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  • Author or Editor: Richard C. Beeson Jr. x
  • Journal of the American Society for Horticultural Science x
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Abstract

Needle starch metabolism was studied during graft development of Colorado blue spruce (Picea pungens Englemann ‘Hoopsi’) scions on Norway spruce [Picea abies (L.) Karst] rootstocks. Starch accumulated during the initial stages of union formation, but the rate of accumulation slowed over time. Peak starch content in developing greenhouse grafts was ≈30% and, in lath house grafts, ≈50% of that in 3-year-old grafts forced in the greenhouse. Prior to budbreak, starch content declined rapidly, stabilizing at pre-grafting levels during shoot elongation. Grafts with misaligned unions accumulated starch during the first week, but the starch content then declined. Preventing photosynthesis in scions during union formation prevented starch accumulation, but did not affect graft success or subsequent scion growth. We concluded that neither starch accumulation nor current photosynthesis in the scion were required during union development.

Open Access

Abstract

The study evaluated the roles of storage carbohydrates and neutral lipids in the success of Colorado blue spruce (Picea pungens Englemann ‘Hoopsi’) grafts. These scions do not require photosynthesis nor receive photosynthates from the rootstock during union development. Carbohydrate and neutral lipid contents, along with respiration and scion water relations, were measured during union development. Stored carbon compounds were sufficient to supply the needs of the scion during the 9 weeks of union development. Estimates of carbohydrate use indicated that decreases in sugar content (bark and needle) were insufficient to account for more than 25% of the estimated respiration. The results indicate that the quantity of carbon storage compounds is not a factor in graft success. We propose that neutral lipids may be the major carbon reserve of the scion during graft formation.

Open Access

Lycopersicon esculentum Mill. cv. Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO2 concentrations (330 or 900 μmol·m-3) for 10 weeks. The elevated CO2 concentration increased the relative growth rate (RGR) of L. esculentum and L. chmielewskii by 18% and 30%, respectively, after 2 weeks of treatment. This increase was not maintained as the plant matured. Net assimilation rate (NAR) and specific leaf weight (SLW) were always higher in C02-enriched plants, suggesting that assimilates were preferentially accumulated in the leaves as reserves rather than contributing to leaf expansion. Carbon dioxide enrichment increased early and total yields of L. esculentum by 80% and 22%, respectively. Carbon exchange rates (CER) increased during the first few weeks, but thereafter decreased as tomato plants acclimated to high atmospheric CO2. The relatively constant concentration of internal C0 with time suggests that reduced stomatal conductance under high CO2 does not explain lower photosynthetic rates of tomato plants grown under high atmospheric CO2 concentrations. Leaves 5 and 9 responded equally to high CO2 enrichment throughout plant growth. Consequently, acclimation of CO2-enriched plants was not entirely due to the age of the tissue. After 10 weeks of treatment, leaf 5, which had been exposed to high CO2 for only 10 days, showed the greatest acclimation of the experiment. We conclude that the duration of exposure of the whole plant to elevated CO2 concentration, rather than the age of the tissue, governs the acclimation to high CO2 concentrations.

Free access

Bud outgrowth dynamics and their implications for shoot architecture were examined in japanese privet (Ligustrum japonicum) plants under well-irrigated [short irrigation cycle (SC)] and water-limitation [long irrigation cycle (LC)] conditions. New buds had limited sensitivity to dormancy, whereas preformed buds required more than one growing season to outgrow naturally. The first spring flush of shoot growth was mostly the result of lateral bud outgrowth, whereas latter flushes had prominent contributions of new apex buds. First flush terminal stems had mainly determinate growth (episodic). First flush lateral stems had increased occurrence of indeterminate growth (continuous). Water limitation influenced shoot architecture by enhancing apical dominance. Lateral branching was diminished 51% in LC plants compared with SC plants. As plants adapted to the stress imposed, indeterminate growth was triggered more often in meristematic regions of terminal buds of LC plants. In shoot flushes that occurred later in the stress treatment, old buds burst more frequently than the newly formed apex lateral buds. Plants under SC were more compact and better formed as an inverse triangle, whereas plants under LC had considerably less new branches and instead had long branches that would require pruning to maintain aesthetically pleasing shapes.

Free access