Temperate Beech Forest Research Articles

High nitrate and sulfate leaching in response to wetter winters in temperate beech forests

Climate models project moderate to large increases in air temperature for most temperate ecosystems with an overall increase in winter precipitation and a shift from snow towards rain. We investigated the effects of increased winter rainfall on the ecosystem functioning of European beech forests at their north-eastern distribution range. In a large-scale field experiment we manipulated winter climate at nine forest sites by increasing the amount of rainfall and excluding snow. Nutrient availability in the topsoil and leaching in 50 cm depth as well as litter decomposition and radial growth of mature European beech trees were analysed. It was hypothesized that (1) wetter winters lead to increased nutrient deposition as well as leaching, with an overall increase in net nutrient availability, (2) decomposition decreases in response to water addition containing also additional nutrients and (3) primary production during the subsequent growing season increases as presumably not all additionally available nutrients would be leached. We found an increase in topsoil nitrate and sulfate availability during winter in response to rain addition, likely as a consequence of collecting more atmospheric deposition, and surprisingly high leaching rates of the additionally available nutrients. During the subsequent early growing season, no difference in nutrient availability could be observed anymore. Enhanced nutrient availability in the topsoil and leaching do not seem to have a strong short-term influence on forest ecosystem processes in ecosystems which are close to their critical load of N deposition. Decomposition rates during winter and early growing season as well as stem diameter growth during the following growing season were not influenced. This indicates that additional nutrients in the topsoil in response to wetter winters are not available for plant growth but pollute ground- and surface waters.

Elevation differentially shapes functional diversity patterns in understorey forest communities when considering intraspecific and interspecific trait variability

AbstractQuestionsWhat is the relative importance of interspecific and intraspecific trait variation and their covariation in the herb layer of European temperate beech forests, and how do they vary with elevation? Is there evidence of interspecific trait convergence at higher elevations, as postulated by the habitat‐filtering hypothesis, and is this convergence enhanced or counteracted by intraspecific variation?LocationNational Park “Foreste Casentinesi, Monte Falterona and Campigna”, Italy.MethodsWe measured four functional traits – plant height, specific leaf area (SLA), leaf dry matter content (LDMC) and leaf area – across 775 individuals from 60 herb‐layer species in 28 forest plots (10 m × 10 m) spanning an 800 m elevation gradient. For each trait in each plot, we computed community‐weighted means (CWMs) and the standardized effect size of functional diversity (SES‐FD). We decomposed total trait variation into its interspecific and intraspecific components, and their covariation. We run linear regression models to assess the impact of elevation on these three components of functional variation. Lastly, we investigated whether higher elevation communities exhibited lower SES‐FD, indicating functional convergence that could hint to a stronger habitat filtering.ResultsInterspecific trait variation was more important than the intraspecific counterpart both for CWMs and SES‐FD. Only CWMs calculated for plant height and LDMC showed a significant relationship with elevation. Low‐elevation communities featured taller, more‐conservative species, whereas shorter, faster‐growing species were more common at higher elevations. SES‐FD remained consistently negative for species turnover and total variation, suggesting stable functional convergence across the gradient.ConclusionsOur findings suggest that interspecific and intraspecific trait variability can be decoupled along an elevation gradient, stressing the importance of individually considering each component of trait variation when studying community composition. Elevation significantly influenced various components of plant community trait variation, with habitat filtering playing a substantial role in selecting plants with specific traits across elevations.

