Girdled Trees Research Articles

Free monoterpenoid accumulation in ‘Riesling’ (Vitis vinifera L.) is light-sensitive and uncoupled from grape hexose accumulation

Monoterpenoid biosynthesis mirrors hexoses accumulation in grape berries during ripening and is affected by environmental factors such as solar radiation. However, no research has confirmed the dependency of monoterpenoid accumulation on grape maturity. Using potted ‘Riesling’ (Vitis vinifera L.) vines, we girdled (GD) shoots at veraison to halt leaf photoassimilate translocation to berries and also utilized light-impenetrable bags to exclude light exposure (LE) to grape clusters to <2 μmol m-2s-1 during ripening. GD and LE were compared to an untreated control (CT), and a combined (GDxLE) treatment. GD caused leaf photosynthetic assimilation to decline from one-week post-treatment until harvest maturity due to feedback inhibition of photosynthesis. This was coupled to a decrease in hexoses and ABA accumulation in GD berries. Meanwhile, LE did not affect photosynthetic assimilation, or hexoses and ABA accumulation. We hypothesized that the accumulation of free and bound monoterpenoids in ‘Riesling’ berries would also be reduced by GD, if monoterpenoid accumulation was dependent on grape maturity. LE significantly decreased free monoterpenoids compared to CT. However, GD did not alter total free and bound monoterpenoid concentrations. GD decreased free Linalool Oxide I and II and bound Linalool Oxide I compared to CT, and increased Citral I and II and α-Terpineol. Although exogenous jasmonate applications stimulate monoterpenoid biosynthesis in grapes, we showed that endogenous jasmonate concentrations were not altered by GD or LE; therefore, any monoterpenoid modulation by GD and LE treatments was not mediated by endogenous jasmonate levels. This study indicates that free monoterpenoid biosynthesis during ripening is “uncoupled” from hexose accumulation and is strongly regulated by solar radiation.

Effect of girdling on phloem and xylem formation in a range of gymnosperms and angiosperms

Summary Girdling is often used as an experimental method to study source/sink controls of cambial growth. However, the phloem responses to girdling have not been well investigated. The aim of this research was to characterize the anatomical changes in the phloem and xylem of different species following trunk girdling. Different species of gymnosperm (Abies sibirica, Pinus sylvestris) and angiosperm (Alnus incana, Populus tremula) woody plants were selected. We girdled trunks during active growth and sampled tissues at two levels (1 cm and 35 cm) above the girdle at the end of the growing season. General responses to girdling were recorded for the studied species, such as increased phloem increments, parenchymatization of conducting tissues, reduction in the size of conducting elements, and an increase in the size of axial parenchyma cells in the phloem and xylem. We observed the suppression of xylogenesis in 3 out of 4 species. Differences in the structure of conducting tissues were found, which are due to species differences in the initial tissue structure. In gymnosperms, noticeable differences in the number of resin ducts in the xylem were observed between control and girdled trees. In angiosperms, we found the formation of cells with thickened cell walls in girdled trees (i.e., the formation of phloem and xylem fibers with thickened cell walls in aspen and sclereids in the phloem of alder). Based on the literature data, the observed responses may be due to both the wounding effect and the influence of the high sugar content above the girdle.

Fungal communities in veteranised oak branches are not a replacement for naturally occurring dead wood communities

ABSTRACT Veteranisation is a promising management technique for dead wood creation at sites where dead wood, and ancient and veteran tree abundance is limited; it aims to replicate the microhabitats associated with ancient and veteran trees in younger trees by controlled physical damage of woody tissues. Five veteranisation treatments were applied, using a chainsaw, to healthy branches within the crowns of three mature oak trees. Treatments consisted of variations of cambium girdling, lopping, and lopping with girdling in combination; in addition, two branches that had died naturally were selected from each tree for comparison. Veteranised branches were harvested after 14 months. The fungal community composition was determined in different parts of the branch and their 3-dimensional structure mapped in representative branches. Stereum gausapatum was the most frequently isolated basidiomycete from veteranised branches, which occurred in all treatment types. The most commonly isolated ascomycete of veteranised branches was Ophiostoma quercus, which caused distinctive pockets of discoloured wood and was associated with half girdle treatments. There were significant differences in fungal species composition between veteranised branches and branches that had died naturally. This compositional difference may influence the development of later stage fungal communities, managers must consider these community compositional differences when prescribing veteranisation.

