Genera of Scrophulariaceae in the páramos of the Venezuelan Andes

A report on the family Scrophulariaceae in the páramos of the Venezuelan Andes is made, which includes 13 genera. A key to the genera is provided.     

Ordination and classification of vegetation along an altitudinal gradient in the Venezuelan páramos

By means of ordination and classification techniques, the relationships between climate, soils, human activities and vegetation along an altitudinal gradient of the Venezuelan páramos are analyzed and interpreted. The altitudinal gradient chosen is characterized by decrease of temperature, precipitation, soil fertility, soil water-holding capacity, and plant cover as altitude increases. The ordination results suggest vegetation changes to be primarily related to environmental changes occurring with altitude, and secondly to disturbances caused mainly by grazing. Some results point toward a disjunction in the vegetational gradient occurring at ca. 3 500 m.a.s.l. and separating low and high páramo. This disjunction might have been caused by the glacial history of the páramos and the occurrence of frequent night-frosts.The soil samples were kindly analyzed by the Laboratorio de Edafologia, Centro Nacional de Investigaciones Agropecuarias. Help in plant identification was generously obtained from the specialists of Instituto Botánico, Instituto Nacional de Parques, Caracas.Nomenclature follows Vareschi (1970).Acknowledgements: This work was supported by the Decanato de Investigaciones, Universidad Simón Bolivar. I wish to thank A. Pacheco for help in the field sampling. Dr O. Arenas help was invaluable in the mathematical treatment of the data. Drs A. Vivas and J. M. B. Smith provided useful criticism to an earlier version of this work.     

Plant functional diversity in tropical Andean páramos

ABSTRACT

Background: Tropical high mountains present extreme daily temperature variations, frequent high air evaporative demands and seasonal differences in soil water availability. Plants have adapted to these conditions through different avoidance-tolerance mechanisms. This review focuses on plant-growth forms and their adaptive strategies.

Aims: This integrated review of páramo plant traits aims at contributing to understanding the functioning of plant-growth forms and their significance on ecosystem properties under environmental climate and land-use changes.

Methods: Plant responses are presented along avoidance-tolerance gradients considering three main aspects: freezing resistance, water relations and gas exchange characteristics. Results from 45 herbaceous and 42 woody species along elevational gradients in the Venezuelan high Andes were analysed.

Results: Leaf supercooling is the common avoidance response of woody plants to night-time freezing temperatures, while herbaceous plants tolerate frost. Trees and caulescent rosettes maintain more positive leaf water potentials under water deficit conditions compared to more tolerant herbaceous species. All plant growth-forms showed strong stomatal control under dry-season conditions.

Conclusions: Páramo plant growth-forms may be separated according to an avoidance-tolerance gradient in response to water deficit and low temperature resistance. Woody growth-forms tend to avoid both freezing and water stress, while herbaceous forms tolerate frost and resist an unfavourable water status. Grasses and cushion plants are at the tolerant extreme of the gradient and coincide in that both reach the highest elevations in the páramo. Andean giant rosettes are freezing avoidant, particularly susceptible to water deficit and the most vulnerable, of all growth-forms, to changing environmental conditions.     

Can soil temperature direct the composition of high arctic plant communities?

Abstract. Low temperatures exert a primary constraint on the growth of high arctic vascular plants. However, investigations into the impact of temperature on high arctic plants rarely separate out the role of air and soil temperatures, and few data exist to indicate whether soil temperatures alone can significantly influence the growth of high arctic vascular plants in a manner that might direct community composition. We examined the response of high arctic plants of three functional types (grasses, sedges/rushes and non‐graminoids) to manipulated soil temperature under common air temperature conditions. Target plants, within intact soil cores, were placed in water baths at a range of temperatures between 4.9 and 15.3 °C for one growing season. Grasses responded most rapidly to increased soil temperature, with increased total live plant mass, above‐ground live mass and total below‐ground live mass, with non‐graminoids having the lowest, and sedges/rushes an intermediate degree of response. The ratio of above‐ground live mass to total live mass increased in all growth forms. Grasses, in particular, responded to enhanced soil temperatures by increasing shoot size rather than shoot number. In all growth forms the mass of root tissue beneath the moss layer increased significantly and to a similar extent with increasing soil temperature. These results clearly indicate that different growth forms, although collected from the same plant community, respond differently to changes in soil temperature. As a consequence, factors influencing soil temperature in high arctic ecosystems, such as global climate change or herbivory (which leads to reduced moss depth and increased soil temperatures), may also direct changes in vascular plant community composition.     

