The cultivation of fast growing tree species on arable land is deemed to be one of the most promising alternatives amongst the approaches to the cultivation of renewable resources currently available. As the site factors influencing the growth of poplar and willow have not yet been sufficiently identified and quantified, it is not possible to provide reliable national yield expectations as a function of the prevailing soil and climate conditions at a particular site on the basis of the data currently available. The main objective of this study, therefore, was to develop a supraregional site-based yield model for the assessment of yield expectations for poplar and willow grown on arable land over short rotations. In order to achieve this goal, a total of 38 research sites were established across as many regions of Germany as possible. The clones selected for the experiment were the poplar clones Max 1, Hybride 275 (H 275) and AF 2, and the willow clones Inger and Tordis. Each site was also characterised, on the basis of climate and soil data. From the site parameters recorded, variables were defined for modelling purposes. The climate variables comprised temperature (T), precipitation (N) and aridity index (TI) derived from total or average values from selected periods during the year and during the vegetation period. Within the variables the months were indexed as numbers (January = 1), periods were separated by comma. Parameters of the German soil appraisal such as the condition grade (ZS), the soil quality index value (BZ) and the arable land quality index value (AZ) were used as soil variables. The selected texture parameters were the proportions of sand (S[%]), silt (U[%]) and clay (T[%]). Variables of the pore space parameters were the available field moisture capacity (nFK), the air capacity (LK) and the dry bulk density (TRD). Both the texture and the pore space variables referred to a soil depth of 0 to 60 cm. To increase the precision of the results, site clusters were derived, differentiated by main soil type, and the variables were aggregated. The dGZ, measured in odt ha-1 a-1,at the end of the first three-year rotation was chosen as the dependent variable. The main results of the study are outlined in the following: Negative correlations between dGZ and temperatures in the vegetation period, especially in the months July to September, were observed on the sandy and loamy soils. Precipitation variables always had a positive effect on the growth of poplar and willow across all clones and site clusters. Taking into consideration all experimental sites, precipitation in the period from May to July was most important. The parameters of the German soil appraisal revealed a moderate correlation with growth for all sites. From the appraisal of all sites and of the individual site clusters it became apparent that U[%] represents the most important texture variable for poplar and willow growth. Considered for all sites simultaneously, the nFK had the greatest significance for growth across all of the parameters examined. The site-based yield models were all univariate and often comprised aggregated variables. Under consideration of all sites, the model predictors for Max 1, Inger and Tordis were (nFK * TI5.7) and (nFK * N5.7) for AF 2. Each model was calculated with the inverse or sigmoid approach and revealed an R²korr between 0.45 and 0.64 with a RMSE of an average of 2.0 odt ha-1 a-1. The division into site clusters improved the accuracy of the models considerably. In the sandy site cluster, the models exhibited an R²korr of 0.77 to 0.97 and an RMSE of 0.95 to 1.36 odt ha-1 a-1. These comprised (U[%]* N6.7) for Max 1 and F 2, (S[%]/ TI6.7) for H 275 and (S[%]* T7.8) for Inger and Tordis. For the silty site cluster, significant models could only be determined for the clones Max 1 and Tordis. The model predictor for Max 1 was (BZ * TI4.5) and for Tordis solely (BZ). The calculated R²korr values were 0.84 and 0.95 with a corresponding RMSE of 0.22 and 0.62 odt ha-1 a-1, respectively. For the loamy soils the models for Max 1 and Inger comprised the variable nFK, for AF 2 the variables (nFK * N5.6). R²korr varied between 0.86 and 0.98 with RMSE between 0.56 and 1.21 odt ha-1 a-1.

No description available.