Responses of a bird community to sporadic outbreaks of woody herbivorous insects in a temperate beech forest in Japan

Sporadic large outbreaks of herbivorous insects alter forest ecosystems via a top-down effect, and a high frequency of outbreaks led to the death of the trees on which the insects fed. The top-down effect of predators, such as other insects and birds, often regulates the outbreaks. Predator insects exert effective top-down control on outbreaks of herbivorous insects, but the effect of bird predation varies because birds have a broader diet range and higher mobility than insects. It was hypothesized that when large insect outbreaks occur during the breeding season of birds, most bird species would not respond owing to a fixed home range during this season and would, therefore, not exert top-down effects. To test this hypothesis, the relationship between bird and beech sawfly abundance was investigated for over nine years in the Tanzawa Mountains of central Japan, where temperate beech forests and large sporadic outbreaks of woody herbivorous insects occur. In this study, 28 649 female beech sawfly adults were captured, and 2515 individuals were identified from 50 bird species. The abundance of most bird species foraging on beech sawfly larvae, except Sitta europaea, did not increase proportionally with the number of beech sawfly adults. Many bird species did not respond to the unpredictable and temporary abundance of food resources in a way that would enhance their density, supporting the hypothesis. These results can be explained by examining the nesting and foraging guilds of the birds. S. europaea is less restricted in nesting sites and nests earlier in the season than other species; therefore, they could select nests in areas where beech sawfly larvae were abundant. Regarding foraging, S. europaea has a unique foot shape that allows it to move down the tree trunk freely and respond rapidly to fluctuations in beech sawfly abundance. Bird species that exert top-down effects on insects show promise for use in an integrated pest management approach to manage sporadic outbreaks of herbivorous insects in forest ecosystems.

Deadwood position matters: Diversity and biomass of saproxylic beetles in a temperate beech forest

Deadwood plays a key role for biodiversity in forests. A significant number of beetles from this group are currently listed as endangered in the Red List. In addition to other management recommendations, there have been recent efforts to enrich stands with dead wood to promote biodiversity. An important parameter for forestry enterprises is the optimization of these interventions. The study investigated the abundance, species richness, gamma diversity, conservation value and biomass of saproxylic beetles in natural forests using window traps. A total of 89 traps were used for saproxylic beetle monitoring, of which 29 were placed on lying logs, 30 on snags and 30 as controls in forest stand space. A total of 35,011 beetles were recorded in 564 species (61 families). Notably, 20,515 of these belong to saproxylic beetles (59%) in 311 species (55%), with 62 classified as Red-List species (20%). In the group of ‘all saproxylic beetles’, the results indicate that α diversity and γ diversity (q ​= ​0) remain consistent across various deadwood types, while β diversity showed significant differences. Significant differences were found in the Red-List species group, where α diversity and γ diversity differed, with higher values observed in snags. Rarefaction based total species richness of site was estimated to be 391 species, including 74 Red-Listed species. Comparing the sample coverage of the studied stand categories showed that all saproxylic species exhibit a pronounced preference for inhabiting areas featuring lying logs. Conversely, Red-List species mainly inhabit snags, with β diversity being more similar to snags and forest stand space. Notably, both the conservation value (weighted average by conservation status) and beetle biomass are significantly highest in snags, whereas stand space shows the lowest values across all measured saproxylic beetle indices. Furthermore, the use of traps set on the poles in forest stand space resulted in an underestimation of the actual stand richness by 20%–25%. Our results support the conclusion that snags are indispensable features in beech forests, playing a key role in promoting high species diversity, especially among Red-List species, and supporting the biomass of saproxylic beetles. Consequently, it becomes crucial to incorporate a higher percentage of standing deadwood in managed forests or actively create equivalent environments by introducing high stumps.

A modeling approach to investigate drivers, variability and uncertainties in O2 fluxes and O2 : CO2 exchange ratios in a temperate forest

