Leaf morphological differences have an impact on light distribution within the leaf, photosynthesis, and photoprotection in Arabidopsis thaliana ecotypes from near the limits of this species' latitudinal distribution in Europe. Leaf morphology, photosynthesis, and photoprotection were characterized in two Arabidopsis ecotypes from near the limits of this species' latitudinal distribution in Europe (63°N and 42°N). The Swedish ecotype formed thicker leaves and upregulated photosynthesis more substantially than the Italian ecotype in high-light environments. Conversely, the smaller rosette formed, and lesser aboveground biomass accumulated, by the Swedish versus the Italian ecotype in low growth-light environments is consistent with a lesser shade tolerance of the Swedish ecotype. The response of the thinner leaves of the Italian ecotype to evenly spaced daily periods of higher light against a background of otherwise non-fluctuating low light was to perform the same rate of photosynthesis with less chlorophyll, rather than exhibiting greater rates of photosynthesis. In contrast, the thicker leaves of the Swedish ecotype showed elevated photosynthetic performance in response to daily supplemental higher light periods in a low-light growth environment. These findings suggest significant self-shading in the lower depths of leaves of the Swedish ecotype by the chloroplasts residing in the upper portions of the leaf, resulting in a requirement for higher incident light to trigger photosynthetic upregulation in the lower portions of its thicker leaves. Conversely, photoprotective responses in the Italian ecotype suggest that more excess light penetrated into the lower depths of this ecotype's leaves. It is speculated that light absorption and the degree of utilization of this absorbed light inform cellular signaling networks that orchestrate leaf structural development, which, in turn, affects light distribution and the level of absorbed versus photosynthetically utilized light in a leaf.
Abstract. In many ecosystems, foundational species create spatial patterns that structure a broader community. It is unclear, however, how robust these patterns are across large areas and strong environmental gradients, and how the landscape-level consequences of these patterns may vary. We investigated the robustness of non-random patterning in the dispersion of the western harvester ant (Pogonomyrmex occidentalis), a widely recognized ecosystem engineer of western North America. We used remote imagery to characterize the spatial structure and densities of western harvester ant mounds at sites spanning their range within the sagebrush steppe and short-grass prairie areas of Wyoming (581 3 450 km area). We found that ant mound densities varied substantially across the study region, but that mounds were strongly and consistently overdispersed (regularly patterned) across both climatic gradients and mound densities. Precipitation was the only abiotic factor that significantly affected either density or pattern, with stronger patterning among mounds at drier sites. This robustness in ecological patterning is likely to have strong effects on community function; mound dispersion increased the fraction of the landscape within typical ant foraging distances up to 30% over what density alone would predict. We estimated how patterning can modify one key ant effect at a landscape level by combining mound dispersion data with information from a seed removal experiment. Randomization tests based on these results showed that in a representative area, overdispersion could increase the mean landscape-wide seed removal rate by 16%, and decrease its spatial variance by 50%. Western harvester ants are known to affect multiple aspects of community function and structure at a relatively fine scale, and our results show that their spatial dispersion may therefore influence many features of interspecific interactions and community dynamics.
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