Influence of ambient and enhanced ultraviolet-B radiation on the plant growth and physiological properties in two contrasting populations of Hippophae rhamnoides

Two contrasting sea buckthorn (Hippophae rhamnoides L.) populations from low and high altitude regions were employed to investigate the effects of prevailing and enhanced ultraviolet-B (UV-B) radiation on plant growth and physiological properties under a UV-B-enhanced/exclusion system. The experimental design included three UV-B regimes, including excluded (-UVB), near-ambient (NA) and enhanced UV-B (+UVB) radiation. Compared with the control (-UVB), NA caused the formation of smaller but thicker plant leaves in both sea buckthorn populations, paralleled with significant increments of carotenoids and UV-absorbing compounds as well as improved water economy. NA also induced more biomass partition from shoot to root, but CO(2) assimilation rate (A), photosynthetic area and biomass accumulation were unaffected. The low-altitude population seemed sensitive to +UVB, as indicated by the decreases in total biomass, A and ascorbic acid content (Asa, an antioxidant) compared with NA. However, little +UVB effect occurred on the high-altitude population, and we suggest that the higher tolerance of this population could be associated with its specific morphological and physiological characteristics, such as small but thick leaves and high-level of Asa content, as well as its greater physiological modification in response to NA, e.g., increases in protective compounds (carotenoids and UV-absorbing compounds) and improvement in water economy, in comparison to the low-altitude population, which form an effective adaptation strategy to enhanced UV-B stress.     

Photosynthetic responses to solar UV-A and UV-B radiation in low-and high-altitude populations of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis>

Two contrasting sea buckthorn (Hippophae rhamnoides L.) populations from the low (LA) and high (HA) altitudinal regions were employed to evaluate the plant physiological responses to solar UV-A radiation and near-ambient UV-B radiation (UV-B+A) under the sheltered frames with different solar ultraviolet radiation transmittance. LA-population was more responsive to solar UV-A. Some modification caused by UV-A only existed in LA-population, such as significant reduction of leaf size, relative water content, and chlorophyll (Chl) b content as well as δ¹³C elevation, coupled with larger increase of contents of total carotenoids (Cars). This higher responsiveness might be an effective pre-acclimation strategy adapting for concomitant solar UV-B stress. Near-ambient UV-B+A radiation caused significant reduction of leaf size and Chl content as well as slight down-regulation of photosystem 2 activity that paralleled with higher heat dissipation, while photosynthetic rate was modestly but significantly increased. The higher photosynthesis under near-ambient UV-B+A radiation could be related to pronounced increase of leaf thickness and effective physiological modification, like the increase of leaf protective pigments (Cars and UV-absorbing compound), constant high photochemical capacity, and improved water economy.     

Differences in growth and physiological traits of Populus cathayana populations as affected by enhanced UV-B radiation and exogenous ABA

During one growing season, the effects of enhanced ultraviolet-B (UV-B) radiation, exogenous abscisic acid (ABA) and their combination on biomass accumulation, gas exchange, endogenous ABA, the concentration of UV-absorbing compounds, antioxidant system and on the carbon (C) and nitrogen (N) content and C/N ratio were investigated in two contrasting Populus cathayana Rehd. populations, originating from high and low altitudes in south-west China. Exogenous ABA was sprayed to the leaves, and enhanced UV-B treatments were applied using a square-wave system to expose the seedlings to ambient (1×) or twice ambient (2×) doses of biologically effective UV-B radiation (UV-B_BE). Enhanced UV-B radiation significantly decreased height, basal diameter, total leaf area, total biomass, net CO₂ assimilation rate (A), stomatal conductance (g_s), transpiration rate (E) and carbon (C) content in leaves, and significantly increased the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPx), and the contents of hydrogen peroxide (H₂O₂) and malonaldehyde (MDA), as well as the accumulation of UV-absorbing compounds and endogenous ABA concentrations among different organs in both populations. In contrast, exogenous ABA induced a significant decrease in A and significant increases in the activities of SOD and GPx, in the content of H₂O₂ and MDA, and in the endogenous ABA concentrations. Compared with the low altitude population, the high altitude population was more tolerant to enhanced UV-B and exogenous ABA. Significant interactions between UV-B and ABA were observed in A, E, and in the activities of SOD and GPx, as well as in endogenous ABA in the leaves and roots of both populations. Across all treatments, the C and N contents of leaves were strongly correlated with their contents in stems and roots. Additionally, the N content of leaves and stems were significantly correlated with the C content of stems.     

