Soil seed bank in and between vegetation patches in arid Patagonia, Argentina

This study was conducted at two sites, 1.5km from 1 to another in arid Argentina (39°S, 69°W). Vegetation is distributed in patches. Four microenvironments can be identified in the soil surface of these patches, and the bare interspaces among them. Hypotheses were that (1) at any time during the sampling periods, buried (viable+damaged) seeds of the most common vegetation in the patches, Larrea divaricata Cav., Atriplex lampa Gill ex Moquin, Stipa neaei Nees ex Steudel and Leymus erianthus (Phil.) Dubcovsky, are present in the soil seed bank at all four microenvironments within any vegetation patch and its associated interspace, and (2) natural plant recruitment from the soil seed bank occurs for L. divaricata, A. lampa, S. neaei, L. erianthus, Bromus tectorum L. and Poa lanuginosa Poiret ap. Lamarck in all study microenvironments. In undisturbed field areas, 32 soil samples were periodically taken using an auger in 1999. Viable and damaged seeds contained in the soil organic matter were counted for L. divaricata, A. lampa, S. neaei, and L. erianthus. In a further study, emergence and subsequent growth of L. divaricata, A. lampa, S. neaei, L. erianthus, B. tectorum and P. lanuginosa from the soil seed bank were evaluated in the various microenvironments; permanent plots (0.04m²) were placed on each of the two study sites using four vegetation patches and their associated interspaces per site. Results supported the first hypotheses only for L. divaricata and A. lampa. However, natural recruitment from the soil only included S. neaei and P. lanuginosa through asexual, and B. tectorum through sexual reproduction. Despite the presence of buried seeds of L. divaricata and A. lampa in microenvironment 4 during most of the sampling period, bare interspaces among vegetation patches can be naturally vegetated through sexual reproduction by B. tectorum, during years of abundant, higher than long-term, annual precipitation.