Isotope Distribution Analysis in H218O Pulse-Labeled Trees Frozen with Liquid Nitrogen.

Tracer injection has long been recognized as a valuable tool for delineating tree hydraulics and assessing water transport pathways. Recently, isotope tracers have emerged as innovative instruments for investigating tree hydraulics, providing new insights into tree water dynamics. Nevertheless, there is a critical need for further research to comprehensively grasp water movement and distribution within trees. A previously introduced technique for analyzing the isotopic ratio of water in wet tissues, offering millimeter-scale resolution for visualizing tracer movement, faces challenges due to its underdeveloped sample preparation techniques. In this study, we introduced an H2 18O tracer into S. gracilistyla samples, exclusively comprising indeterminate roots, stems, and leaves, cultivated through hydroponics and grown within the current year. Our objective was to assess the axial distribution of the tracer in the xylem. Additionally, we devised a novel method for preparing frozen wet tissue samples, enhancing the repeatability and success rate of experiments. The results demonstrated that all frozen wet tissue samples exhibited an average water loss rate of less than 0.6%. Isotopic analysis of these samples unveiled a consistent decline in tracer concentration with increasing height in all Salix specimens, with three out of five samples revealing a significant isotope gradient. Our findings affirm the efficacy and practicality of combining isotopic labeling with freezing, stabilization, and preparation techniques. Looking ahead, our isotopic labeling and analysis methods are poised to transcend woody plants, finding extensive applications in plant physiology and ecohydrology.

Symmetric-logarithmic-derivative Fisher information for kinetic uncertainty relations.

We investigate a symmetric logarithmic derivative (SLD) Fisher information for kinetic uncertainty relations (KURs) of open quantum systems described by the GKSL quantum master equation with and without the detailed balance condition. In a quantum kinetic uncertainty relation derived by Vu and Saito [Phys. Rev. Lett. 128, 140602 (2022)0031-900710.1103/PhysRevLett.128.140602], the Fisher information of probability of quantum trajectory with a time-rescaling parameter plays an essential role. This Fisher information is upper bounded by the SLD Fisher information. For a finite time and arbitrary initial state, we derive a concise expression of the SLD Fisher information, which is a double time integral and can be calculated by solving coupled first-order differential equations. We also derive a simple lower bound of the Fisher information of quantum trajectory. We point out that the SLD Fisher information also appears in the speed limit based on the Mandelstam-Tamm relation by Hasegawa [Nat. Commun. 14, 2828 (2023)2041-172310.1038/s41467-023-38074-8]. When the jump operators connect eigenstates of the system Hamiltonian, we show that the Bures angle in the interaction picture is upper bounded by the square root of the dynamical activity at short times, which contrasts with the classical counterpart.

Electronic and spin states at edges of finite p-orbital helical atomic chain.

In connection to the chiral-induced spin selectivity effect, we theoretically analyze the electronic and spin states of edges of a finite p-orbital helical atomic chain with the intra-atomic spin-orbit interaction. This model can host the spin-filtering state in which two up-spins propagate in one direction and two down-spins propagate in the opposite direction without breaking the time-reversal symmetry (TRS). The enhancement of charge modulations concentrated at the edges due to the evanescent states is induced, although the spin density is absent because of the TRS. A Zeeman field at an edge of the atomic chain, which breaks the TRS, yields a finite spin polarization, whose direction depends on the chirality of the molecule. The chirality change induces a reasonable amount of the energy difference, which may provide an insight into the enantioselective adsorption of chiral molecules on the ferromagnetic surface.

The difference in the functional water flow network between the stem and current-year root cross-sectional surfaces in Salix gracilistyla stem xylem.

The dye injection method has been applied to many species to analyze the xylem water transport pathway in trees. However, traditional dye injection methods introduced dye tracers from the surface of cut stems, including several annual rings. Furthermore, the traditional dye injection method did not evaluate radial water movement from the outermost annual rings to the inner annual rings. In this study, we assessed the difference in radial water movement visualized by an injected dye, between stem base cut and current-year root cut samples of Salix gracilistyla Miq., with current-year roots grown hydroponically. The results showed that the number of stained annual rings in the root cut samples was smaller than that in the stem cut samples, and the percentage of stained vessels in the root cut samples was significantly smaller than that in the stem base cut samples in the second and third annual rings. In the current-year root cut samples, water transport mainly occurred in the outermost rings from the current-year roots to leaves. In addition, the theoretical hydraulic conductivity of stained vessels in the stem cut samples was higher in the current-year root cut samples in the second and third annual rings. These findings indicate that the previously reported dye injection method using stem cut samples overestimated the water transport pathway in the inner part of the stems. Moreover, previous hydraulic conductivity measurement methods might not have considered the effects of radial resistance through the annual ring boundary, and they might have overestimated the hydraulic conductivity in the inner annual rings.

