Transpiration Flow Research Articles

The Péclet effect on leaf water enrichment correlates with leaf hydraulic conductance and mesophyll conductance for CO2

Leaf water gets isotopically enriched through transpiration, and diffusion of enriched water through the leaf depends on transpiration flow and the effective path length (L). The aim of this work was to relate L with physiological variables likely to respond to similar processes. We studied the response to drought and vein severing of leaf lamina hydraulic conductance (K(lamina) ), mesophyll conductance for CO(2) (g(m) ) and leaf water isotope enrichment in Vitis vinifera L cv. Grenache. We hypothesized that restrictions in water pathways would reduce K(lamina) and increase L. As a secondary hypothesis, we proposed that, given the common pathways for water and CO(2) involved, a similar response should be found in g(m) . Our results showed that L was strongly related to mesophyll variables, such as K(lamina) or g(m) across experimental drought and vein-cutting treatments, showing stronger relationships than with variables included as input parameters for the models, such as transpiration. Our findings were further supported by a literature survey showing a close link between L and leaf hydraulic conductance (K(leaf) = 31.5 × L(-0.43) , r(2) = 0.60, n = 24). The strong correlation found between L, K(lamina) and g(m) supports the idea that water and CO(2) share an important part of their diffusion pathways through the mesophyll.

Determination of an aerodynamic perforation of plates by means of numerical simulation

Aerodynamic behavior of transpiration flows through perforated plates finds recently some attention again. In this paper we refer to previous research carried out within the EUROSHOCK projects in nineties (Doerffer and Bohning, 2000 [1]). Those experiments were carried out on plates drilled with a help of lasers where the holes are of low quality, far from being cylindrical. Transpiration flow model proposed there introduced “aerodynamic perforation” which became an effective feature of a plate, instead of holeʼs dimensions. However, in literature there are attempts to use hole dimensions as means to characterize itʼs aerodynamic behavior (Poll and Danks, 1992 [3]; Inger and Babinsky, 2000 [2]). A question arises how all these approaches refer to the aerodynamics of plates with ideal cylindrical hole perforation. Such ideal cylindrical perforation is not achievable in experiment therefore it was decided to base our study on numerical methods. A data bank for different perforations and different holeʼs sizes was built by means of CFD simulations. This data bank was processed in the same way as previous experiments (Doerffer and Bohning, 2000 [1]), allowing for verification of empirical model.

Water status in Mesembryanthemum crystallinum under heavy metal stress

Heavy metals (HMs) are known to have negative effects on plant water status; however, the mechanisms by which plants rearrange their water relations to adapt to such conditions are poorly understood. Using the model plant Mesembryanthemum crystallinum, we studied disturbances in water status and rapid plant defence responses induced by excess copper or zinc. After a day of HM stress, reductions in root sap exudation and water deficits in leaf tissues became evident. We also observed several primary adaptive events, including a rapid decrease in the transpiration rate and progressive declines in the leaf-cell sap osmotic potential. Longer HM treatments resulted in reductions of total and relative water contents as well as proline accumulation, an increase in water retention capacity and changes in aquaporin gene expression. After 3 h of HM exposure, leaf expression of the McTIP2;2 gene, which encodes tonoplast aquaporin, was suppressed more than two-fold, thus representing one of the earliest responses to HM treatment. The expression of three additional aquaporin genes was also reduced starting at 9 h; this effect became more prominent upon longer HM exposure. These results indicate that HMs induce critical rearrangements in the water relations of M. crystallinum plants, based on the rapid suppression of transpiration flow and strong inhibition of root sap exudation. These effects then triggered an adaptive water-conserving strategy involving differential regulation of aquaporin gene expression in leaves and roots, further reductions in transpiration, and an accelerated switch to CAM photosynthesis.

Poiseuille and thermal transpiration flows of a highly rarefied gas: over-concentration in the velocity distribution function

Poiseuille and thermal transpiration flows of a highly rarefied gas are investigated on the basis of the linearized Boltzmann equation, with a special interest in the over-concentration of molecules on velocities parallel to the walls. An iterative approximation procedure with an explicit error estimate is presented, by which the structure of the over-concentration is clarified. A numerical computation on the basis of the procedure is performed for a hard-sphere molecular gas to construct a database that promptly gives the induced net mass flow for an arbitrary value of large Knudsen numbers. An asymptotic formula of the net mass flow is also presented for molecular models belonging to Grad's hard potential. Finally, the resemblance of the profiles between the heat flow of the Poiseuille flow and the flow velocity of the thermal transpiration is pointed out. The reason is also given.

