共查询到20条相似文献，搜索用时 343 毫秒
1.
Jaime Puértolas Juan A. Oliet Douglass F. Jacobs Luis F. Benito Juan L. Peñuelas 《Forest Ecology and Management》2010
Tube shelters were designed to protect against browsing, but they improve seedling survival in Mediterranean dry climates. Mechanisms for this response, however, are not fully understood and this knowledge can be useful to help design optimal tube shelters for Mediterranean species and climates. Our objective in this study was to determine if the positive effect of tube shelters is due to enhanced growth during the wet season or to reduced light stress during the dry season. We performed two independent experiments. In the first, we assessed root growth during the wet season in two Mediterranean species with contrasting light tolerance (Quercus ilex L. and Pinus halepensis Mill.) growing in tubes with varying light transmissivity. In the second experiment, we studied the response of a Quercus ilex plantation to different shelter treatments. Root growth during the wet season was reduced with decreasing light transmissivity in the shade intolerant P. halepensis, but not in the shade tolerant Quercus ilex. Survival of Q. ilex shaded by a mesh shelter only during summer was higher than in unsheltered seedlings and similar to the survival in tube and mesh shelters during the whole season. This suggests that shade during the dry period was the main factor explaining survival in this species. This effect could be related to the lower leaf temperature recorded in sheltered seedlings. We conclude that Q. ilex (and perhaps other late successional, shade tolerant Mediterranean species) should be planted in tubes with the currently used light transmissivity because these shelters reduce light stress in summer without impairing root growth in the wet season. However, current tubes impair root growth in P. halepensis (and likely other pioneer, shade intolerant Mediterranean species), so higher transmissivity tubes may be necessary. Optimal transmissivity for tube shelter in Mediterranean climates is species-specific and identifiable as the point that minimizes light stress during summer without impairing root growth in the wet season. 相似文献
2.
Norway spruce (Picea abies (L.) Karst.) is shade-tolerant and sensitive to high irradiance, summer frosts and winter desiccation, which can impair its reforestation success. In this study, artificial pre- and post-planting shading was examined to determine their effects on post-planting shoot and root growth as well as the vigor of one- and two-year-old Norway spruce seedlings. Three planting experiments were carried out on open nursery fields (Exp. 1, 2) and on a mounded forest clearcut in central Finland (Exp. 3). Before planting, the seedlings were stored over winter either in a freezer or on open fields under snow cover. For two weeks prior to planting, half of the seedlings were placed in the open and the other half under a horizontal shade netting (light transmittance 56 %) (Exp. 1, 2). All seedlings were planted with or without a vertical post-planting shade, which was located on the southern side. Post-planting shading enhanced shoot growth and reduced damage (better visual vigor and needle color and less pine-weevil damage) on Norway spruce seedlings for at least two years after planting (Exp. 2, 3). Those seedlings, that had been stored over winter in the open and kept in shade prior to planting seemed to benefit most from post-planting shading (Exp. 2). However, post-planting shading may give variable results, depending on the seedling quality and weather conditions after planting, and may even reduce shoot growth if no pre-planting shading is used (Exp. 1). Shoot growth may also be improved at the expense of root growth (Exp. 3). The costs of manufacturing and installing post-planting shades may limit their use in practice, for example, to selected regeneration sites where there is high risk of frost damage but where no alternative silvicultural procedure (shelterwood or nurse crop) has been used. 相似文献
3.
Claudia González-Salvatierra Ernesto Iván Badano Joel Flores Juan Pablo Rodas 《林业研究》2013,24(1):23-28
Forest restorations conducted in semiarid, seasonally dry climates must deal with the intense drought stress that affects tree seedlings during the dry season. Although this water deficit is the most commonly invoked source of mortality for seedlings, several other environmental factors may also preclude survival of transplants. For instance, it has been widely reported that excessive light reduces the efficiency of the photosynthetic apparatus, hence decreasing plant survival, but most seedling transplants in deforested areas are conducted under these light conditions. This study is focused in determining whether excessive light affects the photosynthetic performance and survival of Quercus coccolobifolia, a Mexican oak species, when their seedlings are transplanted in semiarid deforested areas. Further, this study tests the possibility of using artificial shade shelters to improve the ecophysiological performance and survival of seedlings. Oak seedlings were transplanted under full sunlight conditions and beneath artificial shade shelters of two different colors: white and black. To reduce water stress, and hence isolate the effects of light treatments, a drip irrigation system was implemented at each experimental plot. Seedling survival was monitored weekly for 128 days and photosynthetic performance was assessed by measuring chlorophyll fluorescence at three opportunities during the experiment. Sun-exposed seedlings showed lower photosynthetic performance and survival rates than those beneath shelters of both colors. These results suggest that sunlight damage can reduce seedling survival when they are transplanted in exposed sites, and that shade shelters can improve the success of forest restoration programs in semiarid climates. 相似文献
4.
