Beech Roots Research Articles

Forest protection and protection forest: Tree root degradation over hydrological shallow landslides triggering

The potential use of protection forests to combat shallow slope instabilities is becoming increasingly important and considerable, especially in the light of the recent landslides and debris/mud flows in regions triggered by rainfalls with increased intensity. Tree vegetation has been constantly subjected to silvicultural activity both in exclusively productive forest areas and in more conservative ones meant to contrast hydrogeological risk. It is important to quantify the root system dynamics in order to correctly evaluate the impact of wood felling or plants death on slope stability. Based on field investigation (on experimental plots and 29 occurred landslides) and numerical modelling (on slope stability and root distribution), the aim of this work is to determine the effects of the evolution of the mechanical characteristics of root systems (and consequently on landslide probability). The paper investigates variations over time in the hazard of rainfall-triggered landslides as a result of root degradation after forest cutting (or death). The case under study is related to experimental investigations aimed at determining the tensile strength and elasticity of root samples of trees dead within a decade, which correspond to decreasing values of soil cohesion (root reinforcement). Two kinds of samples were taken into account: living beech roots from protected wood areas to determine the current characteristics and roots from dead beeches (felled in previous years and at present in degradation) to analyse the evolution of root mechanical characteristics. To analyse the stability of representative slopes, we calculated the return time associated with a rainfall event, which in saturated conditions would lead to the attainment of the limit value of the safety factor and the associated hazard for different rainfall durations during a fixed period of time. Information about the increasing risk of collapse with the degradation of root system was obtained and compared with landslides occurrence in forested slopes of the study area. The results of the present paper show that such slopes may remain stable if they are covered with intact protective vegetation, but they will become unstable if the conditions of the forest deteriorate or after a wooded area dies off: within a decade of tree death the root system of protection forests loses most of its soil-stabilising function.

Root-induced tree species effects on the source/sink strength for greenhouse gases (CH4, N2O and CO2) of a temperate deciduous forest soil

Through their leaf litter and throughfall water, tree species can have a pronounced influence on soil chemistry. However, there is little knowledge of species-specific root effects on greenhouse gas fluxes between forest soils and the atmosphere. By growing saplings of beech (Fagus sylvatica) and ash (Fraxinus excelsior) in monoculture or mixture at defined atmospheric and soil conditions in rhizotrons, we tested four hypotheses related to potential root-induced tree species effects on the uptake of CH4 and the emission of N2O and CO2 from the soil. This design excluded putative effects of leaf litter mineralisation on trace gas fluxes. Gas fluxes were measured biweekly using the closed chamber technique; the CO2 derived from root respiration was estimated, and the concentration of organic acids in the rhizosphere solution was analysed. Rhizotrons planted with ash took up significantly more CH4 and emitted less N2O than control rhizotrons without plants. CH4 and N2O fluxes from beech rhizotrons did not differ from the root-free control but were significantly smaller (CH4) or higher (N2O) than the fluxes from the ash treatment. While root respiration of ash was higher than of beech, root-induced soil respiration was higher in the rhizosphere of beech roots. The concentration of organic acids tended to be higher in the rhizosphere of beech and also the composition was different from that of ash. We conclude that tree species identity may substantially alter the soil source/sink strength for greenhouse gases through root-related processes.

Beech roots are simultaneously colonized by multiple genets of the ectomycorrhizal fungus Laccaria amethystina clustered in two genetic groups

In this study, we characterize and compare the genetic structure of aboveground and belowground populations of the ectomycorrhizal fungus Laccaria amethystina in an unmanaged mixed beech forest. Fruiting bodies and mycorrhizas of L. amethystina were mapped and collected in four plots in the Świętokrzyskie Mountains (Poland). A total of 563 fruiting bodies and 394 mycorrhizas were successfully genotyped using the rDNA IGS1 (intergenic spacer) and seven simple sequence repeat markers. We identified two different genetic clusters of L. amethystina in all of the plots, suggesting that a process of sympatric isolation may be occurring at a local scale. The proportion of individuals belonging to each cluster was similar among plots aboveground while it significantly differed belowground. Predominance of a given cluster could be explained by distinct host preferences or by priority effects and competition among genets. Both aboveground and belowground populations consisted of many intermingling small genets. Consequently, host trees were simultaneously colonized by many L. amethystina genets that may show different ecophysiological abilities. Our data showed that several genets may last for at least 1 year belowground and sustain into the next season. Ectomycorrhizal species reproducing by means of spores can form highly diverse and persistent belowground genets that may provide the host tree with higher resilience in a changing environment and enhance ecosystem performance.

