Water limitation intensity shifts carbon allocation dynamics in Scots pine mesocosms

Area of Science:

• Ecology
• Plant Physiology
• Soil Science

Background:

• Trees globally face water limitation, impacting growth and carbon (C) cycling at the plant-soil interface.
• The effects of soil water loss on belowground carbon transfer are not fully understood.

Purpose of the Study:

• To investigate how increasing water deficit influences the growth of Scots pine (Pinus sylvestris) saplings.
• To trace the movement of assimilated carbon (C) belowground under varying water availability using stable isotope labeling.

Main Methods:

• Mesocosm experiment with Scots pine saplings subjected to different water deficit levels.
• ¹³C-CO₂ pulse labeling to track carbon allocation to needles, fine roots, soil CO₂, and microbial groups.

Main Results:

• Increased water limitation led to greater allocation of biomass belowground, reducing aboveground growth.
• Severe water limitation enhanced ¹³C allocation to fine roots and soil fungi.
• ¹³C transit from needles to soil CO₂ was minimally affected by moderate drought but slowed under severe drought, with less ¹³CO₂ readily respired.

Conclusions:

• Under severe drought, trees exhibit slower internal carbon cycling.
• Carbon allocated belowground may accumulate in fine roots or be transferred to soil and microbes without immediate metabolic use.