Silvicultural canopy gaps improve health and growth of eastern hemlocks infested with Adelges tsugae in the southern Appalachian Mountains

The hemlock woolly adelgid (HWA, Adelges tsugae Annand) is an invasive forest insect threatening the sustainability of eastern hemlock (Tsuga canadensis (L.) Carrière) in eastern North America. In this study, cutting small gaps in the forest canopy above understory eastern hemlocks was evaluated as a potential tool for use in the integrated pest management of HWA. Two gap sizes and two gap creation methods (felling vs. girdling trees) were assessed for effects on HWA density, hemlock crown health, hemlock growth, and regeneration of competing tree species, at three different latitude groups in the southern Appalachian Mountains. In all three latitude groups, the treatment that removed the most canopy competition (Large Fell) increased the production of new hemlock shoots, reduced the percentage of dead shoots, and increased basal area increment of target hemlocks relative to unreleased trees. Smaller gaps and those that removed fewer competing live trees (Girdle treatments) also improved hemlock health in the southernmost latitude group. Positive effects of canopy gaps on hemlock crown condition and growth occurred despite similar or higher HWA densities on gap-released vs. unreleased trees. In regression analysis, more than half the variability in crown transparency change and basal area growth post-treatment was explained by the competition index of live trees remaining, average HWA density index, and tree size (dominant tree height and hemlock dbh). In the southernmost latitude group, the regeneration density of deciduous species increased significantly in the three years following gap creation and were highest in the Large Fell treatment. Results support the hypothesis that the increased availability of sunlight (and possibly other limited resources) resulting from canopy gaps (radius approximately ¼ to ½ dominant tree height) improves the physiological tolerance of eastern hemlock to HWA infestation and could complement biological control by providing a more stable source of new shoots with adelgid prey for predatory insects.

A multifaceted approach to reveal the very-fine root's response of Fagus sylvatica seedlings to different drought intensities.

How temperate trees respond to drier summers strongly depends on the drought susceptibility and the starch reserve of the very-fine roots (<0.5 mm in diameter). We performed morphological, physiological, chemical, and proteomic analyses on very-fine roots of Fagus sylvatica seedlings grown under moderate- and severe drought conditions. Moreover, to reveal the role of the starch reserves, a girdling approach was adopted to interrupt the flux of photosynthates toward the downstream sinks. Results show a seasonal sigmoidal growth pattern without evident mortality under moderate drought. After the severe-drought period, intact plants showed lower starch concentration and higher growth than those subjected to moderate drought, highlighting that very-fine roots rely on their starch reserves to resume growth. This behavior caused them to die with the onset of autumn, which was not observed under moderate drought. These findings indicated that extreme dry soil conditions are needed for significant root death in beech seedlings and that mortality mechanisms are defined within individual compartments. The girdling treatment showed that the physiological responses of very-fine roots to severe drought stress are critically related to the altered load or the reduced transport velocity of the phloem and that the changes in starch allocation critically alter the distribution of biomass. Proteomic evidence revealed that the phloem flux-dependent response was characterized by the decrease of carbon enzymes and the establishment of mechanisms to avoid the reduction of the osmotic potential. The response independent from the aboveground mainly involved the alteration of primary metabolic processes and cell wall-related enzymes.

Evaluating effectiveness of girdle-herbicide containment of below-ground spread of oak wilt (Bretziella fagacearum)

Oaks (Quercus spp) are one of the most important sources of timber, mast for wildlife, and ecosystem services across the eastern US. Increasingly, this genus is at risk from diseases including oak wilt, which is one of the most serious threats to oaks, caused by the fungus, Bretziella fagacearum. The upper Midwest has over 5 million ha of oak forests, much of which is on rocky glaciated soils where traditional methods of containing below-ground spread of oak wilt (e.g., vibratory plow lines) are not feasible. We evaluated an alternative containment method of girdling and herbicide (GH) of oak wilt infected trees as well as neighboring oak trees likely connected via root grafts. Our results demonstrated that GH was effective at controlling below-ground spread of oak wilt (overall success rate: 55 %). Best control was achieved when infection centers were small (≤4 newly infected trees), where GH was 81 % effective at containing oak wilt. Containment was only 29 % in larger infection centers (≥5 newly infected trees). The best predictor of success was the number of newly infected trees (p = 0.02) even when considering other factors that could dictate the size of infection centers (e.g., diameter of trees, or number of neighboring trees treated). Our results illustrate the importance of early and rapid management of oak wilt infections and offer a starting place for continued improvement of the GH methodology.

