Shallow Soil Layers Research Articles

Geodiversity effects on soil quality and geo-ecosystem functioning in drylands

Geodiversity is defined as the natural variability of geologic, geomorphic, and soil features. It has been acknowledged to positively affect biodiversity and species richness. A long-term drought occurring in the semi-arid northern Negev of Israel has led to the mass mortality of shrubs, with the particularly adverse impact on the predominant Noaea mucronata species. Recent observations in these shrublands have suggested that this mass mortality is not uniformly distributed over the landscape, but is confined to hillslopes characterized by low-geodiversity. This type of hillslope is defined by a deep (>1 m) soil layer, lacking rock fragments in its profile and on its surface. Also, the herbaceous vegetation cover of these hillslopes is very high (>90%), but shrubby vegetation cover is very low (<10%) and for the most part, non-vital. At the same time, shrubby vegetation in high-geodiversity hillslopes – defined by a shallow (~10 cm) soil layer, and high rock fragment content (>30% volume) and cover (>20%) – is rather dense (>25%) and vital, but their herbaceous vegetation cover is quite sparse (<30%). Soil was sampled from the 0–10 cm depth in two micro-habitats – shrubby patches and inter-shrub spaces – on both the homogeneous and heterogeneous hillslopes. Overall, soil quality was found to be considerably higher in the heterogeneous hillslopes compared to the homogeneous hillslopes. This included the contents of hygroscopic moisture, total organic carbon, particulate organic carbon, and carbon lability, whose means were 22%, 36%, 27%, and 38%, respectively, greater in the heterogeneous hillslopes. Further, mean clay dispersion index was 18% lower in the heterogeneous hillslopes. At the same time, mean soil electrical conductivity was 13% greater in the heterogeneous hillslopes. Yet, this could be attributed to the greater clay content in the former type (19.1%) than that in the latter type (12.7%) of hillslope, with the assumingly higher salt-adsorption from the soil solution. Overall, the results show that the effect of micro-habitat on the soil properties was relatively moderate, and therefore, suggest that the impact of geodiversity might override that of vegetation patchiness. The results highlight the importance of assessing patch-scale and/or hillslope-scale geodiversity in future studies of dryland ecosystems around the world.

Seasonal changes in water sources used by woody species in a tropical coastal dune forest

Our aim was to investigate the water sources used by woody species under contrasting water availability and the extent of water-sources-use differentiation among dominant woody species in a tropical coastal dune forest. We sampled 15 woody species in a Brazilian restinga forest and, through Bayesian isotope mixing models, we estimated the proportion of water sources used. We tested whether water-sources-use was (i) different between contrasting water availability conditions; (ii) dependent on growth form, plant size or crown illumination; and (iii) influenced by stand density, evenness or biomass. We found a seasonal variation in water-sources-use, but no vertical soil-water partitioning among woody species. In wetter periods, plants used mainly water from top-soil, as a shallow water table limited water uptake to top-soil layers recharged with rainwater. Contrastingly, during drier periods, with the absence of rain and a deeper water table, plants generally relied on deeper (50 cm) soil layers. Only under less-wet conditions, a greater evenness and density implied higher water-uptake depth heterogeneity among plants. However, changes in the main water-sources used by plants were neither evoked in more dense or diverse plots, nor induced by plant size. Our study shows that restinga species have dynamic shifts in water-uptake depth caused by seasonal water availability changes, influenced by the combined effect of insufficient moisture at shallow soil layers and water-table lowering in drier periods. These temporal shifts are common among species, implying that restinga woody community has a homogeneous strategy of water-resources acquisition. This study enhances our understanding of the effects that water variations can have on water-resource use in restinga forests.

