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sw ) of excised and nonexcised strawberry ( Fragaria ×ananassa ‘Camino Real’) leaves. Solid vertical line indicates the time (90 s postinitiation of leaf gas exchange measurements) when the petiole of the excised leaf was cut. The mean separation was
the dynamics of seasonal WUE. The whole canopy gas exchange studies were conducted in July and August because shoot expansion had essentially ceased for the growing season and leaf collection in the fall would be an accurate measurement of leaf area to
Approach-grafted 1-year-old `Gala'/M7 apple trees were grown with both tops for the remainder of the 2003 season in a greenhouse. Trees were supplied with >100% (control, PRD100) or 50% (PRD50, DI50) of daily ETc either applied to one root compartment only (PRD100, PRD50) or divided evenly across both root compartments (control and DI50). ETc was estimated from gravimetric measurements, and irrigation was switched between wet and dry root compartments several times throughout the experiment. Soil moisture was measured both gravimetrically (tripod) and volumetrically (time-domain reflectometry). Predawn leaf water potential (Ï…pd) and single leaf gas exchange (photosynthesis, stomatal conductance, and transpiration) were recorded daily, and sap flow in stems and roots was monitored continuously using the heat-pulse technique. Leaves were collected for abscisic acid (ABA) determination following gas exchange measurements. Regardless of irrigation placement (i.e., PRD or DI), both 50% ETc treatments experienced similar declines in Ï…pd and single leaf gas exchange relative to control levels. In addition, ABA concentrations were similar for PRD50 and DI50, and were significantly higher than the control and PRD100 treatments. PRD100 trees had similar Ï…pd as control trees; however, gas exchange was reduced >25% compared to the control. Bulk leaf ABA concentration did not differ significantly from control levels and does not by itself explain the down regulation of stomata with PRD100.
Abstract
Estimates of photosynthetic rates are obtained routinely in many plants using a number of techniques (1-3). Until recently, however, accurate field estimates of net CO2 exchange have been difficult to obtain, partially because of the limited mobility of the apparatus and the time involved in data collection (4-6). LI-COR, Inc. (Lincoln, Neb.) has developed an integral infrared gas analyzer system (IRGA), which is incorporated in their LI-6000 series of commercially available portable instruments (7). This system consists of a battery powered nondispersive IRGA, a porometer, an RS-232C serial communications interface, and a dedicated datalogger with battery-powered nonvolatile memory. This unit automatically stores measurements of CO2 concentration, chamber relative humidity, chamber temperature, leaf temperature, photosynthetically active radiation, time, and optional operator-supplied comments. Time required for a single measurement is between 30 to 180 sec, with various types of leaf chambers spanning a range of volumes between 250 and 3900 ml (7).
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.
Recent droughts and depleted water tables across many regions have elevated the necessity to irrigate field-grown (FG) nursery trees. At the same time, ordinances restricting nursery irrigation volume (often without regard to plant water requirements) have been implemented. This research investigated gas exchange and growth of two FG maple tree species (Acer × freemanii `Autumn Blaze' and A. truncatum) subjected to three reference evapotranspiration (ETo) irrigation regimes (100%, 60%, and 30% of ETo) in a semi-arid climate. During Spring 2002, nine containerized (11.3 L) trees of each species were field planted in a randomized block design. Each year trees were irrigated through a drip irrigation system. During the first growing season, all trees were irrigated at 100% ETo. Irrigation treatments began Spring of 2003. Gas exchange data (pre-dawn leaf water potential and midday stomatal conductance) were collected during the 2003 and 2004 growing seasons and growth data (shoot elongation, caliper increase, and leaf area) were collected at the end of each growing season. For each species, yearly data indicates irrigation regime influenced gas exchange and growth of these FG trees. However, it is interesting to note gas exchange and growth of these FG maple trees were not necessarily associated with trees receiving the high irrigation treatment. In addition, it appears the influence of irrigation volume on the growth of these FG trees is plant structure and species specific. Our data suggests irrigation of FG trees based upon local ETo measurements and soil surface root area may be a means to conserve irrigation water and produce FG trees with adequate growth. However, continued research on the influence of reduced irrigation on FG tree species is needed.
Five- to six-year-old `Redblush' grapefruit (Citrus paradisi Macf.) trees on `Volkamer' lemon [VL = C. volkameriana (Ten. & Pasq.)] or sour orange (SO = C. aurantium L.) rootstock, were grown individually in 7.9-m3 lysimeters for 2.5 years using low to high rates of fertilizer N. Net CO2 assimilation (ACO2) of leaves and leaf dry mass per area (DM/a) increased with leaf N concentration, whereas leaf tissue C isotope discrimination (Δ) decreased. Leaf tissue Δ was negatively related to ACO2 and DM/a. Transient effects of rootstock on leaf N were reflected by similar effects on Δ. There was no effect of leaf N on water-use efficiency (WUE) of leaves (WUEL = ACO2/transpiration); WUEL was not correlated with Δ. Although photosynthetic N use efficiency (ACO2/N) consistently decreased with increased leaf N, Δ was not consistently related to ACO2/N. Annual canopy growth, tree evapotranspiration (ET), and fruit yield increased with whole tree N uptake. Leaf tissue Δ was negatively related to all of these tree measurements at the end of the second year. By that time, whole-tree WUE (WUET, annual canopy growth per ET) also was negatively related to Δ. Larger trees on VL had higher ET than trees on SO, but there were no rootstock effects on WUET or on Δ. Leaf tissue Δ was consistently higher than Δ values of trunk and woody root tissues. Citrus leaf tissue Δ can be a useful indicator of leaf N, characteristics of leaf gas exchange, tree growth, yield, and WUET in response to N availability.
physiological (drought) stress ( Glenn et al., 2001 ). From ‘Ginger Gold’ [ Malus × sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] leaf gas exchange measurements made in the 2004 season as part of a preliminary study, it appeared that greater rates of
removed to stimulate vegetative growth. In the following season, one fruit-bearing shoot per plant was allowed to grow. The third leaf from the shoot base was used for gas-exchange and leaf-area measurements. The same leaf from individual plants was
. Pecanha, A.L. de Assis, F.A.M.M. de Sousa, E.F. Glenn, D.M. Campostrini, E. 2016 Comparison between single-leaf and whole-canopy gas exchange measurements in papaya ( Carica papaya L.) plants Scientia Hort. 209 73 78 doi: 10.1016/j.scienta.2016.06.014 10