Leaf Chemistry Research Articles

A hyperspectral image can predict tropical tree growth rates in single-species stands.

Remote sensing is increasingly needed to meet the critical demand for estimates of forest structure and composition at landscape to continental scales. Hyperspectral images can detect tree canopy properties, including species identity, leaf chemistry and disease. Tree growth rates are related to these measurable canopy properties but whether growth can be directly predicted from hyperspectral data remains unknown. We used a single hyperspectral image and light detection and ranging-derived elevation to predict growth rates for 20 tropical tree species planted in experimental plots. We asked whether a consistent relationship between spectral data and growth rates exists across all species and which spectral regions, associated with different canopy chemical and structural properties, are important for predicting growth rates. We found that a linear combination of narrowband indices and elevation is correlated with standardized growth rates across all 20 tree species (R2 =53.70%). Although wavelengths from the entire visible-to-shortwave infrared spectrum were involved in our analysis, results point to relatively greater importance of visible and near-infrared regions for relating canopy reflectance to tree growth data. Overall, we demonstrate the potential for hyperspectral data to quantify tree demography over a much larger area than possible with field-based methods in forest inventory plots.

Short-term leaching dynamics of three peatland plant species reveals how shifts in plant communities may affect decomposition processes

Foliar litter is the main input of organic carbon to many soils, and thus litter decomposition processes are integral to our understanding of carbon dynamics in soil systems. Despite the short duration of the leaching phase of decomposition, a considerable amount of mass loss can occur providing a valuable energy source for microbes, and influencing leaf litter chemistry for subsequent microbial decomposition. At the same time, differences in plant species and their functional traits play a role in decomposition dynamics, particularly in consideration of shifting plant communities or changes in leaf chemistry under climate change. Here we investigate the short-term leaching decomposition dynamics of three boreal peatland plant species (Carex magellanica, Chamaedaphne calyculata, Sphagnum magellanicum) grown under ambient and elevated levels of atmospheric CO2. Litter chemistry was significantly different among all three plant species. In addition, plant tissues grown under elevated CO2 showed lower total C and total N than plants grown under ambient CO2. After leaching, however litter from plants grown under elevated CO2 conditions were not significantly different in total C values compared to plants grown under ambient CO2 conditions. Mass loss corresponded with the total dissolved organic carbon release across all species and was greatest in Chamaedaphne, a woody shrub; measures of carbon lability (SUVA254) were significantly greater in vascular plant species compared to Sphagnum moss. Mass loss was reduced in plants grown under elevated CO2 conditions, suggesting allocation to more non-soluble structural compounds. Placing our results within a climate change scenario where peatland plant community compositional shifts from mosses to graminoids and woody shrubs have been observed, we suggest that greater amounts of more labile carbon released from vascular plant species indicates a shift to more decomposable litters with the potential to stimulate microbial growth and activity.

Leaf chemistry of woody species in the Brazilian cerrado and seasonal forest: response to soil and taxonomy and effects on decomposition rates

The Brazilian cerrado occurs interspersed with the semi-deciduous seasonal forest, and soil fertility is considered as the main determinant of the abrupt transitions between both vegetation types. We aimed to study patterns across chemical traits of green leaves in 121 cerrado and seasonal forest woody species from southeastern Brazil, their response to soil nutrient status, and their effects on decomposition rates. We compared leaf traits of both cerrado and forest species and constructed multilevel models to account for partitioning of variance in each trait. We calculated the community-weighted mean of each trait to assess their response to soil nutrient status and their effects on decomposition rates of standard plant material. Most of the traits were significantly correlated among themselves, with cerrado species having lower nutrient concentrations than the seasonal forest. Taxonomy accounted for 52 % of the total variance in leaf traits, whereas vegetation type accounted for 19 %. All leaf traits but leaf manganese and aluminium concentrations were significantly related to soil properties. Decomposition rates were affected indirectly by soil features through its effects on leaf traits. Contrary to the expected, the higher the leaf nitrogen concentration in the surrounding litter, the lower the decomposition rate. Even with a large effect of taxonomy on leaf nutrient-related traits, soil exerted an important role on the chemical traits. Strategies of both cerrado and seasonal forest species were carried out through multi-element control of soil on leaf nutrient composition. The effect of such different strategies on functioning was, however, less prominent.

