Competitive Ability of Native and Non-Native Prairie Species in Response to Soil Nitrogen and Density

The objective of this paper is to determine how competitive response varies between the prairie native Solidago rigida and the closely related Solidago canadensis, an invasive prairie species. I tested the idea that invasive species would exhibit greater biomass under increased nitrogen levels, while native species would not show significant difference across differences in nitrogen. I tested to see if variations in plant density changed how both of these plants respond to increased and ambient nitrogen levels. I found the invasive S. canadensis to have significantly higher biomass than the native S. rigida at high nutrient availabilities (total biomass: F1, 1 = 15.34, p =.0002). I also found that biomass for S. canadensis decreased as soil nitrogen levels decreased, while biomass for S. rigida did not decline from high to ambient nitrogen and at some densities it increased. While change in biomass from high to ambient nitrogen decreased at all densities for S. canadensis, the highest four densities for S. rigida demonstrated an increase in biomass. Our findings suggest that that as soil nutrients decrease, competitive dynamics between native and invasive species change. The results show that when grown under lower soil nitrogen conditions, S. rigida may be able to outcompete invasive neighbors, particularly when local densities are high. The findings also show the importance of considering density when comparing invasive and native responses to soil nitrogen, since S. rigida only exhibits a higher level of competitive ability at high densities and low levels of nitrogen

Adapting an Ecosystem Process Model to Estimate Ecosystem Services in Exurban Ecosystems

Ecosystem services (ES) are the physical goods and associated benefits that are provided to humans by ecological systems. Assessment of ES requires knowledge of ecology and ecosystem processes, and ES estimates can be improved when they include knowledge of nonlinearities, feedbacks, and interactions within ecosystems. A variety of assessment tools have been proposed to estimate the provision of ES. However, they fail to acknowledge interconnectedness of services or connections between ecosystem processes and services. This dissertation examines connections of ecosystem processes and ES with the assumption that knowledge of ecosystem ecology and ecosystem processes can be applied to improve estimates of ES capacity over time and under a variety of management scenarios. To investigate this connection, I modified the ecosystem process model Biome-BGC to simulate the provision of ES in exurban Southeastern Michigan. The modification resulted in a new version of the model, Biome-BGC-Ex, and involved detailed changes to the source code. The modified model included the ability to model competition between turfgrass and open grown trees in a single grid cell, to incorporate residential management practices, and to translate model outputs into well-defined, quantitative estimates of ES. My research was conducted as part of a larger collaboration, the SLUCE (Spatial Land Use Change and Ecological Effects) project and addresses the exurban residential landscape as a coupled human-natural system. It references and builds on previous elements of the SLUCE project including an empirical ecological field study, developer and homeowner interviews, web-based surveys, and modeling in a coupled human-natural system framework. My contributions to the project, specifically modifying Biome-BGC and linking it to ES, can be applied to future research on coupled human-natural systems in exurban residential landscapes. Chapter two describes how Biome-BGC was modified for the exurban landscape and then calibrated and parameterized for Southeastern Michigan. It examined which yard management practices have the greatest effect on carbon sequestration and model results suggested N fertilization was the strongest driver across three major vegetation types. Chapter three describes how Biome-BGC-Ex was modified to estimate ES capacity of ten services and evaluated the impact of yard management practices on ES capacity. Model simulations showed trade-offs between ES relating to high amounts of carbon or biomass and freshwater recharge. Chapter four took a broader approach and evaluated ecosystem process models as a potential tool for ES assessment and discussed how the integration of Biome-BGC-Ex with other tools could improve ES assessment. I found that while process models can improve understanding of interconnected ecosystem processes and biophysical feedbacks that affect the production of ES, they require more detailed data and complex knowledge to run. These chapters also discuss limitations of Biome-BGC-Ex and its ability to adequately address ecological complexities of exurban landscapes. One major limitation was accurately modelling N dynamics of exurban tree cover and model simulations likely overestimating C sequestration under high levels of fertilization. My dissertation research is the first to modify Biome-BGC to measure ES in a residential ecosystem. It is also novel because the work focuses on how human management of the landscape affects ES production as opposed to land use or land cover change. My dissertation research can likely be replicated in similar ecosystems to inform more complex ES modelling frameworks that rely on ES production modelling grounded in the understanding of ecosystem processes and their feedbacks.PHDResource Ecology & Mgt PhDUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169753/1/sekiger_1.pd

Sbf/MTMR13 coordinates PI(3)P and Rab21 regulation in endocytic control of cellular remodeling.

Cells rely on the coordinated regulation of lipid phosphoinositides and Rab GTPases to define membrane compartment fates along distinct trafficking routes. The family of disease-related myotubularin (MTM) phosphoinositide phosphatases includes catalytically inactive members, or pseudophosphatases, with poorly understood functions. We found that Drosophila MTM pseudophosphatase Sbf coordinates both phosphatidylinositol 3-phosphate (PI(3)P) turnover and Rab21 GTPase activation in an endosomal pathway that controls macrophage remodeling. Sbf dynamically interacts with class II phosphatidylinositol 3-kinase and stably recruits Mtm to promote turnover of a PI(3)P subpool essential for endosomal trafficking. Sbf also functions as a guanine nucleotide exchange factor that promotes Rab21 GTPase activation associated with PI(3)P endosomes. Of importance, Sbf, Mtm, and Rab21 function together, along with Rab11-mediated endosomal trafficking, to control macrophage protrusion formation. This identifies Sbf as a critical coordinator of PI(3)P and Rab21 regulation, which specifies an endosomal pathway and cortical control

