growth, physiology, and leachate losses in picea glauca seedlings (1+0)...

Growth, physiology, and leachate losses in Piceaglauca seedlings (1+0) grown in air-slit containersunder different irrigation regimes

Mohammed Lamhamedi, Gil Lambany, Hank Margolis, Mario Renaud, LindaVeilleux, and Pierre Y. Bernier

Abstract: In production tunnels, time domain reflectometry (TDR) was used to manage irrigation and leaching by con-trolling water content in the rhizosphere of air-slit containerized white spruce (Picea glauca(Moench) Voss) seedlings(1+0). Seedlings were exposed to four irrigation regimes (v/v: IR-60%, IR-45%, IR-30%, and IR-15%) during the firstgrowing season to assess IR effects on growth, gas exchange, nutrient uptake, carbohydrates, root architecture, andleaching. In the province of Quebec, seedling producers generally maintain a high substrate water content (>50%, v/v)during all growth phases. The accuracy and feasibility of using TDR to decrease irrigation without affecting the mate-rial attributes of the seedlings at the end of the first growing season was confirmed. However, seedlings grown underIR-15% had significantly lower height, root collar diameter, shoot and root dry masses, root surface, root length, netphotosynthesis, and nutrient contents than seedlings grown under IR-30%, IR-45%, and IR-60%. In comparison withIR-30% and IR-45%, the application of IR-60% produced no increase in shoot or root growth, mineral nutrition, andcarbohydrates. Seedlings grown under IR-15%, IR-30%, and IR-45% used approximately 28, 37, and 46%, respectively,of the amount of water applied under IR-60%. Nutrient losses including anions and cations under IR-60% were higherin comparison with the other IRs. Maintaining a water content in the rhizosphere that changes with the stage of seed-ling development is suggested to optimize growth and to avoid excess irrigation and leaching.

Résumé: La réflectométrie dans le domaine temporel a été utilisée pour gérer l’irrigation et le lessivage en contrôlantla teneur en eau dans la rhizosphère de semis d’épinette blanche (Picea glauca(Moench) Voss) (1+0) produits dansdes récipients à parois ajourées sous tunnel. Les semis ont été soumis à quatre régies d’irrigation (v/v: IR-60%, IR-45%,IR-30% et IR-15%) durant la première saison de croissance afin d’évaluer leurs effets sur la croissance, les échangesgazeux, l’absorption des éléments nutritifs, les glucides, l’architecture des racines et le lessivage. Au Québec, les pro-ducteurs maintiennent généralement des teneurs en eau élevées (>50%, v/v) lors des différentes phases de croissancedes semis. La précision et la faisabilité de diminuer les teneurs en eau ont été confirmées sans affecter les caractéristi-ques des semis à la fin de la première saison de croissance. Cependant, les semis soumis à la régie IR-15% ont montréune hauteur, un diamètre au collet, des masses sèches des racines et des parties aériennes, une surface et une longueurdes racines, une photosynthèse nette et un contenu en éléments nutritifs significativement inférieurs comparativementaux semis croissant sous les régies IR-30%, IR-45% et IR-60%. Par comparaison aux régies IR-30% et IR-45%, lemaintien de la régie IR-60% n’a pas permis une augmentation en termes de croissance des racines, des parties aérien-nes, d’absorption des éléments nutritifs et des sucres. Les semis croissant sous les régies IR-15%, IR-30% et IR-45% ontrespectivement utiliséapproximativement 28, 37 et 46% de la quantité d’eau appliquée dans le cas de la régie IR-60%. Lespertes en éléments nutritifs incluant les anions et les cations sous la régie IR-60% sont plus élevées par comparaisonaux autres régies. Le maintien d’une teneur en eau dans la rhizosphère qui tient compte du stade de développement dessemis a été suggéré en vue d’optimiser la croissance et d’éviter les excès d’irrigation et de lessivage.

Lamhamedi etal. 1980

Can. J. For. Res.31: 1968–1980 (2001) © 2001 NRC Canada

1968

DOI: 10.1139/cjfr-31-11-1968

Received December 12, 2000. Accepted July 24, 2001. Published on the NRC Research Press Web site at http://cjfr.nrc.ca onOctober 20, 2001.

M. Lamhamedi,1 G. Lambany,2 M. Renaud, and L. Veilleux. Direction de la recherche forestière, Forêt Québec, ministère desRessources naturelles, 2700, rue Einstein, Sainte-Foy, QC G1P 3W8, Canada.H. Margolis. Centre de recherche en biologie forestière, Faculté de Foresterie et de Géomatique, Pavillon Abitibi-Price, UniversitéLaval, Sainte-Foy, QC G1K 7P4, Canada.P.Y. Bernier. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du PEPS, P.O. Box 3800,Sainte-Foy, QC G1V 4C7, Canada.

1Corresponding author (e-mail: [email protected]).2Present address: Direction des programmes forestiers, ministère des Ressources naturelles, 880 Chemin Sainte-Foy, Sainte-Foy,QC G1S 4X4, Canada.

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IntroductionIn the province of Quebec (Canada), large seedlings are

used in reforestation programs as one of the possible alterna-tives to herbicide applications (Perreault et al. 1993; Jobidonet al. 1998; Lamhamedi et al. 1998a). These seedlings aregrown for 2 years in air-slit containers with large cavities(350 cm3/cavity) filled with peat-vermiculite mixture(Gingras 1993, 1997). A specific mineral nutrition regimehas been developed for the nursery production of large seed-lings of white spruce (Picea glauca(Moench) Voss) basedon its growth requirements (Langlois and Gagnon 1993;Gingras et al. 1999). The production of this new stock typealso requires modifications in scheduling irrigation to meetmorphological standards at the end of the first growing sea-son. Timmer and Miller (1991) showed that growth, nutrientstatus, and water relations of container-grown red pine(Pinus resinosaAit.) seedlings were more affected by irriga-tion regime than by nutrient fertilization. Gingras et al.(1999) observed that variations in substrate water content inthe rhizosphere was a major factor limiting growth of whitespruce seedlings grown in air-slit containers (containerswhose sides are slit to expose the growing medium to theopen air; Watanabe and Nakamura 1996; Gingras 1997).