Cane Girdling Influence on the Berry Texture Properties of Three Table Grape Varieties

The effects of cane girdling on the berry texture characteristics were studied in three table grape cultivars. The application was carried out at véraison. The total soluble solids (TSS, °Bx) of berry must and berry weight were measured. The berry mechanical properties were investigated by a texture analyser. A double compression test was used to determine berry hardness and its derived parameters. A puncture test was also applied to assess skin hardness, skin elasticity and skin break energy. Skin thickness was also investigated. The sugar concentration of the must and the berry weight after the girdling treatment were significantly higher compared to those of the control. Berry hardness, skin hardness and skin thickness were significantly affected by this technique. The changes in berry mechanical and quality parameters with this application did not show the same pattern as those observed during control ripening. Notably, in our experiment, after the girdling treatments, the higher berry hardness was accompanied with a higher sugar concentration compared to the control. The skin hardness showed lower values as a result of girdling. However, skin thickness was significantly higher in the girdled berries compared to the non-treated vines.

The Effects of Phloem Girdling on Leaf Cell Physiology and Chlorophyll Biosynthesis in Peach Tree

Phloem girdling is used for many fruit trees to promote fruit set and quality. Although many studies showed the pomological and biochemical effects of girdling in fruit trees, there is very little information on how girdling affects cell physiology. The current study aimed to characterize the leaf xylem structure, cortex cell division, and expansion affected by trunk girdling during phloem healing in peach. The experiment was carried out on a two-year-old peach cv. Rich May grafted onto Garnem grown in 10 L pots in greenhouse. The girdling was performed on the trunk end of the May. The leaf samples were collected 1, 2, 3 and 4 weeks after treatment (WAT). The study showed that the girdling decreased tree growth, stomatal conductance and stomatal density. Girdling decreased chlorophyll biosynthesis in peach leaves. Furthermore, girdling treatment increased leaf cell expansion, xylem thickness, and xylem conduit number during two weeks. The results have demonstrated that leaf anatomy changed by girdling during phloem healing.

Response of sink manipulation in ‘Lapins’ sweet cherry (Prunus avium L.) branches to late-deficit irrigation

Photosynthetic traits, leaf soluble sugars and fruit yield and size were evaluated in order to identify the role of early sink manipulation (girdling and fruiting spur thinning applied in winter) in modulating the effect of late-deficit irrigation (recovering 60% of crop evapotranspiration during 36 days pre-harvest) in ‘Lapins’ sweet cherry branches. Photosynthesis (PN), stomatal conductance (gs), and fruit weight were affected by both treatments, whereas intercellular CO2 concentration of leaves (Ci), mesophyll conductance (gm), Rubisco carboxylase activity (Vcmax), electron transport rate (Jmax), leaf soluble sugars and branch yield were exclusively affected by sink manipulation. The effect of sink manipulation on PN was mainly observed in the girdling treatment as it was not altered by thinning. In girdled branches, PN dropped by 34%, accompanied by a two-fold increase in leaf soluble sugars, indicating that sink feedback regulation of carbon assimilation occurred. Irrespective of the irrigation, the higher PN observed in the controls were not sufficient to achieve the fruit weight and yield of the girdled branches, indicating that fruit carbon demand in control branches was source-limited. The depressed PN by girdling was associated with significant reductions in gs, gm, Vcmax and Jmax. Since lowered PN by deficit irrigation was neither attributable to a gs-associated decrease in Ci nor to changes in any other photosynthetic variable, further research is needed to clarify this point. Results showed that irrigation deficit was sufficient to reduce PN in girdled branches, whereas it had no effect in control and thinned branches. Thus, the depressive effect of deficit irrigation on PN appeared to be exacerbated by the sink effect.

