstrated with its genetic diversity based on morphological variations. Samples were collected from different parts of the University of Dhaka growing in different habitats around the University campus area. After the study of its morphology, it has been observed that the population of this taxon shows significant variation in plant size, shape, colour, ventral scales, appendages of scales, rhizoids, and the position of male and female receptacles, etc. The RAPD marker system was employed to estimate the genetic diversity within and between the populations based on such morphological variations. Approximately 82% of the variations have been observed within and between genotypes of Riccia as revealed with both phenotypic and genotypic data. The RAPD markers are being used increasingly to analyse the phylogenetic relationship among the liverworts to give the exact framework of taxonomic identification of naturally occurring liverwort Riccia. Plant Tissue Cult. & Biotech. 32(2): 137-144, 2022 (December)

Cotton Stand Counting from Unmanned Aerial System Imagery Using MobileNet and CenterNet Deep Learning Models

An accurate stand count is a prerequisite to determining the emergence rate, assessing seedling vigor, and facilitating site-specific management for optimal crop production. Traditional manual counting methods in stand assessment are labor intensive and time consuming for large-scale breeding programs or production field operations. This study aimed to apply two deep learning models, the MobileNet and CenterNet, to detect and count cotton plants at the seedling stage with unmanned aerial system (UAS) images. These models were trained with two datasets containing 400 and 900 images with variations in plant size and soil background brightness. The performance of these models was assessed with two testing datasets of different dimensions, testing dataset 1 with 300 by 400 pixels and testing dataset 2 with 250 by 1200 pixels. The model validation results showed that the mean average precision (mAP) and average recall (AR) were 79% and 73% for the CenterNet model, and 86% and 72% for the MobileNet model with 900 training images. The accuracy of cotton plant detection and counting was higher with testing dataset 1 for both CenterNet and MobileNet models. The results showed that the CenterNet model had a better overall performance for cotton plant detection and counting with 900 training images. The results also indicated that more training images are required when applying object detection models on images with different dimensions from training datasets. The mean absolute percentage error (MAPE), coefficient of determination (R2), and the root mean squared error (RMSE) values of the cotton plant counting were 0.07%, 0.98 and 0.37, respectively, with testing dataset 1 for the CenterNet model with 900 training images. Both MobileNet and CenterNet models have the potential to accurately and timely detect and count cotton plants based on high-resolution UAS images at the seedling stage. This study provides valuable information for selecting the right deep learning tools and the appropriate number of training images for object detection projects in agricultural applications.

Multi-factor control of seed mass of species on the eastern part of the Qinghai-Tibetan Plateau: Integration of environmental filters, local adaptation and correlated evolution

Seed mass is a central plant life history trait that varies and evolves due to selection by biotic or abiotic factors. To determine the factors affecting seed mass variation among species and phylogeny, we used linear and regression tree analyses of three biotic traits and four niche traits to quantify the relative importance of each trait on seed mass for 1340 angiosperm species from the eastern part of the Qinghai-Tibetan Plateau. Dispersal mode was the strongest predictor of both species and phylogenetic seed mass variation, whereas life form only had a small impact. These results suggest that seed mass has responded to dispersers rather than the life history or available stored resources. Moreover, in both inter-specific and phylogenetic comparisons, species with similar light, moisture and disturbance niche positions tended to have similar seed mass, indicating that adaptation to local environments is a second force driving species-level seed mass variation. The lack of any relationship between thermal niche and seed mass in the phylogenetic analysis implies that seed mass variation along thermal gradients may be a result of regional species sorting, or alternatively, a plastic response to the variation in plant size. All species and phylogenetic multivariate models showed that both dispersal mode and species light/moisture niche explain seed mass variation, suggesting the importance of coevolution or covariation between seeds and vertebrates and the selection or filter effect of habitats on early life-history stages of plants in affecting individual seed development. Lastly, our results imply that phylogenetic constraints and niche conservatism may operate simultaneously in determining regional patterns of seed mass variation.

