摘要：为探究黄土高原丘陵区不同植物群落的土壤粒径分布特征。选取草地、山杏纯林、油松纯林和油松山杏混交林0~200 cm土壤为研究对象，采用激光衍射技术测定土壤样品粒度组成，计算土壤粒度参数与分形维数，绘制粒度频率曲线。结果表明：（1）研究区土壤属粉壤土，粉粒含量约占总体的56.58%~71.67%，砂粒约占21.37%~38.71%，黏粒约占3.55%~6.96%。（2）各植物群落内土壤粒度组成随土层深度增加分布较为均一，粒径分布整体分选性均较差，呈极正偏度，峰态尖窄，粒度频率曲线为双峰型，曲线波峰一致。不同植物群落土壤粒径分布差异主要集中在土壤表层0~20 cm（P<0.05）。（3）草地、山杏纯林、油松纯林和油松山杏混交林0~200 cm土壤平均分形维数分别为2.63、2.60、2.61、2.58。分形维数与黏粒含量具有极显著正相关关系（P<0.05），其中，草地土壤分形维数与黏粒的相关性最强。总体来看，黄土高原丘陵区草地土壤粒径分布特征显著优于人工林，本研究结果可为黄土高原的生态重建工作提供理论依据。
摘要：土壤盐结皮对土壤水文过程具有重要影响，初始盐分浓度（Initial salt concentration, ISC）的差异会对盐结皮的形成过程产生不同程度的影响，从而导致土壤蒸发的差异。但目前不同ISC下盐结皮形成过程对土壤蒸发的影响机理尚不明确。因此，通过试验模拟与理论分析相结合，动态监测及分析不同ISC下砂土的盐结皮形成、蒸发、土壤表面温度动态变化过程，以期阐明不同ISC下盐结皮形成过程及其对土壤蒸发的影响机理。结果表明：ISC越高，盐结皮在土壤表面出现的时间越早，覆盖率越大，且在同样光照强度和光照时间条件下土表温度增幅越小，蒸发量也越小；对数函数能较好地拟合不同ISC与累积蒸发量之间的关系（R2>0.90）；随着ISC的增加，盐结皮对土壤蒸发抑制效率从24.14%（10 g·L-1）增大到71.99%（250 g·L-1）。ISC会显著影响盐结皮形成的过程，并通过影响土表温度的变化进而导致土壤蒸发出现巨大差异。
The study of the heterogeneity of soil enzyme activities at different sampling locations in canopy gaps will help understand the influence mechanism of canopy gaps on soil ecological processes. In this paper, we analyzed the spatiotemporal variation of soil enzyme activities and soil physicochemical properties at different sampling locations (closed canopy, expanded edge, canopy edge, gap center) in different sampling time (December, February, April, June, August, and October) on the northern slope of the Tianshan Mountains, Northwest China. The results showed that soil catalase, cellulase, sucrase, and acid phosphatase activities were relatively high from June to October and low from December to April, and most of soil enzyme activities were higher at closed canopy than at gap center. Soil urease activity was high during December–February. The soil temperature reached the highest value during June–August and was relatively high at gap center in October, December, and February. Soil water content was significantly higher in December and April than in other months. Soil bulk density was higher at gap center than at closed canopy in December. Soil pH and soil electrical conductivity in most months were higher at closed canopy than at gap center. Soil organic carbon, soil total nitrogen, and soil total phosphorus were generally higher at gap center than at closed canopy. Furthermore, sampling time played a leading role in the dynamic change of soil enzyme activity. The key factors affecting soil enzyme activity were soil temperature and soil water content, which were governed by canopy gaps. These results provide important support for further understanding the influence mechanism of forest ecosystem management and conservation on the Tianshan Mountains.
