Relative humidity predominantly determines long‐term biocrust‐forming lichen cover in drylands under climate change

Abstract

1. Manipulative experiments typically show a decrease in dryland biocrust cover and altered species composition under climate change. Biocrust-forming lichens, such as the globally distributed Diploschistes diacapsis, are particularly affected and show a decrease in cover with simulated climate change. However, the underlying mechanisms are not fully understood, and long-term interacting effects of different drivers are largely unknown due to the short-term nature of the experimental studies conducted so far. 2. We addressed this gap and successfully parameterised a process-based model for D. diacapsis to quantify how changing atmospheric CO 2 , temperature, rainfall amount and relative humidity affect its photosynthetic activity and cover. We also mimicked a long-term manipulative climate change experiment to understand the mechanisms underlying observed patterns in the field. 3. The model reproduced observed experimental findings: warming reduced lichen cover, whereas less rainfall had no effect on lichen performance. This warming effect was caused by the associated decrease in relative humidity and nonrainfall water inputs, which are major water sources for biocrust-forming lichens. Warming alone, however, increased cover because higher temperatures promoted photosynthesis during early morning hours with high lichen activity. When combined, climate variables showed non-additive effects on lichen cover, and effects of increased CO 2 levelled off with decreasing levels of relative humidity. 4. Synthesis. Our results show that a decrease in relative humidity, rather than an increase in temperature, may be the key factor for the survival of the lichen D. diacapsis under climate change and that effects of increased CO 2 levels might be offset by a reduction in non-rainfall water inputs in the future. Because of a global trend towards warmer and drier air and the widespread global distribution of D. diacapsis, this will affect lichen-dominated dryland biocrust communities and their role in regulating ecosystem functions worldwide. This is an open access article under the terms of the Creat ive Commo ns Attri butio n-NonCo mmercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Fire, climate and biotic interactions shape diversity patterns along an Afrotropical elevation gradient

“…These observed correlations apply to the full range and the two parts of our elevation gradient and also align with previous experimental findings (e.g. Baldauf et al, 2021), suggesting that these different responses could be partially explained by contrasting physiological tolerance. However, as with vascular plants, the effect of climate variables on bryophytes–lichens and soil phototrophs was also mediated by other factors, with fire playing a central role (see Palmer et al, 2020 for review).…”

“…Grau et al, 2007). Like vascular plants, non‐vascular terrestrial cryptogams and soil phototrophs, key components of biological soil crusts, are climate sensitive (Baldauf et al, 2021; Di Nuzzo et al, 2021; Rodríguez‐Caballero et al, 2018). Yet, they are also susceptible to disturbance such as fire (Palmer et al, 2020), and the impact of climate variables on their diversity patterns could be indirect.…”

Tissue chemistry of biocrust species along an aridity gradient and comparison to vascular plant leaves

“…Manipulative experiments and process models concur that a warmer, drier future will generally reduce abundance and the rate of carbon fixation in biocrusts (Baldauf et al, 2021;de Guevara et al, 2014;Reed et al, 2016;Zhang et al, 2018). Our stoichiometry results…”

“…Because water availability is so closely tied to carbon fixation in poikilohydric organisms (Raggio et al., 2021), the increasing scarcity of water means that biocrust carbon stocks are likely to decline at the global scale. Manipulative experiments and process models concur that a warmer, drier future will generally reduce abundance and the rate of carbon fixation in biocrusts (Baldauf et al., 2021; de Guevara et al., 2014; Reed et al., 2016; Zhang et al., 2018). Our stoichiometry results along an aridity gradient reinforce the carbon fixation results of prior work and agree with a recent mesocosm study, which found that simulated warming and rainfall reduction led to reduced tissue C:N in a biocrust lichen (Concostrina‐Zubiri et al., 2021).…”

Enhancement of ecosystem carbon uptake in a dry shrubland under moderate warming: The role of nitrogen‐driven changes in plant morphology

“…As already noted by previous research (Amthor et al, 2010 ; Beier et al, 2004 ; Bruhn et al, 2013 ), this effect represents an artifact introduced by experimental temperature manipulation. Dewfall represents an important source of water for ecosystems in arid and semiarid areas (Uclés et al, 2014 ), especially for biocrust formation (Baldauf et al, 2021 ). In our experiment, however, the predawn leaf water potential of C. monspeliensis was not modified by warming, even during dry periods, indicating that both nighttime soil warming and reduced dew formation did not significantly modify plant water balance.…”