Irrigation management has a direct effect on water andaeration conditions in the substrate and the growth ofcontainerized seedlings (Heiskanen 1993, 1995; Bernier etal. 1995; Khan et al. 1996; Lamhamedi et al. 1997). Theamount and timing of irrigation in forest nurseries are usu-ally adjusted after visual and tactile evaluation of the sub-strate, or after successive weighing. For seedling productionin air-slit containers, nursery growers tend to irrigate oftenand maintain high substrate water contents, between 50 and70% (v/v). This high frequency of irrigation maintains ahigh relative humidity around the slits causing low rates ofroot air pruning. Abundant air pruning of roots and the con-sequent development of robust fibrous root systems is themain reason for using air-slit containers. Optimization of ir-rigation could reduce irrigation volume and possibly de-crease nutrient losses from leaching by allowing more timefor nutrients in the substrate solution to be absorbed byroots. Proper scheduling of irrigation is difficult because irri-gation decisions need to be based on the sensitivity of seed-lings in air-slit containers to variations in substrate watercontent during the establishment, growth, and hardeningphases. Maintaining adequate water and nutrients in therhizosphere are key components for maintaining the physio-logical processes in seedlings, which can improveoutplanting performance (Timmer and Miller 1991).

The use of air-slit containers with a 350-cm3 cavity (IPL25-350A) for the production of large seedlings is driving thesearch for improvements to irrigation management. To bettercontrol water content in the rhizosphere, we adapted a soilmoisture measurement system based on the principles oftime domain reflectometry (TDR) to measure real-time sub-strate volumetric water content (Topp et al. 1984; Topp andDavis 1985). Previous studies (Lambany et al. 1996, 1997;Lamhamedi et al. 2000a) show that the simple and nonde-structive measurement procedures based on TDR producedquick, accurate, reproducible results under forest nurseryconditions.

Lamhamedi et al. (2000a) showed that a 15% (v/v) differ-ence between two irrigation regimes (25 and 40%, v/v) hadno significant effect on the morphology and root architectureof 1-year-old white spruce seedlings grown in air-slit con-tainers. These results suggest that it is possible to maintain alower water content in the rhizosphere without any effect onthe growth and physiology of seedlings. Improved under-standing of the direct effect of substrate water content on thegrowth and physiology of air-slit-containerized seedlingswould enable nursery operators to use real-time TDR mea-surements to better control the threshold of water contentsand nutrient leaching.

We hypothesized that various morphological and physio-logical variables of white spruce would be linked to sub-strate water content, when substrate fertility was keptconstant throughout the growing season. Consequently, theobjectives of the current study were (i) to show that TDRcan be used routinely to monitor and control substrate watercontents in air-slit containers; (ii ) to assess the impact of ir-rigation regime on the growth, gas exchange, and carbohy-drate and organic acid concentrations of white spruceseedlings; (iii ) to evaluate nutrient leaching in response todifferent irrigation regimes; and (iv) to propose to nurserygrowers an irrigation program specific to white spruce.

Materials and methods

Seedling production and growth conditionsThe experiment was conducted in unheated tunnels at the “Cen-

tre de production de plants forestiers du Québec”, Sainte-Anne-de-Beaupré, Que., Canada (47°02′N, 70°55′W). Seeds from an uncon-trolled provenance of white spruce (No. X01-034-96) were sown inair-slit containers on May 6, 1998. Each container had 25 square-shaped cavities (IPL 25-350A, IPL Inc., Saint-Damien-de-Bellechasse, Que.; 350 cm3/cavity with a surface area of 34.8 cm2)filled with a moistened 3:1 (v/v) peat–vermiculite mixture whichwas adjusted to a density of 0.11 g/cm3 (Lamhamedi et al. 2000a).Two weeks after germination, seedlings were thinned to one percavity. Seedlings reached a height of 2–3 cm after 3 weeks ofgrowth at which time they were subjected to one of four irrigationregimes (IR): IR-15%, IR-30%, IR-45%, and IR-60% (% v/v:100(cm3 H2O/cm3 substrate)). These substrate water contents werekept constant during the growing season from July to October.There were 162 containers per IR divided among six blocks. EachIR was distributed randomly within each block with buffer zonesof 27 containers to eliminate edge effects. All quantities of waterare reported as volume of water per unit surface of cavity or, moresimply, as water depth in millimetres.

Substrate water contents were monitored using the MP-917TDR-based instrument (ESI Environmental Sensors Inc., Victoria,B.C.), which measures the speed of propagation of an electromag-netic wave in the medium surrounding the probes. This speed islinearly related to the dielectric properties of the material. Waterhas a dielectric constant of 80, whereas the values for dry soilsrange between 2 and 5. Therefore, a change in water content is lin-early related to the speed of propagation of the signal (Topp andDavis 1985). Thus, water content can be accurately determined bymeasuring the propagation time over a fixed-length probe embed-ded in the medium. The probes consisted of two 39 cm long paral-lel stainless steel rods separated by a 1-cm gap and linked with twodiodes (models SDP and SDA, ESI Environmental Sensors Inc.,Victoria, B.C.).

