Mari Paz Esquivias

Gender-specific costs of reproduction on vegetative growth and physiological performance in the dioecious shrub Corema album

BACKGROUND AND AIMS Reproductive costs imply trade-offs in resource distribution at the physiological level, expressed as changes in future growth and/or reproduction. In dioecious species, females generally endure higher reproductive effort, although this is not necessarily expressed through higher somatic costs, as compensatory mechanisms may foster resource uptake during reproduction. METHODS To assess effects of reproductive allocation on vegetative growth and physiological response in terms of costs and compensation mechanisms, a manipulative experiment of inflorescence bud removal was carried out in the sexually dimorphic species Corema album. Over two consecutive growing seasons, vegetative growth patterns, water status and photochemical efficiency were measured to evaluate gender-related differences. KEY RESULTS Suppression of reproductive allocation resulted in a direct reduction in somatic costs of reproduction, expressed through changes in growth variables and plant physiological status. Inflorescence bud removal was related to an increase in shoot elongation and water potential in male and female plants. The response to inflorescence bud removal showed gender-related differences that were related to the moment of maximum reproductive effort in each sexual form: flowering in males and fruiting in females. Delayed costs of reproduction were found in both water status and growth variables, showing gender-related differences in resource storage and use. CONCLUSIONS Results are consistent with the existence of a trade-off between reproductive and vegetative biomass, indicating that reproduction and growth depend on the same resource pool. Gender-related morphological and physiological differences arise as a response to different reproductive resource requirements. Delayed somatic costs provide evidence of gender-related differences in resource allocation and storage. Adaptive differences between genders in C. album may arise through the development of mechanisms which compensate for the cost of reproduction.

Physiological performance and xylem water isotopic composition underlie gender-specific responses in the dioecious shrub Corema album

Gender-specific requirements of reproduction in dioecious species can lead to different physiological responses in male and female plants, made in relation to environmental constraints, and influencing growth, survival and population structure. Gender-related physiological differences and seasonal responses, indicating the existence of compensatory mechanisms of reproduction, were examined during a drought year in the dioecious shrub species Corema album. To integrate aboveground and belowground physiological responses, chlorophyll fluorescence, leaf gas exchange, water potential and xylem water isotopic composition were monitored throughout the diurnal cycle and annual phenological sequence of the species. Sampling was carried out in Doñana Natural Park (SW Spain) in Mediterranean-type climate conditions. The gender which bore greater reproductive effort showed higher physiological stress. Intersexual differences in leaf water potential were interpreted as arising from each genders maximum reproductive allocation; lower values were found during flowering in males and during fruit production in females. Cold temperatures during winter fostered photoinhibitory responses that were most evident in male individuals, as a response to their relatively higher investment in reproduction during flowering. Net assimilation rate was not influenced by reproductive status; however, females tended to show higher values of this parameter at midday. The integrated analysis of photosynthetic variables and water relations indicated a gender effect in the physiological response at midday. The oxygen isotopic composition of xylem water showed a lack of dependence on the water table during the drought period, and indicated intersexual differences in water catchment. Females reached deeper soil layers, suggesting mechanisms compensating for their higher reproductive effort, and giving new evidence of physiological gender dimorphism in the belowground responses of a woody species.

How do Mediterranean shrub species cope with shade? Ecophysiological response to different light intensities

Under natural conditions, light exposure for Mediterranean shrubs can be highly variable, especially during cloudy days or under a canopy, and can interfere with other environmental factors such as temperature and water availability. With the aim of decoupling the effect of radiation and temperature from water availability, we conducted an experiment where two perennial and three summer semi-deciduous shrub species were subjected to different levels of irradiation. In order to follow plant responses to light exposure, we measured gas exchange, photosystem II photochemical efficiency, photosynthetic pigments and leaf mass area in spring and summer. Results showed that all study species presented a plastic response to different light conditions, and that light-related traits varied in a coordinated manner. Summer semi-deciduous species exhibited a more opportunistic response, with higher photosynthesis rates in full sun, but under shade conditions, the two strategies presented similar assimilation rates. Stomatal conductance did not show such a drastic response as photosynthetsis, being related to changes in WUE. Daily cycles of Fv /Fm revealed a slight photoinhibitory response during summer, mainly in perennial species. In all cases photosynthetic pigments adjusted to the radiation level; leaves had lower chlorophyll content, higher pool of xanthophylls and higher proportion of the de-epoxydaded state of xanthophylls under sun conditions. Lutein content increased in relation to the xanthophyll pool under shade conditions. Our results evidenced that radiation is an important driving factor controlling morphological and physiological status of Mediterranean shrub species, independently of water availability. Summer semi-deciduous species exhibit a set of traits with higher response variability, maximising their photosynthetic assimilation under different sun conditions.

