Hydraulic Architecture Research Articles

Hydraulic mechanism of limiting growth and maintaining survival of desert shrubs in arid habitats.

The growth and survival of woody plant species is mainly driven by evolutionary and environmental factors. However, little is known about the hydraulic mechanisms that respond to growth limitation and enable desert shrub survival in arid habitats. To shed light on these hydraulic mechanisms, 9-, 31-, and 56-year-old Caragana korshinskii plants that had been grown under different soil water conditions at the southeast edge of the Tengger Desert, Ningxia, China were used in this study. The growth of C. korshinskii was mainly limited by soil water rather than shrub age in non-watered habitats, which indicated the importance of maintaining shrub survival prior to growth under drought. Meanwhile, higher vessel density, narrower vessels and lower xylem hydraulic conductivity indicated that shrubs enhanced hydraulic safety and reduced their hydraulic efficiency in arid conditions. Importantly, xylem hydraulic conductivity mediated by variation in xylem hydraulic architecture regulated photosynthetic carbon assimilation and growth of C. korshinskii. Our study highlights that the synergistic variation in xylem hydraulic safety and hydraulic efficiency is the hydraulic mechanism limiting growth and maintaining survival of C. korshinskii under drought, providing insights into the strategies for growth and survival of desert shrubs in arid habitats.

Extreme functional specialization of fertile leaves in a widespread fern species and its implications on the evolution of reproductive dimorphism.

Resource allocation theory posits that organisms distribute limited resources across functions to maximize their overall fitness. In plants, the allocation of resources among maintenance, reproduction, and growth influences short-term economics and long-term evolutionary processes, especially during resource scarcity. The evolution of specialized structures to divide labor between reproduction and growth can create a feedback loop where selection can act on individual organs, further increasing specializaton and resource allocation. Ferns exhibit diverse reproductive strategies, including dimorphism, where leaves can either be sterile (only for photosynthesis) or fertile (for spore dispersal). This dimorphism is similar to processes in seed plants (e.g., the production of fertile flowers and sterile leaves), and presents an opportunity to investigate divergent resource allocation between reproductive and vegetative functions in specialized organs. Here, we conducted anatomical and hydraulic analyses on Onoclea sensibilis L., a widespread dimorphic fern species, to reveal significant structural and hydraulic divergences between fertile and sterile leaves. Fertile fronds invest less in hydraulic architecture, with nearly 1.5 times fewer water-conducting cells and a nearly 0.5 times less drought-resistant xylem compared to sterile fronds. This comes at the increased relative investment in structural support, which may help facilitate spore dispersal. These findings suggest that specialization in ferns-in the form of reproductive dimorphism-can enable independent selection pressures on each leaf type, potentially optimizing spore dispersal in fertile fronds and photosynthetic efficiency in sterile fronds. Overall, our study sheds light on the evolutionary implications of functional specialization and highlights the importance of reproductive strategies in shaping plant fitness and evolution.

Primary, seminal and lateral roots of maize show type-specific growth and hydraulic responses to water deficit.

The water uptake capacity of a root system is determined by its architecture and hydraulic properties, which together shape the root hydraulic architecture. Here, we investigated root responses to water deficit (WD) in seedlings of a maize (Zea mays) hybrid line (B73H) grown in hydroponic conditions, taking into account the primary root (PR), the seminal roots (SR), and their respective lateral roots. WD was induced by various polyethylene glycol concentrations and resulted in dose-dependent inhibitions of axial and lateral root growth, lateral root formation, and hydraulic conductivity (Lpr), with slightly distinct sensitivities to WD between PR and SR. Inhibition of Lpr by WD showed a half-time of 5 to 6 min and was fully (SR) or partially (PR) reversible within 40 min. In the two root types, WD resulted in reduced aquaporin expression and activity, as monitored by mRNA abundance of 13 plasma membrane intrinsic protein (ZmPIP) isoforms and inhibition of Lpr by sodium azide, respectively. An enhanced suberization/lignification of the epi- and exodermis was observed under WD in axial roots and in lateral roots of the PR but not in those of SR. Inverse modeling revealed a steep increase in axial conductance in root tips of PR and SR grown under WD that may be due to the decreased growth rate of axial roots in these conditions. Overall, our work reveals that these root types show quantitative differences in their anatomical, architectural, and hydraulic responses to WD, in terms of sensitivity, amplitude and reversibility. This distinct functionalization may contribute to integrative acclimation responses of whole root systems to soil WD.

