•Soil quality is significantly improved by desert reclamation.•The SOC stocks show exponential change with long-term conventional cultivation.•The N:P ratio has an essential influence on SOC and ...nutrient stocks.
Reclamation in desert-oasis areas is effective for improving land productivity and ensuring food supply. However, the understanding of the sustainable productivity of soils under long-term conventional cultivation after desert reclamation is still poor. This study was conducted to determine soil structural properties, organic carbon stocks (SOCS) and nutrient stocks under four desert reclamation ages (0, 30, 60, and 100) in the arid region of northwest China, and evaluate the influence of long-term conventional cultivation on desert soil quality. The results indicated that soil structural stability index (SI) in topsoil improved after desert reclamation, but showed a slight downward trend after 60 years of cultivation, and farmland soil in the study area was still at serious risk of degradation (SI ≤ 5 %) overall. SOCS were enlarged by 4.2 times after desert reclamation, and nitrogen stocks (NS) and phosphorus stocks (PS) were increased by 1.2–6.5 times. However, the regression analysis showed that SOCS and NS in 0–40 cm soil layer and PS in topsoil stopped increasing after about 60-year conventional cultivation. Soil stoichiometry, pH and texture were the key factors affecting SOCS, NS and PS in oasis farmlands. In summary, our study emphasized that soil quality in arid areas was greatly improved after desert reclamation, however, long-term conventional agriculture management measures limited this improvement. Therefore, long-term conventional management of agricultural land in arid areas should introduce appropriate conservation measures to achieve sustainable soil productivity.
This article aims to design and apply a quality evaluation index system based on Bloom's cognitive domain classification method to evaluate the training quality of big data professionals in ...universities. With the rapid development of big data technology, the importance of cultivating big data professionals in universities is becoming increasingly prominent. However, the existing training quality evaluation system often lacks systematicity and scientificity, making it difficult to fully reflect the comprehensive abilities of students. This article combines key knowledge of big data in the field of finance and economics with Bloom’s cognitive domain classification method to divide the cognitive process of talent cultivation into six levels: memory, understanding, application, analysis, evaluation, and creation. Through expert interviews and the Delphi method, specific evaluation indicators for each cognitive level were determined, and 18 indicators were extracted. Through data collection and empirical analysis, the performance of students at various cognitive levels was evaluated. The results showed that third year students performed the best on average at all cognitive levels, reflecting their rich learning experience and practical skills. The analysis also shows that there are significant differences in the performance of students at higher-order cognitive levels, with a coefficient of variation of 0.23 for the A1 indicator and 0.84 for the F3 indicator. This indicates that higher-order cognitive activities require higher demands from students, with significant individual differences. Through correlation analysis between various indicators, it was found that the proficiency level of tool usage in the project is strongly correlated with other indicators. Bloom’s cognitive domain classification system can reflect students’ comprehensive abilities and provide a scientific evaluation method for universities. Through continuous improvement and in-depth research, we hope to provide more scientific and comprehensive support for the cultivation of big data talents in universities.
Purpose
Tea gardens, being a key agroecosystem type, are an important source of nitrous oxide (N
2
O) emissions. However, main factors that regulate N
2
O emissions following urea and organic matter ...amendments have yet to be clarified.
Materials and methods
To investigate the influence of different fertilization management measures on N
2
O emissions in tea garden soil, a 50-day laboratory incubation experiment was conducted. Five treatments were designed for this experiment: control (CK), urea (U), rapeseed cake (R), urea + rapeseed cake (2:1, UR1), and urea + rapeseed cake (1:2, UR2).
Results and discussion
N
2
O emission flux in the R treatment peaked at 14.12 μg kg
−1
h
−1
on day 19, which occurred later than the UR1, UR2, and U treatments. Cumulative N
2
O emissions from the R and UR2 treatments were 6073 and 4296 μg kg
−1
, respectively, which were greater by a factor of 11.2 and 7.9, respectively, compared to the U treatment. Moreover, N
2
O emissions of the UR1 and UR2 treatments were significantly lower than the R treatment. Additionally, N
2
O emissions were also significantly positively correlated to pH levels and microbial biomass carbon (MBC) content. MBC content had the most direct and greatest influence on soil N
2
O emissions, indicating that MBC could be the key limiting factor for N
2
O emissions in this experiment.
