Deep Soil Research Articles

The effect of land use and land cover on soil carbon storage in the Yellow River Delta, China: Implications for wetland restoration and adaptive management

Gaining a comprehensive understanding of the effect of land use/land cover (LULC) and soil depth on soil carbon storage, through the manipulation of external carbon input and turnover processes, is crucial for accurate predictions of regional soil carbon storage. Numerous research investigations have been conducted to examine the impact of LULC on the storage and cycling of carbon in the surface soils of coastal wetlands. Nevertheless, there remains a dearth of understanding concerning the implications of this phenomenon on subterranean soils, a crucial factor in discerning the capacity for carbon sequestration in coastal wetlands and implementing measures for their preservation. The study focused on the Yellow River Delta (YRD) in China, which serves as a representative model system. It aimed to assess the impact of LULC as well as soil depth on carbon storage. This was achieved by a combination of remote sensing interpretation and field samplings. The findings of the study indicate that there was an increase in soil organic carbon storage with both the area covered and the depth of the soil across the four different land use types, namely forest, grass, tidal flat, and cultivated land. Cultivated land was identified as the predominant LULC type, encompassing 41.73% of the entire YRD. Furthermore, it accounted for a substantial carbon storage of 76.08%. In comparison to soil layers at depths of 0–20 cm and 20–40 cm, 40–60 cm was discovered to have the maximum carbon storage, accounting for 42.29% of total carbon storage. Furthermore, one of the main factors influencing carbon storage is salinity, which shows a negative association with carbon storage. Moreover, the aforementioned findings underscore the significance of the conjoined physical and chemical properties induced by LULC in influencing the dynamics of soil carbon. This suggests that the inclusion of deep soil carbon in the estimation and restoration of soil carbon storage is necessary. This inclusion will support the realization of the United Nations' “Toward Zero Carbon” effort and facilitate the implementation of China's national carbon neutrality objectives.

Variation of nitrate sources affected by precipitation with different intensities in groundwater in the piedmont plain area of alluvial-pluvial fan

A substantial reservoir of nitrogen (N) in soil poses a threat to the quality and safety of shallow groundwater, especially under extreme precipitation that hastens nitrogen leaching into groundwater. However, the specific impact of varying precipitation intensities on the concentration and sources of nitrate (NO3−) in groundwater across diverse hydrogeological zones and land uses remains unclear. This study aims to elucidate the fluctuations in NO3− concentration, sources, and controlling factors in shallow groundwater under different intensities of precipitation (extreme heavy precipitation and continuous heavy precipitation) in a typical alluvial-pluvial fan of the North China Plain by using stable isotopes (δ2H–H2O, δ18O–H2O, δ15N–NO3-, δ18O–NO3-), hydrochemical analyses and the SIAR model. Affected by extreme heavy precipitation the depleted isotopes of δ2H–H2O and δ18O–H2O in groundwater of the entire area suggested the rapid recharge of fast flow by precipitation. The enriched isotopes of δ2H–H2O and δ18O–H2O of north part in alluvial fan after continuous heavy precipitation showed the recharge of translatory flow of soil water. NO3−concentrations increased to 78.9 mg/L after extreme heavy precipitation and increased to 105.3 mg/L after continuous heavy precipitation when compared to those in normal year (56.8 mg/L) of north part of the alluvial fan. However, NO3− concentrations had slight variation after continuous heavy precipitation of south part of the fan due to the deep vadose zone. The contribution ratio of sources of NO3− in groundwater by using SIAR analysis revealed manure & sewage (MS) as the primary NO3− source (accounting for 59.7–78.1%) before extreme heavy precipitation, chemical fertilizer (CF) making a minor contribution (6.9–17.3%). Different precipitation events and land use types lead to changes in NO3− sources. Affected by extreme heavy precipitation, the contribution of MS decreased while CF increased, particularly in vegetables (26.2–28.1%) and farmland (29.2–34.7%). After continuous heavy precipitation, MS increased again, particularly in vegetables (50.0%) and farmlands (20.4–66.4%), with CF either increasing or remaining steady. This indicated that continuous heavy precipitation accelerated the leaching of nitrogen (organic manure application) stored in deep soil to groundwater and it has a larger influence on the increasing of NO3− concentrations of groundwater than extreme heavy precipitation which carried nitrogen (chemical fertilizer application) in shallow soil to groundwater by fast flow. These findings underscore the importance of considering soil chemical N stores and their implications for groundwater contamination mitigation under future extreme climate scenarios, particularly in agricultural management practices.

