Nutrition minérale des plantations de peuplier hybride

Specifie leaf area and net photosynthesis

DRIS-BASED FERTLIZATION EFFICIENCY OF YOUNG HYBRID POPLAR PLANTATIONS IN THE BOREAL REGION OF CANADA

Nutritional deficiencies rn plantations of fast-growing spec1es have often been reported in boreal regions both on farrnland and on forest sites (e.g., after a clearcut) (Tullus et al. 2007; Guillemette and DesRochers 2008). In boreal forest environments, soils are generally poor in many available nutrients because of slow decomposition of organic matter and low mineralization rate due to low temperatures and leaching (Piirainen et al. 2007; Allison et al. 2008, 2009). In conventional farming systems, the use of intensively managed monocultures is common and may be a source of nutrient deficiencies (V arallyay 2007; Duggan et al. 2007; Toth et al. 2009). Nitrogen and phosphorus deficiencies can drastically affect yields of fast-growing plantations wh en they are established on farmland (Heilman and Xie 1993; Coleman et al. 2006). In addition to site history, tree growth in plantations may also be affected by inherent soil characteristics such as texture, depth, and pH which should be optimal to maximize growth of hybrid poplars (Stanturf et al. 2001). In an experiment conducted in Europe (Marron et al. 20 10), tree growth of the same hybrid poplar clones (P. deltoides W.Bartram x P. trichocarpa Torrey & A.Gray and P. alba L. x P. alba L.) varied significantly among three sites.

Understanding nutritional requirements of tree spectes used in plantations is important to maximize yields (Gregoire and Fisher 2004; Oskarsson and Brynleyfsdottir 2009). On the one hand, nutritional deficiencies can lead to high mortality, slow early growth rates and low economie profitability (Pitre et al. 2007; Block et al. 2009; Pinno and Bélanger 2009; Rivest et al. 2009). On the other hand, excess fertilization can lead to tree nutrient imbalances and consequently to lower yields (Fageria 2001). It may also negatively affect environment quality (Adler et al. 2007; Van Miegroet and Jandl 2007; Flint et al. 2008) through the contamination of groundwater and surface waters by nutrient leaching or runoff (Lofgren et al. 2009). Nitrates and phosphates are the main constituents of the chemical pollution generated by fertilizer loss and wastage (Nikitishen and Lichko 2008). Therefore, accurate determination of the nutritional requirements of fast-growing trees should ensure high yields while mitigating effects on environmental quality and avoiding higher production costs (Jacobs and Timmer 2005).

Diagnosis methods that are based on foliar analysis have been developed to determine plant nutrient status because they are more reliable than those based on soil nutrient analyses (Beaufils 1973; Bink:ley 1986). Nutrient concentrations vary among the leaves ofthe same tree depending on their age and position (order and height) (Walworth and Sumner 1987) but these factors have much less impact on nutrient ratios than on their absolute concentrations (Beaufils 1973; Fageria 2001). Diagnosis and Recommendation Integrated System (DRlS) is based on the use of nutrient ratios that are standardized as DRlS formulas and then transformed into DRlS indices (Walworth and Sumner 1987). A nutrient index is a mean of the deviations of the nutrient ratios from their respective optimum or norm values (Sumner 1979). DRlS norms are obtained from highly-productive individuals of a population grown under field conditions, and assuming that their nutrient ratios are closest to tree optimal nutritional requirements, allows one to make fertilization recommendations.

DRlS has been successfully used as a fertilizer management tool for a number of agricultural crops (e.g., Walworth and Sumner 1987; Ruiz-Bello and Cajuste 2002; Junior et al. 2003; Hartz et al. 2007; Hundal et al. 2007), but this approach is less common for forest plantations and its effectiveness is still being debated (Drechsel and Zech 1994; Ouimet and Camiré 1994; Campion and Scholes 2008; Lteif et al. 2008). The aim of the current study was to evaluate the efficiency of the DRlS method to correct nutritional imbalances and increase productivity in hybrid poplar plantations that have been established under boreal conditions. We hypothesized that (i) DRlS would accurately diagnose nutrient status oftrees and be a good predictor of tree growth and (ii) DRlS based fertilization would be more efficient to increase growth rates and correct nutrient deficiencies rather than using a standard fertilization formulae.

