Shallow Soil Layers Research Articles

Investigating unproductive water losses from irrigated agricultural crops in the humid tropics through analyses of stable isotopes of water

Abstract. Reliable information on water flow dynamics and water losses via irrigation on irrigated agricultural fields is important to improve water management strategies. We investigated the effect of season (wet season and dry season), irrigation management (flooded and non-flooded), and crop diversification (wet rice, dry rice, and maize) on soil water flow dynamics and water losses via evaporation during plant growth. Soil water was extracted and analysed for the stable isotopes of water (δ2H and δ18O). The fraction of evaporation losses were determined using the Craig–Gordon equation. For dry rice and maize, water in shallow soil layers (0 to 0.2 m) was more isotopically enriched than in deeper soil layers (below 0.2 m). This effect was less pronounced for wet rice but still evident for the average values at both soil depths and seasons. Soil water losses due to evaporation decreased from 40 % at the beginning to 25 % towards the end of the dry season. The soil in maize fields showed stronger evaporation enrichment than in rice during that time. A greater water loss was encountered during the wet season, with 80 % at the beginning of the season and 60 % at its end. The isotopic enrichment of ponding surface water due to evaporation was reflected in the shallow soils of wet rice. It decreased towards the end of both growing seasons during the wet and the dry season. We finally discuss the most relevant soil water flow mechanisms, which we identified in our study to be those of matrix flow, preferential flow through desiccation cracks, and evaporation. Isotope data supported the fact that unproductive water losses via evaporation can be reduced by introducing dry seasonal crops to the crop rotation system.

Characterization of soil water by the means of hydrogen and oxygen isotope ratio at dry-wet season under different soil layers in the dry-hot valley of Jinsha River

AbstractThe soil water was stratified sampling and analyzed with 0–100 cm by three plantation (Leucaena Benth Forest land, Dodonaea angustifolia Shrub land and Heteropogon contortus grassland) at the dry-hot Valley in Jinsha River, at June, September, December of 2016, which were to know about the variation and mechanism of soil water movement. The results showed that (1) soil water in different soil layers is significantly different, and the overall performance is shrub land (11.65%) > grassland (8.29%) > forest land (6.76%); (2) the δD isotope ratio of the soil water from all samples ranged from −146.359% to −54.628% and the δ18O isotope ratio ranged from −20.272% to −2.148%, and there is a good linear relationship between isotope ratios of soil water of three different soils; (3) there is a change with season: the intercept of the isotopes ratio at different months decreased in turn, June < September < December. While the shrub lands and grassland had the same pattern but slightly different, the isotope ratio of soil moisture in December was lower, and the intercepts of shrub land in September were significantly larger than in December; (4) there is a change in space: the total difference isotopes ratio of soil water is larger at the shallow soil layer and changed sharply at all positions of the forestland, while those in the shrub land and grassland changed became relatively weakly. This study provides the theoretical basis for the key problems of plant water using mechanism, ecological water demand, vegetation recovery and so on.

Simulation Analysis of Influencing Factors of Subsidence Based on Mining under Huge Loose Strata: A Case Study of Heze Mining Area, China

Based on the coal seam mining under the condition of thick soil layer, the mechanical mining subsidence process under the condition of thick soil layer was analyzed. Combined with the results of core drilling and laboratory test in the mining area, the mechanical analysis of the special transition strata of “hard soil-soft rock” at the bottom of the soil layer was carried out. Additionally, the characteristics of the shallow buried soil layer were compared and analyzed. Furthermore, the significance of this transitional font to the surface subsidence law was proposed. By using the numerical simulation software of FLAC3D and choosing the thickness of “hard soil-soft rock” transitional font as the influencing factor, a model was established and the surface subsidence characteristics of different stratum combinations were numerically simulated. The research results show that the transitional font is the special strata indicating that the hard soil is transiting to the soft rock, having a significant effect on the ground movement and deformation induced by coal mining. It cannot be designated into the loose strata. Also, it cannot be regarded as the bed rock to study the influence of it on the surface subsidence. The “hard soil-soft rock” transitional font has the support effect on the overlying strata during coal seam mining, which can restrict the surface subsidence. Furthermore, the larger the thickness of the transitional font is, the more obvious the restricting effect of it on the surface subsidence is. Meantime, this restricting effect will not be changed with the variation of the proportion between the loss bed and the bed rock thickness. Only the restricting extent is a little different.

