Search

Volicitin [N-(17-hydroxylinolenoyl)-L-glutamine] and N-linolenoyl-L-glutamine were originally identified in the regurgitant of Spodoptera exigua larvae. These fatty acid amino acid conjugates (FACs) are known to be elicitors that induce plants to release volatile compounds which in turn attract natural enemies of the larvae such as parasitic wasps. FAC concentrations are regulated by enzymatic biosynthesis and hydrolysis in the intestine of Lepidoptera larvae. It has been proposed that FAC metabolism activates glutamine synthetase and plays an important role in nitrogen metabolism in larvae. In this study, we identified candidate genes encoding a FACs hydrolase in Spodoptera litura using genomic information of various related lepidopteran species in which FACs hydrolases have been reported. We analyzed the importance of FAC hydrolysis on caterpillar performance with CRISPR/Cas9 knock outs. Larvae of strains with an inactive FACs hydrolase excreted FACs in their feces. They absorbed 30% less nitrogen from the diet compared to WT caterpillars resulting in a reduction of their body weight of up to 40% compared to wild type caterpillars. These results suggest that the hydrolysis of FACs is an important metabolism for insects and that FACs are important for larval growth. [ABSTRACT FROM AUTHOR]

The role of trees, in addition to that of the soil, must be considered in CH4 budget for forests. Although trees can emit CH4 through their stems, there are uncertainties about the main factors that explain inter- and intraspecific variations, which impedes upscaling of measurements from the stem to the ecosystem level. This study aimed to characterize the variability in CH4 emissions ( F CH 4 ) from stems between species and individuals, and within individuals. We measured F CH 4 in situ during the snow-free period in five species in a temperate mountain forest, using individuals of different sizes and chambers at different heights along the stems. One coniferous species emitted almost no CH4, whereas four broadleaved species exhibited high intraspecific variability in F CH 4 (0–3.7 nmol m−2 s−1). Increasing trends in F CH 4 with tree diameter were observed for four species. The vertical patterns in F CH 4 were complex. Seasonal variations in F CH 4 , measured on two trees per species, were well explained by air temperature with apparent temperature sensitivity coefficients (Q10) between 1.2 and 2, which were not related to the antecedent precipitation indices, whether calculated over 7 or 30 days. Potential CH4 production was detected in wood core segments incubated under anoxic conditions in the majority of individual trees of all species. Our results suggest that the CH4 emitted by trunks can originate either from soil or internal sources. Scaling F CH 4 from trees at the stand level and developing process-based models of F CH 4 will remain challenging until the sources of variation are better explained. [ABSTRACT FROM AUTHOR]

Purpose: Clarification of root architecture is important for understanding tree root functions. 3D laser scanning reconstructs the 3D structure of root system with high accuracy, but the devices are large and expensive. The Structure-from-Motion with multi-view stereo-photogrammetry (SfM-MVS) method reconstructs the 3D structure of an object from multiple images. This method is suitable for field research because it acquires the 3D data with a commercially available digital camera. Our aim in this study was to test the applicability of the SfM-MVS method for morphological measurement of tree root systems. Methods: The 3D root system model was created using a dummy and three black pine (Pinus thunbergii) root systems. Image data were collected from the root systems using a camera and reconstructed using the free software, VisualSfM and MeshLab. We evaluated the accuracy of morphological data estimated from the 3D models by comparing them with real data obtained from manual measurements of the root systems. Results: The 3D reconstructions of the dummy and black pine root systems were successful. The root mean squared error values for the morphological features in the pine root systems ranged from 4 to 24%, which was sufficiently accurate for a successful 3D model. However, the RMSE values were larger than that of dummy root, ranging from 2 to 9%. Conclusion: The SfM-MVS method is a new tool, based on non-specialised equipment and free software, to obtain the 3D structure of tree root systems. The morphological features of it can be successfully measured from the reconstructed models. [ABSTRACT FROM AUTHOR]

