The advantages of being deciduous or evergreen in subtropical forests are poorly understood. The carbon assimilation of senescing leaves has not been investigated, probably because the senescence process is usually short. Carbon assimilation by senescing leaves, however, could be of importance to some deciduous species with prolonged senescence. Dr. ZHANG Yongjiang of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study on Lyonia ovalifolia, the most common deciduous tree species in the subtropical evergreen broadleaf forest of Ailao Mountain (24°32′N, 101°01′E, elevation 2,460 m) in SW China, which maintains red leaves on trees for a long period in winter (more than 2 months) when other deciduous trees are leafless.
The objectives of the study were: (1) to determine the winter photosynthetic performance of Lyonia ovalifolia red senescing leaves; (2) to infer the relative contribution of winter carbon gain to the yearly carbon balance of L. ovalifolia and the importance of maintaining positive winter carbon balances for trees in subtropical forests of SW China; and (3) to test whether L. ovalifolia with extended leaf senescence and anthocyanin accumulation has higher nutrient resorption efficiency than co-occurring deciduous species without extended leaf senescence and anthocyanin accumulation.
The study found that the deciduous plant species Lyonia ovalifolia can use red senescing leaves to assimilate substantial amounts of carbon during 2 months of the winter season. Cold acclimation and photoprotection corresponding with anthocyanins helped winter CO2 assimilation. The importance of maintaining a positive winter carbon balance for achieving high yearly carbon gains and ecological success also provided indirect evidence for the dominance of evergreen species in the subtropical forests of SW China.
The researchers also observed continuing nutrient resorption in L. ovalifolia during the red leaf stage, and higher nutrient resorption efficiency than for co-occurring deciduous species without extended leaf senescence, supporting the hypothesis that anthocyanin accumulation in senescing leaves protects the nutrient resorption process.
The study was supported by a grant from the National Natural Science Foundation of China (30670320).
The study entitled “Extended leaf senescence promotes carbon gain and nutrient resorption: importance of maintaining winter photosynthesis in subtropical forests” has been published online in Oecologia, DOI 10.1007/s00442-013-2672-1
The subtropical evergreen broadleaf forest of Ailao Mountains in winter.