Roots exert pullout resistance under pullout force, allowing plants to resist uprooting. However, the pullout resistance characteristics of taproot-type shrub species of different ages remain unclear. In this study, in order to improve our knowledge of pullout resistance characteristics of taproot systems of shrub species, we selected the shrub species Caragana korshinskii Kom. in different growth periods as the research plant and conducted in situ root pullout test. The relationships among the maximum pullout resistance, peak root displacement, shrub growth period, and aboveground growth indices (plant height and plant crown breadth) were analyzed, as well as the mechanical process of uprooting. Pullout resistance of 4–15 year-old C. korshinskii ranged from 2.49 (±0.25) to 14.71 (±4.96) kN, and the peak displacement ranged from 11.77 (±8.61) to 26.50 (±16.09) cm. The maximum pullout resistance and the peak displacement of roots increased as a power function (R2=0.9038) and a linear function (R2=0.8242) with increasing age, respectively. The maximum pullout resistance and the peak displacement increased with increasing plant height; however, this relationship was not significant. The maximum pullout resistance increased exponentially (R2=0.5522) as the crown breadth increased. There was no significant relationship between the peak displacement and crown breadth. The pullout resistance and displacement curve were divided into three stages: the initial nonlinear growth, linear growth, and nonlinear stages. Two modes of failure of a single root occurred when the roots were subjected to vertical loading forces: the synchronous breakage mode and the periderm preferential breakage mode. These findings provide a foundation for further investigation of the soil reinforcement and slope protection mechanisms of this shrub species in the loess area of northeastern Qinghai-Tibet Plateau, China.
Stemflow is vital for supplying water, fertilizer, and other crop essentials during sprinkler irrigation. Exploring the spatial and temporal variations of crop stemflow and its influencing factors will be essential to preventing soil water and nutrient ion's migration to deeper layers, developing, and optimizing effective sprinkler irrigation schedules. Based on the two-year experimental data, we analyzed the variation patterns (stemflow amount, depth, rate, and funneling ratio) of maize stemflow during the growing season, and clarified its vertical distribution pattern. Meanwhile, effects of sprinkler irrigation and maize morphological parameters on stemflow were investigated. The results showed that stemflow increased gradually as maize plant grew. Specifically, stemflow was small at the pre-jointing stage and reached the maximum at the late filling stage. The upper canopy generated more stemflow than the lower canopy until the flare opening stage. After the tasseling stage, the middle canopy generated more stemflow than the other positions. Variation in canopy closure at different positions was the main factor contributing to the above difference. As sprinkler intensity increased, stemflow also increased. However, the effect of droplet size on stemflow was inconsistent. Specifically, when sprinkler intensity was less than or equal to 10 mm/h, stemflow was generated with increasing droplet size. In contrast, if sprinkler intensity was greater than or equal to 20 mm/h, stemflow tended to decreased with increasing droplet size. Compared with other morphological parameters, canopy closure significantly affected the generation of stemflow. Funneling ratio was not significantly affected by plant morphology. Based on the results of different sprinkler intensities, we developed stemflow depth versus canopy closure and stemflow rate versus canopy closure power function regression models with a high predictive accuracy. The research findings will contribute to the understanding of the processes of stemflow involving the hydro-geochemical cycle of agro-ecosystems and the implementation of cropland management practices.
Drought has pronounced and immediate impacts on agricultural production, especially in semi-arid and arid rainfed agricultural regions. Quantification of drought and its impact on crop yield is essential to agricultural water resource management and food security. We investigated drought and its impact on winter wheat (Triticum aestivum L.) yield in the Chinese Loess Plateau from 2001 to 2015. Specifically, we performed a varimax rotated principal component analysis on drought severity index (DSI) separately for four winter wheat growth periods: pre-sowing growth period (PG), early growth period (EG), middle growth period (MG), and late growth period (LG), resulting in three major subregional DSI dynamics for each growth period. The county-level projections of these major dynamics were then used to evaluate the growth period-specific impacts of DSI on winter wheat yields by using multiple linear regression analysis. Our results showed that the growth period-specific subregions had different major DSI dynamics. During PG, the northwestern area exhibited a rapid wetting trend, while small areas in the south showed a slight drying trend. The remaining subregions fluctuated between dryness and wetness. During EG, the northeastern and western areas exhibited a mild wetting trend. The remaining subregions did not display clear wetting or drying trends. During MG, the eastern and southwestern areas showed slight drying and wetting trends, respectively. The subregions scattered in the north and south had a significant wetting trend. During LG, large areas in the east and west exhibited wetting trends, whereas small parts in south-central area had a slight drying trend. Most counties in the north showed significant and slight wetting trends during PG, EG, and LG, whereas a few southwestern counties exhibited significant drying trends during PG and MG. Our analysis identified close and positive relationships between yields and DSI during LG, and revealed that almost all of the counties were vulnerable to drought. Similar but less strong relationships existed for MG, in which northeastern and eastern counties were more drought-vulnerable than other counties. In contrast, a few drought-sensitive counties were mainly located in the southwestern and eastern areas during PG, and in the northeastern corner of the study region during EG. Overall, our study dissociated growth period-specific and spatial location-specific impacts of drought on winter wheat yield, and might contribute to a better understanding of monitoring and early warning of yield loss.