Mechanisms of enhanced methane emission due to introduction of Spartina anglica and Phragmites australis in a temperate tidal salt marsh

Introductions of exotic plants are widespread ecological threats disturbing the carbon and nutrient cycles in global coastal wetlands. Previous studies have found that the invasion has enhanced methane emission through increased primary production and a changed methanogenic pathway. However, the previous studies did not determine the depth profiles of the changes while the depth in the soil profile to which the disturbance propagates is one of the critical issues to be addressed. In this study, we illustrated the depth profiles of the effect of the introductions of S. anglica and P. australis on the potential methane production, soil biogeochemistry, and soil microbial community which play a substantial role in enhanced methane emission due to the invasions. The in situ field measurements and anaerobic incubation were conducted to determine the mechanistic differences of depth profiles. Both introductions of S. anglica and P. australis increased methane emission through different microbial mechanisms depending on depth profile. Potential methane production was stimulated in shallow and deep soil layer of S. anglica and P. australis-introduced marshes, respectively. S. anglica increased the contribution of methylotrophic methanogenesis in top soil layers while P. australis decreased competitive inhibition by sulfate reducers in all soil layers. These results emphasize the importance of below-ground microbial activity and vertical distribution in carbon cycles in tidal marshes. Further plant invasion studies should focus on depth profiles of microbial processes, as their distribution and activity vary substantially across soil depths.

In-Situ Monitoring and Characteristic Analysis of Freezing-Thawing Cycles in a Deep Vadose Zone

Freeze-thaw cycles play a critical role in affecting ecosystem services in arid regions. Monitoring studies of soil temperature and moisture during a freeze-thaw process can generate data for research on the coupled movement of water, vapor, and heat during the freezing-thawing period which can, in turn, provide theoretical guidance for rational irrigation practices and ecological protection. In this study, the soil temperature and moisture changes in the deep vadose zone were observed by in-situ monitoring from November 2017 to March 2018 in the Mu Us Desert. The results showed that changes in soil temperatures and temperature gradients were largest in soil layers above the 100-cm depth, and variations decreased with soil depth. The relationship between soil temperature and unfrozen water content can be depicted well by both theoretical and empirical models. Due to gradients of the matric potential and temperature, soil water flowed from deeper soil layers towards the frozen soil, increasing the total water content at the freezing front. The vapor flux, which was affected mainly by temperature, showed diurnal variations in the shallow 20-cm soil layer, and its rate and variations decreased gradually with increasing soil depths. The freeze-thaw process can be divided into three stages: the initial freezing stage, the downward freezing stage, and the thawing stage. The upward vapor flux contributed to the formation of the frozen layer during the freezing process.

Fine root capture and phenotypic analysis for tomato infected with Meloidogyne incognita

Nematode Meloidogyne incognita is a damaging herbivore that retards root development, shoot growth and plant production. Meloidogyne incognita parasitizes in plant roots and soil, which makes observation and prediction of infection hard to implement, and always observed in the late stage or in the most serious infecting conditions. In this study, adaptive minirhizotrons (microrhizotrons) were used to observe root traits subjected to nematode Meloidogyne incognita in soil-based environment. Microrhizotrons were preset to observe roots in situ, and root images were transferred and processed to extract root diameter and root hair changes. Root system architecture was quantified and reconstructed with 3D architecture digitizer. The result showed that root began to swell since 25 days after infection. Root hair length in swelling parts was observed elongation in 20 days. The defense mechanism was not only limited to root-knot point, but also to non-knot parts in the nematodes inoculation roots. Lateral roots developed more uniformly into deeper than 100 cm in control group, but in infected group lateral roots gathered and clustered with large root angles in shallow soil layer less than 10 cm. Shoot height and injury was visually obviously after about 40 days after infection. The result indicated that microrhizotron provided a method of micro root traits tracing in situ, and root development observed by microrhizotron could give early estimation of nematodes infection than shoot development.

