中国科学院水利部水土保持研究所机构知识库

水力侵蚀（简称侵蚀）与侵蚀劣地植被恢复（简称植被恢复）是土壤碳库的重要驱动因子，能够显著影响土壤碳库的封存与流失。在过去几十年，国内外学者针对侵蚀与植被恢复过程土壤有机碳库的动态变化进行了广泛探讨，但有关侵蚀与植被恢复环境土壤有机碳动态的微生物作用机制仍缺乏深入了解。因而，进一步研究黄土高原侵蚀与植被恢复环境微生物主导的有机碳矿化与固定潜力及其与土壤生物、非生物因子间的内在联系，对于揭示土壤侵蚀在全球碳循环中的角色定位以及探明微生物在土壤碳循环中所起的作用都具有重要意义。本研究选取黄土高原典型坝控小流域-桥子沟流域为研究对象，应用定量PCR、高通量测序与¹³C稳定同位素标记等分析技术，研究了侵蚀与植被恢复体系微生物主导的有机碳矿化与固定潜力及其影响机制。主要结论如下：

（1）阐明了坡面侵蚀与沉积环境土壤有机碳矿化的微生物作用机制。研究结果表明侵蚀区（坡上、坡中）细菌丰度显著高于沉积区（坡下），而细菌物种多样性与群落组成并无明显差异。此外，沉积区土壤有机碳矿化速率为19.02 mg CO₂-C kg^-1 d^-1，分别是坡上与坡下侵蚀区的1.26和1.07倍；有机碳矿化比呈现出坡中（0.082 g CO₂-C g^-1 SOC）>坡上（0.070 g CO₂-C g^-1 SOC）>坡下（0.064 g CO₂-C g^-1 SOC）的变化规律。侵蚀诱导土壤团聚体的破裂虽增加了侵蚀区土壤有机碳被微生物矿化分解的风险，但表层土壤活性有机碳的大量流失导致其可供微生物分解的有机碳量减少，其CO₂释放速率也相应降低。多元逐步回归分析结果表明碱解氮是土壤有机碳矿化的主要解释变量（60.2%）。相对细菌丰度与物种多样性，活性有机质是侵蚀坡面土壤有机碳矿化的主要调控因子。侵蚀坡面细菌丰度与有机碳矿化速率的空间分布异质性否定了土壤有机碳矿化微生物控制学说。研究结果表明土壤微生物对有机碳矿化表现出明显的功能冗余特征，侵蚀诱导微生物丰度与物种多样性的适度改变不会对土壤有机碳矿化产生显著影响。

（2）揭示了流域沟蚀作用下自养细菌群落与微生物固碳潜力的变化特征。   研究发现坡耕地自养细菌丰度与物种多样性指数分别是淤地坝的1.70和1.10倍，沟蚀诱导养分贫瘠土壤的沉积显著降低了淤地坝总自养细菌丰度与物种多样性，而以大气CO₂为专一碳源的专性自养菌相对丰度却得到显著提升，如硫杆菌（Thiobacillus）。此外，淤地坝微生物固碳速率为5.002 Mg C km^-2 yr^-1，是对应坡耕地的4.67倍；微生物固碳速率与有机碳含量，多数兼性自养菌相对丰度，总自养微生物丰度与物种多样性指数存在显著负相关关系，而与多数专性自养菌相对丰度显著正相关。因而，专性自养菌可能是微生物固碳的主要贡献者。逐步回归分析结果表明，可溶性有机碳是土壤微生物固碳速率的主要解释变量（72.0%），流域侵蚀通过影响活性有机碳的空间分布可有效改变自养微生物群落结构，如兼性自养菌与专性自养菌的占比，进而影响侵蚀与沉积环境土壤微生物固碳潜力。

