Size-mediated ageing reduces vigour in trees.

Area of Science:

• Plant physiology and ecology
• Aging and senescence in perennial organisms
• Tree growth and development

Background:

• Investigating the trade-offs between increased size and prolonged lifespan in plants, particularly trees, is crucial.
• The relationship between tree size, age, and physiological functions like growth rates and mortality is not well understood.
• Existing theories attribute reduced growth to cellular senescence or to the physiological burdens of large size and height.

Discussion:

• Experimental manipulations separated the effects of plant size (extrinsic) from age (intrinsic) across four tree species.
• Measurements included growth, gas exchange, and leaf biochemical properties in field and common garden settings.
• Results indicate that size, rather than cellular senescence, explains age-related declines in relative growth and net assimilation rates.

Key Insights:

• Plant size is the primary driver of age-related declines in growth rates, not cellular senescence.
• Specific leaf area shows genetic control in some species, but size has a stronger independent effect.
• Hydraulic limitations offer partial explanations for reduced tree growth.

Outlook:

• The absence of a clear soma-germline separation, unlimited meristem proliferation, and increasing reproductive effort with size contribute to the lack of senescence-induced decline in trees.
• Further research may explore senescence symptoms in trees significantly older than those studied.
• Understanding these factors is key to predicting forest dynamics and ecosystem responses to climate change.