Effect of water availability and fertilization on water status,growth, vigour and the resistance of Scots pine to fungal mass inoculation with Ophiostoma ips

Abstract

The effect of water and nutrient availability on the performance of Scots pine (Pinus sylvestris L.) against Ophiostoma ips (Rumb.), a bark beetle-associated phytopathogenic blue-stain fungus, was investigated. Field-grown trees were subjected for 18 months to water-stress and/or fertilization, and the effects of such treatments on the needle nutrient status, tree vegetative growth and vigour were examined. At the end of the experimental period, the trees were mass-inoculated (800 inocula m^?2) with the fungus, and the relationship between resource availability and tree performance against pathogen attack was also tested. Predawn shoot water potential (Ψ_PD) of irrigated trees was significantly higher than that of water-stressed trees, and fertilized trees had a significantly lower C/N ratio. The Ψ_PD values and needle nitrogen content suggest that resource-limited trees were under moderate stress. Improved nutrient availability significantly increased tree growth and tree vigour. However, no evidence for an effect of improved nutrient availability on tree fungal resistance was found in our study.     

Pisolithus tinctorius promotes germination and forms mycorrhizal structures in Scots pine somatic embryos in vitro

The results of the present study show that inoculation with the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch potentially enhances the germination of Scots pine (Pinus sylvestris L.) somatic embryos in vitro. Stimulation by Pisolithus tinctorius was only observed in the absence of direct contact between the symbionts; mature embryos were not sufficiently robust for balanced interaction with the fungus on half-strength DCR medium. Subsequently, on MMN medium with a reduced sugar concentration, direct contact between somatic embryo-derived plants and the fungus resulted in in vitro formation of mycorrhiza. Ex vitro inoculation also improved adaptation of the somatic embryo-derived plants, even though mycorrhizal structures were not observed. The reactions to Pisolithus tinctorius varied between different Scots pine cell lines both in vitro and ex vitro.     

Tolerance and biodegradation of m-toluate by Scots pine, a mycorrhizal fungus and fluorescent pseudomonads individually and under associative conditions

The tolerance to, and degradation of m-toluate by Scots pine (Pinus sylvestris), a symbiotic mycorrhizal fungus (Suillus bovinus) and Pseudomonas fluorescens strains, with or without m-toluate-degrading capacity, was determined individually and in all symbiotic/associative plant-microbe combinations. Fungal survival on medium with m-toluate was increased in co-culture with the degradative bacterial strains on agar plates (up to 0.02%, w/v). When fungi were grown in mycorrhizal association with Scots pine seedlings in test-tube microcosms containing expanded clay pellets and growth media, the fungus was able to withstand m-toluate concentrations up to 2.0%, w/v in all treatments. The seedling tolerance remained unaltered regardless of the presence or absence of mycorrhizal fungi or biodegradative bacteria. Reduction in m-toluate levels was only detected in treatments inoculated with bacterial strains harbouring TOL catabolic plasmids. The plant and fungus, alone or in mycorrhizal symbiosis, were unable to cleave m-toluate. The presence of easily available plant-derived carbon sources did not impede m-toluate degradation by the bacteria in the mycorrhizosphere.     

Spermidine and the ectomycorrhizal fungus Pisolithus tinctorius synergistically induce maturation of Scots pine embryogenic cultures

Exogenous spermidine (Spd) and the ectomycorrhizal (ECM) fungus Pisolithus tinctorius (Pers.) Coker and Couch had a synergistic effect on the maturation of Scots pine (Pinus sylvestris L.) somatic embryos. Induced maturation was expressed as a higher number of cell masses able to form embryos and a greater number of embryos formed per cell mass. In contrast, treatment with P. tinctorius alone on the hormone-free medium resulted in the lowest embryo-forming capacity. Retarded proliferation growth appeared to be required for maturation, but did not explain the synergistic effect of the fungus and exogenous Spd. Simultaneous treatment did not result in lower concentrations of putrescine (Put), Spd or spermine (Spm) in the embryogenic cell masses relative to the separate treatments. Our study is the first report on the use of a specific ECM fungus to induce maturation of somatic embryos, and it indicates that P. tinctorius was able to modify the maturation media in a way that, together with exogenous Spd, positively affected embryogenic cultures of Scots pine. Our study also shows that it is possible to enhance plant development other than root formation by using specific ECM fungi.     