Chlorophyll fluorescence, chlorophyll content, growth, and mortality of white spruce (Picea glauca [Moench] Voss) seedlings were monitored for 2 years after planting under three scenarios of artificial shade: no-shade (control),
shade in summer only, and shade all year. The shade frames allowed 50–60% light transmission, with limited effects on air
temperature, relative humidity, soil temperature, and soil moisture around seedlings. Based on fluorescence yield and chlorophyll
content measurements, summer-only shade reduced photoinhibition and photooxidation, especially in summer and fall; extending
to all year shading did not further reduce either photoinhibition or photooxidation. Shade tended to reduce seedling diameter
and mortality, but after 2 years the cumulative effect on mortality was not statistically significant. Study results support
the establishment of white spruce seedlings under partial forest canopy, especially on sites with harsh environmental conditions. 相似文献
5.
The effect of two bud development treatments on post-dormancy shoot growth was investigated with 1-year-old container-grown Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings. A difference in the date of budset and number of overwintering primordia was obtained by applying 8-hour or 17-hour photoperiods in growth rooms during summer months. Seedlings were then chilled for 14 weeks at 4 °C and finally held 2 months at 22 °C under either an 8-hour or 16-hour photoperiod. The new shoot growth of seedlings with early budset had greater length, stem unit numbers, average stem unit length, and dry weight. Stem unit number of the post-dormancy seedlings was unaffected by photoperiod during flushing. Significant free growth occurred only in late budset seedlings and accounted for 40% and 46% of the fixed growth under 16-hour and 8-hour flushing photoperiods, respectively. 相似文献
6.
《Scandinavian Journal of Forest Research》2012,27(2):133-144
The objective of this study was to evaluate the possibility of enlarging the planting window of container-grown silver birch seedlings from spring and autumn to summer by planting young, actively growing seedlings. For over 3 yrs the study investigated the growth, survival and damage of silver birch seedlings grown in containers and planted at different times during the growing season on 18 sites in fields and forest sites in central Finland. In a pot experiment in the greenhouse, the root-egress ability of seedlings planted at different times during the growing season was monitored. Root egress of seedlings was rapid from the beginning of July to the middle of August. Actively growing seedlings planted in summer on a site suitable for silver birch grew and survived at least as well as seedlings planted in spring during the dormant stage. The risk of drought stress increased when seedlings were planted on easily drying, coarse sandy soils. The risk was also high in soils with high levels of fine soil fractions that become hard when dry and when the dry period continued for several weeks before planting. In conclusion, it is possible to enlarge the planting window of birch seedlings to July and the beginning of August by using actively growing container seedlings. 相似文献
7.
Effects of nursery shading on seedling quality and post-planting performance in two Mediterranean species with contrasting shade tolerance 总被引：1，自引：1，他引：0
In Mediterranean climates, seedlings are frequently shaded in the nursery to avoid heat damage and save water. However, the
impact of this shading on the seedling quality and transplanting performance of Mediterranean species is not well known. We
studied the effect of nursery shading on pre-planting features and post-planting performance of two Mediterranean tree species:
the shade-intolerant pioneer Pinus halepensis and the shade-tolerant late-successional Quercus ilex. We grew one-year-old seedlings of both species under 100, 40 and 5% full sunlight. Shade had a low impact on the morphology
and physiology of Q. ilex seedlings. In pines, only the deep shade treatment produced low quality seedlings with poor root development. In both species,
transference to high light at planting in autumn did not impose any additional stress than that caused by frosts, but initial
root growth was impaired in the two shaded treatments in pine. Post-planting growth and survival of oak seedlings showed no
difference between treatments. Pine seedlings grown in deep shade showed higher mortality and lower growth after planting
than those grown in full sun and intermediate light treatments, while intermediate light only reduced growth. For the nursery
culture of Q. ilex seedlings, we advise using low light levels during summer to save water without impairing field performance. In P. halepensis, seedlings should be cultured under full sunlight conditions to maximize post-planting growth, but they can be cultured under
intermediate light without impairing survival. 相似文献
8.
