Engineering topics

Mitton, Jeffry

Publications and source records attributed to Mitton, Jeffry.

3 records

DOE OSTI2018

Comparative Transcriptomics Among Four White Pine Species

Conifers are the dominant plant species throughout the high latitude boreal forests as well as some lower latitude temperate forests of North America, Europe, and Asia. As such, they play an integral economic and ecological role across much of the world. This study focused on the characterization of needle transcriptomes from four ecologically important and understudied North American white pines within the Pinus subgenus Strobus. The populations of many Strobus species are challenged by native and introduced pathogens, native insects, and abiotic factors. RNA from the needles of western white pine (Pinus monticola), limber pine (Pinus flexilis), whitebark pine (Pinus albicaulis), and sugar pine (Pinus lambertiana) was sampled, Illumina short read sequenced, and de novo assembled. The assembled transcripts and their subsequent structural and functional annotations were processed through custom pipelines to contend with the challenges of non-model organism transcriptome validation. Orthologous gene family analysis of over 58,000 translated transcripts, implemented through Tribe-MCL, estimated the shared and unique gene space among the four species. This revealed 2025 conserved gene families, of which 408 were aligned to estimate levels of divergence and reveal patterns of selection. Specific candidate genes previously associated with drought tolerance and white pine blister rust resistance in conifers were investigated.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2017

Subalpine and alpine species range shifts with climate change: temperature and soil moisture manipulations to test species and population responses (Final Report)

The Alpine Treeline Warming Experiment (ATWE) was established in 2008-2009 to experimentally test how climate change would affect species ranges at and beyond the cold edge limits of forest growth. One key finding was that warming can hinder upslope tree migration by increasing seedling water stress and reducing seedling survival. We found evidence for more conservative traits in seedlings from high elevation tree populations, which may further slow tree expansion into the current alpine. In the alpine, warming may only increase productivity if summer rain increases, as dominant alpine life forms were negatively affected by heating unless water was added. The ATWE experimental design and focus on dynamic vegetation were novel, and the setting at the mountain treeline transition was important to understanding effects of climate variability and change on water resources, carbon cycling and biodiversity. We ended climate manipulations and removed associated infrastructure from the field in 2016 following 8 years of data collection. To date, 5 MS theses and 18 peer-reviewed papers have been published or accepted (including one that yielded the cover image in Global Change Biology, left), and 1 PhD thesis and at least 5 papers are in review or active development. Numerous past seasonal and long-term field staff have gone on to graduate school, and subsequently to research positions as university faculty or agency scientists. PI Kueppers continues collecting data on soil microclimate and seedling survival for long-lived tree species to fill a critical gap in knowledge regarding the seedling-to-sapling transition across species and elevations. Primary project data is housed on the project’s virtual server, organized according to topic. Published data and model code is available either through the project website or via other permanent archives. Our results are influencing understanding and modeling of climate and genetic constraints on dynamic vegetation change across the landscape, particularly in the mountains of the Western U.S.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

Linking carbon and water relations to drought-induced mortality in Pinus flexilis seedlings.

Survival of tree seedlings at high elevations has been shown to be limited by thermal constraints on carbon balance, but it is unknown if carbon relations also limit seedling survival at lower elevations, where water relations may be more important. We measured and modeled carbon fluxes and water relations in first-year Pinus flexilis seedlings in garden plots just beyond the warm edge of their natural range, and compared these with dry-mass gain and survival across two summers. We hypothesized that mortality in these seedlings would be associated with declines in water relations, more so than with carbon-balance limitations. Rather than gradual declines in survivorship across growing seasons, we observed sharp, large-scale mortality episodes that occurred once volumetric soil-moisture content dropped below 10%. By this point, seedling water potentials had decreased below -5 MPa, seedling hydraulic conductivity had decreased by 90% and seedling hydraulic resistance had increased by >900%. Additionally, non-structural carbohydrates accumulated in aboveground tissues at the end of both summers, suggesting impairments in phloem-transport from needles to roots. This resulted in low carbohydrate concentrations in roots, which likely impaired root growth and water uptake at the time of critically low soil moisture. While photosynthesis and respiration on a leaf area basis remained high until critical hydraulic thresholds were exceeded, modeled seedling gross primary productivity declined steadily throughout the summers. At the time of mortality, modeled productivity was insufficient to support seedling biomass-gain rates, metabolism and secondary costs. Thus the large-scale mortality events that we observed near the end of each summer were most directly linked with acute, episodic declines in plant hydraulic function that were linked with important changes in whole-seedling carbon relations.

Reinhardt, Keith↗