Seedling Leaf Area Research Articles

Growth, water relations, and survival of drought-exposed seedlings from six maternal families of honey mesquite (Prosopis glandulosa): responses to CO(2) enrichment.

Low water availability is a leading contributor to mortality of woody seedlings on grasslands, including those of the invasive shrub Prosopis. Increasing atmospheric CO(2) concentration could favor some genotypes of this species over others if there exists intraspecific variation in the responsiveness of survivorship to CO(2). To investigate such variation, we studied effects of CO(2) enrichment on seedling survival in response to uniform rates of soil water depletion in six maternal families of honey mesquite (P. glandulosa Torr. var. glandulosa). Three families each from the arid and mesic extremes of the species' distribution in the southwestern United States were studied in environmentally controlled glasshouses. Relative water content at turgor loss and osmotic potential were not affected by CO(2) treatment. Increased atmospheric CO(2) concentration, however, increased growth, leaf production and area, and midday xylem pressure potential, and apparently reduced transpiration per unit leaf area of seedlings as soil dried. Consequently, CO(2) enrichment about doubled the fraction of seedlings that survived soil water depletion. Maternal families of honey mesquite differed in percentage survival of drought and in several other characteristics, but differences were of similar or of smaller magnitude compared with differences between CO(2) treatments. There was no evidence for genetic variation in the responsiveness of survivorship to CO(2). By increasing seedling survival of drought, increasing atmospheric CO(2) concentration could increase the abundance of honey mesquite where establishment is limited by water availability. Genetic types with superior ability to survive drought today, however, apparently will maintain that advantage in the future.

Relations between the invasive Cinnamomum verum and the endemic Phoenicophorium borsigianum on Mané island, Seychelles

Abstract. In the Seychelles the endemic palm Phoenicophorium borsigianum and the aggressively invasive alien Cinnamomum verum are competitors in a series of habitats. The extent to which demographic variables (relative growth rates of leaf area (RGRAL) and height (RGRR) together with mortality and recruitment) were important determinants of the competitive ability of the above species was investigated.It was studied whether competitive relations between Cinnamomum and Phoenicophorium can change with light intensity as a result of different morphological responses and to what extent native plants such as Phoenicophorium can establish, regenerate and potentially outcompete Cinnamomum in important biodiversity sites in mountain mist forest and intermediate forest habitats. The light intensity in terms of diffuse site factors (DifSF) was estimated at 32 microsites from hemispherical photographs using a computerized image analysis system. A new plant growth analysis function, the so‐called leaf area height index (ALHI), has been introduced and a principal components analysis (PCA) was carried out to evaluate the seedling performance of Cinnamomum and Phoenicophorium. Competition between Cinnamomum and Phoenicophorium was greatly influenced by the amount of available photosynthetically active radiation (PAR). For both species there was a negative correlation between mean leaf area of seedlings and light levels. Phoenicophorium responded significantly better in terms of RGRAL and ALHI to low gap light levels than Cinnamomum. Both species showed no further response to direct sunlight with levels of 98.7 % diffuse site factor. Phoenicophorium and probably other palms endemic to the Seychelles such as Deckenia nobilis and Roscheria melanochaetes act as a filter affecting the distribution and abundance of establishing Cinnamomum seedlings. Mortality of Cinnamomum was strongly negatively correlated with levels of PAR while Phoenicophorium showed no such correlation. Unlike Phoenicophorium, Cinnamomum could establish and regenerate only in light levels of >7.5 % diffuse site factor.

Seed treatment with growth regulators and crop productivity. I. 2,4-D as an inducer of salinity-tolerance in wheat (Triticum aestivum L.)