Species-specific effects of the invasive Hieracium pilosella in Magellanic steppe grasslands are driven by nitrogen cycle changes

AimsThe principal objective was to evaluate the interference by the invasive species, H. pilosella, on native grassland species at the physiological performance level. We hypothesised that the invasive species is able to alter the nitrogen uptake of native plant species, and can modify community functioning.MethodsThis study was performed under field conditions in the Magellanic Steppe (Argentina). We compared stable isotope signatures, nutrient content and several functional physiological traits in four grassland species with and without H. pilosella interference.ResultsWe found significant interference effects from the invasive species on native species, mostly through changes in nitrogen uptake. The variation in the natural abundance of foliar δ15N suggests that the native plants switched nitrogen sources due to interference with the exotic species. A linear relationship between chlorophyll and proline content that disappears when species are under H. pilosella interference, suggests major changes in the N allocation of native species. Grassland species under interference with exotic species exhibit lower photochemical efficiency and higher water use efficiency. Canonical discriminant analysis evidenced the existence of a different set of functional traits between invasive and native plants, and also among native species with and without H. pilosella interference.ConclusionsOur results support the hypothesis that H. pilosella exerts intense interference with native species through shifting the N sources available for native species, a lower leaf N content, and increasing water stress.

Reliance on deep soil water in the tree species Argania spinosa

In South-western Morocco, water scarcity and high temperature are the main factors determining species survival. Argania spinosa (L.) Skeels is a tree species, endemic to Morocco, which is suffering from ongoing habitat shrinkage. Argan trees play essential local ecological and economic roles: protecting soils from erosion, shading different types of crops, helping maintain soil fertility and, even more importantly, its seeds are used by the local population for oil production, with valuable nutritional, medicinal and cosmetic purposes. The main objective of this study was to identify the sources of water used by this species and to assess the effect of water availability on the photosynthetic rate and stem water potential in two populations: one growing on the coast and a second one 10 km inland. Stem water potential, photosynthetic rate and xylem water isotopic composition (δ18O) were seasonally monitored during 2 years. Trees from both populations showed a similar strategy in the use of the available water sources, which was strongly dependent on deep soil water throughout the year. Nevertheless, during the wet season or under low precipitation a more complex water uptake pattern was found with a mixture of water sources, including precipitation and soil at different depths. No evidence was found of the use of either groundwater or atmospheric water in this species. Despite the similar water-use strategy, the results indicate that Argania trees from the inland population explored deeper layers than coastal ones as suggested by more depleted δ18O values recorded in the inland trees and better photosynthetic performance, hence suggesting that the coastal population of A. spinosa could be subjected to higher stress.

Morpho-physiological response of Retama monosperma to extreme salinity levels

Retama monosperma (L.) Boiss is a coastal shrub growing on sandy soils in the SW of the Iberian Peninsula and in the NW of Morocco. Although a native species, it has been considered to show an invasive behaviour. Tolerance of R. monosperma to salinity -one of the most limiting factors of coastal systems- was assessed as an eventual explanation to its invasive character. A glasshouse experiment, where young plants were irrigated with different NaCl concentrations (5 to 600 mM), was designed. R. monosperma physiological performance was examined by measuring gas exchange, quantum yield, and water potential, at 7, 30 and 60 days after reaching the assigned NaCl concentration. At the end of the experiment, after measuring free proline content in cladodes, plants were harvested, separated in stems, roots and root nodules and weighted and Na + content was measured in roots and cladodes. Although plants survived to high NaCl concentrations, increasing levels of salinity resulted in a progressive reduction in photosynthetic rate, stomatal conductance and water potential, and also in a progressive increase in proline and Na + content. Roots accumulated more Na+ than cladodes in all situations. Biomass allocation pattern was modified by the NaCl levels. The high tolerance of R. monosperma to a continued exposure to salinity could be one of the factors explaining its high expansion rate in coastal areas.