Ecophysiological and genetic variation in seedling traits and in first-year field performance of eight <Emphasis Type="Italic">Acacia senegal</Emphasis> provenances in the Blue Nile,Sudan

The genetic variation in seed weight, seed number per kg and seedling traits was compared among eight Acacia senegal provenances originating from the clay plain (east) and sand plains (west) of the gum belt in Sudan. The main objective of this study was to identify germplasm sources of A. senegal that have a good seed germination capacity and seedling traits suitable for reforestation in the clay-soil part of the dryland gum belt in the Blue Nile region in Sudan. A specific objective was to tentatively explore the adaptive strategy of A. senegal populations. Seventeen-week-old seedlings were planted in the field at spacing of 3 m × 3 m, giving 100 trees per plot and replication; within a randomized complete block design with four replications. The experimental site was in the clay plain region. Seed variables showed significant differences. Clay plain provenances showed considerable variation in seed weight and seed number. They had the smallest seed weight but the highest seed number, while the sand (western) provenances had the largest seed weight but lowest seed number. Seedling branch number, root length, root to shoot ratio and shoot dry weight differed significantly among the provenances 12 weeks after germination. Clay provenances had the highest branch number and shoot dry weight but the shortest roots and lowest root to shoot ratio. This was interpreted as showing better adaptation to the site in these local provenances in comparison to those originating from the western sandy soil regions. High positive correlations were observed between seedling variables, such as root nodule and branch numbers; this could be used for early selection. The variation was greater between provenance groups than within them, suggesting that especially selection among groups would yield genetic gain.     

Inter- and intra-provenances variations in seed size and seedling characteristics of Khaya senegalensis A. Juss in Burkina Faso

Within- and between-provenance variations in seed and seedling traits of Khaya senegalensis A. Juss were studied at INERA in Burkina Faso. Nursery grown seedlings from four provenances in Burkina Faso were used for the study. The studies revealed significant variability in all traits evaluated. Seed length and weight significantly varied among provenances and families within provenances, where Bopiel and Koyenga had the highest mean values. Height and root collar diameter of 1 year old seedlings significantly varied among families within provenances. Except leaf biomass ratio and carbon isotope ratio which varied significantly among provenances but not among families within provenances, all other seedling biomass traits—total plant biomass, stem biomass ratio, leaf biomass ratio, root biomass ratio, root shoot ratio, specific leaf area, and leaf area ratio were significantly affected by provenances and families within provenances. The magnitude of variation due to family effect ranged from 65 to 93 % for seed size traits, and from 4.5 to 17.8 % for seedling characters. Estimates of family heritability were moderate to high (0.67–0.95) for seed traits, but low to moderate (0.19–0.59) for seedling characters, indicating that much of the total variation in seed traits is due to the genetic effect. The two most prominent provenances, Koyenga and Bopiel, with higher seed size and greater seedling growth could be considered for an eventual K. senegalensis improvement program in Burkina Faso.     

Root growth and water use efficiency of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings

One-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and lodgepole pine (Pinus contorta Dougl.) seedlings were grown for 17 weeks in 100-cm deep, 7.8-liter containers. Two Douglas-fir provenances, one from a wet and one from a dry site in coastal British Columbia, and two lodgepole pine provenances, one from a wet and one from a dry site in interior British Columbia, were grown in wet (522% water content) or dry (318% water content) peat/vermiculite soil in a factorial design. Each container was sealed so that water loss occurred only through the seedling. Five harvests were made at three to five week intervals and water use, dry matter increment, root length and root weight were determined at each harvest. Stomatal conductance and shoot water potentials were measured during the last 12 weeks of the experiment. Lodgepole pine seedlings had greater dry matter production, water use, stomatal conductance and new root length than Douglas-fir seedlings. New root weight of lodgepole pine seedlings exceeded that of Douglas-fir seedlings during the last five weeks of the experiment, and specific root length (root length per unit root weight) of new roots was higher for lodgepole pine seedlings throughout the experiment. Douglas-fir seedlings showed higher water use efficiency (WUE) than lodgepole pine seedlings, and both species showed higher WUE in the dry soil treatment. Douglas-fir seedlings had lower water potentials and higher water uptake rates per unit of new root length than lodgepole pine seedlings, although water uptake rates per unit of root dry weight showed little difference between species. Soil water treatment influenced specific root length of new roots, water uptake per unit of new root length, and WUE in Douglas-fir seedlings more than in lodgepole pine seedlings.     

