Background and aims: There are currently no microsatellite markers available for any American species of Vachellia, and particularly, for V. aroma. Then the aims of this study were to develop SSR ...markers specific for V. aroma, for the first time, and test its amplification in a close related species. M&M: For the development of the SSR in V. aroma, total genomic DNA was extracted and it was sequenced in a one-fourth run on a Roche 454 GS FLX+ platform. The study area included two Argentinean populations: San José and Robles, Santiago del Estero province. Results: We detected 422 sequences containing SSR loci. A set of 39 primer pairs presented amplified products in V. aroma and V. caven, but 12 revealed clear, replicable and polymorphic loci in V. aroma. Conclusions: The results of this work indicate that a new set of SSR markers was developed for V. aroma and their transferability to V. caven was assessed. The analysis of variability, showed that these 12 polymorphic markers are highly informative, and a powerful tool to investigate population genetics parameters in V. aroma and related species.
Based on the niche conservatism hypothesis, i.e. the idea that niches remain unchanged over space and time, climatic niche modelling (CNM) is a useful tool for predicting the spread of introduced ...taxa. Recent advances have extended such predictions deeper in time for plant species dispersed by humans before the modern era. The latest CNMs successfully evaluate niche differentiation and estimate potential source areas for intriguing taxa such as archaeophytes (i.e., species introduced before 1492 AD). Here, we performed CNMs for Acacia caven, a common Fabaceae tree in South America, considered an archaeophyte west of the Andes, in Central Chile. Accounting for the infraspecific delimitation of the species, our results showed that even when climates are different, climatic spaces used by the species overlap largely between the eastern and western ranges. Despite slight variation, results were consistent when considering one, two, or even three-environmental dimensions, and in accordance with the niche conservatism hypothesis. Specific distribution models calibrated for each region (east vs west) and projected to the past, indicate a common area of occupancy available in southern Bolivia-northwest Argentina since the late Pleistocene, which could have acted as a source-area, and this signal becomes stronger through the Holocene. Then, in accordance with a taxon introduced in the past, and comparing regional vs continental distribution models calibrated at the infraspecific or species level, the western populations showed their spread status to be mostly in equilibrium with the environment. Our study thus indicates how niche and species distribution models are useful to improve our knowledge related to taxa introduced before the modern era.
Excessive copper concentrations affect nutrient uptake in sensible species. However, the effects of copper on nutrient uptake in tolerant species have not been studied equally well. Thus, the main ...objective of this study was to determine the effect of rising Cu exposure on nutrient uptake rates and root/shoot nutrient contents in two species with distinct copper tolerance:
Acacia caven
(Mol.) Mol. and
Helianthus annuus
L. To this end, a hydroponic experiment was conducted. Copper treatments were applied at concentrations of 0, 2.0, 3.9, 7.9, and 15.7 μM. Relative root elongation was chosen as the endpoint for Cu toxicity assessment. The results of our study demonstrate that
A. caven
and
H. annuus
differ greatly in their tolerance to Cu. Copper concentration in the solution associated with the calculated EC
25
was found to be six times higher in
A. caven
(15 μM) than in
H. annuus
(2.3 μM). When effective concentrations were instead based on the measured root Cu concentrations, the difference observed was ten times greater (1044 and 98 mg/kg for
A. caven
and
H. annuus
, respectively). Both species showed equal Cu uptake kinetics, with root absorbing power (α) of 7.5 ± 0.7 × 10
–6
and 7.8 ± 0.5 × 10
–6
cm s
–1
for
A. caven
and
H. annuus
, respectively. Rising Cu concentrations in the exposure solution progressively diminished the influx of Ca into the roots of
H. annuus
, whereas no significant effect was noted for
A. caven
.
