Drought shortens subtropical understory growing season by advancing leaf senescence

Subtropical forests, recognized for their intricate vertical canopy
stratification, exhibit high resistance to extreme drought. However, the
response of leaf phenology to drought in the species-rich understory
remains poorly understood. In this study, we constructed a digital camera
system, amassing over 360,000 images through a 70% throughfall exclusion
experiment, to explore the drought response of understory leaf phenology.
The results revealed a significant advancement in understory leaf
senescence phenology under drought, with 11.75 and 15.76 days for the
start and end of the leaf-falling event, respectively. Pre-season
temperature primarily regulated leaf development phenology, whereas soil
water dominated the variability in leaf senescence phenology. Under
drought conditions, temperature sensitivities for the end of leaf
emergence decreased from -13.72 days ℃-1 to -11.06 days ℃-1, with
insignificance observed for the start of leaf emergence. Consequently,
drought treatment shortened both the length of the growing season (15.69
days) and the peak-growth season (9.80 days) for understory plants.
Moreover, this study identified diverse responses among intra- and
inter-species to drought, particularly during the leaf development phase.
These findings underscore the pivotal role of water availability in
shaping understory phenology patterns, especially in subtropical forests.