Maize ZmSRO1e promotes mesocotyl elongation and deep sowing tolerance by inhibiting the activity of ZmbZIP61.

Deep sowing is a traditional method for drought resistance in maize production, and mesocotyl elongation is strongly associated with the ability of maize to germinate from deep soil. However, little is known about the functional genes and mechanisms regulating maize mesocotyl elongation. In the present study, we identified a plant-specific SIMILAR TO RCD-ONE (SRO) protein family member, ZmSRO1e, involved in maize mesocotyl elongation. The expression of ZmSRO1e is strongly inhibited upon transfer from dark to white light. The loss-of-function zmsro1e mutant exhibited a dramatically shorter mesocotyl than the wild-type in both constant light and darkness, while overexpression of ZmSRO1e significantly promoted mesocotyl elongation, indicating that ZmSRO1e positively regulates mesocotyl elongation. We showed that ZmSRO1e physically interacted with ZmbZIP61, an ortholog of Arabidopsis ELONGATED HYPOCOTYL 5 (HY5) and showed a function similar to that of HY5 in regulating photomorphogenesis. We found that ZmSRO1e repressed the transcriptional activity of ZmbZIP61 toward target genes involved in the regulation of cell expansion, such as ZmEXPB4 and ZmEXPB6, by interfering with the binding of ZmbZIP61 to the promoters of target genes. Our results provide a new understanding of the mechanism by which SRO regulates photomorphogenesis and highlight its potential application in deep sowing-resistant breeding.

Assessing and Quantifying the Carbon, Nitrogen, and Enzyme Dynamics Effects of Inter-row Cover Cropping on Soils and Apple Tree Development in Orchards

Cover crops between rows in orchards can improve the development of soil resources and increase agricultural productivity. However, there have been few reports of cover crops that can act as a “green manure” in apple orchards across arid and semiarid zones. This study investigated the effects of planting interrow vegetation on soil properties and apple tree performance during a 32-month experiment. There were six treatments: clean cultivation as a control; natural grass planting; planting with ryegrass; planting with alfalfa; planting with tall fescue; and planting with villous wild pea cover crops. The treatments primarily affected the 0- to 20-cm surface soil layer. Soil carbon, nitrogen, and enzyme levels initially decreased (during the first 12–24 months); then, they increased (24–32 months). The cover crops significantly increased nutrient contents (soluble organic carbon, microbial carbon and nitrogen, alkaline dissolved nitrogen, nitrate nitrogen, and ammonium nitrogen) in the 0- to 20-cm soil layer by more than 19.6% and increased the related enzyme activities by more than 25.2%. The alfalfa and wild pea alleys had a stronger effect on the soil environment than the control, natural grass, ryegrass, and tall fescue alley treatments; however, after 32 months, the alfalfa treatment inhibited fruit tree growth and development. This was unexpected because alfalfa seemed to have a positive effect on soil fertility characteristics. Under local ecological conditions, villous wild pea had the greatest effect on apple orchard productivity and significantly increased short branching by 15.9%, fruit weight per fruit by 12.6%, yield per plant by 8.6%, and soluble sugar content by 10.5% compared with clean cultivation. The correlation analysis showed that there were significant or highly significant positive correlations between fruit tree performance and soil carbon, nitrogen, and enzyme activity levels as the soil layer depth increased. Therefore, under local ecological conditions, cover crops have a greater effect on orchard surface soil fertility than on deeper soils, and intercropping with villous wild pea potentially produces the greatest improvement in apple orchard productivity.

Strategies of invasive snail Pomacea canaliculata during hibernation in rice fields of south China: effects of body size, sex, and soil depth.

