Relationships between climate at origin and seedling traits in eight Panafrican provenances of <Emphasis Type="Italic">Vitellaria paradoxa</Emphasis> C.F. Gaertn. under imposed drought stress

The morphological responses of seedlings of eight African provenances of Vitellaria paradoxa (Shea tree or Karité) to imposed draught stress were compared under nursery experimental conditions. The potted seedlings were subjected to three different watering regimes (87 days after sowing): no water stress (100% of the field capacity, C), moderate water stress (75% of C) and severe water stress (50% of C). Before the application of the stress, we observed genotypical differences in the morphological variables at the scale of leaves and of above-ground parts. The six-month water stress affected aerial growth: all provenances responded to drought by down-regulating growth (in height and in diameter), leaf number and area. Katawki provenance of Uganda performed relatively poorly, possibly of it being a nilotica subspecies, contrary to the others (paradoxa subspecies). There was a lack of correlation between climate of seeds origin, seed characteristics, seeds germination and survival rate of seedlings. The study confirmed the importance of leaf area in the vigor of the initial growth in this species. Thus, Tamale and Karaba provenances performed better than other West African provenances due to their larger leaf area, which was found to be a determining factor of relative growth in height at the seedling stage.     

Growth and biomass partitioning of nine provenances of Quillaja saponaria seedlings to water stress

Information on the morphological and physiological responses of seedlings to stressors, such as water stress, is required for successful early establishment of seedlings. We examined provenance variation in morphological and physiological traits of Quillaja saponaria Molina seeds from nine provenances representing a latitudinal transect across the species range in Chile. The seedlings were subjected to two water regimes (well-watered vs water restriction) in a nursery experiment, and growth, biomass, survival, and gas exchange traits were measured. As expected, well-watered seedlings exhibited a superior performance in all traits analysed. Provenance effects were significant for most of the morphological and physiological traits. In the growth and biomass analysis, the northernmost provenance showed the lowest survival, growth and dry biomass, whereas in the gas exchange analysis, the southern interior provenance showed the highest net photosynthesis, transpiration, stomatal conductance and water use efficiency. The interaction between water regimes and provenance was only significant for diameter and net photosynthesis. These results indicate that different provenances of Q. saponaria show a stable performance across different controlled drought conditions. This information is of relevance for sourcing seeds for the restoration of the species.     

Effects of water stress on growth,dry matter allocation and water-use efficiency of a leguminous species, <Emphasis Type="Italic">Sophora davidii</Emphasis>

The adaptation responses to different water conditions and the drought tolerance of Sophora davidii seedlings were assessed in a greenhouse experiment. Two-month-old seedlings were subjected to the following water supplies for 95 days: 100, 80, 60, 40 and 20% of field water capacity. The seedlings at 100% FC had the greatest productivity, height, basal diameter, branch number, leaf number and leaf area. Water supply <80% FC was the threshold of drought-initiated negative effects on seedling growth, yield and physiological processes; these parameters were severely reduced at 20% FC, however, there was no plant death during the experiment. Moreover, water stress decreased leaf relative water content, specific leaf area, leaf area ratio, and water-use efficiency (WUE), whereas it increased the biomass allocation to roots, which resulted in a higher root:stem mass ratio under drought. The S. davidii seedlings tolerated drought by maintaining high leaf relative water content and by reducing branching and leaf expansion. However, low productivity and WUE at 20% FC suggested that seedlings did not produce high biomass under severe drought. Therefore, prior to introducing S. davidii in forestation efforts, a water supply >40% FC is recommended for seedlings to maintain growth and productivity. These results provide insights into limitations and opportunities for establishment of S. davidii in arid regions.     

干旱胁迫对不同种源马尾松苗木生长的影响

对广东信宜、浙江江山、湖南汝城、重庆黔江和湖北大悟5个种源马尾松容器苗进行不同程度干旱周期性胁迫处理,测定和分析干旱胁迫对各种源马尾松苗木生长的影响。结果表明:干旱胁迫下,各种源马尾松苗木生长均受到抑制,中度胁迫和重度胁迫下的苗高增长量、地上部分干重、地下部分干重、总干重均低于对照。胁迫后期,各种源生长指标的变化幅度不一致。综合分析得出:湖南、湖北、广东种源较为耐旱;浙江、重庆种源耐旱能力较弱。     

Effects of drought stresses induced by polyethylene glycol on germination of Pinus sylvestris var. mongolica seeds from natural and plantation forests on sandy land

