Some disturbances can drive ecological systems to abrupt shifts between alternative stages (tipping points) when critical transitions occur. Drought‐induced tree death can be considered as a ...nonlinear shift in tree vigour and growth. However, at what point do trees become predisposed to drought‐related dieback and which factors determine this (tipping) point? We investigated these questions by characterizing the responses of three tree species, silver fir (Abies alba), Scots pine (Pinus sylvestris) and Aleppo pine (Pinus halepensis), to a severe drought event. We compared basal area increment (BAI) trends and responses to climate and drought in declining (very defoliated and dying) vs. non‐declining (slightly or not defoliated) trees by using generalized additive mixed models. Defoliation, BAI and sapwood production were related to functional proxies of tree vigour measured at the onset and end of the drought (non‐structural carbohydrate concentrations, needle N content and C isotopic discrimination, presence of wood‐inhabiting fungi). We evaluated whether early warning signals (increases in synchronicity among trees or in autocorrelation and standard deviation) could be extracted from the BAI series prior to tree death. Declining silver fir and Scots pine trees showed less growth than non‐declining trees one to three decades, respectively, before the drought event, whereas Aleppo pines showed growth decline irrespective of tree defoliation. At the end of the drought period, all species showed increased defoliation and a related reduction in the concentration of sapwood soluble sugars. Defoliation was constrained by the BAI of the previous 5 years and sapwood production. No specific wood‐inhabiting fungi were found in post‐drought declining trees apart from blue‐stain fungi, which extensively affected damaged Scots pines. Declining silver firs showed increases in BAI autocorrelation and variability prior to tree death. Synthesis. Early warning signals of drought‐triggered mortality seem to be species specific and reflect how different tree species cope with drought stress. Highly correlated declining growth patterns during drought can serve as a signal in silver fir, whereas changes in the content of sapwood soluble sugars are suitable vigour proxies for Scots and Aleppo pines. Longer growth and defoliation series, additional vigour parameters and multi‐species comparisons are required to understand and predict drought‐induced tree death.
We tested the hypotheses that responses to the mountain pine beetle fungal associate Grosmannia clavigera will differ between the evolutionarily co‐evolved host lodgepole pine (Pinus contorta var. ...latifolia) and the naïve host jack pine (Pinus banksiana) and that these responses will be influenced by water availability. G. clavigera inoculation resulted in more rapid stem lesion development in lodgepole than in jack pine; water deficit delayed lesion development in both species. Decreased hydraulic conductivity was observed in inoculated lodgepole pine seedlings, likely because of tracheid occlusion by fungal hyphae and/or metabolite accumulation. Drought but not inoculation significantly impacted bark abscisic acid levels. Jasmonic and salicylic acid were implicated in local and systemic responses of both species to G. clavigera, with salicylic acid appearing to play a greater role in jack pine response to G. clavigera than lodgepole pine. Water deficit increased constitutive levels and/or attenuated induced responses to G. clavigera for several monoterpenes in lodgepole but not jack pine. Instead, inoculation of well‐watered but not water deficit jack pine resulted in a greater number of xylem resin ducts. These findings reveal mechanisms underlying differences in G. clavigera‐induced responses between lodgepole and jack pine hosts, and how water availability modulates these responses.
Western North America is currently experiencing the largest mountain pine beetle epidemic in recorded history; in recent years, this destructive forest pest has undergone host range expansion to jack pine, a boreal forest species. We have examined the effect of water limitation on responses of the evolutionarily co‐evolved host lodgepole pine and the naïve host jack pine, focusing on delineating similarities and differences in responses to inoculation with a mountain pine beetle fungal associate, Grosmannia clavigera. These species show different physiological responses to water limitation and that water deficit alters both constitutive and induced defences. Hormone profiles correlate with treatment‐associated differences in induced defences, and hormone crosstalk may modulate the patterns of induced defences that we observed in this study.