Temperature and soil fertility as regulators of tree line Scots pine growth and survival—implications for the acclimation capacity of northern populations

The acclimation capacity of leading edge tree populations is crucially important in a warming climate. Theoretical considerations suggest that adaptation through genetic change is needed, but this may be a slow process. Both positive and catastrophic outcomes have been predicted, while empirical studies have lagged behind theory development. Here we present results of a 30‐year study of 55,000 Scots pine (Pinus sylvestris) trees, planted in 15 common gardens in three consecutive years near and beyond the present Scots pine tree line. Our results show that, contrary to earlier predictions, even long‐distance transfers to the North can be successful when soil fertility is high. This suggests that present northern populations have a very high acclimation capacity. We also found that while temperature largely controls Scots pine growth, soil nutrient availability plays an important role—in concert with interpopulation genetic variation—in Scots pine survival and fitness in tree line conditions. These results suggest that rapid range expansions and substantial growth enhancements of Scots pine are possible in fertile sites as seed production and soil nutrient mineralization are both known to increase under a warming climate. Finally, as the ontogenetic pattern of tree mortality was highly site specific and unpredictable, our results emphasize the need for long‐term field trials when searching for the factors that control fitness of trees in the variable edaphic and climatic conditions of the far North.     

Asynchrony in larval development of the pine beauty moth, Panolis flammea, on an introduced host plant may affect parasitoid efficacy

In the United Kingdom, Panolis flammea (Den. and Schiff.) (Lepidoptera: Noctuidae) is an important pest species of the introduced lodgepole pine but not of its natural host Scots pine. The timing of P. flammea larval growth must be synchronized with its host tree if the larvae are to succeed. We collected field data during 1990 which revealed that the phenological window starts earlier in Scots pine and is shorter than that observed in lodgepole pine. The larvae are found in the field earlier and within a narrower time frame within a Scots pine forest than in a lodgepole pine forest. The larval developmental period is significantly longer on lodgepole pine than on Scots pine. The synchrony/asynchrony of P. flammea to its natural host (Scots pine) and an introduced tree (lodgepole pine) results in the parasitoids having a different impact on the larvae of the two hosts. At any one time, the host plant, caterpillars and parasitoids are more synchronous on the ancestral Scots pine than on lodgepole pine, resulting in a higher percentage of larvae in the optimal instar for parasitism at that time. In lodgepole pine, the percentage of suitable instars available to parasitoids is lower at any given time. The information presented here furthers our understanding of the possible mechanisms for the observed differential population dynamics of the insect on Scots pine and lodgepole pine in the UK. Handling editor: Robert Glinwood.     

Ectomycorrhizal community structure of different genotypes of Scots pine under forest nursery conditions

In this paper, we report the effect of Scots pine genotypes on ectomycorrhizal (ECM) community and growth, survival, and foliar nutrient composition of 2-year-old seedlings grown in forest bare-root nursery conditions in Lithuania. The Scots pine seeds originated from five stands from Latvia (P1), Lithuania (P2 and P3), Belarus (P4), and Poland (P5). Based on molecular identification, seven ECM fungal taxa were identified: Suillus luteus and Suillus variegatus (within the Suilloid type), Wilcoxina mikolae, Tuber sp., Thelephora terrestris, Cenococcum geophilum, and Russuloid type. The fungal species richness varied between five and seven morphotypes, depending on seed origin. The average species richness and relative abundance of most ECM morphotypes differed significantly depending on pine origin. The most essential finding of our study is the shift in dominance from an ascomycetous fungus like W. mikolae in P2 and P4 seedlings to basidiomycetous Suilloid species like S. luteus and S. variegatus in P1 and P5 seedlings. Significant differences between Scots pine origin were also found in seedling height, root dry weight, survival, and concentration of C, K, Ca, and Mg in the needles. The Spearman rank correlation coefficient revealed that survival and nutritional status of pine seedlings were positively correlated with abundance of Suilloid mycorrhizas and negatively linked with W. mikolae abundance. However, stepwise multiple regression analysis showed that only survival and magnesium content in pine needles were significantly correlated with abundance of ECM fungi, and Suilloid mycorrhizas were a main significant predictor. Our results may have implications for understanding the physiological and genetic relationship between the host tree and fungi and should be considered in management decisions in forestry and ECM fungus inoculation programs.     