The influence of waste pits on species composition and structure of raised bogs’ plant communities in the Middle Ob area

The technologically altered structure of raised bogs plant communities adjacent to the waste pits of the largest oil fields in the Middle Ob (middle taiga subzone) is considered. A list of vascular plants is detected; mosses are the dominant species.     

A new species of Elatine (Elatinaceae) from the Colombian páramos in the northern Andes

Elatine paramoana, a new species from the high Andean region of the Cordillera Oriental in Colombia, is described, illustrated, and compared to its nearest relatives,E. ecuadoriensis andE. fassettiana. Notes on morphological variation and general ecology and a key to the central and northern Andes species are also given.     

The composition and structure of rotiferan and crustacean communities of the lower rio nhamundá, amazonas,Brazil

The crustaceans and rotifers of 17 samples from the plankton and 3 from the littoral from lakes of the lower Rio Nhamundá, an affluent of the Amazon were studied.

145 taxa of rotifers and 46 of crustaceans were found; two rotifers and three crustaceans are new to science: Keratella americana nhamundaiensis, Euchlanis triquetra var. nhamudaiensis, Echinisca superaculeata, E. sioli, and E. mira. In the taxonomical part 24 rotiferan and 22 crustacean taxa are described in more detail, drawings of them given, and partly remarks made about the geographical distribution.

In the biocenotical part the conditions of dominances were studied: Brachionus zahniseri and Keratella americana within the rotifers and Bosminopsis deitersi and Oithona amazonica within the crustaceans are the dominant species in the pelagial. In the littorial Synchaeta stylata and Stre‐blocerus pygmaeus were found to be dominant.

The species diversity and also the evenness is higher within the rotifers than in the crustaceans. By means of an index of similarity dendrograms were drawn where groups of lakes can be differentiated by using the similarity between the crustaceans. The proportion of neotropical species in relation to pantropical and cosmopolitical species is lowest in the rotifers, higher in the cladocerans and highest in the copepods at 100%.     

First report on generalized pollination systems in Melastomataceae for the Andean páramos

Melastomataceae is a megadiverse family with records of transitions from specialized to generalized pollination systems for several species. These transitions are associated with the colonization of new, unpredictable and/or impoverished pollinator habitats or habitats where specialized pollinators are scarce (e.g., in highland environments). The bee species diversity is low in highlands. Therefore, autonomous breeding systems such as apomixis and self-pollination emerge in these environments. In this paper, we studied the floral traits associated with the generalization of pollination systems and registered the floral visitors of two species in the Colombian Andes: Miconia cataractae and M. elaeoides. We investigated the breeding system of M. elaeoides. Both species presented small flowers, short anthers of medium pore size, and nectar-producing stomata on the base of the anthers. Miconia cataractae produced an average of 1.62 μl nectar/flower, a sugar concentration of 6.78%, whereas M. elaeoides produced 0.09 μl nectar/flower, a sugar concentration of 6.13%. We recorded a wide diversity of pollinators for both species, mainly insects from the orders Hymenoptera and Diptera. Miconia elaeoides presented a mixed breeding system and was also capable of setting fruits by apomixis. We conclude that flower and anther morphology, combined with nectar production, thus represent convergent traits resulting in a generalist pollination system shared by M. cataractae and M. elaeoides. Here, we presented the first generalist pollination system recorded for Miconia (and the Melastomataceae) in the Andes, the first report for a species from the small-pored section Amblyarrhena, and the first report for a species from the large-pored section Cremanium in Colombia.     