Abstract. The O2 : CO2 exchange ratio (ER) between terrestrial ecosystems and the atmosphere is a key parameter for partitioning global ocean and land carbon fluxes. The long-term terrestrial ER is considered to be close to 1.10 mol of O2 consumed per mole of CO2 produced. Due to the technical challenge in measuring directly the ER of entire terrestrial ecosystems (EReco), little is known about variations in ER at hourly and seasonal scales, as well as how different components contribute to EReco. In this modeling study, we explored the variability in and drivers of EReco and evaluated the hypothetical uncertainty in determining ecosystem O2 fluxes based on current instrument precision. We adapted the one-dimensional, multilayer atmosphere–biosphere gas exchange model “CANVEG” to simulate hourly EReco from modeled O2 and CO2 fluxes in a temperate beech forest in Germany. We found that the modeled annual mean EReco ranged from 1.06 to 1.12 mol mol−1 within the 5-year study period. Hourly EReco showed strong variations over diel and seasonal cycles and within the vertical canopy profile. The determination of ER from O2 and CO2 mole fractions in air above and within the canopy (ERconc) varied between 1.115 and 1.15 mol mol−1. CANVEG simulations also indicated that ecosystem O2 fluxes could be derived with the flux-gradient method using measured vertical gradients in scalar properties, as well as fluxes of CO2, sensible heat and latent energy derived from eddy covariance measurements. Owing to measurement uncertainties, however, the uncertainty in estimated O2 fluxes derived with the flux-gradient approach could be as high as 15 µmol m−2 s−1, which represented the 90 % quantile of the uncertainty in hourly data with a high-accuracy instrument. We also demonstrated that O2 fluxes can be used to partition net CO2 exchange fluxes into their component fluxes of photosynthesis and respiration if EReco is known. The uncertainty of the partitioned gross assimilation ranged from 1.43 to 4.88 µmol m−2 s−1 assuming a measurement uncertainty of 0.1 or 2.5 µmol m−2 s−1 for net ecosystem CO2 exchange and from 0.1 to 15 µmol m−2 s−1 for net ecosystem O2 exchange, respectively. Our analysis suggests that O2 measurements at ecosystem scale have the potential to partition net CO2 fluxes into their component fluxes, but further improvement in instrument precision is needed.

Host body mass, not sex, affects ectoparasite loads in yellow-necked mouse Apodemus flavicollis

We investigated the presence and potential causes of sex bias in ectoparasite infestations in the yellow-necked mouse Apodemus flavicollis. We compared the natural tick and flea burdens of male and female mice in a temperate beech forest and assessed whether the observed differences were driven by host sex or body mass. We found that males were more heavily infested by ticks compared to female mice. However, this difference was driven by host body mass, and not sex itself. Host body mass positively correlated with flea loads, but there was no evidence of sex bias in flea abundance. In addition, the abundance of both ticks and fleas infesting yellow-necked mice changed over time, both seasonally (month to month) and annually (year to year). Our results underscore the importance of the sexual size dimorphism and the parasite taxon as the primary factors that influence the occurrence of sex-biased parasitism in small mammals.

Future forests and biodiversity: Effects of Douglas fir introduction into temperate beech forests on plant diversity

Introduction of drought-tolerant exotic tree species is seen as an important adaptation measure of forest management to climate change in Central Europe. Douglas fir (Pseudotsuga menziesii) is particularly favored in this context, because it is adapted to summer droughts due to the climate in its natural distribution range in temperate western North America and it is also fast-growing and the wood is readily marketable. In Germany, there are plans to grow Douglas fir on a large scale in mixed forests with other tree species on acidic soils. Potential ecological consequences have not yet been sufficiently scrutinized. Here, we analyze effects of Douglas fir introduction into forests of European beech (Fagus sylvatica), which would naturally predominate Central Europe’s forests. We analyzed vascular plant diversity and species composition of the ground vegetation in a gradient with increasing Douglas fir canopy fraction that ranged from pure beech (0% Douglas fir) via mixed stands (25%, 50%, 75% Douglas fir) to pure (100%) Douglas fir forest. Species richness, Shannon diversity, and Simpson diversity increased with increasing Douglas fir canopy fraction. However, this increase was primarily driven by an increase of nitrogen-tolerant disturbance indicators, whereas the share of forest species that were predominant in pure beech forests decreased. Beech forest species declined gradually with increasing Douglas fir canopy fraction, but these declining species were fewer than the number of species increasing due to Douglas fir introduction. Cover of ∼30% of species remained constant when Douglas fir was introduced. Strong changes in the ground vegetation were observed at Douglas fir canopy fractions > 40 – 50% and the original character of the ground vegetation was completely lost beyond a threshold of 75%. Therefore, we discourage from high Douglas fir proportions beyond these thresholds in production forests and from any introduction of Douglas fir where nature conservation is a priority.

