欧美杨细菌性溃疡病菌的寄主范围调查及其寄主抗性物质的初步分析

目的 为明确欧美杨细菌性溃疡病菌的寄主范围、欧美杨抗性品种及其可能的抗性活性物质。 方法 通过田间接种方法开展欧美杨细菌性溃疡病菌的寄主范围、杨树品系抗性调查,并利用高效液相色谱分析杨树抗感品种树皮中活性物质含量及其染病前后含量变化情况,同时利用抑菌实验验证潜在抗性物质的活性。 结果 研究发现欧美杨细菌性溃疡病主要危害黑杨派美洲黑杨、欧美杂交杨的品系以及旱柳,而欧洲黑杨品系具有高度抗菌能力;本研究的30个美洲黑杨和欧美杂交杨品系中,中林46杨、2025杨、2001杨、313杨、中荷1号杨和16-09杨是高感病品系;16-10杨、豫抗1号杨为高抗病品系,而131杨、03-59杨、02-212杨和03-34杨为抗病杨树品种;杂交柳和垂柳抗病,金丝柳轻微感病;栎属和青杨派的种类和品系具有高度抗性。高效液相色谱分析显示,抗病和高感病品系树皮中的邻苯二酚、苯甲酸、绿原酸、儿茶素的含量较高,其中邻苯二酚和儿茶素在病菌侵染时含量明显增加。 结论 明确了欧美杨细菌性溃疡病的主要危害对象和寄主范围,明确了具有抗性、感病的杨树品系,证明了邻苯二酚和儿茶素与杨树抗病性密切相关,该研究结果为欧美杨的栽培和病害防治提供技术支持和防治建议,该研究结果对我国欧美速生杨的细菌性溃疡病的防治具有重要意义。     

Endophyte-mediated resistance against white pine blister rust in Pinus monticola

Induced resistance responses, including fungal endophyte-mediated resistance, have been well studied in both agricultural crops and grass systems. Yet, the effect of these processes and symbionts in forest trees is poorly known. Fungal endophytes have been found in all conifer forest systems examined to date and have been hypothesised to be involved in resistance-mediated responses. However, in the absence of functional studies the influence of these endophytes on the extended phenotype of the host plant is unclear. In this study we demonstrate that fungal endophytes from Pinus monticola were effective at increasing survival in host plants against the exotic pathogen Cronartium ribicola, which is responsible for the devastating disease called white pine blister rust. Seedlings previously inoculated with fungal endophytes lived longer than endophyte-free seedlings and also showed some reduction in white pine blister rust disease severity. This endophyte-mediated resistance was found to be effective over time, indicating persistence, and is hypothesised to be a form of induced resistance. Overall, this suggests fungal endophytes may play a determinative role in the structure of biological communities and could provide a useful alternative or ancillary management tool for combating pests and diseases.     

Genetic variability of the ‘bark canker resistance’ character in several natural provenances of Cupressus sempervirens

Several Aegean (Greece) and Anatolian (Turkey) cypress provenances were studied for resistance variability to bark canker, a disease caused by the fungal pathogen Seiridium cardinale. The investigation also examined whether the low disease rate within the natural area of cypress was due to genetic or geographic‐climatic reasons. Results demonstrated strong variability for the ‘bark canker resistance’ character, in particular for trees within families. As trees from the provenances studied were not found to have genetic superiority for bark canker resistance, the above‐mentioned low disease rate could be due to geographic‐climatic barriers that inhibit the development of the fungus or its ability to infect the host. Several half‐sib progenies exhibited high resistance, suggesting that this character is totally inherited through the maternal line. Should this finding be confirmed by further research, it would facilitate the task of genetic improvement for resistance, allowing progenies of resistant trees to be obtained.     

