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Land ecosystems are important sources and sinks of atmospheric components. In turn, air pollutants affect the exchange rates of carbon and water fluxes between ecosystems and atmosphere. However, these biogeochemical processes are usually not well presented in the Earth system models, limiting the explorations of interactions between land ecosystems and air pollutants from the regional to global scales. Here, we develop and validate the interactive Model for Air Pollution and Land Ecosystems (iMAPLE) by upgrading the Yale Interactive terrestrial Biosphere model with process-based water cycles, fire emissions, wetland methane (CH4) emissions, and the trait-based ozone (O3) damages. Within the iMAPLE, soil moisture and temperature are dynamically calculated based on the water and energy balance in soil layers. Fire emissions are dependent on dryness, lightning, population, and fuel load. Wetland CH4 is produced but consumed through oxidation, ebullition, diffusion, and plant-mediated transport. The trait-based scheme unifies O3 sensitivity of different plant functional types (PFTs) with the leaf mass per area. Validations show correlation coefficients (R) of 0.59-0.86 for gross primary productivity (GPP) and 0.57-0.84 for evapotranspiration (ET) across the six PFTs at 201 flux tower sites, and yield an average R of 0.68 for CH4 emissions at 44 sites. Simulated soil moisture and temperature match reanalysis data with the high R above 0.86 and low normalized mean biases (NMB) within 7%, leading to reasonable simulations of global GPP (R=0.92, NMB=1.3%) and ET (R=0.93, NMB=-10.4%) against satellite-based observations for 2001-2013. The model predicts an annual global area burned of 507.1 Mha, close to the observations of 475.4 Mha with a spatial R of 0.66 for 1997-2016. The wetland CH4 emissions are estimated to be 153.45 Tg [CH4] yr-1 during 2000-2014, close to the multi-model mean of 148 Tg [CH4] yr-1. The model also shows reasonable responses of GPP and ET to the changes in diffuse radiation, and yields a mean O3 damage of 2.9% to global GPP. The iMAPLE provides an advanced tool for studying the interactions between land ecosystem and air pollutants. [ABSTRACT FROM AUTHOR]

A major limitation in modeling global ozone (O3) vegetation damage has long been the reliance on empirical O3 sensitivity parameters derived from a limited number of species and applied at the level of plant functional types (PFTs), which ignore the large interspecific variations within the same PFT. Here, we present a major advance in large-scale assessments of O3 plant injury by linking the trait leaf mass per area (LMA) and plant O3 sensitivity in a broad and global perspective. Application of the new approach and a global LMA map in a dynamic global vegetation model reasonably represents the observed interspecific responses to O3 with a unified sensitivity parameter for all plant species. Simulations suggest a contemporary global mean reduction of 4.8% in gross primary productivity by O3, with a range of 1.1%-12.6% for varied PFTs. Hotspots with damages > 10% are found in agricultural areas in the eastern U.S., western Europe, eastern China, and India, accompanied by moderate to high levels of surface O3. Furthermore, we simulate the distribution of plant sensitivity to O3, which is highly linked with the inherent leaf trait trade-off strategies of plants, revealing high risks for fast-growing species with low LMA, such as crops, grasses and deciduous trees. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Fire is an important source of surface ozone (O3), which causes damage to vegetation and reduces stomatal conductance. Such processes can feed back to inhibit dry deposition and indirectly enhance surface O3. Here, we apply a fully coupled chemistry-vegetation model to estimate the indirect contributions of global fires to surface O3 through O3-vegetation feedback during 2005-2012. Fire emissions directly increase the global mean annual O3 by 1.2 ppbv (5.0%) with a maximum of 5.9 ppbv (24.4%) averaged over central Africa by emitting substantial number of precursors. Considering O3-vegetation feedback, fires additionally increase surface O3 by 0.5 ppbv averaged over the Amazon in October, 0.3 ppbv averaged over southern Asia in April, and 0.2 ppbv averaged over central Africa in April. During extreme O3-vegetation interactions, such feedback can rise to >0.6 ppbv in these fire-prone areas. Moreover, large ratios of indirect-to-direct fire O3 are found in eastern China (3.7%) and the eastern U.S. (2.0%), where the high ambient O3 causes strong O3-vegetation interactions. With likelihood of increasing fire risks in a warming climate, fires may promote surface O3 through both direct emissions and indirect chemistry-vegetation feedbacks. Such indirect enhancement will cause additional threats to public health and ecosystem productivity. [ABSTRACT FROM AUTHOR]

Ozone-vegetation feedback is essential to tropospheric ozone (O3) concentrations. The O3 stomatal uptake damages leaf photosynthesis and stomatal conductance and, in turn, influences O3 dry deposition. Further, O3 directly influences isoprene emissions, an important precursor of O3. The effects of O3 on vegetation further alter local meteorological fields and indirectly influence O3 concentrations. In this study, we apply a fully coupled chemistry-carbon-climate global model (ModelE2-YIBs) to evaluate changes in O3 concentrations caused by O3-vegetation interactions. Different parameterizations and sensitivities of the effect of O3 damage on photosynthesis, stomatal conductance, and isoprene emissions (IPE) are implemented in the model. The results show that O3-induced inhibition of stomatal conductance increases surface O3 on average by + 2.1 (+ 1.4) ppbv in eastern China, + 1.6 (- 0.5) ppbv in the eastern U.S., and + 1.3 (+ 1.0) ppbv in western Europe at high (low) damage sensitivity. Such positive feedback is dominated by reduced O3 dry deposition, in addition to the increased temperature and decreased relative humidity from weakened transpiration. Including the effect of O3 damage on IPE slightly reduces surface O3 concentrations by influencing precursors. However, the reduced IPE weakens surface shortwave radiative forcing of secondary organic aerosols leading to increased temperature and O3 concentrations in the eastern U.S. This study highlights the importance of interactions between O3 and vegetation with regard to O3 concentrations and the resultant air quality. [ABSTRACT FROM AUTHOR]