Competition for water rather than facilitation in mixed beech-fir forests after drying-wetting cycle

In the present study we investigated water use strategies of mature stands of Fagus sylvatica (European Beech) with and without co-cultivation of Abies alba (Silver fir) during a summer drought and subsequent rewetting through simulated heavy precipitation in a temperate forest in south-west Germany. We used a combination of sap flow analysis, water stable isotope labeling and a simple linear mixing model with physiological restrictions to determine whether both species were able to switch water uptake depths during drought and reverse this switch after restoration of water supply. We showed that both species utilized water from relatively deep soil layers (>0.5 m) during the drought phase, though for beech trees these contributions were not able to support the high transpiration demands. In contrast, the transpiration of firs remained unaffected by drought probably due to a mixture of its isohydric water use strategy and taproot system. The reactions towards high intensity irrigation differed among species but also between beeches of the pure and mixed stands. While beech trees in the pure stand, once water uptake from the topsoil was re-established, used ~70% of water from more shallow soil depths and were able to restore transpiration, beech trees in the mixed stand obtained only 50% and transpiration decreased further. Firs used around 70% of the water in shallow soil layers and transpiration rates again remained unaffected. These differences indicate competition between beech trees and firs in the mixed stand upon drought. We conclude that drought is able to disrupt water relations in mixed temperate forested ecosystems in such a way that facilitation can turn into competition for resources like water.

Can rain suppress smoldering peat fire?

Smoldering wildfire in peatlands contributes significantly to global carbon emissions and regional haze events. Smoldering fire in peatlands is one of the largest and most persistent fire phenomena on Earth. Here we assess the underlying mechanism of rain in suppressing the smoldering peat fire in the shallow soil layer up to 15 cm deep through laboratory experiments. We show that the minimum rainfall intensity to extinguish the peat fire is roughly 4 mm/h, so that the persistent light rain cannot suppress such smoldering wildfire. The required rain duration, ∆t (min), for extinguishing smoldering peat fire decreases with the rainfall intensities, I (mm/h), as log10∆t = − 1.15log10I + 3.3, and is much longer than that for extinguishing flaming wildfire. We also identify that the required rainfall depth for extinguishing peat fire gradually decreases with the rainfall intensity and approaches a minimum value of 13 mm under violent rain. As rainfall intensity increases, the carbon emission flux from peat fire decreases. Therefore, we conclude that the short-term violent rain is most effective for suppressing the persistent smoldering peat fire. This research helps evaluate the impact of weather on the development of peat fire and improve the prediction of carbon emissions from peat fire with the use of regional weather models.

Coffee and shade trees show complementary use of soil water in a traditional agroforestry ecosystem

Abstract. Globally, coffee has become one of the most sensitive commercial crops, being affected by climate change. Arabica coffee (Coffea arabica) grows in traditionally shaded agroforestry systems in tropical regions and accounts for ∼70 % of coffee production worldwide. Nevertheless, the interaction between plant and soil water sources in these coffee plantations remains poorly understood. To investigate the functional response of dominant shade tree species and coffee (C. arabica var. typica) plants to different soil water availability conditions, we conducted a study during near-normal and more pronounced dry seasons (2014 and 2017, respectively) and a wet season (2017) in a traditional coffee plantation in central Veracruz, Mexico. For the different periods, we specifically investigated the variations in water sources and root water uptake via MixSIAR mixing models that use δ18O and δ2H stable isotope composition of rainfall, plant xylem and soil water. To further increase our mechanistic understanding of root activity, the distribution of below-ground biomass and soil macronutrients was also examined and considered in the model as prior information. Results showed that, over the course of the two investigated dry seasons, all shade tree species (Lonchocarpus guatemalensis, Inga vera and Trema micrantha) relied, on average, on water sources from intermediate (>15 to 30 cm depth: 58± 18 % SD) and deep soil layers (>30 to 120 cm depth: 34±21 %), while coffee plants used much shallower water sources (<5 cm depth: 42±37 % and 5–15 cm depth: 52±35 %). In addition, in these same periods, coffee water uptake was influenced by antecedent precipitation, whereas trees showed little sensitiveness to antecedent wetness. Our findings also showed that during the wet season coffee plants substantially increased the use of near-surface water (+56 % from <5 cm depth), while shade trees extended the water acquisition to much shallower soil layers (+19 % from <15 cm depth) in comparison to drier periods. Despite the plasticity in root water uptake observed between canopy trees and coffee plants, a complementary use of soil water prevailed during the dry and wet seasons investigated. However, more variability in plant water sources was observed among species in the rainy season when higher soil moisture conditions were present and water stress was largely absent.

