Julia G. Bryce

Nutrient Supply Rate and Mycorrhizal Colonization Control Patterns of Element Distribution in Ectomycorrhizal Pine

Ectomycorrhizal fungi may provide plants access to nonexchangeable nutrients. We measured nutrients (potassium, calcium, magnesium, manganese, iron, and aluminum) in roots and foliage in nonmycorrhizal and ectomycorrhizal Pinus sylvestris cultured in perlite at two nutrient supply levels. We also measured nutrients in perlite leachates from abiotic experiments using hydrochloric or oxalic acid at pH 2–4. Twenty‐one percent more potassium and 30% more calcium accumulated in nonmycorrhizal plants than in ectomycorrhizal plants, presumably because of nutrient sequestration in extraradical fungal biomass. Plants at low nutrient supply accumulated 22% more potassium and 23% more calcium than at high nutrient supply, presumably because of additional mobilization of nutrients from perlite by plant and fungal acids. Significantly more leaching at pH 2 with oxalic than with hydrochloric acid occurred, probably caused by enhanced ligand‐mediated dissolution with oxalic acid. Leaching of minerals by organic acids may enhance plant nutrient supply, particularly from microsites of low pH.

Submarine and subaerial lavas in the West Antarctic Rift System: Temporal record of shifting magma source components from the lithosphere and asthenosphere

The petrogenesis of Cenozoic alkaline magmas in the West Antarctic Rift System (WARS) remains controversial, with competing models highlighting the roles of decompression melting due to passive rifting, active plume upwelling in the asthenosphere, and flux melting of a lithospheric mantle metasomatized by subduction. In this study, seamounts sampled in the Terror Rift region of the Ross Sea provide the first geochemical information from submarine lavas in the Ross Embayment in order to evaluate melting models. Together with subaerial samples from Franklin Island, Beaufort Island, and Mt. Melbourne in Northern Victoria Land (NVL), these Ross Sea lavas exhibit ocean island basalt (OIB)-like trace element signatures and isotopic affinities for the C or FOZO mantle endmember. Major-oxide compositions are consistent with the presence of multiple recycled lithologies in the mantle source region(s), including pyroxenite and volatile-rich lithologies such as amphibole-bearing, metasomatized peridotite. We interpret these observations as evidence that ongoing tectonomagmatic activity in the WARS is facilitated by melting of subduction-modified mantle generated during 550–100 Ma subduction along the paleo-Pacific margin of Gondwana. Following ingrowth of radiogenic daughter isotopes in high-µ (U/Pb) domains, Cenozoic extension triggered decompression melting of easily fusible, hydrated metasomes. This multistage magma generation model attempts to reconcile geochemical observations with increasing geophysical evidence that the broad seismic low-velocity anomaly imaged beneath West Antarctica and most of the Southern Ocean may be in part a compositional structure inherited from previous active margin tectonics.