The invasive freshwater snail Pomacea canaliculata is an agricultural pest with a certain level of tolerance to abiotic stress. After the harvest of late rice, the snails usually burrow themselves into the soil surface layers to overwinter and pose a renewed threatto rice production in the following year. Revealing the response of snails to environmental stresses is crucial for developing countermeasures to control their damage and spread. In this study, we conducted a 120-day in situ experiment during the winter to investigate the survival and physiological changes of hibernating snails in 0-5 and 5-10 cmsoil depths, aiming to explore their overwintering strategies. Our results showed that 73.61%, 87.50%, and 90.28% of male, female, and juvenile snails survived after hibernation for 120 days in 0-10 cm soil depth, respectively. The differences in survival rates based on sex and size of snailspotentially reflect the countermeasures of snails to rapidly reproduce after hibernation. Simultaneously, the hibernating snails exhibited the ability to maintain a certain level of body weight. During this period, the snails increased their antioxidant enzyme activities to cope with oxidative stress, and enhanced their lipid storage. The hibernation survival of snails was not significantly affected by different soil depths, indicating that they have the potential to hibernate into deeper soils. Furthermore, snails were capable of increasing their contents of bound water and glycerol to cope with sudden cold spells during hibernation. Our findings emphasize the adaptive changes of P. canaliculata snails overwintering in paddy soils. In future studies, the vulnerabilitiesof P. canaliculata during hibernation (e.g. shell characteristics, nutrient reserves, and dehydration tolerance, etc.,) should be investigated to develop effective control methods for this period. © 2024 Society of Chemical Industry.

Experimental study on comprehensive detection technology of shallow gas in deep soft soil layer

This study focuses on the underground shallow gas detection project in the Lingkun Island area of the northern entrance tunnel of the Wenzhou City Light Rail S2 line. Based on geological exploration data of shallow gas, we chose the technique of controlled-release gas with static pressure as the experimental foundation, integrating various technologies such as multi-functional in-situ probing, electrical methods, and seismic waves, comprehensively researching shallow gas detection technology in the Lingkun Island area. We conducted field probing experiments to accurately obtain the physical and mechanical properties of gas-rich soil layers and further studied the possibility of determining gas-rich locations. By applying parallel electrical methods, we can accurately identify and distinguish areas of anomalous resistivity in shallow geological structures. Based on abnormal changes in acoustic impedance in strata, we used seismic wave methods, including seismic CT and seismic wave scattering technology, to accurately reveal the presence and depth of shallow gas, providing reliable basis for accurate determination of shallow gas. Finally, we summarized a comprehensive plan for underground shallow gas detection technology, covering on-site data collection, data processing, and image interpretation of results, which will provide valuable references for future shallow gas exploration in relevant areas.

Deep (200–2,000 cm) Soil Water Use Can Compensate for the Drought Effect on Gas Exchange in Dry Years Better Than in Wet Years for Dryland Tree Plantations

AbstractAnalyzing deep soil water use (DSWU) response to precipitation change and its impact on tree physiology is necessary to understand tree mortality mechanisms, especially in drylands. Using a process‐based model parameterized with in situ measured fine root distribution data for 0–2,000 cm depth, along with a root‐cutting (below 200 cm depth) numerical experiment, this study explored DSWU strategies and their contribution to total water consumption during different precipitation years, as well as their relationship to tree gas exchange traits, in mature apple (Malus pumila Mill) tree and black locust (Robinia pseudoacacia L.) plantations in both wetter (Changwu, 583 mm) and drier (Yan'an, 534 mm) sites on China's Loess Plateau. Results showed that DSWU at 200–2,000 cm depth in different precipitation years of both species mainly occurred during the early growing seasons. On average, DSWU contributed 22.9% and 25.1% to the total water consumption of apple trees and black locust, respectively, and its contribution increased to 26.0% and 36.7% in extremely dry years. Moreover, the lack of DSWU significantly decreased (p < 0.05) stomatal conductance (by 16.9%, 16.9%, 47.4%, and 11.4%, respectively) and photosynthetic rates (by 37.1%, 20.1%, 28.5%, and 16.4%, respectively) of Changwu apple trees, Yan'an apple trees, Changwu black locust and Yan'an black locust in extremely dry years. Similar reductions occurred only in Yan'an for both tree species in normal years. In contrast, no significant differences were found in gas exchange traits in extremely wet years. Our results highlight that DSWU is an important strategy for plantations in the deep vadose zone region to resist extreme drought.

