关键词: 物候工程, 光周期调控, 功能性常绿, 碳汇, 林木适应性, CRISPR/Cas9, 杨树

Abstract:

In response to the practical bottleneck that suitable afforestation land becomes increasingly limited, and the space is limited for carbon sequestration solely relying on area expansion. This study proposes the concept of “functionally evergreen” trees and demonstrates the use of phenological engineering to reprogramm the photoperiod regulatory network, thereby extending the photosynthetic season to enhance carbon sequestration per unit area, providing molecular design strategies for efficient management of short rotation plantations. The core components of the plant photoperiodic pathway are highly conserved across angiosperms and have been successfully used to improve climatic adaptation in crops such as Oryza sativa, Glycine max, Triticum aestivum, and Zea mays. In Populus spp. (poplar), this pathway is reused to regulate seasonal growth: the florigen gene PtFT2 is essential for maintaining apical meristem activity, and under short days the clock proteins PtLHY2, PtGI, PtELF3 and PtLUX cooperatively repress PtFT2 expression, thereby inducing growth cessation. This study proposes concept validation: PtELF3 knockout hybrid poplar lines using CRISPR/Cas9 and PtFT2 overexpressing lines through ectopic expression were formulated. In controlled-environment simulation trials, both engineered lines were insensitive to short days and maintained active growth. A field observation for five years at a subtropical research station showed that the PtELF3 knockout lines remained nearly evergreen throughout the year, with substantially higher biomass and annual carbon storage than the wild type. The PtFT2 overexpressors also performed better, although the effect was weaker (preliminary data from a single site and limited sample size). Phenological engineering can allow poplar to become “functionally evergreen”, and its growth is no longer limited by its inherent developmental rhythms. Thus, precise molecular design can significantly prolong the growth period and enhance carbon storage per unit area. According to climate zone, in the mild-winter south it is advantageous to pyramid freezing-tolerance and phenological genes to achieve year-round growth combined with safe overwintering. In the northern temperate and cold-temperate zones, weak alleles should be used to delay growth cessation only moderately, balancing carbon gain against winter survival. Before large-scale deployment, cold hardiness, multi-site/multi-year validation and ecological risks must be resolved. Because the photoperiodic pathway is highly conserved across angiosperms, this strategy also holds reference value for carbon sequestration improvement in other short-rotation fast-growing broadleaf tree species. If fully validated, phenological engineering holds promise for achieving higher carbon sequestration output on limited land areas, offering a new technological pathway for improving the quality and efficiency of plantations in China.

Key words: phenological engineering, photoperiod regulation, functionally evergreen, carbon sink, tree adaptability, CRISPR/Cas9, Populus