Lateral Water Transport Research Articles

Photosynthesis of rice leaves with a parallel venation is highly tolerant to vein severing.

Vein severing in plants caused by leaf damage is common in fields where crops are cultivated. It is hypothesized that leaves with complex reticulate venation can withstand hydraulic disturbances caused by vein severing, thereby preserving leaf carbon assimilation. However, limited research focuses on vein damage of leaves with parallel venation. We studied how vein-severing affected the photosynthetic traits of rice (Oryza sativa) leaves in seconds, minutes and days, under varying water-demand conditions and differing extents of water supply disruption. Rice leaves completely lost their photosynthetic capacity within 2.5 minutes after excision. Severing the midrib resulted in reduced light-saturated photosynthetic rate (A), stomatal conductance (gsw ) and transpiration rate (E) by 2.6, 6.8 and 5.9%, respectively, already after thirty minutes. We further investigated the photosynthetic trait responses to various extents of leaf width severing, while keeping the midrib functional. Surprisingly, A, gsw and E in the downstream area of the severed leaves largely remained stable, showing minimal variation across different leaf width severing ratios. These traits declined only slightly even under increased ambient light intensity and leaf-to-air vapor pressure deficit. This sustained photosynthesis post-severing is attributed to the efficient lateral water transport. Long-term leaf damage slightly but not significantly, impacted the downstream photosynthetic traits within five days post-severing. However, a more pronounced reduction in gas exchange during leaf senescence was observed nine days after severing. These findings suggested that rice leaves can tolerate hydraulic disturbances from vein severing and maintain functionality under various conditions, which is crucial for crop yield stability. However, long-term consequences require further investigation.

Development of inter-grid-cell lateral unsaturated and saturated flow model in the E3SM Land Model (v2.0)

Abstract. The lateral transport of water in the subsurface is important in modulating terrestrial water energy distribution. Although a few land surface models have recently included lateral saturated flow within and across grid cells, it is not a default configuration in the Climate Model Intercomparison Project version 6 experiments. In this work, we developed the lateral subsurface flow model within both unsaturated and saturated zones in the Energy Exascale Earth System Model (E3SM) Land Model version 2 (ELMv2.0). The new model, called ELMlat, was benchmarked against PFLOTRAN, a 3D subsurface flow and transport model, for three idealized hillslopes that included a convergent hillslope, divergent hillslope, and tilted V-shaped hillslope with variably saturated initial conditions. ELMlat showed comparable performance against PFLOTRAN in terms of capturing the dynamics of soil moisture and groundwater table for the three benchmark hillslope problems. Specifically, the mean absolute errors (MAEs) of the soil moisture in the top 10 layers between ELMlat and PFLOTRAN were within 1 %±3 %, and the MAEs of water table depth were within ±0.2 m. Next, ELMlat was applied to the Little Washita experimental watershed to assess its prediction of groundwater table, soil moisture, and soil temperature. The spatial pattern of simulated groundwater table depth agreed well with the global groundwater table benchmark dataset generated from a global model calibrated with long-term observations. The effects of lateral groundwater flow on the energy flux partitioning were more prominent in lowland areas with shallower groundwater tables, where the difference in simulated annual surface soil temperature could reach 0.3–0.4 ∘C between ELMv2.0 and ELMlat. Incorporating lateral subsurface flow in ELM improves the representation of the subsurface hydrology, which will provide a good basis for future large-scale applications.

Impact of topography on in situ soil wetness measurements for regional landslide early warning – a case study from the Swiss Alpine Foreland

Abstract. Recent studies have demonstrated the potential of in situ soil wetness measurements to predict regional shallow landslides. Increasing availability of monitoring data from sensor networks provides valuable information for developing future regional landslide early warning systems (LEWSs); however, most existing monitoring sites are located on flat terrain. The question arises of if the representativeness for regional landslide activity would improve if sensors were installed on a landslide-prone hillslope. To address this, two soil wetness monitoring stations were installed at close proximity on a steep slope and on a flat location in the Napf region (Northern Alpine Foreland of Switzerland), and measurements were conducted over a period of 3 years. As both sites inhibit similar lithological, vegetation, and precipitation characteristics, soil hydrological differences can be attributed to the impact of topography and hydrogeology. At the sloped site, conditions were generally wetter and less variable in time, and evidence was found for temporary lateral water transport along the slope. These differences were systematic and could be reduced by considering relative soil moisture changes. The application of a statistical landslide forecast model showed that both sites were equally able to distinguish critical from non-critical conditions for landslide triggering, which demonstrates the value of existing monitoring sites in flat areas for the application in LEWSs.

