Loess Plateau Region Research Articles

Ecosystem carbon sequestration service supports the Sustainable Development Goals progress

Ecosystem carbon sequestration service (ECSS) is the benefits humans derive from the ecosystem carbon sequestration process, which is key to regulating climate, stabilising the natural foundation for development, and supporting the Sustainable Development Goals (SDGs) achievement. However, how ECSS contributes to the SDGs still needs to be discovered. Here, based on downscaling localisation SDG indicators, regression methods, and mechanism analysis, we identified the contribution of ECSS to the SDGs, taking China's Loess Plateau (LP) region as an example. The results showed that the LP made higher progress on resource and environmental SDGs, such as SDGs 13, 12, 6, and 7 (climate, consumption and production, water, and energy) in the last two decades. As for the relationships between ECSS and SDGs, the progress of SDGs 6, 7, 13 and 15 (water, energy, climate, and ecosystems) showed positive linear responses to ECSS. The response of SDGs 1, 4, 8, and 12 (poverty reduction, education, economic growth, and consumption and production) to ECSS showed a threshold when the standardised ECSS value was 0.11. To improve ECSS for a more sustainable ecological foundation underpinning the SDGs, ECSS management should be improved to protect the ecosystem carbon pool and improve carbon sequestration function, as well as to promote the social-ecological co-benefits. This work links carbon sequestration service to sustainable development and can help in leveraging nature's contributions towards carbon neutrality and the 2030 Agenda.

近20年黄土高原生态系统服务研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 近20年黄土高原生态系统服务研究进展 DOI: 10.5846/stxb202204291190 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42041007，42171088）；中央高效基本科研业务费专项资金资助 Research progress on the ecosystem services on the Loess Plateau during the recent 20 years Author: Affiliation: 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:生态系统服务是自然生态系统及其物种提供的供给和维持人类生存的条件和过程，是人类通过生态系统的功能直接或间接得到的产品或服务，具有典型的区域性特征。黄土高原是黄河流域重要生态安全屏障，生态建设规模大、历时长，是我国生态系统服务研究的重要案例区。已有研究针对黄土高原生态系统服务进行物质量与价值量估算、权衡与协同关系识别和供需关系评估，但不同结论之间缺少归纳和对比。研究对近20年来黄土高原地区生态系统服务研究的文献总体特征和主要研究发现分析表明：相关中英文论文数量和被引频次整体呈上升趋势，研究内容上主要关注黄土高原生态系统服务的定量估算，近年来逐渐向生态系统服务权衡分析和供需关系评估拓展；黄土高原地区自退耕还林以来，各项生态系统服务总量呈上升趋势，呈现出东南增量较多、西北增量较少的空间格局；黄土高原地区供给服务和调节服务存在较明显的权衡关系，但在不同尺度上强度分异明显；区域内生态系统服务供给量和需求量均呈增加趋势，供需匹配状况具有明显时空差异。面向当前研究中物质量评估种类不足、价值量估算高度不确定、权衡与协同现象缺乏归因、空间流动性体现不足等问题，未来黄土高原生态系统服务研究有待加强面向生态产品价值实现的生态系统服务价值估算，空间流动视角下的生态系统服务供需关系评估，以及基于生态系统服务权衡情景模拟的国土空间优化。 Abstract:Ecosystem services are the conditions and processes provided by natural ecosystems and their species that supply and sustain human existence, and are products or services that human received directly or indirectly through the functions of ecosystems. It has typically regional characteristics. The Loess Plateau is an important ecological security barrier in the Yellow River Basin, with a large scale and long duration of ecological construction, and is an important case area for ecosystem service research in China. Previous studies have estimated the value and quality of ecosystem services, identified their trade-offs and synergies, and evaluated their supply-demand relationship on the Loess Plateau. However, there is a lack of generalization and comparison among different conclusions. We analysed the main findings of the literature on ecosystem services on the Loess Plateau region over the past 20 years, and got the following results. The number of relevant papers in both English and Chinese have been generally increasing, as well as the frequency of citations. The research content was mainly concerned with the quantitative estimation of ecosystem services on the Loess Plateau, and it has gradually expanded to the analysis of ecosystem service trade-offs and the assessment of supply-demand relationship in recent years. Since the Grain-for-Green project, the vegetation cover of the Loess Plateau has increased and the total amount of ecosystem services has been on the rise, presenting a spatial pattern of more increased in the southeast and less increased in the northwest. There are clear trade-offs between provision and regulation services on the Loess Plateau, and the intensity varies apparently at different scales. Both the supply and demand of ecosystem services are increasing in the region, with clear spatial and temporal differences in their matching degree. To address the limitations of insufficient types of quality assessments, high uncertainty in value estimation, lack of attribution of trade-offs and synergies, and insufficient representation of spatial delivery, future research on ecosystem services on the Loess Plateau needs to strengthen the estimation of ecosystem service values towards the realization of ecological product value, improve the assessment of ecosystem service supply and demand from the perspective of spatial delivery, and enhance the simulation of ecosystem service trade-off scenarios to support territorial space optimization. 参考文献 相似文献 引证文献

