Species traits related to the invasion of woody plants in Patagonian deciduous forests

The comparison of ecological, phenological, morphological and developmental traits between exotic invasive species and coexisting native species contributes to understand the driving mechanisms of successful invasions. This study aimed to examine which of these traits are related to the invasion of woody plants in the understory of deciduous North Patagonian forests of Argentina. We compared the phenology, shoot growth rate, number of leaves, biomass allocation, leaf herbivory, and recruitment type of two exotic deciduous trees, Crataegus monogyna and Sorbus aucuparia, with those of four coexisting native woody species (one deciduous, one semi-deciduous, and two evergreen species). Spring shoot growth took place several weeks earlier in both exotic species and in the deciduous native species than in the other native species; growth rates were higher in the exotics. Compared to coexisting native species, both exotic species developed shoots that were as long as or longer, had lower biomass allocation to leaves and higher allocation to roots, suffered lower leaf damage by herbivores and exhibited higher seed than vegetative recruitment. This study supports the idea that a combination of phenological, growth rate and mass allocation traits allow exotic species to preempt resources, thus favouring invasion processes.

Exploring the response of Marchantia polymorpha: Growth, morphology and chlorophyll content in the presence of anthracene

Polycyclic aromatic hydrocarbons (PAHs) were identified as hazardous contaminants that are ubiquitous and persistent in aquatic environments, where bryophytes sensu lato (mosses, liverworts and hornworts) are frequently present. Marchantia polymorpha (Class Hepaticae; thalloid liverwort) is known to respond fast to changes in the environment; it accumulates toxic substances in its tissues due to the lack of vascular and radicular systems and a reduced or absent cuticle. The objective of the present study was to quantify the effects of increasing concentrations of anthracene (0, 50 100, 280 μM) on the germination of propagules, plant morphology and chlorophyll content index (CCI) in M. polymorpha under in vitro cultures. The results show that anthracene had no statistical effect on germination or propagula formation. However, plants exposed to anthracene for 30 days showed significantly lowered the content of chlorophyll (measured as CCI), irregular growth patterns and the induction of thalli asexual reproduction as evidenced by the production of multicellular viable propagules in gemmae cups. Results of epifluorescence microscopy also showed concomitant accumulation of anthracene in the cell walls. All of these distinctive morphological and physiological adaptive responses indicators, clearly suggest that M. polymorpha are capable of resisting high (coal tar) anthracene concentrations.

Desarrollo de especies leñosas nativas y exóticas en cipresales patagónicos

El crecimiento y la arquitectura de las especies leñosas que habitan los bosques inciden en la dinámica de estas comunidades. El objetivo principal de este estudio fue mejorar la comprensión de la dinámica de los cipresales patagónicos a partir del análisis del crecimiento longitudinal y de la arquitectura de las especies leñosas más abundantes en esas comunidades, las nativas: Aristotelia chilensis, Berberis microphylla, Lomatia hirsuta, Maytenus boaria, Myoschilos oblongum y Schinus patagonicus; y las exóticas: Juniperus communis, Prunus avium, Pseudotsuga menziesii y Rosa rubiginosa. El crecimiento longitudinal del eje principal no se relacionó necesariamente con el aumento en altura de las plantas durante el período de estudio (2012-14). Se registraron decrecimientos en altura en todas las especies excepto en P. menziesii y P. avium, exóticas para Patagonia. La mayoría de los individuos presentaron notables desviaciones de su eje principal de la vertical, las que se correlacionaron negativamente con la longitud del brote distal y con la variación en altura de las plantas. Se agruparon las especies en cuatro grupos funcionales, de acuerdo a su arquitectura y crecimiento. La invasión de los cipresales por parte de especies exóticas como P. menziesii y P. avium, asociadas a grupos funcionales distintos a los de las especies nativas más frecuentes, podría impactar significativamente en la dinámica de esas comunidades promoviendo el reemplazo de las especies nativas por las exóticas dominantes.

