氮素营养对闽楠幼苗生长及光合特性的影响

设置0、50、100、150、200、300、400、600 mg·株-1 8个N处理,通过盆栽试验研究氮素对闽楠苗生长及光合特性的影响.结果表明:随着供氮量的增加,闽楠苗高、地径、叶面积和根、茎、叶及整株生物量均呈现先增加后降低的趋势,其中,苗高、地径和叶面积均在供氮量100 mg·株-1时最高,而各器官生物量及整株生物量均在供氮量150 mg·株-1时最大;根冠比则随着供氮量的增加呈现单调递减趋势;闽楠苗光合特性与生长表现是契合的,随供氮水平的提高,闽楠苗叶绿素a、b及总量先升高后降低,净光合速率、气孔导度、胞间二氧化碳浓度和蒸腾速率值也均呈先仰后抑之势,恰在供氮量100 mg·株-1时,以上光合参数值均达最高,且不同氮素处理间闽楠光合气体交换参数和蒸腾速率差异均显著.综合闽楠苗各生长及光合指标的分析结果,100～150 mg·株-1的供氮量为闽楠苗温室培育的适宜范围.     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

Grass interference limits resource availability and reduces growth of juvenile red pine in the field

The effects of competing grasses on resource availability, growth and ecophysiological characteristics of 3-0 red pine (Pinus resinosa Ait.) seedlings were examined the first two years following outplanting in Anoka County, Minnesota, USA. Equal numbers of seedlings were planted into suppressed and undisturbed grass communities in a sandy soil. Grass suppression was maintained throughout the first growing season, but partially discontinued thereafter on the site. During the first field season interference from grass reduced pine seedling root collar diameter, needle length, number of new root tips, and lateral root length by over 40%. Mean pre-dawn needle water potential was 0.55 MPa lower in undisturbed grass plots during a brief drought in year one, but otherwise water stress was not significantly (p=0.05) influenced by grass interference. The presence of grass also reduced, up to 50%, the photosynthetically active radiation reaching the seedling canopy. At the end of year one, total biomass N, P, K, and Ca content were significantly (p=0.05) less in seedlings growing in the undisturbed grass community. Nitrogen was deficient in seedlings growing in grass. After two growing seasons, seedling shoot length (p=0.03), root collar diameter (p=0.001), and needle length (p=0.001) were significantly less (40, 54 and 20%, respectively) for seedlings growing in undisturbed grass. Seedling growth reductions induced by grass competition were associated with multiple environmental stressors in the field and not restricted to water stress as was observed in earlier studies with pine species at low and mid-latitude sites.     

Why seedlings survive: influence of plant attributes

Seedling survival and successful forest restoration involves many silvicultural practices. One important aspect of a successful forest restoration program is planting quality seedlings with high survival capability. Thus the nursery needs to create seedlings with plant attributes that allow for the best chance of success once a seedling is field planted. Since the mid-twentieth century, research foresters have critically examined plant attributes that confer improved seedling survival to field site conditions. This review describes the value of commonly measured seedling quality material (i.e. shoot height, stem diameter, root mass, shoot to root ratio, drought resistance, mineral nutrient status) and performance (i.e. freezing tolerance and root growth) plant attributes defined as important in answering the question of why seedlings survive after planting. Desirable levels of these plant attributes can increase the speed with which seedlings overcome planting stress, become ‘coupled’ to the forest restoration site, thereby ensuring successful seedling establishment. Although planting seedlings with these desirable plant attributes does not guarantee high survival rates; planting seedlings with desirable plant attributes increases chances for survival after field planting.     

Effects of Seedbed Density on One-Year-Old <Emphasis Type="Italic">Fraxinus angustifolia</Emphasis> Seedling Characteristics and Outplanting Performance

To assess the effects of seedling spacing on one-year-old seedling morphology in the nursery, seeds of three provenances of Fraxinus angustifolia were sown at five different seedling spacings within rows of two different spacings in the seedbed. Subsequent growth performance of one-year-old seedlings was assessed by planting in the forest. Within row spacings were: 4.3, 5.0, 6.3, 8.3, and 12.5 cm, and there were five rows at 20 cm apart, or three rows at 33 cm apart across the 1.2 m wide seedbeds. Both spacings within and between rows significantly affected shoot height, root collar diameter, root dry weight and shoot dry weight, but not root/shoot ratio. Wider spacings produced larger seedlings, but only the wider spacing within rows significantly increased fine and coarse root mass. Provenances showed significant differences in diameter, root/shoot ratio, and fine and coarse roots, and they also showed interactions with row spacings in height and diameter measurements. One year after outplanting, diameter growth was significantly related to provenance, and diameter growth was 88% greater for trees from 33 cm nursery row spacing than those from 20 cm nursery row spacing.     