Analysis of soil water potential characteristics of wheat croplands and apple orchards in an agroforestry ecosystem based on the van Genuchten model

Due to intense droughts and water shortages, soil water deficit limits agricultural production in arid and semiarid areas, such as China’s Loess Plateau region. Yet the effects of different cover crops on soil water in these areas have received insufficient attention. This study was conducted in the Weibei rainfed highland to investigate soil water potential dynamics in an agroforestry ecosystem comprising winter wheat (<i>Triticum aestivum</i> L.) and apple (<i>Malus domestica</i>) trees over the apple growth period (March to September of 2020). Soil water characteristic curves (SWCCs) of cropland topsoil (0 to 40 cm), orchard topsoil (0 to 40 cm), dark loessial subsoil (40 to 80 cm), and loess parent material (80 to 150 cm) were determined using the centrifuge method and water vapor equilibrium method. The van Genuchten model was used to fit SWCCs and then convert volumetric soil water content monitored in field plots to soil water potential. A quantitative analysis was conducted to evaluate soil water stress in wheat croplands and apple orchards. The model performed well in fitting SWCCs for all tested soils, yielding a robust accuracy (<i>R</i>² &gt; 0.96). Compared to apple trees, wheat was more threatened by drought. From mid-March to early July, the 0 to 100 cm soil layers of croplands all exhibited high water stress with matric suction pF &gt; 3.98, and unavailable water occurred in the 0 to 20 cm and 0 to 80 cm soil layers in late March to late April and mid-May to mid-July, respectively. Drought threat in apple orchards increased with an increase in tree age. In young orchards (&lt;10 y), high water stress was found only in surface soil layers (0 to 20 cm) in mid-March to late April and late May to early July, which spread to a depth of 70 cm in early June to early July. In mature orchards (10 to 20 y), high water stress was similarly observed in the surface soil layers in mid-March to early May and late May to early July, which extended to the 80 cm depth in late May to early July. In old orchards (&gt;20 y), high water stress initially emerged in the surface soil layers in early April to mid-April and then reached the 70 cm depth in late May to mid-July, whereas unavailable water occurred in the 0 to 60 cm soil layers in mid-June to mid-July. The results indicated that soil water stress zones with low water potential were formed intermittently at different soil depths of apple orchards depending on tree age and growth stage. However, compared to wheat croplands, apple orchards were less influenced by drought stress, so that converting croplands to orchards could alleviate drought threats in the Weibei area.

Gully internal erosion triggered by a prolonged heavy rainfall event in the tableland region of China's Loess Plateau

Gully erosion is a severe form of soil erosion, but gully internal erosion processes are poorly understood, especially at the event scale. To investigate gully internal erosion intensity and understand the related gully development mechanism in an agricultural environment with gully head stabilization and vegetation restoration efforts, two successive field investigations were carried out just before and after a prolonged rainfall event in 2021 in the tableland region of China's Loess Plateau. Thirteen gullies were investigated and all experienced gully internal erosion, while most gully boundaries were stable during the heavy rainfall event based on the comparison of the UAV digital orthograph maps (DOMs acquired with Unmanned Aerial Vehicle) before and after the rainfall event. The proportion of gully internal erosion area to gully internal area of the 13 investigated gullies ranged from 3 to 55%, with average areal erosion proportion of the gully sidewall and gully bed of 21% and 36%, respectively. The erosion area of subdrainage units (SDUs) on the gully sidewall was positively correlated to the SDU area, average SDU slope gradient and vegetation type, while the erosion area on the gully bed was positively correlated to the gully area, gully depth and gully bed slope gradient. Gully internal erosion was not significantly correlated with gully drainage area because the connectivity between the upslope and gully areas was interrupted and the effective drainage area of the gully was obviously reduced by soil erosion conservation measures, including terraces on the upslope drainage area, shrub belts, and water barriers. Thus, gully internal erosion is still active under the heavy rainfall storm against the background of the ‘Grain for Green’ and ‘Gully Stabilization and Tableland Protection’ programs, and integrated measures for preventing both gully expansion and gully internal erosion must be further enhanced in the context of climate change.

