Different responses of non-structural carbohydrates in above-ground tissues/organs and root to extreme drought and re-watering in Chinese fir (Cunninghamia lanceolata) saplings

Abstract

The total NSC concentration in the roots declined more significantly than in the above-ground tissues/organs under drought treatment, and the level did not return to that of the control after re-watering. Non-structural carbohydrates (NSC) reflect the relative balance between C-gain (photosynthesis) and C-loss (respiration) and play a pivotal role in carbon cycling in a forest ecosystem. However, little is known regarding the effects of extreme drought and re-watering on the NSC status in different tissues/organs. This study examined the variation in NSC concentrations in different tissues/organs and the total NSC pool sizes in Chinese fir (Cunninghamia lanceolata) saplings after drought and re-watering. Results showed that significant differences were observed in the concentrations of total NSC and its components in the different tissues/organs. For example, the NSC concentrations were nine times higher in bark than in stemwood. Moreover, the responses of NSC and its components to extreme drought also varied in different tissues/organs. Drought either significantly increased or maintained the total NSC concentration in the above-ground tissues/organs. By contrast, drought reduced the total NSC concentration in the sapling roots. Furthermore, the results also showed that extreme drought leads to sapling death, which is supported by the result of needle staining and the failure of the total NSC concentration to recover after re-watering. The concentrations of NSC and its components further decreased, and a more pronounced decline was observed in the roots than in the above-ground tissues/organs after re-watering. We speculated that drought can cause failure in carbon translocation between the above- and below-ground tissues/organs and thus cause varied responses of different tissues/organs to extreme drought and re-watering. Overall, these findings suggest the need to investigate the potential differential responses of various tissues/organs to climate change.