（3）揭示了侵蚀劣地植被恢复过程土壤微生物与有机碳矿化速率间的内在联系。研究结果表明植被恢复区土壤细菌丰度（1.47 × 10⁷ copies g^-1）显著低于坡耕地（8.39 × 10⁸ copies g^-1），而植被恢复区土壤真菌:细菌比是侵蚀区的7.68倍，侵蚀劣地植被恢复过程土壤微生物由细菌为主导的群落向以真菌为主导的群落演变。此外，植被恢复区土壤有机碳矿化速率是侵蚀区的1.29倍，土壤碳矿化比则表现出相反的变化趋势，侵蚀劣地植被恢复虽降低了土壤有机碳被微生物矿化的风险，但植被恢复区活性有机质含量的增高显著提升了土壤CO₂释放速率。多元统计分析结果表明，可溶性有机碳是土壤有机碳矿化的主要解释变量（68.5%），侵蚀劣地植被恢复过程土壤活性有机质含量的高低在一定程度上调控着土壤CO₂释放速率的快慢。研究指出土壤微生物是有机碳矿化的主要承担者而非关键调控者。

（4）阐明了自养细菌群落与微生物固碳潜力对侵蚀劣地植被恢复的响应特征。研究结果表明侵蚀劣地植被恢复32年，植物碎屑与根系分泌物的大量输入虽有助于土壤碳、氮库的提升，但小冠花植物巨大的蒸腾损耗显著降低了土壤水分含量。植被恢复过程土壤有效水分的降低抑制了自养微生物的快速生长与增殖，致使植被恢复区土壤自养细菌丰度与物种多样性显著低于侵蚀劣地。此外，侵蚀劣地土壤微生物固碳速率为1.114 Mg C km^-2 yr^-1，是植被恢复区的1.748倍。主成分分析结果表明，微生物固碳速率与土壤水分、自养细菌丰度与物种多样性呈正向耦合关系，而与土壤碳、氮养分呈负向耦合关系。干旱半干旱区植被恢复诱导土壤水分的降低是微生物固碳潜力的主要限制因素，且其主要通过改变自养细菌群落来实现。

总的来说，侵蚀与植被恢复环境土壤有机碳矿化主要受有机质自身质量所调控，微生物对土壤有机碳矿化特征表现出明显的功能冗余，微生物是土壤有机碳矿化的主要“承担者”而非关键“调控者”。此外，微生物固碳速率与专性自养微生物相对丰度显著正相关，专性自养菌可能是土壤微生物固碳的主要“贡献者”。植被恢复诱导土壤水分的降低抑制了自养菌群的快速增殖，尤其是兼性自养菌，且进一步降低了微生物固碳潜力。该研究改变了微生物丰度决定土壤有机碳矿化速率的传统观念，证实了微生物在土壤有机碳矿化中的功能冗余与固碳中的关键贡献，为侵蚀与植被恢复体系土壤有机碳动态模拟与研究提供了新的思路。

Water erosion (erosion for short) and vegetation restoration of degraded cropland (vegetation restoration for short) are the important driving factors of soil carbon (C) dynamic, which have significant impacts on the sequestration and mineralization of soil organic carbon (SOC). In the past decades, SOC dynamic induced by erosion and vegetation restoration have been extensively studied, but there is still a lack of understanding of the role of soil microorganisms in them. Therefore, further study on the SOC mineralization and fixation potential dominated by soil microorganisms in erosional and vegetation restoration environemnts of the Loess Plateau and its intrinsic relationship with soil biotic and abiotic factors are of great importance for revealing the role of soil erosion in the global C cycle and exploring the role of microbes in the soil C dynamic. In this study, the typical dam-controlled small watershed-Qiaozigou watershed was selected as the research object. The qPCR, high-throughput sequencing and ¹³C stable isotope labeling were used to study the SOC mineralization and fixation potential dominated by soil microorganisms in the erosional and vegetation restoration system. The main conclusions are as follows:

