Bacterial (Bacillus thuringiensis subsp. thuringiensis and B. thuringiensis subsp. kurstaki) Entomocidal Preparations Decrease Chlorophyll Accumulation in Larch Needles

Chlorophyll a plus b content and absorption spectra of the homogenates from the cotyledonary leaves of 30-day-old seedlings of two larch species, Larix gmelinii (Rupr.) Rupr. and L. sibirica Ldb. were studied. The seedlings were grown on Perlite containing aqueous solutions of entomocidal biopreparations isolated from Bacillus thuringiensis subsp. thuringiensis (bitoxybacillin) and B. thuringiensis subsp. kurstaki (lepidocide) at various final concentrations (2, 6, and 12 g/l). Changes in the form of chlorophyll absorption spectra induced by biopreparations were established. A marked inhibition of pigment accumulation in the needles dependent on the biopreparation concentration was noted. At a low concentration (2 g/l), the biopreparations virtually did not affect the chlorophyll content; an increase in their concentrations resulted in a decrease in chlorophyll content in leaves by 20% (at 6 g/l) and 40% (at 12 g/l). It is concluded that bitoxybacillin and lepidocide inhibited the chlorophyll accumulation in larch needles to a similar extent.     

Latest developments of dendro-archaeology in the French Alps: Assessing changes in mountain forests exploitation over the last millennium

Dendrochronological studies are carried out on rural buildings in the French Alps for twenty years. In this contribution, we examine an extensive dataset of larch timbers (n = 1294) that were dendrochronologicaly dated at 139 buildings. This material yielded felling dates spanning the 11th century to the 20th century and contributed to improve our knowledge of human occupation and exploitation of mountain forests during the second millennium CE. From the 11th to the 14th century, rural populations increasingly exploited older forests. The crises of the 14th century led to a significant decrease in construction and by extension in tree cutting. The beginning of the 15th century marks a resumption of construction and felling which is continuous until the beginning of the 20th century. There is a relationship between the age of harvested trees, the number of dates and population fluctuations, which corroborates findings at the European scale. Regional trade probably influenced the stem diameters used in constructions in the immediate vicinity of the forests. Logging regulations can be perceived through variations in the age of harvested trees. The 14th century gap in felling dates would also mark a transition period in the exploitation of mountain forests and by extension a transformation of the economy.     

日本落叶松LoERF017基因的克隆及生物信息学分析

从日本落叶松中克隆得到的LoERF017基因，该基因全长624 bp，共编码206个氨基酸。预测该基因所编码的蛋白只包括一个AP2结构域，其二级结构包括α-螺旋（30.43%），无规卷曲（54.11%），延伸链（12.56%），β-折叠（2.9%）。对该基因进行亚细胞定位，结果显示LoERF017基因定位在细胞核中。荧光定量PCR结果表明，LoERF017基因在日本落叶松中的表达有一定的组织特异性，该基因在根中的表达量最高，在茎中的表达量最低，在叶中的表达量居中。干旱胁迫下，LoERF017基因的表达量在根中呈上升趋势，复水后，该基因的表达量有下降趋势。可以初步预测该基因主要在日本落叶松根中表达并行使功能，并推测该基因可能与抗旱相关。     

Leaf hydraulic traits of larch and ash trees in response to long-term nitrogen addition in northeastern China

兴安落叶松和水曲柳叶片水力性状对长期氮添加的响应 大气氮沉降影响树木水力结构，进而影响树木的生长和生存。然而，目前关于叶片水力性状对氮沉降的响应尚不明确，而且该响应可能与物种或植物功能型有关。本研究以中国东北地区水曲柳 (Fraxinus mandshurica，阔叶被子植物)和兴安落叶松(Larix gmelinii，针叶裸子植物)人工林为研究对象，利用长达16年的施氮(10 g N m⁻² yr⁻¹)试验研究了氮添加对两种树种叶片水力性状的影响。用自然干燥法测定了叶片压力-容积曲线，用复水动力学法量化了叶片最大水力导度(K_{leaf_max})和抗栓塞阻力(P_50leaf)。研究结果表明，与水曲柳相比，兴安落叶松具有较高的K_{leaf_max}和较强的干旱容忍性(即较低的质壁分离点的相对含水量(RWC_tlp)和弹性模量(ε)，较负的P_50leaf)。此外，氮添加增加了水曲柳的叶膨压损失点水势(π_tlp)、叶饱和含水量时的渗透势(π₀)和叶水容(C_{leaf_mass})，但对兴安落叶松的这些性状影响不显著，表明水曲柳对氮添加更敏感。氮添加增加了水曲柳和兴安落叶松的K_{leaf_max}和P_50leaf。水曲柳的π_tlp和π₀均与叶密度(LD)正相关，而C_{leaf_mass}与LD负相关。兴安落叶松的K_{leaf_max}与LD正相关，P_50leaf与LD负相关。两个树种的K_{leaf_max}与P_50leaf均呈负相关关系。我们的研究表明，长期氮添加降低了这两个重要造林树种的叶片干旱容忍性，这一发现加深了我们对氮沉降背景下树木水力表现的理解。     

The Effect of Larch Casebearer on Larch Growth and Reproductive Organ Formation

Dependencies of larch (Larix sibirica Ledeb.) growth and reproductive organ formation on its infestation by a phyllophagous miner, larch casebearer (Coleophora sibiricella Flkv., Lepidoptera, Coleophoridae) were studied. The work was performed in the sustained outbreak of the larch casebearer in the forest-steppe-larch forest at Kuznetsk Alatau. For the representative tree groups, we determined shoot linear growth, the number of axillary buds, trunk radial growth, the number of micro- and macrostrobili produced, and the contents of water, monoses, starch, and nitrogenous compounds in needles as dependent on the infestation density. We found that infestation exceeding 0.5 larvae per brachyblast significantly suppressed tree growth and reproductive organ formation. At this threshold value of infestation, a significant inhibition of shoot linear growth can serve a marker for suppressed trunk radial growth and reproductive organ formation. The lower degree of infestation did not suppress larch growth and even stimulated it. This observation, along with our data on the changes in the composition of nitrogenous and carbohydrate compounds in damaged needles, demonstrates the active character of interaction between the host tree and the phyllophagous insect, a transit of the source function from damaged needles to healthy ones, and the stimulated reparation of the assimilation apparatus.     