Fungi assigned to the Ophiostomatales are of economic concern as many are blue-stain fungi and some are plant pathogens. The mitogenomes of two blue-stain fungi,
and
, were sequenced and compared ...with currently available mitogenomes for other members of the Ophiostomatales. Species representing various genera within the Ophiostomatales have been examined for gene content, gene order, phylogenetic relationships, and the distribution of mobile elements. Gene synteny is conserved among the Ophiostomatales but some members were missing the
gene. A genome wide intron landscape has been prepared to demonstrate the distribution of the mobile genetic elements (group I and II introns and homing endonucleases) and to provide insight into the evolutionary dynamics of introns among members of this group of fungi. Examples of complex introns or nested introns composed of two or three intron modules have been observed in some species. The size variation among the mitogenomes (from 23.7 kb to about 150 kb) is mostly due to the presence and absence of introns. Members of the genus
appear to have the smallest mitogenomes due to loss of introns. The taxonomy of the Ophiostomatales has recently undergone considerable revisions; however, some lineages remain unresolved. The data showed that genera such as
appear to be polyphyletic and the separation of
from
is justified.
The European spruce bark beetle, Ips typographus (L.), is a major pest of Norway spruce. During outbreaks, the beetles can colonize moderately stressed trees via mass attacks mediated by aggregation ...pheromones, while at endemic population levels, beetles infest trees with impaired defenses. I. typographus introduces ophiostomatoid fungi into the phloem, which can support host colonization. Low-density fungal infections are locally contained by hypersensitive wound reactions; larger necrotic lesions indicate lower tree resistance. Here, we made links between drought stress, susceptibility to fungal infections, and the attractiveness of spruce for host-searching I. typographus males. We sampled bark cores from roofed, non-roofed and untreated control trees of a rainfall exclusion field site. Drought stress was assessed using pre-dawn twig water potentials, and tree defenses were assessed using inoculations with Grosmannia penicillata. Subsequently, we performed Petri dish arena choice tests in the lab, where male beetles could choose between the bark samples of differentially stressed trees. We found that the attractiveness of bark cores increased with drought stress and the extent of hypersensitive wound reactions to fungal infection. Furthermore, beetles stayed longer in those Petri dish sections with the sample of their final choice. The bioassays provide evidence for the primary attraction of male I. typographus to tissues of Norway spruce and preference of beetles for stressed trees.
Considered one of the most devastating plant–parasitic nematodes worldwide, Bursaphelenchus xylophilus (commonly known as pinewood nematode, PWN) is the causal agent of the pine wilt disease in the ...Eurasian coniferous forests. This migratory parasitic nematode is carried by an insect vector ( Monochamus spp.) into the host tree ( Pinus species), where it can feed on parenchymal cells and reproduce massively, resulting in the tree wilting. In declining trees, PWN populations are strongly dependent on fungal communities colonizing the host (predominantly ophiostomatoid fungi known to cause sapwood blue-staining, the blue-stain fungi), which not only influence their development and life cycle but also the number of individuals carried by the insect vector into a new host. Our main aim is to understand if PWN-associated mycobiota plays a key role in the development of PWD, in interaction with the PWN and the insect vector, and to what extent it can be targeted to disrupt the disease cycle. For this purpose, we characterized the fungal communities of Pinus pinaster trees infected and non-infected with PWN in three collection sites in Continental Portugal with different PWD temporal incidences. Our results showed that non-infected P. pinaster mycoflora is more diverse (in terms of abundance and fungal richness) than PWN-infected pine trees in the most recent PWD foci, as opposed to the fungal communities of long-term PWD history sites. Then, due to their ecological importance for PWN survival, representatives of the main ophiostomatoid fungi isolated ( Ophiostoma, Leptographium , and Graphilbum ) were characterized for their adaptative response to temperature, competition in-between taxa, and as food source for PWN. Under the conditions studied, Leptographium isolates showed promising results for PWN control. They could outcompete the other species, especially O. ips , and significantly reduce the development of PWN populations when compared to Botrytis cinerea (routinely used for PWN lab culturing), suggesting this to be a natural antagonist not only for the other blue-stain species but also for the PWN.
► Transpiration began to decline within 10days of beetle infestation. ► Girdled tree water status and foliage growth was similar to healthy trees. ► Blue stain fungi were the primary mortality agents ...following beetle infestation.
