1 Introduction
Land sanding and desertification are the most threatening environmental problems in arid desert areas. More than 70% of arid desert lands suffer from long-term sanding or desertification, and land degradation has resulted in a loss of 19-29 Pg of soil carbon (Lal, 2004; Li et al., 2015). Vegetation construction is one of the main ways to improve land degradation in these areas. Related studies have shown that revegetation of sandy areas leads to changes in soil physicochemical properties, and makes it possible for the soil to capture and sequester atmospheric CO2, increasing the soil carbon sink potential (Huang et al., 2012). Soil carbon pools, including SOC and SIC, are terrestrial ecosystems’ largest carbon pools. Due to the potential rapid response of soil carbon pools to vegetation type changes, SOC has been widely and intensively studied by scholars in China and abroad (Deng et al., 2014; Jackson et al., 2002). Compared to studies on SOC, there are few studies on the dynamics of SIC after revegetation. Since the storage of SIC in arid desert areas far exceeds that of SOC, small revegetation-induced changes in SIC may exert a stronger effect than major changes in SOC in changing the terrestrial carbon balance (Gao et al., 2017; Wang et al., 2016). Therefore, the study of SIC changes after revegetation in arid desert areas is crucial for finding ”lost carbon sinks” in terrestrial ecosystems.
In arid desert areas, changes in SIC after revegetation are highly uncertain. The Colorado Plateaus Desert, USA, showed a 53.8% reduction in SIC content on the soil surface after 10 years of poplar planting (Sartori et al., 2007). In the Badangirin Desert, China, the SIC content at the soil surface increased by 45.7% after 7 years of planting poplar trees (Su et al., 2010). In the Loess Plateau of China, studies have shown that the SIC content of cultivated land at 0-100 cm soil depth is significantly lower than that of restored plantation forests (Wang et al., 2016). In addition, other studies in the region showed that reforestation only affected the distribution characteristics of SIC in different soil layers and did not change the amount of SIC storage (Chang et al., 2012). Inorganic carbon after revegetation showed different or even contradictory findings in the context of similar stand types, climatic conditions, and plant species. These results suggest that the response of SIC content to afforestation in arid desert areas needs further study. In addition, studies on SIC in arid desert areas have mainly focused on soil profiles of 100 cm or even shallower (Shi et al., 2012), while the changing pattern of SIC below 100 cm is still a big question. Recent studies have found that deeper SIC levels in arid desert areas are more than twice as high as those in shallow, In contrast, within 1 to 3 m of the shrub deserts and desert soil profiles, the soil carbon pool is composed mainly of SIC (Naorem et al., 2022). Therefore, the change pattern of SIC after revegetation in arid desert areas needs to be urgently studied.
Located in the interior of northwestern China, Alxa League is a typical arid desert region with the distribution of Ulaanbaatar, Tengger, and Badangirin Deserts. The region’s chronic drought and lack of water, combined with sparse vegetation, make it one of the most active areas of wind-sand in China. The region began vegetating sandy areas in the middle of the last century. As a result, it has extensive artificial sand-fixing forests. To a certain extent, land sanding and sand, and afforestation have typical characteristics of arid desert areas. H. ammodendron belongs to the small tree Quinoa family, which is characterized by its resistance to drought and barrenness. It is the largest sand-fixing tree in the desert area of northwest China, and is called a ”desert plantation”. In this study, we hypothesized that sandy vegetation restoration could increase SIC storage. To test this hypothesis, we selected four stands (5, 11, 22, and 46 years old, respectively) of the H. ammodendron plantation at the edge of the Badangirin Desert in the Alxa League, and used nearby moving sand (MS) as a control. By collecting soils from 0 to 300 cm profiles in the above sample sites, we focused on (1) the characteristics of soil profile changes in SIC along the age sequence of H. ammodendron plantation; (2) the effects of soil moisture(SM) and pH on SIC; and (3) the importance of deep soil SIC in soil carbon storage estimation.