黄土区次生植被恢复对土壤有机碳官能团的影响

以植被空间排列顺序推断时间演替顺序,采用同步辐射软X射线探讨子午岭林区典型植物样地白羊草(Bothriochlor ischaemum)狼牙刺(Sophora viciifolia)辽东栋群落(Quercus liaotungensis)演替过程中土壤有机碳官能团变化。图谱定性分析显示,恢复过程中各植被条件下0-5 cm和20-40 cm土层土壤脂肪-C、酮-C吸收强度明显增加;0-5 cm土层土壤脂肪-C吸收较20-40 cm强,而土壤酮-C吸收较20-40 cm弱。半定量分析结果显示,随植被演替进程,0-5 cm土层土壤各官能团相对百分含量都有所增加,如芳香-C、脂肪-C、酮-C呈现逐渐增加趋势,至辽东栎群落时,20-40 cm土层土壤脂肪-C相对百分含量明显增加。植被恢复过程中,各样地SOC官能团组成基本一致,但植被恢复影响土壤SOC官能团数量变化;植被恢复能促进0-5 cm和20-40 cm土层土壤脂肪-C、酮-C含量增加,并且这种作用随着植被恢复时间的延长逐渐增强,说明植被演替增强了土壤有机碳化学稳定性。

Effect of revegetation on functional groups of soil organic carbon on the Loess Plateau

Vegetation succession affects soil physical and chemical properties, including organic carbon functional group species, quantities, and structural changes. Changes in soil organic carbon (SOC) functional groups during the vegetation restoration process could reveal the processes governing changes in the composition and properties of humus. The study was on the Loess Plateau in the Ziwuling forest region of Shaanxi Province, where various stages of secondary forests have developed. At different phases of development, vegetation systems in this region have changed from pioneer herbage species, which initially colonized abandoned croplands, (Bothriochloa isehemum, Artenmisia giradii, Stipa bungeana, Artenmisia sacrorum, Spodiopogen sibiricus, Sophora flavecens, Themeda japonica, and Arundinella anomala), to secondary shrubs (Hippophae rhamnoides, Sophora viciifdia, and Ostryopsis davidiana), to an early forest community (Populus davidiana, Betula platyphylla, and Platycladus orientalis with groups of trees and/or shrubs), and finally to a Liaotungesis community forming the mature forest. The SOC content in the 0-40 cm soil layer increases significantly during the vegetation succession from abandoned cropland to mature Liaotungesis forest. The rate of increase in SOC is different during vegetation succession, and organic carbon functional groups varied among the different plant communities. Recent studies using synchrotron-based C(1s) near-edge X-ray absorption fine structure (NEXAFS) have shown it to be an effective, non-invasive technique, which can be used to identify and fingerprint the complex structural characteristics of SOC. Consequently it can be used to investigate the impact of management on the composition and biogeochemical cycling of organic C at the molecular level in terrestrial ecosystems. This synchrotron radiation technology has rarely been used to study SOC structure in China before so we used it in this study with the objective of developing a new method to explore the effect of the succession process under typical plant species (Bothriochlor ischaemum, Sophora viciifolia, Quercus liaotungensis) on changes in SOC functional groups. The time succession sequence could be inferred from current vegetation spatial arrangements. Therefore, we collected samples from two soil layers (0-5 cm,20-40 cm) in soil profiles under selected vegetation systems typically representing different vegetation succession stages in the region. Results obtained, which were qualitatively analyzed, indicated that aliphatic-C and ketone-C absorption intensities in samples from the 0-5 cm and 20-40 cm soil layers increased significantly during the vegetation process: the peak intensity of aliphatic-C of the 0-5cm layer was greater than in the 20-40 cm layer; the ketone-C absorption intensity of samples from the 0-5 cm soil layer was less than in the 20-40 cm layer. Results of a semi-quantitative analysis showed that the functional groups' relative percentage content in the 0-5 cm soil layers increased during the plant succession process, and the aliphatic-C aromatic-C, and ketone-C contents followed a gradually increasing trend. For the Quercus liaotungensis community, the aliphatic-C relative percentage content increased significantly in the 20-40 cm soil layer. The results show that the SOC functional groups from different land use-type samples were basically identical, and that the revegetation affected the change in the quantity of SOC functional groups during the revegetation process. Revegetation can promote increases in aliphatic-C and ketone-C contents in both the 0-5 cm and 20-40 cm soil layers, and this effect gradually increased with prolonged revegetation time This illustrated that the vegetation succession enhanced SOC chemical stability.