Abstract
The shrub Nitraria tangutorum is distributed widely in arid desert areas, and plays a critical role in the desert–oasis ecosystem. This study quantified varying characteristics of carbon (C) and nitrogen (N) in the soil at four stages—the initial stage (IS), stable stage (SS), degradation stage (DS), and severe degradation stage (SDS)—in a steppe ecosystem in the desert of northwestern China. The results indicated that N. tangutorum experienced both expansion and deterioration as a decline of 50.7% occurred in the available soil water due to agricultural utilization, and the plant community transformed from being shrub-dominated to annual herb-dominated. At soil layer depths between 0–100 cm in the N. tangutorum nebkha dune ecosystem, organic C and total N storage was 1195.84 g/m2 and 115.01 g/m2 during the SDS, respectively, with an increase of 11.13% and 12.59% from the IS. In addition, the storage of C and N in the soil increased during the IS as well as the SS, when most of the C and N were accumulated, and the storage decreased during the DS and SDS, as the N. tangutorum communities declined. At soil layer depths between 0–100 cm in the desert steppe ecosystem, the highest storage levels of C and N were 8465.97 g/m2 and 749.29 g/m2 during the SS, and the lowest were 1076.12 g/m2 and 102.15 g/m2 during the IS, respectively. The changes and accumulation of C and N were greater in the deeper (40–100 cm) layer than in the surface layer of soil (0–40 cm). Lastly, changes in soil organic carbon (SOC) as well as in the total nitrogen (TN) were strongly related to the coverage degree, water content in soil, and the ratio of fine soil particles (silt and clay). To sum up, the intensive development of water resources has vastly reduced the ability of N. tangutorum vegetation to sequester C and N in the desert of Minqin. Efforts to perform ecological restoration and reverse desertification in the Minqin Desert should focus on preventing the unreasonable exploitation of water resources in order to maintain stable N. tangutorum communities.
Highlights
Understanding the cycles of carbon (C) and nitrogen (N) in soil in ecosystems is essential for estimating their influence on global climate change [1] and determining the ecological strategy of particular land ecosystems [2]
The succession of N. tangutorum vegetation had a significant effect on the distribution of particle size and soil water content in nebkha topsoil (0–5 cm) (P < 0.05) (Table 2)
The contents of clay and silt increased by 259.5% and 94.5% throughout the entire succession process, respectively (Table 2)
Summary
Understanding the cycles of carbon (C) and nitrogen (N) in soil in ecosystems is essential for estimating their influence on global climate change [1] and determining the ecological strategy (i.e., conservation) of particular land ecosystems [2]. Nebkhas are the most common landforms in arid desert areas, and their origination and development are considered the indicators for the change in the local climate and environment [5]. The presence of nebkhas has been considered a distinctive indicator of land degradation and the intensification of wind erosion [6], of a significant decrease in land production, and of the degradation of an ecological environment [7]. Most studies focusing on the formation and development of nebkhas are related to vegetation [8,9], climate change [10], anthropogenic influence [6], geological and hydrogeological conditions [11,12,13], wind strength [14], and sand source [15]. A few papers have considered sand fixation and the reduction of wind erosion [18], the protection of biodiversity [11], or the enrichment of soil water and nutrient content in nebkhas [19,20]
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