Estimating deep soil water depletion and availability under planted forest on the Loess Plateau, China.

Deep soil water (DSW) plays a pivotal role in tree growth, susceptibility to drought-induced mortality, and belowground carbon and nutrient cycling. Assessing DSW depletion is essential for evaluating the resilience and sustainability of planted forests. But, due to the poor accessibility of deep soil layers, little is known about large scale DSW depletion. In this study, we leverage the concept that "plants are reliable indicators of deep soil water" to estimate DSW depletion in planted forests within the arid and semi-arid regions of the Chinese Loess Plateau (CLP). Our approach involves establishing a model that correlates forest age with DSW depletion. We then employ this model to estimate DSW depletion across the region, utilizing readily available data on the distribution of forest age and utilize the boundary models to consider the variability of DSW depletion estimated with forest age. Our results indicate that the model effectively estimates DSW depletion in planted forests, demonstrating a strong fit with an R2 of 0.71 and a low root mean square error (RMSE) of 332 mm. Notably, a substantial portion of the planted forest areas on the CLP has experienced DSW depletion from 800 mm to 1600 mm, and totaling 2.41 × 1010 m3 DSW depletion from 1995 to 2020 based on the general model. However, the available DSW in the existing planted forests on the CLP is estimated at only 1.73 × 1010 m3 by 2038. This suggests that there is potential risks and unsustainability for further afforestation efforts and carbon sequestration on the CLP under the current continuous afforestation measures. Our study holds significant implications for sustainable regional ecological management and quantifying water resources for carbon trading through afforestation.

Anomalous stable hydrogen-oxygen isotope characteristics and water vapor sources of autumn precipitation in the Weihe River basin, Northwest China.

The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.

Comparing dual heat pulse methods with Péclet's number as universal switch to measure sap flow across a wide range.

Accurate determination of sap flow over a wide measurement range is important for assessing tree transpiration. However, this is difficult to achieve by using a single heat pulse method. Recent attempts have been made to combine multiple heat pulse methods and have successfully increased the sap flow measurement range. However, relative performance of different dual methods has not yet been addressed, and selection of the numerical threshold used to switch between methods has not been verified among different dual methods. This paper evaluates three different dual methods with respect to measurement range, precision and sources of uncertainty: (method 1) the heat ratio (HR) and compensation heat pulse method; (method 2) the HR and T-max method; and (method 3) the HR and double ratio method. Field experiments showed that methods 1, 2 with three needles and 3 compare well with the benchmark Sapflow+ method, having root mean square deviations of 4.7 cm h-1, 3.0 cm h-1 and 2.4 cm h-1, respectively. The three dual methods are equivalent in accuracy (P > 0.05). Moreover, all dual methods can satisfactorily measure reverse, low and medium heat pulse velocities. However, for high velocities (>100 cm h-1), the HR + T-max (method 2) performed better than the other methods. Another advantage is that this method has a three- instead of four-needle probe configuration, making it less error prone to probe misalignment and plant wounding. All dual methods in this study use the HR method for calculating low to medium flow and a different method for calculating high flow. The optimal threshold for switching from HR to another method is HR's maximum flow, which can be accurately determined from the Péclet number. This study therefore provides guidance for an optimal selection of methods for quantification of sap flow over a wide measurement range.

Effects of optical and radar satellite observations within Google Earth Engine on soil organic carbon prediction models in Spain.

The modeling and mapping of soil organic carbon (SOC) has advanced through the rapid growth of Earth observation data (e.g., Sentinel) collection and the advent of appropriate tools such as the Google Earth Engine (GEE). However, the effects of differing optical and radar sensors on SOC prediction models remain uncertain. This research aims to investigate the effects of different optical and radar sensors (Sentinel-1/2/3 and ALOS-2) on SOC prediction models based on long-term satellite observations on the GEE platform. We also evaluate the relative impact of four synthetic aperture radar (SAR) acquisition configurations (polarization mode, band frequency, orbital direction and time window) on SOC mapping with multiband SAR data from Spain. Twelve experiments involving different satellite data configurations, combined with 4027 soil samples, were used for building SOC random forest regression models. The results show that the synthesis mode and choice of satellite images, as well as the SAR acquisition configurations, influenced the model accuracy to varying degrees. Models based on SAR data involving cross-polarization, multiple time periods and "ASCENDING" orbits outperformed those involving copolarization, a single time period and "DESCENDING" orbits. Moreover, combining information from different orbital directions and polarization modes improved the soil prediction models. Among the SOC models based on long-term satellite observations, the Sentinel-3-based models (R2 = 0.40) performed the best, while the ALOS-2-based model performed the worst. In addition, the predictive performance of MSI/Sentinel-2 (R2 = 0.35) was comparable with that of SAR/Sentinel-1 (R2 = 0.35); however, the combination (R2 = 0.39) of the two improved the model performance. All the predicted maps involving Sentinel satellites had similar spatial patterns that were higher in northwest Spain and lower in the south. Overall, this study provides insights into the effects of different optical and radar sensors and radar system parameters on soil prediction models and improves our understanding of the potential of Sentinels in developing soil carbon mapping.

