Xeric Environments Research Articles

Can the galling Eriophyidae (Trombidiformes) manipulate leaf structural and histochemical profiles over environmental stressors?

Context Galls are products of an intrinsic relationship between specific parasites and their host plants. Gall formation involves alterations in the developmental pattern of the host organs in which environmental conditions may also impose constraints. Aims We hypothesised that the adaptive features of the host plants reflect the stressors of the xeric and mesic environments and influence the establishment and success of the associated galls. Methods We analysed anatomical, histometric, and histochemical alterations induced by two species of Eriophyidae, on Miconia ibaguensis adapted to the Brazilian Cerrado (xeric environment) and on Miconia notabilis adapted to the forests of the equatorial region (mesic environment). Key results The adaptive leaf characteristics of M. ibaguensis and M. notabilis to both xeric and mesic environments, such as the trichomes, cuticle and mesophyll thickness, number of mesophyll layers, the proportion of intercellular spaces, differences in the intensity detection of phenolic and starch are kept in the galls. The higher density of emergences in M. notabilis may increase the protection against the natural enemies of the eriophyids, which are commonly more abundant in mesic than in xeric environments. Conclusions These traits are important not only for the survival of the two host plants but also for the success of the two species of galling Eriophyidae in distinct environments. Implications These findings indicate the success of the gall inducers of the same taxa in distinct environments, which can be explored in different systems.

Osmotic characteristics of water retention structures of Bursera microphylla in relation to soil salinity

With a worldwide increase in soil salinity, as well as the climate crisis raising global temperatures, it is important to understand the effects of soil salinity on plant survival. One way to understand how plants may evolve to survive in these xeric desert environments is to gain a further understanding of existing halophytic (live in saline environments) and/or xerophytic (live in dry, arid environments) plants. Bursera microphylla in particular is quite interesting because it is both a halophyte and a xerophyte. One reason it is able to survive in dry environments is due to its bulbs at the base of the trunk and major limbs of the tree, which have been shown to store water during droughts. To facilitate mineral uptake, plants use ATP to transport NaCl ions into the plant, which facilitates water uptake. Because observed field conditions in the Baja California Peninsula were extremely xeric, most plants there have distinct evolutionary traits to facilitate water storage or retention. The Elephant Tree (Bursera microphylla) gets its name from the abnormal proportions of the base of its stem, which is much wider than much of the tree, and studies show that this disproportionately wide stem can store water for use during times of drought, which are common in the Baja California Peninsula. Our hypothesis was that sodium chloride was taken up through the plant’s root structure to facilitate this water transportation, and that this sodium chloride accumulation was directly proportional to the soil salinity. We tested this hypothesis via light microscopy of plant tissues to observe cell tonicity under different concentrations of saline solution. soil salinity was measured using saturated extraction. The results of this experiment show that most cells within the “bulb” structures were isotonic at a concentration approximately twice as high as that of root tissue and ambient soil salinity, therefore supporting the presented hypothesis.

Neo-taphonomy of prey bones ingested by pumas in central western Argentina

Pumas are American top predators that commonly frequent places that may also be inhabited by humans. With the aim of contributing to the evaluation of the accumulating processes and agents of vertebrate remains of archaeological and paleontological sites, we analyzed a modern puma scat-derived vertebrate bone assemblage from an area of the central Monte Desert, one of the most arid regions of South America. We evaluated the taphonomic signature of vertebrate remains recovered in such scats without discriminating among the different types of fauna, which strengthens this taphonomic contribution. Despite the high availability of domestic and exotic fauna from livestock fields in the surroundings of the area, the assemblage was dominated by typical native small and medium-sized fauna from xeric environments of the Monte biome. The armadillo Zaedyus pichiy was the most frequent taxon, followed by the caviid rodents Microcavia maenas and Galea leucoblephara, and the Tinamidae Eudromia elegans. The most remarkable taphonomic signatures are high breakage; a high proportion and degree of elements with evidence of digestion; and a low number of tooth marks. We find a good proportion of identifiable specimens, considering the previous assumptions on the extreme destruction of felid scat-derived vertebrate bone assemblages. A first assessment was made of specimens little known from a regional taphonomic perspective, such as armadillo osteoderms or bird remains. The taphonomic analysis of this multi-taxa accumulation enables a solid evaluation of vertebrate bone assemblages from archaeological and paleontological sites.

