Abstract
Aerosols can enhance ecosystem productivity by increasing diffuse radiation. Such diffuse fertilization effects (DFEs) vary among different aerosol compositions and sky conditions. Here, we apply a suite of chemical, radiation, and vegetation models in combination with ground- and satellite-based measurements to assess the impacts of natural and anthropogenic aerosol species on gross primary productivity (GPP) through DFE during 2001–2014. Globally, aerosols increase GPP by 8.9 Pg C yr-1 at clear skies but only 0.95 Pg C yr-1 at all skies. Anthropogenic aerosols account for 41% of the total GPP enhancement though they contribute only 25% to the increment of diffuse radiation. Sulfate/nitrate aerosols from anthropogenic sources make dominant contributions of 33% (36%) to aerosol DFE at all (clear) skies, followed by the ratio of 18% (22%) by organic carbon aerosols from natural sources. In contrast to other species, black carbon aerosols decrease global GPP by 0.28 (0.12) Pg C yr-1 at all (clear) skies. Long-term simulations show that aerosol DFE is increasing 2.9% yr-1 at all skies mainly because of a downward trend in cloud amount. This study suggests that the impacts of aerosols and cloud should be considered in projecting future changes of ecosystem productivity under varied emission scenarios.
Highlights
Diffuse light enhances plant photosynthesis more efficiently than direct light (Gu et al, 2002; Alton et al, 2007; Mercado et al, 2009; Jing et al, 2010; Cirino et al, 2014; Zhou et al, 2021a, c)
We further explore the interannual variations in gross primary productivity (GPP) changes caused by aerosol diffuse fertilization effects (DFEs) from natural and anthropogenic sources (Fig. 7)
We quantified the impacts of sky conditions, emission sources, and aerosol species on terrestrial ecosystem productivity through aerosol DFE
Summary
Diffuse light enhances plant photosynthesis more efficiently than direct light (Gu et al, 2002; Alton et al, 2007; Mercado et al, 2009; Jing et al, 2010; Cirino et al, 2014; Zhou et al, 2021a, c). The cause for such a difference is that diffuse light can penetrate into the deep canopy and enhance photosynthesis of more shaded leaves with higher light use efficiency (LUE = GPP / PAR, gross primary productivity per photosynthetically active radiation) (Roderick et al, 2001; Gu et al, 2003; Rap et al, 2015). As a result, increasing the diffuse radiation can help promote canopy photosynthesis through the diffuse fertilization effect (DFE). Zhou et al.: Distinguishing the impacts of natural and anthropogenic aerosols on global GPP
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