Woody encroachment in savannas represents an ecological process of current global interest given its negative impact on ecosystem functioning, particularly on forage production. Traditional savanna ...models propose competition and niche differentiation as the main mechanisms allowing tree-grass coexistence. Demographic models, instead, propose abiotic and biotic factors as bottlenecks controlling vital rates and transitions from seeds to adult trees. The role played by domestic grazing on woody encroachment is yet controversial. Here, using a multistage tree life approach, we combine both models and evaluate the role of grazing and herbaceous vegetation on woody recruitment in a Neotropical savanna dominated by Vachellia caven, a successful and widely spread encroacher tree species. We performed three experiments to evaluate seed predation, seedling emergence and survival of V. caven by manipulating cattle grazing (grazed and ungrazed areas) and herbaceous vegetation presence (vegetated and unvegetated). Finally, we combined the results of the three experiments to estimate the probability of plant recruitment across these experimental factors. Grazing decreased seed predation by half, did not modify seedling emergence and decreased seedling survival. Herbaceous vegetation did not affect seed predation nor seedling emergence rate, but increased seedling survival. Overall, the net effect of grazing on V. caven recruitment was neutral since the increase in seed availability due to the reduction in seed predation rate was compensated by the negative effect of grazing on seedling survival. Our analysis revealed that cattle grazing and herbaceous vegetation had contrasting effects on the seed and seedling life stages. We propose that in order to restrain the early stages of encroachment, cattle grazing pressure could be managed following the seasonality of demographic tree transitions. Through rotational grazing amongst paddocks, stocking rates could be relaxed during the primary dispersal stage to maximize granivory, and then increased to enhance the chance of seedling consumption and trampling.
Display omitted
•Woody encroachment drivers change whit the encroacher's life stage.•Cattle increased seed availability by a negative effect on seed predation rate.•Cattle decreased seedling survival through consumption and trampling.•Woody encroachment could be limited through rotational grazing amongst paddocks.
Importance of nurse plants structuring plant communities is well‐appreciated at local scales, yet the effect of a single nurse on large scales has been neglected in analyses. So far, studies only use ...environmental gradients within one type of ecosystem and tend to generalize the nurse effects.
To assess how the effect of a single nurse species is modulated by different environmental settings, interactions between the shrub Vachellia caven and the surrounding plant communities were evaluated at 481 paired plots (outside vs. underneath the plant crown), in 39 sites across two distribution ranges, the Mediterranean west and the mostly subtropical east of the Andes Mountains (covering ca. 2 × 106 km2).
Cover, abundance and richness of perennial plants underneath and outside V. caven were used as response variables to estimate an index indicative of plant interactions (relative interaction index RII) and tested how this was affected by the rainfall gradient and distribution range.
Overall, RII responses to rainfall gradients had low conditional R2 (~0.25) in this large scale of analysis, but were significantly different between ranges: the RII followed a quadratic trend across the rainfall gradient in the western range, while this relationship was positive and close to linear at the eastern range.
Then, by projecting the RII models (i.e. for abundance, cover and richness) spatially through a consensus map, we show that most positive effects of V. caven are geographically found in dissimilar areas: the central part of Chile (western range) and across the Paraná River (eastern range).
When local fine‐scale predictors (i.e. annual herbs' cover and height, and herbivores' faeces cover) were used to model each response variable at the plot level (underneath or outside V. caven), we observed similar trends as when we considered only the large‐scale predictors.
Synthesis. Here, we show that the effect of the same nurse species on neighbouring plant communities can be very different depending on ranges of distribution, stressing that its ecological function cannot be generalized and not only depends on local factors but also is large‐scale context‐dependent.
Resumen
La importancia de las plantas nodrizas para estructurar las comunidades de plantas es bien conocida a escala local, pero el efecto de una sola nodriza a gran escala no se ha analizado. Hasta la actualidad, los estudios solo han usado gradientes ambientales dentro de un tipo de ecosistema y tienden a generalizar los efectos de las nodrizas.
Para evaluar cómo el efecto de una misma especie nodriza es modulado por diferentes factores ambientales, se analizaron las interacciones entre el arbusto Vachellia caven y las comunidades de plantas circundantes en 481 contrastes pareados (fuera vs debajo de la copa de la planta), en 39 sitios a lo largo de dos rangos de distribución: al oeste de los Andes (clima Mediterráneo), y al este de las montañas (clima principalmente subtropical), cubriendo entre ambos aprox. 2 × 106 km2.
Se usó la cobertura, abundancia y riqueza de las especies de plantas perennes creciendo debajo y fuera de V. caven como variables respuesta para estimar un indicador de la interacción planta‐planta, el índice de interacción relativa (RII), siendo este último modelado en función del gradiente de lluvia y el rango de distribución.
