Photosynthesis and root respiration of Pinus sylvestris and picea abies seedlings after different root freezing and storage temperatures

Photosynthetic performance and root respiration were measured for seedlings of Scots pine and Norway spruce under constant conditions in an open gas exchange system in the laboratory. Measurements were carried out after root exposure to ‐20, ‐5 and 0°C and subsequent longtime storage in darkness at +1 or +4°C. Stomatal conductance in relation to net photosynthetic rates was also investigated after the same treatment of seedlings. Root respiration was low for seedlings whose root system had been exposed to ‐20°C, Scots pine showing lower rates than Norway spruce. This was probably an indication of root damage. At least for one provenance of Scots pine, respiration rates were higher for seedlings stored at +1 than at +4°C. Photosynthetic performance was also lowest for seedlings whose roots had been exposed to +20°C compared to higher temperatures, the difference being more clear‐cut for Norway spruce than for Scots pine. Storage at +1 gave slightly higher photosynthetic rates than at +4°C. There was a close relation between stomatal conductance measured on individual needles and photosynthetic performance measured on the whole seedling.     

Outdoor winter storage of container stock on raised pallets—effects on root zone temperatures and seedling growth

Containerized seedlings of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) were overwintered on the ground and above ground on pallets. Soil temperatures in elevated containers were lower and showed greater fluctuation than containers on the ground. The lowest temperatures (‐15 to ‐16°C) were observed in containers stored on pallets with little or no snow cover during the winter. Temperatures in the edge rows of containers were lower than interior bed soil temperatures. Lower temperatures were also observed in the top than in the bottom of the container. The storage on pallets resulted in reduced shoot and root growth. Although insulation preventing air movements beneath the container units improved soil temperature conditions and subsequent seedling growth, the best result was obtained when seedlings were stored directly on the ground surface.     

Frost resistance and frost damage in pinus sylvestris seedlings during shoot elongation

No differences were found in the frost resistance of the different‐aged (2–7 weeks) germlings of Scots pine. The critical temperature was ‐6°C to —3°C. A temperature of ‐4°C killed half of the germlings and produced damage in one fifth of the surviving seedlings; the needles turned brown and growth ceased. The frost resistance of the previous year's shoots of two‐year‐old seedlings, measured by the impedance method, decreased during the shoot elongation period from — 10°C to — 4°C. Damage to the current shoots during shoot elongation appeared as deformation and discolouration of the needles and abnormal development or death of the apical bud. The results indicate that frost is not the cause of growth disturbances observed in Finnish nurseries.     

Effect of Scleroderma Spore Density and Age on Mycorrhiza Formation and Growth of Containerized Eucalyptus globulus and E. urophylla Seedlings

Greenhouse trials with containerized Eucalyptus globulus and E. urophylla seedlings were made to determine effective inoculum spore densities (Scleroderma cepa from temperate Australia, and S. citrinum from sub-tropical China) and spore storage conditions (fresh spores or spores stored for 5 years at room temperature or at 4 °C; S. albidum, S. areolatum and S. cepa from Western Australia). Inoculation with 10⁶ or 10⁸ spores/seedling increased eucalypt growth by up to 46% in height and 42% in dry weight compared to non-inoculated seedlings at 12 weeks after inoculation. Mycorrhizal formation was poor at 10² spores/seeding. Spores stored at 4 °C for 5 years were as effective in forming mycorrhizas as freshly collected spores when a standard density of 10⁶ spores/seedling was applied. It is recommended that spore densities ≥10⁴ be used for inoculation of containerised eucalypts and that spores be stored at 4 °C until use.     

Freezing temperatures in the root zone—effects on growth of containerized Pinus sylvestris and Picea abies seedlings

Roots of 1‐year‐old containerized seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were experimentally frozen in December. The seedlings were then grown for 3 weeks in a growth chamber and evaluated with regard to root growth capacity (RGC) and shoot elongation. The subsequent RGC of Scots pine declined as root zone temperatures were lowered from ‐6°C to ‐11°C and from ‐11°C to ‐16°C. Almost no root growth was observed after exposure to ‐20°C. Shoot growth was also negatively affected by low root temperatures but less than root growth. Low root temperatures did not affect Norway spruce as much as Scots pine, although root and shoot growth of Norway spruce were reduced after exposure to the lowest test temperatures (‐16°C and ‐20°C). The length of exposure, ranging between 1 and 8 hours had no effect on subsequent growth.     

