Tulane University is a private research university in New Orleans, Louisiana. It was founded as a public medical college in 1834 and became a comprehensive university in 1847. The institution was made private under the endowments of Paul Tulane and Josephine Louise Newcomb in 1884. Tulane is the 9th oldest private university in the Association of American Universities, which consists of major research universities in the United States and Canada. The Tulane University Law School and Tulane University Medical School are, respectively, the 12th oldest law school and 15th oldest medical school in the United States.Alumni include the former President of Costa Rica; twelve governors of Louisiana; one Chief Justice of the United States Supreme Court; various members of Congress, including one Speaker of the House; two Surgeons General of the United States; 23 Marshall Scholars; 18 Rhodes Scholars; 12 Truman Scholars; 155 Fulbright Scholars; and four living billionaires. Two Nobel laureates have been affiliated with the university.
Plant species distributions are strongly influenced by soil nutrient availability in tropical forests. Yet, the relative importance of abiotic and biotic factors underlying the composition of pervasive fungal symbionts of plants, arbuscular mycorrhizal fungi (AMF), remains unresolved in lowland tropical forests. Utilizing a long-term plot network in central Panama with mapped soil properties and tree species distributions, we aimed to understand the relative contribution of soil properties, geographic distance, root traits, and plant species identity in determining AMF community composition. We further asked how plant-fungal networks vary between sites with contrasting soil phosphorus (P) availability. We sampled fine roots for molecular identification of AMF communities from 140 trees representing 26 species with varied distributions across the soil nutrient availability gradient. We found that plant species identity and soil properties, especially soil P availability and dry-season moisture deficit, independently structured AMF community composition. Taxonomic turnover and a large number of indicator taxa across a soil P availability gradient provide further evidence for the strong abiotic and biotic structuring of AMF communities. Moreover, a significantly nested plant-AMF network in the low-P site points to a role of soil nutrient availability in mediating plant-AMF interactions. Our results lay the foundation for future studies to uncover the functional consequences of this symbiosis for plant distributions and ecosystem function in tropical forests.
Low optically stimulated luminescence (OSL) sensitivity is commonly observed in quartz from tectonically active catchments, suggesting limited or short-lived conditions favorable for sensitization. We characterize the OSL sensitivity of quartz sand within a small, tectonically active catchment in Sicily using modern fluvial samples and a hillslope soil sample. We investigate how OSL sensitivity varies with bedrock lithology, weathering proxies, and topographic metrics. OSL sensitivity spans three orders of magnitude (60-2800 counts/Gy/mm3) with no clear linkage to bedrock source. The soil sample exhibits the highest OSL sensitivity, and positive relationships between OSL sensitivity, magnetic susceptibility, and weathering intensity suggest that pedogenic hillslope processes enhance quartz OSL sensitivity. In contrast, fluvial sediments show low OSL sensitivity and a modest inverse relationship to channel steepness and hypsometry. OSL sensitivity decreases downstream, suggesting that highly sensitized grains from hillslope soils are progressively diluted by low OSL sensitivity sediment likely generated by rapid bedrock erosion in the catchment. These results highlight a hierarchy of controls: bedrock lithology sets the initial OSL sensitivity, hillslope processes enhance it, rapid erosion dilutes it, and fluvial transport modulates it through mixing, explaining why tectonically active catchments rarely preserve quartz with high OSL sensitivity.
Rifts that initiate in mechanically strong, stable continental lithosphere are characterized by M > 5 earthquakes at depths >35 km near or below the crust mantle interface. Current models for deep rift zone earthquakes invoke elevated pore pressures associated with magmatism, and rapid stressing from magma intrusions. We evaluate the role of static stress changes caused by lateral density contrasts (magma intrusions) in the upper mantle and crust-mantle interface on mantle earthquakes. We use numerical models of static stress changes, and test models against seismic data from the Tanganyika rift, East Africa which has upper mantle earthquakes and locally elevated crustal Vp/Vs. The earthquake source mechanisms from these ML2.4-2.8 earthquakes show steep nodal planes and little correlation to crustal source mechanisms and E-W extension direction. Likewise, the direction of fast splitting from seismic anisotropy studies is oblique to predictions from earthquake source mechanisms. The models of density contrasts (magma intrusions) explored in this study predict differential stresses of 1-10 MPa, stresses consistent with average earthquake stress drops. The local stress field rotations around the edges of intrusive bodies can explain the variable source mechanisms and match the local rotation of shear wave splitting direction, providing a plausible mechanism for mantle earthquakes in cratonic rifts. By analogy, exhumed mantle from rift zones reveals pseudotachylites near intrusions. Metasomatic reactions in contact aureoles broaden density contrasts and reduce upper mantle strength, potentially enabling extension of initially cold, strong continental lithosphere.
Seed dispersal services are key to maintaining healthy forest ecosystems, yet our understanding of the factors that influence visitation and frugivory between conspecific plants remains incomplete. Although fruiting neighborhood, plant traits, and fruit traits have been shown to individually influence frugivory, few studies have concurrently evaluated the relative importance of these factors. We address this knowledge gap by simultaneously assessing multiple factors thought to influence frugivory. Specifically, we evaluated how the fruiting neighborhood, defined as the number of fruiting palms in a 35 m radius, and relevant traits at the level of individual plants (e.g., height, crop size) and fruits (e.g., fruit and seed size, water and sucrose content) influenced frugivore visitation and the number of fruits removed per visit in a common understory palm in Northwestern Ecuador, Synechanthus warscewiczianus. A higher number of conspecific fruiting neighbors exhibited a decrease in visitation, suggesting competition among palms that share frugivore mutualists for dispersal services. However, the number of fruits removed per frugivore visit appeared to be affected by crop size and fruit traits of individual palms. Larger crop and fruit sizes were positively associated with the number of fruits removed per visit and indicates frugivore satiation is not a main determinant of fruit consumption during visits. Taken together, our results suggest larger-scale factors like fruiting neighborhood may affect a frugivore's decision to visit a palm, yet finer-scale fruit traits may drive fruit removal once a palm is selected, thereby influencing variation in seed dispersal services at the individual plant level.
Seasonal land motion can be caused by processes above or below Earth's surface, often linked to natural changes in the hydrological cycle. In coastal deltaic systems, the coupling of water level changes between rivers and aquifers may cause significant surface deformation, but this process is poorly understood. In this research, we show that land motion can be a proxy for groundwater level changes in layered and semi-confined aquifers, with implications for other delta systems worldwide. We investigate the processes driving the >15 mm seasonal deformation in the Mississippi River Delta near Baton Rouge, Louisiana. We consider elastic deformation due to surface loading and poroelastic deformation caused by changes in groundwater levels. The underlying aquifer system is formed by almost-independent sands, crossed by the Mississippi and Amite Rivers, and cut by the Baton Rouge fault, which is a leaky barrier. We quantify seasonal deformation using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR), between 2016 and 2022 and validate the results with Global Navigation Satellite Systems (GNSS) data. We find that the amplitude of the seasonal response has spatial variations related to the distance to the Mississippi River and the Baton Rouge Fault. We identify which aquifer layers are in phase with the observations and are thus most likely to cause poroelastic deformation. Our results are supported by hydraulic properties from the literature for the aquifer system. We conclude that seasonal motion in the area is dominantly driven by the poroelastic response to Mississippi River level changes that recharge the shallower aquifer layers.
