Simulated soil crust conditions in a chamber system provide new insights on cyanobacterial acclimation to desiccation

Abstract

Environmental research often faces two major hurdles: (i) fluctuating spatial and temporal conditions and consequently large variability in the organisms' abundance and performance, and (ii) complex, costly logistics involved in field experiments. Measurements of physiological parameters or molecular analyses often represent single shot experiments. To study desiccation acclimation of filamentous cyanobacteria, the founders and main primary producers in desert biological soil crusts (BSC), we constructed an environmental chamber that can reproducibly and accurately simulate ambient conditions and measure microorganism performance. We show that recovery from desiccation of BSC cyanobacteria and Leptolyngbya ohadii isolated thereof are strongly affected by dehydration rate following morning dew. This effect is most pronounced in cells exposed to high light and temperature in the dry phase. Simultaneous measurements of water content, gas exchange and fluorescence were performed during dehydration. Photosynthetic performance measured by fluorescence begins declining when light intensity reaches values above 100 μmol photons m(-2) s(-1), even in fully hydrated cells. In contrast, photosynthetic rates measured using O2 evolution and CO2 uptake increased during rising irradiance to the point where the water content declined below ∼ 50%. Thus, fluorescence cannot serve as a reliable measure of photosynthesis in desert cyanobacteria. The effects of drying on gas exchange are discussed.

Algal richness in BSCs in forests under different management intensity with some implications for P cycling

“…As many other terrestrial algae, Klebsormidium is tolerant to light exposure during dehydration (Gray et al, 2007). This is a typical situation, which BSC algae have to cope with, since the increase in light intensity in the morning is often associated with dehydration (Raanan et al, 2016). A recent study in central Europe, however, observed that Klebsormidium is sensitive to increasing light during cellular water loss (Pierangelini et al, 2017).…”

“…Also, the stand density, another parameter of the SMI, could affect the light regime on the ground: higher density would result in less photosynthetic active radiation for photosynthetically active soil microorganisms. The radiation is often coupled with evaporation of soil moisture (Raanan et al, 2016); hence, the stand density could have an indirect effect on the BSC organisms via an altered water regime. Thus, the SMI was expected to affect the algal richness in BSCs via lower light availability and lower evaporation rates.…”

Changes in aggregation states of light-harvesting complexes as a mechanism for modulating energy transfer in desert crust cyanobacteria

“…Many of these ecosystems are founded on biological desert crusts, which play an essential role in stabilizing shifting sands and enriching them with nutrients (1,2). Cyanobacteria are among the first microorganisms to inhabit these crusts where one of the major sources of water is often dew deposited before dawn (3,4). However, as temperatures elevate, water quickly evaporates.…”

“…However, as temperatures elevate, water quickly evaporates. Such conditions can be extremely harmful for photosynthetic organisms and require adaptations on all cellular levels (3)(4)(5)(6)(7)(8)(9). These include shifts in metabolic profiles and the accumulation of compatible solutes.…”

Potentials of the microalgae inoculant in restoration of biological soil crusts to combat desertification

“…In addition, it is necessary to know how the inoculated communities interact with the biotic and abiotic factors and the best-matched strain for the specific condition. The interaction between soil cyanobacteria and the environmental parameters have been studied and reviewed over a long time period (Gómez et al 2012;Raanan et al 2015). From these results, it could be concluded that water availability and the related factors, such as frequency of rainfall, soil moisture content, together with the clay, and the amount of available phosphate in the soil, have the greatest influence on the cyanobacterial biomass concentration.…”