A series of grazing experiments was conducted, in the summer/autumn of 2001, 2002 and 2003, to investigate the effects of poplar (Populus spp.) and/or willow (Salix spp.) supplementation, during mating, on ewe production and reproduction when grazing drought pasture. Each experiment involved a rotational grazing system with 300 mixed-age Romney ewes, divided into three groups of 100 ewes each. In each year, all ewes were offered low quality simulated drought pasture, containing more than 60% dead matter, at an allowance sufficient to provide a potential desired intake of 0.70 kg dry matter (DM)/day, for periods of 9 to 12 weeks, including two mating cycles. Mean pre-and post-grazing pasture masses averaged over the three years were 1100 and 600 kg DM/ha. The pasture consumed in all years was typical of pasture available to grazing livestock in a drought; it was high in neutral detergent fibre (NDF; approximately 600 g/kg DM), low in organic matter digestibility (OMD, approximately 0.52) and metabolisable energy (ME; approximately 7.5 MJ/kg DM) and contained approximately 20 g nitrogen (N)/kg DM. The supplementary poplar and willow diets were always superior to drought pasture consumed by the ewes, being higher in OMD (approximately 0.67), ME (approximately 10 MJ/kg DM) and total N (approximately 26 g/kg DM) and lower in NDF (approximately 383 g/kg DM). Tree fodder diets also contained substantial concentrations of the secondary compounds condensed tannin (CT; range 7 to 52 g/kg DM), salicin (approximately 2 g/kg DM) and other phenolic glycosides (approximately 21 g/kg DM), with willow (27 to 52 g/kg DM) containing greater concentrations of CT compared with poplar (7 to 19 g/kg DM). Mean diameter of the tree fodder stem consumed during the series of experiments was approximately 7 mm for poplar and 4 mm for willow with the diameter increasing over the experimental periods in four cases out of live (P<0.05). After the supplementation period, the three groups were joined together and grazed on perennial ryegrass/white clover pasture until the conclusion of each experiment at weaning. In all years, the effect of poplar and/or willow supplementation on ewe live weight (LW) and body condition score (BCS) change; the proportion of lambs (reproductive rate) at pregnancy scanning, lambing, docking and weaning; and wool production and staple length from ewe fleeces with approximately 11 months growth, were measured. Experiment 1 was designed to determine how much poplar fodder needed to be fed to increase ewe production and reproduction over a 71-day supplementation period. The experiment involved a high supplementation group, offered 1.5 kg fresh poplar/ewe/day; a low supplementation group, offered 0.75 kg fresh poplar/ewe/day; and a control group that was offered no tree fodder. Ewes in the high and low treatments lost less LW (-67 and -71 vs. -82 g/day; P<0.05) and BCS (-0.78 and -1.27 vs. -1.31 units; P<0.05) compared with unsupplemented ewes. Reproductive rate was relatively low in the control group (121 lambs born/100 ewes mated), with poplar supplementation increasing ewe reproductive rate by approximately 20% units (P<0.05) and 30% units (P<0.001) for the low and high treatment groups, respectively, at scanning, lambing, docking and weaning. The increase in reproductive rate in supplemented ewes was due to increases in both conception rate (number of ewes pregnant/100 ewes mated) and fecundity (number of lambs born/100 ewes mated). Experiment 2 was designed to determine if production and reproduction varied between ewes fed poplar versus willow at the same rate of supplementation, 1.4 kg fresh forage/ewe/day, for 87 days. Again, reproductive rate was relatively low in the control group (133 lambs born/100 ewes mated), with willow supplementation reducing L.W loss (-86 g/day vs. -103 g/day; P<0.01) and increasing reproductive rate by 15%, 17% 21% and 20% units at ultrasound scanning (P=0.097), lambing (P=0.087), docking (P<0.05) and weaning (P=0.058), respectively. The increase in reproductive rate was due to an increase in fecundity; supplementation did not affect conception rate in this experiment. Unlike the previous experiment, poplar supplementation showed no effect on reproductive rate, despite the increase in DM intake and the apparent reduction in LW loss of 9 g/day (P-0.11). It is likely that severe contamination of the poplar fodder with Melampsora larici-populina, or poplar leaf rust, confounded the results. Building on the results of the first two grazing trials, the next step was to determine the period (days) of tree fodder supplementation necessary to achieve a response in reproductive rate. Experiment 3 involved ewes fed 1.3 kg fresh willow/ewe/day for a 'long' period, 63 days including 6 weeks of mating, and a 'short' period, 31 days including 3 weeks of mating. The mating period commenced on the same day for all groups and lasted for 6 weeks. Willow supplementation for 63 days reduced ewe LW loss (-96 g/day vs. -147 g/day; P<0.05) and BCS (-0.79 VS. -1.09; P<0.05) loss, compared with unsupplemented