Abstract
The rate and efficiency of photosynthesis (PS) is unquestionably one of the primary determinants of crop yield. Yet, as this symposium illustrates, many other factors contribute to plant productivity. Indeed, the exact relationship between PS rate and yield remains undefined. For several years we have now been interested in factors that affect PS rate in both C3 and C4 plants, not only within the plant, but also external to it. Internal factors affecting PS that will be discussed include leaf age, leaf canopy, photorespiration, stage of plant development (including both vegetative and reproductive phases), and the occurrence of little-recognized metabolic pathways such as polyol synthesis and transport. External factors that affect PS, in addition to obvious environmental determinants such as temperature, light, and water, include the seasonal growth cycle. While we still do not understand how all of these factors interact to affect yield, we are beginning to understand their singular effects. Control of these factors, once thought to be within reach even before the advent of biotechnology, remains likely, but distant.
. Contradictory results have been reported for NAR. Heraut-Bron et al. (1999) demonstrated that the R:FR did not affect photosynthesis per unit leaf area of white clover ( Trifolium repens L.). However, other reports demonstrated that low-R:FR light reduces the
Cranberry [Vaccinium macrocarpon (Ait.)] yield has been associated with photosynthate supply. However, the impact of temperature and radiation on photosynthesis of the cranberry plant is not well understood. The objective of this experiment was to characterize the photosynthetic response to radiation and temperature in order to develop a model for estimation of cranberry photosynthetic rates. Two cranberry cultivars, `Stevens' and `Ben Lear', were tested for photosynthetic response at air temperatures ranging from 15 to 35 °C and radiation intensities from 200 to 1200 μmol·m-2·s-1. Depending on temperature, maximum photosynthesis (Pmax) was ≈10 or 12 μmol CO2/m2/s (net photosynthesis) and the saturating radiation level was estimated to be 600 to 800 μmol·m-2·s-1. Cranberry quantum yield was estimated as 0.03 mol CO2/mol photon. Both models; Blackman and the nonrectangular hyperbola with a Θ (angle of curvature) of 0.99 were a good fit for measured photosynthetic rates under controlled environment conditions. The disparity between modeled predicted values, and observed values in the field around midday, indicates a reduction in potential photosynthetic rates in a diurnal cycle that is consistent with the phenomenon of midday depression.
chitosan as a soil amendment might also result from its direct effect on plant nutrient status and metabolism, and photosynthesis. Soil-applied chitosan increased the content of nitrogen, phosphorus, potassium, total sugars, and soluble proteins as well as
declines rapidly with small changes in substrate water content ( da Silva et al., 1993 ), making it more difficult for plants to extract water when Θ is low in the substrate. Photosynthesis is central to crop growth and highly sensitive to drought stress
. Leaf gas exchange was measured on 2 Oct. 2009, 1 Oct. 2010, and 5 Nov. 2010. Because ‘Western’ kernel fill continues through October in New Mexico, the early November photosynthesis measurement date was included in 2010 to ensure that we captured the
data and SPAD readings were recorded, and the leaflet had to be located in the middle canopy of the tree. The same leaflet was used for both P n and SPAD. Leaf P n was measured using the LI-COR 6400XT portable photosynthesis system (LI-COR Inc
chamber. Because it is assumed that only one side of the cladode is sunlit, the photosynthesis values referred to half the lateral area, in accordance with the methodology used for Asparagus officinalis ( Guo et al., 2002 ). Spear photosynthesis was
( Connor et al., 1993 ), sink assimilate demand ( Frageria, 1992 ), and availability of water as well as light and nutrients. Photosynthesis is also affected by different stress factors ( Taiz and Zeiger, 2006 ). The capacity of the plant’s photosynthetic
., 2016 ). Silicon is also considered to be a beneficial element for plants ( Epstein and Bloom, 2005 ), and some argue that it is essential ( Ma, 2004 ). Whether essential or not, Si enhances water and solute transport, improves photosynthesis rates, and