Weed seed contaminants in agricultural products from China in recent years have the potential for introducing new invasive plant species. Seeds of 169 weedy species from 39 families were collected from Chinese farmlands. Fifty-eight of these that are currently absent in Canada were evaluated. Two weed risk assessment (WRA) models (modified WRA+ secondary screen tool and weed elsewhere+ modified WRA+ secondary screen tool) rejected all invasive plant species and showed similar accuracy in non-invasvie plant species prediction based on 140 existing alien plant species in Canada, yet the second WRA model took significantly less time to conduct the evaluation. Fifty-five potential invasive species with various negative impacts in Chinese farmlands were rejected to enter Canada by the “weed elsewhere+ modified WRA+ secondary screen tool” model, including eight species that cause significant damage to Chinese farmlands. However, Anemone rivularis and Silene jenisseensis, which have no negative impacts in China, were also rejected. Seed germination characteristics among 18 Chinese weedy species were found with base temperatures for germination (Tb) varying from -2.5°C to 10.9°C, thermal time requirements to reach 50% germination (θ_50) ranging from 23.7 to 209.2℃*Day, and different optimal temperatures for germination, which may facilitate these species to cause different degrees of negative impacts in Canadian prairie provinces. An alien species would have a higher competitive advantage in resource uptake and space occupation than its congeneric with advantageous seed germination characteristics; otherwise it will be less competitive than its congeneric. In addition, plant functional traits that promote invasiveness would make an alien species more invasive. In conclusion, the “weed elsewhere+ modified WRA+ secondary screen tool” model is a fast and highly accurate way to screen out potential invasive species from Chinese environments, and is applicable to other environments with modification. Seed germination characteristics can be used to predict seasonal dynamics of weed seedling populations. The comparison of seed germination characteristics and other plant functional traits between alien plant and its congeneric weed from native areas provides a new way to evaluate the invasive potential of alien plant species.

The biochemistry of leaves merges the fates of trees and the atmosphere. Leaf primary metabolism cycles carbon and indirectly drives atmospheric circulation via the latent heat of transpiration. Tropical forests contain half of global forest carbon, and actively cycle carbon and energy year round, making them critical components of the coupled biosphere-climate system. Climate change threatens tropical forests with rising temperatures and increasing variability of precipitation. Their response will influence future biodiversity as well as the fate of the climate. Understanding the physiological attributes that define tropical tree responses and feedbacks to climate is a current research priority. The emission of isoprene gas from plant leaves has been demonstrated to enhance leaf tolerance to high temperatures and drought. Isoprene is a volatile secondary metabolite produced in the chloroplast by approximately one-third of plant species. While the benefits of isoprene are supported by extensive laboratory and greenhouse-based research, work has only begun to explore how the trait is integrated in plant functional strategies. Whether isoprene influences differential species performance and survival across environments has yet to be tested. An impediment to filling this clear ecological research gap has been a lack of instrumentation capable of quantifying isoprene emissions from leaves in remote field settings. The first study presented here tests the hypothesis that isoprene emission influences plant community assembly shifts across environmental gradients and through time in tropical forests. The capacity for a species to produce isoprene was associated with increased relative abundance at higher temperatures and following drought anomalies. A negative relationship with the length of seasonal drought suggests a trade-off between isoprene emission and other plant traits, such as deciduous leaf habit. The second study presents the development of a new instrument that is uniquely optimized for field-based ecological research on leaf volatiles. The new system, named PORCO (Photoionization of Organic Compounds), utilizes custom leaf cuvettes, precision light control, and an optimized commercial photoionization detector to achieve real-time detection of leaf emissions with detection limits better than 0.5 nmol m⁻² leaf s⁻¹. The third study utilizes PORCO to test hypotheses about the structuring of isoprene within plant functional strategies and across forest microenvironments in an eastern Amazonian evergreen tropical forest. The results support the role of isoprene—and potentially other volatile isoprenoids—in mitigating effects of intermittent sun exposure in the sub-canopy. Emissions are structured in a complex, multivariate manner that depends on taxonomy, leaf and wood characteristics, tree height, and light environment. The results from this dissertation work demonstrate that isoprene emission from leaves affects plant responses to climate at ecologically relevant scales. Isoprene influences climate not only by its effect on primary leaf functions, but also by directly altering atmospheric chemistry, and contributing to aerosol and cloud properties. Understanding isoprene's role in forest responses to increasing temperatures and drought will help to predict the feedbacks between forest ecosystems and climatic change.

