Soutenance mémoire
RÉSUMÉ
Le rendement des plants de bleuets sauvages est étroitement lié à plusieurs caractéristiques intrinsèques et extrinsèques. Pour ainsi améliorer la productivité, une meilleure compréhension de l’influence de l’architecture des plants, de la phénologie spécifique aux espèces et des traitements de fertilisation et de fauchage sur la production de fruit serait importante pour faire de meilleur choix de pratiques agricole en zone nordique. Pour ce faire, la première partie de cette étude porte sur la comparaison des traits phénologiques, architecturaux et allométriques entre les deux espèces présentes auSaguenay-Lac-Saint-Jean, soit Vaccinium angustifolium Aiton et Vaccinium myrtilloides Michaux. Dans la seconde partie de l’étude, ce sont les effets combinés sur les traits allométriques et le rendement de deux pratiques agricoles, soit le fauchage et l’application d’engrais, qui sont comparés dans une bleuetière en zone nordique. L’expérience s’est déroulée du printemps 2017 à l’automne 2018 sur une bleuetière commerciale située au nord du Saguenay-Lac-Saint-Jean. La combinaison de fauchage – mécanique ou mécanique et thermique – et d’engrais – minéral, organique ou sans – a été appliquée sur les champs. La phénologie des bourgeons, la croissance en hauteur et en longueur, la masse des fruits par plant et par parcelle ainsi que le nombre d’éléments sur la plante (bourgeon, feuille, fleur, fruit, etc.) ont été notés selon le type de production en cours dans les champs, soit l’année après fauchage (pruning year) ou l’année de récolte (harvesting year). La surface foliaire spécifique, la biomasse hors-sol des plants, l’aire et la biomasse des feuilles ont été estimées à partir de la prise de donnée sur 192 plants récoltés. La comparaison entre les espèces a permis de montrer des différences entre elles : d’abord leur phénologie diffère et le bourgeonnement des feuilles et des fleurs de V. myrtilloides est retardé, dû à un nombre plus important de composantes structurelles (bourgeon, fleur, feuille) comparativement à V. angustifolium. La biomasse des fruits estsimilaire entre les deux espèces : V. myrtilloides possède des fruits plus petits, mais en plus grande quantité, ce qui peut être expliqué par la limitation de la pollinisation et par une biomasse hors-sol importante. Par son retard dans la phénologie des fleurs, V. myrtilloides pourrait être l’espèce la mieux adaptée à la zone nordique pour résister au gel printanier, mais la pollinisation devrait être augmentée. Pour ce qui est des pratiques agricoles, l’application d’engrais, qu’il soit minéral ou organique, améliore la majorité des traits de la plante, dont la production de fruit après deux années. L’engrais organique n’a cependant réussi à atteindre les résultats de l’engrais minéral qu’après deux années, comme il a dû être dégradé avant d’être rendu disponible pour les plantes. Le fauchage thermique, appliqué en plus du fauchage mécanique, a accru certains traits végétatifs, comme la biomasse des feuilles et de la plante. D’ailleurs, deux modèles prévisionnels ont été produits et qui montre que le nombre de fleurs avec l’application d’engrais ainsi que la longueur des branches et la biomasse de la plante sont les facteurs qui expliquent le mieux le rendement en fruit. L’étude confirme que l’utilisation d’engrais dans les champs de bleuet en zone nordique est essentielle, mais une étude à plus long terme sur le fauchage thermique est nécessaire pour vérifier si ce type de fauchage amène réellement plus de bénéfices que de coûts.
Experimental design
We conducted our study from spring 2017 to autumn 2018 in a commercial wild lowbush blueberry field at the Bleuetière d’Enseignement et de Recherche (BER) of Corporation d’Aménagement Forestier de Normandin (CAFN) in Normandin Quebec,Canada (48°49ʹ35ʺN; 72°39ʹ35ʺW). We established an experimental design that included 2 adjacent sites composed of 2 fields at each site and 4 blocks of 12 experimental units (EU) in each field arranged in a split-plot design (Supplementary Figure SM.1). Each site contained 96 EU, each 15 × 22 m (330 m2 ), separated by 3-m buffer zones. All EU received1 of 12 different treatments (see Table II.7 in chapter 2). These treatments were combinations of mechanical or mechanical and thermal pruning, with or without fungicide application, and mineral, organic or without fertilization (Supplementary Figure SM.1, see Table II.8 in chapter 2). Site 1 was pruned thermally in fall 2016 and mechanically in spring 2017. Site 1 was harvested in 2018. Site 2 was pruned mechanically and thermally in fall 2017. Site 2 was in a pruning year in 2018 and a harvesting year in 2019 (after the completion of this study, Supplementary Figure SM.1). However, the effects of these various treatments are not presented in this paper, but see chapter 2 p.48. As well, 52 beehives were used in spring 2018 to ensure sufficient flower pollination during harvesting year (see Table II.8 in chapter 2).
