Forest subsoils may represent an important C sink in a warming world, but rhizodeposition as the key biogeochemical process determining the C sink strength of mature forests has not yet been ...quantified in subsoils. According to studies conducted in topsoil or laboratory experiments, soil C inputs by root exudation are increasing with increasing temperature and decreasing nutrient availability. We examined whether these relationships apply to forest subsoil by analyzing the response of root exudation to increasing soil depth up to 130 cm in a mature European beech (Fagus sylvatica L.) forest. In two subsequent growing seasons differing in temperature and precipitation, we investigated in situ root exudation with a cuvette-based method and analyzed root morphology, microbial biomass, and soil nutrient availability. We proved that root exudation greatly decreases with soil depth as a consequence of a significant decrease in root-mass specific exudation activity to nearly a fifth of topsoil activity. The decrease in specific metabolic activity from 312 mg C g−1 yr−1 in the topsoil to 80 mg C g−1 yr−1 at 130 cm depth was amplified by an exponential decrease in root biomass per soil volume, leading to a relative decrease in root exudation per volume in the deep subsoil to 2% of topsoil root exudation (1 g C 10 cm−1 m−2 yr−1 at 130 cm depth). Specific root area decreased and mean fine root diameter and root tissue density increased with soil depth, indicating a shift in primary root functionality from fibrous roots in the topsoil to pioneer roots in the subsoil. The decrease in root exudation was accompanied by decreases in soil microbial biomass, extractable organic C (EOC), and N and P availability and increases in the aromatic C portion in SOM, but it did not relate to seasonal differences in climatic conditions. More specifically, it responded positively to an increase in EOC and ETN in the topsoil, but remained at its minimum rate in the SOC-poor subsoil, probably due to a lower organic N and higher mineral N content. The vertical pattern of beech root exudation is in accordance with a strategy to maximize whole-tree carbon-use efficiency, as it reduces C loss by exudation in soil spots where positive priming effects are unlikely, but enhances C exudation where microbes can mine less bioavailable SOM. The exudation patterns further suggest that increased C allocation to root systems as a likely tree response to elevated atmospheric CO2 may not lead to enhanced soil C input by root exudation to subsoils poor in SOM.
•Specific root exudation decreased in the subsoil to less than a fifth.•Root morphology changed from fibrous-type roots in the topsoil to pioneer-type roots in the subsoil.•Root exudation rate was positively related to EOC and ETN in the topsoil.•Exudation was particularly low in subsoil poor in SOM where positive priming effects are unlikely.
We monitored the carbon isotope composition of bulk leaves and specific long-chain alkanes during a four-year litterbag experiment using super(13C-labelled leaves and unlabelled reference leaves of ...the European beech tree (Fagus sylvatica L.). Whereas the isotope composition of alkanes from ) super(1)3C-enriched leaves exhibited a marked decrease in super(13C-content, the isotope composition of unlabelled reference leaves remained nearly constant. We interpreted this difference as evidence for a microbial contribution to the long-chain alkane pool of the decomposing leaves and related it to the progressive invasion of leaves by soil organisms which was revealed upon microscopic examination. These results suggest that long-chain alkanes may not provide an unaltered record of organic carbon isotope composition in soils and sediments.)
• Here, palaeobotanical and genetic data for common beech (Fagus sylvatica) in Europe are used to evaluate the genetic consequences of long-term survival in refuge areas and postglacial spread. • ...Four large datasets are presented, including over 400 fossil-pollen sites, 80 plant-macrofossil sites, and 450 and 600 modern beech populations for chloroplast and nuclear markers, respectively. • The largely complementary palaeobotanical and genetic data indicate that: (i) beech survived the last glacial period in multiple refuge areas; (ii) the central European refugia were separated from the Mediterranean refugia; (iii) the Mediterranean refuges did not contribute to the colonization of central and northern Europe; (iv) some populations expanded considerably during the postglacial period, while others experienced only a limited expansion; (v) the mountain chains were not geographical barriers for beech but rather facilitated its diffusion; and (vi) the modern genetic diversity was shaped over multiple glacial-interglacial cycles. • This scenario differs from many recent treatments of tree phylogeography in Europe that largely focus on the last ice age and the postglacial period to interpret genetic structure and argue that the southern peninsulas (Iberian, Italian and Balkan) were the main source areas for trees in central and northern Europe.