From comfort zone to mortality: Sequence of physiological stress thresholds in Robinia pseudoacacia seedlings during progressive drought.

Introduction: Parameterizing the process of trees from the comfort zone to mortality during progressive drought is important for, but is not well represented in, vegetation models, given the lack of appropriate indices to gauge the response of trees to droughts. The objective of this study was to determine reliable and readily available tree drought stressindices and the thresholds at which droughts activate important physiological responses. Methods: We analyzed the changes in the transpiration (T), stomatal conductance, xylem conductance, and leaf health status due to a decrease in soil water availability (SWA), predawn xylem water potential (ψpd), and midday xylem water potential (ψmd) in Robinia pseudoacacia seedlings during progressive drought. Results: The results showed that ψmd was a better indicator of drought stress than SWA and ψpd, because ψmd was more closely related to the physiological response (defoliation and xylem embolization) during severe drought and could be measured more conveniently. We derived the following five stress levels from the observed responses to decreasing ψmd: comfort zone (ψmd > -0.9 MPa), wherein transpiration and stomatal conductance are not limited by SWA; moderate drought stress (-0.9 to -1.75 MPa), wherein transpiration and stomatal conductance are limited by drought; high drought stress (-1.75 to -2.59 MPa), wherein transpiration decreases significantly (T< 10%) and stomata closes completely; severe drought stress (-2.59 to -4.02 MPa), wherein transpiration ceases (T< 0.1%) and leaf shedding orwilting is > 50%; and extreme drought stress (< -4.02 MPa), leading to tree mortality due to xylem hydraulic failure. Discussion: To our knowledge, our scheme is the first to outline the quantitative thresholds for the downregulation of physiological processes in R. pseudoacacia during drought, therefore, can be used to synthesize valuable information for process-based vegetation models.

Field variation of groundwater recharge and its uncertainty via multiple tracers' method in deep loess vadose zone.

Accurate estimation of groundwater recharge is a precondition for assessing its spatial variation at different scales, especially field scale. In the field, the limitations and uncertainties of different methods are first evaluated based on site-specific conditions. In this study, we evaluated field variation in groundwater recharge via multiple tracers in the deep vadose zone on the Chinese Loess Plateau. Five deep soil profiles (approximately 20 m deep) were collected in the field. Soil water content and particle compositions were measured to analyse soil variation, and soil water isotope (3H, 18O, and 2H) and anion (NO3- and Cl-) profiles were used to estimate recharge rates. Distinct peaks in soil water isotope and nitrate profiles indicated a vertical one-dimensional water flow in the vadose zone. Although the soil water content and particle composition were moderately variable, no significant differences were observed in recharge rates among the five sites (p > 0.05) owing to the identical climate and land use. The recharge rates did not show a significant difference (p > 0.05) between different tracers' methods. However, recharge estimates by the chloride mass balance method indicated higher variations (23.5 %) than those by the peak depth method (11.2 % to 18.7 %) among five sites. Moreover, if considering the contribution of immobile water in vadose zone, groundwater recharge would be overestimated (25.4 % to 37.8 %) using the peak depth method. This study provides a favourable reference for accurate groundwater recharge and its variation evaluated using different tracers' methods in deep vadose zone.

Evaluating potential groundwater recharge in the unsteady state for deep-rooted afforestation in deep loess deposits.

