Abstract
We examined soil surface colour change to green and hydrotaxis following addition of water to biological soil crusts using pigment extraction, hyperspectral imaging, microsensors and 13C labeling experiments coupled to matrix-assisted laser desorption and ionization time of flight-mass spectrometry (MALD-TOF MS). The topsoil colour turned green in less than 5 minutes following water addition. The concentrations of chlorophyll a (Chl a), scytonemin and echinenon rapidly increased in the top <1 mm layer while in the deeper layer, their concentrations remained low. Hyperspectral imaging showed that, in both wet and dehydrated crusts, cyanobacteria formed a layer at a depth of 0.2–0.4 mm and this layer did not move upward after wetting. 13C labeling experiments and MALDI TOF analysis showed that Chl a was already present in the desiccated crusts and de novo synthesis of this molecule started only after 2 days of wetting due to growth of cyanobacteria. Microsensor measurements showed that photosynthetic activity increased concomitantly with the increase of Chl a, and reached a maximum net rate of 92 µmol m−2 h−1 approximately 2 hours after wetting. We conclude that the colour change of soil crusts to green upon water addition was not due to hydrotaxis but rather to the quick recovery and reassembly of pigments. Cyanobacteria in crusts can maintain their photosynthetic apparatus intact even under prolonged periods of desiccation with the ability to resume their photosynthetic activities within minutes after wetting.
Highlights
IntroductionCyanobacteria are ubiquitous in all arid and semi-arid biological soil crusts (referred as crusts hereafter), where they play a vital role in fixing carbon and nitrogen, stabilizing the soil as well as altering the hydrological properties (e.g. water retention) of crust-covered soils [1,2,3,4]
Cyanobacteria are ubiquitous in all arid and semi-arid biological soil crusts, where they play a vital role in fixing carbon and nitrogen, stabilizing the soil as well as altering the hydrological properties of crust-covered soils [1,2,3,4]
The chlorophyll a (Chl a) concentration remained low in the bottom layer, and they slightly increased during the first 10 minutes, this increase could not account for the Chl a increase in the top layer (Fig. 2B)
Summary
Cyanobacteria are ubiquitous in all arid and semi-arid biological soil crusts (referred as crusts hereafter), where they play a vital role in fixing carbon and nitrogen, stabilizing the soil as well as altering the hydrological properties (e.g. water retention) of crust-covered soils [1,2,3,4]. Whereas prolonged periods of desiccation lead to the oxidation and destruction of proteins, nucleic acids and cell membrane components of microorganisms [5], cyanobacteria in crusts have developed a variety of strategies to deal with water scarcity and to respond rapidly to sporadic rehydration during raining events [6,7,8,9,10,11]. Desiccationtolerant cyanobacteria have been shown to regulate their intracellular water potential through the accumulation of compatible solutes such as trehalose and sucrose and to increase water retention through the production of exopolysaccharides [5,14]. A detailed transcriptomic study revealed a rapid induction of genes related to oxidative and osmotic stress responses and to the synthesis of C and N storage polymers when crusts were exposed to desiccation [15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