Responses of ring widths and maximum densities of Larix gmelinii to climate on contrasting north- and south-facing slopes in central Siberia

An analysis was performed of the climatic responses of the radial growth of Larix gmelinii (Rupr.) Rupr. at two sites—both of which included contrasting north- and south-facing slopes—in Tura, central Siberia, with the development of ring width and maximum-density chronologies for each slope. Both residual and standard chronologies of ring widths were positively correlated with temperature from late May until mid June on all four slopes. By contrast, standard chronologies of ring widths were negatively correlated with precipitation during the winter (from October to April) and in May on the north-facing slope at site 1 and on the south-facing slope at site 2 respectively. The negative correlations with precipitation during the winter and in May on some of the slopes suggested that delayed snowmelt in early spring might inhibit the radial growth of L. gmelinii, and the effects of snow are likely to vary with topography. Both residual and standard chronologies of maximum densities were positively correlated with temperature in early July on all four slopes. Maximum densities were also positively correlated with precipitation during summer of the previous year on all the slopes. These suggest that no major differences exist in terms of responses of maximum density to climatic factors between the north- and south-facing slopes.     

Carbon isotope discrimination indicates improving water-use efficiency of trees in northern Eurasia over the last 100 years

We investigated the response of conifer trees in northern Eurasia to climate change and increasing CO₂ over the last century by measuring the carbon isotope ratio in tree rings. Samples from Larix, Pinus and Picea trees growing at 26 high‐latitude sites (59–71°N) from Norway to Eastern Siberia were analysed. When comparing the periods 1861–1890 and 1961–1990, the isotope discrimination and the ratio of the intercellular to ambient CO₂ concentration (c_i/c_a) remained constant for trees growing in mild oceanic climate and under extremely cold and dry continental conditions. This shows a strong coordination of gas‐exchange processes, consisting in a biochemical acclimation and a reduction of the stomatal conductance. The correlation for c_i/c_a between the two investigated periods was particularly strong for Larix (r²=0.90) and Pinus (r²=0.94), but less pronounced for Picea (r²=0.47). Constant c_i/c_a under increasing CO₂ in the atmosphere resulted in improved intrinsic water‐use efficiency (W_i), the amount of water loss at the leaf level per unit carbon gain. We found that 125 out of 126 trees showed increasing W_i from 1861 to 1890 to 1961 to 1990, with an average improvement of 19.2±0.9% (mean±SE). The adaptation in gas exchange and reduced transpiration of trees growing in this region must have had a strong impact on the water and energy budget, resulting in a drier and warmer surface air layer today than would exist without this vegetation–climate feedback.     

The effects of chilling and forcing temperatures on spring synchrony between larch casebearer and tamarack

1. Spring phenological synchrony can be important for tree-insect interactions. Depending on the magnitude and direction of phenological shifts, overwintering insects could be affected in many ways, for example, facing starvation or having to contend with increased chemical or physical defences of host trees. If temperature has different influences on the phenology of trees and insects, climate change can alter spring phenological synchrony.
2. In this experiment, we exposed tamarack seedlings and larch case bearer larvae from Minnesota, USA, to a variety of chilling and forcing temperatures and measured spring phenology (twig bud break and larval activation). We additionally measured case bearer performance on seedlings that were exposed to different forcing × chilling levels, tracking larval survivorship to adulthood.
3. Warmer forcing enhanced larval activation and bud break, but larval development slowed down past 21°C. Higher chilling temperatures accelerated bud break, but the effect was inconclusive for larvae. There was no chilling × forcing interaction for either species. Spring activity accelerated more quickly with increases in temperature for larvae than for seedlings, resulting in increased phenological synchrony at warmer temperatures. Activation rates for overwintering larvae were highest at 27°C, while survivorship to adulthood following spring activation was highest at 21°C. At temperatures at or beyond 27°C, no larvae reached adulthood.
4. Warmer winters and springs will likely initially increase spring synchrony between tamarack and larch case bearer, exposing larvae to younger, potentially more nutritious foliage, but extremely warm spring temperatures may decrease survivorship of larvae to adulthood.

     

Embryogenesis and genetic stability in long term megagametophyte-derived cultures of larch

Embryogenic cultures derived from megagametophytes of Larix decidua were maintained for up to 17 years. A few lines were divided into sub-lines, which were maintained in the same manner as the others. Embryogenic tissue was grown on 1/2 strength LM medium supplemented with glutamine and casein hydrolysate at constant temperature and light regimes. Chromosome counts were conducted at various times. DNA content was assessed by flow cytometry. Embryogenesis was monitored with each transfer and records of all appearances of green mature embryos were kept. Chromosome number was found to vary. DNA content and chromosome number, both of which had doubled a number of years after initiation, stabilized around 24 chromosomes for most cultures. A few lines showed substantial increases in chromosome number. One of these lines lost vigour and died. Another line showed a further doubling of DNA content. No lines were embryogenic over the entire period. Embryogenicity was lost completely in some lines, but in others the loss was temporary, as periodic restoration of embryogenesis was observed.