A peculiar new species of Dione (Agraulis) Boisduval & Le Conte (Lepidoptera, Nymphalidae, Heliconiinae) associated with Malesherbia Ruiz & Pavón (Passifloraceae) in xeric western slopes of the Andes.

Butterflies associated with xerophytic environments of the Andes have been little studied, and they exhibit high levels of endemism. Herein Dione (Agraulis) dodona Lamas & Farfán, sp. nov. (Nymphalidae; Heliconiinae) is described, distributed on the western slopes of the Andes of Peru and northern Chile, between 800 and 3,000 m elevation. Adults of both sexes, and the immature stages, are described and illustrated based on light and scanning electron microscopy. The immature stages are associated with MalesherbiatenuifoliaD. Don (Passifloraceae) found in xeric environments, representing a new record of this genus as a host plant for the subfamily Heliconiinae. Conspicuous morphological differences are presented for all stages at the generic level. Based on a phylogenetic analysis of the COI barcode mitochondrial gene fragment, D. (A.) dodona Lamas & Farfán, sp. nov. is distinguished as an independent lineage within the Agraulis clade of Dione, with ca. 5% difference to congeneric species.

Composition and phenology of the beetle community (Coleoptera: Scarabaeoidea, Staphylinidae, Histeridae, Hydrophilidae) associated to dung of equines in an arid environment

Summary While coprophagous beetles (Scarabaeidae) have been intensively studied in the Mediterranean basin, coprophilous and other equally important dung-associated beetles have received less attention. This study represents the first effort to understand the temporal patterns and dynamic of the whole beetle community in arid conditions, including Scarabaeidae, Staphylinidae, Histeridae and Hydrophilidae. In addition, it is the first specifically to study the fauna attracted to dung of equines in Morocco, which is a key element in promoting the conservation of these insects in xeric environments. The taxonomic identification of 2596 beetles, collected between I.2014 and III.2015 in southern-eastern Morocco, allowed the identification of 53 taxa belonging to six families. Our study has shown that coprophilous and the Staphylinidae members were the major components of dung-associated fauna in xeric conditions in the study area in terms of the total number of individuals, followed by the coprophagous Scarabaeidae. The correspondence analysis has shown that variations of the beetle community over time are governed mainly by temperature. The biocenotic study revealed the presence of three faunal groups: summer species, winter species and a third group composed by eurythermal taxa.

Irrigation and fertilization of Chrysothamnus nauseosus (Asteraceae) affect the attack and gall growth of Rhopalomyia chrysothamni (Cecidomyiidae)

The quality of the environment and the host plant influence the development of the galls as well as the performance of gall inducing insects. The effect of nutrients and water availability on the development of galls induced by Rhopalomyia chrysothamni (Diptera: Cecidomyiidae) on Chrysothamnus nauseosus subsp. hololeucus (Asteraceae) was tested. The study was conducted in a xeric area with no signs of disturbances in Coconino National Forest, Arizona, USA. Individuals of C. nauseosus randomly selected underwent three treatments of water and nutrients availability. At the end of the growing season, the number of attacked plants, abundance and the development of galls in each treatment were evaluated. The differences in habitat quality simulated by the fertility and humidity conditions influenced both the number of attacked plants and the growth of galls. Plants with lower hydric-nutritional quality were more attacked by the galling insect. Otherwise, when both water and nutritional stresses were relieved plants developed galls with higher dry biomass and density. Therefore, this field experimental study indicates that while galling females attacked plants more in xeric environments, the galls grew larger in relatively more mesic conditions. The results showed a trade-off between the quantity and quality of galls of R. chrysothamni depending on the nutritional quality of the host plants.

