Effects of light intensity and quality on needle physiological and biochemical traits of eighteen-year-old Pinus koraiensis trees adapted long-period to real field environment

Abstract

Abstract Regeneration of Korean pine (Pinus koraiensis) has been mostly fraught with failure and light is considered primarily the cause. Considerable experiments concerning it were using seedlings or shaded by black nets or both and thus with conflicting results. Here we investigated the effects of light conditions on eighteen-year-old Korean pines that have been long-period adapted to the under-canopy environment in the field. Photosynthetic pigments, chlorophyll a fluorescence, non-structural carbohydrate metabolism, antioxidant enzyme activity and nutrient concentrations of current-year needles under four light regimes (three understory, one full light, classified by light intensity and quality) were measured. From June to September, light intensity and quality decreased under full light, but understory light conditions got a little better after leaf fall. Photosynthetic pigments content decreased as the light improved, but Car/Chl was the highest in full-light needles. Glucose content and Rubisco activity were all positively correlated with light conditions. APX activity, DPPH scavenging capacity and proline content were all the highest in needles under full light, along with higher NPQ and lower Fv/Fm readings, suggested that full-light Korean pines were under stress and inhibited photosynthesis to some degree. The highest content of ABA in full-light needles in September contrasting with previous results might imply that full light conditions helped trees to adapt to cold earlier than understory ones. This study implied that the understory light during growing season was not always unfavourable, Korean pine trees were capable of living under the canopy of deciduous trees for at least eighteen years.