© 2001 NRC Canada

Lamhamedi et al. 1969



The water content in each container was adjusted during threesuccessive days using the MP-917 to guarantee a uniform substratewater content in all the containers at the beginning of the experi-ment (27 containers × 6 blocks × 4 irrigation regimes). On thefourth day, nine containers per block per treatment were chosen atrandom for measurement of substrate water content. The MP-917probes were then installed for the duration of the growing seasonin six containers of each IR that had shown a substrate water con-tent closest to the mean value of their respective experimentalunits. Individual probes were inserted horizontally through fivecavities halfway up the container (Lambany et al. 1996, 1997;Lamhamedi et al. 2000a). These containers were placed in the cen-tre of the experimental units. They were irrigated as needed tomaintain the target substrate water content with a motorized robot(Aquaboom Harnois model, Saint-Thomas-de-Joliette, Que.)equipped with 22 nozzles and mounted on a ground rail. Water wasapplied at a water pressure of 2.1 bars (1 bar = 100 kPa), and eachpass of the robot increased the water content of the substrate by0.9% (v/v). Substrate water contents were adjusted three times ev-ery week (Monday, Wednesday, and Friday) depending on the irri-gation regime. The coefficient of uniformity of this irrigationsystem varied between 95 and 98%. Details concerning the proce-dures used to precisely monitor each irrigation regime are given inLambany et al. (1996, 1997) and Lamhamedi et al. (2000a).

The confounding effects of substrate fertility and irrigation ongrowth and physiological responses of white spruce seedlings wereeliminated by maintaining similar nutrient concentrations amongthe four irrigation regimes. A preset target level of 250 ppm N(Gingras et al. 1999) was maintained throughout the growing sea-son in all irrigation treatments. Every 2 weeks, samples were col-lected and both seedling tissue and substrate were analyzed todetermine their nutritional status. For each irrigation regime, seed-ling needs for macronutrients and micronutrients were calculateddepending on nutrient concentrations and the growth of whitespruce seedlings according to the PLANTEC software developedby the ministère des Ressources naturelles du Québec (Langloisand Gagnon 1993; Gingras et al. 1999; Girard et al. 2001). For ex-ample, seedlings received 49, 55, 61, and 79 mg N throughout thegrowing season for irrigation regimes IR-15%, IR-30%, IR-45%,and IR-60%, respectively.

Environmental variables including substrate temperature, airtemperature, and relative humidity were recorded continuously us-ing a CR10X data logger (Campbell Scientific, Logan, Utah). Sub-strate temperature was measured in one randomly chosen containerwith thermistors. For each irrigation regime, a rain gauge (modelNo. TE525M, Texas Instruments, Dallas, Tex.) was used to moni-tor the quantity of water applied to plants during fertilization andirrigation. During the active growing season (June–July), mean airand substrate temperatures ranged from 15 to 26°C, whereas meanrelative humidity at 2 m under tunnel conditions varied between 62and 100%.

Morphological variables and growth analysisGrowth trends of the seedlings were followed by destructive

samplings on eight occasions during the 1998 growing season (July6 and 20; August 3, 17, and 31; September 14 and 28; and October13). On each sampling date, 288 seedlings (12 seedlings/containerper IR per block) were randomly selected and gently excavatedfrom their cavities. After measuring root collar diameter andheight, the seedlings were partitioned into needle, stem, and rootcomponents.

Analyses of differences in relative growth rates (RGR) amongtreatments were conducted using an analysis of variance performedon the natural log transformed dry mass measurements of the seed-lings, as described by Poorter and Lewis (1986) and Lamhamedi etal. (1998a). An RGR-based analysis was used to eliminate the ef-

fect of differences in seedling size on growth values. In this analy-sis, natural log transformed plant biomass (dependent variable) ismodeled as a function of sampling date. Significant interactionterms of measurement date and treatment indicate a treatment-related difference in the rate of increase of the natural log trans-formed dry masses over time and, thus, RGR. The degree of eachpolynomial equation was derived from the significance of the lin-ear, quadratic, and cubic orthogonal contrasts performed on thetime × irrigation regime interaction.

To quantify the effect of each irrigation regime on dry matterpartitioning between roots and shoots, an allometric equation wasdeveloped from individual seedling data pooled over all samplingdates using logarithmic transformation:

Ln(shoot dry mass) =a + b ln(root dry mass)

whereb describes the partitioning of biomass between shoots androots and is a measure of the ratio of their relative growth ratesduring the exponential phase of growth (Ledig et al. 1970).

Gas exchange and xylem water potential measurementsOn each sampling date, measurements of gas exchange were

made between 09:00 and 11:00 solar time using a portable open-mode gas analyzer system with a cylindrical coniferous cuvette(model No. LCA-4, Analytical Development Company, Hoddesson,U.K.) on six seedlings randomly selected from each irrigation re-gime. To obtain measurements at light saturation, a sodium vapourlamp was suspended over the cuvette to maintain approximately800µmol·m–2·s–1 at the top of the seedlings. In general, photosyn-thesis of boreal coniferous species attains light saturation between600 and 800µmol·m–2·s–1 (Lamhamedi and Bernier 1994; Dang etal. 1997). After gas-exchange measurements, the number of nee-dles and their average length were determined by image analysisusing the WINNEEDLE software (Instruments Régent Inc., Qué-bec, Que.). To measure the perimeter of cross sections, three needlesfrom each seedling were fixed overnight at 4°C in 4% formaldehydein cacodylate buffer, then rinsed in buffer as described byLamhamedi et al. (2000b), and measured by image analysis. Perime-ters and lengths were used to compute half all-sided leaf area(hemisurface) as used for the Boreal Ecosystem–Atmosphere Study(BOREAS) (Chen et al. 1997). Net photosynthesis (An), transpira-tion (T), and stomatal conductance to water vapour (gsw) were ex-pressed on a hemisurface basis.

The shoots of other randomly selected seedlings in the samecontainers were severed and midday xylem water potential (ΨxMID)was measured with a pressure chamber (P.M.S. Instruments,Corvallis, Oreg.). These measurements were only performed forthe last four sampling dates.

