Photosynthetic characteristics of highbush blueberry (Vaccinium corymbosum cv. Bluecrop) leaves in response to water stress and subsequent re-irrigation

Abstract

SUMMARYGas exchange and photosystem II (PSII) activities in the leaves of 2-year-old ‘Bluecrop’ highbush blueberry (Vaccinium corymbosum) were monitored during water stress and subsequent re-irrigation to investigate the effects of the intensity of water stress on changes in photosynthetic characteristics. The blueberry shrubs were not irrigated for 3 to 5 weeks, then re-irrigated daily up to 8 weeks. The decrease in soil water potential during water stress caused a progressive decrease in leaf water potential. Soil water potentials decreased to -0.26 MPa and -0.34 MPa at 3 and 5 weeks, respectively, following water stress, but recovered following subsequent re-irrigation, while the soil water potential in daily-irrigated shrubs was maintained at over -0.13 MPa throughout the experiment. Chlorophyll concentrations decreased with an increasing duration of water stress. Chlorophyll concentrations in leaves on shrubs subjected to water stress for 5 weeks did not recover following re-irrigation, unlike those subjected to water stress for 3 weeks. The leaves on shrubs subjected to water stress for 5 weeks maintained lower levels of chlorophyll during reirrigation. The net rate of CO2 assimilation (An) decreased significantly with an increasing duration of water stress. Reirrigation reversed the decrease in An in leaves on shrubs subjected to water stress for 3 weeks. Stomatal conductance (gs) exhibited a similar pattern to An. The actual quantum yield of photosystem II (ΦPSII) and the electron transport rate (ETR) also decreased significantly with an increasing duration of water stress, although the Fv/Fm ratio was not affected. ΦPPSII and ETR values in the leaves on shrubs subjected to water stress for 5 weeks did not recover after reirrigation, unlike those subjected to water stress for 3 weeks. Non-photochemical quenching increased with an increasing duration of water stress, but subsequent re-irrigation did not reverse the increase. These results indicate that the timing of re-irrigation of water-stressed ‘Bluecrop’ highbush blueberry is critical in order to maintain their photosynthetic capacity. Among the photosynthetic characteristics measured, ΦPSII and ETR could be used as sensitive indicators to assess the physiological status of leaves of ‘Bluecrop’ highbush blueberry growing under water stress conditions.