Quantification of Phaeocryptopus gaeumannii colonization in Douglas‐fir needles by ergosterol analysis

Current assessments of infection levels of Phaeocryptopus gaeumannii, the incitant pathogen of Swiss needle cast disease on Pseudotsuga menziesii, typically rely on surveys of abundance of fruit bodies on diseased needles. The relationship between this measure and internal fungal colonization is unknown. In this article, a series of experiments to determine whether ergosterol can be used to quantify P. gaeumannii internal colonization within Douglas‐fir needles is reported. It was found that ergosterol content in seven commonly occurring Douglas‐fir foliar fungi is proportionally related to biomass, and in P. gaeumannii this relationship is not affected by age of the culture. Furthermore, at four sites tested, P. gaeumannii was the most common fungus species isolated from Douglas‐fir needles, accounting for approximately 50% of the isolations. Ergosterol content in these needles was best related to P. gaeumannii despite the presence of other fungi. The strong relationship between ergosterol and P. gaeumannii is attributed to its greater contribution to total fungal biomass compared with all other fungi present within Douglas‐fir needles.     

Resistance and tolerance in juvenile interior Douglas‐fir trees Pseudotsuga menziesii var. glauca artificially inoculated with Armillaria ostoyae

Plants utilize two general strategies to cope with pathogen attack. They either limit or resist the pathogen (termed ‘resistance’) or they cope with the disease by surviving and growing (termed ‘tolerance’). Both strategies tend to increase plant fitness; however, there are possible costs, trade‐offs and interactions associated with each strategy. This study focused on five half‐sib interior Douglas‐fir families [Pseudotsuga menziesii var. glauca (Beissn.) Franco] that were putatively classified as either resistant or susceptible to Armillaria ostoyae in a previous greenhouse study of seedling families challenged with A. ostoyae. We compared their survival rates in the greenhouse study with results of juvenile trees from the same five families that were artificially inoculated in field conditions. Both resistance and tolerance appeared to be operating in the field test trees, and a possible trade‐off between resistance and tolerance was detected. Significant differences were detected among the five families for stem radial growth following infection at the tree root collar. Compared with the putatively susceptible families, resistant families had smaller lesions and lower proportional root collar girdling. Tolerant families generally had larger lesions but demonstrated better growth when diseased than resistant families. One tolerant family that was a good survivor in the greenhouse survival study presented vertically shaped lesions that were large in area but had greatly reduced proportional root collar girdling. While a second family showed tolerant traits in the field study, its poor survival in the greenhouse study agreed with the large horizontally spreading lesions associated with high root collar girdling in the field study trees. Survival rankings of the five families in the greenhouse study mostly agreed with results from the field study based on the proportion of collar girdling among families. These host responses are discussed with respect to stability, quantity and quality of stands and products.     

Virulence of Fusarium oxysporum and F. commune to Douglas‐fir (Pseudotsuga menziesii) seedlings

Fusarium species can cause damping‐off and root rot of young conifer seedlings, resulting in severe crop and economic losses in forest nurseries. Disease control within tree nurseries is difficult because of the inability to characterize and quantify Fusarium spp. populations with regard to disease potential because of high variability in isolate virulence. Fusarium isolates were collected from healthy and diseased seedlings of Douglas‐fir (Pseudotsuga menziesii) and western white pine (Pinus monticola) from a nursery in Idaho, USA. Molecular markers such as DNA sequences (mitochondrial small subunit and nuclear translation elongation factor 1‐alpha) and amplified fragment length polymorphism were used to identify isolates as either F. oxysporum or F. commune. In addition, diagnostic primers were developed to detect and distinguish F. commune from F. oxysporum. In vitro and greenhouse virulence tests were completed on Douglas‐fir germinants and seedlings. For Douglas‐fir germinants and seedlings, F. oxysporum isolates generally caused less severe symptoms, whereas most F. commune isolates caused mortality through damping‐off. This is the first report of direct evidence that F. commune can cause damping‐off disease on Douglas‐fir seedlings under greenhouse conditions.     