Hydro‐Thermodynamic Processes at a Large Confluence Under Reservoir Regulation

AbstractConfluences are ubiquitous and important components in river systems, and their hydrodynamic complexity attracts increasing attention. The flow pattern in a confluence is influenced by the planform geometry, momentum, discharge ratio and bed concordance/discordance. In recent years, flow density is found to be a significant factor in natural confluence flow patterns, while the generated hydrodynamic processes that affects mixing within confluences are not fully known, especially in large rivers under heavy human activities. In this study, we investigate the hydro‐thermodynamic processes at a major confluence in the Yangtze River using a three‐dimensional numerical model. The water level in the confluence zone is regulated seasonally by the Three Gorges Reservoir, that is, the zone is within the reservoir's fluctuating backwater reach. The results show that reservoir regulation alters flow patterns in the confluence zone significantly in both horizontal and vertical planes, including shrinking re‐circulation, complicated cross‐sectional vortexes, as well as weakened riverine mixing capacity. The density difference leads to changes in the hydro‐thermodynamic processes, especially in combination with the reservoir regulation. When the tributary water temperature is high, the generated buoyancy strengthens the secondary flow in the mainstream, which further enhances the lateral transport capacity and accelerates the water mixing. More importantly, it is found that the combined effect of reservoir regulation and thermal buoyancy alters the flow structure considerably in the confluence zone, and modifies the water transport mode in the mainstream. Thus, a dimensionless number S is defined to represent the lateral water transport capacity.

Estimating the lateral transfer of organic carbon through the European river network using a land surface model

Abstract. Lateral carbon transport from soils to the ocean through rivers has been acknowledged as a key component of the global carbon cycle, but it is still neglected in most global land surface models (LSMs). Fluvial transport of dissolved organic carbon (DOC) and CO2 has been implemented in the ORCHIDEE LSM, while erosion-induced delivery of sediment and particulate organic carbon (POC) from land to river was implemented in another version of the model. Based on these two developments, we take the final step towards the full representation of biospheric carbon transport through the land–river continuum. The newly developed model, called ORCHIDEE-Clateral, simulates the complete lateral transport of water, sediment, POC, DOC, and CO2 from land to sea through the river network, the deposition of sediment and POC in the river channel and floodplains, and the decomposition of POC and DOC in transit. We parameterized and evaluated ORCHIDEE-Clateral using observation data in Europe. The model explains 94 %, 75 %, and 83 % of the spatial variations of observed riverine water discharges, bankfull water flows, and riverine sediment discharges in Europe, respectively. The simulated long-term average total organic carbon concentrations and DOC concentrations in river flows are comparable to the observations in major European rivers, although our model generally overestimates the seasonal variation of riverine organic carbon concentrations. Application of ORCHIDEE-Clateral for Europe reveals that the lateral carbon transfer affects land carbon dynamics in multiple ways, and omission of this process in LSMs may lead to an overestimation of 4.5 % in the simulated annual net terrestrial carbon uptake over Europe. Overall, this study presents a useful tool for simulating large-scale lateral carbon transfer and for predicting the feedbacks between lateral carbon transfer and future climate and land use changes.

