Information about soil nitric oxide (NO) emissions from subtropical forests is quite limited, and even less is known about the pulse emission of NO when wetting soils after a long period of dryness. In this study, we measured NO fluxes following wetting of dry soil in a broadleaf forest and a pine forest in subtropical China. Large pulses of NO fluxes were observed after soil wetting in both forests. NO fluxes increased significantly within 0.5 h following wetting in both forests and reached peak 1 and 4 h after soil wetting in the pine forest and the broadleaf forest, respectively. In the broadleaf forest, averaged peak flux of NO pulses was 157 ng N m -2 s -1 , which was 8 times the flux value before wetting, and in the pine forest, the averaged peak flux was 135 ng N m -2 s -1 , which was 15.5 times the flux value before wetting. The total pulses-induced NO emissions during the dry season were roughly estimated to be 29.4 mg N m -2 in the broadleaf forest and 22.2 mg N m -2 in the pine forest or made up a proportion of 4.6% of the annual NO emission in the broadleaf forest and 5.3% in the pine forest.
LI De-Jun and WANG Xin-Ming 2 State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China)
应用整合分析(meta-analysis)方法定量研究了大气臭氧(O3)浓度增加对小麦光合色素、气体交换和产量形成的影响.通过Web of Sciences和中国期刊全文数据库检索,共收集39篇原始论文.结果表明,大气臭氧浓度增加可导致小麦的产量在当前环境浓度的基础上降低26%,籽粒重、穗粒数和穗数分别降低18%,11%和5%,收获指数减少11%.叶片生理对大气臭氧浓度增加的响应比产量敏感得多,如光饱和光合速率、气孔导度和叶绿素含量分别下降40%,31%和46%.春小麦和冬小麦对臭氧的响应相似.大部分指标显示了小麦叶片生理和产量的降低随着臭氧浓度增加而线性增加的趋势.在小麦灌浆期,臭氧浓度增加引起叶片的光合速率、气孔导度和叶绿素含量降低得最大.大气CO2浓度升高可以明显减轻或抵消大气臭氧浓度增加引起的减产效应.
采用旋转布气法开顶式气室(Open top chambers,OTCs)装置,研究4种臭氧(O3)浓度水平(过滤大气,O3浓度20nl·L–1;环境大气,O3浓度40nl·L–1;中等O3浓度处理,O3浓度为75nl·L–1;高浓度处理,O3浓度为150nl·L–1)下水稻(Oryzasativa)根系中根系活力、可溶性蛋白含量、膜脂过氧化程度与抗氧化系统的变化差异。主要结果表明与过滤大气处理相比,O3浓度升高(75和150nl·L–1)使植株根系活力显著降低,根系大幅度、过早地衰退;根系可溶性蛋白质含量显著下降;根系MDA含量显著升高,膜脂过氧化程度加剧;SOD活性呈先升高后下降的变化趋势根系中H2O2含量大幅度显著上升,并随着O3处理浓度升高和暴露时间延长变化幅度增大;CAT与POD活性则表现出升高趋势,但处理后期升高幅度略微降低;整个处理期间根系ASA含量无显著变化。环境大气处理与过滤大气处理植株各个指标变化趋势基本一致并略微下降,随着处理时间延长根系活力与蛋白质含量出现显著下降,其他指标无显著差异。试验结果表明O3浓度升高会对植物地下部分根系产生影响;随着O3胁迫时间的延长,植物将面临着缺乏强有力的根系生理代谢活力支持。
