Drought-prone Habitats Research Articles

Sand dune shrub species prioritize hydraulic integrity over transpirational cooling during an experimental heatwave

Plant thermoregulation through transpirational cooling is important when facing heat stress and is suggested as an active mechanism to maintain lower leaf temperature during heatwaves. However, whether the role of cooling through transpiration is constrained in drought-prone habitats for the sake of hydraulic safety remains largely unknown. To evaluate the influence of plant water use characteristics on transpiration-based thermoregulation, we compared responses to natural and experimental heatwave conditions of two sand dune shrub species commonly used in dune revegetation projects but inherently differ in xylem hydraulics and water-use strategies. Salix gordejevii adopts a conservative water-use strategy and has low xylem native embolism and Caragana microphylla uses water less frugally and suffers high degrees of xylem native embolism. Under natural conditions, S. gordejevii exhibited lower transpiration levels, higher leaf temperature and had greater leaf thermotolerance with regard to cell membrane thermostability than C. microphylla. During the experimental heatwave, neither species increased cooling through transpirational water loss and maintained stable leaf water status and xylem embolism levels, suggesting that water conservation for hydraulic integrity is possibly a higher priority than transpirational cooling in sand dune shrubs experiencing heatwaves. This study provides evidence that the water-use behavior of shrubs from water-limited sand dunes prioritizes protection against water stress over heat stress.

Caution needed with the EU forest plantation strategy for offsetting carbon emissions

As part of the 2015 Paris climate agreement and under its Green Deal, the EU proposes to strongly rely on forests for offsetting its carbon footprint. However, planting trees should be avoided in wildfire prone and drought prone habitats, which are expanding significantly as climate warms across Europe. In favorable habitats, tree planting remains a controversial solution and the risk of using inappropriate material is high in the absence of long-term planning, unfortunately typical of the forest seed and nursery sector. The EU forest tree planting strategy should pay close attention to local land-use issues, to within- and among-species genetic diversity and should adopt relevant, pluri-annual funding schemes and planting contracts rather than letting market opportunities govern the future of forest tree plantations.

Late Permian seed-plant evolution

Paleobotany The great evolutionary expansion of seed plants took place in the Mesozoic era, which began after the Permian mass extinction 252 million years ago. Blomenkemper et al. report the discovery of seed-plant fossils from Late Permian (252-million- to 260-million-year-old) deposits on the margins of the Dead Sea in Jordan. This area represents an equatorial habitat with pronounced dry seasons. These fossils, which include the earliest records of conifers, push back the ages of several important seed-plant lineages. Some of these lineages appear to span the mass extinction event at the end of the Permian, which suggests that the communities they supported may have been more stable than expected over this transition. Thus, early evolutionary innovations can occur in drought-prone tropical habitats—which rarely offer the conditions needed for fossil preservation. Science , this issue p. [1414][1] [1]: /lookup/doi/10.1126/science.aau4061

Unscrambling phylogenetic effects and ecological determinants of chromosome number in major angiosperm clades

As variations in the chromosome number are recognized to be of evolutionary interest but are also widely debated in the literature, we aimed to quantitatively test for possible relationships among the chromosome number, plant traits, and environmental factors. In particular, the chromosome number and drivers of its variation were examined in 801 Italian endemic vascular plants, for a total of 1364 accessions. We estimated phylogenetic inertia and adaptation in chromosome number - based on an Ornstein-Uhlenbeck process - and related chromosome numbers with other plant traits and environmental variables. Phylogenetic effects in chromosome number varied among the examined clades but were generally high. Chromosome numbers were poorly related to large scale climatic conditions, while a stronger relationship with categorical variables was found. Specifically, open, disturbed, drought-prone habitats selected for low chromosome numbers, while perennial herbs, living in shaded, stable environments were associated with high chromosome numbers. Altogether, our findings support an evolutionary role of chromosome number variation, and we argue that environmental stability favours higher recombination rates in comparison to unstable environments. In addition, by comparing the results of models testing for the evolvability of 2n and of x, we provide insight into the presumptive ecological significance of polyploidy.