Ectomycorrhizal diversity, taxon-specific traits and root N uptake in temperate beech forests.

Roots of forest trees are colonized by a diverse spectrum of ectomycorrhizal (EM) fungal species differing in their nitrogen (N) acquisition abilities. Here, we hypothesized that root N gain is the result of EM fungal diversity or related to taxon-specific traits for N uptake. To test our hypotheses, we traced 15 N enrichment in fine roots, coarse roots and taxon-specific ectomycorrhizas in temperate beech forests in two regions and three seasons, feeding 1 mM NH4 NO3 labelled with either 15 NH4 + or 15 NO3 - . We morphotyped > 45 000 vital root tips and identified 51 of 53 detected EM species by sequencing. EM root tips exhibited strong, fungal taxon-specific variation in 15 N enrichment with higher NH4 + than NO3 - enrichment. The translocation of N into the upper parts of the root system increased with increasing EM fungal diversity. Across the growth season, influential EM species predicting root N gain were not identified, probably due to high temporal dynamics of the species composition of EM assemblages. Our results support that root N acquisition is related to EM fungal community-level traits and highlight the importance of EM diversity for tree N nutrition.

Microbial responses to soil cooling might explain increases in microbial biomass in winter

In temperate, boreal and arctic soil systems, microbial biomass often increases during winter and decreases again in spring. This build-up and release of microbial carbon could potentially lead to a stabilization of soil carbon during winter times. Whether this increase is caused by changes in microbial physiology, in community composition, or by changed substrate allocation within microbes or communities is unclear. In a laboratory incubation study, we looked into microbial respiration and growth, as well as microbial glucose uptake and carbon resource partitioning in response to cooling. Soils taken from a temperate beech forest and temperate cropland system in October 2020, were cooled down from field temperature of 11 °C to 1 °C. We determined microbial growth using 18O-incorporation into DNA after the first two days of cooling and after an acclimation phase of 9 days; in addition, we traced 13C-labelled glucose into microbial biomass, CO2 respired from the soil, and into microbial phospholipid fatty acids (PLFAs). Our results show that the studied soil microbial communities responded strongly to soil cooling. The 18O data showed that growth and cell division were reduced when soils were cooled from 11 to 1 °C. Total respiration was also reduced but glucose uptake and glucose-derived respiration were unchanged. We found that microbes increased the investment of glucose-derived carbon in unsaturated phospholipid fatty acids at colder temperatures. Since unsaturated fatty acids retain fluidity at lower temperatures compared to saturated fatty acids, this could be interpreted as a precaution to reduced temperatures. Together with the maintained glucose uptake and reduced cell division, our findings show an immediate response of soil microorganisms to soil cooling, potentially to prepare for freezing events. The discrepancy between C uptake and cell division could explain previously observed high microbial biomass carbon in temperate soils in winter.

Geometric configurations of particulate matter in terrestrial solutions of a temperate beech forest

