Soil crusts and disturbance benefit plant germination, establishment and growth on nutrient deficient sand

The influence of cyanobacterial soil crusts combined with mechanical soil disturbance on germination, establishment, growth and nutrition of Lepidium sativum seedlings on nutrient poor sand was analyzed under controlled conditions in a growth chamber. Marked release of nitrate and ammonia into the soil was only found in established and older (aging) crusts. Analyses of the N-15 signatures of the crust and the seedling biomass revealed, that there was clear evidence that the established seedlings took up considerable amounts of the released nitrogen. This positively affected plant performance. Mechanical disturbance of the crust led to a temporal increase of nitrogen release but later to a considerable decrease of the released nitrogen components. Undisturbed crusts had a low stimulating effect on seed germination. In contrast and independent of the presence or absence of crusts mechanical soil disturbance led to significantly higher seed germination rates. It is concluded that the occurrence of small-scale disturbance events of moderate intensity at an intermediate frequency, which is the typical disturbance regime in many natural soil crust habitats, seems to be necessary for the successful coexistence of crust organisms and higher plants in nutrient poor environments. (C) 2007 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.