Soil stoichiometry in typical shrub communities in the Ulan Buh Desert

Different typical shrub communities have made an important contributions to alleviating the problem of soil degradation in the Ulan Buh Desert. Shrub type plays an essential role in ecosystem recovery and affects soil quality, particularly the contents of carbon(C), nitrogen(N), and phosphorus(P). In recent years, stoichiometry has been successfully used to indicate community succession and vegetation restoration, and studies on the effects of different shrub types on soil C, N, and P stoichiometry have contributed to our understanding of the relationships between vegetation restoration and soil quality, and are also beneficial with regards to determining the processes and functions of ecological systems. In this study, standard sampling plots of 10 m × 10 m were established in shrub woodland of Ulan Buh Desert natural vegetation types, and soil stratified sampling was carried out in the marginal sections(east, south, west, and north directions) of plant shrubs, with sampling depths being divided into five layers: 0-20, 20-40, 40-60, 60-80, and 80-100 cm. Soil samples collected from the same levels were mixed, dried, and passed through a 0.15 mm sieve, and subsequently analyzed using the four-point method to determine the contents of C, N, and P in soil. The soil organic C, total N, and total P contents in the 0-100 cm layer of soil were measured and ecological stoichiometric characteristics in different shrubs and soil depths were compared. Correlations between indicators were also determined. The results showed that the mean contents of soil C, N, and P were 2.45, 0.26, and 0.28 g/kg, respectively, which were all below the national levels. In all the four soils, there was a moderate variation in the stoichiometric characteristics of C and P, whereas there was a relatively marked variation in soil N. Correlation analysis of the elements showed extremely significant correlations between C and N, C and P(P < 0.01), and N and P(P < 0.05). Furthermore, C and N showed almost synchronous variation, whereas P invariably showed a lag. The contents of soil C, N, and P in the surface layer(0-20 cm) of soil associated with each shrub type were higher than those in deeper soil. The ratios of both soil C and N decreased significantly with increasing soil depth, whereas the vertical pattern of soil P differed from top to bottom. There was no significant difference in the P content of different soil layers(P > 0.05). The mean soil C∶N, C∶P, and N∶P ratios were 9.41, 8.7