Restoration of Shrub Communities Elevates Organic Carbon in Arid Soils of Northwest China

Arid and semi-arid lands cover approximately 45% of the global terrestrial area and contain 16% of the global soil carbon pool. More importantly, over two-thirds of lands in arid and semi-arid regions have been destroyed by desertification, leading to ca. 20–30 Pg C loss. If efficient restoration measures can be successfully applied on the degraded lands, these lands could sequester 0.9–1.9 Pg C y^-1 during a 25–50-year restoration phase. This value accounts for 30% of the present atmospheric CO2 level. In sandy land, planting shrub has been proved as an efficient restoration measure.

To control desertification development in northern China, researchers implemented a series of work in the Horqin sandy land in eastern Inner Mongolia, China. Fencing and planting shrubs have been regarded as the successful measures for mobile sand dune restoration since 1970s. Previous studies have investigated the vegetation eco-physilological changes, including biomass distribution, plant life-form and morphological traits. However, little information is available on the carbon flux input to soil resulted from fine roots turnover and leaf fallen during restoration.

Relying on the ingrowth core and sequential core methods, researchers investigated the fine-root dynamics and fine-root production of three shrub stands (Artemisia halodendron, Caragana microphylla and Salix gordejevii) which have different life-forms and root architectures in the Naiman Station of Desertification and Farmland Research, Chinese Academy of Sciences. Naiman is located at the southwestern part of the Horqin Sandy Land. The soil carbon and nitrogen stock was also estimated in the restoration, and the relative contribution of carbon input related to fine root mortality and leaf fallen was assessed.

The result showed that the mean standing live and dead fine-root biomass in A. halodendron stand at the primary restoration were significantly less than in C. microphylla stand at moderate restoration and S. gordejevii stand in lowland. Consistent with leaf production, fine root production showed a positive correlation with soil water content and followed the order of A. halodendron < C. microphylla < S. gordejevii. In contrast, the fine-root turnover rate was quicker in primary restoration phase (2.12 year^-1) than in moderate restoration phase (1.55 year^-1) and lowland (1.28 year^-1). The annual carbon and nitrogen inputs via fine root mortality and leaf fallen increased from 74.78 g C m^-2 year^-1 and 1.25 g N m^-2 year^-1 in A. halodendron stand to 189.66 g C m^-2 year^-1 and 1.67 g N m^-2 year^-1 in S. gordejevii stand. Although the share of the fine roots of A. halodendron seized a relatively smaller proportion in the net primary production compared with those in C. microphylla and S. gordejevii, the relative contribution of carbon input related to fine roots mortality in primary restoration phase was higher than in the other two shrub stands. This study proved that the carbon input to soil by fine-root mortality considerably contributed to the restoration of soil carbon and nitrogen stock in semi-arid degraded lands.

The main finding has been published on Soil Biology and Biochemistry, 2012, 47: 123–132. The paper is also archived at http://www.sciencedirect.com/science/article/pii/S0038071711004494.