Description ofroot systems ofundesirable tree species

Description ofroot systems ofundesirable tree species

Covers with capillary barrier effects as mine site reclamation method:

Québec is one of the leading Canadian provinces in exploitation of mineral resources. Nevertheless, mining operations are accompanied by the release of millions tonnes of tailings that may lead to serious ecological problems. To prevent this, the government of Québec issued the Mining Act (I\.1NR 2014) thatrequires the mining companies to work towards sustainable development. Following the regulations of the Mining act, mining companies must rehabilitate tailings impoundment areas to prevent contamination of the environment, thereby obtaining social acceptance.

Nowadays, acid mine drainage (AMD) remains one of the challenging environmental issues for the mining industry (Johnson and Hallberg 2005; Bussière 2009). Acid mine drainage is produced from the oxidation of sulphide minerais, such as pyrite and pyrrhotite, contained in mine tailings (Kleinmann et al. 1981; Blow es et al. 1994 ). T’vian y methods are proposed to control AMD generation (MEND 2001). In humid climates, the construction of covers with capillary barrier effects (CCBE) is frequently used as a closure plan for various mines with AMD generation (Ricard et al. 1997; Dagenais et al. 2005; Bussière et al. 2006). Covers with capillary barrier effects have to maintain a high degree of saturation in one (or more) of its layers in order to limit oxygen migration from the atmosphere to the mine tailings and consequently to prevent AMD generation (Nicholson et al. 1989; Bussière et al. 2003). Basically, CCBEs consist ofthree to five layers. Each layer is made of different materials, each having a specifie function. From the bottom to the top the layers are: a support and capillary break layer made of course-grained materials; a moisture-retention layer made offine-grained materials that serves as oxygen and water barrier; a drainage layer made of coarse-grained material to prevent water loss from evaporation; protection and surface layers to protect against erosion and bio intrusion of the CCBE (Aubertin et al. 1995; Bussière et al. 2003). Schematic illustration of a typical CCBE is presented in Figure 1.1.

Description of root systems of un desirable tree species:

Undesirable trees species, especially their root systems, can threaten the integrity ofCCBE and affect their long-terrn performance. In the following, the root system of the potentially dangerous tree species are described and discussed.

Poplars
The species of the genus Populus, known in the boreal zone as poplar and aspen, can produce new roots from the radical, from a cutting or an abscised branch, and from the pre-existing root system in the case of suckers (Zasada and Phipps 1990). However, roots of healthy parent poplar trees rarely develop suckers without aboveground disturbance (Wan et al. 2006). The root system of a parent poplar trees and its suckers have different root architecture. Euphrates poplar (Populus euphratica Oliv.) seedlings produce one deep vertical tap root, keeping this as adult tree, and radiating coarse lateral roots that are formed from the tap root (Wiehle et al. 2009). Suckers have a ”T”- like root system that originates from lateral roots of a parent tree. Consequent! y, suckers never develop a tap root but have two apparent side roots opposite from each other (Wiehle et al. 2009).

Trembling aspen (Populus tremuloides Michx.) produces strong vertically penetrating roots originating near the tree base and sinker roots that are formed from a network of lateral roots (Peterson and Peterson 1992). The lateral roots of aspen are usually within 15 to 30 cm of the soil surface, whereas the sinker roots may reach 3 rn in depth (Strong and La Roi 1983b; Perala 1990). Root system morphology and depth distribution of aspen vary with stand age and site conditions (Strong and La Roi 1983a,b ). As pen roots can reach a depth of 130 cm with age but on sandy soils. On clay loam, as pen has a maximum rooting depth of 95 cm (Strong and La Roi 1983b).Maximum vertical rooting depth of aspen ranges from 1.5 to > 3 rn, whereas the radial spreadranges from 14.3 to 30.5 rn (see review by Stone and Kalisz 1991). In early growth of trembling aspen and balsam poplar (28-30 days after seed establishment), balsam poplar tends to produce deeper roots, compared to as pen (Wolken et al. 20 10). Root systems ofbalsam poplar penetra te deeply in the soil and possess an extensive system of lateral roots on dry sites (Zasada and Phipps 1990). On wet sites, rooting depth ofbalsam poplar can be reduced (Zasada and Phipps 1990).