Mineral nutritionOn each sampling date, mineral nutrient concentrations of seed-

lings and substrate were determined on six composite samples perIR (one composite sample per block). Each composite sample wascomposed of 12 seedlings or substrate samples from one randomlychosen container per IR per block. For dry matter determination,shoots and roots were separated at the root collar and oven-dried at60°C for 48 h. After grinding and acid digestion, each compositesample was analyzed for nitrogen using Kjeldahl, and for P, K, Ca,and Mg using inductively coupled argon plasma analysis (Parkin-son and Allen 1975; Walinga et al. 1995). Plant nutrient composi-tion is expressed as content (concentration × dry mass) of eachelement per seedling or tissue, because it reflects accurately plantnutrient uptake and accumulation (Timmer 1991).

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1970 Can. J. For. Res. Vol. 31, 2001



Root architectureMeasurements of root architecture including root length, diame-

ter, volume, and surface area were measured on roots of each seed-ling by image analysis using the WINRHIZO software (InstrumentsRégent Inc., Québec, Que.). On each sampling date, six seedlingswere randomly selected from each irrigation regime per block.Roots were carefully separated and washed with tap water. Theywere then stained with acid fuchsin (0.005%) at room temperaturefor 15 min according to the procedures developed by Lambany andVeilleux (1999). Staining with acid fuchsin facilitates scanning allwhite roots.

Nutrient leachingNutrient leaching including NO3-N, NH4-N, P, K, Ca, and Mg

was determined by collecting leachate from one container perblock per IR. The leachate for each selected container was col-lected in plastic containers placed below each selected container.The containers were connected to bottles in which the leachate ac-cumulated. Leachate samples were collected during 30 min aftereach fertilization or irrigation on several sampling dates in 1998(July 27, 29, and 31 and September 8, 11, and 14). Nitrate and am-monium were analyzed using an automated ion analyzer (LachatInstruments, Milwaukee, Wis.). Phosphorus, K, Ca, and Mg weredetermined using coupled argon plasma analysis.

Carbohydrate and organic acid analysesDuring the last two sampling dates, six seedlings were randomly

selected from each IR per block. Roots of each seedling werewashed and separated from the shoot for determination of solublesugars (total glucose, total fructose, sucrose, raffinose), polyols

(manitol, inositol), and organic acids (shikimic and quinic acids).Carbohydrates were extracted immediately with 80% hot ethanoland analyzed by liquid chromatography (Veilleux et al. 1992;Lambany 1994; Lamhamedi et al. 1998b).

Statistical analysisAll morphological and physiological data were analyzed as a

randomized complete block design. Analyses of variance were per-formed with the MIXED procedure of the SAS version 6.08 soft-ware (SAS Institute Inc., Cary, N.C.). Differences among irrigationregimes regarding physiological and morphological variables weredetermined by a priori contrasts (Steel and Torrie 1980). Differ-ences were considered significant atP < 0.05.

Results

Irrigation monitoring and cumulative waterThe irrigation protocol resulted in precise and consistent

control of water contents for each IR (IR-15%, IR-30%,IR-45%, and IR-60%; v/v) in the peat–vermiculite substrate(Fig. 1a) before and after each irrigation throughout the firstgrowing season under tunnel conditions. As practiced in for-est nurseries during germination and early growth, a sub-strate is approximately saturated near a water content of50% (v/v). The combination of the motorized irrigation ro-bot and the moisture point MP-917 provided homogenousand relatively stable substrate water contents in air-slit con-tainers. The four target irrigation regimes tested (IR-15%,

© 2001 NRC Canada


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Fig. 1. (a) The control of volumetric water content in the rhizosphere of air-slit containerized white spruce seedlings (1+0) grown un-der four irrigation regimes (15, 30, 45, and 60%, v/v). (b) The cumulative water quantity used over the course of the growing seasonas a function of irrigation regime. Error bars are SEs (n = 6).



IR-30%, IR-45%, and IR-60%) were generally attained inmid-July.

At the end of the first growing season, the cumulative wa-ter quantities used to maintain different target substrate wa-ter contents in the rhizosphere were 49, 64, 79, and 171 mmfor IR-15%, IR-30%, IR-45%, and IR-60%, respectively(Fig. 1b). Assuming similar amounts of evaporative lossesfrom irrigation water intercepted by the foliage and from thesilica-covered container surface, the IR-15%, IR-30%, andIR-45% used approximately 28, 37, and 46%, respectively,of the quantity of the water applied under IR-60%.

Growth analysisThe IR had a significant effect on all growth variables in-

cluding height (P < 0.0001), root collar diameter (P <0.0001), shoot dry mass (P < 0.0001), root dry mass (P <0.0001), needle dry mass (P < 0.0001), and total dry mass(P < 0.0001) (Table 1, Fig. 2). Sampling date (SD) also wasa significant source of variation (P < 0.0001) on all growthvariables. Because the analysis of variance was performedon natural log transformed growth components, the signifi-cant IR × SD interaction for all growth variables (P <0.0001) indicates significant differences in RGR among irri-gation regimes. Orthogonal contrasts revealed the absence ofsignificant differences between IR-30% and IR-45%, but thecomparison between IR-45% and IR-60% revealed signifi-cant differences in height (P = 0.0342), root collar diameter,and needle dry mass (P = 0.035) (Table 1) under the wetterirrigation regime. The comparison between IR-15% and themean of both IR-30% and IR-45% revealed significantlylower values for all growth variables in the driest irrigationregime (Table 1, Fig. 2). Orthogonal contrasts performed bysampling date showed that differences in all growth compo-nents between IR-15% and the mean of IR-45% and IR-60%were observed beginning in early August. From mid-Augustto late October, morphological variables including height, rootcollar diameter, root and shoot dry masses, and total dry massof seedlings were lower under IR-15% than under IR-30%,IR-45%, and IR-60% (Figs. 2a–2e).