Influence of Soil Pore System Properties on the Degradation Rates of Organic Substances during Soil Aquifer Treatment (SAT)

Soil aquifer treatment (SAT) is a nature-inspired solution for improving the water quality through soil percolation. The biodegradation of organic matter typically occurs in the shallowest soil layer and it depends on the contaminant’s characteristics (water solubility, molecular structure) and specific soil properties (pore size distribution). The present study aims at identifying which grain size fraction of typically used sandy soils in the shallowest layer of SAT systems can provide the optimal conditions for microbiological growth that can be reached by a trade-off between soil moisture as well as nutrients and oxygen supply. For this, soil columns were used at a laboratory scale to determine the relationship between the pore size distribution of four different grain size fractions and biodegradation rates of organic matter from synthetic wastewater. The results obtained from this experimental setup indicate that bacterial colonies reached optimum growth when about 60% of the available pore space was filled with water. For the selected soil, this was achieved by the fraction with grain sizes in the range of 630 µm to 1000 µm, having pore diameters between 87 µm and 320 µm and a mean pore diameter of 230 µm.

A field assessment of bauxite residue rehabilitation strategies

Bauxite residue, the by-product of the alumina industry, is mainly stored in land-based bauxite residue disposal areas (BRDAs). Environmental concern has been raised due to the large volumes in stockpile, the high alkalinity of the material, as well as the presence of elevated concentrations of trace elements. If not adequately managed, BRDAs can act as a source of pollution. In order to minimize the environmental risk, revegetation is implemented to stabilize the residue against water and wind erosion. Currently, two main approaches are used: the use of amendments or the installation of a capping layer. However, few studies evaluating the long-term success and self-sustainability of the rehabilitation programs have been published.A series of field-established rehabilitation strategies reflecting both direct revegetation and revegetation on capping layer were assessed in terms of both soil and plant quality. Soil physico-chemical properties, including pseudo-total and plant-available fractions of nutrients and trace elements, were determined over a summer and winter seasons and aerial portions of vegetation were analysed for nutrients and trace elements.Failure to adequately lower alkalinity remains the major constraint to long-term rehabilitation success of bauxite residue. This is evidenced from poor soil properties in unamended residue and in residue capped with a shallow soil layer, as well from vegetation displaying excessive concentrations of certain elements. Certain elements exceeded typical ranges for non-contaminated soils (i.e. Cr, Fe, Na, Ni and V), with some showing excessive plant-available fractions (i.e. of Al, As, Cr, Hg and V). Vegetation analysis found excessive uptake of some elements (i.e. of Al, Na, Fe, Cr and V). Future attempts for bauxite residue rehabilitation should include both gypsum and organic amendments, while a capping layer may only be effective if either a deep layer (>1 m) is installed or if the underlying residue is sufficiently treated prior to capping.

Hormonal signaling cascades required for phototaxis switch in wandering Leptinotarsa decemlineata larvae.

Many animals exploit several niches sequentially during their life cycles, a fitness referred to as ontogenetic niche shift (ONS). To successfully accomplish ONS, transition between development stages is often coupled with changes in one or more primitive, instinctive behaviors. Yet, the underlining molecular mechanisms remain elusive. We show here that Leptinotarsa decemlineata larvae finish their ONS at the wandering stage by leaving the plant and pupating in soil. At middle wandering phase, larvae also switch their phototactic behavior, from photophilic at foraging period to photophobic. We find that enhancement of juvenile hormone (JH) signal delays the phototactic switch, and vise verse. Moreover, RNA interference (RNAi)-aided knockdown of LdPTTH (prothoracicotropic hormone gene) or LdTorso (PTTH receptor gene) impairs avoidance response to light, a phenotype nonrescuable by 20-hydroxyecdysone. Consequently, the RNAi beetles pupate at the soil surface or in shallow layer of soil, with most of them failing to construct pupation chambers. Furthermore, a combination of depletion of LdPTTH/LdTorso and disturbance of JH signal causes no additive effects on light avoidance response and pupation site selection. Finally, we establish that TrpA1 (transient receptor potential (TRP) cation channel) is necessary for light avoidance behavior, acting downstream of PTTH. We conclude that JH/PTTH cascade concomitantly regulates metamorphosis and the phototaxis switch, to drive ONS of the wandering beetles from plant into soil to start the immobile pupal stage.