Groundwater recharge reduces due to high transpiration from shallow-rooted to deep-rooted afforestation. However, reaching a steady state in recharge process is challenging and no methods are available for assessing potential groundwater recharge under unsteady state. Hence, this study developed a new method to quantify groundwater recharge in the unsteady state by (1) calculating the water age (A2) at maximum root depth (D2) for deep-rooted afforestation using the chloride accumulative age method; (2) determining the soil depth (D1) corresponding to A2 under shallow-rooted vegetation using the multi-year average pore water velocity multiplied by A2; (3) calculating the reduction in groundwater recharge (∆R) from shallow- to deep-rooted afforestation as the depth difference multiplied by the average water content between D1 and D2, divided by stand age. The average groundwater recharge for deep-rooted afforestation is equal to the average annual groundwater recharge under shallow-rooted vegetation minus ∆R. Soil cores with >25 m soil profiles below four land-use types of Hippophae rhamnoides Linn. (H. rhamnoides), Platycladus orientalis (L.) Franco (P. orientalis), Robinia pseudoacacia L. (R. pseudoacacia), and grassland were collected to measure soil water content, root distribution, and chloride and tritium contents. The results revealed that: (1) maximum root depths were 11.0 ± 0.5, 20.2 ± 1.2, and 22.6 ± 0.8 m, with soil water deficits of 373.48, 823.65, and 1847.92 mm under H. rhamnoides, P. orientalis, and R. pseudoacacia, respectively; (2) groundwater recharge following land-use change has not reached a steady state; (3) an average annual groundwater recharge was 89.12 mm yr-1 under grassland, amounting to 16 % of the average annual precipitation; deep-rooted afforestation did not significantly differ, with 83.55, 84.91, and 85.65 mm yr-1 under H. rhamnoides, P. orientalis, and R. pseudoacacia, respectively. This study contributes to a rational assessment of groundwater resources under unsteady state during land-use change.

Effect of Straw and Wood Ash on Soil Carbon Sequestration and Bacterial Community in a Calcareous Soil.

Soil fertility can be improved by effectively utilizing agricultural waste. Straw can supply energy and wood ash adds nutrients to improve soil quality. However, few kinds of research have investigated the effect of wood ash and straw on soil carbon sequestration and the soil bacterial population, particularly in calcareous soils. The main goal of this current study was to quantify the impact of a combination of wood ash and straw on the indicators described above using stable δ13C isotope analyses by applying wheat straw to calcareous soil under a long-term C4 crop rotation. The incubation experiment included four treatments as follows: (i) no amendment (Control); (ii) amendment with wood ash (W); (iii) amendment with straw (S); and (iv) a combined amendment of straw and wood ash (SW). Our results showed that sequestration of soil inorganic carbon (SIC) in the SW and W treatments was higher (an average of 7.78%) than that in the S and Control treatments. The sequestered soil organic carbon (SOC) in the SW treatment was 1.25-fold greater than that in the S treatment, while there was no evident effect on the SOC content compared with straw alone. The microbial biomass carbon increased under SW by 143.33%, S by 102.23%, and W by 13.89% relative to control. The dissolved organic carbon increased under SW by 112.0%, S by 66.61%, and W by 37.33% relative to the control. The pH and electrical conductivity were higher in the SW and W treatments than in the S treatment and the control. The SW was conducive to maintaining soil enzymatic activities and bacterial diversity. Bacteroidetes and Actinobacteriota were dominant in SW, while the Acidobacteria phyla were dominant in the S treatment. The diversity of bacteria in the soil and community composition of the bacteria were predominantly assessed by the levels of water-soluble K, pH, and electrical conductivity. The incorporation of straw and wood ash is probably more effective at improving SIC and SOC sequestration and ameliorates the soil microhabitat.

Long-term vegetation restoration increases deep soil carbon storage in the Northern Loess Plateau.