Helianthus porteri, a Granite Outcrop Endemic, Does Not Have More Drought Resistant Traits Than Congeners

AbstractHelianthus porteri, a sunflower endemic to drought prone granite outcrops, has been hypothesized to be drought resistant. We compared H. porteri to three Helianthus species (H. annuus, H. agrestis, H. carnosus) from less drought prone habitats for traits associated with drought avoidance and tolerance in greenhouse experiments. Under well-watered conditions, H. porteri had high specific root length suggestive of high capacity for water uptake, but intermediate root mass ratio (RMR) and shallow rooting inconsistent with enhanced capacity for drought avoidance. In response to mild drought, none of the species exhibited osmotic adjustment, and H. porteri had no change in RMR and no greater capacity to increase water-use efficiency, again, inconsistent with greater drought avoidance. In response to cessation of watering, H. porteri wilted at a leaf water potential similar to a wet habitat species, inconsistent with greater drought tolerance. Overall, under the conditions assessed, we found no evidence that H. porteri possesses traits that confer a unique ability to avoid or tolerate drought as compared to congeners.

Photosynthetic response of four fern species from different habitats to drought stress: relationship between morpho-anatomical and physiological traits

Ferns flourish in many habitats, from epiphytic to terrestrial and from sunny to shady, and such varied conditions require contrasting photosynthetic strategies to cope with drought. Four species of temperate ferns from different habitats were subjected to drought by withholding irrigation in order to investigate their photosynthetic responses. Lepisorus thunbergianus (epiphytic) had low stomatal density and showed high water-use efficiency (WUE) retaining photosynthetic activity with low relative frond water content under drought stress, which suggested their high adaptation to drought. On the other hand, low WUE with low light-saturated photosynthetic rate in Adiantum pedatum (terrestrial, shady environment) was associated with much lower photosynthesis than in the other species under drought stress, suggesting lower adaptation to drought-prone habitats. Morphological stomatal traits such as stomatal density and photosynthetic response to drought in ferns involved species-specific adaptation to survive and grow in their natural habitats with different levels of drought.

Depletion of Key Meiotic Genes and Transcriptome-Wide Abiotic Stress Reprogramming Mark Early Preparatory Events Ahead of Apomeiotic Transition.

Molecular dissection of apomixis – an asexual reproductive mode – is anticipated to solve the enigma of loss of meiotic sex, and to help fixing elite agronomic traits. The Brassicaceae genus Boechera comprises of both sexual and apomictic species, permitting comparative analyses of meiotic circumvention (apomeiosis) and parthenogenesis. Whereas previous studies reported local transcriptome changes during these events, it remained unclear whether global changes associated with hybridization, polyploidy and environmental adaptation that arose during evolution of Boechera might serve as (epi)genetic regulators of early development prior apomictic initiation. To identify these signatures during vegetative stages, we compared seedling RNA-seq transcriptomes of an obligate triploid apomict and a diploid sexual, both isolated from a drought-prone habitat. Uncovered were several genes differentially expressed between sexual and apomictic seedlings, including homologs of meiotic genes ASYNAPTIC 1 (ASY1) and MULTIPOLAR SPINDLE 1 (MPS1) that were down-regulated in apomicts. An intriguing class of apomict-specific deregulated genes included several NAC transcription factors, homologs of which are known to be transcriptionally reprogrammed during abiotic stress in other plants. Deregulation of both meiotic and stress-response genes during seedling stages might possibly be important in preparation for meiotic circumvention, as similar transcriptional alteration was discernible in apomeiotic floral buds too. Furthermore, we noted that the apomict showed better tolerance to osmotic stress in vitro than the sexual, in conjunction with significant upregulation of a subset of NAC genes. In support of the current model that DNA methylation epigenetically regulates stress, ploidy, hybridization and apomixis, we noted that ASY1, MPS1 and NAC019 homologs were deregulated in Boechera seedlings upon DNA demethylation, and ASY1 in particular seems to be repressed by global DNA methylation exclusively in the apomicts. Variability in stress and transcriptional response in a diploid apomict, which is geographically distinct from the triploid apomict, pinpoints both common and independent features of apomixis evolution. Our study provides a molecular frame-work to investigate how the adaptive traits associated with the evolutionary history of apomicts co-adapted with meiotic gene deregulation at early developmental stage, in order to predate meiotic recombination, which otherwise is thought to be favorable in stress and low-fitness conditions.

Chlorophyll fluorescence varies more across seasons than leaf water potential in drought-prone plants.