No effect of snow on shrub xylem traits: Insights from a snow-manipulation experiment on Disko Island, Greenland

Widespread shrubification across the Arctic has been generally attributed to increasing air temperatures, but responses vary across species and sites. Wood structures related to the plant hydraulic architecture may respond to local environmental conditions and potentially impact shrub growth, but these relationships remain understudied. Using methods of dendroanatomy, we analysed shrub ring width (RW) and xylem anatomical traits of 80 individuals of Salix glauca L. and Betula nana L. at a snow manipulation experiment in Western Greenland. We assessed how their responses differed between treatments (increased versus ambient snow depth) and soil moisture regimes (wet and dry). Despite an increase in snow depth due to snow fences (28–39 %), neither RW nor anatomical traits in either species showed significant responses to this increase. In contrast, irrespective of the snow treatment, the xylem specific hydraulic conductivity (Ks) and earlywood vessel size (LA95) for the study period were larger in S. glauca (p < 0.1, p < 0.01) and B. nana (p < 0.01, p < 0.001) at the wet than the dry site, while both species had larger vessel groups at the dry than the wet site (p < 0.01). RW of B. nana was higher at the wet site (p < 0.01), but no differences were observed for S. glauca. Additionally, B. nana Ks and LA95 showed different trends over the study period, with decreases observed at the dry site (p < 0.001), while for other responses no difference was observed. Our results indicate that, taking into account ontogenetic and allometric trends, hydraulic related xylem traits of both species, along with B. nana growth, were influenced by soil moisture. These findings suggest that soil moisture regime, but not snow cover, may determine xylem responses to future climate change and thus add to the heterogeneity of Arctic shrub dynamics, though more long-term species- and site- specific studies are needed.

Modelling hydraulic plasticity of mangroves

The hydraulic architecture of plants responds to their water availability, mediating between promoting water flow and providing hydraulic safety against embolism. Sites with a constant supply of water favor plants with large vessel diameters, while in dry conditions, narrower vessels are more advantageous. The characteristics of the vessels are primarily shaped by the species’ adaptation to its preferred habitat. However, physiological plasticity enables individual plants to undergo further adaptations to suit specific sites. Mangroves are constantly exposed to low water potentials and therefore hydraulic properties play a pivotal role. Reevaluating studies on vessel diameter distributions and xylem conductivities, we propose a two-parameter gamma distribution description of the hydraulic system. The shape parameter characterizes the species-specific component, and the rate parameter specifies the particular adaptation of the plant to the site salinity. Based on the Hagen–Poiseuille law, we can estimate the xylem conductivity of the plant. Applying this approach to the established single tree model BETTINA, we show the potential plant damage due to salinity shocks for stylized species with different hydraulic properties. Model results suggest that plants with a vessel diameter distribution similar to Rhizophora spp. have an advantage and grow faster under constant salinity conditions due to higher hydraulic conductivities compared to Avicennia-like diameter distributions. This comes at the cost of a higher hydraulic vulnerability to salinity changes of Rhizophora. This approach provides a mechanistic link between site conditions and the hydraulic properties of plants in terms of their ability to physiologically adjust to the site.

Linking functional composition moments of the sub-Mediterranean ecotone with environmental drivers.