Leaf sam pling and fertilizer application 

About two months after trees were planted (end of July 2005), two leaves from each of the five trees that formed the middle row of each fertilizationxclone treatment combination were collected in each block and pooled together to determine the nutrient status of trees prior to fertilization and thereafter quantities of fertilizers to apply for treatments “DRIS I” and ”DRIS II”. Leaves were oven-dried (72 hat 70 °C) and ground through a 60 ~ sieve of a Wiley mill (Thomas Scientific, Swedesboro, NJ, USA). Nitrogen concentrations were obtained by dry combustion method with a LECO N-analyzer (Leco Corp., MI, USA) (Leco Corp. 1986). P, K, Ca and Mg concentrations were determined using inductively-coupled plasma spectrophotometry (ICP) following a nitrichydrochloric acid digestion (Masson and Esvan 1995).

The frrst fertilization treatment (DRIS I) was based on DRIS functions taken from Guillemette and DesRochers (2008) but using foliar nutrient concentrations that were obtained from our trees. These functions had been determined from a study by using 18 combinations of N-P-K fertilizers on three hybrid poplar clones grown in the same region (747210: P. balsamifera x P. trichocarpa, 915005: P. balsamifera x P. ma.ximowiczii and 915319: P. ma.ximowiczii x P. balsamifera). The DRIS I treatment was thus composed of 10 g tree·1 of ammonium nitrate (NJLN03), 70 g tree·1 of potassium sulphate (K2S04 ) and 40 g tree·1 of dolomite (CaMg(C03) 2). The DRIS II treatment was based on Leech and Kim’s (1981) DRIS functions. The latter were obtained from an experiment in which growth response of hybrid poplars to various fertilization treatments was evaluated in northeastem Ontario. DRIS II consisted of 60 g tree· 1 of NJLN03, 20 g tree·1 of triple superphosphate (Ca(H2P04) 2) 3), 30 g tree·1 of K2S04, and 30 g tree·1 of calcium carbonate (CaC03). The third treatment (standard treatment, STD) had a 1:2:1 NPK ratio that is often used in agriculture (Wang et al., 2008) and which consisted of 40 g tree·1 of NJLN03, 20 g tree·1 of Ca(H2P04) 2) 3 and 30 g tree·1 of K2S04 . A control treatment with no added fertilizer was also tested. In May 2006, fertilizers were placed in a 15 cm deep hole 20 cm away from the base of each tree (Guillemette and DesRochers, 2008). To avoid contamination between fertilization treatments, a buffer row of trees without fertilizers was retained between each treatment.

Leaves were sampled at the end of July 2006 (as described above in 2005) for nutrient analyses and to calculate DRIS indices.

Soil analyses 

Five soil samples were collected in l’vfay 2007 at the farmland site and ten at the forest site (more heterogeneous) for chemical and physical characterization . Soil samples were collected diagonally along plots. For each sample, two sub-samples from the 0- 20 cm and 20-40 cm horizons were collected separately. Soil samples were subsequently dried in an oven at 50 °C, ground and sieved through a 60 r-un mesh. The sub-samples at each level were then poo led for analysis. Soil pH was obtained after water-extraction of a saturated paste. Total carbon concentration in the soil was determined by high temperature combustion with a LECO N-analyzer (Leco Corp., Ml, USA) and soil available cations concentrations and the cation exchange capacity (CEC, cmoljkg) were obtained by ICP after an ammonium acetate extraction at the Forest Resources and Soil Testing Laboratory, Lakehead University (Thunder Bay, Ontario).

DRIS norms and indices 

The DRIS approach allows the determination of a nutrient index, which is the degree of deviation of that nutrient from its optimum value or norm. The nutrient norms are obtained from a high-yielding population (Partelli et al. 2007), and a nutrient is considered balanced when its index is around zero. The more positive an index, the greater the degree to which the nutrient is in excess; conversely, the more negative an index, the greater the degree to which the nutrient is limiting (Walworth and Sumner 1987).

Fertiliz er-Growth

Average relative growth rate of the four clones was increased by fertilization at both sites but clones responded differently to fertilization treatments in 2006 . At the forest site, trees fertilized with DRIS I, DRIS II and STD had greater growth rates (average of four clones) than unfertilized trees (3.75, 3.70, 3.70 and 3.49 cm3 cm·3 y”1 , respectively) . A significant Clone x Treatment interaction (?=0.02) was noticed as the ”Treatment” effect depended on clones. Fertilization increased growth rates by 5.04% to 18.44% depending on treatments and clones. DRIS I generated the greatest growth increases for clones 915319 and 915004 (13.55% and 11.90%) and DRIS II for the other two clones (9.84% and 18.44%) .

