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Noninvasive and nondestructive root phenotyping techniques under field conditions are sorely needed to advance plant root science. Soil polarization measured by electrical capacitance (ECsoil) has the potential to meet this requirement, but whether it specifically detects root properties remains unexplored. We carried out manipulative experiments where wheat (Triticum aestivumL.) and maize (Zea maysL.) roots were buried in soil or immersed in hydroponic solution combined with pot trials to reveal the mechanism of root trait detection by ECsoil, while a field experiment was conducted to test its feasibility to determine root depth distribution. We found that ECsoilmeasured at low current frequency (< 1 kHz) was not significantly affected by the addition of roots to the system either by burying roots in soil or immersing them in solution. At frequency greater than10 kHz a shift occurred, and root polarization contributed more to ECsoilwhich was positively correlated with root volume. When ECsoilwas measured at high frequency (30 kHz −100 kHz) it was well correlated with root volume vertical distribution in the field. The measurement error after soil moisture calibration at depths of 10 cm, 20 cm, 30 cm and 40 cm was 0.4%, 12.0%, 1% and 34%, respectively. Our results demonstrate that ECsoilis a robust method to measurein situroot distribution and we believe the newly available high frequency measurement equipment combined with novel root prediction models will enable ECsoilto be widely used for root phenotyping in the future.

Background and aims In this study, the potential of non-intrusive root electrical capacitance (CR) measurements for monitoring the seasonal changes and drought response of root activity was tested on two grassland species in a climate change experiment. Methods CR was detected between a ground electrode inserted into the soil and a plant electrode attached to the stem of the perennial grass Stipa borysthenica and the biennial herb Crepis rhoeadifolia in control and drought plots throughout two growing seasons. A pilot study revealed that CR was strongly correlated with root biomass for a given time and soil water content. The effect of changing soil water content on the measured CR value was accounted for by means of species-specific experimental calibrations. Results Root activity (CR) was found to peak at the flowering stage in late spring (S. borysthenica) or early summer (C. rhoeadifolia). Both the natural shortage of rainfall and the experimental summer drought reduced root activity in both species. Stipa borysthenica displayed great plasticity in root activity, including quick post-treatment recovery during the rainy autumn. The changes observed in root activity were similar to those previously recorded using conventional root investigation techniques (i.e. destructive, minirhizotron, ingrowth core) in temperate grasslands. Conclusions Root capacitance measurements proved to be adequate for monitoring root activity in situ in natural grassland. The method could be particularly useful in studies where plant injury or soil disturbance need to be avoided.

Background and aims This study was the first to test the efficiency of monitoring root electrical capacitance (CR*) non-destructively in the field to evaluate crop development under different environmental conditions. Methods A free-air CO2 enrichment (FACE) experiment was performed with two winter wheat cultivars, two levels (low and high) of nitrogen supply and two (ambient and elevated) of [CO2] in three replicate plots over two years. The validity of CR* as a proxy for root uptake activity was confirmed by tracking the ceptometer-based leaf area index (LAI). Results Repeated CR* measurements clearly demonstrated the seasonal dynamics in root development, with a peak at flowering, and the delayed growth in the second year caused by the unfavourable meteorological conditions. From the vegetative to flowering stages, CR* was strongly correlated with LAI (R2: 0.897–0.962). The positive effect of higher N supply and elevated [CO2] on crop growth was clearly indicated by the higher CR* values, associated with increased LAI, shoot dry mass (SDM) at flowering and grain yield (GY). The maximum CR* was closely related to GY (R2: 0.805 and 0.867) when the data were pooled across the N and CO2 treatments and the years. Unlike CR* and GY, SDM and LAI were significantly lower in the second year, presumably due to the enhanced root/shoot ratio induced by a severe spring drought. Conclusions The present results convincingly demonstrated the potential of the in situ root capacitance method to assess root responses dynamically, and to predict crop GY.

