Student Number : 9906840R - MSc research report - School of Animal, Plant and Environmental Science / The global increased demand for forest products has led to an increase in the area of exotic fast-growing forest plantations. An understanding of nutrient cycling in plantations is essential to enhance their productivity. Sustainable forest productivity involves the managing of nutrients and genetic factors to maximize yields such that they are increasing or non-declining through the maintenance of soil quality and selection of superior tree species and breeds. Komatiland Forests Limited (KFL), a South African forestry company, initiated a permanent sampling plot (PSP) programme in 1998, where it monitors over 30 foliar and soil parameters, as well as tree growth parameters. This study utilized a subset of the permanent sample plots (PSPs) database to compile a suite of foliar and soil parameters that can be used to better interpret stand productivity in pine plantations. Data from PSPs of pine species Pinus patula, Pinus elliottii and the hybrid Pinus elliottii x caribaea planted on dolomite, granite and shale were used in the statistical analyses as they were well represented in the dataset. The geological analysis revealed that parent material significantly affects soil organic carbon content; soil exchangeable K, soil Fe, soil Mn and foliar Mn concentrations. Exchangeable K was found to be low across the geologies ranging on average from 0.08 – 0.11cmol/kg. An accumulative effect was found in foliar concentration of Mn across the geologies and species, with average foliar Mn concentrations being as high as 1086ppm. No statistically significant differences were found at the geological level in soil N, P, exchangeable Ca, Mg & Na, Al, pH or soil texture. Neither were there any significant differences in foliar concentration of N, P, Ca, Mg, Na, Cu, Fe, Zn, B and S at the geological level of analysis. However significant correlations were found between soil cation exchange capacity, soil pH and foliar concentration of Zn, Mn, Mg and Ca. Pinus patula had significantly higher foliar concentrations of N (p<0.001), P (p<0.001). Mg (p=0.001), B (p=0.001) and S (p<0.001) than the other pine variants under analysis. However when species x geology interaction analysis was used P. patula only had significantly higher foliar concentrations with regard to N (p<0.001) and P (p<0.001), and lower foliar concentrations of Zn (p<0.001) and Na (p=0.041) than the other pine variants under analysis. Across the species and geologies, soil acidification resulted in low Ca (0.15-1.6 cmol/kg) and Mg (0.1-0.7cmol/kg) availability. Positive and significant correlations were found between foliar and soil concentrations of N (p=0.022), P (p=0.030), Mg (p<0.001) and Ca (p<0.001). Productivity of the hybrid was significantly higher than the other two species (p<0.001), while P. elliottii had significantly lower productivity than P. patula (p=0.001). Regression models and a principal component analyses revealed that from the dataset of soil and foliar chemical and physical parameters Mg Soil, CEC, N soil, N foliar, P foliar, K foliar, Cu foliar, B foliar, S foliar, C:N soil, Ca:Al soil, N:Ca foliar, N:K foliar, clay and silt are best correlated with stand productivity.

This study investigated a potentially sustainable rice production system in the Mississippi Alluvial Valley (MAV) that uses ecological principles to enhance environmental quality at the field scale. It was hypothesized annual flooding of rice fields to create waterbird habitat would benefit soil health, providing agronomic benefits to the farmer. Two sites were selected: a low-external-input-sustainable-agriculture (LEISA) system with flooded (LF) and nonlooded (LN) fields and a conventional site with flooded (CF) and nonlooded (CN) fields. Soil microbial diversity and nutrient content were quantified and compared. Camera traps were used to document bird activity for estimates of fecal matter input. Soil health variables linked LF high bird activity with soil health and pathogen detection. Evidence from the investigation provided a framework for other producers within the MAV to adopt similar management methods, ultimately improving the overall integrity of soil, water, and environmental quality.

