Biogenic isoprene emissions play a very important role in atmospheric chemistry. These emissions are strongly dependent on various environmental conditions, such as temperature, solar radiation, plant water stress, ambient ozone and CO2 concentrations, and soil moisture. Current biogenic emission models (i.e., Model of Emissions of Gases and Aerosols from Nature, MEGAN) can simulate emission responses to some of the major driving variables, such as short-term variations in temperature and solar radiation, but the other factors are either missing or poorly represented. In this paper, we propose a new modeling approach that considers the physiological effects of drought stress on plant photosynthesis and isoprene emissions for use in the MEGAN3 biogenic emission model. We test the MEGAN3 approach by integrating the algorithm into the existing MEGAN2.1 biogenic emission model framework embedded into the global Community Land Model of the Community Earth System Model (CLM4.5/CESM1.2). Single-point simulations are compared against available field measurements at the Missouri Ozarks AmeriFlux (MOFLUX) field site. The modeling results show that the MEGAN3 approach of using of a photosynthesis parameter (Vcmax) and soil wetness factor (βt) to determine the drought activity factor leads to better simulated isoprene emissions in non-drought and drought periods. The global simulation with the MEGAN3 approach predicts a 17% reduction in global annual isoprene emissions, in comparison to the value predicted using the default CLM4.5/MEGAN2.1 without any drought effect. This reduction leads to changes in surface ozone and oxidants in the areas where the reduction of isoprene emissions is observed. Based on the results presented in this study, we conclude that it is important to simulate the drought-induced response of biogenic isoprene emission accurately in the coupled Earth System model.

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异戊二烯排放对干旱的响应及其对全球大气化学的影响

生物异戊二烯排放在大气化学中发挥着非常重要的作用。这些排放很大程度上取决于各种环境条件，例如温度、太阳辐射、植物水分胁迫、环境臭氧和二氧化碳浓度以及土壤湿度。目前的生物排放模型（即自然界气体和气溶胶排放模型，MEGAN）可以模拟对一些主要驱动变量的排放响应，例如温度和太阳辐射的短期变化，但其他因素要么缺失或代表性较差。在本文中，我们提出了一种新的建模方法，考虑干旱胁迫对植物光合作用和异戊二烯排放的生理影响，用于 MEGAN3 生物排放模型。我们通过将算法集成到现有的 MEGAN2.1 生物排放模型框架中来测试 MEGAN3 方法，该框架嵌入到社区地球系统模型的全球社区土地模型 (CLM4.5/CESM1.2) 中。将单点模拟与密苏里州 Ozarks AmeriFlux (MOFLUX) 现场的可用现场测量进行比较。建模结果表明，MEGAN3使用光合作用参数（Vcmax）和土壤湿度因子（βt）来确定干旱活动因子的方法可以更好地模拟非干旱和干旱时期的异戊二烯排放。与使用默认 CLM4.5/MEGAN2.1 预测的值（没有任何干旱影响）相比，使用 MEGAN3 方法进行的全球模拟预测全球年度异戊二烯排放量将减少 17%。这种减少导致观察到异戊二烯排放量减少的区域的表面臭氧和氧化剂发生变化。根据本研究的结果，我们得出结论，在耦合地球系统模型中准确模拟干旱引起的生物异戊二烯排放响应非常重要。