This study evaluated the concurrent application and the results of the root electrical capacitance (CR) and minirhizotron (MR) methods in the same plant populations. The container experiment involved three winter wheat cultivars, grown as sole crops or intercropped with winter pea under well-watered or drought-stressed conditions. The wheat root activity (characterized by CR) and the MR-based root length (RL) and root surface area (RSA) were monitored during the vegetation period, the flag leaf chlorophyll content was measured at flowering, and the wheat shoot dry mass (SDM) and grain yield (GY) were determined at maturity. CR, RL and RSA exhibited similar seasonal patterns with peaks around the flowering. The presence of pea reduced the maximum CR, RL and RSA. Drought significantly decreased CR, but increased the MR-based root size. Both intercropping and drought reduced wheat chlorophyll content, SDM and GY. The relative decrease caused by pea or drought in the maximum CR was proportional to the rate of change in SDM or GY. Significant linear correlations (R2: 0.77–0.97) were found between CR and RSA, with significantly smaller specific root capacitance (per unit RSA) for the drought-stress treatments. CR measurements tend to predict root function and the accompanying effect on above-ground production and grain yield. The parallel application of the two in situ methods improves the evaluation of root dynamics and plant responses.

This methodological study evaluated the efficiency of predicting aboveground biomass and grain yield in field-grown winter wheat by measuring the saturation root electrical capacitance at anthesis. Three cultivars were grown over a three-year period as sole crops and intercropped with winter pea at halved wheat density. The root capacitance readings were converted into saturation root electrical capacitance using the relevant soil water content, according to an empirical function. At plant scale, saturation root electrical capacitance at anthesis showed a significant (p < 0.001) linear regression with the total aboveground biomass (R2: 0.653-0.765) and grain yield (R2: 0.585-0.686) at maturity for each cultivar. At stand scale, both the mean saturation root electrical capacitance and shoot dry mass at anthesis and grain yield varied over the years, and were consistently higher for the intercrops compared to the sole crops. The relative increase in saturation root electrical capacitance due to intercropping corresponded with the changes in shoot dry mass and grain yield, especially in dry years. Saturation root electrical capacitance was significantly correlated with shoot dry mass (R2: 0.714-0.899) and grain yield (R2: 0.742-0.877) for each cultivar across all cropping systems and years. In conclusion, by mitigating the soil water content effect, the measurement of saturation root electrical capacitance at anthesis is adequate to forecast grain yield and cultivar response to a changing environment.

Tenyészedény-kísérletben vizsgáltuk, hogy a szárazságstressz és az arbuszkuláris mikorrhiza gomba (AMF) oltás milyen változást okoz a búza gyökérnövekedésében, és ez hogyan követhető nyomon a gyökér–talaj rendszer elektromos kapacitásának (CR) in situ mérésével. A kísérletet randomizált blokk elrendezésben végeztük két búzafajtával (Mv. Hombár őszi és TC 33 tavaszi), kétféle öntözéssel (optimális és szárazságstressz) és kétféle oltással (oltatlan és AM-gombával oltott), 12 ismétlésben. A tenyészidőszakban monitoroztuk a CR-t, valamint mértük a sztómakonduktanciát és a levelek klorofilltartalmát (SPAD-értékben). A kísérlet végén TTC-teszttel vizsgáltuk a gyökerek életképességét, mikroszkópos vizsgálattal becsültük az AM gomba gyökérkolonizációját, valamint meghatároztuk a gyökér- és hajtástömeget. A vízhiány szignifikánsan (9–35%-kal) csökkentette a búzafajták gyökértömegét, mely a mért CR-értékekben is tükröződött. A szárazság okozta CRés biomassza-csökkenés jelentősebb volt a TC 33, mint az Mv. Hombár esetében. A CR monitorozásával kimutattuk a növények stressz utáni regenerációját és a fajták eltérő gyökérnövekedési dinamikáját. Az AMF oltás csökkentette a CR-t és a biomassza-produkciót (29–42%-kal), vélhetően az intenzív (84–87%-os) gyökérkolonizáció és a növénynevelés körülményei (erős szárazságstressz) következtében. Az oltás optimális öntözés mellett növelte a sztómakonduktanciát és a gyökér vitalitását. A vízhiány azonban csökkentette a gyökér életképességét. A klorofilltartalom leginkább a búzafajták között mutatott eltérést az Mv. Hombár nagyobb SPAD-értékével. A gyökértömeg és -kapacitás között szoros lineáris korrelációt (R2 = 0,792–0,865) találtunk. A TC 33 fajta regressziós egyenesének nagyobb meredeksége a nagyobb hajtástömegből eredő nagyobb fajlagos vízfelvételre vezethető vissza. Eredményeink alapján a CR-mérés alkalmas a gyökérnövekedési dinamika monitorozására és a környezeti hatások detektálására. A roncsolásmentes eljárás egyéb növénymorfológiai és -élettani vizsgálómódszerek hasznos kiegészítője lehet.

