研究论文 正式出版 版本 3 Vol 10 (3) : 307-315 2019
Evaluation of a modified open-top chamber simulation system on the study of elevated CO2 concentration effects
: 2018 - 05 - 22
: 2018 - 08 - 13
: 2018 - 08 - 21
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摘要:摘要为提高开顶气室(-top chamberOTC)模拟气候变化环境研究植物生理响应的控制效果,基于前期OTC控制系统基础,对气室结构、控制系统及监测系统改进升级。对改进后的OTC控制系统采集了试验期间5月10月OTC气室内CO2浓度、温度及空气相对湿度实时数据分析模拟效果,结果表明改进后的OTC控制系统能够控制CO2浓度达到试验预设浓度梯度,在试验期OTC气室内监测的CO2浓度平均值对照组(CK)为369.33 μmol·mol-1,处理1组(TR1)为558.35 μmol·mol-1,处理2组(TR2)为772.71 μmol·mol-1;CO2浓度波动范围TR1组为551.82572.40 μmol·mol-1,变幅为20.58 μmol·mol-1;TR2组为756.71779.79 μmol·mol-1,变幅为23.08 μmol·mol-1,满足试验预设模拟要求;气室内不同处理间温度、空气相对湿度差异均不显著(>0.05)。改进后的OTC控制系统模拟效果好,可用于研究植物响应气候变化的模拟试验。
Abstract & Keywords
Abstract:  Background, aim, and scope Enhancement of carbon dioxide (CO2) in the atmosphere has received great attention due to its potential repercussion on global warming and direct effects on the vegetation, especially with a potential increase in atmospheric CO2 level from 400 μmol∙mol-1 to 1000 μmol∙mol-1 by the end of 21st century according with currents environmental studies. Therefore, development of new technologies on controlled environment conditions are needed to investigate plant response to CO2 enhancements and its possible repercussion on world food security. Among the controlled environment facilities such as the free air CO2 enrichment (FACE), soil-plant-atmosphere research chambers (SPAR), and CO2-temperature gradient chambers (CTGC), the open-top chambers (OTC) are commonly used to control elevated CO2 concentration for plant science research. In the present study, we aimed to evaluate a modified OTC, designed and constructed based on previous OTC experiences, which provides a precise control of CO2 under different concentrations, with excellent control of air temperature and humidity. Materials and methods Three parts of OTC chamber structure, control system and monitoring system are improved and upgraded. (1) The modified OTC has a regular octagonal prism structure made of plastic steel 4 mm thick high transmittance glass material, an improvement over the previous system. The structure dimensions are 1.08 m length (diagonal), of 2.78 m diameter, and the inner and outer height (top) of 2.55 m and 2.10 m, respectively. (2) The monitoring system consisted of CO2 analyzers, temperature and humidity sensors, and a data acquisition system. (3) The control system is also composed by other features like programmable logic controller, GPRS communication module, a touch screen, a micro-relay, CO2 pressure reducing valves, solenoid valves, perforated windpipes, and CO2 cylinders. The OTC control system automatically collects and uploads data every six minutes using a system control coupled to the PI regulation mode (Proportional integral controller). A linear controller generates deviation monitoring according to a given and an actual output value. The system is also equipped with a GSM communication module connected with the PLC through the Protocol PPI(Point to point interface) to upload all the data to a web server. The OTC control, monitoring system and the data can be accessed in real time through web browser or mobile App, reducing operation costs and allowing environmental variables monitoring. (4) To test the functionality of the modified OTC, Goji berry (Lycium barbarum L.) plants were grown from May to October on 2017 inside the chambers. Real-time data of CO2 concentration, temperature, and air relative humidity of the chambers were collected. Results As a result, the average CO2 levels obtained in the chamber during the study period was 369.33 μmol∙mol-1 for ambient conditions, while elevated group 1 and group 2 showed concentrations of 558.35 μmol∙mol-1 and 772.71 μmol∙mol-1 respectively. The fluctuation for elevated group 1 ranged from 551.82 μmol∙mol-1 to 572.40 μmol∙mol-1 with a variation amplitude of 20.58 μmol∙mol-1. In the elevated group 2, the range of CO2 concentration was from 756.71 μmol∙mol-1 to 779.79 μmol∙mol-1 with variation amplitude of 23.08 μmol∙mol-1. In addition, no significant differences were found in temperature and air relative humidity among the chambers treatments (p > 0.05). Discussion The improved OTC simulation control system can well control the CO2 concentration to meet the preset concentration requirements. In actual control, it needs to further debug and improve to achieve stable operation. Hysteresis usually occurs in the actual control, mainly