The heterogeneous nature of the size and shape of particulate matter (PM) deposited onto forest canopies is acknowledged. However, it is uncertain how PM interacts with the forest canopy and how it is transported and cycled via the hydrological processes of throughfall and stemflow. To improve our understanding of particulate cycling in forested watersheds, this study quantifies the geometric configuration of PM in bulk precipitation, throughfall, stemflow, and upper soil (Oa horizon) solution in both leafed and leafless periods in a European beech (Fagus sylvatica L.) forest in Germany. Circular equivalence diameter, circularity, elongation ratio, perimeter-to-area ratio, and fractal dimension were calculated for all 43,278 individual particulates in bulk precipitation, throughfall, stemflow, and Oa solutions. Loss on ignition measurements were also conducted to determine the organic matter content of the particulates. From a physical point of view, the opposite trends for circular equivalence diameter and perimeter-to-area ratio of PM between stemflow or throughfall and bulk precipitation during both leafless and leafed periods were the most striking. For bulk precipitation, the PM's mean circular equivalence diameter was significantly larger in the leafless period than the leafed period, with the reverse observed for throughfall and stemflow. Mean perimeter-to-area ratios (μm−1) of PM of both stemflow and throughfall were significantly larger in the leafless period than the leafed period. The opposite trend was observed for bulk precipitation and Oa solution. The percent organic matter of PM was not statistically significantly different across solutions or canopy state. Our results indicate that the differential routing of PM through the canopy indeed influences the geometry of PM among solution types as compared to the bulk precipitation. The effects of these changes on the chemistry of the PM and its impact of particulate cycling, and the impacts of shifting seasonality with climate change, warrants further investigation.

Methane emission from stems of European beech (Fagus sylvatica) offsets as much as half of methane oxidation in soil.

Trees are known to be atmospheric methane (CH4 ) emitters. Little is known about seasonal dynamics of tree CH4 fluxes and relationships to environmental conditions. That prevents the correct estimation of net annual tree and forest CH4 exchange. We aimed to explore the contribution of stem emissions to forest CH4 exchange. We determined seasonal CH4 fluxes of mature European beech (Fagus sylvatica) stems and adjacent soil in a typical temperate beech forest of the White Carpathians with high spatial heterogeneity in soil moisture. The beech stems were net annual CH4 sources, whereas the soil was a net CH4 sink. High CH4 emitters showed clear seasonality in their stem CH4 emissions that followed stem CO2 efflux. Elevated CH4 fluxes were detected during the vegetation season. Observed high spatial variability in stem CH4 emissions was neither explicably by soil CH4 exchange nor by CH4 concentrations, water content, or temperature studied in soil profiles near each measured tree. The stem CH4 emissions offset the soil CH4 uptake by up to 46.5% and on average by 13% on stand level. In Central Europe, widely grown beech contributes markedly to seasonal dynamics of ecosystem CH4 exchange. Its contribution should be included into forest greenhouse gas flux inventories.

Tree-ring and remote sensing analyses uncover the role played by elevation on European beech sensitivity to late spring frost.

Extreme climate events such as late spring frosts (LSFs) negatively affect productivity and tree growth in temperate beech forests. However, detailed information on how these forests recover after such events are still missing. We investigated how LSFs affected forest cover and radial growth in European beech (Fagus sylvatica L.) populations located at different elevations at four sites in the Italian Apennines, where LSFs have been recorded. We combined tree-ring and remote-sensing data to analyse the sensitivity and recovery capacity of beech populations to LSFs. Using daily temperature records, we reconstructed LSF events and assessed legacy effects on growth. We also evaluated the role played by elevation and stand structure as modulators of LSFs impacts. Finally, using satellite images we computed Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and LAI (Leaf Area Index) to evaluate the post-LSF canopy recovery. The growth reduction in LSF-affected trees ranged from 36 % to 84 %. We detected a negative impact of LSF on growth only during the LSF year, with growth recovery occurring within 1-2 years after the event. LSF-affected stands featured low vegetation indices until late June, i.e. on average 75 days after the frost events. We did not find a clear relationship between beech forest elevation and occurrence of LSFs defoliations. Our results indicate a high recovery capacity of common beech and no legacy effects of LSFs.

