4.3 The importance of deep SIC
Most previous studies on SIC have focused on the upper layers,
especially the top 1.0 m. However, the excavation of deeper soil
profiles becomes more important for the study of SIC storage (Mi et al.,
2008; NEPSTAD et al., 1994; Veldkamp et al., 2003). (Li et al., 2007)
estimated that the SIC storage from 1 m depth to intact soil is about
57% in sandy soils and 61% in gray desert soils. (Wang et al., 2010)
reported that more than 50% of the SIC in forests, scrub, grasslands,
and sandy areas in temperate regions of northern China were located at a
depth of 100 ~ 300 cm. (Wang et al., 2013) found
stratified storage of SIC at 0 ~ 1 m, 1
~ 3 m, 3 ~ 6 m, and 6 ~
9 m depth in saline and alkaline soils in arid northwest China. SIC
storage below 1 m is above 80%, and SIC storage below 3 m is above
50%. The values estimated in this study were higher than theirs, and we
found more than 60% of SIC storage in the 1m to 3m soil profiles in
sandy and post-afforestation areas. The differences between these values
may be due to different soil sampling depths and vegetation types.
Compared to the estimated total SIC storage in the top 1 m of the soil
of 53.3 Pg, soils below 1 m in the arid desert areas of northwest China
still contain 6.2 Pg or more of SIC storage (Mi et al., 2008). Recent
studies have shown that carbon uptake in saline soils in arid zones can
be as high as 62-622 g C m -2 y−1.
Thus, on a global scale, the deep soil SIC pool and its variability may
be more critical than we have recognized. In China, 47% of the land is
arid and semi-arid, and the deeper layers of the soil are rich in SIC.
The contribution of deep soil SIC storage to total soil carbon storage
after vegetation construction has not been well studied for these areas.
Understanding the changes in deep-section SIC storage is essential for
assessing the climate change mitigation potential of soil carbon
pools(George et al., 2012; Jobbagy and Jackson, 2000). In this study, we
analyzed the soil profile variation of SIC storage along the age of
artificial H. ammodendron plantation and its influencing factors. On the
one hand, the variation characteristics of SIC storage in different
forest age stages provide important data for regional carbon estimation.
On the other hand, understanding the effect of vegetation restoration on
changes in SIC storage under different soil depth conditions helps us to
understand the importance of deep SIC for soil carbon pool estimation.
Our results suggest that considering only shallow SIC when assessing the
impact of regional vegetation restoration on SIC reserves will result in
a significant underestimation of the SIC pool. However, all soil samples
are difficult to reach down to 300 cm due to a large amount of labor and
cost consumption. In this context, the combination of remote sensing
techniques and model simulations for in-depth soil sample collection in
typical areas is a feasible method for estimating the soil inorganic
carbon pool.