Abstract: Mosses are poikilohydric plants. The duration of leaf spreading time is a key factor affecting their growth and development in the field. The dynamics of field growth and development and influencing factors of mosses in arid and semi-arid areas are largely unknown. In the study, we examined leaf spreading situation under natural conditions from September 5th to November 25th for Didymodon vinealis and Barbula unguiculata, two common species in hilly Loess Plateau. The results showed that the leaves of both species showed a regular diurnal dynamic change of ‘spreading-closing-spreading’ from September to October, and that the average leaf closing time of D. vinealis in the morning was 0.68 hours earlier than that of B. unguiculata, while leaf spreading time was delayed by 1.79 hours in the afternoon. Both species spread their leaves for longer time in the rainy season. The average leaf spreading duration of D. vinealis was 251 min, which was 30.4% lower than B. unguiculata of 361 min. The relative humidity near the surface was the key factor affecting leaf spreading duration. The morphological structure of moss species would affect leaf spreading duration. Compared with D. vinealis, B. unguiculata was relatively short, with a large proportion of costa in leaves, and the mosaic structure of stem cortex cells was more prominent. The humidity threshold during leaf spreading of B. unguiculata (54.3%) was lower than that of D. vinealis (60.1%). The leaf spreading duration was mainly affected by humidity. B. unguiculata was more adaptable to the environment than D. vinealis.

Key words: Pottiaceae, morphological structure, leaf spreading duration, humidity, moss crust