Effect of flooding on C metabolism of flood-tolerant (Quercus robur) and non-tolerant (Fagus sylvatica) tree species

Flooding is assumed to cause an energy crisis in plants because-due to a lack of O(2)-mitochondrial respiration is replaced by alcoholic fermentation which yields considerably less energy equivalents. In the present study, the effect of flooding on the carbon metabolism of flooding-tolerant pedunculate oak (Quercus robur L.) and flooding-sensitive European beech (Fagus sylvatica L.) seedlings was characterized. Whereas soluble carbohydrate concentrations dropped in roots of F. sylvatica, they were constant in Q. robur during flooding. At the same time, root alcohol dehydrogenase activities were decreased in beech but not in oak, suggesting substrate limitation of alcoholic fermentation in beech roots. Surprisingly, leaf and phloem sap sugar concentrations increased in both species but to a much higher degree in beech. This finding suggests that the phloem unloading process in flooding-sensitive beech was strongly impaired. It is assumed that root-derived ethanol is transported to the leaves via the transpiration stream. This mechanism is considered an adaptation to flooding because it helps avoid the accumulation of toxic ethanol in the roots and supports the whole plant's carbon metabolism by channelling ethanol into the oxidative metabolism of the leaves. A labelling experiment demonstrated that in the leaves of flooded trees, ethanol metabolism does not differ between flooded beech and oak, indicating that processes in the roots are crucial for the trees' flooding tolerance.

Ectomycorrhizal fungal diversity, tree diversity and root nutrient relations in a mixed Central European forest

Knowledge is limited about whether root nutrient concentrations are affected by mixtures of tree species and interspecific root competition. The goal of this field study was to investigate root nutrient element concentrations in relation to root and ectomycorrhizal (EM) diversity in six different mixtures of beech (Fagus sylvatica), ash (Fraxinus excelsior) and lime (Tilia sp.) in an old-growth, undisturbed forest ecosystem. Root biomass and nutrient concentrations per tree taxon as well as the abundance and identity of all EM fungi were determined in soil cores of a volume of 1 L (r=40 mm, depth=200 mm). Stand-level nutrient concentrations in overall root biomass and H' (Shannon-Wiener diversity) were obtained by pooling the data per stand. At stand level, Shannon H' for roots and aboveground tree species abundance were correlated. H' for roots and EM fungi were not correlated because of the contribution of ash roots that form only arbuscular mycorrhizal but no EM associations. Nutrient element concentrations in roots showed taxon-related differences and increased in the following order: beech ≤ lime < ash with the exception of calcium (Ca), which was lower in ash. Stand-level concentrations of Ca, magnesium, potassium and sulfur in roots increased with increasing tree diversity because of two effects: increasing contribution of ash roots to the mixture and increasing Ca accumulation in beech roots with increasing root diversity. On a small scale, increasing root diversity, but not EM diversity, was correlated with decreasing P concentrations in beech roots pointing to interspecific tree competition. Nitrogen (N) concentrations of beech roots were unaltered in relation to root and EM diversity. Opposing behavior was observed for lime and ash: the N concentrations in lime roots increased, whereas those in ash roots decreased with increasing EM diversity in a given soil volume. This suggests that EM diversity facilitates N acquisition of lime roots at the expense of non-EM ash.

Soil base saturation affects root growth of European beech seedlings§

AbstractTo assess the potential effects of Al toxicity on the roots of young European beech (Fagus sylvatica L.), seeds were sown in soil monoliths taken from the Ah and B horizons of forest soils with very low base saturation (BS) and placed in the greenhouse. The Ah horizons offered a larger supply of exchangeable cation nutrients than the B horizons. After 8 weeks of growth under optimal moisture conditions, the seedlings were further grown for 14 d under drought conditions. Root‐growth dynamics were observed in rhizoboxes containing soils from the Ah and B horizons. The concentrations of Al3+, base cations, and nitrate in the soil solution and element concentrations in the root tissue were compared with above‐ and belowground growth parameters and root physiological parameters. There was no strong evidence that seedling roots suffered from high soil‐solution Al3+ concentrations. Within the tested range of BS (1.2%–6.5%) our results indicated that root physiological parameters such as O2 consumption decreased and callose concentration increased in soils with a BS &lt; 3%. In contrast to the B horizons, seedlings in the Ah horizons had higher relative shoot‐growth rates, specific root lengths, and lengths and branching increments, but a lower root‐to‐shoot ratio and root‐branching frequency. In conclusion, these differences in growth patterns were most likely due to differences in nutrient availability and to the drought application and not attributable to differences in Al3+ concentrations in the soil solution.