Sex-specific physiological and growth responses to water stress in <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> L. populations

Dioecious plant species and those occupying diverse habitats may present special analytical problems to determine effects of environmental stress. Here, sex-specific physiological and growth responses of two contrasting sea buckthorn (Hippophae rhamnoides L.) populations were recorded after exposure to different watering regimes. The populations used were from wet and dry climate regions in China, respectively. In the semi-controlled environmental study, the well-watered and water-deficiency plants which were watered to 100 % and 50 % field capacity were used, respectively. Sexual differences in height growth (HT), dry matter accumulation (DMA), root/shoot ratio (RS), specific leaf area (SLA), net photosynthesis (A), transpiration (E), instantaneous water use efficiency (WUE_i) and carbon isotope composition (δ¹³C) between the male and female individuals were detected under water-deficiency treatment in both populations tested. However, these sexual differences were not detected under well-watered treatment. On the other hand, compared with the wet climate population, the dry climate population showed lower HT, DMA, SLA, A and E, and higher RS under both watering regimes. The dry climate population also showed higher WUE_i and δ¹³C as affected by water deficit than the wet climate population. These morphological and physiological responses to drought showed that the different populations and the different sexual individuals may employ different survival strategies under environmental stress. The male individuals and the dry climate population would have a conservative water-use strategy in response to drought stress.     

Resource economics and coordination among above- and below-ground functional traits of three dominant shrubs from the Chilean coastal desert

Aims Plant functional traits determine how plants respond to environmental factors and influence ecosystem processes. Among them, root traits and analyses of relations between above and below-ground traits in natural communities are scarce. Methods we characterized a set of above- and below-ground traits of three dominant shrub species in a semiarid shrub-steppe that had contrasting leaf phenological habits (deciduous, semideciduous and evergreen). We analysed if there was coordination among above- and below-ground resource economics patterns: i.e. patterns of biomass allocation, construction costs and lifespan.Important findings Above- and below-ground traits and their resource economics relations pointed to species-specific functional strategies to cope with drought and poor soils and to a species ranking of fast to slow whole-plant strategies in terms of resource uptake, biomass construction costs and turnover. The deciduous shrub, Proustia cuneifolia, had relatively deep and even distribution of roots, and high proportion of short-lived tissues of low C construction costs: it had high fine to coarse root and high leaf-to-stem biomass ratios, high specific leaf area (SLA), and stems of low wood density. This strategy allows Proustia to maximize and coordinate above- and below-ground resources uptake as long as the most limiting factor (water) is available, but at the cost of having relative high plant biomass turnover. The evergreen Porlieria chilensis, instead, displayed a more conservative and slow strategy in terms of resource economics. It had ~80% of the roots in the 40cm topsoil profile, low proportion of fine compared with coarse roots and low leaf-to-stem ratios, low SLA and stems of high wood density, i.e. it invested in C costly tissues that, overall, persist longer but probably at the cost of having lower plant resource uptake rates. Traits in the semideciduous Adesmia bedwellii were in between these two functional extremes. Our results revealed high functional diversity and above- and below-ground complementarity in resource economics among these three codominant species in the Chilean coastal desert.     

