Haloxylon ammodendron Adapts to Desert Environments through Seed Polymorphism during Diaspore Germination and Seedling Establishment

Ziyi Wang ¹ Weizhi Chen ¹ Minghao Yang ² Lamei Jiang ^2,3 Ze Wang ⁴ Cai Ren ^2,3* Xianhua Zhang ^1*

• ¹ College of Grassland Science, Xinjiang Agricultural University, Urumqi, China
• ² College of Life Sciences, Xinjiang Agricultural University, Urumqi, China
• ³ Xinjiang Key Laboratory for Ecological Adaptation and Evolution of Extreme Environment Biology, College of Life Sciences, Xinjiang Agricultural University, Urumqi, China
• ⁴ College of Resources and Environment, Xinjiang Agricultural University, Urumqi, China

Seed polymorphism, i.e., the production of two or more types of diaspores with distinct morphology and ecological function in a species, is a bet-hedging strategy of plants to cope with unpredictable spatiotemporally changing environments. Previous studies have mainly focused on annual plants; therefore, little is known about seed polymorphism in perennial plants, particularly in desert constructive species. In this study, we found that Haloxylon ammodendron (a desert constructive shrub which plays an irreplaceable and crucial role in maintaining the fragile desert ecosystem) showed seed polymorphism that was widely present in natural populations within our investigation area. With different plants producing three differently colored diaspores, which we classified as YY (yellow fruit-wing perianth and yellow pericarp), YP (yellow fruit-wing perianth and pink pericarp), and PP (pink fruit-wing perianth and pink pericarp). The polymorphic diaspores differed significantly in terms of morphology, physiology, and behavior. The fruit/diaspore biomass and gibberellic/abscisic acid concentration ratios were the lowest in YY (0.611 and 0.64, respectively) and the highest in YP (0.684 and 1.56). YY plants are more drought-resistant and produces a small amount of robust seedlings to ensure population persistence. YP seeds have a higher germination percentage, germination rate, and emergence percentage, allowing rapid population expansion in a suitable environment. PP seeds mitigate the negative effects of salt stress by having a lower germination percentage and can potentially serve as a seed bank. These results indicate that H. ammodendron employs seed polymorphism to adapt to the unpredictable desert environment during diaspore germination and seedling establishment. This study provides a theoretical basis for investigating the bionomic strategies species employ to adapt to extreme environments, aiming to achieve seedling establishment, maintain population renewal and continuity, and offer diversified germplasm resources for desertification prevention.