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Abstract

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.

Open Access

Abstract

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.

Open Access

Abstract

Although upper limitations on photosynthesis by apple trees are imposed by the structure and biochemistry of the leaf, an apple tree has a considerable potential for the fixation of carbon. Within these limits it is important to determine factors that prevent attainment of the tree’s full biological productivity. This review describes our present knowledge of some of these factors, both environmental and internal, that determine the actual biological productivity of the apple tree.

Open Access

Abstract

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.

Open Access

Dibutylurea (DBU), a breakdown product of benomyl, may be partially responsible for the previously reported phytotoxicity of the fungicide Benlate DF. We quantified the effect of DBU on the growth of two popular bedding plant species, petunia (Petunia × hybrida) and impatiens (Impatiens wallerana Hook. f.). DBU reduced photosynthesis of both species, and its effect strongly depended on the amount of DBU applied. The effects of DBU were most apparent 2 to 4 days after treatment, at which time 1.20 g·m-2 (corresponding to 10% DBU in Benlate DF at maximum labeled drench rate) inhibited photosynthesis completely. DBU also decreased flower number and caused marginal necrosis. DBU effects were more pronounced in low relative humidity. Benlate DF containing 3.1% DBU and an equivalent amount of reagent grade DBU had similar effects on photosynthesis and petunia necrosis. Our results showed that DBU is responsible for at least part of the phytotoxic symptoms that can be caused by Benlate DF. However, other ingredients or breakdown products may also contribute to the phytotoxic symptoms of Benlate DF.

Free access

measured 15 weeks after the N application in each year. Gas exchange measurements were conducted between 1100 and 1300 hr from two fully expanded leaves. Gas exchange measurements were determined using a portable photosynthesis system (LI-6400XT; LI

Free access

net photosynthesis (Pn) were achieved at a higher frequency of kaolin particle film application and that this was particularly the case at leaf temperatures exceeding 35 °C ( Privé et al., 2007 ). Ultraviolet damage and photoinhibition can be additive

Free access

Field experiments with 15 sweet potato [Ipomoea batatas L. (Lam.)] genotypes were conducted to study the physiological basis of yield in 1981 and 1982. The leaf area index differed significantly among the sweet potato genotypes during early and late phases of growth, hut showed an inconsistent relationship with yield. Single leaf net photosynthesis ranged from 0.74 to 1.12 mg CO2/m' per sec. Canopy photosynthesis for sweet potato genotypes differed significantly in 1981, but not in 1982. It ranged from 0.81 to 1.16 mg CO2/m2 per sec in Aug. 1981. and from 0.63 to 0.88 mg CO2/m2 per sec in 1982. Four hours after “C-labeling, 14C-assimilate translocation from the treated leaf ranged from 21% to 46%, but did not differ significantly among the genotypes. At final harvest, harvest index [HI, defined as (storage root yield/total biological yield) × 100] of the genotypes varied from 43% to 77% and 31% to 75% for 1981 and 1982, respectively. Canopy photosynthesis during September was significantly correlated with storage root dry matter yield (r = 0.54*) in 1981 and with phytomass (above-ground biomass plus storage roots) (r = 0.60*) in 1982. Both phytomass and HI were significantly correlated with storage root matter yield. Canopy photosynthetic evaluation of sweet potato germplasm may be-more relevant when the storage root sinks are at an advanced stage of development. Our study suggests that yield is poorly predicted by Pn, particularly when the genotypes have different leaf sizes.

Free access

Abstract

Field experiments were conducted during 1979 and 1980 growing seasons with sweet potato [Ipomoea batatas (L.) Lam.] genotypes at different stages of growth to determine leaf net photosynthetic rates (Pn) and photosynthate partitioning patterns. Net photosynthesis was measured in an open system with an infrared analyzer on the youngest and the fully expanded leaves still attached to the plant. Photosynthesis rates differed significantly in both years. Photosynthesis varied from 19.1 to 32.4 mg CO2dm−2hr−1 in 1979 and from 25.8 to 36.9 mg CO2dm−1hr−1 in 1980. A new selection, 75-96-1, averaged highest both years. Percentages of photosynthate partitioning to storage roots also differed significantly. About 45 days after planting, ‘Centennial’ and ‘Georgia Jet’ diverted the highest percentage, about 28%, of the total dry matter to the storage roots. But ‘Georgia Red’ diverted the highest percentages of photosynthate (51.0 and 56.4) to the storage roots 75 and 90 days after planting, respectively. Photosynthate partitioning to storage roots ranged from 11.2 to 56.4%, 90 days after planting. Final root yield correlated significantly (r = 0.69 to 0.87) with photosynthate partitioning at all stages of growth. During 1980, Pn and total dry matter yield also were significantly correlated. Harvest index was significantly correlated (r = 0.89) with final storage root yield. But Pn did not significantly correlate with either storage root yield or photosynthate partitioned to roots. Stomatal density was 2 to 3 times more on the abaxial than the adaxial surface of the leaves. Percentages of neither leaf nitrogen nor chlorophyll content of leaves differed significantly. High-yielding genotypes generally initiated storage root formation earlier and also partitioned more photosynthate to storage roots than low-yielding genotypes.

Open Access

Abstract

One of the most important aspects of designing an experiment is determining sample size. Without prior experience, estimation of the amount of variation that will be encountered during data collection is difficult. This information is necessary to decide the number of replicates needed. Recently, Marini (1985) and Marini and Trout (1984) have published reports on the sample size needed to determine treatment effects in peach tree growth and yield studies. However, this type of information is lacking for sample sizes required to detect differences in net photosynthesis in peach. This note attempts to assist researchers in determining correct sample size.

Open Access