Consumer-driven nutrient cycling has been shown to be an important process in supplying inorganic nutrients to autotrophic and heterotrophic organisms in aquatic ecosystems. Theory indicates that consumer nutrient excretion is influenced primarily by an organism's nutrient composition; however, an organism's diet should also play an important role in nutrient excretion, especially if the consumer is nutrient limited. This study asks the question, how does diet influence nutrient excretion of consumers at different trophic levels? Macroinvertebrates and fish were collected from six streams and nitrogen (N) and phosphorus (P) excretion were quantified. Epilithon, leaf detritus, and seston (fine particulate organic matter in transport) were collected and analyzed for carbon (C), nitrogen (N), and phosphorus (P) content in an attempt to qualitatively assess the nutritional status of the diet of primary consumers. Macroinvertebrates were also analyzed for C, N, and P content to assess their nutritional composition in relation to their excretion and also to assess the nutritional composition of the diet of predatory insects and fish. Fish were also analyzed for C, N, and P. Similar to theoretical predictions, fish and macroinvertebrate P excretion was negatively related to P content and the N:P excretion ratio was negatively related to the body N:P ratio. However, this relationship was driven primarily by two phosphorus rich species, mottled sculpin in the fish and crayfish in the macroinvertebrates. Some relationships did emerge between consumer excretion and diet. For example, hydropsychid caddisflies had the highest macroinvertebrate P excretion, possibly explained by the low N:P of seston. However, shredders, eating on a very low N and P diet of leaf detritus, had very low N and P excretion. The relationship between consumers, their food, and nutrient excretion is a matter of mass balance. If the food N:P ratio is higher than that of the consumer, then the N:P excretion should be higher than the consumer N:P and the food N:P, especially if organisms are P-limited. However, N:P excretion by macroinvertebrates and fish were very similar despite large differences in diet. The majority of macroinvertebrates and fish had a lower N:P excretion ratio than the predicted N:P of their food, possibly indicating that 1) consumers were either selectively consuming more P-rich foods than the diets that I assigned them or 2) consumers are generally not N or P limited or influenced by the N or P in their diet. Mottled sculpin and crayfish were the only organisms with a higher N:P excretion than their resources and both had a higher %P than the other fish and macroinvertebrates, respectively. High N:P excretion along with high phosphorus content is indicative of P-limitation. Macroinvertebrates and fish, excluding mottled sculpin and crayfish, had a lower N:P excretion and the N:P ratio of the water column. If consumers do play a role in nutrient dynamics, then consumers could alter the relative abundance of nitrogen and phosphorus by supplying more phosphorus. However, the presence of a P-limited organism, such as mottled sclupin or crayfish, could alter the relative abundance of nitrogen and phosphorus by supplying less phosphorus. / Master of Science

Soil microbial communities can be characterized by community structure and function (community composition) across a spectrum of spatial scales, and variation in soil microbial composition has been associated with a number of environmental gradients. This study investigates the structure and function of soil microbial communities under mature, undisturbed forested sites across a range of regional climates in British Columbia and Alberta, and also examines the variation in community composition within sites. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass at each site. Extra-cellular enzyme assays established the functional potential of the soil microbial community at each site. Multivariate analysis of the data showed that the soil microbial communities under different forest types did significantly separate along the regional climate gradient by both community structure and function, despite high local variation in the communities. Soil moisture content and soil organic matter concentration consistently exhibited the strongest relationship with microbial community characteristics, although the functional and structural responses to the external drivers were different. Microbial community function and structure also changed with soil depth but not with time of sampling. Microbial community function was related to the regional annual average precipitation gradient. Most of the locations exhibited unique microbial community functional profiles in their soil layers; however the enzyme activities in the samples from the driest (Ponderosa Pine) and wettest (Mountain Hemlock) locations were notably different from each other and from those of the other locations, especially in the organic layers. The moist maritime-influenced Coastal Western Hemlock (CWH) forest exhibited microbial community structural characteristics which were unique from those of the other forest locations. The higher abundance of bacteria relative to fungi in the CWH forest soils may be related to the significantly higher available nitrogen concentrations at this site.

Soil microbial communities can be characterized by community structure and function (community composition) across a spectrum of spatial scales, and variation in soil microbial composition has been associated with a number of environmental gradients. This study investigates the structure and function of soil microbial communities under mature, undisturbed forested sites across a range of regional climates in British Columbia and Alberta, and also examines the variation in community composition within sites. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass at each site. Extra-cellular enzyme assays established the functional potential of the soil microbial community at each site. Multivariate analysis of the data showed that the soil microbial communities under different forest types did significantly separate along the regional climate gradient by both community structure and function, despite high local variation in the communities. Soil moisture content and soil organic matter concentration consistently exhibited the strongest relationship with microbial community characteristics, although the functional and structural responses to the external drivers were different. Microbial community function and structure also changed with soil depth but not with time of sampling. Microbial community function was related to the regional annual average precipitation gradient. Most of the locations exhibited unique microbial community functional profiles in their soil layers; however the enzyme activities in the samples from the driest (Ponderosa Pine) and wettest (Mountain Hemlock) locations were notably different from each other and from those of the other locations, especially in the organic layers. The moist maritime-influenced Coastal Western Hemlock (CWH) forest exhibited microbial community structural characteristics which were unique from those of the other forest locations. The higher abundance of bacteria relative to fungi in the CWH forest soils may be related to the significantly higher available nitrogen concentrations at this site.