Willows
Most willows (Salix spp.), frequently used in ecological engineering (i.e. soil remediation, short-rotation woody crops for the biomass production, stabilization of slopes, soil erosion control), are fast-growing shrubs (Greger and Landberg 1999; Schaff et al. 2002; Pulford and Watson 2003; Mirck et al. 2005; Meers et al. 2007; Mickovski et al. 2009). The root system architecture ofwillow shrubs differs from willow trees. Willow shrubs are highly dependent on an efficient root system for water and nutrient uptake to maintain its high yield production (Rytter 1999). The root system of willows is characterized by a high production and turnover rate of fine roots (Rytter and Rytter 1998; Rytter 1999) and an extensive gravitropic coarse root system (Mickovski et al. 2009). The majority of its roots are located in the upper soillayers where soil conditions are more favorable for root penetration and growth ( e.g. high nutrients availability, optimal soil density, better soil aeration) (Volk et al. 2001). Black willow (Salix nigra Marsh.), a commercially important species native to North America, is recognized as a shallow-rooting species (Pitcher and McKnight 1990).

Root behaviour in response to environmental stresses:

Root system development in plants is under sorne degree of genetic control (Gale and Grigal 1987). This means that the root architecture that was described above is exhibited in normal conditions. However, roots growth is also influenced by environmental conditions. It can be limited by physical, chemical, and biological soil properties (Bengough et al. 2011). One of the widely recognized plant responses to changes in soil media in the presence of plant species is a shift in biomass partitioning between above- and belowground plant structures (Chapin et al. 1993; Wardle and Peltzer 2003). It is frequently reported that biomass allocation to the roots increases as supplies of water and/ or mineral nutrients ( especially P and N) become growthlimiting (Haynes and Gower 1995; Huante et al. 1995; Bonifas et al. 2005; Murphy et al. 2009). Biomass allocation shifts towards roots and consequently an increase in root-to-shoot ratio is induced by belowground res ource competition (Gersani et al. 200 1; Donaldson et al. 2006; Murphy and Dudley 2007). This response allows plants to maximize the exploitation of insufficient nutrients and water, thereby minimizing resource requirements (Chapin et al. 1987).

Sheep laurel
Sheep laurel is an ericaceous understory shrub native to the eastern Canadian boreal forests that ranges from Newfoundland to Ontario (Titus et al. 1995). It is very efficient at vegetative propagation: by stem base sprouting, belowground rhizomatous growth, and layering (:M:allik 1993). Sheep laurel can tolerate a wide range of edaphic conditions (Damman 1971; Titus et al. 1995). However, this ericaceous shrub is found to be more vigorous (higher values for plant height, leaf area and specifie leaf area) in partial shade, compared to open sites (clear-cut) (Mallik 1994). Earlier studies demonstrated that the presence of sheep laurel inhibits the growth of conifer seedlings, such as black spruce (English and Hackett 1994; Yamasaki et al. 1998; Thiffault et al. 2004; Thiffault and Jo bidon 2006), red pine (Pi nus resinosa Ait.) (I<rause 1986), and balsam fir (Abies balsamea (L.) Mill.) (Thompson and :M:allik 1989). Arisk of conversion of productive to unproductive forest stands occupied by sheep laurel following disturbance in the boreal forest was reported (Thiffault and Jobidon 2006) .

Research context:

Covers with capillary barrier effects represent an efficient measure limiting short-term production of AMD (Bussière et al. 2006). This ~ster’s study was conducted to integrate a bio-barriers made of species with potential allelopathic effects in the design of CCBEs in or der to protect the CCBEs against undesirable tree establishment, thereby improving its long-term efficiency. The main objective of this study was to assess whether two bio barrier species (BBS) with potential allelopathic effects, bluejoint reedgrass (Landhausser and Lieffers 1998; Balandier et al. 2006) and sheep laurel (Yamasaki et al. 1998; Thiffault et al. 2004; Joanisse et al. 2007), can inhibit the growth ofthree target tree species (TS): balsam poplar, willow, and black spruce (most problematic species in the Québec boreal context). The effects ofBBS are assessed on growth increment, biomass (root, shoot, total), and root-to-shoot of three TS. Increased attention was paid to test whether BBS are able to alter the root system architecture ofthree TS (maximum root depth and root radial extension, total root length and volume, root bran ching parameters number of 2nct_and 3rct_order roots) and especially to inhibit downwards root growth of TS because tree roots represent a particular risk to CCBEs. The use of bio-barriers made of species with potential allelopathic effects is a promising ecological solution to control undesirable tree invasions since BBS are native to boreal ecosystems (no pesticides or herbicides are involved to control tree invasions on the CCBEs).

