土壤微生物群落对玉米根茬和茎叶残体碳的利用特征

以沈阳农业大学连续29a棕壤长期定位施肥试验为基础，以¹³C标记的玉米植株为试验试材，采用田间原位培养方法和磷脂脂肪酸-稳定同位素示踪联用（PLFA-SIP）技术，研究土壤不同粒级团聚体中微生物群落对残体碳的同化状况，及土壤有机碳的固定这一关键生物地球化学过程.结果表明：植物残体添加显著增加了全土及各粒级团聚体中各微生物群落PLFAs含量，其中以真菌PLFAs含量增幅最高，细菌中以革兰氏阴性菌含量增幅最高；但不同残体类型并未对全土中各群落PLFAs含量产生显著影响.茎叶碳与根茬碳的矿化率无显著差异；根茬碳对总PLFAs碳库的贡献是茎叶碳的3.9倍，说明根茬碳更有利于通过微生物合成的方式贡献于土壤有机碳库.残体碳占不同微生物群落PLFAs碳库的比例以真菌最高，表明真菌对植物残体碳具有最强的同化能力；而残体碳对PLFAs的贡献在革兰氏阳性菌和革兰氏阴性菌之间却差异不大.残体碳含量、PLFAs含量和残体碳占微生物PLFAs碳库的比例均在较小粒级的团聚体中（0.25~1mm和<0.25mm）更高，而细菌/真菌比在较大粒级团聚体（>2mm和1~2mm）中更高，说明较小粒级团聚体已经成为微生物对残体进行同化固定的主要位点.植物残体在土壤中的腐解过程与残体类型、土壤团聚体组成和微生物群落密切相关.

Characteristics of microbial utilization of maize root- and straw derived carbon

Based on the long-term fertilization experiment station established in 1987, ¹³C labeled maize residues (root or straw) were added into Brown Earth and then in-situ incubated for 150days. We investigated the assimilation dynamics of maize residue carbon (C) by various microbial communities in different soil aggregates with PLFA-SIP technique, as well as the SOC sequestration process. Plant residue addition significantly increased the PLFAs contents, especially fungal PLFAs, in bulk soil and all aggregate fractions. Besides, the increase of gram-negative bacterial PLFA was greater than that of gram-positive bacterial PLFA after residue incorporation. However, residue type did not affect the PLFAs contents in different microbial groups in bulk soil. The difference in the residue C mineralization rate was not significant between the treatments of straw and root additions. The contribution of root C to the total PLFAs C was 3.9 times that of straw C to the total PLFAs C, suggesting that microbial synthesis of root C was more conducive to the sequestration of SOC. Among all microbial groups, the contribution of residue C to fungal PLFA C was highest, indicating that fungi had the strongest ability to assimilate residue C. Whereas, the contribution of residue C to gram-positive PLFA C was similar to that to gram-negative bacterial PLFA C. The contents of residue C and PLFAs and the proportion of residue C in total PLFAs C were higher in the 0.25~1mm and <0.25mm aggregates, while the bacteria/fungi ratio was higher in the >2mm and 1~2mm aggregates which indicated that the 0.25~1mm and <0.25mm aggregates were the main sites for microbial assimilation for residue C. We conclude that the decomposition of plant residue in soil is closely related to residue type, soil aggregate composition and microbial community.