晋西黄土区人工林细根与土壤水碳的耦合关系

PDF HTML阅读 XML下载 导出引用 引用提醒 晋西黄土区人工林细根与土壤水碳的耦合关系 DOI: 10.5846/stxb201901120101 作者: 作者单位: 山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院,山西师范大学生命科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 山西省自然科学基金（201601D021103）；国家自然科学基金项目（41401242） Coupling fine roots with soil moisture and organic carbon in artificial forests in loess region of western Shanxi Province Author: Affiliation: College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university,College of Biology Science,Shanxi normal university Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以晋西黄土区山西离石典型人工林刺槐、侧柏、核桃为研究对象，研究其深剖面（0-500 cm）细根参数、土壤水分和有机碳的分布特征，并以农地为对照，评价各人工林土壤水分亏缺和有机碳积累效应，在此基础上探讨三者的耦合关系。结果表明：（1）3种人工林土壤浅层（0-70 cm）细根累计生物量占整个土层的56%-71%，具有明显表聚性。（2）3种人工林土壤深层（70-500 cm）土壤水分亏缺效应均显著高于浅层（P < 0.05），与农地相比，其亏缺值表现为：侧柏 > 核桃 > 刺槐。（3）3种人工林深层土壤有机碳密度占整个土层的77%-86%；与农地相比，侧柏和核桃土壤有机碳积累效应总体为正向积累作用，刺槐则相反。（4）在土壤浅层，细根参数与土壤水分和有机碳密度均有显著相关性，而在深层，细根主要与有机碳密度显著相关，与土壤水分的相关性仅在刺槐样地显著。晋西黄土区不同人工林深层细根分布有很大差异，且已对其深层土壤水分和有机碳的分布产生影响。综合来看，刺槐的细根分布已造成深层土壤水分亏缺，同时也不利于深层有机碳的积累。 Abstract:In this study, the relationship between fine roots, soil moisture, and soil organic carbon in artificial forests was analyzed. Three tree species, Robinia pseudoacacia, Platycladus orientalis, and Juglans regia were selected in the loess region of western Shanxi Province, China. Soil and root samples were taken from 0-500 cm depths to analyze the distribution pattern of fine root parameters, soil moisture content (SMC), and soil organic carbon density (SOCD). Soil moisture deficit (SMD) and organic carbon accumulation (SOCA) in artificial forests were evaluated with long-term cropland as a control. The results showed that:(1) the cumulative proportion of fine root biomass in shallow soil layers (0-70 cm) ranged from 56% to 71%, which showed obvious surface aggregation in all three forests. (2) The SMD in deep soil layers (70-500 cm) was significantly higher than that in shallow soil layers of all forests (P < 0.05). Compared with the control, the SMD in deep soil layers of artificial forests ranked as P. orientalis > J. regia > R. pseudoacacia. (3) The SOCD in deep soil layers accounted for 77%-86% of total soil profile SOCD across different forests. Compared with the control, the SOCA in P. orientalis and J. regia plots was generally positive, while the SOCA in R. pseudoacacia plot was negative. (4) The fine root parameters were positively correlated with both SMC and SOCD in shallow soil layers. However, in deep soil layers, the positive correlation was observed mainly with SOCD. The significant correlation with SMC was found only in R. pseudoacacia plot. The deep distribution of fine roots considerably differed among three artificial forests in the loess region of western Shanxi, which had an obvious influence on the deep SMC and SOCD distribution. Overall, the fine root distribution of R. pseudoacacia contributed to SMD while negatively affecting SOCA in the deep soil. 参考文献 相似文献 引证文献

Energy balancing in ground heat exchanger for heat pump systems – a case study with simulations

The negative impact of systems based on fossil fuel on the environment and the desire to promote sustainable development is increasingly encouraging building owners to invest in renewable energy sources. One of the possibilities of using a renewable energy source located in shallow soil layers is a brine-to-water heat pump. Ground energy can be used for both heating and cooling buildings. This article presents the advantages of balancing the supply and energy consumption from the ground for the large heat pump systems. Authors presented a case study and the simulation of the system operation with different cooling load share vs heating load. This was done on the basis of the analysis of data from several years of measurements from the actual installation as well as the simulation in Earth Energy Designer software. The results of the simulations shows that the most advantageous strategy for the operation of the analysed installation is to provide 50 to 75% of the cooling load in relation to the heating load.