Fungal endophytes in woody roots of Douglas‐fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa)

The fungal community inhabiting large woody roots of healthy conifers has not been well documented. To provide more information about such communities, a survey was conducted using increment cores from the woody roots of symptomless Douglas‐fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) growing in dry forests on the eastern slope of the Cascade Mountains in Washington state, USA. Fungal isolates were cultured on standard media, and then were identified using a combination of molecular and morphological methods. Fungal genera and species identified in this study will provide baseline data for future surveys of fungal endophytes. Examination of internal transcribed spacer (ITS1 and ITS2) and 5.8S rDNA sequences and morphology of cultured fungi identified 27 fungal genera. Two groups predominated: Byssochlamys nivea Westling (20.4% of isolations) and Umbelopsis species (10.4% of isolations). This is the first report of B. nivea within large woody roots of conifers. Both taxa have been previously identified as potential biological control agents. Although some trends were noted, this study found no significant evidence of host species or plant association effects on total recovery of fungal endophytes or recovery of specific fungal taxa.     

Fungal lesion length and expansion rate for the root pathogen Armillaria ostoyae in Douglas‐fir affecting root colonization and damage

Plant lesions affect disease impact, progression and host resistance. Root lesions caused by Armillaria ostoyae (Romagn.) Herink were inspected on 24‐ to 34‐year‐old planted Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) pulled from the soil in five locations. Four hundred seventy‐nine lesions were measured for length (mm), expansion rate (mm/year) and lesion type. Lesion types were patch lesions on a root side, girdled lesions covering the root circumference and root collar lesions on the stem below ground. Non‐linear mixed modelling revealed that fungal lesion length at girdled and collar lesions increased but the expansion rate slowed as a power function of time, indicating increasing secondary inoculum and host resistance. Average fungal lesion expansion rate in girdled root and collar lesions was 127 mm the first year which then declined non‐linearly to 26 mm/year after 10 years. Fungal lesion length in patch lesions showed little change after the first year of infection. For girdled and collar lesions, fungal lesion length increased with tree size at the time of infection. Sites with a longer frost‐free period had shorter girdled root and stem lesions, probably because of more active host defence. Results indicate that mortality would be rare from one infection event. Furthermore, patch lesions pose a lower risk of mortality than other lesions because of a lower fungal lesion expansion rate and secondary inoculum. Tree size, lesion position, lesion type and fungal lesion expansion rate need to be considered when assessing the risk of lesions to individual tree survival. Techniques to minimize the disease impact are discussed.     

Necrophylactic periderm formation in the roots of western larch and Douglas‐fir trees infected with Armillaria ostoyae. II. The response to the pathogen

Periderm formation was studied in bark samples collected from the roots of western larch (Larix occidentalis) and Douglas‐fir (Pseudotsuga menziesii) trees infected with Armillaria ostoyae. Necrophylactic periderms were formed in advance of infection and successfully restricted continued fungal spread in 68 and 45% of the samples collected from 10‐ and 27‐year‐old western larch, respectively. However, all periderms formed in 11‐ and 25‐year‐old Douglas‐fir had been breached by the advancing fungus. In both species, necrophylactic periderms were commonly breached at the junction of the periderm with the vascular cambium. In western larch, stone phellem often comprised the external phellem layer of necrophylactic periderms with multiple bands of phellem. In 27‐year‐old western larch, infection was often confined to discrete lesions bounded by multiple periderms with multiple bands of phellem. In both tree species, phellem production was greater in response to infection than in response to abiotic wounding.     

Necrophylactic periderm formation in the roots of western larch and Douglas‐fir trees infected with Armillaria ostoyae. I. The response to abiotic wounding in non‐infected roots

The sequence of events leading to necrophylactic periderm formation was studied throughout the year following the abiotic wounding of the non‐infected roots of 10‐ and 27‐year‐old western larch (Larix occidentalis) and 11‐ and 25‐year‐old Douglas‐fir (Pseudotsuga menziesii) trees that were infected with Armillaria ostoyae. The sequence was the same for both ages and species of trees. Wound repair was more rapid in the summer compared with the spring and autumn. Following cell hypertrophy, a zone of lignified impervious tissue was in the initial stages of formation within 10 days of wounding in the summer and 14 days in the spring or autumn. The new phellogen produced a layer of phellem three to four rows of cells thick after 20 days in the summer or 40 days in the spring. Modified cells abutting the inner boundary of the impervious zone frequently developed thick lignified abaxial walls and thin suberized adaxial walls. A typical exophylactic periderm in healthy root bark tissue of both western larch and Douglas‐fir consisted of stone phellem one to four rows of cells thick and a layer of thin‐walled phellem three to six rows of cells thick in western larch and two to three rows thick in Douglas‐fir, a single row of phellogen cells and one to three rows of phelloderm cells. Mature thin‐walled phellem cells had pigmented contents, red in western larch and light brown in Douglas‐fir. In response to wounding, 27‐year‐old western larch and 25‐year‐old Douglas‐fir developed necrophylactic periderms with annual bands of phellem. The bands included a layer of phellem that was six to 12 and nine to 15 rows of cells thicker than the layer of phellem observed in the respective naturally developed exophylactic periderms. Fifty days following wounding in the summer, stone phellem, one to three rows of cells thick, was observed in the necrophylactic periderm of 10‐year‐old trees. When fully developed, the necrophylactic periderm in 27‐year‐old western larch also had a layer of stone phellem three to five rows of cells thick in each band. Stone phellem development was only sporadic in 25‐year‐old Douglas‐fir. Wounds in the winter showed no signs of activity associated with repair until dormancy broke in the spring.     