Among the effects of environmental change, the intensification of drought events is noteworthy, and tropical vegetation is predicted to be highly vulnerable to it. However, it is not clear how tropical plants in drought-prone habitats will respond to this change. In a coastal sandy plain environment, we evaluated the response of six plant species to water deficits across seasons, the relationship between their morpho-physiological traits, and which traits would be the best descriptors of plants' response to drought. Regardless of leaf succulence and phenology, responses between seasons were most strongly related to chlorophyll fluorescence. In this study we have demonstrated that a better comprehension of how tropical species from drought-prone habitats cope with changes in water availability can be based on seasonal variation in leaf water potential and chlorophyll fluorescence. Temporal variation in leaf water potential and chlorophyll fluorescence was found useful for differentiating between groups of sandy soil species that are responsive or unresponsive to water availability. However, chlorophyll fluorescence appeared to be a more sensitive descriptor of their seasonal and short-term responses.

Patterns of Diversification in the Xeric-adapted Fern Genus <I>Myriopteris</I> (Pteridaceae)

Abstract Strong selective pressures imposed by drought-prone habitats have contributed to extensive morphological convergence among the 400 + species of cheilanthoid ferns (Pteridaceae). As a result, generic circumscriptions based exclusively on macromorphology often prove to be non-monophyletic. Ongoing molecular phylogenetic analyses are providing the foundation for a revised classification of this challenging group and have begun to clarify its complex evolutionary history. As part of this effort, we generated and analyzed DNA sequence data for three plastid loci (rbcL, atpA, and the intergenic spacer trnG-trnR) for the myriopterid clade, one of the largest monophyletic groups of cheilanthoid ferns. This lineage encompasses 47 primarily North and Central American taxa previously included in Cheilanthes but now placed in the recircumscribed genus Myriopteris. Here, we infer a phylogeny for the group and examine key morphological characters across this phylogeny. We also include a brief discussion of the...

Improving elms performance under drought stress: The pretreatment with abscisic acid

Hormonal conditioning of plants in order to increase photosynthetic performance and reduce oxidative stress may improve plants’ tolerance to stress. This study aims to elucidate the effects of ABA pretreatment on the photosynthetic apparatus and antioxidant battery of Ulmus minor plants under well watered (WW) and drought stress (DS) conditions. Leaves were sprayed with ABA (50 and 100μM). After 25 days of treatment DS was initiated by withholding water for 6 days. Water deficit decreased the RWC, induced stomatal closure and impaired net CO2 assimilation rate (A). However, independently of the water regime, ABA pretreatment increased plant DW accumulation, A, carotenoids and Chl a contents and reduced water loss. DS induced oxidative stress, but ABA application increased DS tolerance by the enhancement of the antioxidant system. Under WW conditions, the benefits of ABA application in reducing the cell membrane damages were noticeable. ABA pretreatment and DS induced changes in U. minor cell cycle of leaf cells, with a delay in S phase and an increase of FPCV coefficient. We propose that ABA pretreatment improves plant performance by increasing plant DW accumulation and augmenting the antioxidant system of U. minor plants, not only under DS conditions, but also under WW conditions. The use of ABA as pretreatment to alleviate the negative effects of DS seems to be a promising strategy to reduce plant's water loss and improve plant productivity in drought prone habitats.

Modifications in Root and Stem Anatomy for Water Conservation in Some Diverse Blue Panic (Panicum antidotale Retz.) Ecotypes Under Drought Stress

Five ecotypes of Panicum antidotale Retz. adapted to diverse habitats were subjected to drought stress to evaluate their drought tolerance in relation to adaptive anatomical structures. The ecotype from non-stressed habitat had intensive sclerification as well as crystallization in parenchymatous cells, which help prevent water loss. The ecotype from drought-prone habitat had well-developed metaxylem vessel area for better conduction of water and nutrients, and pith area for better storage of water. The ecotype collected from salinity-affected habitat as well as that from saline and waterlogged habitat showed extensive sclerification in the vascular region, which is vital for preventing water loss. The ecotype from a salinity- and drought-prone habitat showed increased metaxylem vessel number and formation of additional metaxylem vessels in the pith region for better conduction, multi-layer exodermis and intensive sclerification for prevention of water loss, and increased parenchymatous region for better storage of water. The most promising anatomical features found in highly drought tolerant ecotypes were increased metaxylem number, multi-layered exodermis, and intensive sclerification in vascular region.