Physiological Response to Water Deficit Stress with Restricted Rooting in Tall Fescue and Zoysiagrass

AbstractUrban soils may restrict turfgrass rooting depth with shallow soil layers in high sand content soils, which may influence water conservation. A greenhouse study sought to quantify water usage and determine the physiological response of turfgrasses at four irrigation levels. ‘ATF-1434′ tall fescue (Schedonorus arundinaceus (Schreb.) Dumort. nom. cons.; syn. Festuca arundinacea Schreb.), ‘Jamur' Japanese lawngrass (Zoysia japonica Steud.), and ‘Zeon' Manilagrass [Zoysia matrella (L.) Merr.] were established in 10 cm (4 in) diameter by 17.8 cm (7 in) tall containers. Each species was irrigated with 16.5, 21.9, 27.3, or 32.7 mm.wk−1 (0.65, 0.86, 1.1, or 1.3 in.wk−1). Gravimetric water loss was determined by pre- and post-irrigation pot weights. Turf quality, leaf discoloration, percent green cover, and gross photosynthesis were evaluated weekly and root parameters were measured at the conclusion of each trial. Although root mass was similar among species, water deficit stress and leaf discoloration occurred sooner in tall fescue than the two Zoysia species, reducing turf quality and green cover. Japanese lawngrass and Manilagrass had greater stomatal conductance, resulting in 109 and 89% higher gross photosynthesis relative to tall fescue. Both zoysiagrasses maintained acceptable turf quality with 27.3 mm water.wk−1. However, tall fescue quality was not acceptable at any irrigation level.Index words: Photosynthesis, gravimetric water loss, tall fescue, Japanese lawngrass, Manilagrass.Species used in this study: Tall fescue (Schedonorus arundinaceus (Schreb.) Dumort. nom. cons.; syn. Festuca arundinacea Schreb.); Japanese lawngrass (Zoysia japonica Steud.); Manilagrass [Zoysia matrella (L.) Merr.].

Effects of long-term warming on the aboveground biomass and species diversity in an alpine meadow on the Qinghai-Tibetan Plateau of China

Ecosystems in high-altitude regions are more sensitive and respond more rapidly than other ecosystems to global climate warming. The Qinghai-Tibet Plateau (QTP) of China is an ecologically fragile zone that is sensitive to global climate warming. It is of great importance to study the changes in aboveground biomass and species diversity of alpine meadows on the QTP under predicted future climate warming. In this study, we selected an alpine meadow on the QTP as the study object and used infrared radiators as the warming device for a simulation experiment over eight years (2011–2018). We then analyzed the dynamic changes in aboveground biomass and species diversity of the alpine meadow at different time scales, including an early stage of warming (2011–2013) and a late stage of warming (2016–2018), in order to explore the response of alpine meadows to short-term (three years) and long-term warming (eight years). The results showed that the short-term warming increased air temperature by 0.31°C and decreased relative humidity by 2.54%, resulting in the air being warmer and drier. The long-term warming increased air temperature and relative humidity by 0.19°C and 1.47%, respectively, and the air tended to be warmer and wetter. The short-term warming increased soil temperature by 2.44°C and decreased soil moisture by 12.47%, whereas the long-term warming increased soil temperature by 1.76°C and decreased soil moisture by 9.90%. This caused the shallow soil layer to become warmer and drier under both short-term and longterm warming. Furthermore, the degree of soil drought was alleviated with increased warming duration. Under the long-term warming, the importance value and aboveground biomass of plants in different families changed. The importance values of grasses and sedges decreased by 47.56% and 3.67%, respectively, while the importance value of weeds increased by 1.37%. Aboveground biomass of grasses decreased by 36.55%, while those of sedges and weeds increased by 8.09% and 15.24%, respectively. The increase in temperature had a non-significant effect on species diversity. The species diversity indices increased at the early stage of warming and decreased at the late stage of warming, but none of them reached significant levels (P>0.05). Species diversity had no significant correlation with soil temperature and soil moisture under both short-term and long-term warming. Soil temperature and aboveground biomass were positively correlated in the control plots (P=0.014), but negatively correlated under the long-term warming (P=0.013). Therefore, eight years of warming aggravated drought in the shallow soil layer, which is beneficial for the growth of weeds but not for the growth of grasses. Warming changed the structure of alpine meadow communities and had a certain impact on the community species diversity. Our studies have great significance for the protection and effective utilization of alpine vegetation, as well as for the prevention of grassland degradation or desertification in high-altitude regions.