Effect of leaf chemistry ofVitis viniferaL. on the performance and development ofEpiphyas postvittana(Lepidoptera: Tortricidae)

Background and Aims In the context of life-history performance, better fitness is evident in insect populations when they correlate positively with the nutritional quality of their host-plants. We determined the chemical differences in the leaves of five cultivars of Vitis vinifera in relation to feeding by Epiphyas postvittana and evaluated larval and adult reproductive performance on the selected cultivars. Methods and Results We determined total nitrogen, carbohydrates, phenolic substances and potassium, iron, sodium and zinc in V. vinifera cv. Chardonnay, Sauvignon Blanc, Merlot, Semillon and Marsanne. The life-history performance of E. postvittana was evaluated by raising it from eggs on leaves of the cultivars. Nitrogen content of Chardonnay was significantly greater than that of the other cultivars. Different cultivars of V. vinifera influenced growth parameters such as larval-developmental time and female-pupal mass. Reproductive-performance, measured as fecundity and fertility rates and adult-male longevity, varied when reared on leaves of the cultivars of V. vinifera. Conclusion Leaves of Chardonnay have the highest nitrogen concentration and enhanced larval performance of E. postvittana. A fitness-index study shows that female-reproductive performance was significantly enhanced when reared on Chardonnay, whereas it declined when reared on Marsanne. Significance of the Study Differences among cultivars of V. vinifera in terms of leaf chemistry are critical for larval performance and adult-reproductive potential. The poor response of E. postvittana on Marsanne could be useful in integrated pest management via push—pull strategy by planting Marsanne either near or among the susceptible cultivars of V. vinifera.

Feeding behavioral response of cotton aphid, Aphis gossypii, to elevated CO2: EPG test with leaf microstructure and leaf chemistry

AbstractEffect of elevated CO2 on feeding behavior of the cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae), was investigated using electrical penetration graphs (EPG) on cotton, Gossypium hirsutum L. (Malvaceae). Leaf microstructures and foliar soluble constituents were also measured simultaneously to quantify the impact of foliar changes on leaf nutritional quantity and quality, owing to elevated CO2, on stylet penetration and food‐quality plasticity of A. gossypii. Significant increases in fresh body weight, fecundity, and population abundances of A. gossypii were found in elevated CO2 in contrast to ambient CO2. Elevated CO2 influenced the feeding behavior, as evidenced by altered EPG recordings, including the increased non‐penetration period (walking and finding the feeding site), E2<8 min (probes with sustained ingestion of <8 min), and first E2>8 min (first occurrence of probes with sustained ingestion of >8 min), and decreased E2>8 min recordings. Moreover, leaf microstructures were significantly affected by CO2 levels, with thinner upside epidermis (UPE) and thicker underside epidermis (UDE), sponge tissues (ST), and fence tissues under elevated CO2 compared to that in ambient CO2. Therefore, it is expected that A. gossypii spend more time penetrating the thicker leaf UDE and ST when the host plant is exposed to elevated CO2. Furthermore, elevated CO2 significantly enhanced foliar soluble matter, including soluble sugars (SS), free amino acids and fatty acids (FFA), and total soluble matter (TSM), which was congruent with significant increase or decrease in leaf turgor or osmotic potential. Increased leaf turgor and leaf soluble constituents favored ingestion in A. gossypii, resulting in increases in fresh body weight, fecundity, and population abundances under elevated CO2. These feeding behaviors and resulting population growth parameters are consistent with the significant positive correlations between aphid fresh body weight and foliar FFA/TSM, between A. gossypii fecundity and foliar SS of cotton plants, and between the time of E2<8 min recordings and leaf turgor.

Elevational divergence and clinal variation in floral color and leaf chemistry in Silene vulgaris.

