外源输入碳在生物结皮土壤各碳组分中的分配特征

研究外源新输入碳进入生物结皮后在各碳组分间的分配特征,可以为理解生物结皮参与碳地球化学循环过程提供数据支持和理论依据。本研究针对黄土高原典型苔藓生物结皮,借助¹³C脉冲标记技术,精确示踪外源新输入碳在生物结皮碳组分中的分配特征及其与无结皮裸地的差异,揭示生物结皮对碳循环的影响。结果表明: 1)由于生物结皮养分循环速率较慢,且与维管束植物相比,其主要生物成分苔藓的生物量有限,导致生物结皮各碳组分的¹³C丰度值均随时间变化表现相对平稳。2)生物结皮的各碳组分¹³C含量均明显高于无结皮裸地,其有机碳、微生物生物量碳、可溶性有机碳中¹³C含量平均分别为0.258、0.078、0.004 mg·kg^-1,分别比裸地高3.1、18.5、2.6倍,且苔藓植株¹³C含量高达1.45 mg·kg^-1。3)生物结皮改变了有机碳各组分的分配特征,其新同化的碳主要分配于活性有机碳库和结皮生物中,表现为¹³C在微生物生物量碳中的分配率(30.6%)高于可溶性有机碳(1.7%),而苔藓植株的¹³C分配率为20.3%。4)生物结皮中微生物生物量¹³C的转移量和库容量分别是裸地的15.7和19.5倍,但其周转率(每月2.94次)略低于裸地(每月3.30次),相应周转期是裸地的1.1倍。综上,生物结皮改变了土壤有机碳组分的分配特征,提升了碳周转速率,在干旱荒漠生态系统碳循环中的作用不容忽视。

Distribution characteristics of exogenous carbon in different carbon fractions in biocrusts-covered soil

The distribution characteristics of exogenous carbon (C) in the C fractions of biocrusts-covered soil are critical for understanding the geochemical cycling of C with biocrusts in drylands. A ¹³C pulse labeling experiment was conducted for moss-dominated biocrusts-covered soil and bare soil on the Loess Plateau of China with semiarid climate, with the content of ¹³C in different C fractions being continuously measured to determine the biocrust effects on the distribution of exogenous C in each C fraction. Our results showed that, 1) the ¹³C abundance of each C fraction in the biocrusts-covered soil was steadily changed with time, due to the relatively low rate of nutrient cycling in the biocrusts-covered soil and also to the relatively low biomass of moss in the biocrusts-covered soil as compared with vascular plants. 2) The ¹³C content of each C fraction in the biocrusts-covered soil was significantly higher than that in the bare soil. Specifically, the ¹³C content of total organic C (TOC), microbial biomass C (MBC), and dissolved organic C (DOC) in the biocrusts-covered soil was 0.258, 0.078, and 0.004 mg·kg^-1, respectively, which was 3.1, 18.5, and 2.6 times higher than that in the bare soil. Moreover, the ¹³C content in the moss of the biocrusts-covered soil was 1.45 mg·kg^-1. 3) The presence of biocrusts changed the distribution characteristics of each C fraction, with the newly assimilated C being mainly distributed in active organic C and biological components of the biocrusts-covered soil. In the biocrusts-covered soil, the ¹³C distribution in MBC (30.6%) was higher than that in DOC (1.7%), and the ¹³C distribution in the C of moss was 20.3%. 4) The transferred amount and storage capacity of MB¹³C in the biocrusts-covered soil were 15.7 and 19.5 times of that in the bare soil, respectively. The turnover rate of MB¹³C in the biocrusts-covered soil and bare soil was 2.94 and 3.30 times per month, respectively, implying that the turnover time of MB¹³C in the biocrusts-covered soil was 1.1 times longer than that in the bare soil. In conclusion, biocrusts could greatly change the distribution characteristics of each C fraction and increase C turnover rate, highlighting its important roles in C cycling in dryland ecosystems.