Drought as an Inciting Mortality Factor in Scots Pine Stands of the Valais, Switzerland

During the 20th century, high mortality rates of Scots pine (Pinus silvestris L.) have been observed over large areas in the Rhône valley (Valais, Switzerland) and in other dry valleys of the European Alps. In this study, we evaluated drought as a possible inciting factor of Scots pine decline in the Valais. Averaged tree-ring widths, standardized tree-ring series, and estimated annual mortality risks were related to a drought index. Correlations between drought indices and standardized tree-ring series from 11 sites showed a moderate association. Several drought years and drought periods could be detected since 1864 that coincided with decreased growth. Although single, extreme drought years had generally a short-term, reversible effect on tree growth, multi-year drought initiated prolonged growth decreases that increased a tree’s long-term risk of death. Tree death occurred generally several years or even decades after the drought. In conclusion, drought has a limiting effect on tree growth and acts as a bottleneck event in triggering Scots pine decline in the Valais.     

Resistance level in Scots pine clones and artificial introductions of Tomicus piniperda (Col., Scolytidae) and Leptographium wingfieldii (Deuteromycetes)

Scots pine trees belonging to clones considered to be resistant or susceptible after mass inoculations of Leptographium wingfieldii , a fungus associated with Tomericus piniperda , were submitted to a low density of fungal inoculations or beetle insertions. The length of the phloem-induced reaction zone, the fungal extension and fungal density inside the reaction zone, and the length of maternal galleries of T. piniperda were measured. The length of the phloem reaction zone never differed between resistant and susceptible trees. The density of the fungus mycelium in histological sections of the phloem, and the length of the maternal galleries in the reaction zone were higher in the susceptible trees than in the resistant ones. These factors could be good indicators of resistance of Scots pine to mass attacks.     

Changing dynamics of the pine beauty moth (Panolis flammea) in Britain: the loss of enemy free space?

1 The pine beauty moth Panolis flammea has two main host plants in Britain: Pinus sylvestris (Scots pine), which is the ancestral food plant where the insect is never abundant enough to cause tree mortality, and Pinus contorta (lodgepole pine), an introduced host tree that has experienced periodic widespread tree mortality due to this pest.
2 We review the recent literature, published mostly after the year 2000, regarding the impact of natural enemies on the population dynamics of P. flammea in Britain.
3 The natural enemies of P. flammea are more diverse and abundant in Scots pine habitat than in lodgepole pine habitat and some of them show differential selection for P. flammea larvae in Scots pine habitat over those located in lodgepole pine habitat.
4 It is concluded that the difference in the population dynamics of this insect in the two different habitats was probably the result of the P. flammea finding enemy-free space in lodgepole pine habitat.
5 Recent evidence on the diversity and impact of natural enemies on lodgepole pine has demonstrated that they currently have a much more significant impact on this pest than they did in the 1970s and 1980s, when outbreaks were frequent.     

大兴安岭北部樟子松树木生长与气候因子的关系

 在大兴安岭北部漠河(MH I、MH II 2个样点)、塔河蒙克山(MKS)、满归(MG)地区共采集樟子松(Pinus sylvestris var. mongolica)年轮样芯139个, 成功地建立了MH I、MH II、MKS和MG 4个样点的樟子松差值年表, 最长达377年(1631–2007年, 有效年表为1743–2007年)。樟子松年轮指数与气候因子的响应函数分析表明, 气温是这4个样点樟子松径向生长的主要限制因子。但4个样点限制其生长的月份有所差异, 漠河的2个样点樟子松年轮指数与6月气温负相关, 满归和塔河蒙克山樟子松年轮指数与前一年10月气温正相关。樟子松年表与区域气候的冗余分析(redundancy analysis, RDA)基本与响应函数分析的结果一致, 进一步验证了气温对大兴安岭北部樟子松生长的限制作用。该研究为全球变暖下大兴安岭北部樟子松林的经营管理及区域气候重建提供了基础数据。     