Effects of drought stresses induced by polyethylene glycol (PEG) (0.0%, 10%, 15%, 20%, 25%, and 30%, with four replicates) on germination of Mongolian pine (Pinus sylvestris var. mongolica) seeds produced in plantations (southern Keerqin sandy land) and natural forests (Hulunbeier sandy plain) were observed. The results indicated that the seeds from both provenances did not germinate when PEG concentration was more than 25%. The time of initial germination and that of its completion of stressed seeds from both provenances were delayed when compared with the unstressed seeds. The germination capacity and germination rate of natural seeds were significantly higher than those of plantation seeds for all treatment levels (P < 0.05). The mean growth rates of radicle and hypocotyl from natural seeds were significantly higher than those from plantation seeds at all treatment levels below 20% PEG treatment (P < 0.05). The ratios of radicle to hypocotyl of 20% PEG treatment were significant higher than those of the corresponding controls for both provenances (P < 0.05). These results suggested that Mongolian pine seeds/seedlings had stronger resistance to PEG drought stresses; 10% PGE stress did not significantly influence germination. Natural seeds exhibited more resistance to PEG stress than plantation seeds. It was concluded that drought stress on seed germination might be one cause of obstructed natural regeneration of Mongolian pine plantations on sandy land. It is recommended that natural seeds be used for afforestation, and light drought stress (e.g., 10% PEG stress) may be useful in improving seed germination and the growth of radicles and hypocotyls.     

Growth,biomass partitioning,and water-use efficiency of a leguminous shrub (<Emphasis Type="Italic">Bauhinia faberi</Emphasis> var. <Emphasis Type="Italic">microphylla</Emphasis>) in response to various water availabilities

Responses of the endemic leguminous shrub Bauhinia faberi var. microphylla, to various soil water supply regimes were studied in order to assess water stress tolerance of seedlings. Two-month-old seedlings were grown under water supply regimes of 100, 80, 60, 40, and 20% water field capacity (FC), respectively, in a temperature and light-controlled greenhouse. Plant height and leaf number were measured monthly over a 4-month period, while water use (WU), water-use efficiency (WUE), leaf relative water content (RWC), biomass production and its partitioning were recorded at the end of the experiment. Seedlings exhibited the greatest biomass production, height, basal diameter, branch number, leaf number, and leaf area when soil content was at 100% FC, and slightly declined at 80% FC. These parameters declined significantly under 60% FC water supply, and severely reduced under 40 and 20% FC. RWC, WU and WUE decreased, while the ratio of root mass to stem mass (R:S) increased in response to decreasing water supply. Water stress caused leaf shedding, but not plant death. The results demonstrated that B. faberi var. microphylla seedlings could tolerate drought by reducing branching and leaf area while maintaining a high R:S ratio. However, low dry mass and WUE at 40 and 20% FC suggested that the seedlings did not produce significant biomass under prolonged severe water deficit. Therefore, before introducing B. faberi var. microphylla in vegetation restoration efforts, water supply above 40% FC is recommended for seedlings to maintain growth.     

红松不同种源种子储藏后对苗木生长的影响

红松是东北地区的重要造林树种之一,主要依靠培育实生苗造林.育苗中经常采用陈年种子,经对6个种源、7个批次的红松种子进行1年生苗木生长情况的测定,认为红松不同种源种子的储放时间长短与苗木生长的变化关系差异极显著;结果表明,有好的种源做保证,有利于苗木正常地生长.     

干旱胁迫对不同种源沙柳苗木水势和水分利用效率的影响

通过人工模拟方式对5个种源沙柳苗木进行干旱胁迫处理,研究干旱处理不同阶段苗木小枝水势日变化、叶片相对含水量、水分饱和亏缺、保水力及水分利用效率。结果表明:干旱胁迫下5个种源的沙柳苗木小枝水势和叶片相对含水量均下降,而水分利用效率在轻度干旱时呈上升趋势,随干旱胁迫的加剧而下降。干旱处理15天后,民勤种源的沙柳日平均小枝水势下降幅度最大为0.77 MPa,然后依次为达拉特旗0.57 MPa、盐池0.36 MPa、榆林0.25 MPa和乌审旗0.12 MPa,其中民勤种源的苗木在充分供水和干旱胁迫下小枝水势差异达到显著。干旱处理18天后叶片相对含水量分别下降:民勤1.68%、盐池7.03%、达拉特旗7.25%,榆林9.35%和乌审旗11.07%,水分饱和亏缺民勤<盐池<达拉特旗<榆林<乌审旗。结果表明,民勤种源的沙柳抗旱的能力较强,而盐池和达拉特旗沙柳苗木在受到水分胁迫时水分利用效率下降幅度较小,即水分胁迫对苗木干物质的积累影响较小,因此具有更高的经济价值。     

