Pulse crops have been long associated with biological dinitrogen fixation and therefore improve the sustainability of cropping systems when included in rotation. However, studies indicate there may be additional benefits of including pulse crops in rotation. To quantify these potential benefits, soil processes and properties related to nitrogen (N) and carbon (C) cycling were examined in five crop rotations with and without field pea (<i>Pisum sativum</i> L.) in Scott, Saskatchewan. Gross mineralization and nitrification rates were determined using the 15N isotope dilution technique in intact soil cores. To estimate the proportion of nitrous oxide (N2O) emissions derived from nitrification related processes rather than denitrification processes tracer techniques using 15N were used. Field incubations were performed in 2008 at seeding (May 13), anthesis (July 8) and just after harvest (October 8). Mean mineralization and nitrification rates were not significantly different among rotations on any date and there was no significant difference in mean N2O emissions among rotations. From labeled 15NO3- cores, it was determined that nitrification-related processes were the major contributors to N2O emissions. There was no difference among the rotations in microbial biomass carbon (MB-C) or microbial biomass N (MB-N) with the exception of MB-C in the continuous field pea (FP) and the canola (<i>Brassica napus</i> L.)-wheat (<i>Triticum aestivum</i> L.)-field pea (CNL-W-FP) rotation at anthesis. There was no effect of rotation on dissolved organic carbon (DOC) and only seasonal differences were observed with DOC levels being lower before seeding than at anthesis and post-harvest. Based on the results obtained from a single growing season, our results show that N benefits of including field pea in rotation, beyond dinitrigen fixation, were not detectable and that the immediate N benefit of including field pea in rotation may be due simply to the direct effects of biological dinitrogen (N2) fixation. However, there have been reports of pulse crop benefits to succeeding crops in rotation. As a result, we investigated both the quantity and quality of crop residues, which can have an impact on soil properties and processes. Plants enriched with isotopic tracers can be used to trace crop residue decomposition to various C pools but only if the tracer is homogeneously distributed throughout the plant. In order to determine if repeat-pulse labeling could be used to trace crop residue decomposition, this method was followed using 13CO2 to enrich plant material of field pea and canola plants in a controlled environment. The distribution of 13C throughout the plant parts (roots, stem, leaves, and pod) and biochemical fractions [acid detergent fiber (ADF) and acid detergent lignin (ADL)] were determined. It was found that 13C was not homogeneously distributed throughout the plant parts or biochemical fractions. The pod fraction in particular was much less enriched in comparison to the other fractions. The ADL fraction was less enriched than the ADF fraction. Because of the heterogeneity of the label throughout the plant, modifications of the method are needed and 13C distribution through out the plant needs to be assessed before the repeat-pulse method can be used to trace C residue through various C pools. Nevertheless, root contributions to below-ground C were successfully determined from the enriched root material and the resulting enriched soil. It was found that canola contributed more above- and below-ground residues than field pea, however canola was also higher in ADF and ADL fractions indicating a more recalcitrant residue. Research should continue to better define the impact of pulse crop residues on C and N cycling and subsequent crops in rotation.

Pulse crops have been long associated with biological dinitrogen fixation and therefore improve the sustainability of cropping systems when included in rotation. However, studies indicate there may be additional benefits of including pulse crops in rotation. To quantify these potential benefits, soil processes and properties related to nitrogen (N) and carbon (C) cycling were examined in five crop rotations with and without field pea (<i>Pisum sativum</i> L.) in Scott, Saskatchewan. Gross mineralization and nitrification rates were determined using the 15N isotope dilution technique in intact soil cores. To estimate the proportion of nitrous oxide (N2O) emissions derived from nitrification related processes rather than denitrification processes tracer techniques using 15N were used. Field incubations were performed in 2008 at seeding (May 13), anthesis (July 8) and just after harvest (October 8). Mean mineralization and nitrification rates were not significantly different among rotations on any date and there was no significant difference in mean N2O emissions among rotations. From labeled 15NO3- cores, it was determined that nitrification-related processes were the major contributors to N2O emissions. There was no difference among the rotations in microbial biomass carbon (MB-C) or microbial biomass N (MB-N) with the exception of MB-C in the continuous field pea (FP) and the canola (<i>Brassica napus</i> L.)-wheat (<i>Triticum aestivum</i> L.)-field pea (CNL-W-FP) rotation at anthesis. There was no effect of rotation on dissolved organic carbon (DOC) and only seasonal differences were observed with DOC levels being lower before seeding than at anthesis and post-harvest. Based on the results obtained from a single growing season, our results show that N benefits of including field pea in rotation, beyond dinitrigen fixation, were not detectable and that the immediate N benefit of including field pea in rotation may be due simply to the direct effects of biological dinitrogen (N2) fixation. However, there have been reports of pulse crop benefits to succeeding crops in rotation. As a result, we investigated both the quantity and quality of crop residues, which can have an impact on soil properties and processes. Plants enriched with isotopic tracers can be used to trace crop residue decomposition to various C pools but only if the tracer is homogeneously distributed throughout the plant. In order to determine if repeat-pulse labeling could be used to trace crop residue decomposition, this method was followed using 13CO2 to enrich plant material of field pea and canola plants in a controlled environment. The distribution of 13C throughout the plant parts (roots, stem, leaves, and pod) and biochemical fractions [acid detergent fiber (ADF) and acid detergent lignin (ADL)] were determined. It was found that 13C was not homogeneously distributed throughout the plant parts or biochemical fractions. The pod fraction in particular was much less enriched in comparison to the other fractions. The ADL fraction was less enriched than the ADF fraction. Because of the heterogeneity of the label throughout the plant, modifications of the method are needed and 13C distribution through out the plant needs to be assessed before the repeat-pulse method can be used to trace C residue through various C pools. Nevertheless, root contributions to below-ground C were successfully determined from the enriched root material and the resulting enriched soil. It was found that canola contributed more above- and below-ground residues than field pea, however canola was also higher in ADF and ADL fractions indicating a more recalcitrant residue. Research should continue to better define the impact of pulse crop residues on C and N cycling and subsequent crops in rotation.

