Theses and Dissertations at Montana State University (MSU)
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Item Recent and historical water use strategies of western U.S. conifers(Montana State University - Bozeman, College of Letters & Science, 2017) Clute, Timothy; Chairperson, Graduate Committee: David Roberts; Jia Hu (co-chair); Jia Hu was a co-author of the article, 'Investigating the variation in inter- and intraspecific physiological plant hydraulic traits across an elevation gradient' which is contained within this thesis.; Jia Hu was a co-author of the article, 'Historic influence of climate on conifer water status in northwestern Montana' which is contained within this thesis.Understanding the physiological traits that trees utilize to manage water use can reveal important insights into how and why they occur in their realized habitat. Among the tools to investigate these traits include measuring trees' seasonal water status, deciphering trees' rooting depth, and measuring the trees' vulnerability to cavitation. However, it is equally important to understand how complex landscape heterogeneity will affect both the inter- and intraspecific variation of these physiological traits. This thesis seeks to quantify the variation of the physiological traits used to manage water status among three common Rocky Mountain conifers; Pseudotsuga menziesii (a plastic species occurring across xeric and mesic sites), Pinus ponderosa (a xeric species), and Picea engelmannii (a mesic species), occurring across an elevation gradient. Furthermore, it aims to link tree maintenance of water status to source water, and understand how the importance of source water is reflected in the tree ring record. In the first chapter, I sought to quantify inter- and intraspecific variation of these three species by measuring diurnal and seasonal water status, seasonal water use, and xylem vulnerability to cavitation at a low elevation xeric site, composed of P. ponderosa and P. menziesii, and a high elevation mesic site, composed of P. engelmannii and P. menziesii. We found good evidence for interspecific variation in the physiological traits to manage water status at both sites. However, we did not find strong evidence for intraspecific variation in these same traits within our plastic species (P. menziesii). In the second chapter, we investigated how stable isotopes in tree rings reflected seasonal source water use as well as the atmospheric conditions the trees were growing under. At the low elevation site, we found evidence that the tree ring isotopes were likely reflecting both seasonal precipitation inputs as well as the atmospheric growing conditions. At the high elevation site, trees likely only reflected the atmospheric growing conditions and did not reflect seasonal water use.Item Conifer transpiration in a montane watershed : environmental controls and methodological uncertainties(Montana State University - Bozeman, College of Letters & Science, 2015) Looker, Nathaniel Thomas; Chairperson, Graduate Committee: Jia Hu; Justin Martin, Zachary Hoylman, Kelsey Jencso and Jia Hu were co-authors of the article, 'Topographic mediation of sap flow dynamics in a forested watershed' submitted to the journal 'Ecohydrology' which is contained within this thesis.; Justin Martin, Kelsey Jencso and Jia Hu were co-authors of the article, 'Uncertainty in conifer transpiration due to sapwood traits' submitted to the journal 'Agricultural and Forest Meteorology' which is contained within this thesis.Transpiration, the evaporative loss of water from vegetation through stomata, is intertwined with biological, meteorological, and hydrologic processes from the scale of leaves to continents. Among the methods of estimating transpiration, thermometric sap flow sensors have gained favor due to their high temporal resolution and capacity to integrate across sub-canopy variability. Heterogeneity in growing conditions through space and time may contribute substantial uncertainty to sap flow-based inferences; hence, quantification of spatiotemporal variability in sap flow dynamics and plant physiological traits is required to improve confidence in transpiration estimates. In this study, I employ sap flow sensors to address the environmental sensitivity of water use dynamics in conifers growing in contrasting topographic positions (elevations, aspects, and hillslope positions) within a watershed; additionally, I explore how variability in sapwood traits may contribute to uncertainty in sap flow-based estimates of whole-tree transpiration. To these ends, I measured sap flow in 32 trees of 5 species throughout the 2014 growing season and estimated sapwood traits in those individuals and in co-occurring trees. I related sap flow dynamics to environmental variables (vapor pressure deficit and soil moisture) through lag analyses and nonlinear regression. A Monte Carlo-based simulation and mixed effects variance decomposition served to quantify the sensitivity of transpiration to variability in sapwood traits and the magnitude of that variability across ecological scales. The response of sap flow to vapor pressure deficit varied with species and across topographic positions, and sap flow dynamics diverged spatially as soil moisture declined during the summer. The simulation suggested that a common assumption (constant wood thermal diffusivity) could impart up to 100% overestimation of transpiration in trees with sapwood properties similar to those I observed. Taken together, these findings underscore the importance of sampling sap flow and sapwood traits at the spatiotemporal scale for which inferences are to be drawn.Item Inhibition of conifers growing under a deciduous canopy : degrees, seasonality and causes of suppression(Montana State University - Bozeman, College of Letters & Science, 2009) Dickman, Garrett Joseph; Chairperson, Graduate Committee: Theodore W. WeaverThe physiological response of conifers to a deciduous overstory is unstudied in the cool temperate zone despite the widespread occurrence of the association. The object of this study is therefore to determine the degree that understory conifers are inhibited by a deciduous overstory, and to identify the factors responsible. Thus, three conifer species (Juniperus scopulorum, Pseudotsuga menziesii, Abies lasiocarpa) growing with and without a deciduous Populus canopy were contrasted in regards to environment, seasonal performance, and physiological response to environmental factors. Understory conifer stands were darker, and especially so when the overstory had leaves. Understory environments of P. menziesii and A. lasiocarpa were cooler and had lower vapor pressure deficits than open sites, but were similar in relative humidity and soil water. In contrast, understory sites of J. scopulorum had similar temperature, vapor pressure deficit, and soil water. Relative to conifers in the open, photosynthesis of understory conifers was reduced by roughly the same amount (~10%), regardless of photosynthetic rate. While at intermittent times photosynthesis was reduced by much greater amounts, the expected increase of summertime suppression (>10%) was not seen. Understory conifer suppression was not linked to any seasonally limited resource, such as light, water, or nutrients. The slight suppression over the year was due to an unidentified factor, perhaps the lower temperature of the understory environment (-2C), or seemingly unlikely, an allelopathic effect from Populus. In instantaneous measures, photosynthesis was better correlated with day of year and RH than light, VPD, or temperature. The correlated phenomena relate to season and precipitation rather than canopy condition under study. Slight photosynthetic inhibition of understory conifers is supported by similar observations of suppression in the diameter growth and one-year's twig growth.