[Quantitative Comparison of Methods to Assess the Airborne Particulate Matter Retention Capacity of Leaves].

The objective of this study was to explore the differences of five methods for evaluating the PM retention capacity of leaves based on the same experimental materials and leaf area measurement method and to summarize the advantages and disadvantages of each method. In this study, four tree species (Pinus tabuliformis, Platycladus orientalis, Ginkgo biloba, and Platanus occidentalis), which are common in Beijing and have greatly different leaf characteristics, were selected as the research objects. The mass subtraction method (MS), the membrane filter method (MF), the aerosol regenerator method(AR), the scanning electron method (SEM), and the elution weighing method coupled with a particle size analysis based on ultrasonic cleaning (ultrasonic-EWPA) were used to evaluate the PM retention capabilities and characteristics of the leaves of the four tree species. The total time needed and the total cost were measured simultaneously during the evaluation process. The results showed that although the values of PM retention efficiency obtained by different methods were quite different, the ranks of the efficiency of four tree species obtained by different methods were the same or partially the same. Additionally, the results obtained by the methods with the same or similar principles were more overlapped (AR and SEM had the most overlapped results). In addition, 89% of the species ranks of the same index obtained by each method were P. orientalis > P. tabuliformis > P. occidentalis > G. biloba, and the remaining 11% were P. occidentalis > G. biloba > P. orientalis > P. tabuliformis. Among the five methods, ultrasonic-EWPA was the one with the largest number of indexes and the highest cost, and MS was the one with the least number of indexes and the lowest cost. The one that needed most time was MF, while the one that needed the least time was AR. ultrasonic-EWPA and SEM are high input and high output methods. That is to say, although they needed more time and cost, they can prove more information; however, MS was opposite, which resulted in less information but lower time and cost needed. So, it is suitable for roughly evaluating the total PM retention capacities of trees; MF had a medium amount of information, low cost, but required too much time, which needs to be weighed and balanced before selecting this method. The AR method had strict requirements for equipment and parameters and should be used with caution. The results of this study can provide a comprehensive and detailed scientific basis for researchers to choose specific methods in the future.

[Effects of water and nitrogen coupling under furrow irrigation on tree growth, absorption and utilization of water and nitrogen of Populus tomentosa]. / 沟灌水氮耦合对毛白杨林木生长及水氮吸收利用的影响.

We explored the coupling effects of water and nitrogen in furrow irrigation on the growth and absorption and utilization of water and nitrogen in young poplar trees (triploid Populus tomentosa), under three irrigation levels (W20, W33, W45; when the soil water potential of 40 cm under the ditch reaches -20, -33 and -45 kPa respectively, irrigate), four N application levels (N120, N190, N260 and N0; the fertilization amount was 120, 190, 260 and 0 kg·hm-2·a-1), and natural conditions (CK). Based on the growth status of trees, the optimal combination of irrigation level and nitrogen application rate under furrow irrigation conditions was determined. The results showed that W20N120 (high water and low fertilizer; soil water potential threshold for initiating irrigation was -20 kPa and N application rate was 120 kg·hm-2·a-1) had the strongest effect on the stand productivity, with a value of 33.37 m3·hm-2·a-1. The significant coupling effect of water and N was detected only for tree height and total individual biomass. The increase of both irrigation amount and N application rate could increase the amount of N uptake, being mainly affected by the latter. The total amount of N uptake was the highest in the W20N260 treatment and reached 112.17 kg·hm-2·a-1, being 74.0% higher than that in CK. Among all the treatments, N uptake efficiency and N fertilizer partial productivity of W20N120 were the highest and significantly higher than those of the other treatments. The N uptake efficiency of the whole plant, aboveground part, and belowground part reached 36.8%, 28.5% and 6.4% in the W20N120 treatment, and its total N partial productivity reached 221.4 kg·kg-1. The effect of irrigation amount under different water-nitrogen coupling treatments on the irrigation water use efficiency was significant. Among them, irrigation water use efficiency in W45N260 was the highest and reached 13.66 g·kg-1. W20N120 had the highest water uptake amount and efficiency, which were 13268.28 t·hm-2 and 129.4%, respectively. To achieve great benefits, adequate irrigation (-20 kPa) and relatively low N application rate (120 kg·hm-2·a-1) should be selected during the young growth of the triploid P. tomentosa.

[Quantitative evaluation for separation of water-soluble and water-insoluble particulate matter on leaf surface of tree species: Taking five tree species as examples.] / 植物叶片表面水溶与非水溶性颗粒物滞纳量分离定量评估­­ä»¥5ç§æ ‘ç§ä¸ºä¾‹.

To accurately and quantitatively evaluate the mass and particle size distribution of water-soluble and water-insoluble particulate matters (PM) on the surface of tree leaves, which would help to improve the accuracy of quantitative assessment of the retention ability of urban trees to atmospheric particles, we collected leaf samples from three broadleaved tree species [Ginkgo (Ginkgo biloba), Chinese scholar tree (Sophora japonica) and weeping willow (Salix babylonica)] and two conifer species [Chinese pine (Pinus tabuliformis) and China savin (Sabina chinensis)] 14 d after the rain (rainfall>15 mm). The PMs retained on leaves were collected by a succeeding procedure of washing + brushing (WC+BC) and ultrasonic cleaning (UC). Then, the extracts at each step were divided into water-soluble and water-insoluble PMs through centrifuge. The mass of water-soluble and water-insoluble particles were dry weighted. Then, the water-soluble and water-insoluble particles were dissolved by anhydrous ethanol and deionized water to measure the particle size distribution. The mass of water-soluble and water-insoluble particles with different particle sizes was calculated. Results showed that the mass (proportion) of water-soluble PMs retained on leaf surfaces of broad-leaved and conifer species were 480.61 (52.3%) and 438.91 (47.7%) mg·m-2, respectively, while that for water-insoluble PMs were 97.93 (12.0%) and 715.84 (88.0%) mg·m-2, respectively. The particle size distribution of water-soluble particles on the leaves of the five tree species showed the unimodal curve with mean size of 40.36 µm. Water-insoluble particles on leaves showed multimodal distribution, with mean size of 105.65 µm. S. japonica and G. biloba had higher PM retention ability in regions suffering with more water-soluble PM pollution, while S. chinensis had higher retention ability to water-insoluble PMs.

