Fritz Lenz

Effects of NaCl or nutrient-induced salinity on growth, yield, and composition of eggplants grown in rockwool

The effects of increasing the salt concentration of a basic nutrient solution from 2.1 up to 4.7 dS m ˇ1 by providing either additional amounts of nutrients or 25 mmol l ˇ1 NaCl on growth, yield, fruit quality and mineral composition of eggplants were investigated. The extra nutrients used to raise the electrical conductivity were added either at the same ionic concentration ratio as in the basic nutrient solution or at an increased ratio of K to total cation concentration. The vegetative growth and the number of flowers per plant were not influenced by any of the salinity treatments. In contrast, the fresh fruit yield of eggplant was significantly reduced to the same extent in all salinity treatments. The yield depression was a result of a decline in mean fruit weight, whereas the number of fruits per plant was not affected. However, recalculation of the data on dry weight basis revealed no significant differences between the treatments. The percentage of eggplant fruits graded Class 1 was significantly reduced at 4.7 dS m ˇ1 , whilst the kind of salts used to induce salinity had no significant effect on fruit quality. The increase of electrical conductivity up to 4.7 dS m ˇ1 by the addition of extra nutrients did not result in a higher nutrient uptake, with the exception of P in roots, and P and organic N in the petioles of older leaves. In contrast, the concentrations of Mg and NO3‐N were reduced in some plant parts when salinity was increased by the addition of extra nutrients, regardless of the proportions of cations in the nutrient solution. All salinity treatments reduced the concentration of Mg in the leaves to the same degree, thus indicating that this salt effect is not ion specific. # 2000 Elsevier Science B.V. All rights reserved.

Responses of strawberry leaf photosynthesis, chlorophyll fluorescence and macronutrient contents to elevated CO2

Summary Gas exchange, chlorophyll fluorescence parameters, and macronutrient contents were investigated in young ( 2 . An increase of the CO 2 level to 600 ppm promoted leaf net photosynthesis, but a further rise led to a decrease of net CO 2 assimilation. The reduction of net photosynthetic rate was less distinct in young leaves exposed to CO 2 levels above 600 ppm for less than 3 weeks, indicating that the reduction might depend on the period of exposition or leaf age. Transpiration and stomatal conductance were significandy affected by leaf age, but not by CO 2 concentrations. Medium leaves were characterised by a higher transpiration rate and stomatal conductance than young and old ones. In leaves growing at high CO 2 levels Chl a and b contents as well as the a/b ratio decreased. The contents of N, P, K, Ca and Mg were lower in leaves growing at high CO 2 concentrations than in those at low ones. An elevated CO 2 level above 750 ppm led to a general macronutrient deficiency and was accompanied by a distinct decrease of optimal quantum yield, due to a rise of basal fluorescence, and an increase of non-photochemical energy dissipation in old leaves.

Effect of fruiting on carbon budgets of apple tree canopies

SummaryCarbon budgets were calculated from net photosynthesis and dark respiration measurements for canopies of field-grown, 3-year-old apple trees (Malus domestica Borkh.) with maximum leaf areas of 5.4 m2 in a temperature-controlled Perspex tree chamber, measured in situ over 2 years (July 1988 to October 1990) by computerized infrared gas analysis using a dedicated interface and software. Net photosynthesis (Pn) and carbon assimilation per leaf area peaked at respectively 8.3 and 7.7 μmol CO2 m−2 s−1 in April. Net photosynthesis (Pn) and dark respiration (Rd) per tree peaked at 3.6 g CO2 tree−1 h−1 (Pn) and 1.2 g CO2 tree−1 h−1 (Rd), equivalent to 4.2 μmol CO2 (Pn) and 1.4 μmol CO2 (Rd) m−2 s−1 with maximum carbon gain per tree in August and maximum dark respiration per tree in October 1988 and 1989. In May 1990, a tree was deblossomed. Pn (per tree) of the fruiting apple tree canopy exceeded that of the non-fruiting tree by 2–2.5 fold from June to August 1990, attributed to reduced photorespiration (RI), and resulting in a 2-fold carbon gain of the fruiting over the non-fruiting tree. Dark respiration of the fruiting tree canopy progressively exceeded, with increasing sink strength of the fruit, by 51% (June–August), 1.4-fold (September) and 2-fold (October) that of the non-fruiting tree due to leaf (i. e. not fruit) respiration to provide energy (a) to produce and maintain the fruit on the tree and (b) thereafter to facilitate the later carbohydrate translocation into the woody perennial parts of the tree. The fruiting tree reached its optium carbon budget 2–4 weeks earlier (August) then the non-fruiting tree (September 1990). In the winter, the trunk respired 2–100 g CO2 month−1 tree−1. These data represent the first long-term examination of the effect of fruiting without fruit removal which shows increased dark respiration and with the increase progressing as the fruit developed.

