Collaborative Research: Recalibrating CO2 and water diffusion through leaves to improve models of photosynthetic responses to the environment

植物生长和作物生产力最初依赖于光合作用捕获的二氧化碳。直接测量光合作用的速率，以了解不同植物在一系列环境条件下生长时的效率。然后，这些数据被用于将光合作用速率与潜在的叶片生物化学联系起来的模型中，以便预测植物在不同环境中的表现。这些模型需要知道树叶内的二氧化碳浓度，但这个值是根据树叶外的二氧化碳和水蒸气的测量计算出来的。原理研究人员最近的工作表明，目前计算树叶内二氧化碳的方法(使用了50多年)经常产生不正确的值。了解二氧化碳进入叶细胞的阻力也是必要的，该原理研究人员的工作还表明，目前的方法可能在估计这些阻力时存在重大错误。这项提议将使用新的方法来重新校准叶片内二氧化碳水平的计算以及二氧化碳进入叶片细胞的阻力。这将提高对不断变化的环境中光合作用的理解，并有助于开发更高产的作物，包括将更有效地利用水分和养分的作物。法夸尔光合作用模型是在35年前开发的，是解释光合作用测量的公认标准。模型中的许多变量可以从基本的酶动力学中分配，但该模型需要测量光合作用电子传递的最大速率、碳同化、对进入和通过叶片的二氧化碳扩散的阻力，以及白天的呼吸速率。要确定这些值中的每一个，都需要准确测量少量的水或二氧化碳通量，以避免在计算关键变量时出现一些潜在的大错误，即叶片气孔下腔内的二氧化碳分压(Ci)和叶绿体基质中的二氧化碳分压(Cc)。支撑确定Ci和cc的基本方法的假设在某些条件下不成立，但偏差的程度尚不清楚。这一建议的主要目的是：1)确定叶片形态(如角质层组成和表皮硬度)和膨压对高温和干旱胁迫期间Ci和cc测量误差的相对贡献；2)发展或改进正确测定Ci和cc的方法，该方法可广泛用于田间和实验室的光合作用测量。

Plant growth and crop productivity initially depend on carbon dioxide capture by photosynthesis. Rates of photosynthesis are measured directly to understand how efficient different plants are when grown across a range of environmental conditions. These data are then used in models that relate the rate of photosynthesis to the underlying leaf biochemistry in order to predict how plants will perform in different environments. The models require knowledge of the concentration of carbon dioxide inside the leaf, but that value is calculated from measurements of carbon dioxide and water vapor outside of the leaf. Recent work by the principle investigators has shown that the current methods for calculating carbon dioxide inside the leaf (in use for over fifty years) are often generating incorrect values. It is also necessary to understand resistances to carbon dioxide movement into leaf cells and the work of the principle investigators also shows current approaches may have major errors in the estimates of these resistances. This proposal will use new methods to re-calibrate the calculation of carbon dioxide levels inside leaves and the resistance to carbon dioxide movement into leaf cells. This will then improve understanding of photosynthesis in changing environments and assist in development of more productive crops, including crops that will use water and nutrients more efficiently.The 'Farquhar' model of photosynthesis was developed over 35 years ago and is the accepted standard for interpreting measurements of photosynthesis. Many of the variables in the model can be assigned from basic enzyme kinetics, but the model requires measurements of maximum rates of photosynthetic electron transport, carbon assimilation, resistance to CO2 diffusion into and through the leaf, and the rate of respiration during the day. Determination of each of these values requires accurate measurement of small fluxes of water or CO2 in order to avoid some potentially large errors in calculation of critical variables, namely the CO2 partial pressure inside the sub-stomatal cavities of leaves (ci) and the CO2 partial pressure in the chloroplast stroma (cc). Assumptions underpinning foundational methods for determining ci and cc are not holding under some conditions, but the extent of the deviations is not known. The major objectives of this proposal are to: 1) determine the relative contribution of leaf morphology (e.g. cuticle composition and epidermal stiffness) and turgor pressure to errors in ci and cc measurement during heat and drought stress, 2) develop or improve methods for correctly determining ci and cc that can be used broadly in both field and laboratory based measurements of photosynthesis.