because in the actual control, CO2 sensor from the monitoring of indoor air CO2 concentration to the control system takes a certain time, the control system automatically adjusts the solenoid valve opening and closing frequency through real-time monitoring data, keeping the CO2 concentration in the air chamber always close to the preset value, the CO2 concentration in the air chamber will be higher than the preset value due to the time difference. In addition, the CO2 concentration is also affected by the outside wind speed and the photosynthetic respiration of the plant, and the CO2 concentration in the air chamber changes greatly. The main purpose of using OTC simulation system in this study is to long-term study the effects of different CO2 concentration treatments on the physiological process of plants. The influencing factors are the same except for the CO2 concentration. This system monitors the temperature and humidity of OTC chambers in real time through different treatment. The results show that the difference in temperature and humidity in different treatment chambers is small, the trend of change is consistent, and the test control effect is good, and the expected purpose of the test is achieved. In addition, if it is necessary to increase temperature simulation in the study, a temperature increase control system may be correspondingly increased to achieve different CO2 concentration and temperature interactive processing simulation test. Conclusions These results demonstrated precise control of CO2 concentration, temperature, and humidity inside the modified OTC chambers, showing an excellent development of CO2 effect improvement on Goji berry, and it can be used to test climate change response in other plant species. Recommendations and perspectives The improved OTC control system realizes automatic unsupervised operation 24 hours a day. All data systems are automatically uploaded to the web server. The system operation status can be monitored in real time through a web browser/mobile phone App, and the system can be controlled and the solenoid valve can be opened and closed. Download data, no geographical restrictions, no manual on-site supervision and save operating costs, improve work efficiency. The system can be used to study the simulation test of plants responding to climate change, and it can also provide reference for other studies related to the simulation of climate change.
Keywords: Open-top chamber; CO2 concentration; Air temperature; Air relative humidity
当前,气候变化已成为人类面临的重大挑战,其已经严重影响了水资源、作物生长以及粮食安全,在半干旱地区更尤为突出Kadiyala et al2015。农业最易受气候变化的影响,气候变暖及CO2浓度升高导致作物生长季节缩短,生物量积累时间减少,进而影响作物产量Supit et al2012。政府间气候变化专门委员会(IPCC)第五次评估报告指出,按目前大气中CO2浓度增长速度,到2100年CO2浓度可能达到1000 μmol·mol-1甚至更高,同时会伴随有热浪、干旱、洪水、气旋和野火极端气象事件;从19世纪工业时代以来,大气中CO2浓度从280 μmol·mol-1上升到380 μmol·mol-1,最近100年(19062005年)全球平均地表温度上升了0.560.92℃,预计21世纪末全球平均气温比初期增高0.34.8℃Change20072014。大气温度升高会影响植物生理进程,促使细胞膨大和分裂,加快器官分化,缩短植物生物量积累时间,降低光合作用。而研究表明碳平衡是植物响应温度变化的一个重要因素,在高CO2浓度或强光条件下,植物光合作用增强,可以有效减弱高温对植物营养组织中生物量积累造成的影响,但高浓度CO2会减小叶片气孔导度,影响植物蒸腾及水分利用效率Lohraseb et al2017Singh et al2017。
为探究气候变化对植物生长及生理进程的影响,研究者通常采用开放式、半开放式和封闭式系统装置模拟气候变化,观察植物在不同CO2浓度或温度等环境条件下生长、产量及品质的变化,以此来评估未来气候变化对植物产生的影响。常见的模拟气候变化的装置主要有:开放式CO2浓度富集系统(ir CO2 FACE)Norby and Zak2011Okada et al2001Pandey et al2017、土壤植物大气研究系统(--SPARS)Reddy et al2001Reddy et al2017、半开放式CO2浓度-温度梯度系统(CO2-CTGC)Yun et al2012李豫婷等2017及开顶气室(,OTC)。
开顶气室OTC控制系统是顶部敞开与外界相通,四周采用透明材料搭建的半封闭环境模拟系统。早在20世纪70年代,科研工作者就设计OTC模拟系统研究烟草对不同O3浓度的响应,以评估大气污染对植物的影响Heagle et al1973。到80年代和90年代,OTC模拟系统使用最为广泛,该技术可以很好的控制植物周围的气体浓度,并可实时监测气体浓度、温度和湿度。但该系统与外界环境存在一定差异,会改变植物生长的小气候环境Piikki et al2008Pleijel and Högy2015。目前,用于试验研究的OTC系统大多根据试验条件设计改进,CO2浓度和温度控制装置也不尽相同。改进设计的OTC模拟控制系统已在早稻万运帆等2014、玉米郭艳亮等2017、大豆张仟雨等2016、小麦张金恩等2015等作物上有研究应用,这些自行设计改进的OTC模拟系统均取得良好效果,在田间条件下精准模拟气候变化,研究CO2浓度和温度对植物生理生态的影响。
1.1   OTC模拟系统改进设计
1.2   模拟控制效果试验
本试验在宁夏大学试验农场(38°13′50.34″N,106°14′22.19″E)进行。以宁夏枸杞“宁杞1号”1年生扦插苗为材料,设置3个处理:对照组CK,OTC气室不通CO2,模拟当前自然生长环境,380±20 μmol·mol-1、处理1组(TR1OTC气室预设CO2浓度为570±20 μmol·mol-1,模拟0.5倍增的大气CO2浓度、处理2组(TR2,OTC气室预设CO2浓度为760±20 μmol·mol-1,1倍增的大气CO2浓度,每个处理下设置组重复(即个气室),共计9个气室(图2),每个气室均匀种植9株生长一致的宁夏枸杞扦插苗,在宁夏枸杞生长期(4月至10月)每天8:00至20:00在处理组TR1及TR2气室内通入CO2,使其浓度保持在预设值。气室内土壤均采用大田土壤(灌淤土),水肥管理均与大田一致。
采用Microsoft 进行数据整理,采用SAS9.4进行数据分析。
2.1   改进开顶气室结构与测控系统
2.1.1   改进开顶气室结构
OTC气室仍然采用正八边形棱柱状结构(图1),气室单边长1.08 m、内径3.0 m、内顶高2.55 m、外顶高2.10 m,气室侧面设有门,气室基部有50 cm厚砖层,气室整体采用塑钢与4 mm厚高透光性能玻璃材料建成。气室内底部安装有补气设备和检测设备,外部电缆和供气管通过气室底部进入气室,沿气室中间位置的PVC支撑管固定,在PVC支撑管根部安装电磁阀,电磁阀负责补气控制动作执行。供气管从电磁阀出口处连接多孔气管,CO2通过气孔释放。