Analysis of natural Fagus sylvatica L. s.l. regeneration in low elevation stands located in the central part of the Evros region in northeastern Greece: Is sprout origin regeneration significant for species maintenance?

The aim of this study was (a) to analyse natural Fagus sylvatica L. s.l. regeneration in low elevation stands located in the central part of Evros region in northeastern Greece in relation to factors such as site productivity, type of silvicultural treatment and regeneration origin and (b) to determine whether or not sprout origin regeneration is significant for the maintenance of beech stands. One hundred and twenty plots (3 m × 3 m) were established in areas where thinnings and regeneration fellings had taken place, and in two site productivity regimes. In each plot, the number of beech seedlings, saplings, and stump or root sprouts (regeneration plants) with a height of up to 3 m was counted, and their height measured. Our findings indicate that even though reproduction by seed is the predominant regeneration mechanism in our stands, in the medium productivity sites sprouts represent a significant percentage of the total number of plants. Moreover, sprouting functions as a mechanism of maintenance of beech stands in medium productivity sites. During the regeneration fellings practised in this area, it is advisable to cut the seedlings and saplings of the advanced regeneration in order to supplement the seed-derived plants with seedling sprouts.

Aggressiveness of Phytophthora cactorum, P. citricola I, and P. plurivora from European Beech.

Phytophthora cactorum, P. citricola I, and P. plurivora cause bleeding cankers on mature European beech (Fagus sylvatica) trees in the northeastern United States. Inoculation experiments were conducted to compare the aggressiveness of the three Phytophthora spp. on stems, leaf disks, and roots of European beech and common lilac (Syringa vulgaris) seedlings. Isolates were obtained from bleeding cankers on European beech from five cities in New York (Albany, Ithaca, Oyster Bay, Plainview, and Rochester) and from a bleeding canker on sugar maple in Ithaca, NY. Stems were inoculated with colonized agar plugs, leaf disks with a zoospore suspension, and roots via infested soil at three inoculum levels. All organs of inoculated beech and lilac developed disease except for lilac roots inoculated with zoospores of P. cactorum. Disease incidence, severity, and plant survival were dependent on isolate and were also influenced by the tissue inoculated and host. Isolates of P. cactorum were the least aggressive and caused less necrosis than isolates of P. citricola I and P. plurivora. Results emphasize the utility of stem and root inoculation for evaluation of this canker disease and underscore critical differences in species aggressiveness.

The presence of amino acids affects inorganic N uptake in non-mycorrhizal seedlings of European beech (Fagus sylvatica)

To investigate the impact of organic N compounds for inorganic nitrogen uptake in the rhizosphere, we fed ammonium nitrate with or without amino acids (i.e., glutamine or arginine) to the roots of non-mycorrhizal beech (Fagus sylvatica L.) seedlings under controlled conditions at different levels of N availability. Uptake of individual N sources was determined from ¹⁵N (inorganic N) and ¹⁵N ¹³C (organic N) accumulation in the roots. In addition, gene fragments encoding proteins involved in N uptake and metabolism were cloned from beech for gene expression analyses by quantitative real-time PCR in the roots. Generally, ammonium was preferred over nitrate as N source. Organic N sources were taken up by beech roots as intact molecules. Uptake of organic N was significantly higher than inorganic N uptake, thus contributing significantly to N nutrition of beech. Depending on the level of N availability, inorganic N uptake was negatively affected by the presence of organic N sources. This result indicates an overestimation of the contribution of inorganic N uptake to N nutrition of beech in previous studies. Apparently, association with mycorrhizal fungi is not essential for organic N uptake by beech roots. Gene expression analyses showed that transcriptional regulation of the amino acid transporters FsCAT3, FsCAT5, FsAAT and FsAAP and the ammonium transporter FsAMT1.2 in the roots is involved in N nutrition of beech.