Wood Scrolls as Highly Efficient All‐Day Steam Generators

AbstractA novel all‐day evaporator in the form of a scroll is developed by rolling a thin layer of wood. Two different wood layers are used to fabricate a wood scroll with diagonal natural water channels (d‐WS) and a wood scroll with parallel natural water channels (p‐WS). Because only diagonal channels allow water transport across the wood layer, d‐WS exhibits good lateral water transport, whereas p‐WS exhibits poor lateral water transport. The gap channels (i.e., spaces between the overlapping wood layers) facilitate vertical water transport in both d‐WS and p‐WS. The synergistic effect of the gap channels and diagonal channels in d‐WS allows for a uniform water flow and sufficient water transport to the top and side surfaces, thus simultaneously increasing evaporation performance and salt resistance. The total evaporation rate of water of d‐WS is 9.08 kg m−2 h−1 in the absence of wind, which increases to 37.95 kg m−2 h−1 in the presence of 2 m s−1 wind. These evaporation rates are among the highest values ever reported under similar conditions. The evaporation rate of d‐WS does not deteriorate even after 5 d, demonstrating the possibility of long‐term operation.

Characteristics of sulfide bearing soil materials in peat extraction areas in N-Finland

Concern has been raised about the potential formation of acid sulfate soils and associated environmental problems related to peat extraction and, thus, peat, sediment and till characteristics of 15 well drained peat extraction fields were investigated in northern and northwestern Finland. The aim was to identify and characterize the occurrence/abundance of potential acid (hypersulfidic) and actual acid sulfate soil materials as well as metals with regards to their depositional environment (marine/non-marine), black schists and soil material properties. Sulfide-bearing marine sediments were commonly found; the highest contents and thickness of sulfide sediments were found in areas <50 m above the current sea level (a.c.s.l.), while the sulfide contents were relatively low in the mineral soil materials (mainly till) in the non-marine areas (>100 m a.c.s.l.). The highest content of sulfides in sediments was typically found just below the peat layer. The sulfides existed mostly as pyrite (up to 3.5 wt% S) but were occasionally also mixed with more reactive metastable sulfide (Fe:S ratio in the order of 1:1), which coincide with high Fe concentrations, indicating that an abundance of Fe2+ can diminish the rate of pyrite formation. Sediments contained very high amounts of potential acidity, but in-field oxidation of the sediments was very limited. Although the sulfur contents were much lower (max 0.3% S), several of the till samples still became acidic (pH < 4) upon oxidation, and contained, thus, some amounts of potential acidity due to a pore buffering capacity. Consequently, during peat extraction most of the acidity is still retained in sediments limiting environmental consequences and, thus, focus should be on appropriate management to prevent oxidation and leaching after peat extraction has been finished. Locally high Mn and Zn concentrations were found in the sediments in black schist areas, indicating that Zn and Mn have migrated with the ground water from the schists to the sediment layers. In several black schist areas, the peat layer contained high amounts of sulfides with a corresponding high potential acidity as well as elevated As, Pb and Zn. This indicates an upward transport of sulfur and some metals (As, Pb and Zn) through capillary rise and/or plant uptake and/or through lateral water transport from surrounding black schist affected soil material. Air pollution, i.e. atmospheric distribution, was most likely a source for high concentrations of Cd, Hg and Sr concentrations in the peat.

Use of Topographic Models for Mapping Soil Properties and Processes

Landscape topography is an important driver of landscape distributions of soil properties and processes due to its impacts on gravity-driven overland and intrasoil lateral transport of water and nutrients. Rapid advancements in aerial, space, and geographic technologies have led to large scale availability of digital elevation models (DEMs), which have proven beneficial in a wide range of applications by providing detailed topographic information. In this report, we presented a summary of recent topography-based soil studies and reviewed five main groups of topographic models in geospatial analyses widely used for soil sciences. We then compared performances of two types of topography-based models—topographic principal component regression (TPCR) and TPCR-kriging (TPCR-Kr)—to ordinary kriging (OKr) models in mapping spatial patterns of soil organic carbon (SOC) density and redistribution (SR) rate. The TPCR and OKr models were calibrated at an agricultural field site that has been intensively sampled, and the TPCR and TPCR-Kr models were evaluated at another field of interest with two sampling transects. High-resolution topographic variables generated from light detection and ranging (LiDAR)-derived DEMs were used as inputs for the TPCR model building. Both TPCR and OKr models provided satisfactory results on SOC density and SR rate estimations during model calibration. The TPCR models successfully extrapolated soil parameters outside of the area in which the model was developed but tended to underestimate the range of observations. The TPCR-Kr models increased the accuracies of estimations due to the inclusion of residual kriging calculated from observations of transects for local correction. The results suggest that even with low sample intensives, the TPCR-Kr models can reduce estimation variances and provide higher accuracy than the TPCR models. The case study demonstrated the feasibility of using a combination of linear regression and spatial correlation analysis to localize a topographic model and to improve the accuracy of soil property predictions in different regions.