Epiphytic lichen diversity in late-successional Pinus sylvestris forests along local and regional forest utilization gradients in eastern boreal Fennoscandia

Pinus sylvestris-dominated forests have been heavily utilized across all of boreal Fennoscandia and the remaining natural forests are generally highly fragmented. However, there are considerable local and regional differences in the intensity and duration of past forest utilization. We studied the impact of human forest use on the diversity of epiphytic and epixylic lichens in late-successional Pinus sylvestris-dominated forests by assessing species richness and composition along both local and regional gradients in forest utilization. The effects of local logging intensity were analysed by comparing three types of stands: (i) near-natural, (ii) selectively logged (in the early 20th century) and (iii) managed stands. The effects of regional differences in duration and intensity of past forest use were analysed by comparing stands in two contrasting regions (Häme and Kuhmo–Viena). The species richness of selectively logged stands was as high as that of near-natural stands and significantly higher in these two stand categories than in managed stands. Species richness increased with the density of small understorey Picea, which correlated strongly with decreasing intensity of local forest use and increasing structural complexity of selectively logged and near-natural stands. Stands in the Häme region hosted a lower number of species, and were less likely to host many old-growth indicator species than the Kuhmo–Viena region, suggesting that species have been lost from stands in the Häme region due to a longer history of intensive forest use. We conclude that selectively logged stands, along with near-natural stands, are valuable lichen habitats particularly for species confined to old-growth structures such as coarse trees and deadwood. In landscapes where natural forests have become fragmented, the management or restoration of the remaining late-successional Pinus-dominated forests, e.g. through the use of fire, should be carefully planned to avoid adverse effects on lichen species richness.     

Population biology of sugar pine (Pinus lambertiana Dougl.) with reference to historical disturbances in the Lake Tahoe Basin: Implications for restoration

Historical logging, fire suppression, and an invasive pathogen, Cronartium ribicola, the cause of white pine blister rust (WPBR), are assumed to have dramatically affected sugar pine (Pinus lambertiana) populations in the Lake Tahoe Basin. We examined population- and genetic-level consequences of these disturbances within 10 sugar pine populations by assessing current population structure and trends for 1129 individuals, genetic diversity for 250 individuals, and frequency of WPBR-resistance for 102 families. Logging had occurred in 9 of 10 sites and fire suppression was evident in all stands. High density of white fir (Abies concolor) is often an indicator of fire suppression and we found a negative relationship between sugar pine survivorship and white fir basal area (r² = 0.31). C. ribicola was present in 90% of stands (incidence range: 0-48%) and we found a significant relationship between mean host survivorship and disease incidence (r² = 0.46). We estimated population growth rates (λ) from size-based transition matrices. For six of 10 sugar pine populations λ was ?1.0, indicating that these populations appear to be stable; for four populations, λ was <1.0, indicating populations that may be in decline. A population specific drift parameter, c_i, which is a measure of genetic differentiation in allele frequencies relative to an ancestral population, ranged from 0.009 to 0.048. Higher values of c_i indicate greater genetic drift, possibly due to a bottleneck caused by historical logging, other agents of mortality or much older events affecting population sizes. Effects of drift are known to be greater in small populations and we found a negative relationship between sugar pine density and c_i (r² = 0.36). Allele frequency of the Cr1 gene, responsible for WPBR-resistance in sugar pine, averaged 0.068 for all populations sampled; no WPBR infection was found in one population in which the Cr1 frequency was 0.112. Historical disturbances and their interactions have likely influenced the population biology of sugar pine in the Tahoe Basin; for some populations this has meant reduced population size, higher genetic drift, and poor survival of small- and intermediate-sized individuals. Possible management strategies include restoring population numbers, deploying WPBR-resistance, treating stands to promote natural sugar pine regeneration, and enhancing genetic diversity.     

Fraxinus nigra (black ash) dieback in Minnesota: Regional variation and potential contributing factors

Extensive tree dieback is a recurrent issue in many regions. Crown dieback of Fraxinus nigra Marsh. (black ash; brown ash) in the northeastern and north central United States is an example. F. nigra is a widely distributed hardwood that is often the dominant species in wetland forests from Manitoba to Newfoundland and West Virginia to Indiana. Widespread crown dieback of F. nigra has been noted in many regions, but there are few quantitative assessments of dieback extent or relationship to potential causes. Most F. nigra dieback episodes are not associated with specific disease or pest agents. Drought, excessive soil moisture, cohort senescense, and road influences, have all been suggested as potential contributing factors. Our objectives were to (1) quantify variable dieback across northern Minnesota, a region described as having extensive dieback, (2) determine the relationship between dieback and site moisture, (3) relate dieback to tree age/size distributions, and (4) assess whether dieback was related to road proximity. Given the increasing threat of Agrilus planipennis (emerald ash borer) in the region, it is important to know the current health status of F. nigra populations before widespread infestation occurs. Many stands in our study exhibited high incidences of crown dieback. However, the incidence of dieback was variable across the region. Spatial variability in dieback was associated with site wetland characteristics; more dieback occurred on jurisdictional wetlands and on sites with a higher wetness index and a deeper depth to a perching layer. Dieback was also positively correlated with mean stand diameter, and tree diameters were generally correlated with age, suggesting that stands with larger and older individuals experienced more dieback. Cohort senescence is a possible explanation for this trend. Finally, dieback occurred with higher frequency nearer to roads. The road influence could be related to hydrological alterations or perhaps toxicity from road deicing salt. The fact that dieback is more severe close to roads may contribute to a general perception that black ash dieback is more severe throughout the region than our study suggests. Collectively, our results indicate that the healthiest F. nigra stands in our study region are likely to be younger and located on relatively drier sites and farther from roads, compared to stands with significant crown dieback.     