Below-ground carbon allocation in mature beech and spruce trees following long-term, experimentally enhanced O 3 exposure in Southern Germany

Canopies of adult European beech ( Fagus sylvatica) and Norway spruce ( Picea abies) were labeled with CO 2 depleted in 13C to evaluate carbon allocation belowground. One-half the trees were exposed to elevated O 3 for 6 yrs prior to and during the experiment. Soil-gas sampling wells were placed at 8 and 15 cm and soil CO 2 was sampled during labeling in mid-late August, 2006. In beech, δ 13CO 2 at both depths decreased approximately 50 h after labeling, reflecting rapid translocation of fixed C to roots and release through respiration. In spruce, label was detected in fine-root tissue, but there was no evidence of label in δ 13CO 2. The results show that C fixed in the canopy rapidly reaches respiratory pools in beech roots, and suggest that spruce may allocate very little of recently-fixed carbon into root respiration during late summer. A change in carbon allocation belowground due to long-term O 3 exposure was not observed.

Competition for nitrogen sources between European beech (Fagus sylvatica) and sycamore maple (Acer pseudoplatanus) seedlings

To investigate the short-term consequences of direct competition between beech and sycamore maple on root N uptake and N composition, mycorrhizal seedlings of both tree species were incubated for 4 days (i.e. beech only, sycamore maple only or both together) in an artificial nutrient solution with low N availability. On the fourth day, N uptake experiments were conducted to study the effects of competition on inorganic and organic N uptake. For this purpose, multiple N sources were applied with a single label. Furthermore, fine roots were sampled and analysed for total amino acids, soluble protein, total nitrogen, nitrate and ammonium content. Our results clearly show that both tree species were able to use inorganic and organic N sources. Uptake of inorganic and organic N by beech roots was negatively affected in the presence of the competing tree species. In contrast, the presence of beech stimulated inorganic N uptake by sycamore maple roots. Both the negative effect of sycamore maple on N uptake of beech and the positive effect of beech on N uptake of sycamore maple led to an increase in root soluble protein in beech, despite an overall decrease in total N concentration. Thus, beech compensated for the negative effects of the tree competitor on N uptake by incorporating less N into structural N components, but otherwise exhibited the same strategy as the competitor, namely, enhancing soluble protein levels in roots when grown under competition. It is speculated that enhanced enzyme activities of so far unknown nature are required in beech as a defence response to inter-specific competition.

Root distribution of under-planted European beech (Fagus sylvatica L.) below the canopy of a mature Norway spruce stand as a function of light

Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings (Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm) soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech with increasing light intensity for both fine and coarse roots.

Carbon and nitrogen balance in beech roots under competitive pressure of soil-borne microorganisms induced by girdling, drought and glucose application

The goal of this work was to increase the understanding of factors regulating nitrogen (N) competition between roots and soil microbes. For this purpose, root assimilate supply was diminished or abolished in beech (Fagus sylvatica L.) seedlings by girdling, drought stress or a combination of both factors. This was revealed by 13C tracer abundance in root tips after 13CO2 pulse labelling of the shoots. Analysis of different root tip fractions revealed that only 6% were ectomycorrhizal. Carbon (C) allocation to ectomycorrhizal and vital non-mycorrhizal root tips was ~26% higher than to distorted root tips. Drought resulted in ~30% increased ammonium (NH4+) and amino acid concentrations in roots and ~65% increased soil NH4+ concentrations, probably because of lower consumption of NH4+ by free-living microorganisms. Root uptake of glutamine of 13 nmol g–1 fresh mass h–1 decreased 2-fold with drought, although the number of vital root tips did not decrease. Carbon content in biomass of free-living microbes increased with glucose application regardless of drought, resulting in significant depletion in soil nitrate (NO3–), root NH4+ and amino acid concentrations. Our results suggest that the root–soil system of young beech trees was C-limited, and this prevented amino acid metabolism in roots and microbial NO3– consumption in the soil, thereby exerting feedback inhibition on uptake of inorganic N by roots. We suggest that rhizodeposition is a key link in regulating the plant–microbial N balance.

Differences in fine root traits between Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) - A case study in the Kysucké Beskydy Mts

Interspecific comparisons of the fine root “behaviour” under stressful situations may answer questions related to resistance to changing environmental conditions in the particular tree species. Our study was focused on Norway spruce (&lt;I&gt;Picea abies&lt;/I&gt; [L.] Karst.) and European beech (&lt;I&gt;Fagus sylvatica&lt;/I&gt; L.) grown in an acidic soil where acidity was caused by past air pollution in the Kysucké Beskydy Mts., North-Western Slovakia. Between April and October 2006, the following fine root traits were studied: biomass and necromass seasonal dynamics, vertical distribution, production, mortality, fine root turnover and production to mortality ratio. Sequential soil coring was repeatedly implemented in April, June, July, September, and October including the soil layers of 0–5, 5–15, 15–25, and 25–35 cm. Results indicated that spruce had a lower standing stock of fine roots than beech, and fine roots of spruce were more superficially distributed than those of beech. Furthermore, we estimated higher seasonal dynamics and also higher turnover of fine roots in spruce than in beech. The production to mortality ratio was higher in beech than in spruce, which was hypothetically explained as the effect of drought episodes that occurred in July and August. The results suggested that the beech root system could resist a physiological stress better than that of spruce. This conclusion was supported by different vertical distributions of fine roots in spruce and beech stands.

