Many studies have shown that the microbial biomass content in paddy soils is much higher than that in upland soils, but a comprehensive review of the underlying mechanisms and processes is lacking. We conducted a meta-analysis of published literature on the microbial biomass content in continuous paddy soils (>1700 data pairs) and paddy-upland rotation soils (>1100 data pairs) as compared to that in adjacent upland soils (>360 data pairs), measured by the fumigation extraction or fumigation incubation method. The microbial biomass carbon (MBC) content in paddy soils was double that in upland soils. This MBC surplus in paddy soils compared to upland soils was explained by (1) higher input of root C and rhizodeposits by rice plants compared with upland crops; (2) lower oxygen availability and consequently slower microbial turnover; (3) higher microbial C assimilation efficiency in paddy soils; and (4) additional C stabilization on iron (oxyhydr)oxides in paddy soils. The proportion of MBC in total soil organic C in paddy-upland rotation, paddy, and upland soils was 3.5%, 2.5%, and 2.1%, respectively. The higher microbial biomass C/N ratio in paddy soils (12.4 ± 0.11) compared to upland soils (9.9 ± 0.21) reflects greater N losses (through nitrate leaching and denitrification) in relation to slower C losses under anoxic conditions. Despite higher temperature and better water availability, microbial biomass turnover was 1.1–1.6 times slower in paddy soils than in upland soils because of oxygen limitation. Multiple stepwise regression and redundancy analyses showed that microbial biomass in continuous paddy and paddy-upland rotation soils was affected by similar soil factors (such as total N and organic C), whereas microbial biomass in upland soils was mainly affected by pH and the organic C content. Paddy-upland rotation soils undergo oxic–anoxic cycles and consequently can absorb and coprecipitate organic compounds with iron (oxyhydr)oxides as an additional advantage for C stabilization. We conclude that the reduced microbial activity and slower microbial turnover under oxygen-limited conditions lead to nearly two times higher microbial biomass content in paddy than in upland soils.

许多研究表明，水稻土中微生物生物量含量远高于旱地土壤，但缺乏对其潜在机制和过程的全面回顾。我们对已发表的关于连续稻田土壤（>1700 个数据对）和稻田-旱地轮作土壤（>1100 个数据对）中微生物生物量含量与相邻旱地土壤（>360 个数据对）的微生物生物量含量进行了荟萃分析，通过熏蒸提取或熏蒸孵育法测定。水稻土中微生物生物量碳（MBC）含量是旱地土壤中的两倍。与旱地土壤相比，稻田土壤中 MBC 过剩的原因是 (1) 与旱地作物相比，水稻植物的根 C 和根际沉积物的输入量更高；(2) 氧气利用率较低，因此微生物周转速度较慢；(3)稻田土壤微生物碳同化效率较高；(4) 稻田土壤中铁（羟基）氧化物的额外 C 稳定性。MBC占水旱轮作、水稻和旱地土壤总有机碳的比例分别为3.5%、2.5%和2.1%。与旱地土壤 (9.9 ± 0.21) 相比，稻田土壤中较高的微生物生物量 C/N 比 (12.4 ± 0.11) 反映了与缺氧条件下较慢的 C 损失相关的更大的 N 损失（通过硝酸盐浸出和反硝化作用）。尽管有更高的温度和更好的可用水量，但由于氧气的限制，稻田土壤中微生物生物量的周转速度比旱地土壤慢 1.1-1.6 倍。多元逐步回归和冗余分析表明，连续水稻和水旱轮作土壤微生物生物量受相似土壤因子（如全氮和有机碳）的影响，而旱地土壤微生物生物量主要受pH和有机碳的影响。内容。稻田-旱地轮作土壤经历好氧-缺氧循环，因此可以吸收和共沉淀有机化合物与铁（羟基）氧化物，作为 C 稳定的额外优势。我们得出的结论是，在缺氧条件下，微生物活性降低和微生物更新较慢导致水稻中微生物生物量含量比旱地土壤高近两倍。稻田-旱地轮作土壤经历好氧-缺氧循环，因此可以吸收和共沉淀有机化合物与铁（羟基）氧化物，作为 C 稳定的额外优势。我们得出的结论是，在缺氧条件下，微生物活性降低和微生物更新较慢导致水稻中微生物生物量含量比旱地土壤高近两倍。稻田-旱地轮作土壤经历好氧-缺氧循环，因此可以吸收和共沉淀有机化合物与铁（羟基）氧化物，作为 C 稳定的额外优势。我们得出的结论是，在缺氧条件下，微生物活性降低和微生物更新较慢导致水稻中微生物生物量含量比旱地土壤高近两倍。