The ‘black box’ of plant demography: how do seed type, climate and seed fungal communities affect grass seed germination?

Abstract

Summary Demographic studies measure drivers of plant fecundity including seed production and survival, but few address both abiotic and biotic drivers of germination such as variation in climate among sites, population density, maternal plants, seed type and fungal pathogen abundance. We examined germination and microbial communities of seeds of Danthonia californica, which are either chasmogamous (external, wind‐pollinated) or cleistogamous (internal, self‐fertilized) and Festuca roemeri, which are solely chasmogamous. Seed populations were sourced across environmental gradients. We tested germination and used high‐throughput sequencing to characterize seed fungal community structure. For F. roemeri, maternal plants significantly influenced germination as did climate and pathogens; germination increased from wetter, cooler sites. For D. californica, the main drivers of germination were maternal plant, seed type and pathogens; on average, more chasmogamous seeds germinated. Fungal communities depended largely on seed type, with fewer fungi associated with cleistogamous seeds, but the communities also depended on site factors such as vapor pressure deficit, plant density and whether the seeds had germinated. Putative pathogens that were negatively correlated with germination were more abundant for both D. californica and F. roemeri chasmogamous seeds than D. californica cleistogamous seeds. In D. californica, cleistogamous and chasmogamous seeds contain vastly different fungal communities.

Improving dryland seedling recruitment using fungicide seed coatings

“…Such systems, appropriately termed disease complexes, are common in wildland settings (Lamichhane & Venturi, 2015). Microbial communities and disease complexes can be highly sensitive to the hydrothermal environment and other stochastic ecological processes (Aanderud et al., 2013; Lamichhane & Venturi, 2015; Lamichhane et al., 2018; Mackin et al., 2021). Thus, the compositions of disease complexes affecting seeds and seedlings in this study were likely unique to each site and year to some degree.…”

“…Thus, it is likely that the pathogenesis of bluebunch wheatgrass seed and seedlings is not a monospecific process, but rather a process involving a community of microbes, some of which may form synergistic relationships (e.g. commensal–pathogen or pathogen–pathogen) affecting disease severity (Lamichhane & Venturi, 2015; Lamichhane et al., 2018; Mackin et al., 2021). Such systems, appropriately termed disease complexes, are common in wildland settings (Lamichhane & Venturi, 2015).…”

“…Pathogenesis is one process that may limit survival of seeds and seedlings. The highest rates of disease‐related mortality of plants in natural systems commonly occur during these demographic stages (Blaney & Kotanen, 2001; Gilbert, 2002; Mackin et al., 2021). Fungi and oomycetes (henceforth referred to collectively as fungi) are particularly important contributors to seed decay and seedling disease (Fawke et al., 2015; Gilbert, 2002).…”

“…In this scenario, seeds and pathogens are in direct competition for endosperm resources, each seeking to utilize the resources before the other. Microsite environmental factors such as soil moisture and temperature may give a competitive advantage to either the seed or the pathogen (Allen et al., 2018; Mackin et al., 2021). Fungal pathogenesis can also be exacerbated by abiotic stressors such as freeze–thaw cycles or drought conditions (Allen et al., 2018; Connolly & Orrock, 2015).…”

“…Fungal pathogens may encounter and colonize seeds and seedlings via seed‐borne or soil‐borne pathways. Each pathway can simultaneously support a diversity of fungal pathogens that may interact to contribute to decay, disease and mortality through a variety of mechanisms (Baskin & Baskin, 2014; Chambers & MacMahon, 1994; Mackin et al., 2021; Nelson, 2018). Given the diversity of fungal pathogens on seeds and in soils, the potential for fungal pathogenesis as a limiting process to plant establishment in a restoration context is high (Franke et al., 2014; Lamichhane & Venturi, 2015; Nelson, 2018).…”