Conclusions
A single application of rapeseed cake caused an increase in N
2
O emissions, whereas the combined application of rapeseed cake and a synthetic N fertilizer (urea) caused a decrease in N
2
O emissions. Results from this study offer potential strategies to mitigate soil N
2
O emissions from tea garden agroecosystems through improved field fertilization management.
Agricultural practices such as fertilization considerably influence soil greenhouse gas fluxes. However, the effects of fertilization on greenhouse gases fluxes remain unclear in tea soil when soil ...nitrogen is low. In the present study, soil CO2 and CH4 fluxes under various fertilization treatments in tea soil were investigated during a 50-day period. The experiment consisted of five treatments: no fertilizer (CK), single nitrogen (urea, N), single oilseed rape cake fertilizer (R), nitrogen + cake fertilizer (2:1, NR1), and nitrogen + cake fertilizer (1:2, NR2). The fertilization proportion of NR1 and NR2 was determined by the nitrogen content of nitrogen fertilizer and cake fertilizer. The results revealed that the single application of nitrogen had no significant effect on soil CO2 flux. However, the addition of cake fertilizer significantly increased CO2 emissions through enhanced soil microbial biomass carbon (MBC). Additionally, CO2 emissions were directly proportional to the amount of carbon (C) in the fertilizer. All treatments were minor sinks for CH4 except for the treatment NR1. Specifically, the cumulative CH4 fluxes of NR1 and NR2 were significantly higher than rest of the three treatments, which implies that application of urea and oilseed rape cake reduced the capability of CH4 oxidation in tea soil. Structural equation models indicated that soil CO2 flux is significantly and positively correlated with soil dissolved organic carbon, MBC and soil pH, while mineral nitrogen content was the main factor affecting CH4 flux. Overall, the application of oilseed rape cake increased the oxidation of CH4 and promoted soil C sequestration but inevitably increased the soil CO2 emissions.
Revegetation of semiarid lands depends upon soil microbial communities to supply nutrients for successive plant species, but microbial activity can be constrained by insufficient water. The objective ...of this study was to quantify the metabolic limitation of microbes by extracellular enzymatic stoichiometry, and to determine how this affected microbial carbon use efficiency (CUE) with biogeochemical equilibrium model. The study occurred in long-term revegetation experiment with seven successional stages (0, 11, 35, 60, 100, 130 and 150 years) in the Loess Plateau, China. Microbes maintained stoichiometric homeostasis in all successional stages, but plants did not. Microbial metabolism was limited by low soil phosphorus (P) concentration throughout the succession, whereas plants were limited by low soil P during the late successional stages (from 60 to 150 years) only. An increase in soil moisture during succession was associated with greater P limitation in microbes and plants. There was less microbial P limitation at the 35-year successional stage, and the greatest microbial P limitation occurred at the 130-year successional stage. The microbial C limitation followed a unimodal pattern through the vegetation succession and reached a maximum at 100 years of succession (the early forest stage). This coincided with the lowest microbial CUE at 100 years of succession (CUE was from 0.24 to 0.41), suggesting a change in the physiological responses from microbes (such as enzyme synthesis and the priming effect), that tended to reduce soil C sequestration. Our results indicate that soil moisture regulated microbial C and P metabolism during the vegetation succession in this semiarid region, which has implications for understanding how microbial metabolism affects soil C dynamics under vegetation restoration.
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•Microbes, but not plants, maintained stoichiometric homeostasis during succession.•Plants were limited by low soil P during late succession (from 60 to 150 years).•Microbial metabolism was limited by low soil P during succession.•Soil moisture was the essential driver of microbial and plant P limitations.•Microbial metabolic limitation negatively affected microbial C use efficiency.