Shading decreases the growth rate of young apple fruit by reducing their phloem import

This study investigates the effects of shading on the biophysical mechanisms of apple ( Malus Domestica Bork.) fruit growth by assessing how vascular and transpiration flows to/from the fruit are affected by shading. At 30 days after full bloom, a 90% neutral shading net was applied to four trees of the cv. Gala, for seven days, while four more trees, chemically thinned, were used as control. Fruit vascular and transpiration flows were assessed from two days before, to the end of shading. The daily patterns of fruit relative growth rate (RGR) and of phloem, xylem and transpiration flows were determined by continuous monitoring of fruit diameter by automatic fruit gauges. Before shading application, no differences between the two groups of trees selected were found for any of the parameters measured. Despite shading induced an immediate drop in canopy photosynthesis, both fruit daily RGR and phloem flow decreased gradually, until reaching 20% of the before treatment values after 7 days of shading. Differences in RGR and phloem flow appeared especially during the afternoon and night, i.e. post carbon assimilation by the tree, and fruit growth rates were higher in control trees. In the same period no, or very small differences were found between treatments for transpiration rates, while xylem flow was affected later than phloem and only at specific times during the day. These results suggest that the decrease in fruit growth rate under shading should be attributed to the reduction of canopy photosynthesis, rather than to a direct effect of shading on fruit sink strength.

A one-dimensional model of water flow in soil-plant systems based on plant architecture

The estimation of root water uptake and water flow in plants is crucial to quantify transpiration and hence the water exchange between land surface and atmosphere. In particular the soil water extraction by plant roots which provides the water supply of plants is a highly dynamic and non-linear process interacting with soil transport processes that are mainly determined by the natural soil variability at different scales. To better consider this root-soil interaction we extended and further developed a finite element tree hydro-dynamics model based on the one-dimensional (1D) porous media equation. This is achieved by including in addition to the explicit three-dimensional (3D) architectural representation of the tree crown a corresponding 3D characterisation of the root system. This 1D xylem water flow model was then coupled to a soil water flow model derived also from the 1D porous media equation. We apply the new model to conduct sensitivity analysis of root water uptake and transpiration dynamics and compare the results to simulation results obtained by using a 3D model of soil water flow and root water uptake. Based on data from lysimeter experiments with young European beech trees (Fagus silvatica L.) is shown, that the model is able to correctly describe transpiration and soil water flow. In conclusion, compared to a fully 3D model the 1D porous media approach provides a computationally efficient alternative, able to reproduce the main mechanisms of plant hydro-dynamics including root water uptake from soil.

An extended macroscopic transport model for rarefied gas flows in long capillaries with circular cross section

Pressure-driven and thermally driven rarefied gas flows in long capillaries with circular cross sections are investigated. For both Poiseuille and thermal transpiration flows, a unified theoretical approach is presented based on the linear form of regularized 13-moment (R13) equations. The captured nonequilibrium effects in the processes are compared to available kinetic solutions, and the shortcomings of classical hydrodynamics, i.e., the Navier–Stokes–Fourier equations, are highlighted. Breakdown of Onsager’s symmetry is proposed as a criterion to determine the range of applicability of extended macroscopic models. Based on Onsager’s reciprocity relation it is shown that linearized R13 equations provide agreement with kinetic data for moderate Knudsen numbers, Kn≤0.25. Two-way flow pattern and thermomolecular pressure difference in simultaneous pressure-driven and temperature-driven flows are analyzed. Moreover, second-order boundary conditions for velocity slip and temperature jump are derived for the Navier–Stokes–Fourier system. The proposed boundary conditions effectively improve classical hydrodynamics in the transition flow regime.

Independent Two-Fields Solution for Full-Potential Unsteady Transonic Flows

The paper introduces a new approach for the numerical solution of full-potential unsteady flows based on an independent approximation of the density and velocity potential fields. The solution procedure relies on an unstructured, node-based, finite volume approximation, with linear shape functions and nonreflecting farfield boundary conditions. An improved upwind density biasing allows us to stabilize the solution in supersonic regions. In view of linearized aeroelastic stability and response analyses, unsteady boundary conditions are accounted for by means of a density flow transpiration. Time marching solutions are dealt using first/second-order implicit schemes, whose unconditional linearized stability properties are demonstrated. A few applications are presented to validate the method.

