Michael M. Blanke

Soil respiration in an apple orchard

Abstract To investigate why the largest CO2 concentration occurred before sunrise at 0.6 m below an apple tree canopy, seasonal and diurnal fluctuations in soil and grass respiration were recorded in an apple orchard near Bonn, Germany between May 1994 and April 1995 with a portable, battery-driven infrared gas analyser and a soil respiration chamber. Respiration from soil on raised nursery beds with fresh organic matter was compared with herbicide treated, flat soil in tree rows and the grass between the rows to study the contribution of soil and grass respiration to the CO2 balance of a fruit orchard. The following results were found. 1. 1. Soil and grass respiration ranged from 0.18 to 24 μmol CO2 m2− s−1. 2. 2. On cold winter days, with soil temperatures below 0°C, soil and grass respiration during the day remained below 0.6 μmol CO2 m−2 s−1 and had the smallest diurnal variation. 3. 3. The largest diurnal variations were in late spring with diurnal temperature differences of 15°C, resulting in respiratory values between 3 in the morning and 5–8 μmol CO2 m−2 s−1 in the afternoon. 4. 4. Soil and grass respiration (up to 40 kg CO2 ha−1 hr−1) exceeded the CO2 exchange of the apple trees per unit surface area, contributed significantly to the CO2 flux in a fruit orchard, and were a pertinent source of CO2 for tree photosynthesis. 5. 5. The temperature coefficient, Q10, ranged from 4 below 0°C, to 2.3 above 0°C, 1.7 above 10°C and 1.3 above 20°C.

A comprehensive overview of the spatial and temporal variability of apple bud dormancy release and blooming phenology in Western Europe

In the current context of global warming, an analysis is required of spatially-extensive and long-term blooming data in fruit trees to make up for insufficient information on regional-scale blooming changes and determinisms that are key to the phenological adaptation of these species. We therefore analysed blooming dates over long periods at climate-contrasted sites in Western Europe, focusing mainly on the Golden Delicious apple that is grown worldwide. On average, blooming advances were more pronounced in northern continental (10 days) than in western oceanic (6–7 days) regions, while the shortest advance was found on the Mediterranean coastline. Temporal trends toward blooming phase shortenings were also observed in continental regions. These regional differences in temporal variability across Western Europe resulted in a decrease in spatial variability, i.e. shorter time intervals between blooming dates in contrasted regions (8–10-day decrease for full bloom between Mediterranean and continental regions). Fitted sequential models were used to reproduce phenological changes. Marked trends toward shorter simulated durations of forcing period (bud growth from dormancy release to blooming) and high positive correlations between these durations and observed blooming dates support the notion that blooming advances and shortenings are mainly due to faster satisfaction of the heating requirement. However, trends toward later dormancy releases were also noted in oceanic and Mediterranean regions. This could tend toward blooming delays and explain the shorter advances in these regions despite similar or greater warming. The regional differences in simulated chilling and forcing periods were consistent with the regional differences in temperature increases.

Effects of flooding and drought on stomatal activity, transpiration, photosynthesis, water potential and water channel activity in strawberry stolons and leaves

Transpiration, xylem water potential and water channel activity were studied in developing stolons and leaves of strawberry (Fragaria × ananassa Duch.) subjected to drought or flooding, together with morphological studies of their stomata and other surface structures. Stolons had 0.12 stomata mm−2 and a transpiration rate of 0.6 mmol H2O m−2 s−1, while the leaves had 300 stomata mm−2 and a transpiration rate of 5.6 mmol H2O m−2 s−1. Midday water potentials of stolons were always less negative than in leaves enabling nutrient ion and water transport via or to the strawberry stolons. Drought stress, but not flooding, decreased stolon and leaf water potential from −0.7 to −1 MPa and from −1 to −2 MPa, respectively, with a concomitant reduction in stomatal conductance from 75 to 30 mmol H2O m−2 s−1. However, leaf water potentials remained unchanged after flooding. Similarly, membrane vesicles derived from stolons of flooded strawberry plants showed no change in water channel activity. In these stolons, turgor may be preserved by maintaining root pressure, an electrochemical and ion gradient and xylem differentiation, assuming water channels remain open. By contrast, water channel activity was reduced in stolons of drought stressed strawberry plants. In every case, the effect of flooding on water relations of strawberry stolons and leaves was less pronounced than that of drought which cannot be explained by increased ABA. Stomatal closure under drought could be attributed to increased delivery of ABA from roots to the leaves. However, stomata closed more rapidly in leaves of flooded strawberry despite ABA delivery from the roots in the xylem to the leaves being strongly depressed. This stomatal closure under flooding may be due to release of stress ethylene. In the relative absence of stomata from the stolons, cellular (apoplastic) water transport in strawberry stolons was primarily driven by water channel activity with a gradient from the tip of the stolon to the base, concomitant with xylem differentiation and decreased water transport potential from the stolon tip to its base. Reduced water potential in the stolons under drought are discussed with respect to reduced putative water channel activity.