Seasonal evolution of water status after outplanting of two provenances of Holm oak nursery seedlings

Forest restoration programs using Holm oak (Quercus ilex ssp. ballota [Desf.] Samp.) have had limited success. The effect of plant provenance on plantation success is uncertain, although some previous studies suggest that some provenances may be better able to tolerate stress. We studied the tolerance to drought in seedlings from two Spanish provenances of Holm oak before and after outplanting. One provenance was from a continental climate with cold winters (GR) and the other was from a xeric climate (HU). Seedlings were subjected to a water stress test in the nursery during the summer and survival was visually assessed after 2?weeks. In addition, 35 healthy seedlings of each provenance that were not subjected to the water stress tests were used for outplanting experiment. In these plants the seasonal changes in water potential at dawn (Ψ), specific leaf area (SLA), cuticular transpiration (E_c), and loss of xylem hydraulic conductance of twigs (PLC) were measured over 18?months. After the water stress test in summer, mortality was 44.3?% for GR seedlings and 12.6?% for HU seedlings. In addition there were differences between the two provenances in plant water status after planting. The HU provenance had a better water status and was more water conservative in the summer (higher Ψ, lower E_c, lower PLC), but not in the winter. The different drought tolerance and water relations parameters of these two provenances indicate that provenance should be considered in forest restoration and conservation programs involving Holm oak.     

Effects of brassinolide on the survival,growth and drought resistance of <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> seedlings under water-stress

We conducted field and pot experiments to investigate the effects of brassinolide on 1-year-old Robinia pseudoacacia L. seedlings. In the field experiment, seedling roots were soaked in brassinolide solutions containing 0–0.4 mg/l pure brassinolide before planting. Survival and growth of the seedlings were determined 8 months later. The results showed that soaking roots in brassinolide prior to planting significantly increased the survival and growth of seedlings. The best results were in the 0.2 mg/l brassinolide treatment. In the pot experiment, roots were soaked in 0–0.4 mg/l brassinolide before planting followed by a foliar application of brassinolide when the seedlings leafed out. After the seedlings were established, the soil water content in the pots was regulated to simulate drought conditions and various physiological parameters were measured. The results showed that treatment with 0.2 mg/l brassinolide decreased the transpiration rate, stomatal conductance and malondialdehyde (MDA) content of seedlings growing under moderate or severe water stress compared to untreated seedlings. Leaf water content, predawn water potential, soluble sugar content, free proline content, and superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were all greater in water-stressed seedlings in the 0.2 mg/l brassinolide treatment compared to the control. The results indicate that the application of brassinolide can ameliorate the effects of water stress and enhance drought resistance of Robinia seedlings. Treatment of seedlings with brassinolide may be a useful management tool for afforestation projects in arid and semiarid areas.     

南酸枣8个种源的早期表现

以南方6个省8个地点的种子为度材，研究发现南酸枣在种子形态，种子大小、苗期生长节律和造林初期生长量上均存在种源差异。西部种源种子明显小于东部种源，偏南部种源的苗木生长停止期较迟，江西会昌种源生长最佳，其2年生幼林树高和胸径生长量超过试验群体平均值的11.75%和8.21%，南酸枣幼年期生长迅速，在优良圃地条件下育苗密度不宜超过每公顷10.8万株。     

Are marginal beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) provenances a source for drought tolerant ecotypes?

Due to the expected increases of number and intensity of summer droughts in Central Europe the identification of drought tolerant ecotypes becomes more important in future forestry. A common garden experiment with seedlings of Fagus sylvatica provenances from the center (Germany) and eastern margin (Poland) of the species’ distribution range was conducted. Responses of morphological, physiological, chemical and growth parameters to three drought treatments were analyzed. Relative growth rates of the marginal provenance were lower as compared to the central provenance. The marginal seedlings showed a tendency to higher total biomasses because of higher seed masses. In both provenances drought decreased biomass production and root/shoot ratio which was lower in the central provenance. A lower specific root area of the marginal provenance indicated a better adaptation to low xylem water potentials. Under moderate drought, lower leaf δ¹³C signatures may indicate lower stomatal limitation (or a reduced rate of CO₂ assimilation) in the marginal provenance. We conclude that marginal beech provenances may exhibit a better drought adaptation.     