Response of soil moisture to rainfall following deep soil drying in China's hilly loess lands

Deep soil drying is a physical soil phenomenon that has become increasingly characteristic to artificial afforestation on China's Loess Plateau. Current research is largely short of conclusive reports on soil moisture recovery following deep soil drying in afforested lands. In this study, a 10-m deep underground column was constructed at Pengyang Experimental Station in Ningxia. The CS650-CR1000 automatic soil moisture monitoring system and BLJW-4 small meteorological observation stations were used to respectively monitor soil moisture and meteorological conditions in the study area for the period 2014–2019. The local rainfall was classified and the characteristics of soil infiltration analyzed at both monthly and annual scales. The results showed that: i) Deep soil moisture recovery in the semi-arid Loess Plateau region depended mainly on 25–49.9 mm and >50 mm types of rainfall; together accounting for 35.44 % of the precipitation. ii) Deep soil moisture replenishment occurred mainly for the period from April to October. While this accounted for 30.13 % of the precipitation, evaporation loss accounted for 69.87 % of it. With increasing monthly rainfall (Pm), the variation in monthly infiltration depth (Zm) was quadratic in shape — where Zm = −0.0094 Pm2 + 3.7702 Pm (R2 = 0.9577). iii) At the annual scale, deep soil moisture replenishment was mainly driven by year-on-year infiltration water accumulation. This is because a single year precipitation infiltration was not enough to replenish deep soil moisture. The cumulative infiltration depth for 2014–2019 was 180, 260, 400, 700, 1000 > 1000 cm. It suggested that soil water infiltration and deep dry soil recovery occurred at different times under rainfed conditions in the semi-arid loess hills in China. This is key for in-depth studies of the hydrological process in dry soil regions.

Variations in water use strategies of Tamarix ramosissima at coppice dunes along a precipitation gradient in desert regions of northwest China.

The precipitation pattern has changed significantly in arid desert areas, yet it is not clear how the water use strategies of Tamarix ramosissima Ledeb. on coppice dunes along a natural precipitation gradient are affected. In this study, the hydrogen and oxygen isotope compositions of xylem water, soil water, precipitation, and groundwater were measured by stable isotope techniques in Huocheng, Mosuowan, and Tazhong. Additionally, the water use strategies of natural precipitation gradient were investigated in conjunction with the MixSIAR model. The results indicated that the water sources of T. ramosissima exhibited significant variation from semi-arid to hyper-arid areas. In semi-arid areas, T. ramosissima mainly absorbed shallow, shallow-middle, and middle soil water; however, T. ramosissima shifted its primary water sources to middle and deep soil water in arid areas. In hyper-arid areas, it mainly utilized deep soil water and groundwater. In contrast, the water source contribution rate of T. ramosissima exhibited relative uniformity across each layer in an arid area. Notably, in hyper-arid areas, the proportion of groundwater by T. ramosissima was significantly high, reaching 60.2%. This is due to the relatively shallow groundwater supplementing the deep soil water content in the area. In conclusion, the proportion of shallow soil water decreased by 14.7% for T. ramosissima from semi-arid to hyper-arid areas, illustrating the occurrence of a gradual shift in potential water sources utilized by T. ramosissima from shallow to deep soil water and groundwater. Therefore, T. ramosissima on coppice dunes shows flexible water use strategies in relation to precipitation and groundwater, reflecting its strong environmental adaptability. The findings hold significant implications for the conservation of water resources and vegetation restoration in arid areas.

Changes in Water Utilization Characteristics of Trees in Forests across a Successional Gradient in Southern China

Elucidating the water utilization strategy of trees during forest succession is a prerequisite for predicting the direction of forest succession. However, the water utilization characteristics of trees in forests across a successional gradient remain unclear. Here, we utilized the hydrogen and oxygen stable isotopes combined with the Bayesian mixed model (MixSIAR) to analyze the water utilization of dominant trees (Pinus massoniana, Castanea henryi, and Schima superba) in forests along a successional gradient in the Dinghushan Biosphere Reserve of China. Furthermore, we determined the primary factor affecting the water utilization of various trees based on variation partitioning analysis and a random forest model. Our results illustrated that in the early-successional forest, the water utilization ratios from shallow soil layers by P. massoniana were significantly lower than that in the mid-successional forest (51.3%–61.7% vs. 75.3%–81.4%), while its water utilization ratios from deep soil layers exhibited the opposite pattern (26.1%–30.1% vs. 9.0%–15.0%). Similarly, the ratios of water utilization from shallow soil layers by C. henryi (18.9%–29.5% vs. 32.4%–45.9%) and S. superba (10.0%–25.7% vs. 29.2%–66.4%) in the mid-successional forest were relatively lower than in the late-successional forest, whereas their water utilization ratios from deep soil layers showed the contrary tendency. Moreover, our results demonstrated that the diverse water utilization of each tree in different successional forests was mainly attributed to their distinct plant properties. Our findings highlight the increased percentage of water utilization of trees from shallow soil layers with forest succession, providing new insights for predicting the direction of forest succession under changing environments.