Vegetation pattern formation: The mechanisms behind the forms

A simple principle relating growth to lateral water transport explains the variety of self-organized vegetation patchiness.

Imaging and Modeling of Passive Water Management in a Miniature Fuel Cell

Fuel cells have potential for small power applications that require long periods, as much as several decades, of uninterrupted power. Small microwatt fuel cell stacks of varying membrane thickness were designed to allow for passive water management. The passive water management system was incorporated into the stack design by use of exposed Nafion membrane for lateral water transport. 1 An experimental and theoretical study of water management across the operating temperature range was conduction, including operando neutron imaging and the development of a multiphysics two-dimensional model. Stack testing was done between -55 °C to 85 °C using a baseline output current of 10 µA and periodic pulses of 4.5 mA lasting 100 ms, every 100 s, or an average current of 16 µA. The stack spatial water concentration was monitored during various operating conditions through in situ neutron imaging. Figure 1 shows the main points of interest on the stack. Operating temperatures ranged from -55 °C to 85 °C to analyze water formation and subsequent water removal. Freezing and below-freezing temperatures were controlled by use of a liquid nitrogen cooled series of insulated boxes to prevent external water condensation during imaging. These measurements suggest successful water transport laterally, enabling operation from the sub-freezing environment to temperatures near the boiling point of water. Figure 2a depicts a constant operation for two hours at 16 µA and -20 ºC and the subsequent drying process in Figure 2b. Water production due to gas crossover in the stacks was quantified at below-freezing temperatures. At temperatures at and below -20 °C, the water production due to gas crossover was greater than the amount of water removal via the passive water management strategy with the current turned off, rather than a drying of the cell as expected. With the gases turned off as well, drying occurs. This indicates that the cell design must allow for water (ice) build-up during operation at these sub-freezing temperatures for successful operation. To avoid large amounts of hydrogen loss due to membrane crossover, we employ multiple layers of membrane to make a thick, mechanically reinforced and chemically stabilized membrane. A two-dimensional multiphysics model for evaluation of water management was also developed to further describe and explore the passive water management system under different conditions. The fundamental model in its present form shows a similar shape but indicates faster water build-up than experimental data. This discrepancy is currently being resolved to allow for a more accurate representation. Acknowledgments: This work was supported by the U.S. Department of Energy.

Warming Alters Hydrologic Heterogeneity: Simulated Climate Sensitivity of Hydrology‐Based Microrefugia in the Snow‐to‐Rain Transition Zone

AbstractIn complex terrain, drifting snow contributes to ecohydrologic landscape heterogeneity and ecological refugia. In this study, we assessed the climate sensitivity of hydrological dynamics in a semiarid mountainous catchment in the snow‐to‐rain transition zone. This catchment includes a distinct snow drift‐subsidized refugium that comprises a small portion (14.5%) of the watershed but accounts for a disproportionate amount (modeled average 56%) of hydrological flux generation. We conducted climate sensitivity experiments using a physically based hydrologic model to assess responses of a suite of hydrologic metrics across the watershed. Experiments with an imposed 3.5 °C warming showed reductions in average maximum snow water equivalent of 58–68% and deep percolation by 72%. While relative decreases were similar across the watershed, much greater absolute decreases in snowpack occurred in the drift‐subsidized site than the surrounding landscape. In drift‐subsidized locations, warming caused a shift from a regime that included both energy‐ and water‐limited evapotranspiration conditions to exclusively water‐limited conditions. Warming also resulted in altered interannual variability of hydrologic metrics. The drift‐subsidized unit was more sensitive to warming than the surrounding landscape, with reduced potential for the effects of warming to be offset by increased precipitation. Despite spatially homogeneous changes in climate, the effects of climate change on the hydrological dynamics were spatially heterogeneous in this watershed due to the presence of lateral water transport in the form of drifting snow. These findings suggest an increase in hydrologic homogeneity across the landscape and relatively large changes in snow drift‐subsidized refugia.