Surfactant-induced phytotoxicity: evidence for interaction with epicuticular wax fine structure

Abstract Phytotoxicity of two homologous series of non-ionic surfactants [octylphenoxy polyethoxyethanol (OP), α-[4-(1,1,3,3-tetramethylbutyl) phenyl]-ω-hydroxypoly-(oxy-1,2-ethanediyl) and nonylphenoxy polyethoxyethanol (NP), α-(nonylphenol)-ω-hydroxypoly-(oxy-1,2-ethanediyl)], of varying oxyethylene (EO) chain length was studied in Brassica oleracea var. gongylodes (L.). Surfactant toxicity following foliar application was determined by visual rating of leaf damage and measurement of ethylene production. Surfactants of medium EO chain length (9.5 and 10 EO) were most phytotoxic; phytotoxicity decreased with decrease to 5 EO or increase to 30 EO. No difference in phytotoxicity was found between OP and NP surfactants. Ethylene production 12 h after application increased with increasing surfactant concentration (0.01–1% w/v) and was greater for droplets of 1.0 μl than for those of 0.5 μl. Regardless of droplet size and surfactant concentration, application of OP+9.5EO enhanced ethylene production more than OP+5EO. After disruption of epicuticular wax fine structure or removal of epicuticular wax, ethylene production following OP+5EO application was significantly greater than that with OP+9.5EO. In Hordeum vulgare (L.), Triticum aestivum (L.) and Vicia faba (L.), OP+5EO induced highest ethylene production, whereas in Brassica napus var. napus (L.) and Brassica oleracea var. gemmifera (DC.) OP+9.5EO was most phytotoxic. Surfactant phytotoxicity is discussed in relation to wetting characteristics of microrough leaf surfaces of Brassica species.

Response of eggplants grown in recirculating nutrient solution to salinity imposed prior to the start of harvesting

Summary The effects of exposing eggplants grown in recirculating nutrient solution to salt stress (6.1 dS m–1) from planting until the beginning of harvesting, on plant growth, yield and macronutrient status was investigated. The salinity was imposed by adding to a basic nutrient solution either additional nutrients at two cation ratios or NaCl. The results showed that the exposure of plants to salinity prior to the beginning of harvesting reduced both vegetative growth during that time and early fruit yield, but the depression of the latter was more severe. The restriction of the early yield was a result of a reduced mean fruit weight due to a lower fruit water content. The detrimental effects of salinity on the mean fruit weight disappeared 25 d after discontinuing the salinity treatments. As a result, the total yield obtained after five months of harvesting was not influenced by exposing the plants to salinity prior to the beginning of harvesting. The salinity source had no specific effect on plant growth. Moreover, the increase of salinity up to 6.1 dS m–1 did not cause any specific nutritional imbalance or toxicity to the plants, irrespective of the salts used to achieve it. It is suggested that the electrical conductivity of the nutrient solution may be raised to 6.1 dS m–1 to control excessive vegetative growth in eggplants grown hydroponically. However, salt treatment should be terminated either at the first harvest, if the total yield is more important than the early yield, or three weeks earlier, if the opposite is true.