Experiments were conducted under laboratory and greenhouse conditions to study the effect of 2,4-D on rooting and salinity tolerance of wheat. Seeds of one commercial wheat (Inqalab-91) and three salt-tolerant wheat lines (WL-41, WL-359, and WL-1073 developed through wide hybridization) were included in the study. Preliminary and short-term experiments were conducted to determine the level of 2,4-D (administered through seed soaking for 24.5 h. at 25 °C in the dark) at which the maximum number of roots emerged. Under hydroponic conditions, 2,4-D treatment of seeds caused an increase of 60 to 100% in the number of primary roots. The maximum increase in the number of roots was observed in one of the salt tolerant wheat lines (WL-41). The roots appeared in bunches but showed stunted growth at higher levels of 2,4-D. Dry matter accumulation decreased markedly; the effect was more pronounced in Inqalab-91 which is less tolerant to stress than other wheat lines. In all wheat types, allocation of dry matter to roots relative to shoot increased due to 2,4-D treatment. In soil, seeds treated with different levels of 2,4-D showed a germination delay of 1–3 days. Although the number of primary roots increased, 2,4-D treatment caused a decrease in total dry matter accumulation by plants grown for 40 days. In another experiment, conducted under greenhouse conditions, seed germination and growth of seedlings was significantly retarded in saline compared to that in non-saline (normal) soil. Initially, the pace of germination of treated seeds as well as seedling growth was slower in both soils, but after six weeks, the leaf area of seedlings raised from treated seeds was greater than those raised from untreated seeds. Towards maturity, plants arising from treated seeds developed wider and longer flag leaves leading to enhanced yield. Root biomass decreased in saline soil as compared to normal soil. However, 2,4-D treatment caused a substantial increase in root biomass in saline soil and the roots were harder in texture in wheats other than Inqalab-91. Seed treatment with 2,4-D led to a significant improvement in the number of productive tillers, yield of straw and grain, and grain protein content of all wheats grown in saline soil. Plants grown in normal soil did not show any marked effect of seed treatment on grain yield and other agronomic parameters. The four wheats showed substantial differences for different parameters but the salt tolerant wheat lines performed better compared to the commercial variety Inqalab-91.

Relationships between early vigour, grain yield, leaf structure and stable isotope composition in field grown barley

Fast growth and early development in barley are used in breeding programmes to improve the water use efficiency and transpiration efficiency of this crop in Mediterranean conditions. Here, we examine the use of several simple traits based on the structure and stable isotope composition of seedling leaves to assess differences in early vigour, phenology and grain yield, and also the interaction with low temperatures in barley. A set of 260 F 8 lines of two-row barley ( Hordeum vulgare L.) derived from the cross of Tadmor and WI 2291 were cultivated in two locations in northwest Syria. Total chlorophyll content on an area basis (SPAD) and specific leaf dry weight (SLDW) were measured in recently fully expanded intact leaves of seedlings. Total leaf area and total dry weight per seedling were evaluated in the same seedlings. The stable isotope compositions of carbon and nitrogen ( δ 13C and δ 15N, respectively) were analyzed in the same leaves on a subset of 75 genotypes. Number of days from planting to heading and grain yield were recorded at both sites. The grain yield measured at both locations was positively correlated with the SPAD value of seedlings, but showed no relationship with SLDW. Days to heading was negatively correlated with SPAD values. Regarding early vigour, a negative relationship between the SLDW and the total leaf area of seedlings was observed. However, no relationship between the δ 13C of seedlings and early vigour was observed, except when only the genotypes most resistant to low temperatures (i.e. showing the highest SPAD values) were considered. This subset of genotypes showed negative relationships between δ 13C and either total leaf area or total dry weight. In addition, δ 15N was negatively correlated with SPAD only within the high-SPAD genotypes. This suggests that within the genotypes resistant to low temperatures, those with higher chlorophyll content assimilate more nitrogen from nitrate.

Growth of pedunculate oak (Quercus robur L.) seedlings on blendsubstrates based on consolidated brackish sludge

