Mature Poplars Research Articles

Effects of nitrogen addition on rhizospheric soil microbial communities of poplar plantations at different ages

The continuous increase of nitrogen (N) deposition has had strong impacts on the structure and health of forest ecosystems globally. An elucidation of the shifts in rhizospheric microbial communities and their interactions with environmental factors under N-addition will assist us with better understanding the responses of forest ecosystems to future environmental changes. In this study, we employed high-throughput sequencing to investigate the responses of rhizosphere soil bacterial and fungal communities to seven-years of N-addition in young (9-year) and mature (14-year) poplar plantations in coastal Eastern China. The experiment included three N-addition levels: 0 (N0), 100 (N1), and 300 (N2) kg N ha−1 yr−1. The results revealed that soil fungal, but not bacterial, alpha-diversity significantly declined under the seven-year N-addition in mature poplars. Moreover, both bacterial and fungal community structures were significantly altered. The total C and NO3− contents controlled the patterns of soil bacteria community structures in mature poplar plantations, while soil pH, NO3−, total N, and C/N were the main factors that shaped the patterns of soil fungi communities in both poplar plantations. However, the relative abundance of plant pathogenic genera Mycoleptodiscus and Plectosphaerella increased strongly with N-addition. The soil microbial communities of mature poplar plantations were sensitive to N-addition. Our findings suggested that long-term simulated N deposition reduced fungal alpha-diversity, altered the composition of bacterial and fungal communities, while boosting the abundance of pathogenic communities, which may induce disease and otherwise damage forest ecosystems.

Biomass of external mycelium of ectomycorrhizal fungi associated with poplars – The impact of tree genotype, tree age and soil environment

The external mycelium (EM) is an important structural element of the symbiosis between mycorrhizal fungi and trees, fulfilling several important functions in their development and playing a significant role in carbon and nitrogen cycling in soil. This study aimed to estimate and compare the EM biomass of ectomycorrhizal fungi associated with mature trees and 6-month-old seedlings representing four different poplar genotypes planted in different soil conditions. The fungal-specific ergosterol biomarker was used to estimate the EM biomass. The results showed similar values of EM biomass for mature trees and seedlings. EM biomass was affected by tree genotype. Soil conditions had a greater effect on the EM biomass of seedlings than mature poplars. Seedling results also demonstrated the importance of soil moisture and carbon and nitrogen content on EM biomass. The soil moisture more than heavy metal pollution influenced the EM biomass of seedlings.

Tree-killing aphid dramatically reduces bark contents in carbohydrates and nitrogen compounds

Abstract Aphids can affect the growth or architecture of their host-trees, but rarely challenge their survival. Nonetheless, the woolly poplar aphid, Phloeomyzus passerinii, can kill healthy, mature poplars during outbreaks. Trees fail to open their buds and flush their leaves in the spring following a severe infestation. This insect develops on poplar trunks, where it induces galls which accumulate amino acids and deplete starch content in the bark tissues. Here, we hypothesized that an infestation may then reduce non-structural carbohydrates (NSC) and non-structural nitrogen compounds (NSNC) contents in the bark, and that the reduction would be positively correlated with the infestation duration. This would in turn compromise the spring reactivation of trees. Consequently we also hypothesized that the bark contents of NSC and NSNC could be positively correlated with the amount of branches exhibiting bud break in spring, and the subsequent radial growth. The bark contents of NSC and NSNC were quantified in autumn for poplars exhibiting different levels of infestation and located in two distant stands. In one stand, NSC and NSNC contents in the bark were also quantified in the following spring and the damage level in the crowns were evaluated. In both stands, the infestation dramatically reduced the NSC and NSNC contents in autumn, especially starch and protein contents. While the drop in protein content was not related to infestation duration, the starch content gradually decreased when infestation duration increased. The infestation effect on starch content was still detectible in spring, after reserves had likely been mobilized for the spring reactivation. Starch content in autumn and spring was strongly positively correlated with crown health and radial increment. These results suggest that poplars infested by P. passerinii may die from carbon reserves deficiency, which would be an unprecedented situation for tree-aphid and tree-gall inducing insects interactions. Further experiments monitoring seasonal dynamics of NSC and NSNC reserves in different organs of infested trees should be conducted to validate this hypothesis. The results also suggest that the starch content in the bark of infested trees, in autumn, might be used as a predictor of tree decay by managers.

