Summary
Wood formation is a crucial process for carbon sequestration on land, yet how variations in phloem-transported carbon affect wood formation, respiration and nonstructural carbon pools remains poorly understood.
To better understand the role of carbon supply on allocation to wood formation, we constrained phloem transport using girdling and compression around the stem of 40 mature white pines to monitor the effects of contrasting carbon supply (enriched above and reduced below the manipulations) on local wood formation and respiration, as well as on nonstructural carbon pools in needles, stems, and roots.
Radial growth and respiration responded to variations in carbon supply. Despite a two-fold difference in the number of tracheids formed above and below the manipulation, cell-wall area only decreased slightly and cell size did not change noticeably. Surprisingly, nonstructural carbon pools and concentrations in the xylem, needles and roots remained largely unchanged, although starch reserves were remobilised and accumulated slightly under the most extreme decreases or increases in carbon supply, respectively.
We conclude that phloem carbon supply does not affect nonstructural carbon concentrations but regulates growth and respiration in mature white pine. Thus, wood formation is controlled by the availability of phloem-transported carbon over timescales of several months.
Competing Interest Statement
The authors have declared no competing interest.