Spatial and temporal variations in soil temperatures over the Qinghai–Tibet Plateau from 1980 to 2017 based on reanalysis products

A change in soil temperature (ST) is a significant indicator of climate change, so understanding the variations in ST is required for studying the changes of the Qinghai–Tibet Plateau (QTP) permafrost. We investigated the performance of three reanalysis ST products at three soil depths (0–10 cm, 10–40 cm, and 40–100 cm) on the permafrost regions of the QTP: the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim), the second version of the National Centers for Environmental Prediction Climate Forecast System (CFSv2), and the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). Our results indicate that all three reanalysis ST products underestimate observations with negative mean bias error values at all three soil layers. The MERRA-2 product performed best in the first and second soil layers, and the ERA-Interim product performed best in the third soil layer. The spatiotemporal changes of annual and seasonal STs on the QTP from 1980 to 2017 were investigated using Sen’s slope estimator and the Mann–Kendall test. There was an increasing trend of ST in the deeper soil layer, which was less than that of the shallow soil layers in the spring and summer as well as annually. In contrast, the first-layer ST warming rate was significantly lower than that of the deeper soil layers in the autumn and winter. The significantly (P < 0.01) increasing trend of the annual ST indicates that the QTP has experienced climate warming during the past 38 years, which is one of the factors promoting permafrost degradation of the QTP.

Bedrock erosion due to hoeing as tillage technique in a hilly agricultural landscape, southwest China

AbstractTillage on hillslopes may not only induce severe soil erosion, but may also cause bedrock erosion under certain conditions. Yet, little is known about bedrock erosion by tillage in a hilly agricultural landscape, southwest China. The aim of this study is to quantify the translocation of rock fragments derived from bedrock fragmentation by hoeing under different conditions, including slope gradient, hoeing depth and soil‐covered thickness using a gravel tracing method. The reliability of the gravel tracing method was confirmed by the bedrock dyeing tracing method. Hoeing depth is a significant factor affecting the translocation rate of rock fragments (Qr). Meanwhile, under the condition of overlying soil layers (0.06−0.10 m thick), the values of Qr were significantly smaller with a reduction of 20.7−25.6%, compared with rock fragmentation by hoeing for bare bedrock. However, slope gradient was found to have insignificant effects on Qr. Fractured bedrock moved as individual small fragments, which was mainly controlled by the hitting force of the hoe, while soil moved in the shape of lumps, which was dominated by both drag force of the hoe and gravity. This study suggests that hoeing into soil‐covered bedrock can diminish bedrock erosion while providing soil matrix for shallow soil layers. Our work presents a quantitative assessment of bedrock erosion by hoeing and an underlying insight into characteristics of bedrock erosion by tillage operations in hilly agricultural regions with mudstone and shale, southwest China. © 2020 John Wiley &amp; Sons, Ltd.

The impact of micro-topography on the interplay of critical zone architecture and hydrological processes at the hillslope scale: Integrated geophysical and hydrological experiments on the Qinghai-Tibet Plateau

As the Third Pole of the Earth, Qinghai-Tibet Plateau (QTP) has been significantly affected by climate change, which makes it an ideal and unique site for critical zone (CZ) research. However, we have limited knowledge of the subsurface CZ structure, hydrologic processes, and their interplays, due to extremely scarce observations in such a harsh environment. In this study, we performed a suite of hillslope-scale experiments that integrated geophysical, hydrological, pedological, and hydrometric observations to investigate the characteristics of the subsurface CZ structure, hydrologic processes, pedological attributes, and their interplays influenced by micro-topography. The results reveal that the subsurface CZ structure and pedological attributes exhibit systematic differences in the aspect gradient (north-facing and south-facing slope). The thickness of the soil, saprolite, weathered layer on the north-facing slope is 0.3 m, 0.2 m, 0.6 m, thicker than that of the south-facing slope. The soil porosity, saturated water content, capillary water content, field capacity, saturated hydraulic conductivity of the shallow soil layer (0–10 cm) in the north-facing slope is 77.2%, 140.1%, 128.2%, 125.8%, 0.67 mm·min−1, which is 8.7%, 26.3%, 24.0%, 22.6%, 0.52 mm·min−1 larger than those of the south-facing slope. In contrast, those properties of the deep soil layer (80-90 cm) in the north-facing slope is 44.3%, 34.3% 32.0%, 29.8%, 0.06 mm·min−1, which is 11.5%, 19.8%, 21.0%, 18.7%, 0.28 mm·min−1 smaller than those of the south-facing slope. The bulk density of the shallow soil layer in the north-facing slope is 0.54 g·cm−3, which is 0.06 g·cm−3 smaller than that of the south-facing slope. In contrast, the bulk density of the deep soil layer is 1.30 g·cm−3, which is 0.26 g·cm−3 larger than that of the south-facing slope. The subsurface CZ structure and micro-topography cause the hydrological processes on the south-facing slope is dominated by surface flow, while those on the north-facing slope is dominated by subsurface flow. The subsurface flow on the north-facing slope accounts for 94.5% of the total runoff, while the surface flow on the south-facing slope accounts for 97.9% of the total runoff. In turn, the dominant runoff regime leads to a decrease of thickness of the soil layer from the top to the bottom of the south-facing slope, with severe slope creep and landslides on the north-facing slope. Our results suggest that the subsurface CZ structure and dominating runoff regime are significantly affected by the micro-topography gradient, which should be parameterized for large-scale research.