Effects of drought and rewatering on growth and transpiration in European beech seedlings late in the growing season

Drought stress is one of the most important environmental factors affecting plant growth and survival. To date, most studies aim at understanding of post-stress physiological and anatomical adaptation to drought stress; however only few studies focus on plant recovery. In the present study, transpiration, shoot water potential, and anatomical and morphological measurements were performed on 4-year-old European beech seedlings with fully developed leaves. The seedlings were exposed to three levels of soil water potential (well-watered, moderate drought stress and severe drought stress) and followed by rewatering under greenhouse conditions. Reduced transpiration rates were observed in the stressed seedlings as a response to drought stress, whereas anatomical and morphological variables remained unchanged. Three days after rewatering, transpiration rates in both moderately and severely stressed seedlings recovered to the levels of those of well-watered seedlings. Drought stress promoted leaf budding, resulting in higher shoot dry mass of stressed seedlings. Our findings indicate that anatomical and morphological adaptations of European beech seedlings to drought stress are visibly limited during late-season growth stages. These results will help us to further understand factors involved in drought adaptation potential of European beech seedlings faced with expected climate-related environmental changes. To complete our findings, further experiments on plant recovery from drought stress should be focused on different periods of growing season.     

不同种源文冠果叶片气孔分布特征对水分胁迫的响应

[目的]探究不同种源文冠果叶片气孔分布特征对水分胁迫的响应,了解其耐旱性差异,为节水耐旱文冠果种源的选择提供依据。[方法]以集中分布在华北地区的3个不同种源文冠果幼苗为研究对象,通过盆栽控水方法设置充足水分(W1)、正常供水(W2)、轻度干旱(W3)和重度干旱(W4)4个水分梯度,采用指甲油印迹技术,研究不同种源文冠果叶片气孔分布特征对水分胁迫的响应。[结果]表明:不同种源文冠果的气孔均分布在叶片的下表皮,随着干旱胁迫程度的加剧,气孔变得小而多,趋于旱生植物的叶片气孔分布结构特征;气孔分布特征对水分胁迫的响应存在显著的差异性,与河南三门峡、山西晋中两个种源相比,河北承德种源叶片在不同水分胁迫处理下均具有小而多的气孔,以及较强的气孔调节能力。[结论] 3个种源文冠果叶片气孔分布特征均存在着不同程度的趋于旱生结构;河北承德种源文冠果叶片气孔器比其他2个种源均相对小而多,且调节能力强,属华北地区抗旱优良种源。     

Functional response of <Emphasis Type="Italic">Quercus robur</Emphasis> L. to taproot pruning: a 5-year case study

Key message

Quercus robur seedling mass was affected more by planting density than by taproot pruning. Root pruning enhanced stem biomass at the expense of roots in later growth stages. Alteration of biomass allocation due to nursery practices may result in greater susceptibility to injury and death of the seedlings under unfavorable environmental conditions.

Context

Plants adjust their growth and modulate the resource allocation in response to applied treatments and environmental conditions.

Aims

The aim was to examine how taproot pruning in seedlings grown at different densities affected long-term growth of Quercus robur.

Methods

Seedlings, sown as acorns at two planting densities, with or without pruned roots were harvested in the second, fourth, and fifth years of growth. The effect of root pruning on biomass allocation was determined by measuring leaf, stem, and root mass fractions; carbohydrate concentrations in the roots; and C/N ratios. Specific leaf area and root length were also determined to assess morphological adaptations to growth conditions.

Results

Total seedling mass was affected more by planting density than by taproot pruning. After 4 years of growth, root mass fractions were lower and stem mass fractions were greater in seedlings planted at a higher density. Five-year old root-pruned seedlings also had a lower root mass fraction and higher stem mass fractions than unpruned seedlings. Specific root length was not affected by root pruning or planting density.

Conclusion

Decrease of relative root biomass with simultaneous increase of stem biomass may be a long-term consequence of taproot pruning of Q. robur, and the effects may manifest years after the seedling stage.

     

干旱胁迫对不同种源北沙柳幼苗生长特性的影响

对7个种源的北沙柳1年生幼苗开展干旱胁迫试验的结果表明,各种源表现出的胁迫症状基本相同,随着胁迫水平的增加,产生的胁迫症状越严重。干旱胁迫使北沙柳的生长受到抑制,株高与基径的生长减缓,总生物量的积累受到抑制。干旱胁迫促进北沙柳根系的生长,以吸收更多的水和营养,从而提高其抗旱性,综合分析可知宁夏盐池种源（SNY）是干旱胁迫下生长表现最优的种源。     

