Harsh Abiotic Conditions Research Articles

More sex at higher altitudes: Changes in the frequency of parthenogenesis in oribatid mites in tropical montane rain forests

We investigated changes in density, proportion of parthenogenetic species and individuals, and community structure of oribatid mites (Oribatida, Acari) along an altitudinal gradient in tropical montane rain forests in southern Ecuador. We hypothesized that the proportion of parthenogenetic species and individuals increases whereas density decreases with increasing altitude due to increased harshness of abiotic conditions known to favor parthenogenetic reproduction. In contrast to our hypothesis, the number of parthenogenetic species and individuals decreased toward higher altitudes indicating that changes in environmental conditions with altitude favor sexual rather than parthenogenetic reproduction. Low density of oribatid mites at high altitudes suggest that high frequency and density of sexual species is favored by the availability of resources and not by factors related to harsh abiotic conditions, finding mating partners or tight coupling with parasites or pathogens. Cosmopolitan decomposer taxa tended to be more frequent at higher altitudes indicating that these species are euryoecious. Overall, our data support the view that the reproductive mode of soil animals is predominantly controlled by the availability and accessibility of resources.

Occurrence of Morphological and Anatomical Adaptive Traits in Young and Adult Plants of the Rare Mediterranean Cliff SpeciesPrimula palinuriPetagna

Cliffs worldwide are known to be reservoirs of relict biodiversity. Despite the presence of harsh abiotic conditions, large endemic floras live in such environments. Primula palinuri Petagna is a rare endemic plant species, surviving on cliff sites along a few kilometres of the Tyrrhenian coast in southern Italy. This species is declared at risk of extinction due to human impact on the coastal areas in question. Population surveys have shown that most of the plants are old individuals, while seedlings and plants at early stages of development are rare. We followed the growth of P. palinuri plants from seed germination to the adult phase and analysed the morphoanatomical traits of plants at all stages of development. Our results showed that the pressure of cliff environmental factors has been selected for seasonal habitus and structural adaptive traits in this species. The main morphoanatomical modifications are suberized cell layers and accumulation of phenolic compounds in cell structures. These features are strictly related to regulation of water uptake and storage as well as defence from predation. However, we found them well established only in adult plants and not in juvenile individuals. These findings contribute to explain the rare recruitment of the present relict populations, identifying some of the biological traits which result in species vulnerability.

The multifaceted role of Lon proteolysis in seedling establishment and maintenance of plant organelle function: living from protein destruction

Intracellular selective proteolysis is an important post-translational regulatory mechanism maintaining protein quality control by removing defective, damaged or even deleterious protein aggregates. The ATP-dependent Lon protease is a key component of protein quality control that is highly conserved across the kingdoms of living organisms. Major advancements have been made in bacteria and in non-plant organisms to understand the role of Lon in protection against protein oxidation, ageing and neurodegenerative diseases. This review presents the progress currently made in plants. The Lon gene family in Arabidopsis consists of four members that produce distinct protein isoforms localized in several organelles. Lon1 and Lon4 that potentially originate from a recent gene duplication event are dual-targeted to mitochondria and chloroplasts through distinct mechanisms revealing divergent evolution. Arabidopsis mutant analysis showed that mitochondria and peroxisomes biogenesis or maintenance of function is modulated by Lon1 and Lon2, respectively. Consequently, the lack of Lon selective proteolysis leading to growth retardation and impaired seedling establishment can be attributed to defects in the oil reserve mobilization pathway. The current progress in Arabidopsis research uncovers the role of Lon in the proteome homeostasis of plant organelles and stimulates biotechnology scenarios of plant tolerance against harsh abiotic conditions because of climate instability.

Potential macro-detritivore range expansion into the subarctic stimulates litter decomposition: a new positive feedback mechanism to climate change?

As a result of low decomposition rates, high-latitude ecosystems store large amounts of carbon. Litter decomposition in these ecosystems is constrained by harsh abiotic conditions, but also by the absence of macro-detritivores. We have studied the potential effects of their climate change-driven northward range expansion on the decomposition of two contrasting subarctic litter types. Litter of Alnus incana and Betula pubescens was incubated in microcosms together with monocultures and all possible combinations of three functionally different macro-detritivores (the earthworm Lumbricus rubellus, isopod Oniscus asellus, and millipede Julus scandinavius). Our results show that these macro-detritivores stimulated decomposition, especially of the high-quality A. incana litter and that the macro-detritivores tested differed in their decomposition-stimulating effects, with earthworms having the largest influence. Decomposition processes increased with increasing number of macro-detritivore species, and positive net diveristy effects occurred in several macro-detritivore treatments. However, after correction for macro-detritivore biomass, all interspecific differences in macro-detritivore effects, as well as the positive effects of species number on subarctic litter decomposition disappeared. The net diversity effects also appeared to be driven by variation in biomass, with a possible exception of net diversity effects in mass loss. Based on these results, we conclude that the expected climate change-induced range expansion of macro-detritivores into subarctic regions is likely to result in accelerated decomposition rates. Our results also indicate that the magnitude of macro-detritivore effects on subarctic decomposition will mainly depend on macro-detritivore biomass, rather than on macro-detritivore species number or identity.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-011-2051-8) contains supplementary material, which is available to authorized users.

