Abstract
In order to estimate vegetation photosynthesis from remote sensing observations; some critical parameters need to be quantified. From all absorbed light; the plant needs to release any excess that is not used for photosynthesis; by non-photochemical quenching; by fluorescence emission and unregulated thermal dissipation. Non-photochemical quenching (NPQ) processes are controlled photoprotective mechanisms which; once activated; strongly control the dynamics of photochemical efficiency. With illumination conditions increasing and decreasing during a diurnal cycle; photoprotection mechanisms needs to change accordingly. The goal of this work is to quantify dynamic NPQ; measured from active fluorescence measurements; based on passive proximal sensing leaf measurements. During a 22-day controlled light and water stress experiment on a tobacco (Nicotiana tabacum L.) leaf we measured the diurnal dynamics of passive fluorescence (Chl F); the Photochemical Reflectance Index (PRI); the Absorbed Photosynthetically Active Radiation (APAR) and leaf temperature in combination with the actively retrieved non-photochemical quenching (NPQ) parameter. Based on a bi-linear combination of diurnal APAR and PRI (plane fit model) we succeeded to estimate NPQ with a RMSE of 0.08. The simple plane fit model estimation represents well the diurnal NPQ dynamics; except for the high light stress phase; when additional reversible photoinhibition processes took place. The present works presents a way of determining NPQ from passive remote sensing measurements; as a necessary step towards estimating photosynthetic rate.
Highlights
Plants must deal with light in extreme ways
We present a proximal sensing experiment at leaf level in which the diurnal behaviour of non-photochemical quenching (NPQ), Absorbed photosynthetically active radiation (APAR), Photochemical Reflectance Index (PRI) and F are investigated during long lasting physiological stress
We address the diurnal evolution of NPQ and leaf temperature along the experiment through the different phases of stress and adaptation of the plant to the environmental conditions
Summary
Plants must deal with light in extreme ways. Both the quantity of solar radiation, varying over several orders of magnitude, as well as the temporal fluctuations, ranging from seconds to seasons, demand a high flexibility of plants to keep the light supply in balance with the demand for healthy metabolic growth. Plants evolved with the remarkable capacity of dissipating absorbed solar energy in ways being profitable (harvesting light for growth) or protective (activating different mechanisms to avoid light damage). During the early morning hours (or low illumination conditions in general) photoprotection is not activated, because the absorbed energy can still be efficiently trapped for photochemical use, driving the light and carbon reactions. When the APAR becomes saturating for the safe and efficient use of the photosynthetic machinery, is hard to be defined on an absolute energy scale. This will depend on the physiological state of the plant, as well as on environmental parameters such as temperature [5]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