This study aimed to demonstrate that single-frequency (1 kHz) measurement of impedance phase angle (Φ) in root–soil systems is suitable for monitoring plant responses to environmental stresses. Potted wheat, soybean and maize plants were exposed to cadmium contamination, alkaline stress, drought or weed competition. Φ was detected at regular intervals between a ground and a plant electrode during plant development, at the end of which root and shoot biomass were measured. Each type of stress significantly reduced both Φ and the root and shoot dry mass, to an extent proportional to the stress level. The decrease in Φ was attributed to various physicochemical changes in root cell membranes, the accelerated maturation of the exo- and endodermis and altered root morphology. These stress responses modified the dielectric properties of the root tissues, influencing the apoplast and symplast pathways of the electrical current inside the roots. The stress-induced increase in the amount of electrically insulating lignin and suberin in root tissues was considered to be an influential factor in decreasing Φ. These results show that in pot experiments the measurement of the impedance phase angle in intact root systems is a potentially useful in situ method for detecting plant responses to stresses affecting roots.

The measurement of electrical capacitance in root–soil system (CR) is a useful method for estimating the root system size (RSS) in situ; however, CR–RSS regressions are often poor. It was hypothesized that this weak relationships could be partly due to the variable energy-loss rate, indicated by the dissipation factor (DF). The values of CR and the associated DF were measured in six plant species grown in quasi-hydroponic pumice medium, arenosol and chernozem soil. The dielectric properties of the plant growth media were also recorded. A modified root–soil capacitance, CDF, was calculated from each CR/DF pair according to the formula CDF = CR·(DF/DFmean)α by estimating α with a standard nonlinear minimization of the sum of squared residuals for CDF–RSS regressions. The capacitive behavior of the medium improved (mean DF decreased) but fluctuated increasingly as the substrate became more complex. The mean DF values in plant–substrate systems were chiefly determined by the plant and were the most variable in chernozem soil. This strengthening substrate effect on CR measurements appeared as a decreasing trend in the R2 values obtained for the CR–RSS regressions. The regression slope was influenced by plant species and medium, while the y-intercept differed only between substrate types. The proposed use of CDF in place of CR could significantly improve the R2 of CDF–RSS regressions, particularly in chernozem soil (R2 increased by 0.07–0.31). The application of CDF will provide more reliable and accurate RSS estimations and more efficient statistical comparisons. The findings are worth considering in future investigations using the root capacitance method.