Functional trait-based approaches are extensively applied to the study of mechanisms governing community assembly along environmental gradients. These approaches have been classically based on studying differences in mean values among species, but there is increasing recognition that alternative metrics of trait distributions should be considered to decipher the mechanisms determining community assembly and species coexistence. Under this framework, the main aim of this study is to unravel the effects of environmental conditions as drivers of plant community assembly in sub-Mediterranean ecotones. We set 60 plots in six plant communities of a sub-Mediterranean forest in Central Spain, and measured key above- and belowground functional traits in 411 individuals belonging to 19 species, along with abiotic variables. We calculated community-weighted mean (CWM), skewness (CWS) and kurtosis (CWK) of three plant dimensions, and used maximum likelihood techniques to analyze how variation in these functional community traits was driven by abiotic factors. Additionally, we estimated the relative contribution of intraspecific trait variability and species turnover to variation in CWM. The first three axes of variation of the principal component analyses were related to three main plant ecological dimensions: Leaf Economics Spectrum, Root Economics Spectrum and plant hydraulic architecture, respectively. Type of community was the most important factor determining differences in the functional structure among communities, as compared to the role of abiotic variables. We found strong differences among communities in their CWMs in line with their biogeographic origin (Eurosiberian vs Mediterranean), while differences in CWS and CWK indicate different trends in the functional structure among communities and the coexistence of different functional strategies, respectively. Moreover, changes in functional composition were primarily due to intraspecific variability. We observed a high number of strategies in the forest with the different communities spreading along the acquisitive-conservative axis of resource-use, partly matching their Eurosiberian-Mediterranean nature, respectively. Intraspecific trait variability, rather than species turnover, stood as the most relevant factor when analyzing functional changes and assembly patterns among communities. Altogether, our data support the notion that ecotones are ecosystems where relatively minor environmental shifts may result in changes in plant and functional composition.

Modeling Xylem Functionality Aspects.

Depending on the questions to be answered, water flow in the xylem can be modelled following different approaches with varying spatial and temporal resolution. When focussing on the influence of hydraulic architecture upon flow dynamics, distribution of water potentials in a tree crown or questions of vulnerability of the hydraulic system, functional-structural plant models, which link representations of morphological structure with simulated processes and with a virtual environment, can be a promising tool. Such a model will then include a network of idealized xylem segments, each representing the conducting part of a stem or branch segment, and a numerical machinery suitable for solving a system of differential equations on it reflecting the hydrodynamic laws, which are the basis of the broadly accepted cohesion-tension theory of water flow in plants. We will discuss functional-structural plant models, the simplifications that are useful for hydraulic simulations within this framework, the deduction of the used differential equations from basic physical conservation laws, and their numerical solution, as well as additional necessary models of radiation, photosynthesis, and stomatal conductance. In some supplementary notes, we are shortly addressing some related questions, for example, about root systems or about the relation between macro-scale hydraulic parameters and fine-grained (anatomical) xylem structure.

Detecting and Quantifying Xylem Embolism by Synchrotron-Based X-Ray Micro-CT.

The vulnerability to xylem embolism is a key trait underlying species-specific drought tolerance of plants, and hence is critical for screening climate-resilient crops and understanding vegetation responses to drought and heat waves. Yet, accurate determination of embolism in plant's xylem is challenging, because most traditional hydraulic techniques are destructive and prone to artefacts. Hence, direct and in vivo synchrotron-based X-ray micro-CT observation of xylem conduits has emerged as a key reference technique for accurate quantification of vulnerability to xylem embolism. Micro-CT is nowadays a fundamental tool for studies of plant hydraulic architecture, and this chapter describes the fundamentals of acquisition and processing of micro-CT images of plant xylem.

