Effect of shoot size on the gas exchange and growth of containerized Picea mariana seedlings under different watering regimes

Containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings of three different sizes (small, medium, and large) were planted in raised sand beds maintained under wet, moderately dry or dry watering regimes during the growing season. The small seedlings were of a conventional stock type. The two larger sizes were novel stock types grown in larger containers. Physiological measurements during the summer showed that the small and medium seedlings maintained nearly similar levels of gas exchanges and water status, but that the large seedlings had reduced net photosynthesis and stomatal conductance under all watering regimes. Analysis of dry masses showed comparable relative growth rates in the small and medium seedlings, but a small to null growth in the large seedlings. Examination of root relative growth rate under wet conditions revealed significant root growth in small and medium seedlings, but negligible growth in the large seedlings. It was concluded that increasing the shoot size of containerized seedlings can be achieved without increasing the susceptibility of the seedlings to water stress, as long as the vigour of the root system is maintained.     

Physiological and growth responses of three sizes of containerized Picea mariana seedlings outplanted with and without vegetation control

Three different stock sizes of containerized black spruce (Picea mariana [Mill.] B.S.P.) seedlings were planted in an abandoned agricultural field. The small planting stock was of a conventional type produced in 110 cm³ containers. The experimental medium and large stock types were produced in 340 and 700 cm³ containers, respectively. Gas exchange, xylem water potential and dry masses were measured six times during each of the first two growing seasons in field plots with and without vegetation control. During the first growing season, the effect of planting shock masked most physiological and growth differences among seedling types. During the second growing season, in plots with vegetation control, small and medium seedlings had similar values of physiological variables and of growth as measured by relative growth rates (RGR), but the large seedlings showed lower values of both net photosynthesis and of RGR, a difference attributed to low initial quality of the root system in the larger seedlings. In plots without vegetation control, the trend was identical, but differences were not significant; the greater height of the larger seedlings, and the resulting greater access to light, compensated for their lower initial quality. The similarity in response between the medium and the small seedlings shows that a fourfold increase in shoot size (1.68–6.82 g) in the initial size and a doubling of the shoot : root ratio (2.17–4.54) of the planting stock did not result in increased planting shock or reduced growth in these containerized conifer stock types. The results also show the importance of the interaction between stock height and the vertical light profile created by the competing vegetation in the final assessment of stock performance.     

Changes in root growth and relationships between plant organs and root hydraulic traits in American elm (Ulmus americana L.) and red oak (Quercus rubra L.) seedlings due to elevated CO2 level

The relationships between plant organs and root hydrological traits are not well known and the question arises whether elevated CO2 changes these relationships. This study attempted to answer this question. A pseudo-replicated experiment was conducted with two times 24 American elm (Ulmus americana L.) and 23 and 24 red oak (Quercus rubra L.) seedlings growing in ambient CO2 (around 360 μmol·L–1) and 540 ± 7.95 μmol·L–1 CO₂ in a greenhouse. After 71 days of treatment for American elm and 77 days for red oak, 14 American elm and 12 red oak seedlings from each of the two CO2 levels were randomly selected in order to examine the flow rate of root xylem sap, root hydraulic conductance, total root hydraulic conductivity, fine root and coarse root hydraulic conductivity. All seedlings were harvested to investigate total plant biomass, stem biomass and leaf biomass, leaf area, height, basal diameter, total root biomass, coarse root biomass and fine root biomass. The following conclusions are reached: 1) plant organs respond to the elevated CO2 level earlier than hydraulic traits of roots and may gradually lead to changes in hydraulic traits; 2) plant organs have different relationships with hydraulic traits of roots and elevated CO2 changes these relationships; the changes may be of importance for plants as means to acclimatize to changing environments; 3) biomass of coarse roots increased rather more than that of fine roots; 4) Lorentzian and Caussian models are better in estimating the biomass of seedlings than single-variable models.     

