On the mechanism of adaptive metabolism of healthy-resistant trees from forest polluted areas

Biochemical comparative studies have been conducted on healthy and diseased forest Picea trees (Picea abies) (30) growing in the polluted area of the Donon Range and on trees growing: A) under controlled conditions in phytotronicchambers with and without subnecrotic levels of SO₂ (208 μg.m^?3) and B) in open-top chambers simulating the pollution conditions of the Donon Range. On the basis of the results obtained, a scheme is presented which summarizes a proposed sequence of metabolic events leading to the development of an adaptive metabolism which can allow trees to become healthy-resistant after passage through the diseased state. Putrescine, polyamines, tryptophan and sugars are proposed to be early biochemical markers of the biochemical and physiological effects of forest pollution.     

Fungal networks in yield-invigorating and -debilitating soils induced by prolonged potato monoculture

Most previous studies on soil microbial communities have been focused on species abundance and diversity, but not the interactions among species. In present study, the Molecular Ecological Network Analysis tool was used to study the interactions and network organizations of fungal communities in yield-invigorating (healthy) and -debilitating (diseased) soils induced by prolonged potato monoculture, based on the relative abundances of internal transcribed spacer sequences derived using pyrosequencing. An emphasis was placed on the differences between the healthy and diseased networks. The constructed healthy and diseased networks both showed scale-free, small world and modular properties. The key topological properties and phylogenetic composition of the two networks were similar. However, major differences included: a) the healthy network had more number of functionally interrelated operational taxonomic units (OTUs) than the diseased one; b) healthy network contained 6 (4%) generalist OTUs whereas the diseased contained only 1 (0.6%) marginal generalist OTU; and c) majority (55%) of OTUs in healthy soils were stimulated by a certain set of soil variables but the majorities (63%) in diseased soils were inhibited. Based on these data, a conceptual picture was synthesized: a healthy community was a better organized or a better operated community than the diseased one; a healthy soil was a soil with variables that encouraged majority of fungi whereas a diseased soil discouraged. By comparing the topological roles of different sets of shared OTUs between healthy and diseased networks, it was found that role-shifts prevailed among the network members such as generalists/specialists, significant module memberships and the OTU sets irresponsive to soil variables in one network but responsive in the counterpart network. Soil organic matter was the key variable associated with healthy community, whereas ammonium nitrogen (NH₄⁺–N) and Electrical conductivity (EC) were the key variables associated with diseased community. Major affected phylogenetic groups were Sordariales and Hypocreales.     

Long-term vegetational history of a Picea abies stand in south-eastern Norway: Implications for the conservation of biological values

The development of a forest stand in south-eastern Norway during the last 9000 years is investigated by pollen and charcoal analyses. The aims are to identify factors that have influenced current biodiversity, which includes the lichen Usnea longissima, and examine the immigration and establishment of the current dominant tree Picea abies. Fire has been a variable but major disturbance factor at the site throughout the study period but has ceased during the last 100 years. Picea immigration was primarily a natural process but local establishment occurred after a major disturbance. Cultural impact began 3500 years ago during the Bronze Age, but was most intensive between AD 1600 and AD 1900. It led to the local extinction of deciduous trees and created a biodiversity bottleneck that facilitated the rise to dominance of Picea. Guidelines are proposed for future management designed to preserve and enhance local biological values.     

Ecological-genetic investigations in environmentally stressed mature sugar maple (Acer saccharum marsh.) populations

In six mature, environmentally stressed sugar maple (Acer saccharum) populations totalling 350 trees, genetic structures were studied within stands. Genetic variation was electrophoretically analyzed for 12 enzyme systems. The populations revealed Hardy-Weinberg proportions for all 11 polymorphic loci. Observed and conditional heterozygosity were. 141 and 899, respectively. Analysis of fixation indices indicated a slight heterozygote deficiency compared to panmictic conditions. Population differentiation was weak (F _ST =.017). Between healthy and declining subpopulations no significant differences were detected in terms of allozyme variation. However in healthy trees, conditional heterozygosity (H _c) and relative genotypic multiplicity (M _rel) were higher in five out of six populations.     

