Effects of Waves and Sediment Disturbance on Seed Bank Persistence at Tidal Flats

Coastal wetlands such as salt marshes have been increasingly valued for their capacity to buffer global climate change effects, yet their long-term persistence is threatened by environmental changes. Whereas, previous studies largely focused on lateral erosion risk induced by stressors like sea level rise, it remains poorly understood of the response of lateral expansion to changing environments. Seedling establishment is a key process governing lateral marsh expansion as seen in many coastal regions such as Europe and East Asia. Here, we evaluate mechanistically the response of seed bank dynamics to changing physical disturbance at tidal flats, using the globally common coastal foundation plant, cordgrass as a model. We conducted a large-scale field study in an estuary in Northwest Europe, where seed bank dynamics of cordgrass in the tidal flats was determined and linked to in situ hydrodynamics and sediment dynamics. The results revealed that wave disturbance reduced the persistence of seeds on the surface, whereas amplified sediment disturbance lowered the persistence of both surface and buried seeds. Overall, this indicates that increasing storminess and associated sediment variability under climate change threatens seed bank persistence in tidal flats, and hence need urgently be incorporated into models for long-term bio-geomorphological development of vegetated coastal ecosystems. The knowledge gained here provides a basis for more accurate predictions on how climatically driven environmental changes may alter the fitness, resilience and persistence of coastal foundation plants, with significant implications for nature-based solutions with coastal vegetation to mitigate climate change effects.

Approaches in demographic modeling for predicting population persistence across a moisture gradient of an invasive, hybridizing weed (Raphanus SPP.)

Human-induced global climate change has altered precipitation patterns, with consequences for weed infestations. Cultivated plants are known to readily hybridize with their wild relatives, which may create more problematic weeds in future environments. I compared the demography and seed bank dynamics of wild radish and crop-wild hybrid radish populations across a soil moisture gradient. In a seed-burial experiment and weekly population censuses, I assessed frequency and timing of various demographic parameters. Germination rates declined with time in the low rain treatment, but increased in the double rain treatment. Wild seedlings tended to emerge later than hybrid seedlings. Hybrid populations had marginally higher population growth rates (λ) than wild populations. Fecundity had the greatest influence on λ. This study better informs weed control measures by predicting seed banks’ role in population persistence and by isolating the most effective life-history stage ‘choke point’ to suppress population growth given new climate change scenarios.

Approaches in demographic modeling for predicting population persistence across a moisture gradient of an invasive, hybridizing weed (Raphanus SPP.)

Human-induced global climate change has altered precipitation patterns, with consequences for weed infestations. Cultivated plants are known to readily hybridize with their wild relatives, which may create more problematic weeds in future environments. I compared the demography and seed bank dynamics of wild radish and crop-wild hybrid radish populations across a soil moisture gradient. In a seed-burial experiment and weekly population censuses, I assessed frequency and timing of various demographic parameters. Germination rates declined with time in the low rain treatment, but increased in the double rain treatment. Wild seedlings tended to emerge later than hybrid seedlings. Hybrid populations had marginally higher population growth rates (λ) than wild populations. Fecundity had the greatest influence on λ. This study better informs weed control measures by predicting seed banks’ role in population persistence and by isolating the most effective life-history stage ‘choke point’ to suppress population growth given new climate change scenarios.

Spatial and temporal dynamics of two cacti seed banks in a xerophytic shrubland in Mexico City

Background: Soil and aerial seed banks directly affect recruitment in plant populations. Soil banks result as the balance between seed inputs and outputs. Seed bank dynamics vary by species and environmental conditions. Few records on cacti seed banks are available. Questions: What types of seed banks do two cacti genera form in a lava-field reserve? Does seasonality influence the seed bank dynamics? Are inputs and outputs associated to the microenvironment? Studied species: Opuntia tomentosa, O. lassiacantha, Mammillaria haageana subsp. san-angelensis, M. magnimamma. Study site and dates: Xerophytic shrubland in the “Reserva Ecológica del Pedregal de San Ángel” in Mexico City. 2016 to 2018. Methods: We collected soil samples from four microenvironments during the rainy and the dry seasons, searched for seeds and tested their viability. We compared the number of inputs, outputs and viable seed by microenvironment and season. For M. magnimamma, each month we registered fruit maturation and searched for seeds remaining between tubercles. Results: Opuntia seed bank inputs occurred in all microenvironments and in both seasons. Rain favored inputs in hollows by secondary seed dispersal. We registered a large number of outputs caused by germination, granivory and loss of viability. Opuntia seed bank was developed in headland, plain and slope. No Mammillaria seed inputs were found, neither an aerial bank in M. magnimamma. Conclusion: Opuntia seed banks were restricted to microenvironments that provided “safe sites” which stored viable seeds. Mammillaria seed dynamics may hinders recruitment for their populations.

Variability of Seed Germination and Dormancy Characteristics and Genetic Analysis of Latvian Avena fatua Populations

Avena fatua is an economically detrimental weed found in cereal growing areas worldwide. Knowledge about the variation of dormancy and germination characteristics, as well as of the genetic diversity and structure can provide additional information about different populations within a region. Identification and development of potential indicators or markers of seed germination behavior, would be useful for modelling emergence and seed bank dynamics. This study aimed to describe the initial germination, dormancy, and morphological characteristics of seeds from different Latvian populations of A. fatua and to investigate the genetic structure of local populations. Seed samples from 26 to 41 locations in different regions of Latvia were collected over three years. Seed morphology, initial germination, and the effect of dormancy-breaking treatments were determined. Seeds from 18 Latvian populations with contrasting seed dormancy characteristics were genotyped. Although morphological differences between seeds from different regions were revealed, genetic analysis of the selected populations indicated that the population structure was not related to geographical location, which probably reflects the impact of anthropogenic dispersal of A. fatua seeds. The effect of dormancy-breaking treatments varied between years, between climatic zones and between populations, indicating environmental influences as well as inherited dormancy.

What are the demographic consequences of a seed bank stage for columnar cacti?

The dynamics of plants populations are often limited by the early stages in their life cycles. The question if the columnar cacti have or not a seed bank in predictable environments. Yet, information regarding seed bank dynamics and how these may influence the full life cycle of plant species is remarkably scarce or ignore. This lack of knowledge is mostly due to the challenges in quantifying seed vital rates. Studies of arid land plant species have historically been focused on the drivers of sporadic recruitment. However, little attention has been given to the demographic consequences of early developmental stages, including seed banks. Here, we evaluate the effects of seed bank survival and seedling recruitment vital rates on the population dynamics and viability of 12 columnar cacti species, recent evidence suggests that cacti seeds may remain viable for the short-term. We assess how changes in the vital rates of these processes, and the inclusion of a seed bank affect population growth rate (λ). We found that a seed bank in the examined matrix population models significantly increased λ as well as the vital rate elasticities of λ to growth and fecundity, whereas that of overall survival decreased. Our numerical simulations showed that seed survival had a larger effect on λ than seedling recruitment and establishment. We suggest that seed bank may explain the structure and population dynamics. Thus, we argue reconsider that this early stage in demographic models will generate more informed decisions on the conservation and management of columnar cacti.