为探索湿地水位变化与土壤气体排放之间的关系，对黄河中游芦苇湿地进行了半注水和满注水样地处理后的动态监测，对比了7 d水位变化过程中土壤气体排放差异。结果表明：注水造成了土壤CO2排放速率的显著差异；随土壤温度上升，H2O、CO2、H2S排放速率都有上升趋势（满注水样地的H2O除外）；半注水和满注水造成的影响，H2O排放速率表现为趋同-异步-消失的特征，在注水前期（63.73 h）半注水和满注水差异基本一致，后期差异较大，直至125.64 h后注水的影响才消失，总体分别造成H2O排放总量76.3%和31.3%的增加；CO2排放速率表现为异步-趋同的特征，注水初期环境的改变造成CO2排放的一致减少，37.69~68.66 h二者出现明显差异，68.66~125.64 h水位虽然恢复，但差异仍然存在，注水分别造成CO2排放总量50.1%和43.2%的减少；H2S排放速率表现为无变化-异步-无变化的特征，总体造成H2S排放总量42.3%和32.3%的增加。研究追踪了水位上升后土壤H2O、CO2和H2S排放速率变化的动态过程，其影响具有异步性和持续性的特点，CO2排放速率表现出较长的响应周期。研究结果对于河流湿地生态功能研究具有重要意义，湿地土壤气体排放对水位变化的响应滞后意味着对湿地生态功能的重要影响，其波动过程需要更长时段的精准研究。
[结果] 结果显示，菌株NT9为枯草芽孢杆菌（Bacullis subtilis），与蜡样芽孢杆菌（B. cereus）YB3不同，具有较强的蛋白酶、淀粉酶活性以及抑菌活性，而纤维素酶活性较弱。同时又与菌株YB3相似，在低营养条件下菌株NT9也仅具有有机氮和氨氮降解作用，其中氨氮降解率可达89.3%。通径分析显示，模型的决定系数为0.55-0.95，其它主要的适配度指标也均符合判定标准。菌株的纤维素酶活性（cel）对大多数环境中菌株的生长（gro）以及有机氮、氨氮的降解（dtan）均具有显著的直接促进效应（P<0.001）。水体起始的菌量（iod）、有机氮含量（ion）、氨氮含量（itann）以及时间阶段（stage）等环境因素对gro和dtan也具有显著的直接影响（P<0.05），但仅限于某些特定的环境。菌株活性与环境因素之间也具有交互作用（P<0.05），对gro和dtan产生间接效应，增强或抵消直接效应，使某些因素表现出显著的总效应（P<0.05），但也导致其它因素的总效应不显著（P>0.05）。gro和dtan在某些环境中相互之间也具有直接的促进效应（P<0.001），并且也相互间接影响。研究表明，菌株特性和环境因素的综合作用对低营养水体中芽孢杆菌的生长和氮转化作用具有重要影响，但是在不同的环境中作用的方式不同。
[结果]结果显示，经过63d的养殖，BFT组对虾成活率（100%）和生产力（1.32 kg/m3）显著高于对照组（P<0.05），同时的对虾平均体重（13.20±1.64 g）、特定生长速率（4.26±0.20%/d）和饵料系数（1.09±0.14）等也均优于对照（P>0.05）。
[结果] 结果显示，菌株NT9属于枯草芽孢杆菌（Bacullis subtilis），在低营养条件下也具有氨氮转化功能，去除率达89.3%，与菌株YB3相比，具有较强的蛋白酶、淀粉酶活性以及抑菌活性，但是生长能力较差。在模拟养殖水体中，2株菌对硝酸氮、亚硝酸氮、溶解氧、pH、碱度等水质条件影响不大，均能够促进有机氮降解，但氨氮转化效果较差，导致水体氨氮显著积累（P< 0.05）。通径分析显示，水体总菌量（cfu）是促进有机氮降解的主要因素，通径系数（直接作用）0.550（P< 0.01），菌株的纤维素酶活性（cel）和生长能力（gro）等都通过cfu对有机氮降解产生较大的间接作用；而微生物的生长增殖活动（总菌增量，dcfu）则是促进氨氮转化的主要因素，通径系数为-0.112（P< 0.01）。
Abstract: Aeolian sandy soil in mining areas exhibits intense evaporation and poor water retention capacity. This study was designed to find a suitable biochar application method to improve soil water infiltration and minimize soil water evaporation for aeolian sand soil. Using the indoor soil column method, we studied the effects of three application patterns (A (0–20 cm was a mixed sample of mixed-based biochar and soil), B (0–10 cm was a mixed sample of mixed-based biochar and soil and 10–20 cm was soil), and C (0–10 cm was soil and 10–20 cm was a mixed sample of mixed-based biochar and soil)), four application amounts (0% (control, CK), 1%, 2%, and 4% of mixed-based biochar in dry soil), and two particle sizes (0.05–0.25 mm (S1) and <0.05 mm (S2)) of mixed-based biochar on water infiltration and evaporation of aeolian sandy soil. We separately used five infiltration models (the Philip, Kostiakov, Horton, USDA-NRCS (United States Department of Agriculture-Natural Resources Conservation Service), and Kostiakov-Lewis models) to fit cumulative infiltration and time. Compared with CK, the application of mixed-based biochar significantly reduced cumulative soil water infiltration. Under application patterns A, B, and C, the higher the application amount and the finer the particle size were, the lower the migration speed of the wetting front. With the same application amount, cumulative soil water infiltration under application pattern A was the lowest. Taking