Relationship Between Dewfall Time and Shadow Soil Moisture

The automated Weather Phenomenon Observation System can observe condensation and record the occurring time of weather phenomena by using image identification technology. The time of condensation occurring and the data of soil moisture in the shallow soil layer are analyzed, and the inverse relationship between dewfall time and shadow soil moisture is confirmed by using the data of the automatic present weather observation system and soil moisture observation equipment installed at Pinggu Station in Beijing from April to September in 2011. The condensation phenomenon appears earlier when the soil moisture of 0 to 10cm layer is higher. On the contrary, the condensation phenomenon appears later when the soil moisture of 1 to 10 cm layer is too low. It can be used to predict soil moisture by exploring the timing of dewfall via the automated Weather Phenomenon Observation System, which is useful to monitor drought.

Towards the development of a baseline for surface movement in the Surat Cumulative Management Area

Ground surface movement can result from several natural and anthropogenic processes. Understanding the mechanisms that drive ground surface movement and their contribution to the net movement is crucial in assessing the impact of resource development projects and other human activities. Consequently, there is an interest in understanding ground surface movement in the Surat Cumulative Management Area (CMA), Queensland, and how it is influenced by coal seam gas (CSG) production, if at all. This paper presents the analysis of a large InSAR (interferometric synthetic aperture radar) dataset covering the CMA regions featuring no active CSG wells. These non-production areas were specifically examined in order to develop an understanding of background surface movement and its contributing processes. Of the regional dataset, four focus areas showing measurable changes over time were selected for more detailed investigation. All the focus areas exhibited an overall downward surface movement (subsidence), with three showing cycles of subsidence and uplift that appeared to be very well correlated with rainfall events. The soil types in these three areas were consistent with the hypothesis that the observed surface movement is due to rainfall infiltration-induced consolidation of the shallow soil layers and subsequent moisture-induced shrinkage and swelling. The fourth focus area, however, did not exhibit a strong seasonal fluctuation, and unravelling the mechanisms driving surface movement in this area was more difficult. This investigation resulted in a foundation for further research into the complex problem of surface movement, and in particular, deconvolution of the various contributions that occur at different depths, lengths, and time scales.

Water uptake by coniferous and broad-leaved forest in a rocky mountainous area of northern China

Extreme drought and precipitation are expected to occur more frequently due to climate change, which may influence the water uptake patterns by vegetation in the rocky mountainous area of northern China. In this work, dual stable isotopes were used to detect the water sources of mixed forest of coniferous and broad-leaved tree species and their response of leaf water potential under differently sized precipitation events (no rain: 0.0 mm; light rain: 9.8 mm; moderate rain: 21.8 mm; large rain: 31.6 mm and rainstorm: 51.2 mm). The results showed that Platycladus orientalis and Quercus variabilis had different water use strategies and opposite responses to precipitation. On dry (no rain) days, P. orientalis and Q. variabilis predominantly obtained water from natural springs (43.3% and 36.2%, respectively) and deep soil layer (32.8% and 31.3%, respectively), while Q. variabilis also used water from shallow soil layer (23.4%). Following the rainfall events, the P. orientalis with dense and shallow fine root system absorbed more water from the soil surface layers (23.1–33.5%) and precipitation (15.2–30.7%). The pre-dawn water potential (ψpd) and the midday water potential (ψmd) of P. orientalis increased with the amount of rainfall, revealing a sensitive response to precipitation. On the other hand, Q. variabilis mostly took up water from natural springs (32.3–36.7%) and deep soil layer (33.8–37.1 %) after the rainfall events through its well-developed taproot system. The ψpd and ψmd of Q. variabilis had no significant variation between no rain and light rain events, though they increased significantly for large rainfall and rainstorm events with > 60 cm of soil water recharge provided by the precipitation. The study provides more insights into reforestation and water management in the region of northern China.