Genotypic variation in drought response of silver birch (Betula pendula Roth): leaf and root morphology and carbon partitioning

This study investigates the drought response of four genotypes of Betula pendula with a focus on leaf and root morphological traits, leaf phenology and carbon partitioning between shoot and root. Potted one-year-old clonal plants of four genotypes from regions with low to high annual rainfall (550–1270 mm year⁻¹) were subjected to drought periods of 12–14 weeks in two subsequent years. Well-watered control plants of the four genotypes differed significantly with respect to total leaf area per plant (LA) and specific leaf area (SLA), whereas differences in total fine root surface area (RA), root specific area (SRA), and the fine root:leaf mass ratio (FR:LM) were not significant. Highest LA and SLA were found in the clone originating from the driest environment. In complementary physiological investigations this clone was found to have the highest water use as well which was interpreted as competitive superiority in terms of water consumption. Drought resulted in an increase in SLA in all genotypes, and a decrease in LA. Leaf area reduction was more pronounced in the genotypes from high than in those from low rainfall origin. The ratio of total root to leaf surfaces remained more or less constant after drought application despite an increase in FR:LM. This is explained by a decrease in SRA resulting from a reduced abundance of very small fine rootlets (diameter <0.2 mm) in the drought-treated plants. The loss in total root surface area due to a reduction in finest root mass was compensated for by a relative increase in total root dry mass per plant. Comparison of results from the first and second drought period indicated a marked influence of timing of drought, root system size, and putative root limitation on plant drought response. We conclude that leaf and root morphology, the total leaf and root surfaces, and the morphological response to drought in birch are to a large extent under genetic control.     

Response of Trifolium repens to UV-B radiation: morphological links to plant productivity and water availability

This study used nine populations of Trifolium repens L. (white clover) to investigate possible relationships between plant morphological attributes and responses to ultraviolet-B (UV-B) radiation. Plants were exposed to 0 or 13.3 kJ·m(-2) ·day(-1) UV-B for 12 weeks. Drought was applied in parallel to these treatments during the last 4 weeks of the experiment to test whether limited moisture availability would alter morphological UV-B responses. UV-B affected plant morphology under well-watered conditions, reducing leaf size by 15%, leaf number by 5% and stolon elongation by 19%. The number of leaf primordia in the apical bud was decreased by 4% under UV-B, and by 12% under drought. In drought-exposed plants, leaf size was reduced by 50%, leaf number by 30% and stolon elongation by 60%. In addition, drought reduced specific leaf area (SLA) by 33% and increased leaf percentage dry mass (PDM) by 40%. UV-B-induced reduction in plant biomass in the T. repens populations was associated with higher plant productivity and this was further linked to larger leaf size as well as to lower PDM. In conclusion, the findings suggest that morphological attributes conferring fast potential growth under productive conditions carry a cost in the form of lower biomass accumulation under UV-B.     

Interactions between drought, ABA application and supplemental UV-B in Populus yunnanensis

To test whether drought and ABA application alter the effects of enhanced UV-B on the growth and biomass allocation of Populus yunnanensis Dode, cuttings were grown in pots at two ABA levels, two watering regimes and two UV-B levels for one growth season. Exposure to enhanced UV-B radiation significantly decreased plant growth and photosynthesis under well-watered conditions, but these effects were obscured by drought, which alone caused growth reduction. Drought may contribute to masking the effects of UV-B radiation. The accumulation of UV-B absorbing compounds and the increase of the ABA content induced by drought could reduce the effectiveness of UV-B radiation. ABA application did not have large direct effects on biomass accumulation and allocation. Evidence for interactions between UV-B and ABA was detected for only a few measured traits. Therefore, there was little evidence to support a pivotal role for ABA in regulating a centralized whole plant response to enhanced UV-B. Yet, we recorded an ABA-induced decrease in stomatal conductance (g(s)) and increase in UV-B absorbing compounds and carbon isotope composition (delta(13)C) in response to enhanced UV-B. The allometric analysis revealed that regression models between root and shoot biomass in response to enhanced UV-B are different for plants under well-watered and drought conditions. Enhanced UV-B led to a significant displacement of the allometric regression line under well-watered condition, while allometric trajectories for both UV-B regimes did not differ significantly under drought condition.     

