Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources
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黄土丘陵区植被与地形特征对土壤和土壤微生物 生物量生态化学计量特征的影响
No full text研究黄土丘陵区植被与地形特征对土壤和土壤微生物生物量生态化学计量特征影 响有助于深入理解黄土丘陵区不同植被带下土壤和土壤微生物相互作用及养分循环规律．选 择黄土丘陵区延河流域 3 个植被区( 森林区、森林草原区、草原区) 和 5 种地形部位( 阴/阳沟 坡、阴/阳梁峁坡、峁顶) 的土壤作为研究对象，利用生态化学计量学理论研究植被和地形对土 壤和土壤微生物生物量生态化学计量特征的影响．结果表明: 土壤及土壤微生物生物量碳、 氮、磷含量在不同地形之间的差别主要表现在沟坡位置和阴坡高于其他坡位和阳坡．植被类 型的变化对两个土层( 0～10、 10～20 cm) 土壤和土壤微生物生物量碳、氮、磷的影响均达到显 著水平，坡向对表层( 0～10 cm) 土壤和土壤微生物生物量碳、氮、磷的影响强于坡位，而在 10～ 20 cm土层，坡位对土壤和土壤微生物生物量碳、氮、磷影响更显著．植被类型显著影响土壤 C ∶ N、 C ∶ P、 N ∶ P 和土壤微生物生物量 C ∶ N、 C ∶ P，坡向和坡位仅影响土壤 C ∶ P 和 N ∶ P， 植被类型的变化是影响土壤 C ∶ N 的主要因素．同时，植被类型对土壤养分和微生物生物量 碳、氮、磷含量及其生态化学计量特征的影响大于地形因子．标准化主轴分析结果表明，黄土 丘陵区不同植被带土壤微生物具有内稳性，特别在草原带，土壤微生物生物量生态化学计量 学特征具有更加严格的约束比例．在黄土丘陵区，土壤微生物生物量 N ∶ P 或许可以作为判断 养分限制的另一个有力工具，若将土壤微生物生物量 N ∶ P 与植物叶片 N ∶ P 配合使用可能 有助于我们更加精确地判断黄土丘陵区的土壤养分限制情况．</p
北洛河上游径流变化特征及其驱动因素研究
No full text研究人类活动及降水变化对北洛河上游径流的影响，分析径流变化的主要驱动因子，为北洛河上游及相类似的其他流域水土保持、水资源合理利用提供决策依据。采用累积距平法、Mann·Kendall趋势检验法、降水一径流双累积曲线法对北洛河上游1971—2014的年降水量和径流量变化进行趋势分析与变异点诊断，并采用双累积曲线法和线性回归模型量化分析降水变化和人类活动对年径流、汛期径流变化的影响程度。结果表明：2003年大规模退耕还林实施后，北洛河上游降水一径流关系发生突变，突变后的年径流和汛期径流显著低于突变前；年径流变化主要是汛期径流减少造成的；人类活动相比降水对年和汛期的贡献率分别为106％和114％；突变后植被调节径流的能力显著增加，日径流量>100、>1.15和<0.5 m3／s所占比例分别为0.27％，59.2％，和8％，径流变化对降水变化的敏感性降低。认为：大规模化植被恢复是北洛河源区径流量减少的直接因素，而退耕还林(草)、水土保持政策是核心驱动力；同时，随着退耕还林时间的延长，北洛河径流不会持续减少，未来将维持在相对低而稳定的水平。
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Aggregate stability and associated organic carbon and nitrogen as affected by soil erosion and vegetation rehabilitation on the Loess Plateau
No full textAlthough soil erosion and land use change have long been focuses in carbon research, the combined influence of soil erosion and vegetation rehabilitation on aggregate stability and the associated soil organic carbon (SOC) and total nitrogen (TN) remains unclear. The current study evaluated the effects of soil erosion on aggregate stability and the associated SOC and TN dynamics in relation to vegetation rehabilitation after the implementation of the "Grain-for-Green" project in the hilly Loess region. A check dam sediment sequence was dated using Cs-137 activity and erosive rainfall events. The SOC and TN in the bulk soil and aggregate fractions were measured in soils from rehabilitated grasslands and sloping croplands and in sediments retained by the check dam. The results showed that vegetation rehabilitation led to 78%, 27% and 9% average increases in the macroaggregate amount, mean weight diameter (MWD) and mean geometric diameter (MGD), respectively. In addition, rehabilitation resulted in the highest SOC and TN concentrations and contents in macroaggregates among all the aggregate size fractions. Soil erosion facilitated the modification of the aggregate size distributions along with soil mineralization and induced the incorporation of deeper SOC-poor soils during transport. These processes resulted in the aggregate-associated SOC and TN concentrations and contents in the sediments being significantly lower than those in the eroding sloping cropland soils. The highest reductions were found in micro aggregates, which exhibited decreases of 48% and 44% for SOC and TN, respectively. Moreover, reaggregation and gully soils incorporated during soil erosion led to higher values of macroaggregate amount and aggregate stability at depositional sites than those at eroding sloping cropland sites in this study. Our study contributes to the understanding of the effects of soil erosion and vegetation rehabilitation on SOC and TN dynamics, which is crucial for understanding the restoration efficiency in soil erosion control and ecosystem security evaluation
Effects of soil aggregate stability on soil N following land use changes under erodible environment
No full textSoil nitrogen (N) dynamics have considerable effects on the terrestrial carbon cycle, and land use changes could affect soil N through impacts on soil aggregate stability. This study selected nine sites including apple orchards of different ages and restored sites to explore the effects of soil aggregate stability on soil total N (STN), ammonium N (AN), and nitrate N (NN) following different stages of apple orchard on the Loess Plateau of China. The results showed that when compared with apple orchard sites, the restored sites had higher contents of STN and lower contents of AN and NN, but when compared with restored sites, inorganic-N storage played a more important role in the apple orchards. Following different stages of apple orchards, the STN, AN and NN contents and mean weight diameter (MWD) of soil aggregates were all improved. MWD had a negative effect on inorganic-N content at 10-30 cm soil depths but had a positive relationship with soil N at 0-10 cm soil depth. In addition, planting apple orchards destroyed soil aggregate stability in this erodible environment, but it could be restored soon after abandonment. Therefore, considering soil N and soil aggregate stability, it is feasible to plant apple trees in this area and we propose that the effects of trade-offs between soil aggregate stability and soil erosion on soil N in terraced agroecosystems should be a focus of future research
