Shuainan Liu’s research while affiliated with Gansu Agricultural University and other places

Progressively higher atmospheric nitrogen (N) deposition increasingly affects soil ecosystems' elemental cycling and stability. Biochar (BC) amendment has emerged as a possible means of preserving soil system stability. Nevertheless, the pattern of soil–microbial nutrient cycling and system stability in response to BC after high N deposition in ecologically sensitive regions remains uncertain. Therefore, we investigated the effects of high N (9 g N·m⁻²·a⁻¹), BC (0, 20, 40 t·ha⁻¹), and combinations of the treatments on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), microbial entropy (qMB), and stoichiometric imbalance (Cimb:Nimb:Pimb). We found that high N addition decreased topsoil (0–20 cm) TP, C:N, qMBN, and Cimb:Nimb values and increased TN, C:P, N:P, qMBP, Cimb:Pimb, and Nimb:Pimb values. However, BC addition increased 0–40 cm soil qMBC and Nimb:Pimb values and decreased qMBN, Cimb:Nimb, and Cimb:Pimb values. Meanwhile, high BC additions attenuated BC's promotion of soil–microbial nutrients. We observed that a mixture of high N and BC increased the 0–40 cm SOC and TP content, promoted the accumulation of MBN and MBP in the subsoil (20–40 cm), and decreased the topsoil Cimb:Pimb and Nimb:Pimb values compared to high N additions. The impact of high N and BC additions on N and P elements varied significantly between the different soil depths. In addition, redundancy analysis identified C:N, MBC, MBN, and C:P as pivotal factors affecting alterations in soil qMB and stoichiometric imbalance. Overall, adding BC reduced the negative impacts of high N deposition on the stability of soil–microbial systems in the Loess Plateau, suggesting a new approach for managing ecologically fragile areas.

Sustainable agriculture faces challenges balancing the need for increasing crop production with environmental protection. Straw mulching is widely used to improve crop productivity, while reducing nitrogen application is an effective strategy to reduce greenhouse gas (GHG) emissions. However, the comprehensive evaluation of soil properties, GHG emissions, and soil quality under straw mulching conditions with different N application rates has not been extensively studied, especially in the Loess Plateau region of Central Gansu. Therefore, a two-year field experiment was conducted, involving two tillage practices (CT: conventional tillage, CTS: conventional tillage + straw mulching) and three fertilization levels (LN: low nitrogen fertilizer, 55 kg N ha⁻¹; MN: medium nitrogen fertilizer, 110 kg N ha⁻¹ HN: high nitrogen fertilizer, 220 kg N ha⁻¹). Based on the greenhouse gas emission intensity (GHGI), the minimum data set (MDS) was constructed by principal component analysis, correlation analysis, and Norm value, and the weighted index method was applied to comprehensively evaluate the soil quality. Our results showed that compared with CT, CTS significantly increased crop yields and improved the content of soil nutrients, and it was more effective when applying moderate amounts of nitrogen fertilizer. Wheat field soil behaves as a nitrous oxide (N2O) emission source and a methane (CH4) absorption sink. CTS–MN and CTS–LN reduced N2O emission by 52.95–87.76%, increased total CH4 uptake by 16.69–43.60%, and slowed down global warming potential (GWP) by 35.70–48.17% compared with CTS–HN in 2021–2022. They also reduced GHGI. Furthermore, CTS enhanced soil quality at different nitrogen application levels compared with CT, with CTS–MN exhibiting the highest Soil Quality Index (SQI) over the two years. Consequently, considering both economic and environmental benefits, CTS–MN can be regarded as a key practice for the sustainable development of agroecosystems in the Loess Plateau region of Central Gansu.