Asymmetric responses of biocrust respiration to precipitation manipulation under a changing semiarid climate

Global climate change is expected to cause both increased and reduced precipitation in the next decades, especially in drylands with semi-arid climates. Biocrusts are an essential soil surface cover in global drylands, and they strongly influence most soil properties and support fundamental ecosystem functions, especially soil carbon (C) cycling. Nevertheless, the response patterns and mechanisms of biocrust respiration rate (Rs) to precipitation changes remain uncertain under changing semi-arid climates. In our study, a field experiment for biocrusts with natural precipitation (CK) and six levels of precipitation manipulation (–50 %, –30 %, –10 %, +10 %, +30 %, and +50 % of CK) were conducted from 2019 to 2021 in a semi-arid climate region of the northern Chinese Loess Plateau. We continuously measured the biocrust Rs of all the treatments in the growing seasons, and the fundamental properties of biocrusts and their temperature and water content at 5 cm depth were also measured. Our results showed that the increased precipitation inhibited biocrust Rs, while moderately reduced precipitation stimulated biocrust Rs. As compared with the CK, the precipitation manipulations of +10 %, +30 %, and +50 % decreased biocrust Rs by 8.9 %, 15.3 %, and 22.1 %, respectively, while the treatments of –10 % and –30 % increased biocrust Rs by 25.5 % and 8.0 %, respectively. However, the precipitation manipulation of –50 % suppressed biocrust Rs by 19.3 %. More importantly, the responses of biocrust Rs to precipitation changes were negative and asymmetric, which indicated a higher sensitivity of biocrust Rs to reduced precipitation in comparison to increased precipitation. Moreover, the increased precipitation (+10 % to + 50 %) raised soil water content (by 29.7 %–55.0 %), moss biomass (by 12.5 %–50.0 %), and organic matter content (by 11.3 %–12.4 %). In contrast, the reduced precipitation (–10 % to –30 %) decreased soil water content (by 5.2 %–17.6 %) and moss biomass (by 12.5 %–25.8 %). The structural equation modeling analysis showed that the responses of biocrust Rs to precipitation manipulation were mainly and directly influenced by soil temperature and biocrust properties. Although soil water content did not have a direct significant effect on biocrust Rs, it indirectly influenced biocrust Rs by affecting the fundamental properties of soil and biocrusts. Consequently, the changed soil properties and biocrust characteristics caused by precipitation shifts aggravated the negative responses of biocrust Rs to precipitation manipulation. Our findings emphasize that biocrusts have a negative and asymmetric response of Rs to precipitation changes, implying that the intensified precipitation variation in semi-arid regions caused by global climate change in future may positively affect the stability of soil C stocks contributed by biocrusts and thus reduce soil C efflux in drylands.

In Situ Rainwater Collection and Infiltration System Alleviates the Negative Effects of Drought on Plant-Available Water, Fine Root Distribution and Plant Hydraulic Conductivity

Soil water status and fine-root characteristics are the foundation for implementing forest water-management strategies in semiarid forest plantations, where rainwater is always the sole source of water for plant growth. Rainwater management and utilization are effective strategies to alleviate water scarcity in semiarid areas as ground water is always inaccessible there. Through the implementation of an in situ rainwater collection and infiltration system (IRCIS), we investigated the effects of IRCIS on soil water and fine-root distributions in the 0–5 m soil profile in a wet (2015, 815 mm) and a dry year (2016, 468 mm) in rainfed Robinia pseudoacacia forests in the Loess Plateau region of China. The results showed drought significantly decreased plant water availability and hydraulic conductivity of roots and branches, but strongly increased soil moisture deficits and fine-root (&lt;2 mm diameter) biomass. With the implementation of IRCIS, soil profile available water and plant hydraulic conductivity can be significantly increased, but soil moisture deficits and fine-root (&lt;2 mm diameter) biomass can be significantly decreased. Drought also significantly influenced the root distribution of Robinia pseudoacacia. The maximum depth of Robinia pseudoacacia roots in the dry year was significantly greater than in the wet year. Therefore, Robinia pseudoacacia can absorb shallow (0–1.5 m) soil water in wet years, while utilizing deep (&gt;1.5 m) soil water in dry years to maintain normal growth and resist drought stress. The results of this study will contribute to the formulation of appropriate strategies for planning and managing rainwater resources in forest plantations.

Diffusion and transformation of methane within the soil profile and surface uptake in dryland spring maize fields under different fertilizer application depths

It is important to assess the potential uptake of methane (CH4) in dryland farming and its contribution to global warming mitigation by elucidating the migration characteristics of CH4 in the soil profile. Therefore, before planting spring maize in the Loess Plateau region of China in 2019–2020, we applied fertilizer at soil depths of 5, 15, 25, and 35 cm (D5, D15, D25, and D35, respectively). The uptake of CH4 and diffusion flux were determined simultaneously in the soil surface and profile. We found that the dryland soil was a sink for CH4 and the cumulative CH4 uptake amount by soil without fertilization during the maize growth stage was 1.54 kg ha–1. Fertilization inhibited the uptake of CH4 by the soil, but deep fertilization promoted its uptake. The cumulative surface CH4 uptake amounts under D15, D25, and D35 were significantly higher than that under D5, i.e., by 42.4%, 105.6%, and 169.1%, respectively. The CH4 concentration and diffusion flux decreased as the soil depth increased, and CH4 diffused downward in the soil profile. The CH4 consumption rate was greater than the production rate in the 0–20 cm soil layer, whereas the opposite was found in the 20–30 cm layer. The surface CH4 uptake flux was significantly positively correlated with the diffusion flux in the 0–30 cm soil layer. Inorganic nitrogen (N) inhibited the diffusion of CH4 from the surface through the soil profile and its diffusion within the profile. The highest maize yield and biomass were obtained under D25. Therefore, increasing the fertilization depth can promote the uptake of CH4 by the soil in maize fields to alleviate climate change, and a fertilization depth of 25 cm is suitable for balancing the requirements for environmental protection and agricultural production. Our findings provide important insights into the production, consumption, diffusion, and uptake of CH4 in dryland farming areas.

