Susceptibility to photoinhibition in seedlings of six tropical fruit tree species native to Malaysia following transplantation to a degraded land

Abstract

To investigate the adaptive capacity to a strong light environment when planted on degraded land, we examined photosynthetic properties in relation to photoinhibition for the sun-leaves of six tropical fruit tree species native to Malaysia before and after transplanting. The six species were: Bouea macrophylla (Bm), Callerya atropurpurea (Ca), Canarium pilosum (Cp), Cynometra cauliflora (Cc), Morinda citrifolia (Mc) and Syzygium sp. (Ssp), which produce edible fruit for endemic animals and birds, and are candidates for corridor plantations. Based on the measurements performed before transplanting, the degree of chronic photoinhibition indicated by the decrease in pre-dawn Fv/Fm was well associated with an accumulation of excessive excitation energy in PSII indicated by a decrease in photochemical quenching (qP). Among the species, Ca and Mc showed lower degrees of photoinhibition with higher qP. Higher electron transport rates (ETR) were observed with higher qP whereas there was no significant relationship between regulatory thermal dissipation (indicated by \(F_{\rm v} /F_{\rm m}\,-\,F^\prime_{\rm v} /F^\prime _{\rm m}\)) and qP. Energy dissipation via electron transport was suggested to be important in keeping qP high and preventing photoinhibition when compared among species. Cc and Bm showed lower ETR and higher susceptibility to photoinhibition before and after transplanting. New Cp and Mc leaves developed after transplanting showed increased area-based leaf nitrogen content (Narea) and stomatal conductance (gs) compared with those before transplanting resulting in higher light-saturated net photosynthetic rates (Amax) and ETR, and contributing to mitigate photoinhibition. In contrast to these species, Ca achieved high Amax with a water conservative manner (indicated by its relatively lower gs), where the higher carboxylation efficiency accompanied with the higher Narea allowed them to maintain relatively high Amax and ETR at lower intercellular CO2 concentration.