Environmental heterogeneity over a species range can lead to divergent selection among populations, leading to phenotypic differences. The plant flavonoid pathway controls key reproductive and defense-related traits and responds to selection and environmental stressors, allowing for hypotheses about phenotypic divergence across environmental gradients. We hypothesized that with increasing elevation, more flavonoids would be produced as a response to increased UV radiation and that plants would be better defended against herbivores. We measured floral color, flavonoids, and herbivory in natural populations of Silene vulgaris (Caryophyllaceae) along elevational transects in the French Alps. We correlated phenotypes with environmental variables and calculated genotypic divergence (FST) to compare with phenotypic divergence (PST). We found significant phenotypic variation in S. vulgaris along elevational gradients. Strong positive correlations were observed between floral color, leaf non-anthocyanidin flavonoid concentration, and elevation. Floral anthocyanin and leaf non-anthocyanidin flavonoid phenotypes negatively covaried with temperature and precipitation seasonality. Comparisons of PST to FST provided evidence for stabilizing selection on floral color among transects and divergent selection along the elevational gradient. Flavonoid production increases along elevational gradients in S. vulgaris, with clinal variation in calyx anthocyanins and increasing leaf non-anthocyanin flavonoid concentrations. Despite the photoprotective and antiherbivore properties of some flavonoids, flavonoid production in flowers and leaves was correlated with population microclimatic variables: temperature and precipitation. Taken together, the results suggest that different flavonoid groups are targeted by selection in different tissues and provide evidence for divergent patterns of selection for flavonoids between high and low elevations.

Intraspecific leaf chemistry drives locally accelerated ecosystem function in aquatic and terrestrial communities.

Resource patchiness influences consumer foraging, movement, and physiology. Fluxes across ecosystem boundaries can extend these effects to otherwise distinct food webs. Intraspecific diversity of these cross-ecosystem subsidies can have large consequences for recipient systems. Here, we show intraspecific variation in leaf defensive chemistry of riparian trees drives local adaptation among terrestrial and riverine decomposers that consume shed leaf litter. We found extensive geographic structuring of ellagitannins, diarylheptanoids, and flavonoids in red alder trees. Ellagitannins, particularly those with strong oxidative activity, drive aquatic leaf decomposition. Further, spatial variation in these leaf components drives local ecological matching: in experiments using artificial food sources distinguished only by the chemical content of individual trees, we found decomposers both on land and in rivers more quickly consumed locally derived food sources. These results illustrate that terrestrial processes can change the chemistry of cross-ecosystem subsidies in ways that ultimately alter ecosystem function in donor and recipient systems.

Growth and leaf chemistry of Atriplex species from Northern Mexico as affected by salt stress

ABSTRACTAtriplex species are tolerant to salinity and water stress and thus they are suitable for restoration of many degraded ecosystems. In addition, many Atriplex species offer good value as forages. We compared growth and leaf chemistry of Atriplex canescens, a well-known halophyte, and A. acanthocarpa, a poorly-studied species, as affected by salinity in a greenhouse study. Seeds and soil were collected in northern Mexico, the native range of these species. Plants were grown in pots containing native soil and irrigated with NaCl solutions of 0, 50, and 100 mM. Shoot growth of A. canescens declined 37% as NaCl treatments increased from 0 to 100 mM while shoot growth of A acanthocarpa was not significantly affected by salinity. The high salt tolerance of A. acanthocarpa was linked to a high accumulation of leaf sodium (Na) (7- to 13-fold higher than A. canescens). A. acanthocarpa had also higher growth rate than A. canescenes, making the former species a good candidate for cultivation, especially under saline conditions. Tissue concentration of potassium (K) in both species was minimally affected by the salinity treatments. Leaf nitrogen (N) concentration increased as plants faced higher salinity treatments, especially in A. canescens. The high salt tolerance and higher Na accumulation of A. acanthocarpa make this species an attractive choice for reclamation of saline areas. We suggest A. acanthocarpa should be explored as viable forage for cultivation and for reclamation of degraded areas just as A. canescens has been throughout the world.