infiltration for 10 min as an example, the reductions of cumulative soil water infiltration under the treatments of A2%(S2), A4%(S1), A4%(S2), A1%(S1), C2%(S1), and B1%(S1) were higher than 30%, which met the requirements of loess soil hydraulic parameters suitable for plant growth. The five infiltration models well fitted the effects of the treatments of application pattern C and S1 particle size (R2>0.980), but the R2 values of the Horton model exceeded 0.990 for all treatments (except for the treatment B2%(S2)). Compared with CK, all other treatments reduced cumulative soil water infiltration, except for B4%(S2). With the same application amount, cumulative soil water evaporation difference between application patterns A and B was small. Treatments of application pattern C and S1 particle size caused a larger reduction in cumulative soil water evaporation. The reductions in cumulative soil water evaporation under the treatments of C4%(S1), C4%(S2), C2%(S1), and C2%(S2) were over 15.00%. Therefore, applying 2% of mixed-based biochar with S1 particle size to the underlying layer (10–20 cm) could improve soil water infiltration while minimizing soil water evaporation. Moreover, application pattern was the main factor affecting soil water infiltration and evaporation. Further, there were interactions among the three influencing factors in the infiltration process (application amount×particle size with the most important interaction), while there were no interactions among them in the evaporation process. The results of this study could contribute to the rational application of mixed-based biochar in aeolian sandy soil and the resource utilization of urban and agricultural wastes in mining areas.
Abstract: Understanding the dynamics of soil organic carbon (SOC) is of fundamental importance in land use and management, whether in the current researches or in future scenarios of agriculture systems considering climate change. In order to evaluate SOC stock of the three districts (Delmiro Gouveia, Pariconha, and Inhapi districts) in the semi-arid region of Brazil in rainfed and irrigated agriculture systems under different climate scenarios using the Century model, we obtained RCP4.5 and RCP8.5 climate scenarios derived from the Eta Regional Climate Model (Eta-HadGEM2-ES and Eta-MIROC5) from the National Institute for Space Research, and then input the data of bulk density, pH, soil texture, maximum temperature, minimum temperature, and rainfall into the soil and climate files of the Century model. The results of this study showed that the Eta-HadGEM2-ES model was effective in estimating air temperature in the future period. In rainfed agriculture system, SOC stock under the baseline scenario was lower than that under RCP4.5 and RCP8.5 climate scenarios, while in irrigated agriculture system, SOC stock in the almost all climate scenarios (RCP4.5 and RCP8.5) and models (Eta-HadGEM2-ES and Eta-MIROC5) will increase by 2100. The results of this study will help producers in the semi-arid region of Brazil adopt specific agriculture systems aimed at mitigating greenhouse gas emissions.