Rhizospheric NO interacts with the acquisition of reduced N sources by the roots of European beech (Fagus sylvatica L.)

The gas phase of the soil plays an important role in plant growth and development. We investigated the effect of rhizospheric NO as a signalling compound for N uptake of beech roots. Following exposure to NO, ammonium and glutamine uptake into roots were determined using 15N-labelling, and gene expression of selected transporters was analysed by quantitative real-time PCR. Uptake of both N sources increased significantly with elevated NO concentration. However, with one exception, this increase was not reflected in up-regulation of expression of the respective transporters.

Ectomycorrhizal communities within beech (Fagus sylvatica L.) forests that naturally regenerate from clear-cutting in northern Spain

The objectives of the work described here were to evaluate the diversity of ectomycorrhizal (ECM) fungi within Spanish beech (Fagus sylvatica L.) forests subjected to clear-cutting and natural regeneration and to elucidate the extent to which the carbohydrate concentration in roots of trees of different ages and sizes is related to ECM colonization. The study concerned an unmanaged forest, a stand clear-cut in 1996 and another clear-cut in 2001. ECM colonization of beech roots showed seasonal dynamics in the disturbed areas, but the percentage of roots colonized by ECM was not always related to the accumulation of non-structural carbohydrates. The composition of ECM communities differed between different stands and 40% of ECM morphotypes only occurred in disturbed ecosystems. However, comparable numbers of different ECM morphotypes (24, 25) were found in the three beech stands. This finding indicates that ECM diversity was quite high and similar within disturbed and unmanaged areas. This finding suggests that (1) ECM diversity was not affected by the size and age of trees and (2) the potential of ECM inocula remained high within clear-cut areas. Consequently, the introduction of ECM inocula by silvicultural practices would not be needed to improve the regeneration of clear-cut areas described in our study.

Combined application of computer tomography and light microscopy for analysis of conductive xylem area in coarse roots of European beech and Norway spruce

Axial water transport in trees is mainly deter- mined by the gradient of negative water pressure and the structure of conductive xylem elements (i.e. conduits) con- necting the fine roots with the foliage. There is still an essential lack of knowledge concerning the relationship between wood structure and hydraulic properties, especially of coarse roots. To this end, the study aimed (1) to work out a novel approach, based on the combination of computer tomography (CT) and light microscopy (LM), for determin- ing the cumulative cross-sectional lumen area of conduits involved in the water transport of coarse roots in European beech (Fagus sylvatica) and Norway spruce (Picea abies) and (2) to demonstrate its adequacy in quantifying the functional relationship between sapwood anatomy and ascending water mass flow in the xylem. The cross-sectional sapwood area of coarse roots was assessed through CT. The cumulative cross- sectional lumen area of conduits in the sapwood (i.e. the lumen area of conductive conduits) was measured by LM in combination with interactive image analysis. The new approach was developed with coarse roots of both the tree species growing in a 60-year-old mixed forest in Bavaria, Germany. The combination of the two methods unveiled spruce to possess a distinct sapwood/heartwood boundary in small-diameter roots, whereas such roots of beech reflected a gradual transition zone; only large-diameter roots displayed a distinct boundary in beech. Additionally, the cumulative lumen area of conductive conduits was found to be approxi- mately 12% of the total coarse root cross-sectional area in both the tree species. The new approach of measuring the conductive lumen area of coarse-root conduits yielded levels of specific sap flow (i.e. axial conductivity) that substantially differed from those derived from commonly applied meth- ods, which were based on sap flow per unit of total cross- sectional root area or xylem cross-sectional area of individual roots. The combination of CT and LM will facilitate func- tional comparisons of woody roots differing in diameter and of tree species of different anatomical xylem structure.