Vergleichende Untersuchungen der Mineralstoffgehalte geschädigter und nicht geschädigter Rotbuchen (Fagus sylvatica) auf Muschelkalkstandorten im Saarland

Comperative study of the mineral content of damaged and visibly healthy red beeches (Fagus sylvatica) on limestone soils in the Saarland 50-80 years old red beeches from a limestone region in the Saarland, differentiated in apparently healthy and diseased trees, were investigated on their mineral content beginning with the roots over stem up to the leaves. Macro- and microelement contents were different between healthy and diseased trees. Magnesium content in the roots of the latter was markedly reduced. Also zinc and phosphorous were decreased in the damaged trees, while manganese was partially accumulated. On the other side, a high sulphur content was observed in the crown area of both types of trees.     

Compound-specific δC and δH analyses of plant and soil organic matter: A preliminary assessment of the effects of vegetation change on ecosystem hydrology

Here we present δ¹³C and δ²H data of long-chained, even-numbered (C₂₇-C₃₁) n-alkanes from C3 (trees) and C4 (grasses) plants and from the corresponding soils from a grassland-woodland vegetation sequence in central Queensland, Australia. Our data show that δ¹³C values of the C4 grassland species were heavier relative to those of C3 tree species from the woodland (Acacia leaves) and woody grassland (Atalaya leaves). However, n-alkanes from the C4 grasses had lighter δ²H values relative to the Acacia leaves, but showed no significant difference in δ²H values when compared with C3 Atalaya leaves. These results differ from those of previous studies, showing that C4 grasses had heavier δ²H values relative to C3 grasses and trees. Those observations have been explained by C4 plants accessing the more evaporation-influenced and isotopically heavier surface water and tree roots sourcing deeper, isotopically lighter soil water (“Two-layered soil-water system”). By comparison, our data suggest that ecosystem changes (vegetation “thickening”) can significantly alter the soil hydrological characteristics. This is shown by the heavier δ²H values in the woodland soil compared with lighter δ²H values in the grassland soil, implying that the recent vegetation change (increased tree biomass) in the woodland had altered soil hydrological conditions. Estimated δ²H values of the source-water for vegetation in the grassland and woodland showed that both trees and grasses in open settings accessed water with lighter δ²H values (avg. −46‰) compared with water accessed by trees in the woodland vegetation (avg. −7‰). These data suggest that in semi-arid environments the “two-layer” soil water concept might not apply. Furthermore, our data indicate that compound-specific δ²H and δ¹³C analyses of n-alkanes from soil organic matter can be used to successfully differentiate between water sources of different vegetation types (grasses versus trees) in natural ecosystems.     

Seasonal levels of water‐extractable cations and anions in soil under blight‐affected and healthy citrus trees

Abstract

Soil samples were collected under blight‐affected and healthy citrus trees at 30‐day intervals for 24 months, at 20‐to 50‐cm depth. Analyses of water extracts (1:1 soil: water) for K, Ca, Mg, Na, SO₄, and Cl showed few differences in cations, but lower anion levels under blighted trees. The cation/anion ratio was significantly higher under blight‐affected trees. Samples collected once at different locations in the same time period showed the same differences. In one location, K was lower and Na higher under healthy trees than under blight‐affected trees, in others K was higher too.     

Long-Term Monitoring Study on Rain, Throughfall, and Stemflow Chemistry in Evergreen Coniforous Forests in Hokkaido, Northern Japan

Long-term study on acid precipitation monitoring at suburban forests in Sapporo city showed that bulk precipitation pH were below 4.8 in recent years. Throughfall and stemflow chemistry for two main coniferous species (Abies sachalinensis and Picea jezoensis) showed different regime for pH and element deposition. The mean annual pH values of throughfall and stemflow in Picea stand were 1.0 to 1.3 units higher than that of rain collected outside the forest. In contrast, mean annual pH of throughfall and stemflow in Abies stand were 0.3 to 0.5 units higher than that of rain. Mean annual inorganic nitrogen input via throughfall and stemflow were estimated 0.41±0.11 gN/m²/yr in Abies stand, 0.44±0.13 gN/m²/yr in Picea stand. Cation input via throughfall, especially for K, in Picea stand was 1.4 times as large as that in Abies stand. Mean annual input of S in both stands was the same level. The possible effects on surface soil properties and nutrient cycling in northern evergreen conifers was discussed.     