Mechanistic assessment of hillslope transpiration controls of diel subsurface flow: a steady‐state irrigation approach

AbstractMechanistic assessment of how transpiration influences subsurface flow is necessary to advance understanding of catchment hydrology. We conducted a 24‐day, steady‐state irrigation experiment to quantify the relationships among soil moisture, transpiration and hillslope subsurface flow. Our objectives were to: (1) examine the time lag between maximum transpiration and minimum hillslope discharge with regard to soil moisture; (2) quantify the relationship between diel hillslope discharge and daily transpiration; and (3) identify the soil depth from which trees extract water for transpiration. An 8 × 20 m hillslope was irrigated at a rate of 3·6 mm h−1. Diel fluctuations in hillslope discharge persisted throughout the experiment. Pre‐irrigation time lags between maximum transpiration and minimum hillslope discharge were 6·5 h, whereas lags during steady‐state and post‐irrigation conditions were 4 and 2 h, respectively. The greatest correlation between transpiration and hillslope discharge occurred during the post‐irrigation period, when the diel reduction in hillslope discharge totalled 90% of total measured daily transpiration. Daily transpiration of trees within the irrigated area remained relatively constant throughout the experiment. Diel fluctuations in soil moisture were greatest at a depth of 0·9–1·2 m prior to irrigation and became more uniform throughout the soil profile during and post‐irrigation. This study clearly demonstrates that when soil moisture is high, hillslope trees can be an important factor in diel fluctuations in stream discharge. We advance a conceptual model for the site whereby the relationship between transpiration and hillslope discharge is a function of soil moisture status and drainable porosity. Copyright © 2010 John Wiley & Sons, Ltd.

The positive effect of skin transpiration in peach fruit growth

The effect of fruit transpiration on the mechanisms driving peach ( Prunus persica (L.) Batsch) daily growth was investigated. In peach, fruit water losses increase during the season and might play a key role in determining fruit growth. Skin transpiration was reduced during the cell expansion stage by enclosing fruit in plastic bags fitted with holes. In the first year, diameter changes of bagged and control fruit were precisely monitored for 15 days, and percentage dry matter and soluble solids content were determined during the experiment and at harvest. In the second year, midday fruit water potential, daily patterns of fruit growth and of vascular and transpiration flows were monitored. Bagging reduced fruit daily growth on some days, and negatively affected both fruit dry matter percentage and soluble solids content. Fruit transpiration rate was reduced during the midday hours, thus increasing midday fruit water potential and lowering xylem inflows. In accordance with the Münch hypothesis on traslocation, these conditions likely decreased the necessary gradient needed for the transport of phloem sap to sink organs, as in the afternoon, bagged fruit showed lower phloem inflows. These data suggest that skin transpiration in peach has a positive effect on fruit growth, as it enhances fruit phloem import.

Changes in vascular and transpiration flows affect the seasonal and daily growth of kiwifruit (Actinidia deliciosa) berry

The kiwifruit berry is characterized by an early stage of rapid growth, followed by a relatively long stage of slow increase in size. Vascular and transpiration flows are the main processes through which water and carbon enter/exit the fruit, determining the daily and seasonal changes in fruit size. This work investigates the biophysical mechanisms underpinning the change in fruit growth rate during the season. The daily patterns of phloem, xylem and transpiration in/outflows have been determined at several stages of kiwifruit development, during two seasons. The different flows were quantified by comparing the diurnal patterns of diameter change of fruit, which were then girdled and subsequently detached while measurements continued. The diurnal courses of leaf and stem water potential and of fruit pressure potential were also monitored at different times during the season. Xylem and transpiration flows were high during the first period of rapid volume growth and sharply decreased with fruit development. Specific phloem import was lower and gradually decreased during the season, whereas it remained constant at whole-fruit level, in accordance with fruit dry matter gain. On a daily basis, transpiration always responded to vapour pressure deficit and contributed to the daily reduction of fruit hydrostatic pressure. Xylem flow was positively related to stem-to-fruit pressure potential gradient during the first but not the last part of the season, when xylem conductivity appeared to be reduced. The fruit growth model adopted by this species changes during the season due to anatomical modifications in the fruit features.