The recent mountain pine beetle outbreak in North American lodgepole pine forests demonstrates the importance of insect related disturbances in changing forest structure and ecosystem processes. Phloem feeding by beetles disrupts transport of photosynthate from tree canopies and fungi introduced to the tree’s vascular system by the bark beetles inhibit water transport from roots to canopy; the implications of these processes for tree mortality are poorly understood. We hypothesized that the fungus must quickly disrupt tree water relations because phloem girdling, reported in other studies, requires much longer than a year to cause mortality. We tested the hypothesis in lodgepole pine (Pinus contorta) by comparing tree water use, foliar expansion and seasonal variation in predawn water potential on 8 mechanically girdled trees, 10 control trees and 17 trees attacked by mountain pine beetle (Dendroctonous ponderosae). Transpiration began to decline within ten days of beetle infestation; two months later, pre-dawn water potential had also dropped significantly as water transport to the canopy declined by 60% relative to healthy trees. There was no water transport or foliar expansion by beetle-infested trees the following year. Experimentally girdled trees continued to transpire, maintain leaf water potential and grow new foliage similar to healthy trees. Our data suggest that fungi introduced by bark beetles in this study are the primary cause of tree mortality following mountain pine beetle attack and significantly reduce transpiration soon after beetle infestation. Rapid decline and the eventual cessation of water uptake by infected trees have important implications for water and nutrient cycling in beetle impacted forests.
Outdoor wood is exposed to various factors that can be described as weathering and cause the wood to grey. The ageing processes can vary greatly depending on the exposure. Parts of wood that are not ...exposed to external factors, e.g. under the overhanging, are less exposed, and the weathering process is therefore slower. This can be accelerated by solutions based on iron ions. In this way, the wood greys quickly and evenly. However, after iron treatment, the colour also depends on the previous exposure of wood to weathering. In our study, the colour change was observed as a function of weathering time. Before treatment, the samples were exposed to outdoor weathering for different periods of time and then treated with a 5 % solution of pure iron (II) sulphate and commercial iron (II) sulphate. It was determined that the pre-weathering time affected the final colour change, as the samples exposed for five weeks before treatment have comparable colour to naturally weathered wood. At the beginning of exposure, iron (II) sulphate limits mould growth, but after two months, staining fungi develop on the treated samples as well. The growth of blue stain fungi on the treated samples did not significantly affect the colour and visual appearance of the wood treated with iron-based solutions.
Drvo za vanjsku uporabu izloženo je različitim čimbenicima koji se mogu opisati kao vremenski utjecaji, a uzrokuju sivljenje drva. Procesi starenja mogu uvelike varirati ovisno o izloženosti drva tim utjecajima. Na dijelovima drva koji nisu izravno izloženi vanjskim čimbenicima, npr. ispod prevjesa, proces starenja je sporiji. Taj se proces starenja može ubrzati otopinama na bazi iona željeza tako da drvo brzo i ravnomjerno posivi. Međutim, boja nakon tretmana željezom također ovisi o prethodnoj izloženosti drva vremenskim utjecajima. U ovom smo istraživanju promatrali promjenu boje kao funkciju trajanja izloženosti drva vremenskim utjecajima. Uzorci su prije tretmana različito vrijeme bili izloženi vremenskim utjecajima, a zatim su tretirani 5 %-tnom otopinom čistog željezova (II) sulfata i komercijalnog željezova (II) sulfata. Utvrdili smo da je prvotna izloženost vremenskim uvjetima utjecala na konačnu promjenu boje jer su uzorci koji su bili pet tjedana izloženi vremenskim utjecajima prije tretmana imali sličnu boju kao i prirodno drvo izloženo vremenskim utjecajima. Na početku izlaganja željezov (II) sulfat ograničavao je razvoj plijesni, ali su se nakon dva mjeseca izlaganja i na tretiranim uzorcima drva razvile gljive promjene boje. Razvoj gljiva plavila na tretiranim uzorcima nije znatnije utjecao na boju i vizualni izgled drva tretiranog otopinama na bazi željeza.