Effect of light on the growth and photosynthesis of an invasive shrub in its native range

Invasive species success may depend on ecophysiological attributes present in their native area or derived from changes that took place in the invaded environment. We studied the growth and photosynthetic capacity of Berberis darwinii shrubs growing under different light conditions (gap, forest edge and below the canopy) in their native area of Patagonia, Argentina. Leaf photosynthesis results determined in the native area were discussed in relation to information provided by studies carried out under the same light conditions in an invaded area in New Zealand. Shoot elongation, leaf production, stem and leaf biomass per shoot and specific leaf area (SLA, cm2 g-1) were determined in five adult plants, randomly selected in each of three light conditions in two forest sites. Net photosynthesis as a function of PPFD (Photosynthetic Photon Flux Density), stomatal conductance (gs), maximum light-saturated photosynthesis rate (Pmax), Pmass (on mass bases) and water-use efficiency (WUEi) were determined in plants of one site. We predicted that functional traits would differ between populations of native and invasive ranges. In their native area, plants growing under the canopy produced the longest shoots and had the lowest values for shoot emergence and foliar biomass per shoot, while their SLA was higher than gap and forest edge plants. Leaf number and stem biomass per shoot were independent of light differences. Leaves of gap plants showed higher Pmax, Pmass and gs but lower WUEi than plants growing at the forest edge. In its native range B. darwinii grows under different light conditions by adjusting shoot and leaf morphology and physiology. Plants of B. darwinii growing under the same light conditions show similar physiology in native and invasive ranges. This means that for B. darwinii, intra-specific variation of the functional traits studied here do not condition successful spread in new areas.

Population rules can apply to individual plants and affect their architecture: an evaluation on the cushion plant Mulinum spinosum (Apiaceae)

BACKGROUND AND AIMS

Plants are regarded as populations of modules such as axes and growth units (GUs, i.e. seasonally produced axis segments). Due to their dense arrays of GUs, cushion plants may resemble crowded plant populations in the way the number of components (GUs in plants, individuals in populations) relates to their individual sizes.

METHODOLOGY

The morphological differentiation of GUs and its relationship with biomass accumulation and plant size were studied for the cushion subshrub Mulinum spinosum (Apiaceae), a widespread species in dry areas of Patagonia. In 2009, GUs were sampled from one-quarter of each of 24 adult plants. Within- and between-plant variations in GU length, diameter, number of nodes and biomass were analysed and related to whole-plant size.

PRINCIPAL RESULTS

Each year, an M. spinosum cushion develops flowering GUs and vegetative GUs. Flowering GUs are larger, twice as numerous and contain two to four times more dry mass (excluding reproductive structures) than vegetative GUs. The hemispherical area of the cushions was positively correlated with the biomass of last-year GUs. The biomass of flowering GUs was negatively correlated with the density of GUs. Mulinum spinosum plants exhibited a notable differentiation between flowering and vegetative GUs, but their axes, i.e. the sequences of GUs, were not differentiated throughout the plants. Flowering GUs comprised a major proportion of each plant's photosynthetic tissues.

CONCLUSIONS

A decrease in the size of flowering GUs and in their number relative to the total number of GUs per plant, parallel to an increase in GU density, is predicted as M. spinosum plants age over years. The assimilative role of vegetative GUs is expected to increase in summer because of their less exposed position in the cushion. These GUs would therefore gain more from warm and dry conditions than flowering GUs.

Fruit mineral contents of six wild species of the North Andean Patagonia, Argentina

The fruit mineral contents (K, Ca, Ba, Br, Zn, Co, Cr, Fe, Na, Rb, Cs, and Sr) of four native and two exotic naturalized shrubs growing in different areas of the Andean Patagonian region of Argentina were investigated. Native species Berberis darwinii, Berberis microphylla (Berberidaceae), Aristotelia chilensis (Elaeocarpaceae) and Ribes magellanicum (Saxifragaceae) produce small berries while the fruits of the exotic species Rosa rubiginosa and Rosa canina (Rosaceae) are aggregates of aquenes. They are used to prepare jams, tea, liquors, and ice creams. Native shrub fruits had higher content of Br, Zn, Co, Cr, Fe, Mo, and Na than those of the exotic naturalized species. Rosa species showed the highest contents of Ca and Ba in their fruits (the mean content doubled those of the native plant fruits). The fruit nutrient content found in the studied species was similar or higher than other values reported for fruits of temperate and tropical species in the world.