Experimental climate warming decreases photosynthetic efficiency of lichens in an arid South African ecosystem

Abstract

Elevated temperatures and diminished precipitation amounts accompanying climate warming in arid ecosystems are expected to have adverse effects on the photosynthesis of lichen species sensitive to elevated temperature and/or water limitation. This premise was tested by artificially elevating temperatures (increase 2.1-3.8°C) and reducing the amounts of fog and dew precipitation (decrease 30.1-31.9%), in an approximation of future climate warming scenarios, using transparent hexagonal open-top warming chambers placed around natural populations of four lichen species (Xanthoparmelia austroafricana, X. hyporhytida , Xanthoparmelia. sp., Xanthomaculina hottentotta) at a dry inland site and two lichen species (Teloschistes capensis and Ramalina sp.) at a humid coastal site in the arid South African Succulent Karoo Biome. Effective photosynthetic quantum yields ([Formula: see text]) were measured hourly throughout the day at monthly intervals in pre-hydrated lichens present in the open-top warming chambers and in controls which comprised demarcated plots of equivalent open-top warming chamber dimensions constructed from 5-cm-diameter mesh steel fencing. The cumulative effects of the elevated temperatures and diminished precipitation amounts in the open-top warming chambers resulted in significant decreases in lichen [Formula: see text]. The decreases were more pronounced in lichens from the dry inland site (decline 34.1-46.1%) than in those from the humid coastal site (decline 11.3-13.7%), most frequent and prominent in lichens at both sites during the dry summer season, and generally of greatest magnitude at or after the solar noon in all seasons. Based on these results, we conclude that climate warming interacting with reduced precipitation will negatively affect carbon balances in endemic lichens by increasing desiccation damage and reducing photosynthetic activity time, leading to increased incidences of mortality.

Warming reduces the growth and diversity of biological soil crusts in a semi-arid environment: implications for ecosystem structure and functioning

“…As these species were the most abundant at our study site in the crust plots subjected to warming (see the electronic supplementary material, appendices S1 and S10), and the community measurements of F v /F m consisted of random measurements over each sampling plot, the later measurements reflected mostly the behaviour of the dominant species (figure 4), and thus did not capture properly the physiological status of the species that were mostly affected by warming. Indeed, significant reductions in the F v /F m of BSC-forming lichens with a 2.1 -3.88C warming and an approximately 30 per cent reduction in dew and fog inputs have been found in South Africa [57]. Why do mosses respond differently to warming than lichens?…”

“…The physiological performance of BSCs was evaluated in the Crust plots by measuring the maximum photochemical efficiency of photosystem II (F v /F m ) as an overall indicator of the status of this photosystem, and as a measure of the efficiency of the photosynthetic process [21,39,43,57,67]. Measurements were taken seasonally at midday from November 2008 until November 2011 on sunny days by using an FMS 2 Pulse Modulated Chlorophyll Fluorometer (Hansatech Instruments Ltd, King's Lynn, UK).…”

Will climate warming exceed lethal photosynthetic temperature thresholds of lichens in a southern African arid region?

“…1). The second warm humid coastal site with a mean annual temperature of 17.2°C and an erratic low rainfall of 39 mm per annum supplemented by frequent fog mea-sured at 214 mm per annum (Maphangwa et al, 2011) were a large lichen field (28°37′S, 16°30′E) situated south-east of the mining town of Alexander Bay, 3.2 km distant from the Atlantic coast (Fig. 2).…”

“…Effective quantum yields of PSII (DF/F m ′) were computed from ratios of variable steady state (F ms -F s ) to maximum steadyhttps://repository.uwc.ac.za/ state (F ms ) fluorescence (DF/F m ′ = F ms -F s /F ms ). Fluorescence measurements were matched with simultaneously recorded ground surface air temperatures and PPFD using radiation-shielded thermocou-ples as described in Maphangwa et al, 2011.…”

“…Lichens are recognized as valuable indicators of climate shifts, especially in temperature and precipitation (Insarov & Insarova, 2002), but there are few data on climatic impacts on lichens in arid and semi-arid ecosys-tems in the southern hemisphere whose diversity is potentially threatened by global climate change, espe-cially in species-rich southern African regions (Zedda et al, 2011). An impact of climatic change on southern African lichens in the arid Succulent Karoo Biome could be a loss of rare and endemic species and a rapid colonization of substrata by globally widespread species, particularly cyanolichens.…”