Phenotypic selection on leaf water use efficiency and related ecophysiological traits for natural populations of desert sunflowers

Plant water-use efficiency (WUE) is expected to affect plant fitness and thus be under natural selection in arid habitats. Although many natural population studies have assessed plant WUE, only a few related WUE to fitness. The further determination of whether selection on WUE is direct or indirect through functionally related traits has yielded no consistent results. For natural populations of two desert annual sunflowers, Helianthus anomalus and H. deserticola, we used phenotypic selection analysis with vegetative biomass as the proxy for fitness to test (1) whether there was direct and indirect selection on WUE (carbon isotope ratio) and related traits (leaf N, area, succulence) and (2) whether direct selection was consistent with hypothesized drought/dehydration escape and avoidance strategies. There was direct selection for lower WUE in mesic and dry H. anomalus populations, consistent with dehydration escape, even though it is the longer lived of the two species. For mesic H. anomalus, direct selection favored lower WUE and higher N, suggesting that plants may be “wasting water” to increase N delivery via the transpiration stream. For the shorter lived H. deserticola in the direr habitat, there was indirect selection for lower WUE, inconsistent with drought escape. There was also direct selection for higher leaf N, succulence and leaf size. There was no direct selection for higher WUE consistent with dehydration avoidance in either species. Thus, in these natural populations of two desert dune species higher fitness was associated with some combination direct and indirect selection for lower WUE, higher leaf N and larger leaf size. Our understanding of the adaptive value of plant ecophysiological traits will benefit from further consideration of related traits such as leaf nitrogen and more tests in natural populations.     

Leaf anatomical structures of <Emphasis Type="Italic">Paphiopedilum</Emphasis> and <Emphasis Type="Italic">Cypripedium</Emphasis> and their adaptive significance

Paphiopedilum and Cypripedium are closely related in phylogeny, but have contrasting leaf traits and habitats. To understand the divergence in leaf traits of Paphiopedilum and Cypripedium and their adaptive significance, we analyzed the leaf anatomical structures, leaf dry mass per area (LMA), leaf lifespan (LL), leaf nitrogen concentration (N _mass), leaf phosphorus concentration (P _mass), mass-based light-saturated photosynthetic rate (A _mass), water use efficiency (WUE), photosynthetic nitrogen use efficiency (PNUE) and leaf construction cost (CC) for six species. Compared with Cypripedium, Paphiopedilum was characterized by drought tolerance derived from its leaf anatomical structures, including fleshy leaves, thick surface cuticles, huge adaxial epidermis cells, lower total stoma area, and sunken stomata. The special leaf structures of Paphiopedilum were accompanied by longer LL; higher LMA, WUE, and CC; and lower N _mass, P _mass, A _mass, and PNUE compared with Cypripedium. Leaf traits in Paphiopedilum helped it adapt to arid and nutrient-poor karst habitats. However, the leaf traits of Cypripedium reflect adaptations to an environment characterized by rich soil, abundant soil water, and significant seasonal fluctuations in temperature and precipitation. The present results contribute to our understanding of the divergent adaptation of leaf traits in slipper orchids, which is beneficial for the conservation of endangered orchids.     

Natural selection on ecophysiological traits of a fern species in a temperate rainforest

Unlike other species of the genus Blechnum, the fern Blechnum chilense occurs in a wide range of habitats in Chilean temperate rainforest, from shaded forest understories to abandoned clearings and large gaps. We asked if contrasting light environments can exert differential selection on ecophysiological traits of B. chilense. We measured phenotypic selection on functional traits related to carbon gain: photosynthetic capacity (A _max), dark respiration rate (R _d), water use efficiency (WUE), leaf size and leaf thickness in populations growing in gaps and understorey environments. We assessed survival until reproductive stage and fecundity (sporangia production) as fitness components. In order to determine the potential evolutionary response of traits under selection, we estimated the genetic variation of these traits from clonally propagated individuals in common garden experiments. In gaps, survival of B. chilense was positively correlated with WUE and negatively correlated with leaf size. In contrast, survival in shaded understories was positively correlated with leaf size. We found positive directional fecundity selection on WUE in gaps population. In understories, ferns of lower R _d and greater leaf size showed greater fecundity. Thus, whereas control of water loss was optimized in gaps, light capture and net carbon balance were optimized in shaded understories. We found a significant genetic component of variation in WUE, R _d and leaf size. This study shows the potential for evolutionary responses to heterogeneous light environments in functional traits of B. chilense, a unique fern species able to occupy a broad successional niche in Chilean temperate rainforest.     