Genetic programming model for estimating soil suction in shallow soil layers in the vicinity of a tree

Soil suction, an important parameter in the safety and risk assessment of geotechnical and green infrastructures, is greatly affected by plants and weather in the shallow soil layers of urban landscapes/green infrastructure. In this study, a computational model consisting of a drying-cycle model and wetting-cycle model was developed by means of a genetic programming method to depict variations in soil suction using select influential parameters. The input data in the model development were measured in a field monitoring test on the campus of the University of Macau. Soil suction was quantified by field monitoring at different distances (0.5 m, 1.5 m, and 3.0 m) from a tree, at a constant depth of 20 cm, with selected influential parameters including initial soil suction, air humidity, rainfall amount, cycle duration, and ratio of distance from tree to tree canopy. Based on the performance analysis, the efficiency and reliability of the proposed computational model are validated. The importance of each input and the coupled effect of each two input variables on the output were investigated using global sensitivity analysis. It can be concluded that the proposed computational model based on the artificial intelligence simulation method describes the relationship between field soil suction in drying–wetting cycles and select input variables within an acceptable degree of error. Accordingly, it can serve as a tool for supporting geotechnical construction design and for assessing the safety and risk of geotechnical green infrastructures.

Variations of water sources for a typical mesophyte vegetation in the Lake Poyang wetland using stable isotopes

