Are Wild Blueberries a Crop with Low Photosynthetic Capacity? Chamber-Size Effects in Measuring Photosynthesis

Wild lowbush blueberries, an important fruit crop native to North America, contribute significantly to the economy of Maine, USA, Atlantic Canada, and Quebec. However, its photosynthetic capacity has not been well-quantified, with only a few studies showing its low photosynthetic rates. Its small leaves make accurate leaf-level photosynthetic measurements difficult and introduce potential uncertainties in using large leaf chambers. Here, we determined the photosynthetic rate for five different wild blueberry genotypes using a big leaf chamber enclosing multiple leaves and a small leaf chamber with a single leaf to test whether using big leaf chambers (branch-level measurements) underestimates the photosynthetic capacity. Photosynthetic rates of wild blueberries were significantly (35–47%) lower when using the big leaf chamber, and they are not a crop with low photosynthetic capacity, which can be as high as 16 μmol m−2 s−1. Additionally, wild blueberry leaves enclosed in the big chamber at different positions of a branch did not differ in chlorophyll content and photosynthetic rate, suggesting that the difference was not caused by variation among leaves but probably due to leaf orientations and self-shading in the big chamber. A significant linear relationship between the photosynthetic rate measured by the small and big leaf chambers suggests that the underestimation in leaf photosynthetic capacity could be corrected. Therefore, chamber-size effects need to be considered in quantifying photosynthetic capacity for small-leaf crops, and our study provided important guidelines for future photosynthesis research. We also established the relationship between the Electron Transport Rate (ETR) and photosynthetic CO2 assimilation for wild blueberries. ETR provides an alternative to quantify photosynthesis, but the correlation coefficient of the relationship (R2 = 0.65) suggests that caution is needed in this case.

Factors influencing the measurement of assimilation and stomatal conductance with the LI-COR 6400XT gas exchange system.

Although CO2 and H2O exchange rates are often measured in experiments as indicators of physiological plant responses these gas exchange measurements are prone to large experimental error. Gas exchange equipment and technology have improved greatly over the past two decades which supports scrutinizing current issues of experimental error in measuring plant photosynthesis and stomatal conductance. This report shows results of a greenhouse experiment with the goal of identifying lessor understood sources of experimental error and variation in measurements with the LI-COR 6400XT gas exchange system. A variety of plant types were used to encompass differing species variation. We found significant sources of experimental error in 1) the time for initial adjustment when placing a leaf in the leaf chamber 2) the time-of-day when measuring 3) leaf age 4) having the chamber window full vs. partially full with leaf tissue 5) using a leaf chamber environment that greatly diverges from the whole plant environment 6) differing degree of experimental error depending upon plant species. A situation with multiple contributors to error would result in useless gas-exchange data. Recommendations for minimizing these experimental errors are given.

New Guinea Impatiens Flower Life and Growth Response to Coal Bottom Ash Level in the Root Substrate

On 26 Mar. 1997, New Guinea impatiens (Impatiens × New Guinea) cultivars `Aglia', `Anaea', `Bora-bora', and `Dark Delias', were planted in 1 peat: 1 vermiculite (v/v) rooting media containing 0%, 25%, or 50% by volume of coal bottom ash (CBA) that had been sieved through 6-mm mesh. Individual flower longevity was recorded from the first day of flower opening until senescence. There was no significant effect among levels of CBA on flower longevity. However, flower life varied significantly among cultivars from 9.5–9.9 days in `Aglia' to 15.1–15.8 days in `Dark Delias'. Per-plant bloom numbers increased linearly with increase in percent CBA for all cultivars. Plant diameters were reduced by CBA in `Aglia', but not affected by CBA in the other three cultivars. Plant heights of `Dark Delias' were increased at 50% CBA over that of plants in 0% CBA. Visual quality indices were significantly greater for plants in CBA media compared to that for plants in 0% CBA. Top fresh and dry weights within each cultivar were equal among CBA levels. Within cultivars, there were no significant differences among plants at different CBA levels in plant transpiration rate, stomatal conductance, and net photosynthesis when measured with an LCA3 Leaf Chamber Analyser. However, there were significant differences in these processes among cultivars.