Effects of forest types on leaf functional traits and their interrelationships of Pinus massoniana coniferous and broad‐leaved mixed forests in the subtropical mountain,Southeastern China

Leaf functional traits are widely used to detect and explain adaptations that enable plants to live under various environmental conditions. This study aims to determine the difference in leaf functional traits among four forest types of Pinus massoniana coniferous and broad‐leaved mixed forests by leaf morphological, nutrients, and stoichiometric traits in the subtropical mountain, Southeastern China. Our study indicated that the evergreen conifer species of P. massoniana had higher leaf dry matter content (LDMC), leaf C content, C/N and C/P ratios, while the three deciduous broad‐leaved species of L. formosana, Q. tissima, and P. strobilacea had higher specific leaf area (SLA), leaf N, leaf P nutrient contents, and N/P ratio in the three mixed forest types. The results showed that the species of P. massoniana has adapted to the nutrient‐poor environment by increasing their leaf dry matter for higher construction costs thereby reducing water loss and reflects a resource conservation strategy. In contrast, the three species of L. formosana, Q. tissima, and P. strobilacea exhibited an optimized resource acquisition strategy rather than resource conservation strategy in the subtropical mountain of southeastern China. Regarding the four forest types, the three mixed forest types displayed increased plant leaf nutrient contents when compared to the pure P. massoniana forest, especially the P. massoniana–L. formosana mixed forest type (PLM). Overall, variation in leaf functional traits among different forest types may play an adaptive role in the successful survival of plants under diverse environments because leaf functional traits can lead to significant effects on leaf function, especially for their acquisition of nutrients and use of light. The results of this study are beneficial to reveal the changes in plant leaf functional traits at the regional scale, which will provide a foundation for predicting changes in leaf traits and adaptation in the future environment.     

Direct and indirect selection on flowering time,water‐use efficiency (WUE, δ13C), and WUE plasticity to drought in Arabidopsis thaliana

Flowering time and water-use efficiency (WUE) are two ecological traits that are important for plant drought response. To understand the evolutionary significance of natural genetic variation in flowering time, WUE, and WUE plasticity to drought in Arabidopsis thaliana, we addressed the following questions: (1) How are ecophysiological traits genetically correlated within and between different soil moisture environments? (2) Does terminal drought select for early flowering and drought escape? (3) Is WUE plasticity to drought adaptive and/or costly? We measured a suite of ecophysiological and reproductive traits on 234 spring flowering accessions of A. thaliana grown in well-watered and season-ending soil drying treatments, and quantified patterns of genetic variation, correlation, and selection within each treatment. WUE and flowering time were consistently positively genetically correlated. WUE was correlated with WUE plasticity, but the direction changed between treatments. Selection generally favored early flowering and low WUE, with drought favoring earlier flowering significantly more than well-watered conditions. Selection for lower WUE was marginally stronger under drought. There were no net fitness costs of WUE plasticity. WUE plasticity (per se) was globally neutral, but locally favored under drought. Strong genetic correlation between WUE and flowering time may facilitate the evolution of drought escape, or constrain independent evolution of these traits. Terminal drought favored drought escape in these spring flowering accessions of A. thaliana. WUE plasticity may be favored over completely fixed development in environments with periodic drought.     