Females of solitary- and group-living sister species of African striped mice show a similar social structure following experimentally imposed group-living

Social systems vary within and between species, ranging along a continuum between solitary-living to complex societies. Social systems are emergent properties of interactions between individuals, and these interactions are often modulated by hormones. We investigated the behavioral and hormonal consequences of experimentally imposed social grouping in two sister species of the African striped mouse Rhabdomys, one of which (R. pumilio) is group-living in its natural xeric environment, while the other (R. dilectus) is solitary-living in its mesic environment. We compared social behavior of triads of age-matched, unfamiliar females of each species, and measured their serum corticosterone and testosterone concentrations in comparison to solitarily housed controls. On day 1, triads of both species displayed mainly amicable behavior. Aggression was rare, but R. pumilio females showed more aggression than R. dilectus females. Triads of both species shared nests from day 2 onwards, and amicable behavior increased over time. Neither species differed in hormonal concentration compared to their solitary controls, but R. dilectus had 1.3 × higher serum corticosterone than R. pumilio. Serum testosterone did not differ between species or treatments. Neither corticosterone nor testosterone concentration measured at the end of the experiment was related to the duration of amicable behavior shown between triad members at the end of the study. Both species established a similar social structure when housed in non-kin triads in captivity. Both displayed high amicability and little aggression, indicating that environmental factors, such as resource distribution and duration of the breeding season, may be more important determinants of social organization in striped mice than social tolerance. Variation in social systems occurs both between and within species, and to date, it is still poorly understood how differences in social tolerance relate to inter-specific variation in social systems. We experimentally imposed social grouping in females of two sister species of the African striped mouse, one naturally group-living and one solitary-living species. We studied interactions between individuals in these experimental groups over 21 days and measured testosterone and corticosterone concentration at the end of the experiment. Both species mainly showed socio-positive behavior and little aggression occurred. Individuals from experimental groups of both species had similar testosterone and corticosterone concentrations compared to solitary-housed control females of the same species. Our results show that both species are tolerant of conspecifics, at least in captivity, indicating that environmental factors might be more important determinants of social organization than social tolerance.

Comparative Micromorphology and Ultrastructure of Resurrection and Non-resurrection Selaginella Species

Most species in the genus Selaginella (Selaginellaceae) are susceptible to desiccation, while a few species are able to withstand the extreme desiccation, recover metabolic functioning, and grow rapidly after rehydration. However, there is limited information about the anatomical features of the resurrection species in Selaginella. In the present study, we compared the microphyll micromorphology and ultrastructure of two resurrection species (S. pulvinata and S. sanguinolenta), and two non-resurrection species (S. kraussiana and S. chrysocaulos). Compared with the two non-resurrection species, the two resurrection species had most of their stomata distributed on the adaxial surface of microphylls that were tightly attached to stems, and possessed smaller and thicker microphylls, smaller stomatal size, higher stomatal density, thicker epidermal cell walls, more chloroplasts, and denser cytoplasm. These micromorphological and ultrastructural features of the two resurrection species were beneficial in reducing the transpiration and dehydration damage and could be considered as ecological adaptations to xeric environments.

Plant–insect interactions from the Late Oligocene of Spain (La Val fossil site, Estadilla, Huesca) and their palaeoclimatological implications

Trace fossils of insect herbivory are an important tool, which provide evidence for palaeoecological and palaeoclimatic interpretations, as well as being a unique and direct record of the plant–insect interactions in the geologic past. In the Iberian Peninsula, these types of surveys have been scarce and purely descriptive. The La Val fossil site is an interesting, new megaflora assemblage from the Late Oligocene of Spain, which encompasses numerous plant–insect interactions and their palaeoclimatic and palaeoecological implications. A total of 1337 fossil specimens from 13 stratigraphic levels were analyzed for this study. We identified 28 different types of plant–insect interactions belonging to seven Functional Feeding Groups (FFGs). Hole feeding was the most common category of external-feeding insect damage, followed by margin feeding, skeletonization, and surface feeding. Among the internal-feeding FFGs, galling was the richest and most abundant FFG. All other internal-feeding FFGs were relatively uncommon: piercing/sucking, and incertae sedis (DT114). Among stratigraphic levels, the mean herbivory frequency was significantly greater at lower levels compared to the upper levels. La Val presents a marked drop in the diversity of plant–insect interactions through time, possibly due to changes in temperature or humidity levels. A marked decrease in galling diversity and a generalized decrease in interactions are observed at the youngest levels. This could be related to an increase in humidity though time in the La Val palaeoforest, since modern xeric environments favour the proliferation of galls. • Reports plant–insect interactions from an Iberian Peninsula Oligocene deposit. • Herbivore interactions decrease in number and richness in the youngest horizons. • A decrease in galling diversity is also observed in the youngest horizons. • Changes in herbivory across horizons may reflect an increase in humidity through time. • The data provide context for previously reported European plant–insect associations.