Nutrient-doped synthetic silicates for enhanced weathering, remineralization and fertilization on agricultural lands of global cold regions- A perspective on the research ahead.

There is now a dire demand for negative emissions technologies (which sequester CO2 from the atmosphere) that can be rapidly deployed, are scalable, and are demonstrably safe and effective. Enhanced weathering of silicate minerals has demonstrated a significant potential for CO2 capture and sequestration by the formation of pedogenic carbonates in soils, subsoils, and sediments. This technique has also been shown to deliver fruitful results in terms of improving soil health, and in turn plant health, through remineralization. The silicate minerals that possess the highest weathering rates (e.g., wollastonite), are relatively rare in nature, whereas the abundant ones (e.g., anorthite and forsterite) have a slower pace of weathering, especially in colder and drier climates such as found in the extensive agricultural lands of Western Canada and the Western United States. Herein, we offer a perspective on the opportunities for computational studies targeting atomic-scale interaction of CO2 with silicates and synthesis of fast-weathering silicates (such as larnite and bredigite), whose composition can be tuned to also support soil fertilization and remineralization, and whose production must be integrated with green and carbon-neutral technologies to ensure net-negative life cycle emissions.

Optimizing fertilization depth can promote sustainable development of dryland agriculture in the Loess Plateau region of China by improving crop production and reducing gas emissions

Optimizing fertilization depth can promote sustainable development of dryland agriculture in the Loess Plateau region of China by improving crop production and reducing gas emissions

Optimization of ridge–furrow mulching ratio enhances precipitation collection before silking to improve maize yield in a semi–arid region

Insufficient soil moisture and heat often limit crop productivity in semiarid regions. The effects of the ridge–furrow mulching system (RFMS) on improving the soil water and temperature conditions have been confirmed in many studies, but the effects of different ridge–furrow ratios on the changes in soil water, temperature, and the interception rate of canopy photosynthetically active radiation (PARIR), and thus crop productivity remain unclear. Therefore, we conducted a field experiment from 2015 to 2020 in the Loess Plateau region of northwest China by testing conventional tillage without mulch (CK) as a control treatment and three ridge–furrow ratios (60:60 cm, 80:40 cm, and 50:10 cm). We studied the changes in the soil hydrothermal characteristics and the response of maize canopy under continuous mulching with different ridge–furrow ratios. Compared with CK, RFMS increased the soil water storage in the 0–200 cm soil layer by 5.2–9.3% and the effective accumulated soil temperature by 10.4–29.1%. The hydrothermal properties affected the maize canopy under RFMS where compared with CK, PARIR increased by 6.3–11.7% at 61 to 90 days after planting (DAP) and the maize yield finally increased by 44.8–77.9%. Correlation analysis showed that the contribution of precipitation from 0 to 90 DAP to the maize yield was greater than that of the effective accumulated soil temperature, whereas the contribution of the effective accumulated soil temperature was greater at 91 to 150 DAP. The precipitation during 61 to 90 DAP was the most important factor that affected the yield during the whole growth period. Thus, increasing the ridge–furrow ratio can improve the soil hydrothermal properties and maize productivity to ensure food security and avoid resource shortages in the Loess Plateau region and similar areas.

Seasonal freeze-thaw characteristics of soil carbon pools under different vegetation restoration types on the Longzhong Loess Plateau

Soil carbon pools are important for maintaining the stability of the carbon cycle in terrestrial ecosystems and regulating climate change. However, it is not clear how soil carbon pools change under different vegetation restoration types at high altitudes during frequent seasonal freeze-thaws (FTs). Therefore, we studied the seasonal FT variability (before freezing, early stages of freezing, stable freeze stage, thawing stage) of soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), and easily oxidized organic carbon (EOC) under three vegetation restoration types (Grassland, GL; Caragana korshinskii, CK; Xanthoceras sorbifolia, XS) on the Longzhong Loess Plateau region. We found that during the seasonal FT, the 0–40 cm SOC, MBC, DOC, and EOC contents were higher in XS vegetation than in GL and CK vegetation, but the sensitivity index of SOC was lower in XS vegetation (sensitivity index = 2.79 to 9.91). In the 0–40 cm soil layer, the seasonal FT process reduced the MBC content and increased the DOC content in the three vegetation soils. Meanwhile, DOC and EOC contents accumulated obviously in the stable freezing period and decreased significantly in the thawing period. We also found that the SOC, MBC, DOC, and EOC contents were higher in the surface soils (0–10 cm) than in the underlying soils (10–20 and 20–40 cm), while the sensitivity of the soil carbon pool fractions to seasonal FT processes differed considerably between soil depths. Redundancy analysis (RDA) showed that soil total nitrogen, temperature, total phosphorus, and soil water content were important environmental factors influencing soil carbon pool fractions during seasonal FT. This study suggested that in the Longzhong Loess Plateau region, soil MBC and DOC were more susceptible to seasonal FT phenomena and that the soil system of the Xanthoceras sorbifolia vegetation had a stronger soil C sequestration function during the seasonal FT process.

