生物土壤结皮演替对土壤生态化学计量特征的影响

生物土壤结皮(生物结皮)是干旱半干旱地区重要的地表覆被物,能够固定碳氮,影响养分循环,从而可能引起土壤化学计量特征的变化。以黄土丘陵区不同演替阶段生物结皮为研究对象,研究该区生态恢复初期生物结皮演替对土壤碳(C)、氮(N)、磷(P)含量及其化学计量特征的影响。结果表明:(1)生物结皮显著增加了生物结皮层C、N、P含量,后期藓结皮较初期藻结皮C、N、P含量分别增加了161%、127%和9%,均显著高于其下0—10 cm土壤;(2)土壤C/N随着生物结皮演替变化较小,范围为10.0—11.8,C/P和N/P在演替后期分别是初期的2.4倍和2.1倍,均显著高于其下0—10 cm土壤;(3)生物结皮土壤C/N、C/P与N/P受坡向影响较大,并与藓生物量显著正相关,与土壤容重显著负相关;(4)生物结皮显著影响土壤C、N、P含量及其化学计量特征,使生物结皮层显著不同于其下层土壤及裸地;(5)生物结皮演替加速表层土壤养分恢复,影响程度可至其下2 cm土层。研究初次从土壤化学计量特征的角度揭示生物结皮对土壤养分循环的贡献,对干旱半干旱地区生态修复和管理具有指导意义。

The effects of biological soil crust succession on soil ecological stoichiometry characteristics

Biological soil crusts (biocrusts) are ubiquitous living surface covers in arid and semi-arid regions. The succession of biocrusts exerts significant influence on soil nutrient cycles owing to their functions of carbon and nitrogen fixation. Therefore, soil ecological stoichiometry characteristics are likely to be affected by the succession of biocrusts. To explore the effects of biocrusts on the contents of organic carbon (C), total nitrogen (N), total phosphorus (P), and their stoichiometric characteristics, biocrusts in six successional stages, totaling 59 sites, were chosen from the hilly Loess Plateau region. Biocrusts and subsoils (0-2 cm, 2-5 cm, and 5-10 cm) were sampled at each site. The contents of C, N, and P were analyzed and their ratios were calculated. The results showed that biocrusts significantly affected the contents of C, N, and P, and their ratios, which resulted in differences between biocrusts and the soils beneath them. Further, the differences increased with the succession of the biocrusts. The contents of C, N, and P significantly increased in the biocrust layers, which were significantly higher than that of the subsoils (0-10 cm). The contents of C, N, and P in biocrusts increased by 161%, 127%, and 9%, respectively, in the later successional stage compared with that in the earlier stage. The ratios of C/N, C/P, and N/P in biocrusts were all significantly higher than in the soils beneath them (0-10 cm). Variances of C/N were lower than that of C/P and N/P, with a range from 10.0 to 11.8. The C/P and N/P ratios in the later successional stage of biocrusts were 2.4 and 2.1 times as high as that in the earlier successional stage, respectively. The slope aspect was the major influencing factor for the ecological stoichiometry characteristics of biocrusts. The ratios of C/N, C/P, and N/P were positively correlated with moss biomass and negatively correlated with soil bulk density. The recovery of topsoil nutrients was improved owing to the succession of biocrusts and the improvement of recovery appeared to be limited to a maximum depth of 2 cm under the biocrusts. Owing to the significant influences of biocrust succession on soil nutrients and their stoichiometric characteristics, and the differences between biocrusts and their subsoil, biocrusts play a crucial role for ecological restoration in arid and semi-arid regions. The results reveal the contribution of biocrusts to nutrient cycles from the perspective of soil stoichiometric characteristics and the study provides scientific basis to the ecological restoration and management in arid and semi-arid regions.