Drought affects the coordination of belowground and aboveground resource‐related traits in Solidago canadensis in China

Quantifying patterns of variation and coordination of plant functional traits can help to understand the mechanisms underlying both invasiveness and adaptation of plants. Little is known about the coordinated variations of performance and functional traits of different organs in invasive plants, especially in response to their adaptation to environmental stressors. To identify the responses of the invasive species Solidago canadensis to drought, 180 individuals were randomly collected from 15 populations and 212 ramets were replanted in a greenhouse to investigate both the response and coordination between root and leaf functional traits. Drought significantly decreased plant growth and most of the root and leaf functional traits, that is, root length, surface area, volume and leaf size, number, and mass fraction, except for the root length ratio and root mass fraction. Phenotypic plasticity was higher in root traits than in leaf traits in response to drought, and populations did not differ significantly. The plasticity of most root functional traits, that is, root length (RL), root surface area (RSA), root volume (RV), and root mass fraction (RMF), were significantly positively correlated with biomass between control and drought. However, the opposite was found for leaf functional traits, that is, specific leaf area (SLA), leaf area ratio (LAR), and leaf mass fraction (LMF). Drought enhanced the relationship between root and leaf, that is, 26 pairwise root–leaf traits were significantly correlated under drought, while only 15 pairwise root–leaf traits were significantly correlated under control conditions. Significant correlations were found between biomass and all measured functional traits except for leaf size. RV, root length ratio, RMF, total area of leaves, and LMF responded differently to water availability. These responses enable S. canadensis to cope with drought conditions and may help to explain the reason of the vast ecological amplitude of this species.     

Differential effect of drought regimes on the seedling performance of six floodplain grassland species

• The performance of seedlings is crucial for the survival and persistence of plant populations. Although drought frequently occurs in floodplains and can cause seedling mortality, studies on the effects of drought on seedlings of floodplain grasslands are scarce. We tested the hypotheses that drought reduces aboveground biomass, total biomass, plant height, number of leaves, leaf area and specific leaf area (SLA), and increases root biomass and root‐mass fraction (RMF) and that seedlings from species of wet floodplain grasslands are more affected by drought than species of dry grasslands.
• In a greenhouse study, we exposed seedlings of three confamilial pairs of species (Pimpinella saxifraga, Selinum carvifolia, Veronica teucrium, Veronica maritima, Sanguisorba minor, Sanguisorba officinalis) to increasing drought treatments. Within each plant family, one species is characteristic of wet and one of dry floodplain grasslands, confamilial in order to avoid phylogenetic bias of the results.
• In accordance with our hypotheses, drought conditions reduced aboveground biomass, total biomass, plant height, number of leaves and leaf area. Contrary to our hypotheses, drought conditions increased SLA and decreased root biomass and RMF of seedlings. Beyond the effects of the families, the results were species‐specific (V. maritima being the most sensitive species) and habitat‐specific. Species indicative of wet floodplain grasslands appear to be more sensitive to drought than species indicative of dry grasslands.
• Because of species‐ and habitat‐specific responses to reduced water availability, future drought periods due to climate change may severely affect some species from dry and wet habitats, while others may be unaffected.

     

Phenotypic plasticity of lianas in response to altered light environment

The growth, morphology and biomass allocation of 11 liana species (six light-demanding and five shade-tolerant) were investigated by growing plants in three contrasting light environments (i.e., field, forest edge and forest interior). Our objectives were to determine: (1) changes in plant traits at the species level; and (2) differences in light-demanding and shade-tolerant species in response to altered light environment. We found that all seedlings of liana species increased in total biomass, total leaf area, relative growth rate (RGR), net assimilation rate (NAR), height, basal diameter, root length, leaf number, root mass/total plant mass (RMR) and root-to-shoot dry biomass (R/S ratio), and decreased in leaf area ratio (LAR), specific leaf area (SLA), leaf size, stem mass-to-total plant mass ratio (SMR) and leaf mass-to-total plant mass ratio (LMR) with increasing light availability. Under the three light environments, the two types of species differed significantly in total biomass, total leaf area, RGR, NAR, LAR, SLA and leaf number, and not in leaf area. Only light-demanding species differed significantly in height, root length, basal diameter, RMR, SMR, LMR and R/S ratio. The mean plasticity index of growth and biomass allocation were relatively higher than the morphological variables, with significant differences between the two groups. Our results showed that liana species respond differently to changing light environments and that light-demanding species exhibit higher plasticity. Such differences may affect the relative success of liana species in forest dynamics.     