Carbon gain is coordinated with enhanced stomatal conductance and hydraulic architecture in coffee plants acclimated to elevated [CO2]: The interplay with irradiance supply

We recently demonstrated that, under elevated [CO2] (eCa), coffee (Coffea arabica L.) plants grown at high light (HL), but not at low light (LL), display higher stomatal conductance (gs) than at ambient [CO2] (aCa). We then hypothesized that the enhanced gs at eCa/HL, if sustained at the long-term, would lead to adjustments in hydraulic architecture. To test this hypothesis, potted plants of coffee were grown in open-top chambers for 12 months under HL or LL (ca. 9 or 1 mol photons m−2 day−1, respectively); these light treatments were combined with two [CO2] levels (ca. 437 or 705 μmol mol−1, respectively). Under eCa/HL, increased gs was closely accompanied by increases in branch and leaf hydraulic conductances, suggesting a coordinated response between liquid- and vapor-phase water flows throughout the plant. Still under HL, eCa also resulted in increased Huber value (sapwood area-to-total leaf area), sapwood area-to-stem diameter, and root mass-to-total leaf area, thus further improving the water supply to the leaves. Our results demonstrate that Ca is a central player in coffee physiology increasing carbon gain through a close association between stomatal function and an improved hydraulic architecture under HL conditions.

Correction to “Hydraulic architecture explains species moisture dependency but not mortality rates across a tropical rainfall gradient”

Correction to “Hydraulic architecture explains species moisture dependency but not mortality rates across a tropical rainfall gradient”

An analytical complete model of root pressure generation: Theoretical bases for studying hydraulics of bamboo.

To better understand the dynamics and functional roles of root pressure, we represent a novel and the first complete analytical model for root pressure, which can be applied to complex roots/shoots. The osmotic volume of a single root is equal to that of the vessel lumen in fine roots and adjacent apoplastic spaces. Water uptake occurs via passive osmosis and active solute uptake ( , osmol s-1 ), resulting in the osmolyte concentration Cr (mol·kg-1 of water) at a fixed osmotic volume. Solute loss occurs via two passive processes: radial diffusion of solute Km (Cr - Csoil ) from fine roots to soil, where Km is the diffusional constant and Csoil is the soil-solute concentration, and the mass flow of solute and water into the plant from the fine roots. The proposed model predicts the quadratic function of root pressure (Pr ), , where b and c are the functions of plant hydraulic resistance, soil water potential, solute flux and gravitational potential. The model demonstrates the root pressure-mediated distribution of water through the hydraulic architecture of a 6.8-m-tall bamboo shoot. This model provides a theoretical basis to test the functional roles of root pressure in shaping the hydraulic architecture and refilling potential xylem embolisms.

Dendroanatomy of xylem hydraulics in two pine species: Efficiency prevails on safety for basal area growth in drought-prone conditions

Xylem structure optimizes water conductivity while preventing hydraulic failure via embolism resistance, but how this process is modulated by climate variability and how it affects secondary growth in mature trees is still not fully understood, particularly in water-limited environments. Using quantitative wood anatomy techniques, we estimated xylem anatomical proxies for hydraulic efficiency (xylem specific conductivity, Ks) and safety (cell wall reinforcement, wrein) in two western US conifers, Pinus flexilis and Pinus longaeva, at a montane and subalpine location respectively. We built two large datasets (570 rings for P. flexilis, 635 rings for P. longaeva) to investigate 1) the variability of anatomical parameters (i.e lumen diameter, cell wall thickness) and hydraulic proxies along the stem in the five outermost rings (2009–2013); 2) the response of hydraulic proxies to daily climate over a period of 24 years (1990–2013); and 3) the relationship between xylem hydraulic architecture and basal area increment (BAI). Lumen diameter scaled along the stem following a power function, but the scaling patterns of cell wall thickness and hydraulic proxies differed significantly between species. From 1990–2013, Ks decreased in both species, whereas wrein increased only in P. longaeva, while no trends were observed in BAI. Climate sensitivity of Ks peaked over a longer period (84–102 days) compared to wrein (20–55 days), responding to increasing minimum temperature. In both species, Ks was a better predictor of BAI than wrein, indicating that, even under severely water-limited conditions, radial growth is linked to hydraulic efficiency rather than safety. Based on the variability of cell density along the stem, the trade-off between hydraulic efficiency and safety in P. longaeva appeared to be controlled by a strategy of space occupation. Characterizing the mechanistic relationship between xylem anatomy, plant hydraulic functioning, and stem growth is necessary to better understand climate-growth relationships in the western US and species’ growth plasticity under future climate change scenarios.