BIO-INTRUSION BARRIERS OF CALAMAGROSTIS CANADENSIS AND KAIMIA ANGUSTIFOLIA HAVE SPECIFIC IMPACTS ON ROOT SYSTEM ARCHITECTURE AND GROWTH OF TREE SPECIES EST ABLISHED ON MINE CO VERS :

Along with the economie benefits that are derived from the exploitation of mineral resources in Canada, the mining industry produces substantial quantities of wastes that may incur adverse environmental impacts. Acid mine drainage (AMD), which results from the oxidation of sulphide-containing minerais in mine wastes (Kleinmann et al. 1981; Blowes et al. 1994), represents one of the most challenging environmental problems for the mining industry (Bussière et al. 2006). Many methods have been proposed to control AMD generation (MEND 2001). Covers with capillary barrier effects (CCBE) are considered to be an efficient means of limiting oxygen migration in humid climates, thereby controlling AMD generation from mine wastes (Ricard et al. 1997; Bussière et al. 2003; Dagenais et al. 2005; Bussière et al. 2006).

Colonization of undesirable plant species, which naturally invade CCBEs from the adjacent forest, can however compromise long-term CCBE efficiency (Trépanier et al. 2006). The main risks that are associated with vegetation invasion of the cover system are: 1) extraction ofwater from fine grained soil by plant roots, which reduce the degree of saturation and the capacity of the CCBE to cons train oxygen migration; (2) creation of macropores by roots and consequent! y an increase in water infiltration and oxygen migration through the cover system; and (3) physical damage to the CCBE through up rooting of shallow-rooting trees (such as Picea spp.) (USDOE 1990; Handel et al. 1997; Hutchings 2001).

Root architecture measurements and analyses
Coarse root systems of TS were digitized in three dimensions with a Polhemus Fastrak lowmagnetic field digitizer (Polhemus, Colchester, VT, USA; http://polhemus.com/) and PiafDigit software (Danjon and Reubens 2008) following the method described by Danjon et al. ( 1999a). The root systems were positioned according to the reference direction (north). Since metal might interfere with the magnetic field and measurements (Danjon et al. 1999b; Nicoll et al. 2006), digitizing was performed outdoors and far away from large metallic objects. The topology, Cartesian XYZ coordinates, and diameter of each digitized point were simultaneously recorded. The diameter corresponding to the frrst digitized point was measured in two directions (north-south and east-west), considering that the roots had oval crosssectional areas (Danjon et al. 2005; Nicoll et al. 2006). Measurements along the length of the roots were taken at 2 cm intervals when the root was straight and every 0.5 cm when the root was highly curved or when its diameter changed abruptly. Appendix B shows sorne examples of how coarse root systems were digitized from August to September 2012 at the Lac Duparquet Research Station ofUQAT.

Statistical analyses
Characteristics of TS (stem height and basal diameter increment; above-, belowground, and total dry mass; root-to-shoot ratio; root architectural characteristics) were analyzed in R (Version 2.15.2, R Development Core Team 20 12) with linear mixed effects models (Zuur et al. 2009). Each TS and treatment (BBS) was analyzed separately. Homoscedasticity and normality of residuals were verified for all data prior to analysis. Data were ln- transformed whenever necessary. The block and treatment-within block were treated as random effects. Two candidate models were identified to assess the effects of BBS on height and diameter increment of TS during the experimental period 2011-2012 for bluejoint and 2009-2012 for sheep laurel. The models included the fixed effects of zone (wet vs. dry), treatment (control, bluejoint, and sheep laurel) and their interaction (zone x treatment). The respective reference levels for these categorical variables were dry zone and control plot. Effects of zone, treatment, dry mass of BBS (aboveground, belowground, and total), and their interactions (zone x treatment, zone x BBS dry mass) on TS dry mass and root characteristics were assessed. The correlated parameters, such as the treatment and BBS dry mass, were not included in the same mo del.