The effects of shade and soil temperature on growth of Eucalyptus marginata Donn ex Sm (jarrah) seedlings were studied in greenhouse experiments. Plant dry weight and that of all plant parts declined in response to shade, as did root/shoot ratio. Plant leaf area was less in unshaded plants than in plants grown in shade, and specific leaf area increased with shade. Unshaded seedlings had a higher light-saturated rate of photosynthesis, a higher light compensation point and a higher light saturation point than seedlings grown in 70% shade. The relationship between plant dry weight and leaf dry weight was independent of shading, whereas the relationship between plant dry weight and plant leaf area was dependent on shading. Therefore, leaf dry weight may be a better predictor of biomass production than leaf area in forest stands where shade is likely to affect growth significantly. Soil temperature had a significant effect on the growth of all plant parts except cotyledons. Total plant growth and shoot growth were maximal at a soil temperature of 30 degrees C, but root growth had a slightly lower temperature optimum such that the root/shoot ratio was highest at 20 degrees C. Roots grown at 15 degrees C were about 30% shorter per unit of dry weight than roots grown at 20 to 35 degrees C. We conclude that increases in irradiance and soil temperature as a result of overstory removal in the forest will cause significant increases in growth of E. marginata seedlings, but these increases represent a relatively small component of the growth response to overstory removal. 相似文献
9.
The influence of shading intensity on growth, morphology and leaf gas exchange of mangosteen (Garcinia mangostana L.) seedlings was investigated over a 2-year period. Diurnal gas exchange studies revealed significantly higher carbon gain for leaves grown in 20 or 50% shade compared to leaves grown in 80% shade. Seedlings grown in 20 or 50% shade accumulated significantly more dry weight than seedlings grown in 80% shade during the 2-year study period. Seedlings grown in decreased shade showed decreased leaf size, increased leaf thickness, lower specific leaf area (SLA) and higher stomatal frequency. Less shaded seedlings also allocated relatively more dry matter to roots than shaded seedlings and exhibited a significant reduction in leaf area relative to total plant dry weight (leaf area ratio). Increased leaf number, enhanced branching and shorter internodes resulted in a more compact appearance of less shaded seedlings. Irrespective of light conditions, mangosteen seedlings exhibited inherently slow growth because of low photosynthetic rates per unit leaf area, low SLA, low leaf area ratios and inefficient root systems. 相似文献
10.
11.
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. 相似文献
12.
Simon M. Landh?usser Javier Rodriguez-Alvarez Eckehart H. Marenholtz Victor J. Lieffers 《New Forests》2012,43(5-6):679-693
Aspen (Populus tremuloides Michx) has great potential as a reclamation species for mining sites in the boreal forest, but planting stock has shown poor field performance after outplanting. In this study we tested how different aspen seedling characteristics and planting times affect field outplanting performance on reclamation sites. We produced three different types of aspen planting stock, which varied significantly in seedling size, root-to-shoot ratio (RSR), and total non-structural carbohydrate (TNC) reserves in roots, by artificially manipulating shoot growth during seedling production. All three stock types were then field-planted either in late summer, late fall, or early spring after frozen storage. Seedlings were outplanted onto two reclaimed open-pit mining areas in the boreal forest region of central and east-central Alberta, Canada, which varied significantly in latitude, reclamation history, and soil conditions. Overall, height growth was better in aspen stock types with high RSR and TNC reserves. Differences in field performance among aspen stock types appeared to be more strongly expressed when seedlings were exposed to more stressful environmental site conditions, such as low soil nutrients and moisture. Generally, aspen seedlings planted with leaves in the summer showed the poorest performance, and summer- or fall-planted seedlings with no shoot growth manipulation had much greater stem dieback after the first winter. This indicates that the dormancy and hardening of the stem, as a result of premature bud set treatments, could improve the outplanting performance of aspen seedlings, particularly those planted during summer and fall. 相似文献
13.
北欧、北美的许多地区在夏季造林前对云杉苗木进行2 ~ 3周的短日照处理,以促进苗木提前形成顶芽和进入休眠,提高苗木的木质化程度,增强苗木抗机械损伤和抵御生物或非生物胁迫的能力;通过抑制苗木的高生长,使碳水化合物更多地向根系分配,可促进根系的生长发育,增强苗木吸收水分、养分的能力,显著改善夏季造林苗木的质量,取得了较好的造林效果。目前,应用短日照处理调控夏季造林苗木质量的相关研究受到广泛关注。文中重点分析短日照处理的起始时间、持续时间和日照长度等主要技术参数对苗木木质化及其抗旱性和抗寒性的影响,并对短日照处理技术在我国夏季造林中的应用提出展望。 相似文献
14.