Abstract Plants have evolved various adaptive strategies for balancing the benefits and costs of having a high affinity for resources, plasticity of growth allocation and mycorrhizal symbiosis. The relative growth rates of mycorrhizal and non-mycorrhizal plants were modelled for stable and variable nutrient availability. Mycorrhizal plants had higher growth rates at low and non-mycorrhizal plants at high nutrient availability. Variation in nutrient availability reduced the growth rate of mycorrhizal plants due to a high affinity for nutrients. However, mycorrhizal plants may be able to buffer against external fluctuations and therefore experience less environmental variation than non-mycorrhizal plants. Non-mycorrhizal plants may even benefit from variation. The optimal allocation of growth between shoot and roots depends on the availability of energy and nutrients. The optimisation model predicted that the requirement for phenotypic plasticity of shoot/root allocation is greatest in environments with low resource availability. Plants with a high affinity for resources required more plasticity in order to tolerate variation than plants with a low affinity. The model predicted a trade-off between the ability to deplete resources and the ability to tolerate resource fluctuations. Changes in the availability and ratio of resources lead to changes in the structure and composition of vegetation during primary succession. The field study of the forested phases of the land uplift island Hailuoto showed a successional change in the vegetation from the dominance of bryophytes and deciduous dwarf shrubs to dominance by lichens and evergreen dwarf shrubs. The humus layer became thinner and the availability of nutrients declined, while the C/N ratio of soil organic matter increased during succession indicating a decline in the quality of organic matter. The increased soil respiration rate indicates a successional increase in the energetic costs of decomposing organic matter. Nutrients mediate both direct and indirect trophic interactions. Indirect interactions of nutrient cycling are not explicit in continuous time models. A transformation to a discrete time model was shown to make the indirect interactions explicit as transition probabilities and allowed their dynamic contribution to be evaluated with an elasticity analysis. The importance of indirect interactions was greater in tundra than temperate forest and increased with the rate of nutrient cycling.

Soil microbial communities can be characterized by community structure and function (community composition) across a spectrum of spatial scales, and variation in soil microbial composition has been associated with a number of environmental gradients. This study investigates the structure and function of soil microbial communities under mature, undisturbed forested sites across a range of regional climates in British Columbia and Alberta, and also examines the variation in community composition within sites. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass at each site. Extra-cellular enzyme assays established the functional potential of the soil microbial community at each site. Multivariate analysis of the data showed that the soil microbial communities under different forest types did significantly separate along the regional climate gradient by both community structure and function, despite high local variation in the communities. Soil moisture content and soil organic matter concentration consistently exhibited the strongest relationship with microbial community characteristics, although the functional and structural responses to the external drivers were different. Microbial community function and structure also changed with soil depth but not with time of sampling. Microbial community function was related to the regional annual average precipitation gradient. Most of the locations exhibited unique microbial community functional profiles in their soil layers; however the enzyme activities in the samples from the driest (Ponderosa Pine) and wettest (Mountain Hemlock) locations were notably different from each other and from those of the other locations, especially in the organic layers. The moist maritime-influenced Coastal Western Hemlock (CWH) forest exhibited microbial community structural characteristics which were unique from those of the other forest locations. The higher abundance of bacteria relative to fungi in the CWH forest soils may be related to the significantly higher available nitrogen concentrations at this site. / Forestry, Faculty of / Graduate