Soil water consumption along the profile in response to soil water content variations in a black locust plantation with a rainfall exclusion in Loess Plateau

Soil drying is frequently observed in mature forests in water-limited regions, and poses a threat to sustainable development of the ecosystems. Herein, we assessed the effects of rainfall reduction on the water-use characteristics of a black locust (Robinia pseudoacacia) plantation in a sub-humid region of the Loess Plateau, China. Paired plots were established in the plantation, including a treatment with 30 % throughfall exclusion and a control. We comparatively investigated the dynamics of soil water content (SWC) throughout the profile in the two plots after four years of the treatment and determined the contribution of soil water storage (SWS) in each soil layer to water consumption according to the SWS budget. While SWC across the profile in the control plot showed general responses to replenishment and consumption under rainy and dry weather conditions, respectively, the treatment plot had smaller replenishment and consumption in deep layers, causing an aggravated deficiency in SWS and the formation of a temporary dried soil layer (DSL) at a depth of 55–100 cm. The cumulative decrement in SWS during each dry event (consecutive rainless days of ≥ 5-day duration) in the control plot was significantly correlated with SWC at 100–160 cm, suggesting a substantial contribution of water consumption from this layer. However, the treatment plot showed a major contribution to water consumption from the 0–100 cm soil layer during dry events. The vertical distribution of the root system supports these findings, which differed from our hypothesis that deep soil water would be used in response to reduced rainfall input. The distribution of fine root density in the treatment plot was relatively shallower (0–22 and 0–73.1 cm accounting for 50 % and 90 % of fine roots, respectively) than in the control plot (0–31.2 and 0–103.5 cm for corresponding values). These findings indicate that soil water deficiency resulted in the formation of DSL, which hindered water consumption and root development deeper in the soil profile. The severity and recovery of the DSL may be jointly determined by the vertical distribution of SWS and transpiration demand of the plantation. These findings provide insights for water resource management and sustainable development of the plantations in this region.

Can we identify tipping points of resilience loss in Mediterranean rangelands under increased summer drought?

Mediterranean ecosystems are predicted to undergo longer and more intense summer droughts. The mechanisms underlying the response of herbaceous communities to such drier environments should be investigated to identify the resilience thresholds of Mediterranean rangelands. A 5-year experiment was conducted in deep and shallow soil rangelands of southern France. A rainout shelter for 75 days in summer imposed drier and warmer conditions. Total soil water content was measured monthly to model available daily soil water. Aboveground net primary production (ANPP), forage quality, and the proportion of graminoids in ANPP were measured in spring and autumn. Plant senescence and plant cover were assessed in summer and spring, respectively. The experimental years were among the driest ever recorded at the site. Therefore, manipulated summer droughts were drier than long-term ambient conditions. Interactions between treatment, community type, and experimental year were found for most variables. In shallow soil communities, spring plant cover decreased markedly with time. This legacy effect, driven by summer plant mortality and the loss of perennial graminoids, led to an abrupt loss of resilience when the extreme water stress index exceeded 37 mm 10 day-1, characterized by a reduction of spring plant cover below 50% and a decreased ANPP in rainy years. Conversely, the ANPP of deep soil communities remained unaffected by increased summer drought, although the presence of graminoids increased and forage nutritive value decreased. This study highlights the role of the soil water reserve of Mediterranean plant communities in modulating ecosystem responses to chronically intensified summer drought. Communities on deep soils were resilient, but communities on shallow soils showed a progressive, rapid, and intense degradation associated with a loss of resilience capacity. Notably, indexes of extreme stress were a better indicator of tipping points than indexes of integrated annual stress. Considering the role of soil water availability in other herbaceous ecosystems should improve the ability to predict the resilience of plant communities under climate change.

