Drought responses,phenotypic plasticity and survival of Mediterranean species in two different microclimatic sites

• Climate models predict a further drying of the Mediterranean summer. One way for plant species to persist during such climate changes is through acclimation. Here, we determine the extent to which trait plasticity in response to drought differs between species and between sites, and address the question whether there is a trade‐off between drought survival and phenotypic plasticity.
• Throughout the summer we measured physiological traits (photosynthesis – A_max, stomatal conductance – g_s, transpiration – E, leaf water potential – ψl) and structural traits (specific leaf area – SLA, leaf density – LD, leaf dry matter content – LDMC, leaf relative water content – LRWC) of leaves of eight woody species in two sites with slightly different microclimate (north‐ versus south‐facing slopes) in southern Spain. Plant recovery and survival was estimated after the summer drought period.
• We found high trait variability between species. In most variables, phenotypic plasticity was lower in the drier site. Phenotypic plasticity of SLA and LDMC correlated negatively with drought survival, which suggests a trade‐off between them. On the other hand, high phenotypic plasticity of SLA and LDMC was positively related to traits associated with rapid recovery and growth after the drought period.
• Although phenotypic plasticity is generally seen as favourable during stress conditions, here it seemed beneficial for favourable conditions. We propose that in environments with fluctuating drought periods there can be a trade‐off between drought survival and growth during favourable conditions. When climate become drier, species with high drought survival but low phenotypic plasticity might be selected for.

     

Sequence of plant responses to droughts of different timescales: lessons from holm oak (Quercus ilex) forests

The functional traits of plants in regions of the world with a Mediterranean climate have been shaped to tolerate periods of water deficit. These species are adapted to summer droughts but may not be able to cope with future increases in drought intensity, duration, and/or frequency. Here, we review the mechanisms and traits of drought resistance and recovery of the well-studied holm oak (Quercus ilex), which we propose as a model species for Mediterranean-type ecosystems. Our aim was to understand the differences and links between the responses of Q. ilex to summer droughts, extreme droughts, and long-term drought experiments. A main goal was to provide an integral picture of drought responses across organisational and temporal scales for identifying the most relevant processes that are likely to contribute to determining the future of Mediterranean vegetation. Evidence from long-term drought experiments showed that acclimation processes from the molecular (e.g. epigenetic changes) to the ecosystem level (e.g. reductions in stand density) mitigate the effects of drought. Changes in leaf morphology and hydraulics, leaf-to-shoot allometry, and root functioning are among the key mechanisms for overcoming increasing drought. The duration of drought determines its severity in terms of canopy loss and stem mortality. Although Q. ilex can vigorously resprout after such episodes, its resilience may be subsequently reduced. In the future, higher frequency of return of extreme droughts will challenge thus the capacity of these forests to recover. The insights provided by this review of the complex interplay of processes that determine the response of trees to droughts of different duration, intensity, and frequency will also help us to understand the likely responses of other resprouting angiosperms in seasonally dry ecosystems that share similar functional traits with Q. ilex.     

Constraints on the evolution of phenotypic plasticity in the clonal plant Hydrocotyle vulgaris

The evolution of phenotypic plasticity of plant traits may be constrained by costs and limits. However, the precise constraints are still unclear for many traits under different ecological contexts. In a glasshouse experiment, we grew ramets of 12 genotypes of a clonal plant Hydrocotyle vulgaris under the control (full light and no flood), shade and flood conditions and tested the potential costs and limits of plasticity in 13 morphological and physiological traits in response to light availability and flood variation. In particular, we used multiple regression and correlation analyses to evaluate potential plasticity costs, developmental instability costs and developmental range limits of each trait. We detected significant costs of plasticity in specific petiole length and specific leaf area in response to shade under the full light condition and developmental range limits in specific internode length and intercellular CO₂ concentration in response to light availability variation. However, we did not observe significant costs or limits of plasticity in any of the 13 traits in response to flood variation. Our results suggest that the evolution of phenotypic plasticity in plant traits can be constrained by costs and limits, but such constraints may be infrequent and differ under different environmental contexts.     

