Aspen is a key resource in the Rocky Mountain Region for wildlife forage and habitat, lumber products, scenery, and plays important roles in fire ecology and hydrological processes. There is evidence of aspen decline over much of the Intermountain West for approximately 100 years. In Dixie and Fishlake National Forests, UT, aspen distribution has decreased by nearly half. Causes of this decline are not well understood, although wildlife browsing by ungulates has been implicated as playing a major role. The objective of this research was to examine what soil or plant factors might be involved in wildlife browse choice in aspen. Twenty-two pairs of moderately and intensively browsed sites were studied to identify factors related to browse preferences over two field seasons. In the summer of 2008, sites were sampled in June, July, and August, and in the summer of 2009 sites were sampled in August only. Soils were analyzed for pH, EC, total nitrogen and carbon, and mineral nutrients. Leaf tissue samples were analyzed for defense chemical (tannin and phenolic glycoside) concentrations, mineral nutrients (via acid digestion), acid-detergent fiber, water content, carbon:nitrogen ratio, and non-structural carbohydrate (sugar) concentration. No significant difference in phenolic glycoside concentrations between moderately and intensively browsed sites was found. Tannins were highest in sites with intensive levels of browsing. Iron was significantly higher and zinc lower in intensively than moderately browsed sites. Leaf moisture was also significantly lower in intensively browsed sites. In the absence of differences in phenolic glycosides, ungulates may be selecting browse sites based on iron requirements. Seasonal changes in the studied factors could be identified in 2008. Over the course of the summer, we found significant decreases in nitrogen, phosphorus, potassium, sulfur, zinc, iron, copper, phenolic glycosides, and moisture concentration. Seasonal increases in calcium, sodium, tannins, sugars, acid-detergent fiber, and carbon:nitrogen ratios were observed. The need for large ungulates to obtain specific nutrients may indicate that aspen is in higher demand as a forage at different times of the year, particularly in areas with forages low in these nutrients. Our data suggest that aspen high in iron may be at risk since other factors explaining browsing choice were not significantly different in our study. This information can help identify clones that are at risk and direct resources where and when they are needed most.

This thesis includes two studies. The first study examined changes in soil characteristics as a result of prolonged conifer dominance in successional aspen-conifer forests. Changing disturbance patterns in aspen-conifer forests appear to be altering successional dynamics that favors conifer expansion in aspen forests. The primary objective of this paper was to identify how increasing conifer dominance that develops in later successional stages alters forest soil characteristics. Soil measurements were collected along a stand composition gradient: aspen dominated, aspen-conifer mix, conifer dominated and open meadow, which includes the range of conditions that exists through the stages of secondary succession in aspen-conifer forests. Soil chemistry, moisture content, respiration, and temperature were measured. There was a consistent trend in which aspen stands demonstrated higher mean soil nutrient concentrations than adjacent meadows, mixed or conifer stands. Soil moisture was significantly higher in aspen stands and meadows in early summer. Soil respiration was significantly higher in aspen stands than conifer stands or meadows throughout the summer. The results indicate that soil resource availability and respiration peak within aspen dominated stands that are present during early succession and then decrease as conifer abundance increases along our stand composition gradient, representative of stand characteristics present in mid to late successional stages. Emerging evidence from other studies suggest that these observed changes in soil characteristics with increasing conifer dominance may have negative feedbacks on aspen growth and vigor. The second study examined the facilitation effect between aspen and subalpine fir establishment. In subalpine forests, conifer species are often found intermixed with broadleaf species. However, few if any studies have explored the existence and influence of facilitation between broadleaf tree species and conifers. We have observed the general establishment of subalpine fir seedlings at the base of aspen trees in a subalpine forest, indicating that a facilitative relationship may exist. To explore the potential facilitative relationship during secondary succession in subalpine forests, subalpine fir seeds were planted across a stand composition gradient (aspen dominated → mixed → conifer dominated stands) at six study sites in the Fishlake National Forest. Seeds were placed during the fall of 2010, at distances of 0 cm and 25 cm in each cardinal direction at the base of mature aspen and subalpine fir trees in each of the three stand types. Seeds were also planted within stand interspaces and in adjacent meadows. Seedling emergence was recorded at the beginning of the summer of 2011 and seedling mortality was recorded in October 2011. Soil moisture content was measured at the position that seeds were placed during the summers of 2009 and 2011. Aspen dominated stands had subalpine fir germination that was on average 11 times greater than mixed or conifer dominated stands. Germination was 2.3 fold greater at the base of aspen trees than fir trees and two fold greater at the base of aspen trees than interspaces. Seedling mortality was lower in aspen stands but was not significantly influenced by position relative to mature trees. Soil moisture was highest in aspen dominated stands, with better soil moisture conditions at the base of aspen trees and in interspaces compared to the base of fir trees. Few if any studies regarding conifer facilitation have provided evidence for facilitation at the germination life stage, rather they focus on seedling survival. However, our study illustrates a strong facilitative interaction in which both aspen dominated stands and aspen trees increase the likelihood of subalpine fir seedling establishment by drastically increasing rates of subalpine fir germination. Because of aspen's primary role in initiating secondary succession through post-disturbance sucker regeneration, and the subsequent dependence of conifers on aspen for establishment, aspen mortality via competition with conifers under longer fire cycles, droughts, or intensive ungulate browsing may result in a loss of aspen-conifer forest communities in some locales.