Adverse Effects of Long-Term Continuous Girdling of Jujube Tree on the Quality of Jujube Fruit and Tree Health

In order to improve fruit yield, girdling technology is widely used in fruit production. However, in the practice of Hui jujube planting in Southern Xinjiang, it was found that the jujube fruit quality declined and the health problems and death rate of jujube trees increased after jujube trees have been girdled continuously for many years, which seriously affected the economic benefits of jujube planting. So, this study was carried out to explore the specific influence law of continuously jujube-tree girdling for many years on the main nutrients (soluble solid, protein, total acid, vitamin C, total sugar, fat and so on), physical quality attributes (single-fruit weight, hardness and geometric-mean diameter) of jujube fruit and tree health. Through the detection of the nutrients of jujube fruit, it was found that the long-term girdling of jujube trees significantly reduced the main nutrients of jujube fruit. The total sugar and reducing sugar content of jujube-fruit samples from the trees without girdling were 134.23% and 109.62% of the corresponding indexes of jujube-fruit samples from girdled ones, respectively; furthermore, the sugar–acid ratio of jujube samples from the girdled trees was 149.95, while the sugar–acid ratio of fruit from non-girdled trees reached 183.78. Moreover, the protein content of fruit from non-girdled trees was 5.91% higher than that of fruit from girdled ones. In addition, the single-fruit weight, hardness and geometric-average diameter of jujube from non-girdled jujube trees were 20.25%, 13.31% and 20.21% higher than those of jujube from girdled ones, respectively. Moreover, microstructural analysis of the callus and the newly formed phloem showed that the adverse effects of girdling on the phloem function were persistent and permanent. It was also found that jujube-tree girdling can also cause damage, to a certain extent, to the xylem around the girdling wound. The above research results further explained the internal cause of jujube-tree death caused by long-term continuously jujube-tree girdling. The results of this study can provide some scientific basis for the effective application of fruit-tree-girdling technology in fruit production.

Removal of non-native trees fosters but alone is insufficient for forest regeneration in Hawaiʻi

Across the globe, non-native plant species have become abundant in many tropical forests, resulting in altered patterns of biological diversity and species composition, and impacting important ecosystem functions. However, long-term experimental research on the efficacy of non-native tree removal for tropical forest restoration remains limited. We investigated the removal of non-native tree species in a mesic tropical forest in Hawaiʻi, where rates of endemism and endangerment of plant species is high and multiple non-native tree species are abundant. As a collaboration between resource managers and researchers, we tested the effects of non-native tree removal on overstory and understory metrics of restoration using three restoration approaches: “total cut” (cutting all non-native trees); “girdle” (girdle of all non-native trees); and “selective cut” (cutting approximately 50% of non-native trees). Prior to removal, we established permanent plots (four 10 × 10 m plots per restoration treatment, with 10 1 × 1 m subplots in each), then monitored them over 10 years. Across all treatments, canopy openness increased significantly post restoration, peaked after three years, then decreased to pre-treatment levels or lower. The increase was largest for the total cut treatment, but there was large variation within treatments. By the end of the experiment, the total cut and girdle treatments performed similarly for all our metrics of restoration, including survival, growth, density, and basal area of native trees; density and richness of native species in the understory; and total weed biomass. The selective treatment performed worse, showing lower relative gains in basal area of native trees and density of native understory individuals. Overall, tree removal was effective in restoring a native canopy. However, understory native species richness and density remained at pre-treatment levels, likely due to limited seed dispersal, seed predation by non-native rodents, and continued competition from non-native herbaceous species. Nonetheless, subplots with the best starting conditions performed the best. More intensive and longer-term weeding of non-native species in the understory, focused on areas with the best starting conditions and combined with out-planting of native seeds, seedlings and/or saplings, is likely necessary to foster effective native species regeneration. Overall, our research shows that removal of non-native trees using the total cut and girdle techniques can foster native forest restoration in the mesic forests of Hawaiʻi, but that on-going long-term management in the understory is critical.

