Archaeal and Bacterial Diversity and Distribution Patterns in Mediterranean-Climate Vernal Pools of Mexico and the Western USA

Biogeographic patterns in microorganisms are poorly understood, despite the importance of microbial communities for a range of ecosystem processes. Our knowledge of microbial ecology and biogeography is particularly deficient in rare and threatened ecosystems. We tested for three ecological patterns in microbial community composition within ephemeral wetlands—vernal pools—located across Baja California (Mexico) and California (USA): (1) habitat filtering; (2) a latitudinal diversity gradient; and (3) distance decay in community composition. Paired water and soil samples were collected along a latitudinal transect of vernal pools, and bacterial and archaeal communities were characterized using 16S rDNA sequencing. We identified two main microbial communities, with one community present in the soil matrix that included archaeal and bacterial soil taxa, and another community present in the overlying water that was dominated by common freshwater bacterial taxa. Aquatic microbial communities were more diverse in the north, and displayed a significant but inverted latitudinal diversity pattern. Aquatic communities also exhibited a significant distance-decay pattern, with geographic proximity, and precipitation explaining part of the community variation. Collectively these results indicate greater sensitivity to spatial and environmental variation in vernal pool aquatic microbial communities than in soil microbial communities. We conclude that vernal pool aquatic microbial communities can display distribution patterns similar to those exhibited by larger organisms, but differ in some key aspects, such as the latitudinal gradient in diversity.

Archaeal and bacterial diversity and distribution patterns in Mediterranean vernal pools of Mexico and the western USA

Biogeographic patterns in microorganisms are poorly understood, despite the importance of microbial communities for a range of ecosystem processes. Our knowledge of microbial ecology and biogeography is particularly deficient in rare and threatened ecosystems. We tested for three ecological patterns in microbial diversity and community composition within ephemeral wetlands—vernal pools—located across Baja California (Mexico) and California (USA): 1) habitat filtering; 2) a latitudinal diversity gradient; and 3) distance-decay in community composition. Paired water and soil samples were collected along a latitudinal transect of vernal pools, and bacterial and archaeal communities were characterized using 16S rDNA sequencing. We identified two distinct microbial communities, with one community present in the soil matrix that included archaeal and bacterial soil taxa, and another community present in the overlying water that was dominated by common freshwater bacterial taxa. Aquatic microbial communities were more diverse in the north and displayed a significant but inverted latitudinal diversity pattern. Aquatic communities also exhibited a significant distance-decay pattern, with geographic proximity explaining 9%, and precipitation explaining 16% of community variation. Collectively these results indicate greater sensitivity to spatial and environmental variation in vernal pool aquatic microbial communities than in soil microbial communities. We conclude that vernal pool aquatic microbial communities can display distribution patterns similar to those exhibited by larger organisms, but differ in some key aspects, such as the latitudinal gradient in diversity.

Phytoplankton Communities of Temporary Ponds Under Different Climate Scenarios: Experiments on Vernal Pool Microcosms

Temporary water bodies, especially vernal pools, are the most sensitive to climate change, yet the least studied aquatic environments. Their functioning largely depends on the phytoplankton communities structure. This study aimed to determine how temperature and photoperiod length (simulating inundation in different parts of the year under six climate scenarios) affect the succession and the structure of phytoplankton communities soon after inundation. For longer photoperiods and at lower temperatures in vernal pool microcosms (simulating a cold spring after a warm snowless winter), the phytoplankton community evolved into chlorophytes and cryptophytes. At short photoperiod (inudation in winter, followed by freezing of the water surface) the communities evolved into the euglenoids. Medium temperatures and long photoperiods (late inundation during cool spring) promoted the development of chlorophytes, with high total phytoplankton abundance as well as species richness and diversity. The lack of cyanobacteria dominance, suggests that they will not be the leading group in vernal pools in the temperate zone with progressive global warming. Our study shows that climate change will result in the seasonal shifts of the species abundance or even in their disappearance, and finally in strong changes in the biodiversity and food web of aquatic ecosystems in the future.