Evaporation-driven internal hydraulic redistribution alleviates root drought stress: Mechanisms and modeling.

Many tree species have developed extensive root systems that allow them to survive in arid environments by obtaining water from a large soil volume. These root systems can transport and redistribute soil water during drought by hydraulic redistribution (HR). A recent study revealed the phenomenon of evaporation-driven hydraulic redistribution (EDHR), which is driven by evaporative demand (transpiration). In this study, we confirmed the occurrence of EDHR in Chinese white poplar (Populus tomentosa) through root sap flow measurements. We utilized microcomputed tomography technology to reconstruct the xylem network of woody lateral roots and proposed conceptual models to verify EDHR from a physical perspective. Our results indicated that EDHR is driven by the internal water potential gradient within the plant xylem network, which requires 3 conditions: high evaporative demand, soil water potential gradient, and special xylem structure of the root junction. The simulations demonstrated that during periods of extreme drought, EDHR could replenish water to dry roots and improve root water potential up to 38.9% to 41.6%. This highlights the crucial eco-physiological importance of EDHR in drought tolerance. Our proposed models provide insights into the complex structure of root junctions and their impact on water movement, thus enhancing our understanding of the relationship between xylem structure and plant hydraulics.

Response mechanism of growth and gypenosides content for Gynostemma longipes cultivated at two altitude habitats to fine root morphological characteristics.

Introduction: Fine roots are the critical functional organs of plants to absorb water and nutrients from the soil environment, while the relation between fine root morphological characteristics and yield & quality has received less attention for medicinal plants. Methods: Therefore, we investigated the relationship between fine root morphological characteristics and biomass & gypenosides content. We explored the primary environmental drivers of fine root indicators for Gynostemma longipes from three provenances cultivated at two altitude habitats. Results: At the end of the growing season, compared with the low-altitude habitat, the underground biomass of G. longipes in the high-altitude habitat increased significantly by 200%~290% for all three provenances. The response of gypenosides content to different altitude habitats varied with provenance and plant organs. The biomass of G. longipes strongly depended on the fine root characteristic indicators (P < 0.001), fine root length density, and fine root surface area. Our results also showed that the harvest yield of G. longipes could be effectively increased by promoting the growth of fine roots per unit leaf weight (P < 0.001, R2 = 0.63). Both fine root length density and fine root surface area had strong positive correlations with soil nutrient factors (R2 > 0.55) and a strong negative correlation with soil pH (R2 > 0.48). In a word, the growth of G. longipes is strongly controlled by the fine root morphological characteristics through the response of fine roots to soil nutrient factors and pH. Discussion: Our findings will help to deepen the understanding of the root ecophysiological basis driven by soil factors for the growth and secondary metabolites formation of G. longipes and other medicinal plants under changing habitat conditions. In future research, we should investigate how environmental factors drive plant morphological characteristics (e.g., fine roots) to affect the growth & quality of medicinal plants over a longer time scale.

Unlocking Drought-Induced Tree Mortality: Physiological Mechanisms to Modeling.

Drought-related tree mortality has become a major concern worldwide due to its pronounced negative impacts on the functioning and sustainability of forest ecosystems. However, our ability to identify the species that are most vulnerable to drought, and to pinpoint the spatial and temporal patterns of mortality events, is still limited. Model is useful tools to capture the dynamics of vegetation at spatiotemporal scales, yet contemporary land surface models (LSMs) are often incapable of predicting the response of vegetation to environmental perturbations with sufficient accuracy, especially under stressful conditions such as drought. Significant progress has been made regarding the physiological mechanisms underpinning plant drought response in the past decade, and plant hydraulic dysfunction has emerged as a key determinant for tree death due to water shortage. The identification of pivotal physiological events and relevant plant traits may facilitate forecasting tree mortality through a mechanistic approach, with improved precision. In this review, we (1) summarize current understanding of physiological mechanisms leading to tree death, (2) describe the functionality of key hydraulic traits that are involved in the process of hydraulic dysfunction, and (3) outline their roles in improving the representation of hydraulic function in LSMs. We urge potential future research on detailed hydraulic processes under drought, pinpointing corresponding functional traits, as well as understanding traits variation across and within species, for a better representation of drought-induced tree mortality in models.

Lack of phenotypic plasticity in leaf hydraulics for 10 woody species common to urban forests of North China.

