Are above- and below-ground phenology in sync?

Area of Science:

• Ecology
• Plant Physiology
• Biogeochemistry

Background:

• Root production is a major component of terrestrial net primary productivity (33-67%).
• Root dynamics significantly influence decomposition, carbon cycling, and nutrient availability.
• Understanding below-ground phenology is crucial for a complete picture of terrestrial ecosystem function, yet it remains poorly understood compared to above-ground phenology.

Purpose of the Study:

• To investigate the phenology of root production in relation to environmental factors and above-ground phenology.
• To synthesize existing data on root growth timing across different biomes.
• To explore the drivers of variation in the timing of root growth.

Main Methods:

• Synthesized data from 87 whole-plant phenology observations across 40 independent studies.
• Analyzed the relationship between root growth timing, shoot growth timing, temperature, and soil moisture.
• Compared phenological offsets across boreal, temperate, Mediterranean, and subtropical biomes.

Main Results:

• On average, root growth initiation occurs 25 ± 8 days after shoot growth initiation.
• The time lag between peak root and shoot growth varies significantly across biomes, exceeding 200 days in some cases.
• Root and shoot growth showed positive correlations with median monthly temperature and mean monthly precipitation in most studied biomes.
• Observed temperature hysteresis suggests internal carbon allocation controls are significant drivers of root phenology.

Conclusions:

• Root phenology exhibits a distinct timing relative to shoot phenology, with substantial biome-specific variation.
• While temperature and precipitation influence root growth, internal plant mechanisms governing carbon allocation appear to be equally or more important.
• Further research is needed to elucidate the precise mechanisms (e.g., photoassimilate supply, hormonal signaling) driving root phenology.