三年桐、千年桐感染枯萎病病原菌后的生理反应

枯萎病是油桐毁灭性病害。中国广泛种植的油桐有三年桐和千年桐,三年桐易感枯萎病,千年桐抗枯萎病。为探讨三年桐与千年桐在枯萎病应答过程中的差异,在对油桐枯萎病灾区调研的基础上,进行枯萎病病原菌的分离、鉴定,并进一步探讨三年桐、千年桐接种枯萎病病原菌后超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性和丙二醛(MDA)含量的变化。结果表明:油桐枯萎病病原菌为尖孢镰刀菌,接种试验显示千年桐在接种尖孢镰刀菌后SOD、POD、CAT较三年桐均呈现较高活性,在接种后SOD、POD活性先升高后降低,CAT活性升高并维持高活性,MDA含量变化不明显;三年桐SOD活性和MDA含量均先升高后降低,POD活性先降低再升高,CAT活性先降低后升高又降低。千年桐作为抗病种,其抗病性可能与其本身具有较高的SOD、POD、CAT活性有关,并且和病原菌感染后酶活上升有关;三年桐为易感病种,接种后SOD、POD、CAT活性有变化,但仍不能抵御病原菌的危害。     

Eutypella canker of maple: first report from Germany and situation in Austria

Eutypella canker of maple, caused by Eutypella parasitica (which is native to North America), is reported for the first time from Germany. From 2013 to 2015, this perennial canker disease was recorded on 105 maple trees in Munich. Six maple species were affected: Acer pseudoplatanus, A. campestre, A. platanoides, A. cappadocicum, A. heldreichii ssp. trautvetteri and A. hyrcanum. Occurrence on the latter three species represents new host records for E. parasitica. In Austria, Eutypella canker was newly discovered on two trees at a second locality in 2011, and it is now known to occur on seven A. pseudoplatanus trees at two localities, which are separated nearly 150 km. A. pseudoplatanus was the most frequent host of E. parasitica in Munich and Austria, which is in agreement with previous studies in Europe. The identity of the causative pathogen as E. parasitica was verified by ITS rDNA sequencing of fungal cultures obtained from cankers in Munich and at both Austrian localities. The presence of large and old cankers in both countries suggests that introduction of E. parasitica dates back a long time, probably several decades. The new records of Eutypella canker in Germany and Austria show that the disease is more widely distributed in central Europe than previously recognized.     

河北省葡萄座腔菌科菌物系统分类研究

【目的】葡萄座腔菌科菌物是引起众多经济及生态造林树种枝干溃疡、枝枯类病害的病原生物,在世界各地均有广泛的分布。本研究对河北省内,与经济林木病害相关的葡萄座腔菌科菌物进行系统分类研究,目的在于揭示该科菌物在特定地区的地理分布特征,明确该类菌物所致树木枝干溃疡、枝枯类病害的寄主植物范围,为河北省树木溃疡、枝枯类病害的控制提供理论依据。【方法】在对河北省树木溃疡类病害系统调查的基础上,本研究根据菌物无性型及有性型的形态学特征、rDNA-ITS序列特征对包括河北省石家庄在内的8个市(县、区)25个不同地点的葡萄座腔菌科菌物进行分类鉴定和系统分类。【结果】共获得葡萄座腔菌科菌物5种73株,分别属于Botryosphaeria dothidea、B.stevensii、B.obtusa、B.sarmentorum和Phyllosticta citrichinaensis。其中B.dothidea为河北省葡萄座腔菌科优势菌物种,占全部检出菌物菌株总数的77%。葡萄座腔菌科菌物侵染杨树、柳树、苹果、核桃等28种植物,其中包括大叶黄杨、构树、火炬树、连翘、花椒和刺梅等6种新寄主植物。【结论】B.dothidea不仅危害杨树等传统寄主,而且危害花椒等新寄主植物以及入侵树种火炬树,是危害河北省树木健康生长的最为重要、分布最为广泛的枝干病原菌物,有必要对其溃疡致病性分化和种群遗传分化进行深入分析。来自柿树、花椒等寄主的10个具有Dothiorella型分生孢子的菌株形成单系类群,提示这些菌株可能是与B.sarmentorum和B.iberica不同的一个系统发育学新种。     