Adaptation potential of Neotropical montane oaks to drought events: Wood anatomy sensitivity in Quercus delgadoana and Quercus meavei

Abstract Climate and local water availability are major evolutionary drivers of adaptive variation and plasticity in the hydraulic architecture of Tropical Montane Cloud Forest (TMCF) tree species. Between‐year xylem vessel variability is key to understanding the adaptation potential of wood anatomy of trees to drought. How wood anatomical features have been influenced by the typical TMCF climate and how tree species persist in these environments remain open questions, particularly in the context of predicted extreme climate events in the future. Here, we evaluated the effects of changes in temperature, precipitation and evapotranspiration during drought events on ring‐width and anatomical vessel traits (hydraulic diameter, vessel density, vessel grouping index and vulnerability index) for two relict endemic and threatened oak species (Quercus delgadoana and Q. meavei) from a Mexican TMCF. The study species differed in their functional and ecological vessel anatomical traits, and their wood anatomical differences are related to specific environmental requirements. However, the ring‐width indices (RWIs) calculated for these species indicate that both have high resistance and recovery, and thus high resilience to drought events. Ring‐width and vessel functional traits show differences in the between‐year variability of xylem traits associated with the hydraulic efficiency of these oak species, which is crucial to understanding how they avoid drought‐induced embolism and cavitation in vessel conduits. These results provide evidence for the existence of specific hydraulic systems that determine functional wood anatomy in response to climatic variation and drought in the study species. Further research assessing the wood anatomical adaptation to different climatic variables and identifying the xylem functional traits that underlie these adaptations, along with the mechanisms allowing tree species persistence in these environments, is essential to gain insight into the responses of TMCF to future drought events. Read the free Plain Language Summary for this article on the Journal blog.

Plant height shapes hydraulic architecture but does not predict metaxylem area under drought in Sorghum bicolor.

Climate change-induced variations in temperature and precipitation negatively impact plant growth and development. To ensure future food quality and availability, a critical need exists to identify morphological and physiological responses that confer drought tolerance in agro-economically important crop plants throughout all growth stages. In this study, two Sorghum bicolor accessions that differ in their pre-flowering responses to drought were exposed to repeated cycles of drying and rewatering. Morphological, physiological, and histological traits were measured across both juvenile and adult developmental stages. Our results demonstrate that plant height is not predictive of metaxylem area but does influence the hydraulic path and water management in an accession-specific manner. Further, when drought-responsive changes to the plant architecture are unable to compensate for the hydraulic risk associated with prolonged drought exposure, tight control of stomatal aperture is crucial to further mitigate hydraulic damage and prevent xylem embolism.

Natural variation of maize root hydraulic architecture underlies highly diverse water uptake capacities.

Plant water uptake is determined by the root system architecture and its hydraulic capacity, which together define the root hydraulic architecture. The current research aims at understanding the water uptake capacities of maize (Zea mays), a model organism and major crop. We explored the genetic variations within a collection of 224 maize inbred Dent lines and successively defined core genotype subsets to access multiple architectural, anatomical, and hydraulic parameters in the primary root (PR) and seminal roots (SR) of hydroponically grown seedlings. We found 9-, 3.5-, and 12.4-fold genotypic differences for root hydraulics (Lpr), PR size, and lateral root size, respectively, that shaped wide and independent variations of root structure and function. Within genotypes, PR and SR showed similarities in hydraulics and, to a lesser extent, in anatomy. They had comparable aquaporin activity profiles that, however, could not be explained by aquaporin expression levels. Genotypic variations in the size and number of late meta xylem vessels were positively correlated with Lpr. Inverse modeling further revealed dramatic genotypic differences in the xylem conductance profile. Thus, tremendous natural variation of maize root hydraulic architecture underlies a high diversity of water uptake strategies and paves the way to quantitative genetic dissection of its elementary traits.