Spintronic reservoir computing without driving current or magnetic field.

Recent studies have shown that nonlinear magnetization dynamics excited in nanostructured ferromagnets are applicable to brain-inspired computing such as physical reservoir computing. The previous works have utilized the magnetization dynamics driven by electric current and/or magnetic field. This work proposes a method to apply the magnetization dynamics driven by voltage control of magnetic anisotropy to physical reservoir computing, which will be preferable from the viewpoint of low-power consumption. The computational capabilities of benchmark tasks in single MTJ are evaluated by numerical simulation of the magnetization dynamics and found to be comparable to those of echo-state networks with more than 10 nodes.

Asymptotic expansion of the solution of the master equation and its application to the speed limit.

We investigate an asymptotic expansion of the solution of the master equation under the modulation of control parameters. In this case, the nondecaying part of the solution becomes the dynamical steady state expressed as an infinite series using the pseudoinverse of the Liouvillian, whose convergence is not granted in general. We demonstrate that for the relaxation time approximation model, the Borel summation of the infinite series is compatible with the exact solution. By exploiting the series expansion, we obtain the analytic expression of the heat and the activity. In the two-level system coupled to a single bath, under the linear modulation of the energy as a function of time, we demonstrate that the infinite series expression is the asymptotic expansion of the exact solution. The equality of a trade-off relation between the speed of the state transformation and the entropy production [Shiraishi, Funo, and Saito, Phys. Rev. Lett. 121, 070601 (2018)PRLTAO0031-900710.1103/PhysRevLett.121.070601] holds in the lowest order of the frequency of the energy modulation in the two-level system. To obtain this result, the heat emission and absorption at edges (the initial and end times) or the differences of the Shannon entropy between the instantaneous steady state and the dynamical steady state at edges are essential: If we ignore these effects, the trade-off relation can be violated.

Nutrients exported from upland stream water enlarge perennial biomass crops.

Rawanbuki, a variety of Japanese butterbur (Petasites japonicus subsp. giganteus), grow naturally along the Rawan River, Hokkaido, northern Japan. Most plants reach 2-3 m in height and 10 cm in diameter in 2 months and are much larger than those grown along other rivers. We examined the hypothesis that nutrients exported from upland streams enhance the growth of the Rawanbuki. Nutrient concentrations, including nitrogen, phosphorus, and base cations, in the Rawan River were much higher than those in rivers of adjacent watersheds. High nutrient concentrations and moisture contents were found in soil along the Rawan River and a significant relationship was found between physicochemical soil conditions and aboveground biomass of butterburs. This indicates that extremely large Rawanbuki plants could be caused by these high nutrient concentrations and moisture contents in the soils. A manipulation experiment showed that fertilization simulated the growth environment along the Rawan River and enhanced the stem height and stem diameter of butterburs. This study concluded that the extremely large butterburs are caused by a large amount of nutrients exported from upland areas. These results are the first demonstration of the role of stream water nutrients in enlarging agricultural crops.

Xylem Water Distribution in Woody Plants Visualized with a Cryo-scanning Electron Microscope.