Dark CO2 fixation in temperate beech and pine forest soils

Soils are the largest terrestrial organic carbon pool and the largest terrestrial source of atmospheric CO2. Non-phototrophic CO2 fixation by microbes re-fixes and recycles CO2 respired in soils. Our previous study showed that in temperate deciduous forest soil profiles, rates of dark CO2 fixation were proportional to microbial biomass, irrespective of soil depth. However, the amount and quality of organic matter entering different soil depths vary for different temperate forest types and these influence microbial communities with unknown consequences for CO2 fixation rates. To test whether differences in the amount and quality of SOC caused by tree species affect dark CO2 fixation rates with depth, we conducted a study using acidic soils from two forest plots from the Schorfheide-Chorin Exploratory, Germany. These soils, dominated by either beech (deciduous) or pine (coniferous) tree stands differ in their SOC content and quality. We traced the incorporation of 2% (v:v) 13C–CO2 label into microbial biomass and estimated the CO2 fixation rates relative to microbial biomass carbon content (in μg C g MBC−1 d−1) across the soil profiles. The rates of dark CO2 fixation per g MBC were similar across the beech soil profiles, but significantly lower in the pine soils at the B2 and BC horizons, suggesting that while dark CO2 fixation rates are linked to MBC in deciduous forest soils, other factors influence dark CO2 fixation rates in coniferous forest soils. The pine subsoils had low SOC content and quality, with a microbial community enriched with heterotrophic fermenters like Chloroflexi that are predicted to have a lower potential for heterotrophic CO2 fixation compared to the other dominant bacteria phyla. In contrast, the beech soil profiles, characterized by higher SOC inputs, featured higher fractions of copiotrophs like Proteobacteria, Acidobacteria, and Actinobacteria predicted to have high heterotrophic CO2 fixation potential. We thus speculate that in contrast to the beech soils, lower SOC inputs in the pine subsoils affected the community composition, leading to lower CO2 fixation rates. We further made comparisons to soils dominated by mixed deciduous trees and featuring a higher MBC and SOC content. Over this range of temperate forest soils, CO2 fixation rates were highest in the mixed deciduous forest soils, with MBC and Shannon index (used as a proxy parameter for community composition) showing the strongest correlations with the varying CO2 fixation rates. Our study suggests that predictions of dark CO2 fixation rates need to consider tree-species specific or site-specific conditions, as these may alter root carbon inputs and affect microbial community composition and their metabolic CO2 fixation potentials in soil.

Microbial community responses to phosphorus and nitrogen inputs in the organic soil horizons of two contrasting temperate beech forests

Due to increasing nitrogen (N) deposition from the atmosphere, temperate forests are progressively becoming phosphorus (P) limited. Trees take up P mainly from the soil solution, which soil microorganisms can replenish by mineralizing organic P through enzymatic hydrolysis (e.g. using phosphatases). We investigated how bacterial (including phosphatase harboring bacteria) and fungal communities in organic horizons with contrasting nutrient status respond within months to changes in soil N and P concentrations. A field experiment with water-soluble N (NH4NO3) and P (KH2PO4) additions was conducted at a high-P and a low-P beech (Fagus sylvatica L.) forest site in Germany. Bacterial (16S rRNA), fungal (ITS), and alkaline (phoD) and acid (acpA) phosphatase harboring community structure was investigated by molecular fingerprinting. Bacterial and fungal community structure was mainly related to available P (resin P) in the high-P site but related to more stable P pools (sequentially extracted NaOH/EDTA P) and total P in the low-P site. The increased importance of strategies to access more stable P forms in the low-P site was reflected by a higher relative abundance of some dominant alkaline phosphatase harboring taxa. In the high-P site, increased available P following P addition was the main influencing factor on community structure. By contrast, in the low-P site predominantly N addition induced differences in the microbial communities, which was linked to decreased P concentrations in several soil pools. Increasing N deposition might thus pose greater impacts on microbial communities in low-P compared to high-P sites, by further increasing the already high competition for P. Our findings illustrate that the soil P status in the organic horizon can shape the structure of microbial communities and their roles in the P cycle.

