Carbon and nitrogen isotopes in grasslands of northern China

<p>Carbon (C) and nitrogen (N) isotopes are important traits to characterize terrestrial ecosystems. Studying the relationships between carbon and nitrogen isotopes of soils and plants in different grassland types and under different environmental conditions is of great importance to the reconstruction of past climate. In this study, we selected three different grassland ecosystems (temperate meadow steppe, temperate typical steppe and temperate desert steppe) in northern China, collected meteorological data and plant and soil samples, determined the basic physical and chemical properties, C and N isotopes to explore the patterns and controlling factors of C and N isotopes in plants and soils of grasslands in northern China. The results showed that there were significant differences in soil δ<sup>13</sup>C and δ<sup>15</sup>N between different grassland types in the northern temperate zone. The soil δ<sup>13</sup>C and δ<sup>15</sup>N of different depths of the northern temperate grassland soil increased with the increase of soil depth. The surface soil δ<sup>13</sup>C of temperate meadow steppe and temperate desert steppe had a good correlation with plant sample δ<sup>13</sup>C. The surface soil δ<sup>15</sup>N temperate typical steppe and temperate desert steppe had a good correlation with plant sample δ<sup>15</sup>N. Mean annual temperature (MAT) and mean annual precipitation (MAP) had a complicated relationship with carbon and nitrogen isotopes of surface soil and plant sample in northern temperate grassland. The surface soil δ<sup>13</sup>C and δ<sup>15</sup>N and the plant sample δ<sup>15</sup>N can be used as indicators of the change of MAT.</p><p><em>Keywords:</em> carbon isotopes, nitrogen isotopes, grasslands, climate, soil depth</p>