Growth, nutrition, photosynthesis and transpiration responses of longleaf pine seedlings to light, water and nitrogen

Early growth and physiology of longleaf pine (Pinus palustris Mill.) seedlings were studied in response to light, water and nitrogen under greenhouse conditions. The experiment was conducted with 1-year-old seedlings grown in 11.3 l pots. The experimental design was a split-plot factorial with two levels (low and high) of each of the factors, replicated in three blocks. The four factorial combinations of water and nitrogen were randomly applied to 15 pots (sub-plots) in each of the light treatment (main plot). Data were collected on survival, root collar diameter (RCD), and height on a monthly basis. Biomass (shoot, root and needle), leaf area index, specific needle area, and needle nutrient (N, P, K, Ca, and Mg) concentrations were determined following final harvest after 16 months. Physiological data (net photosynthesis and transpiration) were collected monthly from March to July during the second growing season.

Height and RCD were significantly influenced by nitrogen and water and by the interaction between them with no apparent effect of light. Seedlings grew 93% taller in the high nitrogen and well watered (HNWW) treatment compared to the low nitrogen and water stressed (LNWS) treatment. Similarly, a significant increase (78%) in RCD was observed for seedlings in the HNWW treatment over the LNWS treatment. Light, along with water and nitrogen, played an important role in seedling biomass growth, especially when water was not limiting. Biomass partitioning (as measured by root:shoot ratio) was affected only by nitrogen and water. Nutrient stress had a greater influence on carbon allocation (69% increase in root:shoot ratio) than water stress (19% increase). Net photosynthesis (P_net) was significantly higher for seedlings in the high resource than in the low resource treatments with significant light×water and nitrogen×water interactions. Transpiration rate was higher (75%) under the WW treatment compared to the WS treatment. Longleaf pine seedlings grown under the LNWW treatment had the lowest foliar nitrogen (0.71%) whereas seedlings in the HNWS treatment had the highest (1.46%). Increasing the availability of light (through larger canopy openings or controlling midstory density) and soil nitrogen (through fertilization) may not result in greater P_net and improved seedling growth unless soil water is not limiting.     

Growth and nutrition of nonmycorrhizal and mycorrhizal pitch pine (Pinus rigida) seedlings under phosphorus limitation

The association of ectomycorrhizal fungi with tree roots enhances the acquisition of phosphorus (P) from the soil. In addition to increasing the uptake of H(2)PO(4) (-) (P(i)), mycorrhizal fungi may increase the spectrum of P sources utilized by tree roots by mediating the dissolution of insoluble metallophosphate salts or the hydrolysis of organic P compounds. To investigate the role of ectomycorrhizal fungi in enhancing P acquisition by tree roots, pitch pine (Pinus rigida Mill.) seedlings were grown in sand culture with or without the ectomycorrhizal symbiont Pisolithus tinctorius Coker and Couch under various conditions of P limitation. Compared with nonmycorrhizal seedlings, seedlings inoculated with P. tinctorius exhibited a greater capacity to function under P limitation as evidenced by superior growth and the maintenance of normal foliar ion composition at low P(i) concentrations. Nonmycorrhizal seedlings subjected to P-limiting conditions exhibited depressed K and P and elevated Na concentrations in foliage. The association of P. tinctorius with pitch pine seedling roots maintained foliar K concentrations and prevented the accumulation of Na under P limitation. Nonmycorrhizal seedlings were unable to obtain P from either solid AlPO(4) or inositol hexaphosphate (IHP), whereas seedlings inoculated with P. tinctorius utilized AlPO(4), but not IHP as a P source. Root surface acid phosphatase (APase) activity was depressed in roots infected with the mycorrhizal symbiont and was negatively correlated with seedling growth on all P sources. Root APase activity was negatively correlated with foliar P concentrations in seedlings grown on P(i), but was not correlated with foliar P concentrations in seedlings cultured with AlPO(4) or IHP.     