水分是维持植物生长、决定种群分布的关键因子，研究植物水分利用来源是揭示水文过程与植被演替作用机制的基础，作为中国最大的淡水湖泊系统，鄱阳湖水文情势的显著改变已直接影响到湿地生态系统的水分补给来源.本文通过测定降水、土壤水、地下水、湖水和植物茎水中δ¹⁸O、δD同位素组成，识别鄱阳湖湿地典型中生植被——茵陈蒿（Artemisia capillaris）群落的土壤水分补给来源，并应用直接对比法和IsoSource多源混合模型估算优势种茵陈蒿的主要吸水区间及水源利用比例.结果发现：（1）与降水同位素相比，湖水和湿地土壤水同位素较为富集，地下水同位素较少发生分馏；（2）湿地地下水主要受历史长期降水和湖水共同补给，土壤水在雨季4—6月和秋季9—10月主要受降水补给，夏季7—8月深层土壤水受湖水侧向入渗和地下水的共同补给，并在蒸发作用下水分向浅层土壤传输；（3）茵陈蒿主要利用0~80 cm深度的土壤水，且能够在不同土层水源间灵活转换.当土壤含水量较高时（4—5月），主要利用0~40 cm浅层土壤水，利用率约49%~68%；当浅层土壤含水量较低时（6—8月），主要利用40~80 cm深层土壤水，利用率高达74%~95%；当植物进入生长后期（9—10月），主要利用0~15 cm表层土壤水，利用率介于41%~70%.总体发现，湖水是鄱阳湖湿地中生植物群落土壤水分的重要补给来源，优势种茵陈蒿能够响应土壤含水量的变化改变吸水深度，具有较强的干旱适应能力.研究结果可为鄱阳湖湿地植被生态系统演变和科学保护提供理论参考.;Water availability is a key factor that sustains plant growth and determines vegetation distribution pattern. Plant water uptake pattern is regarded as a foundation to reveal the interaction mechanism between hydrological changes and vegetation succession. As the largest freshwater lake in China, the hydrological regime of Lake Poyang has been encountering a dramatic change in terms of water level variations, which generated a large influence on the water recharge of the wetland ecosystem. In this study, the replenishment sources of soil water in the Artemisia capillaris community, a typical mesophyte vegetation in the Lake Poyang wetland, were explored by using the stable isotopes (δ¹⁸O and δD). The stable isotopes composition of rainfall, lake water, groundwater, soil water and the plant water were analyzed. The main water uptake depth and the proportions of water uptake by A. capillaris were further investigated, using a direct inference method and the IsoSource mixing model. The results showed that the lake water and soil water isotopes were enriched, while the groundwater isotopes were rarely fractionated, relative to local precipitation isotopes. The wetland groundwater is likely to be recharged by the long-term rainfall and the lake water. During the rainy season (April-June), soil water in the A. capillaris community was mainly recharged by the local rainfall. During the summer months (July-August), the deep soil water was most likely to be supplied by lateral lake water and the groundwater. Accordingly, the soil water moved upward from deep to shallow soil layers under strong evaporation. In the growing season, A. capillaris mainly absorbed soil water at 0-80 cm depths and showed plasticity in switching water sources from different soil layers. When the soil water content was high (April-May), A. capillaris mainly used water from shallow soil layers (0-40 cm), accounting for 49%-68% of the total water uptake. When the shallow soil becomes dry (June-August), A. capillaris mainly absorbed deep soil water from deep soil layers (40-80 cm). The proportions of soil water uptake at 40-80 cm were up to 74%-95%. However, the main water source of A. capillaris again switched to the soil water at top soil layer (0-15 cm) during the mature stage (September-October), and the proportions of water uptake were in the range of 41%-70%. Overall, these findings reveal that lake water is an important replenishment source of the soil water in mesophyte vegetation community in the Lake Poyang wetland. A. capillaris could adjust water uptake depth according to the soil water availability, suggesting a strong drought tolerance. This study is helpful to provide scientific reference for the ecosystem evolution and wetland protection in the Lake Poyang-floodplains.

Castanea sativa Mill. plantations as a low-carbon landslide hazard mitigation measure

In the last twenty years, several rainfall-induced landslides occurred in areas surrounding Mount Vesuvius (Campania, Italy). Landslides usually involve the shallow pyroclastic soil layers (2-3 m thick) covering the steep slopes of the Lattari Mountains. The cultivation of trees for fruit production on the pyroclastic cover is a common practice by local farmers. Woody vegetation contributes to slope stability through the mechanical reinforcement of soil by roots. We investigated the use of Sweet chestnut (Castanea sativa Mill.) trees as a low-carbon landslide mitigation measure to be applied in large areas where conventional geotechnical engineering solutions would be costly and extremely invasive, in order to respond to the demand in energy and environmental geotechnics for eco-friendly approaches. The root distribution of C. sativa in terms of root volume ratio was determined from soil cores. The mechanical reinforcement of soil by tree roots was quantified based on root-soil interaction models. Slope stability was analysed by means of limit equilibrium analyses performed on an infinite slope. The safety factor calculated for a cultivated slope was higher than for a fallow slope due to the mechanical reinforcement provided by roots. Therefore, the cultivation of C. sativa is a useful mitigation measure against shallow landslides.

Age- and climate- related water use patterns of apple trees on China’s Loess Plateau