Munkank soran tenyeszedeny-kiserlettel teszteltuk az elektromos gyokerkapacitas (EC) meres alkalmazhatosagat szojafajtak gyokernovekedesenek es szarazsagtűresenek in situ vizsgalata celjabol. A kontroll es a szarazsagstressznek kitett novenyek EC-jet rendszeresen mertuk, vegul biomasszajukat destruktiv eljarassal meghataroztuk. Az EC meresevel jol detektalhato volt a fajtak elterő gyokernovekedesi dinamikaja es biomassza-produkcioja. Az EC — fajtatol es kortol fuggő intenzitassal — a viragzas kezdeteig folyamatosan emelkedett, majd kozel allandova valt. A fajtak EC-je es gyokertomege szoros korrelaciot mutatott a kontroll (R2=0,844) es a szarazsagkezelt (R2=0,936) novenyeknel egyarant. A vizhiany 28,8–50,5%-kal csokkentette az egyes fajtak EC-jet, ami osszhangban allt azok hajtastomegeinek 25,5–49,1%-os, es levelfeluleteinek (transzspiraciojanak) 23,6–51,5%-os csokkenesevel, ugyanakkor tobb fajtanal lenyegesen meghaladta a gyokertomegben mutatkozo veszteseget (12,6–47,3%). Ennek oka, hogy a szarazsag hata...

A pot experiment was designed to demonstrate that the parallel, single-frequency detection of electrical capacitance (CR), impedance phase angle (ΦR), and electrical conductance (GR) in root–substrate systems was an adequate method for monitoring root growth and some aspects of stress response in situ. The wheat cultivars ‘Hombar’ and ‘TC33’ were grown in a rhyolite-vermiculite mixture under control, and low, medium, and high alkaline (Na2CO3) conditions with regular measurement of electrical parameters. The photochemical efficiency (Fv/Fm) and SPAD chlorophyll content were recorded non-intrusively; the green leaf area (GLA), shoot dry mass (SDM), root dry mass (RDM), and root membrane stability index (MSI) were determined after harvest. CR progressively decreased with increasing alkalinity due to impeded root growth. Strong linear CR–RDM relationships (R2 = 0.883–0.940) were obtained for the cultivars. Stress reduced |ΦR|, presumably due to the altered membrane properties and anatomy of the roots, including primarily enhanced lignification. GR was not reduced by alkalinity, implying the increasing symplastic conductivity caused by the higher electrolyte leakage indicated by decreasing root MSI. Fv/Fm, SPAD value, GLA, and SDM showed decreasing trends with increasing alkalinity. Cultivar ‘TC33’ was comparatively sensitive to high alkalinity, as shown by the greater relative decrease in CR, SDM, and RDM under stress, and by the significantly lower MSI and higher (moderately reduced) |ΦR| compared to the values obtained for ‘Hombar’. Electrical root characterization proved to be an efficient non-intrusive technique for studying root growth and stress responses, and for assessing plant stress tolerance in pot experiments.

Soybean (Glycine max L. Merr.) is regarded worldwide as indisputably one of the most important crops for human food and animal feed. The presence of symbiotic bacteria and fungi is essential for soybean breeding, especially in low-input agricultural systems. Research on the cooperation between different microbial symbionts is a key to understanding how the health and productivity of the plant is supported. The symbiotic effectivity of dual and tripartite symbiotic agents was investigated in two pot experiments on different soybean cultivars with special regard to compatibility. In the Selection experiment, two out of sixteen soybean cultivars (Aliz, Emese) were chosen on the basis of their drought tolerance and used in all the other investigations. In the Compatibility experiment, the compatible coupling of symbiotic partners was selected based on the efficiency of single and co-inoculation with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in the infectivity and effectivity of the microsymbionts. The rhizobial and AMF inoculation generally improved plant production, photosynthetic efficiency and root activity, but this effect depended on the type of symbiotic assotiation. Despite the low infectivity of AMF, inocula containing fungi were more beneficial than those containing only rhizobia. In the Drought Stress (DS) experiment, co-inoculated and control plants were grown in chernozem soil originating from organic farms. Emese was more resistant to drought stress than Aliz and produced a bigger root system. Under DS, the growth parameters of both microbially inoculated cultivars were better than that of control, proving that even drought tolerant genotypes can strengthen their endurance due to inoculation with AMF and nitrogen fixing bacteria. Root electrical capacitance (CR) showed a highly significant linear correlation with root and shoot dry mass and leaf area. The same root biomass was associated with higher CR in inoculated hosts. As CR method detects the absorptive surface increasing due to inoculation, it may be used to check the efficiency of the microbial treatment.