Spatial and Temporal Characteristics of Water Use Efficiency in Typical Ecosystems on the Loess Plateau in the Last 20 Years, with Drivers and Implications for Ecological Restoration

The water use efficiency (WUE) is an essential indicator of carbon–water coupling between terrestrial ecosystems and the atmosphere, and it is an important parameter for studying ecosystem responses to global climate change. A comprehensive understanding of the water–carbon coupling process in the Loess Plateau can reflect the balance between the “carbon absorption” and “water consumption” in vegetation, which drives the ecosystem succession process. In recent years, scholars have gained a more comprehensive understanding of the WUE and the driving factors of the Loess Plateau. However, there is still a need to study the carbon and water coupling mechanisms of different land use types in the Loess Plateau region. In this article, based on the gross primary productivity (GPP), evapotranspiration (ET), surface cover remote sensing products, and meteorological observation data, the trend of WUE changes for different vegetation types in the Loess Plateau from 2001 to 2020 and the correlations with the Normalized Difference Vegetation Index (NDVI), precipitation, and temperature values were analyzed using the Theil–Sen median (SEN) trend analysis method and correlation coefficient analysis method. The spatial distribution patterns of the changes with the drought index showed that the multi-year average WUE value of the Loess Plateau was 1.24 g C mm−1 H2O, and the mean WUE values in different seasons were ranked as follows: summer &gt; autumn &gt; spring. The WUE growth rates of all vegetation types showed a decreasing trend with the increase in drought index, and the size of the WUE response rate for each vegetation type to drought was ranked as follows: grassland &gt; forest &gt; shrub &gt; crop. The annual average WUE increase rate of the Loess Plateau was 0.02 g C mm−1 H2O yr−1, of which 93.36% of the area showed an increasing trend. The NDVI was the dominant factor affecting the spatial and temporal variations in WUE rates in the Loess Plateau, and the correlation between the NDVI and WUE was strongest in summer. In the more arid regional ecosystems, the WUE was negatively correlated with the precipitation and temperature, but in summer the precipitation had a positive effect on the WUE. The correlation of grassland and shrub WUE rates with temperature was more sensitive to the drought index than that of the forest and crop areas, but there was also a threshold effect. Therefore, when vegetation restoration is carried out in arid and semi-arid regions, the carbon and water coupling mechanisms of different vegetation types and the reasonable allocation of regional water resources should be fully considered.

Carbon Sequestration Characteristics of Different Restored Vegetation Types in Loess Hilly Region

Since 1999, the "Grain for Green" Program has been extensively implemented in the Loess Plateau region. This measure has largely been of concern not only for its contribution to soil erosion reduction but also for its effects on carbon sequestration. The aim of this study was to assess the carbon sequestration characteristics of different restored vegetation types in areas with severe soil erosion on the Loess Plateau and to compare the effects of restoration age and slope direction on the vegetation carbon sequestration. To evaluate the carbon density and composition characteristics of different ecosystem types, six typical vegetation types (including farmland, grassland, Hippophae rhamnoides Linn., Caragana korshinskii Kom., Robinia pseudoacacia L., and Populus davidiana Dode.) were selected in the Loess Hilly Region, i.e., Wuqi County and Zhidan County in Northern Shaanxi province, which is a typical area for the implementation of artificial vegetation restoration. The results showed that:① vegetation restoration in the semi-arid loess region had a profound impact on carbon sequestration. The carbon density of different vegetations, as well as different vegetation components including above-ground vegetation, below-ground roots, and litter, shared the same pattern as tree>scrub>grassland>farmland. The 0-40 cm soil layer of the farmland showed the lowest soil organic carbon density (1355.5 g·m-2), compared to which those of grassland, H. rhamnoides Linn., C. korshinskii Kom., R. pseudoacacia L., and P. davidiana Dode. were higher by 91.4%, 125.2%, 144.0%, 124.5%, and 232.6%, respectively. ② It was common in grassland, H. rhamnoides Linn., C. korshinskii Kom., and P. davidiana Dode. for the carbon density of different vegetation components as well as soil organic carbon density of different soil layers (0-5, 5-20, and 20-40 cm) to generally show an increasing trend with increased restoration age. ③ Slope direction had a significant impact on the vegetation carbon density only for H. rhamnoides Linn., C. korshinskii Kom., R. pseudoacacia L., and P. davidiana Dode., while showing the contrary for farmland and grassland. Soil organic carbon densities for sunny slopes were significantly lower than those for shaded slopes by 22.9%, 34.3%, 75.8%, 49.1%, 22.4%, and 69.4%, respectively, for farmland, grassland, H. rhamnoides Linn., C. korshinskii Kom., R. pseudoacacia L., and P. davidiana Dode. ④ Ecosystem carbon density varied significantly for different ecosystem types, among which farmland showed the lowest (2022.1 g·m-2), and grassland, H. rhamnoides Linn., C. korshinskii Kom., R. pseudoacacia L., and P. davidiana Dode. showed values higher by 48.7%, 152.8%, 125.1%, 166.3%, and 530.7%, respectively. The carbon density of each ecosystem component showed a pattern as follows:soil layer>above-ground vegetation layer>root layer>litter layer. Soil organic carbon constituted the main part of the ecosystem carbon density and accounted for 67.0%, 86.3%, 59.7%, 72.7%, and 56.5%, respectively, for farmland, grassland, H. rhamnoides Linn., C. korshinskii Kom., and R. pseudoacacia L. These results can provide an essential basis for scientific management of ecosystem carbon pools and promote ecological environment management on the Loess Plateau.