Either in its pure form or as a base for a blend-substrate, brackish sludge can be used as a growth medium for trees. The objectives of the experiment were (1) to evaluate the quality of consolidated brackish sludge as a growth medium, (2) to assess the influence of substrate blending on tree growth (leaf area, tree height, biomass), and (3) to evaluate the need for substrate blending. Germinated acorns of the same mother tree were planted in containers and grown under controlled conditions. The substrate consisted of pure brackish sludge or of brackish sludge blended with peat, sand or wood chips, in stages of 25 volume percentage. Chemical analysis of the brackish sludge showed a neutral pH, a conductivity of 3.60 mS/cm and a sufficient amount of macro elements. The addition of sand contributed to an accelerated desalination of the substrate. The treatments with 100 % sludge and 25 % peat yielded a leaf area, a tree height and a biomass which were among the top three growing results. The growing results of the treatments with 25% sand and 50% peat were consistently among the top five. The blending of peat in brackish sludge had no influence on leaf area, tree height and biomass of seedlings. The use of wood chips or of more than 25 % sand resulted in a significant decrease of these three growth parameters. Foliage analyses of the trees grown on a substrate containing more than 50% sand or wood chips revealed deficits in available nutrients. These deficits manifested themselves in a loss of leaf area, tree height and biomass production. The nutritional status and the growth parameters of oak seedlings on brackish sludge were favourable. No influence of the salt and the heavy metal concentrations on growth was observed. Consolidated brackish sludge is a suitable growth medium for trees.

Sensitivity of Selected Vegetable and Weed Seedlings to Ultraviolet-B Radiation

Relative sensitivity of selected vegetable and weed seedlings to ultraviolet-B (UV-B) radiation (280–320 nm) was investigated. Seedlings were grown for 4 weeks in a greenhouse, in chambers equipped with UV-B-emitting fluorescent tubes and Mylar (control) and cellulose acetate (UV-B) filters. UV-B radiation reduced seedling height, leaf area, and leaf fresh weight in tomato (Lycopersicon esculentum `Cour Di Bue'), broccoli (Brassica oleracea var. Italica `Purple Sprouting'), cabbage (Brassica oleracea var. Capitata `Red Drumhead'), and cucumber (Cucumis sativus `Straight Eight'), leaf area and leaf fresh weight in beet (Beta vulgaris `Cylindra' and `Early Wonder'), seedling height and leaf area in spinach (Spinacia oleracea `Long Standing Bloomsdale'), lettuce (Lactuca sativa ``Red Salad Bowl Everest') and `Savoy' cabbage, and seedling height in `Chinese Tip Top' cabbage and lettuce (`Saladin'). `Winterton' cabbage was not affected. UV-B radiation decreased leaf area and leaf fresh weight in common chickweed (Stellaria media) and corn spurry (Spergula arvensis) and seedling height in green foxtail (Setaria viridis) and redroot pigweed (Amaranthus retroflexus). Tillering was stimulated in response to UV-B in green foxtail. There was no effect of UV-B on lady's-thumb (Polygonum persicaria) growth. Leaf number was not affected by exposure to UV-B in any species. The differential morphological sensitivity of vegetable and weed seedlings may result in altered competitive relationships under enhanced UV-B levels expected with the depletion of the earth's ozone layer.

The effects of seed size, cotyledon reserves, and herbivory on seedling survival and growth in Quercus rugosa and Q. laurina (Fagaceae)

In a greenhouse experiment, seedling survival of two oak species (Quercus rugosa and Q. laurina) was greatly affected by the excision of cotyledons 1 mo after germination, with a greater impact on Q. laurina. The effect of seed size was also significant for both species, with a positive correlation between seed mass and survival and growth. The effect of cotyledon excision on seedling growth persisted throughout the first growing season in Q. rugosa and was not analyzed for Q. laurina due to the low number of seedlings that survived cotyledon excision. Seed size significantly affected seedling height, diameter, leaf area, and biomass at 6 mo. Seed size and cotyledon retention affected the ability of Q. rugosa to recover from herbivory, as both factors had a significant effect on relative growth rates after aerial biomass removal. The results show that seedlings originating from large seeds can better endure loss of cotyledons and aerial biomass and thus are better equipped to confront stress early in their lives.

