DO<sub>3</sub>SE modelling of soil moisture to determine ozone flux to forest trees

Abstract

Abstract. The DO3SE (Deposition of O3 for Stomatal Exchange) model is an established tool for estimating ozone (O3) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O3 precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O3 flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (gsto), and subsequent O3 flux. This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on gsto for a variety of forest tree species. This DO3SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plant-atmosphere system and empirical data describing gsto relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to gsto, to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system. These methods are evaluated against field data describing a variety of soil water variables, gsto and transpiration data for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), birch (Betula pendula), aspen (Populus tremuloides), beech (Fagus sylvatica) and holm oak (Quercus ilex) collected from ten sites across Europe and North America. Modelled estimates of these variables show consistency with observed data when applying the simple empirical methods, with the timing and magnitude of soil drying events being captured well across all sites and reductions in transpiration with the onset of drought being predicted with reasonable accuracy. The more complex methods, which incorporate hydraulic resistance and plant capacitance, perform less well, with predicted drying cycles consistently underestimating the rate and magnitude of water loss from the soil. A sensitivity analysis showed that model performance was strongly dependent upon the local parameterisation of key model drivers such as the maximum gsto, soil texture, root depth and leaf area index. The results suggest that the simple modelling methods that relate gsto directly to soil water content and potential provide adequate estimates of soil moisture and influence on gsto such that they are suitable to be used to assess the potential risk posed by O3 to forest trees across Europe.

Deciphering the ozone-induced changes in cellular processes: a prerequisite for ozone risk assessment at the tree and forest levels

“…That new function is being increasingly used, but more knowledge is needed to determine if the effects of O3 on trees should really be integrated in the same way as to link the O3 function to another function than phenology function so far. Further research is needed (i) to characterize O 3 impacts on stomatal function as well as the interaction with other abiotic stresses like drought and (ii) to improve stomatal conductance models like the DO3SE model (Büker et al 2012). In these models, we need to improve the estimation of the start and end of the growing season today and in the future.…”

“…An alternative, flux-based methodology emerged from the International Cooperative Programme on the effects of air pollution on vegetation (Mills et al 2013) under the UNECE Convention on Long-Range Transboundary Air Pollution (LRTAP). In this approach, the European Monitoring and Evaluation Program (EMEP) and Rossby Centre Regional Climate (RCA3) models provided O 3 and meteorological input data that fed the Deposition of Ozone for Stomatal Exchange (DO 3 SE) model, which simulates O 3 dry deposition (Büker et al 2012) and subsequently O 3 stomatal fluxes and phytotoxic O 3 doses (POD Y ) as described in the LRTAP convention manual (2010). O 3 flux-response relationships were applied to calculate biomass and carbon losses for tree species groups and representative species.…”

Impact of regional climate change and future emission scenarios on surface O<sub>3</sub> and PM<sub>2.5</sub> over India

“…Calculation of non-stomatal sinks, in conjunction with an ecosystemspecific calculation of vertical O 3 profiles, is an important part of this calculation, as discussed in Tuovinen et al (2004Tuovinen et al ( , 2009 or Simpson et al (2003). The methodology and robustness of the calculations of O 3 deposition and stomatal conductance have been explored in a number of publications (Tuovinen et al, 2004(Tuovinen et al, , 2009Emberson et al, 2007;Büker et al, 2012). …”

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Whether it is possible to separate the components of R ns (R c2 -external surfaces; R c3 -soil; R c4 -in-canopy chemistry) depends on the nature of the measurement site and canopy, and there are some models available based on measurements over bare soil, senescent vegetation and in-canopy chemistry (Launiainen et al, 2013;Fares et al, 2013bFares et al, , 2012Büker et al, 2012;Tuzet et al, 2011;Stella et al, 2011). Many research groups have taken this approach, and Table 1 provides a summary of some of the different estimates of the values for R ns in the literature.…”