Sheep laurel
As observed in the bluejoint plots, only one root characteristic, i.e., maximum root depth of balsam poplar, varied among zones (estima te wet zone = -0.36, 95% CI: -0.61, -0.12).  When compared to the dry zone, the maximum root depth ofbalsam poplar in the wet zone was 37% (17 cm) and 23% (13.4 cm) lower in the control and sheep laurel plots, respectively (Table 2.4). In the presence of sheep laurel, the maximum root depth of bals am poplar increased by 38% (estimatesheeplaurel = 0.32, 95% CI: 0.09, 0.55) and its total root volume was 57% greater, compared to the control plot ( estimatesheep laurel = O. 57, 95% CI: 0.08, 1.07). The number of 2nd_ order roots of balsam poplar in the sheep laurel plots was 36% greater than in the control (estimatesheeplaurel = 1.63, 95% CI: 0.37, 2.88). No difference between plots was observed for maximum root radial extension, total root length, and the number of 3rct_order roots of bals amµ poplar (Table 2.4, Appendix L).

GENERAL CONCLUSION :

In Québec, mining tailings accumulation areas must be rehabilitated to protect the environment from AMD production (l\1RN 2014 ). Covers with capillary barrier effects are recognized as one of the most effective engineered methods to rehabilitate AMD generating mining sites (Dagenais et al. 2005; Bussière et al. 2006). Nevertheless, the rapid establishment of tree species and shrubs on CCBEs was a cause of concem since uncontrolled vegetation can reduce long-term CCBE efficiency (Trépanier et al. 2006; Smimova et al. 2009). This project was developed to improve the ability of CCBEs to control AMD production. The main objective of this study was to introduce two native species with potential allelopathic effects (bluejoint and sheep laurel) at the L TA tailings impoundment, which was rehabilitated with a CCBE in order to test whether these species can be used as effective BBS that are able to impede the growth ofundesirable TSµ (balsam poplar, willow, and black spruce).

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Table des matières

CHAPTERI GENERAL INTRODUCTION 
1.1 Covers with capillary barrier effects as mine site reclamation method
1.2 Description ofroot systems ofundesirable tree species
1.2.1 Pop lars
1.2.3 Black spruce
1.3 Root behaviour in response to environmental stresses
1.4 Bio-barriers to improve long-term performance of mining covers
1.4.1 Bluejoint reedgrass
1.4.2 Sheep laurel.
1. 5 Research context
CHAPTERII BIO-INTRUSION BARRlERS OF CALAMAGROSTIS CANADENSIS AND KALMIA ANGUSTIFOLIA HAVE SPECIFIC IMPACTS ON ROOT SYSTEM ARCHITECTURE AND GROWTH OF TREE SPECIES EST ABLISHED ON MINE COVERS 
2.1 Résumé
2.2 Abstract
2.3 Introduction
2.4 Materials and methods
2.4.1 Study site
2.4.2 Experimental design and treatment
2.4.3 Seedling measurements and sampling
2.4.4 Root architecture measurements and analyses
2.4.5 Statistical analyses
2.5 Results
2.5.1 Bio-barrier species responses .
2.5.2 Target tree species mortality
2.5.3 Target tree species growth
2.5.3.1 Bluejoint
2.5.3.2 Sheep laurel
2.5.4 Target tree species biomass and root-to-shoot ratios
2.5.4.1 Bluejoint
2.5.4.2 Sheep laurel
2.5.5 Target tree species root system architecture
2.5.5.1 Bluejoint
2.5.5.2 Sheep laure1.
2.6 Discussion
2.6.1 Influence ofbluejoint on above- and belowground growth oftarget trees
2.6.2 Influence of sheep laurel on above- and belowground growth of target trees2.7 Conclusion
CHAPTER III GENERAL CONCLUSION

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