Growth,morphology and gas exchange responses of two-year-old Quercus castaneifolia seedlings to flooding stress

Tolerance to flooding is crucial when thinking in promissory species for restoration of ecosystems prone to suffer soil water excess. In this study, we tested the flooding tolerance of two-years-old seedlings of Chestnut-leaved oak (Quercus castaneifolia C.A.Mey.) to determine whether it can be recommended for use in wetland restoration programs. Seedlings of Q. castaneifolia were subjected to three treatments: (1) control (C), (2) flooding for 60 days followed by a 42-day recovery period (F?+?R) and (3) continuous flooding for 102 days (F). Physiological performance, plant morphological changes and biomass accumulation were assessed. Results showed that, although net photosynthetic rates, stomatal conductance and transpiration decreased with prolonged flooding, when flood waters were removed, plants were able to recover their physiological activity (49–80% compared to controls). By contrast, when plants were continually flooded, their physiological activity decreased as well as the leaves experienced precocious senescence and wilting. Biomass responses paralleled physiological responses: leaf and root biomass were 42–49% higher under F?+?R treatment than under continuous flooding, and all plants under the F?+?R survived. Therefore, Q. castaneifolia appears as a promising species to be further studied when thinking re-vegetation of riverine areas and other temporarily flooded wetlands.     

Acid phosphatase activity and phosphorus nutrition in Scots pine needles

From March to October, acid phosphatase activity and phosphorus (P) concentration were measured in four needle age classes of the upper and lower crowns of fertilized and unfertilized Scots pine (Pinus sylvestris L.) trees. Negative correlations between acid phosphatase activity and P concentration were observed in current-year needles and in needles in the upper part of the crown, whereas there was a positive correlation between enzyme activity and P concentration in older needles and in needles in the lower part of the crown. In May and October, needles of all ages showed increased acid phosphatase activity. The most sensitive response of acid phosphatase activity to phosphate supply and phosphorus status of the whole tree was seen in current-year needles on the first whorl where a 300% increase in acid phosphatase activity was observed in response to a decrease in foliar P concentration of 1.7-1.8 mg P g(DW) (-1).     

Growth responses of red pine seedlings to the chemical bioregulator,DCPTA

The chemical bioregulator, 2-(3, 4-dichlorophenoxy)-triethylamine (DCPTA), which has markedly stimulated photosynthesis, carbon allocation, and above- and below-ground growth of several agricultural crops, caused small growth effects on red pine (Pinus resinosa L.) germinants and one and two-year-old seedlings, mainly to foliage and stems. At low DCPTA concentrations, i.e. 10 ppm, growth tended to be promoted, whereas at 100 ppm growth appeared to be suppressed. Continued testing of the bioregulator's effect on growth and physiology of other tree species is recommended.     

Blister rust in maritime pine

Maritime pine (Pinus pinaster Ait.) seedlings from four stands of central Italy were inoculated with a suspension of 75,000 basidiospores/ml. Significant differences among the stands were found for the following traits: percentages between nonspotted and inoculated seedlings; and percentages between seedlings with spermagonia of Cronartium flaccidum and spotted seedlings. Genetic variation in blister rust resistance among the stands and among the families within a stand confirms the validity of the idea to select the stands which are exposed to heavy rust infection and then within the selected stands to choose trees able to supply the highest possible number of nonspotted seedlings and seedlings with needle spots but without spermagonia.     

Photosynthetic responses of cottonwood seedlings grown in glacial through future atmospheric [CO2] vary with phosphorus supply

Plants often exhibit proportionately larger photosynthetic responses to the transition from glacial to modern [CO(2)] than from modern to future [CO(2)]. Although this pattern may reflect increased nutrient demand with increasing [CO(2)], few studies have examined the role of nutrient supply in regulating responses to the range of [CO(2)] from glacial to future [CO(2)]. In this study, we examined the effects of P supply (0.004-0.5 mM) on photosynthetic responses of Populus deltoides (cottonwood) seedlings to glacial (200 micromol mol(-1)), modern (350 μmol mol(-1)) and future (700 micromol mol(-1)) [CO(2)]. The A(sat) (light-saturated net photosynthetic rates at the growth [CO(2)]) response to future [CO(2)] decreased with decreasing P supply such that there was no response at the lowest P supply. However, P supply did not affect A(sat) responses to an increase from glacial to modern [CO(2)]. Photosynthetic capacity [e.g., final rubisco activity, apparent, maximal Rubisco-limited rate of photosynthesis (V(cmax)), apparent, maximal electron transport-limited rate of photosynthesis (J(max))], stomatal conductance (g(s)) and leaf P generally increased with increasing P supply but decreased with increasing [CO(2)]. Measures of carbohydrate sink capacity (e.g., leaf mass per unit leaf area, leaf starch) increased with both increasing P supply and increasing [CO(2)]. Changes in V(cmax) and g(s) together accounted for 78% of the variation in A(sat) among [CO(2)] and P treatments, suggesting significant biochemical and stomatal controls on photosynthesis. However, A(sat) responses to increasing [CO(2)] did not reflect the changes in the carbohydrate sink capacity. These results have important implications because low P already constrains responses to increasing [CO(2)] in many ecosystems, and our results suggest that the P demand will increasingly affect A(sat) in cottonwood as [CO(2)] continues to increase.     