Provenance-specific growth responses to drought and air warming in three European oak species (Quercus robur, Q. petraea and Q. pubescens)

Provenance-specific growth responses to experimentally applied drought and air warming were studied in saplings of three European oak species: Quercus robur, Quercus petraea and Quercus pubescens. Four provenances of each species were grown in large open-top chambers and subjected to four climates: control, periodic drought, air warming or their combination in 3 subsequent years. Overall growth responses were found among species and provenances, with drought reducing shoot height growth and stem diameter growth and air warming stimulating shoot height growth but reducing stem diameter growth and root length growth. Differential growth responses in shoots, stems and roots resulted in altered allometric growth relations. Root length growth to shoot height growth increased in response to drought but decreased in response to air warming. Stem diameter growth to shoot height growth decreased in response to air warming. The growth responses in shoots and stems were highly variable among provenances indicating provenance-specific sensitivity to drought and air warming, but this response variability did not reflect local adaptation to climate conditions of provenance origin. Shoot height growth was found to be more sensitive to drought in provenances from northern latitudes than in provenances from southern latitudes, suggesting that genetic factors related to the postglacial immigration history of European oaks might have interfered with selective pressure at provenance origins.     

Variation in seed traits and seedling vigour of Cordia africana Lam.provenances in Ethiopia

Cordia africana is a very important indigenous tree species for timber and other products and services in Ethiopia.Seed traits and seedling vigour of seeds from 12 provenances of the species were compared.Mean seed mass for each provenance was assessed for 1000 seeds in10 replications,and seed length and width were measured for 100 seeds in four replications per provenance.Germination was assessed in a glasshouse taking 400 seeds from each provenance.Root collar diameter and height of 440 seedlings grown in a nursery for 290 days in Addis Ababa were measured.Seed length,seed width,seed mass,and shoot height and root collar diameter of seedlings showed significant differences(P0.001) among provenances.Correlation analysis between seed and seedling traits and environmental variables revealed significant positive correlations between seed width and germination percentage,seed width and altitude,seed width and longitude and seed length and latitude.Negative correlations were obtained between seed width and temperature,seed width and rainfall,seed mass and temperature,and germination and temperature of the seed source.As expected,differences in seed trait did not explain the variability in seedling vigour.Determining quantitative variations in seed traits and seedling vigour among provenances and the patterns along environmental gradients are essential for informing decisions on the tree improvement programme of the species.     

林芝云杉不同地理种源苗期性状变异

正林芝云杉(Picea likiangensis var.linzhiensis Cheng et L.K.Fu)是松科(Pinaceae)云杉属(Picea Dietr.)常绿高大乔木,为西藏高原亚高山暗针叶林主要、特有的建群树种之一[1-2]。主要分布在西藏东南的林芝、米林、波密等地,并向西分布至朗县、错那、洛扎、隆子、工布江达。林芝云杉是云杉属中木材品质系数最高的树种[3],生长迅速,寿命持久,在水热条件优越的地区能长成罕见的巨树,胸径可达2.5 m,最大树高可达73 m,单株立木材积达到50     

南方红豆杉苗木性状种源分化和育苗环境对苗木生长的影响

利用来自10个省区27个产地的南方红豆杉种子在福建明溪和浙江淳安2个地点开展种源苗期遗传测定,系统研究苗木生长、苗高生长参数、根系特征和干物质积累等性状的种源差异及育苗环境对种源苗木生长的影响.研究结果显示:南方红豆杉苗高、地径和侧枝数存在显著的种源差异.基于苗高生长参数分析表明:种源苗高的增加主要是由于线性生长量、最高生长速率和线性生长速率的提高,而不是由于线性生长期的延长.相对于其它树种,南方红豆杉线性生长速率虽较小,但线性生长期较长.试验虽然未发现根系形态、干物质积累量的种源差异达到统计学上的显著水平,但这些性状的种源绝对值却相差较大,达20%以上.育苗环境对南方红豆杉种源生长影响较大,良好的水热资源和庇荫条件将显著促进苗木的高、径生长.苗木生长性状存在显著的种源与地点互作,但种源与遮阳处理的互作却很小.不同育苗地点南方红豆杉苗高和地径呈现出的地理变异模式是不同的:在福建明溪点,种源苗木高、径生长与产地的地理气候因子相关性较小,苗期速生种源不仅有来自自然分布区偏东部和偏北部的种源,而且还有来自偏南部和偏西部的种源;在浙江淳安点,来自偏东部和偏北部的种源苗高生长量较大,而来自偏南部和偏西部的种源生长则较慢,类似于作者对南方红豆杉有限分布区种源试验的已有研究结果.     