Hydraulic architecture of crown in three Brazilian species

Summary The hydraulic limitation hypothesis postulates an increase in resistance to water conductivity as trees become taller. Accordingly, we expect that the hydraulic architecture of trees shares a close relationship with the crown architecture and that anatomical traits can directly or indirectly influence hydraulic conductivity. The aim of this work was to investigate the variations in vessels, hydraulic properties and wood density of three native Brazilian tree species. We selected 40-year-old Balfourodendron riedelianum, Cariniana legalis and Handroanthus vellosoi trees and measured maximum vessel length, specific hydraulic conductivity, the percentage loss of conductivity, leaf hydraulic conductivity, and density of branches at three different positions of the crown. Variability in anatomical and hydraulic properties was mostly explained by differences between species, while small differences were related to the position of the branch along the crown-position gradient. Within the measured variables, only the maximum vessel length differed between one crown position and the other. We posit that poor differences between anatomical and hydraulic positions in the crown-position gradient could be related to sample positions within the crown, which were relatively close to each other, with branches having similar ages and diameters. Our findings demonstrate that despite growing in the same environment and having the same age, our species deploy contrasting carbon allocation and hydraulic species-specific strategies. These strategies mirror different growth performances resulting from a different trade-off between hydraulic capacity and safety.

Wood trait trade‐offs in desert plants: A triangular model to understand intra‐ and interspecific variations along an aridity gradient

AbstractThe hydraulic architecture of woody plants may show intra‐ and interspecific variations along aridity gradients as a result of wood trait trade‐offs, which depend on species‐specific abilities to withstand or evade drought. Plant hydraulic architecture can be defined as the set of different cell types involved in water transport through the soil–plant‐atmosphere continuum. At the present time, there are two models designed to understand trade‐offs among xylem wood functional traits, developed by Baas and Pratt, respectively. The first model presents a triangular trade‐off space where three main plant xylem functions are linked to each other to provide resistance to embolism in evolutionary time. The second model depicts xylem cell types associated with their main functions, namely vessel‐transport, parenchyma‐storage and fibre‐support. We propose here a new model considering the same relative xylem cell trait abundance for three desert species with different drought tolerance strategies along an aridity gradient of more than 300 mm. Hence, our model may account for both intra‐ and interspecific variations in wood traits for species from different localities along an aridity gradient. The tree Neltuma flexuosa showed little intraspecific variation in the medium drought resistance portion of the trade‐off space, suggesting this species is independent from rainfall. Larrea divaricata showed a similar low intraspecific variation, but the spatial location in the trade‐off space suggests it has a high tolerance to drought. The third species, Bulnesia retama, showed a higher intraspecific variation within the trade‐off space, changing its hydraulic architecture in more fibre area with increasing aridity. Our model seems to be a generalized tool to assess both intra‐ and interspecific variations in trade‐offs for hydraulic architecture among woody plants as a response to drought.

Experimental and Modelling Analysis of a Downstream Compensation System: Energy Optimization of the Directional Control Valves

