Plant Ecophysiological Traits Research Articles

Influence of Vegetation Dynamics on Soil Organic Carbon and Its Fractions in a Coastal Wetland

Coastal wetland ecosystems are highly efficient in sequestering carbon (C) to mitigate climate change. However, it is still unclear how vegetation dynamics affect soil organic carbon (SOC) and its fractions (labile and recalcitrant C (LC and RC)) in coastal wetlands. Here, we quantified the effects of saltmarsh vegetation dynamics on the SOC and its fractions using the invasiveSpartina alternifloraand co-occurring nativePhragmites australiscommunities as a model. SOC contents in these 2 communities showed similar spatial patterns with an inverted U-shaped curve from tidal mudflats to vegetated marshes. Our results suggested that plant ecophysiological traits play a primary role in regulating the spatial distribution of SOC. In addition, the lower ratio of leaf to shoot inP. australiscommunity facilitates the accumulation of RC, while the lower soil pH inS. alternifloramay accelerate the decomposition of RC. The findings indicated thatS. alternifloracould accumulate more C in the soil owing to its greater plant biomass and photosynthesis rate. However, the reduced soil pH byS. alterniflorainvasion might restrain SOC accumulation. Our findings shed light on the impacts of long-term species invasion on SOC and its fractions in coastal wetlands under global changes.

Ectomycorrhizal fungi with hydrophobic mycelia and rhizomorphs dominate in young pine trees surviving experimental drought stress

Mycorrhizal fungi can help plants to cope with drought, but research on the fungal communities that are more resistant to drought or alleviate drought stress of trees is still scarce. In this study, we investigated effects of drought on soil fungal communities and explored potential fungal traits related to drought resistance under greenhouse conditions. We manipulated water availability in pine seedlings belonging to three Spanish Pinus pinaster populations from geographical areas subjected to contrasting summer drought. A set of plant ecophysiological traits were quantified and soil fungi was quantified and profiled using ergosterol and Pacific Biosciences sequencing. Abundance of ectomycorrhizal (ECM) fungi in plants subjected to drought was lower than in well-watered plants. Most ECM taxa in plants surviving drought had long exploration types and were taxa typically forming rhizomorphs and hydrophobic mycelia. By contrast, ECM taxa in well-watered plants had wider range of distinct exploration types. No differences in fungal communities were found among P. pinaster populations. No associations between ECM fungi and plant ecophysiological traits were found, but significant interactions between drought treatments and belowground plant biomass were found for the relative abundances of ECM fungi, particularly ECM with long exploration types. Plants subjected to drought may benefit by associating to ECM taxa previously shown to transport water efficiently.

Contrasting responses in growth, photosynthesis and hydraulics of two subtropical tree species to cadmium contamination as affected by elevated CO2 and nitrogen addition.

Plant growth, photosynthesis, and hydraulics are affected by heavy metals but also by elevated atmospheric CO2 concentration (e[CO2]) and nitrogen (N) deposition. However, few studies have investigated the response of woody species to the combined effects of these three factors. We conducted an open-top chamber experiment with two common subtropical trees (Acacia auriculiformis and Syzygium hainanense) to explore the effects of cadmium (Cd)-contamination, e[CO2], and N addition on plant eco-physiological traits. We found that the growth of A. auriculiformis was insensitive to the treatments, indicating that it is a Cd-tolerant and useful afforestation species. For S. hainanense, in contrast, e[CO2] and/or N addition offset the detrimental effects of Cd addition by greatly increasing plant biomass and reducing the leaf Cd concentration. We then found that e[CO2] and/or N addition offset the detrimental Cd effects on S. hainanense biomass by increasing its photosynthetic rate, its N concentration, and the efficiency of its stem water transport network. These offsetting effects of e[CO2] and/or N addition, however, came at the expense of reduced xylem hydraulic safety resulting from wider vessels, thinner vessel walls, and therefore weaker vessel reinforcement. Our study suggests that, given future increases in global CO2 concentration and N deposition, the growth of Cd-tolerant tree species (like A. auriculiformis) will be probably stable while the growth of Cd-sensitive tree species (like S. hainanense) might be enhanced despite reduced hydraulic safety. This also suggests that both species will be useful for afforestation of Cd-contaminated soils given future global change scenarios.

