Respiratory carbon use and carbon storage in mid‐rotation loblolly pine (Pinus taeda L.) plantations: the effect of site resources on the stand carbon balance

Abstract

We used estimates of autotrophic respiration (R A ), net primary productivity (NPP) and soil CO 2 evolution (S ff ), to develop component carbon budgets for 12-year-old loblolly pine plantations during the fifth year of a fertilization and irrigation experiment. Annual carbon use in R A was 7.5, 9.0, 15.0, and 15.1 Mg C ha À1 in control (C), irrigated (I), fertilized (F) and irrigated and fertilized (IF) treatments, respectively. Foliage, fine root and perennial woody tissue (stem, branch, coarse and taproot) respiration accounted for, respectively, 37%, 24%, and 39% of R A in C and I treatments and 38%, 12% and 50% of R A in F and IF treatments. Annual gross primary production (GPP 5 NPP 1 R A ) ranged from 13.1 to 26.6 Mg C ha À1 . The I, F, and IF treatments resulted in a 21, 94, and 103% increase in GPP, respectively, compared to the C treatment. Despite large treatment differences in NPP, R A , and carbon allocation, carbon use efficiency (CUE 5 NPP/GPP) averaged 0.42 and was unaffected by manipulating site resources.Ecosystem respiration (R E ), the sum of S ff , and above ground R A , ranged from 12.8 to 20.2 Mg C ha À1 yr À1 . S ff contributed the largest proportion of R E , but the relative importance of S ff decreased from 0.63 in C treatments to 0.47 in IF treatments because of increased aboveground R A . Aboveground woody tissue R A was 15% of R E in C and I treatments compared to 25% of R E in F and IF treatments. Net ecosystem productivity (NEP 5 GPP-R E ) was roughly 0 in the C and I treatments and 6.4 Mg C ha À1 yr À1 in F and IF treatments, indicating that non-fertilized treatments were neither a source nor a sink for atmospheric carbon while fertilized treatments were carbon sinks. In these young stands, NEP is tightly linked to NPP; increased ecosystem carbon storage results mainly from an increase in foliage and perennial woody biomass.

Aboveground sink strength in forests controls the allocation of carbon below ground and its [CO 2 ]-induced enhancement

“…However, a closer assessment of individual studies shows that TBCA or belowground NPP (BNPP; roughly 50% of TBCA) (4), may increase, decrease or be insensitive to an increase in ANPP (17)(18)(19)(20)(21)(22)(23)(24). These apparently inconsistent responses of TBCA or BNPP to aboveground productivity might be explained by the range of L in each study and site-and species-specific conditions that control canopy photosynthesis and the aboveground C sink.…”

Contrasting growth and water use efficiency after thinning in mixed Abies pinsapo-Pinus pinaster-Pinus sylvestris forests

“…The higher iWUE values for P. pinaster could therefore be attributed to a higher overall assimilation capacity of this species, to a better stomatal control of water losses than in the P. sylvestris, or to a combination of both factors (Seibt et al 2008;Moreno-Gutierrez et al 2012). On the other hand, shade-tolerant species such as A. pinsapo generally have stomata that are more responsive to elevated CO 2 than intolerant coniferous species (Maier et al 2004). It is this 'active response' to thinning that produces the 'physiological response' via a reduction in stomatal conductance, and an increase in the carbon assimilation rate (Moreno-Gutiérrez et al 2012).…”

“…Shadetolerant species such as A. pinsapo generally have stomata that are more responsive to elevated CO 2 than intolerant coniferous species (Maier et al 2004). Therefore, the silviculture of a mixed forest must put under consideration different active response to thinning in the context of global change (D'Amato et al 2011).…”

Carbon allocation in forest ecosystems

“…For most of these studies, R root was estimated with chamber measurements and scaling techniques. Three additional studies used for our analyses estimated R root as: (i) coarse root respiration from biomass, temperature and stem respiration rates, and fine root respiration as a residual term of GPP (where GPP was estimated from annual gas-exchange rates and crown leaf area measurements; Benecke & Nordmeyer, 1982), (ii) maintenance respiration from tissue temperature and nitrogen content and growth respiration assuming a construction cost of 0.25 (Maier et al, 2004), or (iii) F soil differences between control and trenched (root-free) plots (Ewel et al, 1987). These methods for estimating R root and, thus, TBCF do not include carbon used for mycorrhizae and root exudates, a potentially large portion of flux to belowground (Fogel & Hunt, 1979;Sylvia, 1998).…”