Impacts of microtopographic snow redistribution and lateral subsurface processes on hydrologic and thermal states in an Arctic polygonal ground ecosystem: a case study using ELM-3D v1.0

Abstract. Microtopographic features, such as polygonal ground, are characteristic sources of landscape heterogeneity in the Alaskan Arctic coastal plain. Here, we analyze the effects of snow redistribution (SR) and lateral subsurface processes on hydrologic and thermal states at a polygonal tundra site near Barrow, Alaska. We extended the land model integrated in the E3SM to redistribute incoming snow by accounting for microtopography and incorporated subsurface lateral transport of water and energy (ELM-3D v1.0). Multiple 10-year-long simulations were performed for a transect across a polygonal tundra landscape at the Barrow Environmental Observatory in Alaska to isolate the impact of SR and subsurface process representation. When SR was included, model predictions better agreed (higher R2, lower bias and RMSE) with observed differences in snow depth between polygonal rims and centers. The model was also able to accurately reproduce observed soil temperature vertical profiles in the polygon rims and centers (overall bias, RMSE, and R2 of 0.59 ∘C, 1.82 ∘C, and 0.99, respectively). The spatial heterogeneity of snow depth during the winter due to SR generated surface soil temperature heterogeneity that propagated in depth and time and led to ∼ 10 cm shallower and ∼ 5 cm deeper maximum annual thaw depths under the polygon rims and centers, respectively. Additionally, SR led to spatial heterogeneity in surface energy fluxes and soil moisture during the summer. Excluding lateral subsurface hydrologic and thermal processes led to small effects on mean states but an overestimation of spatial variability in soil moisture and soil temperature as subsurface liquid pressure and thermal gradients were artificially prevented from spatially dissipating over time. The effect of lateral subsurface processes on maximum thaw depths was modest, with mean absolute differences of ∼ 3 cm. Our integration of three-dimensional subsurface hydrologic and thermal subsurface dynamics in the E3SM land model will facilitate a wide range of analyses heretofore impossible in an ESM context.

Internal morphology and histology of blueberry Vaccinium corymbosum L. (Ericaceae) in Lima, Peru

Although there is a lot of information about cultivation, use and medicinal properties of blueberry Vaccinium corymbosum, there is still little information about its internal morphology and histology. Therefore, we proposed to know more of those aspects and to understand the low seed germination. The material used was composed of seeds and mature plants obtained from a farm located in Trujillo, Peru. All histological work was made in the Laboratory of Plant Anatomy and Pharmacognosy belongs to Faculty of Biological Science in Universidad Nacional Mayor de San Marcos in Lima, Peru. Each organ was analyzed in cross and longitudinal sections, as well as in external or superficial view. Lugol and Sudan IV were used for seed sections, Safranin for stem and root sections, and Lugol for leaf sections. We found some variation in seed size and color, being assigned to the category of oil seeds. Germination was limited by the embryos viability, as well as thickness of the seed coat. Stems and roots have punctuated xylem vessels, which facilitate the lateral water transport. The radical system is highly branched, apparently due to mycorrhizal symbiosis. Leaves are bifacial, with all the stomata on the abaxial side, and features that are characteristic of C3 plants.

