Continuous monitoring of chlorophyll a fluorescence and microclimatic conditions reveals warming-induced physiological damage in biocrust-forming lichens

Abstract

Purpose: Biocrust communities, which are important regulators of multiple ecosystem functions in drylands, are highly sensitive to climate change. There is growing evidence of the negative impacts of warming on the performance of biocrust constituents like lichens in the field. Here, we aim to understand the physiological basis behind this pattern.

Methods: Using a unique manipulative climate change experiment, we monitored every 30 minutes and for 9 months the chlorophyll a fluorescence and microclimatic conditions (lichen surface temperature, relative moisture and photosynthetically active radiation) of Psora decipiens, a key biocrust constituent in drylands worldwide. This long-term monitoring resulted in 11,847 records at the thallus-level, which allowed us to evaluate the impacts of ~2.3 °C simulated warming treatment on the physiology of Psora at an unprecedented level of detail.

Results: Simulated warming and the associated decrease in relative moisture promoted by this treatment negatively impacted the physiology of Psora, especially during the diurnal period of the spring, when conditions are warmer and drier. These impacts were driven by a mechanism based on the reduction of the length of the periods allowing net photosynthesis, and by declines in Yield and Fv/Fm under simulated warming.

Conclusion: Our study reveals the physiological basis explaining observed negative impacts of ongoing global warming on biocrust-forming lichens in the field. The functional response observed could limit the growth and cover of biocrust-forming lichens in drylands in the long-term, negatively impacting in key soil attributes such as biogeochemical cycles, water balance, biological activity and ability of controlling erosion.

Supplementary information: The online version contains supplementary material available at 10.1007/s11104-022-05686-w.

Keywords: Drylands; Global change ecology; Lichen physiology; Photosynthesis; Plant-soil interactions; Soil erosion control.

Fig. 1

Experiment setup details and pluviogram. a) Open top chambers located at the facilities of Rey Juan Carlos University. b) A plastic circular pot with squared fragments of Psora decipiens. c) Close up view of a measuring head of the HexPAM monitoring device. d) Daily precipitation (mm) during the experiment

Fig. 2

Violin plots showing the distribution of lichen surface temperature (upper panels) and relative moisture (bottom panels) recorded for the diurnal (PAR > 0; left panels) and nocturnal (PAR = 0; right panels) periods across seasons and treatments. Black dots and vertical lines inside each violin represent mean values ± standard deviation of each variable by treatment and season. Letters above each violin plot indicate significant differences (p < 0.05, Tukey Contrasts post-hoc test) after a Mixed-Effect model. A total of 1482 observations were used for this analysis

Fig. 3

Violin plots showing the distribution of daily lichen surface temperature when the individuals were active (i.e., Yield >0) recorded for the diurnal period (PAR > 0) and for autumn, winter, spring seasons. Black dots and vertical lines inside each violin represent mean lichen surface temperature ± standard deviation by warming treatment level and season. Letters above each violin plot indicate significant differences (p < 0.05, Tukey Contrasts post-hoc test) after a Mixed-Effect model. 1111 observations were used for this analysis

Fig. 4

Violin plots showing the distribution of a – b) daily % of activity, c) daily yield and d) daily Fv/Fm for the diurnal (PAR > 0; left panels) and nocturnal (PAR = 0; right panels) periods and for autumn, winter, spring seasons. Black dots and vertical lines inside each violin represent mean values ± standard deviation of each variable by treatment and season. Letters above each violin plot indicate significant differences (p < 0.05, Tukey Contrasts post-hoc test) after a Mixed-Effect model. A total of 1482, 1111 and 1138 observations were used for the analysis of a-b, c and d panels respectively. Daily yield and Fv/Fm values result from averaging only positive values (i.e., reflecting the situations where the lichen is metabolically active)

Fig. 5

Violin plots showing the distribution of daily % of activity when PAR ≥ 70 for autumn, winter, spring seasons. Black dots and vertical lines inside each violin represent mean daily % of activity ± standard deviation by treatment and season. Letters above each violin plot indicate significant differences (p < 0.05, Tukey Contrasts post-hoc test) after a Mixed-Effect model. 1482 observations were used for this analysis)