Root diseases in bareroot and container nurseries of the Pacific Northwest: epidemiology, management, and effects on outplanting performance

In forest and conservation nurseries in the Pacific Northwest USA, seedling production can be limited by root diseases caused by fungi in the genera Fusarium Link:Fr., Cylindrocarpon Wollenw., Phytophthora de Barry, and Pythium Pringsh. Fusarium, Cylindrocarpon, and Pythium are the most ubiquitous, whereas incidence of Phytophthora is mostly associated with coastal bareroot nurseries. All of these root pathogens are encouraged by water saturated soils or media. Seedlings infected with Fusarium, Phytophthora, or Pythium often appear chlorotic or necrotic with extensive root decay. Cylindrocarpon often causes serious root decay without shoot symptoms. The best approach to mitigate losses from these diseases is to use a holistic integrated pest management program. This program should combine chemical controls with cultural practices, particularly those that increase soil permeability and drainage and reduce potential sources of inoculum, especially by disinfesting seeds and containers reused for crops. In general, we found that seedlings meeting nursery specifications for outplanting on forest soil (proper height, root collar diameter, healthy shoot color, lack of disease symptoms) but having these disease organisms on their root systems perform as well as non-infected seedlings.     

Seed mass effects on performance of Pinus halepensis Mill. seedlings sown after fire

Pinus halepensis is a widely distributed species in the Mediterranean basin. It is generally well adapted to regenerate after wildfire, except when fire intervals are too short (≤15 years). In these latter situations, direct seeding could be a good alternative for restoring pine woodland after fire. Under dry climate, low seedling growth and survival can greatly limit the use of seeding. Early studies have shown that seedlings grown from large seeds have higher seedling establishment, growth and survival. Seed size grading may however reduce the genetic diversity of a seed lot by eliminating part or all of the families with relatively small seeds. An alternative to improve seed lot quality without losing genetic variability could be collecting and sieving seeds from each family separately. In order to explore the influence of seed mass on P. halepensis seedling performance, seeds from five half-sib families differing in mean seed mass were sown under greenhouse and field conditions. Final seedling emergence was unrelated to seed mass and half-sib family. The time of emergence was also unrelated to seed mass but it varied among families. Seed mass showed a positive effect on seedling height and diameter, both at population level and within family throughout the study period (9 months under greenhouse conditions and 20 months under field conditions). We also observed a negative relationship between seed mass and relative growth rate for seedling diameter, but it was not high enough to fully compensate the initial differences due to seed mass at the end of the 20-month study period. Seedling predation had a considerable impact on seedling survival, and it was not related to seed mass. When seedlings killed by predation were excluded from the survival analysis, larger seedlings, coming from larger seeds, showed slightly better survival, but only during the first growing period. The small advantages obtained from large seed mass in seedling development do not seem to justify the increased operational costs derived from seed mass selection for each family.     

Assessing the Quality of Seedlings in Small-scale Nurseries in the Highlands of Cameroon: The Use of Growth Characteristics and Quality Thresholds as Indicators

