ABSTRACT
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.
Subject(s)
Bryophyta , Soil , Carbon , China , EcosystemABSTRACT
Nitrogen (N) labeled with 15N was evenly added into plots of moss-dominated biological soil crusts (BSCs) and bare soil on the Chinese Loess Plateau. After that, the surface BSCs and bare soil samples were continuously collected within 1-30 days. The 15N content of each N fraction in soil, microorganisms, and mosses was measured for each sample. The effects of BSCs on soil N fate and cycling was determined through analyzing the differences in the distribution of 15N fractions between the BSCs and bare soil. Our results showed that: 1) The 15N content of total N (TN), microbial biomass N (MBN), and dissolved organic N (DON) in the BSCs was 2.9, 17.5, and 9.0 times higher than that in the bare soil, respectively. The 15N content of moss plants in the BSCs was 4.73 mg kg-1. 2) The residual rate of 15N in the BSCs and bare soil was 13.0% and 3.3%, respectively, indicating that the N fixing and holding ability of BSCs was four times higher than that of bare soil. The percentage of each 15N fraction in T15N in the BSCs was in the order of MBN (54.3%)>moss plant N (22.5%)>DON (6.2%), while that in the bare soil was in the order of MBN (11.5%)>DON (2.6%). Over all, microorganisms and mosses in the BSCs had 65.3% higher capacity of N fixation as compared with the bare soil. 3) The transferred amount and storage capacity of MB15N in the BSCs were 17.2 and 20.5 times higher than that in the bare soil, respectively. Accordingly, the turnover rate of MB15N in the BSCs and bare soil was 5.8 and 7.2 times per month, respectively, with the turnover time of MB15N in the BSCs being 1.2 times longer than that in bare soil. In conclusion, BSCs fix and hold more N than bare soil and change the distribution of each N fraction, implying that BSCs play a critical role in N cycling in dryland ecosystems.
Subject(s)
Bryophyta , Soil , Ecosystem , Nitrogen , Soil MicrobiologyABSTRACT
The 30-year-old biological soil crusts dominated by mosses (hereafter moss crusts) and corresponding uncrusted soil (hereafter no crust) were sampled on loess soil and aeolian soil at 0-12 cm depth on the Loess Plateau of China. Afterwards, the hydrolase activities of the samples were measured, and their correlations with soil physicochemical properties were analyzed. Compared with no crust, the activities of urease, alkaline phosphatase, invertase, and protease of the moss crusts were 2.4, 7.6, 20.7, 2.4 times higher on loess soil, respectively; while they were 3.5, 22.2, 22.3, 2.0 times higher on aeolian soil, respectively. Compared with no crust, the soil water content of the moss crusts was decreased by 6.5% and 0.8% on loess soil and aeolian soil, and the soil temperature of the moss crusts was decreased by 0.8 and 2.5 â, respectively; the contents of soil organic matter, alkali-hydrolyzable nitrogen, and available phosphorus of the moss crusts were 2.5, 2.9 and 3.6 times higher on the loess soil, and they were 3.6, 3.0 and 6.6 times higher on the aeolian soil, respectively. The soil hydrolase activities were positively correlated with the soil nutrient content and negatively correlated with the soil water content. Soil temperature was positively correlated with the urease activity and negatively correlated with the protease activity. The moss crusts significantly improved soil nutrients and fertility through increasing soil enzyme activities on the Loess Plateau of China, and these effects were reasonably attributed to the moderate soil water content and temperature regulated by the moss crusts.
