Changes in soil organic carbon content and their causes during the degradation of alpine meadows in Zoigê Wetland

doi:10.17521/cjpe.2020.0231

Abstract

Abstract:

Aims The balance between soil organic carbon (SOC) input and output processes determines SOC content. However, it is not clear which of the two processes dominantly affect SOC content during the degradation of alpine meadows in Zoigê Wetland. In this study, the changes in SOC contents of alpine meadows and their causes at different degradation stages (alpine meadow (AM), slightly degraded alpine meadow (SD), and heavily degraded alpine meadow (HD)) in the Zoigê Wetland were investigated using the method of spatial sequence instead of temporal successional sequence.
Methods First, the changes in C input to soil and their causes along the degradation gradient were analyzed by investigating main soil physicochemical properties, microbial biomass, plant biomass and community composition of plant functional groups at different degradation stages. Secondly, the changes in the C output from soil were estimated based on lab incubation experiments of soil C mineralization and the temperature sensitivity of soil respiration (Q₁₀) and monthly average air temperature of the Zoigê Wetland. Finally, the main causes and processes leading to changes in SOC content along the degradation gradient were analyzed.
Important findings The results showed that soil water content (SWC), SOC content, total nitrogen (TN) content, microbial biomass C and N content decreased with the increase of degradation. Plant community composition gradually changed from sedges and grasses dominated community to forbs dominated community. Plant biomass and SOC mineralization rate decreased during the degradation of alpine meadows. The potential accumulation of organic C reduced during the degradation (compared with AM, the potential input, output and accumulation of organic C in SD and HD decreased by 16%, 18%, 15% and 59%, 63%, 41%, respectively). The decrease in SWC changed soil physical and chemical properties, including bulk density, SOC content, TN content, total phosphorus content, and C:N, which led to the shifts in the distribution pattern of plant functional groups and in soil microorganisms, consequently reducing the inputs and outputs of SOC. The decrease in potential plant-derived C input to soil caused by decreased SWC was the main reason for the decline in SOC content along the degradation gradient of alpine meadows in Zoigê Wetland.

Key words: alpine meadow, soil organic carbon, carbon input, soil accumulative carbon mineralization

DONG Li-Jun, LI Jin-Hua, CHEN Shan, ZHANG Rui, SUN Jian, MA Miao-Jun. Changes in soil organic carbon content and their causes during the degradation of alpine meadows in Zoigê Wetland[J]. Chin J Plant Ecol, 2021, 45(5): 507-515.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2020.0231

https://www.plant-ecology.com/EN/Y2021/V45/I5/507

Figures/Tables 5

Table 1 Classification basis of degradation stages of alpine meadows in Zoigê Wetland

草地类型 Grassland type	优势种 Dominant species	主要伴生种 Major associated species	塔头情况 Condition of grass hill	鼠兔洞穴 Pika cave	总盖度 Total coverage (%)
高寒草甸 Alpine meadow (AM)	木里薹草 Carex muliensis	鹅绒委陵菜、矮生嵩草 Potentilla anserine, Kobresia humilis	塔头高10-20 cm The height of grass hill was 10-20 cm	无 No	92
轻度退化高寒草甸 Slightly degraded alpine meadow (SD)	木里薹草 C. muliensis	鹅绒委陵菜、华扁穗草 P. anserine, Blysmus sinocompressus	无塔头 No grass hill	有 Yes	97
重度退化高寒草甸 Heavily degraded alpine meadow (HD)	二裂委陵菜 P. bifurca	鹅绒委陵菜、木里薹草 P. anserine, C. muliensis	无塔头, 出现斑块化裸地, 部分土地沙化 No grass hill, there were patches of bare land, and partially desertifield land	有 Yes	64

Fig. 1 Soil physicochemical characteristics along degradation gradients (mean ± SE). AM, alpine meadow; HD, heavily degraded alpine meadow; SD, slightly degraded alpine meadow. Different lowercase letters indicate significant difference among the degradation stages (p < 0.05).

Fig. 2 Principal component analysis (PCA) of plant functional groups (grasses, sedges, and forbs) importance value and degradation gradient. AM, alpine meadow; HD, heavily degraded alpine meadow; SD, slightly degraded alpine meadow.

Fig. 3 Redundancy analysis (RDA) of plant functional groups importance value (A), cumulative soil carbon mineralization (B) and soil physicochemical properties. C1, C15, and C31 represent the cumulative mineralization amount of soil carbon during 1day, 15 days, and 31 days of incubation, respectively. BD, bulk density; MBC, microbial biomass carbon content; MBN, microbial biomass nitrogen content; MBP, microbial biomass phosphorus content; SOC, soil organic carbon content; SWC, soil water content; TN, total nitrogen content; TP, total phosphorus content.

Fig. 4 Characteristics of potential input, output, and accumulation of soil organic carbon along degradation gradients (mean ± SE). AM, alpine meadow; HD, heavily degraded alpine meadow; SD, slightly degraded alpine meadow. Different lowercase letters indicate significant difference among the degradation stages (p < 0.05).

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