Abstract
The photochemical reflectance index (PRI) and red-edge region of the spectrum are known to be sensitive to plant physiological processes, and through measurement of these optical signals it is possible to use non-invasive remote sensing to monitor the plant photosynthetic status in response to environmental stresses such as drought. We conducted a greenhouse experiment using Quercus ilex, a Mediterranean evergreen oak species, to investigate the links between leaf-level PRI and the red-edge based reflectance ratio (R690/R630) with CO2 assimilation rates (A), and photochemical efficiency (FV/FM and Yield) in response to a gradient of mild to extreme drought treatments (nine progressively enhanced drought levels) and corresponding recovery. PRI and R690/R630 both decreased under enhanced drought stress, and had significant correlations with A, FV/FM and Yield. The differential values between recovery and drought treatments of PRI (ΔPRIrecovery) and R690/R630 (ΔR690/R630recovery) increased with the enhanced drought levels, and significantly correlated with the increases of ΔArecovery, ΔFV/FMrecovery and ΔYieldrecovery. We concluded that both PRI and R690/R630 were not only sensitive to enhanced drought stresses, but also highly sensitive to photosynthetic recovery. Our study makes important progress for remotely monitoring the effect of drought and recovery on photosynthetic regulation using the simple physiological indices of PRI and R690/R630.
Highlights
The increasing occurrence of drought in the Mediterranean region is widely reported [1,2,3] and during the last 20 years observations show that it has affected ecosystem functioning and structure [4,5], decreased plant growth [6] and primary production [7,8], and triggered vegetation mortality [9].The increase of drought has enhanced water scarcity [10], and elicited ecological damage [11] and crop failures [12]
2017, 8, 386 of 14 decreased gradually. Both changes in photochemical reflectance index (PRI) and reflectance at 690 nm (R690)/R630 were highly consistent with the decreases decreases in soil water(SWC), contentA,(SWC), FV/FYield
Photosynthesis, and chlorophyll fluorescence (ChlF) at 690 nm probably plays a role in the relationship of R690/R630 with photosynthesis. Both PRI and R690/R630 can be used for remotely monitoring the effect of drought on the carbon uptake and productivity of Mediterranean species
Summary
The increase of drought has enhanced water scarcity [10], and elicited ecological damage [11] and crop failures [12] Faced with these negative impacts, monitoring the timing of drought onset and the extent of the effects on vegetation ecosystems is being increasingly warranted. One of the key constraints of Mediterranean ecosystems [4], elicits a water deficit in the leaf tissue that can down-regulate photosynthesis [13]. This reduction in photosynthesis for Mediterranean species such as Quercus ilex L. is generally caused by stomatal closure in response to drought stress [14,15,16]. Quercus ilex is a broadleaved evergreen tree or shrub that is widely distributed
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