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Abstract
An inexpensive, well-stirred chamber for measuring net fluxes of CO2 and H2O vapor from single leaves was constructed from readily available materials. It incorporates a fan that maximizes air turbulence and boundary-layer conductance. Leaf temperature can be maintained within ± 0.5°C of air temperature. Temperatures can be varied for experimental purposes or can be maintained constant even under varying heat loads using a temperature-controlled water circulator. When used in conjunction with such a circulator and CO2 and H2O vapor analyzers, this chamber can become an inexpensive yet useful component of a gas-exchange system.
Abstract
The purpose of this study was to evaluate seasonal changes in the free proline content of citrus roots, leaves, fruit peel, and juice in response to low-temperature and water stress. Nonirrigated trees generally had higher proline in all tissues than did irrigated trees except immediately after a freeze. At this time, nonirrigated trees were less water-stressed because of the greater amount of freeze-induced defoliation that nonirrigated trees had sustained. Using data from an entire year, proline concentration was not correlated with water stress of leaves or fruit. This lack of correlation probably was due to the interacting effects of water stress and low temperature on proline accumulation. Leaves accumulated proline in response to stress before roots and fruit. These data support the idea that the free proline increases first in the leaves in response to stress and subsequently is transported to other tree tissues. Even though proline content in the juice increased with fruit maturity, proline may not be a good indicator of juice quality since it did not always correspond with Brix:acid ratio and fruit in the most exposed canopy positions tended to have the highest proline content.
Abstract
‘Duncan’ grapefruit (C. paradisi Macf.) and ‘Pineapple’ sweet orange (Citrus sinensis L.) seedlings were grown in full sunlight, 50% and 90% shade; maximum photosynthetic photon flux densities (PPFD) of 2300, 1100 and 200 μmol s−1m−2, respectively. In fully expanded matured (hardened) leaves, leaf thickness, specific leaf weight (SLW), tissue density, and nitrogen content were highest in full sun leaves and lowest in 90% shade leaves. Leaf chlorophyll content was highest in 90% shade leaves. Half of the seedlings which were grown in full sunlight were transferred into 50% shade to simulate normal canopy development; half of the seedlings from 50% and 90% shade were moved into full sunlight to simulate changes that occur after hedging. Specific leaf weight and tissue density changed in the same direction as PPFD. Leaf nitrogen content decreased temporarily when leaves were exposed to new PPFD conditions regardless of the PPFD levels. Total leaf chlorophyll content initially decreased when seedlings were transferred into full sunlight but began to increase after 4–6 weeks. Chlorophyll content increased in seedlings transferred from full sun to 50% shade. Percentage of air space within leaf tissues did not change during acclimation to new PPFD levels. Changes in leaf anatomy, physical characteristics, and chemical components are mechanisms that enable citrus leaves to acclimate to a wide range of changing light environments, even after leaves are fully mature.