Climate and plants regulate the spatial variation in soil multifunctionality across a climatic gradient

A patchy distribution of soil resources is a characteristic of most natural terrestrial biomes, potentially resulting in spatial variation in multiple soil functions (soil multifunctionality). However, less is known about how soil multifunctionality and its spatial variability respond to increasing dryness across extensive climatic gradients, making it difficult to predict changes in ecosystem functions under climate change scenarios. We surveyed 150 sites along a 1500 km climatic gradient in eastern Australia, from humid forests to arid shrublands, to explore the spatial variation in soil multifunctionality with increasing aridity. We assessed four functional groups (carbon stocks, organic matter decomposition, plant structure, soil stability) of multifunctionality and average (net) multifunctionality across four vegetation patch types (tree, shrub, grass and unvegetated open interspaces). We then used average dissimilarity across these four patches as our measure of spatial variability. Our results showed that 1) net soil multifunctionality remained unchanged as aridity increased, because increases in soil stability and plant structure compensated for reductions in carbon stocks and organic matter decomposition; 2) the response of soil multifunctionality to increasing aridity differed among vegetation patch types, with the greatest increases in plant structure and reductions in carbon stocks in the open, but with marginal changes beneath trees; 3) variation in soil multifunctionality increased with increasing aridity and was driven by changes in climate (aridity, rainfall seasonality), soil (pH, sand) and to a lesser extent, variation in plant size, with impacts varying with the target functional group. Our study provides empirical evidence that soils can sustain an average level of multifunctionality across the climatic gradient by regulating the trade-offs between nutrient cycling and soil stability. Furthermore, our results demonstrate that forecasted increases in aridity will increase the spatial variation in soil multifunctionality and enhance the dominance of biocrusts, which would be critical for stabilizing soils under drier global climates.

Intraspecific trait variation across elevation predicts a widespread tree species' climate niche and range limits.

Global change is widely altering environmental conditions which makes accurately predicting species range limits across natural landscapes critical for conservation and management decisions. If climate pressures along elevation gradients influence the distribution of phenotypic and genetic variation of plant functional traits, then such trait variation may be informative of the selective mechanisms and adaptations that help define climatic niche limits. Using extensive field surveys along 16 elevation transects and a large common garden experiment, we tested whether functional trait variation could predict the climatic niche of a widespread tree species (Populus angustifolia) with a double quantile regression approach. We show that intraspecific variation in plant size, growth, and leaf morphology corresponds with the species' total climate range and certain climatic limits related to temperature and moisture extremes. Moreover, we find evidence of genetic clines and phenotypic plasticity at environmental boundaries, which we use to create geographic predictions of trait variation and maximum values due to climatic constraints across the western US. Overall, our findings show the utility of double quantile regressions for connecting species distributions and climate gradients through trait‐based mechanisms. We highlight how new approaches like ours that incorporate genetic variation in functional traits and their response to climate gradients will lead to a better understanding of plant distributions as well as identifying populations anticipated to be maladapted to future environments.

In Arabidopsis thaliana Heterosis Level Varies among Individuals in an F1 Hybrid Population

Heterosis or hybrid vigour is a phenomenon in which hybrid progeny exhibit superior yield and biomass to parental lines and has been used to breed F1 hybrid cultivars in many crops. A similar level of heterosis in all F1 individuals is expected as they are genetically identical. However, we found variation in rosette size in individual F1 plants from a cross between C24 and Columbia-0 accessions of Arabidopsis thaliana. Big-sized F1 plants had 26.1% larger leaf area in the first and second leaves than medium-sized F1 plants at 14 days after sowing in spite of the identical genetic background. We identified differentially expressed genes between big- and medium-sized F1 plants by microarray; genes involved in the category of stress response were overrepresented. We made transgenic plants overexpressing 21 genes, which were differentially expressed between the two size classes, and some lines had increased plant size at 14 or 21 days after sowing but not at all time points during development. Change of expression levels in stress-responsive genes among individual F1 plants could generate the variation in plant size of individual F1 plants in A. thaliana.

