Non-rainfall water input determines lichen and cyanobacteria zonation on limestone bedrock in the Negev Highlands

- Belts of lithobionts (zonation) of different appearance are common in the Negev.
- Rain and dust could not have explained the zonation.
- The zonation was explained by variable non-rainfall water input (NRWI).
- Differences in NRWI stem from temperature gradients.
- Lithobiont zonation may serve as bio-indicator for variable NRWI.

Lichen zonation on bedrock in accordance with the rock contours is a common phenomenon. This is also the case in the Negev Desert Highlands, where zonation along a continuum of lichens-cyanobacteria or different groups of lichens (epiliths-endoliths) within a distance of as short as <1 m can be observed. In an attempt to evaluate the factors responsible for the zonation, two plots with zonal distribution were demarcated in a north-facing slope and two at a south-facing slope, and their chlorophyll content and species composition were defined. In addition, rock properties, surface temperatures, dust input, rain amount, and the amount of non- rainfall water input, NRWI (dew, fog and high water vapor content) were measured. Whereas rock properties and aeolian input failed to explain the observed zonation, a clear temperature-induced NRWI gradient was found. The findings suggest that differential amounts of NRWI are responsible for the zonation observed, and subsequently for the clear gradient in chlorophyll content. The findings also suggest that lithobiont zonation may serve as a biomarker for subtle gradients in surface temperatures and subsequently in NRWI.