Tree genotype influences ectomycorrhizal fungal community structure: Ecological and evolutionary implications

Abstract Although the eco-evolutionary dynamics of multicellular organisms are intertwined with the microorganisms that colonize them, there is only a rudimentary understanding of how a host's genotype influences its microbiome. We utilize Populus angustifolia to test whether communities of essential symbionts, ectomycorrhizal fungi (EMF), vary among host genotypes. Further, we test whether EMF communities covary among tree genotypes with the chemistry of senescent leaves and aboveground biomass, traits important to tree fitness, and carbon and nutrient cycling. We found: 1) EMF composition, colonization and the Basidiomycota to Ascomycota ratio varied among tree genotypes (broad-sense heritability = 0.10–0.25). 2) EMF composition did not covary among genotypes with aboveground biomass but it did covary with senescent leaf chemistry ( rho = 0.29), primarily due to a single genotype. These findings demonstrate a link between tree genotype and EMF communities, which has implications for fungal diversity, host-symbiont interactions and aboveground-belowground linkages in ecological and evolutionary contexts.

Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora

Salinity and tidal inundation induce physiological stress in vascular plant species and influence their distribution and productivity in estuarine wetlands. Climate change-induced sea level rise may magnify these abiotic stressors and the physiological stresses they can cause. Understanding the potential of invasive plants to respond to predicted salinity increases will elucidate their potential niche breadth. To examine potential phenotypic plasticity and functional trait responses to salinity stress in the invasive cordgrass Spartina densiflora, we collected rhizomes from four invasive populations occurring from California to Vancouver Island, British Columbia on the Pacific Coast of North America. In a glasshouse common garden experiment, we measured plant traits associated with growth and allocation, photosynthesis, leaf pigments, and leaf chemistry and calculated plasticity indices across imposed salinity treatments. Fifteen of 21 leaf chemistry, pigment, morphological and physiological traits expressed plastic responses to salinity. When averaged across all measured traits, degree of plasticity did not vary among sampled populations. However, differences in plasticity among populations in response to salinity were observed for 9 of 21 measured plant traits. Leaf chemistry and adaxial leaf rolling trait responses demonstrated the highest degree of plasticity, while growth and allocation measures were less plastic. Phenotypic plasticity of leaf functional traits to salinity indicates the potential of S. densiflora to maintain invasive growth in response to rising estuarine salinity with climate change.

Topographic distributions of emergent trees in tropical forests of the Osa Peninsula, Costa Rica

Tropical rainforests are reservoirs of terrestrial carbon and biodiversity. Large and often emergent trees store disproportionately large amounts of aboveground carbon and greatly influence the structure and functioning of tropical rainforests. Despite their importance, controls on the abundance and distribution of emergent trees are largely unknown across tropical landscapes. Conventional field approaches are limited in their ability to characterize patterns in emergent trees across vast landscapes with varying environmental conditions and floristic composition. Here, we used a high‐resolution light detection and ranging (LiDAR) sensor aboard the Carnegie Airborne Observatory Airborne Taxonomic Mapping System (CAO‐AToMS) to examine the abundance and distribution of tall emergent tree crowns (ETC) relative to surrounding tree crowns (STC) across the Osa Peninsula, a geologically and topographically diverse region of Costa Rica. The abundance of ETC was clearly influenced by fine‐scale topographic variation, with distribution patterns that held across a variety of geologic substrates. Specifically, the density of ETC was much greater on lower slopes and in valleys, compared to upper slopes and ridges. Furthermore, using the CAO high‐fidelity imaging spectrometer, ETC had a different spectral signature than that of STC. Most notably, ETC had lower remotely sensed foliar nitrogen than STC, which was verified with an independent field survey of canopy leaf chemistry. The underlying mechanisms to explain the topographic‐dependence of ETCs and linkages to canopy N are unknown, and remain an important area of research.

Evolutionary correlations in flavonoid production across flowers and leaves in the Iochrominae (Solanaceae)

Plant reproductive and vegetative tissues often use the same biochemical pathways to produce specialized metabolites. In such cases, selection acting on the synthesis of specific products in a particular tissue could result in correlated changes in other products of the pathway, both in the same tissue and in other tissues. This study examined how changes in floral anthocyanin pigmentation affect the production of other compounds of the flavonoid pathway in flowers and in leaves. Focusing on the Iochrominae, a clade of Solanaceae with a wide range of flower colors, liquid chromatography coupled with mass spectrometry and UV detection was used to profile and quantify the variation in two classes of flavonoids, anthocyanins and flavonols. Purple, red, orange and white-flowered Iochrominae produced all of the six common anthocyanidin types, as well as several classes of flavonols. Differences in anthocyanin and flavonol production were significantly correlated in flowers, particularly with respect to B ring hydroxylation pattern. However, these differences in floral flavonoids were not strongly related to differences in leaf chemistry. Specifically, most species made only flavonols (not anthocyanins) in leaves, and these comprised the two most common flavonols, quercetin and kaempferol, regardless of the color of the flower. These results suggest that shifts in flower color may occur without significant pleiotropic consequences for flavonoid production in vegetative tissues. Similar studies in other systems will be important for testing the generality of this pattern in other groups of flowering plants.