Precipitation variations, rather than N deposition, determine plant ecophysiological traits in a desert steppe in Northern China

Understanding how plant ecophysiological traits of coexisting species within a community respond to environmental changes could help to predict the shift in plant community structure and function, but it remains limited in the scenarios of co-occurring precipitation variations and N deposition. A two-year field experiment was conducted to explore the effects of large precipitation changes (reduced and increased precipitation amount by 25% and 50% relative to ambient control) and high N deposition (10 g N m−2 yr−1) on a series of leaf ecophysiological traits of three dominant species (Stipa tianschanica, a C3 grass; Cleistogenes squarrosa, a C4 grass; and Artemisia capillaris, a C3 forb) in a desert steppe in Northern China. Increasing precipitation significantly linearly promoted the leaf light-saturated photosynthesis rate (Asat) and N use efficiency of the two C3 species, irrespective of N addition. The rises in Asat of both C3 species were mainly caused by increased soil moisture, which strongly induced increases in leaf stomatal conductance (gs) and declines in quantum yield of photosystem II (ΦPSII). However, the Asat of the two C3 species was weakly correlated with their specific leaf area and leaf N concentration, whereas the Asat of the C4 grass was negatively related to its leaf N. Moreover, the Asat, height, and aboveground biomass of the forbs were much more water-sensitive than those of both grass species, with a consequence of the most dominant species turning from grass to forbs as precipitation increased. Our findings highlight that water limitation, rather than N deficit, is the largest factor controlling plant growth in drylands, and plant species-specific ecophysiological responses to precipitation fluctuations will cause a substantial shift in the production and composition of plant community.

Differences in Ecological Traits between Plants Grown In Situ and Ex Situ and Implications for Conservation

Ex situ conservation plays an important role in maintaining global plant biodiversity and protects thousands of wild plants. Plant conservation in botanical gardens is an important part of ex situ conservation; however, little attention has been given to whether plant ecophysiological traits change and whether plant conservation goals are reached following ex situ conservation. In this study, tree and shrub plants were selected from Shanxi, Beijing of China and from Beijing Botanical Garden, and plants with good growth and similar ages were randomly selected to measure their light response curves, CO2 response curves with a portable photosynthesis system (Li-6400XT), relative chlorophyll contents using a chlorophyll meter (SPAD-502) and leaf water potential using a dew point water potential meter (WP4C). In comparison with cultivated plants, wild plants had higher water use efficiencies among all plants considered (by 92–337%) and greater light use efficiencies among some of plants considered (by 107–181%), while light response curves and CO2 response curves for wild plants were either higher or lower compared with cultivated plants. Ecological traits of wild and cultivated plants changed more as a result of habitat factors than due to plant factors. The initial slope of the light response curve, net photosynthetic rate at light saturation, light saturation point, maximum light energy utilization efficiency, maximum water use efficiency, leaf water content, and the leaf water potential of wild plants were larger or equal to those of cultivated plants, while dark respiration rate (by 63–583%) and light compensation point (by 150–607%) of cultivated plants were higher than those of wild plants. This research compared the ecophysiological traits of common green space plants cultivated in botanical gardens and distributed in different areas in wild environments. The response of plant ecophysiological traits to the changing environment has important theoretical and practical significance for wild plant conservation and urban green space system construction.

Effect of lignosulfonate application to sandy soil on plant nutrition and physiological traits

The application of nutrient-rich substrates to soils characterized by low natural fertility is discussed as a strategy to improve soil fertility and, consequently, affect plant physiological traits. This study aimed to evaluate if sodium lignosulfonate (LS), a by-products of pulp and paper industry, may improve plant ecophysiological traits under contrasting nutrient conditions. A pot culture experiment was conducted with cucumber plants, using LS concentrations of 0, 1, 2.5, 5, and 10 vol.% in sandy soil, and two soil nutrient levels: sufficient and low nutrient availability (SNA and LNA, accordingly). The LS increased N and P content in SNA leaves when 1% of LS was used and decreased N content in LNA leaves regardless of soil LS content. The LS did reduce mass-, N-, and P-based respiration rates of the SNA leaves, and increased the N-based respiration rate under LNA. The LS did not have a significant impact on the ratio of respiration to photosynthesis in SNA leaves, but decreased it under LNA. The LS application contributed to a slight activation of some physiological processes in LNA plants, but it was not successful to recover these activities to the level of plants grown under SNA.

