农田土壤有机碳固定机制及其影响因子研究进展

全球气候变暖引起的环境问题已经引起各国政府及科学家的密切关注。农田土壤作为大气CO2的源和库,在全球碳循环中的重要角色日渐被认识。本文围绕土壤固碳的基本问题,总结了农田土壤固碳潜力、土壤有机碳固定机制及其影响因素的国内外研究进展。国内研究表明,目前耕地的地力不稳,土壤有机碳密度较低,农田土壤固碳的潜力较大。因此,加强不同区域农田土壤固碳潜力、固碳过程、固碳机理等方面的研究,设计合理优化的农业管理措施,是今后研究的重点。     

模拟干旱对藏北高寒草甸植物物候期和生产力的影响

为探究生长季不同时期干旱事件对高寒草甸植物物候期和生产力的影响,采用截雨棚于藏北高寒草甸生长季前期和后期进行为期2年(2016-2017年)的截雨试验.结果表明:1)植物物候期对不同时期干旱处理响应不同,高寒草甸关键物种植物物候期对生长季前期干旱(SE)响应较为敏感,SE会导致植物返青期大幅推迟,生长季长度和繁殖期明显...     

Role of green roofs in urban connectivity,an exploratory approach using landscape graphs in the city of Paris,France

Green roofs provide many ecosystem services, but little is known about the way they contribute to urban functional connectivity. This paper has the following four objectives: (1) to compare the potential green roofs’ role to connectivity in relation to other urban green spaces, (2) to specify the green roofs contribution’s type, (3) to explore the influence of building height integration method and finally (4) to assess the impact on connectivity of simulated greening new roofs. Using a landscape graph approach, we modeled ecological networks of three species groups with different dispersion capacities in the Paris region (France). Then, we computed several connectivity metrics to assess the potential contribution of green roofs to functional connectivity. At a large scale (metropole scale), our results show that green roofs can slightly improve the global connectivity largely through the connections rather than the addition of habitat area. More than a stepping stone function, green roofs would have a dispersion flux function at a local scale. Furthermore, when the difficulty of crossing movement is exponential to the height of buildings, green roofs over 20 m high are mostly disconnected from the ecological networks. In addition to the green roof’s height, our analysis highlights the very strong role played by buildings’ configuration. This study raises promising directions for the integration of building height into the analysis of urban connectivity. Detailed research and long-term biological data from green roofs and green spaces are needed to confirm our results.     

Estimating aboveground biomass of urban forest trees with dual-source UAV acquired point clouds

Urban forest is a crucial part of urban ecological environment. The accurate estimation of its tree aboveground biomass (AGB) is of significant value to evaluate urban ecological functions and estimate urban forest carbon storage. It has a high accuracy to estimate the forest AGB with field measured canopy structure parameters, but unsuitable for large-scale operations. Limited by low spatial resolution or spectral saturation, the estimated forest AGBs based on various satellite remotely sensed data have relatively low accuracies. In contrast, Unmanned Aerial Vehicle (UAV) remote sensing provides a promising way to accurately estimate the tree AGB of fragmented urban forest. In this study, taking an artificial urban forest in Ma'anxi Wetland Park in Chongqing City, China as an example, we used UAVs equipped with a digital camera and a LiDAR to acquire two point cloud data. One was produced from overlapping images using Structure from Motion (SfM) photogrammetry, and the other was resolved from laser scanned raw data. The dual point clouds were combined to extract individual tree height (H) and canopy radius (R_c), which were then input to the newly established allometric equation with tree H and R_c as predictor variables to obtain the AGBs of all dawn redwood trees in study area. In accuracy assessment, the coefficient of determination (R²) and Root Mean Square Error (RMSE) of extracted H were 0.9341 and 0.59 m; the R² and RMSE of extracted R_c were 0.9006 and 0.28 m; the R² and RMSE of estimated AGB were 0.9452 and 17.59 kg. These results proved the feasibility and effectiveness of applying dual-source UAV point cloud data and the new allometric equation on H and R_c to accurate AGB estimation of urban forest trees.     

Analysing urban trees on verges and slopes along a highway using machine learning methods

In arboricultural research, data analysis is important to the understanding of the characteristics of urban forest. This study attempted to apply machine learning techniques on a relatively small data set. This research aimed at exploring the biodiversity and structure of tree stands on verges and slopes along a highway, and analysing the influences of habitat characteristics on the tree stands with the aid of machine learning techniques. 53 slopes and 52 verges along San Tin Highway, Hong Kong were surveyed. 7209 trees belonging to 23 species were found. Dimension reduction proved successful in the concise characterisation of urban forest by a biodiversity component and an abundance component. The biodiversity component score of the slopes (0.625) was higher than that of the verges (−0.637). However, the abundance component scores of slopes (−0.059) and verges (0.060) showed slight difference, reflecting comparable tree abundance. A 75–25 train/test split was applied on a data subset consisting of slopes registered under a scheme called Systematic Identification of Maintenance Responsibility of Slopes in the Territory for regression analysis. The scores of the two components were regressed on several slope geophysical variables. Slope height and slope area served as significant predictors explaining biodiversity. Boosting improved the explanatory power and predictive accuracy of the regression model on the biodiversity component, as evidenced by an increase in adjusted R² by 0.23 and a decrease in RMSE by 0.40. This research proved that component scores can serve as inputs for regression models for the explanation of urban forest characteristics by habitat-related variables. In future, small data sets from tree surveys can be analysed using the workflow demonstrated in this study for the generation of more management insights.     

