Phenotypic Markers Reflecting the Status of Overstressed Tea Plants Subjected to Repeated Shade Cultivation

Abstract

Shade cultivation is a traditional Japanese tea cultivation method in which the shoot buds are shaded for several weeks. This technique is increasingly used for green tea production because it produces tea of high quality (as indicated by umami and nutritional content) and commands high prices. However, given that shaded tea plants are grown under low-light stress, concerns exist regarding damage to tea plants caused by repeated shade cultivation. To understand basic physiological responses and accumulative changes in photosynthetic ability and metabolites of tea plants subjected to repeated shading, we performed a pot experiment on immature tea plants grown in a growth chamber subjected to repeated shading treatments. The results demonstrated that shade cultivation caused a decrease in non-structural carbohydrate content and an increase of several degrees in leaf surface temperature, reflecting transpiration through the leaf stomata, as a result of a reduction in photosynthetic ability. An increase of several degrees in canopy temperature and a reduction in photosynthetic ability in the field in the midsummer season was also observed in overstressed tea plants subjected to repeated shading. Metabolomic analysis identified several candidate biomarkers, such as citrulline and glycine betaine, that were significantly changed in individuals affected by shade cultivation. These physiological changes may be an indicator of the stress status of tea plants grown under repeated shade cultivation.

Mechanism Underlying the Shading-Induced Chlorophyll Accumulation in Tea Leaves

“…During tea plant cultivation, providing plants with sufficient shade can significantly improve tea color quality. To produce Japanese matcha, tea plants are often shaded by 60–98% for 10–30 days ( Yamashita et al, 2020 ). The chlorophyll content of tea leaves increases significantly after shading treatment.…”

“…Previous studies revealed that significant increases in the chlorophyll content of fresh leaves due to shading are unaffected by leaf age, shading season, and number of shading treatments but are related to the duration and degree of shading ( Lee et al, 2013 ; Sano et al, 2018 ; Yamashita et al, 2020 ). Using an electron microscope, Liu observed that shading induces the development of tea leaf plastids, leading to an increase in the number of chloroplasts and in thylakoid compactness ( Liu et al, 2020 ).…”

Impacts of Ecological Shading by Roadside Trees on Tea Foliar Nutritional and Bioactive Components, Community Diversity of Insects and Soil Microbes in Tea Plantation

“…Ecological shading by roadside trees is a special shading method in tea plantations, and here, for the first time, we investigated the influence of roadside tree ecological shading on the soluble nutrients and bioactive compounds, population occurrence of key pests, and the community diversity of insects and microbes. Shade management in tea plantations is a general approach for augmenting the quality-related metabolite contents in pre-harvest tea [ 23 , 33 ]. However, prolonged shading may result in a decreased tea biomass, which in turn affects the synthesis of quality indices and is considered non-conducive to tea production [ 23 , 34 ].…”

“…Tea, Camellia sinensis (L.), an evergreen perennial subtropical plant that prefers shade and can withstand humidity, is one of China’s most important cash crops. Shading immediately after the emergence of new shoots can improve the quality of the tea [ 23 ]. It has been reported that shading treatment in two consecutive production periods reduced the yield of late-emerging tea leaf buds and that timely removal of shading stress could reverse the yield reduction [ 24 , 25 ].…”

HPLC–MS2 Analysis of Chlorophylls in Green Teas Establishes Differences among Varieties

“…As photosynthesis is the process that sustains photosynthetic organisms, light is the most important factor influencing plant growth and productivity. For that reason, plants have developed a high capacity to adapt their metabolisms to changes in light intensity [ 16 ]. One of these adaptations consists not only in an increase of the total amount of chlorophyll molecules, but also in rearrangements of the photosynthetic apparatus through the interconversion of chlorophyll a to chlorophyll b through the “chlorophyll cycle” ( Figure 1 ).…”