The effects and regulatory mechanisms of co-inoculation of plant-growth-promoting rhizobacteria (PGPRs) and rhizobium in plant-soil systems remain unclear, despite numerous reports that PGPRs or ...rhizobium can alleviate metal toxicity. We used the co-inoculation of the PGPR Paenibacillus mucilaginosus and the metal-resistant rhizobium Sinorhizobium meliloti for exploring the physiological and biochemical responses of the plant-soil system in metal-contaminated soil. The co-inoculation with the PGPR and rhizobium significantly increased the nutrient (N, P, and K) contents in plant tissues and promoted plant growth in soil contaminated with copper (Cu). Stress from Cu-induced reactive oxygen species and lipid peroxidation were largely attenuated by the co-inoculation by increasing the activities of antioxidant enzymes. The contents and uptake of Cu in plant tissues increased significantly in the co-inoculation treatment compared with the uninoculated control and individual inoculation treatment. Co-inoculation with PGPR and rhizobium significantly increased soil microbial biomass, enzymatic activities, total nitrogen, available phosphorus, and soil organic matter contents compared with the uninoculated control. Interestingly, co-inoculation also affected the composition of the rhizospheric microbial community, and slightly increased rhizospheric microbial diversity. These improvements of the soil fertility and biological activity also had a beneficial impact on plant growth under Cu stress. Our results suggested that alfalfa co-inoculated with PGPR and rhizobium could increase plant growth and Cu uptake in metal-contaminated soil by alleviating plant Cu stress and improving soil biochemical properties. These results indicate that the co-application of PGPR and rhizobium can have a positive effect on the biochemical responses of alfalfa-soil systems in soil contaminated by heavy metals and can provide an efficient strategy for the phytomanagement of metal-contaminated land.
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•Co-inoculation with PGPR and rhizobium enhanced plant tolerance under Cu stress.•Soil biological activity significantly improved in the co-inoculation treatment.•The uptake of Cu in plant significantly increased in the co-inoculation treatment.•Co-inoculation can modulate the biochemical responses of the alfalfa-soil system.
•Evaluation of green manure application effect by meta-analysis.•Green manure can significantly improve soil nutrient content.•Green manures’ type affects succeeding crops yield.
The application of ...green manure is a traditional and valuable practice for agroecosystem management. In northern China, the effects of green manure on production of the region’s major crops have been extensively investigated, but the inconsistent conclusions that these case studies have yielded cannot provide effective guidance for practical local agricultural production. Here, we conducted a meta-analysis to generate a comprehensive evaluation of the effects of green manure on soil properties and crop yield in this region. Our results shown that green manure improves soil quality effectively, decreasing soil bulk density by ∼ 5.6 %, increasing microbial biomass carbon by 28 %, and improving the activities of soil enzymes by 14 % ∼ 39 %. Among the different types of green manure, legume green manure more markedly increased both nitrate and hydrolysable nitrogen, while non-legume green manure more markedly increased available potassium. Soil gravimetric water content was decreased under green manure treatment. Maize yield was significantly increased under green manure by 11 % on the whole, while effects of green manure on wheat and potato were inconsistent. In summary, the application of green manure in northern China can improve soil quality significantly, and proper green manure use can improve cash crop yields.
Soil microbial metabolism is vital for nutrient cycling and aboveground ecosystem stability. A general understanding of microbial metabolism and nutrient limitation under human disturbance in arid ...and semi-arid regions, which are the largest and most fragile oligotrophic ecosystems globally, however, is still limited. We quantified and compared the characteristics of nutrient limitation of soil microbes under natural/artificial grassland and shrubland, an ecological forest, an economic forest, and sloped cropland in typical arid and semi-arid ecosystems on the Loess Plateau, China. Vegetation restoration significantly affected the activities of extracellular enzymes and ecoenzymatic stoichiometry mainly by affecting soil nutrients and nutrient stoichiometry. A vector analysis of enzyme activity indicated that microbial communities were co-limited by carbon (C) and phosphorus (P) in all types of vegetation restoration. Linear regression indicated that microbial C and P limitations were significantly correlated with the stoichiometry of soil nutrient, suggesting that the balance of nutrient stoichiometry is an important factor maintaining microbial metabolism and elemental homeostasis. C and P limitations in the microbial communities were the lowest in the natural grassland. This implies that both vegetation and microbial communities under the restoration pattern of natural grassland were more stable under environmental stress, so the restoration of natural grassland should be recommended as the preferred option for ecosystem restoration in these arid and semi-arid regions.