The Loess Plateau of China is a major apple-cultivating region, but much of the Plateau is water-limited, and the expansion of apple-growing is putting pressure on soil water resources. Plants’ water consumption patterns have been intensively studied to facilitate formulation of robust agricultural strategies, but previous studies have generally applied indirect methods to characterize their water use. Moreover, the few studies that have applied direct (isotopic) methods have mostly focused on shallow (0–200 cm) soil layers, usually in stands of a single age or single climatic region. To avoid these limitations, we have investigated the primary water sources of apple trees of three ages (10, 15 and 22 years) in semiarid and semihumid climatic regions of the Plateau using both natural stable isotopic signatures (δ2H values) and injections of 2H2O into deep soil layers. We found that water content in apple orchards’ soil decreased with increases in depth and stand age, and was higher in the semihumid area than in the semiarid area. Nevertheless, patterns of apple trees’ water uptake from shallow (0–300 cm) soil layers were similar in the two climatic regions and the main water sources became shallower with increases in stand age. However, water uptake from deep (400–500 cm) soil layers was also detected, particularly in the blossom and young fruit stage in apple orchards of the semiarid area. Moreover, older trees absorbed more water from these layers than younger trees in the semiarid area (but not in the semihumid area) throughout the growing season. Excessive consumption of deep soil water inevitably results in deep soil drying and severely threatens the sustainability of apple cultivation. Our work suggests that it is necessary to take actions (e.g. supplementary irrigation, landscaping and mulching combinations) to reduce the proportion of deep soil water used by apple trees to prevent the development of dried soil layers. It also highlights the need to assess uptake patterns of plants at multiple developmental stages and ages to identify times when and places where interventions may be required or most effective.

Altered water uptake patterns of Populus deltoides in mixed riparian forest stands

Plant water uptake plays an important role in regulating ecosystem water balance and its productivity. However, previous studies regarding plant water uptake were primarily conducted in wet areas under seasonal drought conditions, with a limited understanding of the proportion and drivers of plant water uptake under humid conditions. Actually, climate change and variations in global precipitation patterns could simultaneously trigger seasonal drought and flooding. Therefore, it is critical to explore patterns and mechanisms for plant water uptake under humid conditions in wet regions. Here, we employed dual stable isotopes of hydrogen and oxygen coupled with a Bayesian mixing model (MixSIAR) to explore the water uptake patterns of Populus deltoides in two types of riparian forests (pure vs. mixed stand of P. deltoides), under different magnitudes of rainfall (7.9, 15.4 and 34.1 mm), in the Middle-Lower Reaches of the Yangtze River in China. We further used both partial correlation and variation partitioning analyses to determine the relative importance of soil variables and plant properties affecting the proportion of P. deltoides water uptake from different soil layers. Our results revealed that compared to pure stands, P. deltoides in mixed stands had a lower water uptake proportion from deep soil layers (60–80, 80–100 cm) and had higher water uptake from shallow soil layers (0–20, 20–40 cm) under 15.4 mm and 34.1 mm rainfall events. Our results also revealed that plant properties such as leaf biomass, fine root biomass, and diameter at breast height were the primary factors influencing water uptake by P. deltoides. This suggests that P. deltoides in mixed stands could increase the proportion of water uptake from shallow soil layers through altering plant attributes. These findings indicate that mixed stands could restrain frequent extreme rainfall events and subsequent flooding, suggesting more resilience towards future climatic variability.

Transference of Robinia pseudoacacia water-use patterns from deep to shallow soil layers during the transition period between the dry and rainy seasons in a water-limited region

Soil water plays a critical role in determining plant survival and growth globally, especially in water-limited regions. This study explores water-use characteristics of Robinia pseudoacacia during the transition period between the dry and rainy seasons in the Chinese Loess Plateau (CLP). A stable isotope technique (δ18O and δD) and two complementary approaches (i.e., the direct inference method and the MixSIAR model) were used to distinguish water source changes during this transition period. Based on δ18O and δD distribution patterns, we subdivided a 500 cm soil profile into four potential water sources: shallow (0–40 cm), intermediate-shallow (40–120 cm), intermediate (120–200 cm) and deep (200–500 cm). During the transition period, R. pseudoacacia exhibited different water uptake patterns. In April 26.2% and 48.4% of water uptake derived from the 40 to 120 and 200 to 500 cm soil profile layers; in May, 21.5%, 24.5% and 37.4% of water was absorbed from the 0 to 40, 40 to 120 and 200 to 500 cm soil profile layers. In June and July, 51.6% and 53.6% of the water mainly derived from the 0 to 120 cm soil profile layer, respectively. During the dry season (April), the trend in water uptake shifted to the deep soil layer, potentially a key period for the onset of soil desiccation in this soil layer. As precipitation increased, the proportion of water uptake from the shallow and intermediate-shallow soil layers increased. Because water-use pattern characteristics could provide important information on the development of the dried soil layer (DSL), the stable isotope technique could help reveal the water sources used by trees while also offering insight into water movement mechanisms of local ecosystems. Given its usefulness, the application of the stable isotope technique should be expanded in analyzing practical ecohydrological issues that occur in deep soils in the future.