As florestas subtropicais têm um papel importante nos serviços ecossistêmicos, embora pouco se conheça sobre a sua dinâmica e funcionamento, especialmente na porção sul da Mata Atlântica. A dinâmica florestal é frequentemente avaliada pela variação líquida da biomassa de árvores. Essa dinâmica de biomassa é influenciada por processos demográficos nas comunidades, os quais correspondem ao crescimento (de sobreviventes), recrutamento e mortalidade de indivíduos. Avaliamos a influência de fatores bióticos (atributos funcionais de plantas e a estrutura inicial da floresta) e fatores abióticos (variáveis do solo) sobre a dinâmica de biomassa de uma floresta subtropical, em um intervalo de 18 anos. Também avaliamos o efeito dos processos demográficos sobre a mudança de biomassa líquida da floresta. O estudo foi realizado no sul do Brasil, em uma área de transição entre a Floresta com Araucária e a Floresta Estacional, sem registro de distúrbio há pelo menos 60 anos, mas com histórico anterior de corte seletivo de madeira. Os levantamentos foram realizados em 1999 e em 2017, em 24 parcelas permanentes de 500 m2 cada, mensurando todos os indivíduos com CAP > 30 cm. Atributos funcionais foliares, de densidade de madeira e altura potencial foram obtidos para todas as espécies. Modelos lineares foram utilizados para avaliar o efeito de atributos funcionais (considerando valores médios da comunidade inicial (CWM= ‘community-weighted mean’) e a diversidade funcional (FD)), da estrutura inicial (área basal no tempo inicial) e de variáveis do solo sobre as variáveis resposta (taxa anual de crescimento, recrutamento e mortalidade). Modelos lineares também foram utilizados para avaliar o efeito dos processes demográficos (taxa de crescimento, recrutamento e mortalidade) e incremento em biomassa (biomassa de sobreviventes + recrutas) sobre a variação líquida de biomassa na comunidade. Observamos um efeito positivo do CWM da altura máxima sobre o crescimento de sobreviventes, e um efeito negativo do CWM do conteúdo de fósforo foliar, do FD de conteúdo de matéria seca foliar (LDMC) e da FD da altura máxima. A biomassa de recrutados teve um efeito positivo do pH e negativo do K do solo, enquanto a mortalidade foi positivamente associada à estrutura inicial da comunidade. Observamos ainda que a mudança líquida de biomassa desta floresta teve influência significativa da mortalidade e do incremento total (biomassa de sobreviventes + recrutados). Comunidades com indivíduos mais altos e com atributos relacionados à conservação de recursos em média crescem mais, enquanto que o menor crescimento teve relação com comunidades funcionalmente mais diversas em termos de LDMC e altura, potencialmente associado a espécies de sub-bosque. Solos menos ácidos permitiram o maior recrutamento, enquanto que a alta concentração de K limitou o recrutamento. Comunidades com maior cobertura inicial apresentaram maior mortalidade de espécies no período. Este trabalho traz importantes resultados sobre a dinâmica de florestas subtropicais, demonstrando que as características iniciais da comunidade, tanto bióticas quanto abióticas, tiveram influência no incremento e/ou perda em biomassa deste ecossistema num período de quase duas décadas. / Subtropical forests play an important role on ecosystem services, but the drivers of biomass dynamics and ecosystem functioning specially at the southern portion of Mata Atlântica are poorly understood. The forest dynamics is often evaluated by tree net biomass change, which is underlied by the community demographic processes. These demographic processes correspond to the growth of survival trees, recruitment and mortality. Here we evaluated the influence of biotic factors (plant functional traits and the initial forest structure) and abiotic factors (soil variables) on biomass dynamics of a subtropical forest in an interval of 18 years. We also evaluated the effect of demographic processes on the net biomass change of the forest. This study was carried out in a subtropical forest in southern Brazil and the region is characterized by the Atlantic forest s.l, in a transitional area between Araucaria and Seasonal forest. The study area corresponds to a protected area (Chapecó National Forest) that did not suffer disturbance since at least 60 years but had some selective logging before. The forestry inventories were realized in 1999 and 2017, in 24 permanent plots with 500 m2 each one. All the individuals with circumference at breast height > 30 cm were measured, identified and tagged. Leaf functional traits, wood density and maximum height were obtained for all species. We performed linear models to evaluate the effect of functional traits (following the mean values of initial community, community-weighted mean (CWM) and functional trait diversity (FD)), initial forest structure (community basal area in initial time) and soil variables, on the response variables (annual rate of growth of survival, recruits and mortality). Linear models were also used to evaluate the effect of tree demographic processes (biomass growth of survival, recruits, mortality and biomass increment (growth of survival + recruits)) on the net biomass change. We observed a positive effect of CWM and FD of maximum height, FD of leaf dry matter content (LDMC) and a negative of CWM of leaf nitrogen content on the growth of survivors. The biomass of recruits had a negative effect of soil K content, and a positive effect of soil pH. Biomass mortality was positive related to the initial forest structure. The net biomass change was negatively influenced by the biomass mortality and positively related to the biomass increment. Communities with taller individuals in mean and traits related to resources conserving grew more. The lower growth was related to more diverse communities in terms of LDMC and maximum height, probably associated to understory species. Less acid soils allowed more recruitment, and high availability of soil K limited the recruitment. Communities with more initial tree cover had more mortality along the time. This work provided important results about the biomass dynamics in subtropical forests, showing that biotic and abiotic community initial characteristics influenced the gain or loss of biomass of this ecosystem in a period of almost two decades.