Secondary buds in Scots pine trees infested with <Emphasis Type="Italic">Gremmeniella abietina</Emphasis>

In winter 2000–2001, there was a serious outbreak of Gremmeniella abietina Morelet in southeastern Norway. During the outbreak, we noted that injured Scots pine trees (Pinus sylvestris L.) developed secondary buds in response to the fungus attack, and we decided to study the relationship between injury, appearance of secondary buds and recovery of the trees thereafter. For this purpose, 143 trees from 10 to 50 years of age were chosen and grouped into crown density classes. Injury was assessed in detail, and buds were counted before bud burst in the spring of 2002. In addition, a subset of 15 trees was followed through the summer of 2002 to assess recovery. All injured trees developed secondary buds, with a clear overweight of dormant winter buds in proportion to interfoliar buds. Healthy control trees did not develop secondary buds at all. The secondary buds appeared predominantly on the injured parts of the tree; interfoliar buds in particular developed just beneath the damaged tissue. Most of the secondary buds died during the winter of 2001–2002, mainly because the fungus continued to spread after the first outbreak. Many of the remaining buds developed shoots with abnormal growth during the summer. Secondary buds may help trees to recover from Gremmeniella attacks, but this strategy may fail when the fungus continues to grow and injure the newly formed buds and shoots.     

Changes in fungal community of Scots pine (Pinus sylvestris) needles along a latitudinal gradient in Sweden

Conifer needles are typically long lived and can host a diverse community of fungal species with various effects on their host tree. The purpose of this study was to analyse shifts in the fungal community of Scots pine (Pinus sylvestris) needles on different spatial scales using 454 pyrosequencing. The fungal community composition changed gradually along a north-south gradient through Sweden, representing boreal to temperate vegetation zones. OTU richness and Shannon's diversity index increased with increasing latitude, but only in naturally regenerated forests. On the tree level, needles with symptoms of disease hosted a more diverse mycobiota compared to healthy needles, presumably supporting more pathogenic or saprotrophic species. This study provides a better insight into the patterns of fungal communities of Scots pine needles and highlights the need for further experimental research to identify specific environmental factors shaping the abundance of different fungal species.     

Habitat indicators for cavity-nesters: The polypore Phellinus pini in pine forests

Foresters and arborists have long used fruit-bodies of heart-rot fungi as signs of advanced live-tree decay, but such usage has not been elaborated for forest conservation. I analysed relationships between a heart-rot fungus, tree-cavity supply, and cavity-nesting bird assemblage in wet hemiboreal Scots pine (Pinus sylvestris) forests in Estonia. The focal species, Phellinus pini, is the main heartwood decayer of live pines; it typically forms fruit-bodies at the stage of advanced decay on old trees. I found that the pine wetlands had few tree-cavities (mostly in snags) and cavity-nesting birds (woodpeckers being almost absent) despite abundant snag supply. Only one fruit-body of P. pini was found on cavity-tree but stand-scale abundance of the fruit-bodies correlated well with cavity-nester densities. Multifactor models indicated that cavity formation, not tree death, was the limiting process for secondary cavity-nesters, and P. pini could indeed be used (in combination with old-pine abundance) for assessing their habitat quality. This fungus could also serve as an educational flagship species to bridge conservation biology and forest pathology, and its fruit-bodies can signal trees to be retained at harvesting in pine forests. The conclusion is that there is hope for developing practical indicators to manage for the hidden decay processes that govern tree-cavity development.     

