Shoot buds of subtropical running bamboos demonstrate endodormancy and chilling requirements for their release

Bamboos, widely distributed in tropical and subtropical regions and significant in ecological, economic and cultural values, are similar to trees in the above-ground growth and to geophytes in the below-ground structure. However, contrary to well-studied endodormancy and the related chilling requirement that synchronize the seasonal development of above-ground buds of tree species and the well-studied below-ground buds of geophytes, it is unknown whether bamboos demonstrate the endodormancy and chilling requirements as those of trees and geophytes, which limits our understanding of how bamboos phenology cope with climate change. Our work mainly examined the effect of temperature on the dormancy release of underground shoot buds of two important subtropical running bamboo species, Lei bamboo (Phyllostachys violascens) and Moso bamboo (Phyllostachys edulis). In the experiments, the bamboo seedlings were first subjected to different durations of natural chilling and subsequently to a regrowth test under high-temperature forcing conditions in whole-tree chambers. In the regrowth test the dormancy state of the shoot buds was examined by observing shoot development, i.e., the emergence of the new shoot aboveground, a significant spring phenological event in many bamboo species. The time required for shooting under the forcing conditions decreased with prolonged chilling, indicating that the shoot buds of these two bamboo species demonstrate the phenomena of endodormancy and a chilling requirement for endodormancy release. For Lei bamboo, the chilling requirement was estimated as 45 Chill Portions (CP) and heat requirement was 9978 ± 6713 GDH℃. As for Moso bamboo, the estimated chilling requirement was 35CP and heat requirement was 6713 ± 3087 GDH℃. Meanwhile, the Vegis effect (an interaction of previous chilling accumulation and forcing temperature) was also found in Lei bamboo: there was a large difference in the time required for shoot development between low and high forcing temperatures after short durations of chilling, but the difference decreased with prolonged chilling. It was also shown that bamboo shoot buds almost received the same heat requirements for emergence at different forcing temperatures under the same chilling requirements. Our results will improve the understanding of temperature regulation of spring phenology in subtropical bamboo forests and promote bamboo production and management.