Terrestrial ecosystems are essential to human well-being, but their future remains highly uncertain, as evidenced by the huge disparities in model projections of the land carbon sink. The existence of these disparities despite the recent explosion of novel data streams, including the TRY plant traits database, the Landsat archive, and global eddy covariance tower networks, suggests that these data streams are not being utilized to their full potential by the terrestrial ecosystem modeling community. Therefore, the overarching objective of my dissertation is to identify how these various data streams can be used to improve the precision of model predictions by constraining model parameters. In chapter 1, I use a hierarchical multivariate meta-analysis of the TRY database to assess the dependence of trait correlations on ecological scale and evaluate the utility of these correlations for constraining ecosystem model parameters. I find that global trait correlations are generally consistent within plant functional types, and leveraging the multivariate trait space is an effective way to constrain trait estimates for data-limited traits and plant functional types. My next two chapters assess the ability to measure traits using remote sensing by exploring the links between leaf traits and reflectance spectra. In chapter 2, I introduce a method for estimating traits from spectra via radiative transfer model inversion. I then use this approach to show that although the precise location, width, and quantity of spectral bands significantly affects trait retrieval accuracy, a wide range of sensor configurations are capable of providing trait information. In chapter 3, I apply this approach to a large database of leaf spectra to show that traits vary as much within as across species, and much more across species within a functional type than across functional types. Finally, in chapter 4, I synthesize the findings of the previous chapters to calibrate a vegetation model's representation of canopy radiative transfer against observed remotely-sensed surface reflectance. Although the calibration successfully constrained canopy structural parameters, I identify issues with model representations of wood and soil reflectance that inhibit its ability to accurately reproduce remote sensing observations.