Factors influencing Rhizophora mangle L. seedling development in Everglades carbonate soils

Nutrient limitation, soil waterlogging, and soil salinity have been hypothesized as the principal factors limiting the development of neotropical mangrove forests. A mesocosm experiment was initiated to investigate these alternative factors, using low-nutrient soils from the south Florida Everglades. Nitrogen (N), phosphorus (P), aeration, and salinity treatment effects on Rhizophora mangle L. seedling leaf area, stem elongation, and biomass development were determined. Phosphorus rather than nitrogen was the important macro-nutrient limiting R. mangle leaf area, and root and leaf biomass development in the mesocosm experiment. A subsequent P enrichment experiment was conducted in the field to substantiate mesocosm findings. Under P enrichment in the field, seedling stem elongation rates increased from 0.03 mm d −1 to 0.20 mm d −1 and leaf area increased from 25 cm 2 to 75 cm 2, relative to unfertilized controls. Soil aeration stimulated root biomass development 40% in the mesocosm experiment. Sodium chloride at 32‰ resulted in branch initiation with no leaf response; however, hypersaline conditions greater than 45‰ caused denaturing of terminal buds. Thus, without hypersalinity stress, P is identified as a dominant factor limiting R. mangle foliar and stem development in low nutrient carbonate soils. Soil anoxia also influences root development and may moderate stem elongation responses to P fertilization in the field.

Relationship between the Effects of Salinity on Seedling Leaf Area and Fruit Yield of Six Muskmelon Cultivars

Six muskmelon (Cucumis melo L.) Galia-type cultivars (`Delada', `Gallicum', `Galor', `Melina', `Regal' and `Revigal') were tested for salt tolerance at the seedling stage and during growth in the field. Three levels of salinity (ECW 2.5 (control), 5.0 and 7.5 dS·m-1), established by adding NaCl to fresh water, were used. The effect of salinity on seedling growth was assessed by measuring the total leaf area 36 days after sowing. `Melina' was the most tolerant at this stage and during subsequent growth in field, with a relative seedling leaf area of 60 and a relative yield of 66 at 7.5 dS·m-1 salinity, both expressed as a percentage of the values obtained at the control level of salinity. `Delada' was the most sensitive to the highest level of salinity at both stages, with relative seedling leaf area and yield of 51 and 56, respectively. For all cultivars, a highly significant correlation (r = 0.99) was established between the influence of salinity on seedling leaf area reduction and on decrease in yield during field culture. The results indicate that the reduction in seedling leaf area can be a good selection criterion to facilitate rapid screening for salt tolerance in muskmelon.

Identification and mode of action of quantitative trait loci affecting seedling height and leaf area in Eucalyptus nitens

Regions of the genome influencing height and leaf area in seedlings of a three-generation outbred pedigree of Eucalyptus nitens have been identified. Three QTLs affecting height and two QTLs affecting leaf area were located using single-factor analysis of variance. The three QTLs affecting height each explained between 10.3 and 14.7% of the phenotypic variance, while the two QTLs for leaf area each explained between 9.8 and 11.6% of the phenotypic variation. Analysis of fully informative marker loci linked to the QTLs enabled the mode of action of the QTLs to be investigated. For three loci the QTL effect segregated from only one parent, while for two loci the QTL showed multiple alleles and the effect segregated from both parents in the pedigree. The two QTLs affecting leaf area were located in the same regions as two of the QTLs affecting height. Analysis of these regions with fully informative markers showed that both QTLs were linked to the same markers, but one had a similar size of effects and a similar mode of action for both height and leaf area, whilst the other showed a different mode of action for the two traits. These regions may contain two closely linked genes or may involve a single gene with a pleiotrophic effect on both height and leaf area. The QTL with the greatest effect showed multiple alleles and an intra-locus interaction that reduced the size of the effect. Assessment for two of the QTLs in a second related family did not show an effect associated with the marker loci; however, this was consistent with the mode of action of these QTLs and the pattern of inheritance in the second family.

Size structure of a dominant Neotropical forest tree species, Dicymbe altsonii, in Guyana and some factors reducing seedling leaf area

There has recently been a renewal of interest in the phenomenon of tree species dominance in tropical forests (Condit et al. 1992, Connell & Lowman 1989), following the observations of Richards more than 40 years ago that tropical tree communities often show marked patterns of species dominance (Richards 1952). Thus, whilst a large tree species pool is present in tropical forests there may be factors operating, such as the ectomycorrhizal associations suggested by Connell & Lowman (1989), which facilitate a marked dominance by one or more species, resulting in a reduction of ecological diversity. The quantification of such dominance and the investigation of the factors contributing to dominance are therefore primary goals of tropical forest ecology.