Exploring rock fissures: does a specialized root morphology explain endemism on granite outcrops?

Worldwide, many plant species are confined to open, shallow-soil, rocky habitats. Although several hypotheses have been proposed to explain this habitat specificity, none has been convincing. We suggest that the high level of endemism on shallow soils is related to the edaphic specialization needed to survive in these often extremely drought-prone habitats. Previous research has shown that species endemic to ironstone communities in SW Australia have a specialized root morphology that enhances their chance to access fissures in the underlying rock. Here we test the generality of these findings for species that are confined to a shallow-soil habitat that is of much greater global significance: granite outcrops. We compared temporal and spatial root growth and allocation of three endemic woody perennials of SW Australian granite outcrop communities with those of congeners occurring on nearby deeper soils. Seedlings of all species were grown in 1·2 m long custom-made containers with a transparent bottom that allowed monitoring of root growth over time. The granite outcrop endemics mostly differed in a predictable way from their congeners from deeper soils. They generally invested a larger portion of their biomass in roots, distributed their roots faster and more evenly over the container and had a lower specific root length. In different species pairs the outcrop endemics achieved their apparent advantage by a different combination of the aforementioned traits. Our results are consistent with earlier work, indicating that species restricted to different types of drought-prone shallow-soil communities have undergone similar selection pressures. Although adaptive in their own habitat in terms of obtaining access to fissures in the underlying rock, these root system traits are likely to be maladaptive in deeper soil habitats. Therefore, our results may provide an explanation for the narrow endemism of many shallow-soil endemics.

Strategies of a Bornean tropical rainforest water use as a function of rainfall regime: isohydric or anisohydric?

Although Bornean tropical rainforests are among the moistest biomes in the world, they sporadically experience periods of water stress. The observations indicate that these ecosystems tend to have little regulation of water use, despite episodes of relatively severe drought. This water-use behaviour is often referred to as anisohydric behaviour, as opposed to isohydric plants that regulate stomatal movement to prevent hydraulic failure. Although it is generally thought that anisohydric behaviour is an adaptation to more drought-prone habitats, we show that anisohydric plants may also be more favoured than isohydric plants under very moist environments where there is little risk of hydraulic failure. To explore this subject, we examined the advantages of isohydric and anisohydric species as a function of the hydroclimatic environment using a stochastic model of soil moisture and carbon assimilation dynamics parameterized by field observations. The results showed that under very moist conditions, anisohydric species tend to have higher productivity than isohydric plants, despite the fact that the two plant types show almost the same drought-induced mortality. As precipitation decreases, the mortality of anisohydric plants drastically increases whereas that of isohydric plants remains relatively constant and low; in these conditions, isohydric plants surpass anisohydric plants in their productivity.

The role of altitude and associated habitat stability in determining patterns of population genetic structure in two species of Atalophlebia (Ephemeroptera: Leptophlebiidae)

Summary 1. Previous studies have identified lowland areas as barriers to gene flow (dispersal) between distinct mountain ranges in montane species of aquatic insects. In this study, we investigated the population genetic structure of two closely related Atalophlebia (mayfly) species inhabiting lowland areas of south-east Queensland, Australia, with the expectation of widespread gene flow throughout the low-altitude environment and associated homogeneous genetic structure. 2. In particular, we asked whether species with lower-altitude distributions demonstrate greater spatial distribution of mtDNA (COI) alleles than the upland species studied previously. This pattern would be expected if good dispersal ability is associated with population persistence in these drought-prone habitats. 3. The two species demonstrated contrasting genetic population structure. Atalophlebia sp. AV13 D revealed strong population structure, with populations on each side of the low-altitude area isolated from each other for a long time (c.350 kya), and the presence of an isolation-by-distance pattern over relatively small geographical distances (<40 km). In contrast, Atalophlebia sp. AV13 A was panmictic at the scale investigated (≤160 km), with no history of past population fragmentation. 4. Examination of sample distribution along the altitudinal gradient reveals that Atalophlebia sp. AV13 D may have a more upland distribution (associated with greater habitat stability) than previously supposed, while Atalophlebia sp. AV13 A inhabits more xeric lowland areas, where freshwater habitats are less stable. We consequently hypothesise that these contrasting genetic population structures result from differences in habitat stability along the altitudinal gradient, only species with good dispersal ability being able to persist in unstable habitats. These findings may be applicable to other regions of the globe where habitat instability is associated with altitudinal gradients.