The review deals with the stands of the alien Austrian pine (Pinus nigra Arn.) in Hungary, emphasizing the ecological consequences of the afforestation. A short historical overview about the establishment of pine cultures is presented with outlining the distribution of the stands among the major forestry regions of Hungary. The nature conservation and economic problems associated with Austrian pine are summarized, including: the local extinction of the species-rich native flora, the less valuable timber, the rapid physiological decay of trees followed by pathogen epidemics, the insufficient soil amelioration effect, as well as the special vulnerability to forest fires and non-native plant invaders. Applicability of the conifer for land reclamation purposes is also introduced. Finally, we describe some directives and proposals concerning the alteration of Austrian pine plantations to native woody associations complying with the sustainable forest management policy.

Symbiotic effectivity of two- and tripartite symbiotic agents was investigated in a pot experiment on three soybean ( Glycine max L. Merr.) cultivars with special regard to compatibility. Host plants were single and co-inoculated with two Bradyrhizobium japonicum strains and two commercial arbuscular mycorrhizal fungal (AMF) products. Significant differences were found in infectivity and effectivity of the microsymbionts. While infectivity of AMF inocula was very poor, the benefits of AMF treatments were more expressed than that of the rhizobial ones. In case of commercial AMF inoculants we should also check the effect of the ingredients of the explain medium. Keywords: Bradyrhizobium sp., arbuscular mycorrhizal fungi, soybean, host compatibility, biomass

The root electrical capacitance (CR) method is suitable for assessing root growth and activity, but soil water content (SWC) strongly influences the measurement results. This study aimed to adapt the method for field monitoring by evaluating the effect of SWC on root capacitance to ensure the comparability of CR detected at different SWC. First a pot experiment was conducted with maize and soybean to establish CR–SWC functions for the field soil. Ontogenetic changes in root activity were monitored under field conditions by simultaneously measuring CR and SWC around the roots. The CR values were normalized using SWC data and experimental CR–SWC functions to obtain CR*, the comparable indicator of root activity. The effect of arbuscular mycorrhizal fungi (AMF) inoculation on the CR* and biomass of field-grown soybean was investigated. The pot trial showed an exponential increase in CR with SWC. CR–SWC functions proved to be species-specific. CR showed strong correlation with root dry mass (R2 = 0.83–0.87). The root activity (CR*) of field-grown crops increased until flowering, then decreased during maturity. This was consistent with data obtained with other methods. AMF inoculation of soybean resulted in significantly higher CR* during the late vegetative and early flowering stages, when destructive sampling concurrently showed higher shoot biomass. The results demonstrated that the root capacitance method could be useful for time course studies on root activity under field conditions, and for comparing single-time capacitance data collected in areas with heterogeneous soil water status.

A b s t r a c t. Pot experiments were designed to test the applicability of root electrical capacitance measurement for in situ monitoring of root water uptake activity by growing cucumber and bean cultivars in a growth chamber. Half of the plants were inoculated with Funneliformis mosseae arbuscular mycorrhizal fungi, while the other half served as non-infected controls. Root electrical capacitance and daily transpiration were monitored during the whole plant ontogeny. Phenology-dependent changes of daily transpiration (related to root water uptake) and root electrical capacitance proved to be similar as they showed upward trends from seedling emergence to the beginning of flowering stage, and thereafter decreased continuously during fruit setting. A few days after arbuscular mycorrhizal fungi-colonization, daily transpiration and root electrical capacitance of infected plants became significantly higher than those of non-infected counterparts, and the relative increment of the measured parameters was greater for the more highly mycorrhizal-dependent bean cultivar compared to that of cucumber. Arbuscular mycorrhizal fungi colonization caused 29 and 69% relative increment in shoot dry mass for cucumbers and beans, respectively. Mycorrhization resulted in 37% increase in root dry mass for beans, but no significant difference was observed for cucumbers. Results indicate the potential of root electrical capacitance measurements for monitoring the changes and differences of root water uptake rate. K e y w o r d s: mycorrhiza, phenology, root electrical capacitance, transpiration, water uptake