The slope (b) in the allometric equation for biomass parti-tioning between root and shoot dry mass was less than 1.0

under all irrigation regimes (Fig. 3), indicating, on average,a greater allocation to the roots during the first growing sea-son. This ratio varied significantly (P < 0.0001) among theIRs. Orthogonal contrasts showed that this among-regimedifference was solely due to a significantly smallerb coeffi-cient in IR-15% than in that of the other IRs tested, i.e., aproportionally smaller allocation to shoots in IR-15%.

Gas exchange and midday xylem water potentialDuring the growing season,ΨxMID, An, T, water use effi-

ciency (WUE), intercellular CO2 (Ci), intercellular/ambientCO2 ratio (Ci/Ca), and gsw were significantly influenced byIR and by SD. Strong interactions between IR × SD (Ta-ble 2) for all physiological variables indicate that the differ-ences among the four IRs tested were not constant over time(Figs. 4 and 5). With the exception ofΨxMID andAn, the sea-sonal course of physiological responses of IR-45% was notsignificantly different from that of IR-60% but was signifi-cantly different from those of IR-30%. There was a strongdifference in all physiological variables between IR-15%and both IR-30% and IR-45%. For several sampling dates,values of An, T, gsw, and ΨxMID were lowest in seedlingsgrown under IR-15% and highest in seedlings grown underIR-45% and IR-60% (Figs. 4a–4c and 5). The lower valuesof An in seedlings subjected to IR-15% were also associatedwith lower gsw andCi/Ca ratio, thus indicating that the waterstress induced stomatal limitations to gas exchange. In mid-October,An abruptly dropped to half the maximumAn rateobserved over the growing season. The decline ofAn in theautumn corresponded with the decrease in air and substratetemperature and in photoperiod.

Mineral nutrient and carbohydrate contentsShoot and root nutrient contents per seedling were signifi-

cantly influenced by IR and SD (Table 3). For shoots, theIR × SD interaction was significant for all nutrients. Forroots, this interaction was significant only for N and Ca con-tents, indicating a relative consistency of IR effects on P, K,and Mg contents. IR-30%, IR-45%, and IR-60% generallyhad higher nutrient contents in both shoots and roots for allnutrients than that observed for seedlings grown under the

© 2001 NRC Canada

1972 Can. J. For. Res. Vol. 31, 2001

Source of variation Height

Rootcollardiameter

Shootdrymass

Rootdrymass

Needledrymass

Totaldrymass

Irrigation regime (IR) 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001Sampling date (SD) 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001IR × SD 0.0002 0.0012 0.0001 0.0001 0.0095 0.0001Linear 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001Quadratic 0.0650 0.0180 0.2405 0.3361 0.0100 0.1494Lack-of-fit 0.2007 0.6997 0.7855 0.0352 0.6859 0.7071Orthogonal contrastsIR-45% vs. IR-60% 0.0342 0.0365 0.0537 0.0815 0.0350 0.0502IR-30% vs. IR-45% 0.0930 0.1003 0.4326 0.5196 0.4779 0.5480IR-15% vs. (IR-30% and IR-45%) 0.0001 0.0001 0.0001 0.0001 0.0007 0.0001

Note: Orthogonal contrasts test the significance of the irrigation regime (IR-15%, IR-30%, IR-45%, and IR-60%)effect on growth components.

Table 1. Tests of fixed effects (P >F) on height, root collar diameter, shoot, root, needle, and total drymasses.



drier IR-15%, as shown by the orthogonal contrasts (Ta-ble 3). Similar results were observed for total nutrient con-tent of shoot and root systems combined (Figs. 6a–6e). Forexample, on the last sampling date, total N contents were14.2, 21.3, 22.9, and 22.1 mg for IR-15%, IR-30%, IR-45%,and IR-60%, respectively (Fig. 6a).

Seasonal dynamics of nutrient contents also varied amongirrigation regimes. Contents in N, P, K, Ca, and Mg in seed-lings grown in IR-15% dropped at the end of August (Fig. 6).In contrast, the other IR treatments (IR-60%, IR-45%, andIR-30%) showed very similar seasonal patterns of nutrientcontents, except for a decrease at the end of September inIR-30%.

Carbohydrate contents including soluble sugars (total glu-cose, total fructose, sucrose, raffinose), polyols (manitol,inositol), and organic acids (shikimic and quinic acids) werenot affected by the irrigation regime at the end of the grow-ing season (September 28 and October 13, 1998; data notshown).

Root architectureIrrigation regimes significantly influenced root length

(P < 0.0001), root surface (P < 0.0001), root diameter (P =0.0125), and root volume (P < 0.0001) (Table 4). Samplingdate also had a significant effect (P < 0.0001) on all root ar-chitecture variables, but the IR × SD interaction was signifi-cant only for length (P = 0.0105) and root diameter (P <0.0001). Comparisons of means using orthogonal contrastsshowed that seedlings grown under IR-15% had root lengths

© 2001 NRC Canada


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0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00

G 15%

E 30%

C 45%

J 60%

IR (v/v) Equation R2 n

15% y=1.8673+0.8076x 0.91 57430% y=1.8770+0.8571x 0.94 57545% y=1.9197+0.8621x 0.95 57360% y=1.9639+0.8601x 0.94 574

. ...

.

.

.

..

.

.

.

.

.

.

.

.

..

..

.

Fig. 3. Relationship of relative growth rates of shoots and rootsof air-slit containerized white spruce seedlings (1+0).