Influence of nursery culture on western red cedar

Western red cedar (Thuja plicata Donn) seedlings were grown in a greenhouse and subjected to six nursery cultural treatments (long-day wet (LDW), long-day moderate (LDM), long-day dry (LDD), short-day wet (SDW), short-day moderate (SDM), and short-day dry (SDD)) during mid-summer. Seedling attributes were measured before fall and spring planting.Short-day and moisture stress treatments reduced shoot but not root growth, resulting in reduced shoot to root ratios. Fall tested LDW seedlings had a higher osmotic potential at saturation and turgor loss point than other treatments. Fall tested short-day seedlings had lower resistance to plant water movement. The LDW seedlings had the greatest new root growth in fall testing, while one of the lowest in spring testing. In the fall, LDW seedlings had the greatest net photosynthesis (P_n) at 25 °C root temperature, with all treatments having a similar decline in P_n as root temperatures decreased to 1 °C. In the spring, all treatments had a similar decline in P_n with decreasing predawn shoot water potential. Moisture stress and short-day nursery cultural treatments applied in mid-summer will not harden western red cedar seedlings for all potential field conditions.Spring, compared to fall, tested seedlings had two times the shoot and three times the root dry weight. Spring tested seedlings had a lower osmotic potential, maximum modulus of elasticity, relative water content at turgor loss point and greater dry weight fraction. Fall, compared to spring, tested seedlings had lower resistance to plant water movement and greater cuticular transpiration. In general, fall tested seedlings had more root growth than spring tested seedlings. Spring, compared to fall, tested seedlings generally had greater stress resistance.     

Root water flow and growth of aspen (Populus tremuloides) at low root temperatures

Effects of root zone temperature on growth, shoot water relations, and root water flow were studied in 1-year-old aspen (Populus tremuloides Michx.) seedlings. Seedlings were grown in solution culture and exposed to day/night air temperatures of 22/16 degrees C and solution culture temperatures of 5, 10, or 20 degrees C for 28 days after bud flush. Compared with root growth at 20 degrees C, root growth was completely inhibited at 5 degrees C and inhibited by 97% at 10 degrees C. The 5 and 10 degrees C treatments severely reduced shoot growth, leaf size, and total leaf area. Root water flow was inhibited by the 5 and 10 degrees C treatments. However, when seedlings were grown for 28 days at 5 degrees C and root water flow was measured at 20 degrees C, there was an increase in flow rate. This increase in root water flow was similar in magnitude to the decrease in root water flow observed when seedlings were grown for 28 days at 20 degrees C and root water flow was measured at 5 degrees C. Reduced root water flow of seedlings grown at 5 and 10 degrees C resulted in decreased stomatal conductance, net assimilation, and shoot water potentials. Root water flow was positively correlated with leaf size, total leaf area, shoot length, and new root growth. Transferring seedlings from 5 to 20 degrees C for 24 h significantly increased root water flow, shoot water potential, and net photosynthesis, whereas transferring seedlings from 10 to 20 degrees C resulted in only a slightly increased shoot water potential. Transferring seedlings from 20 to 5 degrees C greatly reduced root water flow, stomatal conductance, and net photosynthesis, whereas shoot water potential decreased only slightly.     

Importance of root growth in overcoming planting stress

Root growth is critical to the establishment of planted seedlings. Seedlings can undergo stress just after planting if root growth is not sufficient to couple the seedling to available soil water. Stress occurs when a newly planted seedling’s root system can not supply enough water to transpiring needles to maintain a proper water balance and ensure survival. Thus, a newly planted seedling’s ability to overcome planting stress is affected by its root system size and distribution, root–soil contact, and root hydraulic conductivity. This paper describes how factors of root growth and water status of newly planted seedlings are important in overcoming the phenomenon of planting stress which then allows a newly planted seedling to enter the establishment phase of development.     

Covariances between morphological characteristics in bareroot Pinus sylvestris nursery stock

In this study an attempt was made to gather information on the relationships of morphological attributes of bareroot Pinus sylvestris seedlings in order to determine the possible use of these attributes for grading purposes. The covariance structure of different morphological variables was studied in commercially produced crops. From each selected batch of Scots pine seedlings, 300 seedlings were sampled, three successive living seedlings from each of the 100 systematically selected sampling points ("clusters"). Variance in the seedlings crop was described using a linear model: total covariance was divided into variance between batches, between clusters and between individual seedlings (error).