The tropical forests on the island of Borneo are among of the richest in the world in terms of tree diversity, and their capacity to store a large reservoir of carbon. The Southeast Asian forests are fundamentally different from Neotropical and African forests, with their single-family dominance by dipterocarp trees, and with inherently greater stature and biomass. The carbon productivity and allocation in Asian tropical forests is still poorly quantified, and their responses to environmental drivers are still poorly understood. Almost all recent advances in tropical forest carbon cycling research have occurred in the Neotropics, with very few studies in Asia. The principal aim of this thesis is to quantify the carbon budget of a lowland dipterocarp forest in the Lambir Hills National Park, Miri, Sarawak, Malaysian Borneo. I examined and explored the productivity and carbon cycling processes and their responses to environmental factors across two major and contrasting soil types, in particular the clay and sandy loam soils. I recorded and analysed the Net Primary Productivity (NPP) and respiration for the above- and below-ground components, and observed the responses to seasonal variation and environmental drivers. Total soil respiration was relatively high and contributed a great deal to ecosystem respiration. Variation in soil respiration rates appeared closely related to soil moisture content. I found a strong diurnal cycle in soil respiration. On the basis of the first soil carbon dioxide (CO2) efflux partitioning study undertaken in a tropical forest, the diurnal cycle in total soil respiration appeared to be entirely driven by the diurnal cycle in litter respiration, and in turn litter is strongly controlled by moisture. There was little seasonal variation in allocation of net primary productivity (NPP), but there was evidence showing potential inter-annual variability for several components of NPP. Further, the allocation of NPP showed a strong seasonal shift between the forest plots on clay and sandy loam soils. Combining all the data measured and obtained in this D.Phil. thesis, the overall carbon budget assessed in this lowland dipterocarp forest showed a high level of agreement with other studies in Asia using micrometeorological techniques and the situation appears to be comparable to tropical forests in Amazonia. The key difference is that the aboveground NPP is higher and is the largest component contributing to the overall carbon budget, with relatively higher carbon use efficiency (CUE). The lowland dipterocarp forest in Lambir shows higher allocation in the above-ground NPP, and there were also differences in NPP and its allocation between sandy and clay-rich plots.

Wetlands serve important ecosystem functions such as carbon sequestration but are often affected by disturbances like urban development, agriculture, and road building. For wetlands created to mitigate losses, it is important that the ecosystem functions successfully replicate those of natural wetlands. Created wetlands have frequently not provided these functions due to issues including low organic carbon (OC), high soil bulk density (BD), lost topsoil, incorrect hydrology, and failure of targeted vegetation establishment. Organic matter (OM) amendments help created wetlands attain these functions quicker, but, their long-term effects are seldom reported. This research's purpose was to measure the long-term effects of treatments at a sandy tidal freshwater wetland created in 2003 (WWE) and a fine-textured, non-tidal wetland created in 2002 (CCW). We tested OM treatments, topsoil amendment, and microtopography effects on soil and vegetation properties at WWE and OM treatments at CCW. Pedogenic changes in soil morphology, physical and chemical properties were detected by comparing data to previous studies at these sites. At both sites, litter and biomass parameters were measured to estimate total mass C. Herbaceous biomass was measured at WWE. At WWE, no long-term OM treatment effects from 78 or 156 Mg ha-1 were observed. Soils in pits had higher OC, lower BD, and lower chroma than soils on mounds. Sandy and loamy HSFI's developed at WWE within four years, but there were fewer sandy indicators after 12 years. Loamy HSFI's were lost at CCW from 2003 to 2016. Plots at WWE that were amended with topsoil had higher soil mass C than the sandy soil due to a finer texture, but total mass C did not vary. At CCW, long-term OM treatment effects were observed, including lower BD, higher soil mass C, and higher tree mass C with increasing compost rates up to 224 Mg ha-1. Overall, the ideal compost loading rate for constructed wetlands varied with wetland type and mitigation goals. Compost rates of 112 Mg ha-1 are sufficient for short term establishment of wetland vegetation and hydric soil properties, but higher rates near 224 Mg ha-1 may be required for effects that last over 10 years. / Ph. D.