En general, las respuestas del RII al gradiente de lluvia tuvieron un R2 condicional bajo (~0.25) a esta gran escala de análisis, pero fueron significativamente diferentes entre rangos: el RII mostró una tendencia cuadrática a lo largo del gradiente de lluvia en el rango occidental, mientras que esta relación fue positiva y cercana a lineal en el rango oriental de la cordillera.
Luego, al proyectar espacialmente los modelos RII (es decir, estimados con abundancia, cobertura o riqueza) a través de un mapa de consenso, se halló que la mayoría de los efectos positivos de V. caven se encuentran geográficamente en áreas disímiles: la parte central de Chile (rango occidental) y a través del río Paraná (rango oriental).
Cuando se modelaron las variables respuesta en función de predictores a escala fina (i.e., cobertura y altura de hierbas anuales, y cobertura de fechas de herbívoros) para cada a tipo de condición (debajo o fuera de V. caven), se mantuvieron tendencias similares a las halladas con solo predictores a gran escala.
Síntesis: El efecto de una misma especie nodriza en las comunidades de plantas vecinas pueden ser muy diferentes dependiendo de los rangos de distribución, enfatizando que su función ecológica no se puede generalizar y que esta no solo depende de factores locales sino también es dependiente de un contexto a gran escala.
The effect of a single key shrub that acts as a nurse species is dependent on its distribution range. The co‐inhabiting plant communities and the environment of the distribution range, exemplified in this study through the rainfall gradients, shape the final effect of the shrub. Image generated using Dall‐E AI, by Nicolás Velasco and Cristina Soto‐Agurto.
•Shadier conditions were observed in the invaded than native woodlands.•Emergence was similar but seedling survival tended to be lower in invaded woodlands.•Success of the exotic species was equal or ...lower than native species.•Lower light quantity was related with a reduction in the growth of seedlings.•C. ehrenbergiana seems to be the most suitable species to start restoration.
Nowadays forests, which were formerly considered resistant to invasion due to its shady understories, are been transformed to invaded landscapes. Thus, the aim of this study was to evaluate the regeneration of native woody species in Ligustrum lucidum invaded woodlands. In addition, we aim to identify the main environmental differences between the native and invaded woodlands and evaluate the effect of those conditions in the regeneration phase of dominant native woody species. Finally, we analyze how is the emergence and survival of the exotic species in relation to that exhibited by native species in both environmental situations. For this, we performed a seed addition experiment placing three native woody species (Celtis ehrenbergiana, Lithraea molleoides, Vachellia caven) and the dominant exotic (L. lucidum) in native and invaded woodlands of the Chaco mountains, central Argentina. Also, we performed a laboratory experiment simulating the differences in light recorded at the field (main abiotic difference between both woodland types). Our field experiment indicated that, if seeds are actively added, the percentage of seedlings emergence of native species could be similar in invaded and native woodlands. However, we observed a trend of lower seedling survival after winter within the exotic monospecific stands, which was significant only for the native species C. ehrenbergiana. We suggest that this constraint could be partly related to the shadier conditions imposed by L. lucidum, since this is the major environmental change within the invaded woodlands in comparison with native ones. Consistently, the experimental simulation showed that the increased in shade reduced the overall growth of seedlings. As was mostly observed in temperate biome, our study in a subtropical seasonally dry region indicates that invaded areas may not affect the emergence stage but limit the survival of seedlings. Among the native species, C. ehrenbergiana seems to be the most suitable species to start restoration, showing the highest performance throughout the year. Combined actions of seed addition and canopy opening might counteract the abiotic constraint and contribute to restoration success of this invaded landscape.