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•Microbial metabolisms were co-limited by C and P in arid and semi-arid regions•Vegetation restoration affected the characteristics of soil microbial metabolism•Microbial C and P limitations were the lowest in the natural grassland•Microbial metabolic limitations depend on the balance of nutrient stoichiometry
Natural restoration of degraded grasslands following livestock removal changed soil nutrient and carbon concentrations, soil aggregate distributions, and patterns of extracellular enzyme activities. ...Here, we used an ecoenzymatic stoichiometry model to quantify microbial resource limitations in semiarid grassland soil aggregates at 0, 11, 26, and 36 years after livestock removal and linked these limitations to microbial carbon use efficiency (CUE), which was estimated from stoichiometry theory (CUEST). Overall, livestock removal altered the size distribution of soil aggregates, increased microbial resources and stimulated extracellular enzyme activities. Long-term livestock removal increased the proportion of small macroaggregates (2–0.25 mm). Microbial carbon (C) and phosphorus (P) limitations in soil aggregates declined to minimum levels at 26 years following livestock removal and then increased after 36 years, with an opposite trend for CUEST. Additionally, the greatest resource limitations to microorganisms were found in smaller aggregates (<2 mm) under long-term livestock removal. Random forest and structural equation models revealed that soil abiotic factors, especially total nitrogen and pH, were key determinants of microbial resource limitation in soil aggregates. Moreover, microbial C and P limitations had significant direct effects on the CUEST. Thus, increasing microbial metabolic limitations after long-term livestock removal could reduce microbial C turnover, potentially reducing soil C sequestration. Overall, this study revealed that livestock removal altered soil aggregate development as well as the allocation of resources in aggregates and consequent microbial resource limitations, providing information that may be useful for developing grassland management strategies to enhance C sequestration.
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•Livestock removal altered soil aggregate size distribution and associated resources.•Resource distributions and limitations are nonlinear across time and aggregates.•Microbial C and P limitations declined to minimum levels after 26 years.•Livestock removal gradually increased resource limitations in smaller aggregates.•Increased microbial metabolic limitation reduced C sequestration in aggregates.
The effects of precipitation patterns on the metabolism of soil microbes are poorly understood, especially in water-limited ecosystems where soil microorganisms play crucial roles in the turnover of ...soil organic carbon (SOC) and nutrients. We investigated the influence of the gradient levels of mean annual precipitation (MAP from 300 to 900 mm) on soil microbial metabolism in an arid and semi-arid grassland region located in Loess Plateau, China and identified relationships between microbial metabolic limitations and the variation of soil organic matter (SOM). Microbial metabolism in this arid and semi-arid region was limited by soil C and phosphorus (P) or nitrogen (N). Microbial C and P limitations decreased with the increase of MAP. Microbial C and P limitations were lowest in the areas with MAPs of 700–900 mm, whereas N limitation was observed in the areas with MAPs >700 mm. The results of a variation-partitioning analysis and partial least squares path modeling indicated that the microbial C and N/P limitations on regional scales were mainly determined by climate factors (MAP and mean annual temperature (MAT)), followed by vegetation biomass and soil properties. The extents of soil drying-rewetting processing caused by different MAPs directly affected microbial nutrient limitation. Our results suggested that the influence of precipitation variation on microbial metabolic limitation strongly governed SOM stability and that an increase in the rate of SOM decomposition with increasing precipitation could be caused by increased microbial nutrient limitation. SOM may be most stable at a MAP of 700 mm in the arid and semi-arid regions (300–900 mm MAP) where microbial nutrient limitation was lowest. This study provided novel insights into the responses of soil microbial metabolism to precipitation change and is an important step toward understanding the mechanisms of SOM stability in an arid and semi-arid grassland ecosystem under scenarios of precipitation variation.
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•C and P limitation of soil microbes decreased as MAP increased (300 to 900 mm).•Microbial N limitation is observed in the areas of MAPs above 700 mm.•Precipitation is one of the most important drivers of microbial metabolic limitation.•SOM variations are correlated with microbial metabolic limitation.
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