Accurate and reliable predictions of site index (height of dominant trees at a reference age, usually 50 years at breast-height) for timber crop species is essential for silvicultural site-specific decision making. Site index can be predicted from site quality once the relationship between site index and site quality has been quantified. Site quality is defined as the sum of all environmental factors affecting the biotic community, such as the factors directly influencing the growth of vascular plants (light, heat, soil moisture, soil nutrients, and soil aeration). Since these factors vary greatly in time, indirect estimates of site quality have widely been used as predictors for site index in various multiple regression models. Trembling aspen (Populus tremuloides Michx.) is the most widely distributed broadleaf species in British Columbia, especially in the Boreal White and Black Spruce (BWBS) biogeoclimatic zone. Growing this species for sustainable timber production requires a good understanding of its productivity attributes and accurate predictions of its growth. This extension note presents (1) relationships between trembling aspen site index and some indirect measures of site quality, and (2) site index prediction models using the indirect measures of site quality as predictors.

No description available.

No description available.

The general objectives of this thesis project were to describe and to understand the dynamics creating occurrence patterns of saproxylic wood-feeding Coleoptera in snags (i.e., standing dead trees) of black spruce and aspen along the decay gradient. The first part of this thesis focuses on pre-landing host-selection behaviours in coniferophagous species, i.e. the use of host-produced volatiles to locate potential hosts. Results presented suggest that most saproxylic wood-feeding beetles studied herein use volatiles to orient towards potential habitat patches but that olfactive information does not allow the identification of suitable hosts at close range prior to landing. The second part of the thesis focuses on the occurrence patterns themselves and on underlying mechanisms. Sampling was conducted using snag dissection, a novel method allowing a better characterization of larval stage wood-feeding assemblages. Opposite patterns were observed between the two host species studied, as abundance and species richness were highest in early stages of decay in spruce, and in middle to late stages of decay in aspen. In aspen, numerous nutritional and physical parameters of dead wood correlated significantly with wood-borer occurrence. However, most of these parameters were strongly auto-correlated, and the explanatory model most highly ranked by model selection consisted of only a snag age term. Also, a simple neutral model based on temporal autocorrelation in occurrence probability produced patterns similar to those observed through sampling. In the last original paper presented, results suggest that wood-boring larvae select for specific types of substrate in highly variable aspen snags. This selection on the part of the larvae likely decreases the impact of the oviposition site on subsequent larval performance, and could explain the lack of strong selection seen on the part of the mother. My results suggest very different host-selection dynamics in black spruce and aspen, as assemblages of the former were dominated by early-decay species with volatiles-driven colonization dynamics, while middle- to late-decay species dominated the later, seemingly through mostly neutral colonization mechanisms. Some of my findings suggest that patterns observed in black spruce and aspen could be extrapolated to a coniferous/deciduous host dichotomy in colonization dynamics of woodfeeding species, based on divergent secondary chemistry and wood structure.

Primary cell walls are a composite of cellulose microfibrilsand hemicelluloses. Xyloglucan is the principal hemicelluloseof primary cell walls of dicotyledons. Xyloglucanendotransglycosylases (XETs) cleave and religate xyloglucanpolymers in plant cell walls. A XET (PttXET16A) from hybridaspen has been heterologously expressed and characterized inour lab. To study XETs enzymology on a molecular level a series ofnovel xyloglucan oligosaccharides (XGOs) have been synthesized.The chromogenic 2-nitrophenol XGO and fluorogenic XGOs havebeen used as kinetic probes for PttXET16A. The first 3-Dstructure of the XET and of the enzyme-substrate complexrevealed new insights into the requirements fortransglycosylation. Cellulose fibers are an important raw material for manyindustries. In a novel chemo-enzymatic approach, thetransglycosylating activity of XET was used for biomimeticfiber surface modification. The aminoalditol XGO derivate wasused as key intermediate to incorporate novel chemicalfunctionality into xyloglucan. TheXGO derivatives wereintegrated into xyloglucan with PttXET16A. The resultingmodified xyloglucan was used as a versatile tool fiber surfacemodification.