Contrasting Morphology and Ecophysiology of Cooccurring Broad and Terete Leaves in Hakea trifurcata (Proteaceae)

We studied the morphology, anatomy, phyllotaxy and daily seasonal ecophysiology of the two leaf types (broad and terete) of Hakea trifurcata (Smith) R.Br., a widespread shrub in south-western Australia. Both leaf types may be present on the same branchlet, with one or two broad leaves forming first during the annual growth period (late winter) followed by many terete leaves in spring. Terete leaves were more xeromorphic than broad leaves, including greater thickness, denser tissues and fewer veins. Broad leaves fixed more carbon and transpired more water per unit mass than terete leaves, in a well ventilated leaf chamber, and had lower (more negative) xylem pressure potentials. Broad leaf temperatures only exceeded those of terete leaves under hot, dry conditions, with no relationship between transpiration rates and leaf temperature. Terete leaves possessed many structural and physiological characteristics commonly associated with drought-tolerant leaves, whereas broad leaves were characteristic of leaves which keep their stomates open during periods of water and heat stress. Both leaf types appear to increase the fitness of this species in a mediterranean climate, with broad leaves having the potential to supply extra photosynthates and nutrients to the new season's growth.

RELATIONSHIP OF PHOTOSYNTHESIS MEASUREMENTS TO FRUIT SOLUBLE SOLIDS AND SPECIFIC LEAF WEIGHT IN APPLE AND GRAPE WITH VARIOUS MEASURING TECHNIQUES

Photosynthesis, light (PAR) and transpiration were measured with an ADC portable infrared gas analyzer on apples and grapes. Measurements were taken on north and south sides of the rows, in the morning and afternoon, on sun and shade leaves, and with the leaf chamber in a horizontal position and in a natural leaf orientation position. Measurements were made on three cloudless days in August 1990 and 1991. Subsequently, fruit adjacent to sampled leaves were harvested and soluble solids determined. Sampled leaves were then harvested and leaf areas and dry weights measured. Correlation coefficients of variables were then subjected to analysis of variance to determine which techniques gave the best correlations. Grapes and apples responded differently. For grapes, soluble solids were most closely correlated to light and photosynthesis measurements when measured on south side shade leaves, while with apples, blush side soluble solids were best correlated with measurements on south side sun leaves in the afternoon. Specific leaf weight was best correlated to photosynthesis and light with grapes when measured on north side sun leaves and with apples when measured on the south side in the morning.

Repeated Mechanical Stress from Leaf Cuvette Influences Leaf Gas Exchange

Long-term effects on stomatal conductance of mechanical stress from repeated clamping of a porometer leaf cuvette to laminae of avocado (Persea americana Miller), carambola (Averrhoa carambolu L.), hibiscus (Hibiscus rosa-sinensis L.), mango (Mangifera indica L.), and sugar apple (Annona squamosa L.) plants were determined under glasshouse conditions. Following 10 weeks of applying the mechanical stimulus seven times during every 4th day to mature leaves, stomatal conductance was lower than for untreated leaves of all species except mango. Similarly, following 10.5 weeks of applying the stimulus one time every 4th day to expanding leaves of avocado, carambola, hibiscus, and sugar apple, stomatal conductance was lower than for untreated leaves of the same age in all species except hibiscus. Carambola and sugar apple were more sensitive to the mechanical stress than the other species. Thus, the indirect effect of leaf chamber clamping on gas exchange should be known before any conclusions are formulated regarding environmental, cultural, or genetic effects on gas exchange. Random leaf samples from a canopy instead of measurements on a fixed set of leaves may be more appropriate for repeated determinations of leaf gas exchange on a set of plants.

GAS EXCHANGE CHARACTERISTICS OF FIELD-GROWN `SHAWNEE' BLACKBERRY

Gas exchange (assimilation, transpiration, water use efficiency, and conductance) of `Shawnee' blackberry were measured under field conditions with a portable system (ADC-IRGA with Parkinson Leaf Chamber). Gas exchange primocane pentifoliate leaflets were similar. Gas exchange rates of leaves along a cane exhibited a quadratic function of leaf position with leaves in lower-mid sections (relative position 0.3 - 0.5) having higher A, TR, WUE, gs than either basal or apical leaves. Leaves subtending fruiting laterals on fruiticanes had higher assimilation than similar age leaves on primocanes but did not differ in Tr, WUE, or gs. Primocanes had estimated dark respiration rates of 0.33mg·dm-1.hr-1, estimated light compensation at 14-20 mol.m-2.s-1, estimated light saturation at 1000-1100 mol.m-2.s-1 with maximum A rates ranging from 24-30 mg CO2.dm-1.hr-1. Measurements were made at field temperatures ranging from 24-35 C. Although temperature response was not measured, correlation indicated that Tr, WUE, and gs were more closely related to temperature than A. Similarly, Tr and WUE were more closely related to gs than A (r = 0.6 to 0.8).