In developing countries seedlings are often produced in small-scale nurseries as a means to raise tree planting materials and, provided they are of high quality, these can form the basis for successful forest plantation initiatives. This study uses morphological characteristics to assess the quality of seedlings of three tree species (Persea americana, Cola acuminata and Dacryodes edulis) in the Western Highlands of Cameroon. The growth characteristics and quality indicators of seedlings produced in two nursery categories were compared—three nurseries collaborating with the tree domestication program implemented by the World Agroforestry Centre (Category 1) and three nurseries collaborating with government and non-governmental projects (Category 2). Seedlings produced in nurseries in the first nursery category were found to be uniform in terms of growth characteristics and quality indicators. In the second category, there were relatively higher seedling proportions having measured parameters out of threshold standards for root to shoot ratio and for sturdiness quotient. Significant differences between nursery categories (at α = 0.05) were detected in root collar diameter of C. acuminata and D. edulis and in shoot dry weight of D. edulis. These differences could be attributed to better nursery management as a results of training and technical backstopping received by nursery operators in Category 1. The level of experience of nursery operators in both categories was found to be insufficient and greater exposure to skills and knowledge could enhance the production of high quality seedlings.     

Influence of initial age and size on the field performance of <Emphasis Type="Italic">Larix olgensis</Emphasis> seedlings

Quality of seedlings is important for the success of plantations. The field performance of five stock types of Olga Bay larch (Larix olgensis Henry) seedlings three seasons after planting was evaluated. High survival rates were achieved for all five types of planting stock in the first-year growing season when weeds were controlled. In the second and third-year growing seasons, significant differences were observed in survival rates among different stocktypes. The 1 + 1 type of Olga Bay larch seedling demonstrated better survival than 1 + 0 type of seedlings. 1 + 1 seedlings with diameter larger than 5.0 mm as well as 1 + 0 seedlings with diameter larger than 4.5 mm were suitable for reforestation. The 1 + 1 stocktype with a root collar diameter between 6.0 and 7.5 mm was considered optimal for the establishment of fast-growing and high-yield plantations. The number of lateral roots > 1 cm in length was the best predictor of field performance, however, the number of first order lateral roots with diameter > 1 mm at the tap root junction (FOLR (D > 1 mm)) was more feasible and sufficiently reliable to predict the field performance of the deciduous conifers. The initial height and root collar diameter of seedlings showed a significant correlation with the field performance for both 1 + 1 and 1 + 0 seedlings in the first and second-year growing seasons and thus can be adopted as an indicator for predicting potential field performance of seedlings.     

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.     

林芝云杉不同地理种源苗期性状变异

正林芝云杉(Picea likiangensis var.linzhiensis Cheng et L.K.Fu)是松科(Pinaceae)云杉属(Picea Dietr.)常绿高大乔木,为西藏高原亚高山暗针叶林主要、特有的建群树种之一[1-2]。主要分布在西藏东南的林芝、米林、波密等地,并向西分布至朗县、错那、洛扎、隆子、工布江达。林芝云杉是云杉属中木材品质系数最高的树种[3],生长迅速,寿命持久,在水热条件优越的地区能长成罕见的巨树,胸径可达2.5 m,最大树高可达73 m,单株立木材积达到50     

Prediction of planted seedling survival of five Mediterranean species based on initial seedling morphology

Field performance can be predicted by evaluating nursery stock quality, but optimal morphological variables for use in these assessments may vary by species especially under dry Mediterranean conditions. Our objective was to identify initial seedling morphological characteristics that successfully predict field performance of five Mediterranean species (Pinus halepensis, Quercus ilex, Quercus coccifera, Ceratonia silqua and Pistacia lentiscus). Container seedling morphology was evaluated following the nursery phase, and then seedlings were outplanted in the field where field survival was monitored for two successive years. Results indicate that survival can successfully be predicted from seedling initial morphological characteristics for all these species, yet not all the initial characteristics were good predictors. Survival of P. halepensis and Pist. lentiscus seedlings was positively correlated to initial seedling root-collar diameter, total dry weight and Dickson’s quality index, and can be reliably predicted by these variables. In contrast, seedling field survival of the two Mediterranean evergreen oak species was correlated with few initial morphological attributes; initial diameter provided an accurate index to predict second-year outplanting survival for both species while height/diameter was a good survival predictor for Q. coccifera seedlings. For C. siliqua seedlings, seedlings with larger initial diameter and total biomass survive better in the field. Thus, diameter was the common variable that accurately predicted survival for all species, which should be >5 mm for P. halepensis seedlings and >7 mm for the remaining species.     