Ecophysio-optical traits of semiarid Nebraska grasslands under different Juniperus virginiana and Pinus ponderosa canopy covers

Despite conservation efforts in the U.S. Great Plains, woody species have continued to expand at an unprecedented rate, threatening key ecosystem services and resilience. Cross-scale monitoring of these grasslands is key to successful integrative management strategies. In this study we measured plant optical traits derived from hyperspectral proximal sensing techniques with a field spectrometer, coupled with field-based measurements, including fluorescence and chlorophyll content, to determine the impacts of Juniperus virginiana and Pinus ponderosa expansion on grasslands health in Nebraska Sandhills, and investigated the use of optical-based approaches as indicators of successful monitoring of grasslands. Our results showed that higher woody species cover in grasslands was associated with lower soil moisture, decline in forbs, shrubs, and grasses cover and productivity, as well as herbaceous chlorophyll content and fluorescence, compared to non-invaded grasslands. We derived 13 vegetation indices (VIs) from optical-based methods and validated them against traditional handheld measurements of plant ecophysiological traits and vegetation biomass and composition. VIs, including Normalized Difference Vegetation Index (NDVI), Water Index (WI) and Chlorophyll Index at red edge (CIred edge) performed best when tested against biomass, and chlorophyll content and fluorescence (Fv/Fm), suggesting their potential use for assessing grasslands vegetation health. We demonstrate that optical-based approaches can serve as efficient non-invasive tools that can be part of multi-scale successful integrative management strategies.

Physiological response of onion (Allium cepa L.) seedlings to shungite application under two soil water regimes

The application of carbon-rich substrates to agricultural soils is discussed as a strategy to improve soil properties and fertility, which can affect plant physiological traits and enhance agricultural crop yield. The aim of this study was to evaluate if shungite, carbon-rich sedimentary-volcanic rock, may improve plant ecophysiological traits under sufficient water supply as well as soil water deficit. A pot culture experiment was conducted with onion (Allium cepa L.) seedlings, using four shungite concentrations (0, 5, 10 and 20 g kg−1) in an Umbric Podzols and two water regimes: well-watered and drying-wetting cycles. Soil water deficit decreased root nutrient content, depressed seedlings growth, net CO2 assimilation rate (An), stomatal conductance (gs) and the respiration rates in both darkness (Rd) and the light (Rl), but increased water use efficiency (WUE) at leaf level. Shungite application decreased the leaf necrosis under both water regimes and increased total leaf length of DW seedlings. Compared with the well-watered conditions, under drying-wetting cycle shungite stimulated the increase of the An rate and WUE at low measurement temperature. No significant effect of shungite was found for Rd, Rl, Rl/Rd, Rd/Ag (Ag = An + Rl) and Rl/Ag regardless soil water regimes. Shungite application was not so successful to eliminate the negative effects of soil water deficit on growth and physiological processes of A. cepa. The observed positive effects of shungite on the physiological traits of onion seedlings were more likely associated with the increase in the content of nutrients than with the improvement in soil water properties.

Tree canopy arthropods have idiosyncratic responses to plant ecophysiological traits in a warm temperate forest complex

Biodiversity studies on forest canopies often have narrow arthropod taxonomic focus, or refer to a single species of tree. In response, and to better understand the wide range of drivers of arthropod diversity in tree canopies, we conducted a large-scale, multi-taxon study which (a) included effect of immediate surroundings of an individual tree on plant physiological features, and (b), how these features affect compositional and functional arthropod diversity, in a warm, southern Afro-temperate forest. We found that tree species differed significantly in plant physiological features and arthropod diversity patterns. Surprisingly, we found negative correlation between surrounding canopy cover, and both foliar carbon and arthropod diversity in host trees, regardless of tree species. Subtle, tree intraspecific variation in physiological features correlated significantly with arthropod diversity measures, but direction and strength of correlations differed among tree species. These findings illustrate great complexity in how canopy arthropods respond to specific tree species, to immediate surroundings of host trees, and to tree physiological features. We conclude that in natural forests, loss of even one tree species, as well as homogenization of the crown layer and/or human-induced environmental change, could lead to profound and unpredictable canopy arthropod biodiversity responses, threatening forest integrity.

