Alan N. Lakso

Effects of cluster light exposure on 3-isobutyl-2-methoxypyrazine accumulation and degradation patterns in red wine grapes ( Vitis vinifera L. Cv. Cabernet Franc).

The effects of light exposure on 3-isobutyl-2-methoxypyrazine (IBMP) accumulation and degradation in Vitis vinifera L. cv. Cabernet Franc berries were assessed by comparison of shaded and exposed clusters within the same vine throughout a growing season. Twenty-seven vines were shoot-thinned to create regions of high and low cluster-light exposure within each vine. Samples were collected at 10 time points starting from 5 to 130 days postbloom. The experimental design allowed for intravine comparison of IBMP levels between treatments at each time. Vine-to-vine variability of IBMP and the correlation of IBMP to malic acid were also evaluated. Cluster exposure reduced accumulation of IBMP at all preveraison time points by 21-44%, but did not increase postveraison degradation. Significant vine-to-vine variability in IBMP content was observed, with the highest level of IBMP in shaded berries in the most vigorous block of vines. Although IBMP concentration by weight decreased significantly due to dilution just prior to color change (veraison), no significant IBMP degradation per berry occurred until after color change (day 70 postbloom). By contrast, malic acid degradation began prior to color change, and malic acid concentrations were not affected by cluster exposure preveraison, but were affected postveraison. A survey of 13 sites in New York state (Seneca Lake) showed that IBMP concentrations at 2 weeks preveraison were highly correlated (R(2) = 0.936, p < 0.0001) to levels at harvest, whereas classic grape maturity indices at harvest were uncorrelated with IBMP at harvest. In summary, light exposure conditions critically influence IBMP accumulation but not IBMP degradation.

A comparison of ‘Empire’ apple fruit size and anatomy in unthinned and hand-thinned trees

SummaryA stereological method was developed to analyze the anatomical features of fresh ‘Empire’ apple fruit sectors cut in the transverse equatorial plane. Fruits were from unthinned trees or trees hand-thinned to one fruit per cluster at –7, 0, 10, 20 or 40 d after full bloom. At final harvest (140 DAFB), fruits representing the size range within each treatment were analyzed for the effects of thinning on fruit size, weight and cortex anatomy, namely, parenchyma cell size, cell number and the proportion of cortex volume occupied by intercellular space (IS). A dissecting stereobinocular microscope fitted with a ten-by-ten reticule was used to count cells and proportion of IS in three fields in each of two cortex sectors per fruit. Cell volume in each field was derived by knowing only the grid area, a point-count for proportion of IS and a count of cell numbers within the grid. Fruit size and weight decreased as thinning was prolonged and unthinned trees had the smallest fruit. Within a thinning treatment...

An expolinear model of the growth pattern of the apple fruit

SummaryThe expolinear growth model of Goudriaan and Monteith (1990) is proposed as a new model for the inherent growth pattern of fruit of apple (Malus domestica Borkh.), defined as growth pattern under apparently non–limiting conditions This function has three parameters: maximum relative growth rate, maximum absolute growth rate, and “lost time” (x intercept of the linear growth phase). Apple fruit growth (weight basis) at very low crop loads and apparently optimum environmental conditions, displays an early positive curvilinear growth followed by linear growth to harvest, and is described well by the expolinear function. The model also fits growth patterns of ‘Empire’ and ‘Golden Delicious’ apple fruit differing in the rate of growth in the exponential phase due to differences in the crop load. Estimates of cortical cell numbers in ‘Empire’ fruit from related studies suggest that during the linear phase in mid–season, different growth rates among crop load treatments were apparently controlled by diffe...