Les forêts tropicales constituent le principal réservoir de biodiversité et de carbone (C). Cependant, la plupart des forêts tropicales, en particulier les forêts de Bornéo en Asie du Sud-Est, subissent une pression intense et sont menacées par des activités anthropiques telles que l'exploitation forestière, l'industrie minière l’agriculture et la conversion en plantations industrielles. En 2010, la superficie des forêts de production de Bornéo était de 26,8 millions d’ha (environ 36% de la superficie totale de l’île, dont 18 millions ha (environ 24%) déjà exploités. Par conséquent, les forêts de production occupent donc une place importante à Bornéo et jouent un rôle essentiel dans la compensation des biens fournis et la maintenance des services écosystémiques, tels que la conservation du C et de la biodiversité.L’exploitation sélective réduit la biomasse aérienne et souterraine par l’élimination de quelques grands arbres, et augmente les stocks de bois mort par des dommages collatéraux. En créant des trouées dans la canopée, le microclimat dans les sous-étages et au sol change localement et accélèrent la décomposition de la litière et de la matière organique. L'importance des dégâts, de l'ouverture de la canopée et de la rapidité du rétablissement du C s'est avéré principalement liée à l'intensité de l'exploitation forestière. Cependant, les évaluations empiriques de l'effet à long terme de l'intensité de l'exploitation forestière sur l'équilibre du C dans les forêts de production restent rares.La présente thèse se concentre principalement sur l'évaluation de l'effet à long terme de l'intensité de l'exploitation forestière sur la séquestration de carbone dans une forêt à Diptérocarpées de Nord Bornéo (District de Malinau, Kalimantan Nord) exploitée en 1999/2000. Cinq principaux réservoirs de C, à savoir le C aérien dans les arbres vivants (AGC), le C souterrain dans les arbres vivants (BGC), le bois mort, la litière et le C organique du sol (SOC) ont été estimés le long d’un gradient d'intensité d'exploitation (0-57% de la biomasse perdue).Nos résultats ont montré que les stocks totaux de C, 16 ans après l'exploitation, variaient de 218 à 554 Mg C ha-1 avec une moyenne de 314 Mg C ha-1. Une différence de 95 Mg C ha-1 a été observée entre une faible intensité d'exploitation forestière (<2,1% de la biomasse initiale perdue) et une intensité d'exploitation élevée (>19%). La plus grande partie du C (environ 77%) était présente dans les arbres vivants, suivie par les stocks du sol (15%), les stocks de bois mort (6%) et une fraction mineure des stocks de litière (1%). L'empreinte de l'intensité de l'exploitation forestière était encore détectable 16 ans après l'exploitation et a été le principal facteur expliquant la réduction des AGC>20, BGC>20, du bois mort et des stocks de C et une augmentation du bois mort. L'intensité de l'exploitation expliquait à elle seule 61%, 63%, 38% et 48% des variations des AGC>20, BGC>20, du bois mort et des stocks de C totaux, respectivement. L'intensité de l'abattage a également réduit considérablement les stocks de SOC dans la couche supérieure de 30 cm. Pour l'ensemble des stocks de SOC (0-100 cm), l'influence de l'intensité de l'exploitation était encore perceptible, en conjonction avec d'autres variables.Nos résultats quantifient l'effet à long terme de l'exploitation forestière sur les stocks de C forestier, en particulier sur les AGC et les bois morts. L'intensité élevée de l'exploitation forestière (réduction de 50% de la biomasse initiale) a réduit les stocks totaux de C de 27%. La récupération de l'AGC était plus faible dans les parcelles d'intensité d'exploitation forestière élevée, ce qui suggère une résilience plus faible de la forêt à l'exploitation forestière. Par conséquent, une intensité d'exploitation forestière inférieure à 20%, devrait être envisagé afin de limiter l'effet à long terme sur les AGC et le bois mort. / Tropical forests are a major reservoir of biodiversity and carbon (C), playing a pivotal role in global ecosystem function and climate regulation. However, most of the tropical forests, especially Bornean forests in Southeast Asia, are under intense pressure and threatened by anthropogenic activities such as logging, mining industry, agriculture and conversion to industrial plantation. In 2010, the area of production forests in Borneo was 26.8 million ha (approx. 36% of the total land area of Borneo) including 18 million ha (approx. 