Key Message: Annual shoot length is useful for analyzing the climate influence on tree level leaf production because it is proportional to leaf mass, and their yearly variations are synchronized within trees. Recent global warming could cause boreal forests to become carbon sources instead of large carbon sinks. A robust prediction of carbon uptake capacity of such forests is, therefore, necessary. However, even though leaf production is a determinant of forest carbon sink capacity, reconstructing annual leaf production in evergreen conifers is still challenging. A new method was proposed to reconstruct the past yearly variation in leaf production of evergreen conifers and was applied to an open stand of Picea mariana in Canada. A clear linear relationship was obtained between annual shoot length and leaf dry mass. Annual shoot lengths on primary branches were measured for over twenty years on ten mature trees. Yearly variations in these lengths were synchronized within trees, which suggests that the measured variation could be scaled up from the branch to the tree level. They were also synchronized among most of the sampled trees; however, two trees showed their own variation. These differences must be considered before scaling up from the tree to the stand level. Neither tree-ring width nor radial area increment of the stem at breast height predicted leaf production. Temperature and rainfall during the growing season were the dominant climatic drivers of leaf production reconstructed from annual shoot lengths. Leaf production may increase under future global warming if the temperature continues to rise and precipitation during the growing season does not decrease, which would otherwise negate the growth benefits of a warmer climate. [ABSTRACT FROM AUTHOR]

Aim: Ground-penetrating radar (GPR) has been used for estimating root biomass, estimating pull-out resistance force of roots, and reconstructing root system architecture. Although GPR can estimate the diameter of a single root, it has not yet been verified whether it can successfully estimate the diameters of adjacent roots or whether rock fragments occurring in the soil matrix can be misidentified as roots. This study aimed to (1) evaluate the visual properties of GPR images of root bundles and rock fragments, and (2) clarify whether they have the potential to create non-negligible errors in GPR surveys. Methods: Root bundle samples buried in a sandy soil bed were scanned using 900 MHz and 1500 MHz antennas. Sole roots of Cryptomeria japonica and rock fragments in the bed were also scanned. Results: A bundle of root formed one hyperbola with an apex in the radar profile, like a sole root. However, the contrast of the hyperbolas was weak and GPR indices relating to diameter were reduced compared to those of the comparably sized sole root. Stones did not form clear images, but boulders were faintly visible with non-negligible GPR indices. Conclusions: For evaluation of root biomass, adjacent roots had the potential to lead to significant errors. Similarly, in reconstructions of root system architecture, adjacent roots might lead to incorrect modelling of root point connections, because of incorrect diameters. For pull-out resistance force, adjacent roots could lead to only underestimation, i.e., safe-side error. Misidentification of rock fragments as roots depends on their sizes. [ABSTRACT FROM AUTHOR]

Main conclusion: We developed simple algorithms for reconstructing tree root system architecture using only the root point coordinate and diameter, which can be systematically obtained without digging up the root systems.Root system architecture (RSA) is strongly related to various root functions of the tree. The aim of this study was to develop a three-dimensional (3D) RSA model using systematically obtained information on root locations and root diameters at the locations. We excavated root systems of Cryptomeria japonica and systematically obtained XYZ coordinates and root diameters using a 10-cm grid. We clarified the patterns of the root point connections and developed a reconstructed root system model. We found that the root diameters farther from the stump centre are smaller. Additionally, we found that the root lengths of the segments running between the base and the connected root point were smaller than those of other root segments, and the inner angle between the base and the stump and between the base and the connected root point was narrower than for the other pairs. The new RSA model developed according to these results had average accuracies of 0.64 and 0.80 for estimates of total volume and length, respectively. The developed model can estimate 3D RSA using only root point data, which can be obtained without digging up root systems. This suggests a wide applicability of this model in root function evaluation. [ABSTRACT FROM AUTHOR]

Key message: Use of ground-penetrating radar (GPR) can non-destructively estimate diameter and distribution of coarse roots in Cryptomeria japonica in weathered granite soils under field conditions.Abstract: Ground-penetrating radar (GPR) has been used as an assessment tool for non-destructive detection of tree root biomass, but few studies have estimated root diameter under forest field conditions. The aim of this study was to clarify whether coarse root diameter of C. japonica in weathered granite soils can be estimated using GPR in a forest. Roots of mature C. japonica were scanned using a 900 MHz GPR antenna before being excavated. The diameter and distribution of excavated roots were compared with those identified by GPR, and the relationships between the diameter and waveform indices in radar profiles were also examined. The detection frequency of the number of roots larger than 5 mm in diameter was 47.7%. Limiting factors affecting root detection using GPR in forest field conditions were small root diameter, increasing root depth, and number of adjacent roots. Only one waveform index, using the sum of time intervals between zero crossings (ΣT, ns) of all reflection waveforms of GPR within the range from the first break time at the root top to the delay point time at the root bottom, had a significant relationship with excavated root diameters. A linear regression model was constructed to estimate root diameter using ΣT, and a significant positive relationship in diameter between GPR-estimated and excavated roots was confirmed. The results in this study indicate that the diameter and distribution of C. japonica coarse roots under forest field conditions could be estimated using GPR and this technique could contribute to future evaluation of slope stability by evaluating tree roots under vulnerable soils, such as weathered granite. [ABSTRACT FROM AUTHOR]