A b s t r a c t. Importance of phase angle measurement during the application of electrical impedance spectroscopy was studied by executing pot experiments with maize. Electrical impedance, phase angle (strength of capacitive character), and dissipation factor in the plant-soil system were scanned between 100 and 10 000 Hz current frequency. The frequency-dependent change in the phase angle could be described by optimum curves culminating within 920-3 650 Hz. Since the rate of energy dissipation is independent of root extent, the higher phase angle and lower energy dissipation were associated with the higher coefficient of determination achieved for the root electrical impedance – root system size (root dry mass and root surface area) regressions. The characteristic frequency selected on the basis of phase angle spectra provided a higher significance level at statistical comparison of plant groups subjected to stress conditions influencing root development. Due to the physicochemical changes observable in aging root tissue, the apex of phase angle spectra, thus the characteristic frequency, shifted continuously toward the higher frequencies over time. Consequently, the regularly repeated phase angle measurement is advisable in time-course studies for effective application of the electrical impedance method, and the systematic operation at the same frequency without determination of phase angle spectra should be avoided. K e y w o r d s: dissipation factor, root capacitance, electrical impedance spectroscopy, phase angle, root surface area

Applicability of root electrical impedance (EI) and electrical capacitance (EC) measurements for the detection of arbuscular mycorrhizal fungal (AMF) colonization was studied. AMF-inoculated and non-inoculated maize plants were compared whilst growing them under well-watered and drought-stressed condition with regular measurement of root EI and EC. AMF-colonized maize plants showed lower EI and higher EC than control counterparts independently of moisture condition, indicating an enhanced root–soil interface. Root scanning revealed lower root surface area in mycorrhizal plants than in non-mycorrhizal ones growing under well-watered condition, while in plants exposed to drought no significant difference between root surface areas was detected. Since fungal colonization didn't provoke an increase in root surface area, the higher root–soil interface showed by EI and EC values was apparently due to the increased absorption surface area caused by the growth of AMF hyphae. Consequently, the simple, non-destructive EI and EC method is considered an appropriate technique for in situ investigation of AMF-colonization and function, which may partially substitute the intrusive techniques commonly used in mycorrhizal research.

The applicability of root electrical capacitance (EC) measurement for in situ investigation of root activity and drought tolerance was tested in soybean cultivars. Well-watered and drought-stressed plants were grown in pots with repeated EC measurements, followed terminally by harvest to determine root dry mass (RDM), shoot dry mass (SDM), root/shoot ratio (RSR) and leaf area (LA). EC measurement showed the cultivar differences in root growth and biomass production. EC increased till the beginning of flowering, then became nearly constant. Terminal EC was highly correlated with RDM for non-stressed (R 2 = 0.844) and stressed plants (R 2 = 0.936). Drought reduced the EC of cultivars by 28.8–50.5 %, consistently with the corresponding changes of SDM (25.5–49.1 %) and LA (23.6–51.5 %), but considerably exceeded the loss of RDM (12.6–47.3 %) in some cultivars. The reason is drought increased the RSR (by 3.9–21.9 %), leading to decreased water uptake, and thus EC per unit of RDM. This was confirmed by the significantly decreased slope of EC–RDM regression line from 0.437 to 0.317 nF g−1 RDM calculated for well-watered and drought-stressed plants, respectively. As EC referred to root uptake activity, it was better indicator of the actual root status than RDM. EC measurement was adequate for monitoring the cultivar-specific differences in root growth and for estimation of biomass loss caused by drought. By supplementing the conventional methods, this in situ technique could be useful for various fields of agriculture, including cultivar selection or stress tolerance studies.