Plastic responses of 4 tree species of successional subalpine coniferous forest serals to different light regimes

The morphological and physiological plasticity to 6 light conditions was investigated for seedlings of 4 tree species dominating at different successional serals in subalpine coniferous forests in eastern Qinghai-Tibet Plateau, China. Abies faxoniana is a late successional species, while Betula albo-sinensis is a pioneer tree species, with Picea asperata and Acer davidii among other mid-late successional species. To compare the responses of photosynthetic characters to different growth light conditions, the seedlings were potted and placed in artificially shaded chambers with gradients of 100%, 55%, 40%, 25%, 15% and 7% of the full sunlight, respectively. During two and a half years' cultivation, various morphological and photosynthetic parameters were measured and analyzed. The results were: 1) all seedlings of the four species under the low growth light conditions showed decrease in root collar diameter, relative growth rate, leaf thickness, root mass ratio, leaf area-based photosynthetic capacity, dark respiration rate, light saturation point and light compensation point, while showed increase in specific leaf area, above-ground to under-ground mass ratio, specific stem length, leaf mass ratio and stem mass ratio; 2) under most light conditions, A. faxoniana of the two conifers revealed lower values in both leaf area-based photosynthetic capacity and respiration rates than P. asperata; the same fact held true for the two broad-leaved trees with lower values observed in B. albo-sinensis; 3) under higher light conditions, relative growth rates of P. asperata and B. albo-sinensis got higher values than those of A. faxoniana and A. davidii, while contrary results were obtained under lower light regimes; 4) the means of phenotypic plastic indices of the eleven morphological and physiological parameters of P. asperata and B. albo-sinensis were higher than those of A. faxoniana and A. davidii, respectively. The findings indicate that A. faxoniana has better adaptation to low light regimes, but as a shade-tolerant species, it is not so adapted to low light regimes as the trees of earlier successional serals, especially P. asperata and B. albo-sinensis. Of the four tree species, physiological plastic indices were higher than morphological plastic indices, suggesting that morphological plasticity plays an important role in their adaptation to different growth light conditions. The results also support the hypothesis that ecophysiological traits of tree species determine their successional status and associate habitats of their seedlings.     

Variation in and adaptive plasticity of flower size and drought-coping traits

Although phenotypic plasticity of morphological and physiological traits in response to drought could be adaptive, there have been relatively few tests of plasticity variation or of adaptive plasticity in drought-coping traits across populations with different moisture availabilities. We measured floral size, vegetative size, and physiological traits in four field populations of Leptosiphon androsaceus (Polemoniaceae) that were distributed across a rainfall gradient in California, USA. Measurements were made over 5 years that varied in precipitation. We also conducted a growth chamber experiment in which half-sibs from three populations were divided equally among a well-watered and a drought treatment. We tested for selection on traits in each of the watering treatments, and evaluated whether traits exhibited plasticity. In the field, plant traits exhibited substantial variation across populations and years. Flower size, leaf size, and water-use efficiency (WUE) were generally higher for populations that received greater average rainfall. However, in dry years, we observed a decrease in flower and leaf size, but an increase in WUE across the populations. In the growth chamber experiment, leaf and physiological traits exhibited plasticity, with smaller leaves and higher WUE found in the drought, as compared to the well-watered treatment. Only specific leaf area exhibited differentiation in plasticity among populations. Although there was no observed plasticity in floral size, selection favored smaller flowers in the drought treatment and larger flowers in the well-watered treatment. Our results suggest that moisture availability has led to trait variation in L. androsaceus via a combination of selection and phenotypic plasticity.     

Heritable variation in the survival of seedlings from Patagonian cypress marginal xeric populations coping with drought and extreme cold

The rear edges of tree species have begun to be perceived as highly valuable for genetic resources conservation and management. In view of expected climatic changes, the responses of trees at their xeric limits may largely be determined by their capacity to cope with augmented environmental variance. We assess the heritability of early survival of Patagonian cypress in two common-garden field tests with contrasting summer water deficits, comprising 140 and 163 open-pollinated families from 10 marginal xeric populations. The first experiment underwent less rigorous conditions than the average mesic, Mediterranean climatic conditions, which were sufficient to reveal additive genetic effects of summer drought on seedling survival. The second trial suffered strong summer water-deficit stress and a winter extreme cold event. In this harsher environment, the heritabilities of survival under summer water-deficit stress were high in all the populations (h ²?=?0.84 on average), while the heritabilities of seasonal, extreme cold survival were moderate or even nil (h ²?=?0.28 on average). We did not find evidence of genetic differentiation among populations in their capabilities to survive droughts and cold extremes. Our results indicate that even when climatic changes were strong enough to cause the extinction of the most threatened populations, heritable variation for traits underlying drought and cold tolerances may allow the marginal xeric edge of cypress to persist under augmented environmental variance, without losing overall genetic diversity.     