Bryophyte species richness on boulders: relationship to area, habitat diversity and canopy tree species

Bryophytes growing on siliceous boulders (diameter 50-200 cm) were studied in two forests in east-central Sweden to investigate the influence of different canopy tree species on the bryophyte species richness. Granite boulders lying below crowns of Ulmus glabra (elm), Fraxinus excelsior (ash), Acer platanoides (maple), Quercus robur (oak), Betula pendula (birch), and Picea abies (Norway spruce) were studied in two mixed stands. Both boulder area and within-boulder habitat diversity were positively related to species richness. Boulders below the base-rich deciduous trees F. excelsior, U. glabra and A. platanoides held roughly twice as many species as those below P. abies, with Q. robur and B. pendula as intermediates. The rank order among trees was as expected from bark pH and litter decomposability in the literature. We also used sample plots to investigate species richness at a smaller scale. Within plots, intermediate levels of litter, inclination and exposed rock promoted species richness, and also the covering tree species had an effect. Individual plots were on average not more species-rich on large boulders than on small ones. This leads us to conclude that population extinctions on the plot-level, and re-colonisations from other parts of the boulder, are less important for species richness than within-boulder habitat diversity. Since species richness was lower under P. abies it is important to favour a diversity of tree species and to include base-rich deciduous trees in otherwise homogeneous Picea forests.     

Replant diseases: Bacterial community structure and diversity in peach rhizosphere as determined by metabolic and genetic fingerprinting

Peach tree replant disease, though reported on in the literature for more than two centuries, has yet to have its causes clearly defined. Decline in peach productivity has been attributed to toxic agents, insects, nutritional disturbances, spray residues, fungi and nematodes. Bacteria has also been indicated as a contributing factor.Peach replant disease was reproduced by using two successive cultures on the same soil. Bacterial communities were isolated and characterized from healthy and diseased peach trees. The potential role of cyanide production by rhizobacteria in the replant problem of peaches was studied. Culture-dependent (evaluation of the number of culturable bacteria, metabolic activities, Biolog^® GN2) and independent (ribosomal intergenic spacer analysis, RISA) methods were used, in order to compare bacterial community structure and diversity in healthy and sick soils and to evaluate the possible role of cyanide.Bacterial densities were significantly increased in sick soils. Metabolic activities (Biolog^® GN2) and genetic structure, observed through RISA, were also significantly modified in sick soils. Changes in the composition of individual microbial groups in the rhizosphere of peach trees excavated from healthy or sick soil indicated the involvement of rhizobacteria in the etiology of the replant sickness of peach soil. More than 60% of the strains isolated from healthy soils corresponded to Pseudomonas sp. and 58% of the isolates from sick soils were Bacillus sp. This study determined that Bacillus were able to produce in vitro HCN. It also appeared that in sick soil, there was a shift in the structure of bacterial communities with an increase noted in phytotoxic microorganisms capable of producing HCN compounds.     

The rhizosphere soil of diseased tomato plants as a source for novel microorganisms to control bacterial wilt