Species effect on allometric characteristics
During the pruning years, both species had similar plant heights (Figure I.2a, Table I.4), ramification numbers (Table I.4), plant BM (Figure I.2d), and SLA (Figure I.2j, Table I.4). In the pruning years, however, we observed significantly higher leaf numbers for V. myrtilloides than for V. angustifolium (Figure I.2h, Table I.4).Furthermore, we also observed a significant difference between years for leaf number (Table I.4) and SLA (Table I.4) in thepruning years, with both traits lower in 2018. We observed no significant year and speciesinteractions (Table I.4). During the harvesting year, plant BM (Figure I.2e), branch length (Figure I.2c), ramification numbers, SLA (Figure I.2j), and fruit BM (Figure I.2o) did not differ between the two species (Table I.4). All other characteristics differed significantly between the twoblueberry species; for example, V. angustifolium had a greater flower bud number (FigureI .2k) and BM per fruit (Figure I.2r) than V. myrtilloides. All other allometric traits had higher values for V. myrtilloides (Table I.4), including plant height (Figure I.2b), number of leaf buds (Figure I.2f), leaves (Figure I.2i), branches (Figure I.2e), apical flowers (Figure I.2m), total flowers (Figure I.2l), flowers by bud (Figure I.2n), apical fruits (Figure I.2q), and total fruits (Figure I.2p). Branch growth slowed around the DOY 185, as fruits began to develop.
Fertilizer Effects
In the pruning year, compared to CF, adding MF and OF increased plant height(Figure II.6e), aboveground plant BM (Figure II.6f), ramification number (Supplementary Table SM.1), leaf number (Figure II.6a), leaf area (Figure II.6c) and leaf BM significantly (Figure II.6d). On the contrary, SLA was significantly reduced by adding fertilizers, and this effect was more pronounced with MF compared to OF (Figure II.6b). In the harvesting year, adding MF and OF increased plant height (Figure II.6g), aboveground plant BM (Figure II.6h), leaf BM (Figure II.6j), and fruit yields (Figure II.7a). Adding MF also increased the flower bud number (Figure II.8a), flower number (Figure II.8b) and branch length (Figure II.6i). However, in most of these traits, the effect of OF was like those of MF or CF.
Pruning Effects
Pruning method had no significant effect on fruit yields (Figure II.7b). However, compared to M, MT slightly but significantly improved several allometric traits by reducing plant ramification in the pruning year and increasing plant height and BM during the harvesting year (Figure II.9). Interactions between fertilizers and pruning were only significant for leaf area and plant height during the harvesting year (Figure II.10, Supplementary Table SM.1 and Table SM.3). However, the only useful information we can extract from these results is that using M and CF produced shorter plants (Figure II.10).
Relationships Between Allometric Traits and Fruit Yields
For both plant-leaf and flower models, the null mixed-effect model presented significant residual effects of random variables, so random variables – i.e. blocks nested infields, and fields – were kept in the models. We chose the best models according to the minimum AIC, AICC and BIC to predict fruit yields (Table II.9). Because no treatment had a significant effect on plant density (P > 0.05, results not shown),upscaling was done in orderto predict fruit yields (t ha-1) EU scale with plant-based allometric traits. For the leaf-plant mixed-effect model, the aboveground plant BM and branch length were significant variables, whereas SLA, number of leaf buds, ramifications and branches were not significant so were removed from the model (Table II.9, Figure II.11). Treatments were not significant because aboveground plant BM proportionally increased with fertilizer, from CF to MF (Table II.9, Figure II.11). The predicted fruit yield linearly increased with aboveground plant BM and branch length (Figure II.11). For the flower mixed-effect model, fertilizer and flower number effects were used in the model after building a backward process that removed flower bud number and flowers by bud to predict fruit yields (Table II.9, Figure II.12). The predicted yields increased linearly as a function of the number of flowers per plant (Figure II.12). A lower predicted fruit yield was observed for control fertilizer CF while OF and MF increased the predicted yield in a similar manner (Figure II.12).
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Table des matières
Résumé
Avant-Propos
Remerciement
Liste des figures
Liste des tableaux
Liste des annexes
Introduction générale
Chapitre 1: How plant allometry influences bud phenology and fruit yield in two vaccinium species
I. Abstract
I.1. Introduction
I.2. Material and Methods
I.2.1. Experimental design
I.2.2. Data collection
I.2.3. Meteorological data
I.2.4. Statistical analysis
I.3. Results
I.3.1. Phenological differences between species
I.3.2. Species effect on allometric characteristics
I.3.3. Link between species, phenology, and allometric characteristics
I.4. Discussion
I.4.1. Link between species, phenology, and allometric characteristics
I.4.2. How plant allometry determines fruit attributes
I.5. Conclusion
I.6. Reference
Chapitre 2: Mineral or organic fertilizers and thermal pruning improve allometric traits related to fruit yields in a wild blueberry field
II. Abstract
II.1. Introduction
II.2. Material and Methods
II.2.1. Experimental Design
II.2.2. Data Collection
II.2.3. Meteorological Data
II.2.4. Statistical Analysis
II.3. Results
II.3.1. Fertilizer Effects
II.3.2. Pruning Effects
II.3.3. Relationships Between Allometric Traits and Fruit Yields
II.4. Discussion
II.4.1. Fertilizer Effects
II.4.2. Pruning Effects
II.4.3. Relation Between Allometric Traits and Fruit Yields
II.5. Conclusion
II.6. References
Conclusion générale
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