Small tropical forest trees have a greater capacity to adjust carbon metabolism to long-term drought than large canopy trees

The response of small understory trees to long-term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long-term drought is, however, also likely to expose understory trees to increased light availability driven by drought-induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (J_max, V_cmax), leaf respiration (R_leaf), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world's longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased J_max, V_cmax, R_leaf and LMA (71, 29, 32, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.     

Is seasonal variation in leaf traits adaptive for the annual plant Dicerandra linearifolia?

Empirical studies of phenotypic plasticity have often relied on the plausibility that a plastic response to the environment would increase fitness in order to diagnose the response as adaptive. I conducted a test of the hypothesis that seasonal variation in leaf traits is an adaptive response to seasonal variation in environmental conditions faced by the annual plant Dicerandralinearifolia. This species exhibits variation in leaf morphology and anatomy in response to temperature that is consistent with the expectations for adaptive plasticity. I examined variation in the size, thickness and density of stomata of leaves that develop in summer and winter and used analysis of phenotypic selection during winter and summer seasons to test the hypothesis that seasonal variation in these traits is adaptive. Regression analyses of estimated dry mass (as a proxy for fitness) on leaf traits revealed no evidence supporting the adaptive hypothesis. Selection favoured individuals with large and thick leaves in both winter and summer, and density of stomata had little or no effect on estimated relative fitness in any season. Correspondence between seasonal variation in leaf thickness and density of stomata and expectations for adaptive plasticity appears to be purely fortuitous. Seasonal variation in leaf traits may persist simply because there is no selection against individuals in which these traits vary. My results underscore the importance of definitive tests of the hypothesis of adaptation to distinguish adaptive plasticity from neutral or nonadaptive phenotypic plasticity.     

Twig morphology and anatomy of Mediterranean trees and shrubs related to drought tolerance

De Micco V. and Aronne G. 2008. Twig morphology and anatomy of Mediterranean trees and shrubs related to drought tolerance. Bot. Helv. 118: 139 – 148. Woody species populating Mediterranean ecosystems have evolved phenological, physiological and morphological adaptations to summer drought, but their degree of drought tolerance varies, so that different species dominate along gradients from xeric to more mesic environments. In this study, we analysed morpho-anatomical properties of leaves and twigs of eight Mediterranean woody species. To test whether there is a consistent pattern of adaptation to drought, we hypothesised that the rank order of species along the xeric-mesic gradient would be reflected by increasing or decreasing trends in twig properties or in relationships between leaf area and branch size. One-year-old twigs were sampled from plants growing in a common site on the Tresino promontory in southern Italy. Measurements included leaf number and area, branch length and diameter, as well as the relative amounts of pith, xylem and cortex tissues at the basis of branches. All traits varied significantly among species, but none of them correlated with the rank order of species along the xeric-mesic gradient. In addition, the relationship between leaf area and branch size (length or diameter) was not consistently related to the drought tolerance of the species. Inconsistencies could partly be explained by variations in twig anatomy. These results support the view that not single traits, but combinations of morpho-anatomical features influence the overall capability of species to withstand dry conditions. Submitted 12 May 2008; Accepted 24 September 2008 Subject editor: Sabine Güsewell     

Adaptive plasticity in response to light and nutrient availability in the clonal plant Duchesnea indica

克隆植物蛇莓对光照强度和养分条件的适应性可塑性 表型可塑性可帮助植物缓冲环境压力并使其表型与当地环境相匹配,但目前仅少数性状的可塑性被广泛认为是适应性的。为充分理解可塑性的适应性意义,仍需进一步研究更多的植物功能性状及其环境因子。本研究将匍匐茎克隆植物蛇莓(Duchesnea indica)的21个基因型种植于不同的光照和养分条件下,并利用选择梯度分析检测了形态和生理可塑性对光照强度和养分有效性变化的适应性值。在遮荫条件下,蛇莓适合度(果实数、分株数和生物量)降低,节间缩短变细,成熟叶叶绿素含量降低,但叶柄长度、比叶面积、老叶叶绿素含量均增加。在低养分条件下,植株叶柄缩短,叶面积缩小变厚,叶绿素含量降低,但果实数量和根冠比增加。选择梯度分析表明,叶柄长度和老叶叶绿素含量对光照变化的可塑性是适应性的,老叶和成熟叶叶绿素含量对养分变化的可塑性也是适应性的。因此,不同性状的可塑性适应值取决于特定的生态背景。该研究的发现有助于理解克隆植物表型可塑性响应环境变化的适应性意义。     

