Diego E. Gurvich

Germination Characteristics of Four Argentinean Endemic Gymnocalycium (Cactaceae) Species With Different Flowering Phenologies

Abstract We analyzed germination percentages and germination rates at four temperature treatments (5/15, 10/20, 15/25 and 20/35 °C) and in light or darkness in four endemic species of the genus Gymnocalycium with different flowering phenologies from the Córdoba Mountains (Argentina). Gymnocalycium bruchii flowered and dispersed its seeds very early in the season in comparison to the other three species. No seeds germinated in darkness or at the coldest temperature regime. For all species except G. bruchii, germination was higher at the two warmest treatments. Gymnocalycium bruchii germination was maximum at the second warmest temperature (15/25 °C) and did not germinate at all at the highest temperature treatment (20/35 °C). Germination varied strongly among species, from about 80% in G. quehliaum to 20% in G. monvillei. Germination rate (t50) varied more strongly among temperature treatments (from 15 to 7 days in the coldest and warmest treatments respectively) than among species. The lack of germination of G. bruchii at 20–35 °C could be related to its early flowering phenology.

Seed mass, germination and seedling traits for some central Argentinian cacti

Seed size is one of the most important traits in the regenerative phase of a plant’s life cycle; however, for cactus species the relationship of seed size and germination characteristics and seedling traits is still unclear. We studied the relationship between seed mass and germination and seedling characteristics in 17 cactus species from central Argentina, belonging to different genera and life forms. We measured seed mass, total seed germination, light requirements for germination and mean time to germination for these 17 cacti species; in addition, we recorded seedling size and shape in 15 species. To test light requirements we performed germination experiments under laboratory conditions at 25/158C (day/night temperatures) and under light or dark conditions. We also calculated seedling volume by measuring seedling height and width. A shape index was obtained by dividing height by width (a value of 1 indicates ‘globose’ seedlings, whereas, as this value increases, seedlings become ‘columnar’). We found no significant relationship between seed mass and any of the germination characteristics considered. However, species with heavier seeds produced bigger seedlings, which were more cylindrical. Adult growth was not totally determined by seedling ‘growth form’, because some species that had globose seedlings were columnar at the adult stage.

Tree morphology in seasonally dry montane forest in Argentina: Relationships with shade tolerance and nutrient shortage

Abstract Question: How does form (leaf and trunk morphology) relate to function (tolerance of shade and nutrient storage) in trees? Location: Los Toldos montane valley in NW Argentina. Methods: We analysed the relationships amongst (1) ten vegetative and four reproductive traits across 40 tree species, (2) a distribution based measure of recruitment under shade and (3) a distribution based measure of recruitment over a soil fertility gradient. Results: Ordinations revealed three main axes of species morphological differentiation: (1) evergreen species had leaves with a lower specific leaf area, greater tensile resistance and slower decomposition rate, denser wood and thinner bark than deciduous species; (2) tall tree species that lack spines and are anemochorous were separated from short, spinescent and zoochorous species and (3) species were distinguished according to clonal growth, seed mass and pollination syndromes. Notably, species recruitment under shade and over a soil fertility gradient were independent of each other, but both were correlated with species scores along the first axis of morphological variation (tolerant species have attributes that favour resource conservation). Different sets of traits were correlated with recruitment under shade and over a soil fertility gradient when traits where assessed individually. Amongst shade tolerant species, recruitment under shade was negatively correlated with species maximum height, suggesting differential responses to vertical gradients of light. Conclusions: These results provide new evidence of integration between leaf and stem morphology which is consistent with an evolutionary compromise between high rate of resource acquisition and resource conservation. Generalizations about the functional value of individual morphological characteristics and of ‘strategies’ vary with the resolution of analyses. Nomenclature: Zuloaga & Morrone (1999) for species; Anon. (2003) for families and orders.