Summer pruning reduces whole-canopy carbon fixation and transpiration in apple trees

Summary Canopy size control is one of the major purposes of summer pruning. However, reducing canopy size might also result in less light interception, consequently decreasing canopy photosynthetic efficiency and carbohydrate production, which might lead to the imbalance of carbohydrate supply and fruit demand. To document the effectiveness of summer pruning on canopy control and the impact on canopy gas exchange, pruning treatments at four levels of intensity (unpruned, light, moderate, and severe) were carried out on mature ‘Empire’/M.9 slender spindle apple trees (Malus domestica Borkh.) on 30 July 1998 and 4 August 1999. Changes in canopy leaf area after summer pruning were estimated. Canopy net carbon exchange rate (NCER) and canopy transpiration before and after summer pruning were monitored. Canopy growth was suppressed by summer pruning and the post-pruning regrowth was insignificant. Canopy NCER was reduced in proportion to the amount of leaf area removed by summer pruning. The result suggests that commercial pruning intensity similar to the moderate to severe treatments in this study could cause a significant reduction in canopy NCER and carbohydrate production. In addition, canopy transpiration was reduced in proportion to pruning intensity. Lower water consumption and improved water status during the growing season after summer pruning might benefit fruit growth and relieve the potential detriment due to carbohydrate shortage.

Estimating nitrogen uptake of individual roots in container- and field-grown plants using a 15N-depletion approach

We only have a limited understanding of the nutrient uptake physiology of individual roots as they age. Despite this shortcoming, the importance of nutrient uptake processes to our understanding of plant nutrition and nutrient cycling cannot be underestimated. In this study, we used a 15N depletion method that allowed for the measurement of nitrate-N uptake rates on intact, individual, fine roots of known age. We expected that N uptake would decline rapidly as fine roots aged, regardless of the environmental conditions and species used. We compared age dependent uptake patterns of young grape cuttings with those of mature vines and with those of tomato. Although patterns of declining uptake with increasing root age were similar for all species and conditions tested, large differences in maximum N uptake rates existed between young cuttings and mature vines, and between woody and herbaceous species. Maximum rates were 10-fold higher for tomato and 3-fold higher for the grape cuttings, when compared with uptake rates of fine roots of mature vines. Coefficients of variation ranged from 43 to 122% within root age groups. The large variability in physiological characteristics of fine roots of the same age, diameter and order suggests that there is a functional diversity within fine roots that is still poorly understood.

Summer pruning effects on fruit size, fruit quality, return bloom and fine root survival in apple trees

Summary While many undesirable effects of summer pruning on apple (Malus domestica Borkh.) growth and development have been reported, the results are inconsistent and difficult to interpret. This study resolves the inconsistency by supplying a model that integrates pruning effects with tree physiological crop load, i.e. canopy net carbohydrate exchange rate per fruit. Our previous study suggests that the potential impact of reducing canopy photosynthesis after summer pruning depends on the balance of carbohydrate supply and demand. To test the hypothesis that summer pruning affects carbohydrate balance, we measured fruit growth, fruit quality, return bloom, and root growth in 20 year old slender spindle ‘Empire’/M.9 apple trees in response to different severities of summer pruning. Results were interpreted in relation to pruning severity, fruit number per tree, and the physiological crop load. Within commercial cropping ranges, light and moderate summer pruning had slight influences on fruit size and fresh weight. Summer pruning did not affect fruit colour, soluble solids content, starch, firmness, and internal breakdown after storage. Summer pruning alone did not affect return bloom or root growth. However, the potential negative effects of summer pruning on fruit growth, return bloom, and fine root survival can be predicted through their relationships with physiological crop load. This study suggests that the carbohydrate supply and demand balance model feasibly explains summer pruning influences. In addition, the impact of carbohydrate shortage after summer pruning is likely to be mediated by the reduction in canopy transpiration. However, the interaction between canopy carbon balance and water status after summer pruning is also likely to be manipulated by annual weather pattern.