Spatial estimation of the density and carbon content of host populations for Phytophthora ramorum in California and Oregon

Outbreak of the emerging infectious disease sudden oak death continues to threaten California and Oregon forests following introduction of the exotic plant pathogen Phytophthora ramorum. Identifying areas at risk and forecasting changes in forest carbon following disease outbreak requires an understanding of the geographical distribution of host populations, which is unknown. In this study, we quantify and map the population density and carbon contents of five key host species for P. ramorum in California and Oregon, including four hosts killed by the pathogen (Notholithocarpus densiflorus, Quercus agrifolia, Quercus kelloggii and Quercus chrysolepis) and the foliar host Umbellularia californica which supports high sporulation rates. We integrate multiple sources of vegetation data, assembled from sparsely distributed (regional-scale) forest inventory and analysis (FIA) plots and more densely distributed (landscape-scale) plots for monitoring sudden oak death, and develop spatial prediction models based on correlation with environmental variables and spatial dependencies in host abundance. We estimate that 1.8 billion N. densiflorus trees (68 Tg C) and 2.6 billion Quercus host trees (227 Tg C) occur across 3.9 and 17.7 million ha of their respective habitat. A total of 436 million U.californica trees (14 Tg C) occur across 4.2 million ha which frequently overlap with Quercus and N. densiflorus host populations. Combination of landscape-scale data with FIA data resulted in more accurate estimation of host populations and their carbon contents. Forests of northern California and southwest Oregon have the highest concentration of the most susceptible hosts along with climatic conditions that favor pathogen spread. This study represents the first spatially-explicit estimate of P. ramorum host populations and their carbon contents which exceed previously published estimates. Our results will inform landscape- to regional-scale models of disease dynamics and guide management decisions regarding ecosystem impacts including risk of C release following widespread tree mortality.     

管芯片技术通量检测杨树溃疡病病菌的应用

正基因芯片技术因能对生物样本进行快速、高通量的定性和定量分析,而在植物病害诊断中也得到普遍的应用[1]。树木溃疡病是指引起木本植物树皮上出现溃疡腐烂等症状的病害[2]。引起杨树溃疡病的真菌种类较多,加之其无性型和有性型多样,所以,关于杨树溃疡病病原菌的报道多有不同。另外,受地理位置、寄主植物关系及分类体系的限制,迫切需要发展不依赖于常规分离培养的病原鉴定新技术。     

Evidence for the occurrence of induced resistance to pitch canker,caused by Gibberella circinata (anamorph Fusarium circinatum), in populations of Pinus radiata

Pitch canker, caused by Gibberella circinata, was discovered in California in 1986. Although initially quite damaging to Monterey pines (Pinus radiata), the severity of pitch canker has moderated in areas where the disease was first observed and some trees appear to have recovered completely. The absence of symptoms on trees that were once severely affected implies they have become more resistant to the disease. Experimental work has shown that P. radiata can manifest systemic induced resistance (SIR) in response to infection by the pitch canker pathogen and observations of disease remission may indicate that SIR is operative under natural conditions as well. As a test of this hypothesis, the susceptibility of trees in remission was assessed by inoculating them with G. circinata and recording the extent of lesion development. In addition, randomly selected trees in areas that differed in residence time of pitch canker were inoculated to determine if trees with a longer period of exposure to the pathogen were more resistant to the disease. The results of these tests showed that 89% of trees observed to be in remission sustained very limited lesion development, consistent with resistance to pitch canker. Furthermore, trees in areas where pitch canker was well established tended to be more resistant than trees in areas where the disease was of more recent occurrence. In sum, these findings support the view that SIR occurs in P. radiata and is contributing to a moderation of the impact of pitch canker under natural conditions.     