Planting cover crop has been suggested as a way of increasing soil organic carbon in agricultural land. Ryegrass (Lolium multiflorum L.), as a cover crop, could improve soil fertility and lower soil CO2 emission. However, effects of soil water content and nitrogen on soil carbon mineralization after ryegrass incorporation are not fully understood. The present study was to investigate the effect of soil water content and nitrogen rate on soil carbon mineralization after ryegrass incorporated into upland red soil (Ferralsols). A laboratory experiment was established, including soil water contents [15% (W1), 30% (W2), 45% (W3)] and nitrogen rates [0 (N1), 60 mg/kg(N2), 120 mg/kg(N3)]. The results showed that the highest soil carbon mineralization accumulation was observed in W3N3. Nitrogen application inhibited carbon mineralization rate and accumulation in the late stage of ryegrass incorporation at W1, but increased carbon mineralization rate and accumulation at W2. With increasing soil water content, nitrogen application could improve soil carbon mineralization at the early stage of ryegrass incorporation. In conclusion, soil nitrogen and water content could regulate soil carbon mineralization. Considering to reduce the soil CO2 emissions, rational nitrogen application should be taken seriously during cover crop (ryegrass) incorporated into the upland red soil.
Soil salinization has adverse effects on the soil physical-chemical characteristics. However, little is known about the changes in soil salt ion concentrations and other soil physical-chemical characteristics within the Qarhan Salt Lake and at different soil depths in the surrounding areas. Here, we selected five sampling sites (S1, S2, S3, S4, and S5) alongside the Qarhan Salt Lake and in the Xidatan segment of the Kunlun Mountains to investigate the relationship among soil salt ion concentrations, soil physical-chemical characteristics, and environmental variables in April 2019. The results indicated that most sites had strongly saline and very strongly saline conditions. The main salt ions present in the soil were Na+, K+, and Cl–. Soil nutrients and soil microbial biomass (SMB) were significantly affected by the salinity (P<0.05). Moreover, soil salt ions (Na+, K+, Ca2+, Mg2+, Cl–, CO32–, SO42–, and HCO3–) were positively correlated with electrical conductivity (EC) and soil water content (SWC), but negatively related to altitude and soil depth. Unlike soil salt ions, soil nutrients and SMB were positively correlated with altitude, but negatively related to EC and SWC. Moreover, soil nutrients and SMB were negatively correlated with soil salt ions. In conclusion, soil nutrients and SMB were mainly influenced by salinity, and were related to altitude, soil depth, and SWC in the areas from the Qarhan Salt Lake to the Xidatan segment. These results imply that the soil quality (mainly evaluated by soil physical-chemical characteristics) is mainly influenced by soil salt ions in the areas surrounding the Qarhan Salt Lake. Our results provide an accurate prediction of how the soil salt ions, soil nutrients, and SMB respond to the changes along a salt gradient. The underlying mechanisms controlling the soil salt ion distribution, soil nutrients, and SMB in an extremely arid desert climate playa should be studied in greater detail in the future.
Soil salinization is a major problem affecting soils and threatening agricultural sustainability in arid and semi-arid regions, which makes it necessary to establish an efficient strategy to manage soil salinity and confront economic challenges that arise from it. Saline soil recovery involving drainage of shallow saline groundwater and the removal of soil salts by natural rainfall or by irrigation are good strategies for the reclamation of salty soil. To develop suitable management strategies for salty soil reclamation, it is essential to improve soil salinity assessment process/mechanism and to adopt new approaches and techniques. This study mapped a recovered area of 7200 m2 to assess and verify variations in soil salinity in space and time in Kairouan region in Central Tunisia, taking into account the thickness of soil materials. Two electromagnetic conductivity meters (EM38 and EM31) were used to measure the electrical conductivity of saturated soil-paste extract (ECe) and apparent electrical conductivity (ECa). Multiple linear regression was established between ECe and ECa, and it was revealed that ECa-EM38 is optimal for ECe prediction in the surface soils. Salinity maps demonstrated that the spatial structure of soil salinity in the region of interest was relatively unchanged but varied temporally. Variation in salinity at the soil surface was greater than that at a depth. These findings can not only be used to track soil salinity variations and their significance in the field but also help to identify the spatial and temporal features of soil salinity, thus improving the efficiency of soil management.