A scanning electron microscope installed cryo-unit (cryo-SEM) allows specimen observation at subzero temperatures and has been used for exploring water distribution in plant tissues in combination with freeze fixation techniques using liquid nitrogen (LN2). For woody species, however, preparations for observing the xylem transverse-cut surface involve some difficulties due to the orientation of wood fibers. Additionally, higher tension in the water column in xylem conduits can occasionally cause artifactual changes in water distribution, especially during sample fixation and collection. In this study, we demonstrate an efficient procedure to observe the water distribution within the xylem of woody plants in situ by using a cryostat and cryo-SEM. At first, during sample collection, measuring the xylem water potential should determine whether high tension is present in the xylem conduits. When the xylem water potential is low (< ca. -0.5 MPa), a tension relaxation procedure is needed to facilitate better preservation of the water status in xylem conduits during sample freeze fixation. Next, a watertight collar is attached around the tree stem and filled with LN2 for freeze fixation of the water status of xylem. After harvesting, care should be taken to ensure that the sample is preserved frozen while completing the procedures of sample preparation for observation. A cryostat is employed to clearly expose the xylem transverse-cut surface. In cryo-SEM observations, time adjustment for freeze-etching is required to remove frost dust and accentuate the edge of the cell walls on the viewing surface. Our results demonstrate the applicability of cryo-SEM techniques for the observation of water distribution within xylem at cellular and subcellular levels. The combination of cryo-SEM with non-destructive in situ observation techniques will profoundly improve the exploration of woody plant water flow dynamics.

Short-time xylem tension relaxation prevents vessel refilling and alleviates cryo-fixation artifacts in diffuse-porous Carpinus tschonoskii and Cercidiphyllum japonicum.

Xylem tension relaxation is an important procedure that closely resembles the in vivo xylem water distribution when measuring conductivity or observing water distribution of plant tissue samples by cryo-scanning electron microscopy (cryo-SEM). Recent studies have shown that partial xylem embolism occurs when samples under tension are cut under water and that gas-filled vessels are refilled during tension relaxation. Furthermore, the frequency of gas-filled vessels has been reported to increase in samples without tension relaxation before cryo-fixation by liquid nitrogen, particularly in samples with significant tension. Here, we examined the effect of tension relaxation on these artifacts in Carpinus tschonoskii and Cercidiphyllum japonicum using magnetic resonance imaging. We observed that xylem embolism rarely occurs in bench-dried samples cut under water. In both species, a small portion of the xylem was refilled within ~1 h after tension relaxation. Cryo-SEM observations revealed that short-time (<1 h) xylem tension relaxation decreases the frequency of gas-filled vessels in samples frozen after xylem tension relaxation regardless of the water potential compared with that in samples frozen without rehydration in both species. Therefore, short-time tension relaxation is necessary to retain xylem water distribution during sample preparation against artifacts.

Suppression of growth and death of meristematic tissues in Abies sachalinensis under strong shading: comparisons between the terminal bud, the terminally lateral bud and the stem cambium.

The suppression of apical growth and radial trunk growth in trees under shade is a key factor in the competition mechanism among individuals in natural and artificial forests. However, the timing of apical and radial growth suppression after shading and the physiological processes involved have not been evaluated precisely. Twenty-one Abies sachalinensis seedlings of 5-years-old were shaded artificially under a relative light intensity of 5% for 70 days from August 1, and the histological changes of the terminal bud and terminally lateral bud of terminal leader and the cambial zone of the trunk base were analyzed periodically. In shade-grown trees, cell death of the leaf primordia in a terminal bud of terminal leader was observed in one of the three samples after 56 and 70 days of shading, whereas the leaf primordia in a terminal bud of terminal leader in all open-grown trees survived until the end of the experiment. In addition, the leaf primordia of the terminally lateral buds of terminal leader retained their cell nuclei until the end of the experiment. No histological changes were observed in the cambial cells after shading, but the shade-grown trees had less cambial activity than the open-grown trees through the experiment. Strong shading appeared to inhibit the formation and survival of cells in the terminal bud of terminal leader rather than the terminally lateral buds of terminal leader and the cambium. The suppression of the terminal bud growth and elongation of the surviving lateral buds would result in an umbrella-shaped crown under shade.

Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading.

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.

Differences in drought- and freeze-induced embolisms in deciduous ring-porous plant species in Japan.