Research on the Reinforcement Characteristics of Thick Cushion Layer and Rigid Pile Composite Foundation

The rigid pile composite foundation method is the most commonly used method for strengthening weak soil foundations. In this method, piles usually need to pass through weak soil layers, and the pile end falls on a bearing layer with good bearing capacity. Under existing technical conditions, the thicker the weak soil layer, the longer the pile body, and the more difficult it is to ensure the construction quality of the pile. In response to this issue, some scholars have adopted the rigid pile composite foundation method with a thick cushion layer for reinforcement treatment. This article uses PLAXIS 3D (V20.04.00.790) software to establish a finite element model of rigid pile composite foundation with a thick cushion layer and simulate the process of foundation reinforcement. The influence of parameters such as thickness, compression modulus, and shear strength index of the cushion layer on foundation settlement and pile–soil stress distribution is studied, and the reasonable range of these parameters is analyzed under the condition of considering reinforcement effect. Through comparative analysis, it can be concluded that for deep and weak soil areas, the thickness of the cushion layer can range from 0.5 to 2.6. The thickness and compressive modulus of the cushion layer have a significant impact on the settlement of the foundation, the pile–soil stress ratio, and the stress of the pile body, while the shear strength index of the cushion layer has a relatively small impact on these parameters. Reasonably selecting the geometric and mechanical parameters of the cushion layer can effectively reduce stress concentration at the pile top and better play the role of the soil between piles.

Precipitation patterns impact soil aggregates and organic carbon of an alpine wetland on the Qinghai-Tibetan Plateau

Global climate change is predicted to influence both precipitation amount and frequency in many regions. However, little is known about how precipitation changes affect soil aggregates and soil organic carbon (SOC) in alpine wetlands. Plots of an alpine wetland on the Qinghai-Tibetan Plateau were subjected to two precipitation frequencies (high vs. low, i.e., 1 and 3 times of nature rainfall intervals) crossed with two precipitation amounts (high vs. low, i.e., 100 % and 70 % of the amount of natural rainfall). Two years later, we investigated changes of soil aggregates (silt + clay, < 53 μm; microaggregates, 53∼250 μm; and macroaggregates, >250 μm) and SOC in three soil depths, i.e., 0–15 cm, 15–30 cm and 30–50 cm. Averaged across the three soil depths, the content of SOC and dissolved organic carbon (DOC) in the simulated natural precipitation (high amount, high frequency treatment) were 127.22 g kg−1 and 0.19 g kg−1, respectively. Reducing precipitation amount or frequency led to a 19.6 %-26.2 % increase in SOC, and 28.7 %-44.4 % increase in DOC. Microbial biomass carbon in natural precipitation was 1.33 g kg−1 across the three soil depths, and its response to precipitation varied with soil depths. The fraction of macroaggregates in the 0–15 cm soil depth was 63.5 % in the simulated natural precipitation treatment, and decreased by 18.6 %–21.9 % in response to reduced precipitation amount or frequency. Aggregate fractions in the 15–30 cm soil depth did not respond significantly to the changes of precipitation patterns. Reducing precipitation frequency or amount decreased the contribution of macroaggregate-associated organic carbon to SOC compared to the simulated natural precipitation, but increased the contribution of microaggregate-associated organic carbon, especially in the 0–15 cm soil depth. Structural equation models revealed that SOC was regulated by soil aggregate composition and microbial biomass carbon. The buffering of the surface soil weakened the effects of precipitation changes on aggregates and aggregate-associated organic carbon in the deep soil. These results suggest that reducing precipitation frequency or amount can decrease the fraction of macroaggregates in the surface soil, and weaken the physical protection of macroaggregates for SOC. Thus, changes in precipitation patterns may have a significant impact on SOC storage and stability in alpine wetlands through their influence on soil aggregate composition.

The heterogeneous distribution of heavy metal(loid)s at a smelting site and its potential implication on groundwater

The downward migration of soil heavy metal(loid)s (HMs) at smelting sites poses a significant risk to groundwater. Therefore, it is requisite for pollution control to determine the pollution characteristics of soil HMs and their migration risks to groundwater. 198 soil samples collected from a Pb-Zn smelting site were classified into 6 clusters by self-organizing map (SOM) and K-means clustering. Cd, Zn, As, and Pb were identified as the characteristic contaminants of the site. The driving factors for the heterogeneous distribution of HMs have been validated through the implementation of K-means clustering and multiple-hits calculation. Using ultrafiltration extraction and microscopic analysis, the soil colloids were identified as crucial carriers facilitating the migration of HMs. Specifically, the colloidal fractions of Cd, Zn, and As, Pb in deep soil (3–4 m) accounted for 91 %, 78 %, 88 %, and 82 %, respectively, consistently surpassing those found in topsoil (0–0.5 m). It was primarily attributed to the strong affinity of HMs toward soil colloids (franklinite, PbS, and kaolinite) and dissolved organic matter (humic acids and protein). The research findings highlight the potential risk of colloidal HMs to groundwater contamination, providing valuable insights for the development of targeted management and remediation strategies.

