Environmental, Population, and Organismic Biology, University of Colorado, Boulder, CO, 80309, USA.
Department of Ecology and Evolution, State University of New York, 11794, Stony Brook, NY, USA.
Oecologia. 2001 Apr;127(2):214-221. doi: 10.1007/s004420000594. Epub 2001 Jan 19.
Tropical forest soils are known to emit large amounts of reactive nitrogen oxide compounds, often referred to collectively as NOy (NOy = NO + NO2 + HNO3 + organic nitrates). Plants are known to assimilate and emit NOy and it is therefore likely that plant canopies affect the atmospheric concentration of reactive nitrogen compounds by assimilating or emitting some fraction of the soil-emitted NOy. It is crucial to understand the magnitude of the canopy effects and the primary environmental and physiological controls over NOy exchange in order to accurately quantify regional NOy inventories and parameterize models of tropospheric photochemistry. In this study we focused on nitrogen dioxide (NO2), which is the component of NOy that most directly catalyzes the chemistry of O3 dynamics, one of the most abundant oxidative species in the troposphere, and which has been reported as the NOy species that is most readily exchanged between plants and the atmosphere. Leaf chamber measurements of NO2 flux were measured in 25 tree species growing in a wet tropical forest in the Republic of Panama. NO2 was emitted to the atmosphere at ambient NO2 concentrations below 0.53-1.60 ppbv (the NO2 compensation point) depending on species, with the highest rate of emission being 50 pmol m(-2) s(-1) at <0.1 ppbv. NO2 was assimilated by leaves at ambient NO2 concentrations above the compensation point, with the maximum observed uptake rate being 1,550 pmol m(-2) s(-1) at 5 ppbv. No seasonal variation in leaf NO2 flux was observed in this study and leaf emission and uptake appeared to be primarily controlled by leaf nitrogen and stomatal conductance, respectively. When scaled to the entire canopy, soil NO emission rates to the atmosphere were estimated to be maximally altered ±19% by the overlying canopy.
热带森林土壤被认为会排放大量的活性氮氧化物化合物，通常统称为 NOy（NOy = NO + NO2 + HNO3 + 有机硝酸盐）。已知植物会同化和排放 NOy，因此植物冠层很可能通过同化或排放土壤排放的部分 NOy 来影响大气中活性氮化合物的浓度。了解冠层效应的幅度以及对 NOy 交换的主要环境和生理控制因素至关重要，这对于准确量化区域 NOy 清单和参数化对流层光化学反应模型至关重要。在这项研究中，我们专注于二氧化氮（NO2），它是 NOy 的组成部分，最直接催化臭氧动力学化学，是平流层中最丰富的氧化物种之一，并且据报道是最容易在植物和大气之间交换的 NOy 物种。在巴拿马共和国的一个湿润热带森林中生长的 25 种树种中测量了叶片室中 NO2 通量。NO2 在环境 NO2 浓度低于 0.53-1.60 ppbv（NO2 补偿点）时被排放到大气中，具体取决于物种，最低排放率为 50 pmol m(-2) s(-1)在 <0.1 ppbv。NO2 在补偿点以上的环境 NO2 浓度下被叶片同化，最大观测到的吸收速率为 5 ppbv 时的 1,550 pmol m(-2) s(-1)。在本研究中未观察到叶片 NO2 通量的季节性变化，叶片排放和吸收似乎主要分别受叶片氮和气孔导度控制。当将其扩展到整个冠层时，估计土壤 NO 排放到大气中的速率最多可被上层冠层改变 ±19%。