Florivory shapes both leaf and floral interactions

AbstractFlorivory, or the consumption of flowers, is a ubiquitous interaction that can reduce plant reproduction directly by damaging reproductive tissues and indirectly by deterring pollinators. However, we know surprisingly little about how florivory alters plant traits or the larger community of species interactions. Although leaf damage is known to affect floral traits and interactions in many systems, the consequences of floral damage for leaf traits and interactions are unknown. We manipulated floral damage in Impatiens capensis and measured effects on floral attractive traits and secondary chemicals, leaf secondary chemicals, floral interactions, leaf herbivory, and plant reproduction. We also examined relationships between early season floral traits and floral interactions, to explore which traits structure floral interactions. Moderate but not high florivory significantly increased relative selfed reproduction, leading to a shift in mating system away from outcrossing. Florivory increased leaf secondary compounds and decreased leaf herbivory, although mechanisms other than leaf chemistry may be responsible for some of the reduced leaf damage. Florivory altered four of seven measured interactions, including increased subsequent florivory and reduced flower spiders, although only leaf damage effects were significant after correcting for multiple tests. Pretreatment concentrations of floral anthocyanins and condensed tannins were associated with reduced levels of many floral antagonisms, including florivory, nectar larceny, and flower spider abundance, suggesting these traits play a role in floral resistance. Overall, our results indicate a broad range of community and potential evolutionary consequences of florivory through structuring subsequent floral interactions, altering leaf secondary chemicals, and shaping leaf herbivory.

Do you speak chemistry? Small chemical compounds represent the evolutionary oldest form of communication between organisms.

In his famous fantasy epic, The Lord of the Rings , British writer and Professor of English Language and Literature, J. R. R. Tolkien, invented the Ents: tree‐like creatures who were some of the oldest beings in his fantasy world of Middle‐earth. In Tolkien's story, the Ents used a unique and ancient language to communicate with each other in a very deliberate way. Tolkien described this language as “unhasty” and “slow, sonorous, agglomerated, repetitive, indeed long‐winded”. > … the intriguing idea of plants chatting with each other proved fascinating to the general public Of course, Entish is a fantasy language, but the idea of a “language of trees” touches on the real‐world question of whether plants actually do communicate. In 1983, Ian T. Baldwin and Jack C. Schultz answered this question in an article in Science : “Rapid Changes in Tree Leaf Chemistry Induced by Damage: Evidence for Communication Between Plants”. In their paper, Baldwin and Schultz suggested that airborne signals originating from damaged plant tissues stimulate biochemical changes in adjacent plants. These changes in turn affect or deter herbivorous insects [1]. The publication inspired numerous articles, features, and comments in the press about “talking trees”—the intriguing idea of plants chatting with each other proved fascinating to the general public. Nevertheless, although they do not chat in Entish, plants do communicate. In a very basic sense, and according to Shannon & Weaver's The mathematical theory of communication (1963), communication involves a sender, a signal, and a receiver, the last of which is able to recognize and decode the signal. Plant communication definitely fits this model (Fig 1). However, communication between living organisms is actually much older than the 450 million years that land plants have lived on land. The oldest form of communication is probably the chemical interactions that …

Decomposition and release of nutrients from leaf litter in rubber plantations

<p>Establishment of cover crop has been a standard scientific agronomic intervention in rubber (<em>Hevea brasiliensis</em>) plantations. Natural leaf fall in rubber plantations is an unaccounted phenomenon which also improves the physicochemical properties and biological activities of soil. A comparison of the decomposition of leaf litter from different sources in soil and the release of utrients from them has been attempted in this study through a field experiment. Studies indicated that the degradation and release of nutrients to the soil pool was mainly decided by the leaf chemistry and degradability of the litter. Rubber litter had its own edge over other leguminous cover crop litter, in providing a sustained release of potassium, calcium and magnesium owing to its slow and steady mineralization rate compared to cover crops. Higher content of nutrients was recorded in degraded litter in comparison to fresh sources. Legume cover crops are capable of enhancing the bacterial and fungal populations in soil compared to nonleguminous crops in rubber plantations.</p>