High-performance thin-film encapsulation for organic light-emitting diodes

Organic light-emitting diodes degrade rapidly by means of local cathode oxidation when exposed to the ambient atmosphere, resulting in visible non-emissive areas called black spots. High performance inorganic based encapsulations are required to protect the OLED. We have applied a hybrid thin-film encapsulation stack consisting of two inorganic barrier layers of silicon nitride deposited at low temperature with an organic layer in between. The resulting water permeation mechanism into the OLED is solely by means of lateral pinhole-to-pinhole transport. With the application of CaO nanoparticles in the organic layer the lateral water transport rate is reduced and we show that black spot formation in 8 cm2 OLEDs is delayed by 6000 h at accelerated climate conditions of 60°C/90% relative humidity. This is estimated to correspond to 20 years at ambient conditions.

Functional water flow pathways and hydraulic regulation in the xylem network of Arabidopsis.

In vascular plants, the xylem network constitutes a complex microfluidic system. The relationship between vascular network architecture and functional hydraulic regulation during actual water flow remains unexplored. Here, we developed a method to visualize individual xylem vessels of the 3D xylem network of Arabidopsis thaliana, and to analyze the functional activities of these vessels using synchrotron X-ray computed tomography with hydrophilic gold nanoparticles as flow tracers. We show how the organization of the xylem network changes dynamically throughout the plant, and reveal how the elementary units of this transport system are organized to ensure both long-distance axial water transport and local lateral water transport. Xylem vessels form distinct clusters that operate as functional units, and the activity of these units, which determines water flow pathways, is modulated not only by varying the number and size of xylem vessels, but also by altering their interconnectivity and spatial arrangement. Based on these findings, we propose a regulatory model of water transport that ensures hydraulic efficiency and safety.

CryoSEM Investigation of Latex Coatings Dried in Walled Substrates

Nonuniformities, such as heavy edges or "coffee rings", frequently develop as particulate coatings dry. One idea for avoiding these nonuniformities is to engineer the substrate edges. In this work, monodisperse latex coatings were deposited on substrates with photoresist walls around their edges. Cryogenic scanning electron microscopy (cryoSEM) results show particle accumulation near the walls and at the free surface. The contact line, pinned at the wall, generates lateral transport of water and particles, leading to a nonuniform coating thickness. Still, coatings on substrates with walls were shown to have a higher degree of thickness uniformity after drying than those without walls.

Pyrolysis‐Gas Chromatography/Mass Spectrometry Characterization of Humic Acids in Coastal Spodosols from Southeastern Brazil

This study on humic acids (HAs) of podzol horizons from the southeastern region of Brazil investigated the accumulation and degradation of soil organic matter (SOM) in warm‐climate podzols. Humic acids from sandy coastal Spodosols (Histic Alaquod and Arenic Alorthod) from Cardoso Island in Sao Paulo State were characterized by pyrolysis in combination with gas chromatography and mass spectrometry (Py‐GC/MS). The soils developed on quartzitics, andy, nutrient‐poor parent materials under restinga forest in a coastal area. The Py‐GC/MS results show that the chemical composition of HAs in B horizons in one out of three profiles was influenced by both dissolved organic C (DOC) and C from in situ decaying roots. Carbon derived from DOC dominated in the deepest part of the B horizons. In the Arenic Alorthod (H9) profile, SOM from the B horizon seemed to be largely derived from roots. The DOC‐derived SOM was characterized by large contributions of phenol, methylphenols, and degraded polysaccharide products, while root contributions were mainly characterized by lignin products. Aliphatics were most abundant in A horizons (E and EB horizons were not analyzed). Both DOC‐derived and lignin‐derived SOM showed distinct degradation patterns. The Py‐GC/MS results corroborate those obtained by 13C variable amplitude cross polarization magic angle spinning nuclear magnetic resonance spectroscopy and Fourier‐transform infrared spectroscopy. Molecular chemistry showed that podzol B horizons are variable in composition, and local influences, such as drainage and vertical or lateral water transport, and SOM decomposition play an important role in podzolization processes in warm climates.

Visualization of lateral water transport pathways in soybean by a time of flight-secondary ion mass spectrometry cryo-system.