Planting performance potential of Pinus sylvestris seedlings as evaluated by root growth capacity and triphenyl tetrazolium chloride reduction methods

Root growth capacity (RGC) and root viability by the reduction of triphenyl tetrazolium chloride (TTC) of Scots pine (Pinus sylvestris L.) seedlings were measured in the winter and spring after freeze‐induced stress (0, ‐10, ‐15, ‐20°C). After freezing, seedlings were also stressed with different storage temperatures, and drying. Field performance during two years at two sites was used to determine the prediction abilities of the two test methods. RGC and TTC differed between the winter and spring tests. Coefficients of variation (CV) for RGC were larger in the winter than in the spring. The opposite applied for TTC. RGC was significantly lower in the winter than in the spring. TTC reduction was lower in the spring than in the winter. RGC‐ and TTC‐values decreased as freezing temperatures were lowered. Correlation coefficients between treatment means of RGC and TTC were low. Coefficients of determination (r ²) of linear regressions of RGC to the field performance attributes, first and second year diameter increment, height increment, and survival, were between 0.30 and 0.40. For TTC the revalues ranged from 0.50 to 0.80. In general, the TTC‐method seemed to be a better indicator of Scots pine seedling performance in the field.     

Effects of nutritional factors on frost hardening in Larix leptolepis (Sieb & Zucc.) Gord.

A method for estimating frost hardiness in seedlings of Larix leptolepis in their first stage of acclimation is demonstrated. Cuttings of the shoot tip were frozen linearly from +2°C to ‐36°C. The viability was determined by TTC‐assay. Data were fitted to a logistic regression model, and hardiness was calculated from the fitting parameters. It was shown that hardiness is influenced by the duration of the fertilizer application period. No effect of the nutrient status of N, P or K in the shoots was found.     

Evaluating methods for storability assessment and determination of vitality status of container grown Norway spruce transplants after frozen storage

ABSTRACT

Autumn sown small seedlings for later transplanting into large containers have been introduced in Swedish forest tree nurseries. Containerized transplants of Norway spruce (Picea abies (L.) Karst.) from three Swedish nurseries were frozen stored during the autumn of 2014 to find out storability and post-storage vitality. Seedling storability was determined by measuring electrolyte leakage after freezing shoots to ?25°C (SE L _diff?25), by measurements of dry matter content (DMC) of seedling shoots and by the commercial molecular test ColdNSure?. Vitality of seedlings after storage was determined by measuring the leakage of electrolytes from shoots (SEL), and seedlings were also tested in regrowth tests. All three methods for storability assessment gave similar predictions, except in one case where DMC showed “not storable” for successfully stored seedlings. Our results indicated that young transplants can be successfully short term stored before reaching the target levels for safe long-term storage of conventional seedlings. Early storage of young transplants resulted in low post-storage survival and vitality expressed as root growth capacity and shoot electrolyte leakage (SEL). A prolonged duration in storage generally resulted in lower survival as well as lower root growth capacity and higher levels of SEL, especially for seedlings stored at earlier dates.     

Longevity of <Emphasis Type="Italic">Juniperus procera</Emphasis> seed lots under different storage conditions: implications for ex situ conservation in seed banks