ewes; however, it did not increase reproductive rate at scanning and lambing. The lack of response in willow-supplemented ewes was likely to be due to toxic concentrations of zearalenone (1.5 mg/kg DM), an oestrogenic mycotoxin, in the drought pasture during mating, which confounded the results by negating any potential benefits due to increased nutrient intakes. Willow supplementation for 63 days did increase reproductive rate at weaning by 13% units, due to a 9% unit (P<0.05) reduction in post-natal lamb mortality, from 17.1 to 8.4%. Supplementation for 31 days did not appear to influence ewe reproduction and production parameters. Overall, the rate of LW loss was greater in Experiment 3 compared with the first two experiments. Seven indoor in vivo digestibility experiments were conducted at the following times; early April 2001 (poplar), February, March and April 2002 (all poplar), and December, March and April 2003 (all willow). Each 14-day trial involved 6 male cryptorchid lambs, individually fed in metabolism cages. The experiments showed that the digestibility of poplar and willow tree fodder declined from late spring to autumn (P<0.05), but that the decline was much smaller than the decline in digestibility of grass-based pastures in New Zealand over the same time period. The experiments also showed that mean ME and digestibilities were generally higher for willow than for poplar. The seven in vivo digestibility coefficients were then used to develop a standard curve for in vitro prediction of in vivo digestibility, this standard was used to analyse all unknown tree fodder samples from the three grazing experiments. Results from the three grazing experiments showed that supplementing ewes grazing drought pasture during mating with poplar and willow tree fodder consistently increased DM intake by 0.25 to 0.33 kg DM/ewe/day for ewes offered 1.3 to 1.5 kg fresh willow or poplar each day and increased calculated total DM intakes from 0.67 to 1.03 kg DM/ewe/day in Experiment 1, from 0.59 to 0.86 kg DM/ewe/day in Experiment 2 and from 0.47 to 0.75 kg DM/ewe/day in Experiment 3. Supplementation also consistently reduced LW loss and loss in BCS and substantially increased lambing rate through increased conception rate and fecundity and reduced post-natal lamb mortality. The effects on LW and BCS gradually declined in the post-treatment period and were no longer evident by commencement of lambing. There was no effect of supplementation on wool production or staple length in any of the experiments. One of the unexpected results of the experiments was an average 34% reduction in post-natal lamb mortality over three years, due to willow/poplar supplementation of ewes during mating. Initial results showed that despite significant increases in fecundity in supplemented ewes in 2001 and 2002, post-natal lamb mortality was not increased. This result, combined with a statistically significant reduction in lamb mortality in Experiment 3 (P<0.05), in the absence of any differences in fecundity between the groups, suggested that tree fodder supplementation during mating may have reduced lamb mortality in all three years, but that the effect was masked by the increase in reproductive rate in the first two experiments. Therefore, data from the three field trials were combined and analysed by adjusting all mortality data to equal birth rank and sex; this showed a significant reduction due to supplementation (P<0.05) with no treatment-year interaction. The increase in ewe production and reproduction in supplemented ewes was likely due to increases in nutrient intake, through increased DM, ME and CP intakes, prior to and during mating and to increased outputs of undegradable dietary protein and microbial protein from the rumen, per unit of crude protein consumed, thus increasing amino acid absorption. An increase in ovulation rate of 1.5 % units/MJ of digestible energy consumed (Smith 1985) should result in increases in ovulation rate due to tree fodder supplementation of only 5 and 4% units in 2001 and 2002, respectively; however, the increases in scanning rate were substantially greater at 41 and 16% units. Therefore, it is possible that the majority of the increase in reproductive rate was due to increased essential amino acid absorption, which is consistent with increases found in ewes mated on CT-containing forages such as Lotus corniculatus (Birdsfoot trefoil). Gross margin analyses using actual data from unsupplemented ewes in each of the three grazing trials compared with Riverside Farm's commercial ewes from the same years showed that drought reduced scanning rates by an average of 22.4% and wool production by 20% and that this reduction decreases sheep production income by approximately $14/ewe. Further analysis showed that almost half the cost ($6/ewe) could be recovered by supplementing ewes with tree fodder in a drought. On a whole farm basis this represents $58/hectare cost benefit due to tree fodder supplementation. Fungal contamination was a significant factor in the results obtained in Experiments 2 and 3. In all years, simulated