Abstract
As an important successional stage and main type of biological soil crusts (BSCs) in Shapotou region of China (southeastern edge of Tengger Desert), lichen soil crusts (LSCs) often suffer from many stresses, such as desiccation and excess light intensity. In this study, the chlorophyll fluorescence and CO2 exchange in the rehydrated LSCs were detected under a series of photosynthetically active radiation (PAR) gradients to study the photosynthetic acclimation of LSCs. The results showed that although desiccation leaded to the loss of photosynthetic activity in LSCs, the fluorescence parameters including Fo, Fv and Fv/Fm of LSCs could be well recovered after rehydration. After the recovery of photosynthetic activity, the effective photosynthetic efficiency ΦPSII detected by Imaging PAM had declined to nearly 0 within both the lichen thallus upper and lower layers when the PAR increased to 200 μE m-2 s-1, however the net photosynthesis detected by the CO2 gas analyzer in the LSCs still appeared when the PAR increased to 1000 μE m-2 s-1. Our results indicate that LSCs acclimating to high PAR, on the one hand is ascribed to the special structure in crust lichens, making the incident light into the lichen thallus be weakened; on the other hand the massive accumulation of photosynthetic pigments in LSCs also provides a protective barrier for the photosynthetic organisms against radiation damage. Furthermore, the excessive light energy absorbed by crust lichens is also possibly dissipated by the increasing non-photochemical quenching, therefore to some extent providing some protection for LSCs.
Highlights
In desert regions, most of vegetation is limited due to the extreme environmental stresses such as drought, UV radiation, salinity, wind and sand-scouring
biological soil crusts (BSCs) gradually develop to the stages of lichen soil crusts (LSCs), in which lichens are dominant many other organisms, such as cyanobacteria, algae, and mosses, co-exist in the crusts [6, 7]
No photosynthetic activity was detected in BSCs when they are in dry state, once water is gained, Harel et al [13] reported cyanobacterial soil crusts would rapidly recover their photosynthetic activity, and energy transfer to photosystem II (PS II) and PS I by the respective antennae was fully established within 10 to 20 min of rehydration
Summary
Most of vegetation is limited due to the extreme environmental stresses such as drought, UV radiation, salinity, wind and sand-scouring. Biological soil crusts (BSCs) can survive those stresses and develop in these regions, because of their unique physiological and ecological characteristics, and even accounting for up to 70% of the living cover in some areas [1, 2]. Crust photosynthetic recovery and acclimation organism such as lichens and mosses emerge after the topsoil is stabilized [3,4,5]. No photosynthetic activity was detected in BSCs when they are in dry state, once water is gained, Harel et al [13] reported cyanobacterial soil crusts would rapidly recover their photosynthetic activity, and energy transfer to PS II and PS I by the respective antennae was fully established within 10 to 20 min of rehydration. The dry lichen photosynthetic apparatus could reconstitute and their photosynthetic activity could recover rapidly [19,20,21]
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