MAIN CONCLUSION: Deciduous ring-porous species in Japan shed all of their leaves under severe water stress before large vessels in earlywood are embolized, and embolization take place during winter. Water in deciduous ring-porous species is mainly conducted upward via large earlywood vessels of the current year. Water columns in large vessels are vulnerable to drought-induced and freeze stress-induced embolisms. Although a vulnerability curve can be created to estimate the hydraulic capacity of plants, it remains unclear why the loss of conductivity in potted plants of ring-porous species does not reach 100 % under severe drought stress. In this study, two deciduous ring-porous species in Japan (Kalopanax septemlobus and Toxicodendron trichocarpum) were used to explain the species-specific pattern in the water-conducting pathway of the stem. We monitored and visualized the spatial distribution of xylem embolisms in the stem of K. septemlobus saplings under drought stress and freeze stress using compact magnetic resonance imaging and cryo-scanning microscopy. In addition, we evaluated the water ascent in the stems of both species using a dye uptake method. Although embolisms of large vessels were observed under drought stress and in winter, all leaves were dropped to avoid fatal water loss after embolization of some large vessels. In contrast, all large vessels were embolized in winter. Larger-diameter vessels of latewood in T. trichocarpum tended to function in trees growing in the warm temperate zone. Thus, our results suggest that the unclear curve may be derived from a discrepancy between leaf water potential and actual water potential in the xylem under severe drought stress. The frequency of xylem embolisms in deciduous ring-porous species in Japan mainly depends on the number of freeze-thaw cycles.

Spatial distribution of xylem embolisms in the stems of Pinus thunbergii at the threshold of fatal drought stress.

Although previous studies have suggested that branch dieback and whole-plant death due to drought stress occur at 50-88% loss of stem hydraulic conductivity (P50 and P88, respectively), the dynamics of catastrophic failure in the water-conducting pathways in whole plants subjected to drought remain poorly understood. We examined the dynamics of drought stress tolerance in 3-year-old Japanese black pine (Pinus thunbergii Parl.). We nondestructively monitored (i) the spatial distribution of drought-induced embolisms in the stem at greater than P50 and (ii) recovery from embolisms following rehydration. Stem water distributions were visualized by cryo-scanning electron microscopy. The percentages of both embolized area and loss of hydraulic conductivity showed similar patterns of increase, although the water loss in xylem increased markedly at -5.0 MPa or less. One seedling that had reached 72% loss of the water-conducting area survived and the xylem water potential recovered to -0.3 MPa. We concluded that Japanese black pines may need to maintain water-filled tracheids within earlywood of the current-year xylem under natural conditions to avoid disconnection of water movement between the stem and the tops of branches. It is necessary to determine the spatial distribution of embolisms around the point of the lethal threshold to gain an improved understanding of plant survival under conditions of drought.

Cutting stems before relaxing xylem tension induces artefacts in Vitis coignetiae, as evidenced by magnetic resonance imaging.

It was recently reported that cutting artefacts occur in some species when branches under tension are cut, even under water. We used non-destructive magnetic resonance imaging (MRI) to investigate the change in xylem water distribution at the cellular level in Vitis coignetiae standing stems before and after relaxing tension. Less than 3% of vessels were cavitated when stems under tension were cut under water at a position shorter than the maximum vessel length (MVL) from the MRI point, in three of four plants. The vessel contents remained at their original status, and cutting artefact vessel cavitation declined to <1% when stems were cut at a position farther than the MVL from the MRI point. Water infiltration into the originally cavitated vessels after cutting the stem, i.e. vessel refilling, was found in <1% of vessels independent of cutting position on three of nine plants. The results indicate that both vessel cavitation and refilling occur in xylem tissue under tension following stem cutting, but its frequency is quite small, and artefacts can be minimized altogether if the distance between the monitoring position and the cutting point is longer than the MVL.

Fluctuation theorem for a small engine and magnetization switching by spin torque.

We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.

Freeze stabilization and cryopreparation technique for visualizing the water distribution in woody tissues by X-ray imaging and cryo-scanning electron microscopy.

The protocol of freeze stabilization and cryopreparation techniques to examine the distribution of water in living tree stems by X-ray imaging and cryo-scanning electron microscopy have been developed and described. The brief procedures are as follows. Firstly, a portion of transpiring stem is frozen in the standing state with liquid nitrogen to stabilize the water that is present in the conducting tissue. After filling with liquid nitrogen, discs are then collected from the frozen portion of the stem and stored in liquid nitrogen. In a low-temperature room, the samples for X-ray imaging are sectioned with a fine handsaw, and trimmed sample blokes for cryo-scanning electron microscopy are cleanly planed using a sliding microtome. Finally, the frozen sections are irradiated in a soft X-ray apparatus, and the small blocks are examined in cryo-scanning electron microscope after freeze-etching and metal coating.

The function of intercellular spaces along the ray parenchyma in sapwood, intermediate wood, and heartwood of Cryptomeria japonica (Cupressaceae).