The survival and performance of urban forests are increasingly challenged by urban drought, consequently compromising the sustainability and functionality of urban vegetation. Plant-water relations largely determine species drought tolerance, yet little is known about the hydraulics of urban forest species. Here, we report the leaf hydraulic and carbon traits that govern plant growth and drought resistance, including vulnerability to embolism, hydraulic conductivity and leaf gas exchange characteristics, as well as morphological traits that are potentially linked with these physiological attributes, with the aim of guiding species selection and management in urban forests. Plant materials were collected from mature shrubs and trees on our university campus in Beijing, representing 10 woody species common to urban forests in north China. We found that the leaf embolism resistance, represented by the water potential inducing 50% loss of hydraulic conductivity (P50), as well as the hydraulic safety margin (HSM) defined by P50 and the water potential threshold at the inception of embolism (P12), varied remarkably across species, but was unrelated to growth form. Likewise, stem and leaf-specific hydraulic conductivity (Kstem and kl) was also highly species-specific. Leaf P50 was positively correlated with hydraulic conductivity. However, neither P50 nor hydraulic conductivity was correlated with leaf gas exchange traits, including maximum photosynthetic rate (Amax) and stomatal conductance (gs). Plant morphological and physiological traits were not related, except for specific leaf area, which showed a negative relationship with HSM. Traits influencing plant-water transport were primarily correlated with the mean annual precipitation of species climatic niche. Overall, current common woody species in urban forest environments differed widely in their drought resistance and did not have the capacity to modify these characteristics in response to a changing climate. Species morphology provides limited information regarding physiological drought resistance. Thus, screening urban forest species based on plant physiology is essential to sustain the ecological services of urban forests.

Characteristics of airborne particles retained on conifer needles across China in winter and preliminary evaluation of the capacity of trees in haze mitigation.

To fully understand the characteristics of particulate matter (PM) retained on plant leaves (PMR) and the effect of vegetation on haze on a large spatial scale, we investigated needle samples collected from 78 parks and campuses in 31 cities (30 provincial cities) of China and developed a comprehensive method to characterise PMR. Both the PMR load (including water-insoluble particulate matter (WIPM), water-soluble inorganic ions (WSIS) and water-soluble organic matter (WSOM)), with a mean value of 554 ± 345 mg m-2 leaf area, and component profiles of PMR showed obvious spatial variation across the cities. Though haze pollution levels vary greatly among the 31 cities, the PM retention capacity of needles does not depend on haze level because PMR generally reaches saturation before precipitation in winter. The water-soluble component (WSC, the sum of WSIS and WSOM) accounted for 52.3% of PMR on average, among which WSIS and WSOM contributed 21.4% and 30.9% to PMR, respectively. The dominant ions of WSIS in PMR in the cities were Ca2+, K+ and NO3-, indicating that raised dust, biomass combustion and traffic exhaust are significant sources of PM in China. Compared with previous reports, the particle size distributions of PMR and PM across China were consistent, with fine PM (PM2.5) constituting a substantial proportion (43.8 ± 17.0%) of PMR. These results prove that trees can effectively remove fine particles from the air, thereby reducing human exposure to inhalable PM. We proposed a method to estimate the annual amount of PMR on Cedrus deodara, with an average value of 11.9 ± 9.6 t km-2 canopy yr-1 in China. Compared with the load of dust fall (atmospheric particles naturally falling on the ground, average of 138 ± 164 t km-2 land area yr-1 in China), we conclude that trees play a significant role in mitigating haze pollution.

Corrigendum: Unlocking drought-induced tree mortality: Physiological mechanisms to modelling.

[This corrects the article DOI: 10.3389/fpls.2022.835921.].

Global distribution of soapberries (Sapindus L.) habitats under current and future climate scenarios.

Sapindus (Sapindus L.) is a widely distributed economically important tree genus that provides biodiesel, biomedical and biochemical products. However, with climate change, deforestation, and economic development, the diversity of Sapindus germplasms may face the risk of destruction. Therefore, utilising historical environmental data and future climate projections from the BCC-CSM2-MR global climate database, we simulated the current and future global distributions of suitable habitats for Sapindus using a Maximum Entropy (MaxEnt) model. The estimated ecological thresholds for critical environmental factors were: a minimum temperature of 0-20 °C in the coldest month, soil moisture levels of 40-140 mm, a mean temperature of 2-25 °C in the driest quarter, a mean temperature of 19-28 °C in the wettest quarter, and a soil pH of 5.6-7.6. The total suitable habitat area was 6059.97 × 104 km2, which was unevenly distributed across six continents. As greenhouse gas emissions increased over time, the area of suitable habitats contracted in lower latitudes and expanded in higher latitudes. Consequently, surveys and conservation should be prioritised in southern hemisphere areas which are in danger of becoming unsuitable. In contrast, other areas in northern and central America, China, and India can be used for conservation and large-scale cultivation in the future.