Aims: The different root systems of Pinus thunbergii observed after the tsunami in 2011 were possibly influenced by different groundwater levels before the tsunami. The aims of this study were to quantify the tap and horizontal root structure and evaluate their relationship with the above-ground parts under different groundwater levels in a coastal P. thunbergii forest.Methods: Two plots, sea- and land-side, with different groundwater levels, in a P. thunbergii stand, were established, and the entire root-systems of three select trees each were harvested to evaluate the biomass, lengths, and cross-sectional areas of the tap and horizontal roots.Results: In the sea-side plot, which had a shallower groundwater level, plate root systems with thicker and longer horizontal roots, but fewer tap roots were observed, whereas tap root systems were well developed in the land-side plots, where the groundwater level was deeper. The root-to- shoot ratio was significantly higher in the sea-side plot than in the land-side plot.Conclusion: We confirmed that quantitative contrasting root systems of P. thunbergii develop under different groundwater levels and higher biomass allocation to horizontal roots occur under shallower groundwater depths, emphasizing the need for management practices that promote the development of tap root systems to enhance resistance to tsunamis. [ABSTRACT FROM AUTHOR]

Climate changes are mainly characterized by an increase in air temperature and a decrease in rainfalls. Potassium (K) nutrition is generally considered to alleviate plants tolerance to water deficit, especially by improving photosynthesis and phloem transport of carbohydrates from leaves to roots. The main objective of this study was to measure the effect of K on sugar transport and allocation under water-stressed conditions on maize ( Zea mays L.). Maize plants were grown in pots under different water and K treatments. We used CO pulse-labelling to determine carbon exportation from leaves with δC analysis, within 1 week. The diurnal sugar content in leaves was measured, and net carbon assimilation accessed. Water deficit strongly reduced plant growth, while K nutrition appeared to be efficient in attenuating these effects. K deficiency significantly decreased starch content in leaves under well-watered but not under water-stressed treatment. A leaf carbon mass balance showed that K increased sugar export on a daily time scale, while instantaneous δC measurements did not show any significant effect, partly because of the very rapid δC decline after labelling. Our home-made labelling chamber proved to be successful in monitoring diurnal changes in δC for a C4 plant with high photosynthetic rates and fast carbon export, and also in determining the effect of a K deficiency on sugar export. Our results highlight a need for research into carbon export on leaves of different ages in fast-growing crops under the combined effect of water and nutrient stress. [ABSTRACT FROM AUTHOR]

Aim: Ground penetrating radar (GPR), a nondestructive tool that can detect coarse tree roots, has not yet become a mature technology for use in forests. In this study, we asked two questions concerning this technology: (i) Does the leaf litter layer influence root detection and major indices based on the time interval between zero crossings ( T) and the amplitude area ( A)? (ii) Can GPR images discriminate roots of different plant species? Methods: Roots buried in a sandy bed, which was covered with different thicknesses of leaf litter, were scanned using a 900 MHz GPR antenna. Roots of four plant species in the bed were also scanned. Results: Leaf litter decreased root reflections without distorting the shape of the hyperbolas in the radar profile. A values decreased with increasing litter thickness, whereas T was independent of litter thickness. For all species combined, GPR indices were significantly correlated with root diameter. Conclusions: Leaf litter dramatically decreased root detection, but the influence of the litter could be ignored when the sum of T for all reflection waveforms (Σ T) is adopted to estimate root diameter. To use A values to detect roots, litter should be removed or equalized in thickness. Radar profiles could not reliably differentiate among roots belonging to plants of different species. [ABSTRACT FROM AUTHOR]

Introduction: We showed that root orientation affected a parameter of ground penetrating radar (GPR), amplitude area ( A) (Tanikawa et al. Plant Soil 373:317-327, ). The aims of this reply to Wu et al. () are (i) to correct the two inaccuracies in Tanikawa et al. () and (ii) to improve our method of estimating A(90°) using A( x) of root angle x. Methods: Measured A values of Tanikawa et al. () were analyzed with the modified equations. Results: The first inaccuracy was the use of incorrect units for the coefficient b (the phase shift) in the sinusoidal waveform of A( x). The units should have been radians instead of degrees. The second inaccuracy was the mis-derivation of A( x) into A( x + 90°). In the modified method, A(90°) was estimated by A( x) from two orthogonally intersecting transect lines and a transect line at a diagonal to them. Conclusions: The two inaccuracies did not affect the previous main conclusions that the parameter T was suitable for estimating root diameter and that grid transects are likely to identify clear hyperbolas reflecting roots in radar profiles (Tanikawa et al. ). By the improved method, we could accurately estimate root diameter by scanning using three transect lines intersecting at angles of x, x + 45°, and x + 90°. [ABSTRACT FROM AUTHOR]