1. The influence mechanism of soil microorganisms on SOC mineralization in slope erosional and depositional areas was elucidated. The results showed that lower bacterial abundance was observed in the down-slope site (depositional site) relative to the upper- and middle-slope sites (erosional sites), while there was no significant difference in bacterial species diversity and community composition. The SOC mineralization rate in down-slope site is 19.02 mg CO₂-C kg^-1 d^-1, which is 1.26 and 1.07 times of that in upper- and middle-slope sites, respectively. The SOC mineralization ratio shows middle-slope (0.082 g CO₂-C g^-1 SOC) > upper-slope (0.070 g CO₂-C g^-1 SOC) > bottom-slope (0.064 g CO₂-C g^-1 SOC). Erosion-induced destruction of soil aggregates increases the risk of SOC mineralization, but the lateral migration of SOC leads to a decrease in CO₂ release rate. Multiple stepwise regression analyses showed that available nitrogen was the main explanatory factor for the variation in SOC mineralization (60.2%, P = 0.009). Relative to bacterial abundance and species diversity, labile organic matter is the more important regulator for SOC mineralization. Microbial communities in soil appear to be characterized by a high functional redundancy, and erosion-induced moderate changes in microbial abundance and species diversity did not significantly affect SOC mineralization.
2. The study pointed out spatial redistribution of labile organic carbon induced by gully erosion can effectively change the autotrophic bacterial community composition, and then determine the microbial C-fixing potential in erosional and depositional sites. The results showed that autotrophic bacterial abundance and species diversity in slope cropland is 1.70 and 1.10 times of those in check dam, respectively. Gully erosion induced deposition of nutrient-poor soils significantly reduced the total autotrophic bacterial abundance and species diversity in check dam, while the relative abundance of obligate autotrophic bacteria, such as Thiobacillus, were significantly increased. In addition, the microbial C-fixing rate in check dam is 5.002 Mg C km^-2 yr^-1, which is 4.67 times of that in slope cropland. Microbial C-fixing rate was negatively correlated with SOC, relative abundances of most facultative autotrophs, total autotrophic bacterial abundance and Shannon index, while positively correlated with the relative abundances of most obligative autotrophs. Obligative autotrophs may be the major ‘contributor’ to microbial CO₂ fixation. Multiple stepwise regression analyses showed that dissolved organic carbon (DOC) was the main explanatory factor for the variation in microbial C-fixing rate (72.0%, P = 0.000). Gully erosion can effectively change the autotrophic bacterial community composition (such as the proportion of obligative autotrophs) by affecting the spatial distribution of labile organic carbon, and then determine the microbial C-fixing potential in erosional and depositional sites.
3. It reveals that soil microbe is the main ‘undertaker’ of SOC mineralization rather than the key regulator of it in the process of vegetation restoration. The results showed that bacterial abundance in the secondary garssland (1.47 × 10⁷ copies g^-1) was significantly lower than that in the cropland (8.39 × 10⁸ copies g^-1), while the fungi: bacteria in the secondary grassland was 7.68 times higher than that of cropland. Microbial communities transitioned from bacteria-dominant to fungi-dominant communities during vegetation restoration. Additionally, SOC mineralization rate in the secondary grassland was 1.29 times higher than that in the cropland, while the soil C mineralization ratio showed the opposite trend. Although vegetation restoration reduces the risk of SOC being mineralized, the increase in SOC during vegetation restoration significantly enhances the CO₂ release rate from soil. Multiple stepwise regression analysis showed that DOC explained up to 68.5% of the variation in SOC mineralization. Labile organic matter is the primary rate-limiting factor for SOC mineralization rate, and soil microbe may be the main ‘undertaker’ of SOC mineralization rather than the key regulator.
4. It clarified that great transpiration loss induced by vegetation restoration inhibits autotrophic bacteria growth, and which further reduced the potential of CO₂ fixation by autotrophic bacteria. Although the large input of plant debris and root exudates during vegetation restoration contributed to the improvement of soil C and nitrogen (N) pools, the huge transpiration loss induced by Coronilla varia plant reduced the soil moisture content. The reduction in soil available water inhibited the rapid growth of autotrophic bacteria, resulting in the abundance and species diversity of autotrophic bacteria in vegetation restoration sites were significantly lower than those in erosional sites. Microbial C-fixing rate in abandoned cropland (1.114 Mg C km^-2 yr^-1) was significantly (P<0.05) higher than that in secondary grassland, and it was positively influenced by soil moisture, autotrophic bacterial abundance and diversity. Overall, vegetation restoration of eroded agricultural land has negative impacts on autotrophic bacterial community and microbial C-fixing potential. In arid and semi-arid regions, great transpiration loss induced by vegetation restoration may inhibit autotrophic bacteria growth, and which further reduces the potential of CO₂ fixation by autotrophic bacteria.