Altitudinal distribution,diversity and endemicity of Carabidae (Coleoptera) in the páramos of Ecuadorian Andes

Species richness and diversity of Carabidae (Coleoptera), as well as rates of endemicity, are studied along altitudinal transects in the páramo of Ecuadorian Andes, from 3500 to 5000 m. Whereas a global tendency to reduction of species richness is evident from 4200 m upwards, two zones of high diversity and high proportion of endemic species occur at 3800–4000 m and at 4200–4400 m. Species turnover between grass páramo and superpáramo is significantly higher in drier mountains, especially in the Western Cordillera, than in humid mountains of the Eastern Cordillera. The altitudinal range of Carabid species tends globally to decrease along the vertical gradient, but with important local variations due to microenvironmental factors, especially humidity rate. When compared with recent phytogeographical studies, these results tend to support the idea that the majority of tussockgrass páramo is a secondary anthropogenic ecosystem. On the contrary, it is argued that the xeric landscape of the Chimborazo “arenal” is primordial, based on the presence of a stenotopic and possibly relict species, Pelmatellus andium Bates 1891.     

Three new species of Lysipomia (Lobeliaceae) endemic to the páramos of southern Ecuador

Three species of Lysipomia, L. caespitosa, L. cylindrocarpa, and L. speciosa, from a tropical alpine ecosystem called páramo, are described, illustrated, and compared to related species. Notes on morphology, especially floral presentation, and general ecology are given where possible. A published key to the species in Ecuador is revised to include the three new species plus L. multiflora McVaugh, a species previously known only from northern Peru.     

Light participates in the auxin‐dependent regulation of plant growth

Light is the energy source for plant photosynthesis and influences plant growth and development. Through multiple photoreceptors, plant interprets light signals through various downstream phytohormones such as auxin. Recently, Chen et al. (2020) uncover a new layer of regulation in IPyA pathway of auxin biosynthesis by light. Here we highlight recent studies about how light controls plant growth through regulating auxin biosynthesis and signaling.     

Habitat variability of the Littorelletea uniflorae plant communities in Polish Lobelia lakes

Research was carried out to determine aquatic oligochaete habitat preferences in the Rokytná River (Thaya River basin), a sixth order highland stream in the Czech Republic during the period of April 1999–April 2001. Quantitative samples were collected and current velocity and basic physico-chemical variables were measured monthly in four typical habitats in the Rokytná River. During this study, 28, 842 individuals representing 44 oligochaete species or higher taxa were collected. Temporal variability of proportional occurrence of trophic groups found on selected habitats (gathering collectors and grazers) was analysed. Habitat preferences of oligochaete species were evaluated by Canonical Correspondence Analysis (CANOCO). Biochemical oxygen demand (BOD) and nitrate (NO₃⁻) ion concentration were the most important variables explaining the distribution of Oligochaeta along the first axis. Current velocity (at 40% of the depth) and presence of oligochaetes associated with the habitat where gravel bars never formed were the most important variables along the second axis. Both axes were correlated with the temperature, reflecting the sampling in summer along the first axis and sampling in late spring along the second axis. The amount of organic matter (BOD) and concentrations of NO₃⁻ ions represented both oligochaete food source and decomposition products contributing to the growth of algae. Current velocity and preferred habitat explained the spatial pattern of oligochaete distributions.     

Factorial and ‘self vs. other’ plant soil feedback experiments produce similar predictions of plant growth in communities

Plant and Soil - In species-factorial plant–soil feedback (PSF) experiments plants are grown on replicate soils from each other potential plant in a community. Species-factorial experiments...     

The effects of grazing and burning on soil and plant nutrient concentrations in Colombian páramo grasslands

The impact of extensive livestock farming on the physical and chemical characteristics of the volcanic soils and on the nutrient status of green plant tissues of neotropical alpine grasslands (páramo) is studied. Soil and plant samples were taken over a one-year period at five sites with different agricultural (grazing and burning) management. In the undisturbed páramo ecosystem, soil moisture (50–250%) and organic matter content are high (7–27%) and decomposition (11–35% yr^-1) and element concentrations are low. Low temperatures (max < 10°C) and phosphorus fixation by the soil (5 mg P g^-1 soil) determine the low mineralization and turn-over rates.Multivariate analysis of laboratory results indicates that the season of sampling and the agricultural practice are the most important explanatory factors for variation of soil characteristics. After long-term heavy grazing, soils have a higher bulk density and a lower moisture content. The outcome of a litterbag experiment confirms the hypothesis of higher decomposition rates at grazed sites. In the intermediate (wet-dry) season, conditions were somewhat better for plant growth but the system remained nutrient limited.Surprisingly, no relation between soil density, moisture or carbon content and concentrations of available nutrients in the soil is found. This is supported by the rather uniform nutrient concentrations in green plant tissue among the sites. It is concluded therefore that the effect of burning and grazing on páramo soils is principally restricted to physical characteristics, and that differences in chemical characteristics of the soil do not cause differences in vegetation structure between grazed, burned and undisturbed sites.The Netherlands Centre for Geo-ecological Research, ICG.     