Central Europe wet meadows are characterized by considerable species richness. The biodiversity maintenance of the wet meadows is connected with regular management (i.e. grazing or mowing). As their area drastically decreased due to changes in land use in the last century, they have become the object of interest among scientists, conservation biologists. This thesis is composed of three original studies which are focused on escribing diversity patterns of the whole spectra of wet meadows at landscape level and dynamic of their changes depending on different management regimes (mowing/abandonment,fertilizing/unfertilizing). The synthesis of these studies reveals the description of the processes underlying the wet meadows species loss depending on land use changes and proposes the principles for sustainable conservation management.

abstract: Functional traits research has improved our understanding of how plants respond to their environments, identifying key trade-offs among traits. These studies primarily rely on correlative methods to infer trade-offs and often overlook traits that are difficult to measure (e.g., root traits, tissue senescence rates), limiting their predictive ability under novel conditions. I aimed to address these limitations and develop a better understanding of the trait space occupied by trees by integrating data and process models, spanning leaves to whole-trees, via modern statistical and computational methods. My first research chapter (Chapter 2) simultaneously fits a photosynthesis model to measurements of fluorescence and photosynthetic response curves, improving estimates of mesophyll conductance (gm) and other photosynthetic traits. I assessed how gm varies across environmental gradients and relates to other photosynthetic traits for 4 woody species in Arizona. I found that gm was lower at high aridity sites, varied little within a site, and is an important trait for obtaining accurate estimates of photosynthesis and related traits under dry conditions. Chapter 3 evaluates the importance of functional traits for whole-tree performance by fitting an individual-based model of tree growth and mortality to millions of measurements of tree heights and diameters to assess the theoretical trait space (TTS) of “healthy” North American trees. The TTS contained complicated, multi-variate structure indicative of potential trade-offs leading to successful growth. In Chapter 4, I applied an environmental filter (light stress) to the TTS, leading to simulated stand-level mortality rates up to 50%. Tree-level mortality was explained by 6 of the 32 traits explored, with the most important being radiation-use efficiency. The multidimentional space comprising these 6 traits differed in volume and location between trees that survived and died, indicating that selective mortality alters the TTS. / Dissertation/Thesis / Doctoral Dissertation Biology 2017

Andean montane forests are one of the most diverse ecosystems on Earth, but are also highly vulnerable to climate change. Therefore, the link between plant distribution and ecosystem productivity is a critical point to investigate in these ecosystems. Are the patterns in productivity observed in montane forest due to species turnover along the elevational gradients? Methodological constraints keep this question unanswered. Also, despite their importance, belowground biomass remains poorly quantified and understood. I measured two plant functional traits in seedlings, root:shoot ratio and specific leaf area, to identify different strategies in growth and biomass allocation across elevations. A tradeoff in specific leaf area with elevation was found in only one species, and no generalized directional change was detected with elevations for root:shoot ratio. Lack of information for the ontogeny of the measured plant traits could confounding the analysis.

No description available.

abstract: Climate change has the potential to affect vegetation via changes in temperature and precipitation. In the semi-arid southwestern United States, heightened temperatures will likely lead to accelerated groundwater pumping to meet human needs, and altered storm patterns may lead to changes in flood regimes. All of these hydrologic changes have the potential to alter riparian vegetation. This research, consisting of two papers, examines relationships between hydrology and riparian vegetation along the Verde River in central Arizona, from applied and theoretical perspectives. One paper investigates how dominance of tree and shrub species and cover of certain functional groups change along hydrologic gradients. The other paper uses the Verde River flora along with that river's flood and moisture gradients to answer the question of whether functional groups can be defined universally. Drying of the Verde River would lead to a shift from cottonwood-willow streamside forest to more drought adapted desert willow or saltcedar, a decline in streamside marsh species, and decreased species richness. Effects drying will have on one dominant forest tree, velvet ash, is unclear. Increase in the frequency of large floods would potentially increase forest density and decrease average tree age and diameter. Correlations between functional traits of Verde River plants and hydrologic gradients are consistent with "leaf economics," or the axis of resource capture, use, and release, as the primary strategic trade-off for plants. This corresponds to the competitor-stress tolerator gradient in Grime's life history strategy theory. Plant height was also a strong indicator of hydrologic condition, though it is not clear from the literature if plant height is independent enough of leaf characteristics on a global scale to be considered a second axis. Though the ecohydrologic relationships are approached from different perspectives, the results of the two papers are consistent if interpreted together. The species that are currently dominant in the near-channel Verde River floodplain are tall, broad-leaf trees, and the species that are predicted to become more dominant in the case of the river drying are shorter trees or shrubs with smaller leaves. These results have implications for river and water management, as well as theoretical ecology. / Dissertation/Thesis / M.S. Plant Biology 2011