Contribution of root growth responses to leaf traits and relative growth rate of Populus alba under different water-table conditions

Water-table depth variations alter root growth response and may affect whole-plant growth in arid and semi-arid regions. We examined how root biomass allocation and root morphological traits affect the leaf physiological and morphological traits and whole-plant growth of Populus alba growing under different water tables. We exposed 1-year-old P. alba cuttings to contrasting soil–water conditions via water table changes in a greenhouse for 90 days. We examined relationships among net assimilation rate (NAR) and other growth components obtained from our published data for trees harvested every 30 days. Strongly negative correlations were found between RMR and root morphological traits. Root mass ratio had a strong negative relationship with LMR, and proportion of fine-root biomass per total root biomass was positively correlated with SLA and NAR. Both NAR and leaf area ratio were important determinants of variation in relative growth rate (RGR). Leaf mass ratio (LMR) and specific leaf area (SLA) were positively correlated with RGR; the correlation was stronger in the case of LMR. Along a water-table gradient, negative relationships between root growth responses are likely to indirectly influence RGR through changes in NAR, LMR, and SLA.     

狭叶红景天幼苗对水分及遮阴的生长及生理生化响应

研究植物对水分和遮阴胁迫的响应及其生理机制对制定合理的栽培管理措施十分必要。以红景天属植物为研究对象,设置土壤含水量分别为田间持水量的80%(过湿水分)、70%(正常水分)、60%(轻度干旱)、40%(中度干旱)、20%(重度干旱)5个水分梯度;设置2个遮阴处理,以全光照(遮阴率为0)为对照、黑色遮阴网遮阴(遮阴率为85%),研究狭叶红景天生长及生理生化指标的变化特征。结果表明:在不同水分处理下,与对照相比,叶绿素含量、茎干重和茎重比(SMR)显著增加(P0.05),株高、总生物量、叶面积、叶干重、叶重比(LMR)、比叶面积(SLA)、叶面积比(LAR)和叶面积根干重比(LARMR)增加,根冠比和根重比(RMR)减少;随着干旱程度加剧,丙二醛(MDA)、脯氨酸(Pro)和可溶性糖(Ss)含量增加,超氧化物歧化酶(SOD)活性总体呈先增加后减小的趋势。在遮阴处理下,株高、SMR、SLA、LAR和LARMR显著增加(P0.05),叶绿素SPAD值和叶面积增加,总生物量、根干重、根冠比和LMR显著减少(P0.05),茎干重和叶干重减少,MDA含量显著增加,Pro含量略有下降,Ss含量减少。在水分胁迫下,狭叶红景天中度干旱时通过增加酶活性抵御伤害,重度干旱超过其阈值,SOD活性下降,植物体受到伤害,Ss可能是主要的渗透调节物质。在遮阴处理下,狭叶红景天通过增加SLA避免遮阴伤害。狭叶红景天在受到环境胁迫时会通过形态改变、调节MDA含量、抗氧化酶活性和渗透调节物质来保证自身正常的生长发育。     

Sources of Variation in Leaf Shape among Two Populations of Achillea Lanulosa

Achillea lanulosa has complex, highly dissected leaves that vary in shape and size along an altitudinal gradient. Plants from a high and an intermediate altitude population were clonally replicated and grown in a controlled environment at warm and cool conditions under bright light. There were genetic differences among populations and among individuals within populations in leaf size and shape. Heritabilities for leaf size and shape characters were moderate. Leaves of the lower altitude population were larger and differed from the higher altitude plants in both coarse and fine shape. Plastic response to temperature of the growth environment paralleled the genetic differentiation between low and high altitude populations. There was no apparent trade-off between genetic control over morphology and the capacity for directional plastic response to the environment. Differences in leaf dissection and size at contrasting altitudes in this species are the result of both genetic divergence among populations and of acclimative responses to local environments.     