No description available.

Cellulosabaserade material är världens rikligast förekommande förnyelsebara råvara. Växters cellväggar är naturliga kompositmaterial där den kristallina cellulosan är inbäddad i en väv av hemicellulosa, strukturproteiner och lignin. Xyloglukaner är en viktig hemicellulosagrupp som omger och korslänkar den kristallina cellulosan i cellväggarna. I denna avhandling undersöks undersöks sambanden mellan struktur och funktion hos olika xyloglukan-aktiva enzymer. En modell för effektiv enzymatisk omvandling av biomassa ges av cellulosomen hos den anaeroba prokaryota organismen Clostridium thermocellum. Cellulosomen är ett proteinkomplex med hög molmassa och flera olika enzymaktiviteter, bl.a. det inverterande xyloglukan-endohydrolaset CtXGH74A. Proteinstrukturen för CtXGH74A har lösts i komplex med xyloglukanoligosackarider, som stabliliserar vissa loopar/slingor som är oordnade i apostrukturen. Ytterligare detaljerade kinetiska och produktananalyser har genomförts för att entydigt visa att CtXGH74A är ett endoxyloglukanas vars slutliga nedbrytningsprodukt är Glc4-baserade xyloglukanoligosackarider. Som jämförelse innehåller glykosidhydrolasfamilj 16 (GH16) såväl hydrolytiska endoxyloglukanaser som xyloglukantransglykosylaser (XETs) från växter. För att utreda vad som bestämmer förhållandet mellan transglykosylering och hydrolys i xyloglukanaktiva enzymer från familj GH 16 jämfördes struktur och kinetik hos ett strikt transglykosylas, PttXET16-34 från hybridasp, med ett nära besläktat hydrolytiskt enzym, NXG1 från krasse. I NXG1 identifierades en viktig förlängningsloop, som vid trunkering gav ett muterat enzym med högre transglykosyleringshastighet och minskad hydrolytisk aktivitet. Kinetikstudierna genomfördes med hjälp av nyutvecklade känsliga provmetoder med väldefinerade XGO:er och ett antal kromogena XGO-arylglykosider. En detaljerad förståelse av enzymologin inom GH16 möjliggjorde utvecklingen av en ny kemoenzymatisk metod för biomimetisk fiberytmodifiering med hjälp av PttXET16-34s translgykosyleringsaktivitet. Aminoalditolderivat av xyloglukanoligosackarider användes som nyckelintermediärer för att introducera ny kemisk funktionalitet hos xyloglukan, såsom kromoforer, reaktiva grupper, proteinligander och initiatorer för polymeriseringsreaktioner. Tekniken innebär ett nytt och mångsidigt verktyg för fiberytmodifiering. / Zellulosehaltige Materialien sind die häufigsten erneuerbaren Rohmaterialien auf der Welt. Pflanzenzellwände sind natürliche Kompositmaterialien, sie enthalten kristalline Zellulose, die in einer Matrix aus Hemizellulosen, Proteinen und Lignin eingebettet sind. Xyloglukane sind eine wichtige Gruppe der Hemizellulosen, sie ummanteln und verbinden Zellulose in der pflanzlichen Zellwand. In dieser Abhandlung werden Strukturen von drei Xyloglukanaktiven Enzymen in Beziehung zu ihrer Funktion untersucht. Ein Paradigma für effizienter Nutzung von Biomasse ist das Cellulosom des anaerob lebenden Bakteriums Clostridium thermocellum. Das Cellulosom ist ein hochmolekularer Komplex von Proteinen mit vielen verschiedenen Aktivitäten, darunter ist auch die invertierende Xyloglukan Endohydrolase CtXGH74A. Die Proteinstruktur von CtXGH74A wurde im Komplex mit Xyloglukanoligosacchariden (XGO) gelöst, welche ungeordnete Loops der apo-Struktur stabilisierten. Durch weitere detaillierte Analyse der Kinetik und Reaktionsprodukte konnte schlüssig gezeigt werden, daß CtXGH74A eine Endoglukanase ist, die Glc4-basierte XGO produziert. Im Vergleich dazu enthält die retentierende Glykosidhydrolasefamilie 16 (GH16) sowohl hydrolytische Endoxyloglukanasen als auch Transglykosidasen von Pflanzen. Um zu erklären welche Faktoren das Verhältnis zwischen Transglykosidase und Hydrolase Aktivität bei GH16 Xyloglukanaktiven Enzymen bestimmen wurde eine reine Transglykosidase PttXET16-34 von Hybridaspen mit einem nah verwandten hydrolytischen Enzym NXG1 von Kapuzinerkresse strukturell und kinetisch verglichen. Als Schlüsselstelle wurde eine Verlängerung eines Loops in NXG1 identifiziert, Verkürzung des Loops führte zu einer Mutante mit erhöhter Transglykosylierungsrate bei verminderter hydrolytischer Aktivität. Kinetische Studien wurden erleichtert durch neu entwickelte