Water movement between cells in a plant body is the basic phenomenon of plant solute transport; however, it has not been well documented due to limitations in observational techniques. This paper reports a visualization technique to observe water movement among plant cells in different tissues using a time of flight-secondary ion mass spectrometry (Tof-SIMS) cryo-system. The specific purpose of this study is to examine the route of water supply from xylem to stem tissues. The maximum resolution of Tof-SIMS imaging was 1.8 μm (defined as the three pixel step length), which allowed detection of water movement at the cellular level. Deuterium-labelled water was found in xylem vessels in the stem 2.5 min after the uptake of labelled water by soybean plants. The water moved from the xylem to the phloem, cambium, and cortex tissues within 30–60 min after water absorption. Deuterium ion counts in the phloem complex were slightly higher than those in the cortex and cambium tissue seen in enlarged images of stem cell tissue during high transpiration. However, deuterium ion counts in the phloem were lower than those in the cambium at night with no evaporative demand. These results indicate that the stem tissues do not receive water directly from the xylem, but rather from the phloem, during high evaporative demand. In contrast, xylem water would be directly supplied to the growing sink during the night without evaporative demand.

Precipitation determines the persistence of hollow Sphagnum species on hummocks

On raised bogs, the distribution of Sphagnum species is determined by their distance to the water table, but occasionally species are able to survive outside their niche. Hollow species that persist in hummock vegetation are assumed to profit from the higher water content of the surrounding hummock species, although the mechanism responsible is unclear. In this study, we elucidated the role of lateral hummock water transport (LHWT) and precipitation on the water content of hollow species occurring in hummocks. This was tested using a full factorial field transplantation experiment with cores of Sphagnum cuspidatum in a high and a low hummock. Treatments included direct precipitation (present or absent) and LHWT (present or absent). Fresh weights of the cores were measured at regular time intervals. Our results show a relatively large effect of precipitation on the water content in both the high and low hummock, whereas LHWT only seemed to be an important source of water in the high hummock, which was relatively dry. Furthermore, LHWT played an important role only after large precipitation events, suggesting that lateral water transport is indirectly affected by rain. This study shows that precipitation alone can explain the persistence of hollow species in high hummocks, whereas it was less important for hollow species in low hummocks. Our data suggest that the survival and potential expansion of hollow species in higher hummocks strongly depends on the intensity and frequency of rain events. Changes in precipitation patterns may result in a loss of Sphagnum diversity in hummocks.

Comparative sectoriality in temperate hardwoods: hydraulics and xylem anatomy

In wood, lateral transport of water and minerals occurs readily in ‘integrated’ trees but is more restricted in ‘sectored species’. Dye distribution and a novel hydraulic technique are used to quantify species-specific differences in sectoriality in three temperate hardwoods, Betula papyrifera, Acer saccharum and Quercus rubra. Sectoriality was related to key elements of xylem structure: intervascular pitting, vessel diameter and vessel grouping. Perfusion of 0.5% safranin through isolated roots showed root-to-branch dye transport was most extensive in B. papyrifera and least extensive in Q. rubra. To test sectorialty using hydraulics, 20 m m KCl solution was pushed at 0.1 MPa through 5-cm wood segments, before and after occluding the direct axial outlet with glue, with flow rate measured in grams of solution expelled over time. Direct (axial) conductance (g MPa−1 s−1) through unglued outlets was compared with indirect (tangential) conductance around occluded outlets. Species with high indirect/direct conductance ratios (Integration Index) are the most integrated. Integration Index ranged from 0.26 in B. papyrifera to 0.02 in Q. rubra. Macerates showed that B. papyrifera has much greater percentage of cell wall area covered with intervascular pits than does A. saccharum or Q. rubra. Vessel grouping was closest in B. papyrifera and vessels were most isolated in Q. rubra. Widest diameter vessels occurred in Q. rubra, where they concentrated in springwood. Intervascular pitting, vessel diameter and grouping are wood traits that contribute to the continuum of sectoriality in trees, and may influence the ability of tree species to dominate in homogeneous or in patchy environments. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150, 61–71.