Effects of decay level of fallen trees and their formed microsite types on soil physicochemical properties in a spruce-fir forest.

To reveal the effects of decay level of fallen trees and their formed microsite types on soil physicochemical properties, the differences in soil physicochemical properties (bulk density, capillary porosity, total porosity, capillary water holding capacity, saturated moisture capacity, soil organic carbon, total nitrogen, total phosphorous, available phosphorous, available potassium, and pH) and stoichiometry (C/N, N/P, and C/P) among different decay levels of treefalls and between different microsite types in the formed gaps by fallen trees were analyzed in a spruce-fir fore-st in a valley of Liangshui National Nature Reserve in Xiaoxing' an Mountains. The results showed that the effects of the decay levels of fallen trees on soil physical properties was not significant. In contrast, we found significant effects of the formed microsite types in soil physical properties. Except for saturated soil water holding capacity, the other soil physical properties were the best under the fallen trees and the worst in the pit bottom. Except of available phosphorus, the contents of the other soil nutrients exhibited a significant increase trend with the increasing decay levels of fallen trees. Among three microsites, the contents of soil nutrients were the lowest and pH were highest in the pit. As for the shallow soil layer, C/N, N/P and C/P of three microsites decreased with the increasing decay levels of fallen trees, while C/N in mound top and in pit bottom increased, N/P and C/P decreased, and the variation of C/P was consistent with that of available phosphorus. In conclusion, with the increasing decay levels of fallen trees, the contents of soil nutrients were signifi-cantly increased. There are significant differences of soil nutrients among different microsites, with the lowest values in the pit.

Dynamics of storage and relative availability of soil inorganic nitrogen along revegetation chronosequence in the loess hilly region of China

In the Loess Hilly Region of China, the widespread conversion of farmland to forestland and grassland has resulted in great changes in soil carbon (C) and nitrogen (N) storage in the shallow soil layers. However, knowledge regarding changes in the status and relative availability of inorganic nitrogen (IN) is still limited. To determine the responses of soil IN storage and its relative availability to revegetation patterns and chronosequence, a 0–200 cm soil profile was collected from two typical vegetation restoration patterns in the heartland of the region, artificial forestland (Robinia pseudoacacia) and natural grassland, with a stand age sequences of 15, 20, 25, 30 and 40 years. The farmland near the sites was selected as a control. As a whole, the NH4-N, NO3-N and total inorganic nitrogen (TIN) concentrations and stocks in the forestlands were significantly higher than those in the grasslands, especially in the topsoil (0–10 cm). With increasing revegetation chronosequence, afforestation improved soil NH4–N, NO3–N and TIN concentrations and stocks until Robinia pseudoacacia reached maturity at an age of 25–30, but abandoned on former farmland had minor effects on soil IN. After revegetation, soil NH4–N was higher than NO3–N, and the NH4–N/NO3–N ratio (ANR) was greater than 1 and increased with soil depth. The soil at 40–200 cm accounted for 60–90% of the total IN stock of the 0–200 cm soil profile, and the soil at 100–200 cm accounted for more than 35% of the total levels. Moreover, soil physicochemical properties were significantly correlated with soil IN variables, and ANR had a greater correlation coefficient with soil physicochemical properties than the other IN variables. It was concluded that afforestation was a better choice for soil IN restoration of degraded land, and subdeep and deep soil provided an extremely important resource for evaluating soil IN pools and their relative availability. Furthermore, soil IN dynamics, particularly ANR, could be regarded as indicators for assessing the dynamics of soil fertility.