Fig. 2. Height, root collar diameter, shoot dry mass, root drymass, and total dry mass of air-slit containerized white spruceseedlings over the growing season as affected by irrigation re-gime. Error bars are SEs (n = 72).



and root areas that were significantly lower than those of theother IRs tested (Table 4, Figs. 7a and 7b). Comparisons bydate showed that these differences were evident from mid-August to late October. On the last sampling date, root sur-face area was 100, 131, 148, and 133 cm2, whereas lengthwas 529, 723, 834, and 770 cm, for IR-15%, IR-30%, IR-45%,and IR-60%, respectively (Figs. 7a and 7b). Our observa-tions revealed that the proportion of white roots was greaterunder the three higher irrigation regimes (IR-30%, IR-45%,and IR-60%) than under IR-15%. In contrast, IR-15% pro-moted highly branched and brown root systems generally lo-cated at 0–8 cm depth in the cavity.

Nutrient leachingTotal leaching over the growing season of substrate solution

varied as an exponential function of IR (Fig. 8). The meanrates of leaching through the sampling period were 2.5, 7.5,10.1, and 51.4% for IR-15%, IR-30%, IR-45%, and IR-60%,respectively. When substrate fertility was maintained constantat 250 ppm N among the four IRs during the growing season,excess of nutrient losses of N, P, K, Ca, and Mg were greaterunder IR-60% than under the other IRs (IR-15%, IR-30%, andIR-45%). Figure 9 presents an example of leaching losses fol-lowing an irrigation in July during which all treatments hap-pened to require an equal amount of the fertilizers to maintain

© 2001 NRC Canada

1974 Can. J. For. Res. Vol. 31, 2001

Source of variation ΨxMID An T WUE Ci/Ca gsw

Irrigation regime (IR) 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001Sampling date (SD) 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001IR × SD 0.0021 0.0001 0.0001 0.0001 0.0073 0.0001Orthogonal contrastsIR-45% vs. IR-60% 0.0125 0.0019 0.0816 0.1097 0.2582 0.1497IR-30% vs. IR-45% 0.0001 0.0001 0.0001 0.0026 0.0070 0.0002IR-15% vs. (IR-30% and IR-45%) 0.0001 0.0001 0.0001 0.0001 0.0003 0.0001

Note: Orthogonal contrasts test the significance of the irrigation regime (15, 30, 45, and 60%, v/v) effect onphysiological variables.

Table 2. Tests of fixed effects (P >F) on midday xylem water potential (ΨxMID), net photosynthesis(An), transpiration (T), water use efficiency (WUE), intercellular CO2 (Ci), intercellular/ambient CO2 ra-tio (Ci/Ca), and stomatal conductance (gsw).

Net

photo

synth

esis

(µ)

Sto

mata

lconducta

nce

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nspiration

((

mm

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oo

ll

lm

mm

22

2s

ss

))

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Fig. 4. Net photosynthesis (An), shoot conductance to watervapour (gsw), and transpiration (T) of air-slit containerized whitespruce seedlings (1+0) grown under four irrigation regimes. Errorbars are SEs (n = 6).

ΨxM

ID(M

Pa)

-1.8

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-1.4

-1.2

-1

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Fig. 5. Midday xylem water potential (ΨxMID) of air-slitcontainerized white spruce seedlings (1+0) grown under four irri-gation regimes. Error bars are SEs (n = 6).



the target substrate fertility. The mean N losses in leachingsolution were 0.7, 0.9, 1.7, and 11.3%, whereas those of Pwere 1.1, 2.0, 11.1, and 54.9%, for IR-15%, IR-30%, IR-45%,and IR-60%, respectively, despite the fact that all of the IRsreceived equal amounts of the fertilizers for only this sam-pling date (Fig. 9).

Although the peat–vermiculite substrate has a high capac-ity to retain cations, mineral nutrients such as K, Ca, and Mgwere always present in leachate with concentrations that var-ied depending on the IR (Fig. 9).

Discussion

During the first growing season under tunnel conditions,soil moisture monitoring using the TDR-based measure-ments permitted precise and consistent control of the fourIRs, resulting in constant volumetric water content of thesubstrate (Fig. 1a). Similar control of root-zone water con-tent of containerized seedlings had been achieved in otherstudies with TDR-based measurements (Richardson et al.1992; Lambany et al. 1996, 1997; Cameron et al. 1999;Lamhamedi et al. 2000a). By comparison, the control of wa-ter content in the rhizosphere using tensiometers was incon-sistent, especially when water content dropped below 20%(v/v), because the contact between the substrate and porouscup of the tensiometer is lost under dry conditions (Rundeland Jarrell 1991; Cameron et al. 1999; Hansen and Pasian1999; Testezlaf et al. 1999).

Although there were small differences in morphologicaland physiological variables among the three wettest irriga-tion regimes (IR-30%, IR-45%, and IR-60%), seedlingsgrown under these IRs all reached the targets for final seed-ling growth parameters. In contrast, seedlings grown underIR-15% had significantly lower morphological and physio-logical responses than seedlings grown under the other IRs(Figs. 2–7). Since substrate fertility was kept constant acrossall fertilization regimes, all differences between IR-15% and

the other regimes were due to differences in water availabil-ity.

Lack of clear growth advantage in IR-60% seedlings com-pared with IR-45% and IR-30% seedlings shows that themaintenance of such high substrate water content is unneces-sary. In addition, the maintenance of an overly high substratewater content requires high irrigation volumes and largequantities of fertilizer, with substantial losses of both waterand nutrients through leaching throughout the growing sea-son. Proper controlling of irrigation and substrate fertilitycan significantly limit leaching (Fig. 9) and water use, whileoptimizing growth and nutrient use. This has economic aswell as environmental advantages for growers. In the prov-ince of Quebec, current environmental regulations do notpermit groundwater N levels to exceed 10 mg (NO3-N +NO2-N)·L–1 according to theRèglement sur l’eau potable(ministère de l’Environnement du Québec 1984). Similarregulations are found in the European Economic Community(Bacon 1995, p. 307) and the United States (Hamilton andHelsel 1995).