Community structure, trophic position and reproductive mode of soil and bark-living oribatid mites in an alpine grassland ecosystem

The community structure, stable isotope ratios (15N/14N, 13C/12C) and reproductive mode of oribatid mites (Acari, Oribatida) were investigated in four habitats (upper tree bark, lower tree bark, dry grassland soil, forest soil) at two sites in the Central Alps (Tyrol, Austria). We hypothesized that community structure and trophic position of oribatid mites of dry grassland soils and bark of trees are similar since these habitats have similar abiotic characteristics (open, dry) compared with forest soil. Further, we hypothesized that derived taxa of oribatid mites reproducing sexually dominate on the bark of trees since species in this habitat consume living resources such as lichens. In contrast to our hypothesis, the community structure of oribatid mites differed among grassland, forest and bark indicating the existence of niche differentiation in the respective oribatid mite species. In agreement with our hypothesis, sexually reproducing taxa of oribatid mites dominated on the bark of trees whereas parthenogenetic species were more frequent in soil. Several species of bark-living oribatid mites had stable isotope signatures that were similar to lichens indicating that they feed on lichens. However, nine species that frequently occurred on tree bark did not feed on lichens according to their stable isotope signatures. No oribatid mite species could be ascribed to moss feeding. We conclude that sexual reproduction served as preadaptation for oribatid mites allowing them to exploit new habitats and new resources on the bark of trees. Abiotic factors likely are of limited importance for bark-living oribatid mites since harsh abiotic conditions are assumed to favor parthenogenesis.

Demographic Consequences of the Two Reproductive Modes in Poa alpina L. along a Primary Succession Gradient in the Central Alps

Poa alpina grass plays a predominant role across the entire range of primary succession on alpine glacier forelands. One demographic factor that reacts clearly to changing environmental conditions is reproduction. Using permanent plot data, the complete life cycle of Poa alpina was studied along a successional gradient of the Rotmoos glacier foreland (2300–2400 m a.s.l., Central Alps, Austria) over a period of three years. We used matrix modeling to study the importance of the generation of plantlets and seedlings along the successional gradient and their ability to form adult individuals, and we hypothesized that plantlets develop faster to adults than seedlings because they start already with 3–4 developed leaves.The study showed that plantlet and seedling fecundities of Poa alpina changed differently in the course of succession: seedling establishment was observed over the entire range of the successional stages, whereas plantlet establishment almost vanished with ongoing succession. In the pioneer stage, plantlets were more important than reproduction by seedlings. But we found neither a higher survival rate nor a significant advantage in development to adults for plantlets compared to seedlings. Opportunistic reproduction—plantlets under harsh abiotic conditions, seeds under increasing density—may therefore explain the fact that the species is ubiquitous along the whole glacier foreland.

Is the hyporheic zone a refugium for aquatic macroinvertebrates during severe low flow conditions?

The potential role of the hyporheic zone as a refugium for stream invertebrates during hydrological perturbations was acknowledged more than five decades ago. However, field evidence to support the hyporheic refuge hypothesis during periods of flow recession and severe low flow remains equivocal. Some studies report fauna using the hyporheic zone during periods of flow cessation whilst others have recorded little or no refuge use due to limited habitat availability or harsh abiotic conditions. We assessed aquatic macroinvertebrate community changes associated with severe low flow conditions during a severe supra-seasonal drought on the Little Stour River (UK). Paired benthic and hyporheic samples were collected from four sites (two perennial, two intermittent) on the upper reaches of the river. The number of benthic taxa and the proportion of benthos (particularly the amphipod Gammarus pulex) within the hyporheic zone relative to those in the benthic samples increased significantly during the latter stages of the drought at all sites. These changes coincided with elevated benthic and hyporheic water temperatures rather than a reduction in river discharge alone. The abundance of obligate hypogean macroinvertebrates also increased during the latter stages of the event, suggesting that hypogean taxa may also utilise the shallow hyporheic zone during adverse environmental conditions. Our results, based on paired surface-hyporheic field samples at multiple sites, support the hyporheic refuge hypothesis within a temperate groundwater-dominated stream during severe drought. The results also clearly demonstrate the importance of considering surface-subsurface linkages when assessing responses to disturbance in streams.