Damage to containerized forest seedlings due to freezing can occur in the fall or early winter in Canadian forest nurseries. The following spring, damage to shoots and impairment of growth is observed. The objectives of this experiment were to measure the impact of late fall low temperatures (0° to --30°C) on whole seedlings of the three most common species used for reforestation in Quebec: black spruce (BS), white spruce (WS) and jack pine (JP). Impacts of freezing temperatures on (i) whole seedling and apical bud mortality, (ii) shoot growth and root mortality, (iii) stem electrical resistance, (iv) shoot and root water relations, (v) concentrations of N, P, K, Ca, Mg, and total sugars in shoots were assessed. JP showed the highest rate of whole seedling mortality while WS showed the highest rate of apical bud mortality. JP was the most severely affected: destruction of the root system at low temperatures as well as a reduction of shoot growth and stem diameter and a decrease (more negative) in shoot and root water potential. WS showed a reduction of shoot growth despite no apparent damage to the root system at low temperatures. BS was not affected by temperatures as low as --30°C. Nutrient and sugar concentrations were not affected by low temperature treatments. 相似文献
15.
Finney MA 《Tree physiology》1993,12(3):301-309
The effects of wounding, shading, and indole-3-acetic acid (IAA) on sprouting responses were examined in coast redwood (Sequoia sempervirens D. Don (Endl)) seedlings. In August, two-year-old seedlings were given one of three thermal wounding treatments made with a blowtorch at the stem base. After 8 months, the heat-wounded seedlings were decapitated above the burl and IAA (0.00% to 1.00% by weight in lanolin) was applied to the cut surface every week for 8 weeks. Throughout the 8-week hormone treatment, the decapitated seedlings were subjected to one of three shading treatments (no shade, 70% shading and complete darkness). At the beginning of June, sprouts were harvested from each stump and measurements made of the length of the tallest sprout, number of sprouts, dry weight of all sprouts, and mean dry weight per sprout. All sprouting parameters showed negative responses to IAA. Shading decreased sprout number and sprout dry weight. Wounding increased maximum sprout length and dry weight per sprout but decreased the number of sprouts. Only the 2-way interaction between IAA and wounding was not significant for any of the responses. 相似文献
16.
Shade and irrigation are frequently used to increase the success of Mediterranean Quercus spp. plantations. However, there is controversy about the combined effects of these treatments on plant performance. We assessed the effects of two irradiances (full sunlight and moderate shade) and two summer watering regimes (high (daily) and low (alternate days)) on leaf and whole-plant traits of 1-year-old seedlings of Quercus coccifera, Q. ilex subsp. ballota and Q. faginea grown outdoors for 8.5 months. Leaf traits included measures of morphology, nitrogen concentration, gas exchange and photochemical efficiency, and measures of whole-plant traits included biomass allocation patterns, growth phenology, across-summer leaf area change and relative growth rate (RGR). Moderate shade reduced leaf mass per area, increased photochemical efficiency, maximum carbon assimilation rate (Amax) and allocation to leaves, and prolonged the growing period in one or more of the species. Daily watering in summer increased Amax of Q. ilex and prolonged the growing period of Q. ilex and Q. faginea. Both treatments tended to increase RGR. The effect of shade was greater in the low-watering regime than in the high-watering regime for two of the 15 studied traits, with treatment effects being independent for the remaining 13 traits. Leaf nitrogen and the ability to maintain leaf area after the arid period, rather than biomass allocation traits, explained the variation in seedling RGR. Trait responsiveness to the treatments was low and similar among species and between study scales, being unexpectedly low in Q. faginea leaves. This may be because selective pressures on leaf plasticity act differently in deciduous and evergreen species. We conclude that moderate shade and daily summer watering enhance the performance of Mediterranean Quercus seedlings through species-specific mechanisms. 相似文献
17.
《Scandinavian Journal of Forest Research》2012,27(4):322-328
Abstract Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings. 相似文献
18.