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 cavity size, seedling growing density and fungicide applications on Keithia blight of western redcedar seedling growth and field performance

To determine the influence of cavity size, seedling density and fungicide application on severity of Keithia blight caused by the fungus Didymascella thujina (Durand) Maire, western redcedar (Thuja plicata Donn) seedlings were grown in styroblocks of 3 cavity sizes, thinned to 3 growing densities and sprayed several times monthly with mancozeb fungicide. After two growing seasons cavity size, seedling growing density and number of fungicide applications all significantly (p0.05) affected blight severity. Blight severity was inversely related to the number of mancozeb fungicide applications. The only significant two-way interaction was for cavity size and seedling growing density.Eighteen seedlings from each of the nine cavity sizes and seedling densities combinations were assessed for shoot height, root collar diameter and blight severity, prior to planting at both Holt Creek and Salmon Creek on Vancouver Island, British Columbia in March 1994. Growth was reassessed during October 1994. Seedling height and root collar diameter increased significantly (p0.05) with certain cavity size and seedling density combinations. Blight severity increased significantly (p0.05) for all nine treatments at both sites, however, between sites blight severity increased significantly (p0.05) only at the wetter, Salmon Creek site.     

The relative importance of different regeneration mechanisms in a selectively cut savanna-woodland in Burkina Faso,West Africa

Savanna plant species are capable of regenerating both sexually and asexually. The importance of each regeneration mechanism depends on the species, the type and the intensity of disturbance. This paper describes the relative importance of sexual and asexual regeneration for the restoration of a selectively cut savanna woodland in Burkina Faso. Plantlets regenerated sexually or asexually were determined by excavating the below ground system and assessing basal and aerial sprouts within 144 quadrats along transects in 2, 5, 10 year-cut and control plots. The result shows that seedling sprouts were predominant (83%) compared to root sucker (4%), coppice (5%), water sprout (2%) and layering (less than 1%). True seedlings constituted a minor component (5%) of the plantlet population. A total of 54 woody species was found in the plantlet population with 52 presenting seedling sprouts. Twelve species were found regenerating from both seeds and root buds; of which Dichrostachys cinerea, Pteleopsis suberosa and Detarium microcarpum had the highest number of plantlets. Feretia apodanthera was the only layering species encountered in the sampled area. Coppices, root suckers and water sprouts showed higher height and bigger collar diameter compared to seedling sprouts and true seedlings. It can be concluded that sexual reproduction is the dominant mechanism of seedling recruitment in this disturbed savanna-woodland, and that its success relies on the ability of plantlets of seed origin to resprout abundantly.     

Relative contribution of initial root and shoot morphology in predicting field performance of hardwood seedlings

Single and multiple linear regression techniques were used to explain the capacity of initial seedling root volume (Rv) and first-order lateral roots (FOLR) relative to shoot height, diameter, and fresh mass to serve as important indicators of stock quality and predictors of first- and second-year height and diameter on an afforestation site in southern Indiana, USA. This was accomplished for northern red oak (Quercus rubra L.), white oak (Quercus alba L.), and black cherry (Prunus serotina Ehrh) seedlings graded into four Rv categories at establishment. Field survival was high (85–97%) for all species. Initial diameter, height, fresh mass, and Rv provided similar predictive ability of second-year field response for absolute height (R² = 0.59–0.77) and diameter (R² = 0.50–0.73) for both oak species. Initial seedling Rv was a better predictor of field response than FOLR for both oak species, though not for cherry. Multiple-variable models accounted for a greater proportion of the total variation in seedling field height and diameter than did single-variable equations. The high R² (up to 0.95) of regression models suggests field performance of these species can be reliably predicted and confirms the importance of initial seedling morphology in dictating early plantation performance.     

Comparison of container-grown Pinus taeda L. seedlings raised outdoors and in a growth chamber in sunlight

Two annual crops of container-grown loblolly pine (Pinus taeda L.) seedlings raised outdoors differed from those grown inside a covered chamber with a clear top. After a 90-day growth period, outside-grown container seedlings had shorter heights, smaller root collar diameters, and lower root, stem, foliage, shoot, and total dry weights than chamber-grown seedlings. Fall-planted, outside-grown seedlings raised the first year had up to 10% higher field survival than those from the chamber. However, chamber-grown container seedlings that survived retained their initial height and diameter advantages following one complete growing season. Fall-planted seedlings raised the second year showed no differences due to growth treatments when favorable weather for seedling growth occurred after field-planting. Container-grown seedlings raised outdoors during the summer months are well suited for fall-outplanting.     