Practical considerations

Overall, our study showed that even at an early age, fertilization increases hybrid poplar growth. At the farmland site, mean tree volumes of DRIS 1, DRIS II and STD treatments exceeded those ofunfertilized trees by 16.07%, 10.51% and 62.61%, respectively , which represents volume gains of 0.17 m3 ha.1 y”\ 0.11 m3 ha.1 y” 1 and 0.68 m3 ha. 1 y”1 (at 4x1m spacing). At the forest site, mean tree volumes of the three fertilization treatments were respectively 33.63%, 30.02% and 30.68% greater than those ofunfertilized trees, which corresponds to volume gains of0.68 m3 ha.1 y”\ 0.6 m3 ha.1 y” 1 and 0.62 m3 ha.1 y”1 . The positive effect offertilization on tree growth was carried through the year following fertilizer application (2007), especially at the forest site where the volume gains associated with DRIS 1, DRIS II and STD for the four clones were 1.09 m3 ha.1 y”1 , 0.47 m3 ha. 1 y” 1 and O. 87 m3 ha. 1 y”1 , respectively (Fig. 2.2). Productivity gains following fertilization were in the range of previous experiments on hybrid poplar plantations in North America i.e., between 15% and 80% (Vance 2000; Brown and van den Driessche 2002; Coleman et al. 2006). The volume gains that were obtained in the first (2006) and the second growing season (2007) following fertilization are promising for successful plantation establishment in northwestem Québec. Fertilization also improves tree vigour and subsequent hybrid poplar resistance to pests (Weih 2004, Coleman et al. 2006), which may compensate for the costs of the fertilizer application.

EFFECTS OF MIXING CLONES ON HYBRID POPLAR PRODUCTIVITY, PHOTOSYNTHESIS AND ROOT DEVELOPMENT IN NORTHEASTERN CANADIAN PLANTATIONS

Much research has been conducted over the past twenty years to evaluate effects of diversity on ecosystem functioning, and has demonstrated that biomass production increases with increasing diversity (Loreau et al. 2001). The mechanisms underlying the positive effects of diversity on productivity have been classified into (i) complementarity and facilitation interactions between species, based on niche partitioning theory or the benefit that one species can receive from another, and (ii) sampling effects, which stipulate that within a group of species, one or more would dominate and increase overall ecosystem yield (Loreau et al. 2001). Most earlier trials tested this relationship on grass and shrub species, but many studies have now attempted to demonstrate the universality ofthis principle and are trying to elucidate the mechanisms that might explain diversity productivity relationships (Menalled et al. 1998; Petit and Montagnini 2006; Homer-Devine et al. 2003). Results from forest ecosystems would appear to confirm previous findings and overall, a positive effect of tree diversity on biomass production in both natural stands and plantations has been found (Tilman 1999; Balvanera and Aguirre 2006; Potvin and Gotelli 2008; Lei et al. 2009; Paquette and Messier 2011).

Site description and plant material 

The study sites were located in the Abitibi-Témiscamingue region of northwestem Québec, Canada, under a humid continental climate. Replicate plantations were established on three different sites. The first site was abandoned farmland located in the municipality of Duhamel (47°32’N, 79°59’W) in the sugar maple (Acer saccharum Marshall)-yellow birch (Betula alleghaniensis Britton) western bioclimatic sub-domain (Grondin 1996). The site had been previously cultivated for hay. The soil at Duhamel was a clayey Luvisol ( 45% clay; Agriculture and Agri-food Canada 2012) with mean annual precipitations and temperature of 820 mm and 2.8 oc, respectively (Environment Canada 20 13).The second site was previously forested before being harvested in 2004 ( 48°29’N, 97°9’W). It was located near the municipality of Duparquet in the balsam fir (Abies balsamea L.)-paper birch (Betula papyrifera Marshall) bioclimatic western sub-domain (Grondin 1996) with mean annual precipitations and temperature of 918 mm and 1.2 °C, respectively. The soil at this site was classified as heavy clay Brunisol (70% clay; Agriculture and Agri-food Canada 20 12). The third site was located in the municipality of Villebois and had been previously farmed organically for cereals and hay. This site (49°09’N, 79°10’W) was in the black spruce (Picea mariana (I’vfill.) BSP)-feather moss (Pleurozium spp.) domain (Grondin 1996) and the soil type was clay Grey Luvisol (50% clay). Mean annual precipitations and temperature at this site are 890 mm and 1.2 °C, respectively (Environment Canada 2013).