Flowering phenology, fruit set and seed mass and number of five coexisting Gymnocalycium (Cactaceae) species from Córdoba mountain, Argentina1

Abstract Flowering phenology may play a critical role in plant coexistence, allowing not only a temporal partitioning of resources but also conditioning the relationship between seed mass and number in these species. We analyzed how flowering phenology was related to seed mass and number, and how these seed traits were related in five coexisting Gymnocalycium (Cactaceae) species in two consecutive flowering seasons. The flowering phenology of each species was characterized in terms of timing (onset and peak), duration, and flowering synchronicity. Although species showed differences in duration and synchronicity, the earliest flowering species tend to have higher reproductive success than species flowering later. However, we did not find a clear relationship between the flowering time and seed traits. A trade-off between seed mass and number in these species was highlighted, as species with higher seed mass were those producing a lower number of seeds per fruit and individual, whereas species with lower seed mass had a higher number of seeds. Our results showed a temporal resource partitioning associated with differences in flowering timing among species, which may lead to differences in reproductive success (number of mature fruits and fruit set) and highlight the importance of the trade-off between colonization vs competitive ability in promoting plant coexistence.

Response to Vergara et al. (2015)—Fruiting phenology as a “triggering attribute” of invasion process: Do invasive species take advantage of seed dispersal service provided by native birds?

In a recent article, Vergara et al. (2015) present the results of a study aimed at testing our triggering attribute model (TA, Gurvich et al. 2005) in a woodland ecosystem in central Argentina. To that end, they compared the bird assemblage that consumes fruits of three woody species, a native tree (Celtis ehrenbergiana) and two congeneric invasive shrubs (Pyracantha angustifolia and P. coccinea). C. ehrenbergiana disperses its fruit in summer, P. angustifolia does so in winter, and P. coccinea shows some overlap in the dispersal period with the native tree [see Fig. 2 in Vergara et al. (2015)]. The authors predicted that, according to the TA approach, the diversity and abundance of frugivorous birds, and their fruit consumption, should be greater for P. angustifolia than for the other two species. They found no difference among the three species and conclude that the TA theory is not at play in the system. While the study provides valuable insight into the frugivorous bird assemblage, we disagree on the main conclusion, in particular regarding the logic behind the testing of the TA approach. According to Gurvich et al. (2005), a TA is defined as a vegetative or regenerative attribute of an exotic species that is discontinuously distributed in comparison to those of the resident community. This attribute allows the exotic species to benefit from a resource that is permanently or temporarily unused by the resident community, triggering its spread over the landscape. The winter fruit phenology of two fleshyfruited invaders (P. angustifolia and Ligustrum lucidum) was proposed as an example of TA that would allow these two species to take advantage of a resource (bird dispersal) that resident fleshy-fruited species—whose fruits are ripe in summer and autumn—cannot tap during the winter. Therefore, the empirical prediction under the TA model is that P. angustifolia should show dispersal rates similar to those of the dominant fleshy-fruited resident of the invaded system. Indeed, the data provided by Vergara et al. (2015) support this prediction, showing that P. angustifolia has the same assemblage of bird dispersers as C. ehrenbergiana, but operating during a different seasonal period. Unlike what Vergara et al. (2015) have done, to test whether P. coccinea benefits from bird dispersal (compared to native fleshy-fruited species) would require the assessment of bird assemblages in both the coupled and uncoupled dispersal periods [see Fig. 2 in Vergara et al. (2015)]. The release from bird predators in the overlapping period is quite interesting and remains to be tested in the unfavorable (cold) season. However, we agree with the authors that dispersal would probably not be the TA that underlies the success of P. coccinea in the D. E. Gurvich (&) P. A. Tecco S. Dı́az Instituto Multidisciplinario de Biologı́a Vegetal (FCEFyN, CONICET-UNC), Av. Vélez Sarsfield 1611, CC495, CP5000, Córdoba, Argentina e-mail: degurvich@gmail.com