Through a study on the Fluid Power innovations in the last years emerged that still few solutions have been successfully implemented for the optimization of the hydraulic circuits. The recent machine electrification offers a potential for investment in energy-saving hydraulic systems to ensure greater performance and higher battery autonomy. From different studies emerged that in the specific field of ICE Off-road Vehicles, only about 10–15% of the available power at fuel level is actually transformed into useful energy for the actuators. Particularly the losses in the Directional Control Valves represent about 35–40% of the hydraulic energy available at the pump level. The traditional Directional Control Valves design solutions, in fact, neglects important opportunities for reducing losses and improving internal regeneration. Especially, energy recovery is rarely applied and in any case by means of important superstructures which considerably increase the costs of the system. This paper presents a new hydraulic architecture: an original Directional Control Valve layout based on a Downstream Compensation approach. In particular, a Flow Sharing system is implemented in this new architecture with the goal to minimize the wasted energy. In fact, this system realizes an important energy recovery from both the inertial loads and the simultaneous use of multiple actuators at different pressure level. The circuit enables recovered energy to be stored in a high-pressure accumulator. The paper presents the simulation results and the energy saving estimation realized through a lumped parameter environment “Amesim Simcenter”. Additionally, the results of experimental activities show the innovative system performance, benefits and physical applicability. This idea is based on concrete objectives and pays particular attention to cost sustainability, industrial manufacturability and system scalability.

Nitrogen addition alleviates drought effects on water status and growth of Moso bamboo (Phllostachys edulis)

Forest ecosystems are increasingly exposed to climate-change-induced drought and nitrogen deposition. However, the role of nitrogen deposition in shaping the responses of plant water use and growth to drought remains unclear. In this study, we conducted an ecosystem-scale manipulation experiment with sixteen plots of 400 m2 to explore responses of water use and growth patterns in a Moso bamboo (Phllostachys edulis) forest to throughfall reduction treatment (TRT) (-50%) and nitrogen (N) addition (100 kg ha−1 yr−1 of nitrogen) for two years. We found that TRT significantly reduced daily total canopy transpiration (EL), leaf water potential, leaf area index (LAI) and basal area increment in a unit stand area (BAI) by decreasing hydraulic conductance (K) and photosynthetic rate. N addition pronouncedly caused lower EL and higher LAI due to increased stomatal conductance sensitivity to vapor pressure deficit, photosynthetic rate, and intrinsic water use efficiency (WUEi) as well as decreased ratio of cross-sectional area of the culm wall to total leaf area (AS/AL) and root/ leaf ratio. The interaction of TRT and N addition caused an increase in leaf water potential at midday (20.6%) and BAI (+25%) compared with the TRT, accounting for the increased stomatal conductance sensitivity, K, photosynthetic rate and WUEi. Our results suggest that N addition alleviates drought effects on foliar water state and growth of Moso bamboo through altered stomatal conductance sensitivity, hydraulic architecture, and photosynthesis. Our findings highlight the key role of coupling processes of forest carbon, nitrogen and water in shaping plant water use and growth, suggesting that interactive effect of drought and nitrogen deposition on plant hydraulic properties should be considered under a changing environment.

Yerba mate (Ilex paraguariensis) agroforestry systems: intraspecific differences in water relations and hydraulic architecture.

Intensive farming systems benefit from the additional ecosystem services provided by tree integration, which generate different growing conditions for the main crop. We studied yerba mate (Ilex paraguariensis ) responses to growing conditions in monoculture (the conventional cropping system of yerba mate) and in three agroforestry systems: (1) yerba mate+Balfourodendron riedelianum ; (2) yerba mate+Peltophorum dubium ; and (3) yerba mate+Toona ciliata . Mainly, we focused on water relations and the hydraulic architecture of yerba mate. Agroforestry cropping systems provided a shade cover of around 34-45% and yielded as high as the conventional system. The shade cover influenced the allocation pattern to enhance leaf light capture, incrementing the leaf area to the sapwood area at the branch level. We also found a higher specific hydraulic conductivity in stems of yerba mate plants in consortium with T. ciliata than in the conventional cropping system, as well as higher resistance to water deficits due to lower vulnerability to embolism in the stems. During a severe drought, yerba mate plants had a similar stem and leaf water potential in both agricultural systems. Still, plants in monoculture had lower hydraulic safety margins and higher signs of leaf damage and mortality. This indicates that integrating trees into the yerba mate cultivation increases water stress resistance which would be beneficial to avoid restrictions on crop productivity under severe droughts induced by climate change.