The effects of varied soil properties induced by natural grassland succession on the process of soil detachment
No full textThe changes in soil properties caused by vegetation succession might have great effects on the process of soil detachment by overland flow. This study was carried out to quantify the effects of varied soil properties induced by natural grass succession on soil detachment capacity by overland flow and soil resistance to flowing water erosion on the Loess Plateau. 300 undisturbed soil samples (without roots) were collected from ten typical grasslands, and subjected to flow scouring under six shear stresses ranging from 4.98 to 16.37 pa. The results showed that the maximum soil detachment capacity (3.80 kg m(-2) s(-1)) was found in Astragalus melilotoides Pall. grassland, where it was 49.0 times greater than that of the minimum found in Poa sphondylodes Trin. grassland. Soil properties induced by fibrous root herbage have strong effects on the process of soil detachment. In comparison to grasslands with tap root systems, grasslands with fibrous root herbage have lower soil detachment and rill erodibility by 84.6% and 84.3%, respectively, and critical shear stress which is higher by 15.2%. Stream power was a better parameter than velocity, shear stress or unit stream power for simulating soil detachment capacity. Soil cohesion, bulk density, organic matter and median soil grain size were the main factors affecting the process of soil detachment. Rill erodibility decreased with cohesion or clay content as an exponential or power function, and increased with the median soil grain size as an exponential function. A model was developed to estimate soil detachment capacity based on hydraulic parameters and soil properties on the Loess Plateau. The result was satisfactory and the performance of model was greatly improved in comparison to previous studies (R-2 = 0.77; NSE = 0.61; p < 0.01)
Vertical distribution of soil total nitrogen and soil total phosphorus in the critical zone on the Loess Plateau, China
No full textIt is important to determine the vertical distributions of soil total nitrogen (SIN) and soil total phosphorus (STP) as well as the factors that influence them in the Earth's critical zone (CZ) in order to understand the N/P cycle in the CZ. However, few data are available regarding the vertical distributions of STN and STP in deep soil profiles in the CZ. Thus, this study investigated the vertical distributions of the STN and STP as well as related factors in a deep soil profile on the Loess Plateau, China. Soil drilling was used to collect 703 soil samples throughout the soil profile from five sites. The STN decreased initially at all of the sampling sites (except at Shenmu), before fluctuating with increasing depth throughout the profile, whereas the STP exhibited a fluctuating trend at all sites. The mean STN and STP concentrations ranged from 0.12 g kg(-1) to 0.25 g kg(-1) and from 0.45 g kg(-1) to 0.58 g kg(-1), respectively. The adjusted r(2) values based on stepwise multiple linear regressions for STN and SIP ranged from 35% to 83% and from 4% to 17%, respectively, and thus, SIN was explained better by the measured soil variables compared with STP. The mean STN and STP stocks ranged from 1.87 to 3.90 mg ha(-1) and from 6.75 to 9.09 mg ha(-1), respectively. The results of this study facilitate evaluations of STN and STP stocks and studies of the N/P cycle in the CZ on the Loess Plateau
Transcriptional Profiles of SmWRKY Family Genes and Their Putative Roles in the Biosynthesis of Tanshinone and Phenolic Acids in Salvia miltiorrhiza
No full textSalvia miltiorrhiza Bunge is a Chinese traditional herb for treating cardiovascular and cerebrovascular diseases, and tanshinones and phenolic acids are the dominated medicinal and secondary metabolism constituents of this plant. WRKY transcription factors (TFs) can function as regulators of secondary metabolites biosynthesis in many plants. However, studies on the WRKY that regulate tanshinones and phenolics biosynthesis are limited. In this study, 69 SmWRKYs were identified in the transcriptome database of S. miltiorrhiza, and phylogenetic analysis indicated that some SmWRKYs had closer genetic relationships with other plant WRKYs, which were involved in secondary metabolism. Hairy roots of S. miltiorrhiza were treated by methyl jasmonate (MeJA) to detect the dynamic change trend of SmWRKY, biosynthetic genes, and medicinal ingredients accumulation. Base on those date, a correlation analysis using Pearson's correlation coefficient was performed to construct gene-to-metabolite network and identify 9 SmWRKYs (SmWRKY1, 7, 19, 29, 45, 52, 56, 58, and 68), which were most likely to be involved in tanshinones and phenolic acids biosynthesis. Taken together, this study has provided a significant resource that could be used for further research on SmWRKY in S. miltiorrhiza and especially could be used as a cue for further investigating SmWRKY functions in secondary metabolite accumulation.</p
Discriminating the precipitation phase based on different temperature thresholds in the Songhua River Basin, China