Age‐related water uptake patterns of alpine plantation shrubs in reforestation region of Qinghai–Tibetan Plateau based on stable isotopes

AbstractSea buckthorn (Hippophae rhamnoides L.) plantations play crucial roles in the prevention of soil erosion and control of desertification on the Qinghai–Tibetan Plateau; however, the limited information on the age‐related water uptake patterns of H. rhamnoides and their relationships with associated grasses species weakens our understanding of how these factors influence the management of H. rhamnoides plantations. Therefore, this study investigated the seasonal variations in water uptake patterns of different‐aged H. rhamnoides and their associated species via stable isotopes and leaf water potential analyses. The model results showed that seedling (Hs) and juvenile (Hj) H. rhamnoides extracted water mainly from shallow and middle soil layers throughout the growing seasons, whereas mature H. rhamnoides (Hm) exhibited high plasticity, shifting water source between shallow soil water and groundwater when the former become less available. By contrast, the associated grasses (Taraxacum mongolicum, Thermopsis lanceolata, and Polygonum sibiricum) mainly absorbed shallow soil water across the whole growing seasons, suggesting that direct competition for shallow soil water occurred between grasses and H. rhamnoides. In addition, the obviously higher δ13C values of Hj with more negative predawn (mean Ψpd, −1.37 MPa) and midday (mean Ψmd, −2.23 MPa) leaf water potential indicated the Hj experienced greater water stress relative to Hs and Hm. These results provide new understanding of the seasonal water use strategies of different‐aged H. rhamnoides, which will be important for the successful management of plantations in this region.

Shaking Table Test and Numerical Verification for Free Ground Seismic Response of Saturated Soft Soil

This paper investigates shaking table test (1g) and numerical simulation (fully coupled) of vertically propagating shear waves for saturated soft free field. A large-scale shaking table model test was performed to study seismic response characteristics of saturated soft soil free field. According to test results of seismic response features of free field system in saturated soft soil, the free field nonlinearity fully coupled numerical model of dynamical effective stress of saturated soft soil was established using OpenSEES, based on the u-p formulations of dynamic consolidation equation as well as effective stress solution method for saturated two-phase media. The numerical simulation of the free field seismic response of saturated soft soil under various test conditions was performed and the calculated results were compared with the shaking table test results. The results show the following. (1) With the increase of input ground motion intensity, the characteristic frequency of the saturated soft free ground decreases and the damping ratio increases gradually. (2) The saturated soft soil ground has short period filtering and long period amplification effect on the horizontal input seismic loads. The failure foundation takes on the isolation and shock absorption under strong ground motions. (3) The peak pore pressure ratio of the saturated soft soil ground is located in the shallow buried soil layer, and with the increase of the input ground motion intensity, the advantage of dynamic pore pressure ratio in this area is gradually weakened. (4) The numerical simulation results are consistent with the results of the shaking table test. This fully coupled effective stress numerical method can reasonably simulate the seismic response characteristics of free field in saturated soft soil, which lay the foundation for other more complex parameter extrapolation models of saturated soft soil sites. This research can provide the necessary technical experience for experimental study on non-free field.

Aboveground overyielding in a mixed temperate forest is not explained by belowground processes.

The relationship between forest productivity and tree species diversity has been described in detail, but the underlying processes have yet to be identified. One important issue is to understand which processes are at the origin of observed aboveground overyielding in some mixed forests. We used a beech-maple plantation exhibiting aboveground overyielding to test whether belowground processes could explain this pattern. Soil cores were collected to determine fine root (FR) biomass and vertical distribution. Correlograms were used to detect spatial arrangement. Near-infrared reflectance spectroscopy was used to identify the tree species proportion in the FR samples and spatial root segregation. An isotopic approach was used to identify water acquisition patterns. The structure and the composition of the ectomycorrhizal fungal community were determined by high-throughput sequencing of DNA in the soil samples. We found no spatial pattern for FR biomass or for its vertical distribution along the gradients. No vertical root segregation was found, as FR density for both species decreased with depth in a similar way. The two species displayed similar vertical water acquisition profiles as well, mainly absorbing water from shallow soil layers; hence, niche differentiation for water acquisition was not highlighted here. Significant alterations in the fungal community compositions were detected in function of the percentage of maple in the vicinity of beech. Our findings do not support the commonly suggested drivers of aboveground overyielding in species-diverse forests and suggest that competition reduction or between-species facilitation of belowground resource acquisition may not explain the observed aboveground overyielding.