Decline of Mediterranean oak trees and its association with Phytophthora cinnamomi: a review

Mortality events in cork and holm oaks have occurred in the Mediterranean basin since the beginning of the XX century, but severity of decline increased during the 1980s. By that time, the exotic soil borne pathogen Phytophthora cinnamomi was often recovered from declining stands and since then it has been considered the main factor associated with decline. This work analyses data concerning P. cinnamomi surveys in cork and holm oaks trees, pathogenicity tests carried out in controlled experiments, studies about the influence of site characteristics in tree decline and approaches to control the disease. Results of field surveys showed that the pathogen is widespread and pathogenicity tests suggested that host susceptibility to the pathogen is moderate when seedlings are in appropriate watering conditions, particularly cork oaks. Occurrence of decline is also associated with soil characteristics that interfere with root expansion and water retention. We assessed the relative importance of each factor involved in decline and revised the role of P. cinnamomi in cork and holm oak decline.     

Canopy gap dynamics and development patterns in secondary Quercus stands on the Cumberland Plateau, Alabama, USA

Forest disturbances of various spatial extents and magnitudes shape species composition, structure, and stand development patterns. The disturbance regimes of most complex stage hardwood stands of the deciduous forests of eastern North America are typified by asynchronous and localized disturbance events. The overwhelming majority of gap-scale disturbance studies in hardwood forests of the region have analyzed late-successional stands. As such, there is a paucity of data on gap dynamics in hardwood stands prior to a complex developmental stage. We quantified biophysical characteristics of 60 canopy gaps in secondary Quercus stands on the Cumberland Plateau in Alabama to analyze gap-scale disturbance processes in developing systems. We found most gaps (90%) were caused by the removal of a single tree. Of the three gap formation mechanisms, snag-formed gaps were most common (40%). However, based on the number of uprooted and snapped stems we speculate that wind was also an important disturbance agent in these stands. Gap size and shape patterns were similar to what has been reported in other hardwood forests of the southern Appalachian Highlands. We did not find differences in gap size or shape based on formation mechanisms; a finding that may be related to the number of single-tree gap events. Gaps projected to close via subcanopy recruitment were significantly larger than those projected to close through lateral crown expansion. Most gaps (65%) were projected to close by lateral crown expansion of gap perimeter trees. However, the number of gaps projected to fill by subcanopy recruitment indicated the stands were approaching a transition in their developmental stage. Gap-scale processes modify residual tree architecture and stand structure. Through time these alterations result in progressively larger gaps, eventually reaching a size when most will fill by subcanopy recruitment, thus marking the complex stage of development. Gap capture by Quercus was restricted to relatively xeric sites that did not contain abundant shade-tolerant mesophytes in the understory. However, the majority of gaps contained abundant subcanopy Fagusgrandifolia, Acer saccharum, and Acer rubrum leading us to project that the forest will undergo a drastic composition shift under the current disturbance regime. Liriodendron tulipifera was projected to capture several relatively small gaps illustrating the role of topography on gap closure mechanisms.     

Crown transparency, tree mortality and stem growth of Pinus sylvestris, and colonization of Tomicus piniperda after an outbreak of Gremmeniella abietina

In the year 2000, large areas of forest in Sweden, mainly 30-50 year old Pinus sylvestris (L.) stands, were attacked by the fungus Gremmeniella abietina (Lagerb.) Morelet. The aims of this study were to investigate: (i) the relationship between G. abietina-induced tree crown transparency (CT) and P. sylvestris (L.) tree mortality; (ii) the influence of CT levels on stem growth; (iii) the recovery of the crown; and (iv) the association of CT and colonization by Tomicus piniperda (L.). Thirty-five permanent sample plots were established in five P. sylvestris stands (38-46 years old), infested by G. abietina, and 23 plots in four reference stands, not obviously infested.During the 5 years following the attack, the total mortality amounted to 454 trees ha⁻¹ and 7.8 m² ha⁻¹, on average, in the five infested stands, corresponding to 42% of the trees and 34% of the basal area at the time of the attack. Most of the mortality occurred within 2 years of the attack. The mortality of individual trees (2002-2005) was found to be related to the crown transparency (CT), the position of needle loss within the crown and the tree diameter at breast height. Based on our modeling, the probability of mortality was substantially increased if the initial CT-value was higher than 85%.Growth reductions were detected for individual trees with an initial CT of >c. 40%. In contrast, trees with a low initial CT (<c. 40%) were not affected and even exhibited increased growth. In the five infested stands, the reductions in basal area and volume increment were estimated to be 26-58%, and, 42-73%, respectively, during the five growing seasons after the attacks.The trees in the infested stands that were still alive in spring 2005 had started to recover in terms of CT. Breeding of T. piniperda on the P. sylvestris (L.) stems occurred almost exclusively on stems with a CT > 90%.The data from this study suggest that when a P. sylvestris (L.) stand has been attacked by G. abietina, trees with a CT above 80% should be felled; the remaining trees will have a high probability of survival and resistance to successful breeding by the T. piniperda.     