Water‐use efficiency in a semi‐arid woodland with high rainfall variability

As the ratio of carbon uptake to water use by vegetation, water‐use efficiency (WUE) is a key ecosystem property linking global carbon and water cycles. It can be estimated in several ways, but it is currently unclear how different measures of WUE relate, and how well they each capture variation in WUE with soil moisture availability. We evaluated WUE in an Acacia‐dominated woodland ecosystem of central Australia at various spatial and temporal scales using stable carbon isotope analysis, leaf gas exchange and eddy covariance (EC) fluxes. Semi‐arid Australia has a highly variable rainfall pattern, making it an ideal system to study how WUE varies with water availability. We normalized our measures of WUE across a range of vapour pressure deficits using g₁, which is a parameter derived from an optimal stomatal conductance model and which is inversely related to WUE. Continuous measures of whole‐ecosystem g₁ obtained from EC data were elevated in the 3 days following rain, indicating a strong effect of soil evaporation. Once these values were removed, a close relationship of g₁ with soil moisture content was observed. Leaf‐scale values of g₁ derived from gas exchange were in close agreement with ecosystem‐scale values. In contrast, values of g₁ obtained from stable isotopes did not vary with soil moisture availability, potentially indicating remobilization of stored carbon during dry periods. Our comprehensive comparison of alternative measures of WUE shows the importance of stomatal control of fluxes in this highly variable rainfall climate and demonstrates the ability of these different measures to quantify this effect. Our study provides the empirical evidence required to better predict the dynamic carbon–water relations in semi‐arid Australian ecosystems.     

Host plant trichomes and the advantage of being big: progeny size variation of the pipevine swallowtail

1. Plants possess numerous traits that confer resistance against insect herbivores, and herbivores, in turn, can evolve traits to ameliorate the effectiveness of these traits. The pipevine swallowtail, Battus philenor, is an extreme specialist on plants in the genus Aristolochia. The only host plant available to the California population of B. philenor is A. californica. Aristolochia californica is distinct from most other B. philenor host plants in that it is pubescent. 2. The progeny of B. philenor are larger in California compared with populations examined in Texas. Size differences persist throughout larval development. 3. Regardless of maternal host plant, population differences in progeny size persist, and crosses between California (large progeny) and Texas (small progeny) B. philenor populations resulted in offspring producing intermediate sized progeny, indicating a heritable component to progeny size variation. 4. California neonate caterpillars more easily overcame the trichomes of A. californica compared with Texas neonates. When trichomes were removed from A. californica, time to feeding establishment was reduced for caterpillars from both populations. Texas caterpillars established feeding sites on A. californica with trichomes removed, in the same time required to establish feeding on their non‐pubescent host plant, A. erecta. 5. This study shows that plant trichomes might impose selection pressure on progeny size.     

Role of micromorphological leaf traits and molecular data in taxonomy of three sympatric white oak species and their hybrids (Quercus L.)

Hybridisation and introgression occur with high frequency in the genus Quercus and interspecific hybrid individuals show patterns of morphological traits that might be influenced in different ways. Micromorphological leaf traits appear to be positive and stable in Quercus species, and by combining genetic and micromorphological analyses, it is possible to compare the patterns of variation in micromorphological leaf traits of pure and hybrid individuals. Trichomes and stomatal traits were examined using scanning electron microscopy at 150–2000 × magnification in sympatric oak species collected in a natural deciduous wood. Q. frainetto, Q. petraea and Q. pubescens appear to have a relatively predictable complement of trichome types. Both the pattern and quantitative values of each micromorphological trait examined (stomata and trichomes) have an important role in identifying hybrids and pure species; putative hybrids show a pattern of trichomes that is a combination of the parental types. These results, combined with the fact that micromorphological traits generally exhibit higher consistency, indicate that this source of information can be an excellent clue to hybridisation and introgression and useful in taxonomical, systematic and evolutionary studies on the European white oaks.     

A tropical epiphytic orchid uses a low‐light interception strategy in a spatially heterogeneous light environment

Light is considered a non‐limiting factor for vascular epiphytes. Nevertheless, an epiphyte's access to light may be limited by phorophyte shading and the spatio‐temporal environmental patchiness characteristic of epiphytic habitats. We assessed the extent to which potential light interception in Rodriguezia granadensis, an epiphytic orchid, is determined by individual factors (plant size traits and leaf traits), or environmental heterogeneity (light patchiness) within the crown of the phorophyte, or both. We studied 104 adult plants growing on Psidium guajava trees in two habitats with contrasting canopy cover: a dry tropical forest edge, and isolated trees in a pasture. We recorded the number of leaves and the leaf area, the leaf position angles, and the potential exposure of the leaf surface to direct irradiance (silhouette area of the leaf blade), and the potential irradiance incident on each plant. We found the epiphytes experience a highly heterogeneous light environment in the crowns of P. guajava. Nonetheless, R. granadensis plants displayed a common light interception strategy typical of low‐light environments, resembling terrestrial, forest understory plants. Potential exposure of the total leaf surface to direct irradiance correlated positively with plant size and within‐plant variation in leaf orientation. In many‐leaved individuals, within‐plant variation in leaf angles produced complementary leaf positions that enhanced potential light interception. This light interception strategy suggests that, in contrast to current wisdom, enhancing light capture is important for vascular epiphytes in canopies with high spatio‐temporal heterogeneity in light environments.     

