Zongrui Lai

Influence of Environmental Factors on Carbon Dioxide Exchange in Biological Soil Crusts in Desert Areas

The influence of water and light on CO2 exchange in cyanobacteria, lichen, and moss crusts at five temperature levels under controlled laboratory conditions was explored using a portable photosynthesis system. Across the range of temperatures, average optimum water content values for cyanobacteria, lichen and moss crusts were 0.38 ± 0.17 mm, 0.92 ± 0.06 mm, and 2.10 ± 0.02 mm (mean ± SE), respectively, whereas the respective average light saturation points were 900 ± 23, 870 ± 45, and 1200 ± 32 µ mol m−2 s−1. Optimum temperatures for photosynthesis were 20–27°C, 15°C, and 20°C, respectively, with maximum photosynthetic rates for the three types of crust of 2.67 ± 0.09, 3.06 ± 0.08, and 6.62 ± 0.06 µ mol m−2 s−1, respectively, under these optimum temperatures. Based on the observed data and climate information, the potential net photosynthetic carbon sequestration rates were estimated at 5.16, 3.46, and 6.05 g C m−2 a−1, respectively. These results indicate that the range of environmental conditions required for photosynthetic carbon sequestration in biological soil crusts is wide. Furthermore, moss crusts covering the smallest distribution area made the greatest contribution of C to the soil ecosystem, followed by cyanobacteria crusts, which covered the largest area.

Influence of Disturbance on Soil Respiration in Biologically Crusted Soil during the Dry Season

Soil respiration (Rs) is a major pathway for carbon cycling and is a complex process involving abiotic and biotic factors. Biological soil crusts (BSCs) are a key biotic component of desert ecosystems worldwide. In desert ecosystems, soils are protected from surface disturbance by BSCs, but it is unknown whether Rs is affected by disturbance of this crust layer. We measured Rs in three types of disturbed and undisturbed crusted soils (algae, lichen, and moss), as well as bare land from April to August, 2010, in Mu Us desert, northwest China. Rs was similar among undisturbed soils but increased significantly in disturbed moss and algae crusted soils. The variation of Rs in undisturbed and disturbed soil was related to soil bulk density. Disturbance also led to changes in soil organic carbon and fine particles contents, including declines of 60–70% in surface soil C and N, relative to predisturbance values. Once BSCs were disturbed, Q 10 increased. Our findings indicate that a loss of BSCs cover will lead to greater soil C loss through respiration. Given these results, understanding the disturbance sensitivity impact on Rs could be helpful to modify soil management practices which promote carbon sequestration.

Effect of Vegetation Rehabilitation on Soil Carbon and Its Fractions in Mu Us Desert, Northwest China

Although vegetation rehabilitation on semi-arid and arid regions may enhance soil carbon sequestration, its effects on soil carbon fractions remain uncertain. We carried out a study after planting Artemisia ordosica (AO, 17 years), Astragalus mongolicum (AM, 5 years), and Salix psammophila (SP, 16 years) on shifting sand land (SL) in the Mu Us Desert, northwest China. We measured total soil carbon (TSC) and its components, soil inorganic carbon (SIC) and soil organic carbon (SOC), as well as the light and heavy fractions within soil organic carbon (LF-SOC and HF-SOC), under the SL and shrublands at depths of 100 cm. TSC stock under SL was 27.6 Mg ha−1, and vegetation rehabilitation remarkably elevated it by 40.6 Mgha−1, 4.5 Mgha−1, and 14.1 Mgha−1 under AO, AM and SP land, respectively. Among the newly formed TSC under the three shrublands, SIC, LF-SOC and HF-SOC accounted for 75.0%, 10.7% and 13.1% for AO, respectively; they made up 37.0%, 50.7% and 10.6% for AM, respectively; they occupied 68.6%, 18.8% and 10.0% for SP, respectively. The accumulation rates of TSC within 0–100 cm reached 238.6 g m−2y−1, 89.9 g m−2y−1 and 87.9 g m−2y−1 under AO, AM and SP land, respectively. The present study proved that the accumulation of SIC considerably contributed to soil carbon sequestration, and vegetation rehabilitation on shifting sand land has a great potential for soil carbon sequestration.

Changes in soil organic carbon and its density fractions after shrub-planting for desertification control

ABSTRACT: Planting shrubs on sand land and degraded pasture are two main measures for desertification control particularly in northwest China. However, their effects on soil organic carbon (SOC) and its fractions remain uncertain. We assessed the changes in stocks of SOC, light fraction of SOC (LF—SOC) and heavy fraction of SOC (HF—SOC) after planting Artemisia ordosica (AO, 17 years), Astragalus mongolicum (AM, 5 years) and Salix psammophila (SP, 16 years) in sand land and planting Caragana microphylla (CM, 24 years) on degraded pasture. Results show that: 1) after planting AO, AM and SP on sand land, SOC stocks increased by 162.5%, 45.2% and 70.8%, respectively, and LF—SOC accounted for a large proportion in the increased SOC. Dry weights of LF—SOC, rather than carbon concentrations, were higher in shrublands than that in sand land; 2) after planting CM on degraded pasture, SOC stock decreased by 9.3% and all the loss was HF—SOC in 60–100 cm soil layer where both herbaceous fine root biomass (HFRB) and soil water content (SWC) also decreased. The results indicate that planting shrubs can result in an increase of SOC in sand land, whereas that can lead to a decrease of SOC in degraded pasture. The increase of SOC in sand land mainly bases on the accumulation of dry weight of LF—SOC. The loss of SOC in degraded pasture is caused by the decrease of carbon concentrations of HF—SOC, which can be related to the reduction of HFRB and SWC in deep soil layer. Therefore, shrub-planting for desertification control not always improve the quantity and stability of SOC in northwest China.