Most of the correlations between different plant parts were large and positive. Only needle length and root length seemed to vary independently of other “length”; variables. Within one batch, at the end of the growing season, height‐diameter was more clearly size‐independent than shoot‐root ratio. Needle biomass increased exponentially with seedling height but the smallest seedlings had relatively less needle biomass than the biggest seedlings. It is not necessary to include dry mass in the requirements for seedling quality since it correlates well and can be described with other variables that can be measured more easily. Of the principal components for morphological characteristics, the “stem”; component explained 69% of the height variation and 77% of the diameter variation, the “needle”; component explaining 79% of the variation in current needle length, and the “root”; component 58% of the variation in root length. Together the three components explain 76% of the total variance in the original crops.     

不同育苗方式对薄壳山核桃苗木生长及根系结构的影响

该文报道了薄壳山核桃大田播种育苗和火箭盆、无纺布、塑料钵容器等育苗方式对苗木生长及根系结构的影响。结果表明:不同育苗方式对薄壳山核桃苗木高度和地径生长影响显著,其中火箭盆容器培育的苗高、地径生长量最大,为39.14 cm和0.96 cm;无纺布容器苗和大田播种苗次之;塑料钵容器苗的苗高、地径生长量最小。多重比较分析表明,不同育苗方式对薄壳山核桃苗木的主根长度、主根直径、1级侧根数、1级侧根平均长度、根鲜质量、根干质量、茎鲜质量、茎干质量、根茎鲜质量比和根茎干质量比等指标影响显著,火箭盆容器和无纺布容器培育的苗木侧根系发达,根系质量好;而大田播种苗和普通塑料容器苗的主根发达,侧根少,根系质量较差。     

Influence of irradiance on photosynthesis, morphology and growth of mangosteen (Garcinia mangostana L.) seedlings

The influence of shading intensity on growth, morphology and leaf gas exchange of mangosteen (Garcinia mangostana L.) seedlings was investigated over a 2-year period. Diurnal gas exchange studies revealed significantly higher carbon gain for leaves grown in 20 or 50% shade compared to leaves grown in 80% shade. Seedlings grown in 20 or 50% shade accumulated significantly more dry weight than seedlings grown in 80% shade during the 2-year study period. Seedlings grown in decreased shade showed decreased leaf size, increased leaf thickness, lower specific leaf area (SLA) and higher stomatal frequency. Less shaded seedlings also allocated relatively more dry matter to roots than shaded seedlings and exhibited a significant reduction in leaf area relative to total plant dry weight (leaf area ratio). Increased leaf number, enhanced branching and shorter internodes resulted in a more compact appearance of less shaded seedlings. Irrespective of light conditions, mangosteen seedlings exhibited inherently slow growth because of low photosynthetic rates per unit leaf area, low SLA, low leaf area ratios and inefficient root systems.     

Performance of loblolly pine (Pinus taeda L.) seedlings and micropropagated plantlets on an east Texas site: I. Above- and belowground growth

East Texas contains the western extent of the natural range of loblolly pine (Pinus taeda L.) and, therefore, many planted seedlings there experience water deficit sometimes leading to plantation failure. One solution may be to regenerate with clonally propagated drought-hardy planting stock. The objective of this research was to compare the field performance of loblolly pine seedlings and plantlets of diverse genetic origin, produced via micropropagation technology.Two adjacent sites were established (Site I in 1993 and Site II in 1994) with trees produced from four genetic families: Liberty (LIB) and Montgomery (MON) Counties from southeast Texas, and Fayette (FAY) and Bastrop (BAS) Counties from the “Lost Pines” in Central Texas. Height, groundline diameter (GLD), leaf area, survival, root/shoot ratio, and root system architecture were measured throughout the 1994 and 1995 growing seasons. In addition, height and diameter at breast height on Site II were measured at the end of 1999 and 2000 growing seasons.Height and GLD growth for seedlings was significantly greater than for plantlets on both sites. However, mean relative growth rates for height were greater for plantlets during the first growing season, but comparable thereafter. Survival for all treatments was >85% on Site I and >90% on Site II at the end of the 1995 growing season. Survival was significantly different, but by a negligible margin, between families and stock types on Site II at the end of the 1995 growing season, and by a margin of 7% (89% for seedlings vs. 82% for plantlets) at the end of the 2000 growing season. Seedlings had greater leaf area growth than plantlets after two growing seasons. Root/shoot ratio was significantly greater for plantlets after two growing seasons, whereas their specific root length was significantly smaller than that of seedlings. This was attributed to root system architecture. Whereas plantlets produced thicker roots with less length per unit dry weight, seedlings produced more branching with thinner roots for similar dry weights.     