Effect of cutting on ascorbic acid oxidation and recycling in fresh-cut baby spinach (Spinacia oleracea L.) leaves

Fresh-cut spinach during processing undergoes several mechanical procedures such as cutting, which may induce stress responses. These stresses may trigger the accumulation of harmful reactive oxygen species (ROS). Plants respond through a wide range of mechanisms and ascorbic acid (AsA) has an important role. The combined effect of cutting, temperature and storage time on AsA recycling route in spinach fresh-cut leaves was studied. AsA, gene expression and activities of the enzymes involved in the AsA oxidation and recycling were considered. Spinach leaves were cut in six pieces and stored at 4 °C or 20 °C. AsA content and enzymes activities were measured over six days of storage, while gene expression analyses were performed in a time-point experiment within 24 h after cutting. Results showed that AsA decreased after cutting (from 19.41 mg/100 g FW to 15 mg/100 g FW) and generally was higher in samples stored at 4 °C. After six days, AsA was 10 mg/100 g in control and 5 mg/100 g FW in cut leaves. The expression of genes and activities of the enzymes involved in the AsA oxidation and recycling route were, for some enzymes, in accordance with AsA levels. The APX (EC 1.11.1.11) activity after cutting increased up to 290 nmol AsA mg⁻¹ prot min⁻¹ compared to the control with 190 nmol AsA mg⁻¹ prot min⁻¹. AsA reduction is firstly affected by temperature and aggravated by cutting procedures. AsA represents a valuable postharvest quality indicator of freshness in spinach leaves.     

A comparison between battery-powered and human-powered ascents by a climbing arborist

Climbing arborists often use a throwline and weight to set a climbing line in a primary support point (PSP) from the ground, which improves efficiency but can increase risk because the climbing arborist cannot carefully inspect the PSP. Efficiency may be further improved if the climbing arborist ascends using a powered device, but few studies have investigated their performance. The author measured loads at and inclination of fifteen PSPs as he ascended by hand or by a battery-powered device. We also measured the climbing arborist’s heartrate and ascent duration. When the climbing arborist ascended by hand, loads were similar to when he used the powered device, even though the device increased the weight of the climbing system. Normalized by load, inclination at and below the PSP was also similar between the two ascent techniques; it was also related to both the distance of PSP from the main stem and PSP diameter, as expected from beam theory. The powered device reduced ascent duration by 56% and the climbing arborist’s heartrate was also less than when he ascended by hand. The powered device conferred advantages in efficiency without increasing the likelihood of PSP failure. Climbing arborists should be careful to inspect the PSP and the stem below it for load-bearing capacity.     

鸡粪生物炭吸附固定铅的研究

随着规模化养殖的快速发展，畜禽粪便的产量随之增加，如何对其进行有效处理与资源化利用已成为研究热点。选取鸡粪为原料，在400 ℃下限氧热解制备生物炭（CMBC-400），探究其对水体中铅离子（Pb²⁺）的吸附性能。通过批处理试验考察吸附时间、Pb²⁺初始含量、吸附温度等因素对CMBC-400吸附Pb²⁺性能的影响，并利用吸附动力学、等温线和热力学计算模型对吸附数据进行拟合，进一步阐述吸附过程。结果表明，CMBC-400吸附Pb²⁺的过程更符合准二级动力学模型，表明该吸附过程的吸附速率主要受化学吸附控制；相比Freundlich和Dubinin-Radushkevich （D-R）模型，Langmuir等温线模型具有更高的拟合相关系数，表明CMBC-400表面均一，Pb²⁺吸附位点的吸附能大致相同；吸附热力学数据表明CMBC-400对Pb²⁺的吸附过程是自发的吸热反应。扫描电镜和X-射线衍射表征结果表明，CMBC-400主要通过在表面形成含Pb微晶的形式固定水体中的Pb²⁺。此外，向土壤中添加CMBC-400还可促进有效态Pb转化为稳定态，降低Pb的生物有效性。     

Novel sediment source fingerprinting quantifying erosion-induced total nitrogen and total phosphorus outputs from an intensive agricultural catchment,North China

Intensive farming is a primary cause of increased sediment and associated nitrogen (N) and phosphorus (P) loads in surface water systems. Determining their contributing sources, pathways and loads present major challenges in the high-intensity agricultural catchments. Herein, we quantify the sediment sources and magnitude of sediment total N and total P from different sources using a novel application of compound-specific stable isotope (CSSI) and fallout radionuclides (FRNs) of ¹³⁷Cs and ²¹⁰Pbex in an intensive agricultural catchment in North China. Sediment sources from surface and sub-surface soils were estimated from FRNs fingerprint and accounted for 62 ± 7% and 38 ± 7% respectively, while surface soil from land uses that originated from hillslope were identified by CSSI fingerprint. Using a novel application of FRNs and CSSI sediment fingerprinting techniques, the dominant sediment source was derived from maize farmland (44 ± 0.1%), followed by channel bank (38 ± 7%). The sedimentation rate (13.55 ± 0.30 t ha⁻¹ yr⁻¹) was quantified by the ¹³⁷Cs cores (0–60 cm) at the outlet of this catchment. The total N and total P in sediment were both mostly derived from maize farmland and least from channel banks. The channel banks are significant sediment sources but contribute little to the input of sediment N and P for eutrophication. It implies that chemically-applied farmlands are the main hotspots for catchment erosion control and pollution prevention. The novel application of FRNs and CSSI techniques cost-effectively quantified sediment N and P loads from different sources with a single visit to the catchment, enabling rapid assessment for optimizing soil conservation strategies and land management practices. Keywords: Sediment sources, Land use, N and P loads, Compound-specific stable isotope, Fallout radionuclides.