Soil carbon and nitrogen pools are crucial for maintaining the balance of carbon and nitrogen cycling in ecosystems and also for reducing the impacts of global climate change. However, current research lacks an understanding of the effects of long-term vegetation restoration on soil carbon and nitrogen pools and their storage in vulnerable ecosystems. Therefore, we studied the characteristics of soil carbon (soil organic carbon, microbial biomass carbon, dissolved organic carbon) and nitrogen pools (total nitrogen, ammonium nitrogen, nitrate nitrogen) and their storage under four types of vegetation restoration (Stipa bungeana Trin., SB; Caragana korshinskii Kom., CK; Xanthoceras sorbifolia Bunge., XS; Picea asperata Mast., PA) in the Longzhong Loess Plateau area. We found that the carbon and nitrogen pools in the 0–40 cm soil layer under the XS and PA vegetation restoration types were higher compared to those under the SB and CK vegetation, and the values of soil ammonium–nitrogen ratios ranged from 0.72 to 0.83 under different vegetation types. Carbon and nitrogen interactions were stronger in the 0–40 cm soil under PA vegetation, which had significantly higher soil carbon (49.06 t·ha⁻¹) and nitrogen (1.78 t·ha⁻¹) storage than did the other vegetation types. We also found that soil carbon and nitrogen stores differed among different types of vegetation restoration. These elements were mainly distributed in soils from 0 to 20 cm depth, where the carbon and nitrogen pools in soils from 0 to 10 cm exceeded those in the lower layers. Furthermore, we discovered that redundancy analysis (RDA) supported by soil enzyme activity and physical properties significantly explained the variation in soil carbon and nitrogen triggered by vegetation restoration. According to this research, the stability and transformation of soil carbon and nitrogen pools in the region can be influenced by various forms of vegetation restoration. Additionally, the findings highlight that forest vegetation restoration can be a successful strategy for effectively sequestering soil carbon and nitrogen within the Longzhong Loess Plateau area.

Nitrous oxide (N2O) is one of the significant greenhouse gases in the atmosphere. Different land use patterns are the sink or source of N2O, which plays a vigorous role in controlling N2O emissions. Yet, how different land use patterns affect soil N2O emissions in the Loess Plateau of Central Gansu is still not clear. Therefore; in order to fill this gap, six different land use patterns, including Picea asperata (PA), Hippophae rhamnoides (HR), Medicago sativa (MS), No-tillage wheat field (NT) and Conventional tillage wheat field (T) were studied. The objective of this study was to examine the impact of different land use patterns on soil properties and N2O emission flux. Our results showed that compared with other treatments, Picea asperata woodland increased the soil bulk density, organic matter and soil water content, total nitrogen accumulation and microbial biomass nitrogen whilst reduced the soil pH. The wheat field is more favorable to accumulating soil nitrate nitrogen and ammonium nitrogen. Moreover, soil N2O emission rates followed the trend of T>NT>HR>GL>MS>PA. In addition, soil physicochemical properties were closely related to N2O emission flux and soil temperature was the most significant factor affecting N2O emission. General, Picea asperata woodland could significantly increased soil nutrient and reduce N2O emissions. We suggest that more forest land should be selected as the optimal site for nitrogen fixation and emission reduction for sustainable development of the terrestrial ecosystem on the Loess Plateau in Central Gansu.

The frequent occurrence of extreme rainfall events may greatly affect soil organic carbon (SOC) fractions and carbon (C) pool of wet meadow in the Qinghai-Tibet Plateau (QTP). However, it remains unclear how SOC fractions will change under different extreme rainfall frequency. Therefore, we set five extreme rainfall frequency treatments in the QTP wet meadow: CK (control plots), DF1 (once a week), DF2 (once every-two weeks), DF3 (once every-three weeks), DF4 (once every-four weeks), all treatments received ambient rainfall. We found that soil particulate organic carbon (POC) content increased with the increasing of extreme rainfall frequency in 0–40 cm layer. Extreme rainfall frequency significantly decreased dissolved organic carbon (DOC) content in 0–10 cm layer. DF2, DF3 and DF4 significantly decreased the soil easily oxidizable carbon (EOC) content, DF2 significantly increased and DF4 significantly decreased SOC content in 0–10 cm layer. Soil organic carbon storage (SOCS) decreased with the increase of extreme rainfall frequency, the lowest value in DF1 treatment (85.61 mg·hm⁻²) and the highest value in DF4 treatment (139.92 mg·hm⁻²). The EOC/SOC and DOC/SOC values at 20–40 cm were greater than those at 0–10 cm under each treatment, and the proportion of SOC fractions in the surface layer (0–10 cm) was more sensitive to the extreme rainfall frequency, while in the deep soil layer (10–20, 20–40 cm) was relatively stable. Redundancy analysis (RDA) showed that soil bulk density (BD) (Explanation = 31.8 %), total phosphorus (TP) (Explanation = 12.8 %), NH4⁺-N (Explanation = 8.8 %) were important environmental factors affecting the SOC fractions content under extreme rainfall frequency. Our study suggests that the increase of extreme rainfall frequency in the future will lead to significant differences in the content of SOC fractions and will reduce the SOCS by affecting soil physicochemical properties, and this may have a serious impact on the C sequestration function and C pool stability of QTP wet meadow soil.