An Object-Based Image Analysis Approach to Assess Persistence of Perennial Ryegrass (Lolium perenne L.) in Pasture Breeding

Perennial ryegrass (Lolium perenne L.) is one of the most important forage grass species in temperate regions of the world, but it is prone to having poor persistence due to the incidence of abiotic and biotic stresses. This creates a challenge for livestock producers to use their agricultural lands more productively and intensively within sustainable limits. Breeding perennial ryegrass cultivars that are both productive and persistent is a target of forage breeding programs and will allow farmers to select appropriate cultivars to deliver the highest profitability over the lifetime of a sward. Conventional methods for the estimation of pasture persistence depend on manual ground cover estimation or counting the number of surviving plants or tillers in a given area. Those methods are subjective, time-consuming and/or labour intensive. This study aimed to develop a phenomic method to evaluate the persistence of perennial ryegrass cultivars in field plots. Data acquisition was conducted three years after sowing to estimate the persistence of perennial ryegrass using high-resolution aerial-based multispectral and ground-based red, green and blue(RGB) sensors, and subsequent image analysis. There was a strong positive relationship between manual ground cover and sensor-based ground cover estimates (p < 0.001). Although the manual plant count was positively correlated with sensor-based ground cover (p < 0.001) intra-plot plant size variation influenced the strength of this relationship. We conclude that object-based ground cover estimation is most suitable for use in large-scale breeding programs due to its higher accuracy, efficiency and repeatability. With further development, this technique could be used to assess temporal changes of perennial ryegrass persistence in experimental studies and on a farm scale.

“The Biological Yield and Harvest Index of Cereals as Agronomic and Plant Breeding Criteria” by C.M. Donald and J. Hamblin, Advances in Agronomy (1976) 28:361–405

This article is part of a series of brief commentaries to highlight papers that have resulted in important and distinctly new perspectives in crop science. A criterion for selection of papers is that they must have been published at least 20 yr ago to allow for a long‐range perspective in assessment of the papers. The current article briefly reviews the paper by C.M. Donald and J. Hamblin published in 1976 that provided original insights about the role of harvest index (defined by them as the ratio of economic yield to aboveground mass) in influencing crop yield. Donald and Hamblin reviewed experimental results showing that harvest index was relatively stable across variations in plant size, had high heritability, and was associated with high grain yield. Although their observations were confirmed in subsequent tests, inconsistent results in plant selection in breeding programs for high yield based on harvest index has discouraged the use of harvest index as a basis for selection. Nevertheless, high harvest index is now well ingrained as an essential plant characteristic for high crop yields.

Ontogenetic stage, plant vigor and sex mediate herbivory loads in a dioecious understory herb

Plant-herbivore interactions can be mediated by plant apparency, defensive and nutritional quality traits that change through plant ontogeny, resulting in age-specific herbivory. In dioecious species, opposing allocation patterns in defense may lead to sex-biased herbivory. Here, we examine how onto stage and plant sex determine levels of herbivore damage in understory herb Mercurialis perennis under field conditions. We analyzed variation in plant size (height, total leaf area), physical (specific leaf area) and chemical (total phenolic and condensed tannins contents) defense, and nutritional quality (total water, soluble protein and nonstructural carbohydrate contents) during the shift from reproductive to post-reproductive stage. Furthermore, we explored correlations between the analyzed traits and levels of foliar damage. Post-reproductive plants had lower levels of chemical defense, and larger leaf area removed, in spite of having lower nutritive quality. Opposing patterns of intersexual differences were detected in protein and phenolic contents during reproductive stage, while in post-reproductive stage total leaf area was sexually dimorphic. Female-biased herbivory was apparent only after reproduction. Plant size parameters combined with condensed tannins content determined levels of foliar damage during post-reproductive stage, while the only trait covarying with herbivory in reproductive stage was total nonstructural carbohydrate content. Our results support claims of optimal defense theory – sensitive stage of reproduction was better defended. We conclude that different combinations of plant traits mediated interactions with herbivores in mature stages. Differences in reproductive allocation between the sexes may not immediately translate into different levels of damage, stressing the need for considering different ontogenetic stages when exploring sex bias in herbivory.