An undiscovered facet of hydraulic redistribution driven by evaporation-a study from a Populus tomentosa plantation.

Maintaining the activity and function of the shallow root system of plants is essential for withstanding drought stress, but the associated mechanism is poorly understood. By investigating sap flow in 14 lateral roots (LRs) randomly selected from trees of a Chinese white poplar (Populus tomentosa) plantation receiving three levels of irrigation, an unknown root water transport mode of simultaneous daytime bi-directional water flow was discovered. This mode existed in five LRs confined to the surface soil without attached sinker roots. In the longer term, the bi-directional water flow was correlated with the soil water content. However, within the day, it was associated with transpiration. Our data demonstrated that bi-directional root sap flow occurred during the day, and was driven by evaporative demand, further suggesting the existence of circumferential water movement in the LR xylem. We named this phenomenon evaporation-driven hydraulic redistribution (EDHR). A soil-root water transport model was proposed to encapsulate this water movement mode. EDHR may be a crucial drought-tolerance mechanism that allows plants to maintain shallow root survival and activity by promoting root water recharge under extremely dry conditions.

The retention characteristics for water-soluble and water-insoluble particulate matter of five tree species along an air pollution gradient in Beijing, China.

The air purification potential of plants has been widely studied and recognized. However, their specific capacities in retaining water-soluble (WSPM) and water-insoluble (WIPM) atmospheric particulate matter (PM) are still unclear. In order to recommend tree species with high air phytoremediation ability, the retention characteristics for WSPM and WIPM of five tree species under different haze pollution levels and PM retention durations in Beijing were evaluated after introducing ultrasonic cleaning procedure to the conventional leaf cleaning methods. The daily PM amount retained these species in the six central districts in Beijing (SCBD) was roughly estimated based on the field tree survey data in 171 plots randomly distributed within the Fifth Ring Road. The updated leaf cleaning method improved the evaluation accuracy for WSPM and WIPM by 54% and 31%, respectively. The particles retained by the broadleaf and coniferous species were mainly composed of WSPM (71%) and WIPM (64%), respectively. The diameter distribution of PM varied markedly with species, PM retention duration, and pollution level. However, it always showed a unimodal pattern for WSPM and no uniform patterns for WIPM. The average relative capacities of different species in retaining WSPM of TSP (PM ≤ 100 µm) were more stable with time, and the corresponding rank was Sophora japonica > Salix babylonica > Ginkgo biloba > Pinus tabuliformis > Sabina chinensis. Whereas, as to the WIPM of TSP, their order changed to S. japonica > P. tabuliformis > S. babylonica > G. biloba > S. chinensis. During the study period, the TPM (WIPM+WSPM) of TSP retained by these species per day in the SCBD reached 132.6 t (76.1 t WSPM + 56.5 t WIPM), accounting for a considerable proportion of the daily dust-fall amount. These findings can contribute to selecting greening tree species and managing the urban forest to improve urban air quality.

[Quantitative Comparison of Methods to Assess the Airborne Particulate Matter Retention Capacity of Leaves].

The objective of this study was to explore the differences of five methods for evaluating the PM retention capacity of leaves based on the same experimental materials and leaf area measurement method and to summarize the advantages and disadvantages of each method. In this study, four tree species (Pinus tabuliformis, Platycladus orientalis, Ginkgo biloba, and Platanus occidentalis), which are common in Beijing and have greatly different leaf characteristics, were selected as the research objects. The mass subtraction method (MS), the membrane filter method (MF), the aerosol regenerator method(AR), the scanning electron method (SEM), and the elution weighing method coupled with a particle size analysis based on ultrasonic cleaning (ultrasonic-EWPA) were used to evaluate the PM retention capabilities and characteristics of the leaves of the four tree species. The total time needed and the total cost were measured simultaneously during the evaluation process. The results showed that although the values of PM retention efficiency obtained by different methods were quite different, the ranks of the efficiency of four tree species obtained by different methods were the same or partially the same. Additionally, the results obtained by the methods with the same or similar principles were more overlapped (AR and SEM had the most overlapped results). In addition, 89% of the species ranks of the same index obtained by each method were P. orientalis > P. tabuliformis > P. occidentalis > G. biloba, and the remaining 11% were P. occidentalis > G. biloba > P. orientalis > P. tabuliformis. Among the five methods, ultrasonic-EWPA was the one with the largest number of indexes and the highest cost, and MS was the one with the least number of indexes and the lowest cost. The one that needed most time was MF, while the one that needed the least time was AR. ultrasonic-EWPA and SEM are high input and high output methods. That is to say, although they needed more time and cost, they can prove more information; however, MS was opposite, which resulted in less information but lower time and cost needed. So, it is suitable for roughly evaluating the total PM retention capacities of trees; MF had a medium amount of information, low cost, but required too much time, which needs to be weighed and balanced before selecting this method. The AR method had strict requirements for equipment and parameters and should be used with caution. The results of this study can provide a comprehensive and detailed scientific basis for researchers to choose specific methods in the future.

