Carbon unloading in roots in relation to root senescence in Cercis chinensis seedlings under drought stress

When Cercis chinensis seedlings suffered from drought treatment,net photosynthetic rates had been significantly reduced at the end of the drought treatment. Compared with the control,the activities of acid invertases in roots had increased 5 and 11 days after drought treatment. Seventeen days after drought treatment,the activities of acid invertases in roots were significantly decreased,while activities of alkaline invertases in roots had also been significantly reduced. As the moisture in culture media dec...     

Effects of nutrition spatial heterogeneity on root traits and carbon usage by roots of Cercis chinensis seedlings in split root rooms

In natural ecosystems, nutrition available for plants shows great spatial heterogeneity. Much is known about plant root responses to the spatial heterogeneity of nutrition, but little is known about carbon usage in roots in nutrition-deficient patches and its effect on root longevity. In this study, split-room boxes were used for culture of Cercis chinensis seedlings, and the small rooms were supplied with different nutrition levels. The number of the first-order roots in the rooms with nutrition supply was significantly higher than that in the rooms with deficient nutrition. Specific root length （SRL） of the first-order roots in the rooms with deficient nutrition reached its peak at day 64 after nutrition treatment. There was no significant SRL differences between the two order roots during the experiment. Biomass of the first-order roots in the rooms without nutrition supply was significantly less than that of the first-order roots in the rooms with nutrition supply from day 64 to 96. The total biomass of the lateral roots in the rooms without nutrition supply decreased from day 64 to 96. The activities of the enzymes in roots in the rooms without nutrition supply increased and the activities of alkaline invertases in roots in the two sides of split box did not change significantly. The activities of the enzymes in roots in the rooms without nutrition supply increased gradually. These results suggest that nutrition spatial heterogeneity induced the changes in root traits and plants actively controlled carbon usage in roots in nutrition-deficient patches by regulating the activities of invertases and sucrose synthases, resulting in the reduction in carbon usage in the roots in nutrition-deficient patches.     

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.     

Effects of nutrition spatial heterogeneity on root traits and carbon usage by roots of Cercis chinensis seedlings in split root rooms

In natural ecosystems, nutrition available for plants shows great spatial heterogeneity. Much is known about plant root responses to the spatial heterogeneity of nutrition, but little is known about carbon usage in roots in nutrition-deficient patches and its effect on root longevity. In this study, split-room boxes were used for culture of Cercis chinensis seedlings, and the small rooms were supplied with different nutrition levels. The number of the first-order roots in the rooms with nutrition supply was significantly higher than that in the rooms with deficient nutrition. Specific root length (SRL) of the first-order roots in the rooms with deficient nutrition reached its peak at day 64 after nutrition treatment. There was no significant SRL differences between the two order roots during the experiment. Biomass of the first-order roots in the rooms without nutrition supply was significantly less than that of the first-order roots in the rooms with nutrition supply from day 64 to 96. The total biomass of the lateral roots in the rooms without nu-trition supply decreased from day 64 to 96. The activities of the enzymes in roots in the rooms without nutrition supply increased and the activities of alkaline invertases in roots in the two sides of split box did not change significantly. The activities of the enzymes in roots in the rooms without nutrition supply increased gradually. These results suggest that nutrition spatial heterogeneity induced the changes in root traits and plants actively controlled carbon usage in roots in nutrition-deficient patches by regulating the activities of invertases and sucrose synthases, resulting in the reduction in carbon usage in the roots in nutrition-deficient patches.     

