No abstract

Seedlings of several conifer species were artificially subjected to freezing temperatures. Microscopic examination of sections, taken at intervals after the frost, revealed the way in which frost rings developed. Differentiating tracheids and xylem mother cells were killed by the frost, leaving a permanent band of underlignified and crumpled tracheids inside a band of dead cell tissue. Most of the cambial initials remained alive but developed abnormally into short irregular tracheids. Parenchyma cells proliferated mainly from the xylem ray cells. With subsequent growth, the growing stresses, which had become subnormal because of the collapse of killed cells, were restored. This was accompanied by the reestablishment of the cambium to its normal form.

-Picea mariana (Mill.) B.S.P. seedlings were hardened for overwintering under four regimes. In three regimes, seedlings were kept inside a heated greenhouse for 11 weeks during and after dormancy induction (August to mid-November), with either 1. Natural daylengths (46°31' N) and warm temperatures of 20 °C or more (NDW), 2. As 1, but fertilized (NDWF) or 3. As 1, but with shortened daylengths (SD). In the fourth regime (OD), seedlings were hardened outside at naturally declining temperatures and daylengths without fertilizer. Seedlings hardened in any warm temperature treatment had buds with more needle primordia and shoots more resistant to desiccation than OD seedlings. Initially, cold hardiness tended to be greatest in SD seedlings. As hardening progressed OD seedlings became equally cold hardy to SD. In late November when all trees were outside, NDW seedlings were usually least cold hardy. Spring root growth potential was least in OD seedlings.cold hardiness / desiccation / needle primordia / transpiration / water potential Résumé -Effets de la longueur du jour, de la température et de la fertilisation sur la résistance à la dessiccation et au froid, et au potentiel de croissance de plants de Picea mariana. On a soumis des semis de Picea mariana (Mill.) à quatre traitements pour les endurcir au froid en vue de la période hivernale. Pour trois traitements les plants ont été installés sous serre chauffée pendant 11 semaines, pendant et après l'induction de la dormance, avec les 3 modalités suivantes : (1) longueur naturelle du jour (latitude 46° 31' N) et chauffage à une température égale ou supérieure à 20 °C (NDW); (2) comme le traitement 1, mais avec fertilisation (NDWF); (3) comme le traitement 1 mais en jours courts (SD). Pour le quatrième traitement (OD) les plants ont été endurcis à l'extérieur avec la baisse de température et la diminution de la longueur des jours des conditions naturelles, sans faire appel à une fertilisation. Les plants issus des traitements comportant une phase sous serre chaude présentaient des bourgeons ayant davantage d'ébauches foliaires et des pousses plus résistantes à la dessication que les plants du traitement OD. Dans un premier stade, l'endurcissement au froid des plants SD tendait à être plus élevé. Ultérieurement celui des plants OD est devenu équivalent à celui des SD. Fin novembre, tous les plants étaient à l'extérieur, les plants NDW étaient moins résistants au froid. Le potentiel de croissance racinaire au printemps était moins élevé pour les plants OD. endurcissement pour la résistance au froid / dessication / ébauche racinaire / transpiration / potentiel hydrique

Five Pinus banksiana (Lamb.) seedlings were fed 50 μCi of 14CO2 (1 Ci = 37 GBq) per seedling in August and at 2-week intervals another set of five trees was fed until December for a total of 10 feedings. Trees of each set were sampled from January to June, in their dormant frost hardy phase and in their growing phase. Sampled trees were separated into needles, bark, xylem, and roots, freeze-dried, and ground. Samples of ground tissues were extracted sequentially for saponifiable and nonsaponifiable lipids, starch, lignin, hemicelluloses, and cellulose. Some protein, amino acids, and sugars were also extracted.In the dormant trees the total amount of 14C in the tissues decreased from August to December except for the needles where it increased towards December. Considerable amounts of 14C occurred in the structural components of the early feedings. The 14C distribution among the chemical components within the tissues was fairly similar over the entire feeding period except for an increase in root starch, xylem lipids, and sugars. No 14C occurred in the amino acids. A drastic reduction in 14C occurred with the onset of growth from all chemical components and little 14C occurred in the new growth.The photosynthate produced during the autumn contributes substantially more to respiration than to the buildup of reserves. In conifers the important forms of food reserves are carbohydrates and lipids. There is an increase in lipid synthesis in early fall which is chiefly restricted to the xylem. All tissue components of the tree are important for storage of food reserves but they are not of equal importance simultaneously. Food reserves do not play a direct role in wood formation of the secondary meristem which is dependent on current photosynthate. Some hemicelluloses appear to be a form of food reserve in trees.