Afforestation plays an important role in soil carbon storage and water balance. However, there is a lack of information on deep soil carbon and water storage. The study investigates the effect of returning farmland to the forest on soil carbon accumulation and soil water consumption in 20-m deep soil profile in the hilly and gully region of the Chinese Loess Plateau. Four sampling sites were selected: Platycladus orientalis (Linn.) Franco forest (PO: oriental arborvitae), Pinus tabulaeformis Carr. Forest (PT: southern Chinese pine), apple orchard (AO) and farmland (FL, as a control). Soil organic carbon (SOC) and soil inorganic carbon (SIC) content were measured in 50-cm sampling intervals of 20-m soil profiles, as well as the associated factors (e.g. soil water content). The mean SOC content of PT was the highest in the 1-5 m layer and that of FL was the lowest (p < 0.05). Compared with FL, the SOC storages of PO, PT and AO increased by 2.20, 6.33 and 0.90 kg m-2 (p > 0.05), respectively, in the whole profile. The SIC content was relatively uniform throughout the profile at all land-use types and SIC storage was 9-10 times higher than SOC storage. The soil water storage of PO, PT and AO was significantly different from that of FL with a decrease of 1169.32, 1161.60 and 1139.63 mm, respectively. After the 36-yrs implementation of the "Grain for Green" Project, SOC in 20 m soil profiles increased as a water depletion cost compared with FL. Further investigation is still needed to understand the deep soil water and carbon interactions regarding ecological restoration sustainability in the Northern Loess Plateau.

Stable isotopes of deep soil water retain long-term evaporation loss on China's Loess Plateau.

Evaporation from the land surface enriches heavy isotope ratios (2H/1H and 18O/16 O) in shallow soils, and downward water movement will carry the fractionation signal to deep soils. However, how to acquire the evaporation from water stable isotopes in deep soils remains untested. Here, we measured water stable isotope composition in the deep soils (2-10 m) across 20 sites on China's Loess Plateau. Our results show that the line-conditioned excess (lc-excess) in deep soils of these sites was invariable with depth at each site, but ranged between -14.0‰ and - 4.1‰ among these sites, indicating differing degree of enrichment in heavy water isotopes between sites. Moreover, the mean lc-excess in deep soils water was significantly correlated to mean annual precipitation (R2 = 0.57), potential evapotranspiration (R2 = 0.25), and the Budyko dryness (R2 = 0.68), indicating that deep soil water lc-excess reflects land surface climate conditions. Furthermore, the deep soils correspond to a timescale of approximately 100 years at one site and more than 27 years at the remaining sites. These results together indicate that stable isotopes of deep soil water retained long-term land surface evaporation effects. Further, by implementing the steady-state isotope mass balance model into the lc-excess framework, we derived a new method to estimate evaporation loss fraction (f). Our f estimates at these sites varied between 5% and 15%, which may represent the lower bound of the actual evaporation to precipitation ratio. Nevertheless, our work suggests that in these and the other similar regions, deep soil is a novel archive for long-term soil evaporation loss, and f may be estimated through a snapshot field campaign of stable isotope measurements.

[Hydrochemistry and Its Controlling Factors and Water Quality Assessment of Shallow Groundwater in the Weihe and Jinghe River Catchments].

The Weihe and Jinghe Rivers catchments are important tributaries of the Yellow River, where it is of great significance to evaluate groundwater hydrochemistry and quality for ecological protection and sustainable development. Piper diagrams, Gibbs, Na-normalized molar ratios, and ion correlation methods were used to analyze the chemical composition of groundwater in these two catchments. Furthermore, the WQI method, Wilcox diagrams, USSL diagrams, and Doneen diagrams were used to evaluate the suitability of groundwater quality for drinking and irrigation. The results showed that the Weihe and Jinghe River catchments are dominated by fresh and weakly alkaline water. Groundwater ion concentration in the Weihe River are higher than in Jinghe River except for Na+, and the major groundwater types are HCO3-Ca-Mg(accounted for 50%), and HCO3-Ca-Mg and HCO3-Na-K (accounted for 32.5%), respectively. The hydrochemistry of the Weihe and Jinghe River catchments is mainly controlled by rock weathering, primarily silicate weathering. Moreover, the groundwater chemistry in the research area is affected by mining and chemical fertilizer application for agriculture. Furthermore, the hydrochemistry of the Weihe River catchment is affected by cation exchange, although this was not obvious in some regions of the Jinghe River catchment. The overall groundwater quality of the two catchments was good, with the Jinghe River water quality being better than in the Weihe River catchment. Based on SSP, SAR, and PI, the groundwater in some parts of the study area cannot be directly used for irrigation as this would result in salinization and, thus, inhibit plant growth. Overall, the groundwater quality in the south of the study area is better than in the north, and is better in the Jinghe River catchment than in the Weihe River catchment according to these three indicators. This study provides a basis for the sustainable development of two catchments, providing baseline data for groundwater quality management.

