Plant response to water stress of native and non-native Oenothera drummondii populations

Invasive plants can spread over climatically diverse areas. We explore the effects of drought on gas exchange and water relations on the invasive dune species Oenothera drummondii, using plants from four populations with different rainfall and temperatures regimes. Plant material was obtained germinating plants from one native and three non-native populations in a greenhouse. Drought stress was induced by withholding water. Responses to drought stressed plants were then compared to well-watered controls. Measurements of gas exchange, chlorophyll fluorescence and leaf traits were taken initially and every 10 days after water was withheld, until day 36 when plants were re-watered and recover capacity was measured. The effect of water stress was more evident in F_v/F_m and gas exchange variables. The results suggest that this species possess a mechanism of thermal dissipation of energy. Leaf relative water content was significant lower in drought stressed than control plants. At the end of withholding water period, stressed plants are separated from control plants along the axis I of the ordination analysis evidencing differences in functional traits. All plants recovered well after re-watering. Our results provide evidence for permanent differences in morphological traits and functional responses to drought stress among native and invasive populations of O. drummondii. Although we have only studied four populations, these results may provide evidence for the role of plasticity in contributing to the invasion success of this species.

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.

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 F_v /F_m 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.

Applicability of the MoCA-S test in populations with little education in Colombia

OBJECTIVES

The objectives of this study were to report on the use of the Spanish version of the Montreal Cognitive Assessment (MoCA-S) as cognitive screening tool in a population aged 65 to 74 years in the Andes Mountains of Colombia, assessing the influence of education, and to examine its test-retest reliability.

METHODS

We performed a cross-sectional study of 150 subjects aged 65 to 74 years recruited from older community social centers in Manizales, Colombia. The Leganes Cognitive Test (LCT), a cognitive screening test for populations with low education, was used to exclude those who were likely to have dementia. The associations between the MoCA total score and cognitive domains and education were examined in the total sample and in those likely free of dementia. MoCA-S test-retest reliability was estimated by the intraclass correlation coefficient (ICC) between two measurements taken 7 days apart.

RESULTS

Participants had low levels of formal education (mean years of schooling, 4.8). According to the LCT, the proportion of people screening positive for dementia was 16% (n = 24). The mean MoCA-S scores were 16.1/30 among illiterate subjects, 18.2/30 among those with incomplete primary school, and 20.3/30 among those with complete primary school (p < 0.001). Errors were frequent in the cube and clock drawing, attention-serial subtraction, verbal fluency, and abstraction. Test-retest reliability was high, ICC = 0.86, 95% CI (0.76-0.93).

CONCLUSION

The MoCA-S has high reliability in low-educated older Colombians, but scores were strongly dependent on years of education. Social and cultural factors must be considered when interpreting MoCA-S given the high error rates on items that depend on the ability to read and write and on culture.