Stable isotope analysis of water sources for Tamarix laxa in the mega-dunes of the Badain Jaran Desert, China

The complex interactions in desert ecosystems between functional types and environmental conditions could be reflected by plant water use patterns. However, the mechanisms underlying the water use patterns as well as the water sources of Tamarix laxa in the mega-dunes of the Badain Jaran Desert, China, remain unclear. This study investigated the water sources and water use patterns of T. laxa using the stable oxygen isotope method. The δ18O values of xylem water, soil water in different layers (0–200 cm), rainwater, snow water, lake water, atmospheric water vapor, condensate water, and groundwater were measured. The sources of water used by T. laxa were determined using the IsoSource model. The results indicate that T. laxa mainly relies on soil water. At the beginning of the growing season (in May), the species is primarily dependent on water from the middle soil layer (60–120 cm) and deep soil layer (120–200 cm). However, it mainly absorbs water from the shallow soil layer (0–60 cm) as the rainy season commences. In September, water use of T. laxa reverts to the deep soil layer (120–200 cm). The water use patterns of T. laxa are closely linked with heavy precipitation events and soil water content. These findings reveal the drought resistance mechanisms of T. laxa and are of significance for screening species for ecological restoration.

Species‐specific differences in water uptake depth of mature temperate trees vary with water availability in the soil

Temperate tree species differ in their physiological sensitivity to declining soil moisture and drought. Although species-specific responses to drought have often been suggested to be the result of different water uptake depths, empirical evidence for such a mechanism is scarce. Here we test if differences in water uptake depths can explain previously observed species-specific physiological responses of temperate trees to drought and if the water uptake depth of different species varies in response to declining soil moisture. For this purpose, we employed stable oxygen and hydrogen isotopes of soil and xylem water that we collected over the course of three growing seasons in a mature temperate forest in Switzerland. Our data show that all investigated species utilise water from shallow soil layers during times of sufficient soil water supply. However, Fraxinus excelsior, Fagus sylvatica and Acer pseudoplatanus were able to shift their water uptake to deeper soil layers when soil water availability decreased in the topsoil. In contrast, Picea abies, was not able to shift its water uptake to deeper soil layers. We conclude from our data that more drought-resistant tree species are able to shift their water uptake to deeper soil layers when water availability in the topsoil is becoming scarce. In addition, we were able to show that water uptake depth of temperate tree species is a trait with high plasticity that needs to be characterised across a range of environmental conditions.

Dynamic variations in profile soil water on karst hillslopes in Southwest China

Precipitation in the karst regions of southwest China is plentiful, however, soils are shallow and highly permeable, which results in rapid transportation of surface water through a soil profile. Therefore, the presence and amount of water stress in a soil layer can be unpredictable. This study will investigate the soil water conditions on karst hillslopes in southwest China through dynamic in situ observations of profile soil moisture (θ). Three profiles at two slope positions on two shrub-grasslands (S1 and S2) were selected, respectively. At each profile, TDR 100 probes were set at 10, 20, 30, 50, and 70 cm and for 100 cm, only on downslopes. Soil samples (undisturbed and disturbed) were collected to measure basic physical and chemical properties. Precipitation and θ were monitored manually each week between July 15, 2012 and November 25, 2014. Results show that soil properties, which have an important effect on θ, varied among slope positions and between the two hisllslopes. A higher clay content, which led to greater water holding capacity, explained a higher θ in downslopes and on S2. Shallow soil layers (0–30 cm), especially in the coarse textured soil layers of S1, were susceptible to water stress due to the limited availability of soil water. Water stress was low during water supplying (December through April) and relatively stable periods (May to June). However, during water consuming periods (July to November), profile θ decreased greatly which resulted in severe water stress for the whole profile. Although precipitation was seasonally uneven, based on weekly observations, profile θ on both hillslopes was not temporally active (coefficients of variation of θ was smaller than 20%) and the variance of each depth was similar. Generally, the effects of precipitation on θ can last two (0–50 cm) to five (70–100 cm) weeks. Nevertheless, θ of downslope deep soil, which was (or near) saturated all year round, was barely affected by precipitation. These results can provide valuable information for hydrological models and rational strategies for ecological restoration designing in karst regions.