[Effects of water and nitrogen coupling under furrow irrigation on tree growth, absorption and utilization of water and nitrogen of Populus tomentosa]. / 沟灌水氮耦合对毛白杨林木生长及水氮吸收利用的影响.

We explored the coupling effects of water and nitrogen in furrow irrigation on the growth and absorption and utilization of water and nitrogen in young poplar trees (triploid Populus tomentosa), under three irrigation levels (W20, W33, W45; when the soil water potential of 40 cm under the ditch reaches -20, -33 and -45 kPa respectively, irrigate), four N application levels (N120, N190, N260 and N0; the fertilization amount was 120, 190, 260 and 0 kg·hm-2·a-1), and natural conditions (CK). Based on the growth status of trees, the optimal combination of irrigation level and nitrogen application rate under furrow irrigation conditions was determined. The results showed that W20N120 (high water and low fertilizer; soil water potential threshold for initiating irrigation was -20 kPa and N application rate was 120 kg·hm-2·a-1) had the strongest effect on the stand productivity, with a value of 33.37 m3·hm-2·a-1. The significant coupling effect of water and N was detected only for tree height and total individual biomass. The increase of both irrigation amount and N application rate could increase the amount of N uptake, being mainly affected by the latter. The total amount of N uptake was the highest in the W20N260 treatment and reached 112.17 kg·hm-2·a-1, being 74.0% higher than that in CK. Among all the treatments, N uptake efficiency and N fertilizer partial productivity of W20N120 were the highest and significantly higher than those of the other treatments. The N uptake efficiency of the whole plant, aboveground part, and belowground part reached 36.8%, 28.5% and 6.4% in the W20N120 treatment, and its total N partial productivity reached 221.4 kg·kg-1. The effect of irrigation amount under different water-nitrogen coupling treatments on the irrigation water use efficiency was significant. Among them, irrigation water use efficiency in W45N260 was the highest and reached 13.66 g·kg-1. W20N120 had the highest water uptake amount and efficiency, which were 13268.28 t·hm-2 and 129.4%, respectively. To achieve great benefits, adequate irrigation (-20 kPa) and relatively low N application rate (120 kg·hm-2·a-1) should be selected during the young growth of the triploid P. tomentosa.

Assessing the Particulate Matter Removal Abilities of Tree Leaves.

Based on the conventional cleaning methods (water cleaning (WC) + brush cleaning (BC)), this study evaluated the influence of ultrasonic cleaning (UC) on collecting various sized particulate matter (PM) retained on leaf surfaces. We further characterized the retention efficiency of leaves to various sized PM, which will help to assess the abilities of urban trees to remove PM from ambient air quantitatively. Taking three broadleaf tree species (Ginkgo biloba, Sophora japonica, and Salix babylonica) and two needleleaf tree species (Pinus tabuliformis and Sabina chinensis) as the research objects, leaf samples were collected 4 days (short PM retention period) and 14 days (long PM retention period) after the latest rainfall. PM retained on the leaf surfaces was collected by means of WC, BC, and UC in sequence. Then, retention efficiencies of leaves (AEleaf) to three types of the various sized PM, including easily removable PM (ERP), difficult-to-remove PM (DRP), and totally removable PM (TRP), were calculated. Only around 23%-45% of the total PM retained on leaves could be cleaned off and collected by WC. When the leaves were cleaned through WC+BC, the underestimation of the PM retention capacity of different tree species was in the range of 29%-46% for various sized PM. Almost all PM retained on leaves could be removed if UC was supplemented to WC+BC. In conclusion, if the UC was complemented after the conventional cleaning methods, more PM on leaf surfaces could be eluted and collected. The procedure developed in this study can be used for assessing the PM removal abilities of different tree species.