Applicability of root electrical capacitance (EC) measurement for monitoring of crop–weed competition was studied in a pot experiment. Maize (Zea mays L.) was grown both alone and with Echinochloa crus-galli or Abutilon theophrasti in different densities with regular measurement of root EC. Plants were harvested 42 days after planting to determine above- and belowground biomass. Depending on weed density, E. crus-galli-A. theophrasti interaction reduced the root EC of maize by 22–66% and 3–57%, respectively. Competitive effect of crop on weeds and intraspecific competition among weeds could also be detected by EC values: E. crus-galli was less sensitive both to the presence of maize and to intraspecific competition than A. theophrasti. Strong linear correlations between root dry mass and root EC for crop and weeds (with R2 from 0.901 to 0.956) were obtained by regression analyses at the end of the experiment. EC monitoring informed us on the emergence time of competition: E. crus-galli interfered with maize root growth a week earlier then A. theophrasti, and increasing weed densities accelerated the emergence of competition. In conclusion, the simple, non-destructive EC method should be considered a potential in situ technique for pot studies on crop–weed competition, which may partially substitute the intrusive techniques commonly used in agricultural researches.

Pinus nigra and Robinia pseudoacacia are exotic trees used for afforestation in Hungary. Pinus nigra was non-invasive, however R. pseudoacacia escaped from cultivation and invaded several vegetation types including pine plantations. It has recently been planned to cut P. nigra plantations and replace them by native tree stands, especially in nature reserves. The scattered presence of R. pseudoacacia specimens in pine stands might place constraints on planned tree replacement because of their vegetative resprouting and recolonization from an established seed bank. The aim of this study was to investigate the soil seed bank under the canopy of solitary R. pseudoacacia specimens found in P.nigra plantations. Altogether 250 soil samples were collected from the 0-6 and 6-12 cm soil layers under solitary Robinia trees of varying ages (with basal areas between 62.4 and 1089.3 cm2). Seeds were separated by sieving then scarified and germinated. Seed bank density ranged between 640 and 2285 seedsm-2 with an average distribution of 82.7% and 17.3% in the upper and lower soil layer, respectively. Total density of the seed bank and also the seed bank ratio of the lower soil layer increased with tree age. The accumulated seed bank of R. pseudoacacia should be considered in the careful planning of tree replacement operations in Pinus nigra stands.

Monitoring of herbicide effect in maize based on electrical measurements The effect of the herbicide acetochlor on root growth was studied by a non-destructive electrical impedance and capacitance method in pot experiments on maize. Acetochlor was applied both as single active ingredient and mixed with safener AD-67 in two dosages. Without safener addition, acetochlor had a permanent inhibiting effect on plant root expansion. The safener AD-67 was capable of providing protective effect against herbicide application. High correlations between root electrical impedance or capacitance and the root dry mass or surface area under our laboratory conditions were confirmed by plant harvest method. Root electrical impedance and capacitance measurements proved to be valid for monitoring the effect of the herbicide influencing root development and for distinguishing plant groups subjected to different stress conditions.

Fire risk in Austrian pine (Pinus nigra) plantations under various temperature and wind conditions The Austrian pine (Pinus nigra), an introduced conifer in Hungary, forms a highly flammable vegetation type. The fire risk of such stands was examined using McArthur's empirical forest fire danger model. Our study focused on the effects of temperature and wind speed on fire behaviour. By keeping the input parameters of the model constant while changing temperature andwind speed within a specified interval the resulting fire danger index (FDI) and fire behaviour were examined. The applied fixed parameters were: 30 °C temperature, 30% relative humidity, 30 km h-1 wind speed, 30 degree of slope and drought factor value 10. The annual trends of the Byram-Keetch drought index (BKDI) and the drought factor were also calculated. Our results show that increasing temperature and wind speed raises the FDI, flame height, rate of fire spread (ROS) and spotting distance. The amount of fuel does not influence the FDI, but increasing the amount promotes the ROS and raises the flame height. Wind speed was the most important factor in the ROS. A serious fire risk of these plantations was determined. The reliability of McArthur's model was proved by comparison of our results with experimental laboratory data based on literature.