1. Introduction
Climate system and the global carbon cycle have formed a positive
feedback loop to reinforce each other(Friedlingstein, Dufresne, Cox, &
Rayner, 2003). Carbon as an important influence factor of the greenhouse
effect has become a research hotspot in the scientific community. About
1,500 Gt of carbon is stored in the soil in the form of organic matter,
which is 2 to 3 times as much as the carbon pool of terrestrial
vegetation or global atmospheric carbon pool. Subtle changes in soil
organic carbon pool may cause large fluctuations in atmospheric
CO2 concentration, which in turn will affect the
greenhouse effect and global climate change (Davidson, Trumbore, &
Amundson, 2000). Therefore, study of the stabilization mechanism of
organic carbon and its controlling factors is essential for a correct
understanding of the biosphere carbon cycle, the importance of soil
organic carbon to ecosystem processes and the feedback to climate
change(Jobbagy & Jackson, 2000).
Changes of land use and vegetation cover pattern have key influence on
the carbon cycle of terrestrial ecosystems (Willcock et al., 2016), All
of them affect greenhouse gas production and emission by altering the
soil microenvironmen, soil physicochemical processes and microbial
activities(Ball, McTaggart, & Watson, 2002) (Flechard et al., 2007).
Due to the character of fast growing,drought resistance, thinness
resistance and hardwood propertie, Black locust has become an important
tree for afforestation and plays an important role in the carbon cycle
of ecosystem on the hilly losee platea of china. The stabilization
mechanism of soil organic carbon in Robinia pseudoacaciaplantation on the Loess Plateau is of great significance for further
understanding of regional climate changes caused by pattern changes in
the organic carbon under conversion of cropland to forest.
The stability of organic carbon in the soil depends on soil properties,
environmental factors and influence of human activities. Most of the
current understanding of the process of soil carbon storage and release
comes from the study of the main surface soil (Richter & Mobley, 2009;
Zabowski, Whitney, Gurung, & Hatten, 2011). However, deep soil serves
as a huge organic carbon pool in terrestrial ecosystems, its carbon
storage is three times as much as that of surface soil (Fontaine, Barot
et al. 2007). A little change in the organic carbon (SOC) cycle of deep
soils may cause the release of large amounts of CO2 and
have a significant impact on the global carbon cycle (X. Wang et al.,
2014).
Although the vertical distribution of soil organic carbon decreasing
with the increase of soil profile depth has already been recognized,
people pay less attention to the dynamics of deep soil carbon due to the
low content of deep soil organic carbon (Davidson & Ackerman, 1993;
Post & Kwon, 2000). Most studies focus on spatial and temporal
variation in organic carbon mineralization and soil CO2flux at soil surface layer (ArchMiller, Samuelson, & Li, 2016; Mande,
Abdullah, Aris, & Ainuddin, 2015; Pang, Bao, Zhu, & Cheng, 2013),
reports on CO2 flux in deep soil layers are very rare
(Jassal R, 2005; Liang N S, 2003; Wiaux F, 2015). In addition, since the
CO2 flux at the soil-atmosphere interface is a
superposition of CO2 emissions caused by organic carbon
mineralization from different depths of soil layers. For lack of
comprehensive understanding of contribution of soil resources at
different depths to SOC mineralization, it will produce larger errors to
predict the overall soil carbon pool variation characteristics based on
soil surface layers (Takahashi, Hiyama, Takahashi, & Fukushima, 2004).
Therefore, distinguishing the characteristics of SOC mineralization
variation at different depths, especially in deep layers, will help to
improve the accuracy of the soil carbon emission prediction model and
further understand the carbon emission mechanism (Subke, Reichstein, &
Tenhunen, 2003; Takahashi et al., 2004).
In summary, understanding the stability of soil organic carbon is the
key to the study of soil carbon sequestration in plantation forests. How
does the process of soil organic carbon mineralization change with soil
depth in the Robinia pseudoacacia plantation ecosystem on the
Loess Plateau? Which characteristics of carbon fluxes changes in
different sections of deep layers and which factors affecte them? All of
these issues need to be further studied. In this study, we monitored the
CO2 concentration and soil physico-chemical environment
at different soil profiles in the artificial Robinia pseudoacaciaof different stand ages and crop land on the hilly losee platea. The
aims of this research were: (1) to determine distribution of soil
CO2 flux at different profiles based on Fick’s first
law; (2) to understand the response of soil CO2 flux to
soil temperature ,moisture and soil organic carbon(SOC) at different
profiles; (3) to define the contribution of CO2 flux in
deep layers to soil-atmosphere interface; (4) to explore multi-factor
coordination and construct prediction model. The results of this study
contribute to clarify the production process of soil CO2in deep layers and the response mechanism of CO2 flux at
different profils for scientifically assessing soil carbon emission
effects of vegetation restoration, and to provide a theoretical basis
for further clarifying the stability of soil carbon and the dynamic
change of soil carbon pool in Robinia pseudoacacia on the hilly
losee platea.