Variation in seed traits and seedling vigour of <Emphasis Type="Italic">Cordia africana</Emphasis> Lam. provenances in Ethiopia

Cordia africana is a very important indigenous tree species for timber and other products and services in Ethiopia. Seed traits and seedling vigour of seeds from 12 provenances of the species were compared. Mean seed mass for each provenance was assessed for 1000 seeds in 10 replications, and seed length and width were measured for 100 seeds in four replications per provenance. Germination was assessed in a glasshouse taking 400 seeds from each provenance. Root collar diameter and height of 440 seedlings grown in a nursery for 290 days in Addis Ababa were measured. Seed length, seed width, seed mass, and shoot height and root collar diameter of seedlings showed significant differences (P < 0.001) among provenances. Correlation analysis between seed and seedling traits and environmental variables revealed significant positive correlations between seed width and germination percentage, seed width and altitude, seed width and longitude and seed length and latitude. Negative correlations were obtained between seed width and temperature, seed width and rainfall, seed mass and temperature, and germination and temperature of the seed source. As expected, differences in seed trait did not explain the variability in seedling vigour. Determining quantitative variations in seed traits and seedling vigour among provenances and the patterns along environmental gradients are essential for informing decisions on the tree improvement programme of the species.     

Influence of different nursery container media on rooting of Scots pine and silver birch seedlings after transplanting

Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) seedlings were grown in containers filled with growth media based on medium-textured sphagnum peat, coarse perlite and fine sand. The seedlings were then planted into fine and coarse sandy soils in 2.2 l pots, which were subjected to two water-content treatments (only one for birch). After the seedlings had grown five weeks in a greenhouse, rooting into the surrounding soil and shoot growth were measured. Addition of perlite and sand to peat medium slightly affected rooting; thus suggesting minor effects on seedling establishment. However, nitrogen concentration of the seedlings varied between growth media and correlated positively with rooting into the soil. The particle size and water content of the soil affected considerably rooting of the seedlings. Seedling height at the time of planting did not affect rooting or shoot growth. The fact that the fewest out-grown roots occurred in the dry fine sandy soil, suggests that dry soil together with high strength and resistance to root penetration reduce rooting and water uptake by container seedlings most and may thus cause water and nutrient stresses to seedlings after outplanting.     

木荷苗木性状的种源变异和地理模式

利用来自7省区36个木荷种源在浙江淳安和福建建瓯两试验点的苗期测定材料,研究其苗木生长、根系特征和叶片形态等12个性状的种源差异及其地理变异模式。方差分析结果显示,除主根长、侧根长和叶片颜色在种源间无显著差异外,其它性状的种源效应都达到显著或极显著水平。种源苗木性状与产地地理气候因子的相关分析发现,苗高、叶片特征(叶片数、叶片宽、叶片厚)及秋末嫩叶颜色等呈典型的纬向变异模式,产地温度则是造成这种纬向变异模式的主要环境作用因子。与北部种源比较,南部种源生长快,叶片数量多,但叶片较薄较窄,其秋末嫩叶颜色变化对寒冷信号反应敏感。影响木荷种子性状表型差异的主导因素是产地的年降水量。以苗高为标准,分别在两地点初选出优良种源10个,它们多来自25°N左右的木荷自然分布区。     

Effects of soil temperature on biomass and carbohydrate allocation in Scots pine (Pinus sylvestris) seedlings at the beginning of the growing season

We studied effects of soil temperature on shoot and root extension growth and biomass and carbohydrate allocation in Scots pine (Pinus sylvestris L.) seedlings at the beginning of the growing season. One-year-old Scots pine seedlings were grown for 9 weeks at soil temperatures of 5, 9, 13 and 17 degrees C and an air temperature of 17 degrees C. Date of bud burst, and the elongation of shoots and roots were monitored. Biomass of current and previous season roots, stem and needles was determined at 3-week intervals. Starch, sucrose, glucose, fructose, sorbitol and inositol concentrations were determined in all plant parts except new roots. The timing of both bud burst and the onset of root elongation were unaffected by soil temperature. At Week 9, height growth was reduced and root extension growth was much less at a soil temperature of 5 degrees C than at higher soil temperatures. Total seedling biomass was lowest in the 5 degrees C soil temperature treatment and highest in the 13 degrees C treatment, but there was no statistically significant difference in total biomass between seedlings grown at 13 and 17 degrees C. In response to increasing soil temperature, below-ground biomass increased markedly, resulting in a slightly higher allocation of biomass to below-ground parts. Among treatments, root length was greatest at a soil temperature of 17 degrees C. The sugar content of old roots was unaffected by soil temperature, but the sugar content of new needles increased with increasing soil temperature. The starch content of all seedling parts was lowest in seedlings grown at 17 degrees C. Otherwise, soil temperature had no effect on seedling starch content.     