Large altitudinal increase in tree root/shoot ratio in tropical mountain forests of Ecuador

Tropical rain forests decrease in tree height and aboveground biomass (AGB) with increasing elevation. The causes of this phenomenon remain insufficiently understood despite a number of explanations proposed including direct or indirect effects of low temperature on carbon acquisition and carbon investment, adverse soil conditions and impaired nutrient supply. For analysing altitudinal patterns of aboveground/belowground carbon partitioning, we measured fine (<2 mm in diameter) and coarse root (2–5 mm) biomass and necromass and leaf area index (LAI), and estimated AGB from stand structural parameters in five tropical mountain rain forests at 1050, 1540, 1890, 2380 and 3060 m along an altitudinal transect in the South Ecuadorian Andes. Average tree height and AGB were reduced to less than 50% between 1050 and 3060 m, LAI decreased from 5.1 to 2.9. The leaf area reduction must have resulted in a lowered canopy carbon gain and thus may partly explain the reduced tree growth in the high-elevation stands. In contrast, both fine and coarse root biomass significantly increased with elevation across this transect. The ratio of root biomass (fine and coarse) to AGB increased more than ten-fold from 0.04 at 1050 m to 0.43 at 3060 m. Under the assumption that fine root biomass does reflect root productivity, our data indicate a marked belowground shift in C allocation with increasing elevation. Possible explanations for this allocation shift are discussed including reduced N supply due to low temperatures, water logging or adverse soil chemical conditions. We conclude that the fine root system and its activity may hold the key for understanding the impressive reduction in tree size along tropical mountain slopes in Ecuador. Analyses of fine root turnover and longevity in relation to environmental factors along altitudinal transects in tropical mountains are urgently needed.     

Variation for phenotypic plasticity among populations of an invasive exotic grass

Phenotypic plasticity is a common feature of plant invaders, but little is known about variation in plasticity among invading populations. Variation in plasticity of ecologically important traits could facilitate the evolution of greater plasticity and invasiveness. We examined plasticity among invasive populations of Microstegium vimineum (Japanese stiltgrass), a widespread and often dominant grass of forests in the eastern U.S. with two separate experiments. First, we exposed seven Microstegium populations to a drought treatment in growth chambers and monitored growth and physiological responses. Then, we established a greenhouse experiment using a subset of the populations; two that exhibited the most divergent responses and one intermediate population. In the greenhouse, we manipulated drought and shade and evaluated biomass production and specific leaf area (SLA). Microstegium exhibited plasticity for biomass production and SLA in the greenhouse experiment, and populations significantly varied in the degree of plasticity under drought and shade treatments. Two populations significantly increased biomass production under favorable conditions, unlike the third population. The most productive populations also responded to shade stress via greater SLA, possibly allowing for greater utilization of available light, while the third population did not. These results show that Microstegium can exhibit plastic responses to environmental conditions. Moreover, variation for plasticity among populations provides the potential for further evolution of plasticity. Future studies should focus on the relative importance of plasticity for the success of Microstegium and other plant invaders and evaluate post-introduction evolution of plasticity.     