Absolute and relative growth of Douglas-fir seedlings of different sizes

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings of a single seed source were grown in a bare-root nursery for two years to produce five different stock types by varying spacing and transplanting treatments. They were then planted in the forest together with one-year-old container seedlings of the same seed source, which constituted a sixth treatment. Stem volume mean relative growth rate (R(v)) was low immediately after planting for all stock types except the container seedlings, and increased over the following 7.6 years. An 8-week greenhouse test of the six stock types showed that dry weight mean relative growth rate (R(w)) generally decreased with seedling dry weight, but this effect was less obvious after planting, because only the three smaller stock types showed a decrease in R(w) with size. In another experiment, bare-root Douglas-fir seedlings were grown at five different spacings in a nursery for two years, and seedlings from each spacing treatment were sorted into large or small by height. The resulting 10 treatments were planted in the forest and stem volumes determined over 6.7 years. The linear effect of nursery spacing on stem volume was no longer evident 3.6 years after planting, but large seedlings had greater stem volume than the small seedlings throughout the 6.7 years of the study. There was no indication that R(v) declined with time, but small seedlings had higher R(v) than large seedlings. Relative growth rates of two-year-old Douglas-fir were depressed for a year or two after planting, but then remained relatively constant, or increased during the ensuing 5 years. Relative growth rates of smaller seedlings were greater than those of larger seedlings so that relative biomass differences decreased with time, and the time advantage (the time necessary for small seedlings to reach the present biomass of large stock) of larger stock decreased. Absolute size differences increased with time.     

Influence of photosynthetic photon flux density on growth and transpiration in seedlings of Fagus sylvatica

Beech seedlings (Fagus sylvatica L.) were grown in various combinations of three photosynthetic photon flux densities (PPFD, 0.7, 7.3 or 14.5 mol m(-2) day(-1)) for two years in a controlled environmental chamber. Dry mass of leaves, stem and roots, leaf area and number of leaves, and unit leaf rate were affected by both previous-year and current-year PPFD. Number of shoots and length of the main shoot were affected by previous-year PPFD but not by current-year PPFD. Number of leaves per shoot did not change with PPFD, whereas leaf dry mass/leaf area ratio was mainly affected by current-year PPFD. During the first 10 days that newly emerged seedlings were grown at a PPFD of 0.7 or 14.5 mol m(-2) day(-1), transpiration rate per unit leaf area declined. Thereafter, transpiration increased to a constant new rate. Transpiration rate per seedling was closely related to leaf area but the relationship changed with time. In two-year-old seedlings grown at various PPFD combinations of 0.7, 7.3 and 14.5 mol m(-2) day(-1) during Years 1 and 2, leaf area and transpiration rate per seedling were closely correlated at Weeks 7 and 11 after bud burst. Weak correlations were found between root dry mass and transpiration rate per seedling. During Year 2, transpiration rate per leaf area was higher at a particular PPFD in seedlings grown at a previous-year PPFD of 0.7 mol m(-2) day(-1) than in seedlings grown at a previous-year PPFD of 14.5 mol m(-2) day(-1). After transfer of two-year-old seedlings at the end of the experiment to a new PPFD (7.3 or 14.5 mol m(-2) day(-1)) for one day, transpiration rates per leaf area, measured at the new PPFD, were correlated with leaf area and root dry mass, irrespective of former PPFD treatment.     