Effects of sustainable forest management on tree diversity, timber volumes, and carbon stocks in an ecotone forest in the northern Brazilian Amazon

The tension between the large global demand for tropical timber, and ecological sustainability and local socioeconomic development in the fragile natural ecosystems of the Amazon region has challenged many generations. In this case study, carried out in an ecotone forest in the northern Brazilian Amazon, we seek to demonstrate how forest management can became more sustainable through silvicultural prescriptions that reduce forest degradation and soil erosion. We evaluated the effects of the sustainable forest management (SFM) on tree diversity, timber volumes, and carbon stocks. A continuous forest inventory was carried out in nine 1-ha permanent plots (900 subplots of 100 m²), distributed in three treatments with three repetitions: T1 = control without selective logging, T2 = SFM, and T3 = SFM + silvicultural treatment of thinning release by tree girdling and poisoning. SFM was carried out with an average of three commercial timber trees harvested per hectare with DBH (diameter at breast height) ≥ 50 cm, corresponding to a timber volume of 20 ± 6 m3 ha-1, equivalent to the removal of 7 ± 2 Mg C ha-1 (5% of the original C). The formation of clearings (gaps) arising from the falling of exploited trees (0.12 ± 0.09 ha) resulted in greater impacts on the forest structure than the construction of 4 m skidder trails (0.06 ± 0.04 ha), with an average of 7 ± 4 damaged trees ha-1 and 5 ± 3 dead trees ha-1. Although six trees species became locally extinct, tree diversity was little altered, and timber volumes and forest carbon volume stocks remained essentially constant at this average logging intensity. Based on our results, sustainable forest management can become an efficient model for land use in the Amazon when harvesting is carried out using this average logging intensity. However, long-term monitoring studies using permanent plots in ecotone forests in the Brazilian Amazon will still be necessary. Quantifying, evaluating, and reporting impacts related to forest management will enable the formation of an empirical basis to support sustanaible forestry practices and for updating environmental legislation, contributing to local socioeconomic development, and maintaining the environmental services provided globally by tropical forests.

Effects of Girdling and Foliar Fertilization with K on Physicochemical Parameters, Phenolic and Volatile Composition in ‘Hanxiangmi’ Table Grape

Aroma is one of the most important indicators of grape quality. Girdling and foliar fertilization with K (K2O) are common agronomic practices applied to improve berry quality in grape production. However, little is known about its effect on the accumulation and biosynthesis of the entire aromatic profile. Our study was aimed to explore the influences of girdling and foliar fertilization with K (alone or in combination) on the general properties, phenolic composition, volatile free aroma compounds, spatial and temporal expression of terpene-related genes and sensory properties in ‘Hanxiangmi’ table grape. In this study, we found that girdling and foliar fertilization with K (alone or in combination) facilitated fruit enlargement and increased the accumulation of phenolic compounds in skin. The combination treatment of girdling and foliar fertilization with K significantly promoted the concentrations of total soluble solids (TSS) in the pulp and proanthocyanidins in the berry skin, and had a lower titratable acidity (TA) compared to those of the control. In contrast, girdling treatment alone increased the concentrations of titratable acidity. Volatile free aroma composition analysis revealed that the combination treatment increased the volatile compounds and concentrations significantly, most notably in terpenes, such as nerol, citronellol and linalool. Spatial and temporal expression analysis showed that the expression level of VvDXS was significantly correlated with linalool and total terpenes concentrations, as a result of which, we speculated that VvDXS is the candidate gene for the regulation of important grape terpenes. We hope that our results can direct farmers to better apply girdling and foliar fertilization with K in grape production.

Tree Girdling for Potential Bat Roost Creation in Northwestern West Virginia

Cavity/crevice tree-roosting bats in North America face an uncertain future with many factors impacting their populations. To benefit crevice/cavity roosting bat species, forests are often enhanced with the use of tree girdling. In October 2015, 20 maples, 22 oaks, and 18 hickories were girdled using a method with fell cut and herbicide (frilling) or double-girdling with a chainsaw. From 2016–2021, targeted trees were observed and the tree’s decay state was collected. The average time for trees to display suitable roosting characteristics for frilling trees was 3.23 years while it was 4.46 years for double girdling. The average time frilling trees contained suitable roosting characteristics was 3.20 years while it was 1.63 years for double girdling. The frilling method resulted in a quicker kill of trees than double girdling and frilling trees had suitable roosting characteristics for a longer duration. Frilling was effective killing all three types of trees, while the double girdling was less effective, especially on oaks. When grouping species and treatment in analysis, only average decay states between maple frill and oak double girdling and hickory frill and oak double girdling were significantly different. This evaluation demonstrates that roost tree creation relating to tree species and girdling methodology has a temporal component that should be considered when managing for crevice/cavity bat roosts and multiple habitat creation methods should be used in conjunction with snag creation to provide sustainable bat habitat over longer time periods.

