Partitioning of canopy and soil CO2 fluxes in a pine forest at the dry timberline across a 13-year observation period

Biogeosciences. 2020. Vol. 17. P. 699–714.

Qubaja R., Fyodor Tatarinov, Rotenberg E., Yakir D.

Partitioning carbon fluxes is key to understanding
the process underlying ecosystem response to change.
This study used soil and canopy fluxes with stable isotopes
(13C) and radiocarbon (14C) measurements in an 18 km2, 50-
year-old, dry (287mm mean annual precipitation; nonirrigated)
Pinus halepensis forest plantation in Israel to partition
the net ecosystem’s CO2 flux into gross primary productivity
(GPP) and ecosystem respiration (Re) and (with
the aid of isotopic measurements) soil respiration flux (Rs)
into autotrophic (Rsa), heterotrophic (Rh), and inorganic
(Ri) components. On an annual scale, GPP and Re were
655 and 488 g Cm􀀀2, respectively, with a net primary productivity
(NPP) of 282 g Cm􀀀2 and carbon-use efficiency
(CUEDNPP = GPP) of 0.43. Rs made up 60% of the Re and
comprised 244%Rsa, 234%Rh, and 131%Ri. The
contribution of root and microbial respiration to Re increased
during high productivity periods, and inorganic sources were
more significant components when the soil water content was
low. Comparing the ratio of the respiration components to Re
of our mean 2016 values to those of 2003 (mean for 2001–
2006) at the same site indicated a decrease in the autotrophic
components (roots, foliage, and wood) by about 􀀀13% and
an increase in the heterotrophic component (Rh=Re) by about
C18 %, with similar trends for soil respiration (Rsa=Rs decreasing
by 􀀀19% and Rh=Rs increasing by C8 %, respectively).
The soil respiration sensitivity to temperature (Q10)
decreased across the same observation period by 36% and
9% in the wet and dry periods, respectively. Low rates of
soil carbon loss combined with relatively high belowground
carbon allocation (i.e., 38% of canopy CO2 uptake) and low
sensitivity to temperature help explain the high soil organic
carbon accumulation and the relatively high ecosystem CUE
of the dry forest.

Keywords: soil respiration, Eddy covariance, метод турбулентных пульсаций, semiarid forests, carbon flux partitioning, почвенное дыхание