Preliminary assessment on exposure of four typical populations to potentially toxic metals by means of skin wipes under the influence of haze pollution.

To investigate the exposure risk of human beings to nine potentially toxic metals (PTMs), namely, Cu, Cr, Zn, As, Cd, Pb, Ni, Mn, and Co, skin wipe samples were collected from four types of populations, namely, children, undergraduates, security guards, and professional drivers, under different haze pollution levels in Xinxiang, China by using Ghost wipes. The Ghost wipes were quantitatively analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after microwave digestion. Generally, Zn (ND-1350µg/m2 for undergraduates, ND-2660µg/m2 for security guards, ND-2460µg/m2 for children, and ND-2530µg/m2 for professional drivers) showed the highest concentration among the four populations, followed by Cu (0.02-83.4µg/m2 for undergraduates, ND-70.2µg/m2 for security guards, 23.2-487µg/m2 for children, and ND-116µg/m2 for professional drivers). As (ND-5.7µg/m2 for undergraduates, ND-2.3µg/m2 for security guards, ND-21.1µg/m2 for children, and ND-11.0µg/m2 for professional drivers) and Co (ND-6.0µg/m2 for undergraduates, ND-7.9µg/m2 for security guards, ND-13.4µg/m2 for children, and ND-2.1µg/m2 for professional drivers) showed the lowest concentrations in all populations. Remarkable differences were found among the four populations and PTM levels decreased in the following order: children, professional drivers, security guards, and undergraduates. Gender variation was discovered for undergraduates and children. Generally, PTM contamination in skin wipes collected during a light haze pollution level was generally higher than that during a heavy haze pollution level, but PTM contamination was comparable between the two haze pollution levels for children. Non-carcinogenic exposure risks to As, Cd, and Pb for all populations were higher than those for the other six elements but all of them were within the acceptable safety threshold, indicating no apparent non-carcinogenic risk.

An investigation of the leaf retention capacity, efficiency and mechanism for atmospheric particulate matter of five greening tree species in Beijing, China.

Urban trees have the potential to reduce air pollution, but the retention capacity and efficiency of different tree species for atmospheric particulate matter (PM) accumulation and the underlying mechanism hasn't been well understood. To select tree species with high air purification abilities, the supplementing ultrasonic cleaning (UC) procedure was first introduced into the conventional leaf cleaning methods [single water cleaning (WC) or plus brush cleaning (BC)] for eluting the leaf-retained PM. Further updates to the methodology were applied to investigate the retention capacity, efficiency, and mechanism for PM of five typical greening tree species in Beijing, China. Meanwhile, the particle size distribution of PM on the leaves, the PM retention efficiencies of easily removable (ERP), difficult-to-remove (DRP) and totally removable (TRP) particles on the leaf (AEleaf), and the individual tree scales were estimated. The experimental leaf samples were collected from trees with similar sizes 4 (SDR) and 14days (LDR) after rainfall. When the leaves were cleaned by WC+BC, there was, on average, 29%-46% of the PM remaining on the leaves of different species, which could be removed almost completely if UC was supplemented. From SDR to LDR, the mass of the leaf-retained PM increased greatly, and the particle size distribution changed markedly for all species except for Sophorajaponica. Pinus tabuliformis retains particles with the largest average diameter (34.2µm), followed by Ginkgo biloba (20.5µm), Sabina chinensis (16.4µm), Salix babylonica (16.0µm), and S. japonica (13.1µm). S. japonica and S. chinensis had the highest AEleaf to retain the TRP and ERP of both PM1 and PM1-2.5, respectively. Conversely, S. babylonica and P. tabuliformis could retain both TRP and ERP of PM2.5-5 and PM5-10, and PM>10 and TSP with the highest AEleaf, respectively. In conclusion, our results could be useful in selecting greening tree species with high air purification abilities.

[Effects of fertilization method and nitrogen application rate on soil nitrogen vertical migration in a Populus xeuramericana cv. 'Guariento' plantation].