Variations of the Oxidative Ratio across Ecosystem Components and Seasons in a Managed Temperate Beech Forest (Leinefelde, Germany)

The oxidative ratio (OR) of organic material integrates the ratio of CO2 sequestered in biomass vs. O2 produced over longer timescales, but the temporal and spatial variability within a single ecosystem has received very limited attention. Between October 2017 and October 2019, we repeatedly sampled leaves, twigs, bark, outer stem wood, understorey vegetation and litter in a temperate beech forest close to Leinefelde (Germany) for OR measurements across a seasonal and spatial gradient. Plant component OR ranged from 1.004 ± 0.010 for fine roots to 1.089 ± 0.002 for leaves. Inter- and intra-annual differences for leaf and twig OR exist, but we found no correlation with sampling height within the canopy. Leaf OR had the highest temporal variability (minimum 1.069 ± 0.007, maximum 1.098 ± 0.002). This was expected, since leaf biomass of deciduous trees only represents the signal of the current growing season, while twig, stem and litter layer OR integrate multiple years. The sampling years 2018 and 2019 were unusually hot and dry, with low water availability in the summer, which could especially affect the August leaf OR. Total above-ground OR is dominated by the extremely stable stem OR and shows little variation (1.070 ± 0.02) throughout the two sampling years, even when facing extreme events.

B and δ11B biogeochemical cycle in a beech forest developed on a calcareous soil: Pools, fluxes, and forcing parameters

Rock weathering and biological cycling hold the development and sustainability of continental ecosystems, yet the interdependence of macro- and micro-nutrients biogeochemical cycles and their implications for ecosystem functioning remains unclear, despite being of particular importance in the context of global changes. This study focuses on the stocks, fluxes and processes constituting the biogeochemical cycle of boron. Vegetation, soils and solutions were monitored for a full year in a temperate beech forest developed on calcareous soil. Despite an overwhelmingly large B pool in soils, this study points to limited influence of weathering emphasizing the importance of vegetation cycling on this site. The biological imprint on the B cycle is marked by (1) a strong 11B enrichment of solutions compared to the mineral source and (2) systematic correlations observed between B and other strongly recycled elements in all water samples. B isotopes are fractionated within the beech stand with higher values in leaves (23.5‰) and lower in fine roots (−11.7‰), suggesting that the light 10B isotope is preferentially assimilated during plant growth. B isotopic data are consistent with a Rayleigh-like behaviour during xylem transfer leading to an 11B enrichment in the higher parts of the trees, putting internal B transfer as the main driver of the large range of isotopic compositions between plant tissues. B apparent isotopic fractionations are observed in the annually produced biomass and total beech stand, albeit with different values: αxylem-biomass = 0.980 ± 0.009 and 0.990 ± 0.002, respectively, suggesting 11B transfer from old to new tissue. The developed model also points to an isotopic fractionation factor during B uptake much higher than previously evaluated (0.979 < αuptake < 0.994). Overall, this study demonstrates that B isotopes appear as a promising tracer of soil-plant interactions with particular emphasis on tree adaptation to B bioavailability in soil.

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.

Microbial Utilisation of Aboveground Litter-Derived Organic Carbon Within a Sandy Dystric Cambisol Profile