Long-term physiological and morphological acclimation by the evergreen shrub <Emphasis Type="Italic">Buxus sempervirens</Emphasis> L. to understory and canopy gap light intensities

Physiological and morphological plasticity are essential for growth and reproduction in contrasting light environments. In dry forest ecosystems, light generalists must also cope with the trade-offs involved in synchronous acclimation to light availability and drought. To understand how the broadleaf evergreen tree-shrub Buxus sempervirens L. (common box) inhabits both understory and successional terrain of Mediterranean forest, we measured photosynthesis–fluorescence light response, morphological traits and architectural characteristics across a light gradient. Our results show that B. sempervirens exhibits stress resistance syndrome, with little change in net photosynthesis rate across a light availability gradient, due to compensatory physiological and morphological acclimation. Light energy processing and dissipation potential were highest in leaves of well-illuminated plants, with higher electron transport rate, fraction of open photosystem II reaction centres, non-photochemical quenching, photorespiration and dark respiration. In contrast, traits reducing light capture efficiency were observed in high light shrubs, including higher leaf mass per unit area, leaf clumping, leaf inclination and branch inclination. We suggest that both physiological and morphological plasticity are required for B. sempervirens to survive across a light gradient in a dry forest ecosystem, while exhibiting homoeostasis in photosynthetic gas exchange. We further speculate that the low growth rate of B. sempervirens is effective in full sun only due to a lack of competition in low resource microsites.     

四种亚高山针叶林树种的表型可塑性对不同光照强度的响应

以青藏高原东缘亚高山针叶林群落演替后期种岷江冷杉、演替中后期种粗枝云杉和青榨槭、及先锋树种红桦为材料,研究了不同光强下生长的4种树苗生长、生物量分配、叶片形态和光合特性,探讨植物幼苗的形态和生理特征的表型可塑性与光适应的关系。结果表明：（1）弱光环境中生长的4种植物的基茎、相对生长速率、叶片厚度、根重比、最大净光合速率、光饱和点、光补偿点、暗呼吸速率较低,而比叶面积、地上／地下生物量、茎长／茎重、叶重比和茎重比较高。（2）大部分光环境下岷江冷杉幼苗的最大净光合速率和暗呼吸速率低于粗枝云杉,青榨槭幼苗的最大净光合速率和暗呼吸速率略低于红桦。（3）高光强下生长的粗枝云杉和红桦幼苗的相对生长速率分别大于岷江冷杉和青榨槭,但在低光强下则与之相反。（4）粗枝云杉和红桦幼苗的11种可塑性指数平均值则分别大于岷江冷杉和青榨槭。岷江冷杉适应弱光环境的能力略强于粗枝云杉和红桦,但适应强光的能力较差。生理适应的可塑性指数大于形态适应的可塑性指数,表明前者在4种植物幼苗光适应方面起到了重要的作用。研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。     

Rapid Plant Invasion in Distinct Climates Involves Different Sources of Phenotypic Variation

When exotic species spread over novel environments, their phenotype will depend on a combination of different processes, including phenotypic plasticity (PP), local adaptation (LA), environmental maternal effects (EME) and genetic drift (GD). Few attempts have been made to simultaneously address the importance of those processes in plant invasion. The present study uses the well-documented invasion history of Senecio inaequidens (Asteraceae) in southern France, where it was introduced at a single wool-processing site. It gradually invaded the Mediterranean coast and the Pyrenean Mountains, which have noticeably different climates. We used seeds from Pyrenean and Mediterranean populations, as well as populations from the first introduction area, to explore the phenotypic variation related to climatic variation. A reciprocal sowing experiment was performed with gardens under Mediterranean and Pyrenean climates. We analyzed climatic phenotypic variation in germination, growth, reproduction, leaf physiology and survival. Genetic structure in the studied invasion area was characterized using AFLP. We found consistent genetic differentiation in growth traits but no home-site advantage, so weak support for LA to climate. In contrast, genetic differentiation showed a relationship with colonization history. PP in response to climate was observed for most traits, and it played an important role in leaf trait variation. EME mediated by seed mass influenced all but leaf traits in a Pyrenean climate. Heavier, earlier-germinating seeds produced larger individuals that produced more flower heads throughout the growing season. However, in the Mediterranean garden, seed mass only influenced the germination rate. The results show that phenotypic variation in response to climate depends on various ecological and evolutionary processes associated with geographical zone and life history traits. Seeing the relative importance of EME and GD, we argue that a “local adaptation vs. phenotypic plasticity” approach is therefore not sufficient to fully understand what shapes phenotypic variation and genetic architecture of invasive populations.     

