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Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.

Net photosynthetic rate, radiation use efficiency, chlorophyll (Chl) fluorescence, photochemical reflectance index (PRI), and leaf water potential were measured during a 25-<1 period of progressive water deficit in quinoa plants grown in a glasshouse in order to examine effects of water stress and ontogeny. All physiological parameters except Fv/F m were sensitive to water stress. Ontogenic variations did not exist in Fv/F m and leaf water potential, and were moderate to high in the other parameters. The complete recovery of photosynthetic parameters after re-irrigation was related with the stability in FyIF m . PRI showed significant correlation with predawn leaf water potential, Fm', and midday FyIF m . Thus PRI and Chl fluorescence may help in assessing physiological changes in quinoa plants across different developmental stages and water status.

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Abstract. A model for the distribution of radiation incident on leaves in an isolated apple tree is presented. The simulated area of shadow cast by a tree compared well with measured values. The radiation model is combined with leaf models of photosynthesis and stomatal behaviour to simulate diurnal variations in the exchanges of carbon dioxide and water by the tree. Satisfactory correspondence was obtained when observed rates of transpiration and photosynthesis were compared with simulations. Further simulations indicated the diurnal patterns of transpiration and photosynthesis to be expected for trees with various shapes and leaf areas.

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