Growth and physiological responses of Carex schmidtii to water-level fluctuation

Water-level fluctuations are common abiotic stresses influencing growth and physiological processes of wetland plants. Nonetheless, little is known about plant eco-physiological responses and growth strategy under multi-hydrological processes. Carex schmidtii was grown under the conditions with interaction of initial water-level depth (DW) and water-level amplitude (AW). Dynamics of plant eco-physiological traits and growth strategy were investigated continuously during the entire growth stages. Results indicated that leaf morphology was significantly affected by DW and lasted time, and leaf width was sensitive to AW. The SLA and LDMC of C. schmidtii varied significantly at different lased time, and their relationships indicated the trade-off in leaves between matter production and nutrient conservation. Increasing DW inhibited matter production of C. schmidtii in early growth stage, but increased nutrient conservation in late growth stage. However, increasing AW contributed to both increase of matter production and nutrient conservation of C. schmidtii. The photosynthetic pigments of C. schmidtii are relatively sensitive to DW, AW and their interaction. Slowing down water-level fluctuations and appropriate water management in the key growth stage will assist with the adaption of Carex schmidtii. The findings provide invaluable supporting information for the management and conservation of C. schmidtii tussock wetlands.

Changes in Plant Functional Groups during Secondary Succession in a Tropical Montane Rain Forest

Aggregating diverse plant species into a few functional groups based on functional traits provides new insights for promoting landscape planning and conserving biodiversity in species-diverse regions. Ecophysiological traits are the basis of the functioning of an ecosystem. However, studies related to the identification of functional groups based on plant ecophysiological traits in tropical forests are still scarce because of the inherent difficulties in measuring them. In this study, we measured five ecophysiological traits: net photosynthetic capacity (Amax), maximum stomatal conductance (gmax), water use efficiency (WUE), transpiration rate (Trmmol), and specific leaf areas (SLA) for 87 plant species dominant in a chronosequence of secondary succession, using four time periods (5 year-primary, 15 year-early, and 40 year-middle successional stages after clear cutting and old growth) in the tropical montane rainforest on Hainan Island, China. These species were grouped using hierarchical cluster analysis and non-metric multidimensional scaling. Finally, the changes in the composition of functional groups and species richness along the chronosequence were analyzed. Results showed that the plant species in the tropical montane rainforest could be classified into eight distinct functional groups. The richness of functional groups was low during the initial early stage and increased as the early and middle stages progressed, and then declined in the late successional stage. The dominant functional groups in the primary stages had the highest Amax, gmax, Trmmol, and SLA, as well as the lowest WUE, while those in the early and middle successional stages had functional traits at a moderate level, and at the late stage they had the lowest Amax, gmax, Trmmol, and SLA, and highest WUE. Our study showed that the diverse plant species in the tropical montane rainforest could be grouped into a few functional groups according to major ecophysiological traits, and the composition and relative abundance of different groups changed with the successional dynamics of the forest ecosystem.

Earthworms suppress thrips attack on tomato plants by concomitantly modulating soil properties and plant chemistry

How plants cope with herbivore attack is partially modulated by the biotic and abiotic environment where the plant lives. For instance, theory predicts that soil fertility should drive patterns of plant resource allocation and defensive strategies. Earthworms, by their burrowing and casting activities, modify soil physicochemical properties and soil fertility. Therefore, earthworm-mediated changes in soil properties could alter plant physiology, plant nutritional quality, and ultimately, plant resistance against insect herbivores. We tested this hypothesis by measuring the combinatorial effects of two earthworm species, an epi-endogeic earthworm (Amynthas corticis) and an endo-anecic earthworm (Metaphire guillelmi), on soil properties, tomato plants’ physiological traits and plant resistance against the western flower thrips (Frankliniella occidentalis). We found that A. corticis alone increased plant resistance more than M. guillelmi alone or the combination of two species. The increased plant resistance was associated with a significant increase in the defence-related phytohormone jasmonic acid and the production of phenolic compounds. Furthermore, we observed a strong link between earthworm-mediated changes in soil properties and plant eco-physiological traits. Our results thus build toward a better predictive model of how earthworms can simultaneously influence soil parameters, plant productivity and resistance against herbivore pests.