NaCl胁迫下沙枣幼苗的离子代谢特性

[Objective]To further understand the ion metabolism characteristics of Elaeagnus angustifolia L. under NaCl stress.[Method]The seedlings of two E. angustifolia L. provenances, which were Alaer (salt tolerance provenance) and Yinchuan (salt sensitive provenance), were treated by three NaCl concentrations (0,150,300 mmol·L^-1) and sampled at the 7th day and the 30th day to measure the Na⁺ , K⁺, Ca²⁺, and Mg²⁺ contents, K⁺/Na⁺ ratio and selective absorption and transportation of K⁺ in tissues (roots, stems and leaves). [Result]The results showed that the Na⁺ content in the organizations of E. angustifolia L. sharply increased with the increase of NaCl concentration. With prolonging of stress time, the Na⁺ content increased in roots, and decreased in stems and leaves. After seedlings of the two provenances were treated with 150 mmol·L^-1 NaCl for 7 days, the Na⁺ content was 2.10 times and 2.23 times in leaves, respectively, compared with the control groups, and was 1.79 times and 1.57 times in root. Meanwhile, the difference between two provenances showed a expanding trend with the increase of NaCl concentration and stress time. With the increase of NaCl concentration and extension of stress time, the K⁺ content, Ca²⁺ content and K⁺/Na⁺ ratio in organizations decreased gradually. Meanwhile, the Alaer provenance seedlings accumulated more Na⁺ in roots and less Na⁺ in leaves than that of Yinchuan provenance, and the K⁺ content, Ca²⁺ content and K⁺/Na⁺ ratio decreased less in the Alaer provenance seedlings than those of Yinchuan provenance. With the increase of NaCl concentration, the Mg²⁺ content in leaf gradually decrease, but the Mg²⁺ content in root increased 22.8~64.4% after salt stress for 7 days, and Alaer provenance seedlings increased more than Yinchuan provenance. After 30 days, there was non-significant difference with the control group on the Mg²⁺ content of root. K⁺ selective absorption of E. angustifolia L. seedlings significantly increased with increasing salt concentration of the media at the 7th days, whereas not obvious at the 30th days. When the concentration of NaCl in the media increased, the change of K⁺ selective transportation was not significant. [Conclusion]E. angustifolia L. seedlings increase Mg²⁺ content and K⁺ selective absorption in the roots at the early stage of salt stress to adapt saline environment. The salt-tolerance E. angustifolia L. provenance can cut off more Na⁺ in roots and reduce Na⁺ content in leaves, which cause less K⁺, Ca²⁺ and Mg²⁺ contents loss, especially the roots and leaves, so as to ensure that all kinds of metabolisms can go well.     

土壤温度和水分变化对川西云杉幼苗氮和磷含量的影响

【目的】研究不同梯度的土壤温度和水分对川西云杉幼苗生长性状和各器官氮和磷含量的影响,以期为全球气候变暖背景下解释川西云杉树线形成的原因提供参考和数据积累。【方法】以5年生川西云杉幼苗为试验材料,采用人工气候室结合嵌套设计,设置5个土壤温度梯度(2、7、12、17、22℃)和3个土壤水分梯度(干旱处理、正常水分含量处理、饱和水分含量处理)。每处理9株幼苗,共135株幼苗。实验处理4个月后,测定并比较分析不同梯度的土壤温度和水分对幼苗的生长性状、各器官干物质含量、各器官全氮、全磷浓度和含量以及土壤全氮和全磷浓度的影响。【结果】土壤温度处理对幼苗基径和株高生长量均无显著影响,而土壤水分处理对幼苗株高生长量有显著影响;在2℃和7℃土壤温度干旱处理下显著降低了幼苗的株高生长量,但随着土壤温度的升高其影响效应不显著。土壤温度处理对土壤氮和磷浓度无显著影响,而干旱处理显著升高了土壤氮和磷浓度。川西云杉幼苗各器官的氮和磷浓度以及当年生叶氮含量随土壤温度降低显著降低;干旱和饱和水分处理显著降低了当年生叶和当年生枝的氮浓度,饱和水分处理显著降低了当年生叶的磷浓度,干旱处理显著降低了当年生枝、茎和根的磷浓度,干旱和饱和水分处理显著降低了当年生叶和根的氮和磷含量,且随着土壤温度升高影响效应更显著。【结论】在短期内,土壤低温对川西云杉幼苗的生长性状没有明显的制约作用,但对川西云杉幼苗各器官的氮和磷浓度及含量影响显著,尤其是当年生叶和根的氮和磷浓度及含量。在川西地区,低温、干旱等极端气候胁迫导致的云杉幼苗氮、磷含量的不足很可能是限制川西云杉垂直分布的重要因素。此外,土壤温度和水分处理存在显著的交互作用,随着土壤温度的降低,水分胁迫对幼苗各器官氮和磷含量的影响由显著变得不再显著,说明随着海拔升高,与水分因子相比,土壤低温成为造成云杉各器官营养元素亏缺的主导因子。     