Heat damage in boxed white spruce (Picea glauca [Moench.] Voss) seedlings: Its pre-planting detection and effect on field performance 总被引：2，自引：0，他引：2
This study investigated the effects of holding 1+0 PSB313a white spruce (Picea glauca (Moench.) Voss) seedlings in storage boxes at air temperatures of 5, 10, 20, 30 and 40°C for 12, 24, 48, 72 and 96 h before planting. The ability to detect physiological damage to seedlings as a result of such treatment, before planting, was also examined. After one growing season, no needle damage or mortality >8% was found for temperature treatments up to 20°C for 4 days. At 30°C and above, seedling damage and mortality increased, while bud flush, shoot height, stem diameter and shoot dry weight decreased with increasing temperature and duration of treatment. Seedling mortality in the field was 100% after the 40°C treatment exposure for 72 h or longer. Pre-planting needle electrolyte leakage was indicative of visible needle damage 14 days after planting, whereas stem electrolyte leakage and root growth potential were more closely related to end of season plantation mortality. Despite the lack of damage observed at 20°C or below, preplanting exposure of white spruce seedlings to temperatures above 5°C, during transportation and field storage, is not recommended. 相似文献
19.
Thirty forages, including eight introduced cool-season grasses, four native warm-season grasses, one introduced warm-season
grass, eight introduced cool-season legumes, five native warm-season legumes, and four introduced warm-season legumes, were
grown in 7.6 L (two gallon) pots in full sun, 50%, and 80% shade created by shade cloth over a greenhouse frame. Experiments
were conducted during summer--fall 1994, spring--early summer 1995, and summer--fall 1995. A complete randomized experimental
design was used and above ground dry weight was measured in each shade environment. Tukey's studentized range test was used
to compare mean dry weights (MDW) within a species. Warm-season grasses displayed significant reductions in MDW under shade
regardless of growing season. All cool-season forages grown during spring--early summer showed a decrease in MDW under shade;
however, the reductions in dry weights of ‘Benchmark’ and ‘Justus’ orchardgrass, ‘KY 31’ tall fescue, Desmodium canescens
and D. paniculatum were not significant under 50% shade. Cool-season grasses showed more shade tolerance when grown during
the summer--fall than when grown during the spring--early summer. Seven of the selected cool-season grasses grown during the
summer--fall did not display significant reductions in MDW under 50% shade as compared to full sun. Smooth bromegrass grown
under 50% shade showed a significantly increased MDW production compared to growth in full sun. With the exception of Justus
orchardgrass and smooth bromegrass, growth of cool-season grasses was inhibited at 80% shade. Among the legumes harvested
during the fall, the dry weights of both Desmodium species tested and hog peanut (Amphicarpaea bracteata L.) increased significantly
under 50% and 80% shade. In addition, ‘Cody’ alfalfa, white clover, slender lespedeza and ‘Kobe’ lespedeza showed no significant
reductions in MDW under 50% shade.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
Ecophysiology of seedlings of three Mediterranean pine species in contrasting light regimes 总被引：2，自引：0，他引：2
Seasonal dynamics of net photosynthesis (Anet) in 2-year-old seedlings of Pinus brutia Ten., Pinus pinea L. and Pinus pinaster Ait. were investigated. Seedlings were grown in the field in two light regimes: sun (ambient light) and shade (25% of photosynthetically active radiation (PAR)). Repeated measures analyses over a 12-month period showed that Anet varied significantly among species and from season to season. Maximum Anet in sun-acclimated seedlings was low in winter (yet remained positive) and peaked during summer. Maximum Anet was observed in June in P. pinea (12 micromol m-2 s-1), July in P. pinaster (23 micromol m-2 s-1) and August in P. brutia (20 micromol m-2 s-1). Photosynthetic light response curves saturated at a PAR of 200-300 micromol m-2 s-1 in winter and in shade-acclimated seedlings in summer. Net photosynthesis in sun-acclimated seedlings did not saturate at PAR up to 1900 micromol m-2 s-1 in P. brutia and P. pinaster. Minimum air temperature of the preceding night was apparently one of the main factors controlling Anet during the day. In shade-acclimated seedlings, photosynthetic rates were reduced by 50% in P. brutia and P. pinaster and by 20% in P. pinea compared with those in sun-acclimated seedlings. Stomatal conductance was generally lower in shaded seedlings than in seedlings grown in the sun, except on days with a high vapor pressure deficit. Total chlorophyll concentration per unit leaf area, specific leaf area (SLA) and height significantly increased in P. pinea in response to shade, but not in P. pinaster or P. brutia. In response to shade, P. brutia showed a significant increase in total chlorophyll concentration but not SLA. Photosynthetic and growth data indicate that P. pinaster and P. brutia are more light-demanding than P. pinea. 相似文献