Evolution in stressful environments II: adaptive value and costs of plasticity in response to low light in Sinapis arvensis

Plants possess a remarkable capacity to alter their phenotype in response to the highly heterogeneous light conditions they commonly encounter in natural environments. In the present study with the weedy annual plant Sinapis arvensis, we (a) tested for the adaptive value of phenotypic plasticity in morphological and life history traits in response to low light and (b) explored possible fitness costs of plasticity. Replicates of 31 half-sib families were grown individually in the greenhouse under full light and under low light (40% of ambient) imposed by neutral shade cloth. Low light resulted in a large increase in hypocotyl length and specific leaf area (SLA), a reduction in juvenile biomass and a delayed onset of flowering. Phenotypic selection analysis within each light environment revealed that selection favoured large SLA under low light, but not under high light, suggesting that the observed increase in SLA was adaptive. In contrast, plasticity in the other traits measured was maladaptive (i.e. in the opposite direction to that favoured by selection in the low light environment). We detected significant additive genetic variance in plasticity in most phenotypic traits and in fitness (number of seeds). Using genotypic selection gradient analysis, we found that families with high plasticity in SLA had a lower fitness than families with low plasticity, when the effect of SLA on fitness was statistically kept constant. This indicates that plasticity in SLA incurred a direct fitness cost. However, a cost of plasticity was only expressed under low light, but not under high light. Thus, models on the evolution of phenotypic plasticity will need to incorporate plasticity costs that vary in magnitude depending on environmental conditions.     

Strong leaf morphological, anatomical, and physiological responses of a subtropical woody bamboo (Sinarundinaria nitida) to contrasting light environments

Dwarf bamboos are an important understory component of the lowland and montane forests in the subtropical regions of Asia and South America, yet little is known about their physiology and phenotypic plasticity in response to changing light environments. To understand how bamboo species adapt to different light intensities, we examined leaf morphological, anatomical, and physiological differentiation of Sinarundinaria nitida (Mitford) Nakai, a subtropical woody dwarf bamboo, growing in open and shaded natural habitats in the Ailao Mountains, SW China. Compared with leaves in open areas, leaves in shaded areas had higher values in leaf size, specific leaf area, leaf nitrogen, and chlorophyll concentrations per unit area but lower values in leaf thickness, vein density, stomatal density, leaf carbon concentration, and total soluble sugar concentration. However, stomatal size and leaf phosphorus concentration per unit mass remained relatively constant regardless of light regime. Leaves in the open habitat exhibited a higher light-saturated net photosynthetic rate, dark respiration rate, non-photochemical quenching, and electron transport rate than those in the shaded habitat. The results of this study revealed that the bamboo species exhibited a high plasticity of its leaf structural and functional traits in response to different irradiances. The combination of high plasticity in leaf morphological, anatomical, and physiological traits allows this bamboo species to grow in heterogeneous habitats.     

Plasticity in reproduction and growth among 52 range‐wide populations of a Mediterranean conifer: adaptive responses to environmental stress

A plastic response towards enhanced reproduction is expected in stressful environments, but it is assumed to trade off against vegetative growth and efficiency in the use of available resources deployed in reproduction [reproductive efficiency (RE)]. Evidence supporting this expectation is scarce for plants, particularly for long‐lived species. Forest trees such as Mediterranean pines provide ideal models to study the adaptive value of allocation to reproduction vs. vegetative growth given their among‐population differentiation for adaptive traits and their remarkable capacity to cope with dry and low‐fertility environments. We studied 52 range‐wide Pinus halepensis populations planted into two environmentally contrasting sites during their initial reproductive stage. We investigated the effect of site, population and their interaction on vegetative growth, threshold size for female reproduction, reproductive–vegetative size relationships and RE. We quantified correlations among traits and environmental variables to identify allocation trade‐offs and ecotypic trends. Genetic variation for plasticity was high for vegetative growth, whereas it was nonsignificant for reproduction. Size‐corrected reproduction was enhanced in the more stressful site supporting the expectation for adverse conditions to elicit plastic responses in reproductive allometry. However, RE was unrelated with early reproductive investment. Our results followed theoretical predictions and support that phenotypic plasticity for reproduction is adaptive under stressful environments. Considering expectations of increased drought in the Mediterranean, we hypothesize that phenotypic plasticity together with natural selection on reproductive traits will play a relevant role in the future adaptation of forest tree species.     