Plant growth promoting rhizobacteria (PGPRs) are used for biocontrol of bacterial wilt caused by Ralstonia solanacearum. They are commonly isolated from the rhizosphere of healthy plants and are scarce in the rhizosphere of diseased plants. We hypothesized that a pathogen-prevalent environment, such as the rhizosphere of infected plants, would be a good or better source for isolating PGPRs than the rhizosphere of healthy plants. In order for these PGPRs to survive successfully in a pathogen-prevalent environment, they must have particularly well-developed survival strategies under the stresses exerted by pathogen activities, which would be of value for their use as biocontrol agents. To test this hypothesis, R. solanacearum-antagonistic bacteria were screened from the rhizospheres of diseased and healthy tomato plants. In total, 110 rhizobacteria were isolated, 18 of which showed antagonism to R. solanacearum in vitro. Among the 18 antagonistic strains, 11 (out of 60) were from the rhizosphere of diseased plants, with inhibition diameter zones ranging from 11.2 to 15.2 mm, whereas 7 (out of 50) were from the rhizosphere of healthy plants, with inhibition diameter zones ranging from 11.5 to 30.5 mm. Strains WR4, WR21, and WR42 from diseased plants rhizosphere, and HR61, HR62, and HR92 from healthy plants rhizosphere, were chosen to investigate their biocontrol efficacies (BCEs) in greenhouse condition. Results showed that WR-isolates performed better in reducing disease incidence (DI) than those HR-isolates. Population densities of R. solanacearum in the rhizosphere soil and crown section of tomato plants were lower in WR-isolate treatments than those in HR-isolate treatments. The best biocontrol effect was achieved by inoculating the strain WR21, followed by WR4, WR42, HR92, HR62, and HR61. Root colonization test showed WR21 had the highest root-colonizing capacity compared with 5 other antagonists. BCEs were positively (r = 0.747) correlated with root-colonizing capacities, but were negatively (r = −0.797) correlated with inhibition zones. In conclusion, the rhizosphere of diseased tomato plants is a good reservoir of biocontrol bacteria.     

Evidence of short-term belowground transfer of nitrogen from Acacia mangium to Eucalyptus grandis trees in a tropical planted forest

The short-term belowground transfer of nitrogen from nitrogen-fixing trees to companion trees has never been studied in the field. A ¹⁵N pulse-labeling study was conducted in a mixed plantation of Acacia mangium and Eucalyptus grandis at the peak of leaf area, 26 months after planting. ¹⁵N–NO₃⁻ was injected into the stem of one big Acacia tree in three plots. ¹⁵N was traced over 2 months in the labeled Acacia tree as well as in neighboring Eucalyptus trees. For both species, young leaves were sampled, as well as fine roots and the rhizosphere at a distance of 0.75 m and 2.25 m from the labeled tree. The ¹⁵N atom% was also determined in the wood, bark, branches and total foliage of the 3 labeled Acacia trees and 9 Eucalyptus trees, 60 days after labeling. Most of the leaves, fine roots and rhizosphere samples of both species were ¹⁵N enriched from 5 days after labeling. The δ¹⁵N values were higher at a distance of 0.75 m than at 2.25 m in Acacia roots, but were similar at both distances in Eucalyptus roots and the rhizospheres. The wood and bark of Eucalyptus trees sampled at a distance of 6.2 m from the labeled Acacia trees were ¹⁵N enriched. This shows belowground N transfer from Acacia to Eucalyptus trees in the field during the first few days after labeling. This facilitation process may provide a significant amount of the nitrogen requirements of trees close to N-fixing trees in mixed forests.     

Responses of transpiration and canopy conductance to partial defoliation of Eucalyptus globulus trees

Partial defoliation has been shown to affect the water relations and transpiration (gas exchange) of plants. Over one growing season, the water relations in response to partial (∼45%) defoliation were examined in four-year-old Eucalyptus globulus trees in southern Australia. Daily maximum transpiration rates (E_max), maximum canopy conductance (GCmax), and diurnal patterns of tree water-use were measured over a period of 215 days using the heat-pulse technique in adjacent control (non-defoliated) and defoliated trees. Sap-flux measurements were used to estimate canopy conductance and soil-to-leaf hydraulic conductance (K_P); leaf water potential (Ψ) and climate data were also collected. Following the removal of the upper canopy layer, defoliated trees exhibited compensatory responses in transpiration rate and canopy conductance of the remaining foliage. Defoliated E. globulus had similar predawn but higher midday Ψ_l, transpiration rates (E), canopy conductance (G_C) and K_P compared to the non-defoliated controls, possibly in response to increased water supply per unit leaf area demonstrated by higher midday Ψ_l. Higher E in defoliated E. globulus trees was the result of higher G_C in the morning and early afternoon. This paper also incorporates the cumulative effect of defoliation, in a phenomenological model of maximum canopy conductance of E. globulus. These results contribute to a mechanistic understanding of plant responses to defoliation, in particular the often observed up-regulation of photosynthesis that also occurs in response to defoliation.     