Towards an integration of plant ecophysiological traits for the conservation of endangered species in ecosystems under water stress

espanolLa conservacion de la biodiversidad en las zonas aridas es un desafio importante en todo el mundo. El conocimiento de la biodi-versidad presente es clave para promover y facilitar la conservacion de plantas nativas en peligro de extincion, la cual contribuye a su persistencia. El desierto de Atacama, ubicado en el sur de Peru y norte de Chile, se considera un area prioritaria para la conservacion de la biodiversidad, debido principalmente a los altos niveles de endemismo presentes en este ecosistema. Sobre esta base, las variables hidricas de las comunidades vegetacionales son una herramienta util para el estudio de las relaciones de causa y efecto de los efectos del ambiente sobre los rasgos ecofisiologicos de las plantas. Sin embargo, en la actualidad existe una falta de informacion acerca de la influencia de los factores ecologicos sobre los parametros de reproduccion, y la interaccion entre las variables climaticas y las relaciones hidricas de las plantas que influyen en la produccion de semillas en las plantas que habitan en entornos limitados de agua. Esta revision describe la importancia de incorporar las variables fisiologicas hidricas de la vegetacion en peligro de extincion, como una herramienta predictiva para llevar a cabo planes de manejo y conservacion. Por otra parte, se destaca la necesidad de incorporar nuevas areas protegidas, debido al reciente aumento de las especies incluidas en peligro de extincion en el desierto de Atacama. Finalmente, se concluye que estos dos temas deben ser considerados para promover la recuperacion de la biodiversidad en las zonas hiperaridas, teniendo en cuenta otras influyentes variables como la erosion del suelo, el cambio climatico y los procesos de industrializacion. EnglishConservation of biodiversity in arid lands is a major issue worldwide. Knowledge of the biodiversity present is key to promote and facilitate the conservation of endangered native plants and will contribute to their persistence. The Atacama Desert, located in southern Peru and northern Chile, is considered a priority area for biodiversity conservation, principally due to high levels of endemism in the ecosystem. On this basis, water traits of plants are a useful tool for developing cause-and-effect relationships of abiotic variables under water stress environments. Nevertheless, currently there is lack of information about the influence of ecological factors on reproduction parameters, and the interaction among climatic variables and plant water relations that influence seed production in plants that inhabit water-limited environments. This report reviews the importance of incorporating plant physiology for the conservation of endangered vegetation as a predictive tool for management and preservation plans. Moreover, the report highlights the necessity of incorporating new protected areas, due the recent increase of species listed as endangered in the Atacama Desert. In brief, these two topics must be considered to promote the recovery of endangered biodiversity in hyperarid areas, taking into consideration soil erosion, climate change and industrialization processes.

A global synthesis of below‐ground carbon responses to biotic disturbance: a meta‐analysis

AbstractAimClimate change, especially the wider occurrence of extreme events, is likely to increase the intensity and frequency of insect/pathogen outbreaks (referred to as biotic disturbance), which may considerably affect plant ecophysiological traits and thus the ecosystem carbon (C) cycle. Little is known, however, about the ways in which biotic disturbance quantitatively affects ecosystem C processes, especially those that occur below ground. We reveal the general patterns of below‐ground C responses to biotic disturbance from field manipulative experiments and opportunistic events.LocationGlobal.MethodWe carried out a meta‐analysis examining the effects of biotic disturbance on 16 variables associated with below‐ground C processes, based on 64 experimental studies.ResultsBiotic disturbance significantly decreased below‐ground C pools with relatively long residence times (e.g. root biomass and soil organic carbon, SOC), but increased labile C pools (e.g. microbial biomass carbon, MBC; dissolved organic carbon, DOC), soil respiration (Rs) and its components, and microbial population sizes. Compared with the neutral or positive effects of other environmental changes on below‐ground C pools and fluxes, biotic disturbance had a negative effect on plant biomass and SOC but a larger positive effect on MBC, DOC and Rs.Main conclusionsBiotic disturbance can have stronger impacts on below‐ground C processes than other environmental changes, and the sensitive responses of soil labile C pools and C fluxes to biotic disturbance decrease long‐term below‐ground C sequestration. More research efforts are, however, needed to reduce the uncertainties in quantifying the effects of biotic disturbance and to improve forecasting of the feedback between the carbon cycle and climate.

