Microtopography creates small‐scale refugia for boreal forest floor bryophytes during clear‐cut logging

The biotic response of ecological systems to disturbances has traditionally been explained by attributes of the disturbance event itself, such as its intensity, the distribution of traits within a community related to resistance (e.g. physiological, morphological or life‐history) or their interaction. Another less investigated mechanism explaining variation in response to disturbance is microtopographic heterogeneity, which might modify survival rates unevenly. We tested the hypothesis that forest floor microtopography creates small‐scale refugia for bryophytes following conventional clear‐cut logging by comparing a) survival of transplanted bryophytes and b) compositional changes of forest floor bryophytes among three different positions: on the northern side of boulders and stumps and on unsheltered forest floor. The investigation was carried out as a before‐and‐after study in 12 Swedish boreal forests (eight stands subjected to clear‐cutting and four reference stands). Significantly more bryophyte transplants survived where they were sheltered by boulders and stumps (30 and 29% respectively) compared to on level forest floor (10%) and less compositional changes occurred in sheltered microtopographic positions than on level forest floor. Shelter from boulders and stumps increased survival from both microclimatic stress and mechanical disturbance but not from burial by logging residues. Our findings provide evidence that microtopography can modify initial responses to disturbances by creating small‐scale refugia. Further studies are needed to determine whether this phenomenon is commonly occurring among other organisms and in other ecosystems and to what extent scattered in‐situ survivors can increase the recovery rate following disturbances.     

Modifications of the 7-Hydroxyl Group of the Transthyretin Ligand Luteolin Provide Mechanistic Insights into Its Binding Properties and High Plasma Specificity

Amyloid formation of the plasma protein transthyretin (TTR) has been linked to familial amyloid polyneuropathy and senile systemic amyloidosis. Binding of ligands within its natural hormone binding site can stabilize the tetrameric structure and impair amyloid formation. We have recently shown that the flavonoid luteolin stabilizes TTR in human plasma with a very high selectivity. Luteolin, however, is inactivated in vivo via glucuronidation for which the preferred site is the hydroxy group at position 7 on its aromatic A-ring. We have evaluated the properties of two luteolin variants in which the 7-hydroxy group has been exchanged for a chlorine (7-Cl-Lut) or a methoxy group (7-MeO-Lut). Using an in vitro model, based on human liver microsomes, we verified that these modifications increase the persistence of the drug. Crystal structure determinations show that 7-Cl-Lut binds similarly to luteolin. The larger MeO substituent cannot be accommodated within the same space as the chlorine or hydroxy group and as a result 7-MeO-Lut binds in the opposite direction with the methoxy group in position 7 facing the solvent. Both 7-Cl-Lut and 7-MeO-Lut qualify as high-affinity binders, but in contrast to luteolin, they display a highly non-specific binding to other plasma components. The binding of the two conformations and the key-interactions to TTR are discussed in detail. Taken together, these results show a proof-of-concept that the persistence of luteolin towards enzymatic modification can be increased. We reveal two alternative high-affinity binding modes of luteolin to TTR and that modification in position 7 is restricted only to small substituents if the original orientation of luteolin should be preserved. In addition, the present work provides a general and convenient method to evaluate the efficacy of TTR-stabilizing drugs under conditions similar to an in vivo environment.     

Production of diaspores at the landscape level regulates local colonization: an experiment with a spore‐dispersed moss

Effective dispersal is crucial to species inhabiting transient substrates in order for them to be able to persist in a landscape. Bryophytes, pteridophytes, lichens and fungi all have wind‐dispersed small diaspores and can be efficiently dispersed if their diaspores reach air masses above canopy height. However, empirical data on dispersal over landscape scales are scarce. We investigated how the colonization of an acrocarpous clay‐inhabiting pioneer moss, Discelium nudum, varied between sites that differed in connectivity to potential dispersal sources at spatial scales from 1 to 20 km in a region in northern Sweden. We recorded the colonization on ?25 introduced clay heaps at each of 14 experimental sites some months after the dispersal period. The colonization rate ranged from 0–82% and had a statistically significant relationship with a proxy for potential habitats (amount of clay‐dominated soil) in a buffer of 20 km radius surrounding the experimental sites (and also weakly with the amount of substrate in a 10 km buffer). There were no significant relationships between colonization rate and connectivity at smaller scales (1 and 5 km). We made a rough estimate of the number of spores available for dispersal in a landscape, given the amount of clay‐dominated soil, by recording the number of Discelium nudum colonies in two 25 × 25 km landscapes. The estimated available spore numbers in the different 20 km buffers were of the same order of magnitude as the deposition densities at the experimental sites calculated from the colonization rates. The results suggest that the spores of species with scattered occurrences and small diaspores (25 μm) in open landscapes can be deposited over extensive areas, at rates high enough to drive colonization patterns. This also implies that regional connectivity may be more important than local connectivity for these kinds of species.