Interactive effects of P-Cu fertilizers on growth and mineral nutrition of maritime pine

The interaction between copper and phosphorus was studied in a pot experiment involving a factorial combination of three levels of copper and three levels of phosphorus applied to maritime pine seedlings growing in podzolic sand.Biomass measurement showed that a single copper fertilization could be toxic to the plant and that better growth was obtained with a combination of both phosphorus and copper fertilization. Copper toxicity was shown to be dependent on phosphorus levels in the plant, and better growth was obtained with an appropriate balance between phosphorus and copper concentrations. A reciprocal inhibition between phosphorus and copper uptake was assumed to explain this pattern.     

Osmotic adjustment in three-year-old seedlings of five provenances of maritime pine (Pinus pinaster) in response to drought

Three-year-old seedlings of five provenances of Pinus pinaster Ait. that differed in climatic conditions at their geographical origin were subjected to decreasing soil water availability. The degree of needle osmotic adjustment (OA) was estimated based on logarithmic plots of needle relative water content (RWC) against needle osmotic potential (Psi(pi)); i.e., lnRWC versus -ln(-Psi(pi)). There were significant differences among provenances in active OA (0.13 to 0.30 MPa for a decrease in RWC to 80%), and a clear negative relationship was found between OA and precipitation (650 to 1280 mm of mean annual rainfall) at the geographical origins of the provenances. A high osmoregulatory capacity contributes to the maintainance of positive turgor at low water potentials. We conclude that OA is one of the mechanisms underlying adaptation to drought in P. pinaster. Solute accumulation was about 2.3 times higher in the provenance from the driest site than in the provenance from the wettest site. The contribution of osmotic adjustment to differences in drought tolerance mechanisms among provenances is discussed.     

Maturation of maritime pine (Pinus pinaster Ait.) seedlings after exposure to a period of continuous light

Nine half-sib families of maritime pine (Pinus pinaster Ait.) of known adult performance were grown in continuous light at either 25 degrees C or 25/20 degrees C for 18 weeks. They were then exposed to a dormancy induction period followed by a dormancy release period and then grown for a further 9 weeks in a 16-h photoperiod at a day/night temperature of 25/20 degrees C. Seedlings exhibited great diversity in morphology at the end of the first growth period. The number of morphogenetic cycles varied between one and three and the form of the apical meristem ranged from a typical rosette to an adult-like bud. The type of seedling obtained at the end of the first growth period strongly influenced later growth, independently of the temperature regime. Maturity was proportional to the number of morphogenetic cycles achieved during the first growth period and was characterized by short growth duration, small primary needles and a high degree of fixed growth. The state of the apical meristem that underwent the dormancy period had less influence on the rate of maturation than the number of morphogenetic cycles. The time course of maturation was endogenously controlled and varied among traits. Conspicuous morphological differences were not associated with changes in the relationship between growth components at the phenotypic level. However, there seemed to be a shift in the genetic correlations between growth components after first budset.     

不同光照条件下红松幼苗光合作用诱导反应的研究

无论光通量密度(PPFD)为200靘ol穖-2穝-1还是500靘ol穖-2穝-1,生长在林冠下的红松幼苗光合速率达稳定净光合速率的50%和90%的诱导时间均长于全光条件下生长苗木。全光下生长的红松幼苗在PPFD为500靘ol穖-2穝-1时的诱导反应较PPFD为200靘ol穖-2穝-1时缓慢,而林冠下生长苗木则恰好相反。表明林冠下生长红松幼苗的光合作用诱导期与光斑强度有关。图3参6。     

Photosynthetic acclimation of shade-grown red pine (Pinus resinosa Ait.) seedlings to a high light environment