Genetic variation in seed and seedling traits of six <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> shrub provenances in desert areas of China

China is one of the countries most severely affected by desertification. Haloxylon ammodendron is an ecologically important component of the desert ecosystem and is one of the main shrub species used for ecological restoration. We compared the genetic variation in seed and seedling traits among six H. ammodendron provenances arrayed from east to west in China. The experiment was carried out in a greenhouse in well-prepared seedling beds (lines 1.5 m apart and seeds with in lines 1.0 m apart, 2.0 cm deep) with five lines (seven seeds per line) per provenance in a randomized block design with six replicates. The seed traits of fruit wing length, kernel weight, germination rate, and survival rate were compared, as were the seedling traits of internode length, branch number, assimilation shoot diameter, height, collar diameter, new shoot length, main root number, main root length, aboveground fresh weight, and underground fresh weight. Moreover, correlations between each seed and seedling trait and climate and geographical factors were assessed. The results show that the seeds from Dengkou County, Inner Mongolia had the best performance. Germination rate and survival rate were significantly positively correlated with longitude; and fruit wing length, kernel weight, seedling height, and new shoot length were significantly negatively correlated with latitude. Fruit wing length was significantly correlated with altitude. Among the climatic factors, the temperature in January had a strong direct effect on fruit wing length, germination rate, seedling height, and new shoot length. The mean annual rainfall had a strong direct effect on collar diameter. Humidity had a strong direct effect on survival rate. Seedling height, aboveground weight, and collar diameter could be important criteria for early provenance selection in the seedling stage. This study provides a reference for the selection of high-quality H. ammodendron seeds for drylands of northwest China.     

木荷种源苗高生长参数变异研究

利用28个木荷种源苗高生长节律的观测材料,通过采用Logistic方程拟合其苗高生长,求算和揭示最大生长速率(MGR)、线性生长速率(LGR)、线性生长量(TLG)和线性生长期(LGD)4个苗高生长参数的种源差异和地理变异模式.研究结果显示:利用Logistic方程可较好地拟合木荷种源苗高生长的动态变化,其决定系数皆在0.92以上.不管是Logistic方程的3个生物学参数a、b、c,还是上述4个苗高生长参数在种源区间和种源区内种源间都存在显著的遗传变异.研究发现:种源MGR、LGR、TLG与产地纬度呈显著的负相关,都表现出明显的纬向渐变地理模式,其变异主要来源于种源区内种源间(42.84%～43.41%),其次来源于种源区间(11.07%～13.15%);LGD在种源区和种源区内种源两个层次的方差分量都相对较小(6.9%和8.4%),且未发现与产地经纬度的显著相关性.苗高生长参数间的相关分析发现:木荷种源苗高线性生长量的增加并非由于线性生长期的延长,而是由于最高生长速率和线性生长速率的提高所致.     

Effects of soil compaction on growth variables in Cappadocian maple(Acer cappadocicum) seedlings

This study investigates the effects of increasing soil penetration resistance(SPR) on seedling morphology and seedling architecture. When seedlings of deciduous Cappadocian maple(Acer cappadocicum Gled.) were grown in a greenhouse in a loamy soil under a wide range of soil compactions, all morphological variables studied changed significantly with increasing SPR. The relationships between increasing SPR and all morphological responses except lateral root length followed a negative quadratic curve. All biomass variables except lateral root biomass showed a bell-shaped response with respect to SPR, with a maximum biomass variable between 0.6 and1.2 MPa, decreasing at higher soil compaction values. All allocation ratios were significantly affected by soil penetration resistance. Biomass allocation to roots was also affected by soil compaction. There was not a significant relationship between the specific stem length and increasing soil penetration resistance. The specific root length showed two trends to increasing SPR; it first decreased in response to the moderate compaction treatment(up to about 1.2 MPa), then increased significantly. We concluded that increasing soil compaction caused morphological changes to root and shoot sections of A.cappadocicum seedlings.     