Influence of girdling on growth of litchi (Litchi chinensis) roots during cold-dependent floral induction

Girdling is extensively applied to promote litchi flowering via the acceleration of bud dormancy and accumulation of carbohydrate in terminal shoots and leaves, but little is known about the response of root growth to girdling treatment during low temperature-mediated floral induction. In this study, litchi plants were girdled before exposure to inductive-cold in the field, and the growth of roots were monitored until floral initiation. The results showed that the length density and growth rate of fine roots increased during cold-dependent floral induction in the entire soil profile, but significantly decreased during flower development. The girdling treatment suppressed the emergence and growth of distal roots but induced that of proximal roots. More fine roots were distributed in shallower soil layers (15–45 cm) where the roots showed more rapid responses to cold and the girdling treatment. Roots reduced starch and sucrose content across the floral induction period and in response to the girdling treatment, which possibly accounted for the suppression of distal root growth. It is suggested that litchi root growth is more sensitive to carbohydrate availability than cold temperatures during floral induction.

Vegetative rescue and in vitro propagation of Persea willdenovii

Persea willdenovii is a native species popularly known for its high potential for medicinal use. Due to problems in low seed production and germination, vegetative propagation appears promising. Thus, we seek with this work to evaluate techniques of vegetative rescue and the potential use of shoots obtained in tissue culture. Adult trees of the species were used to apply total and partial girdling treatments and obtain pruned branches as vegetative rescue techniques. Shoot production was monitored over time (90 to 240 days). Sprouts were used for in vitro propagation, and disinfestation treatments were carried out using biocides such as NaClO and Plant Preservative Mixture PPMTM (PPMTM), changing the time and concentrations of the products. Multiplication was also tested using doses of 6-benzylaminopurine (BAP) and media and the potential for callogenesis under combinations of BAP and Naphthalene Acetic Acid (ANA). The vegetative rescue by complete or semi-girdling has the potential to produce shoots, though pruned branches proved to be one of the best techniques for rescue. In the micropropagation, the use of biocides such NaOCl for a long period of time (2 % for 20 min) with PPMTM added to the culture medium shows a potential for disinfestation in the in vitro establishment. For in vitro multiplication, the usage of WPM and BAP (2 a 4 g L-1) promotes higher shoot length, shoot number and leaf number. For indirect organogenesis by leaf segments, the cultivation with BAP and ANA was not responsive to the induction of callogenesis.

Effects of different trunk girdlings on fruit yield and pomological characteristics of persimmon (Diospyros kaki L. cv. Hachiya)

Objective: This study was performed to determine the effects of two girdling practices on yield and some pomological properties of persimmon trees in 2019. Material and Methods: The gridling practices were applied to Hachia variety, common in Çanakkale, as single girdling, double girdling and control. Girdling treatments were performed after full blossom in full yield trees. Fruit yield and some pomological properties of the variety were determined. Fruit weight, fruit width, fruit size, fruit skin colour (L, a, b), pH, titratable acidity (TA) (%), fruit flesh firmness (kg / cm2) and total soluble solid content (TSS) were determined. Results: The highest yield per tree was obtained from the control (120.74 kg tree-1) treatment. The largest fruits with a value of 383.23 g were obtained from double girdling treatment. The double girdling application provided the highest values in terms of fruit length and fruit width (79.22 mm, 94.71 mm, respectively). There was a significant difference (p

Effects of clearcutting and girdling on soil respiration and fluxes of dissolved organic carbon and nitrogen in a Japanese cedar plantation

