Barrett C. Wilson

Quality Assessment of Temperate Zone Deciduous Hardwood Seedlings

Research regarding seedling quality issues has been performed for decades and focused primarily on conifer species, which comprise the greatest proportion of nursery production worldwide. Demand for hardwood seedlings, particularly for conservation purposes, has increased steadily in recent years, emphasizing the need for seedling quality assessment protocols specific to these species. Important differences between conifer (gymnosperm) and hardwood (angiosperm) species require the creation of seedling evaluative programs specific to each group. Variation in phenology and ecological adaptability of hardwood species limits the validity of inferences made between and within genera. Annual cycles of leaf emergence followed by abscission in temperate hardwoods necessitate examination of seasonal variation in indicators of physiological condition that do not require leaf tissue (e.g., mineral nutrition, electrolyte leakage). Also, it is crucial to identify appropriate sampling periods and plant tissues for testing such that test results may be accurately compared. Though certain parameters (e.g., morphological) may be readily used in both conifer and hardwood seedling quality testing programs with little modification, additional refinement is needed to improve predictive capacity for hardwoods across a variety of environments. We review the current state of knowledge regarding seedling quality testing of temperate deciduous hardwood species, discuss limitations in incorporating traditional components of quality testing programs, and set priorities for future study.

Short-day treatment alters Douglas-fir seedling dehardening and transplant root proliferation at varying rhizosphere temperatures

We tested effects of shortened day length during nursery culture on Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) seedling development at dormancy release. Seedlings from a 428N source were grown either under ambient photoperiods (long-day (LD)) or with a 28 day period of 9 h light: 15 h dark photoperiods (short-day (SD)). Seedlings were periodically removed from freezer storage from January to May. Sensitivity of plant tissues to cold temperatures was investigated via electrolyte leakage at nine test temperatures ranging from 2 to -40 8C. New root growth was assessed with rhizosphere temperatures of 10, 15, 20, and 25 8C. From 2 to -13 8C, there was no difference between treatments in cold hardiness. However, at or below -18 8C, LD seedlings exhibited higher indices of damage than SD seedlings. The LT50 (temperature at which 50% cell electrolyte leakage occurred) was consistently lower for SD than LD seedlings. Rhizosphere temperature differentially influenced new root proliferation: LD seedlings had greater new root pro- duction than SD seedlings at 20 8C, whereas the opposite response was detected at 10 8C. Our results confirm photoperiod sensitivity of Douglas-fir sources from relatively low (i.e., <458N) latitudes. Increased spring cold hardiness and greater rooting at lower rhizosphere temperatures may improve field performance potential of SD-treated seedlings.

Cold hardiness and transplant response of Juglans nigra seedlings subjected to alternative storage regimes

Abstract• Effects of overwinter storage regimes on seedling cold hardiness and physiological vigor are relatively unexplored, particularly for temperate deciduous forest tree species.• We evaluated influence of storage duration (0, 66, 119, or 175 d) on electrolyte leakage of stem and root collar tissues following exposure to a series of freeze-test temperatures in black walnut (Juglans nigra L.) seedlings sampled from cold (3 °C) or freezer (−2 °C) storage. Seedlings were subsequently transplanted into a controlled growth chamber environment for two months.• Regardless of storage temperature, mean LT50 was lowest for seedlings stored for 66 d (≤ −34 °C) and increased dramatically after 119 d (≥ −13 °C).• Root collar tissue had lower LT50 than stem tissue after 119 d for cold-stored seedlings, reflecting importance of evaluative tissue type. Days to bud break shortened with increasing storage duration up to 119 d and stabilized thereafter for both storage regimes. Root growth potential was maximized after 119 d of storage, and subsequently declined for cold-stored seedlings. Height growth increased following storage, regardless of duration.• To promote stress resistance and transplant growth response, we recommend that black walnut seedlings from this genetic source be outplanted after approximately 66–119 d of storage.Résumé• Les effets de différentes modalités de stockage hivernal sur la résistance au froid des semis et sur leur vigueur physiologique ont été relativement inexplorés, en particulier pour les arbres forestiers décidus tempérés.• Nous avons évalué l’influence de la durée de stockage (0, 66, 119 ou 175 jours) sur la perte d’électrolyte de la tige et des tissus du collet racinaire exposés à une série de tests (témoin 4 %C, −10 °C, −20 °C, −40 °C) de température de congélation de semis de noyer noir (Juglans nigra L.), après stockage au froid (3 °C) ou au gel (−2 °C). Les semis étaient ensuite transplantés dans une chambre climatisée pour une durée de deux mois. Indépendamment de la température de stockage, la moyenne de LT50 (température létale correspondant à un endommagement de 50 % des plants) a été plus basse pour les semis stockés pendant 66 jours (≤ −34 °C) et s’est accrue de façon spectaculaire après 119 jours (≥ −13 °C).• Les tissus du collet racinaire avaient un plus bas LT50 que les tissus de la tige, après 119 jours pour les semis stockés au froid, reflétant l’importance du type de tissu pour l’évaluation. Le nombre de jours jusqu’au débourrement a été raccourci avec l’accroissement de la durée de stockage jusqu’à 119 jours et s’est stabilisé par la suite pour les deux modalités de stockage. Le potentiel de croissance racinaire a été maximisé après 119 jours de stockage et a décliné par la suite, pour les semis stockés au froid. La croissance en hauteur s’est accrue à la suite du stockage, indépendamment de sa durée.• Pour promouvoir une résistance élevée au stress et une forte reprise de croissance des semis transplantés, nous recommandons que les semis de noyer noir de cette source génétique soient plantés après approximativement 66 à 119 jours de stockage.