Plastic Allometry in Coarse Root Biomass of Mature Hybrid Poplar Plantations

In this study, we sampled coarse root biomass of three poplar clones in four 13-year-old hybrid poplar (Populus spp.) plantations, with the objective of developing an allometric relationship between diameter at breast height (DBH) and coarse root biomass. A second objective was to test significance of site, clone and ×site clone interaction effects on coarse root biomass, using analysis of covariance (ANCOVA), with DBH as a covariate. Across the four sites, the general allometric relationship between DBH and coarse root biomass was highly significant (R 2 = 0.78, p < 0.001). However, given the high significance of the site effect (p < 0.001) in the ANCOVA and the differences in data distribution between sites, two allometric relationships were developed based on the fertility class of sites (high and moderate). Environment-specific allometric relationships developed for two site fertility classes had a better fit (R 2 = 0.81-0.90, p < 0.001). ANCOVA, with DBH as a covariate and site fertility class as a main effect, also showed that both of these variables significantly affected (p < 0.001) coarse root biomass allocation. Environment-specific equations showed that higher coarse root biomass was allocated in harsher environments for a given DBH, probably to improve access to growth limiting soil nutrients or to build-up larger storage sites for amino acids and non-structural carbohydrates. Consequently, poplar coarse root biomass growth is both driven by ontogeny (size) and environment, reflecting the plasticity of the root system of mature poplars. Implications of using general vs. environment-specific equations in estimating stand-level root biomass and shoot to root ratios are discussed. Shoot to root ratios calculated using environment-specific equations were more strongly correlated to key environmental variables than ratios calculated using the general equation, with soil NO3 supply rate being the strongest predictor of the ratio (R 2 = 0.90, p < 0.001).

Exceptional plant penetration and feeding upon cortical parenchyma cells by the woolly poplar aphid

Forty percent of aphids live wholly or partly on trees, most species being associated with leaves or petioles. Species able to exploit woody parts have either specific adaptations, such as extra long stylets that allow them to reach the phloem, or the ability to induce galls. The woolly poplar aphid, Phloeomyzus passerinii (Signoret) (Hemiptera: Aphididae), colonizes the trunks and base of the lower branches of mature poplars and causes cortical necrosis leading to the death of trees where infestation is heavy. Very little is known about the mode of feeding of P. passerinii. This study looked at the feeding behavior of P. passerinii on stem-cuttings of Populus x canadensis Moench using: (i) histological analyses of the feeding site and stylet pathway and (ii) electrical penetration graphs (EPG, DC) based on parthenogenetic apterous females on woody tissues. The histological and EPG results showed that stylets of P. passerinii penetrated into the plant tissues following a straight unbranched extracellular and intracellular pathway to reach the cortical parenchyma. Compared to EPGs for phloem sap feeding aphids, there were differences in the waveforms A and C whereas a new waveform Icp was described. Based on histological analyses and previous descriptions of EPG waveforms, correlations with the stylet tip position and aphid activities within bark tissues are discussed. A pathway and a sustained intracellular phase were distinguished, both occurring in the cortical parenchyma cells. The bark aphid feeding mode is discussed in relation to the damage caused and in terms of changes in the aphid’s diet.

