PATTERNS AND DRIVERS OF CARBON FLUXES IN TEMPERATE FORESTS

Despite decades of carbon cycling research in terrestrial ecosystems, a complex suite of biotic and abiotic interactions make a complete understanding of the natural carbon cycle elusive. This thesis aims to advance our understanding of the carbon cycle, and stems from several ongoing projects aimed at quantifying carbon dynamics in forest ecosystems across a range of scales, with a specific effort to include both above and belowground components of forest ecosystems. I begin with a project using detailed chemical measurements on specific segments of root systems from two different tree species, in order to help refine methods that quantify the production of symbiotic root-associated mycorrhizal fungi. Next, I use top-down and bottom-up approaches to determine a comprehensive carbon budget (including the production of mycorrhizal fungi), as well as interannual drivers of carbon fluxes in a northern temperate forest stand. Lastly, I compare patterns of carbon allocation to plant and fungal components in temperate forest stands spanning a range of species composition. Chapter 1 presents results from a project done in collaboration with Dr. Dali Gou and researchers at the Maoershan research station in China, focusing on fine scale patterns of root anatomy, chemistry, and function. I used patterns in fine root chemistry to assess the importance of symbiotic root-colonizing (mycorrhizal) fungi to two important tree species in China that differ in their mycorrhizal associate type — arbuscular mycorrhizal versus ectomycorrhizal fungi. Results indicated a strong fungal association in ectomycorrhizal Larix gmelinii, with fungal material comprising over 50 % of nitrogen and 36 % of the biomass of root tips in Larix. Data from this work helped refine an approach to quantify the production of mycorrhizal fungi in forest ecosystems using stable isotopes. Chapter 2 is the result of a long term effort to quantify carbon fluxes within northern hardwood temperate forest stands at the Bartlett Experimental Forest, New Hampshire. The stands used in this study are centered on an eddy covariance flux tower (part of the Ameriflux network), and are also part of NASA’s North American Carbon Program (NACP) Tier-2 field research sites. I present a detailed carbon budget of net and gross ecosystem fluxes using measurements collected from 2004-2016. Comparison of interannual fluxes suggested the presence of direct climate controls on wood growth (growing season temperature and moisture), and indirect controls on gross carbon uptake related to conditions in the winter and spring preceding the growing season. The data resulting from this work provide an ideal data set for assessing the capability of ecosystem models to simulate a number of aspects of forest ecosystem carbon dynamics. Chapter 3 is an extension of the carbon measurements around the flux tower at Bartlett, and spans a range of forest stands with varying species composition. This work was unique in its attempt to quantify the production of both plant components and mycorrhizal fungi. Results indicate that as biomass of conifer tree species increased relative to deciduous species, the production of foliage, wood, and fine roots significantly decreased. In contrast, the production of mycorrhizal fungi was more than twice as high in nearly pure conifer stands than in pure deciduous broadleaf stands, at times equaling or exceeding rates of wood production. Stable isotope data indicated that both the tree species present (e.g. conifers), as well as soil nutrient availability were important in influencing rates of fungal production

Mycorrhizal roots in a temperate forest take up organic nitrogen from 13C- and 15N-labeled organic matter

Background and Aims The importance of the uptake of nitrogen in organic form by plants and mycorrhizal fungi has been demonstrated in various ecosystems including temperate forests. However, in previous experiments, isotopically labeled amino acids were often added to soils in concentrations that may be higher than those normally available to roots and mycorrhizal hyphae in situ, and these high concentrations could contribute to exaggerated uptake. Methods We used an experimental approach in which we added 13C-labeled and 15N-labeled whole cells to root-ingrowth cores, allowing proteolytic enzymes to release labeled organic nitrogen at a natural rate, as roots and their associated mycorrhizal fungi grew into the cores. We employed this method in four forest types representing a gradient of soil pH, nitrogen mineralization rate, and mycorrhizal type. Results Intact uptake of organic nitrogen was detected in mycorrhizal roots, and accounted for at least of 1-14% of labeled nitrogen uptake. Forest types did not differ significantly in the importance of organic uptake. Conclusions The estimates of organic N uptake here using 13C-labeled and 15N-labeled whole cells are less than those reported in other temperate forest studies using isotopically labelled amino acids, and likely represent a minimum estimate of organic N-use. The two approaches each have different assumptions, and when used in tandem should complement one another and provide upper and lower bounds of organic N use by plants

Warming Up to Dance/Movement Therapy Through Humor

This thesis examined the effects humor has on a Dance/Movement Therapy (DMT) warm-up intervention in increasing engagement for individuals in a grief setting who are new to DMT practices. Studies have demonstrated the positive effects humor has on individuals’ sense of comfort and there were notable similarities with the benefits of DMT. The healing advantages of humor were thoroughly studied and the comedic principle of the “Rule of Threes” was chosen and translated into a movement warm-up intervention to create a space that allowed for humor and laughter. This humor strategy for the warm-up intervention was used in a group and individual DMT sessions. Data were collected regarding the individuals’ feelings on movement prior to the intervention as well as after completion of the intervention. The data collected showed that laughter occurred throughout the sessions and individuals felt a sense of readiness to continue with the rest of the DMT session. These findings suggested that utilizing humor and laughter with DMT interventions could lead to increased engagement from participants. Further study is needed to demonstrate effective uses of humor with DMT practices