A novel approach for estimating groundwater use by plants in rock-dominated habitats

Plant water use is an important component in the function of Earth’s critical zone and this can be examined by decomposing isotope composition of xylem water into contributions from precipitation stored in shallow soil layers and deeper groundwater. The usual procedure for estimating the proportional use of groundwater by plants is to sample the isotope composition of soil and groundwater and determine the most probable mixing coefficients from all potential sources. Here we propose and test a novel method for achieving the same goal without sampling soil water. The method is based on analyzing variability in the stem water isotope ratios of several members of a community and the known isotope ratio of groundwater to ‘triangulate’ the unknown isotope ratio of stored rainwater. Using a simple water balance model, parameterized to produce the best fit between actual and estimated stem water isotope ratios, we simulated seasonal variation in the volume and isotope ratio of rainwater storage, along with species-specific groundwater use ratios. The method was applied to eight woody plant species growing on two rocky outcrops in the South China karst. Estimated average proportional groundwater use over two seasons varied between 14% and 62% and was site-dependent. For the majority of species, groundwater use increased as estimated stored rainwater volume declined. The two species with highest groundwater use were taller, deciduous or semi-deciduous trees with lower wood densities. While the new method was inspired by the inability to sample water stored in the rocky outcrops, it may have broader use in any environment where the spatial variability of soil water isotope composition is a barrier to estimating average groundwater use ratios. The broader adoption of this or equivalent methods would greatly improve the study of the Earth’s critical zone.

Physiological mechanisms contributing to the QTL qDTY3.2 effects on improved performance of rice Moroberekan x Swarna BC2F3:4 lines under drought

BackgroundTraditional rice (Oryza sativa) varieties are valuable resources for the improvement of drought resistance. qDTY3.2 is a drought-yield quantitative trait locus that was identified in a population derived from the traditional variety Moroberekan and the drought-susceptible variety Swarna. In this study, our aim was to characterize the physiological mechanisms associated with qDTY3.2. Our approach was to phenotype fifteen BC2F3:4 lines for shoot and root drought resistance-related traits as compared to Swarna in the field under well-watered and drought stress conditions. Four BC2F3:4 lines contrasting for yield under drought were selected for detailed characterization of shoot morphology, water use related traits, flowering time and root system architecture in the field as well as in controlled environments (lysimeters in a greenhouse, and gel imaging platform in a growth chamber).ResultsAcross five field experiments, grain yield correlated significantly with root growth along the soil profile, flowering time, and canopy temperature under drought conditions. The four selected BC2F3:4 lines showed earlier flowering time, reduced distribution of root growth to shallow soil layers which resulted in lower water uptake (between 0 and 30 cm) and drought-induced increased distribution of root growth to deep soil layers (between 30 and 60 cm) as compared to Swarna in the field. Root system architecture phenotypes were confirmed in whole root systems in lysimeters, and corresponded to higher numbers of root tips in a gel imaging platform, highlighting the potential stability of some root traits across different growth stages and systems.ConclusionsWe conclude that earlier flowering time, reduced shallow root growth, and drought-induced increased deep root growth are associated with the presence of qDTY3.2 since these phenotypes were consistently observed in the selected QTL lines with full introgression of qDTY3.2. We hypothesize that the qDTY3.2 associated RSA phenotypes led to better use of water and metabolic resources which, combined with earlier flowering time, improved yield under drought.