Litter-derived dissolved organic carbon (DOC) is considered to be a major source of stabilised C in soil. Here we investigated the microbial utilisation of litter-derived DOC within an entire soil profile using a stable isotope labelling experiment in a temperate beech forest. The natural litter layer of a Dystric Cambisol was replaced by 13C enriched litter within three areas of each 6.57 m−2 for 22 months and then replaced again by natural litter (switching-off the 13C input). Samples were taken continuously from 0 to 180 cm depths directly after the replacement of the labelled litter, and 6 and 18 months thereafter. We followed the pulse of 13C derived from aboveground litter into soil microorganisms through depth and over time by analysing 13C incorporation into microbial biomass and phospholipid fatty acids. Throughout the sampling period, most of the litter-derived microbial C was found in the top cm of the profile and only minor quantities were translocated to deeper soil. The microbial 13C stocks below 30 cm soil depth at the different samplings accounted constantly for only 6–12% of the respective microbial 13C stocks of the entire profile. The peak in proportional enrichment of 13C in subsoil microorganisms moved from upper (≤ 80 cm soil depth) to lower subsoil (80–160 cm soil depth) within a period of 6 months after switch-off, and nearly disappeared in microbial biomass after 18 months (&amp;lt; 1%), indicating little long-term utilisation of litter-derived C by subsoil microorganisms. Among the different microbial groups, a higher maximum proportion of litter-derived C was found in fungi (up to 6%) than in bacteria (2%), indicating greater fungal than bacterial dependency on litter-derived C in subsoil. However, in contrast to topsoil, fungi in subsoil had only a temporarily restricted increase in litter C incorporation, while in the Gram-positive bacteria, the C incorporation in subsoil raised moderately over time increasingly contributing to the group-specific C stock of the entire profile (up to 9%). Overall, this study demonstrated that microorganisms in topsoil of a Dystric Cambisol process most of the recently deposited aboveground litter C, while microbial litter-derived C assimilation in subsoil is low.

High Fungal Diversity but Low Seasonal Dynamics and Ectomycorrhizal Abundance in a Mountain Beech Forest

Forests on steep slopes constitute a significant proportion of European mountain areas and are important as production and protection forests. This study describes the soil fungal community structure in a European beech-dominated mountain forest stands in the Northern Calcareous Alps and investigates how it is determined by season and soil properties. Samples were collected at high spatial resolution in an area of ca. 100 m × 700 m in May (spring) and August (summer). Illumina MiSeq high-throughput sequencing of the ITS2-region revealed distinct patterns for the soil fungal communities. In contrast to other studies from temperate European beech forest stands, Ascomycota dominated the highly diverse fungal community, while ectomycorrhizal fungi were of lower abundance. Russulaceae, which are often among the dominant ectomycorrhizal fungi associated with European beech, were absent from all samples. Potentially plant pathogenic fungi were more prevalent than previously reported. Only subtle seasonal differences were found between fungal communities in spring and summer. Especially, dominant saprotrophic taxa were largely unaffected by season, while slightly stronger effects were observed for ectomycorrhizal fungi. Soil characteristics like pH and organic carbon content, on the other hand, strongly shaped abundant taxa among the saprotrophic fungal community.

Dynamics of dwarf bamboo populations and tree regeneration over 40 years in a clear-cut beech forest: effects of advance weeding and herbicide application

ABSTRACT We explored the dynamics of dwarf bamboo populations in a beech forest 11 years before and 30 years after clear-cutting. Repeated weeding or herbicide application (sodium chlorate) was used experimentally to reduce or eliminate dwarf bamboo prior to clear-cutting. At the beginning of the study, the understory comprised dense populations of two Sasa species, the dominant S. palmata and the less common S. kurilensis. Both weeding and herbicide application rapidly reduced the cover of S. palmata, but it began to recover prior to clear-cutting and soon exceeded initial cover values. Both weeding and herbicide application reduced the cover of S. kurilensis to near-negligible levels; the cover increased slowly after clear-cutting but remained below initial levels. Weeding or herbicide application resulted in different patterns with respect to height; height decreased rapidly in response to weeding, whereas herbicide application had more gradual effects. Height began to increase after clear-cutting, and S. palmata exceeded its initial height, reaching 1.5–2.0 m in the 10–15 years following clear-cutting. No tree recruits were found in sites where dwarf bamboo was left unmanaged. Weeding and herbicide application facilitated recruitment of Betula ermanii after clear-cutting, but recruits of Fagus crenata, which originally dominated the forest canopy, remained scarce or non-existent at 30 years after clear-cutting. We postulate that natural regeneration of Fagus is nearly impossible following clear-cutting in temperate beech forests in Japan with dense undergrowth of Sasa, even with advance measures to reduce or eliminate Sasa.