The hydraulic conductance of Fraxinus ornus leaves is constrained by soil water availability and coordinated with gas exchange rates

Leaf hydraulic conductance (Kleaf) is known to be an important determinant of plant gas exchange and photosynthesis. Little is known about the long-term impact of different environmental factors on the hydraulic construction of leaves and its eventual consequences on leaf gas exchange. In this study, we investigate the impact of soil water availability on Kleaf of Fraxinus ornus L. as well as the influence of Kleaf on gas exchange rates and plant water status. With this aim, Kleaf, leaf conductance to water vapour (gL), leaf water potential (Psileaf) and leaf mass per area (LMA) were measured in F. ornus trees, growing in 21 different sites with contrasting water availability. Plants growing in arid sites had lower Kleaf, gL and Psileaf than those growing in sites with higher water availability. On the contrary, LMA was similar in the two groups. The Kleaf values recorded in sites with two different levels of soil water availability were constantly different from each other regardless of the amount of precipitation recorded over 20 days before measurements. Moreover, Kleaf was correlated with gL values. Our data suggest that down-regulation of Kleaf is a component of adaptation of plants to drought-prone habitats. Low Kleaf implies reduced gas exchange which may, in turn, influence the climatic conditions on a local/regional scale. It is concluded that leaf hydraulics and its changes in response to resource availability should receive greater attention in studies aimed at modelling biosphere-atmosphere interactions.

Ecological and evolutionary consequences of desiccation tolerance in tropical fern gametophytes

Ferns have radiated into the same diverse environments as spermatophytes, and have done so with an independent gametophyte that is not protected by the parent plant. The degree and extent of desiccation tolerance (DT) in the gametophytes of tropical fern species was assessed to understand mechanisms that have allowed ferns to radiate into a diversity of habitats. Species from several functional groups were subjected to a series of desiccation events, including varying degrees of intensity and multiple desiccation cycles. Measurements of chlorophyll fluorescence were used to assess recovery ability and compared with species ecology and gametophyte morphology. It is shown that vegetative DT (rare in vascular plants) is widely exhibited in fern gametophytes and the degree of tolerance is linked to species habitat preference. It is proposed that gametophyte morphology influences water-holding capacity, a novel mechanism that may help to explain how ferns have radiated into drought-prone habitats. Fern gametophytes have often been portrayed as extreme mesophytes with little tolerance for desiccation. The discovery of DT in gametophytes holds potential for improving our understanding of both the controls on fern species distribution and their evolution. It also advances a new system with which to study the evolution of DT in vascular plants.

Isotopic carbon composition and related characters of dominant species along an environmental gradient in Inner Mongolia, China

Carbon isotope composition ( δ 13C value) provides a useful measure of integrated water-use efficiency (WUE) of plants and can be used to rank the drought tolerance of different species. We determined the δ 13C values, leaf water content (LWC) and free proline content of 52 plant species selected from eight plant communities along a moisture gradient in the Xilin River Basin, Inner Mongolia. The δ 13C values and WUE of C 3 plant species tended to increase as the occurrence frequency and relative biomass of the species increased in the entire basin. The mean foliage proline concentration of all species in a community was higher when the habitat was drier and the mean LWC of plants decreased with increasing soil aridity. Significantly positive relationships existed between the foliar proline concentration and occurrence frequency and relative biomass of the species, respectively. Our results indicated that inter- and intra-species variations in WUE might significantly influence the outcome of competitive interactions and played a large role in determining species composition of plant communities. In addition, proline accumulation in leaves might strengthen competitive ability of plants growing in drought prone habitats.