Containerized Muskmelon Transplants: Cell Volume Effects on Pretransplant Development and Subsequent Yield

Muskmelon (Cucumis melo L. cvs. Superstar and Mission) transplants were grown in cellular seedling trays of polystyrene or styrofoam, with individual cells ranging in volume from 7 to 100 cm3, transplanted to the field, and grown to maturity in Florida and Indiana during the 1993 and 1994 growing seasons. Seedling leaf area, shoot and root weights before transplanting, and shoot dry weight 20 days after transplanting increased linearly with increasing cell volume in Florida. Thirty days after transplanting, vine length showed significant linear and quadratic trends with respect to cell volume in Indiana. In Florida, early and total yields increased linearly as transplant cell volume increased for `Mission' in both years and for `Superstar' in 1994. In Indiana, early yields increased linearly as transplant cell volume increased for `Mission' in 1994 and for `Superstar' in both years, but cell volume did not consistently affect total yield. Transplant tray effects on early and total yield unrelated to linear or quadratic effects of cell volume occurred in both locations, but these effects were not consistent.

Performance, plasticity, and acclimation of the nonindigenous shrub Lonicera maackii (Caprifoliaceae) in contrasting light environments

Growth and photosynthetic capability of the eastern Asiatic shrub Lonicera maackii (Rupr.) Herder were measured in shadehouses and in artificial canopy gaps. In shadehouses providing 5, 25, and 100% of full sun, total dry mass, and leaf area of seedlings increased with light availability; specific leaf area and leaf area ratio decreased with light availability. When small suppressed shrubs were transplanted from a forest site to the shadehouse environments, rapid (13 day) acclimation in existing leaves initially produced the highest mean photosynthetic rate (8.12 μmol∙m−2∙s−1) and the highest mean relative stem growth at 25% light. However, maximum mean photosynthetic rate (10.36 μmol∙m−2∙s−1), higher mean stomatal density, and increased mean leaf thickness were measured only in new leaves formed in 100% light. This plastic response was associated with higher relative stem growth later in the experiment. Naturally established seedlings in both artificial canopy gaps and sites with intact canopies had low and negative relative stem growth, presumably as a result of light limitation. The results support the observation that L. maackii is a shade intolerant species that performs best in forests where large disturbances or edge effects create enhanced light availability. Key words: acclimation, forest edge, invasive species, Lonicera maackii, plasticity, shade tolerance.

Seedling White Clover Response to Defoliation

Defoliation during the early stages of seedling development can influence growth of white clover (Trifolium repens L.). Our objective was to determine the response of cultivars with diverse leaf sizes to defoliation across a range of seedling growth stages. ‘Regal’ (large‐leaf), ‘Louisiana S‐1’ (medium‐large‐leaf), ‘Grasslands Huia’ (medium‐smallleaf), and ‘Aberystwyth S184’ (small‐leaf) were grown in the greenhouse and were initially clipped to remove all leaf (except cotyledons) and petiole tissue (1.0‐cm stubble) when seedlings attained a unifoliolate leaf or one, two, four, and eight trifoliolate leaves. Seedlings were subsequently clipped in the same manner every 7 or 28 d for the next 28 d. Plant response to defoliation was assessed 7, 14, 21, and 28 d after the last clipping. Seedling shoot dry weight of all cultivars increased linearly in response to initial leaf stage when subsequent clipping occurred every 7 d after the initial defoliation. When subsequent clipping was delayed 28 d, defoliation after the four‐trifoliolate stage did not influence shoot weight of any cultivar except Regal. Despite fewer numbers of leaves after regrowth, seedling leaf area of Regal was always greater than that of the other cultivars. Number of stolon branches of Regal and Louisiana S‐1 increased in response to leaf stage at initial defoliation (0.15 branches stage−1), while that of Grasslands Huia and Aberystwyth S184 was relatively unchanged after the four‐ to six‐trifoliolate stage. Permitting white clover seedlings to attain advanced leaf stages before initial defoliation and increasing the time interval before subsequent defoliation will enhance seedling growth and potential survival.