Optimizing biochar application to improve soil physical and hydraulic properties in saline-alkali soils.

Biochar application has been a promising approach to improve soil quality but their optimal amount in improving physical and hydraulic properties remains contradictory and inconclusive. The objective of this study was to examine and propose an optimal biochar application amount in saline alkali soil considering their impact on soil physical and hydraulic properties. A three-year field experiment was conducted in the saline-alkali soils under plastic film-mulched drip irrigation in Xinjiang, China. The studied physical and hydraulic properties included bulk density, soil porosity, saturated soil water content (θs), permanent wilting point (PWP), field capacity (FC), plant available water (PAW), spatial distribution of soil water content, planar soil water storage (PSWS), and soil evaporation. The treatments included biochar application amounts of 0 (CK), 10 (B10), 50 (B50), and 100 t ha-1 (B100) in 2018. Additional two treatments with 25 t ha-1 (B25) and 30 t ha-1 (B30) were added in 2019 and 2020, respectively. A four-parameter Gaussian function was fitted to the single-peak curves of the studied hydraulic properties vs. biochar application amounts to determine the most optimal biochar application amount. The results indicated that: (1) All of the biochar treatments significantly decreased bulk density and increased soil porosity over CK; (2) B10 and B25 treatments significantly increased θs, FC, PAW, PWP, and PSWS of root zones in the film-mulched zones over CK, but reverse results were observed in the B50 and B100 treatments; (3) Daily and cumulative soil evaporation were increased in no mulch zones of all biochar treatments over CK; (4) A dose of 21.9 t ha-1 was recommended as the most optimal biochar application amount for improving physical and hydraulic properties of saline-alkali soil. This research provided useful information on biochar application amounts for improving physical and hydraulic properties in saline-alkali soil.

[Hydrochemical and Isotopic Characteristics in the Shallow Groundwater of the Fenhe River Basin and Indicative Significance].

The Fenhe River basin is the second largest tributary of the Yellow River. Piper diagrams, Gibbs, PCA, correlation analysis and forward derivation modeling were used to analyze the distribution characteristics and the controlling factors of the groundwater chemistry and stable isotopes in the Fenhe River basin, which revealed the water cycle and water quality evolution process. The results indicated that the groundwater is a weakly alkaline, micro-hard water, the dominant anions and cations are HCO3- and Ca2+, the major groundwater types are Mg-Ca-HCO3 and Mg-Ca-Cl-SO4, the groundwater quality is good, and more than 94% of the samples belong to classes Ⅰ-Ⅲ. The average values of δD and δ18O of the Fenhe River groundwater are -70.2‰ and -9.6‰, which are similar to the isotope values of the precipitation from July to September, indicating that the groundwater may have originated from this period and that the groundwater recharge mode (dominant flow and piston flow) has a spatial variation. Rock weathering is the dominant source of ions in the groundwater, with an average contribution of 87%, while the contributions of atmospheric input and human activity are 8% and 5%, respectively. For rock weathering, silicate, evaporate, and carbonate rock contribute equally to the groundwater solutes, accounting for 32%, 28%, and 26%, respectively. The results of this study provide the basis for promoting the sustainable development and utilization of groundwater resources in the Fenhe River basin.

[Analysis of Hydrogen and Oxygen Stable Isotope Characteristics and Vapor Sources of Precipitation in the Guanzhong Plain].