Grapevine (Vitis spp.) dynamics in association with manual tending,physiography, and host tree associations in temperate deciduous forests

The role of lianas (woody vines) in the development and diversity of both tropical and temperate forests under differing management scenarios has not been thoroughly explored. We examined changes in grapevine (Vitis spp.) densities over time in clearcut stands as influenced by manual tending, physiography, and host tree associations. We used data from long-term studies on 66 clearcut stands dominated by temperate deciduous forest tree species on the Hoosier National Forest in south-central Indiana, USA. Fourteen of the stands had grapevines removed manually, approximately during the stem exclusion stage of development. Grapevine densities steadily increased from age 5 until age 15, which coincides with the period of stem exclusion of these stands. Subsequent grapevine mortality may have been related to light competition. Manually treated stands had similar grapevine densities as untreated stands after 20 years across sites, and it appeared that only on the most xeric area was the grapevine treatment effective in reducing grapevine densities. During early stand development, ranging from ages 5 to 17, grapevine density was strongly related to slope position, but as stands developed through the stem exclusion stage, aspect emerged as a stronger factor influencing grapevine density. Black cherry (Prunus serotina Ehrh.), walnut (Juglans spp.), and elm (Ulmus spp.) were the most common grapevine host trees under both treated and untreated scenarios, which may be associated with the crown architecture of these species. Results suggest lianas play a critical role in the early development of disturbed forest sites in temperate deciduous forests. With concerns that lianas are increasing in abundance and distribution in these forest types, understanding their role in forest dynamics, such as host tree associations at different stages of development, competition dynamics on different sites and corresponding influences on tree growth, species composition, and diversity, will be critical to decision-making processes in achieving desired management goals in the future.     

Assessment of molecular detection of Fusarium circinatum in insects and passive spore traps in Pinus radiata plantations

Fusarium circinatum is the causal agent of pitch canker, a destructive disease that threatens natural and planted pine forests around the world. Although pitch canker has caused problems in Spain and Portugal, concerning Europe as a whole, the fungus is not established across the pine distribution area. Its dispersion by wind and/or insect vectors could nevertheless play a role in the colonization of currently uninfected stands. It is therefore crucial to develop monitoring tools for its detection. To this end, we assessed the molecular detection of the pathogen in environmental samples of bark beetles and passive spore traps, collected in two infected Pinus radiata plantations in Basque country, Spain. The spread pattern of F. circinatum was assessed by an experimental design that included insect and spore traps installed at the centre, at the edge and outside the plots. Our results showed that F. circinatum was detected in both types of samples, at almost all collection dates. In both type of samples, positive detections were mainly found at the centre of the plots, a lower proportion at the edge, and very few outside. This suggests that long‐distance dispersion of Fusarium circinatum does not rely on wind spore dispersal neither on insect flight. Our study also shows that molecular methods are a powerful tool to monitor the pathogen in environmental samples.     