Modelling field scale water partitioning using on-site observations in sub-Saharan rainfed agriculture

Abstract. Smallholder rainfed farming systems generally realise sub-optimal crop yields which are largely attributed to dry spell occurrences during crop growth stages. However, through the introduction of appropriate farming practices, it is possible to substantially increase yield levels even with little and highly variable rainfall. The presented results follow research conducted in the Makanya catchment in northern Tanzania where gross rainfall amounts to less than 400 mm/season which is insufficient to support staple food crops (e.g. maize). The yields from farming system innovations (SIs), which are basically alternative cultivation techniques, are compared against traditional farming practices. The SIs tested in this research are runoff harvesting used in combination with in-field trenches and soil bunds (fanya juus). These SIs aim to reduce soil and nutrient loss from the field and, more importantly, promote in-field infiltration and water retention. Water balance components have been observed in order to study water partitioning processes for the "with" and "without" SI scenarios. Based on rainfall, soil evaporation, transpiration, runoff and soil moisture measurements, a water balance model has been developed to simulate soil moisture variations over the growing season. Simulation results show that, during the field trials, the average productive transpiration flow ranged between 1.1–1.4 mm d−1 in the trial plots compared to 0.7–1.0 mm d−1 under traditional tillage practice. Productive transpiration processes accounted for 23–29% while losses to deep percolation accounted for 33–48% of the available water. The field system has been successfully modelled using the spreadsheet-based water balance 1-D model. Conclusions from the research are that the SIs that were tested are effective in enhancing soil moisture retention at field scale and that diversions allow crop growth moisture conditions to be attained with early rains. From the partitioning analysis, it is also concluded that there is more scope for efficient utilisation of the diverted runoff water if storage structures could be installed to minimise runoff and deep percolation and, hence, regulate water flow to the root zone when required.

The actual consumption of water by selected cultivated and weed species of plants and the actual values of evapotranspiration of the stands as determined under field conditions

 In the years 2005 to 2008, the consumption of water by selected cultivated and weed species under the field conditions and the values of the actual evapotranspiration in selected stands of cultivated crops were evaluated. The values of the transpiration flow were measured with a T4.2 EMS Brno (CZ) 12 channel sap-flow meter, and the actual evapotranspiration by BREB method (Bowen Ratio-Energy Balance) using the equipment of the same firm. The recording of the values obtained during the measurements was carried out in 10-min intervals. The sap flow was measured on the following weed plants <I>Amaranthus retroflexus</I>, <I>Artemisia vulgaris</I>, <I>Cirsium arvense</I>, <I>Conyza Canadensis</I>, and <I>Lactuca serriola </I>as weeds in the cultivated crops of <I>Brassica napus </I>and <I>Zea mays</I>. The actual evapotranspiration using the BREB method was determined over the stands of <I>Beta vulgaris</I>, <I>Brassica napus</I>, <I>Hordeum vulgare</I>, <I>Medicago sativa</I>, and <I>Zea mays</I>. On the basis of the measurements carried out, the average daily values of the sap flow of the evaluated plants ranged from 0.016 to 0.193 kg/day of water per plant. The maximum daily values ranged from 0.025 to 0.309 kg/day of water per plant. The average daily value of the evapotranspiration flow in <I>Hordeum vulgare </I>during the period under observation amounted to 2.9 mm, while the daily values ranged from 1.2 to 4.6 mm H<SUB>2</SUB>O/day. In the other evaluated plants, the daily values of evapotranspiration ranged from 0.9 mm to 5.9 mm/day of water, on average 3.4 mm/day of water (<I>Beta vulgaris</I>), and from 1.7 mm to 5.2 mm/day of water, on average 3.2 mm/day of water (<I>Brassica napus</I>).

Detailed analysis of double girdling effects on stem diameter variations and sap flow in young oak trees

Stem diameter variations are not solely driven by the water status of a tree, but also by the carbon status in the phloem. We mechanically changed the carbon status in young oak trees ( Quercus robur L.) by girdling the stem in order to investigate its effect on stem diameter variations. The stem was girdled at two heights by removing the bark which contains the carbon conducting phloem. The upper stem zone (U) still received new assimilates from the leaves, while the lowest stem zone (L) received only stored carbon from the roots. The middle stem zone (M) was completely isolated from crown and roots. As downward carbon transport was interrupted after girdling, the stem expansion and the roots. We argue that expedited growth in U was driven by both irreversible radial growth and reversible swelling. In contrast to U, stem expansion and carbohydrate content decreased in the two lower stem zones (M and L). Time lags were observed between the moments of morning shrinkage when comparing the three stem zones (U, M and L). Since these time lags correlated with the soluble carbohydrate content, it seems that daily dynamics in stem diameter variations were influenced by changes in carbon status. Furthermore, a decrease in xylem sap flow rate was observed, which could be attributed to an indirect effect of girdling. This decrease seems to be provoked by a feedback inhibition of net photosynthesis rate via stomatal closure. Such feedback inhibitions are often described in literature as a consequence of the reduced sink strength after girdling. This study, hence, demonstrates that a disturbance in tree carbon status not only changes carbon-related processes (i.e. radial stem growth, photosynthesis, carbon storage), but also water-related processes (i.e. stem swelling and shrinkage, transpiration and sap flow).

