Red and Blue Netting Alters Leaf Morphological and Physiological Characteristics in Apple Trees.

Richard M Bastías,Pasquale Losciale,Camilla Chieco,Luca Corelli-Grappadelli

doi:10.3390/plants10010127

Abstract

There is little information about the role of red and blue light on leaf morphology and physiology in fruit trees, and more studies have been developed in herbaceous plants grown under controlled light conditions. The objective of this research was to evaluate the effect of red and blue screens on morpho-anatomy and gas exchange in apple leaves grown under ambient sunlight conditions. Apple trees cv. Fuji were covered by 40% red and blue nets, leaving trees with 20% white net as control. Light relations (photosynthetic photon flux density, PPFD; red to far-red light ratio, R/FR and blue to red light ratio, B/R), morpho-anatomical features of the leaf (palisade to spongy mesophyll ratio, P/S, and stomata density, SD) and leaf gas exchange (net photosynthesis rate, An; stomatal conductance, gs; transpiration rate, E; and intrinsic water use efficiency, IWUE) were evaluated. Red and blue nets reduced 27% PPFD, reducing by 20% SD and 25% P/S compared to control, but without negative effects on An and gs. Blue net increased gs 21%, leading to the highest E and lowest IWUE by increment of B/R light proportion. These findings demonstrate the potential use of red and blue nets for differential modulation of apple leaf gas exchange through sunlight management under field conditions.

Highlights

Netting is a cultural practice in apple orchards to ensure sustainable fruit production and quality
These results demonstrate that the lowest leaf mass area (LMA) found under blue net was mainly due to decreases in thickness of palisade tissue and increases in the air space of mesophyll, which are normal adaptive responses of leaves grown under shading conditions to allow a better light transmission towards the chloroplasts [25]
The differences in leaf chlorophyll content between colored nets cannot be explained by changes in light intensity because the leaves grown under red and blue nets received the same quantity of photosynthetic photon flux density (PPFD) (Figure 1A)

Summary

Introduction

Netting is a cultural practice in apple orchards to ensure sustainable fruit production and quality. Covering apple trees with nets alters orchard microclimate, with changes in the incoming solar radiation, air temperature, relative humidity, wind speed and soil moisture with ensuing effects on physiological plant and fruit responses [3,6]. The use of photo-selective colored nets demonstrates the interest in modifying the solar light quality conditions to promote desired plant physiological responses, improving the yield and fruit quality in different horticultural crops [7]. Colored nets have been tested under field conditions with different effects on productivity and fruit quality traits, depending on the net color and fruit crops. In ‘Fuji’ apple, blue and gray nets increased significantly fruit growth compared to red net [11], while fruit quality traits such as color, sweetness, hardness and fruit peel antioxidant content were affected by colored nets [12,13]

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