干旱胁迫及复水对绿竹容器苗生理特征的影响

[目的]探究模拟干旱环境下水分亏缺对绿竹容器苗主要营养器官生理特性的影响,为绿竹规模化育苗栽培制定适宜的经营管理及节水灌溉技术方案提供理论依据。[方法]以绿竹组培苗为试验材料,采用盆栽苗控水方式,测定分析不同干旱胁迫条件下绿竹叶片及根系抗氧化酶、膜脂渗透性、叶片光合色素含量、以及根系活力等生理指标。[结果]表明:随着干旱胁迫加重,绿竹叶片叶绿素a、叶绿素b和类胡萝卜素含量明显下降,各处理间均达到差异显著(P0.05),复水后叶绿素a、叶绿素b、及类胡萝卜素含量均明显升高,其中叶绿素a、叶绿素b达到差异显著(P0.05),但类胡萝卜素差异不显著(P0.05);干旱胁迫下,根系活力呈明显下降趋势,中度干旱胁迫(MS)和重度干旱胁迫(SS)根系活力分别比对照(CK)下降14.35%、33.31%,均达到差异显著(P0.05),复水后,根系活力均明显升高,分别达到了CK处理根系活力的96.75%、73.84%;干旱胁迫下,根系及叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性和丙二醛(MDA)含量均呈上升趋势,且在复水后均呈现一定下降趋势,表现为中度干旱胁迫后复水(MS-CK)降低程度高于重度干旱胁迫后复水(SS-CK),各处理间均达到差异显著(P0.05)。[结论]模拟干旱环境下,增加干旱胁迫程度,绿竹的根系活力及叶片色素含量呈显著降低,MDA含量及SOD、CAT、POD活性均升高。复水后,根系活力及叶片色素含量较干旱胁迫时有所提高,MDA含量及SOD、CAT、POD活性有明显下降,不同干旱程度补偿能力不同,表现为中度干旱胁迫后复水高于重度干旱胁迫后复水,且不同营养器官对于解除干旱后消除活性氧及修复适应能力也不尽相同。绿竹根系活力和叶绿素含量与干旱胁迫程度呈负相关,而保护酶SOD、CAT、POD活性以及MDA含量均与干旱胁迫程度呈正相关。     

丛枝菌根化香椿、秋枫幼苗对干旱胁迫生理响应

以香椿（Toona sinensis）、秋枫（Bischofia javanica）实生种子苗为试验材料,研究干旱胁迫下丛枝菌根化香椿、秋枫幼苗叶片质膜透性、游离脯氨酸含量及超氧化物歧化酶（SOD）活性的变化.结果表明：随着干旱胁迫程度加重及胁迫时间延长,香椿、秋枫幼苗叶片质膜透性、游离脯氨酸含量呈增加趋势,SOD活性在胁迫处理4天时明显增加,之后随着胁迫时间延长无明显变化趋势.中度干旱胁迫（田间持水量40％）处理20天时,菌根化香椿、秋枫幼苗叶片质膜透性、游离脯氨酸含量及SOD活性均高于非菌根化苗.这说明,接种丛枝菌根能有效促进香椿、秋枫幼苗生理抗旱性,且干旱胁迫程度越重效果越显著.     