Ecophysiological variation in two provenances of Pinus flexilis seedlings across an elevation gradient from forest to alpine

Climate change is predicted to cause upward shifts in forest tree distributions, which will require seedling recruitment beyond current forest boundaries. However, predicting the likelihood of successful plant establishment beyond current species' ranges under changing climate is complicated by the interaction of genetic and environmental controls on seedling establishment. To determine how genetics and climate may interact to affect seedling establishment, we transplanted recently germinated seedlings from high- and low-elevation provenances (HI and LO, respectively) of Pinus flexilis in common gardens arrayed along an elevation and canopy gradient from subalpine forest into the alpine zone and examined differences in physiology and morphology between provenances and among sites. Plant dry mass, projected leaf area and shoot:root ratios were 12-40% greater in LO compared with HI seedlings at each elevation. There were no significant changes in these variables among sites except for decreased dry mass of LO seedlings in the alpine site. Photosynthesis, carbon balance (photosynthesis/respiration) and conductance increased >2× with elevation for both provenances, and were 35-77% greater in LO seedlings compared with HI seedlings. There were no differences in dark-adapted chlorophyll fluorescence (Fv/Fm) among sites or between provenances. Our results suggest that for P. flexilis seedlings, provenances selected for above-ground growth may outperform those selected for stress resistance in the absence of harsh climatic conditions, even well above the species' range limits in the alpine zone. This indicates that forest genetics may be important to understanding and managing species' range adjustments due to climate change.     

Effects of soil temperature on shoot and root growth and nutrient uptake of 5-year-old Norway spruce seedlings

Soil temperature is a main factor limiting root growth in the boreal forest. To simulate the possible soil-warming effect of future climate change, 5-year-old Norway spruce (Picea abies (L.) Karst.) seedlings were subjected to three simulated growing seasons in controlled environment rooms. The seedlings were acclimated to a soil temperature of 16 degrees C during the first (GS I) and third growing seasons (GS III), but were assigned to random soil-temperature treatments of 9, 13, 18 and 21 degrees C during the second growing season (GS II). In GS II, shoot diameter growth was lowest in the 21 degrees C treatment and root growth was lowest in the 9 degrees C treatment. In GS III, shoot height and root length growth improved in seedlings that had been kept at 9 degrees C during GS II, indicating compensatory growth in response to increased soil temperature. The temporary decrease in soil temperature had no long-lasting significant effect on seedling biomass or total nutrient uptake. At the end of GS III, fine roots of seedlings exposed to a soil temperature of 21 degrees C in GS II were distributed more evenly between the organic and mineral soil layers than roots of seedlings in the other treatments. During GS II and GS III, root growth started earlier than shoot growth, decreased during the rapid shoot elongation phase and increased again as shoot growth decreased.     

Carbon and phosphorus partitioning in Pinus serotina seedlings growing under hypoxic and low-phosphorus conditions

Ten-week-old pond pine (Pinus serotina Michx.) seedlings were grown in solution culture at 5 or 100 microM P and under aerobic or hypoxic solution conditions. After 6 and 10 weeks in the treatments, changes in relative growth rate (RGR), P acquisition and allocation, and carbohydrate partitioning were determined by analyzing tissue for total P, soluble sugars and starch. Six weeks of low-P growth conditions decreased seedling dry weight and the ratio of shoot dry weight to root dry weight (S/R) by 39 and 51%, respectively, in comparison to seedlings from the aerobic, high-P (control) treatment. Mean RGRs of shoots in the low-P treatment were reduced by 33%, whereas root growth was unaffected. After 10 weeks of low-P growth conditions, however, both shoot and root RGRs were significantly reduced, and plants had lower S/R ratios than in any other treatment. Slowed shoot growth was accompanied by starch and nonstructural carbohydrate accumulation in needles, indicating that needle growth was not limited by carbohydrate supply. Six weeks of low-P growth conditions decreased total seedling P by 75%, reflecting a 97% reduction in the net uptake rate (NUR). Shoot NUR as a fraction of seedling NUR was also greatly reduced in the low-P treatment, indicating that low-P growth conditions affected P translocation to the shoot more than P accumulation by roots. In contrast, 6 weeks of hypoxic growth conditions decreased total dry weight of seedlings in the high-P treatment by 41% relative to their aerobic counterparts. Root growth was affected more than shoot growth, however, and S/R ratios increased. After 10 weeks, S/R ratios doubled, primarily because of the reduction in root RGR. Nevertheless, roots of hypoxic seedlings contained a higher percentage of total seedling P than their aerobic counterparts. Net P acquisition per seedling decreased by more than 50% under hypoxic growth conditions, as a result of reductions in both root RGR and seedling NUR. Starch accumulation in shoots of hypoxic seedlings reflected reductions both in root growth and in transport of carbohydrates to nonwoody roots. Carbohydrate availability did not appear to be limiting growth of hypoxic woody roots, which are well-aerated internally, but it may have limited metabolic processes in nonwoody roots of seedlings from the high-P treatment.     

