Dynamics and ecological functions of Cryptogam Soil Crusts (CSC) in planitial landscapes of continental-temperate regions

Dry grasslands and heathlands are important habitats for biodiversity conservation and host cryptogam soil crusts (CSC) that greatly contribute to ecosystem functioning. This thesis aims at exploring: the terricolous lichen diversity in dry habitats in a human-impacted lowland (Po Plain, N Italy); the compositional patterns of CSC across dry grasslands and heathlands, also accounting for the dynamic stage of the vegetation (pioneer vs mature); the effects of small-scale disturbances on the three main taxa found in cryptogam-rich dry grasslands (vascular plants, lichens, bryophytes); the potential of CSC in delivering the ecosystem service of storing seeds of vascular plants, in the perspective of habitat restoration. Diversity and dynamics were studied by means of vegetation surveys in circular plots, whose number was area-dependent, located along transects in each habitat patch (= 185 plots in 60 grasslands, 114 plots in 22 heathlands). The % cover of each plant, bryophyte and lichen was recorded, with environmental (soil pH and texture, vegetation structure, altitude, bare soil %), disturbance-related (human trampling, cattle and lagomorphs fecal pellets, wild boar scratches) and climate variables (mean annual temperature and precipitation). The composition in lichens and bryophytes was compared among the 3 habitat types (3 groups) and between their dynamic stages (pioneer vs mature, 6 groups) to understand whether it is habitat- and stage-specific by means of NMDS, PERMANOVA and Indicator Species Analysis. Drivers of cover and species richness of the 3 taxa were analyzed for dry grasslands by means of generalized linear models. The seed storing function was studied taking 5 samples of CSC in 4 acidic grassland patches (= 20 samples), each sample taken at the centre of one plot surveyed in the previous spring. The samples were dryed, crumbled on sterile gardening soil in a controlled situation. All the germinated seedlings were identified and counted. Data were analyzed in comparison to data from the donor plots by means of Kruskal-Wallis test and linear regression, considering all the species and then native and non-native species separately . 33 terricolous lichen species were recorded, of which 13 of conservation concern. In spite of the widespread presence of few common species and the generally low species richness, composition differs significantly between the 3 habitat types and between pioneer vs mature heathlands, less markedly between dynamic stages within each grassland type. Three well-characterized assemblages which include many species of conservation concern were found for both lichens and bryophytes. Cryptogam assemblages are influences also by rainfall, soil features and vegetation structure. Increase of soil pH and disturbance by lagomorph fecal pellets have a negative effect on lichens, as well as their interaction (the negative effect of pellets is more evident at the increase of soil pH). Soil pH, fecal pellets and precipitation have a positive effect on bryophytes. Human trampling and fecal pellets have a negative effect on vascular plants, while increase of soil pH has a positive effect. The interaction of soil pH and pellets has an effect opposite than on lichens (the negative effect of pellets is more evident at the decrease of soil pH). CSC are able to store and release vascular plant seeds which are viable and can germinate when placed in proper conditions. The number of species and individuals of vascular plants germinated from CSC is comparable to what recorded in nature in the donor plots. Native species richness was higher, while native species germinated with less individuals than non-native species. These results are useful in addressing conservation towards the management and protection of all the lowland dry habitats, due to the differentiation among the cryptogam assemblages they host and to the presence of several species of conservation concern.