Photosynthesis and photoassimilate transport during root hypoxia in Melaleuca cajuputi, a flood-tolerant species, and in Eucalyptus camaldulensis, a moderately flood-tolerant species

We compared the photosynthetic and photoassimilate transport responses of Melaleuca cajuputi Powell seedlings to root hypoxia with those of Eucalyptus camaldulensis Dehnh. Control and hypoxia treated roots were maintained in a nutrient solution through which air or nitrogen was bubbled. Under root hypoxic conditions, seedlings of M. cajuputi, a flood-tolerant species, maintained height growth, whereas seedlings of E. camaldulensis, a moderately flood-tolerant species, showed markedly decreased height growth compared with control seedlings. Root hypoxia caused decreases in whole-plant biomass, photosynthetic rate and stomatal conductance in E. camaldulensis, but not in M. cajuputi. Photoassimilate transport to roots decreased significantly in E. camaldulensis seedlings 4 days after treatment and starch accumulated in mature leaves. Photoassimilate supply to hypoxic roots of E. camaldulensis seedlings was, thus, limited by reduced photoassimilate transport rather than by reduced photosynthesis. In contrast, M. cajuputi seedlings showed sustained photoassimilate transport to hypoxic roots and persistent photosynthesis, which together provided a substantial photoassimilate supply to the roots. Sucrose accumulated in hypoxic E. camaldulensis roots, but not in hypoxic M. cajuputi roots. A stable, low sucrose concentration in hypoxic roots would let M. cajuputi seedlings prolong photoassimilate transport to the roots. Photoassimilate partitioning among the water-soluble carbohydrates, starch and structural carbohydrates within the roots was unaffected by root hypoxia in E. camaldulensis, but in M. cajuputi, partitioning was shifted somewhat from structural carbohydrates to water-soluble carbohydrates. This suggests that M. cajuputi seedlings are able to increase photoassimilate utilization in metabolism and sustain energy production under root hypoxic conditions.     

滇重楼种子内源激素含量与种胚长度和萌发的关系

[目的]通过研究滇重楼种子层积过程中不同阶段内源激素含量与种胚长度的动态变化情况来探讨种子休眠机理.[方法]应用酶联免疫吸附法测定不同阶段种子内激素含量.[结果]种子萌发过程中,脱落酸(ABA)含量由54.34 ng·g^-1·FW降至32.16 ng·g^-1·FW,赤霉素(GA)、玉米素核苷(ZR)显著升高,吲哚乙酸(IAA)含量波动较大,但整体呈逐渐升高趋势,随层积时间延长,未萌发种子中ABA含量持续降低,GA含量与GA/ABA值持续升高,仍显著低于已萌动种子中激素含量(p<0.05);种子在层积42天后,种胚开始膨胀,胚率快速增加;相关性分析结果,内源激素含量及比值与种胚生长呈显著相关(p<0.05),其中,GA/ABA值对种胚生长的影响最大.[结论]种子萌发过程中仅ABA含量降低不足以解除滇重楼种子休眠,同期GA含量升高和GA/ABA值达到某一阈值时能有效的解除滇重楼种子的休眠和促进胚的发育;种子在层积40天左右后,由于各项激素的综合作用,滇重楼种子由休眠状态逐步转变为破除休眠状态和萌发状态.     

