The Impact of Heat Stress and Water Deficit on the Photosynthetic and Stomatal Physiology of Olive (Olea europaea L.)—A Case Study of the 2017 Heat Wave

Abstract

Heat waves are predicted to increase in frequency and duration in many regions as global temperatures rise. These transient increases in temperature above normal average values will have pronounced impacts upon the photosynthetic and stomatal physiology of plants. During the summer of 2017, much of the Mediterranean experienced a severe heat wave. Here, we report photosynthetic leaf gas exchange and chlorophyll fluorescence parameters of olive (Olea europaea cv. Leccino) grown under water deficit and full irrigation over the course of the heat wave as midday temperatures rose over 40 °C in Central Italy. Heat stress induced a decline in the photosynthetic capacity of the olives consistent with reduced ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity. Damage to photosystem II was more apparent in plants subject to water deficit. In contrast to previous studies, higher temperatures induced reductions in stomatal conductance. Heat stress adversely affected the carbon efficiency of olive. The selection of olive varieties with enhanced tolerance to heat stress and/or strategies to mitigate the impact of higher temperatures will become increasingly important in developing sustainable agriculture in the Mediterranean as global temperatures rise.

Resilient and Sensitive Key Points of the Photosynthetic Machinery of Coffea spp. to the Single and Superimposed Exposure to Severe Drought and Heat Stresses

“…Since g s was maintained at very low values, similar to those of SWD plants at 25/20°C, this additional P n reduction has been likely to be related to further non-stomatal impacts which lead P n to the minimal values observed over the entire experiment. In fact, severe drought may predispose the leaves to photoinhibitory damage given that a strong stomata closure will impose drastic restriction of CO 2 diffusion into the chloroplast, reducing photochemical energy use and promoting energy overcharge (Baker and Rosenqvist, 2004;Haworth et al, 2018), with the concurrent need to an increased thermal energy dissipation (Y (NPQ) ). However, it seems relevant that in some cases at 42/30°C, the SWD plants displayed better values (e.g.…”

“…Heat and drought stresses, which are major environmental constraints to plant growth and crop productivity, have been associated with decreases in both stomatal conductance ( g s ) and net CO 2 assimilation rates ( P n ) ( Long et al., 2006 ). These decreases predispose leaves to photoinhibitory damage due to decreased energy use through photosynthesis ( Baker and Rosenqvist, 2004 ; Lambers et al., 2008 ; Haworth et al., 2018 ), which can be exacerbated when these stresses are superimposed. As a consequence, growth and productivity of agricultural crops are depressed under these conditions to a greater extent than to each single applied stress ( Sehgal et al., 2017 ; Urban et al., 2018 ).…”

Lipid Peroxidation and Chlorophyll Fluorescence of Photosystem II Performance during Drought and Heat Stress is Associated with the Antioxidant Capacities of C3 Sunflower and C4 Maize Varieties

“…Analysis of the physiological mechanisms involved in crop responses to drought and heat stress may elucidate the photosynthetic and protective behaviors that underpin tolerance to these stresses. Chlorophyll fluorescence ( ChlF ) allows rapid non-destructive collection of data relating to the performance of photosystem II (PSII) [ 14 ] and is highly sensitive to the deleterious effects of drought [ 15 , 16 ] and heat [ 17 , 18 ] stress. To protect and stabilize the thylakoid membrane where PSII electron transport occurs, plants possess protective antioxidant mechanisms [ 19 , 20 ].…”

“…The thylakoid membranes are also vulnerable to heat stress [ 17 , 26 , 27 , 28 , 29 ]. Heat stress also induces a decrease in P N by reducing the affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) for CO 2 [ 30 ] and the activity of RubisCO activase [ 9 , 26 ], possibly reducing the capacity for photosystem I (PSI) to act as an electron receiver for PSII [ 16 , 31 ], thus impairing the use of energy for photochemistry through PSII [ 14 ]. As such, the thylakoid membranes are particularly sensitive to the effects of both drought and heat stress, and any disruption to the structure and function of the thylakoid membranes is evident in reductions in the efficiency of electron transport during PSII [ 17 , 26 , 32 ].…”

Crop Coefficients and Transpiration of a Super Intensive Arbequina Olive Orchard using the Dual Kc Approach and the Kcb Computation with the Fraction of Ground Cover and Height

“…Meanwhile, impacts of water deficit on olives growth and yield are relatively well known [6][7][8][9][10][11]. That knowledge about olives evapotranspiration and responses to water deficits is also essential to assess scenarios of climate change expected for the region, mainly referring to higher temperature during summer and less rainfall in winter and autumn [12,13].…”