Bark beetles form multipartite symbiotic associations with blue stain fungi (Ophiostomatales, Ascomycota). These fungal symbionts play an important role during the beetle's life cycle by providing ...nutritional supplementation, overcoming tree defences and modifying host tissues to favour brood development. The maintenance of stable multipartite symbioses with seemingly less competitive symbionts in similar habitats is of fundamental interest to ecology and evolution. We tested the hypothesis that the coexistence of three fungal species associated with the mountain pine beetle is the result of niche partitioning and adaptive radiation using SNP genotyping coupled with genotype–environment association analysis and phenotypic characterization of growth rate under different temperatures. We found that genetic variation and population structure within each species is best explained by distinct spatial and environmental variables. We observed both common (temperature seasonality and the host species) and distinct (drought, cold stress, precipitation) environmental and spatial factors that shaped the genomes of these fungi resulting in contrasting outcomes. Phenotypic intraspecific variations in Grosmannia clavigera and Leptographium longiclavatum, together with high heritability, suggest potential for adaptive selection in these species. By contrast, Ophiostoma montium displayed narrower intraspecific variation but greater tolerance to extreme high temperatures. Our study highlights unique phenotypic and genotypic characteristics in these symbionts that are consistent with our hypothesis. By maintaining this multipartite relationship, the bark beetles have a greater likelihood of obtaining the benefits afforded by the fungi and reduce the risk of being left aposymbiotic. Complementarity among species could facilitate colonization of new habitats and survival under adverse conditions.
Surface mould growth contributes to the colour changes of outdoor exposed wood over time. Modelling mould growth can thus help visualize wooden facades’ colour development, which can improve facade ...design and service life. However, existing wood mould models do not consider transient wetting effects that occur outdoors due to precipitation and condensation. To address this, four mould models were evaluated using laboratory experimental data that included exposure to transient wetting. First, the models (the original and the updated VTT model, the biohygrothermal model and the mould resistance design (MRD) model) were evaluated for Scots pine sapwood. For this evaluation, the transient wetting effect was implemented in the models by using hourly wood surface relative humidity (RH), calculated from electrical resistance measurements, as input. This showed that the original and the updated VTT model gave best fit to the experimental data. However, further evaluation of these two models for more wood materials showed that the updated VTT model was sensitive to the choice of material parameters. Large discrepancies occurred when varying the material parameters in the updated VTT model. Finally, different estimates of RH were tested in the original VTT model. Using wood surface RH as input gave best fit to the experimental data, and ambient air RH gave poorest fit. Overall, the results indicate that the original VTT model is fairly reliable and can be used to predict mould growth on wooden claddings exposed to transient wetting as long as the wood surface climate is used as climatic input data.
•Four existing mould growth models were evaluated using experimental data.•Eight climatic conditions and eight wood materials were included in the evaluation.•The transient wetting effect was implemented in the models by using wood humidity as input data.•The original VTT model gave the most reliable estimates.
Ips acuminatus (Coleoptera, Scolytinae) is a pine-infesting bark beetle that occurs throughout Europe and Asia. Recently, the insect has killed numerous Scots pines (Pinus sylvestris) in eastern ...Poland. Several species of ophiostomatoid fungi are associated with I. acuminatus in Europe, but no research has been done on the fungi associated with this bark beetle in Central Europe specifically. The aim of this study was to identify the ophiostomatoid fungal associates of I. acuminatus in eastern Poland, where tree mortality caused by this beetle species has recently increased. Field surveys in Puławy and Mircze Forest Districts yielded a total of 2 269 fungal isolates from 237 beetles and 204 beetle galleries. Isolates were grouped based on morphology and representatives of each group were identified based on DNA sequences of the ITS, LSU, β-tubulin, calmodulin and elongation factor 1-α gene regions. A total of seven previously described species of ophiostomatoid fungi were identified. The dominant species were Graphilbum acuminatum and Sporothrix pseudoabietina. This study revealed that the community of ophiostomatoid fungi associated with I. acuminatus in Poland is different from those reported in other regions of Europe. In addition, molecular data suggest that S. pseudoabietina is a synonym of S. villosa in the Sporothrix gossypina & S. stenoceras species complexes.
PDF
