若尔盖湿地高寒草甸退化过程中土壤有机碳含量变化及成因分析

doi:10.17521/cjpe.2020.0231

摘要/Abstract

摘要：

土壤碳输入与输出之间的收支差决定土壤有机碳(SOC)含量。若尔盖湿地高寒草甸退化过程中, 土壤碳输入和输出哪个过程对SOC含量的影响占主导作用还不明确。该研究用空间序列代替时间序列的方法研究了若尔盖湿地高寒草甸不同退化阶段(高寒草甸(AM)、轻度退化高寒草甸(SD)和重度退化高寒草甸(HD)) SOC含量变化及原因。首先, 通过测定高寒草甸退化阶段上主要的土壤理化性状、微生物生物量、植物生物量和功能群组成的变化, 分析了退化阶段上土壤碳输入量的变化及原因; 其次, 结合室内土壤碳矿化培养实验结果和研究区的月平均气温以及土壤呼吸温度敏感性(Q₁₀)估算了该区域土壤碳输出, 并分析了其变化原因; 最后, 分析了造成SOC含量变化的主要原因和过程。结果表明: 在退化梯度上, 土壤含水量(SWC)、SOC和全氮(TN)含量、微生物生物量碳氮含量降低; 植物群落组成逐渐从莎草科、禾本科占优势过渡到杂类草占优势, 且植物生物量降低; SOC矿化量降低; 有机碳潜在积累量降低(与AM阶段相比, SD和HD阶段有机碳潜在输入量、输出量和积累量分别降低了16%、18%、15%和59%、63%、41%)。SWC降低引起土壤容重、SOC含量、TN含量、全磷含量、C:N的改变, 进而导致植物功能群分布模式和土壤微生物的变化, 最终引起SOC输入和输出量的降低。SWC降低导致的植物碳潜在输入量的降低是若尔盖湿地高寒草甸退化过程中SOC含量下降的主要原因。

关键词: 高寒草甸, 土壤有机碳, 碳输入, 土壤累积碳矿化

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

董利军, 李金花, 陈珊, 张瑞, 孙建, 马妙君. 若尔盖湿地高寒草甸退化过程中土壤有机碳含量变化及成因分析. 植物生态学报, 2021, 45(5): 507-515. DOI: 10.17521/cjpe.2020.0231

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. Chinese Journal of Plant Ecology, 2021, 45(5): 507-515. DOI: 10.17521/cjpe.2020.0231

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2020.0231

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

图/表 5

表1 若尔盖湿地高寒草甸退化阶段划分依据

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

图1 若尔盖湿地高寒草甸退化梯度上土壤理化性质变化特征(平均值±标准误)。AM, 高寒草甸; HD, 重度退化高寒草甸; SD, 轻度退化高寒草甸。不同小写字母表示在退化梯度上差异显著(p < 0.05)。

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).

图2 植物功能群(禾本科、莎草科、杂类草)重要值与退化梯度主成分分析(PCA)。AM, 高寒草甸; HD, 重度退化高寒草甸; SD, 轻度退化高寒草甸。

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.

图3 植物功能群重要值(A)和土壤碳累积矿化量(B)与土壤因子的冗余分析(RDA)。C1、C15、C31分别表示第1、15、31天的土壤碳累积矿化量。BD, 容重; MBC, 微生物生物量碳含量; MBN, 微生物生物量氮含量; MBP, 微生物生物量磷含量; SOC, 土壤有机碳含量; SWC, 土壤含水量; TN, 全氮含量; TP, 全磷含量。

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.

图4 退化梯度上土壤有机碳潜在输入量、输出量、积累量变化特征(平均值±标准误)。AM, 高寒草甸; HD, 重度退化高寒草甸; SD, 轻度退化高寒草甸。不同小写字母表示该指标在退化梯度上差异显著(p < 0.05)。

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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