Winter variation in physiological status of cold stored and freshly lifted semi-evergreen Quercus nigra seedlings

Abstract• Water oak (Quercus nigra L.) is a tardily deciduous species commonly planted in afforestation projects in the Lower Mississippi River Alluvial Valley, USA. Field performance is often marked by low survival rates and top dieback, which may be associated with poor physiological quality of planting stock.• We investigated physiological status of cold stored (2–4 °C; CS) and freshly lifted (FL) seedlings during the period between lifting and planting (December — February). In mid-February, seedlings were transplanted into a controlled greenhouse environment for 90 d to evaluate post-transplant growth performance.• Net photosynthetic rates were positive until late January (generally greater in CS seedlings) and became negative thereafter. FL seedlings generally had lower LT50 values from freeze-induced electrolyte leakage (FIEL), reflecting greater cold hardiness. FIEL of foliage provided the best indicator of physiological status, though terminal buds may serve as a suitable substitute. All seedlings experienced top dieback following transplant; CS seedlings had less relative root-collar diameter, height, and root volume increments.• Cold storing seedlings did not appear to prolong dormancy, increase stress resistance, or hold promise as a means to improve outplanting success. Regardless of storage regime, seedlings appeared to be most cold hardy and perhaps stress resistant until late January.Résumé• Quercus nigra L. est une espèce semi décidue, plantée dans les projets de reboisement dans la Basse vallée alluviale du fleuve Mississippi aux Etats-Unis. Les performances en plantation sont souvent marquées par un faible taux de survie et un dépérissement de la flèche du plant, ce qui peut être associé à leur mauvaise qualité physiologique.• Nous avons étudié l’état physiologique de jeunes plants stockés au froid (2–4 °C ; CS) et récemment arrachés (FL), au cours de la période entre l’arrachage et la plantation (Décembre — Février). Á la mifévrier, les plants ont été transplantés pour 90 jours dans une serre climatiquement contrôlée, pour évaluer les performances concernant la croissance après transplantation.• Les taux de photosynthèse nette ont été positifs jusqu’ à la fin janvier (généralement plus élevés pour les jeunes plants CS) et sont devenus négatifs par la suite. Les plants FL ont eu généralement des valeurs LT50 inférieures de perte d’électrolyte induit par le gel (FIEL), reflétant une plus grande tolérance au froid. Le FIEL du feuillage fourni le meilleur indicateur de l’état physiologique, même si les bourgeons terminaux peuvent servir comme un substitut approprié. Tous les plants on présenté une perte des feuilles de la flèche à la suite de la transplantation ; les plants CS avaient un rapport relatif racine-diamètre du collet, une hauteur, et des accroissements du volume de racines, moindres.• Le stockage au froid des plants ne semble pas prolonger la dormance, ni accroître la résistance au stress de transplantation, ou tenir la promesse d’un moyen d’amélioration de la réussite du reboisement. Indépendamment du régime de stockage, les plants semblent être plus tolérants au froid et peut-être plus résistants au stress jusqu’à la fin janvier.

Chlorophyll fluorescence of stem cambial tissue reflects dormancy development in Juglans nigra seedlings

Assessment of chlorophyll fluorescence (CF) of forest tree seedlings can provide important insight into physiological function, dormancy status, and stress resistance. This evaluative tool has been measured routinely using foliage on conifer seedlings to assess seedling physiological status during winter dormancy. Absence of foliage during dormancy has thus far precluded the potential application of CF to seedling quality assessment of temperate deciduous hardwood seedlings. Because stems contain chlorophyll, however, assessment of CF using stem tissue may serve as an effective alternative tissue type to facilitate CF measurements. We collected Juglans nigra L. (black walnut) seed from two provenances (Alabama and Indiana, USA) and subjected 1-year-old container seedlings from these provenances to a simulated hardening regime (i.e., progressively decreasing temperatures and photoperiods) in a growth chamber environment over an 18-week period; CF of stem tissue (evaluated as ΦPSII, efficiency of photosystem II) was sampled periodically at seven time intervals. Though both provenance and measurement period significantly affected ΦPSII, measurement period had a much more pronounced effect. Values for ΦPSII fluctuated (ranging from 0.45 to 0.72) during the simulated growth and hardening regimes, generally decreasing over time for both provenances. Our results suggest that physiological status of temperate deciduous seedlings may be effectively evaluated during dormancy by assessing CF of stem tissue.