Juniperus procera Endl. is economically important timber species, but its populations are extremely small and fragmented in its natural habitat, thus, calling for immediate ex situ conservation. Here we examined the effects of seed sources and storage temperature on the longevity of Juniperus procera seed lots through collection and preservation of seeds in seed banks. Seeds were collected from nine sites across the species natural distribution in Ethiopia and stored in four warehouses: modern cold room (5℃), mud house (15℃), concrete block house (17℃ or corrugated iron house (20℃) for 42 months. Every three months, a random sample of stored seeds were drawn and tested for germination. A highly significant variation (p < 0.01) in germination of stored seeds was observed among different storage environments, seed lots, and duration of storage. Over the storage period, seeds stored in the cold room had the highest mean percentage germination, followed by the mud house, corrugated house and blocket house. The cold room (41%) and the mud house (38%) maintained the same level of germination as the intitial germination of the seedlotds (42%). The variation in longevity of stored seeds was significnatly correlated with the initial germination of seed lots (r > 0.80; p < 0.01). Cold storage also resulted in enhancement of germination through its stratification effect that terminated the non-deepphysiological dormancy of juniper seeds. In conclusion, seed lots with good initial germination can be effectively stored in cold room (5℃) up to four years. In the absence of modern cold stores, mud houses can be used as a good alternative to store seeds at local level.     

Chlorophyll fluorescence,root growth potential,and stomatal conductance as estimates of field performance potential in conifer seedlings

After cold storage, conifer seedlings in British Columbia are tested for field growth potential before planting. We compared three tests of performance potential using container-grown seedlings of Douglas-fir, interior spruce, lodgepole pine, and western larch (14 seedlots total). On several autumn dates, seedlings were lifted and stored at −2°C. The following spring we tested stored seedlings for root growth potential (RGP), chlorophyll fluorescence (CF), and stomatal conductance (Gs), and then planted seedlings in nursery beds. We assessed survival and shoot dry weight (SDW) after one growing season. Performance test results were significantly correlated with each other (r ≥ 0.47) but showed different relationships with field performance, which varied with lift date. The best performance predictor was the sum of CF and RGP (R ² = 0.79 for 78 seedlot by lift-date combinations), which minimized the risk of planting poor seedlings and not planting good seedlings. A sum of 83 for CF (Fv/Fm %) and RGP (new roots >1 cm) provided a threshold above which survival and growth were good. For evergreen conifers, Gs was a good performance predictor, but required extra time to measure leaf area. We recommend a combination of CF and RGP to assess vigor of shoot and root systems before planting. Wolfgang D. Binder––Scientist Emeritus.     

Seed storage behavior of <Emphasis Type="Italic">Knema attenuata</Emphasis>, an endemic species of Western Ghats,India

We performed desiccation and storage trials to better under- stand storage behavior of Knema attenuata seeds. Mature seeds with moisture content (MC) of 31% exhibited 73% germination. During the period of desiccation (open lab condition) seeds with MC 23% showed 40% germination. After further drying to MC 21% germination was reduced to 16%. Complete loss in viability resulted when seed moisture was reduced to 18%. The seeds stored at -10°C, 0°C, 10°C and 28±2°C (open lab condition) lost their viability within 10 days. Seeds stored in sealed polythene bags and moist sand retained viability for more days than did seeds stored under all other storage conditions. Sensitivity of seeds to lower temperature and desiccation suggest that the storage be- havior of K. attenuata seeds is recalcitrant. Seeds stored in moist condi- tions can, at best, be stored for a period of two months.     

Calophyllum inophyllum: recalcitrant or intermediate seed?

We studied seed storage behaviour of a multipurpose tree Calophyllum inophyllum (Clusiaseae). Seeds were collected at Roslyn bay (23°7′60″ S, 150°43’60″ E) Central Queensland. Seed drying and desiccation tolerance tests were carried out according to International Seed Testing Association (ISTA) rules. We found C. inophyllum seeds to be recalcitrant and vulnerable to chilling injury, hence, unsuited for cold storage. C. inophyllum seeds maintained their viability for an appreciable period (> 8 months) if stored in warmer environments.     

Temperature step response of dehardening in Pinus sylvestris seedlings

The time constant of the dehardening of one‐year‐old Scots pine (Pinus sylvestris L.) seedlings was studied in three experiments started at different times of the year. The seedlings were transferred from outside to the different controlled conditions in January (Exp. 1), March (Exp. 2) and April (Exp. 3). Changes in the frost resistance of the seedlings were followed on the basis of the temperature response of the specific impedance difference in the shoot. The time constant for dehardening at a temperature of 7.5°C was found to be about 12 days in Exp. 1, about 8 days in Exp. 2, and about 5 days in Exp. 3. the terminal bud burst when the frost resistance of the shoot had risen to about ‐10°C.     