Interacting effects of irradiance and water stress on dry weight and biomass partitioning in Fagus sylvatica seedlings

Abstract

Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings.     

Stomatal conductance,growth and root signaling in Betula pendula seedlings subjected to partial soil drying

Seedlings of Betula pendula Roth were grown with their root systems separated between two soil compartments. Four treatments were imposed: (i) adequate irrigation in both compartments (WW, controls); (ii) adequate irrigation in one compartment and drought in the other compartment (WD); (iii) drought in both compartments (DD); and (iv) half of the root system severed and the remainder kept well-watered (root excision, RE). Predawn leaf water potential, stomatal conductance, soil-to-leaf specific hydraulic conductance, and root and leaf growth decreased in DD-treated seedlings, which also displayed severe leaf shedding (30% loss in leaf area). The DD treatment also resulted in increased concentrations of abscisic acid (ABA) and its glucose ester in the xylem sap of roots and shoots compared to concentrations in control seedlings (about 200 versus 20 nM). Despite the difference in xylem sap concentrations, total ABA flux to the shoots was similar in the two treatments (1-2 pmol ABA m(-2) leaf area s(-1)) as a result of reduced transpiration in the DD-treated seedlings. Compared with root growth in control plants, root growth increased in the RE-treated plants and decreased in the drying compartment of the WD treatment; however, the RE and WD treatments only slightly reduced leaf expansion, and had no detectable effects on shoot water relations or ABA concentrations of the root and shoot xylem sap. We conclude that short-term soil water depletion affecting only 50% of the root system does not cause a measurable stress response in birch shoots, despite root growth cessation in the fraction of drying soil.     

Water relations of loblolly pine seedlings from diverse geographic origins

Leaf conductance at three absolute humidity deficits (AHDs) (7, 14 and 21 g m(-3)), hydraulic conductance and components of tissue water potential were measured in one-year-old loblolly pine seedlings from six origins representing the geographic range of the species. Measurements were made on seedlings grown (a) with ample water (moist regime) and (b) with recurring severe drought (dry regime). However, all seedlings were well-watered prior to and during measurements. Seedlings grown in the moist regime had greater mean leaf conductances (0.30 versus 0.13 cm s(-1)) and greater responses to AHD than seedlings grown in the dry regime. They also exhibited greater hydraulic conductances (0.53 versus 0.35 microg cm(-2) s(-1) MPa(-1), less negative osmotic potentials (-1.45 versus -1.57 MPa) and higher relative water contents at turgor loss (0.72 versus 0.65). Seed source differences in water relations characteristics were detected only in seedlings grown in the moist regime. In these, trees from the three interior origins had greater mean leaf conductances than those from the three coastal sources (0.32 versus 0.28 cm s(-1)), but no differences in response to changing AHD were observed. Seedlings from North Carolina had lower osmotic potentials at turgor loss than those from Florida, Georgia or Texas. These differences in water relations characteristics are not clearly related to the observed greater survival ability of trees from interior origins compared with those from coastal origins.     

Phosphorus Enhanced Establishment,Growth, Nutrient Uptake,and Productivity of Dalbergia sissoo Seedlings Maintained at Varying Soil Water Stress Levels in an Indian Arid Zone

We assessed interactive effects of varying levels of applied phosphorus fertilizer and water stress on growth, productivity, and mineral accumulation in container-grown Dalbergia sissoo L. seedlings. Height, collar diameter, leaf size and area, root volume and total biomass were reduced, and dry matter allocation to root was increased with increasing levels of soil water stress. The reduction was >32% in growth, >50% in leaf, and >77% in biomass when seedlings were grown with <50% of soil field capacity. Phosphorus application at the level of 10 mg kg^?1 soil enhanced stems and leaf biomass and nutrient accumulation at all irrigation levels, and thus tolerance to drought. Phosphorus responses to growth and biomass production increased with irrigation levels. Thus, 20 mg P kg^?1 soil is beneficial at sufficient soil water availability and a lower dose (i.e., 10 mg P kg^?1) is recommended under high soil water stress conditions to benefit growth and productivity of D. sissoo.     