Using check dam deposits to reconstruct changes in the sediment response of a small catchment on the Loess Plateau in China, during the period 1960–1990

AbstractInformation on both the magnitude and relative contributions of inter‐gully and gully areas to the sediment yield from small catchments in the Loess Plateau of China represents an important requirement for understanding catchment sediment dynamics, assessing the sensitivity of catchment sediment budgets to environmental change and developing effective soil and water conservation strategies. Contemporary catchment monitoring programmes can provide such information, but there is also a need to consider past behaviour. Where long‐term records are lacking, attention has been directed to the potential for using the sediment deposits behind check dams to reconstruct the sediment response of the upstream catchment. This contribution reports a study of the 0.181 km2 Nianyangou catchment located in the hilly region of the Chinese Loess Plateau, in Shaanxi Province, China, which has extended a previous study aimed at using individual flood couplets preserved in the check dam deposits to reconstruct the record of annual sediment yield, to include the use of sediment source fingerprinting techniques to document changes in the annual sediment contribution from inter‐gully and gully areas for the period 1960–1990. The sediment response of the catchment provided evidence of two change points in 1964 (Period 1–Period 2) and 1983 (Period 2–Period 3), which reflect the introduction of soil and water conservation measures in the mid 1960s through to the 1970s and a change in the land tenure system in 1983. The annual sediment yields from inter‐gully and gully areas follow the trend P1 &gt; P3 &gt; P2, whereas the equivalent information on the relative contribution of inter‐gully and gully areas follow different trends P3 &gt; P1 &gt; P2 and P2 &gt; P1 &gt; P3, respectively.

An Empirical Analysis of the Role of Forage Product Trade on Grassland Quality and Livestock Production in China

The restoration of grassland ecosystems and the development of the livestock industry in China are constrained by a gap in livestock feed supply and demand. The importation of forage products, as an important means to bridge this feed gap, deserves attention for its relationship with grassland quality and livestock production. This paper empirically examines the relationship between forage products trade and grassland quality, as well as livestock production. The paper uses a cointegration test and error correction model based on data on forage product trade, grassland quality, and livestock production in seven livestock-type regions from 2006 to 2020. The results show that forage product trade has a long-term stable equilibrium relationship with grassland quality in China. The relationships between forage product trade and livestock production in different livestock-type regions are heterogeneous. Among these heterogeneous results, livestock production in the Qinghai-Tibet Plateau region, Loess Plateau Region, Southwest Mountain Region, and Northeast Region are closely related to forage product trade. It appears that importation of feed reduces pressure on natural grasslands, as well as providing high-quality feed that improves livestock production. The above findings can help explain the characteristics of livestock production in different livestock-type regions in China, as well as provide empirical evidence and new ideas for restoring grassland environments and developing herbivorous animal husbandry.