Soil Solution Chemistry in Forests with Granite Bedrock in Japan

Soil solutions were taken from three forest areas with granite bedrock in Japan (Abukuma, Tateyama and Hiroshima) to investigate pH values, forms of Al and the molar BC/Al ratios. In each area, 10 sites were chosen for study. At each site, a target tree was selected, and two soil solution samples were taken from 10 cm depth at points 10 cm and 100 cm from the trunk of the tree to evaluate the effects of stemflow and throughfall on soil solution chemistry. Values of pH of samples taken 10 cm from the trunks (referred to as S samples) and 100 cm from the trunks (referred to as T samples) ranged from 3.66 to 6.52 and from 4.55 to 6.48, respectively. For Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) trees, S samples showed lower pH than T samples, whereas the inverse relation was observed for broadleaf trees. In the Abukuma and Tateyama areas, the concentrations of monomeric Al (Al_m) were mostly below 30 µmol L^?1. In the Hiroshima area, however, extremely high Al_m concentrations (up to 293 µmol L^?1) were observed at some sites. The molar ratio of BC (= Ca + Mg + K) to inorganic monomeric Al was higher than 1 for all samples, except for an S sample from the Hiroshima area having a ratio of 0.72.     

Effect of land-use on soil water dynamic in dehesas of Central–Western Spain

Dehesa ecosystems are open woodlands with scattered oak trees as their main component. As a result of differing land-uses, the structure of vegetation found within dehesas varies between: (i) oak trees and intercropped cereals (cropped), (ii) oak trees and native grass vegetation (grazed), and (iii) oak trees with abundant understorey shrubs (encroached). The aim of this study is to investigate whether land-use influences the water dynamics of dehesas by measuring available soil water content (AWC) in the upper 250 cm of the soil at different distances from tree trunks (maximum 30 m) at four Quercus ilex dehesas in Central–Western Spain. The technique used was Time Domain Reflectometry and the study was undertaken between May of 2002 and December of 2005. Leaf water potential (Ψ) was also measured on trees at one site by mean of a pressure chamber. Within the upper meter of the soil, it appears that trees, grasses and shrubs extracted soil water resources in a similar way from both beneath and beyond the tree canopy. However, encroached plots in general showed lower average AWC values than cropped or grazed plots (3.7, 5.6, and 6.2% in encroached, cropped and grazed, respectively). Cereal crops do not compete more strongly than grasses with trees for available soil water resources. The similar Ψ values found at cropped and grazed plots supported these results. From our results, it could be hypothesized that ploughed dehesas could facilitate soil re-watering in the plots with pronounced slopes. The decrease of AWC values at encroached plots with respect to the cropped and grazed plots was found mostly beyond the tree trunk at deeper soil layers, indicating that shrubs use water partly not accessible to trees. The presence of an understory of shrubs seems to have slightly increased the water constraints on trees during the summer period (Ψ_d values of − 0.5, − 0.5, and − 0.8 MPa in cropped, grazed, and encroached plots, respectively). In cropped and grazed plots, an important amount of water seems to have remained unused for trees and grasses.     

