Application of the Herbicide, Simazine, and its Effect on Soil Surface Parameters and Vegetation in a Patchy Desert Landscape

Abstract

Semiarid regions are characterized by spatial heterogeneity with two patch types: (a) shrub patches with an annual vegetation understorey, and (b) biological soil crusts. Runoff as overland flow from the crust patch is a source of water and nutrients for the shrub patch and, thus, influences annual plant productivity. The aim of this study was to quantify the effects of the herbicide, simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], a photosynthesis inhibitor, on biological soil crusts and the consequences for the patchy desert landscape, in the northern Negev Desert, Israel. We studied the direct effect of the herbicide on the factors that compose the crusts (polysaccharides production, moss density, chlorophyll level), indirect effects on plant productivity (vegetation index and annual biomass), and resources (water, soil, organic matter and nutrients) on the landscape. We carried out a 2-year experiment, which entailed applying simazine on 20 (0.5 m2) plots with combinations of crust and shrub patches, and 20 control plots. Results indicated that 41.3% of the runoff water that flow overland from the crust patches was intercepted and absorbed by the shrub patches. Destruction of live crust components, such as cyanobacteria and soil algae, reduce polysaccharide production (from 0.12 to 0.06 µg mL−1 of crust extraction) and moss density (from 66 to 4 moss caulidia cm−2), which led to soil (12 g m−2 yr−1), organic matter (0.5 g m−2 yr−1) and nitrate (600 µg m−2yr−1) erosion. Degradation of shrub patch productivity was due to the removal of annual vegetation by simazine. We conclude that applying simazine to biological soil crusts in this fragile semiarid ecosystem, affected the crust organisms and in turn, the flow of water, soil and nutrients.