不同种源白刺幼苗生理生长对水分梯度的响应差异

在乌兰布和沙漠东北部地区,依据多年平均月降水量,对5个种源的白刺幼苗进行极度干旱、干旱、轻度干旱和正常降雨水平4种不同的水分梯度处理,开展水分梯度试验.通过测定不同水分梯度、不同种源的光合生理指标表明:水分梯度显著影响白刺幼苗的净光合速率、蒸腾速率、气孔限制值、气孔导度、光合水分利用效率、表观光能利用效率、表观CO2利用效率等生理生态特征,并影响植株的苗高和最大新枝长等生长量指标;不同种源之间的净光合速率、水分利用效率、表观光能利用效率、表观CO2利用效率存在显著差异,且在苗高和最大新枝长之间也存在显著差异,但不同种源、不同水分梯度对幼苗的地径均无显著影响.相比于临河、乌拉特后旗种源,磴口、阿拉善盟和民勤种源的蒸腾速率和资源利用效率在不同水分处理之间表现出显著差异,且3个种源的各个资源利用效率都较大.白刺幼苗在光合活动中的气体交换及资源利用效率的生理反应和外在的生长量表型指标的差异,反映了各白刺种源对不同水分环境表现出的响应差异.     

Survival and growth of drought hardened <Emphasis Type="Italic">Eucalyptus pilularis</Emphasis> Sm. seedlings and vegetative cuttings

Forestry requires low mortality of transplanted seedlings. Mortality shortly after planting is often associated with inadequate hydration of transplants. Seedlings can be hardened to the drought conditions they may experience after transplanting by exposing them to controlled drought conditions in the nursery. Eucalyptus pilularis Sm. seedlings were drought hardened by providing nil (severe treatment) or half (mild treatment) the daily irrigation routinely received (control treatment) for up to two non-consecutive days per week during the last 4 weeks of growth in the nursery. Drought hardening reduced stem diameter, seedling leaf area, leaf area per root biomass and seedling quality measured by the Dickson quality index, but increased root:shoot ratio. Hardened seedlings had lower stomatal conductance and leaf water potential on the days they received less irrigation that the control treatment. Hardened seedlings had greater stomatal conductance and were less water stressed than seedlings experiencing drought for the first time indicating hardened seedlings had adjusted physiologically to drought. Survival after transplanting in the controlled drought environment in a glasshouse was enhanced by the hardening treatments. Non hardened seedlings that had had their upper leaves manually removed immediately prior to transplanting to reduce leaf area (top-clipped) had similar survival to hardened seedlings. Stomatal conductance and leaf water potential after transplanting were higher in hardened and top-clipped seedlings than unhardened control seedlings or vegetative cuttings. Survival in the field trial was over 95% for all treatments, possibly as rain fell within 4 days of planting and follow-up rain occurred in the subsequent weeks. Neither the hardened or top-clipped seedlings planted in the field trial had reduced growth, increased propensity to form double leaders or worse stem form than control seedlings when measured at age 3 years.     

Correlations and clines in tree growth and wood density of <Emphasis Type="Italic">Balanites aegyptiaca</Emphasis> (L.) Delile provenances in Niger

Balanites aegyptiaca (L.) Delile provides wood and other essential products for farming and pastoralist communities in the West African Sahel. In this region, mean annual rainfall decreases in general from south to north and from west to east, so one might expect clinal variation in fitness-related traits in relation to the rainfall gradients. This paper presents results from a provenance/progeny test of 11 provenances sampled in Niger and established at one relatively dry site in Niger. The objectives were to evaluate phenotypic correlations (Pearson r) between tree growth (height, stem diameter) and basic density of the wood, and clines in growth and density at 13 years. Tree growth and wood density were positively correlated, and the correlations differed among provenances. Mean tree height and stem diameter of provenances increased, in general, from the more humid to the drier parts of the sample region. Results suggest that selection of faster-growing trees could lead to an increase in wood volume and density in the subsequent generation, especially in certain provenances; that provenances from drier areas are better adapted to drought; and that tree improvement and conservation programs should collect seeds from populations in the drier areas for planting and conservation.     

马尾松苗木叶绿素荧光参数及相对水分亏缺测定

对广东信宜、浙江江山、湖南汝城、重庆黔江和湖北大悟等5个种源的马尾松苗木进行干旱胁迫处理,并测定其叶绿素荧光参数Fv/Fm值及相对水分亏缺。结果表明:大部分种源马尾松苗木叶绿素荧光参数Fv/Fm值在中度或重度干旱胁迫下低于对照,相对水分亏缺在中度或重度干旱胁迫下高于对照,均表现出积极的抗旱反应。