Respiration of apple trees between leaf fall and leaf emergence

Abstract Respiratory CO2 loss of apple (Malus domestica Borkh.) was measured in situ, using tree chambers and computerized infrared gas analysis with a dedicated interface and software, over two years, from November 1988 to March 1990 in which the first autumn/winter period was relatively cold and the second period was relatively warm. In the first, the colder winter of the study, respiration of a three-year-old apple tree declined from 60–120 mg CO2 tree−1 hr−1 after leaf fall in November to minimum values of 30–50 mg CO2 hr−1 (0.2–0.3 μmol CO2 s−1) in December/January. In the second, the warmer winter of the study, the then four-year-old apple tree with still attached leaves assimilated 1500 mg CO2 hr−1 during daytime in November, with dark respiration of 500 mg CO2 hr−1, attributed to translocation of carbohydrates into the woody perennial parts of the tree later in the year in the warmer autumn. With daytime CO2 assimilation exceeding dark respiration, the leaves of the apple tree still gained carbon in the warmer November, while the tree lost carbon in the colder November. Associated with the date of leaf fall, the switch from net photosynthesis to net respiration during the day occurred earlier in the colder winter (November) than in the warmer winter (mid-December), a time when the tree lost excessive carbon. Minimum respiration values exceeded 50 mg CO2 hr−1 tree−1 in the warmer December/January compared to 30 mg CO2 hr−1 tree−1 in the colder December/January. Minimum carbon losses were encountered in December (colder winter) or January (warmer winter), with date and minimum values depending on ambient temperature. After leaf fall, the temperature response of the trunk plus branches gave an averaged Q10 of 2.55 (5°C/15°C). These data represent the first comprehensive carbon balances of apple trees in situ between leaf fall and leaf emergence.

Diurnal CO2 fluctuations in an apple orchard

Abstract Diurnal CO 2 fluctuations were recorded in an apple orchard at Bonn, Germany. The CO 2 concentration was measured continuously for 24-hr periods with a portable, battery-driven infrared gas analyzer with combined datalogger at 0.60, 1.20 and 1.80 m heights within an apple tree canopy and 1.50 m above the grass between tree rows. Measurements were conducted on typical sunny or cloudy days during the vegetation period in 1992. The largest diurnal variations on sunny summer days were ca 300 ppm CO 2 , i.e. between 328 and 632 ppm CO 2 . On these days, CO 2 concentrations declined to 328 ppm in the afternoon between 1400 and 1600 hr and reached a maximum of either 466 ppm during warm or 632 ppm during hot nights between 200 and 400 hr in the lower part of the apple tree canopy 0.60 m above ground. The low afternoon CO 2 concentrations in the canopy may be a result of tree photosynthesis during the day, whereas the large CO 2 concentrations were attributed to lack of wind or turbulence and considerable dark respiration of the apple trees and grass and soil as dependent on night temperature. On cloudy and overcast summer days, in contrast, the CO 2 concentrations during the day remained constant around 340–350 ppm CO 2 with a slight increase to 370–380 ppm CO 2 during the night.

Sink-Source Relationships in Fruit Trees

Investigations of the effects of fruit (mainly citrus) on growth, flower formation, water consumption, nutrient uptake, photosynthesis, and respiration of plants are reviewed. The main emphasis is on photosynthetic efficiency of leaves as affected and perhaps regulated by fruit.

Utilization of bicarbonate by apple fruit Phosphoenolpyruvate carboxylase

Abstract Phosphoenolpyruvate carboxylase (PEPC), was partially purified from apple fruit cv Golden Delicious. Kinetic values for PEP and HCO − 3 suggest a capacity for efficient carbon dioxide refixation. PEPC activity was maximal between 5–10 mM carbonate (HCO − 3 ) and inhibition was observed above 10 mM HCO − 3 . In conditions of PEP-saturation, HCO − 3 inhibition of apple fruit PEPC activity appeared non-competitive with respect to PEP and was partially reversible.