An improved MUSLE model incorporating the estimated runoff and peak discharge predicted sediment yield at the watershed scale on the Chinese Loess Plateau

An accurate prediction of sediment yield at the watershed scale is critical not only for sustainable watershed management but also for improving knowledge regarding the relationship between sediment yield and its determinant factors, which often rely on the varying model complexity. In this study, a modified sediment yield formula based on the modified universal soil loss equation (MUSLE) model was developed by introducing a channel factor into the original formula. The reliability of the proposed method was tested using data from 1,341 storm events in 38 watersheds and was applied to 256 storm events in five application watersheds using the optimized parameters. Results indicated that the proposed method is very accurate, as demonstrated by the Nash–Sutcliffe efficiency (NSE) values of 88.18 %, 85.72 %, and 85.51 % during calibration, validation, and application, respectively. The performance of the proposed model was superior to that of the original MUSLE model. Subsequently, the proposed method was used to predict sediment yield from the last five typical watersheds. This prediction utilized the parameters derived from the initial 38 watersheds; the peak discharge predicted by the modified Chemicals, Runoff, and Erosion from Agricultural Management Systems (CREAMS); and the runoff estimated by the modified Soil Conservation Service Curve Number (SCS-CN) method. Elevated NSE (61.88–81.42 %) and low root mean square error values (2.35–11.40 t ha−1) were calculated for the five watersheds. From the results, the proposed sediment yield model, combined with the modified SCS-CN method and CREAMS, was found to accurately predict the event-based sediment yield, peak discharge, and runoff in the Loess Plateau region under varying hydrological and geomorphic conditions.

An experimental investigation of the erosion process and morphological characteristics of the tile-back type slope with non-uniform slopes based on a 3D reconstruction method

Tile-back type slopes comprise ephemeral gullies (EGs) and hillslopes; they are a unique and widely distributed micro-landform in the Loess Plateau region of China. Gully erosion from these landforms is a serious issue, but the micro-landform makes the erosion process and its estimation complex. Quantifying soil erosion processes and their distribution characteristics at different positions on tile-back type slopes will provide a clearer picture for ecological restoration to control further soil degradation. This study investigated the erosion process of tile-back type slope with non-uniform slopes using a 3D photo-reconstruction method during eight successive simulated rainfall events. The results showed that EG erosion began with a chain of intermittent headcuts. When the accumulated rainfall reached 76 mm, serious collapses dramatically increased the amount of sediment by 216% after the first rainfall (cumulative rainfall was about 15 mm). We quantified the sediment contribution of EG erosion (46.20%), rill erosion (35.62%), and inter-rill erosion (18.18%) to total soil loss. The erosion area of the steep slope section and extremely steep slope section accounted for 33.26% and 66.74% of the total erosion area, respectively. Moreover, sediment amounts significantly correlated with morphological parameters, particularly the amount of EG erosion and maximum gully depth, with a correlation coefficient of 0.98. Cumulative gully length and erosion area had the greatest effect on rill erosion, with a correlation coefficient of 0.97. These results provide insight into the qualitative and quantitative understanding of EG erosion process on Loess Plateau of China and an important reference for the rational arrangement of EG control measures.

Interactive effect between tree ageing and trunk-boring pest reduces hydraulics and carbon metabolism in Hippophae rhamnoides.

Sea-buckthorn (Hippophae rhamnoides) is widely distributed across the Eurasian continent. Recently sea-buckthorn has shown premature ageing and decline when confronted with water deficiency and Holcocerus hippophaecolus damage in northwest China and the Loess Plateau region. However, the physiological process of sea-buckthorn senescence in response to drought and pest damage is still unknown. In this study, 4-year-old (4y), 15-year-old normal growth (15yN) and 15-year-old seriously moth-damaged sea-buckthorn plants (15yH) were used as the research objects. The growth of branches and roots, branch water potential and percentage loss of conductivity (PLC), branch vulnerability to embolism (quantified by P50, xylem water potential at 50 % of PLC), branch xylem parenchyma cell viability, photosynthesis and the non-structural carbohydrate (NSC) content in branches and roots in dry and wet seasons were measured. The results showed that the length, basal diameter of 1-year-old branches and the leaf area of 4y trees were significantly larger than that of 15yN and 15yH trees, and the fine root density of 15yH trees was significantly lower than that of 15yN trees in all measured areas. The branch-specific hydraulic conductivity of 15yN and 15yH trees was only 50.2 % and 12.3 % of that of 4y trees, and the P50 of 4y, 15yH and 15yN trees was -3.69 MPa, -2.71 MPa and -1.15 MPa, respectively. The midday water potential and photosynthetic rate were highest in 4y trees, followed by 15yN and then 15yH trees in both the dry season and wet seasons, while branch PLC declined in the opposite direction (15yH trees highest, 4y trees lowest). The degree of PLC repair within a day was highest in 4y trees, followed by 15yN and then 15yH trees, and the viability of xylem cells was consistent with this pattern. The branch xylem starch and NSC content of 4y and 15yN trees were significantly higher than that of 15yH trees in the dry season, and the root starch and NSC content of 4y trees were significantly higher than that of 15yH trees in the two seasons. The above results suggest that the hydraulic properties of the normal elderly and seriously pest-damaged sea-buckthorn were significantly worse than in juvenile plants. Narrower early wood width and vessel density, high embolism vulnerability and weak embolism repair capacity led to the decline in water-conducting ability, and similarly further affected photosynthesis and the root NSC content. The decline in xylem parenchyma cell viability was the main reason for the limited embolism repair in the branches.