The effect of positive interactions on community structure in a multi-species metacommunity model along an environmental gradient

Positive interactions are widely recognized as playing a major role in the organization of community structure and diversity. As such, recent theoretical and empirical works have revealed the significant contribution of positive interactions in shaping species’ geographical distributions, particularly in harsh abiotic conditions. In this report, we explore the joint influence of local dispersal and an environmental gradient on the spatial distribution, structure and function of communities containing positive interactions. While most previous theoretical efforts were limited to modelling the dynamics of single pairs of associated species being mutualist or competitor, here we employ a spatially explicit multi-species metacommunity model covering a rich range of interspecific interactions (mutualism, competition and exploitation) along an environmental gradient. We find that mutualistic interactions dominate in communities with low diversity characterized by limited species dispersal and poor habitat quality. On the other hand, the fraction of mutualistic interactions decreases at the expense of exploitation and competition with the increase in diversity caused by higher dispersal and/or habitat quality. Our multi-species model exemplifies the ubiquitous presence of mutualistic interactions and the role of mutualistic species as facilitators for the further establishment of species during ecosystem assembly. We therefore argue that mutualism is an essential component driving the origination of complex and diverse communities.

Intraspecific differentiation of social behavior and shelter selection in Mesobuthus gibbosus (Brullé, 1832) (Scorpiones: Buthidae)

We compared seasonal shelter selection and social behavior of Mesobuthus gibbosus from autumn to mid-summer in two similar phryganic ecosystems, in continental Greece (near Volos city) and in insular Greece (eastern Crete), and in the laboratory under simulated abiotic conditions. Our results showed that shelter selection is a critical indicator of the seasonal social behavior of the species. The abrupt climatic changes in spring caused a differentiation in shelter selection between the cold period (November–February) and the warm period (March–June) at both sites. Sociality was exhibited only during winter in the field and was more extensive under cold conditions in the laboratory. Co-occurrence of scorpions proved to be age-specific, facilitated by population density and by harsh abiotic conditions during winter, and negatively influenced by intraspecific competition, which was higher in continental Greece. The response of scorpions to changes of abiotic factors reveals synchronization of seasonal shelter selection with climatic changes.

The function of stilt roots in the growth strategy of Socratea exorrhiza (Arecaceae) at two neotropical sites

Arboreal palms have developed a variety of structural root modifications and systems to adapt to the harsh abiotic conditions of tropical rain forests. Stilt roots have been proposed to serve a number of functions including the facilitation of rapid vertical growth to the canopy and enhanced mechanical stability. To examine whether stilt roots provide these functions, we compared stilt root characteristics of the neotropical palm tree Socratea exorrhiza on sloped (>20 degrees) and flat locations at two lowland neotropical sites. S. exorrhiza (n=80 trees) did not demonstrate differences in number of roots, vertical stilt root height, root cone circumference, root cone volume, or location of roots as related to slope. However, we found positive relationships between allocation to vertical growth and stilt root architecture including root cone circumference, number of roots, and root cone volume. Accordingly, stilt roots may allow S. exorrhiza to increase height and maintain mechanical stability without having to concurrently invest in increased stem diameter and underground root structure. This strategy likely increases the species ability to rapidly exploit light gaps as compared to non-stilt root palms and may also enhance survival as mature trees approach the theoretical limits of their mechanical stability.

Temporal Patterns in Rates of Community Change during Succession

While ecological dogma holds that rates of community change decrease over the course of succession, this idea has yet to be tested systematically across a wide variety of successional sequences. Here, I review and define several measures of community change rates for species presence-absence data and test for temporal patterns therein using data acquired from 16 studies comprising 62 successional sequences. Community types include plant secondary and primary succession as well as succession of arthropods on defaunated mangrove islands and carcasses. Rates of species gain generally decline through time, whereas rates of species loss display no systematic temporal trends. As a result, percent community turnover generally declines while species richness increases--both in a decelerating manner. Although communities with relatively minor abiotic and dispersal limitations (e.g., plant secondary successional communities) exhibit rapidly declining rates of change, limitations arising from harsh abiotic conditions or spatial isolation of the community appear to substantially alter temporal patterns in rates of successional change.

