Factors controlling germination and dormancy processes in dimorphic fruits of Atriplex inflata (Chenopodiaceae)

Background and aims – Seed dimorphism is an adaptive feature to harsh environments such as arid and saline habitats. This is explained as an escape from inadequate conditions. In the current study, we investigated the seed germination of a dimorphic species Atriplex inflata Muell. (Chenopodiaceae). A. inflata occurs in saline habitats, namely in arid regions. Its bracteoles enclose a brown or a black fruit. This unit constitutes the diaspore. Methods – Mature fruits were collected from Kelbia (35°46'06"N 10°07'34"E), located in the centre of Tunisia, with semi-arid climate. The effect of cold stratification, nitrate (KNO 3, 10 mM), light, dry storage (for seven months), chemical scarification and salt pretreatment on germination were determined in order to assess the factors that control germination and dormancy. Key results – The results show that brown fruits germinated rapidly and the final germination percentage was 98% after twenty days. However, germination of black fruits was slower and reached only 19%. This confirms the fact that the difference in morphology is accompanied by a difference in germination capacity and dormancy in A. inflata. Chemical scarification and dry storage increased germination capacity of black fruits. Thus, the black fruit showed a physical dormancy and a non-deep physiological dormancy. Conclusion – The production of two types of fruit in A. inflata, one dormant and the other non-dormant, is of high ecological importance for the survival of populations. Actually, this ensures both rapid germination (brown fruits) and a permanent seed bank (black fruits), which permit the persistence of the species and population establishment in disturbed environments

The mericarp of the halophyte Crithmum maritimum (Apiaceae): Structural features, germination, and salt distribution

At maturation and during seed fall and dispersal, halophyte seeds may be subjected to invasion by salt ions. How these seeds remain viable in such hostile environments is however still unclear, depending for instance on the species and the family. In the Apiaceae, the mericarp (fruit) shows a wide range of morphological and anatomical modifications, many of which may enhance the adaptation to severe environmental conditions. Therefore, structural features, ion accumulation, and long-term floating capacity were investigated in the fruit (mericarp) of the halophyte Crithmum maritimum L. The mericarp was composed of a spongy outer coat, a secretory envelope, a thin endocarp reduced to a unicellular layer delimiting the endosperm, and an embryo. Both of the secretory canals and the endocarp adhered after complete ripening of the mericarp, while the epicarp and much of the mesocarp formed the spongy coat. Assessing long-term floating ability of the fruit under laboratory conditions revealed that even after 60 d, more than 98% of C. maritimum L. mericarps still floated over seawater. Seed germination was delayed and reduced by the spongy coat. The X-ray microanalysis revealed that the spongy coat and the secretory canals contained essentially Cl and Na, while seeds, i.e. endosperm and embryo, accumulated mostly Mg, K and P. In a subsequent experiment designed to simulate salt leaching by rain, most of the salt accumulated in the spongy coat and seeds was released after 2 h imbibition in distilled water. Taken together, these results highlight the protective role of the mericarp and the likely involvement of this structure in the seed dispersal of C. maritimum L. This may ultimately have eco-physiological implications explaining the successful establishment of this halophyte in its native saline biotopes

Effects of two composts and two grasses on microbial biomass and biological activity in a salt-affected soil

The effectiveness of compost supply at several doses (0, 50, 100, and 150 t/ha) to a saline soil was studied using municipal solid waste (MSW) and palm waste (PW) composts. The experiment was carried out in pots under cultivation of Polypogon monspeliensis (halophyte forage species) and Hordeum vulgare (common forage species) and lasted three months. The investigation focused on some selected soil physico-chemical properties, soil microbial biomass, and ten soil enzymatic activities; Arylsulfatase (ARY), dehydrogenase (DEH), β-glycosidase (β-GLU), protease (PRO), urease (URE), invertase (INV), Fluorescein diacetate hydrolase (FDAH), catalase (CAT), acid and alkaline phosphatases (PHO). Both amendments improve markedly the saline soil quality. They ameliorate the physico-chemical properties. The increase of soil pH is regarded as an interesting fact and is usually proportional to the compost application rate. Electrical conductivity increased proportionally to the applied rates. Soil carbon and nitrogen amounts were also improved and the highest raise (7.5-folds) was noted for carbon. According to the substantial increase of the organic matter, levels of measured microbial biomass and several enzyme activities in saline soil were improved. DEH activity which proposed as a measure of overall microbial activity exhibited a significant increase only at dose 2 (100 t/ha). Consequently, One hundred tones of composts per hectare, under which some enzymes exhibited an optimal of activity and metal accumulation can be minimized, appeared an interesting rate for saline soil amendment