The role of seed appendage in improving the adaptation of a species in definite seasons: a case study of Atriplex centralasiatica

Trade-offs between diaspore dispersal and dormancy within a spike of the invasive annual grass Aegilops tauschii

MAIN CONCLUSION

Differences in dispersal and dormancy of heteromorphic diaspores of Aegilos tauschii may increase its flexibility to invade/occupy weedy unpredictable habitats by spreading risk in space and time. In plant species that produce dimorphic seeds, there often is a negative relationship between dispersal and dormancy, with high dispersal-low dormancy in one morph and low dispersal-high dormancy in the other, which may function as a bet-hedging strategy that spreads the risk of survival and ensures reproductive success. However, the relationship between dispersal and dormancy and its ecological consequences in invasive annual grasses that produce heteromorphic diaspores is not well studied. We compared dispersal and dormancy responses of diaspores from the basal (proximal) to the distal position on compound spikes of Aegilops tauschii, an invasive grass with heteromorphic diaspores. Dispersal ability increased and degree of dormancy decreased as diaspore position on a spike increased from basal to distal. There was a significant positive correlation between length of awns and dispersal ability, and awn removal significantly promoted seed germination. Germination was positively correlated with GA concentration and negatively correlated with ABA concentration, and the ABA: GA ratio was high in seeds with low germination/high dormancy. Thus, there was a continuous inverse-linear relationship between diaspore dispersal ability and degree of dormancy. This negative relationship between diaspore dispersal and degree of dormancy at different positions on a spike of Aegilops tauschii may facilitate seedling survival in space and time.

The environmental adaptation strategy of seed germination, and roles of the seed pappus on dispersal and hypocotyl hairs on seedling anchorage in Tamarix ramosissima

Seed dispersal, germination and seedling establishment are affected by various ecological factors in desert plant species. Tamarix ramosissima has evolved multiple strategies to facilitate its survival in harsh environments during the early stages of development. In this study, we investigated the effects of different ecological factors on seed germination and seedling growth, the function of the seed pappus in seed dispersal, as well as the function of the hypocotyl hairs in seedling establishment. We found that the seed germination of T. ramosissima was rapid and could occur under a wide range of temperatures (5-30 °C), after long periods of storage (at least 12 months on dispersal), under high concentrations of salts (700-900 mmol·L^-1) and polyethylene glycol (PEG) 6000 (500 g·L^-1) and under medium concentrations of alkalis (300-500 mmol·L^-1). Lower concentrations of salts and PEG promoted seedling growth. The seed pappus had no effect on seed germination, but it might function as an accessory structure that provides a buoyancy force and promotes long-distance seed dispersal. The hypocotyl hairs located on the edge of the hypocotyl end might aid the upright positioning of the seedlings during early development, especially when seed germination occurs under floating or flooding conditions. In conclusion, the germination of T. ramosissima seeds and seedling development can occur under diverse types of abiotic stress, and the seed pappus and hypocotyl hairs played an important role in seed dispersal and seedling establishment.

Dormancy and germination of the trimorphic achenes of a cold desert annual: spreading the risk over time

Many studies have been done on the relationship between variation in morphology, dispersal ability and degree of dormancy of heterocarpic species with dimorphic diaspores. However, there are far fewer such studies on species that produce trimorphic diaspores. Our aim was to compare dormancy and germination of achenes from peripheral, intermediate and central positions in the capitulum of the diaspore-trimorphic cold desert annual Asteraceae species Heteracia szovitsii, an important component of plant communities in the cold deserts of NW China. Dormancy breaking/germination responses of the three achene morphs and of seeds isolated from the pericarp were tested in the laboratory using standard procedures, and seedling emergence phenology of the achene morphs was monitored under natural cold desert temperature conditions in an experimental garden with and without supplemental watering. Depth of dormancy of the three achene morphs was peripheral > intermediate > central. Seedlings from the three morphs emerged in spring and in autumn. Cumulative seedling emergence percentage from achenes during 47 months of burial was central > intermediate > peripheral. Central achene morphs emerged over a period of ~12 months after sowing, while intermediate and peripheral achene morphs did so for ~40 and 47 months, respectively. Thus, H. szovitsii exhibits a temporal dispersal strategy. No viable central or intermediate achene morphs were present after 16 and 40 months, respectively, but ~60 % of the non-emerged peripheral achenes morphs were viable after 47 months. Based on our results on diaspore dormancy and those of a previous study of diaspore spatial dispersal of H. szovitsii, we conclude that this species has a high-intermediate-low risk diaspore dispersal/dormancy strategy that likely increases the chances for population persistence over time and space.

Extreme drought alters progeny dispersal unit properties of winter wild oat (Avena sterilis L.)

The dead husk is a vital component of the dispersal unit whose biochemical properties can be modified following exposure to drought. This might affect seed performance and fate, soil properties and consequently plant biodiversity. We investigated the effects of extreme drought on the dispersal unit (DU) properties of winter wild oat (Avena sterilis L.) in the Mediterranean ecosystems focusing on a commonly ignored component of the DU, namely the dead floral bracts (husk). DUs were collected from a climate change experimental research station in the Judean Hills, Israel, simulating extreme drought and from two additional sites differing in the rainfall amounts. Our results showed that drought conditions significantly affected A. sterilis reproductive traits displaying reduced DUs and caryopses weights. The husk contributes profoundly to seed performance showing that germination from the intact DUs or the intact florets 1 was higher, faster and more homogenous compared to naked caryopses; no effect of drought on germination properties was observed. The husk stored hundreds of proteins that retain enzymatic activity and multiple metabolites including phytohormones. Changes in rainfall amounts affected the composition and levels of proteins and other metabolites accumulated in the husk, with a notable effect on abscisic acid (ABA). The husk of both control and drought plants released upon hydration substances that selectively inhibited other species seed germination as well as substances that promoted microbial growth. Our data showed that the dead husk represents a functional component of the DU that have been evolved to nurture the embryo and to ensure its success in its unique habitat. Furthermore, drought conditions can modify husk biochemical properties, which in turn might affect seed performance and fate, soil microbiota and soil fertility and consequently plant species diversity.

Retraction Note to: The role of seed appendage in improving the adaptation of a species in definite seasons: a case study of Atriplex centralasiatica

An amendment to this paper has been published and can be accessed via the original article.