Maria Karatassiou

Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils.

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre‐adapted to serpentine soils.

Changes of the photosynthetic behaviour in annual C3 species at late successional stage under environmental drought conditions.

Differences in structural, physiological, and biochemical features between C3 and C4 species resulted in different wateruse efficiencies and different adaptations to climate. This paper aimed at investigating, at a late successional stage, the water-use efficiency of two forage species, Dichanthium ischaemum and Dasypyrum villosum, which exhibit different growth forms (perenial, annual) and photosynthetic mechanisms (C4 and C3, respectively). The annual C3 species Avena fatua, at an early successional stage, was included in our experiments to contrast its behaviour against D. villosum. The experiment was conducted during the growing season in low-elevation grasslands of North Greece. Midday leaf water potential, net photosynthetic rate, transpiration rate and stomatal conductance were measured. Instantaneous water-use efficiency (WUE) and intrinsic water-use efficiency (WUEi) were calculated in D. ischaemum, D. villosum, and A. fatua. The results suggest that, under natural rainfall conditions, the annual C3 grass species D. villosum exhibits a similar WUE with higher values of WUEi than the perennial C4 species D. ischaemum at late stage of succession on the low elevation Mediterranean grasslands. Moreover, A. fatua at an early successional stage, exhibited different photosynthetic behaviour than D. villosum at a late successional stage. These findings indicate that the annual C3 species D. villosum under drought and at a late successional stage seems to modify the WUE obtaining values similar to those of C4 species. The extent to which the ecophysiological characteristics of D. villosum are environmentally or intrinsically determined remains to be answered.

Effect of selenium on mineral content and nutritive value of Melilotus officinalis L.

Plants of Melilotus officinalis L. were subjected to two different treatments: a) no selenium (Se), and b) addition of 3 mg Se L−1 irrigation water for 45 days and samples of leaves, stems and roots were analyzed for Se, potassium (K), sodium (Na), magnesium (Mg), iron (Fe), copper (Cu), calcium (Ca), manganese (Mn) and zinc (Zn). Crude protein (CP) content, neutral detergent fiber (NDF), acid detergent fiber (ADF) and in vitro organic matter digestibility (IVOMD) were also estimated for the aerial plant tissues. In Se-treated plants Se mainly accumulated in leaf tissues, various changes in macronutrient concentrations were detected, while the micronutrient content decreased significantly. In addition, leaf CP, NDF and ADF content decreased, while IVOMD increased, possibly indicating ameliorated nutritive value. According to our findings, M. officinalis could be used either as a dietary supplement, in mixture with non-accumulator species, for livestock feed deficient in Se or for restoration of grasslands in seleniferous soils.

Lotus corniculatus L. response to carbon dioxide concentration and radiation level variations

Carbon dioxide concentration and light conditions may greatly vary between mountainous and lowland areas determining the photosynthetic performance of plants species. This paper aimed to evaluate the photosynthetic responses of Lotus corniculatus, growing in a mountain and a lowland grassland, under low and high radiation and CO2 concentration. Net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration were measured while the water-use efficiency and the ratio of variable to maximal fluorescence were calculated. Photosynthetic response curves to different levels of radiation and intercellular CO2 partial pressure were estimated. Our results showed that high radiation and CO2 concentration enhanced water-use efficiency of plants at both sites, enabling them to use more efficiently the available water reserves under drought conditions. The increase of radiation and CO2 concentration would enhance the photosynthetic performance of the mountainous population of L. corniculatus, which overall seems to express higher phenotypic plasticity.

Comparative investigation of physiological responses of field-grown alfalfa and tall fescue to cutting under different water regimes

An important consideration in designing and managing forage systems is the knowledge of the physiological response mechanisms to cutting, especially when water deficit conditions are prevailing. The objective of this study was to determine the physiological response of Medicago sativa and Festuca arundinacea to cutting under different water regimes in a semi-arid Mediterranean region. In a field experiment, two cutting intensities were applied under irrigation and under rainfed (water deficit) conditions. Water potential, transpiration rate and stomatal conductance were measured. Based on the results, M. sativa showed higher transpirational water losses under rainfed conditions when compared to those of F. arundinacea, regardless of cutting treatment, because of the higher stomatal conductance. However, leaf water potential remained higher in M. sativa, suggesting a more effective root, stem or leaf related water uptake system. In addition, under water deficit, stomata of M. sativa were less sensitive to low values of water potential, probably resulting in higher productivity when compared to F. arundinacea. Cutting resulted in higher stomatal conductance and, therefore, higher transpiration in both species. Moreover, under water deficit, cutting positively affected water potential, especially in F. arundinacea, alleviating the effect of ageing.