Peter Vitousek, Doctoral (Program)
Nitrogen dynamics along a climate gradient on geologically old substrate, Kaua'i, Hawai'i.
We evaluated N dynamics on a climate gradient on old (>4 million year) basaltic substrate on the Island of Kaua'i, Hawai'i, to evaluate the utility of pedogenic thresholds and soil process domains for understanding N cycling in terrestrial ecosystems. Studies of nitrogen dynamics on the climate gradient on a younger basaltic substrate (~150,000year) had found a good match between soil process domains and N cycling processes. Here we measured net N mineralization and nitrification by incubation, and delta15N of total soil N, to determine whether the soil process domains on the older gradient were equally useful for interpreting N cycling and thereby to explore the general utility of the approach. Net N mineralization varied from 0 to 1.7mgkg-1 d-1 across the old Kaua'i gradient, and delta15N varied from +3 to +11omicron/omicronomicron, both ranges similar to those on the younger substrate. However, while the pattern of variation with climate was similar for delta15N, the highest rates of mineralization on the old gradient occurred where forests were dominated by the native N fixer Acacia koa. This occurred in sites wetter than the process domain associated with high net N mineralization on the gradient on younger substrate. We conclude that soil process domains based on rock-derived nutrients are not always useful for evaluating N dynamics, especially where the distribution of biological N fixers is controlled by factors other than rock-derived nutrients.
View details for PubMedID 30377769
SLC39A14 deficiency alters manganese homeostasis and excretion resulting in brain manganese accumulation and motor deficits in mice
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2018; 115 (8): E1769–E1778
Solute carrier family 39, member 14 (SLC39A14) is a transmembrane transporter that can mediate the cellular uptake of zinc, iron, and manganese (Mn). Studies of Slc39a14 knockout (Slc39a14-/-) mice have documented that SLC39A14 is required for systemic growth, hepatic zinc uptake during inflammation, and iron loading of the liver in iron overload. The normal physiological roles of SLC39A14, however, remain incompletely characterized. Here, we report that Slc39a14-/- mice spontaneously display dramatic alterations in tissue Mn concentrations, suggesting that Mn is a main physiological substrate for SLC39A14. Specifically, Slc39a14-/- mice have abnormally low Mn levels in the liver coupled with markedly elevated Mn concentrations in blood and most other organs, especially the brain and bone. Radiotracer studies using 54Mn reveal that Slc39a14-/- mice have impaired Mn uptake by the liver and pancreas and reduced gastrointestinal Mn excretion. In the brain of Slc39a14-/- mice, Mn accumulated in the pons and basal ganglia, including the globus pallidus, a region susceptible to Mn-related neurotoxicity. Brain Mn accumulation in Slc39a14-/- mice was associated with locomotor impairments, as assessed by various behavioral tests. Although a low-Mn diet started at weaning was able to reverse brain Mn accumulation in Slc39a14-/- mice, it did not correct their motor deficits. We conclude that SLC39A14 is essential for efficient Mn uptake by the liver and pancreas, and its deficiency results in impaired Mn excretion and accumulation of the metal in other tissues. The inability of Mn depletion to correct the motor deficits in Slc39a14-/- mice suggests that the motor impairments represent lasting effects of early-life Mn exposure.
View details for DOI 10.1073/pnas.1720739115
View details for Web of Science ID 000425495000012
View details for PubMedID 29437953
View details for PubMedCentralID PMC5828629