Tobacco, Microbes, and Carcinogens: Correlation Between Tobacco Cure Conditions, Tobacco-Specific Nitrosamine Content, and Cured Leaf Microbial Community.

Tobacco-specific nitrosamines are carcinogenic N-nitrosamine compounds present at very low levels in freshly harvested tobacco leaves that accumulate during leaf curing. Formation of N-nitrosamine compounds is associated with high nitrate levels in the leaf at harvest, and nitrate is presumed to be the source from which the N-nitrosation species originates. More specifically, nitrite is considered to be a direct precursor, and nitrite is linked with N-nitrosation in many environmental matrices where it occurs via microbial nitrate reduction. Here, we initiate work exploring the role of leaf microbial communities in formation of tobacco-specific nitrosamines. Leaves from burley tobacco line TN90H were air cured under various temperature and relative humidity levels, and 22 cured tobacco samples were analyzed for their microbial communities and leaf chemistry. Analysis of nitrate, nitrite, and total tobacco-specific nitrosamine levels revealed a strong positive correlation between the three variables, as well as a strong positive correlation with increasing relative humidity during cure conditions. 16S rRNA gene amplicon sequencing was used to assess microbial communities in each of the samples. In most samples, Proteobacteria predominated at the phylum level, accounting for >90% of the OTUs. However, a distinct shift was noted among members of the high tobacco-specific nitrosamine group, with increases in Firmicutes and Actinobacteria. Several OTUs were identified that correlate strongly (positive and negative) with tobacco-specific nitrosamine content. Copy number of bacterial nitrate reductase genes, obtained using quantitative PCR, did not correlate strongly with tobacco-specific nitrosamine content. Incomplete denitrification is potentially implicated in tobacco-specific nitrosamine levels.

Plant hydraulic responses to long-term dry season nitrogen deposition alter drought tolerance in a Mediterranean-type ecosystem.

Anthropogenic nitrogen (N) deposition represents a significant N input for many terrestrial ecosystems. N deposition can affect plants on scales ranging from photosynthesis to community composition, yet few studies have investigated how changes in N availability affect plant water relations. We tested the effects of N addition on plant water relations, hydraulic traits, functional traits, gas exchange, and leaf chemistry in a semi-arid ecosystem in Southern California using long-term experimental plots fertilized with N for over a decade. The dominant species were Artemisia california and Salvia mellifera at Santa Margarita Ecological Reserve and Adenostoma fasciculatum and Ceanothus greggii at Sky Oaks Field Station. All species, exceptCeanothus, showed increased leaf N concentration, decreased foliar carbon to N ratio, and increased foliar N isotopic composition with fertilization, indicating that added N was taken up by study species, yet each species had a differing physiological response to long-term N addition. Dry season predawn water potentials were less negative with N addition for all species except Adenostoma, but there were no differences in midday water potentials, or wet season water potentials. Artemisiawas particularly responsive, as N addition increased stem hydraulic conductivity, stomatal conductance, and leaf carbon isotopic composition, and decreased wood density. The alteration of water relations and drought resistance parameters with N addition in Artemisia, as well as Adenostoma, Ceanothus, and Salvia, indicate that N deposition can affect the ability of native Southern California shrubs to respond to drought.

Genotypic richness predicts phenotypic variation in an endangered clonal plant.