drought pasture contained metabolites of zearalenone and the trichothecenes nivalenol and deoxy-nivalenol, produced by Fusarium fungi, while in Experiment 2 the poplar was severely contaminated with Melampsora larici-populina, or poplar leaf rust. Zearalenone concentrations in pasture were at their greatest in Experiment 3 and increased to over 2 mg/kg DM during the mating period. This may explain the lack of increase in reproductive rate expected in willow-supplemented ewes in Experiment 3, which was a feature of previous experiments; however, it did not explain the much greater loss in ewe LW in Experiment 3. Nivalenol (NIV) and deoxy-nivalenol (DON) are common trichothecene toxins found in New Zealand pasture and were found in pasture samples from all three experiments, however, the concentration in Experiment 3 was three- to four-fold greater than in previous experiments. Reports have suggested that trichothecenes may be partly responsible for the reduced growth of otherwise healthy livestock grazing dry autumn pasture, often referred to as 'ill thrift'. However, based on evidence from dosing experiments, it is unlikely that the quantities of NIV and DON present in pasture in Experiment 3 accounted for all of the greater LW loss seen in this experiment. This suggests that these toxins are likely to be indicators of other more potent fungal toxins, which have a much bigger impact on livestock health and production. It is likely that fungal toxins contribute more to reduced reproduction in breeding ewes and to ill thrift in young stock grazing dry autumn pastures in East Coast regions than is currently acknowledged

New Zealand, having large areas of hilly landscapes, is subject to the risk of soil erosion, and summer and autumn droughts that limit pasture growth, which in turn affects the livestock-based economy. The nitrogen and phosphorus input in fertilisers coupled with livestock excreta and soil disturbance impose a serious threat to downstream water quality. The planting of trees is one option used to decrease soil erosion, increase the quantity of forage and manage runoff. To date, research has mainly focused on wide spaced poplar trees for feed quality and their effects on understorey pasture growth. However, there is increasing interest in the use of densely planted willow and poplar for fodder purpose. The effects of young (< 5 yrs old) willow and poplar planted at close spacing on runoff, soil erosion, growth of understory pasture and nutrient losses have never been studied in New Zealand. Three field trials (two at Crop and Research Unit, Moginie, Manawatu and one at Riverside Farm, Masterton) were conducted between October 2004 and November 2006 that incorporated comparative establishment and growth of densely planted willow and poplar and their effects on soil moisture, runoff, sediment load and nutrient losses from grazed and fertilised farmland. It was concluded that densely planted willow and poplar (3-4 yrs) reduced total nitrogen (TN) and dissolved reactive phosphorus (DRP) by 47 % each and sediment load by 52 %. Young trees reduced surface runoff and soil moisture more as they aged. However, due to their deciduous nature willow and poplar were not effective in reducing surface runoff in winter and early spring. Sheep preferred camping under trees, especially in late spring and summer, and this led to greater deposition of dung and urine under trees than open pasture. Sheep grazing, especially in winter, significantly increased sediment and nutrient loads in runoff water. The N and P fertiliser application increased nutrient load in runoff water well above the threshold level required to initiate algal growth to create eutrophication. Densely planted willow and poplar significantly reduced understorey pasture growth by 23 % and 9 %, respectively, in their second year at Moginie, mainly due to shade, but coupled with soil moisture deficit in summer. The pasture growth in a willow browse block was 52 % of that in open pasture as a result of shade and differences in pasture species composition. Sheep browsing reduced willow leaf area significantly. Willow and poplar survival rates were similar (P > 0.05) after two years of establishment (100 % vs 90.5 %, respectively). However, willow grew faster than poplar in height (1.90 vs 1.35 m), stem diameter (43.5 vs 32.6 mm), canopy diameter (69 vs 34 cm) and number of shoots (8.7 vs 2.3) at the age of two years, respectively. The research clearly demonstrated that densely planted young willow and poplar trees can reduce runoff, sediment load and nutrient losses from farmland to freshwater, but shade and soil moisture can limit pasture growth under trees. It is recommended that willow and poplar should be planted at wide spacing on the whole farm to minimise loss of pasture. Where blocks of trees are necessary, such as willow browse blocks, sheep browsing can be used as a tool to reduce shade to improve pasture growth. Livestock access to riparian strips should be minimal to avoid livestock camping that can have deleterious effects on water quality.