Distribution of eriophyoid mites (Acari: Eriophyoidea) on coniferous trees

The aim of the paper was to determine the infestation parameters and species composition of eriophyoid mites for different parts of Norway spruce and Scots pine as well as for different age groups of the trees. The observations on the occurrence of the mites were conducted in 2004 and 2005 in 4 locations distributed in various regions of Poland, accounting for 11 environments (location x year). Three plant age groups were studied: (1) adult trees: 40–60 years old, additionally divided into three levels: top, middle and bottom; (2) young trees: 6–10 years old; and (3) seedlings: 2–3 years old. The same number of species (five) occurred on each coniferous tree, but only one, the rarest, was common on both tree species. Out of 500 samples for each species, mites were found on 279 pine (55.8%) and 252 spruce samples (50.2%). No tendency for the mites to choose any particular level on Scots pine and Norway spruce was observed. In addition, no tendency for the mites to choose trees from any of the age groups was observed for both Scots pine and Norway spruce, in the latter case the result obtained also for mite species subdivided into vagrant and refuge-seeking ones. Final conclusions were that in case of adult trees samples can be taken from the bottom part of a tree; however, sampling from young trees growing among adult trees may be seen as the most efficient sampling method.     

Growth patterns in relation to drought-induced mortality at two Scots pine (Pinus sylvestris L.) sites in NE Iberian Peninsula

Drought-related tree mortality has become a widespread phenomenon. Scots pine (Pinus sylvestris L.) is a boreal species with high ecological amplitude that reaches its southwestern limit in the Iberian Peninsula. Thus, Iberian Scots pine populations are particularly good models to study the effects of the increase in aridity predicted by climate change models. A total of 78 living and 39 dead Scots pines trees were sampled at two sites located in the NE of the Iberian Peninsula, where recent mortality events have been recorded. Annual tree rings were used to (1) date dead trees; (2) investigate if there was an association between the occurrence of tree death and severe drought periods characterized by exceptionally low ratios of summer precipitation to potential evapotranspiration (P/PET); and (3) to compare the growth patterns of trees that died with those of surviving ones. Mixed models were used to describe the relationships between tree growth (in terms of basal area increment, BAI, and the percentage of latewood, LW%) and climate variables. Our results showed a direct association between Scots pine mortality and severe drought periods characterized by low summer water availability. At the two sites, the growth patterns of dead trees were clearly distinguishable from those of the trees that survived. In particular, the BAI of dead trees was more sensitive to climate dryness (low P/PET_summer, high temperatures) and started to decline below the values of surviving neighbors 15–40 years before the time of death, implying a slow process of growth decline preceding mortality.     

Branch transpiration of pine and spruce scaled to tree and canopy using needle biomass distributions

Branch water exchange and total tree water uptake were measured in a mixed Norway spruce and Scots pine stand in central Sweden during the 1995 and 1996 growing seasons. Branch transpiration was scaled to canopy level on the basis of a branch conductance model, using vertical needle-area distributions obtained by destructive sampling. Comparison with total tree water uptake scaled to canopy level showed agreement within 10%, for periods when the canopy was not affected by climatically induced stress. Comparison of scaled fluxes on individual trees showed that measurements of transpiration at branch level provide information on the direct response of transpiration to variations in weather, and furthermore that the time-lag between transpiration and tree water uptake was as much as 3 h. The vertical needle-area distribution of Scots pine was similar to that found by other authors. Needle-area distribution on Norway spruce, which has not been described before, showed that it has its largest needle area at the top of the crown. Specific needle area varied considerably both within trees and between trees. For spruce, mean specific needle area (±SD) varied from 2.4±0.5 mm² mg^–1 at the top of the crown to 7.1±1.9 mm² mg^–1 at the base. Corresponding figures for Scots pine were 3.4±2.0 and 9.1±2.1. Received: 5 March 1999 / Accepted: 17 March 2000     

Understanding 3D structural complexity of individual Scots pine trees with different management history