Germination and seedling growth of <Emphasis Type="Italic">Dimorphandra jorgei</Emphasis> MF Silva and <Emphasis Type="Italic">Swartzia macrostachya</Emphasis> Benth. var. <Emphasis Type="Italic">riedelii</Emphasis> Cowan

Dimorphandra jorgei MF Silva (Caesalpinaceae) and Swartzia macrostachya Benth. var. riedelii Cowan (Fabaceae) are tree species from the southern Bahian Atlantic Forest, identified for the restoration of degraded areas. The objective of this research is to study their seed germination and seedling growth to develop simple methods for seedling production in small scale nurseries. Because the species have distinct dormancy and germination characteristics, the seeds were submitted to different treatments. D. jorgei seeds were immersed in hot water, scarified and stored for 12 weeks in the laboratory environment (25°C). S. macrostachya seeds were submitted to different combinations of drying and storage in the laboratory environment or refrigerator (4°C). Seedlings were submitted to two light treatments for 3 months: partial shade (52% of full sun) and full shade (12% of full sun). In D. jorgei, the highest germination occurred for scarified seeds (87%) and for seeds stored for 12 weeks and then scarified (69%). In S. macrostachya the undried control seeds had the highest germination, followed by that of the refrigeration storage treatment, without predrying (99% and 97%, respectively). The average values for the growth parameters were greater in full shade for D. jorgei, while S. macrostachya seedlings showed greater growth rates in partial shade. Two months growth is recommended before D. jorgei seedlings are of the sufficient size and leaf number for field planting. On the other hand, a period of 4 months is recommended for S. macrostachya, due to its relatively slow growth.     

Storability measures of Norway spruce and Scots pine seedlings and assessment of post-storage vitality by measuring shoot electrolyte leakage

As indoor frozen storage is increasing in forest tree nurseries it is important to have accurate methods for assessing seedling storability in autumn and methods to determine post-storage vitality. Storability of spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.) seedlings can be based on determination of dry matter content (DMC) of seedling shoots or by freezing shoots at –25°C and thereafter measure electrolyte leakage (SEL_diff–25). To compare these two methods we stored 1-year-old spruce and pine seedlings at different occasions during the autumn. To test if leakage of electrolytes from shoots (SEL) could indicate deteriorated vitality, we measured SEL at the end of storage. After storage seedling viability was determined in a three-week growth test, measuring shoot and root growth capacity (RGC). Determination of freezing tolerance (SEL_diff–25) before storage had a better ability to predict the outcome of storage compared to the DMC test. Measuring SEL at the end of the frozen storage period accurately indicated seedling vitality. Seedlings with SEL of 0–5% had a high survival rate whereas SEL over 10% indicated low survival and growth capacity after storage. The SEL method has a potential to become a screening test for identifying batches of seedlings that have been damaged during storage in the nursery.     

西南桦种子贮藏试验

本研究设置干燥、布袋与保鲜袋包装以及系列温度处理，开展了3a西南桦种子贮藏试验。结果表明：布袋与保鲜袋处理对西南桦种子贮藏影响极不影响；在常温常规条件下，西南桦种子贮藏3个月即失去生活力，而在常温干燥条件下，西南桦种子贮藏10个月种子发芽率尚未显著下降；在15℃条件下贮藏10个月几乎丧失发芽能力，非常有趣的，西南桦种子在10、5、0℃和－5℃各温度条件下贮藏3a，效果十分理想，10℃似乎是西南桦种子低温贮藏的临界温度。本研究促进了西南桦的扩大栽培和基因资源的保存。     

Overwinter Storability of Conifer Planting Stock: Operational Testing of Fall Frost Hardiness