Regulation of the structure and catalytic properties of plasma membrane H&lt;sup&gt;+&lt;/sup&gt;-ATPase involved in adaptation of two reed ecotypes to their different habitats

The properties and kinetics of ATP and p-nitrophenyl phosphate (PNPP) hydrolysis activities of plasma membrane H+-ATPase from the two reed ecot ypes, swamp reed (SR) and dune reed (DR), were investigated. The pH optimum of the plasma membrane H+-ATPase in both reed ecotypes was similar but the sensitivity of the enzyme to the reaction medium pH seemed to be higher in DR than that in SR. Compared to SR, the DR exhibited a higher Vmax value for ATP hydrolysis whereas the Km value was almost similar in both reed ecotypes. The PNPP hydrolysis of the plasma membrane H+-ATPase was also studied in both reed ecotypes at increasing PNPP concentrations. Km and Vmax for PNPP hydrolysis showed great differences in the two reed ecotypes and in DR the Km and Vmax values were 2- and 10-fold, respectively, higher than those in SR. The ATP hydrolysis activity of the plasma membrane was markedly inhibited by hydroxylamine in both reed ecotypes, and the percentage inhibition of ATP hydrolysis rate seemed higher in DR than that in SR. In addition, the structure or property of the C-terminal end of the plasma membrane H+-ATPase were also different in the two reed ecotypes. These data suggest that different isoforms of the plasma membrane H+-ATPase might be developed and involved in the adaptation of the plant to the long-term drought-prone habitat.

Genotypic variation in drought response of silver birch (Betula pendula): leaf water status and carbon gain.

To assess genotypic variation in drought response of silver birch (Betula pendula Roth), we studied the plasticity of 16 physiological traits in response to a 12-14-week summer drought imposed on four clones in two consecutive years. In a common garden experiment, 1-year-old clonal trees from regions with low (550 mm year(-1)) to high rainfall (1270 mm year(-1)) were grown in 45-l pots, and leaf gas exchange parameters, leaf water potentials, leaf osmotic potentials and leaf carbon isotope signatures were repeatedly measured. There were no clonal differences in leaf water potential, but stomatal conductance (gs), net photosynthesis at ambient carbon dioxide concentration, photosynthetic water-use efficiency, leaf carbon isotope composition (delta13C) and leaf osmotic potentials at saturation (Pi0) and at incipient plasmolysis (Pip) were markedly influenced by genotype, especially gs and osmotic adjustment. Genotypes of low-rainfall origin displayed larger osmotic adjustment than genotypes of high-rainfall origin, although their Pi0 and Pip values were similar or higher with ample water supply. Genotypes of low-rainfall origin had higher gs than genotypes of high-rainfall origin under both ample and limited water supply, indicating a higher water consumption that might increase competitiveness in drought-prone habitats. Although most parameters tested were significantly influenced by genotype and treatment, the genotype x treatment interactions were not significant. The genotypes differed in plasticity of the tested parameters and in their apparent adaptation to drought; however, among genotypes, physiological plasticity and drought adaptation were not related to each other. Reduction of gs was the first and most plastic response to drought in all genotypes, and allowed the maintenance of high predawn leaf water potentials during the drought. None of the clones exhibited non-stomatal limitation of photosynthesis. Leaf gs, photosynthetic capacity, magnitude of osmotic adjustment and delta13C were all markedly lower in 2000 than in 1999, indicating root limitation in the containers in the second year.

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PLANT SCIENCE Is it better to grow efficiently within a limited range of conditions or safely across a broader range? Factors that influence this choice are illustrated by comparing water-conducting tissues (xylem) in plants. Wide and long vessels support low-resistance flow of water, but are susceptible to catastrophic failure provoked by a few untoward bubbles. Narrower, shorter xylem vessels struggle to carry as much water, but are a more robust conduit for facing the vagaries of life. Because transpiration and photosynthesis go hand in hand, the amount of water delivered to the leaves determines the amount of photosynthesis that can be supported. Kocacinar and Sage, examining xylem structure in relation to metabolism and environment, find that some species favor a secure water supply and others favor a maximized water supply that supports more leaf area. An increased leaf canopy is a competitive solution in resource-rich habitats, whereas reliability of water supply is the solution favored for species growing in drought-prone habitats. In either case, C4 photosynthetic plants, which use water more efficiently than do C3 photosynthetic plants, have the advantage of being able to go further with a given amount of xylem tissue. Thus, the advantages of C4 metabolism include not only metabolic efficiency, but also doing more with less in plant infrastructure. — PJH Plant Cell Environ. 26 , 2015 (2003).