Multi‐scale heterogeneity in vegetation and soil carbon in exurban residential land of southeastern Michigan, USA

Exurban residential land (one housing unit per 0.2–16.2 ha) is growing in importance as a human‐dominated land use. Carbon storage in the soils and vegetation of exurban land is poorly known, as are the effects on C storage of choices made by developers and residents. We studied C storage in exurban yards in southeastern Michigan, USA, across a range of parcel sizes and different types of neighborhoods. We divided each residential parcel into ecological zones (EZ) characterized by vegetation, soil, and human behavior such as mowing, irrigation, and raking. We found a heterogeneous mixture of trees and shrubs, turfgrasses, mulched gardens, old‐field vegetation, and impervious surfaces. The most extensive zone type was turfgrass with sparse woody vegetation (mean 26% of parcel area), followed by dense woody vegetation (mean 21% of parcel area). Areas of turfgrass with sparse woody vegetation had trees in larger size classes (> 50 cm dbh) than did areas of dense woody vegetation. Using aerial photointerpretation, we scaled up C storage to neighborhoods. Varying C storage by neighborhood type resulted from differences in impervious area (8–26% of parcel area) and area of dense woody vegetation (11–28%). Averaged and multiplied across areas in differing neighborhood types, exurban residential land contained 5240 ± 865 g C/m2 in vegetation, highly sensitive to large trees, and 13 800 ± 1290 g C/m2 in soils (based on a combined sampling and modeling approach). These contents are greater than for agricultural land in the region, but lower than for mature forest stands. Compared with mature forests, exurban land contained more shrubs and less downed woody debris and it had similar tree size‐class distributions up to 40 cm dbh but far fewer trees in larger size classes. If the trees continue to grow, exurban residential land could sequester additional C for decades. Patterns and processes of C storage in exurban residential land were driven by land management practices that affect soil and vegetation, reflecting the choices of designers, developers, and residents. This study provides an example of human‐mediated C storage in a coupled human–natural system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122437/1/eap1313.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122437/2/eap1313_am.pd

Student Voice report

Student Voice report and recommendation

Starvation‐induced MTMR13 and RAB21 activity regulates VAMP8 to promote autophagosome–lysosome fusion

Autophagy, the process for recycling cytoplasm in the lysosome, depends on membrane trafficking. We previously identified Drosophila Sbf as a Rab21 guanine nucleotide exchange factor (GEF) that acts with Rab21 in endosomal trafficking. Here, we show that Sbf/MTMR13 and Rab21 have conserved functions required for starvation-induced autophagy. Depletion of Sbf/MTMR13 or Rab21 blocked endolysosomal trafficking of VAMP8, a SNARE required for autophagosome-lysosome fusion. We show that starvation induces Sbf/MTMR13 GEF and RAB21 activity, as well as their induced binding to VAMP8 (or closest Drosophila homolog, Vamp7). MTMR13 is required for RAB21 activation, VAMP8 interaction and VAMP8 endolysosomal trafficking, defining a novel GEF-Rab-effector pathway. These results identify starvation-responsive endosomal regulators and trafficking that tunes membrane demands with changing autophagy status

Sbf/MTMR13 coordinates PI(3)P and Rab21 regulation in endocytic control of cellular remodeling.

Cells rely on the coordinated regulation of lipid phosphoinositides and Rab GTPases to define membrane compartment fates along distinct trafficking routes. The family of disease-related myotubularin (MTM) phosphoinositide phosphatases includes catalytically inactive members, or pseudophosphatases, with poorly understood functions. We found that Drosophila MTM pseudophosphatase Sbf coordinates both phosphatidylinositol 3-phosphate (PI(3)P) turnover and Rab21 GTPase activation in an endosomal pathway that controls macrophage remodeling. Sbf dynamically interacts with class II phosphatidylinositol 3-kinase and stably recruits Mtm to promote turnover of a PI(3)P subpool essential for endosomal trafficking. Sbf also functions as a guanine nucleotide exchange factor that promotes Rab21 GTPase activation associated with PI(3)P endosomes. Of importance, Sbf, Mtm, and Rab21 function together, along with Rab11-mediated endosomal trafficking, to control macrophage protrusion formation. This identifies Sbf as a critical coordinator of PI(3)P and Rab21 regulation, which specifies an endosomal pathway and cortical control

Comparison of air-displacement plethysmography results using predicted and measured lung volumes over a protracted period of time

Background Air-displacement plethysmography (ADP) systems can either measure or predict lung volume (LV) in their test trials. The repeatability of the predicted and the measured value is an important factor in the accuracy of the final test result. Objective Compare the variability and accuracy of ADP tests using predicted and measured LV over a protracted period of time. Methods Twenty-four adults (18–30 years) participated in the study. Each subject underwent three ADP tests over a period of 3 weeks, with 1 week between tests. At each testing session, subjects were tested using a predicted LV protocol and a measured LV protocol in random order. LV, body volume (BV) and per cent body fat (% BF) were compared between testing modes and between assessment times. Results A two-way ANOVA examined the effect of the mode of LV assessment (measured or predicted) and trial (week) for LV and BV and the effect of the LV mode assessment (measured or predicted) and trial (week) on % BF results. LV and BV did not differ significantly (P\u3e0·05) between the two modes of assessment (measured or predicted). Time (day of assessment) also was not significantly different between trials (P\u3e0·05). Neither mode nor trial was significant (P\u3e0·05), therefore neither had an effect on the % BF results. Conclusion In this investigation, the method used to determine LV during ADP testing did not significantly affect the final % BF result. Also, tests performed over an extended period of time was not affected by LV measurement method