Effects of foliar apple trichomes on Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae): preferences,fecundity and prey consumption

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Oviposition,larval survival and leaf damage by the willow leaf blotch miner,Micrurapteryx salicifoliella,in relation to leaf trichomes across 10 Salix species

1. Foliar trichomes clearly reduce chewing damage and efficiency of movement by some insect herbivores, but the effect of trichomes on insect oviposition is less well characterised. Trichomes are likely to have particularly strong, negative effects on species that require secure attachment of the egg to the leaf epidermis for successful transition to the feeding stage – a group that includes many leaf mining insects. 2. One such species, Micrurapteryx salicifoliella, must initially enter leaf cells directly from an egg adhered to the cuticle, but later instars can move between leaves and initiate new mines from the leaf exterior. 3. Natural patterns of occurrence by M. salicifoliella were quantified on 10 sympatric Salix species varying in trichome expression to test whether trichomes were associated with reduced oviposition, larval survival and leaf damage. 4. Mean egg density and leaf mining damage were negatively related to mean trichome density across Salix species. Survival of M. salicifoliella from egg to pupa was positively related to trichome density, suggesting that initiation of new mines by late‐instar larvae was not adversely affected by trichomes. There was no evidence that trichomes benefited leaf miner larvae indirectly by decreasing density‐dependent mortality; rather, the positive relationship between trichome density and larval survival may reflect less effective chemical defence by Salix species expressing high trichome density. 5. The results suggest that foliar trichomes serve as an effective defence against M. salicifoliella by deterring oviposition, but do not reduce the survivorship of those individuals that successfully transition from egg to larva.     

Anatomical inferences on aerial bud protection of three Eugenia shrub species from the Cerrado

• Location and degree of protection of aerial buds are important functional traits in disturbance- or stress-prone environments since aerial buds ensure the development of new organs under favourable growing conditions. This study was carried out in a Brazilian Cerrado area under regeneration after long-term Pinus cultivation, where the trees were clear-cut in 2012 and the remaining material was burned in 2014.
• After the fire treatment, several species resprouted from belowground organs and their aboveground organs were directly exposed to full sunlight. We collected 15 terminal branches with fully expanded leaves from three individuals of each of three Eugenia species to investigate if those with well-developed belowground organs invest in bark for aboveground bud protection. The samples were analysed using light and electron microscopy.
• In addition to terminal and axillary buds, all species presented accessory buds, and the number varied according to the node analysed. None of the aerial buds were protected by bark, but all were well protected by cataphylls and densely pubescent leaf primordia. There were also inter- and intra-petiolar colleters that released a mucilaginous protein exudate. The distance between the shoot apical meristem and the outer surface was longer in the terminal bud than in axillary buds. The bud leaf primordia covering the shoot apical meristem had a thick cuticle, unicellular non-glandular trichomes that accumulate phenolic and lipophilic compounds, and secretory cavities.
• Our study shows that all three Eugenia species studied here had highly protected aerial buds allocated from belowground organs. These morphological traits may improve the chances of the species' persistence in areas subjected to frost events, low relative humidity, high irradiance and harmful UV levels.

     

Soybean leaf pubescence affects aphid vector transmission and field spread of soybean mosaic virus

A study was undertaken to determine the influence of trichome density on the spread of non-persistently transmitted plant viruses by aphid vectors. A system using soybean plants and soybean mosaic virus (SMV) tested the hypothesis that greater leaf trichome density inhibits probing activity of vector species, leading to reduced virus spread and retarded virus epidemics under field conditions. Probing activity of three important aphid vectors of SMV, Myzus persicae, Rhopalosiphum maidis, and Aphis citricola, was affected by the density of soybean leaf trichomes. Less pubescent and glabrous isolines elicited greater probing activity than did densely pubescent isolines. Among the parameters considered, probe duration was found to be species specific, whereas the following traits were consistent among species for the denser isolines: reduced numbers of probes, greater length of time to first probe, and less time spent probing. Laboratory transmission of soybean mosaic virus was reduced in the more densely pubescent isolines by the vector species tested. Field spread of SMV was negatively correlated with density of pubescence. In our system, we found that denser leaf pubescence retards field epidemics of non-persistently transmitted plant viruses.     