The similarity in patterns of growth responses, nutrientuptake, and carbohydrate concentrations of white spruceseedlings in all but the driest irrigation regimes suggest thatwhite spruce is not very sensitive to variations in substratewater content. The maintenance of higherAn in white spruceseedlings grown under IR-60% indicates that these youngseedlings can probably maintain similar vigour above thisrather high rhizosphere water content. Field studies haveshown that with the exception of stagnant water saturatedconditions white spruce seedlings can tolerate a wide rangeof soil moisture contents (Nienstaedt and Zasada 1990).However, the lower slope of the allometric equation forseedlings grown under IR-15% (Fig. 3) indicates that theshoot–root balance can be controlled to some extent by theirrigation regime.

Differences in biomass partitioning between roots andshoots can be related to the differences in the rates of net

© 2001 NRC Canada


Fixed effects N P K Ca Mg

Shoot nutrient contentIrrigation regime (IR) 0.0001 0.0001 0.0001 0.0001 0.0001Sampling date (SD) 0.0001 0.0001 0.0001 0.0001 0.0001IR × SD 0.0130 0.0012 0.0001 0.0001 0.0475Orthogonal contrastsIR-45% vs. IR-60% 0.0781 0.1421 0.0520 0.0534 0.2021IR-30% vs. IR–45% 0.6381 0.6398 0.7145 0.5257 0.7409IR-15% vs. (IR-30% and IR-45%) 0.0001 0.0001 0.0001 0.0001 0.0001Root nutrient contentIrrigation regime (IR) 0.0001 0.0001 0.0001 0.0001 0.0001Sampling date (SD) 0.0001 0.0001 0.0001 0.0001 0.0001IR × SD 0.0008 0.9342 0.8379 0.0001 0.7668Orthogonal contrastsIR-45% vs. IR-60% 0.9523 0.3720 0.1309 0.0065 0.3857IR-30% vs. IR-45% 0.2183 0.0966 0.1329 0.6695 0.1104IR-15% vs. (IR-30% and IR-45%) 0.0001 0.0001 0.0001 0.0001 0.0001

Note: Orthogonal contrasts test the significance of the irrigation regime (IR-15%, IR-30%, IR-45%, and IR-60%)effect on nutrient content.

Table 3. Tests of mineral nutrient content (P >F) of both shoots and roots of air-slit containerizedwhite spruce seedlings grown under different irrigation regimes.



photosynthesis (An) among the different irrigation regimes.Seedlings grown under IR-15% showed lower rates ofAnthan those grown under the other IRs (Fig. 4, Table 2). TheAn rate is affected by water and nutrient availability, whichin turn affects shoot and root growth, the latter having beenshown to be at least partially dependent on current

© 2001 NRC Canada

1976 Can. J. For. Res. Vol. 31, 2001

0

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Fig. 6. Total nitrogen, phosphorus, potassium, calcium, and mag-nesium content in air-slit containerized white spruce seedlings(1+0) grown under four irrigation regimes. Error bars are SEs(n = 6 composite samples, each composite sample was formedfrom 12 seedlings).

0

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Fig. 7. Seasonal patterns of root surface and root length of air-slit containerized white spruce seedlings (1+0) grown under fourirrigation regimes. Error bars are SEs (n = 36).

Fixed effectsRootlength

Rootsurface

Rootdiameter

Rootvolume

Irrigation regime (IR) 0.0001 0.0001 0.0001 0.0001Sampling date (SD) 0.0001 0.0001 0.0001 0.0001IR × SD 0.0105 0.1013 0.0001 0.0672Orthogonal contrastsIR-45% vs. IR-60% 0.5310 0.9783 0.0401 0.6117IR-30% vs. IR-45% 0.4225 0.7506 0.1656 0.8874IR-15% vs. (IR-30% and

IR-45%)0.0001 0.0001 0.2642 0.0001

Table 4. Analysis of variance (P >F) and comparisons betweenirrigation regimes for their effects on root architecture parame-ters.



photosynthates from the shoot in conifer seedlings (van denDriessche 1987; Kozlowski 1992; Pellicer et al. 2000).These patterns are very similar to those reported by Kuhnsand Gjerstad (1988) who showed that the decrease in14Ctranslocation from shoots to roots inPinus taedaL. seed-lings was closely linked to the intensity of water stress. Ourmeasurements of physiological and growth patterns of whitespruce grown under tunnel conditions show that IR-15%should not be recommended to nursery growers during theactive growing season.

In this experiment, substrate fertility was kept constantamong the IRs. Therefore, the level of nutrient uptake wascontrolled by the availability of the substrate solution, whichin turn was controlled through the irrigation regime. One in-direct effect in IR-15% seedlings was the lowering of rootgrowth elongation and the predominance of suberized roots.Suberized roots have a lower hydraulic conductance and alower ability to absorb water than unsuberized roots in sev-eral woody species (Chung and Kramer 1975; Sands et al.1982). Our results are consistent with the results of otherstudies showing that IR significantly affects conifer seedlingroot growth and nutrient uptake (Timmer and Miller 1991;Haase and Rose 1994), as well as nutrient leaching in orna-mental and horticultural crops (Biernbaum 1992; Cresswell1995; Tyler et al. 1996; Groves et al. 1998; Hansen andPetersen 1998).