To improve the understanding of hydrogen and oxygen stable isotope characteristics and vapor sources in the Guanzhong Plain, we collected 98 precipitation samples and corresponding meteorological data between 2015 and 2018 in Yangling, Shanxi Province, which is located in the central area of the Guanzhong Plain. The composition characteristics of the local hydrogen and oxygen stable isotopes of precipitation (δ2H, δ18O, and δ17O) and their environmental controls were analyzed, and the local meteoric water line (LMWL) and the meteoric water line of the triple oxygen isotopes were established. Three indicators (δ18O, d-excess, and 17O-excess) were used to explore the possible vapor sources of local precipitation and to quantify the contributions of ocean-source and inland-source water vapor to the precipitation. The results showed that there were obvious seasonal changes in the hydrogen and oxygen stable isotopes of precipitation in the Yangling area:water isotopes were depleted in the wet season (May to October) and enriched in the dry season (November to April of the next year). Both the slope (7.7) and intercept (9.1) of the LMWL were lower than those of the global meteoric water line (GMWL), indicating that the annual precipitation in the research area experienced variable degrees of secondary evaporation under cloud cover. The slope of the meteoric water line of the triple oxygen isotopes is 0.528, which is between that of seawater equilibrium fractionation (0.529) and water vapor diffusion into dry air (0.518), consistent with the fact that the Guanzhong area is located on the migration path of marine air mass to inland arid regions. Comprehensive analysis of δ18O, d-excess, and 17O-excess confirmed that the precipitation in the study area is jointly contributed to by the warm and humid air mass from the southeast monsoon and the dry and cold air mass from the westerly wind. Of these, approximately 55%-79% of the precipitation water vapor comes from the ocean, mainly in June to August, and about 21%-45% of the water vapor comes from inland and local evaporation, mainly from October to April. The water vapor sources of precipitation in May and September are complex and may intermittently originate from ocean and inland water vapor.

Chloride tracer of the loess unsaturated zone under sub-humid region: A potential proxy recording high-resolution hydroclimate.

A high-resolution hydroclimate archive is critical to understanding the past changes, but such hydroclimatic reconstructions are extremely limited. Our study aims to examine the potential of the chloride tracer (Cl) within unsaturated zone (USZ) to reconstruct high-resolution hydroclimate records. We investigated a representative sub-humid monsoon area of the Chinese Loess highland, where piston flow recharge dominates and a constant rate of Cl input occurs. We successfully reconstructed a 1007-yr hydroclimate record with a 2-yr sampling resolution using a 95-m USZ Cl profile. Excluding the recycling and mixing zone, and the groundwater affecting zone, six relatively humid phases and five relatively dry phases were discernible. The uncertainty in the time of wet/dry phase decreases as the accumulated time increases, and the minimal recharge uncertainty is 16% over a 10-yr time scale. The reconstructed hydroclimate record from the semi-humid region has a much higher resolution than that of the arid zones, likely because the semi-humid, fine-grained thick USZ, possesses higher velocity piston flow, relatively to diffusion and dispersion of Cl signals. The record compared well with other related records, suggesting that the Cl proxy can be used in sub-humid areas, and is sensitive to wet/dry alternations that are largely driven by the Asian monsoon intensity. To the best of our knowledge, this is the first investigation of the USZ Cl to hydroclimatic reconstruction in a non-arid region. The high-resolution hydroclimate record may deepen our understanding of the hydrological process in the deep USZ, past climate and water resources, and promote developments of the hydropedology and global change science.

Deep soil water extraction by apple sequesters organic carbon via root biomass rather than altering soil organic carbon content.

Soil water and carbon stocks have always been research hotspots. However, the interaction between soil water and carbon in deep soil (>1 m below surface) remains poorly understood. The present study used the chronosequence approach to investigate water extraction and carbon input by roots to a depth of 25.2 m in 8-, 11-, 15-, 18-, and 22-year-old afforested apple (Malus pumila Mill.) orchard stands in a sub-humid region of the Chinese Loess Plateau. Three long-term cultivated farmlands were used as a benchmark of soil water and carbon status before land use change. Measurements showed that the apple trees accessed deep soil water reserves by growing deep roots, with the resulting desiccated soil possibly stimulating apple trees to extend their roots into deeper, moister soil. Accordingly, soil water content in the root zone decreased progressively with increasing stand age. For example, the roots of apple trees in the 22-year-old stand extended to 23.2 m below the soil surface and extracted 1530 ±â€¯43 mm deep soil water. Consequently, carbon input from root biomass correlated well with the water storage loss in deep soil (R2 = 0.88). Deep roots accounted for 49 ±â€¯22% of the total root biomass and contributed 0.44 ±â€¯0.15 Mg C ha-1 yr-1 to the deep soil. However, the roots of apple trees did not significantly change the soil organic carbon content in the root zone possibly because there was limited root biomass per unit soil depth and because soil water content in the root zone gradually decreased. These findings demonstrate the importance of deep soil in regulating water and carbon cycles, advancing our understanding of interactions among water, roots, and carbon in this zone.

Temporal variability of water footprint for cereal production and its controls in Saskatchewan, Canada.