Accounting for deep soil carbon in tropical forest conservation payments

Secondary tropical forests are at the forefront of deforestation pressures. They store large amounts of carbon, which, if compensated for to avoid net emissions associated with conversion to non-forest uses, may help advance tropical forest conservation. We measured above- and below-ground carbon stocks down to 1 m soil depth across a secondary forest and in oil palm plantations in Malaysia. We calculated net carbon losses when converting secondary forests to oil palm plantations and estimated payments to avoid net emissions arising from land conversion to a 22-year oil palm rotation, based on land opportunity costs per hectare. We explored how estimates would vary between forests by also extracting carbon stock data for primary forest from the literature. When tree and soil carbon was accounted for, payments of US$18–51 tCO2–1 for secondary forests and US$14–40 tCO2–1 for primary forest would equal opportunity costs associated with oil palm plantations per hectare. If detailed assessments of soil carbon were not accounted for, payments to offset opportunity costs would need to be considerably higher for secondary forests (US$28–80 tCO2–1). These results show that assessment of carbon stocks down to 1 m soil depth in tropical forests can substantially influence the estimated value of avoided-emission payments.

Germination Biology of Three Cyperaceae Weeds and Their Response to Pre- and Post-Emergence Herbicides in Paddy Fields

(1) Background: Cyperaceae weeds have become a major type of weed in local paddy fields in China. (2) Methods: We assessed the impact of environmental factors, including temperature, light, salinity, water stress and soil depth, on the germination and emergence of three dominant Cyperaceae weeds: Cyperus difformis L., C. iria L. and Fimbristylis littoralis Gaudich. Using the dish dipping method, the performances of the pre- and post-emergence herbicides commonly used in paddy fields on three Cyperaceae weeds were evaluated using the pot method. (3) Results: The seeds optimally germinated at 35 °C in constant conditions and 25 °C/40 °C in alternating conditions. The seeds of the three Cyperaceae weeds were sensitive to light and could not germinate under dark conditions. The germination rate of the three weeds decreased with the increase in the NaCl concentration and water potential; the three weeds could not germinate at a 320 mmol·L−1 NaCl concentration and −0.1 MPa water potential. When the pH levels were 4 to 9, the germination rates of the three weeds were all greater than 80%. The burial depths to inhibit 50% of the emergence of C. difformis, C. iria and F. littoralis were 0.27, 1.06 and 0.42 cm, respectively. The control efficacy of the pre-emergence herbicides of pretilachlor, butachlor and oxyfluorfen on the three weeds were all above 90% at the recommended dose in the field. Halosulfuron-methyl, florpyrauxifen-benzyl and bentazone could effectively control the three Cyperaceae weeds; their performances on the three weeds at the 3- to 4-leaf stage were all above 82%. (4) Conclusions: The three Cyperaceae weed seeds have a strong adaptability to temperature, water potential, salinity and soil depth, and these weeds are sensitive to most pre- and post-emergence herbicides. Therefore, taking Cyperaceae weed seeds into the deep soil layer by tillage or selecting appropriate herbicides according to their growth stages can effectively control Cyperaceae weeds in rice fields.

