稻田与旱地土壤中真菌和细菌对秸秆碳的利用特征

微生物将植物残体矿化为CO₂和同化为微生物细胞组成部分是新鲜有机物料转化为土壤有机质的关键环节.以亚热带两种典型农业利用（稻田和旱地）土壤为对象,采用40 d室内模拟培养试验结合磷脂脂肪酸-稳定同位素示踪联用(¹³C-PLFA-SIP)技术,研究¹³C标记秸秆的矿化特征以及参与秸秆降解的细菌和真菌类群变化规律.结果表明,培养前期（0.25～1 d）,秸秆碳在稻田土壤中的矿化速率高于旱地土壤,中期（2～20 d）以稻田土壤低于旱地土壤（P<0.05）,后期（21～40 d）两者矿化速率相当.培养结束时,秸秆碳在稻田土壤中的累积矿化率（11%）约为旱地（20%）的一半.尽管稻田土壤中总微生物量（PLFA总量）比旱地高,但两种土壤中秸秆碳被微生物同化为细胞组分的量(¹³C-PLFA)相当,且稻田中秸秆碳的富集比例(PLFA中¹³C占总碳量的百分比)低于旱地,说明稻田土壤中参与秸秆碳降解的活性微生物占比少.整个培养期内,稻田土壤中秸秆碳被微生物利用的优势类群为细菌(占^1...

Characteristics of Microbial Utilization for Crop Residue-Derived C in Paddy and Upland Soils

Two typical subtropical agricultural soils, a flooded paddy soil and its adjacent upland, were collected and then incubated with or without ¹³C-labeled crop residue (maize straw) for 40 days. During the incubation, the mineralization rate of the crop residue was monitored, and the ¹³C incorporated into fungal and bacterial phospholipid fatty acid (PLFA) was quantified. At the early stage (0.25-1 days), the mineralization rate of crop residue was faster in paddy soil than that in upland soil, whereas the opposite trend was observed from 2 to 20 days. At the late stage (21-40 days), the mineralization rate was similar in both soils. At the end of incubation, 11% of the total crop residue was mineralized in paddy soil, which was about half of that in upland soil (20%). Although paddy soil had a higher amount of microbial biomass (indicated by total PLFA), the total amounts of ¹³C-PLFA were comparable in both soils, and the enrichment ratio (proportion of ¹³C to total C in PLFA) was lower in paddy soil than that in upland soil. This indicated that the microbial community in paddy soil was less active in the uptake of crop residue C than that in upland soil. During the incubation, the residue-derived ¹³C was mainly distributed in bacterial PLFA (up to 86% of total ¹³C-PLFA, including 59% in gram-positive and 27% in gram-negative bacteria) in paddy soil, and up to 75% of total ¹³C-PLFA distributed in fungal PLFAs was in upland soil. Thus, bacteria dominated the utilization of crop residue in paddy soil versus fungi in upland soil. Compared with that in upland soil, the microbial activity was suppressed in the anaerobic condition caused by flooding in paddy soil, with a stronger inhibition of fungi than bacteria. Considering the discrepancies of life strategies and necromass turnover between bacteria and fungi, the different dominant microbial groups in the utilization of crop residue in water-logged and well-drained conditions could lead to the distinct accumulation and stabilization of microbial-derived organic matter in paddy and upland soils.