图1   改进开顶气室结构图
Fig.1 Improved structure diagram of OTC
1:气体释放管道;2:气孔;3:温湿度传感器;4:CO2传感器;5:PVC支撑管;6:电磁阀。1: gas release pipe; 2: release hole; 3: temperature and humidity sensor; 4: CO2 sensor; 5: PVC support tube; 6: electromagnetic valve.

图2   气室布置示意图
Fig.2 Layout drawing of chambers
2.1.2   测控系统
监测系统主要有CO2传感器、温湿度传感器及数据采集系统构成,CO2传感器采用北京昆仑海岸公司的JQAW-12AC传感器(量程02000 μmol·mol-1),该传感器采用美国GE双通道CO2模块设计,双通道非分光红外原理,响应时间≤2 min,CO2浓度精度经标定在01000 μmol·mol-1可达±20 μmol·mol-1;温湿度传感器采用北京昆仑海岸公司的JWSK-6ACW传感器,空气相对湿度量程0100%,精度±3%;温度量程-2060℃,精度±0.5℃。传感器固定在气室正中间PVC固定管上,可随植株生长调节高度。传感器采集气室内CO2浓度、温度、空气相对湿度等物理量,转换为电流信号传回核心控制器(PLC),经过AD转换、运算后转换(1)为可视的数字量;采集原理如图3a所示。

图3   OTC测控系统
Fig.3 OTC measurement and control system
Mo 转换公式为:
\({\mathrm{M}}_{\mathrm{O}}=\left[\frac{\left({\mathrm{O}}_{\mathrm{s}\mathrm{h}}-{\mathrm{O}}_{\mathrm{s}\mathrm{l}}\right)×\left({\mathrm{I}}_{\mathrm{v}}-{\mathrm{I}}_{\mathrm{s}\mathrm{l}}\right)}{{\mathrm{I}}_{\mathrm{s}\mathrm{h}}-{\mathrm{I}}_{\mathrm{s}\mathrm{l}}}\right]+{\mathrm{O}}_{\mathrm{s}\mathrm{l}}\) (1)
式中:Mo为可视数字量数据;Mr为实际检测物理量;ICO2 为420mA电流信号;Iv为换算对象;Osh为换算结果的高限;Osl为换算结果的低限;Ish为换算对象的高限;Isl为换算对象的低限
2.1.3   远程监测系统