Canopy occupancy: How much of the space in plant communities is filled?

A major gap in our knowledge of plant communities is how much of their volume is occupied by plant material (stem, leaf or reproductive structure). This is basic knowledge and may be crucial for the concept of competition for space. We sampled two grassland communities and two shrublands in both Italy and New Zealand. The height of the canopy was measured by a point quadrat method, and the volume of plant material, after cutting, by displacement of water. From 0.5% to 2.9% of the canopy was occupied by plant material. Occupancy was lower in the Italian communities, which we tentatively attribute to the climate. It did not differ significantly between grasslands and shrublands. Our data suggest that physical space is probably never limiting by itself in terrestrial higher-plant communities, so that competition for space, distinct from competition for resources such as light, water and nutrients, is not likely to exist.     

Soil fertility alters the nature of plant–resource interactions in invaded grassland communities

Resource competition theory suggests that the nature of diversity–resource–invasibility interactions will vary along fertility gradients, concurrent with changes in the relative availability of limiting above- versus below-ground resources. Experimental support for this contingency is lacking. Here, we manipulated resident diversity, baseline fertility, and the availabilities of light and soil nitrogen in grassland communities invaded by two functionally distinct non-native plant species (Lolium arundinaceum and Melilotus alba). We tested the hypotheses that increased resident diversity reduces community invasibility and dampens the effects of light and soil nitrogen pulses, and that the relative effects of light versus soil nitrogen additions on diversity–invasibility relationships depend on the baseline fertility of the study system. Our results reveal an overall weak negative effect of resident diversity on Lolium performance, but in contrast to our expectations, this diversity effect did not vary with light or soil nitrogen additions or with baseline fertility. However, the relative effects of above- versus below-ground resource additions on invader performance varied with baseline fertility as expected: Lolium responded most strongly to soil nitrogen additions in low-fertility mesocosms and most strongly to increased light availability in high-fertility mesocosms. In contrast to Lolium, nitrogen-fixing Melilotus was overall less responsive to diversity and resource manipulations. Together, these patterns do not lend support for the dependence of diversity–resource–invasibility relationships on either baseline fertility or invasive species identity, but they do highlight the dominant role of resources over diversity in determining invader performance, as well as the manner in which fertility alters the relative importance of above- versus below-ground resource pulses in promoting invasions.     

The more the better? The role of polyploidy in facilitating plant invasions

Background

Biological invasions are a major ecological and socio-economic problem in many parts of the world. Despite an explosion of research in recent decades, much remains to be understood about why some species become invasive whereas others do not. Recently, polyploidy (whole genome duplication) has been proposed as an important determinant of invasiveness in plants. Genome duplication has played a major role in plant evolution and can drastically alter a plant''s genetic make-up, morphology, physiology and ecology within only one or a few generations. This may allow some polyploids to succeed in strongly fluctuating environments and/or effectively colonize new habitats and, thus, increase their potential to be invasive.

Scope

We synthesize current knowledge on the importance of polyploidy for the invasion (i.e. spread) of introduced plants. We first aim to elucidate general mechanisms that are involved in the success of polyploid plants and translate this to that of plant invaders. Secondly, we provide an overview of ploidal levels in selected invasive alien plants and explain how ploidy might have contributed to their success.

Conclusions

Polyploidy can be an important factor in species invasion success through a combination of (1) ‘pre-adaptation’, whereby polyploid lineages are predisposed to conditions in the new range and, therefore, have higher survival rates and fitness in the earliest establishment phase; and (2) the possibility for subsequent adaptation due to a larger genetic diversity that may assist the ‘evolution of invasiveness’. Alternatively, polyploidization may play an important role by (3) restoring sexual reproduction following hybridization or, conversely, (4) asexual reproduction in the absence of suitable mates. We, therefore, encourage invasion biologists to incorporate assessments of ploidy in their studies of invasive alien species.