Tree functional traits together with processes such as forest regeneration, growth, and mortality affect forest and tree structure. Forest management inherently impacts these processes. Moreover, forest structure, biodiversity, resilience, and carbon uptake can be sustained and enhanced with forest management activities. To assess structural complexity of individual trees, comprehensive and quantitative measures are needed, and they are often lacking for current forest management practices. Here, we utilized 3D information from individual Scots pine (Pinus sylvestris L.) trees obtained with terrestrial laser scanning to, first, assess effects of forest management on structural complexity of individual trees and, second, understand relationship between several tree attributes and structural complexity. We studied structural complexity of individual trees represented by a single scale‐independent metric called “box dimension.” This study aimed at identifying drivers affecting structural complexity of individual Scots pine trees in boreal forest conditions. The results showed that thinning increased structural complexity of individual Scots pine trees. Furthermore, we found a relationship between structural complexity and stem and crown size and shape as well as tree growth. Thus, it can be concluded that forest management affected structural complexity of individual Scots pine trees in managed boreal forests, and stem, crown, and growth attributes were identified as drivers of it.     

Assessing forest vulnerability to climate warming using a process‐based model of tree growth: bad prospects for rear‐edges

Growth models can be used to assess forest vulnerability to climate warming. If global warming amplifies water deficit in drought‐prone areas, tree populations located at the driest and southernmost distribution limits (rear‐edges) should be particularly threatened. Here, we address these statements by analyzing and projecting growth responses to climate of three major tree species (silver fir, Abies alba; Scots pine, Pinus sylvestris; and mountain pine, Pinus uncinata) in mountainous areas of NE Spain. This region is subjected to Mediterranean continental conditions, it encompasses wide climatic, topographic and environmental gradients, and, more importantly, it includes rear‐edges of the continuous distributions of these tree species. We used tree‐ring width data from a network of 110 forests in combination with the process‐based Vaganov–Shashkin‐Lite growth model and climate–growth analyses to forecast changes in tree growth during the 21st century. Climatic projections were based on four ensembles CO₂ emission scenarios. Warm and dry conditions during the growing season constrain silver fir and Scots pine growth, particularly at the species rear‐edge. By contrast, growth of high‐elevation mountain pine forests is enhanced by climate warming. The emission scenario (RCP 8.5) corresponding to the most pronounced warming (+1.4 to 4.8 °C) forecasted mean growth reductions of ?10.7% and ?16.4% in silver fir and Scots pine, respectively, after 2050. This indicates that rising temperatures could amplify drought stress and thus constrain the growth of silver fir and Scots pine rear‐edge populations growing at xeric sites. Contrastingly, mountain pine growth is expected to increase by +12.5% due to a longer and warmer growing season. The projections of growth reduction in silver fir and Scots pine portend dieback and a contraction of their species distribution areas through potential local extinctions of the most vulnerable driest rear‐edge stands. Our modeling approach provides accessible tools to evaluate forest vulnerability to warmer conditions.     

Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality

Key message

The retrospective analysis of wood anatomical features evidences how a long-term deterioration of hydraulic performance and carbon use portend drought-induced mortality in Scots pine.

Abstract

Widespread episodes of drought-induced tree mortality are predicted to become more frequent as climate becomes warmer and drier. Nevertheless, growth trends and their links to changes in wood anatomy before tree dies are still poorly understood. Wood anatomical features provide valuable information that can be extracted to infer the mechanisms leading to tree death. In this study, we characterize drought-induced mortality affecting two Scots pine (Pinus sylvestris) sites (Prades and Arcalís) located in the North Eastern Iberian Peninsula. Co-occurring now-dead and living Scots pine trees were sampled and their wood anatomical features were measured and compared. We aimed to detect differences in anatomical features between living and dead trees, and to infer past physiological performances that might have determined their subsequent death or survival. Now-dead trees showed lower tracheid and resin duct production, and smaller radial lumen diameters than co-occurring living trees. At the more xeric Prades site, these anatomical differences were larger and chronic, i.e. were observed over the three studied decades, whilst they were less pronounced at the other, more mesic Arcalís site, where tree mortality episodes were more recent. This indicates that dead trees’ hydraulic conductivity was severely affected and that carbon investment in xylem formation and resin duct production was constrained prior to tree death. Our findings show that both hydraulic deterioration and low carbon allocation to xylem formation were associated to drought-induced mortality in Scots pine. Nevertheless, the temporal dynamics of these processes differed between populations as a function of site climatic conditions.