短期NaCl胁迫对西伯利亚白刺幼苗Na~+、K~+分配和平衡的影响

[目的]为探究西伯利亚白刺盐适应机制。[方法]以1年生西伯利亚白刺水培幼苗为材料,研究不同浓度NaCl(0、200、300 mmol·L-1)胁迫24 h后根系Na~+、K~+离子流的动态变化(利用扫描离子选择微电极技术,SIET)及植株各器官中Na~+、K~+含量的静态变化(利用电感耦合等离子体光谱仪,ICP-OES)。[结果]表明:(1)短期NaCl胁迫显著提高了西伯利亚白刺根、茎、叶中Na~+含量,其中,叶中Na~+含量是根中的3倍以上;西伯利亚白刺根、茎、叶中K~+含量保持稳定或上升;(2)盐胁迫下,西伯利亚白刺根、茎、叶中K~+/Na~+呈下降趋势,其中,在200、300 mmol·L-1NaCl胁迫下,根中K~+/Na~+差异不显著;(3)离子流结果显示,NaCl胁迫显著提高了西伯利亚白刺根系Na~+的外流;对照和200 mmol·L-1NaCl胁迫下,K~+净流量分别为156、159 pmol·cm-2·s-1,差异不显著;300 mmol·L-1NaCl胁迫显著提高了K~+的内流,净流量为-370 pmol·cm-2·s-1。[结论]综合分析认为,西伯利亚白刺通过叶片对Na~+区隔,加强根系对Na~+的外排和K~+内流,进而维持植株根系K~+/Na~+的相对平衡,以此适应盐渍环境。     

Growth and biomass production in Azadirachta indica seedlings in response to nutrients (N and P) and moisture stress

Production of quality seedlings is an important aspect of successful tree planting. No information is available on the effect of nutrients and water on the growth and development of the seedlings of neem (Azadirachta indica A. Juss), an important component of many tropical agroforestry systems. In an experiment in central India, the growth and nutrient-use efficiency of neem seedlings grown at various levels of light, nutrients (N and P), and water stress were determined. Seedlings were given light (diffused and complete) and nutrient (N and P) treatments comprising either high N-high P, high N-low P, low N-high P, or low N-low P. Seedlings grown in complete light (800 mol/m²/s) had four times more biomass than those grown in diffused light (200 mol/m²/s). Significant increase in seedling biomass was observed with nitrogen application, while phosphorus had no effect on biomass. Leaves contributed maximum biomass, followed by roots and stem. Nutrient use efficiency decreased with an increase in the supply of nutrients. In another experiment, containerized and bare-root seedlings were subjected to five watering treatments, viz., watering twice a week, watering weekly, watering every alternate week, watering every third week, and natural precipitation. Plant moisture stress affected both growth and survival of neem seedlings. Only 50 per cent of seedlings survived in severe drought treatment (no. 4) whereas 90 to 95 per cent seedlings showed growth in all other treatments. Plant moisture stress in severe drought treatment averaged –21 bar while in other treatments it ranged from –9 to –12 bar. Shoot-root ratio was high in bare-root seedlings as compared to containerized seedlings. Containerized seedlings had shown better endurance against drought than the bare-root seedlings. The results suggest that neem seedlings adjust their nutrient use efficiency and can be grown even under limited available resources. It is also inferred that the species can tolerate soil resource depletion caused by competitor species.This revised version was published online in November 2005 with corrections to the Cover Date.     

干旱胁迫对垂柳生理特性的影响

试验在田间条件下研究了干旱对垂柳2年生苗生理特性的影响规律,结果表明:随着干旱时间的延长,垂柳叶片内叶绿素a、叶绿素b、总叶绿素含量均有所降低,6月9日,干旱处理与对照相比分别降低了1.45、0.30、1.45mg·g^-1;干旱胁迫提高了保护酶活性,其中POD、SOD、CAT活性分别比对照提高了14.30、17.42、9.67U·g^-1;渗透物质含量在干旱持续时间超过25d后显著升高,其中可溶性蛋白、可溶性糖、游离脯氨酸含量与对照相比分别提高了40.10%、25.33%、69.46%;电导率在干旱持续15d后显著升高,MDA含量在干旱持续10d后显著升高,试验结束时分别比对照提高了21.47%、35.62%。综合分析认为,浇水25d后垂柳生理特性会发生显著变化。     

盐旱交叉胁迫对皂角幼苗保护酶活性的影响

以一年生皂角Gleditsia sinensis Lam.实生苗为材料,研究干旱和盐分交叉胁迫对其膜质过氧化和保护酶活性的影响.结果表明:盐旱交叉胁迫下,丙二醛(MDA)含量、膜透性呈上升趋势,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性先上升后下降;在相同的处理下,随着处理时间的延长,膜透性和MDA含量呈上升趋势,SOD、POD活性均下降,CAT活性先上升后下降.分析认为皂角幼苗在盐旱交叉胁迫下表现出交叉适应性,适度的干旱胁迫可增加皂角的抗盐能力.     