Seasonal variations in locomotor activity rhythm and diurnal activity in the dromedary camel (Camelus dromedarius) under mesic semi-natural conditions

ABSTRACT The dromedary camel (Camelus dromedarius) is a large ungulate that copes well with the xeric environment of the desert. Its peculiar adaptation to heat and dehydration is well-known. However, its behavior and general activity is far from being completely understood. The present study was carried out to investigate the ecological effect of the various seasons on the locomotor activity (LA) rhythm and diurnal activity of this species. Six adult female camels were maintained under mesic semi-natural conditions of the environment during four periods of 10 days in each season: autumn, winter, spring and summer. In addition, three female camels were used to test the effect of rain on the LA rhythm during a period of 18 days during the winter. The animal’s LA was recorded using the locomotion scoring method. Camels displayed a clear 24.0h LA rhythm throughout the four seasons. Activity was intense during Day-time (6–22 fold higher in comparison to night) and dropped or completely disappeared during nighttime. Mean daytime total activity was significantly higher in the summer as compared to winter. Regardless of the season, the active phase in camels coincided with the time of the photophase and thermophase. Furthermore, the daily duration of the time spent active was directly correlated to the seasonal changes of photoperiod. The diurnal activity remained unchanged over the four seasons. For each season, the start and the end of the active phase were synchronized with the onset of sunrise and sunset. At these time periods, temperature remained incredibly stable with a change ranging from 0.002 to 0.210°C; whereas, changes of light intensity were greater and faster with a change from 0.1 to 600 lux representing a variation of 3215–7192 fold in just 25–29 min. Rainfall affected the pattern of the LA rhythm with occurrence of abnormal nocturnal activity during nighttime disturbing nocturnal rest and sleep. Here we show that the dromedary camel exhibits significant seasonal changes of its activity within daylight hours. However, the diurnal pattern remains unchanged regardless of the season; whereas, abnormal nocturnal activity is observed during periods of rain. The activity onset and offset in this species seems to be primarily driven by the changes in light intensity at dusk and dawn.

Cololobus ruschianus (Vernonieae, Asteraceae), a Threatened Narrow Endemic Species from Atlantic Forest Inselbergs, Espírito Santo, Brazil

Abstract— The Atlantic Forest is the most species rich vegetation in Brazil and holds several phytophysiognomies, including the vegetation on inselbergs, which is a very stressful xeric environment that selects for very specialized biota. Cololobus is an endemic genus from Atlantic Forest inselbergs of eastern Brazil, and Cololobus ruschianus is a new species based on morphological evidence, differing from other species of the genus by its morphological traits in petioles, subinvolucral bracts, and outer involucral bracts. Cololobus ruschianus occurs in Santa Teresa, Espírito Santo State, Brazil and would likely be considered Critically Endangered (CR), based on the criteria of the IUCN red list.

