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

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.

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.

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.

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.