Au sein des communautés végétales, les traits fonctionnels dirigent et influencent les processus sol-plantes. Le ruissellement et l'érosion concentrés, causes principales de la dégradation des sols, peuvent être contrôlés par des végétations herbacées qui créent une rugosité hydraulique induisant la réduction de la vitesse des flux de ruissellement et la rétention des sédiments. L'approche des traits, plutôt que taxonomique, permet de comprendre et caractériser les effets directs de la végétation sur le ruissellement et la rétention des sédiments. Ce projet de recherche vise à approfondir les connaissances vis-à-vis des effets (i) des traits fonctionnels (Chapitre 1), (ii) de la complémentarité des traits (Chapitre 2), et (iii) de la diversité fonctionnelle (Chapitre 3) sur les écoulements concentrés et la rétention des sédiments afin d'évaluer l'efficacité et le design de haies herbacées pour réduire les impacts de l'érosion des sols dans les bassins versants limoneux d'Europe. Parmi les combinaisons de traits principaux identifiées comme augmentant la rugosité hydraulique (densité et diamètre des tiges, et densité et surface foliaire), certains traits sont négativement corrélés. Un meilleur effet pourrait donc être atteint au sein d'assemblage d'espèces par un effet complémentaire des traits. Cependant, des effets non-additifs des diversités en espèces et fonctionnelle ont été trouvés, chacun généré par un effet dominant des traits dans les communautés testées. Ces effets des traits et de la diversité fonctionnelle sur la rugosité hydraulique et la rétention des sédiments constituent une nouvelle avancée dans la compréhension des effets de l'assemblage des traits sur les processus d'écoulement et d'érosion des sols ainsi qu'une base pour le design et la modélisation des haies herbacées pour le contrôle du ruissellement et de l'érosion. / Plant-soil processes are driven and influenced by plant functional traits in vegetation communities. Concentrated runoff and erosion constitute the main cause of soil degradation and can be managed by herbaceous vegetation creating hydraulic roughness that induces flow velocity reduction and sediment retention. Using plant trait-based approach, unlike taxonomical approach, allows to understand and characterise the direct effects of the vegetation on runoff and sediment retention. This research project aims to deepen the knowledge regarding the effects of (i) plant functional traits (chapter 1), (ii) traits' complementarity (chapter 2) and (iii) functional diversity (chapter 3) on concentrated runoff and sediment retention processes, in order to evaluate the efficiency and design of herbaceous hedges to reduce the impacts of soil erosion in loamy European agricultural catchments. The identification of the main efficient traits and traits' combinations towards hydraulic roughness increase (stem density, diameter, leaf area and density) highlighted negatively correlated traits, suggesting that a trade-off could be reached within a plant species assemblage through a complementarity effect of the traits. However, non-additive effects of plant species diversity and functional diversity were found, both driven by dominant traits in the community. The effects of traits and functional diversity on the hydraulic roughness and sediment retention constitute a new advance in the understanding of plant trait assemblage on runoff and soil erosion processes and a baseline for the design and modelling of herbaceous hedges for runoff and erosion control.