Long-term coordinated morphological and hydrological traits of desert mosses in an arid temperate desert.

BACKGROUND AND AMIS: The adaptive plasticity of xerophytic vegetation in response to hydrological fluctuations serves as a critical determinant of ecosystem stability in arid regions. However, it is still unclear how mosses respond to long-term changes in water availability. METHODS: We investigated Bryum argenteum, Didymodon vinealis and Syntrichia caninervis, which have sequentially colonized an arid revegetated area of the Tengger Desert (northern China). The study focused on altered above-ground morphological, physiological and hydrological traits at different periods of restoration (35, 41 and 66 years) of artificial sand-fixing vegetation. RESULTS: Bryum argenteum had the smallest shoot size, biomass, PSII quantum efficiency (Fv/Fm), non-structural carbohydrate (NSC) content and the highest population density. In contrast, D. vinealis and S. caninervis exhibited larger shoot size, greater biomass, higher Fv/Fm and NSC content but lower population densities. Moreover, for B. argenteum and D. vinealis, there was a trade-off between water absorption and retention. Bryum argenteum had the slowest water absorption and lowest dehydration rate, whereas D. vinealis exhibited greater water absorption and a faster dehydration rate. Syntrichia caninervis, however, had both high water absorption and a slow dehydration rate, which may have been facilitated by its awns. CONCLUSIONS: Our findings revealed that the succession of moss species in a restored desert followed three sequential adaptive trajectory shifts: from species with small shoot sizes, prioritizing high-density colonization and conservative hydrological functions (low water absorption and strong water retention capacities), to those with larger shoot sizes, prioritizing low-density colonization and competitive hydrological functions (high water absorption and rapid dehydration), and finally to species with even larger shoot sizes, featuring morphological innovations (awns) that have excellent water-holding capacity (awn-mediated absorption-retention synergy). This study demonstrated that moss species can progressively optimize their adaptive strategies under prolonged ecological restoration.