English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Percent instantaneous incident photosynthetic photon flux density (%INPPFD) was measured within an apple (Malus domestica Borkh.) canopy for various sky conditions and used to predict the percent cumulative incident photosynthetic photon density (PPD) for the last 10 weeks of the growing season (%CPPD LS) and the total growing season (%CPPDTS). Instantaneous measurements from overcast conditions were superior to measurements from clear or hazy conditions for the prediction of %CPPD LS in 1989 and 1990. A one-to-one relationship between %INPPFD and %CPPDLS was found for overcast conditions in both years, even though there was an 11% difference in total cumulative PPD between the years. The models had good predictive accuracy, with prediction coefficients of deter- mination (R 2 Pred ) >0.83 in both years (n = 30). %lNPPFD from overcast conditions also yielded accurate predictive models for %CPPDTS (R 2 Pred > 0.84, n = 30), which differed from the models for %CPPD LS. Predictive models (for both %CPPDLS and %CPPDTS) from %lNPPFD made before the canopy was fully developed differed from the models developed after canopy development was complete. The models still had good predictive accuracy, with R 2 Pred >0.76 (n = 30). Predictive models developed for cloudless conditions had inferior predictive accuracy (R 2 Pred = 0.49 to 0.80, n = 30) compared to models for overcast conditions. R 2 Pred were higher for hazy than for clear conditions. Time of day (1000 to 1400 HR) had no consistent effect on the development of predictive models for any weather condition. The most reliable models resulted from the average of several measurements within a day, particularly for cloudless conditions. Many instruments and measurement techniques have been used to characterize the light environment of plant communities and individual tree canopies (Anderson, 1964a; Jackson, 1980). The introduction of the quantum sensor allowed for the rela- tively quick and simple selective measurement of the photosyn- thetically active waveband 400 to 700 nm, expressed as a photosynthetic photon flux density (PPFD). Instantaneous mea- surements with quantum sensors (and other instruments) have been used extensively for light environment studies within apple tree canopies and have been related to spur, leaf, and fruit qual- ity characteristics within the canopy (Barritt et al., 1987; Marini and Barden, 1982; Marini and Marini, 1983; Morgan et al., 1984; Patten and Proebsting, 1986). Instantaneous light mea- surements, often based on only a few measurements during the season, have been used to represent total seasonal (cumulative) light levels. The validity of instantaneous measurements as es- timates of total cumulative light levels has been questioned due to the complicated nature of canopy/light interactions, such as weather variations, proportions of direct and diffuse light, sun- flecks, spectral changes, and the timing of measurements (An- derson, 1964a; Monselise, 1951). For the measurement of PPFD, Grappadelli and Coston (1988) described the construction of an inexpensive silicon photocell sensor that had a similar measurement response to commercially produced quantum sensors. Combined with a datalogger, these sensors provide an affordable method of measuring the total cumulative photosynthetic photon density (PPD) impinging on

Instantaneous Light Measurements Predict Relative Cumulative Light Levels within an Apple Canopy