Agricultural practices are significant to increase the soil nitrogen and organic carbon sequestration to adapt and mitigate the climate change in a recent climate change scenario. With this background, we carried out research in the Longzhong Loess Plateau region of China. This research was conducted under a randomized complete block design, with three replicates. Adopt the method of combining outdoor positioning field test with indoor index measurement to explore the soil bulk density (BD), nitrogen components (viz., nitrate nitrogen (NO3⁻-N), ammonia nitrogen (NH4⁺-N), total nitrogen (TN), microbial biomass nitrogen (MBN) and nitrogen storage (NS), and carbon components [viz., soil organic carbon (SOC), easily oxidized organic carbon (EOC), microbial biomass carbon (MBC) and carbon storage (CS), carbon pool index (CPI), carbon pool activity (A) and carbon pool activity index (AI) and carbon pool management index (CPMI)] and C/N, ratio under different tillage practices [namely., conventional tillage (CT), no tillage (NT), straw mulch with conventional tillage (CTS) and straw mulch with no tillage (NTS)]. Our results depicted that different conservation tillage systems significantly increased soil BD over conventional tillage. Compared with CT, the NTS, CTS and NT reduced soil NO3⁻-N, increased the soil NH4⁺-N, TN, MBN and NS, among them, NS under NTS, CTS and NT treatment was 25.0, 14.8 and 13.1% higher than that under CT treatment, respectively. Additionally, conservation tillage significantly increased SOC, EOC, MBC, CS, CPI, AI, CPMI and C/N, ratio than CT. Inside, CS under NTS, CTS and NT treatment was 19.4, 12.1 and 13.4% higher than that under CT treatment, respectively. Moreover, during the 3-year study period, the CPMI under NTS treatment was the largest (139.26, 140.97, and 166.17). Consequently, we suggest that NTS treatment was more sustainable strategy over other investigated conservation tillage practices and should be recommended as climate mitigation technique under climate change context.

The principal channel of carbon export from ecosystems to the atmosphere, and an important connection in carbon exchange between land and atmosphere, is ecosystem respiration (ER). It has a significant impact on the global carbon cycle and the rate of CO2 increase in the atmosphere. The effects of different vegetation types [Medicago sativa grassland (MS); Xanthoceras sorbifolium forestland (XS); Caragana korshinskii bushland (CK); Hippophae rhamnoides shrubland (HR); and Stipa bungeana grassland (SB)] on ecosystem respiration fluxes in Loess Hilly Region (LHR) were studied via the static chamber technique. The results showed that different vegetation types had significant effects on ER fluxes, and the decreasing order of the cumulative fluxes was HR > MS > SB > CK > XS. Throughout the study period, the largest value of ER occurred in the summer and the lowest value occurred in the winter. Temperature (air temperature, soil temperature) and soil moisture were both significantly and positively linked with ER. For the temporal change of ER, the joint effect of soil temperature and moisture was a key regulating factor. The temperature sensitivity of ecosystem respiration varies greatly between vegetation types and seasons. In the process of LHR vegetation restoration, the ER, carbon sequestration capacity and ecological benefits of different plant types should be considered in order to select the vegetation type that is most conducive to reducing the greenhouse effect.