Stored root carbohydrates can maintain root respiration for extended periods

Abstract

Tight coupling between below-ground autotrophic respiration and the availability of recently assimilated carbon (C) has become a paradigm in the ecophysiological literature. Here, we show that stored carbohydrates can decouple respiration from assimilation for prolonged periods by mobilizing reserves from transport roots to absorptive roots. We permanently disrupted the below-ground transfer of recently assimilated C using stem girdling and root trenching and measured soil CO efflux for over 1 yr in longleaf pine (Pinus palustris), a species that has large reserves of stored carbohydrates in roots. Soil CO efflux was not influenced by girdling or trenching through the 14-month observation period. Stored carbohydrate concentrations in absorptive roots were not affected by the disrupted supply of current photosynthate for over 1 yr; however, carbohydrate concentrations in transport roots decreased. Our results indicate that root respiration can be decoupled from recent canopy assimilation and that stored carbohydrates can be mobilized from transport roots to absorptive roots to maintain respiration for over 1 yr. This refines the current paradigm that canopy assimilation and below-ground respiration are tightly coupled and provides evidence of the mechanism and dynamics responsible for decoupling the above- and below-ground processes.

The role of understory phenology and productivity in the carbon dynamics of longleaf pine savannas

“…We show that longleaf pine savannas are resilient to the disturbance of fire and drought, as a result of their ability to rapidly mobilize nonstructural carbohydrates when photosynthate supply is low, in agreement with a previous study conducted at our sites (Aubrey and Teskey 2018). However, we found that the magnitude and timescale of recovery was site-dependent.…”

Belowground Carbohydrate Reserves of Mature Southern Pines Reflect Seedling Strategy to Evolutionary History of Disturbance

“…Twelve trees from each species between 20 to 25 cm dbh were randomly selected and inspected to ensure there were no diseases or obvious visible injuries that could have potentially affected the amount of carbon stored. Stem cores and coarse root samples were collected from the same individual trees in October and the following March, periods that reflect the seasonal minimum and maximum, respectively, for starch [3] which is the NSC component believed to play the largest role in storage [20]. We focused our belowground efforts on coarse roots because they represent the largest belowground storage reservoir-both in terms of overall mass and starch concentration-and they exhibit more dynamic seasonal patterns of accretion and depletion relative to the finest roots [3].…”

“…Under these circumstances, non-structural carbohydrates (NSCs) are mobilized to compensate for the insufficient supply of current photosynthate required to maintain the metabolism of existing cells as well as to refoliate the canopy, thereby decreasing the stored carbohydrate pool. This strategy of storing carbohydrates may provide an advantage for mature individuals experiencing frequent disturbances [1][2][3]. Alternatively, the advantage conferred by increased stored carbohydrate reserves under chronic disturbance could be a trait favored by selection at a critical life history stage that maintains benefits at later stages-a concept analogous to developmental inertia as described by Minelli [4,5].…”

Using Metabolic Energy Density Metrics to Understand Differences in Ecosystem Function During Drought

“…We estimated energy invested into growth by multiplying monthly biomass increments (kg m −2 ) with the proportional energy contents of cellulose, lignin, starch, and sugar. Starch and sugar content of nonstructural carbohydrate (NSC) contents of mature longleaf pine roots were measured during a study conducted at our sites during 2011 and 2012 (Aubrey & Teskey, ). Starch and sugar contents varied by season but were similar on an annual basis, as well as among sites, ranging from ~5–10% for starch and ~3–4% for sugars.…”