This diploma thesis deals with the cultivation of fast-growing wood and concentrates on the influence of particular factors like e.g. location, agrotechnology and fertilizers, which have a crucial impact on the phytomass production. Moreover, the thesis evaluates the economic efficiency of this type of sustainable energy ressource, which can be a source of local business. Introductory theoretical chapters describe essentials rules of the cultivation of fast-growing wood. Furthermore the thesis presents general information in this field and proposes suitable wood clones. In addition, the thesis outlines the process of choice and preparation of the agricultural parcel, the usage of various fertilizes, herbicides and agrotechnology. The applied core characterises the business case itself. The primary research compares financial investment and its return of two examined agricultural parcels under the prerequisit of suitable choice of location and agrotechnology. A trail phase depictes the cultivation of fast-gworing wood and discuss presumptions for succesfull business. This thesis is mainly based on primary research. The acquired data are further analyzed and the final chapter attempts to outline the results and suggest measures.

En climat tempéré, le changement climatique aura pour conséquence une augmentation de la fréquence et de l’intensité des sécheresses. Parmi les facteurs influençant la survie des espèces à cet environnement fluctuant, la plasticité d’ajustement des traits de réponse semble constituer un atout majeur. Ce travail de thèse a étudié de façon intégrée la réponse physiologique et transcriptionnelle du peuplier noir à une carence hydrique progressive jusqu’à un niveau sévère. Dans le cadre d’une analyse globale, la plasticité des traits de réponse physiologiques de la plante et, pour la première fois, celle de l’expression des gènes foliaires a été estimée. Différentes échelles d’étude ont été prise en compte : les génotypes issus de populations différentes, les clones d’un même génotype et les structures de la feuille (nervure principale versus limbe). Un continuum de réponses phénotypiques au déficit hydrique sévère a été identifié permettant de classer la majorité des génotypes étudiés comme évitants avec un seul génotype tolérant, maintenant son développement foliaire, conservant ses feuilles matures et limitant la tension hydrique. Le transcriptome du limbe était profondément remodelé en réponse au déficit hydrique maximal (41% des transcrits différentiellement exprimés) et présentait des fonctions en lien avec la modification de la composition membranaire, le maintien de l’homéostasie cellulaire et la détoxication. L’expression des gènes liés au transport intra- et extra-cellulaire et aux flux d’eau (par les aquaporines) était également fortement régulée. Ces gènes étaient associés aux fonctions de maintien de l’intégrité et de l’hydratation cellulaire du limbe. La modulation du transcriptome était partiellement spécifique de la nervure principale par rapport au limbe. Les 958 transcrits spécifiquement régulés de la nervure principale indiquaient une sur-expression des gènes liés aux métabolismes du glyoxylate et des carbohydrates, et une sous-expression des gènes liés au transport intra- et extra-cellulaire. Ceci pourrait favoriser une accumulation de sucres dans la nervure principale, ce qui permettrait de maintenir les flux de sève et de limiter l’embolie. Les plasticités phénotypiques et transcriptionnelles moyennes calculées étaient différentes entre génotypes. Le nombre de feuilles et le potentiel hydrique foliaire étaient les deux traits permettant de discriminer statistiquement les génotypes par leur plasticité. Le niveau de plasticité de certains transcrits était également spécifique des génotypes : la plasticité transcriptionnelle était forte pour les gènes impliqués dans la fixation du carbone et le transport des messagers secondaires pour le génotype, qui en moyenne, était le moins plastique. L’ensemble de ces résultats permettent de conclure que le génotype le plus tolérant à la sécheresse possédait les plus faibles degrés de plasticités phénotypiques et transcriptionnelles. A l’inverse, les génotypes les plus sensibles détenaient des plasticités phénotypiques et transcriptionnelles plus fortes. Enfin, la régulation du degré de plasticité dépendrait à la fois de mécanismes conservés et d’autres acquis par les génotypes. / In temperate climates, climate change will result in an increase of the frequency and intensity of droughts. Among the factors influencing the species survival in fluctuating environment, trait responses plasticity seems to be a major asset. This thesis has focused on the integrated study of physiological and transcriptional responses of black poplar responding to a progressive water deficit until a severe level. For an overall analysis, plant phenotypic traits responses plasticity and, for the first time, plasticity of the leaf genes expression has been estimated. Different scales of study were taken into account: genotypes from different populations, clones