Forest inventory-based assessments of the invasion risk of Pseudotsuga menziesii (Mirb.) Franco and Quercus rubra L. in Germany

European Journal of Forest Research - In Europe, some non-native tree species (NNT) are classified as invasive because they have spread into semi-natural habitats. Yet, available risk assessment...     

The relationship between the needle age and the growth rate in Scots pine (Pinus sylvestris): a retrospective analysis by needle trace method (NTM)

Variation in annual radial and height increments (RI and HI, respectively) as well as the number of needles belonging to different needle sets of successive annual shoots, determined by the needle trace method (NTM), was studied retrospectively in Scots pine stands, one in southern Finland and two in Estonia. The connection between different needle sets and tree growth was studied by correlation and covariance analyses. The numbers of needles of the three youngest needle sets were positively correlated with growth, whereas the number of needles older than 3 years had no significant correlation. The covariance analysis emphasized the negative relationship of older needle sets with tree growth. It is generally concluded that the two or three youngest needle sets are important and all older needles minimally contribute to growth, possibly because of their small quantity. Older needles may remain on the tree if assimilation is impeded for some reason, e.g. due to premature loss in the two youngest needle sets. The trees having attached old needles grew less than those that had already totally lost these needle sets.     

沙地樟子松不同林龄树高、胸径等生长指标的关系研究

对沙地樟子松人工林10~60 a林龄样地进行树高、胸径等生长指标调查、观测,使用SPSS20.0进行分析,结果表明:不同林龄树高与胸径、冠幅大小、第一活枝下高高度各生长量两两之间有极显著相关关系,林木树高与胸径、冠幅之间存在正相关关系;树高生长量随胸径变化模型为y=0.405x1.104,树高生长量随冠幅变化模型为y=e2.895-2.836/x。     

沙地樟子松天然更新与降水因子的灰色关联度分析

沙地樟子松人工固沙林的天然更新在大部分引种地不能很好地进行，其天然更新存在着某些障碍因子。通过对辽宁省昌图县傅家林场樟子松天然更新情况的调查，采用灰色关联度分析的方法，对更新与降水因子的关系进行了分析。结果表明，更新产生的当年12月和翌年1，2月的降水量，即冬季降雪情况与天然更新关联最大。说明了冬季降雪是影响樟子松天然更新的一个关键因子。     

Fungal colonization patterns in necrotic rootstocks and stem bases of dieback‐affected Fraxinus excelsior L.

European ash (Fraxinus excelsior) trees currently face the major threat of ash dieback caused by an invasive fungus, Hymenoscyphus fraxineus. Collar rots in F. excelsior have been increasingly associated with infections by this pathogen. However, the aetiology of the collar rots is still unclear and remains heavily debated. In contrast to most studies of this kind, entire rootstocks of four diseased ash trees were dug out to examine necrotic tissues in these rootstocks and stem bases in detail and to sample necrotic wood for fungal isolation. With the aid of morphological and molecular identification techniques, five to twelve fungal taxa were detected per tree. Members of the Nectriaceae family and Botryosphaeria stevensii, the causal agent of stem and branch cankers on many tree species, were frequently isolated from outer xylem. In contrast, H. fraxineus was the dominating species in interior wood layers. Microsatellite genotyping of 77 H. fraxineus isolates helped to identify up to six different genotypes per tree. The role of H. fraxineus and other isolated fungi in the aetiology of ash collar rots are discussed.     