Breeding System, Insect Flower Visitation, and Floral Traits of Two Alpine Cerastium Species in Norway

Many alpine/arctic flowering plant species have presumably evolved the ability to self-pollinate as a reproductive assurance mechanism under harsh abiotic environmental conditions that restrict insect flower visitation. We compared self-pollination, pollen limitation, insect flower visitation, and dichogamy of low- and high-elevation populations of Cerastium alpinum, a species in established alpine communities, and Cerastium cerastoides, a pioneer species in disturbed habitats. Cerastium alpinum has large showy flowers, while C. cerastoides has smaller and paler flowers. The temporal separation of pollen release and stigma receptivity within a flower (dichogamy) was smallest in C. cerastoides, which was also more highly self-compatible. No pollen limitation on seed set occurred in any species, possibly due to their high selfing ability. Despite a substantially higher pollinator visitation to C. alpinum compared to C. cerastoides, the latter had the higher seed set. Pollen limitation, autogamy, and pollinator visitation did not differ between altitudes for either species. Differences in habitat and flower size, color, and development between the species are consistent with their different selfing ability.

Precipitation during El Niño correlates with increasing spread of Phragmites australis in New England, USA, coastal marshes

The grass Phragmites australis has historically been restricted to the relatively benign upper border of coastal marshes, but over the past century, and particularly in recent decades, it has been spreading aggressively in New England throughout brackish and salt marshes with high soil salinities that are physiologically stressful to the plant. Here I tested the hypothesis that variations in climatic conditions, particularly increased precipitation during the 1997-98 El Nino event, buffer harsh abiotic conditions and enhance the performance of this nuisance species. I monitored the growth and reproductive output of P. australis in the year before, dur- ing, and after the 1997-98 El Nino in coastal brackish marshes of southern New England, USA. During the El Nino year, P. australis produced on average 30% more shoots, which were 25% taller, and yielded an order of magnitude more inflores- cences than in the other 2 years. Soil porewater salinities were negatively related to precipitation during the 3 years of the study, and the growing season during the El Nino year was one of the wettest of the past century. Consequently, increased precipitation during El Nino may facilitate the spread of less salt-tolerant nuisance and invasive species throughout brackish and salt marshes.

Facilitation of Leymus mollis by Honckenya peploides on coastal dunes in subarctic Quebec, Canada

Plant recruitment in the very first stages of primary succession is limited by seed availability and harsh abiotic conditions. Facilitation, the positive effect of an earlier successional species on a later successional one, is often significant during primary succession and may result from the trapping of seeds and (or) the improvement of seed germination, seedling emergence, establishment, growth, and survival. We examined the effect of mature Honckenya peploides (L.) Ehrh. (Caryophyllaceae) plants on Leymus mollis Trin. (Poaceae) seedling recruitment on a coastal dune in subarctic Quebec, Canada. Facilitative effects of H. peploides on L. mollis may be critical because the latter species is a key element in the dynamics of the coastal dunes at high latitudes in eastern Canada. Honckenya peploides forms small mounds on the upper beach (the embryo dunes) that are typically distinct from the foredune. Leymus mollis progression towards the upper beach occurs through clonal growth, but seedling recruitment is also significant and contributes to the population genetic diversity. We determined L. mollis seedling emergence and growth and estimated various abiotic variables in two habitats on the upper beach: the embryo dunes and the bare, flat areas beside embryo dunes. Sand accumulation and substrate salinity were higher on the embryo dunes than beside them. Leymus mollis seedling emergence was more important on embryo dunes, although seedling growth was lower there. Our results suggest that the embryo dunes formed by H. peploides facilitate L. mollis recruitment possibly by trapping seeds and improving seed germination and seedling emergence.Key words: coastal dunes, facilitation, Honckenya peploides, interspecific interactions, Leymus mollis, sand burial.

Environmental destruction called desertification

Abstract Desert ecosystems are fragile. Arid lands easily deteriorate under modest impact, and the process of human‐induced decrease in their stability is called desertification. Desert ecosystems are characterized by a number of harsh abiotic conditions, such as heat, drought, wind, salt, occasional floods, high‐lime and/or rocky and sandy soil. These combined in various groupings, sometimes with intense animal activity, make for the fragile ecosystems so easily subject to desertification when arid lands are cultivated. When human‐made stresses are further superimposed upon these stresses, results can be devastating because of the additive and synergistic nature of the stresses. Even non‐arid lands are subject to desertification because of mismanagement. Destruction of vegetation can change climate and accompanying soil erosion can create desert conditions. Salinity is a major cause of desertification in irrigated lands. Air pollution is another.