Stomatal density, leaf area and plant size variation of Rhizophora mangle (Malpighiales: Rhizophoraceae) along a salinity gradient in the Mexican Caribbean

In community ecology, the knowledge of abiotic factors, that determine intraspecific variability in ecophysiological and functional traits, is important for addressing major questions, such as plant community assembly and ecosystem functioning. Mangroves have several mechanisms of resistance to salinity and most species exhibit some xeromorphic features in order to conserve water. Leaf area and stomatal density play an important role in maintaining water balance, and gas exchange is regulated by their aperture and density, two traits that vary intraspecifically in response to environmental conditions, such as water stress and salinity. In this study, we evaluated the effects of salinity on stomatal density, leaf area and plant size in R. mangle and we tested for associations among the three variables, across three sites along a natural salinity gradient in the Xel-Há Park, Quintana Roo, Mexico. We hypothesized that high salinity sites would produce smaller plants, with smaller leaves, and fewer stomata. Three sampling sites with different environmental conditions were chosen and salinities were monitored monthly. A total of 542 plants were tagged and tree heights and diameters were measured for each individual within each of the three sampling sites. Three leaves from 20 trees from each site were measured to determine leaf area. Stomatal densities were determined in each leaf using nail polish casts, examining ten 1 mm squares per leaf under an optical microscope. A principal component analysis was used to assess association between tree height, leaf area, and stomatal density for each plot. The salinity gradient was reflected in plant size, producing smaller plants at the higher salinity site. The largest leaves were found at the low salinity site (51.2 ± 24.99 cm2). Leaf length was not correlated to plant size (LL vs. tree height: r= 0.02, P= 0.8205; LL vs. trunk diameter: r= 0.03, P= 0.7336), so we concluded that leaf length is an environmentally plastic trait of red mangroves that may vary as a function of environmental conditions, such as hydric stress caused by elevated salinity. The larger leaves from the low salinity site had lower densities of stomata (65.0 stomata.mm2 SD= 12.3), and increasing salinities did not decrease stomatal density (intermediate salinity site: 73.4 stomata.mm2 SD= 13.5; high salinity site: 74.8 stomata.mm2 SD= 17.3). Our results confirm that stomatal density is inversely related to leaf area (r= -0.29, P < 0.001), especially leaf width (r= -0.31, P < 0.001), and that salinity may increase stomatal density by causing reduction of leaf size.

Taxonomic Study of Japanese Deparia petersenii (Woodsiaceae) Based on Cytological and Molecular Information

Deparia petersenii has a large morphological variation in plant size and leaf shape in Japan. To reveal possible distinct biological units of this species, we determined the chromosome numbers and nuc

A global method for calculating plant CSR ecological strategies applied across biomes world‐wide

Summary Competitor, stress‐tolerator, ruderal (CSR) theory is a prominent plant functional strategy scheme previously applied to local floras. Globally, the wide geographic and phylogenetic coverage of available values of leaf area (LA), leaf dry matter content (LDMC) and specific leaf area (SLA) (representing, respectively, interspecific variation in plant size and conservative vs. acquisitive resource economics) promises the general application of CSR strategies across biomes, including the tropical forests hosting a large proportion of Earth's diversity. We used trait variation for 3068 tracheophytes (representing 198 families, six continents and 14 biomes) to create a globally calibrated CSR strategy calculator tool and investigate strategy–environment relationships across biomes world‐wide. Due to disparity in trait availability globally, co‐inertia analysis was used to check correspondence between a ‘wide geographic coverage, few traits’ data set and a ‘restricted coverage, many traits’ subset of 371 species for which 14 whole‐plant, flowering, seed and leaf traits (including leaf nitrogen content) were available. CSR strategy/environment relationships within biomes were investigated using fourth‐corner and RLQ analyses to determine strategy/climate specializations. Strong, significant concordance (RV = 0·597; P < 0·0001) was evident between the 14 trait multivariate space and when only LA, LDMC and SLA were used. Biomes such as tropical moist broadleaf forests exhibited strategy convergence (i.e. clustered around a CS/CSR median; C:S:R = 43:42:15%), with CS‐selection associated with warm, stable situations (lesser temperature seasonality), with greater annual precipitation and potential evapotranspiration. Other biomes were characterized by strategy divergence: for example, deserts varied between xeromorphic perennials such as Larrea divaricata, classified as S‐selected (C:S:R = 1:99:0%) and broadly R‐selected annual herbs (e.g. Claytonia perfoliata; R/CR‐selected; C:S:R = 21:0:79%). Strategy convergence was evident for several growth habits (e.g. trees) but not others (forbs). The CSR strategies of vascular plants can now be compared quantitatively within and between biomes at the global scale. Through known linkages between underlying leaf traits and growth rates, herbivory and decomposition rates, this method and the strategy–environment relationships it elucidates will help to predict which kinds of species may assemble in response to changes in biogeochemical cycles, climate and land use.