Energy Consumption of Household Consumer Products

This article describes the energy consuming characteristics of the U.S. household both in quantative and qualitative terms. Alternative household definitions for energy consuming household consumer products are used to illustrate and assess the potential consequences of mandatory energy efficiency and labeling standards

Readout and Control of a Power-recycled Interferometric Gravitational-wave Antenna

Interferometric gravitational wave antennas are based on Michelson interferometers whose sensitivity to small differential length changes has been enhanced by adding multiple coupled optical resonators. The use of optical cavities is essential for reaching the required sensitivity, but sets challenges for the control system which must maintain the cavities near resonance. The goal for the strain sensitivity of the Laser Interferometer Gravitational-wave Observatory (LIGO) is 10^-21 rms, integrated over a 100 Hz bandwidth centered at 150 Hz. We present the major design features of the LIGO length and frequency sensing and control system which will hold the differential length to within 5 10^-14 m of the operating point. We also highlight the restrictions imposed by couplings of noise into the gravitational wave readout signal and the required immunity against them.Comment: Presentation at ICALEPCS 2001, San Jose, November 2001, (WECT003), 3 page

Thermal limits across life stages do not predict contemporary geographic distributions

Rapid and ongoing climate change is causing a complete redistribution of life on Earth. To predict species’ geographic responses to climate change, it is critical that we establish the role of species’ thermal tolerances in shaping their climatic envelopes. Using experimentally-derived measures of thermal limits and a database of georeferenced occurrence records, we test whether thermal limits can predict the hottest and coldest temperatures experienced within the geographic distributions of 13 North American odonate species. We measure thermal limits in both odonate larvae and adults to account for potential life stage-related differences. Lastly, we use a time-calibrated phylogeny of North American odonates to estimate the effects of evolutionary history on the relationship between species’ thermal and climatic limits. We find that, even after accounting for ontogenetic differences and phylogeny, thermal limits do not translate into climatic limits. Further, we determine that species’ thermal limits are constrained by phylogeny, while climatic limits appear to have evolved free from phylogenetic associations. This suggests that the evolvability of odonates’ thermal limits is limited and that currently, species are in disequilibrium with their environment. Additionally, other traits or processes, such as biotic interactions, are potentially shaping odonates’ geographic distributions. In the face of climate change, odonates are unlikely to adapt to novel environmental conditions and thus will likely have to continue to shift their geographic distributions in order to track their ancestral thermal niches. Further, purely climate-based models will likely be insufficient for predicting odonates’ geographic responses to climate change

The role of surface roughness, albedo, and Bowen ratio on ecosystem energy balance in the Eastern United States

Land cover and land use influence surface climate through differences in biophysical surface properties, including partitioning of sensible and latent heat (e.g., Bowen ratio), surface roughness, and albedo. Clusters of closely spaced eddy covariance towers (e.g., \u3c10 \u3ekm) over a variety of land cover and land use types provide a unique opportunity to study the local effects of land cover and land use on surface temperature. We assess contributions albedo, energy redistribution due to differences in surface roughness and energy redistribution due to differences in the Bowen ratio using two eddy covariance tower clusters and the coupled (land-atmosphere) Variable-Resolution Community Earth System Model. Results suggest that surface roughness is the dominant biophysical factor contributing to differences in surface temperature between forested and deforested lands. Surface temperature of open land is cooler (−4.8 °C to −0.05 °C) than forest at night and warmer (+0.16 °C to +8.2 °C) during the day at northern and southern tower clusters throughout the year, consistent with modeled calculations. At annual timescales, the biophysical contributions of albedo and Bowen ratio have a negligible impact on surface temperature, however the higher albedo of snow-covered open land compared to forest leads to cooler winter surface temperatures over open lands (−0.4 °C to −0.8 °C). In both the models and observation, the difference in mid-day surface temperature calculated from the sum of the individual biophysical factors is greater than the difference in surface temperature calculated from radiative temperature and potential temperature. Differences in measured and modeled air temperature at the blending height, assumptions about independence of biophysical factors, and model biases in surface energy fluxes may contribute to daytime biases

Régulation de l’identité des membres postérieurs par le facteur de transcription à boîte T Tbx4

