Diurnal kinetics related to physiological parameters in Pistacia vera L. versus Pistacia atlantica Desf. under water stress conditions

Abstract

This study tests the diurnal variations of water status, leaf gas exchanges and chlorophyll fluorescence in Pistacia vera L. (P. vera L.) and Pistacia atlantica Desf. (P. atlantica Desf.) seedlings. At 40% of field capacity, diurnal variations in water uptake, relative water content (RWC) were estimated every hour between 5:00 am and 7:00 pm. The daily course of light, temperature, photosynthesis (A), stomatal conductance (gs), transpiration rate (E), intrinsic water use efficiency (A/gs), mesophyll efficiency (A/Ci), internal CO 2 concentration (Ci) and chlorophyll fluorescence were measured every 3 h from 05:30 am to 7:30 pm in irrigated and stressed seedlings of the two studied species. The results showed a significant variation in all surveyed parameters over diurnal cycle. The stressed seedlings of P. atlantica exhibited considerably higher RWC, water uptake, A, gs, E, A/gs and A/Ci over diurnal cycles compared to P. vera stressed seedlings. In contrast, P. vera was more sensitive to water stress and excess light and temperature over the diurnal cycle. The midday stomatal conductance and photosynthesis decrease was more likely the result of low RWC caused by high transpiration rates, stomatal closture and photoinhibition. Photoinhibition is a protective mechanism of PSII, rather than a result of photo-damage of photosynthetic apparatus. P. atlantica revealed an important physiological feature that is maintaining photosynthesis at midday compared to P. vera. This might be due to internal regulation through several mechanisms mainly better osmotic adjustment, photoprotective mechanisms of PSII.

Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

“…However, although much information is available on the midday depression of photosynthesis in rice plants (Oryza sativa L.) [11,27,28,66,67], there is limited information on wild aquatic plant species. This situation contrasts with the plentiful information on terrestrial plants in diverse habitats, including both woody species [30,31,37,42,43,54,55,58,61,[68][69][70] and herbs [39,56,60,71,72]. Previous studies on midday depression of emergent plants are equivocal.…”

“…Fourth, although the leaves of this emergent plant species exist in the air, the water temperature surrounding the roots may also affect whole-plant physiology [104]; however, the effect of water environment was not investigated in the present study. Finally, we only investigated one species from one climate; however, the stress responses and degree of photosynthetic limitation vary among different species [32,37,105,106], cultivars [30,31,35,64,107], and plants in different growth conditions [42,66]. Furthermore, even within a single site, causes of photosynthetic limitation change seasonally [9,13,42] and annually [70].…”

“…Photosynthesis of plants greatly affects global [1,2] and regional [3][4][5][6][7][8][9][10][11][12][13][14][15][16] carbon cycles. Since ecosystem-level photosynthesis is the sum of single-leaf photosynthesis [16][17][18][19][20][21][22], understanding of stress responses of leaves to diurnal and seasonal environmental change is necessary to improve ecosystem carbon cycles modeling [6,8,9,11,12,[23][24][25][26][27] and to increase agricultural [22,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] and forestry…”

“…Midday depression of photosynthesis is a phenomenon where photosynthetic rate decreases during the midday hours when light is not a limiting factor for photosynthesis [6,8,11,21,50,[54][55][56][57][58]. The degree of photosynthetic limitation is affected not only by the atmospheric environment surrounding leaves, but also by the soil water content and resultant whole-plant water status [21,31,32,37,38,[41][42][43]48,50,54,[59][60][61][62][63][64][65]. Thus, it is expected that plants in environments with different water availability will show different degrees of midday depression.…”