Declines in genetic diversity within a species can affect the stability and functioning of populations. The conservation of genetic diversity is thus a priority, especially for threatened or endangered species. The importance of genetic variation, however, is dependent on the degree to which it translates into phenotypic variation for traits that affect individual performance and ecological processes. This is especially important for predominantly clonal species, as no single clone is likely to maximise all aspects of performance. Here we show that intraspecific genotypic diversity as measured using microsatellites is a strong predictor of phenotypic variation in morphological traits and shoot productivity of the threatened, predominantly clonal seagrass Posidonia australis, on the east coast of Australia. Biomass and surface area variation was most strongly predicted by genotypic richness, while variation in leaf chemistry (phenolics and nitrogen) was unrelated to genotypic richness. Genotypic richness did not predict tissue loss to herbivores or epiphyte load, however we did find that increased herbivore damage was positively correlated with allelic richness. Although there was no clear relationship between higher primary productivity and genotypic richness, variation in shoot productivity within a meadow was significantly greater in more genotypically diverse meadows. The proportion of phenotypic variation explained by environmental conditions varied among different genotypes, and there was generally no variation in phenotypic traits among genotypes present in the same meadows. Our results show that genotypic richness as measured through the use of presumably neutral DNA markers does covary with phenotypic variation in functionally relevant traits such as leaf morphology and shoot productivity. The remarkably long lifespan of individual Posidonia plants suggests that plasticity within genotypes has played an important role in the longevity of the species. However, the strong link between genotypic and phenotypic variation suggests that a range of genotypes is still the best case scenario for adaptation to and recovery from predicted environmental change.

Nutrient availability and flooding stress interact to affect growth and mercury concentration in Taxodium distichum (L.) Rich. seedlings

Plant growth can be limited by nutrient availability and/or flooding stress but their relationship is understood too poorly to predict when they act independently or to predict which dominates the relationship. Nutrient availability also reduces uptake of toxic metals under some conditions but enhances uptake under others. We studied how flooding stress and nutrient availability affected growth and mercury uptake by Taxodium distichum (L.) Rich., which is a tree that dominates freshwater wetlands in the southeastern United States. We hypothesized that nutrients would negate flooding stress and enhance mercury uptake. We also hypothesized that leaf chemistry could serve as an indicator of factors limiting growth. We planted 432 one-year old seedlings in soil with one of four nutrient availabilities (no enhancement, or enhanced with 57, 283, or 1132gNm−2 and other nutrients) and allowed the seedlings to grow for two seasons with one of six flooding regimes ranging from <1% to 96% flooding each month. The highest level of nutrient availability killed 82% of the seedlings almost immediately but after one year, nutrient availability and flooding interacted such that seedlings given 57gNm−2 negated effects of flooding stress on stem length. After two years, nutrient availability and flooding stress interacted such that seedlings given 283gNm−2 grew more than less fertilized seedlings except in the most flooded treatment. Mercury in leaves was related to flooding after the first year but to nutrient availability after the second year. The C:N and N:P ratio in leaves could not be used to indicate nutrient limitation in T. distichum because flooding also altered those ratios. The Ca:Mg ratio was related to nutrient availability but we found no chemical indicator of flooding stress. Research is needed to determine if flooding enhanced uptake of atmospheric mercury by leaves or soil mercury by roots.

Elevated CO2 impacts bell pepper growth with consequences to Myzus persicae life history, feeding behaviour and virus transmission ability.

Increasing atmospheric carbon dioxide (CO2) impacts plant growth and metabolism. Indirectly, the performance and feeding of insects is affected by plant nutritional quality and resistance traits. Life history and feeding behaviour of Myzus persicae were studied on pepper plants under ambient (aCO2, 400 ppm) or elevated CO2 (eCO2, 650 ppm), as well as the direct impact on plant growth and leaf chemistry. Plant parameters were significantly altered by eCO2 with a negative impact on aphid’s life history. Their pre-reproductive period was 11% longer and fecundity decreased by 37%. Peppers fixed significantly less nitrogen, which explains the poor aphid performance. Plants were taller and had higher biomass and canopy temperature. There was decreased aphid salivation into sieve elements, but no differences in phloem ingestion, indicating that the diminished fitness could be due to poorer tissue quality and unfavourable C:N balance, and that eCO2 was not a factor impeding feeding. Aphid ability to transmit Cucumber mosaic virus (CMV) was studied by exposing source and receptor plants to ambient (427 ppm) or elevated (612 ppm) CO2 before or after virus inoculation. A two-fold decrease on transmission was observed when receptor plants were exposed to eCO2 before aphid inoculation when compared to aCO2.