Forest trees facing climate change may persist in a short term through acclimation within the limits of their phenotypic plasticity. In the longer term, however, evolutionary adaptation would be ...needed for populations to thrive in the changed climate, or species may migrate to new areas as climate becomes favorable there. European beech is one of the most important tree species in western and central Europe, and projections indicate that it may contract its southern range and migrate towards northern and north-eastern Europe in the future climates. It is therefore important to recognize the level of variation in climatic adaptation and climatic responsiveness of populations which are likely the source of genetic material for expanding the species range. In this study we examined variation in growth and productivity among 39 European beech populations, which represent the north-eastern margin of the species distribution range. We employed the transfer function and the Universal Response Function approaches to analyze populations’ performance in response to the climatic transfer across five provenance test sites and in relationship to climate at the populations’ origin and planting sites. We found significant but low variation among tested populations in tree diameter (DBH; cm) and Volume index (m3 ha−1) and significant population × site interaction at age 30 years. That variation, however, was only weakly related to gradients of climatic variables represented by the set of sampled populations. The variable performance of populations across planting sites, and the importance of planting sites’ climate in explaining traits’ variation in this experiment confirm the plastic response of examined populations to climate change. Our findings indicate that beech populations from the analyzed region have a high acclimation potential to the projected changes in climate, although for high-altitude populations (from > 600 m a.s.l) the negative effect of transfers to warmer and drier conditions was observed. Detailed knowledge of the plasticity of response and adaptive potential of marginal beech populations in the longer term would be needed to guide management decisions to help future forests to cope with climate change.
•Beech populations at species north-east margin would contribute to range expansion.•Those populations vary in diameter growth and productivity across planting sites.•Variation was related more to the climate of planting site than population origin.•The pattern on variation reflects plastic response to climate change.•Beech populations from analyzed region have overall a high acclimation potential.
The evolutionary potential of long‐lived species, such as forest trees, is fundamental for their local persistence under climate change (CC). Genome–environment association (GEA) analyses reveal if ...species in heterogeneous environments at the regional scale are under differential selection resulting in populations with potential preadaptation to CC within this area. In 79 natural Fagus sylvatica populations, neutral genetic patterns were characterized using 12 simple sequence repeat (SSR) markers, and genomic variation (144 single nucleotide polymorphisms (SNPs) out of 52 candidate genes) was related to 87 environmental predictors in the latent factor mixed model, logistic regressions and isolation by distance/environmental (IBD/IBE) tests. SSR diversity revealed relatedness at up to 150 m intertree distance but an absence of large‐scale spatial genetic structure and IBE. In the GEA analyses, 16 SNPs in 10 genes responded to one or several environmental predictors and IBE, corrected for IBD, was confirmed. The GEA often reflected the proposed gene functions, including indications for adaptation to water availability and temperature. Genomic divergence and the lack of large‐scale neutral genetic patterns suggest that gene flow allows the spread of advantageous alleles in adaptive genes. Thereby, adaptation processes are likely to take place in species occurring in heterogeneous environments, which might reduce their regional extinction risk under CC.
The effect of extreme climate events on ecosystems is an important driver of biotic responses to climate change. For forests, extreme drought has been linked to negative effects such as large‐scale ...mortality and reduced primary production. However, the response of plant communities to extreme drought events remains poorly understood. We used mortality data from a long‐term monitoring programme in the core of the focal species' ranges, in combination with annual growth data from tree‐rings, to study the effect of, and recovery from, an extreme drought event. We examined both the intraspecific and interspecific drought response and explored how differential responses affect competitive dominance between the dominant species Fagus sylvatica and Quercus petraea. Mortality for the most drought‐susceptible species, F. sylvatica, occurred alongside a temporary reduction in competition‐induced mortality of Q. petraea, resulting in the long‐term alteration of the relative abundance of the two species. Significant intraspecific variation occurred in post‐drought recovery in surviving F. sylvatica, with two distinct cohorts identified. A prolonged recovery period was coupled with the failure to regain pre‐drought growth levels in this species, whereas for Q. petraea, no severe drought impacts were observed. This species instead experienced competitive release of growth. Our results demonstrate that ecosystem responses to extreme drought can involve rapid, nonlinear threshold processes during the recovery phase as well as the initial drought impact. These sudden changes can lead to the reordering of dominance between species within communities, which may persist if extreme events become more frequent.
•High survival was found for beech and oak seedlings under different light regimes.•Growth and biomass decreased as shade increased.•Both species had morphological acclimation to shade.
The survival, ...morphological, and growth responses of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) seedlings to different light intensities, from full sunlight to heavy shade, were studied over two growing seasons in a shadehouse experiment. Although shade treatments significantly affected seedling growth, they did not influence seedling survival. Both growth and biomass increased as light intensity increased. Diameter growth of oak seedlings was higher than that of beech. Beech and oak seedlings showed typical acclimation to shade, including greater specific leaf area and height to diameter ratios, and lower leaf thickness and root:shoot ratios with increasing shade. Beech seedlings exhibited greater specific leaf area, and lower leaf thickness and root:shoot ratios than oak seedlings. In spite of the greater growth at full sunlight, the results from this study suggest that beech and oak seedlings would have high survival rates and would acclimate well if underplanted below overstories that reduce the available light to as low as 28% of full light.