Impacts of nursery cultural treatments on stress tolerance in 1 + 0 container white spruce (<Emphasis Type="Italic">Picea glauca</Emphasis> [Moench] Voss) seedlings for summer-planting

Impacts of nursery cultural treatments (T) on stress tolerance of greenhouse-grown 1 + 0 container white spruce (Picea glauca [Moench] Voss) seedlings (mean height 24 cm, root collar diameter 3.1 mm) for summer planting were studied. Seedlings were subjected to 12-h short-day treatments of 0 (T0), 3 (T3), 7 (T7), 10 (T10), or 15 (T15) days, followed by 0, 7, 17, 40, or 46 days of reduced N supply, respectively. Relevant physiological and morphological factors were examined concurrently. Foliar N concentrations exceeded optimal levels and differed little among treatments, suggesting a minor confounding role for N reduction. Both frost and drought tolerance increased incrementally from T0 through T15. Electrolyte leakage index decreased steadily from T0 (25% for roots, 17% for needles) to T15 (1% for roots, 2% for needles) after 2-h exposure of fine roots to − 2°C and of needles to − 8°C. Withholding soil watering for 19 days caused 80% mortality among seedlings in T0, 50% in T3, and < 10% in T7–T15. The transpiration decline curve suggested that enhanced drought tolerance was largely attributable to quicker stomatal closure during water stress and lower cuticular transpiration rate. The treatments increased root growth capacity on a per-seedling, but not per-root-mass, basis. Needle primordia were developed in all T7-T15 seedlings but not in T0 and T3 treatments, suggesting that nurseries may need no more than 7 days of blackout application for conditioning spruce seedlings for summer planting. Shoot dry weight fraction increased gradually from T0 through T15 and was linearly correlated with needle specific weight and frost tolerance, and may thus be useful in monitoring progress of conditioning treatments.     

Effect of NaCl stress on ion distribution in roots and growth of Cyclocarya paliurus seedlings

We studied ion distribution in roots and the growth of Cyclocarya paliurus seedlings of three provenances, Huangshan in Anhui, Jiujiang in Jiangxi and Kunming in Yunnan, under conditions of 0, 1, 3 and 5 g/L NaCl stress using X-ray microanalysis. Results show that under NaCl stress of 3 and 5 g/L, the relative contents of Na⁺ and Cl⁻ in root tissues increased, while the relative contents of K⁺, Ca²⁺ and Mg²⁺ decreased. With an increase in salinity, the relative content of Na⁺ in the epidermis and cortex of the root increased, while the relative content of Cl⁻ in the stele and cortex of the root increased markedly. Thus, ions in the root tissues were unbalanced and the ratios K⁺/Na⁺ and Ca²⁺/Na⁺ decreased, while Na⁺/(K⁺+ Na⁺+Ca²⁺+Mg²⁺) increased. The decrease of the K⁺/Na⁺ ratio and the substantial increase of Cl⁻ in root tissues contributed to a decline in seedlings survival and reduced the increments for seedling leaf area, height, basal diameter as well biomass. Our preliminary conclusion is that the level of salt tolerance for the tested provenance seedlings was in the order of Huangshan > Kunming > Jiujiang, and the threshold of salt tolerance for C. paliurus seedlings was about 1 g/L. __________ Translated from Scientia Silvae Sinica, 2008, 44(6): 66–72 [틫自: 쇖튵뿆톧]     

Effects of nitrogen source on growth and activity of nitrogen-assimilating enzymes in Douglas-fir seedlings