Why do Pinus species have different growth dominance patterns than Eucalyptus species? A hypothesis based on differential physiological plasticity

It has been observed that Eucalyptus stands show high growth dominance levels while Pinus stands show null or low growth dominance levels. We hypothesized that this differential behaviour is linked to a higher degree of physiological-biochemical plasticity in Eucalyptus than in Pinus species related to photosynthetic capacity. This leads to an increment in growth efficiency (GE) difference between the largest and the smallest trees of a stand, and therefore to high growth dominance levels in Eucalyptus. To test our hypothesis we carried out a bibliographical survey and reanalyzed data from Pinus ponderosa and Pinus taeda plantations in Argentina. We found that some species within the genus Eucalyptus present higher growth dominance levels, physiological plasticity and GE differentiation than Pinus species. The mean maximum values of these traits reported for any Eucalyptus species were: growth dominance coefficient, 0.48; photosynthetic capacity increment when resource availability increases, 175%; GE difference between the largest and the smallest trees of a stand, 300%. Mean maximum values for the same traits reported for any Pinus species were 0.13, no phostosynthetic plasticity as the most frequent pattern, and 51%, respectively. In Pinus species the most frequent response to an increase in resource availability is characterized by an increase in leaf area or biomass, maintaining a similar photosynthetic capacity per unit area. However, it appears that in P. ponderosa there are some situations, characterized by a high degree of intraspecific competition, leading to a very high degree of GE differentiation which deserve future research. Although we did not find any study reporting simultaneously all variables concerning our hypothesis (growth dominance, growth efficiency differentiation and physiological plasticity) any of the circumstantial evidence found in the bibliography contrasts our hypothesis.     

Forest management effects on in situ and ex situ slash pine forest carbon balance

In this study we analyzed the effect of silviculture on carbon (C) budgets in Pinus elliottii (slash pine) plantations on the southeastern U.S. Coastal Plain. We developed a hybrid model that integrates a widely used growth and yield model for slash pine with allometric and biometric equations determined for long-term C exchange studies to simulate in situ C pools. The model used current values of forest product conversion efficiencies and forest product decay rates to calculate ex situ C pool. The model was validated from a variety of sources, accurately simulating C estimates based on multiple measurement techniques and sites. Site productivity was the major factor driving C sequestration in slash pine stands. On high productivity sites, silvicultural schemes that promote sawtimber-type products are more suitable for increasing C storage (even not taking in account the consequent economical revenues associated with sawtimber production). When rotation length was increased from 22 to 35 years on unthinned and thinned stands, respectively, we estimated net increments of 26 and 20 MgC ha⁻¹ in average C stock of the first five rotations. Even though in situ C pool in slash pine accounts for most of this net increment, C in sawtimber products increased from 8 and 14 to 23 and 24 MgC ha⁻¹, on unthinned and thinned stands, respectively. Thinning effects on net C stock depended on intensity and timing of intervention, mainly due to changes in diameter classes that promote higher proportion of long-lived products. Emissions associated with silvicultural activities, including transportation of logs to the mill, are small compared to the magnitude of net C sequestration, accounting for between 2.2 and 2.3% of gross C stock. This slash pine plantation C sequestration model, based on empirical and biological relationships, is appropriate for use in regional C stock assessments or for C credit verification.     

Field survey,isolation, identification and pathogenicity of Phytophthora species associated with a Mediterranean‐type tree species

Corymbia calophylla (marri), a keystone tree species in the global biodiversity hot spot of southwestern Australia, is suffering decline and mortality associated with a canker disease caused by the endemic fungus Quambalaria coyrecup. Phytophthora species are frequently isolated from the rhizosphere of C. calophylla, and a hypothesis is that Phytophthora root infection is predisposing C. calophylla to this endemic canker pathogen. Field surveys were conducted in both anthropogenically disturbed and undisturbed C. calophylla stands, from where a total of 100 rhizosphere soil samples, from both healthy and cankered trees, were collected. Phytophthora species were isolated from 26% of the samples collected, with Phytophthora incidence significantly higher on disturbed stands than in natural forests (73% and 27%, respectively). Five Phytophthora species were recovered, including P. cinnamomi, P. elongata, P. multivora, P. pseudocryptogea and P. versiformis. Under‐bark inoculations with the Phytophthora isolates caused significant lesion lengths in excised C. calophylla stems. Corymbia calophylla response to pot infestation trials in the glasshouse varied between Phytophthora species and isolates, with isolates of P. cinnamomi and P. multivora causing a significant reduction in seedling root volume and often leading to seedling death. This study demonstrates that root disease caused by Phytophthora species, especially P. cinnamomi and P. multivora, has the ability to adversely affect C. calophylla health. This study leads the way to do a dual inoculation trial with the canker pathogen Q. coyrecup, and different Phytophthora species to investigate if Phytophthora root infection predisposes C. calophylla to this canker disease.