胡杨叶功能性状特征及其对地下水埋深的响应

叶片性状反映了植物对环境的适应能力及其自我调控能力。以塔里木干旱荒漠区建群种胡杨（Populus euphratica）为研究对象,通过分析自然生长状况下胡杨叶功能性状对地下水埋深（GWD）的响应及功能性状间的权衡关系,揭示胡杨对极端干旱荒漠环境的生态适应策略。结果表明：胡杨7个叶功能性状种内变异程度不同（9.20%-40.02%）,叶面积（LA）变异程度最大,叶干物质含量（LDMC）与叶片含水量（LWC）变异程度较低,GWD梯度上表现出较大的分化变异特征。叶性状在不同GWD之间差异显著（P<0.05）,与GWD呈极显著相关（P<0.01）。比叶面积（SLA）、LA、LWC与叶干重（LDM）呈极显著正相关（P<0.01）,与叶厚度（LT）、叶组织密度（LTD）、LDMC呈极显著的负相关（P<0.01）;LDMC与LT、LTD,LWC与LA、SLA呈极显著正相关（P<0.01）,反映胡杨通过叶性状间的相互调节与权衡来适应干旱荒漠环境。逐步回归分析表明LA、LT对GWD变化最敏感,可间接借助这2个性状来预测干旱荒漠区地下水埋深变化。随GWD降低,胡杨SLA、LA、LDM、LWC减小,而LT、LTD、LDMC增大,其由高生长速率、资源利用能力的开拓型策略转变为以增强自身养分储存、防御能力的保守型策略,拓宽了生态幅和增强其在干旱逆境的适合度。可见,极端干旱荒漠区胡杨形成了小的LA、SLA、LDM,大的LT、LDMC、LTD等一系列有利于减少水分散失、储存养分和增强耐旱能力的干旱性状组合,这可能是其适应干旱贫瘠环境的生态策略。     

Relationships between gas-exchange characteristics and stomatal structural modifications in some desert grasses under high salinity

Two populations, one from lesser saline Derawar Fort (DF) and the other from highly saline Ladam Sir (LS) in the Cholistan desert, for each of the five grass species, Aeluropus lagopoides, Cymbopogon jwarancusa, Lasiurus scindicus, Ochthochloa compressa, and Sporobolus ioclados were examined to investigate the influence of salinity on structural and functional characteristics of stomata. Salinity tolerance in A. lagopoides mainly depended on controlled transpiration rate (E) and high water-use efficiency (WUE), which was found to be regulated by fewer and smaller stomata on both leaf surfaces as well as stomatal encryption by epidermal invaginations. C. jwarancusa had sunken stomata on the abaxial surface only, which largely reflected a reduced E, but less affected stomatal conductance (g _s) or WUE. L. scindicus had fewer but larger stomata along with hairs/trichomes which may function to avoid water loss through transpiration, and hence, to attain a high WUE. In O. compressa stomata were found only on the abaxial surface and these were completely encrypted by epidermal invaginations as well as a dense covering of microhairs, which was associated with a low E and high WUE under salinity stress. In S. ioclados, the traits of increased stomatal density and decreased stomatal area may be critical for stomatal regulation under salt-prone environments. High stomatal regulation depended largely on stomatal density, area, and degree of encryption under salinity, which is of great ecophysiological significance for plants growing under osmotic stresses.     