Photosynthetic light acclimation in red pine (Pinus resinosa Ait.) seedlings was examined in a greenhouse study to better understand the physiological response of this species to increased light intensity following release from competition. Seedlings grown in a high (HL), medium (ML) or low (LL) light environment for 12 weeks were transferred to high light. Gas exchange and chlorophyll fluorescence of ML and LL seedlings were measured prior to and following transfer and compared with the HL control treatment. Photosynthetic characteristics were related to initial light treatment and time after transfer. Acclimation of gas exchange features to high light in shade formed ML and LL foliage was relatively rapid, with similar values among light treatments within 57 days of transfer. Acclimation of net photosynthetic rate was similar in ML and LL seedlings, and was associated primarily with increased mesophyll conductance to CO₂. The ratio of variable to maximal chlorophyll fluorescence (F_v/F_m) decreased initially after transfer, especially in LL seedlings, but recovered to normal values after 57 days. Red pine seedlings appear to be well adapted for photosynthetic acclimation to high light intensity, consistent with that reported for other early successional tree species.     

Transverse shrinkage in maritime pine juvenile wood

Summary This paper reports experimental results concerning the transverse shrinkage variability within and between trees of two samples composed of 17 eleven-year-old and 20 twenty-year-old maritime pine trees harvested in two stands at the Forest Research Centre of INRA Pierroton in Aquitaine. The within tree variations are divided into a height effect and a radial effect, both related to the occurrence of juvenile wood. It is shown that the tangential shrinkage and the anisotropic ratio between radial and tangential dimensional variations are increasing from the top to the base of the stems (+14.9% and +16.9%, respectively), and that this effect is independent of the tree. The variations from the pith outward are also significant for these parameters (+25.0% for at and –9.5% for the ratio) and for the radial shrinkage (+37.2% ), but in this case, the amplitude of the effect is depending on a tree effect. The relationship between shrinkage and density is also studied, showing poorly significant correlation when considering each sampling positions independently.     

Micronutrient distribution in 16-year-old maritime pine

Concentrations and contents of the micronutrients Fe, Mn, Zn, Cu, and B were measured in various tree compartments of a 16-year-old stand of maritime pine (Pinus pinaster Soland in Ait.). The micronutrients were actively redistributed within the tree. The longer-lived aerial tissues, trunks and branches, constituted the major micronutrient reservoirs, with the exception of manganese which accumulated in the needles.     

Physiological and morphological responses to nitrogen limitation in jack pine seedlings: potential implications for drought tolerance

The morphological and physiological responses to nitrogen (N) limitation in jack pine (Pinus banksiana Lamb.) seedlings were studied following the initiation of four different dynamic N treatments for six and 15 weeks. The N treatments produced needle N concentrations from 11 to 31 mg g^-1dry weight, and seven-fold difference in dry weight at 15 weeks. Low-N jack pine seedlings: 1) had an higher root/shoot ratio; 2) extended their tap root more rapidly; 3) were better able to maintain turgor when shoot water potential declined; and 4) had a larger dry weight fraction and apoplasmic fraction than seedlings with higher foliar N concentrations. These responses may contribute collectively to enhance drought tolerance in N-limited plants, thereby affecting seedling quality. Modifying nursery fertilization regimes, other than optimal as usually applied, may thus be needed to produce stock for use on particularly droughty sites. Knowledge of the nature of drought at a particular site could be an important consideration when making decisions related to fertilization.     

Photosynthetic responses to lightflecks ofFagus crenata seedlings grown in a gap and understory of a deciduous forest