Naphthenic acids inhibit root water transport,gas exchange and leaf growth in aspen (Populus tremuloides) seedlings

Effects of sodium naphthenates (NAs) on root hydraulic conductivity (Lp) and gas exchange processes were examined in aspen (Populus tremuloides Michx.) seedlings grown in solution culture. Exposure of roots to NAs for 3-5 weeks significantly decreased Lp and stomatal conductance. Root-absorbed NAs also decreased leaf chlorophyll concentration, net photosynthesis and leaf growth. Short-term (< or = 2 h) exposure of excised roots to NAs significantly decreased root water flow (Qv) with a concomitant decline in root respiration. We conclude that NAs metabolically inhibited Lp, likely by affecting water channel activity, and that this inhibition could be responsible for the observed reductions in gas exchange and leaf growth.     

Morphological indicators of stock quality and field performance of red oak (Quercus rubra L.) seedlings underplanted in a central Ontario shelterwood

The value of initial stem diameter near the root collar, shoot length and number of first-order lateral roots (FOLR) as morphological indicators of stock quality and field performance was examined for bareroot (1+0, undercut) red oak (Quercus rubra L.) underplanted in a shelterwood in central Ontario. These three attributes were measured on more than 400 seedlings prior to planting, and their relationship with height and basal diameter growth two years after planting was determined using correlation and regression analysis. Initial diameter, shoot length and number of FOLR were positively and significantly correlated with second-year height and diameter. These relationships were strongest for diameter, but this variable explained less than 25% of the total variation in growth. Of the three indicators, diameter was also the best predictor of several physical characteristics of root systems two years after planting. Initial diameter was significantly correlated with root volume, root area and lateral root, taproot and total root dry mass. Weaker relationships existed between initial shoot length and number of FOLR and second-year root system features. Stem diameter two years after planting was more strongly related to root volume, area and dry mass than was initial diameter, the probable result of adjustment in root-shoot balance of planting stock to the shelterwood environment.     

Stomatal conductance, growth and root signaling in young oak seedlings subjected to partial soil drying

Leaf conductance, water relations, growth, and abscisic acid (ABA) concentrations in xylem sap, root apices and leaves were assessed in oak seedlings (Quercus robur L.) grown with a root system divided between two compartments and subjected to one of four treatments: (a) well watered, WW; (b) half of root system exposed to soil drying and half kept well watered, WD; (c) whole root system exposed to drought, DD; and (d) half of root system severed, RE. Sharp decreases in plant stomatal conductance, leaf water potential, hydraulic conductance and leaf growth were observed during DD treatment. No significant differences in plant leaf water potential and stomatal conductance were detected between the WW and WD treatments. Nevertheless, the WD treatment resulted in inhibition of leaf expansion and stimulation of root elongation only in the well-watered compartment. Abscisic acid concentrations did not change in leaves, root tips, or xylem sap of WD- compared to WW-treated plants. Increased concentrations of ABA were observed in xylem sap from DD-treated plant roots, but the total flux of ABA to shoots was reduced compared to that in WW-treated plants, because of decreases in transpiration flux. Similar plant responses to the WD and RE treatments indicate that the responses observed in the WD-treated plants were probably not triggered by a positive signal originating from drying roots.     

Water movement in yellow-cedar seedlings and rooted cuttings: comparison of whole plant and root system pressurization methods

One-year-old yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) seedlings and rooted cuttings were taken from cold-storage facilities and grown in aerated water in a controlled environment room for 21 days. Root areas of seedlings and rooted cuttings were initially comparable, but after 21 days seedlings had produced more than twice as much new root area as rooted cuttings. Water flow resistance through the plant-atmosphere continuum decreased in both stock types over the 21-day period. In both seedlings and rooted cuttings, transpirational flux density increased in a curvilinear manner as new root area increased. Root resistance to water movement decreased sharply with increasing new root area up to 20 cm(2) in both seedlings and rooted cuttings. Further increases in new root area did not result in further changes in root resistance of either stocktype. Plant water movement was measured by both the whole plant and the root system pressurization methods with results differing between the two techniques.