Pasture production and composition under poplar in a hill environment in New Zealand

Traditionally, poplar (Populus spp.) have been planted to control erosion on New Zealand’s hill-slopes because of their capacity to dry out and bind together the soil. Two systems: (1) widely spaced, planted poplar for soil conservation, and (2) non-eroded open pasture were compared to determine the relative effect of the poplar–pasture system on the production, nutritive value and species composition of the pasture, and on the water balance. Measurements were made at three sites with mature poplar (>29 years and 37–40 stems ha−1) and at a replicated experiment with young poplar (5 years, 50–100 stems ha−1). Soil water relations did not suggest strong competition for water between poplar and pasture. Pasture accumulation under mature poplar was 40% less than in the open pasture, but under young poplar was similar to that in the open pasture. Chemical composition of pasture suggested that feed quality of pasture in the open was better than under the poplar canopy, except during spring, when most chemical components were similar. At the most, in vitro digestibility of pasture dry matter was 8.9% lower and metabolisable energy of pasture dry matter was 1.5 MJ kg lower under the poplar canopy than in the open pasture. Shade tolerant species were not dominant in the plant community under the poplar canopy with grasses such as browntop (Agrostis capillaris, L.) and ryegrass (Lolium perenne, L.) being a high proportion of the plant community. Differences in chemical composition were related to differences in the botanical composition between the open pasture and the poplar understorey. It was concluded that the greatest effect of poplar was on pasture production due to shading, and that management of this silvopastoral system needs to focus on control of the tree canopy to lessen the decrease in pasture production.

Soil properties of a widely spaced, planted poplar (Populus deltoides)–pasture system in a hill environment

Planting poplars is an effective technology for controlling hill soil erosion in New Zealand pastureland. However, the effects of widely spaced poplars on soil properties are not documented. Soil was sampled from 3 soil depths (0-75, 75-150, and 150-300 mm) in poplar-pasture (PP) and adjacent open pasture (OP) systems. Four sites were examined, 3 unreplicated sites with mature poplars (&amp;gt;29 years, 37-40 stems/ha) and a replicated experiment with immature poplars (5 years, 50-100 stems/ha). Pastures at all sites were dominated by low fertility species and were grazed by sheep and cattle. Pasture species were used in a glasshouse experiment to assess the production potential of the topsoil media (0-20 mm) from the PP and OP soils, and the OP topsoil amended with 5% poplar leaf litter.

Factors affecting the regeneration and distribution of riparian woodlands along a northern prairie river: the Red Deer River, Alberta, Canada

Abstract. Flooding patterns and variations in the composition and successional trends of riparian vegetation in the upper and lower Red Deer River in southern Alberta, Canada, were studied in order to establish which flood regimes were most important in the regeneration and maintenance of riparian vegetation communities, with a particular focus on riparian poplars. The dominant riparian tree in the upper river is Populus balsamifera with some Picea glauca and in the lower river Populus deltoides (the plains cottonwood). Dendrochronological studies of the poplars along the river show that major periods of regeneration correspond with major flood events during the record period. Extensive cottonwood regeneration occurred in the period 1900–20, corresponding with a series of floods, some as high as the 1 in 100‐year event. In addition, just prior to and during this period there was a significant reduction in use of the floodplain by bison, clearance of forests and a higher incidence of fires in upper reaches of the river and a series of high rainfall years. A series of floods greater than the 1 in 10‐year flood occurred in the 1950s and stimulated the most extensive regeneration of poplars experienced since the 1920s. Parts of the lower Red Deer floodplain are now at elevations well above the 1 in 100‐year flood event. It is suggested that fringe replenishment of riparian poplars is currently the dominant form of regeneration and that the large stands of mature poplars found on the floodplain, initiated during the end of the last century and first decades of this century, are unlikely to be replaced unless large floods (&gt;1 in 50‐year events) occur again. Construction of the Dickson Dam above the city of Red Deer in 1983 has led to attenuation of floods and a reduced likelihood that extensive flooding and poplar regeneration will occur again. A number of recommendations are made regarding flow management to both retain the fringe regeneration of poplars currently occurring and to stimulate more widespread regeneration of poplars on the floodplain.