Short-term stem diameter variations in irrigated and non-irrigated stone pine (Pinus pinea L.) trees in a xeric non-native environment

Irrigation of adult stone pine trees growing in a xeric non-native habitat had positive effects not only in stem diameter growth but also in tree response to climatic variability. Stone pine is a key species from Mediterranean Europe increasingly planted in South America. The knowledge about irrigation impact on short-term stem diameter dynamics is still limited in non-native arid areas. To improve our understanding of the effect of irrigation on (1) stem diameter changes of stone pine trees in a drought-prone environment in Chile and (2) the sensitivity of the species to weather conditions. We studied daily stem diameter changes in irrigated and non-irrigated 31-year-old stone pine trees during a growing season with below average precipitation in Chile. Short-term diameter changes were recorded using high-resolution dendrometers. The detrended daily stem diameter changes, expressing tree water status, were correlated with weather variability in both irrigated and non-irrigated trees. The growth period lasted longer and the cumulative sum of daily changes increased by 130% in irrigated trees. Moreover, a similar correlation of tree water status with climatic variables was found in non-irrigated, with the exception of precipitation. Irrigation increased stone pine productivity in this xeric environment and reduced the correlations between daily stem diameter variations and local climatic variability.

The Mediterranean species of genus Loxosceles Heineken amp; Lowe, 1832 (Araneae: Sicariidae): Loxosceles imazighen sp. n. from Morocco and first description of the female of L. mrazig Ribera amp; Planas, 2009 from Tunisia.

The aim of this paper is to describe a new species of the genus Loxosceles Heineken Lowe, 1832 from Morocco, Loxosceles imazighen sp. n., and to describe for the first time a female of Loxoxceles mrazig Ribera Planas, 2009 from Tunisia. Both species live in xeric and desert environments and are located in southern Atlas Range. Molecular phylogenetic analyses, using mitochondrial (cox1, 16S) and nuclear (H3, 28S) markers, revel that these species are closely related and that they constitute a separate evolutionary lineage of L. rufescens (Dufour, 1820) and of the set of endemic species of the Canary Islands. L. imazighen sp. n. differs from L. mrazig, the closest species morphologically and geographically, in the shapes and proportions of the male palpal tibia and the shapes and dispositions of the female seminal receptacles. In addition, L. mrazig females show morphological variability in their genitalia, mainly in the inner and outer lobes. Although that variability cannot be associated with different populations, since it also appears within individual populations, and is not related to genetic or geographic distances.

Atlas of leaf surface micromorphology in Aloe L. (Asphodelaceae) from the Horn of Africa region

The confident identification to species rank of fragmentary and sterile plant material is often challenged by the absence of diagnostic characters, which are present in intact specimens, reproductive parts, and plants in habitat. Here, we consider leaf surface micromorphology for the identification of the genus Aloe in the Horn of Africa region. Primary and secondary sculpturing of the leaf epidermis and stomata were characterised from SEM micrographs of 35 taxa representing 31 species of Aloe (Asphodelaceae subfam. Alooideae). Detailed comparison revealed that leaf surface characters are conserved between species and within-species variation is modest. Closely related taxa in the Aloe adigratana—A. camperi—A. sinana species complex could be distinguished using leaf surface micromorphology alone. These characters also guide species delimitation; in the species complex including A. schoelleri and A. steudneri, a narrow circumscription is supported, whereas with A. ankoberensis and A. pulcherrima, a wider circumscription merits consideration. The observed trait combinations are characteristic of plants in xeric environments, with the most notable feature being stomata that are most deeply sunken in species in more arid habitats. Our findings support the use of comparative study of micromorphological leaf surface characters for species identification and taxonomy in the genus Aloe.

The fossil flora of the Dead Sea region, Jordan – A late Permian Garden of Delights

The Umm Irna Formation, Jordan, holds one of the most peculiar late Permian plant–fossil assemblages worldwide. Over the last decades of field work, several localities close to the eastern shore of the Dead Sea have yielded a highly diverse ‘mixed flora’ of mesic to xeric environments encompassing elements that are typical either for different floral realms or for different time periods of Earth History. Taxa typical for particular floral realms include, e.g. Cathaysian gigantopterids and Lobatannularia, Euramerican conifers such as Otovicia hypnoides, or the characteristic Gondwanan seed ferns Glossopteris and Dicroidium. Moreover, most taxa are typical for the Permian, some assemblages have also yielded precocious occurrences of taxa that have so far been considered typical for the Mesozoic, such as Umkomasiaceae, Bennettitales, and podocarp conifers. In most cases, fossils from the Umm Irna Formation show well–preserved cuticles that allow sound systematic placement and contribute to the reconstruction of dispersed plant parts into whole–plant–taxa. Altogether, the Umm Irna Formation provides an exceptional window into depositional environments and vegetation types that are rarely preserved in the fossil record but that are crucial for our understanding of plant evolution.