Aim: Ground-penetrating radar (GPR) has been applied to detect coarse tree roots. The horizontal angle of a root crossing a scanning line is a factor that affects both root detection and waveform parameter values. The purpose of this study was to quantitatively evaluate the influence of root orientation ( x, degree) on two major waveform parameters, amplitude area ( A, dB × ns) and time interval between zero crossings ( T, ns). Methods: We scanned four diameter classes of dowels in a sandy bed as simulated roots using a 900 MHz antenna from multiple angles to clarify the relationships between the parameters and x. Results: Angle x strongly affected reflection images and A values. The variation in A( x) fitted a sinusoidal waveform, whereas T was independent of x. The value of A scanning at 90° was estimated by A values of arbitrary x in two orthogonal transects. The sum of T in all reflected waveforms showed a significant linear correlation with dowel diameter. Conclusions: We clarified that root orientation dramatically affected root detection and A values. The sum of T of all reflected waveforms was a suitable parameter for estimating root diameter. Applying grid transects can overcome the effects of root orientation. [ABSTRACT FROM AUTHOR]

Aims: Tree roots in forest soils can be detected using nondestructive ground-penetrating radar (GPR). However, few studies have investigated root detection frequency; i.e., how many and which roots are identified in a radar profile out of the total quantity of roots present in a forest stand. The objective of this study was to quantify root detection frequency and uncertainty, including relationships between root detection and radar parameters using 1.5 GHz GPR in a Pinus thunbergii forest on sandy soils. Methods: We compared the vertical distribution of 829 excavated roots with distributions identified visually in radar profiles using GPR on 17 transects. Results: The detection frequency for number of roots less than 1.0 cm in diameter was only 6.6 %, but 54 % of roots that were larger than 1.0 cm were detected. Roots larger than 2.0 cm were identified with less frequency by GPR at deeper depths (20-30 cm) than were shallower roots. Conclusion: Our study indicates that GPR methods estimate root biomass to be 68 % of the excavated root biomass and that the detection frequency for number of roots in radar profiles using GPR is related to root biomass, although there is uncertainty in the attenuation of radar waves with depth, soil water condition and root orientation. [ABSTRACT FROM AUTHOR]

It has been reported that ground-penetrating radar (GPR) is a nondestructive tool that can be used to detect coarse roots in forest soils. However, successful GPR application for root detection has been site-specific and numerous factors can interfere with the resolution of the roots. We evaluated the effects of root diameter, root volumetric water content, and vertical and horizontal intervals between roots on the root detection of Cryptomeria japonica in sand using 900-MHz GPR. We found that roots greater than 19 mm in diameter were clearly detected. Roots having high volumetric water content were easily detected, but roots with less than 20% water content were not detected. Two roots that were located closely together were not individually distinguished. These results confirm that root diameter, root water content, and intervals between roots are important factors when using GPR for root detection and that these factors lead to an underestimation of root biomass. [ABSTRACT FROM AUTHOR]

The original version of this article unfortunately contained a mistake. Table 3 was published erroneously. This Table has now been corrected. [ABSTRACT FROM AUTHOR]

Drought-induced tree death has become a serious problem in global forest ecosystems. Two nonexclusive hypotheses, hydraulic failure and carbon starvation, have been proposed to explain tree die-offs. To clarify the mechanisms, we investigated the physiological processes of drought-induced tree death in saplings with contrasting Huber values (sapwood area/total leaf area). First, hydraulic failure and reduced respiration were found in the initial process of tree decline, and in the last stage carbon starvation led to tree death. The carbohydrate reserves at the stem bases, low in healthy trees, accumulated at the beginning of the declining process due to phloem transport failure, and then decreased just before dying. The concentrations of non-structural carbohydrates at the stem bases are a good indicator of tree damage. The physiological processes and carbon sink-source dynamics that occur during lethal drought provide important insights into the adaptive measures underlying forest die-offs under global warming conditions. Yuri Kono et al. show that drought-induced tree death is caused by initial hydraulic failure followed by carbon starvation. They find that the loss of the carbon sink-source balance in stem bases due to phloem transport failure is the key factor governing wilting, providing insight to developing adaptive measures to prevent forest die-offs under global warming conditions. [ABSTRACT FROM AUTHOR]