hochempfindliche Methoden für Aktivitätsmessung, die auf XGO oder chromogene Aryl-XGO als definierte Substrate zurückgreifen. Detailliertes Verständnis von GH16 Enzymologie hat den Weg für die Entwicklung für eine neuartige Methode für biomimetische Oberflächenmodifikation von Zellulosefibern geebnet, dafür wurde die transglykosylierende Aktivität von PttXET16-34 angewendet. Aminoalditol-derivate von XGO wurden als wichtigste Zwischenprodukte angewendet, um neue chemische Funktionalitäten in Xyloglukan einzuführen, darunter waren Chromophore, reaktive Gruppen, Proteinliganden und Initiatoren für Polymerisationsreaktionen. Die modifizierten Xyloglukane wurden an eine Reihe von verschiedenen Zellulosematerialien gebunden und veränderten die Oberflächeneigenschaften dramatisch. Diese Methode ist ein neues wertvolles Werkzeug für Oberflächenmodifikation von Zellulosen. / Cellulosic materials are the most abundant renewable resource in the world; plant cell walls are natural composite materials containing crystalline cellulose embedded in a matrix of hemicelluloses, structural proteins, and lignin. Xyloglucans are an important group of hemicelluloses, which coat and cross-link crystalline cellulose in the plant cell wall. In this thesis, structure-function relationships of a range of xyloglucan-active enzymes were examined. A paradigm for efficient enzymatic biomass utilization is the cellulosome of the anaerobic bacterium Clostridium thermocellum. The cellulosome is a high molecular weight complex of proteins with diverse enzyme activities, including the inverting xyloglucan endo-hydrolase CtXGH74A. The protein structure of CtXGH74A was solved in complex with xyloglucan oligosaccharides (XGOs) which stabilized disordered loops of the apo-structure. Further detailed kinetic and product analyses were used to conclusively demonstrate that CtXGH74A is an endo-xyloglucase that produces Glc4-based XGOs as limit digestion products. In comparison, the retaining glycoside hydrolase family 16 (GH16) contains hydrolytic endo-xyloglucanases as well as xyloglucan transglycosylases (XETs) from plants. To elucidate the determinants of the transglycosylase/hydrolysis ratio in GH16 xyloglucan-active enzymes, a strict transglycosylase, PttXET16-34 from hybrid aspen, was compared structurally and kinetically with the closely related hydrolytic enzyme NXG1 from nasturtium. A key loop extension was identified in NXG1, truncation of which yielded a mutant enzyme that exhibited an increased transglycosylase rate and reduced hydrolytic activity. Kinetic studies were facilitated by the development of new, sensitive assays using well-defined XGOs and a series of chromogenic XGO aryl-glycosides. A detailed understanding of GH16 xyloglucan enzymology has paved the way for the development of a novel chemo-enzymatic approach for biomimetic fiber surface modification, in which the transglycosylating activity of PttXET16-34 was employed. Aminoalditol derivates of XGOs were used as key intermediates to incorporate novel chemical functionality into xyloglucan, including chromophores, reactive groups, protein ligands, and initiators for polymerization reactions. The resulting modified xyloglucans were subsequently bound to a range of cellulose materials to radically alter surface properties. As such, the technology provides a novel, versatile toolkit for fiber surface modification. / QC 20100624

Trembling aspen (Populus tremuloides Michx.) is one of the most common tree species in the boreal and temperate forests of North America. It grows on many different sites and associates with a variety of tree species. In BC, aspen is frequent throughout all submontane and montane continental forested zones. Relationships between environmental factors and forest productivity have been the subjects of many studies. Most of these studies, using various topographic, soil, physical and chemical properties as independent variables, had limited success in accounting for the variation in SI over a large geographic area. The objectives of this study were (1) to quantify relationships between aspen SI and environmental factors at two spatial scales, and (2) to develop predictive SI models from easily measurable environmental factors.