The water footprint (WF) of crop production is a user-friendly means to analyze the consumption of water resource in agricultural production systems. This study assessed the inter-annual variability of grain yield, protein yield, and their corresponding WFs and determined the major factors influencing the WFs in Saskatchewan of Canada. Both spring wheat and barley showed a significant trend of increasing grain and protein yield from 1965 to 2014, at 194.1 and 179.2kgha-1decade-1 for grain yield (P<0.01) and 18.6 and 17.3kgha-1decade-1 for protein yield, respectively. Coincident with this was that both the grain yield-based and protein yield-based WFs of spring wheat and barley in Saskatchewan showed a downward trend. The grain yield-based WFs ranged from 1.08 to 1.80m3kg-1 for spring wheat, and from 0.90 to 1.38m3kg-1 for barley, whereas the protein yield-based WFs ranged from 7.93 to 10.44m3kg-1 for spring wheat and from 8.14 to 16.47m3kg-1 for barley. The grain yield-based WFs were affected by local precipitation followed by expenses on inputs from farms and the scientific and technological contributions. Under the same protein yield, the protein yield-based WFs tended to be lower in spring wheat than barley. The grain yield-based WFs of cereal crops have large potential for improvement in the future.

Thermal Transport of Graphene Sheets with Fractal Defects.

Graphene combined with fractal structures would probably be a promising candidate design of an antenna for a wireless communication system. However, the thermal transport properties of fractal graphene, which would influence the properties of wireless communication systems, are unclear. In this paper, the thermal transport properties of graphene with a Sierpinski fractal structure were investigated via the reverse non-equilibrium molecular dynamics simulation method. Simulation results indicated that the thermal conductivity of graphene with fractal defects decreased from 157.62 to 19.60 (W m-1 K-1) as the fractal level increased. Furthermore, visual display and statistical results of fractal graphene atomic heat flux revealed that with fractal levels increasing, the real heat flux paths twisted, and the angle distributions of atomic heat flux vectors enlarged from about (-30°, 30°) to about (-45°, 45°). In fact, the fractal structures decreased the real heat flow areas and extended the real heat flux paths, and enhanced the phonon scattering in the defect edges of the fractal graphene. Analyses of fractal graphene thermal transport characters in our work indicated that the heat transfer properties of fractal graphene dropped greatly as fractal levels increased, which would provide effective guidance to the design of antennae based on fractal graphene.

[Profile Distribution of Soil Organic and Inorganic Carbon Under Different Land Use Types in the Loess Plateau of Northern Shaanxi].

Carbon storage in the Loess Plateau is affected by land use. In order to assess the differences in soil organic carbon (SOC) and soil inorganic carbon (SIC) under different land use patterns in deep soil profiles, we investigated the distribution characteristics of SOC and SIC at 0-20.0 m soil depth at three locations in the northern Shaanxi province (i.e., an economical plantation in Mizhi, a reforestation area in Shenmu, and a wind break and sand fixation forest district in Yuyang). The results showed that the order for SOC content was:pruning jujube tree (2.00 g·kg-1) > jujube tree (1.54 g·kg-1) > Caragana (0.97 g·kg-1) > degraded artificial grassland (0.81 g·kg-1) > pine forests (0.70 g·kg-1) > natural grass field (0.45 g·kg-1), which indicated significant differences between SOC content and land use types (P<0.05). Similarly, the order of SIC content was:pruning jujube tree (11.66 g·kg-1) > jujube tree (11.59 g·kg-1) > Caragana (9.62 g·kg-1) > degraded artificial grassland (8.07 g·kg-1) > pine forests (4.32 g·kg-1) > natural grass field (0.47 g·kg-1). There were no significant differences between SIC content and soil profiles under the economical plantation of Mizhi and the reforestation area of Shenmu. There were significant differences for SIC content between an artificial economic forest, an area returning farmland to a forest (grass) profile, and a windbreak and sand fixation forest (P<0.05). The SIC densities for pruning jujube tree, jujube tree, Caragana, degraded artificial grassland, pine forest, and natural grass field were 6.19, 7.71, 10.70, 10.78, 5.91, and 1.03 times that of its corresponding SOC density, respectively. It has been concluded that the soil carbon storage was significantly different for different land use patterns, and the SIC content was much higher than the SOC content in the soil profile.