Influence of Different Harvesting Stages and Cereals-Legume Mixture on Forage Biomass Yield, Nutritional Compositions, and Quality under Loess Plateau Region.

One of the main problems in the animal industries currently is the constant provision of forage in sufficient amounts with acceptable nutritional content for large and small ruminants, as livestock is a significant source of income for rural people in the Loess Plateau region. Cereals and legumes are essential forage crops because of their nutritional significance, particularly the protein concentration in legumes and the fiber content in cereals. Therefore, combining cereal and legume crops may be a practical solution to the problems of inadequate forage nutrition, an insufficient amount of forage, unsustainable agricultural methods, and declining soil fertility. The current study predicts that mixed cropping of cereals and legumes at the harvesting stage of the soft dough stage and maturity stage based on the cereal growth stage will have different effects on forage biomass output, forage quality index, and nutritional value of the forage. In this study, wheat (Triticum aestivum) and ryegrass (Lolium multiflorum) are used as cereal crops and pea (Pisum sativum), and alfalfa (Medicago sativa) are used as legume crops. Three sample replicates and a split-plot design with a randomized block design are used. The study is conducted in the 2020–2021 and 2021–2022 cropping seasons. The experimental results show that cereal–legume mixed cropping, particularly the cereal–alfalfa combination, has a positive impact on the biomass yield and nutritional composition of the forage. However, adding peas to cereal has a negative impact on biomass yield, nutritional composition, mineral composition, and forage quality index. Among the treatments, ryegrass–alfalfa mixed cropping was shown to have higher values of WSC%, CP%, EE%, CF%, and ash% in both growing seasons. The values are WSC (15.82%), CP (10.78%), EE (2.30%), CF (32.06%), and ash (10.68%) for the 2020–2021 cropping seasons and WSC (15.03%), CP (11.68%), EE (3.30%), CF (32.92%), and ash (11.07%) for the 2021–2022 cropping seasons, respectively. On the other hand, the current study finds that cereal–alfalfa mixed cropping had a detrimental impact on NDF and ADF concentrations. All nutritional indices, including CP, WSC, EE, CF, ash, NDF, and ADF, have favorable correlations with one another. Furthermore, in both growing seasons, RA, ryegrass–alfalfa mixed cropping, has higher mineral compositions and forage quality indicators. Furthermore, harvesting times have a significant impact on the fresh biomass yield, dry matter yield, nutritional compositions, mineral compositions, and forage quality parameters (p < 0.001), with the highest values being shown when harvesting at the soft dough stage. The current study concludes that, based on chemical composition and quality analysis, the soft dough stage is the greatest harvesting period, and that the cereal–alfalfa mixed cropping is the most preferable due to its maximized quality forage production and nutritional content in livestock feedstuff in the Loess Plateau region.

Combined effects of the earthworm casts application and fallow time on runoff and sediment loss by raindrop splashing in the Loess Plateau, China

The importing of sources of exogenous organic carbon is an effective method for the prevention of soil degradation in sloping soils. Earthworm casts (ECs) have been recognised as a contributor to long-term carbon protection, but relatively few studies have examined the temporal impact ECs have on the achievement of this goal and its efficacy in the mitigation of soil erosion challenges in the Loess Plateau region in China. This study conducted field simulated rainfall experiments as a means of investigating the effects of five ECs (0, 200, 400, 600 and 800 g/m2, labelled CG, E1, E2, E3 and E4) on runoff, sediment and soil aggregate composition after 60, 90 and 150 days of fallow. As E4 was fallow for 150 days, the total runoff, runoff coefficient and total sediment amount decreased by 34.0%, 37.6% and 82.80% in comparison to CG. The runoff and sediment analytical models were able to accurately simulate the runoff and sediment yield processes through ECs application (R2≥0.704, RMSE≤1.108, NSE≥0.513). After being fallow for 150 days, soil sorptivity (S) increased from 0.151 cm/min0.5 to 0.310 cm/min0.5 as ECs application quantity increased. In contrast, the calibration constants of splash erosion (Cr) decreased from 0.150 to 0.090 and runoff erosion (Cf) decreased from 0.120 to 0.081. ECs were found to considerably enhance the number of aggregates that were more prominent than 0.25 mm in size. When E4 was fallow for 150 days, the fraction of >0.25 mm aggregate (WSA0.25) increased by 120.69% in comparison to CG. The mean weight diameter (MWD) grew by 105.96%, the geometric mean diameter (GMD) increased by 98.81% and the soil erodibility value K improved by 43.78%. When the amount of ECs was 800 g/m2, the stability of soil aggregates was effectively improved against water erosion while runoff and sediment transport were controlled. This can help improve the current soil and water loss situation in the Loess Plateau while also improving cultivated land soil quality. At the same time, a longer fallow period time promotes soil aggregate formation. This study is focused on the exceptional performance of ECs in limiting soil erosion on the Loess Plateau in China, which may provide novel solutions for soil and water conservation and the prevention of non-point source pollution.