Pattern of water use by Tamarix ramosissima seedlings in floodplains under varied groundwater depths in the hinterland of the Taklimakan Desert

The water use of Tamarix ramosissima Ledeb. seedlings after flooding were analyzed both to explore the maintenance mechanism and pattern of natural regeneration of riparian forest, which will provide a scientific basis for restoration of desert riparian forest and ecosystem stability in the lower reaches of inland rivers of arid regions. This study area was located in the hinterland of the Taklimakan Desert in Xinjiang, China. Tamarix ramosissima seedlings growing on different groundwater depths at the river floodplain were used as the study system. The rooting depths of T. ramosissima seedlings with different basal stem diameters were ascertained by the root excavation method. The water source for the T. ramosissima seedlings was clarified using hydrogen and oxygen stable isotope methods, and the water use efficiency of T. ramosissima seedlings was investigated by stable carbon isotope (δ13C) analysis. As the basal stem diameter classes of the T. ramosissima seedlings increased, their root depths increased. As the groundwater depth increased, the seedlings changed from primarily utilizing deep soil water to utilizing shallow soil water. In the three sample sites, the average depth of water uptake of the seedlings with basal stem diameters of 0–5 mm was 110.5, 44.1 and 39.1 cm, respectively, and that of seedlings with basal stem diameters of 5–11 mm was 83.8, 73.6 and 37.7 cm, respectively. As groundwater depth increased, the average water uptake depth of the seedlings gradually became shallower. There was no significant difference in the δ13C values of leaves under different groundwater depths, indicating that the seedlings were not subjected to water stress. Thus, surface water played a greater role than groundwater in T. ramosissima seedling water utilization. Therefore, when analyzing ecological water conveyance patterns, attention should be paid to T. ramosissima located in areas with deep groundwater. Shallow-rooted seedlings with small basal stem diameters face an increased risk of wilting if they do not receive timely recharges of surface water. Data AvailabilityAll data generated or analyzed during this study are included in this published article.

Water uptake patterns and rooting depths of Tamarix ramosissima in the coppice dunes of the Gurbantünggüt Desert, China: a stable isotope analysis.

Tamarix ramosissima has an important role in stabilizing sand dunes in desert ecosystems. Understanding the water use strategies of T. ramosissima is essential to understand its adaptations on coppice dunes. We utilized the stable isotopes δ2H and δ18O in soil water, groundwater, and xylem water to identify monthly differences in water sources. Additionally. we explored rooting depth using 2H2O as an artificial tracer. In May, T. ramosissima derived 75% of its water from shallow and middle soil layers. In July, it absorbed 90% water from middle and deep soil layers. In August and September, it acquired approximately 80% of its water from deep soil layers. The labelling using 2H as an artificial tracer indicated that the root system of T. ramosissima could reach depths >500 cm in the coppice dunes. 2H absorption was observed at depths of 100, 200, 300 and 400 cm. Soil water is the dominant water source for T. ramosissima in the coppice dunes because groundwater is at depths >30 m. The flexible water-use strategies of T. ramosissima enable it to effectively utilize different available water sources to adapt to the arid environment. These findings improve our understanding of water uptake patterns and drought adaptation strategies of T. ramosissima in the coppice dunes of desert ecosystems.

Topographic and Climatic Factors Effect Spatiotemporal Coupling Relationship of Soil Water Conservation Function with Vegetation in Source of the Yellow River

The Gannan Water Conservation area is an indispensable part of the ecological barrier on the Tibetan Plateau and is a key ecological area for the water supply. Exploring the coupled coordination relationship between vegetation and soil contributes to the conservation and planning of the natural environment. In this study, soil water conservation function (SWCF) was investigated with Moderate Resolution Imaging Spectroradiometer (MODIS) data in the Gannan Water Conservation Area at the source of the Yellow River, and the spatiotemporal coupling relationship between the SWCF and vegetation was explored. Meanwhile, their responses to topographic and climatic factors were investigated with structural equation models. The main results indicated that the coupling coordination degree (DVS) in the soil depth was in a barely coordinated state, with 0–10 cm &gt; 20–30 cm &gt; 10–20 cm, showing that the area proportion of ‘Basic balanced–Synchronous development of VEG and SWCF’ was the highest, and the spatial aggregation feature was obvious. As the gradient of topographic factors varied, the coupling coordination also varied at various soil depths. Meanwhile, the absolute values of the correlation coefficients of the temperature and precipitation with the coupling coordination were the highest at 20–30 cm compared to the other soil depths, demonstrating that the effect was more significant in deeper soils than in shallower ones. Furthermore, the path coefficients of the topographic factors were larger than those of the climatic factors in the 10–20 cm and 20–30 cm layers, while the opposite was true in the 0–10 cm layer. In general, the vegetation conditions and water conservation function of soil in the source area of the Yellow River are basically developing synchronously, and the topographic factor is the key factor for the geographical difference in the coupling relationship between the two factors.