Effects of Thermal Acclimation on the Tolerance of Bactrocera zonata (Diptera: Tephritidae) to Hydric Stress.

Insects, similarly to other small terrestrial invertebrates, are particularly susceptible to climatic stress. Physiological adjustments to cope with the environment (i.e., acclimation) together with genetic makeup eventually determine the tolerance of a species to climatic extremes, and constrain its distribution. Temperature and desiccation resistance in insects are both conditioned by acclimation and may be interconnected, particularly for species inhabiting xeric environments. We determined the effect of temperature acclimation on desiccation resistance of the peach fruit fly (Bactrocera zonata, Tephritidae) – an invasive, polyphagous pest, currently spreading through both xeric and mesic environments in Africa and the Eurasian continent. Following acclimation at three constant temperatures (20, 25, and 30°C), the survival of adult flies deprived of food and water was monitored in extreme dry and humid conditions (<10 and >90% relative humidity, respectively). We found that flies acclimated at higher temperatures were significantly heavier, and contained more lipids and protein. Acclimation temperature significantly and similarly affected the survival of males and females at both high and low humidity conditions. In both cases, flies maintained at 30°C survived longer compared to 20 and 25°C – habituated counterparts. Regardless of the effect of acclimation temperature on survival, overall life expectancy was significantly shortened when flies were assayed under desiccating conditions. Additionally, our experiments indicate no significant difference in survival patterns between males and females, and that acclimation temperature had similar effects after both short (5–10 days) and long (11–20 days) acclimation periods. We conclude that acclimation at 30°C prolongs the survival of B. zonata, regardless of ambient humidity levels. Temperature probably affected survival through modulating feeding and metabolism, allowing for accumulation of larger energetic reserves, which in turn, promoted a greater ability to resist starvation, and possibly desiccation as well. Our study set the grounds for understanding the phenotypic plasticity of B. zonata from the hydric perspective, and for further evaluating the invasion potential of this pest.

Vasopressin and oxytocin expression in hypothalamic supraoptic nucleus and plasma electrolytes changes in water-deprived male Meriones libycus

ABSTRACT In mammals, plasmatic osmolality needs to be stable, and it is highly related to the hydric state of the animals which depends on the activity of the hypothalamic neurohypophysial system and more particularly by vasopressin secretion. Meriones, a desert rodent, can survive even without drinking for more than one month. The mechanism(s) by which they survive under these conditions remains poorly understood. In this study, we examine the water’s deprivation consequences on the: (1) anatomy, morphology, and physiology of the hypothalamic supraoptic nucleus, (2) body mass and plasma electrolytes changes in male desert rodents ‘Meriones libycus’ subjected to water deprivation for 30 days. The effect of water deprivation was evaluated on the structural and cellular organization of the supraoptic nucleus by morphological observations and immunohistochemical approaches, allowing the labeling of AVP but also oxytocin. Our finding demonstrated that upon water deprivation (1) the body weight decreased and reached a plateau after a month of water restriction. (2) The plasmatic osmolality began to decrease and return to values similar to control animals at day 30. (3) The SON, both in hydrated and water-deprived animals, is highly developed.(4) The AVP labeling in the SON increased upon dehydration at variance with OT. These changes observed in body mass and plasma osmolality reveal an important adaptive process of male Meriones in response to prolonged water deprivation. Overall, this animal represents an interesting model for the study of water body homeostasis and the mechanisms underlying the survival of desert rodents to xeric environments.