Determination of soil volumetric water content θ in forest ecosystems is particularly challenging due to deep rooting systems and unknown soil vertical and spatial heterogeneity. This research aims ...to test two undisturbed methods, electrical resistivity tomography (ERT) and HYDRUS 2D/3D, for 2D θ determination in a thorny forest ecosystem. The experiment consisted of infiltrating 10 L of water lasting 60 min. During infiltration, ERT measured apparent resistivity by time‐lapse measurements, and θ was measured with an FDR probe (EnviroSCAN) at 33, 63, 83, 97, and 163 cm depth close to the infiltration site. At the end of infiltration, a soil pit was dug, and 100 measurements of θ were performed with a TDR in a 10 × 10 cm regular grid. Archie law transformed soil resistivity (ERT) into θ using manual calibration, verified by an independent dataset. The 2D θ profile obtained by ERT was qualitatively compared with the HYDRUS 2D/3D one. HYDRUS 2D/3D was parametrized with calibrated parameters obtained with HYDRUS 1D using 106 days of θ obtained with EnviroSCAN. The results of HYDRUS 1D calibration and verification were satisfactory, with RMSE and Nash‐Sutcliffe coefficients ranging from 0.021 to 0.034 cm3 cm−3 and 0.11 to 0.77, respectively. The forward HYDRUS 2D/3D θ simulation disagrees with EnviroSCAN data for 33 cm depth. However, it follows the trend with near to zero variation of water content at 63 cm depth. Water content determination by ERT was satisfactory with RMSE for calibration and verification of 0.017 and 0.021 cm3 cm−3. HYDRUS 2D/3D and ERT comparisons were not equal, with a shallower wetting front by ERT and a deeper one for HYDRUS. Still, both wetting fronts agree with the wetting depth estimated by EnviroSCAN. We conclude that both methods are an alternative for θ determination in heterogeneous and deep soils of forest ecosystems.
A detailed dataset is used for the calibration of HYDRUS 1D and set up HYDRUS 2D/3D
The Water content θ can be satisfactorily determined using Electrical Resistivity Tomography (ERT).
Comparison of ERT and HYDRUS 2D/3D partially match the wetting front.
Urbanisation is one of the main drivers of insect species loss worldwide. However, its impacts on ecological interactions involving insects still deserve further research, especially seed predation ...and parasitism of seed predators.
Here, we evaluated the seed predation rate by the specialist bruchid beetle Pseudopachymerina spinipes and its parasitism rate in the native tree Vachellia caven (Fabaceae) along an urbanisation gradient in Cordoba (Argentina). Since resource availability can influence these ecological interactions, we also investigated whether seed and prey availability could affect seed predation and parasitism rates, respectively.
We sampled trees in 10 sampling sites along an urbanisation gradient estimated by the Normalised Difference Vegetation Index (NDVI) within a 100 m radius. In our system, sites with low NDVI, beyond representing the low amount of vegetation cover, also indicate high surface temperature and low availability of host trees.
Seed predation in V. caven and the parasitism rate of P. spinipes were significantly reduced with increasing urbanisation. Notably, seed availability at the pod level did not affect seed predation rate, while prey availability was negatively correlated with parasitism rate.
These findings suggest a deleterious effect of urbanisation on the studied antagonistic interactions, giving no support to the idea of resource limitation effects.
We evaluated how urbanisation degree and resource availability per pod affect the seed predation rate of a native Fabaceae tree by a specialist bruchid beetle and its parasitism rate. Seed predation rate and parasitism rate significantly decreased with increasing urbanisation. Seed number per pod did not affect seed predation, but prey availability negatively influenced the parasitism rate. Our results suggest a deleterious effect of urbanisation on the studied antagonistic interactions, giving no support to the idea of resource limitation effects.
•A cellular automata model synthetizes the transition from the Chilean evergreen forest to savanna.•The patch-size distribution of the forest provides a leading indicator of the transition.•The ...indicator of the transition suggests a robust criticality before the collapse of the forest.•Indicators of transition can support livestock management in forest landscapes.
Semi-desert areas are sensitive to changes in rainfall and agricultural pressure, prone to abrupt changes and to the collapse of ecological functions. The sclerophyllous evergreen forest of central Chile, known as matorral, has been extensively overgrazed by domestic livestock. As a consequence, the native and endemic species of this forest community have been replaced by a savanna-type environment dominated by the species Acacia caven, known as espinales. It has been hypothesized that the collapse of matorral forest can be abrupt, and the two ecosystems represent two alternative stable states. To understand the ecological dynamics that occur during this transition, their signature in space, and the consequences of livestock management, a cellular automata model that considers the local interaction among forest vegetation, Acacia, and livestock management was developed. By simulating and analyzing the process of fragmentation in space and time, in a gradient of livestock pressure and aridity, the results show that the system exhibits properties of "robust criticality", with a shift of patch-size distributions from models matching power-laws to models matching truncated power-laws as livestock pressure increases nearby the point of collapse. Simulation results in scenarios with rotation of livestock at the tipping point reveal the interaction between resting frequency and forest conservation. These results provide information to design better management strategies in human-modified landscapes in the remaining Chilean matorral.
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