Thesis advisor: Jeremy Shakun / Thesis advisor: Tony Wang / To better understand ice sheet and nutrient cycling dynamics in the North Atlantic, three geochemical paleo-proxies have been analyzed in Pleistocene marine sediments: cosmogenic nuclides (10Be and 26Al) in ice-rafted debris (IRD), 40Ar/39Ar in IRD, and foraminifera-bound nitrogen isotopes (FB-δ15N). For Chapter 1, we analyzed 10Be and 26Al concentrations in quartz separates of IRD from last-glacial North Atlantic sediments and used these data to constrain the history of Laurentide Ice Sheet (LIS) cover over Canada during the Pleistocene. While LIS history is well constrained since the Last Glacial Maximum (LGM) (~20,000 years ago), there is little evidence available from earlier times. 26Al/10Be ratios are depressed in these samples, the result of long-term decay under cover, which we suggest is best explained by a persistent LIS over much of the last million years. This finding implies that the LIS did not fully disappear during many Pleistocene interglacials, making the current ice-free Holocene interglacial relatively unique. For Chapter 2, we synthesized 3,762 40Ar/39Ar ages from North Atlantic IRD, including 670 new analyses. 595 of these single-grain analyses come from some of the same sample intervals as Chapter 1. These 40Ar/39Ar ages in IRD, a tracer of IRD provenance, clarify changes in North Atlantic ice sheet extent during the past few glacial cycles. Comparison of 40Ar/39Ar ages with hypothesized ice margins and cosmogenic nuclide data (from Chapter 1) aid in our interpretations. For last-glacial samples, results suggest ice sheets around the basin may have been in a retracted state during Marine Isotope Stage (MIS) 3 (~29-57 ka), an interval of debated ice extent for the LIS. Our synthesis also allows us to present the first complete records 40Ar/39Ar ages in IRD during Heinrich intervals – times when the LIS exhibited iceberg discharge events. These results support the suggestion made by previous work that Heinrich events 3 and 6 are anomalous relative to other intervals. 40Ar/39Ar analyses from earlier glacial periods – the first yet published – highlight that IRD provenance data may be reflecting iceberg survivability in addition to changes in ice extent. Lastly, analyzing cosmogenic nuclides and 40Ar/39Ar ages in IRD from the same sample intervals indicates that both proxies may be used to infer changes in ice sheet provenance; this is the first time cosmogenic nuclides in IRD have been considered in this way. For Chapter 3, we analyzed FB-δ15N at Site U1313 in North Atlantic samples during the Plio-Pleistocene to reconstruct marine nutrient cycling. In the North Atlantic, nutrient cycling is known to play an important role in regulating surface ocean productivity and CO2 drawdown via photosynthesis. We nevertheless lack a complete understanding of nutrient cycling evolution for the Plio-Pleistocene, during which Northern Hemisphere ice sheets and climate exhibited dramatic fluctuations. We find increasing FB-δ15N values at the transition from the Pliocene to the Pleistocene. Additionally, FB-δ15N values are generally higher during glacials compared to interglacials. We suggest these observations can best be explained by an expansion or increase of N2 fixation in the North Atlantic during warmer intervals (interglacials, Pliocene) and a retraction or decrease of N2 fixation during cold intervals (Pleistocene glacials). Considered alongside previously published paleo-proxy data from Site U1313 we suggest these changes in nutrient cycling reflect climate-driven migrations of the North Atlantic Current. In Chapter 4, I reflect upon how I have worked to integrate broader impacts into my Ph.D. work. Using a combined approach, I focused on fostering an inclusive environment within paleoclimate research spaces as well as engaging non-scientists in paleoclimate-and Earth science-related activities. These approaches ranged from K-12 partnership activities to mentoring students to more experimental avenues, such as a collaborative art project. I have evaluated the success of this work using a combination of quantitative metrics and subjective assessments. Participating in these efforts was also crucial for reminding me of the importance of making science accessible to everyone as well as for helping me hone my mentorship and science communication skills. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Les invasions biologiques sont une cause majeure de perte de biodiversité à l’échelle mondiale. L’impact direct des espèces exotiques envahissantes (EEE) sur la structure et la composition des communautés a été bien documenté. Par contre, leur impact sur le fonctionnement des écosystèmes a été comparativement moins étudié. Dans le présent travail, j’ai mesuré sur le terrain et en conditions expérimentales l’impact de 7 espèces de plantes exotiques particulièrement envahissantes en Europe sur les propriétés chimiques du sol, sur la productivité et sur le stock d’éléments minéraux dans la biomasse. Malgré la diversité des groupes fonctionnels considérés dans notre échantillon (des espèces annuelles aux arbres), des impacts récurrents ont pu être mis en évidence. Les EEE ont toujours une biomasse et une productivité supérieures à celles de la végétation qu’elles envahissent. Il en va de même pour le stock d’éléments minéraux dans la biomasse aérienne. En ce qui concerne le sol, les traits fonctionnels des espèces ne permettent pas de prédire la direction et l’amplitude des impacts. Par contre, ces impacts sur le sol se sont révélés partiellement prévisibles en fonction des conditions écologiques initiales (contexte pédologique). La disponibilité des cations et du P et la concentration en C et N organiques augmentent suite à l’invasion dans les sites initialement pauvres alors que ces mêmes paramètres baissent dans les sites plus eutrophes au départ. Les EEE entraînent, dans une certaine mesure, une homogénéisation des conditions écologiques dans les écosystèmes envahis. Dans un deuxième temps, je me suis attaché à identifier les mécanismes de l’impact de Fallopia japonica