Effects of enhanced UV-B radiation and nitrogen deposition on the growth of invasive plant Triadica sebifera

Aims Exotic plant invasions are important components of global change, threatening both the stability and function of invaded ecosystems. Shifts in competitive ability of invasive plants versus their native congeners have been documented. Enhanced UV-B radiation and nitrogen (N) deposition might interact with soil biota communities impacting the invasion process of exotic plant species. To understand the potential effects by UV-B and N with soil biota on plant growth would enhance our understanding of the mechanisms in plant invasions in the context of global change.
Methods We conducted a full-factorial pot experiment in the native range (China) of Triadica sebifera invading US to investigate how UV-B radiation, N and soil biota together determined their seedling growth.
Important findings The results showed that UV-B radiation, N and soil sterilization together impacted the growth of T. sebifera seedlings. UV-B radiation induced changes in biomass allocation with larger leaf biomass observed in response to UV-B radiation. In addition, N increased aboveground biomass and decreased root biomass simultaneously. Soil biota imposed positive effects on growth of T. sebifera, and the addition of N amplified these positive effects. The negative effects by UV-B radiation on growth of T. sebifera showed no response to N addition. Plant height, leaf biomass and total biomass of the invasive T. sebifera populations out- performed those of the native ones. In addition, invasive T. sebifera populations weakened the dependence of root/shoot ratio and root biomass on local soil microorganisms than native populations, but enhanced that of leaf area ratio.     

The role of seed provenance in the early development of Arbutus unedo seedlings under contrasting watering conditions

In the last decades, several studies have reported the increase of land degradation and desertification in the Mediterranean Basin. Depending on degradation severity, ecological restoration might be needed in order to promote ecosystem recovery. The ecology of the selected species and intra specific variability should be considered in order to improve restoration options, especially facing climate change.The present study tested the hypothesis that seedlings from drier provenances would be better adapted to low water content conditions. Seeds were germinated under controlled temperature after which seedlings were grown in a phytotron under two contrasting watering regimes. Seedling performance was analysed using morphological and physiological parameters.Low water content had a clear negative effect on the seedlings’ aboveground biomass (total dry weight, root collar diameter, leaf dry weight and leaf weight ratio) and a positive effect on belowground biomass (root weight and root:shoot ratio). This response was not unequivocal, since provenances differed in morphological adaptations to low water content. Seedlings from the wettest provenance revealed a higher relative growth rate under high water content but a poor adaptation to limited water availability when compared to the other two provenances. This was observed by the absence of a significant belowground investment in this provenance. Seedlings from the wettest provenance also presented a significant reduction of total leaf area that was not observed in the other two provenances. This can however be hardly considered as a successful adaptation to cope with drought since this provenance produced less sclerophyllous leaves, less belowground biomass and also lower sapwood to leaf area ratio independently from the water content conditions. By contrast, seedlings from the dry provenance with the hottest summer had similar root collar diameter, leaf dry weight and physiological performance under both watering regimes.The observed adaptations to water regimes seem to be related with the climate of the seed source and highlighted the importance of seed provenance in ecological restoration actions using Mediterranean species. This knowledge could improve early establishment success predictions for different plant populations, allowing more reliable and cost-effective management decisions under climate change scenarios.     

Drought tolerance in two perennial bunchgrasses used for restoration in the Intermountain West,USA

An ideal restoration species for the semi-arid Intermountain West, USA would be one that grows rapidly when resources are abundant in the spring, yet tolerates summer’s drought. We compared two perennial C_3, Triticeae Intermountain-native bunchgrasses, the widely occurring Pseudoroegneria spicata and the much less widespread Elymus wawawaiensis, commonly used as a restoration surrogate for P. spicata. Specifically, we evaluated seedlings of multiple populations of each species for biomass production, water use, and morphological and physiological traits that might relate to drought tolerance under three watering frequencies (WFs) in a greenhouse. Shoot biomass of E. wawawaiensis exceeded that of P. spicata regardless of WF. At low WF, E. wawawaiensis displayed 38% greater shoot biomass, 80% greater specific leaf area (SLA), and 32% greater precipitation use efficiency (PUE). One E. wawawaiensis population, E-46, displayed particularly high root biomass and water consumption at high WF. We suggest that such a plant material could be especially effective for restoration of Intermountain rangelands by preempting early-season weeds for spring moisture and also achieving high PUE. Our data explain how E. wawawaiensis has been so successful as a restoration surrogate for P. spicata and highlight the importance of measuring functional traits such as PUE and SLA when characterizing restoration plant materials.