P. 1989, Winter hardening in first-year black spruce (Picea mariana) seedlings, Physiol, Plant, 76: 1-9, Winter hardening of first-year black spruce [Picea mariana (Mill,) B,S,P,] seedlings was studied by assessing a nutnber of morphological and physiological changes under three hardening regimes: 1) early removal (ER), in which seedlings were exposed to natural daylengths and low ambient temperatures outside, 2) extended greenhouse culture (EG), in which seedlings were exposed to natural daylengths and warm temperatures, and 3) short day (SD), in which seedlings were exposed to short daylengths and low ambient temperatures outside. Measurements included needle primordia initiation, embryonic shoot volume, terminal bud mitotic index, embryonic shoot average cell volume, and shoot tip frost hardiness, EG seedlings formed buds containing 4 times as many needle primordia as ER stock. Embryonic shoot volume increased with number of needle primordia initiated, until late in the hardening period, when significant reductions in meristem volumes of SD and EG stock were observed. Frost hardiness increased sooner in seedlings which set bud in response to short days, but SD treatment did not result in significantly greater frost hardiness at the end of the trial. Frost hardiness was correlated with mitotic index of the embryonic shoot. Cell size in the embryonic shoot declined in seedlings of all treatments during hardening, however, EG seedlings had significantly lower cell volumes by the end of the trial in comparison to ER and SD seedlings.

Greenhouse-grown black spruce and jack pine container seedlings were fertilized weekly with a 20–8–20 fertilizer at four concentrations during the fall. Seedlings were sampled when 23 weeks old towards the end of the greenhouse cultural period to determine the effect of fertilization on the free amino acid concentrations. All amino acids, except tryptophan, showed significant increases in concentration with higher levels of fertilizer; the concentration of tryptophan decreased with increasing fertilizer concentration. Amino acids with the highest concentrations in black spruce were arginine, glutamic acid, and proline, while in jack pine, besides these three, aspartic acid and glutamine were also found in high concentrations. Black spruce had significantly higher amino acid concentrations than jack pine. The concentrations of certain free amino acids may be more sensitive indicators of seedling nitrogen status than total foliar nitrogen.

We investigated the effects of a 4-week exposure to an 8-h or 18-h photoperiod at 5 or 25 degrees C on the development of hardiness to -20 degrees C and the accumulation of proline (Pro), arginine (Arg) and tryptophan (Trp) in shoots of black spruce (Picea mariana (Mill.) B.S.P.) seedlings. The greatest degree of hardening to -20 degrees C occurred in seedlings exposed to an 8-h photoperiod at 25 degrees C, and some hardening occurred in seedlings exposed to 5 degrees C in either an 8-h or 18-h photoperiod. Proline accumulated in shoots in response to 5 degrees C and either an 8-h or 18-h photoperiod, whereas Trp accumulated in response to an 8-h photoperiod at either temperature, and Arg only accumulated in shoots in the 5 degrees C + 8-h photoperiod treatment. Only the accumulation of Trp was significantly related to the degree of hardiness to -20 degrees C.

The electrical impedance of 1-year-old twigs of three hardwoods and conifers was measured at several frequencies before and after boiling. In all species the impedance before killing decreased as frequency increased from 100 to 40 000 c.p.s. The rate of decrease in conifers was greater than in hardwoods, particularly at low frequencies. After the twigs were killed, the drastically reduced impedance exhibited only a slight dependence on frequency. The variability relative to the mean was about the same at all frequencies.The contribution of xylem and bark (i.e., periderm, phloem, and cambium combined) to the impedance was determined by measuring the impedance of the two tissues together and separately. The importance of uniform electrode penetration was demonstrated.