PREMISE OF THE STUDY: Intercellular spaces along ray parenchyma (ISRP) are common in many conifer xylems, but their function is uncertain because the in-situ structural network among ISRP, ray parenchyma, and tracheids has not been evaluated. Analysis of water distribution in ISRP from sapwood to heartwood is needed to elucidate the function of ISRP in sapwood, intermediate wood, and heartwood. METHODS: We used cryo-scanning electron microscopy, x-ray photography, and water content measurement in xylem to analyze the presence of liquids in ISRP, ray parenchyma, and tracheids from sapwood to heartwood in Cryptomeria japonica (Cupressaceae). KEY RESULTS: In sapwood, almost all ISRP were empty. "Cingulate-cavitated regions", which lose water along the tangential direction within one annual ring, formed in the earlywood tracheids, and their frequency increased toward the inner annual rings, whereas ray parenchyma cells were alive and not involved in the partial cavitation. In intermediate wood, almost all ISRP and earlywood tracheids and many of the ray cells were empty, and only some latewood tracheids retained liquid in their lumina. The ISRP were connected with tracheids via gas-filled ray parenchyma cells. CONCLUSIONS: The ISRP work as a pathway of gas for aspiration of ray parenchyma cells in sapwood. On the other hand, the occurrence of a gas network between ISRP, ray parenchyma, and tracheids facilitates cavitation of tracheids, resulting in the generation of low-moisture, intermediate wood.

Determination and potential importance of diterpene (kaur-16-ene) emitted from dominant coniferous trees in Japan.

Reactive volatile organic compounds (VOCs) are known to affect atmospheric chemistry. Biogenic VOCs (BVOCs) have a significant impact on regional air quality due to their large emission rates and high reactivities. Diterpenes (most particularly, kaur-16-ene) were detected in all of the 205 enclosure air samples collected over multiple seasons at two different sites from Cryptomeria japonica and Chamaecyparis obtusa trees, the dominant coniferous trees in Japan,. The emission rate of kaur-16-ene, was determined to be from 0.01 to 7.1 µg dwg(-1) h(-1) (average: 0.61 µg dwg(-1) h(-1)) employing branch enclosure measurements using adsorbent sampling followed by solid phase-liquid extraction techniques. The emission rate was comparable to that of monoterpenes, which is known major BVOC emissions, collected from the same branches. In addition, total emission of kaur-16-ene at 30°C was estimated to exceed that of total anthropogenic VOC emissions.

Photosynthetic, hydraulic and biomechanical responses of Juglans californica shoots to wildfire.

Leaf gas exchange and stem xylem hydraulic and mechanical properties were studied for unburned adults and resprouting burned Juglans californica (southern California black walnut) trees 1 year after a fire to explore possible trade-offs between mechanical and hydraulic properties of plants. The CO(2) uptake rates and stomatal conductance were 2-3 times greater for resprouting trees than for unburned adults. Both predawn and midday water potentials were more negative for unburned adult trees, indicating that the stems were experiencing greater water stress than the stems of resprouting trees. In addition, the xylem specific conductivity was similar in the two growth forms, even though the stems of resprouting trees were less vulnerable to water-stress-induced embolism than similar diameter, but older, stems of adult trees. The reduced vulnerability may have been due to less cavitation fatigue in stems of resprouts. The modulus of elasticity, modulus of rupture and xylem density were all greater for resprouts, indicating that resprouts have greater mechanical strength than do adult trees. The data suggest that there is no trade-off between stem mechanical strength and shoot hydraulic and photosynthetic efficiency in resprouts, which may have implications for the success of this species in the fire-prone plant communities of southern California.

Nonequilibrium fluctuation relations in a quantum coherent conductor.

We experimentally demonstrate the validity of nonequilibrium fluctuation relations by using a quantum coherent conductor. In equilibrium the fluctuation-dissipation relation leads to the correlation between current and current noise at the conductor, namely, the Johnson-Nyquist relation. When the conductor is voltage biased so that the nonlinear regime is entered, the fluctuation theorem has predicted similar nonequilibrium fluctuation relations, which hold true even when the Onsager-Casmir relations are broken in magnetic fields. Our experiments qualitatively validate the predictions as the first evidence of this theorem in the nonequilibrium quantum regime.