Bien que partageant une homologie structurelle évidente, les membres antérieurs (MA) sont toujours différents des membres postérieurs (MP). Ceci suggère l’existence d’un programme générique de formation d’un membre, un bauplan, qui doit être modulé de façon spécifique pour engendrer cette différence antéro-postérieure de l’identité. Nous avons donc voulu identifier les mécanismes déployés durant l’évolution pour permettre la mise en place de l’identité des membres. Le laboratoire avait précédemment caractérisé, chez les souris où le gène Pitx1 est inactivé, une transformation partielle des MP en MA couplée à une perte de croissance. Nous avons donc cherché à comprendre les mécanismes en aval de Pitx1 dans la détermination de l’identité postérieure. Notre démarche nous a permis d’identifier les gènes affectés par la perte de Pitx1 dans les MP, où nous avons confirmé une dérégulation de l’expression de Tbx4. Tbx4 et Tbx5 sont des candidats évidents pour déterminer l’identité, leur expression étant restreinte aux MP et MA, respectivement, mais leur implication dans ce processus était sujette à controverse. Nous avons donc évalué l’apport de Tbx4 en aval de Pitx1 dans les processus d’identité en restaurant son expression dans les MP des souris Pitx1-/-. Ce faisant, nous avons pu montrer que Tbx4 est capable de pallier la perte de Pitx1 dans le MP, en rétablissant à la fois les caractères d’identité postérieure et la croissance. En parallèle, nous avons montré que Tbx5 était capable de rétablir la croissance mais non l’identité des MP Pitx1-/-, démontrant ainsi de façon définitive une propriété propre à Tbx4 dans la détermination de l’identité des membres postérieure. La caractérisation de l’activité transcriptionnelle de Tbx4 et Tbx5 nous a permis de mettre en évidence un domaine activateur conservé mais aussi un domaine spécifique à Tbx4, répresseur de la transcription. Par ailleurs, une mutation faux-sens de TBX4 dans les patients atteints du syndrome coxo-podo-patellaire, TBX4Q531R, inactive le domaine répresseur, empêchant la compensation de l’identité mais non de la croissance des MP dépourvus de Pitx1, démontrant l’importance de cette fonction dans l’identité postérieure. La caractérisation de l’activité répressive de Tbx4, qui se manifeste seulement dans les membres postérieurs démontre l’importance de cette fonction dans l’identité postérieure. Nous avons aussi été en mesure d’identifier un corépresseur qui est suffisant pour supporter cette activité de Tbx4. Enfin, nous avons pu aussi démontrer l’activité transcriptionnelle d’un représentant du gène ancestral, présent chez Amphioxus, qui se comporte strictement comme un activateur et semble dépourvu du domaine répresseur. En somme, nous avons précisé le rôle de Tbx4 et Tbx5, ainsi que leur mécanisme, dans la détermination de l’identité des membres. Globalement, nos travaux permettent d’élaborer une théorie où une divergence d’activité transcriptionnelle de Tbx4 et Tbx5 est responsable de l’identité des membres et même entrevoir que cette divergence d’activité soit à la base de son apparition durant l’évolution.Forelimbs and hindlimbs are a classical example of serial homology, suggesting they share an evolutionary common generic program that directs their formation. Identity is presumably derived from specific modulations of that program in different limb type. Transcription factors are prime candidates to link these structural differences to specific modulations and three factors with limb-specific expression have been identified. Pitx1 and Tbx4 expression is restricted to the hindlimbs while Tbx5 is restricted to the forelimbs and they have all been ascribed functions in both growth and identity from knockout and overexpression studies. Recent studies have produce evidence that Tbx4 and Tbx5 are interchangeable, sharing identical properties to support growth but not identity of the limbs, the latter being a direct consequence of Pitx1 expression. Indeed, Pitx1 deficient mice have been previously described as undergoing a hindlimb-to-forelimb transformation in addition of growth defects. To better assess the shared and specific properties of Tbx4 and Tbx5, we assessed their capacities to rescue identity and growth defects by expression studies in Pitx1-/- hindlimbs. Specifically, previous studies had shown that Pitx1 deficiency causes the loss of hindlimb features, the transformation of hindlimb features toward forelimb-like morphology, the gain of a forelimb feature and the asymmetric loss of growth at the level of the femur. Targeted expression in the limbs of both Tbx4 and Tbx5 rescued the growth defects similarly. Interestingly, only Tbx4 was able to restore identity features affected in absence of Pitx1. To further assess these shared and specific properties, we conducted transcriptional assays that revealed the presence of a shared and conserved transactivating domain in the C-terminal moiety of these proteins. Moreover, we could identify a repressor domain specific to Tbx4. Human small patella syndrome maps to TBX4 and a coding mutation, TBX4Q531R, that specifically inactivates the repressive properties of Tbx4 prevents it from rescuing identity to the Pitx1-/- hindlimbs but not from rescuing growth. We also conducted a yeast two-hybrid assay that allowed the identification of putative co-factors of Tbx4, of which one seems to act as a co-repressor. Together, our results support the presence of a Tbx4/Tbx5 conserved activating domain required for limb outgrowth that is an integral part of the limb bauplan. Importantly, we identified a molecular basis for the determination of limb identity through the Tbx4-specific repressor domain and reveal a novel path through which limb identity may have emerged during evolution