Experimental warming studies on tree species and forest ecosystems: a literature review

Temperature affects a cascade of ecological processes and functions of forests. With future higher global temperatures being inevitable it is critical to understand and predict how forest ecosystems and tree species will respond. This paper reviews experimental warming studies in boreal and temperate forests or tree species beyond the direct effects of higher temperature on plant ecophysiology by scaling up to forest level responses and considering the indirect effects of higher temperature. In direct response to higher temperature (1) leaves emerged earlier and senesced later, resulting in a longer growing season (2) the abundance of herbivorous insects increased and their performance was enhanced and (3) soil nitrogen mineralization and leaf litter decomposition were accelerated. Besides these generalizations across species, plant ecophysiological traits were highly species-specific. Moreover, we showed that the effect of temperature on photosynthesis is strongly dependent on the position of the leaf or plant within the forest (canopy or understory) and the time of the year. Indirect effects of higher temperature included among others higher carbon storage in trees due to increased soil nitrogen availability and changes in insect performance due to alterations in plant ecophysiological traits. Unfortunately only a few studies extrapolated results to forest ecosystem level and considered the indirect effects of higher temperature. Thus more intensive, long-term studies are needed to further confirm the emerging trends shown in this review. Experimental warming studies provide us with a useful tool to examine the cascade of ecological processes in forest ecosystems that will change with future higher temperature.

Herbivores Modify Selection on Plant Functional Traits in a Temperate Rainforest Understory

There is limited evidence regarding the adaptive value of plant functional traits in contrasting light environments. It has been suggested that changes in these traits in response to light availability can increase herbivore susceptibility. We tested the adaptive value of plant functional traits linked with carbon gain in contrasting light environments and also evaluated whether herbivores can modify selection on these traits in each light environment. In a temperate rainforest, we examined phenotypic selection on functional traits in seedlings of the pioneer tree Aristotelia chilensis growing in sun (canopy gap) and shade (forest understory) and subjected to either natural herbivory or herbivore exclusion. We found differential selection on functional traits depending on light environment. In sun, there was positive directional selection on photosynthetic rate and relative growth rate (RGR), indicating that selection favors competitive ability in a high-resource environment. Seedlings with high specific leaf area (SLA) and intermediate RGR were selected in shade, suggesting that light capture and conservative resource use are favored in the understory. Herbivores reduced the strength of positive directional selection acting on SLA in shade. We provide the first demonstration that natural herbivory rates can change the strength of selection on plant ecophysiological traits, that is, attributes whose main function is resource uptake. Research addressing the evolution of shade tolerance should incorporate the selective role of herbivores.

Understanding plant-microbe interactions for phytoremediation of petroleum-polluted soil.

Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of petroleum pollution, however relatively little is known about how these interactions are influenced by petroleum pollution. In this experimental study using a microcosm approach, we examined how plant ecophysiological traits, soil nutrients and microbial activities were influenced by petroleum pollution in Phragmites australis, a phytoremediating species. Generally, petroleum pollution reduced plant performance, especially at early stages of plant growth. Petroleum had negative effects on the net accumulation of inorganic nitrogen from its organic forms (net nitrogen mineralization (NNM)) most likely by decreasing the inorganic nitrogen available to the plants in petroleum-polluted soils. However, abundant dissolved organic nitrogen (DON) was found in petroleum-polluted soil. In order to overcome initial deficiency of inorganic nitrogen, plants by dint of high colonization of arbuscular mycorrhizal fungi might absorb some DON for their growth in petroleum-polluted soils. In addition, through using a real-time polymerase chain reaction method, we quantified hydrocarbon-degrading bacterial traits based on their catabolic genes (i.e. alkB (alkane monooxygenase), nah (naphthalene dioxygenase) and tol (xylene monooxygenase) genes). This enumeration of target genes suggests that different hydrocarbon-degrading bacteria experienced different dynamic changes during phytoremediation and a greater abundance of alkB was detected during vegetative growth stages. Because phytoremediation of different components of petroleum is performed by different hydrocarbon-degrading bacteria, plants’ ability of phytoremediating different components might therefore vary during the plant life cycle. Phytoremediation might be most effective during the vegetative growth stages as greater abundances of hydrocarbon-degrading bacteria containing alkB and tol genes were observed at these stages. The information provided by this study enhances our understanding of the effects of petroleum pollution on plant-microbe interactions and the roles of these interactions in the phytoremediation of petroleum-polluted soil.

