Effects of phytochemical crusts formed under two desert shrubs on physical properties of soils in arid ecosystems

Xerophytic shrubs are usually dominant in arid environments. Because of environmental pressures both biotic and abiotic, many plants have developed a huge diversity of carbon based secondary metabolites (CBSM). Several functions have been found for these CBSM, although their fate after being released is not clear. One of the hypothesis, tested here, is that CBSM accumulate in the soil under the plant's canopy. Particularly, we tested the hypothesis that terpene and polyphenolic resins present in Grindelia chiloensis (Asteraceae) and Larrea divaricata (Zigophyllaceae) would accumulate in the soil under their canopies and change its physical properties. Our results show that resins accumulate in the soil, and increase hardiness and hydrophobicity, while they reduce water infiltration. These changes in soil properties, compared to non-CBSM producing shrubs and bare soil, were more evident close to the plants' center and decreased towards the edge and surrounding soil. As they alter water dynamics, chemical crusts may have consequences both to the individual plant and to the ecosystem, and should be present in other arid lands, outside Patagonia.