of the same genotype and leaf structures (midrib versus leaf blade). A continuum of phenotypic responses to severe water deficit was identified allowing classifying the majority of the genotypes as sensitive with only one tolerant genotype, maintaining its foliar development, preserving its mature leaves and limiting hydraulic tension. The leaf blade transcriptome was deeply remodeled under severe drought (41% differentially expressed transcripts) and exhibited functions related to the modification of the membrane composition, maintenance of cellular homeostasis and detoxication. Transcripts related to intra- and extra-cellular transport and water flows (by aquaporins) were also highly regulated and associated with integrity and cellular hydration functions of the leaf blade. The transcriptome modulation was in part specific to the midrib compared to the leaf blade. The 958 specifically regulated transcripts of the midrib indicated up-regulation of genes implied in glyoxylate and carbohydrates metabolisms and down-regulation of genes involved in intra- and extra-cellular transport. In consequence, these modifications may favor sugar accumulation in the midrib and could force the sap flow and limit embolism. The estimated mean phenotypic and transcriptional plasticities were different between genotypes. The number of leaves and the leaf water potential were the two traits allowing discriminating statistically the genotypes by their plasticity. The plasticity level of some genes expression was also specific to genotypes: transcriptional plasticity was high concerning genes involved in carbon fixation and transport of secondary messengers for the genotype, which on average was the least plastic. All these results allowed concluding that the most drought-tolerant genotype possessed the lowest degrees of phenotypic and transcriptional plasticities. Conversely, the most sensitive genotypes hold high phenotypic and transcriptional plasticities. Finally, the regulation of the plasticity degree would depend on both preserved mechanisms and others acquired by the genotypes.

Les taillis à courte rotation (TCR) permettent de produire de la biomasse ligneuse, alternative aux combustibles fossiles. L'intégration d’espèces d’arbres fixateurs d'azote atmosphérique en mélange avec les essences à croissance rapide peut être un moyen de limiter le risque d'appauvrissement des sols dans les TCR. Le succès d'un tel mélange va dépendre des interactions entre les deux espèces : facilitation, compétition ou complémentarité pour la lumière et les ressources du sol (eau, nutriments). L’objectif de cette étude était d’évaluer l’impact du mélange peuplier / robinier, sur la croissance, la production de biomasse et l'acquisition de l'azote d'une plantation à courte rotation. Un dispositif instrumenté composé de monocultures de peuplier et robinier et le mélange des deux espèces a été étudié pendant quatre ans. La quantification répétée des biomasses aériennes et souterraines associée au suivi des dimensions des arbres a permis de mettre en évidence que la présence des robiniers n'avait pas d'influence sur la croissance, la production et l'allocation de biomasse des peupliers à l'échelle de l'arbre comme à l'échelle du peuplement. En revanche, les robiniers souffraient de la compétition interspécifique : mortalité augmentée, croissance et production de biomasse diminuée. De plus, une approche isotopique (15N) couplée à l'analyse des minéralomasses a montré que les teneurs en azote des robiniers dans le mélange étaient plus faibles que dans la monoculture dues à une fixation de l'azote atmosphérique réduite. Le stock global d'azote dans le milieu était comparable dans les mélanges et les monocultures de chaque espèce. Le mélange n'a pas montré d'intérêt sur la période d'étude en raison notamment des conditions pédoclimatiques inappropriées (en particulier pour le robinier) et d'une incompatibilité entre les deux espèces sur ce site / Biomass from short rotation coppice (SRC) plantations may help reducing fossil fuel consumption. The development of mixed-species plantations, introducing a nitrogen-fixing species could be a solution to reduce the risk of fertility decline in SRC. Nevertheless, the success or failure of the mixture will depend on the competition and complementarity processes, for light and soil resources (water and nutrients), between both species. The objectives of this study were to determine the impact of a mixture of poplar and black locust, on growth, biomass production and nitrogen uptake in the plantation. Instrumented monocultures and mixed plantations of both species have been studied during four years. Repeated above-and belowground biomass estimations associated with tree dimension monitoring have shown that the presence of black locust affected neither growth, nor biomass production and allocation of poplar trees both at tree and plot level. On the other hand, the black locusts trees suffered from interspecific competition: high mortality, decrease in growth and biomass production. Moreover, an isotopic approach (15N) coupled with mineralomass analyses allowed to highlight that nitrogen concentration in black locust trees in the mixture was lower than in the monoculture due to a reduction of the percentage of nitrogen derived from atmospheric fixation. The total nitrogen contents were close in the mixture and in the monocultures of each species. No advantage of the mixture was found during the study period because of inappropriate pedoclimatic conditions (especially for the black locust) and incompatibility between both species on this site