Effects of drought and canopy ozone exposure on antioxidants in fine roots of mature European beech (Fagus sylvatica)

We quantified ascorbate, glutathione and alpha-tocopherol in fine roots of mature Fagus sylvatica L. under free-air canopy ozone (O(3)) exposure (twice ambient O(3) concentration, 2x[O(3)]) during two growing seasons that differed in the extent of summer drought (exceptional drought year 2003, average year 2004). This design allowed us to test whether O(3) exposure or drought, or both, affected root antioxidants during the growing season. In both years, root ascorbate and alpha-tocopherol showed a similar relationship with volumetric soil water content (SWC): ascorbate concentrations on a root dry mass basis increased from about 6 to 12 micromol g(-1) when SWC dropped from 25 to 20%, and a-tocopherol increased from 100 to 150 nmol g(-1) at SWC values below 20%. Root glutathione showed no relationship with SWC or differences between the dry and the average year, but it was significantly and consistently diminished by 2x[O(3)]. Our results were inconclusive as to whether shoot-root translocation of glutathione or glutathione production in the roots was diminished. Phloem glutathione concentrations in the canopy remained constant, but reduced transport velocity in the phloem and, as a consequence, reduced mass flow of glutathione cannot be ruled out.

Genotypic variation and phenotypic plasticity in the drought response of fine roots of European beech

How temperate trees respond to drier summers, as predicted by climate change models for parts of Europe and eastern North America, will depend on the drought susceptibility of the root systems. We investigated the importance of the genetic constitution for the belowground drought response of European beech (Fagus sylvatica L.), in four populations from regions differing in precipitation (520-970 mm year(-1)). Saplings were grown at ample (10 vol.%; well-watered) or reduced (5 vol.%; drought treatment) soil water content in the Göttingen Rhizolab Facility for two consecutive summers, and the responses of fine root biomass, root morphology, root depth distribution, and fine root production and turnover were investigated by a combined mini-rhizotron and harvest technique approach. In the drought treatment, total root mass per plant was reduced by 30-40% as a result of: (1) a reduction in median fine root lifespan by roughly 50% and hence an increase in fine root turnover; and (2) a 10-fold reduction in relative fine root growth rate (productivity per standing root biomass). The root:shoot ratio did not increase with drought. Although beech plants originating from drier climates tended to reduce their root biomass in response to drought less than those from wetter climates, analyses of variance revealed no significant influence of genotype on root mass, morphology, growth rate or turnover. However, most fine root traits showed marked differences between the well-watered and drought treatments. We conclude that beech saplings respond to summer drought primarily by shortening root lifespan, whereas root system structure and root:shoot carbon partitioning pattern are unaltered. Beech fine root growth and turnover exhibited high phenotypic plasticity, but genotypic variation was of minor importance. In contrast, genotype had a strong influence on leaf and shoot morphogenesis and growth.

Dating of small gully formation and establishing erosion rates in old gullies under forest by means of anatomical changes in exposed tree roots (Southern Poland)

Small gullies occur in forested gully systems on the undulating loess plateau in southern Poland. The old gully hillslopes are mainly covered with 200-year old beech trees in contrast with the surface of the summit plateau, which is cultivated agricultural land. Beech roots are exposed in the gullies through erosion. Wood vessels in the root tree rings divide into early wood and late wood and, after the roots are exposed, start to make fewer vessels. These anatomical changes in root tree rings allow us to date erosion episodes. Small gullies form in a different manner on the valley floor and on hillslopes. In valley bottoms, erosion features are often formed at some distance from one another, and in time small gullies combine to form a single, longer one. Depending on local conditions, such as the hillslope profile, hillslopes may exhibit headward erosion or may be eroded downwards. Hilllope gullies may be transformed into side valleys as a result of gradual widening and deepening. Dating the exposure of roots indicates that small gullies had already formed in the valley system by 1949. Intensive gully erosion was recorded between 1984 and 2002, during intense precipitation in 1984 and, of particular note, during the extraordinary flood of 1997 which affected all of Central Europe. The mean rate of small gully erosion in the old gully system studied is 0.63 m/year. On hillslopes the mean gully erosion rate is 0.21–0.52 m/year, and on the valley bottoms 0.18–1.98 m/year. High bottom erosion rates resulted from the emergence of long gullies during the erosion episodes in 1984 and 1997. Sheet flow in valley floors intensifies at times of heavy rainfall which causes long gullies to form. Taking into account the fact that conditions favoured erosion, the rate at which the old gullies under forest were transformed should be considered slow. New side gullies form slowly within the valley and it appears that if erosion progressed at the rate observed, new side valleys would take a few hundred years to form.