Tracking endolithic microbiomes to support the sustainabilityand functioning of global drylands

Drylands cover almost half of the planet and support >25% the global population. In this era of global warming, they are expected to continue expanding by the end of the century as a consequence of predicted increases in aridity, which will affect multiple global locations that are already characterised by extreme temperatures, low and variable rainfall, and low soil fertility. In these fragile ecosystems, where microorganisms are integral to maintain functioning and primary productivity, endoliths (i.e., rock-inhabiting microorganisms) play a key role in soil formation and dynamics and are and critical drivers of ecological succession. Here, we posit that endolithic microbes could also function as early alarm warning indicators for environmental changes in the most arid ecosystems. Nevertheless, studies on endoliths are still rather fragmentary and mainly focused in a few specific dry areas such as the Antarctic or Atacama deserts. A global appraisal of the structure and function of the endolithic microbiome is needed for the assessment of the current state of dryland biodiversity worldwide, and to identify the regions that are more vulnerable to global changes. Such an effort will provide new knowledge and will implement official and international initiatives to track and conserve biodiversity on global drylands.