Photosynthetic responses to a series of 1-min lightflecks (1,000μmol m⁻² s⁻¹) superimposed on a background with different duration (1, 5, and 10 min) and intensity (25 and 50μmol m⁻² s⁻¹) of low background photosynthetic photon flux density (PPFD) were measured in the leaves ofFagus crenata grown in a gap and understory of aFagus crenata forest in the Naeba Mountains. The two background PPFD intensities most frequently occurred in understory and gap sites respectively. The maximum net photosynthetic rate (P _Nmax) and maximum stomatal conductance (g _smax) were higher in the gap seedlings than in the understory seedlings. However, when the background PPFD was 25μmol m⁻²s⁻¹, the net photosynthetic rate (P ₂₅) and stomatal conductance (g _s25) were almost the same between the gap and understory. When the background PPFD duration was 1-min, the net photosynthetic rate (P _N ) at the end of each lightfleck increased progressively. When the background PPFD duration was 5- and 10-min, the increase inP _N at the end of each lightfleck was less. This indicates that background PPFD duration is important to photosynthetic responses to lightflecks. The higher ratios ofP ₂₅/P _Nmax andg _s25/g _smax in the understory seedlings indicate that the understory seedlings can maintain relatively lower levels of biochemical and stomatal limitations than the gap seedlings under low light conditions. The ratios ofP _N /P _Nmax at the end of each lightfleck (IS) and light utilization efficiency of single lightflecks (LUE _s) that showed the influence of lightflecks on carbon gain were higher in the understory seedlings than in the gap seedlings when the background PPFD was 25μmol m⁻² s⁻¹. This means that understory seedling are capable of utilizing fluctuating light more efficiently under low light conditions than the gap seedlings although the net carbon gain of single lightflecks (CG _s) in the understory seedlings was not higher than that in the gap seedlings. There were no significant differences inIS andLUE _s between understory seedlings at a background PPFD of 25μmol m⁻² s⁻¹ and gap seedlings at a background PPFD of 50μmol m⁻² s⁻¹. However,CG _s in gap seedlings was higher than in understory seedlings. These results provide more evidence thatF. crenata acclimate to a natural light environment in respect to relative induction state at low background PPFD and can capture the fluctuating light at the same efficiency in both the gap and understory seedlings under natural light environments. This study was funded by the research project, Evaluation of Total CO₂ Budget in Forest Ecosystems, coordinated by the Ministry of Agriculture, Forestry and Fisheries of Japan.     

Early frost damage on Sitka spruce seedlings and the influence of phosphorus nutrition

A frost on 8 September 1972 caused widespread damage to youngSitka spruce (Picea sitchensis (Bong.) Carr.) plantations. Inan experiment designed to examine the interaction of climateand P nutrition on the growth of young transplants in southScotland damage was greater on plants growing at low elevationand with high P content. This effect was attributed to theirextended growth period compared to those with low P supply.The lack of low temperatures prior to the frost resulted ininsufficient hardening of tissues to avoid damage from relativelyhigh temperatures. Damage and recovery were assessed by thereduction in height and dry weight increase compared to undamagedplants.     

Growth and visible responses of Scots pine (Pinus sylvestris L.) seedlings to simulated summer frost

Scots pine seedlings, 20–30 days old, were exposed to simulated summer frost in controlled environment growth chambers. The responses observed showed extreme variation between individual seedlings; seedlings suffering from needle-necrosis, healthy-looking, and dead seedlings were found in the same treatment. Four days exposure to temperatures below –4.5°C caused multiple-leaders maximally in 7.7 % of the pine seedlings and resulted in decreased shoot and root dry weight and shoot length.     

Nitrogen availability modifies the ozone responses of Scots pine seedlings exposed in an open-field system

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were exposed to either ambient or elevated (1.5-1.6 x ambient) ozone concentration ([O3]) for three growing seasons in an open-field fumigation facility where they were irrigated during the growing season with a nutrient solution providing nitrogen (N) at 70 (LN treatment), 100 (control) or 150% (HN treatment) of the optimum supply rate. Treatment effects were most evident during the third year of exposure, when the ambient [O3] + HN treatment enhanced whole-plant biomass, root/shoot dry weight ratio, needle pigment concentrations and the number of chloroplast plastoglobuli in the mesophyll cells in current-year (C) needles, whereas it reduced starch accumulation in C needles and abscission of 2-year-old (C+2) needles. In the control fertilization, 3 years of exposure to elevated [O3] decreased stem-base diameter and increased K concentration and electron density of chloroplast stroma in C needles. Plants in the HN treatment exposed for 3 years to elevated [O3] had significantly lower heights, current-year main shoot length and root/shoot dry mass ratio than control plants, and increased abscission of C+2 needles. In contrast, O3-induced changes in the ultrastructure of mesophyll cells were most evident in seedlings grown for 3 years in the LN treatment. We conclude that, in Scots pine, a relatively O3-tolerant species, chronic O3 exposure leads to cumulative growth reduction, increased needle abscission and changes in carbon allocation that are strongly influenced by plant N availability.