The relative tolerance of some Eucalyptus species to ozone exposure

Surface ozone (O₃) concentrations have proved to be difficult to control and regional (0₃) concentrations appear to be increasing in many parts of the world. Eucalyptus species are widely used as plantation trees in many regions that have Mediterranean, warm temperate and subtropical climates. An increased knowledge of the effects of tropospheric O₃ on Eucalyptus trees may assist in the management of these plantations. The present study was set up to evaluate injury and measure growth reduction caused by O₃ in eight Eucalyptus species. Seven month old saplings were exposed to diumally varied concentrations of 26 or 172 nil^?1 (0₃) (7h mean) 7h day^?1, 5 days in every 14 days, for 18 weeks. The plants were grown in open top field chambers fitted with rain excluders. Significant differences were found between the responses of different species. There was no visible injury or dry weight reduction in E. globulus. However O₃ exposure caused a 30% weight reduction and 90% leaf injury in E. microcorys. E. gomphocephala also experienced a 30% weight reduction but no significant leaf injury. Hence Eucalyptus plantations in regions with the potential for photochemical smog formation, such as some of the rapidly developing industrialising nations in Asia and South America, will need to consider O₃ tolerance when selecting plantation trees.     

NaCI contamination in pine trees determined by neutron activation techniques

The NaCl content in samples of pine needles was measured to establish the extent of contamination from rock salt which is used for deicing roadways. Neutron activation analysis techniques were used to determine the NaCl content in the samples, and the irradiation neutrons were obtained from a portable²⁵²Cf neutron source. The average Na content in samples from the diseased trees was 50 times greater than in the control samples.     

Ammonium,nitrite, and nitrate nitrogen levels in the soil under blight‐affected and healthy citrus trees

Abstract

Ammonium, nitrite, and nitrate nitrogen levels in the root zone of blight‐affected and healthy trees in a 35‐year‐old commercial orange grove were monitored at 30‐day intervals for 2 years. There was essentially no difference in NH₄‐N and NO₂‐N; however, at four sampling dates and overall, the NO₃‐N level was slightly higher under healthy trees.     

Strong seasonal variations in net ecosystem CO2 exchange of a tropical pasture and afforestation in Panama

Pasture and afforestation are land-use types of major importance in the tropics, yet, most flux tower studies have been conducted in mature tropical forests. As deforestation in the tropics is expected to continue, it is critical to improve our understanding of alternative land-use types, and the impact of interactions between land use and climate on ecosystem carbon dynamics. Thus, we measured net ecosystem CO₂ fluxes of a pasture and an adjacent tropical afforestation (native tree species plantation) in Sardinilla, Panama from 2007 to 2009. The objectives of our paired site study were: (1) to assess seasonal and inter-annual variations in net ecosystem CO₂ exchange (NEE) of pasture and afforestation, (2) to identify the environmental controls of net ecosystem CO₂ fluxes, and (3) to constrain eddy covariance derived total ecosystem respiration (TER) with chamber-based soil respiration (R_Soil) measurements. We observed distinct seasonal variations in NEE that were more pronounced in the pasture compared to the afforestation, reflecting changes in plant and microbial activities. The land conversion from pasture to afforestation increased the potential for carbon uptake by trees vs. grasses throughout most of the year. R_Soil contributed about 50% to TER, with only small differences between ecosystems or seasons. Radiation and soil moisture were the main environmental controls of CO₂ fluxes while temperature had no effect on NEE. The pasture ecosystem was more strongly affected by soil water limitations during the dry season, probably due to the shallower root system of grasses compared to trees. Thus, it seems likely that predicted increases in precipitation variability will impact seasonal variations of CO₂ fluxes in Central Panama, in particular of pasture ecosystems.     

Elemental and chemical concentration in peach tree short life and healthy trees

Abstract

Elemental concentrations of N, P, K, Ca, Mg, Fe, Al, Zn, Mn, and Cu in peach tree short life (PTSL) trees were compared to concentrations in apparently healthy trees in the same orchard. Leaf and stem concentration of K were significantly less and concentrations of Fe and Al were significantly greater in PTSL trees than healthy trees. Leaf concentrations of Ca and Mg and stem concentrations of N, P, and Cu were also significantly less in PTSL trees than healthy trees. Increased levels of Fe and Al and a K:Fe ratio of less than 150:1 in the leaves and stems was associated with PTSL.

There were no detected differences in prunasin, amino acid, or sugar content of PTSL and healthy trees in leaf and stem samples, but significant differences in elemental content suggest some type of stress on the root system of PTSL trees.