Numerical simulation of gas-phonon coupling in thermal transpiration flows

Thermal transpiration is a rarefied gas flow driven by a wall temperature gradient and is a promising mechanism for gas pumping without moving parts, known as the Knudsen pump. Obtaining temperature measurements along capillary walls in a Knudsen pump is difficult due to extremely small length scales. Meanwhile, simplified analytical models are not applicable under the practical operating conditions of a thermal transpiration device, where the gas flow is in the transitional rarefied regime. Here, we present a coupled gas-phonon heat transfer and flow model to study a closed thermal transpiration system. Discretized Boltzmann equations are solved for molecular transport in the gas phase and phonon transport in the solid. The wall temperature distribution is the direct result of the interfacial coupling based on mass conservation and energy balance at gas-solid interfaces and is not specified a priori unlike in the previous modeling efforts. Capillary length scales of the order of phonon mean free path result in a smaller temperature gradient along the transpiration channel as compared to that predicted by the continuum solid-phase heat transfer. The effects of governing parameters such as thermal gradients, capillary geometry, gas and phonon Knudsen numbers and, gas-surface interaction parameters on the efficiency of thermal transpiration are investigated in light of the coupled model.

Increasing productivity in irrigated agriculture: Agronomic constraints and hydrological realities

Irrigation is widely criticised as a profligate and wasteful user of water, especially in watershort areas. Improvements to irrigation management are proposed as a way of increasing agricultural production and reducing the demand for water. The terminology for this debate is often flawed, failing to clarify the actual disposition of water used in irrigation into evaporation, transpiration, and return flows that may, depending on local conditions, be recoverable. Once the various flows are properly identified, the existing literature suggests that the scope for saving consumptive use of water through advanced irrigation technologies is often limited. Further, the interactions between evaporation and transpiration, and transpiration and crop yield are, once reasonable levels of agricultural practices are in place, largely linear—so that increases in yield are directly and linearly correlated with increases in the consumption of water. Opportunities to improve the performance of irrigation systems undoubtedly exist, but are increasingly difficult to achieve, and rarely of the magnitude suggested in popular debate.

Rate-Independent Hysteresis in Terrestrial Hydrology

The goal of this article is twofold. The first objective is to demonstrate the role of hysteresis in hydrology. The second objective is to describe a class of simple and convenient mathematical models of hydrological systems with hysteresis and to briefly discuss methods for the quantitative and qualitative analysis of such models. This article is organized as follows. In the first section we discuss the role of the Preisach model. We then present an explicit expression for analogues of wetting and drying curves in the Preisach model context. The central role in this section is occupied by special one-parameter classes of Preisach operators which are useful as models of soil-water hysteresis for particular soils. Fitting is discussed in the context of the GRIZZLY database of hysteretic soil-water characteristics. The second section introduces a simple but instructive example of a differential equation coupled with a Preisach nonlinearity. This equation serves as a basis for modeling vegetated soil in terrestrial hydrology. The third section is dedicated to the FEST model, where FEST stands for "fully vegetated slab of soil with transpiring plants". This model describes drainage, transpiration, and infiltration flows in a fully vegetated slab of soil. We demonstrate that hysteresis effects are critical, both on qualitative and quantitative levels, for modeling hydrological systems and flows in soil, while theoretical analysis and numerical implementation of the models raise interesting mathematical questions. To demonstrate the application of this model we use rainfall data gathered in the Feale region in County Kerry, Ireland, covering a period of 19 months between July 2002 and February 2004. The FEST model includes a quantitative description of the dynamics of the plant biomass, which depends on the amount and regularity of precipitation and soil type, including details of soil-water hysteresis. Hence, the FEST model can be used as a component of ecological system models. Finally, the qualitative properties of the FEST model are discussed.