Maqui (Aristotelia chilensis [Mol.] Stuntz) morphological and phenolic traits associated with forests type and latitudinal gradient in natural populations of Patagonia Argentina

Maqui (Aristotelia chilensis [Mol.] Stuntz) is a native berry of the Patagonia Andean forests, which has one of the highest antioxidant levels currently known. This biochemical characteristic strongly depends on the phenolic profile and is highly influenced by the growing environment. The objective of this study was to characterize natural maqui populations in the immediate lee (Argentina) of the Northern Patagonian Andes, distributed in a latitudinal gradient and associated with coihue (Nothofagus dombeyi) and cypress (Austrocedrus chilensis) forests, humid and xeric environments, respectively. Twenty-five natural populations that spanned the geographical distribution of the species in Argentina, were identified. The sites were associated with two forests (coihue and cypress) and three latitudinal groups (north, center and south). Canopy cover and light interception were measured in the selected sites, as well as plant morphology, fruit yield components, phenolic profiles and oxygen radical absorbance capacity (ORAC) of mature berries. Maqui populations associated to cypress are exposed to greater incident total solar radiation and lesser rainfalls, and showed shorter plants with several main stems, multiple branching and smaller specific leaf area (SLA) as compared to those of coihue forest. Maqui populations associated to coihue presented an increase in the number of berries per bunch, and also in the accumulation of phenols and ORAC. The evaluation of the acclimation responses of the natural populations by different environments can contribute to the development of high-yield and quality maqui crops as source of bioactive compounds.

Responses to Salinity in Four Plantago Species from Tunisia.

The genus Plantago is particularly interesting for studying the mechanisms of salt tolerance in plants, as it includes both halophytes and glycophytes, as well as species adapted to xeric environments. In this study, the salt stress responses of two halophytes, P. crassifolia and P. coronopus, were compared with those of two glycophytes, P. ovata and P. afra. Plants obtained by seed germination of the four species, collected in different regions of Tunisia, were subjected to increasing salinity treatments for one month under greenhouse conditions. Morphological traits and biochemical parameters, such as ion accumulation and the leaf contents of photosynthetic pigments, osmolytes, oxidative stress markers and antioxidant metabolites, were measured after the treatments. Salt-induced growth inhibition was more pronounced in P. afra, and only plants subjected to the lowest applied NaCl concentration (200 mM) survived until the end of the treatments. The biochemical responses were different in the two groups of plants; the halophytes accumulated higher Na+ and proline concentrations, whereas MDA levels in their leaves decreased, indicating a lower level of oxidative stress. Overall, the results showed that P. coronopus and P. crassifolia are the most tolerant to salt stress, and P. afra is the most susceptible of the four species. Plantago ovata is also quite resistant, apparently by using specific mechanisms of tolerance that are more efficient than in the halophytes, such as a less pronounced inhibition of photosynthesis, the accumulation of higher levels of Cl− ions in the leaves, or the activation of K+ uptake and transport to the aerial part under high salinity conditions.

PHYSICAL AND CHEMICAL DEFENSES OF Cenostigma pyramidale (FABACEAE): A PIONEER SPECIES IN SUCCESSIONAL CAATINGA AREAS

ABSTRACT Cenostigma pyramidale, a pioneer species presents in all different successional stage (early, intermediate and late) of fifteen natural regeneration areas of Caatinga after land used changed and abandonment was used to investigates the morphological and physiological attributes that are very important to xeromorphic conditions as against herbivories. Leaf samples were collected to evaluate the percentage of the herbivory and index of sclerophylly. Anatomy, histochemistry, total phenolic content, epicuticular wax load, and n-alkanes profile were also performed. The results showed an inverse relationship between the percentage of herbivory and the index of sclerophylly. The leaves showed typical morphological and anatomical characteristics of xeric environments plants such as uniseriate epidermis and trichomes. Furthermore, it was also noticed a decrease in the overall thickness and the tissues according to the advancement of the successional stages. The histochemical revealed the presence of lipidic substances coating the epidermal layers, phenolics compounds stored in secretory structures, and starch in the mesophyll. The concentration of phenolics compounds indicating the difference from health leaves of plants between different stages of regeneration, but no difference when they were herbivored. The amount of cuticle wax did not change significantly with the successional stage. The profile of n-alkanes was characterized by the predominance of nonacosane (C29) and hentriacontane (C31). The C29 content decreases with the advancement of the successional stage, while the C31 content increases. All those attributes have a role to protect the plants to acclimate to the various environmental conditions of Caatinga.