Operational stock-testing facilities that estimate overwinter storability of seedlings (ability to survive and grow after storage) need a reliable method that provides fast results to forest nurseries. We compared three methods using container-grown seedlings of Douglas-fir, interior spruce, lodgepole pine, and western larch from forest nurseries in British Columbia. On three to nine dates in autumn, frost hardiness at −18°C was estimated using visible injury of foliage or stems (VI), electrolyte leakage from needles or stems (EL), and chlorophyll fluorescence of shoots (CF). Seedlings were placed into overwinter cold storage (−2°C). In the spring, stored seedlings were planted in nursery beds; survival and growth were assessed after one growing season. There were close correlations (r ≥ 0.93) between the assessment methods. Seedlings lifted after they reached thresholds of 69% or higher for CF and 25% or lower for EL and VI had over 90% survival at harvest and doubled shoot dry weight compared with seedlings lifted earlier. Measuring CF was the fastest and most easily replicated method to estimate successful storability, and reduced testing time by 6 days relative to VI tests.     

The effect of photosynthetic photon flux density on development of frost hardiness in top and roots of Larix leptolepis seedlings

Seedlings of Larix leptolepis were grown in a growth chamber under short day conditions (8 h day) at 4 different photosynthetic photon flux densities (PPFD's). After a period of 8 weeks frost hardiness of the shoot tips and roots, dry matter content, dry weight (dw), content of glucose and starch were determined. The frost hardiness in the shoot tips increased from ‐15°C at a PPFD of 55μmol m^‐2s^‐1 to about ‐35°C at 440 μmol m^‐2s^‐1. No effect of PPFD was found on frost hardiness of the roots. A high PPFD results in a high dry matter content. The effect on dry matter content was most pronounced for the shoot tips and less pronounced for the roots. The total dry weight increased for both root and top with increasing PPFD. The height of the plants increased when the PPFD increased up to 220 μmol m^‐2s^‐1.     

Germination and seedling growth in Abies lasiocarpa (Hook.) Nutt. as affected by provenance,seed pretreatment,and temperature regime

Abies lasiocarpa (Hook.) Nutt. seeds germinated and the seedlings grew on under controlled environments (18 h photoperiod and 16/8 h thermoperiods; 10/10^oC, 20/20°C, 20/10°C, and 25/10°C). The experiment was concluded after 180 days, and the seedlings were scored for stem diameter and length. Four provenances were included: Colorado “high elevation”; (CO), Oregon 1 600 m a.s.l. (OR), British Columbia 1200 m a.s.l. (BC), and Finland (BCF; originally from British Columbia 1800 m a.s.l.). A cold‐moist pretreatment for 30 days improved germination and seedling growth in the BC and BCF seed lots, while the CO and OR seed lots were less affected. Daily fluctuating temperatures improved germination in the BC and BCF seed lots, the widest fluctuation 25/10°C producing the greatest germination. The average length of the seedlings was 34 mm at 20/20°C, 33 mm at 20/10°C, and 37 mm at 25/10°C; differences in hypocotyl length being most important. There were small but significant differences between the provenances in their reaction to temperature regime. The major part of the seedlings produced 2 or 3 flushes of growth in the 180 days period, the CO provenance having the most stabile buds and the OR provenance being the most labile.     

First-year growth response of cold-stored,nursery-grown aspen planting stock

This research examined the first year growth characteristics of cold stored and transplanted nursery-produced aspen (Populus tremuloides) seedlings (container and bareroot (BR)) and compared it to the growth of seedlings that had not been transplanted (established from germinants in the field) and therefore had an unrestricted root system (UR). Prior to planting, nursery-produced seedlings were placed in cold storage (−3°C) and root growth potential (RGP) and total non-structural carbohydrate (TNC) root reserves were tested at 0, 10, 75 and after 150 (container) and 190 days (BR) of storage. Both container and BR stock had much lower root to shoot ratios (RSRs) and root carbohydrate reserves compared to UR seedlings after 170 days. During storage, root reserves in container stock declined faster than in the BR and UR seedlings. RGP in all nursery stock was the highest after 75 days of storage, while longer storage resulted in shoot dieback and reduced root growth. After the first growing season, UR seedlings were one tenth the size of the nursery stock; however, in the second growing season they had no stem dieback and grew twice the height and stem diameter. The higher RSRs and root reserves in the UR seedlings was likely caused by early bud set in its first year of growth. This suggests that inducing bud set earlier in the growing regime might allow seedlings to increase root mass and carbohydrate reserves.