Within-population variation in the relation between node number and flowering time in Rhinanthus angustifolius (Orobanchaceae)

Background and aims – The annual hemiparasitic plant genus Rhinanthus displays large variation in the date of onset of flowering, and ecotypes have been described from populations with different flowering times. Much less is known, however, about the variation in flowering time within populations of an ecotype, which is important for the adaptive capacity of a population. The number of nodes produced before the first flower is an important trait linked to flowering time differences among populations, and this trait and its relation with flowering date were investigated. Methods – Seeds from a natural, early-flowering population of Rhinanthus angustifolius, mown in early July, were used to establish a new field population in 2003, mown after summer, and to cultivate plants in the greenhouse in 2001 and 2004. The onset of flowering, node number and plant size were recorded in the field population in 2005 and in 2008. In the greenhouse, germination date, node number and flowering date were recorded. Key results – Flowering time was strongly correlated with node number in all years: the production of more nodes before the first flower was associated with a delay in flowering. There was always considerable variation around the median flowering date among plants with the same number of nodes, even in the greenhouse. Removing variation in the timing of germination in the greenhouse experiment did not reduce variation in flowering date. Part of the remaining variation was due to variation in plant size: larger plants flowered earlier. After five years, the relaxed selection on flowering time by mowing later had increased node number and delayed flowering in the new field population. Conclusions – Both genetically determined (node number) and phenotypically plastic (plant size) traits contribute to variation in flowering time within populations, and even under strong selection against late flowering, wild populations may harbour enough variation to react to a decrease in this selection pressure by later mowing.

Flexible three-dimensional modeling of plants using low- resolution cameras and visual odometry

The three-dimensional reconstruction of plants using computer vision methods is a promising alternative to non-destructive metrology in plant phenotyping. However, diversity in plants form and size, different surrounding environments (laboratory, greenhouse or field), and occlusions impose challenging issues. We propose the use of state-of-the-art methods for visual odometry to accurately recover camera pose and preliminary three-dimensional models on image acquisition time. Specimens of maize and sunflower were imaged using a single free-moving camera and a software tool with visual odometry capabilities. Multiple-view stereo was employed to produce dense point clouds sampling the plant surfaces. The produced three-dimensional models are accurate snapshots of the shoot state and plant measurements can be recovered in a non-invasive way. The results show a free-moving low-resolution camera is able to handle occlusions and variations in plant size and form, allowing the reconstruction of different species, and specimens in different stages of development. It is also a cheap and flexible method, suitable for different phenotyping needs. Plant traits were computed from the point clouds and compared to manually measured reference, showing millimeter accuracy. All data, including images, camera calibration, pose, and three-dimensional models are publicly available.

Contrasting Effects of Long-Term Grazing and Clipping on Plant Morphological Plasticity: Evidence from a Rhizomatous Grass.