•Assessment of tree species composition effects on communities of 13 species groups.•Oak, pine or spruce admixtures to beech affect diversity and community composition.•Effects often depend on tree ...species identity and on the proportion of admixture.•Admixture increases gamma diversity through heterogeneity and associated species.•Forest managers can assess ecological effects of altering tree species composition.
Central Europe's temperate forests are heavily shaped by centuries of human activity. Their natural vegetation, mainly consisting of beech-dominated (Fagus sylvatica) deciduous forests, has been widely replaced by more profitable species grown outside of their natural ranges. This has strongly influenced forest-dwelling communities. Necessary adaptations to changing climatic conditions and the increasing demand for forest ecosystem multifunctionality are reversing these shifts in tree species composition. Integrative approaches that seek to balance production and conservation goals promote mixed forests of beech with spruce (Picea abies), pine (Pinus sylvestris), or oak (Quercus spp.). These mixed forests more closely resemble the natural vegetation and have reduced vulnerability to disturbances compared to coniferous monocultures, but higher commercial value compared to pure beech forests. However, our understanding of how different levels of admixture of commercially relevant tree species to beech forests affect multi-trophic diversity and community composition remains limited.
We investigated herbaceous plants, fungi, oribatid mites, springtails, true bugs, beetles, birds and bats in 41 mature forest stands differing in tree species composition. We assessed the effects of admixtures on abundances and alpha and gamma diversity, i.e. the total number of species per forest type, and a measure of multidiversity by comparing reference beech stands with stands containing varying proportions of admixed species. At the plot level, the proportion of admixtures was especially important regarding oak and pine. Increasing shares of oak positively affected birds, true bugs and herbivorous beetles. Increasing shares of pine benefitted herbivorous true bugs and understory plants but negatively affected other true bugs, bats, and litter-decomposing fungi. Spruce admixture resulted in higher saproxylic beetle and bird diversity. At the landscape level, admixture significantly increased gamma diversity in plants, mycorrhizal and litter decomposing fungi and herbivorous and saproxylic beetles. Only springtail gamma diversity decreased in the presence of admixture. Admixture also significantly altered community composition for six out of 13 taxa. Indicator species were found for all forest types, and seven species groups included species significantly associated with pure beech stands.
Our results indicate that forestry decisions determine forest biodiversity across trophic levels via tree species composition, combining habitat heterogeneity effects and tree species-specific associations. Even low shares of admixed species affect local abundances and diversity. By displacing some species while benefitting others, admixing also alters community composition. This study provides a basis for estimating how altering tree species composition in Central European forests changes the diversity and composition of forest communities.
Key message
In case of a prolonged drought, the stored carbohydrates in trees were remobilized to fuel survival functions until their nearly depletion at death stage.
Dynamic global vegetation models ...project forest tree mortality in response to the recurrent severe droughts likely in the future. However, these models should better take into account the physiological processes involved in tree mortality. Faced with severe drought, the
Fagus sylvatica L.
tree strongly limits its cambial growth. This suggests that readjustments in carbon (
C
) allocation among sink functions are taking place in response to the lack of water and this could allow tree’s survival. For 3 years, we induced a water shortage on 8-year-old beech trees in a rain exclusion system. During this period, we analysed the consequences of severe drought on survival rate, growth, and non-structural carbohydrate (NSC) dynamics in the aboveground and belowground compartments of control, water-stressed living, and dead trees. The survival rate after 3 years of drought was 87%, while primary and secondary growth was strongly reduced. The first 2 years, NSC concentrations increased in all tree compartments (stem, branches, and roots) in response to drought. However, during the third year, starch dropped markedly in water-stressed trees, while soluble sugar concentrations remained similar to control trees. All the compartments in dead trees were virtually empty of starch and soluble sugars. Maintaining an active
C
storage function at the expense of growth was certainly key to
F. sylvatica
survival under prolonged extreme drought conditions. Process-based models predicting mortality should better take into account
C
storage and remobilization processes in forest trees.
In the course of global climate change, Central Europe is experiencing more frequent and prolonged periods of drought. The drought years 2018 and 2019 affected European beeches (
L.) differently: ...even in the same stand, drought-damaged trees neighboured healthy trees, suggesting that the genotype rather than the environment was responsible for this conspicuous pattern. We used this natural experiment to study the genomic basis of drought resistance with Pool-GWAS. Contrasting the extreme phenotypes identified 106 significantly associated single-nucleotide polymorphisms (SNPs) throughout the genome. Most annotated genes with associated SNPs (>70%) were previously implicated in the drought reaction of plants. Non-synonymous substitutions led either to a functional amino acid exchange or premature termination. An SNP assay with 70 loci allowed predicting drought phenotype in 98.6% of a validation sample of 92 trees. Drought resistance in European beech is a moderately polygenic trait that should respond well to natural selection, selective management, and breeding.
PDF