Four hybrid poplar clones that had been recommended for the region by the ministère des Ressources Naturelles du Québec (MRNQ) were selected for planting: clone 747215 (Populus trichocarpa Torrey & A Gray x balsamifera L.), clones 915004 and 915005 (P. balsamifera x maximowiczii Henry), and clone 915319 (P. maximowiczii x balsamifera). Prior to plantation establishment, stumps and woody debris at the Duparquet site were removed with a bulldozer. This site was then ploughed to a depth of 30 cm in autumn 2004 with a forestry plough pulled by a sk:idder and disked in spring 2005 to level the soil before planting. Duhamel and Villebois sites were ploughed using an agricultural cultivator in autumn 2004. Trees were planted in June 2005 at 4 x 3 rn spacing, corresponding to a density of about 833 trees/ha. Stock type was bare-root dormant trees and the average tree height at planting was 96.3 cm. Following planting, weeds were mechanically removed twice a year by cultivating between rows with a farm tractor and by tilling between trees with a Weed Badger (model 4020-SST, Marion, ND, USA). The experimental design was comprised of three monoclonal and three polyclonal replicates (blocks) of the four hybrid poplar clones at each site. A monoclonal plot consisted of five rows of five trees of one clone, while a polyclonal plot consisted of a mixture of eight rows of eight trees where the position of the four clones was randomly assigned (N = 14 76).

Specifie leaf area (SLA) and chemical analyses 

In May 2007, five soil samples were collected at Duhamel, and 10 at Duparquet and Villebois (more heterogeneous) for chemical and physical characterization . Soil samples were collected diagonally along plots (periphery and centre of the two diagonals) .Two sub-samples from the 0-20 cm and 20-40 cm horizons were collected separately for each sample. Soils were subsequently dried in an oven at 50 °C, ground, sieved to pass a 60 mn mesh, and then pooled for analysis. Total carbon concentrations in the soil were determined by high temperature combustion with a LECO N-analyzer (Leco Corp., St. Joseph, MI, USA). Soil concentrations of available cations (Ca2 +, K+, Mg2 + and Na+) and cation exchange capacity (CEC, cmolc kg-1 ) were determined after ammonium acetate extraction. Soil samples pH were obtained from a water-saturated paste. Leaf and soil nitrogen concentrations were quantified with the LECO N -analyzer. KCl (2 M) extraction was frrst performed on the soil, according to application bulletin CHNP2-84 (Leco Corp. 1986).

Photosynthesis

Net photosynthesis (Pn) was measured on two trees within each replicate, for each clone and for each layout type (monoclonal and polyclonal) at the three sites with a CIRAS-2 portable photosynthesis system using an infra-red analyzer (PP Systems, Amesbury, MA, USA) for the period 13-17 July 2009 (N = 144). Measurements were made on recently matured and well exposed leaves that did not show any apparent sign of senescence. The CIRAS-2 system was coupled with a broadleaf cuvette (PLC6-U, 25 mm diameter), which was equipped with a LED unit for automatic light control. Air flow and C02 concentrations in the cuvette were maintained at 300 mL min·1 and 360 J.l1llOl mol1 , respectively. Photosynthetically active radiation (PAR) was set at 1600 J.l1llOl rn -z s – 1 and measurements were taken between 8h30 and 12h00. During measurements, air temperature ranged between 18 oc and 25 oc, while relative humidity was between 50% and 70%. The order of tree measurements was randomized to reduce the time effect on photosynthesis parameters between 8h30 and 12h00. To avoid edge effect, trees of a buffer row around each plot were not sampled for photosynthesis, SLA and nutrients measurements.

Destructive sam pling

The root and shoot systems of two randomly chosen trees per replicate for each clone and layout type (N = 24) were selected for destructive sampling at the Duparquet site. Roots were excavated, either using an AIR-SPADE (Arbortools, Hong Kong) or hydraulically with a high pressure water pump (Mark III, Wajax, Lachine, QC, Canada). Small roots were dug out manually using pickaxes, shovels and trowels. Roots were grouped into three classes according to their distance ( d) from the stem: (i) d «:; 30 cm; (ii) 30 cm < d «:; 60 cm; (iii) d > 60 cm. Maximum depth (Dmax, cm) and maximum radial elongation (Lmax, cm) of roots were also measured for each excavated tree. After roots were dried, the totallength of coarse roots (diameter > 2 mm) and the mass of each root group were measured. Stems, branches and leaves of excavated trees were separated, dried (at 75°C) and weighed to calculate biomass allocation to roots and shoots. At the beginning of each tree excavation, a root sample of about 1 cm in diameter and 10 cm in length was collected for total non-structural carbohydrates (TNC) determination. Samples were located 50 to 70 cm from the stem to homogenize sampling.