sur le cycle de l’azote. Cette espèce, perenne rhizomateuse, adopte une gestion très conservatrice de l’azote en retransloquant jusqu’à 80 % de l’azote des tiges et des feuilles vers le système racinaire en automne avant l’abscission des feuilles. La litière restituée est, de ce fait, pauvre en azote. Ce paramètre, combiné à une teneur élevée en lignine, explique sa faible vitesse de décomposition par rapport à celle de la végétation non envahie. Une grande partie de l’azote de l’écosystème tourne donc en cycle quasi fermé entre les organes de réserve et les parties aériennes de la plante, tandis que l’azote restant est en grande partie bloqué dans la nécromasse de la plante et est donc non disponible pour les espèces concurrentes indigènes. Ce mécanisme explique, sans doute, en partie le succès invasif de l’espèce. A l’avenir, les implications des impacts sur le sol en terme de restauration des communautés devront être étudiées. L’hypothèse d’une influence positive de ces impacts sur l’aptitude compétitive des espèces envahissantes devra être testée. Enfin, une étude plus fonctionnelle des impacts de ces espèces dans des sites contrastés devrait permettre d’identifier les mécanismes impliqués./Biological invasions are a major cause of biodiversity loss worldwide. The direct impact of alien invasive species (AIS) on community structure and composition has been well documented. On the other hand, their impact on ecosystem functioning has been comparatively less studied. In this work, I measured, on the field and in experimental conditions, the impact of 7 highly invasive alien plant species in Europe on soil chemical properties, biomass and aboveground nutrient stock. Despite the high diversity in considered functional groups (from annuals to trees), recurring impacts have been found. AIS had always higher biomass and aboveground nutrient stocks than invaded resident vegetation. Concerning soil, species functional traits did not allow us to predict impact direction and intensity. On the other hand, impacts on soil were partially predictable based on initial ecological conditions (pedologic context). Thus, cations and P availability and organic C and N concentrations increased in initially poor sites and decreased in eutrophic ones. AIS tend to homogenize soil properties across invaded landscapes. In a second part, i tried to identify the mechanisms of the impacts of Fallopia japonica on N cycling. This perrennial rhizomatous species manage N in a very conservative way. About 80 % of aboveground N is translocated to rhizomes before leaves abscission. The litter is therefore poor in N. This parameter combined with a high lignin concentration explains its slow decomposition rate compared to that of uninvaded vegetation. A big part of the ecosystem N is engaged in a nearly closed cycle between above and belowground organs while the remaining N is blocked in the necromass and is thus not available for the indigenous competitors. This mechanism probably explains the invasive success of this species. In the future, the implications of soil properties modifications in terms of community restoration should be studied. The hypothesis of a positive influence of these modifications on the competitive ability of AIS should be tested. At last, a functional study of these soil impacts in contrasted sites should allow us to identify the implied mechanisms.

Microbial activity occurs year-round in Arctic soils, including during the winter when soils are frozen. From 2004 to 2008 I monitored soil microbial and nutrient dynamics in low Arctic wet and dry sedge meadows near Churchill, Manitoba. I documented a consistent annual pattern in which soil microbial biomass (MB) and soil nutrients peak in late winter, and decrease during the early stages of spring thaw, remaining in low abundance during the summer. Based on a series of experiments, resource shortages do not appear to be the cause of the microbial decline, as has been hypothesized. Observations and theoretical considerations regarding soil physical properties indicate that this decrease is driven by the influx of liquid water at thaw that brings about a rapid change in the chemical potential of water, leading to cell lysis. I have used 15N isotope tracing to show that inorganic nitrogen is taken up very quickly at thaw by the roots of the dominant plant, Carex aquatilis. This represents a critical window of opportunity for these plants, as nitrogen remains abundant only for a short time. The described annual pattern was pronounced in wet sedge sites, but some inter-annual variation is evident, for example a post-thaw soil nitrogen pulse in 2006, and low winter MB in 2008. In the dry sedge meadow, fluctuations in MB and nutrients were dampened relative to wet sites, and the annual pattern was variable, particularly after 2006. Over four years, peak winter values of soil MB and nutrient variables declined in both wet and dry sites, and this could be related to a drying trend. This work improves our understanding of the controls on decomposition and primary productivity in a system that is experiencing climate warming and increased precipitation. Changes to hydrology, carbon and nitrogen cycling, and primary productivity will have further effects on vegetation communities and higher trophic levels, including several species of migratory birds.