Source and sink limitations in vascular flows in peach fruit

SummaryThe daily patterns of vascular and transpiration flows to and from peach fruit were compared between heavily-thinned (LCL) and unthinned (HCL) trees, in order to assess when these flows were limited by resource availability (source-limited) or by the genetic potential of the fruit (sink-limited) during the day. Minute variations in fruit growth and in phloem, xylem, and transpiration flows were determined at cell division (stage I) and at cell expansion (stage III) during fruit development on several fruit per treatment, using highly sensitive fruit gauges. During cell expansion, the thinning treatments were also compared for their effects on fruit water potential. At stage I, no difference between treatments was found in any of the flows, suggesting that fresh matter (FM) import from phloem and xylem is sink-limited during early fruit development. At stage III, HCL fruit were smaller and had higher specific transpiration rates during the day. Xylem flow did not show any source limitations due to high crop load. However, it was “sink-strengthened” in the afternoon, in HCL, as these fruit reached lower water potentials during the day. Phloem flow to HCL fruit was source-limited during the afternoon, and at night, due to fruit-to-fruit competition. However, HCL fruit appeared to take advantage of their lower water potential at midday, when they showed higher rates of phloem flow. Although daily growth in HCL fruit undergoes periods of source limitation, this study showed how, at certain times of day, fruit may be more active sinks in attracting resources in high cropping conditions than at low crop loads.

Numerical Analysis of Thermal Transpiration Flows for a Nano-Pore Aerogel Membrane

Thermal transpiration flows in nano-pore aero-gel membranes are investigated for the performance optimization of a Knudsen compressor. Critical elements that drive the Knudsen compressor are its thermal transpiration membranes. The membranes are based on aerogel, or on machined aerogel. In our study, aerogel is modeled as a single microflow channel. The effects of wall temperature distribution on thermal transpiration flow patterns are examined. The flow has a pumping effect, and the mass flow rates through the channel are calculated. The results show that a steady one-way flow is induced for a wide range of Knudsen numbers. The direct simulation Monte Carlo (DSMC) method, with a variable hard sphere (VHS) model and no time counter (NTC) technique, is applied to obtain numerical solutions.

GREENFALL LINKS GROUNDWATER TO ABOVEGROUND FOOD WEBS IN DESERT RIVER FLOODPLAINS

Groundwater makes up nearly 99% of unfrozen freshwater worldwide and sustains riparian trees rooted in shallow aquifers, especially in arid and semiarid climates. The goal of this paper is to root animals in the regional water cycle by quantifying the significance of groundwater to riparian animals. We focused our efforts on the cricket, Gryllus alogus: a common primary consumer found in floodplain forests along the San Pedro River, in southeast Arizona, USA. Cottonwood trees make groundwater available to G. alogus as dislodged, groundwater‐laden leaves (greenfall). We hypothesized that groundwater fluxes mediated by greenfall sustain G. allogus through the prolonged dry season and link these aboveground consumers to belowground aquifers.To test this hypothesis, we first characterized gradients in absolute humidity (air) and water stress in field‐collected G. alogus. Absolute humidity declined with distance from river across wide stands of floodplain cottonwood forest during the dry season, but not during the rainy season. Similarly, G. alogus body water content declined along this gradient. Second, we measured evaporative water loss (EWL) by field‐captured G. alogus in the laboratory at temperatures bracketing field conditions. EWL ranged from 0.05 ± 0.009 g·individual−1·d−1 to 0.13 ± 0.03 g·individual−1·d−1 (mean ± SD, at 30° and 40°C, respectively). These daily losses are high, but still less than the water content of a single cottonwood leaf (0.296 ± 0.124 g H2O/leaf). Third, we designed field experiments to quantify the relative dependence of G. alogus on greenfall. G. alogus more frequently consumed greenfall than various controls consisting of dried leaves. This preference occurred in distal habitats and during the dry season, but not proximal to the river or in the rainy season. Finally, we compared estimated daily water fluxes via greenfall to (1) estimates of water demand of the entire G. alogus population at our field site, and (2) reports of cottonwood transpiration and San Pedro River base flow from other authors. By our estimates, groundwater fluxes via greenfall sustain G. alogus populations despite their trivial magnitude compared to stream discharge and cottonwood transpiration. Primary consumers in turn provide dietary water to higher trophic levels (e.g., abundant and speciose birds in the region) through trophic pathways, thereby fueling secondary production from the bottom up. Thus, riparian trees root animals in the regional water cycle.