Seedling Crown Orientation and Interception of Diffuse Radiation in Tropical Forest Gaps

In forest gaps, the geometry of canopy openings above a plant determines the spatial distribution of diffuse and direct radiation, which may be received from different sectors of the sky. We examined crown orientation and light interception by seedlings of four species of pioneer trees, Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum, and Trema micrantha, transplanted into natural forest gaps at the Los Tuxtlas Tropical Biology Station, Veracruz, Mexico. The four species differed in the number and mean size of leaves, but total leaf area was not significantly different among equal age plants. The mean azimuth and zenith angle of diffuse and direct radiation were determined from hemispherical photographs taken above each plant. Mean diffuse radiation vectors were distributed around the zenith, with a significant clustering in an easterly direction, while mean direct radiation vectors were distributed along the solar track in the southern portion of the sky. The mean orientation of the crown of each seedling was determined from detailed, three—dimensional reconstruction of leaf display using a canopy architecture model. A directional correlation test indicated that seedling crowns were orientation of individual leaves. The mechanisms of this differential response to diffuse vs. direct radiation are not known. For diffuse radiation, the total light capture capacity integrated over all sky directions increased with seedling leaf area, while efficiency of capture per unit area decreased. Based on simulations, the light interception efficiency of each plant in its own microsite was 5—25% greater than would be achieved in the sites of conspecifics of in symmetric canopy openings centered on the zenith. These analyses provide a quantitative estimate of the value of nonrandom leaf and crown orientation for whole—plant light interception in natural environments.

Water movement through Quercus rubra I. Leaf water potential and conductance during polycyclic growth

ABSTRACTTwo experiments examined simultaneous changes in leaf area (AL), root length (Lr), stomatal conductance (gs), leaf water potential (ΨL), transpiration and hydraulic plant conductance per unit leaf area (G) during the first three shoot cycles of northern red oak (Quercus rubra L.) grown under favourable and controlled conditions. Each shoot cycle consisted of bud swell, stem elongation, leaf expansion and rest; roots grew almost continuously. The gs of all leaves decreased substantially while leaves of the newest flush were expanding and increased modestly when seedling leaf area remained constant. Overall, gs decreased. The ΨL of mature leaves decreased during leaf expansion and increased by an equivalent amount during intervening periods. Possible explanations for the paired changes in gs and ΨL are considered. Changes in G closely paralleled those of canopy gs. These parallel changes during polycyclic seedling growth should act to keep seedling ΨL relatively constant as plant size increases and thereby help prevent ΨL from dropping to levels that would cause runaway embolism.

Seed germination, seedling demography, and growth of Salix setchelliana on glacial river gravel bars in Alaska

This study examines the recruitment from seed of Salix setchelliana Ball, a prostrate clonal willow, which grows in the gravel-bar habitat of glacial rivers in Denali National Park, Alaska. Seeds of this species did not exhibit any dormancy. Under laboratory conditions, seeds moistened immediately after collection showed 100% germination, and percent germination decreased with an increase in the length of dry storage. Since summer precipitation is generally frequent in this region, this is probably not a factor limiting recruitment. Most seedlings observed in the field were located on gravel bars with greater plant cover, as opposed to those with sparse plant cover. The survivorship of seedlings over their first winter averaged 11%; in comparison, yearly survivorship in years 1–6 averaged 69%. The most likely cause of mortality was insufficient carbohydrate accumulation. Seedling leaf area differed between years and locations. An inverse relationship was found between leaf area and age-class for seedlings of younger age-classes. Key words: alpine, clonal, recruitment.