Ecophysiological responses of two dominant grasses to altered temperature and precipitation regimes

Ecosystem responses to climate change will largely be driven by responses of the dominant species. However, if co-dominant species have traits that lead them to differential responses, then predicting how ecosystem structure and function will be altered is more challenging. We assessed differences in response to climate change factors for the two dominant C 4 grass species in tallgrass prairie, Andropogon gerardii and Sorghastrum nutans, by measuring changes in a suite of plant ecophysiological traits in response to experimentally elevated air temperatures and increased precipitation variability over two growing seasons. Maximum photosynthetic rates, stomatal conductance, water-use efficiency, chlorophyll fluorescence, and leaf water potential varied with leaf and canopy temperature as well as with volumetric soil water content (0–15 cm). Both species had similar responses to imposed changes in temperature and water availability, but when differences occurred, responses by A. gerardii were more closely linked with changes in air temperature whereas S. nutans was more sensitive to changes in water availability. Moreover, S. nutans was more responsive overall than A. gerardii to climate alterations. These results indicate both grass species are responsive to forecast changes in temperature and precipitation, but their differential sensitivity to temperature and water availability suggest that future population and community structure may vary based on the magnitude and scope of an altered climate.

Variability in water use efficiency at the leaf level among Mediterranean plants with different growth forms

Assessing natural variability of leaf water use efficiency in plants adapted to extreme conditions of the Mediterranean climate represents an important step in the evaluation of the usefulness of some plant ecophysiological traits under water stress. Eleven Mediterranean species naturally inhabiting the Balearic Islands and corresponding to different growth forms (herbs, semi-deciduous shrubs, woody evergreen shrubs and woody evergreen semi-shrubs) were subject to progressive soil water depletion. Leaf intrinsic water use efficiency was measured by gas exchange at four different degrees of water stress. Under well watered conditions, differences in leaf intrinsic water use efficiency (A N/g s) among growth forms were limited to woody evergreen semi-shrubs, which presented the highest values. Under water stress conditions, differences became more evident, with a trend for an increase in A N/g s from woody evergreen shrubs, through semi-deciduous shrubs and herbaceous to woody evergreen semi-shrubs. The observed variation in A N/g s correlated with several physiological (leaf water potential, soil to leaf hydraulic conductance and stomatal conductance) and morphological (stomatal density) parameters, displaying a general relationship for all growth forms. This suggests that the capacity for withstanding water limitation is adaptive for all Mediterranean species. However, when A N/g s was related to leaf mass area, this relationship was not generally applicable, and depended on growth forms, suggesting that different growth forms display specific morphological adjustments in response to water shortage.

Natural selection on and predicted responses of ecophysiological traits of swamp milkweed (Asclepias incarnata)

Summary Given the rapid and reversible impact of the environment on plant ecophysiological traits, it has been speculated that such traits may have low heritabilities, high phenotypic plasticity and experience selection which is highly variable. We estimated heritabilities, phenotypic plasticity and natural selection on five ecophysiological traits (carbon : nitrogen (C : N) ratio, leaf water content, specific leaf area (SLA), trichome density and water use efficiency (WUE)) of swamp milkweed Asclepias incarnata. In a 2‐year field experiment, we studied 49 full‐sibling families in a common garden and assessed phenotypic and genotypic selection. Consistent evidence indicated selection for increased leaf trichome density and reduced WUE. Less strong evidence suggested selection for reduced SLA and leaf water content, and there was no selection on C : N of leaves. Although the ecophysiological traits showed many phenotypic and genetic correlations, we found little evidence that these correlations would constrain adaptive evolution. To evaluate the phenotypic plasticity of the same traits, we conducted a separate growth chamber experiment and found evidence that leaf water content, SLA and C : N responded to environmental conditions (herbivory, water stress, nutrient addition). Synthesis. We have demonstrated natural selection on ecophysiological traits and their probable response to selection with a genotypic selection analysis. We cautiously reject the notion that these traits lack heritable variation and that genetic correlations among them constrain their response to selection. Thus, plants such as A. incarnata appear capable of adaptive responses in their ecophysiological traits.