Reduced water availability in the rhizosphere can beachieved without affecting seedling quality of white spruceduring the first growing season. Using peat–vermiculite–perlite as a growing medium, Khan et al. (1996) showed thatDouglas-fir seedlings exhibited optimum growth, bud devel-opment, and nutrient and starch reserves when the growingmedium was maintained at a moderate water content varyingfrom 29 to 53%. From our results and previous studies(Lambany et al. 1996, 1997; Lambany 1998; Gingras et al.1999; Lamhamedi et al. 2000a; Stowe 2001), it appears that

under tunnel conditions white spruce seedlings (1+0) can beproduced by changing the water contents in the rhizospherewith respect to different growth phases (Fig. 10) as definedby Landis et al. (1999). During the establishment phase, thewater content of the rhizosphere should be maintained be-tween 40 and 45% (v/v) to favour germination and earlygrowth. This range of water content under nursery condi-tions successfully prevents moss and algae from developing.During the rapid growth phase, the water content can be de-creased and maintained between 30 and 45% (v/v). Thehardening phase must be induced when white spruce seed-lings reach 80–90% of the target height (7–8 cm) accompa-nied by a reduction in photoperiod, air temperature, andfertilization. At the beginning of the hardening phase, thewater content in the rhizosphere should be decreased to 18–25% (v/v); during the remainder of this phase it can bemaintained between 25 and 35%. The objective of this de-crease is to stop shoot growth and to initiate development ofterminal bud and frost hardiness. White spruce seedlings re-spond favourably to slight moisture stress by reducinggrowth and entering dormancy (Macey and Arnott 1986).Our observations revealed that bud formation was initiatedand completed rapidly in seedlings grown under IR-15%compared with the other irrigation regimes. When bud for-mation is complete, the substrate water content should be in-creased to 60% (v/v), and seedlings can be moved out of thetunnel during the first week of November.

Irrigation management is now successfully carried out us-ing TDR in several nurseries in the province of Quebec. Thisstudy has shown that the technique can be used to minimizeleachate losses under the controlled environment of the tun-nel. However, most production schedules for largercontainerized seedlings extend for two growing seasons,with the seedlings being grown outdoors during the secondgrowing season. Therefore, it will be necessary to examine,during the second growing season, the major container-

© 2001 NRC Canada


y = 0.0459e0.0913x

R2= 0.76

0

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6

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10

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16

18

0 20 40 60 80

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Leach

ing

losses

(mL

/cavit

y)

Fig. 8. Leaching of substrate solution as a function of irrigationregime. Each data point represents the mean of leaching obtainedfrom six containers per irrigation regime during the sampling pe-riod (July–September). Each cavity of an air-slit container has asquare shape with a surface area of 34.8 cm2.

NH4 NO3 Nmin P K Ca Mg

0

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30%

45%

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Nu

trie

nt

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ing

(mg

/ca

vity)

Fig. 9. Effect of irrigation regime on leaching of different nutri-ents (NH4-N, NO3-N, Nmin (mineral N), P, K, Ca, and Mg) ofair-slit containerized white spruce seedlings (1+0) on one sam-pling date (July) when the IRs received similar amounts of fertil-izers. Each cavity of an air-slit container has a square shape witha surface area of 34.8 cm2.



grown species’ optimum water and fertilization regimes forachieving the most efficient growth regimes while reducingwater use and nutrient losses. Under such semicontrolledconditions, the next challenge is to use similar techniques toreach morphological and physiological targets of seedlingswhile minimizing fertilizer use and loss through leaching.

Acknowledgments

This study was conducted in collaboration with the Centrede production de plants forestiers (CPPFQ, Sainte-Anne-de-Beaupré, Que.). The authors thank Richard Gohier, RosaireTremblay, Lyne Lachance, Daniel Girard, Munyonge AbweWa Masabo, Jean Gagnon, and Debbie Stowe for technicalassistance and helpful discussions and Pamela Cheers andIsabelle Lamarre for their editorial work. The statistical ad-vice on experimental design and analyses of France Savardand Barbara Sochanski is gratefully acknowledged. Thanksare also extended to the Laboratoire de chimie organique etinorganique (Direction de la recherche forestière, Forêt Qué-bec, ministère des Ressources naturelles) for substrate andplant analyses. This research program was supported by agrant to Dr. Hank Margolis and Dr. Mohammed Lamhamedifrom the ministère des Ressources naturelles du Québec(project Nos. 281S and 271S) and the Fonds international decoopération universitaire de l’Agence universitaire de laFrancophonie (project No. 2000/PAS/15).

References

Bacon, P.E. 1995. Nitrogen fertilization in the environment. MarcelDekker, Inc., New York.

Bernier, P.Y., Stewart, J.D., and Gonzalez, A. 1995. Effects of thephysical properties ofSphagnum peat on water stress incontainerizedPicea mariana seedlings under simulated fieldconditions. Scand. J. For. Res.10: 184–189.

Biernbaum, J.A. 1992. Root-zone management of greenhouse con-tainer-grown crops to control water and fertilizer use. Hortic.Technol.2: 127–132.

Cameron, R.W.F., Harrison-Murray, R.S., and Scott, M.A. 1999.The use of controlled water stress to manipulate growth of con-tainer-grown Rhododendron cv. Hoppy. J. Hortic. Sci.Biotechnol.74: 161–169.

Chen, J.M., Rich, P.M., Gower, S.T., Norman, J.M., and Plummer,S. 1997. Leaf area index of boreal forests: theory, techniques,and measurements. J. Geophys. Res.102: 429–443.

Chung, H.-H., and Kramer, P.J. 1975. Absorption of water and32Pthrough suberized and unsuberized roots of loblolly pine. Can. J.For. Res.5: 229–235.

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© 2001 NRC Canada

1978 Can. J. For. Res. Vol. 31, 2001

Wate

rconte

nt(%

,v/v

)

0

10

20

30

40

50

60

70

maximum

minimum

M J J A S O N

Establishment

phase Rapid growth

phase Hardening

phase

Month

Fig. 10. Irrigation regime and leaching under tunnel conditions of containerized white spruce seedlings (1+0) can be optimized bymaintaining water content between minimum and maximum thresholds depending on growth phases.



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growth, physiology, and leachate losses in picea glauca seedlings (1+0)...

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