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were grown for 68 days in a growth chamber in nutrient solutions with ammonium, nitrate or ammonium nitrate as the nitrogen source. Among the nitrogen sources tested, whole-seedling biomass, relative growth rate (RGR), root and shoot elongation, and number of lateral roots, were greatest in seedlings grown with ammonium. In the absence of nitrogen, plant growth and formation of lateral roots were poor. Initially, glutamine synthetase, NAD-glutamate dehydrogenase and aspartate aminotransferase activities were high in young roots and shoots, but all three enzymatic activities decreased after one month of culture. In root apices, glutamine synthetase and aspartate aminotransferase activities were higher than NAD-glutamate dehydrogenase activity. Enzymatic activities were often higher in ammonium-fed seedlings than in seedings supplied with the other forms of nitrogen. Activities of all three enzymes were significantly reduced in seedlings grown in the absence of nitrogen. The beneficial effect of ammonium is discussed on the basis of its involvement in the assimilation pathways of Douglas-fir.     

Effects of simulated drought stress on the fine roots of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) in a plantation forest on the Kanto Plain,eastern Japan

Drought stress was simulated in a 28-year-old Japanese cedar plantation (Kanto Plain, Japan) between April and October 2004 by removing throughfall using rain shelters. Changes in fine-root parameters caused by this drought treatment were examined by sequential soil coring. Drought effects on fine roots were analyzed separately for particular soil depths (0–5, 5–15, and 15–25 cm) and root diameters (<1 and 1–2 mm). Generally, fine-root biomass and root tip numbers decreased by the drought treatment. Drought stress was most intense for fine roots in the topsoil and weakest for fine roots in the deepest soil layer. Fine roots less than 1 mm in diameter were affected more severely than 1- to 2-mm roots. The effect of drought treatment was most remarkable for the number of white root tips, which decreased to 17% of the control at the soil depth of 0–5 cm. These results suggest that white root tip is the most suitable indicator of drought stress. Simulated drought reduced production of fine roots less than 1 mm and 1–2 mm in diameter. Fine-root mortality was stimulated for roots less than 1 mm, but not for 1- to 2-mm roots. These results suggest that fine roots with larger diameters can survive drought stress at a level simulated in this study, but processes of fine-root production were inhibited regardless of the diameter classes. The duration of drought stress and phenology of fine roots should also be considered in diagnosing the effects of drought on fine-root parameters.     

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 the extreme drought in 2003 on soil respiration in a mixed forest

We present a field study on the drought effects on total soil respiration (SR_t) and its components, i.e., “autotrophic” (SR_a: by roots/mycorrhizosphere) and “heterotrophic” respiration (SR_h: by microorganisms and soil fauna in bulk soil), in a mature European beech/Norway spruce forest. SR_a and SR_h were distinguished underneath groups of beech and spruce trees using the root exclusion method. Seasonal courses of SR_a and SR_h were studied from 2002 to 2004, with the summer of 2003 being extraordinarily warm and dry in Central Europe. We (1) analyzed the soil temperature (T _s) and moisture sensitivity of SR_a and SR_h underneath both tree species, and (2) examined whether drought caused differential decline of SR_a between spruce and beech. Throughout the study period, SR_a of beech accounted for 45–55% of SR_t, independent of the soil water regime; in contrast, SR_a was significantly reduced during drought in spruce, and amounted then to only 25% of SR_t. In parallel, fine-root production was decreased during 2003 by a factor of six in spruce (from 750 to 130 mg l⁻¹ a⁻¹), but remained at levels similar to those in 2002 in beech (about 470 mg l⁻¹ a⁻¹). This species-specific root response to drought was related to a stronger decline of SR_a in spruce (by about 70%) compared to beech (by about 50%). The sensitivity of SR_a and SR_h to changing T _s and available soil water was stronger in SR_a than SR_h in spruce, but not so in beech. It is concluded that SR_a determines the effect of prolonged drought on the C efflux from soil to a larger extent in spruce than beech, having potential implications for respective forest types. This article belongs to the special issue "Growth and defence of Norway spruce and European beech in pure and mixed stands."