Impacts of forest management practices on soil carbon (C) and nitrogen (N) dynamics remain under debate due to complex interactions between belowground biogeochemical processes. To optimize practices that minimize soil C and N losses, we investigated the effects of management practices on soil C and N fluxes, including the leaching of dissolved organic C (DOC) and N, by comparing clearcutting, stem girdling (removal of the bark and phloem tissue), and control treatments in a Japanese cedar plantation. Canopy opening by clearcutting is hypothesized to have a greater effect on soil C loss and the leaching of nitrate-N relative to girdling. Results showed that clearcutting increased soil heterotrophic respiration (organic matter decomposition) and lead to a loss of soil organic C (2.9–3.7 Mg C ha−1 yr−1). Higher litter inputs from girdled tree dieback caused an increase in DOC fluxes from the organic horizon, whereas the loss of fresh litter inputs decreased DOC fluxes from the organic horizon following clearcutting. Clearcutting increased nitrate-N leaching by 3.3–4.8 kg N ha−1 yr−1 due to the loss of plant N uptake and the increased mineralization of soil organic matter, but high C/N ratios in dissolved organic matter limited nitrate leaching in the girdled treatment. Effects of forest management practices on soil C loss and nitrate leaching loss could be variable, but the slash application in clearcutting and the slow dieback in stem girdling could mitigate soil C loss and nitrate leaching loss.

Metabolomics Analysis of Litchi Leaves during Floral Induction Reveals Metabolic Improvement by Stem Girdling.

Prolonged exposure to cold temperatures often results in a relatively low flowering rate in litchi (Litchi chinensis Sonn.) trees with younger leaves. This study aimed to verify the impact of stem girdling on litchi flowering by identifying and characterizing the induced metabolic changes. After a 60 day exposure to cold treatment at 15 °C/10 °C (12 h/12 h), the flowering rate of the girdled trees was 100%, while that of the non-girdled trees was 20%, indicating that girdling improved litchi flowering at its turning stage. The metabolic profiles of litchi leaves with and without stem girdling during floral induction were compared and 505 metabolites potentially associated with litchi flowering were detected. Most metabolites were involved in the metabolism of starch and sucrose, fatty acid, and phenylpyruvic acid. The metabolic pathways concerned with the biosynthesis of epinephrine, sucrose, and d-maltose were induced in leaves after girdling treatment. The level of galactitol, phenylpyruvic acid, acetyl-CoA, linoleic acid, alpha-linolenic acid, and 13-HPOT biosynthesis remained stable in the leaves from girdled trees but changed drastically in the leaves from non-girdled trees. In addition, 379 metabolites concerning flowering rate were characterized. Metabolism pathways of starch and sucrose, galactose, and linoleic acid are of great significance to the flowering of litchi. Linoleic acid exhibited the most significant variations between girdled trees and non-girdled trees with fold changes of up to 13.62. These results contribute to understanding the biological mechanism of litchi floral induction and the metabolic changes after stem girdling.

Phosphorus Availability Alters the Effect of Tree Girdling on the Diversity of Phosphorus Solubilizing Soil Bacterial Communities in Temperate Beech Forests

Phosphorus (P) solubilization is an important process for P acquisition by plants and soil microbes in most temperate forests. The abundance of inorganic P solubilizing bacteria (PSB) is affected by the P concentration in the soil and the carbon input by plants. We used a girdling approach to investigate the interplay of root-derived C and initial P content on the community composition of gcd-harboring bacteria as an example of PSB, which produce gluconic acid. We hypothesized that gcd-harboring PSB communities from P-poor sites are more vulnerable to girdling, because of their lower diversity, and that a shift in gcd-harboring PSB communities by girdling is caused by a response of few, mostly oligotrophic, taxa. We used a high-throughput metabarcoding approach targeting the gcd gene, which codes for the quinoprotein glucose dehydrogenase, an enzyme involved in the solubilization of inorganic P. We compared the diversity of gcd-harboring PSB in the mineral topsoil from two temperate beech forests with contrasting P stocks, where girdling was applied and compared our data to the respective control plots with untreated young beech trees. At both sites, gcd-harboring PSB were dominated by Proteobacteria and Acidobacteria, however, with differences in relative abundance pattern on the higher phylogenetic levels. The P-poor site was characterized by a high relative abundance of Kaistia, whereas at the P-rich site, Dongia dominated the gcd-harboring bacterial communities. Girdling induced an increase in the relative abundance of Kaistia at the P-poor site, whereas other bacterial groups of the family Rhizobiaceae were reduced. At the P-rich site, major microbial responders differed between treatments and mostly Bradyrhizobium and Burkholderia were positively affected by girdling in contrast to uncultured Acidobacteria, where reduced relative abundance was found. Overall, these effects were consistent at different time points analyzed after the introduction of girdling. Our data demonstrate that plant-derived carbon influences community structure of gcd-harboring bacteria in temperate beech forest soils.