On the fate of seasonally plastic traits in a rainforest butterfly under relaxed selection

Many organisms display phenotypic plasticity as adaptation to seasonal environmental fluctuations. Often, such seasonal responses entails plasticity of a whole suite of morphological and life‐history traits that together contribute to the adaptive phenotypes in the alternative environments. While phenotypic plasticity in general is a well‐studied phenomenon, little is known about the evolutionary fate of plastic responses if natural selection on plasticity is relaxed. Here, we study whether the presumed ancestral seasonal plasticity of the rainforest butterfly Bicyclus sanaos (Fabricius, 1793) is still retained despite the fact that this species inhabits an environmentally stable habitat. Being exposed to an atypical range of temperatures in the laboratory revealed hidden reaction norms for several traits, including wing pattern. In contrast, reproductive body allocation has lost the plastic response. In the savannah butterfly, B. anynana (Butler, 1879), these traits show strong developmental plasticity as an adaptation to the contrasting environments of its seasonal habitat and they are coordinated via a common developmental hormonal system. Our results for B. sanaos indicate that such integration of plastic traits – as a result of past selection on expressing a coordinated environmental response – can be broken when the optimal reaction norms for those traits diverge in a new environment.     

Rapid evolution of Medicago polymorpha during invasion shifts interactions with the soybean looper

The Enemy Release Hypothesis posits that invasion of novel habitats can be facilitated by the absence of coevolved herbivores. However, a new environment and interactions with unfamiliar herbivores may impose selection on invading plants for traits that reduce their attractiveness to herbivores or for enhanced defenses compared to native host plants, leading to a pattern similar to enemy release but driven by evolutionary change rather than ecological differences. The Shifting Defense Hypothesis posits that plants in novel habitats will shift from specialized defense mechanisms to defense mechanisms effective against generalist herbivores in the new range. We tested these ideas by comparing herbivore preference and performance of native (Eurasia)‐ and invasive (New World)‐range Medicago polymorpha, using a generalist herbivore, the soybean looper, that co‐occurs with M. polymorpha in its New World invaded range. We found that soybean loopers varied in preference and performance depending on host genotype and that overall the herbivore preferred to consume plant genotypes from naïve populations from Eurasia. This potentially suggests that range expansion of M. polymorpha into the New World has led to rapid evolution of a variety of traits that have helped multiple populations become established, including those that may allow invasive populations to resist herbivory. Thus, enemy release in a novel range can occur through rapid evolution by the plant during invasion, as predicted by the Shifting Defense Hypothesis, rather than via historical divergence.     

Leaf traits of two Mediterranean perennial tussock grass species in relation to soil nitrogen and phosphorus availability

Studying relationships of plant traits to ecosystem properties is an emerging approach aiming to understand plant's potential effect on ecosystem functioning. In the current study, we explored links between morphological and nutritional leaf traits of two Mediterranean perennial grass species Stipa tenacissima and Lygeum spartum, widely used to prevent desertification process by stabilizing sand dunes. We evaluated also relationships in terms of nitrogen (N) and phosphorus (P) availability between leaves of the investigated species and the corresponding soil. Our results showed that leaf P was very low in comparison with leaf N for the two investigated species. In fact, chlorophyll content, photosynthesis capacity and water conservation during photosynthesis are mainly linked to leaf nitrogen content. Our findings support previous studies showing that at the species levels, morphological and nutritional leaf traits were not related. On the other hand, significant relationships were obtained between soil N and leaf N for S. tenacissima (P = 0.011) and L. spartum (P = 0.033). However, leaf P was not significantly related to soil P availability for both species. We suggest that any decrease in soil N with the predicted increasing aridity may result in reduction in leaf N and thus in worst dysfunction of some biological processes levels.     

Photosynthetic innovation broadens the niche within a single species

Adaptation to changing environments often requires novel traits, but how such traits directly affect the ecological niche remains poorly understood. Multiple plant lineages have evolved C₄ photosynthesis, a combination of anatomical and biochemical novelties predicted to increase productivity in warm and arid conditions. Here, we infer the dispersal history across geographical and environmental space in the only known species with both C₄ and non‐C₄ genotypes, the grass Alloteropsis semialata. While non‐C₄ individuals remained confined to a limited geographic area and restricted ecological conditions, C₄ individuals dispersed across three continents and into an expanded range of environments, encompassing the ancestral one. This first intraspecific investigation of C₄ evolutionary ecology shows that, in otherwise similar plants, C₄ photosynthesis does not shift the ecological niche, but broadens it, allowing dispersal into diverse conditions and over long distances. Over macroevolutionary timescales, this immediate effect can be blurred by subsequent specialisation towards more extreme niches.