Case study of a mature Populus deltoides-pasture system in a hill environment

Pasture characteristics, soil moisture relations and water balance were measured in open pasture and in a mature poplar understorey, to assess how land conservation practices modify a pastoral system. Mature poplars changed the environment of the understorey pasture, with light intensity decreased from September to April, and the soil generally colder and drier in autumn and early winter. Soil moisture relations did not suggest strong competition for water between trees and pasture in spring. Pasture under the poplars accumulated 40% less herbage mass and was of lower feed quality than pasture in the open. The case study highlights the complexity of silvipastoral systems in hill country and the need for a more complete understanding of the interactions if the potential of a multipurpose tree and livestock farming systems is to be realised. Keywords: conservation, pasture characteristics, poplar, Populus deltoides, sapflow, soil moisture, silvipasture, trees, water balance

Betaines and free amino acids in salt stressed vitroplants and winter resting buds of Populus trichocarpa X deltoides

Organic solutes, in particular glycine betaine and proline, have been detected as osmoprotective compounds in many microorganisms and herbaceous species. However, for woody plants, very little information is available on mechanisms of adaptation to salt stress. In the present study, effects of NaCI treatment on betaine and free amino acid contents in a clone of Populus trichocarpa X deltoides micropropagated vitroplants were analyzed using HPLC and silicate plate chromatography. The application during 12 days of 50 to 200 mM NaCI to viroplants cultured on Murashige and Skoog medium (Murashige and Skoog 1962. Physiol. Plant. 15: 473–497) led to a progressive decrease of growth, leaf senescence, abscission, and apical necrosis. Populus trichocarpa X deltoides was characterized by the absence of glycine betainc and/or proline accumulation. However, trigonelline was found to increase in vitroplants subjected to 100 mM NaCI. Trigonelline was also present in dormant buds harvested in natural conditions and missing in active buds. In vitroplants, the content of some amino acids was strongly modified by salt stress. A progressive accumulation of alanine and γ‐amino butyrate was particularly significant in roots, whereas the relative concentration of glutamine was strongly enhanced in leaves. Leaf content of glutamate and ornithine attained maximum in the presence of 100 and 150 mM NaCI concentrations, and then decreased. Arginine and serine pools were not significantly modified by salt treatment. The variations in vitroplants were of small amplitude compared to those observed in mature poplars where winter rest was associated with a very high arginine level and with a disappearance of nearly all other free amino acids. The results are discussed in relation to previous data obtained with herbaceous species and in relation to some metabolic pathways in poplars where trigonelline could be considered as a sensitive stress indicator.

Forest Succession and Sedimentation on a Meandering-River Floodplain, Northeast British Columbia, Canada

An examination of primary forest succession within two migrating bends along the Beatton River in northeast British Columbia provides information on the interrelationships between the geomorphic and biotic components of a meandering-river floodplain. Overbank sedimentation rates are estimated from changes in the wood structure of partially buried balsam poplars, and from distinct changes in floodplain slope. Particular emphasis is placed upon the changing age-structure of dominant tree species to describe successional changes within the floodplain forest. Rapid sedimentation on the youngest ridges favours the establishment of a dense, non-reproducing balsam poplar stand of uniform age, and prevents the establishment of white spruce seedlings. Following an abrupt decline in overbank sedimentation on surfaces approximately 50 years old, white spruce rapidly colonize the bare mineral soil beneath the poplar canopy and form a dense, relatively even-aged stand. With the death of mature poplars on surfaces 100-150 years in age, the spruce seedlings are released and develop into a mature, non-reproducing stand. This stand persists until its senescence on ridges 350-400 years old. Here, a second, similar, although less even-aged spruce stand establishes, maturing in a like manner to the flrst, to eventually decline on ridges 500-550 years in age. On this older surface there is the suggestion of yet a third generation of spruce seedlings. These oscillations are reflected in changes of the vascular understory-species during succession, and compare to the cyclic regeneration and climax instability described by Watt (1947) and Whittaker (1953). Tree densities and overbank sedimentation achieve minimum values on floodplain surfaces greater than approximately 200 years in age. A reasonable explanation to account for negligible sediment deposition on these older surfaces is that the more open trunk density there permits relatively rapid overland flow, preventing the deposition of suspended sediment load. Sedimentation and vegetation appear to be strongly interrelated components within the total floodplain system.