This research is part of continued efforts to correlate the hydrology of East Fork Poplar Creek (EFPC) and Bear Creek (BC) with the long term distribution of mercury within the overland, subsurface, and river sub-domains. The main objective of this study was to add a sedimentation module (ECO Lab) capable of simulating the reactive transport mercury exchange mechanisms within sediments and porewater throughout the watershed. The enhanced model was then applied to a Total Maximum Daily Load (TMDL) mercury analysis for EFPC. That application used historical precipitation, groundwater levels, river discharges, and mercury concentrations data that were retrieved from government databases and input to the model. The model was executed to reduce computational time, predict flow discharges, total mercury concentration, flow duration and mercury mass rate curves at key monitoring stations under various hydrological and environmental conditions and scenarios. The computational results provided insight on the relationship between discharges and mercury mass rate curves at various stations throughout EFPC, which is important to best understand and support the management mercury contamination and remediation efforts within EFPC.

Depuis quelques années la sylviculture intensive prend une grande ampleur afin de rapprocher la source de fibres des usines, d'accroître la productivité des plantations, et de diminuer la pression de coupe sur les forêts naturelles. Toutefois un débat sur le type d'aménagement optimal des plantations oppose l'aménagement mono- et pluri-spécifique. Il est important de mieux comprendre le fonctionnement de ces écosystèmes pour en effectuer une bonne gestion et d'optimiser les services écosystémiques que ces plantations fournissent. La décomposition des litières et le recyclage des nutriments sont des processus complexes essentiels au fonctionnement des écosystèmes. Ainsi mon projet de thèse visait à mieux comprendre l'influence de la mixité de deux essences forestières, à savoir l'épinette blanche et le peuplier hybride, en comparaison à des plantations pures sur le processus de décomposition des litières et le stockage de carbone. Les résultats de cette étude ne montrent pas d'amélioration du processus de décomposition avec le mélange du peuplier et de l'épinette ou de leurs litières. En revanche, le mélange de ces deux espèces en plantation tamponne les effets contrastés du peuplier et de l'épinette observés dans les plantations monospécifiques. De plus, le stockage de carbone et la productivité du peuplier sont améliorés dans les plantations mixtes par rapport aux plantations monospécifiques. Les herbacées semblent être bénéfiques pour la diversité d'organismes et favorisent la libération d'azote des litières d'arbres. Cet aspect pourrait contrebalancer l'effet négatif de la présence d'herbacées qui entrent en compétition avec les arbres pour les ressources. / The use of trees under intensive management is particularly important for rapid fibre production and for reduce cutting pressure on natural forests in boreal regions. However, a debate on the best type of plantation management opposes the mono-and pluri-specific management. Despite the possible antagonistic effects on productivity, it seems that mixed plantations would have benefits on soil properties, environmental stability, but also to maintain biodiversity and aesthetic value. It is important to better understand the functioning of these ecosystems to make good management in order to optimize ecosystem services of these plantations. Litter decomposition and nutrient cycling are essential process for the ecosystems functioning. My thesis project was to better understand the influence of the mixing of two tree species planted in comparison to monospecific plantations, namely white spruce and hybrid poplar, on the litter decomposition process and carbon storage. The results of this study showed no improvement in the decomposition process with the mixture of poplar and spruce in plantation or by their litters mixture. However, the mixture of the two species in plantation buffers the contrasting effects of poplar and spruce observed in monospecific plantations. In addition, carbon storage and productivity of poplars are improved in mixed plantations compared to monospecific plantations. Herbaceous litter appears to be beneficial for the abundance of organisms and promote the release of nitrogen from tree litter. This could offset the negative effect of the presence of grasses that compete with trees for resources.