贵州不同种源棕榈苗期生长性状比较及评价

为给贵阳地区棕榈人工造林的优良种源选择提供参考,以贵州省内遵义、毕节等18个市(县)的棕榈种子为试验材料,采用大田育苗的方法进行培育。对不同种源2年生棕榈苗的地上部分和地下部分的生长指标进行观测,并采用聚类分析法对棕榈种源进行类别划分,对其与种源地地理位置的相关性进行分析,采用主成分分析法对18个种源棕榈苗的生长性状进行综合评价。结果表明:不同种源2年生棕榈苗的高、地径、总根长、主根长、总根表面积、总根体积、根尖数及总生物量等指标均有显著差异(P<0.05),各指标的变幅分别为28.78~51.09cm、8.40~21.93mm、37.41~85.02cm、14.73~41.20cm、127.13~362.82cm2、5.52~19.55cm3、902~1536、4.64~12.32g。聚类分析结果表明,18个种源可分为2大类,其中罗甸、兴义、毕节为苗期生长性状表现较好的一类。相关性分析结果表明,原产地是低纬度和湿润地区的棕榈苗在试验区生长表现较好。主成分分析及综合得分排序的前3名分别为罗甸、兴义、毕节种源,与聚类分析结果一致。初步评价出罗甸、兴义和毕节种源为贵阳地区首选的棕榈种源。     

Seedling growth and mycorrhizal formation in clearcut and adjacent,undisturbed soils in montana: A green-house bioassay

In a series of greenhouse bioassays, tree seedling growth and root-tip development were compared among soils from two areas that had been clearcut and site prepared 16 years earlier and adjacent, undisturbed forest. Seedlings grown in soil from logged areas were shorter and had fewer root tips than those grown in undisturbed forest soil; however, effects on seedling weights were not consistent among species or experimental series. Fertilizing with nitrogen eliminated size differences due to soil source. In Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco], the only species tested in sterilized soils, sterilization of logged soils resulted in increased seedling size and root-tip formation, whereas sterilization of unlogged soils had either no or a negative effect.     

Growth and phenology of seedlings of four contrasting slash pine families in ten nitrogen regimes

Seedlings of two fast- and two slow-growing families of slash pine, Pinus elliottii Englm. var. elliottii, were grown in a greenhouse for one growing season in one of 10 nitrogen (N) regimes. Increasing the N concentration in the nutrient solution resulted in both increased growth rates during the exponential growth phase and extended duration of the growing season. The two components of total height, free growth (epicotyl length to the first bud) and summer growth (height growth after the first bud), both increased significantly with increasing N concentrations up to 40-60 mg l(-1) but decreased at N concentrations above 180 mg l(-1). Compared to seedlings grown in the presence of an optimum N concentration, seedlings grown in the presence of trace amounts of N were smaller and had less summer growth as a percentage of total growth, earlier cessation of height growth, fewer flushes, lower shoot/root ratio, higher root fibrosity, and lower N concentrations in all seedling tissues. Compared to slow-growing families, fast-growing families had more summer height growth, more flushes and later growth cessation, higher shoot/root ratios and higher root fibrosity at all N concentrations. In the presence of an optimum or higher concentration of N, the fast-growing families also had higher needle and total N concentrations than the slow-growing families. Strong family by N-treatment interactions occurred for height, phenology and biomass traits because of the extra responsiveness of one family to increasing N concentration. Several seedling traits were identified that appear promising for predicting field performance in slash pine. The results indicated that the nutrient environment greatly influences genetic expression (e.g., family patterns of summer growth were most closely related to field rankings for seedlings in the trace-N treatment).