[Effects of fertilization method and nitrogen application rate on soil nitrogen vertical migration in a Populus xeuramericana cv. 'Guariento' plantation].

A field experiment was conducted to investigate the effects of fertilization methods, i.e., drip (DF) and furrow fertilization (GF), and nitrogen (N) application rates (25, 50, 75 g N · plant(-1) · time(-1)) on the dynamics of soil N vertical migration in a Populus x euramericana cv. 'Guariento' plantation. The results showed that soil NH4(+)-N and NO3(-)-N contents decreased with the increasing soil depth under different fertilization methods and N application rates. In the DF treatment, soil NH4(+)-N and NO3(-)-N were mainly concentrated in the 0-40 cm soil layer, and their contents ascended firstly and then descended, reaching their maximum values at the 5th day (211.1 mg · kg(-1)) and 10th day (128.8 mg · kg(-1)) after fertilization, respectively. In the GF treatment, soil NH4(+)-N and NO3(-)-N were mainly concentrated in the 0-20 cm layer, and the content of soil NO3(-)-N rose gradually and reached its maximum at the 20th day (175.7 mg · kg(-1)) after fertilization, while the NH4(+)-N content did not change significantly after fertilization. Overall, N fertilizer had an effect within 20 days in the DF treatment, and more than 20 days in the GF treatment. In the DF treatment, the content and migration depth of soil NH4(+)-N and NO3(-)-N increased with the N application rate. In the GF treatment, the NO3(-)-N content increased with the N application rate, but the NH4(+)-N content was not influenced. Under the DF treatment, the hydrolysis rate, nitrification rate and migration depth of urea were higher or larger than that under the GF treatment, and more N accumulated in deep soil as the N application rate increased. Considering the distribution characteristics of fine roots and soil N, DF would be a better fertilization method in P. xeuramericana cv. 'Guariento' plantation, since it could supply N to larger distribution area of fine roots. When the N application rate was 50 g · tree(-1) each time, nitrogen mainly distributed in the zone of fine roots and had no risk of deep leaching, consequently improving the fertilizer utilization efficiency.

[Exploration of a quantitative methodology to characterize the retention of PM2.5 and other atmospheric particulate matter by plant leaves: taking Populus tomentosa as an example].

Taking Populus tomentosa as an example, a methodology called elution-weighing-particle size-analysis (EWPA) was proposed to evaluate quantitatively the ability of retaining fine particulate matter (PM2.5, diameter d ≤ 2.5 µm) and atmospheric particulate matter by plant leaves using laser particle size analyzer and balance. This method achieved a direct, accurate measurement with superior operability about the quality and particle size distribution of atmospheric particulate matter retained by plant leaves. First, a pre-experiment was taken to test the stability of the method. After cleaning, centrifugation and drying, the particulate matter was collected and weighed, and then its particle size distribution was analyzed by laser particle size analyzer. Finally, the mass of particulate matter retained by unit area of leaf and stand was translated from the leaf area and leaf area index. This method was applied to a P. tomentosa stand which had not experienced rain for 27 days in Beijing Olympic Forest Park. The results showed that the average particle size of the atmospheric particulate matter retained by P. tomentosa was 17.8 µm, and the volume percentages of the retained PM2.5, inhalable particulate matter (PM10, d ≤ 10 µm) and total suspended particle (TSP, d ≤ 100 µm) were 13.7%, 47.2%, and 99.9%, respectively. The masses of PM2.5, PM10, TSP and total particulate matter were 8.88 x 10(-6), 30.6 x 10(-6), 64.7 x 10(-6) and 64.8 x 10(-6) g x cm(-2) respectively. The retention quantities of PM2.5, PM10, TSP and total particulate matter by the P. tomentosa stand were 0.963, 3.32, 7.01 and 7.02 kg x hm(-2), respectively.

[Simulation of soil water dynamics in triploid Populus tomentosa root zone under subsurface drip irrigation].

Based on the observed data of triploid Populus tomentosa root distribution, a one-dimensional root water uptake model was proposed. Taking the root water uptake into account, the soil water dynamics in triploid P. tomentosa root zone under subsurface drip irrigation was simulated by using HYDRUS model, and the results were validated with field experiment. Besides, the HYDRUS model was used to study the effects of various irrigation technique parameters on soil wetting patterns. The RMAE for the simulated soil water content by the end of irrigation and approximately 24 h later was 7.8% and 6.0%, and the RMSE was 0.036 and 0.026 cm3 x cm(-3), respectively, illustrating that the HYDRUS model performed well in simulating the short-term soil water dynamics in triploid P. tomentosa root zone under drip irrigation, and the root water uptake model was reasonable. Comparing with 2 and 4 L x h(-1) of drip discharge and continuous irrigation, both the 1 L x h(-1) of drip discharge and the pulsed irrigation with water applied intermittently in 30 min periods could increase the volume of wetted soil and reduce deep percolation. It was concluded that the combination of 1 L x h(-1) of drip discharge and pulsed irrigation should be the first choice when applying drip irrigation to triploid P. tomentosa root zone at the experiment site.