Les facteurs de transcription (FT) de la famille R2R3-MYB chez les plantes jouent un rôle important dans la formation de la paroi secondaire des cellules de bois, que ce soit en activant ou en réprimant leurs gènes cibles au sein d’un réseau régulationnel complexe. Dans ce travail, nous avons utilisé la transgénèse et l’immunoprécipitation de chromatine associée à un séquençage haut-débit (ChIP-SEQ) pour déterminer la fonction de 3 FT R2R3-MYB chez le peuplier. Les peupliers surexprimant MYB090 ont des rayons moins lignifiés ; les tiges présentent une réduction de croissance et de teneurs en lignines. MYB090 régule ses cibles à l’aide d’un motif très conservé, similaire au motif Gamyb. Ses cibles sont impliquées notamment dans la biosynthèse des lignines, cellulose et xylanes, constituants principaux des parois. Les plantes surexprimant MYB221-SRDX et MYB156 présentent une nette réduction de la lignification des parois de leurs fibres, associée à une réduction de croissance. MYB221 semble avoir pour cibles des gènes codant pour des enzymes du métabolisme, ainsi qu’un autre FT de type R2R3-MYB, dont la régulation passe par un motif conservé de type SMRE (Secondary wall MYB-Responsive Element). En conclusion, la combinaison des approches ChIP-SEQ et de transgénèse montre que MYB090 semble être un répresseur transcriptionnel de la lignification, notamment dans les rayons, et de la formation de la paroi secondaire. De même, MYB156 et MYB221 seraient également des répresseurs de la lignification, dans les fibres et les rayons. Cette thèse ouvre des perspectives sur l’établissement de réseaux de régulation transcriptionnelle de la formation de la paroi secondaire. / Plant R2R3-MYB transcription factors (TF) play an important role in secondary cell wall formation in wood cells, by activating or repressing their target genes within a complex regulatory network. Here, we used genetic engineering and chromatin immunoprecipitation technique, associated to next-generation sequencing (ChIP-SEQ) to determine the function of 3 R2R3-MYB TF in poplar. Plants overexpressing MYB090 had less lignified parenchyma rays. The stem growth and total lignin content were reduced. MYB090 regulates target genes through a highly conserved motif, similar to Gamyb. Its target genes are involved in lignin, cellulose and xylan biosynthesis, which are the major components of secondary cell wall. Poplars overexpressing MYB221-SRDX and MYB156 showed a decrease in fiber cell wall lignification, and a reduced growth. MYB221 have targets encoding for metabolic enzymes but also for another R2R3-MYB TF. MYB221 recognizes its target genes, most probably through SMRE (Secondary wall MYB-Responsive Element) conserved motif. In conclusion, the combination of ChIP-SEQ and genetic engineering approaches shows that MYB090 seems to be a transcriptional repressor of lignification, especially in parenchyma rays. MYB156 and MYB221 are also negative regulators of secondary cell wall lignification, in fibers and parenchyma rays. This work opens new avenues on the building of transcriptional regulatory networks involved in secondary cell wall formation.