Photosynthetic Efficiency and Yield of Cucumber (Cucumis sativus L.) Grown under HPS and LED Lighting in Autumn-Winter Cultivation

The objective of this study was to evaluate the effect of the supplemental lighting of cucumber with sodium pressure lamps (HPSs) and light-emitting diodes (LEDs) on photosynthetic efficiency and yield in autumn-winter cultivation. Cucumber plants of the 'Svyatogor' F1 midi-cucumber parthenocarpic type cultivar were grown on mineral wool mats in three compartments, differing only in the type of light, i.e., (1) HPS top lighting (HPS) in the first compartment, (2) HPS top lighting and LED panel interlighting (HPS + LED) in the second compartment and (3) LED top lighting and inter-row LED panels (LED) in the third compartment. The photosynthetically active radiation was the same in each compartment. The study showed that the highest commercial yields of cucumber could be achieved under LED light (top and inter-row). The chlorophyll content in the leaf blade of younger leaves was higher in plants under LED lighting. This type of lighting also had a positive effect on the gas exchange of plants (net carbon assimilation, stomatal conductance, transpiration). LED and HPS + LED lighting increased the chlorophyll a fluorescence parameters, such as Fs, Fm' and vitality index (PI), in both younger and older leaves, which also increased the fruit yield in the tested combinations.

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon-juniper woodland

Plant hydraulic conductance (k_s) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine (Pinus edulis) and juniper (Juniperus monosperma) woodland. We examined the relationship between k_s and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (E_C) and conductance (G_C). For both species, we observed significant reductions in plant transpiration (E) and k_s under experimentally imposed drought. Conversely, supplemental water additions increased E and k_s in both species. Interestingly, both species exhibited similar declines in k_s under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant k_s also reduced carbon assimilation in both species, as leaf-level stomatal conductance (g_s) and net photosynthesis (A_n) declined strongly with decreasing k_s. Finally, we observed that chronically low whole-plant k_s was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy E_C and G_C. Our data indicate that significant reductions in k_s precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.