No full textDifferent precipitation phases (rain, snow or sleet) differ greatly in their hydrological and erosional processes. Therefore, accurate discrimination of the precipitation phase is highly important when researching hydrologic processes and climate change at high latitudes and mountainous regions. The objective of this study was to identify suitable temperature thresholds for discriminating the precipitation phase in the Songhua River Basin (SRB) based on 20-year daily precipitation collected from 60 meteorological stations located in and around the basin. Two methods, the air temperature method (AT method) and the wet bulb temperature method (WBT method), were used to discriminate the precipitation phase. Thirteen temperature thresholds were used to discriminate snowfall in the SRB. These thresholds included air temperatures from 0 to 5.5 degrees C at intervals of 0.5 degrees C and the wet bulb temperature (WBT). Three evaluation indices, the error percentage of discriminated snowfall days (Ep), the relative error of discriminated snowfall (Re) and the determination coefficient (R-2), were applied to assess the discrimination accuracy. The results showed that 2.5 degrees C was the optimum threshold temperature for discriminating snowfall at the scale of the entire basin. Due to differences in the landscape conditions at the different stations, the optimum threshold varied by station. The optimal threshold ranged 1.5-4.0 degrees C, and 19 stations, 17 stations and 18 stations had optimal thresholds of 2.5 degrees C, 3.0 degrees C, and 3.5 degrees C respectively, occupying 90% of all stations. Compared with using a single suitable temperature threshold to discriminate snowfall throughout the basin, it was more accurate to use the optimum threshold at each station to estimate snowfall in the basin. In addition, snowfall was underestimated when the temperature threshold was the wBT and when the temperature threshold was below 2.5 degrees C, whereas snowfall was overestimated when the temperature threshold exceeded 4.0 degrees C at most stations. The results of this study provide information for climate change research and hydrological process simulations in the SRB, as well as provide reference information for discriminating precipitation phase in other regions
Effect of terrain slope on water distribution and application uniformity for sprinkler irrigation
No full textIn order to provide practical parameters for sprinkler irrigation system design on sloping land, the effect of terrain slope on water distribution, sprinkler throw radius and water application uniformity were analyzed for the Rainbird LF1200 sprinkler. The results show that, the water distribution curve is roughly "heart-shape" on slope, and the water has the trend of focusing on the upslope with the increase of the slope. Throw radius decreases for the upslope and increases for the downslope as the slope increases. For the convenience of sprinkler irrigation system design on sloping land, a formula for computing throw radius on sloping land was put forward by the theoretical derivation, and it was verified by the experimental data. The impact of sprinkler pressure and spacing on CU for sloping land is more significant than that for flat ground. Under the experimental condition, no significant change is found regarding the influence of terrain slope on water application uniformity at the confidence level of 95%. Taking irrigation quality and economy into account, the Rainbird LF1200 sprinkler should operate at the manufactures' recommended pressure, rather than low pressure, with sprinkler spacing from 8 mx8 m to 10 mx10 m below the slope of 0.15 in practice
The Agricultural Water Rebound Effect in China
No full textAlthough the water productivity of the agricultural sector in China continuously increased over the last twenty years, by improvements in irrigation technology, the total agricultural water use did not decline as expected, mainly due to continuous increases in agricultural output partially derived from technological progress. Thus, agricultural water use in China may experience a rebound effect. This study defines the water rebound effect (WRE), using macro-scale indicators of water use and water productivity, establishes a simplified direct comparison method using the contribution rate of technological progress, and evaluates the magnitude of the macro scale water rebound effect in the Chinese agricultural sector using provincial panel data from 1997 to 2014. The magnitude of the agricultural WRE in China (1998-2014) is 61.49%. The northern and western regions of China experience a greater WRE than the southern and eastern regions, and the changes in the inter-annual WRE are distinct. These observations indicate that much of the expected water savings from efficiency improvement could be offset by increased water use for increased agricultural production due to technology enhancement. The control of water use growth is effective for reducing the water rebound effect. The study confirmed the existence of the agricultural WRE in China