Plant and soil indicators for relating land management to plant conservation

In the Mediterranean area, the use of land for agriculture and pastoralism dates to the Neolithic and the land surface devoted to these activities represents roughly 40% of the total available area. In central Italy, similarly to other zones, common feature of the present landscapes is a high environmental fragmentation, with a mosaic of unmanaged semi-natural areas encircled by agricultural land and highly anthropized areas. The contiguity of natural and disturbed areas creates a huge amount of edge effects, which poses great challenges for plant conservation. In this framework, policy decisions on agroecosystems considering the issues of plant and biodiversity conservation are required, and an assessment of habitat overall quality is essential. Soil seed banks play an important part in defining healthy ecosystems, containing seeds dropped from standing vegetation, so as those survived from past vegetation, or dispersed from surrounding habitats by wind, animals, and human activities. In fragmented landscapes the composition of soil seed banks may significantly differ from that of the standing vegetation, thus reducing ecosystem resilience. On the other hand, storing seeds for more than a decade, seed banks allow us to study the history of the soil, providing relevant information on the soil’s health over the years. Soil properties can be analysed through expensive physical and chemical analyses, whereas seed bank analyses require good botanical competence but are cheaper. Our study, within the SHARInG-MeD project, aims to create a tool for farmers to assess soil health using seed bank composition indicators, and to set standards of certification for policy makers. In the present experiment we estimated the potential flora present in the viable seed bank of soils collected from different land uses within a highly fragmented agroecosystem. Differences in the abundance and functional composition of species among the seed bank communities were investigated by means of the seedling emergence method and related to land management and disturbance. The analyses focused also on identifying species or functional traits that could be used as a proxy for assessing soil health, specifically regarding nitrogen quantity and other chemical physical parameters. Soil samples up to 20 cm in depth were collected in summer 2024 in three contiguous land uses from central Italy: farmland under conventional management, abandoned land previously used for agriculture, and an un-managed semi-natural forest. Soil samples from nearby evergreen and deciduous forests were also included for comparison. For each land use we sampled soil in 16 different points which were merged in four replicates. After being stored in a refrigerated room for three months to enhance seed germination, the soils were sieved with a 4 mm mesh and then spread in a thin layer (2 cm max) into germination trays filled with expanded clay up to a half. Seed trays, four replicates for each land use, were placed in a greenhouse and regularly irrigated. The number of emerged seedlings was determined at week intervals, and after eight weeks, the abundance of the seed bank expressed as the number of seedlings emerged per unit soil surface and the composition in species and functional groups, were determined. Open agricultural fields in general allow seed to travel easier than dense woods, thus abundance of seeds and the biodiversity of species could be higher in the agricultural or uncultivated land uses, despite lack of rare species and high proportion of invasive weeds. In forest or rewilded areas, habitat specialist species could be more present. However, due to fragmentation seeds of ruderal species may accumulate in these soils.