Planting mahogany in canopy gaps created by commercial harvesting

Attempts at natural forest management of mahogany (Swietenia macrophylla King) have so far met with limited success, whilst many plantations are beset by the shoot borer Hypsipyla spp. In this paper we present preliminary results of an approach to enrichment planting that aims to balance economic returns (rapid growth and good silvicultural form) with intervention costs and changes to forest structure. Mahogany seedlings were planted in gaps created by selective timber harvesting and that ranged in vertical projected area from 91 to 542 m² (mean = 257 m²). Seedlings grew within the matrix of gap regrowth, with limited control of competing vegetation. Sixty-one percent of seedlings had survived by 4.4 years (equivalent to an annual mortality rate of 10.5% year⁻¹), and had reached a mean height of 4.5 m. Stocking levels of mahogany were similar to that of naturally regenerated commercial species in unplanted gaps of the same age, but mahogany seedlings were significantly taller. The incidence of shoot borer attack on mahogany stems was relatively low (54.7%), but, more importantly, most damaged stems (58%) responded by producing a single replacement leader. The cost of the proposed methodology (US$ 94 per gap over 4.4 years) was low compared to the high value of mahogany timber relative to other species in the forest. The implications of planting mahogany in gaps for forest management and the potential benefits to conservation of the species are considered.     

水分胁迫对毛红椿幼苗生长和生物量分配的影响

以我国亚热带落叶阔叶优势树种毛红椿的1年生幼苗为试验材料,设置4个水分胁迫处理,模拟研究不同水分胁迫强度下毛红椿幼苗生长和生物量分配规律。结果表明:水分胁迫对毛红椿幼苗根系生长的限制作用明显大于对苗高生长的限制作用,对地径生长限制作用不明显;随着水分胁迫程度增加,根质量比表现出先增大后减小的趋势;叶质量比在处理初期和中期增大,在处理后期和末期降低;在整个处理阶段,茎质量比始终保持增加趋势;根系平均直径在处理中期和后期逐渐减小,处理末期则有所上升;细根/总根长比值则在处理中期和后期逐渐增大,处理末期则有所降低;不同水分胁迫程度导致根尖数量差异显著。在整个处理阶段,水分首先保证苗高和叶片生长,根系生长受到限制;随着水分胁迫程度增加,通过落叶和根系二次生长来保障根系的水分需求和提高水分吸收效率,以此来缓解水分胁迫对生存的胁迫。     

老鼠簕幼苗在潮汐环境下对不同光强的生理生态响应

采用自制潮汐模拟系统培养红树植物老鼠簕幼苗,设置7个相对于自然光5％、15％、20％、45％、60％、75％、100％的光照强度,研究了不同光强对老鼠簕幼苗从发芽至生长10个月的生理生态影响.随着光照强度的升高,幼苗的保存率、苗高、地径、根干质量、茎干质量、叶干质量、单株生物量、根冠比、根系活力、叶面积、叶绿素a、b含量均是先升后降;可溶性糖含量、净光合速率、蒸腾速率、气孔导度、最大净光合速率随光强增大而增加.在淹浸30 min内,不同光照强度的净光合速率均有增大的表现,而气孔导度均降低,且最终均稳定在初始值以下.试验表明:光照强度为45％时,多数生理生态指标表现为促进植物的生长;当光照强度为20％时,老鼠簕幼苗通过降低根冠比、光补偿点,增加苗高、叶绿素含量、叶面积和表观量子利用效率来提高自身光能获取的效率;当光照强度为5％时,光照会显著抑制幼苗的生长,但保存率依然在60％以上.可以认为,极低的光照强度致使幼苗生长缓慢,但并不影响其自然定居的密度;同时,在不同光强下,老鼠簕光饱和点和光补偿点均很低.以上可以解释淇澳岛红树林林下存在高密度老鼠簕的原因是由于其自身拥有高的耐阴能力,同时对光照减弱有极强的适应能力.