Understanding the mechanism of plant morphological plasticity in response to grazing and clipping of semiarid grassland can provide insight into the process of disturbance-induced decline in grassland productivity. In recent studies there has been controversy regarding two hypotheses: 1) grazing avoidance; and 2) growth limiting mechanisms of morphological plasticity in response to defoliation. However, the experimental evidence presented for the memory response to grazing and clipping of plants has been poorly reported. This paper reports on two experiments that tested these hypotheses in field and in a controlled environment, respectively. We examined the effects of long-term clipping and grazing on the functional traits and their plasticity for Leymus chinensis (Trin.) Tzvelev (the dominate species) in the typical-steppe grassland of Inner Mongolia, China. There were four main findings from these experiments. (i) The majority of phenotypic traits of L. chinensis tended to significantly miniaturize in response to long-term field clipping and grazing. (ii) The significant response of morphological plasticity with and without grazing was maintained in a hydroponic experiment designed to remove environmental variability, but there was no significant difference in L. chinensis individual size traits for the clipping comparison. (iii) Plasticity indexes of L. chinensis traits in a controlled environment were significantly lower than under field conditions indicating that plants had partial and slight memory effect to long-term grazing. (iv) The allometry of various phenotypic traits, indicated significant trade-offs between leaf and stem allocation with variations in plant size induced by defoliation, which were maintained only under grazing in the hydroponic controlled environment experiment. Taken together, our findings suggest that the morphological plasticity of L. chinensis induced by artificial clipping was different with that by livestock grazing. The miniaturization of plant size in long-term grazed grassland may reflect retained characteristics of dwarf memory for adaptation to long-term grazing by large herbivores.

Species richness loss after nutrient addition as affected by N:C ratios and phytohormone GA3contents in an alpine meadow community

Aims From the light-competition hypothesis, competition for light is asymmetric and the observed increases in plant-size variability with increasingly denser canopies are primarily due to competition for light. Greater plant height provides pre-emptive access to light and produces increased height differences among species. The question is what produces these differences in plant height or height growth response among species in response to fertilization. Methods In 2009, a field experiment of N, P and N + P enrichments at three levels each was initiated in an alpine meadow on the northeast Qinghai- Tibet Plateau. Effects of fertilization on species richness, aboveground net primary production (ANPP), relative light intensity and plant height of different plant functional groups were determined. Festuca ovina (grass), Kobresia humilis (sedge), Oxytropis ochrocephala (legume), Taraxacum lugubre (rosette forb) and Geranium pylzowianum (upright forb) were selected as exemplars of each of the indicated functional groups. The N: C ratios in aboveground biomass, gibberellic acid (GA3) concentrations in leaves, plant heights and height relative growth rate (RGR) of these exemplar species were analyzed in detail. Important Findings Species richness of grasses significantly increased with increasing N + P levels. Species richness of legumes and upright forbs decreased after N and N + P additions. P addition had no significant effect on species richness. The effects of N + P addition on species richness and ANPP were consistently stronger than those of the single N or P fertilization. Reductions in species richness caused by nutrient addition paralleled the increases in ANPP and decreases in light intensity under the canopies, indicating indirect effect of nutrient addition on species richness via ANPP-induced light competition. The exemplar species that responded most positively to fertilization in height and RGR also displayed stronger increases in their GA3 content and N:C ratios. GA3 concentrations and N: C ratios were positively correlated with height RGR when the data were pooled for all species. The tallest and the fastest-growing grass, F. ovina, had the largest increase in N: C ratios and the highest leaf GA3 concentrations after nutrient addition. These results indicated that differential responses of GA3 concentrations and N: C ratios to fertilization were related to the inequality in plant heights among species.

Explaining within‐community variation in plant biomass allocation: a balance between organ biomass and morphology above vs below ground?

