Abstract
Chlorophyll-containing oxygenic photoautotrophs have been well known to play a fundamental role in the development of biological soil crusts (BSCs) by harvesting solar radiations and providing fixed carbon to the BSCs ecosystems. Although the same functions can be theoretically fulfilled by the widespread bacteriochlorophyll-harboring aerobic anoxygenic phototrophic bacteria (AAnPB), whether AAnPB play a role in the formation of BSCs and how important they are to this process remain largely unknown. To address these questions, we set up a microcosm system with surface sands of the Hopq desert in northern China and observed the significant effects of near-infrared illumination on the development of BSCs. Compared to near-infrared or red light alone, the combined use of near-infrared and red lights for illumination greatly increased the thickness of BSCs, their organic matter contents and the microalgae abundance by 24.0, 103.7, and 1447.6%, respectively. These changes were attributed to the increasing abundance of AAnPB that can absorb near-infrared radiations. Our data suggest that AAnPB is a long-overlooked driver in promoting the development of BSCs in drylands.
Highlights
Global drylands cover about 41% of the Earth’s terrestrial surface with arid, semiarid and dry subhumid areas (Feng and Fu, 2013)
We took advantage of the different light absorption properties in chlorophyll-containing photoautotrophs and bacteriochlorophyll a (BChl a)-containing aerobic anoxygenic phototrophic bacteria (AAnPB) (Kolber et al, 2001) and set up a microcosm system provided with different light conditions (Red vs. NIR vs. Red + NIR)
The system did not fully mimic the environmental factors in desert, e.g., hard light, wind blow, drought stress and diurnal temperature variations, we did observe the strong effects exerted by NIR on the development of biological soil crusts (BSCs), which could be attributed to the activities of microbial seeds in BSCs
Summary
Global drylands cover about 41% of the Earth’s terrestrial surface with arid, semiarid and dry subhumid areas (Feng and Fu, 2013). These regions are expanding on an appreciable scale, due to climate changes, deterioration in water supplies and land degradation (Hallenbeck, 2017). BSCs can help in maintaining soil fertility and reducing erosion, and play a vital role in global carbon (Elbert et al, 2012; Porada et al, 2013, 2014) and nitrogen cycling (Belnap, 2003). BSCs consist of cyanobacteria, eukaryotic microalgae, microfungi, lichens, bryophytes and heterotrophic bacteria, among which phototrophs play a crucial role in the development of BSCs (Belnap et al, 2016). Cyanobacteria are one of the key players in the development of BSCs, as they can enhance soil nutrition content through fixation of atmospheric carbon and nitrogen and by secretion of polysaccharide that can condense sand
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