Composition and partition of biomass in a smith fir (<Emphasis Type="Italic">Abies georgei</Emphasis> var. <Emphasis Type="Italic">smithii</Emphasis>) timberline forest on the Sergyemla Mountain,southeastern Tibetan Plateau

The southeastern Tibetan Plateau has the highest timberlines in the world and climate change affects this area to a considerable extent.Quantification of vegetation biomass in the forests at the timberline is essential for understanding carbon balance,forest structure and functional changes in the forests at timberlines.We describe biomass and its constituent components of a smith fir timberline forest occurring at an elevation of 4320 m on the Sergyemla Mountain in the southeastern Tibetan Plateau.The results show that,in the tree layer,the average diameter at breast height(DBH) was 35.6 cm,the density 251 trees per hectare with a total biomass of 309.9 t.ha-1.Of the total biomass,the trunks accounted for 70.49%,branches for 9.09%,leaves for 5.57% and roots for 14.85%.The total biomass in the shrub layer was 77.9 t.ha-1 of which the biomass of trunks,branches,leaves and roots accounted for 42.8,14.9,4.6 and 15.6 t.ha-1,respectively.The total biomass in the herb layer was 3.0 t.ha-1.The total vegetation biomass in the smith fir timberline forest was 390.9 t.ha-1,to which the tree layer contributed the most(79.3%),followed by shrubs(19.9%) and herbs(0.8%).We estimate that the smith fir forest stand at the timberline had a higher total biomass than other fir or spruce forest stands in the surrounding area.     

Root architecture might account for contrasting establishment success of <Emphasis Type="Italic">Pseudotsuga menziesii</Emphasis> var. <Emphasis Type="Italic">menziesii</Emphasis> and <Emphasis Type="Italic">Pinus sylvestris</Emphasis> in Central Europe under dry conditions

Key message

Pinus sylvestris seedlings quickly expand their roots to deeper soil layers while Pseudotsuga menziesii concentrates its root system in the topsoil, thereby running the risk of desiccation during long dry spells, as indicated by lower survival after simulated summer drought.

Context

Pseudotsuga menziesii (Douglas-fir) is regarded as a promising species to maintain the productivity of Central European lowland forests given the projected increase of long dry spells.

Aims

Will the species be able to regenerate from seed and spread outside plantations in a drier temperate Europe?

Methods

We measured the relative growth rate, biomass allocation, root architecture, and phenotypic plasticity of Pseudotsuga menziesii seedlings sown in a common garden and grown under current precipitation and prolonged drought, respectively. The species’ competitive ability with respect to Pinus sylvestris L., the most drought-tolerant native conifer in Central Europe, was assessed during three growing seasons.

Results

Pinus sylvestris seedlings had higher relative growth rates than did Pseudotsuga menziesii seedlings, first in terms of aboveground biomass and later in terms of shoot height. This resulted in heavier and taller seedlings after three growing seasons under both moist and dry conditions. Shorter vertical roots corresponded with lower survival of Pseudotsuga menziesii seedlings under dry conditions.

Conclusion

Fast root proliferation allows Pinus sylvestris seedlings to reach deeper water pools that are less rapidly depleted during transient drought. By contrast, the shallow root system might put Pseudotsuga menziesii seedlings at the risk of desiccation during prolonged dry spells.

     

Age trends in the genetic parameters of wood density and the relationship with growth rates in hybrid larch (Larix gmelinii var. japonica × L. kaempferi) F1

Age trends in variance components and heritability of overall wood density, earlywood and latewood density, and latewood proportion were investigated in 29-year-old trees of 19 full-sib families of hybrid larch (Larix gmelinii var. japonica × Larix kaempferi) F₁. The age–age correlation and optimum selection age for these traits were also estimated and genetic and phenotypic correlations between wood density and radial growth rate were calculated for each growth ring. Intraring wood density data were obtained using X-ray densitometry. The coefficient of additive genetic variance was stable over all ages, whereas the coefficient of environmental variances gradually decreased with increasing age, resulting in increases in heritability estimates with age for overall density. The latewood proportion had the highest heritability estimates at all ages, ranging from 0.44 to 0.66. Overall density and its various components at 28 years of age showed strong genetic correlations with their respective traits at all younger ages. Optimum selection ages for the wood density traits ranged from 8 to 14 years, at which point maximum gain efficiencies per year were obtained. There were negative correlations between wood density and radial growth rate at early ages, although these relationships tended to be weaker with increasing age. These results suggest that selection at a young age is effective for wood density, but particular care must be taken in selecting trees with an improved radial growth rate because rapid growth will result in a low-density wood product, especially in the early growth period.     

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.