24%) of logged forests. Production forests are thus emerging as a dominant land-use, playing a crucial role in trading-off provision of goods and maintenance of ecosystem services, such as C and biodiversity retention.Selective logging is known to reduce both above- and below-ground biomass through the removal of a few large trees, while increasing deadwood stocks through collateral damages. By creating large gaps in the canopy, microclimates in the understory and on the forest floor change locally speeding up the decomposition of litter and organic matter. The extent of incidental damages, canopy openness, as well as the speed of C recovery, was shown to be primarily related to logging intensity. However, empirical evaluations of the long-term effect of logging intensity on C balance in production forests remain rare.The present thesis aims to assess the long-term effect of logging intensity on C sequestration in a north Bornean Dipterocarp forests (Malinau District, North Kalimantan) logged in 1999/2000. Five main C pools, namely above-ground (AGC) and below-ground (BGC) carbon in living trees, deadwood, litter, and soil organic carbon (SOC) were estimated along a logging intensity gradient (ranging from 0 to 57% of initial biomass removed).Our result showed that total C stocks 16 years after logging, ranged from 218-554 Mg C ha-1 with an average of 314 Mg C ha-1. A difference of 95 Mg C ha-1 was found between low logging intensity (<2.1% of initial biomass lost) and high logging intensity (>19%). Most C (approx. 77%) was found in living trees, followed by soil (15%), deadwood (6%), and a minor fraction in litter (1%). The imprint of logging intensity was still detectable 16 years after logging, and logging intensity thus was the main driver explaining the reduction of AGC>20, BGC>20, deadwood, and total C stocks and an increase in deadwood. Solely, logging intensity explained 61%, 63%, 38%, and 48% of variations of AGC>20, BGC>20, deadwood, and total C stocks, respectively. Logging intensity also significantly reduced SOC stocks in the upper 30 cm layer. For total SOC stocks (0-100 cm), the negative influence of logging intensity was still perceptible, being significant in conjunction with other variables.Our results quantify the long-term effect of logging on forest C stocks, especially on AGC and deadwood. High logging intensity (50% reduction of initial biomass) reduced total C stocks by 27%. AGC recovery was lower in high logging intensity plots, suggesting lowered forest resilience to logging. Our study showed that maintaining logging intensity, below 20% of the initial biomass, limit the long-term effect of logging on AGC and deadwood stocks.

La coltivazione dei sistemi colturali poliennali su terreni marginali combina la produzione sostenibile di biomassa per diversi utilizzi a benefici di carattere ambientale come il sequestro del C atmosferico nel suolo. La limitata longevità di questi sistemi colturali (10-20 anni), fornisce la possibilità di sfruttarli come una tecnica temporanea per rigenerare la fertilità dei terreni marginali e di studiare il loro effetto nel lungo periodo sul carbonio del suolo. Con questa tesi, avevo l'obiettivo di studiare l'effetto della riconversione a coltura annuali dei sistemi agricoli poliennali sul carbonio del suolo: per raggiungere questo obiettivo, ho combinato ad una meta-analisi di letteratura sull'effetto della riconversione, con un esperimento di campo di lungo periodo, un esperimento di incubazione in laboratorio e l'uso di un modello matematico del carbonio del suolo. L'uso combinato di questi approcci mi ha permesso di mostrare il potenziale che i sistemi colturali poliennali hanno nel sostenere il sequestro del C ne suolo anche dopo la loro riconversione. Quindi i sistemi colturali poliennali sono una pratica sostenibile promettente che può essere integrata in rotazioni agricole di 13 anni sui terreni marginali del nord d'Italia per ripristinare il carbonio del suolo. / The cultivation of perennial cropping systems on marginal lands combines the production of sustainable biomass for multiple uses with environmental benefits such as carbon (C) sequestration in soil. In this thesis, we studied the effect of perennial cropping system on soil C considering the scenario of perennial cropping systems reversion to arable land. The limited longevity (10-20 years) of perennial cropping systems, gives the possibility of using these crops as a temporary- option to restore soil fertility of marginal lands and to study the long-term legacy of these cropping systems on soil C. In this thesis I aimed to study the effect of perennial cropping systems reversion to arable land on soil C: to achieve this objective, I combined a literature meta-analysis on the effect of reversion of perennial cropping systems on soil C, with a long-term field experiment on perennial cropping systems, an incubation experiment and the use of a process-based soil C model. The combined use of these approaches gave me the chance to show the potential of perennial cropping systems to support C sequestration even after their reversion. Therefore, perennial cropping systems are a promising sustainable practice which could be integrated on a 13-year agricultural rotation on marginal lands of northern Italy to restore soil C.