In general, SOC mineralization in erosional and vegetation restoration system is mainly regulated by labile organic carbon, and microorganisms show obvious functional redundancy. soil microorganism is the main ‘undertaker’ of SOC mineralization rather than the key regulator. Furthermore, microbial C-fixing rate is positively correlated with the relative abundances of obligate autotrophs. Obligate autotrophs may be the main ‘contributor’ to microbial CO₂ fixation. Great transpiration loss induced by vegetation restoration inhibits autotrophic bacteria growth, and which further reduces the potential of CO₂ fixation by autotrophic bacteria. This study changed the traditional concept that microbial biomass determines the rates of SOC mineralization, and confirmed the microbial functional redundancy and the key contribution of soil autotrophic bacteria in SOC fixation, which provides a new idea for the simulation and research of SOC dynamic in erosional and vegetation restoration system.

第一章   绪论... 1

1.1 选题的背景与意义... 1

1.2 国内外研究进展... 2

1.2.1 土壤侵蚀及其生态环境效应... 2

1.2.2 侵蚀影响下土壤有机碳动态过程... 5

1.2.3 侵蚀劣地植被恢复过程土壤生物地球化学特性的改变... 11

1.2.4 土壤碳循环的微生物作用机制... 14

1.3存在的问题和不足... 18

1.4 研究目标与内容... 19

1.4.1 研究目标... 19

1.4.2 研究思路... 19

1.4.3 主要研究内容... 19

1.4.4 技术路线... 20

第二章  研究区域概况与分析方法... 21

2.1 研究区概况... 21

2.2 实验设计... 23

2.2.1 室内矿化培养实验... 23

2.2.2 室内固碳培养实验... 24

2.3 相关指标测定... 25

2.3.1 土样¹³⁷Cs含量测定与侵蚀速率估算... 25

2.3.2 土壤水分、容重、pH与颗粒组成测定... 26

2.3.3 土壤碳、氮养分测定... 27

2.3.4 土壤细菌、真菌与Cbbl固碳细菌群落分析... 28

2.4 数据处理与统计... 29

第三章  细菌群落与有机碳矿化对坡面侵蚀的响应... 30

3.1 材料与方法... 30

3.2 坡耕地各坡位侵蚀-沉积速率估算... 32

3.3 侵蚀作用下土壤理化参数动态特征... 33

3.4 侵蚀作用下土壤微生物群落变化特征... 36

3.5 侵蚀作用下土壤有机碳矿化动态特征... 41

3.6 土壤有机碳矿化与生物、非生物因子间的关系... 44

3.7 本章小结... 45

第四章  自养菌群与微生物固碳潜力对土壤侵蚀-沉积的响应    47

4.1 材料与方法... 47

4.2 ¹³⁷Cs活度对土壤沉积的负响应... 49

4.3 侵蚀作用下土壤理化参数动态特征... 51

4.4 侵蚀作用下固碳自养菌群变化特征... 55

4.5 侵蚀影响下微生物固碳潜力变化特征... 61

4.6 本章小结... 64

第五章  侵蚀劣地植被恢复对微生物群落与有机碳矿化的影响    66

5.1 材料与方法... 66

5.2 植被恢复土壤理化参数变化特征... 68

5.3 细菌与真菌丰度和物种多样性对植被恢复的响应特征... 72

5.4 细菌与真菌群落组成对植被恢复的响应特征... 76

5.5 植被恢复诱导土壤有机碳矿化变化特征... 83

5.6 本章小结... 86

第六章  侵蚀劣地植被恢复对自养菌群与微生物固碳潜力的影响    88

6.1 材料与方法... 88

6.2 植被恢复诱导土壤理化参数变化特征... 90

6.3 自养菌群丰度与物种丰富度对植被恢复的响应... 94

6.4 自养细菌群落组成对植被恢复的响应... 96

6.5 植被恢复诱导微生物固碳潜力变化特征... 103

6.6 本章小结... 106

第七章  主要结论与进一步研究设想... 108

7.1 主要结论... 108

7.2 主要创新点... 110

7.3 研究展望... 111

参考文献    112

致 谢... 126

作者简历及攻读学位期间发表的学术论文与研究成果    128