Advances in the studies of plant diversity and ecological adaptation in the subnival ecosystem of the Qinghai-Tibet Plateau

Abstract

<p indent=0mm>The alpine subnival belt, located at the front of the alpine life zone, very close to the snowline at high elevations, is the highest habitat of all terrestrial ecosystems. Due to various harsh environmental factors, the alpine subnival belt offers the most hostile conditions for the survival, growth and development of plant species. However, due to its highly varied climates, extremely diverse types of microhabitats, and unique corridor or isolation barrier for plant species, the Qinghai-Tibet Plateau (QTP) hosts the richest alpine subnival plant biodiversity in the world; and the driver for speciation, as well as the mechanisms of sustaining plant diversity in the alpine subnival ecosystem in this region are areas of interest for many researchers. Many recent studies have revealed: Highly specialized morphological features, such as large semi-translucent bracts, dense hairy inflorescences, and nodding flowers that appear in various systematically distant plant species, have multifold functions to protect their vegetative and reproductive organs from high intensity UV radiation, low temperatures, and high humidity, therefore improving the survival rate of these plant species in such a hostile environment. Numerous other researches have reported how advantageous reproductive strategies that have evolved in subnival plant species of the QTP, including the hermaphroditism system, dry fruits, delayed germination behavior and persistent seed bank, promote the probability of reproductive success. In addition, some studies have highlighted the critical role of plant-plant interactions, in particular the facilitation of other plant species by keystone species (e.g. <italic>Arenaria polytrichoides</italic>, <italic>Potentilla articulata </italic>with cushion morphology), and unique plant-pollinator interactions between flagship species (e.g. <italic>Rheum nobile</italic> with large semi-translucent bracts covering inflorescence) and insects on the composition and sustainability of plant diversity in the subnival ecosystem of the QTP. On the other hand, as a region extremely sensitive to climate changes, the subnival habitat has experienced great changes in appearance over the past decades. Recent reports have stated that as a result of warmer climates, the expansion of areas for plant migration and colonization has brought increasing species richness in some subnival areas of the QTP (e.g. the Hengduan Mountains, SE QTP). Yet at the same time, by taking advantage of the continuous rise in temperature, many lowland and middle-elevation plant species will be able to invade this cold-edge ecosystem, causing in a great compression in the niche of some typical and/or endemic subnival plant species and finally resulting in a dramatic decrease in the diversity and functions of the subnival ecosystem. Undoubtedly, the findings obtained from numerous studies on all aspects of terrestrial evolution in recent decades have improved our understanding of ecological adaptation and sustainability of plant diversity in the subnival ecosystem of the QTP. In the future, we still need to focus on: (1) Unveiling the adaptive mechanisms of the striking morphological characteristics of subnival plant species from a molecular and/or genome level; (2) exploring how the buffer effects of the safety net produced by keystone species (e.g. cushion plant) influence global warming on the plant diversity of subnival ecosystem; (3) examining the beneficiary feedback effect on benefactor species and changes in the plant-pollinator co-evolutionary interaction, under global warming and human activity disturbance; (4) investigating how species richness, phenological pattern, and the functional traits of subnival plant species respond to global warming; and (5) testing the importance of plant diversity on the functions and evolution of the subnival ecosystem, and the potential influence of plant diversity loss on the stability and integrity of the subnival ecosystem, through field experiments in permanent plots and historical records of plant collections and vegetation surveys.