CONCLUSION GÉNÉRALE 

Les plantations forestières d’essences améliorées à haut potentiel productif sont d’ores et déjà une composante des plans d’aménagement forestiers au Québec. En effet, la nouvelle loi sur l’aménagement durable du territoire forestier, entrée en vigueur en 2013, exige la création de zones dites« aires d’intensification de la production ligneuse» (AIPL) qui occuperaient 2% du territoire forestier à moyen terme et 15 % à long terme (ministère des Ressources Naturelles du Québec 2013). Le peuplier hybride, une espèce à croissance rapide, est particulièrement intéressant pour la production ligneuse intensive à courte rotation. L’établissement des AIPL a été recommandé sur des sites productifs en région boréale pour atteindre les rendements escomptés. Cela est d’autant plus important pour le peuplier hybride dont les exigences nutritionnelles sont relativement élevées. Dans ce contexte, il est important de mieux connaître et d’une façon précise les caractéristiques nutritionnelles des clones de peuplier à planter et leur tolérance à la compétition. Par ailleurs, on en connaît peu sur leur réponse à la variation des conditions du milieu le long de gradients climatiques, un paramètre particulièrement important sur le territoire forestier du Québec.

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Table des matières

CHAPITRE1 INTRODUCTION GÉNÉRALE
1.1 Problématique de recherche
1.2 Nutrition minérale des plantations de peuplier hybride
1.3 Intérêt du diagnostique foliaire dans la fertilisation des plantations de peuplier hybride
1.4 L’effet diversité-productivité dans la foresterie à courte rotation
1. 5 Plasticité phénotypique et productivité
1.6 Méthodologie et objectifs de recherche
CHAPITRE II DRIS-BASED FERTLIZATION EFFICIENCY OF YOUNG HYBRID POPLAR PLANTATIONS IN THE BOREAL REGION OF CANADA
2.1 Abstract
Résumé
2.2 Introduction
2.3 Materials and methods
2.3.1 Study sites and plant material
2.3.2 Leaf sampling and fertilizer application
2.3.3 Soil analyses
2.3.4 DRIS norms and indices
2.3.5 Nutrient balance index (NBI) and correction index (CI)
2.3.6 Statistical analyses
2.4 Results
2.4.1 Fertilizer-Growth
2.4.2 DRIS indices
2.4.3 DRIS indices vs. Growth
2.5 Discussion
2.6 Practical considerations
2.7 Acknowledgements
CHAPITRE III EFFECTS OF MIXING CLONES ON HYBRID POPLAR PRODUCTIVITY, PHOTOSYNTHESIS AND ROOT DEVELOPMENT IN NORTHEASTERN CANADIANPLANTATIONS 
3.1 Abstract
Résumé
3.2 Introduction
3.3 Materials and methods
3.3 .1 Site description and plant material
3.3.2 Growth
3.3 .3 Specifie leaf area (SLA) and chemical analyses
3.3.4 Photosynthesis
3.3.5 Destructive sampling
3.3.6 Statistical analyses
3.4 Results
3.4.1 Stem volume
3.4.2 Nutrient concentrations
3.4.3 Specifie leaf area and net photosynthesis
3.4.4 Biomass allocation
3.4.5 Radial distribution of roots
3.4.6 TNC content ofroots
3.5 Discussion
CHAPITRE IV PLASTICITY OF BUD PHENOLOGY AND PHOTOSYNTHETIC CAPACITY IN HYBRID POPLAR PLANTATIONS ALONG A LATITUDINAL GRADIENT AND IN RESPONSE TO SPACING IN NORTH EASTERN CANADA. 
4.1 Abstract
Résumé
4.2 Introduction
4.3 I’viaterials and methods
4.3 .1 Study sites and plant material
4.3.2 Phenology
4.3 .3 Meteorological data
4.3 .4 Growth
4.3 .5 Leaf nitrogen concentration and specifie leaf area (SLA)
4.3 .6 Photosynthesis
4.3.7 Plasticity
4.3 .8 Statistical analysis
4.4 Results
4.4.1 Clonai growth patterns
4.4.2 Growth stability
4.4.3 Bud phenology
4.4.4 Kinetics ofbud burst (BB) and bud set (BS)
4.4.5 Physiological response pattern
4.4.6 Plot density and leaf traits
4.4.7 Relationships between variables
4.4.8 Plasticity
4.5 Discussion
CHAPITRE V CONCLUSION GÉNÉRALE

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