AbstractQuestionsIt remains unresolved why, despite the obvious functional importance of leaves and roots, co‐existing plant species can display highly contrasting biomass distributions of these organs. Building on the ‘functional equilibrium’ hypothesis, we hypothesize that co‐existing species can each achieve balanced resource acquisition above vs below ground by trading off the biomass vs morphology of structures responsible for resource acquisition, i.e. leaves and fine roots.MethodsWe tested this hypothesis in a natural field setting by measuring plant above‐ and below‐ground biomass and morphological traits associated with resource uptake – specific leaf area (SLA) and specific root length (SRL) – of 18 dominant angiosperm species from a sub‐alpine plant community.LocationNew Zealand South Island.ResultsWe found a significant negative relationship between the species leaf mass to fine root mass ratio and the SLA to SRL ratio when we considered eudicot species only. The SLA to SRL ratio and plant size explained 31% and 34% of the total variation in the species leaf to fine root mass ratio respectively, and 45% when used in combination (P < 0.05 in all cases). Within a given plant size, 90% of the variation among species in total leaf area was due to differences in SLA, whereas variation in the fine root mass fraction was responsible for 71% of the variation among species in fine root length.ConclusionsIn support of our hypothesis, part of the difference between co‐occurring species in leaf and fine root biomass distribution could be explained by the variable morphologies of these organs as well as variation in plant size, independent of the plant economic strategy. We expect that this outcome may result from environmental and evolutionary constraints on plant species‐average traits, as well as plastic responses to local environmental conditions. These findings help explain why a diversity of strategies for achieving balanced resource acquisition can co‐exist within a single plant community.

Intraspecific variation in plant size, secondary plant compounds, herbivory and parasitoid assemblages during secondary succession

During secondary succession on abandoned agricultural fields the diversity and abundance of insect communities often increases, whereas the performance and nutritional quality of early successional plants often declines. As the diversity and abundance of insects on a single plant are determined by characteristics of the environment as well as of the host plant, it is difficult to predict how insects associated with a single plant species will change during succession. We examined how plant characteristics of the early successional plant species ragwort (Jacobaea vulgaris), and the herbivores and parasitoids associated with these plants change during secondary succession. In ten grasslands that differed in time since abandonment (3–26 years), we measured the size and primary and secondary chemistry of individual ragwort plants. For each plant we also recorded the presence of herbivores in flowers, leaves and stems, and reared parasitoids from these plant parts. Ragwort plants were significantly larger but had lower nitrogen concentrations in recently abandoned sites than in older sites. Pyrrolizidine alkaloid (PA) composition varied among plants within sites but also differed significantly among sites. However, there was no relationship between the age of a site and PA composition. Even though plant size decreased with time since abandonment, the abundance of stem-boring insects and parasitoids emerging from stems significantly increased with site age. The proportion of plants with flower and leaf herbivory and the number of parasitoids emerging from flowers and leaves was not related to site age. Parasitoid diversity significantly increased with site age. The results of our study show that ragwort and insect characteristics both change during secondary succession, but that insect herbivore and parasitoid abundances are not directly related to plant size or nutritional quality.

Allometric analysis of the effects of density on reproductive allocation and Harvest Index in 6 varieties of wheat (Triticum)

Plants produce biomass and then allocate some of this biomass to reproduction. The pattern of reproductive allocation is an important aspect of a plant's reproductive strategy in nature and is closely linked to yield and Harvest Index in cereal crops. Recent research has concluded that reproductive allocation should be analyzed and interpreted allometrically because ratios or fractions such as Reproductive Effort or Harvest Index are size dependent. We investigated reproductive allocation of individuals in 6 varieties of Triticum (wheat) grown at a wide range of densities. We harvested leaves, stems, spikes and grains of individual plants and analyzed the relationship between grain mass and vegetative mass allometrically. The large variation in density created large variation in plant mass and reproductive output. Most of the variation in individual yield (grain mass) was due to variation in plant size. There were significant differences among the varieties in the allometric exponent (slope of log–log relationship) of grain versus vegetative mass, such that some varieties produced higher yield (and therefore had a higher Harvest Index) than others when plants were small, while others had higher yield at larger sizes. Thus, the Harvest Index and its rank among varieties changed with plant size, which puts into question the practice of selecting for Harvest Index when crop performance varies greatly among individuals, years or environments. Selection for a high Harvest Index when individuals are large may mean unintentional selection for a lower Harvest Index when individuals are smaller. We conclude that cereal breeders should focus on reproductive allometry when interpreting Harvest Index, and select for allometric patterns that are most advantageous in a given agronomic context, especially when there is large variation in productivity among individuals, locations or years.