Growth and morphology of rhizome cuttings and seedlings of salal (Gaultheria shallon): effects of four light intensities

Rhizome cuttings and seed of salal (Gaultheria shallon) were cultured in nursery beds at four light intensities (20, 50, and 70%, and full sunlight) created by various thicknesses of shade cloth. After each of two growing seasons, growth and morphological characteristics were compared among light intensities and between life stages. Under all light intensities, rhizome cuttings produced aerial stems and new rhizomes within 1 year and produced fruit within 2 years. Seedlings produced numerous aerial stems but few rhizomes. In general, 70% light induced the greatest production of aerial stems and rhizomes for both cuttings and seedlings. In 70% light, cuttings averaged more than three times the number of rhizomes and rhizome biomass and nearly twice the aerial stem biomass of cuttings in 20% light. Morphology of aerial stems, rhizomes, leaves, and seedling canopies was also affected by light quantity. Aerial stems produced by cuttings were shortest (9.9 cm) in full light and rhizome lengths were longer (27.6 cm) in 50% light than in 20% or full light. Specific leaf area of both cuttings and seedlings was highest (99.9 cm2/g and 146 cm2/g, respectively) under the most shaded treatment. The implications of these results with respect to the ecology of salal under field conditions are discussed. Key words: Gaultheria shallon, seedlings, rhizome cuttings, shade treatment, morphology, vegetative growth.

Phenotypic variation in seedlings of a "keystone" tree species (Quercus douglasii): the interactive effects of acorn source and competitive environment.

Blue oak (Quercus douglasii) is a deciduous tree species endemic to California that currently exhibits poor seedling survival to sapling age classes. We used common garden techniques to examine how genetic variation at regional and local scales affected phenotypic expression in traits affecting oak seedling growth and survival. Between-population variation was examined for seedlings grown from acorns collected from a northern, mesic population and a southern, xeric population. Within-population variation was examined by comparing seedlings from different maternal families within the mesic population. Acorns were planted into neighborhoods of an annual dicot (Erodium botrys), an annual grass (Bromus diandrus), and a perennial bunchgrass (Nassella pulchra). By varying the species composition of herbaceous neighborhoods into which acorns were planted, the interactive effects of competition and acorn germplasm source on phenotypic expression could also be examined. Potential maternal effects, expressed as variation in acorn size, were assessed by weighing each acorn before planting. Probability of seedling emergence increased significantly with acorn size in the xeric population but not in the mesic population. Similarly, the effect of acorn size on seedling leaf area, stem weight, and root weight was also population-dependent. At a within-population level, acorn size effects on seedling traits varied significantly among maternal families. In addition to acorn size effects, rates of oak seedling emergence were also dependent on an interaction of population source and competitive environment. Interactions between maternal family and competitive environment in the expression of seedling leaf characters suggest the possibility of genetic variation for plasticity in traits such as specific leaf area. Using carbon isotope discrimination (Δ) as an index of relative water-use efficiency (WUE), higher water use efficiency was indicated for oak seedlings grown in the annual plant neighborhoods compared to seedlings grown in the bunchgrass neighborhood. This trend may represent an adaptive plastic response because, compared to the bunchgrass neighborhood, soil water depletion was more rapid within annual plant neighborhoods.

Leaf and root growth dynamics in Eucalyptus globulus seedlings grown in drying soil

Seedlings of Eucalyptus globulus growing in soil columns were subjected to a 24 day soil drying treatment. Water and solute potentials of both young expanding and fully expanded leaves declined under reduced soil water availability, while slightly higher turgor was sustained by the fully expanded leaves. Although leaf area of unwatered seedlings was smaller, the corresponding leaf dry weight was quite similar to that of well-watered seedlings. Soon after rewatering, leaf area of plants experiencing water shortage was comparable to that of well-watered plants. It seems that a difference in wall properties between juvenile and mature leaves allows for an effective pattern of water use by eucalypt plants growing in drying soil. Some stomatal opening is sustained and therefore, presumably, some carbon may be fixed, keeping the carbon balance of the whole plant positive, and allowing a continuous cell division despite the limited water supply. The highest root density of both well-watered and unwatered plants was found in the upper soil layers. However, root growth of unwatered seedlings was gradually increased in the deeper soil layers, where thicker root apices and higher soil water depletion rates per unit root length were recorded. As a consequence, root absorbing surface area was as large in unwatered plants as in well-watered plants.