Composition of photosynthetic organisms and diurnal changes of photosynthetic efficiency in algae and moss crusts

In Dalateqi region of Inner Mongolia (at eastern edge of Qubqi Desert), man-made algae crusts were constructed with two filamentous cyanobacteria. Two to three years later, the algae crusts began to succeed to moss crusts under some microterrain conditions. In order to characterize the community structure and compare the photosynthetic characteristics in different successional stages of biological soil crusts (BSCs). This paper studied composition of photosynthetic organisms and diurnal changes of photosynthetic efficiency, with microscopic observation and chlorophyll fluorescence monitoring techniques. Compared with the early successional algae crusts, later moss crusts had a higher photosynthetic efficiency, which was closely related with the different community structure of photosynthetic organisms. Further, moss crusts had a higher total photosynthetic biomass, although the algal biomass decreased along the successional sequence. Similar to higher vascular plants, a midday depression of photosynthetic efficiency was detected in BSCs, although the depression extents were different in different successional stages. Analysis demonstrated the depression was mainly caused by non-stomata limitations, and photosynthetically active radiation (PAR) was a significant influencing factor in the down-regulation of photosynthetic efficiency. We conclude, cyanobacterial inoculation effectively promotes the formation, development and seccession of BSCs. Furthermore, the later successional BSCs have a better photosynthetic performance and thus are expected to play a more effective role in desertification control.