图4   Web端数据监测示意图
Fig.4 Schematic diagram of web data monitoring
2.2   改进开顶气室模拟CO2浓度控制系统运行效果
利用改进升级后的OTC模拟系统调控气室内的CO2浓度达到预设值,并实时监测记录CO2浓度,预设处理组TR1气室内CO2浓度为570±20 μmol·mol-1,处理组TR2气室内CO2浓度为760±20 μmol·mol-1,对照组CK不通入CO2模拟当前自然环境,系统设定通入CO2时间为白天(08:00—20:00)。试验期OTC气室内CO2浓度监测效果如图5a所示,对照组CK气室内CO2浓度波动范围为364.04373.50 μmol·mol-1,气室内CO2浓度平均值为369.33 μmol·mol-1;处理组TR1气室内CO2浓度平均值为558.35 μmol·mol-1,波动范围为551.82572.40 μmol·mol-1,变幅为20.58 μmol·mol-1,实际控制效果在预设范围内;处理组TR2气室内CO2浓度平均值为772.71 μmol·mol-1,波动范围为756.71779.79 μmol·mol-1,变幅为23.08 μmol·mol-1,实际控制效果接近预设值。
对试验监测期每天08:0020:00时间段的CO2浓度计算平均值,获得OTC气室内不同时间段均值动态变化情况如图5b所示,对照组CK气室内CO2浓度波动范围为365.43368.54 μmol·mol-1,平均值为366.68 μmol·mol-1;TR1气室内CO2浓度波动范围为538.91577.27 μmol·mol-1,平均值为550.76 μmol·mol-1,偏差范围为-22%,误差范围为-25%,变幅为38.36 μmol·mol-1;TR2气室中CO2浓度波动范围为741.93783.96 μmol·mol-1,平均值为752.52 μmol·mol-1,偏差范围为-11%,误差范围为-20%,变幅为42.03 μmol·mol-1,实际控制效果均在预设范围内。通过对试验期内(5月10月)OTC气室内CO2浓度监测,同时对系统不断进行调试改进,改进的OTC控制系统可以精确控制CO2浓度达到预设试验要求,系统运行稳定,满足模拟试验条件。

图5   OTC气室内CO2浓度控制效果
Fig. 5 Control effect of CO2 concentration
2.3   改进开顶气室内温度监测比较

图6   OTC内温度监测效果
Fig.6 Effect of temperature in OTC chambers
2.4   改进开顶气室内空气相对湿度监测比较

图7   OTC内空气相对湿度监测效果
Fig.7 Effect of air relative humidity in OTC chambers
3   讨论
改进后的OTC模拟控制系统能够较好的控制CO2浓度达到模拟试验条件。本试验通过对前期OTC控制系统全新改进升级,在气室内安装CO2传感器,在白天(08:00—20:00)通过控制系统调控通入CO2,处理组TR1气室内CO2浓度预设范围为570±20 μmol·mol-1,TR2气室内CO2浓度预设范围为760±20 μmol·mol-1。通过对宁夏枸杞生长期(5月10月)OTC气室内CO2浓度实时监测,对照组CK气室内CO2浓度平均值为369.33 μmol·mol-1;处理组TR1气室内CO2浓度平均值为558.35 μmol·mol-1,处理组TR2气室内CO2浓度平均值为772.71 μmol·mol-1,控制效果均达到预设范围,满足试验要求;但在试验过程中还需要不断调试系统,以达到最佳控制状态,通常在实际控制中会出现滞后现象,这主要是因为在实际控制中,CO2传感器从监测气室内CO2浓度到传输至控制系统需要一定时间,控制系统通过实时监测数据自动调整电磁阀开闭频率,保持气室内CO2浓度始终接近预设值,由于时间差原因就会造成气室内CO2浓度高于预设值,此外,CO2浓度还受外界风速及植物光合呼吸作用影响,气室内CO2浓度变化幅度较大。本试验中,OTC控制系统达到了试验控制目标,模拟效果较好,但在后期试验中还要进一步根据试验目标改进,提高控制效果和精度,保证系统稳定运行。
4   结论
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MA Yaping
WAHG Naigong
CAO Bing
曹 兵,E-mail: bingcao2006@126.com
National Natural Science Foundation of China (31660199, 31160172)
出版时间: 2018年8月21日 (版本3
Journal of Earth Environment