Stomatal Activity of the Grape Berry cv. Riesling, Müller-Thurgau and Ehrenfelser

Summary Developing grape berries of the cvs. Riesling, Muller-Thurgau and Ehrenfelser were grown in the greenhouse and examined by SEM, using fresh specimens without prior fixation. Stomata were observed from anthesis onwards and were situated on top of a rectangular or conal peristomatal protuberance, four weeks after full bloom, which may be characteristic for the grape berry. The stomatal frequency of cv. Riesling and Ehrenfelser exceeded that of cv. Muller- Thurgau by about 50%, but was small relative to their respective leaves. Transpiration was measured in the laboratory using whole bunches of grape berries still attached to the vine. The stomatal activity of the grape berry was demonstrated and decreased with fruit ontogeny. It is concluded that the transpiration rate does not reflect the ratio of stomatal frequency between tissues at all stages of fruit ontogeny, and the proportion of the cuticular transpiration is greater on the berry than on the leaf and increases with fruit development.

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.

Coloured hailnets alter light transmission, spectra and phytochrome, as well as vegetative growth, leaf chlorophyll and photosynthesis and reduce flower induction of apple

In view of alleged positive effects of coloured (red) hailnets on phytochrome, photosynthesis, yield and fruit quality, the objective of the present work was to investigate a range of red and green hailnets using apple as a model crop with cvs. ‘Pinova’ and ‘Fuji Kiku 8’. Light transmission of green or red hailnets peaked between 500 and 570 nm (green) or above 570 nm (red–orange) and was reduced by 12% (white) or 14% (red–white), 18% (red–black) and 23% (green–black) hailnets; there were no effects on phytochrome. Leaf chlorophyll concentration increased under coloured hailnets by up to 46% under the green–black hailnet, while air temperature was reduced by 0.2°C. Under sunny conditions, photosynthesis of ca. 18 μmol CO2 m−2 s−1 was not reduced under coloured hailnets, in contrast with a 21% reduction under cloudy conditions with a concomitant reduction in transpiration by 13%. Vegetative growth was affected in different ways: shaded trees showed smaller trunk diameter, but increased the number and length of their 1-year shoots under coloured hailnets, particularly with cv. ‘Fuji’ when grown under green–black hailnet. Hailnets reduced flower induction in June and return bloom in the next spring to the same extent as they reduced the light transmission. Overall, tree growth under coloured hailnets was genetically influenced, with cv. ‘Fuji’ being more prone and sensitive to adverse effects of coloured hailnets than cv. ‘Pinova’, but is also influenced by the environment.

Bioenergetics, Respiration Cost and Water Relations ofDeveloping Avocado Fruit

Summary Avocado fruit of cultivars with different susceptibility to physiological fruit disorders were examinedin situ for respiration, stomatal conductance, transpiration and xylem water potential. Therein, attached fruit of cv. Fuerte (susceptible to mesocarp discolouration) were compared with Hass (susceptible to small fruit) over the 3-month period from anthesis until the fruit reached 60 g fresh matter: o 1. Avocado fruit respired more CO2 in the dark than in the light due to fruit photosynthesis. Respirationrates decreased with fruit ontogeny from 14.5 to 1.5 μmol CO2 m−2 s−1 and increased from 1 to 4.5 μmol CO2 fruit−1 h−1, reflecting the higher energy requirement of the avocado relative to other fruits and of cv. Hass relative to Fuerte fruit. 2. Fruit respiration accumulated to 4.8 g (Fuerte) or 5.1 g (Hass) CO2 (= 63 or 66kJoule), with growthrespiration (Fuerte) of 0.324 kg CO2 (7.35 MJ) kg−1 dry matter twice as large as found in fruits of other species and maintenance respiration of 1.98 kg CO2 or 26MJ kg−1 dry matter. 3. Stomatal conductance decreased from 0.17 mmol m−2s−1 at pre-anthesis to 0.01 mmol m−2s−1 at 60gfruit weight. 4. Fruit of cv. Hass transpired more water than those of Fuerte, i.e. 0.2 to 1 mmol H2O m−2 s−1 or 0.2 to2 mmol H2O fruict−1 day−1. 5. A 60-g fruit accumulated 51 mL water and transpired 155 mL or 171 mL H2O, resulting in a waterconsumption of 206 mL (Fuerte) or 222 mL (Hass) water with a fruit water use efficiency (FWUE), i.e. mol CO2 respired per mol water transpired, of 9.5 × 10−3. 6. Midday fruit water potentials ranged between −0.4 to −0.9MPa with values obtained for cv. Fuertefruit exceeding those of the respective leaf. These results present the first data on energy requirement, maintenance and growth respiration, transpiration,water use and water potential of developing avocado fruit, which are discussed with respect to physiological fruit disorders.