Morphological and Physiological Adaptations for Maintaining Photosynthesis under Water Stress in Apple Trees

The apple tree has evolved several mechanisms, both morphological and physiological, to ameliorate the effects of water stress on photosynthesis. Drought escape or avoidance occurs by rapid leaf area development in the spring. Drought tolerance at high water potentials is accomplished by good water use efficiency through tight coupling of photosynthesis and stomatal conductance. Stomatal responses to humidity in field trees appears to be modified by the stomatal sensitivity to photosynthetic activity. In addition to stomatal behavior, the reduction in leaf area and the folding of exposed leaves reduce radiation interception and increase water use efficiency. Increases in the root hydraulic conductivity in response to evaporative demand also helps maintain high water potentials. Drought tolerance at low water potentials is mediated by marked osmotic adjustment in mature leaves although shoot tips show little osmotic adjustment. These mechanisms are effective primarily due to the slow physiological aging of apple leaves.

A microtensiometer capable of measuring water potentials below −10 MPa

Tensiometers sense the chemical potential of water (or water potential, Ψw) in an external phase of interest by measuring the pressure in an internal volume of liquid water in equilibrium with that phase. For sub-saturated phases, the internal pressure is below atmospheric and frequently negative; the liquid is under tension. Here, we present the initial characterization of a new tensiometer based on a microelectromechanical pressure sensor and a nanoporous membrane. We explain the mechanism of operation, fabrication, and calibration of this device. We show that these microtensiometers operate stably out to water potentials below -10 MPa, a tenfold extension of the range of current tensiometers. Finally, we present use of the device to perform an accurate measurement of the equation of state of liquid water at pressures down to -14 MPa. We conclude with a discussion of outstanding design considerations, and of the opportunities opened by the extended range of stability and the small form factor in sensing applications, and in fundamental studies of the thermodynamic properties of water.

Light responses of photosynthesis and transpiration of two tomato cultivars under ambient and altered CO2 and O2

Abstract Young plants of two tomato (Lycopersicon esculentum L.) cultivars, ‘Sonatine’ and ‘F6-IVT’, were examined for whole plant photosynthesis and transpiration in a closed gas-exchange system under different light levels and a combination of high or low oxygen (21 or 1%) and high or low carbon dioxide concentrations (1850 or 550 mg m−3). With saturating light, both cultivars showed approximately equivalent increases in photosynthesis in response to lowering the oxygen concentration, raising the carbon dioxide, or both. Under non-saturating light, ‘F6-IVT’ responded positively to lowered oxygen but CO2 had little effect. In ‘Sonatine’, changes in O2 as well as CO2 gave photosynthetic enhancement under low light. Stomates responded primarily to CO2 with little response to O2. As a result of the stomatal behavior to light, plant water-use efficiency in the short term peaked at moderate light levels, was enhanced by low O2, but was enhanced most by high CO2, regardless of O2 concentration.

The influence of water stress on grapevine (Vitis vinifera L.) shoots in a cool, humid climate: growth, gas exchange and hydraulics

Recent climatic trends of higher average temperatures and erratic precipitation patterns are resulting in decreased soil moisture availability and, consequently, periods of water stress. We studied the effects of seasonal water stress on grapevine (Vitis vinifera L. cv. Riesling grafted onto 101-14 (Vitis riparia Michx.×Vitis rupestris Scheele) rootstock) shoot growth, leaf gas exchange, xylem morphology and hydraulic performance in the cool-climate Finger Lakes region of New York. A plastic rain exclusion tarp was installed on the vineyard floor to create a soil moisture deficit and consequently induce vine water stress. Weekly measurements of predawn leaf and midday stem water potentials (Ψmd) were made, and two contrasting shoot length classes, long (length >2.0m) and short (length <1.0m), were monitored. Growth of both long and short shoots was positively correlated with Ψmd but no difference in water status was found between the two. Compared with rain-fed vines, water-stressed vines had lower photosynthesis and stomatal conductance later in the season when Ψmd dropped below -1.2MPa. Long shoots had three-fold higher xylem-specific hydraulic conductivity values than short shoots. Long shoots experiencing water stress were less vulnerable to xylem cavitation than shorter shoots even though they had more large-diameter vessels. The lower vulnerability to cavitation of long shoots may be attributed to less xylem intervessel pitting being found in long shoots, consistent with the air-seeding hypothesis, and suggests that a hydraulic advantage enables them to maintain superior growth and productivity under water stress.