Amazonia trees have limited capacity to acclimate plant hydraulic properties in response to long‐term drought

The fate of tropical forests under future climate change is dependent on the capacity of their trees to adjust to drier conditions. The capacity of trees to withstand drought is likely to be determined by traits associated with their hydraulic systems. However, data on whether tropical trees can adjust hydraulic traits when experiencing drought remain rare. We measured plant hydraulic traits (e.g. hydraulic conductivity and embolism resistance) and plant hydraulic system status (e.g. leaf water potential, native embolism and safety margin) on >150 trees from 12 genera (36 species) and spanning a stem size range from 14 to 68 cm diameter at breast height at the world's only long‐running tropical forest drought experiment. Hydraulic traits showed no adjustment following 15 years of experimentally imposed moisture deficit. This failure to adjust resulted in these drought‐stressed trees experiencing significantly lower leaf water potentials, and higher, but variable, levels of native embolism in the branches. This result suggests that hydraulic damage caused by elevated levels of embolism is likely to be one of the key drivers of drought‐induced mortality following long‐term soil moisture deficit. We demonstrate that some hydraulic traits changed with tree size, however, the direction and magnitude of the change was controlled by taxonomic identity. Our results suggest that Amazonian trees, both small and large, have limited capacity to acclimate their hydraulic systems to future droughts, potentially making them more at risk of drought‐induced mortality.     

木本植物应对干旱胁迫的响应机制：基于水力学性状视角

干旱最显著的影响表现在区域尺度的森林死亡事件中,可以在短时间内杀死数百万棵树木。鉴于未来极端干旱事件的频率和强度可能随温度的升高而增加,迫切需要明确树木对干旱胁迫的响应对策以及衰退死亡机理,揭示木本植物在干旱环境中存活和死亡的生理机制,了解树木在未来气候下的适应机制,提高预测树木对干旱反应的准确性。在常用植物功能性状的基础上,重点纳入与植物水分运输能力及耐旱性相关的水力学性状,系统总结了:1)植物木质部水分运输的物理机制;2)植物应对干旱胁迫的水力响应过程:3)干旱胁迫下木本植物水分利用对策;以及4)干旱胁迫下木本植物衰退/死亡机理。最后,提出3个尚待解决的主要问题:1)加强纳入水力性状阐明植物对干旱胁迫的响应和调节机制;2)加强从全株植物的角度考虑植物不同组织性状间的关系;3)深入探究树木干旱致死机理。     

Different combinations of morpho‐physiological traits are responsible for tolerance to drought in wild tomatoes Solanum chilense and Solanum peruvianum

Herbaceous species can modify leaf structure during the growing season in response to drought stress and water loss. Evolution can select combinations of traits in plants for efficient water use in restricted environments. We investigated plant traits that mediate adaptation and acclimation to water stress in two herbaceous drought‐tolerant species. Anatomical, morphological and physiological traits related to stems and leaves were examined under optimal watering (OW) and a long period of restricted watering (RW) in 11 accessions from three Solanaceae species (Solanum chilense, S. peruvianum and S. lycopersicum). The relationships between these traits were tested using linear regression and PCA. There were significant differences in anatomical traits between the species under both OW and RW, where leaf area correlated with stem diameter. Proline and total carbohydrates accumulated highly in S. chilense and S. peruvianum, respectively, and these osmolytes were strongly correlated with increased osmotic potential. Stomatal density varied between species but not between acclimation treatments, while stomatal rate was significantly higher in wild tomatoes. There was a strong positive relationship between stem growth rate and a group of traits together expressed as total stomatal number. Total stomata is described by integration of leaf area, stomatal density, height and internode length. It is proposed that constitutive adaptations and modifications through acclimation that mediate RW play an important role in tolerance to drought stress in herbaceous plants. The capacity for growth under drought stress was not associated with any single combination of traits in wild tomatoes, since the two species differed in relative levels of expression of various phenotypic traits.