Leaf senescence is characterized by programmed degradation of cellular constituents such as proteins, nucleic acids, and lipids, together with organelles and structures of leaf cell, resulting in a significant photosynthetic decline. Photosynthesis
exchange and chlorophyll fluorescence parameters were measured using a portable photosynthesis system (LI-6400 XT, LI-COR, Inc., Lincoln, NE). The P n , T r , g S , and intercellular CO 2 concentration ( C i ) were measured on the upper, third fully
The impact of environmental factors on the photosynthetic potential of tree fruits is largely uncontrollable, but one can affect photo synthetic efficiency through the manipulation of various cultural practices. Application of pesticides and other chemicals; tree size and shape; mineral nutrition; and pest damage are all important factors and should be carefully considered in maximizing net photosynthesis (Pn) and ultimate tree performance.
Light perception in plants is critical to their survival because light regulates three important processes: skotomorphogenesis, photomorphogenesis, and photosynthesis. At ground level the composition of sunlight is ≈3% ultraviolet, 44% visible (380
·ha −1 in 2014) ( APCQ, 2015 ). A decline in photosynthesis is one of the first physiological responses to soil waterlogging ( Liao and Lin, 2001 ). Poor aeration in the root zone generally leads to a reduction in root cellular respiration and
rates of all ABA treatments were ≥90% of controls. Fig. 2. The effect of abscisic acid rate on photosynthesis ( P n ) of ‘Bartlett’ pear leaves in Expt. 3 ( A ) and Expt. 2 ( B ). Measurements were taken at solar noon (±1 h). Data are means of four
. Photosynthesis is one of the most important and sensitive metabolic processes in plants. The BDE-47 treatments significantly affected not only the light reaction process but also the carbon assimilation ability of Chinese cabbage leaves. The chlorophyll
The relationships of net photosynthesis (Pn) to soil water potential, leaf diffusive resistance, leaf water potential, and relative water content were studied with hybrid geranium (Pelargonium × hortorum Bailey cv Sprinter Scarlet) grown under conditions of greenhouse pot culture. Net photosynthesis went through 4 stages according to the effects of water stress on the plants. As water stress increased, Pn went from a steady-state maxiumum rate to slow decline, to rapid decline, to total inhibition. During rapid Pn decline, soil water potential rapidly decreased from −4 bars to −14 bars, and leaf diffusive resistance increased from 4 s cm−1 to 80s cm−1. Leaf water potential was −7 bars, and relative leaf water content was 81–87%. Leaf water potential appeared to be the best indicator of imminent Pn decline. After rewatering water-stressed plants, 3 days were required to elevate Pn to a steady-state maximum which was only 90% of initial steady-state Pn.
Photosynthesis and transpiration rates of seedlings of 4 citrus rootstocks under flooded conditions were measured over a 10-day period. For all rootstocks photosynthesis and transpiration decreased, but photosynthesis decreased relatively less than transpiration. Stomatal closure is inferred to account in part for the reductions observed.
Flooding did not increase ethanol concentration in either tops or roots, suggesting that ethanol is not an end-product of. anaerobic respiration in citrus seedlings. Only in the neutral soil was rough lemon (Citrus limon L. Burm. f.) found to be more tolerant to short-term flooding than ‘Cleopatra’ mandarin (Citrus reticulata Blanco) and trifoliate orange (Poncirus trifoliata L. Raf.). Tolerance to flood injury was greater at a soil pH of 7 than 4.5.
Simulated pest injury to expanding or fully expanded apple leaves (Malus domestica Borkh. ‘McIntosh’) by midrib cutting, lamina pricking, or heat injury from ironing reduced net photosynthesis (Pn). Only cutting of the basal half of the midrib of fully expanded leaves reduced transpiration (Tr). Application of gibberellic acid (GA3), and particularly of 6 benzylamino purine (BA), to lamina lesions damaged by pricking, stimulated Pn. This Pn compensation of injured apple leaves mediated by phytohormones may overcome otherwise damaging levels of some pests.