A field experiment was conducted to investigate the effects of fertilization methods, i.e., drip (DF) and furrow fertilization (GF), and nitrogen (N) application rates (25, 50, 75 g N · plant(-1) · time(-1)) on the dynamics of soil N vertical migration in a Populus x euramericana cv. 'Guariento' plantation. The results showed that soil NH4(+)-N and NO3(-)-N contents decreased with the increasing soil depth under different fertilization methods and N application rates. In the DF treatment, soil NH4(+)-N and NO3(-)-N were mainly concentrated in the 0-40 cm soil layer, and their contents ascended firstly and then descended, reaching their maximum values at the 5th day (211.1 mg · kg(-1)) and 10th day (128.8 mg · kg(-1)) after fertilization, respectively. In the GF treatment, soil NH4(+)-N and NO3(-)-N were mainly concentrated in the 0-20 cm layer, and the content of soil NO3(-)-N rose gradually and reached its maximum at the 20th day (175.7 mg · kg(-1)) after fertilization, while the NH4(+)-N content did not change significantly after fertilization. Overall, N fertilizer had an effect within 20 days in the DF treatment, and more than 20 days in the GF treatment. In the DF treatment, the content and migration depth of soil NH4(+)-N and NO3(-)-N increased with the N application rate. In the GF treatment, the NO3(-)-N content increased with the N application rate, but the NH4(+)-N content was not influenced. Under the DF treatment, the hydrolysis rate, nitrification rate and migration depth of urea were higher or larger than that under the GF treatment, and more N accumulated in deep soil as the N application rate increased. Considering the distribution characteristics of fine roots and soil N, DF would be a better fertilization method in P. xeuramericana cv. 'Guariento' plantation, since it could supply N to larger distribution area of fine roots. When the N application rate was 50 g · tree(-1) each time, nitrogen mainly distributed in the zone of fine roots and had no risk of deep leaching, consequently improving the fertilizer utilization efficiency.

[Exploration of a quantitative methodology to characterize the retention of PM2.5 and other atmospheric particulate matter by plant leaves: taking Populus tomentosa as an example].

Taking Populus tomentosa as an example, a methodology called elution-weighing-particle size-analysis (EWPA) was proposed to evaluate quantitatively the ability of retaining fine particulate matter (PM2.5, diameter d ≤ 2.5 µm) and atmospheric particulate matter by plant leaves using laser particle size analyzer and balance. This method achieved a direct, accurate measurement with superior operability about the quality and particle size distribution of atmospheric particulate matter retained by plant leaves. First, a pre-experiment was taken to test the stability of the method. After cleaning, centrifugation and drying, the particulate matter was collected and weighed, and then its particle size distribution was analyzed by laser particle size analyzer. Finally, the mass of particulate matter retained by unit area of leaf and stand was translated from the leaf area and leaf area index. This method was applied to a P. tomentosa stand which had not experienced rain for 27 days in Beijing Olympic Forest Park. The results showed that the average particle size of the atmospheric particulate matter retained by P. tomentosa was 17.8 µm, and the volume percentages of the retained PM2.5, inhalable particulate matter (PM10, d ≤ 10 µm) and total suspended particle (TSP, d ≤ 100 µm) were 13.7%, 47.2%, and 99.9%, respectively. The masses of PM2.5, PM10, TSP and total particulate matter were 8.88 x 10(-6), 30.6 x 10(-6), 64.7 x 10(-6) and 64.8 x 10(-6) g x cm(-2) respectively. The retention quantities of PM2.5, PM10, TSP and total particulate matter by the P. tomentosa stand were 0.963, 3.32, 7.01 and 7.02 kg x hm(-2), respectively.

[Simulation of soil water dynamics in triploid Populus tomentosa root zone under subsurface drip irrigation].

Based on the observed data of triploid Populus tomentosa root distribution, a one-dimensional root water uptake model was proposed. Taking the root water uptake into account, the soil water dynamics in triploid P. tomentosa root zone under subsurface drip irrigation was simulated by using HYDRUS model, and the results were validated with field experiment. Besides, the HYDRUS model was used to study the effects of various irrigation technique parameters on soil wetting patterns. The RMAE for the simulated soil water content by the end of irrigation and approximately 24 h later was 7.8% and 6.0%, and the RMSE was 0.036 and 0.026 cm3 x cm(-3), respectively, illustrating that the HYDRUS model performed well in simulating the short-term soil water dynamics in triploid P. tomentosa root zone under drip irrigation, and the root water uptake model was reasonable. Comparing with 2 and 4 L x h(-1) of drip discharge and continuous irrigation, both the 1 L x h(-1) of drip discharge and the pulsed irrigation with water applied intermittently in 30 min periods could increase the volume of wetted soil and reduce deep percolation. It was concluded that the combination of 1 L x h(-1) of drip discharge and pulsed irrigation should be the first choice when applying drip irrigation to triploid P. tomentosa root zone at the experiment site.