Structure and elemental compositon of grape berry stomata

Summary Former SEM work without cryotechnique of the fruit surface had shown grape (Vitis vinifera L.) berry stomata surrounded by large, conspicuous protuberant tissue. This led to speculation of artifacts resulting from microscopic preparation techniques. This work examined the existance of these alleged protuberances and a possibly distinguished tissue by low temperature scanning electron microsopy (LT-SEM), freezesectioning, energy dispersive X-ray analysis, and light microscopy with staining. LT-SEM showed that peristomatal protuberances of up to 200 Jlm diameter developed two weeks after anthesis in all four grape cultivars examined and consisted of small, compact cells of 10 to 15Jlm length. These cells were distinctly different from the typically larger cells (30-40 Jlm) in the epidermis, hypodermis and outer fruit pericarp. Energy dispersive X-ray analysis revealed no differences in the distribution of sulphur, chlorine and iron between the peristomatal protuberance and non-protuberant tissue. Although potassium concentrations in the peristomatal protuberance were low, silicon and calcium were abundant in marked contrast to the non-protuberant tissue. During the later stages of fruit development, polyphenolics accumulate preferentially in the protuberant tissues and these specialised structures become heavily suberised.

Bioenergetics, maintenance respiration and transpiration of pepper fruits

Summary Structure and function of chile pepper Capsicum annuum var. annuum L. fruit tissues were examined by SEM, GC and porometry. Stomata were absent from the inner (endocarp) and outer (exocarp) epidermis of mature chile pepper fruits of cvs. Serrano, Jalapeno, Hungarian Wax, Anaheim and MexiBell. Fruit transpiration of 0.4 to 2.4 mmol H2O m−2 s−1 was hence attributed solely to cuticular transpiration. Chlorophyll contents of mature fruits ranged from 4.1 μg/g to 76 μg/g fresh weight with chlorophyll a:b ratios of 1.68:1 to 2.35:1. Locular space volumes and CO2 concentrations ranged respectively from 22% to 52% (v/v) and from 0.6 to 2.1% CO2 with concomitant locular oxygen concentrations from 18.4 to 20.6% O2 and RQ of between 0.89 to 1.81. Immature seeds and placenta were the primary sources of accumulated CO2, while respiration of the endocarp was comparatively low. The large maintenance respiration from 0.81 to 2 mg CO2 [g dwt day]−1 and 0.54 to 1.3 mg glucose [g dwt day]−1 provided 0.05 to 1.3 kJoule fruit−1 h−1 for biochemical conversions.

Stomatal and cuticular transpiration of the cap and berry of grape

Summary Pictorial evidence is given of the existence and developmental stage of stomata in the grape cap and young grape berry; transpiration measurements in dark/light showed the stomata to be functional. In cv. Muller-Thurgau, the number of stomata varied with development of the inflorescence, with 24–30 per cap or 8–10 stomata per berry. Based on the same diameter of the cap and berry at particular developmental stages, from two weeks before to two weeks after petalfall, and commensurate appearance of stomata in these tissues, transpiration per berry was greater than transpiration per cap. This discrepancy was attributed to different proportions of cuticular or stomatal transpiration. These proportions were estimated by two methods, either relating the transpiration of the tissue to the number of stomata or by assuming the transpiration in the dark to be equal to cuticular transpiration. The two methods gave good agreement. The cuticular transpiration of the grape berry as estimated by the two methods accounted for either 87 % or 81 % respectively of the overall transpiration in the light one week after petalfall.