长期施肥下水稻根际和非根际土壤微生物碳源利用特征

Microbial Carbon Source Metabolic Profile in Rice Rhizosphere and Non-rhizosphere Soils with Different Long-term Fertilization Management

以红壤丘陵区典型稻田长期定位施肥试验土壤为研究对象,选取不施肥(CK)、化肥(NPK)、秸秆还田+化肥(NPKS)、30%有机肥+化肥(LOM)和60%有机肥+化肥(HOM)这5种处理,研究长期不同施肥条件下水稻根际和非根际土壤微生物碳源利用特征.基于^(18)O-H_2O示踪的结果表明,土壤微生物量碳(MBC)和微生物生长速率(CGrowth)均以HOM处理最高,CK处理最低.根际土中,土壤微生物基础呼吸速率以HOM最高,CK和NPK最低;微生物碳源利用效率(CUE)以NPK最高,LOM和HOM最低.非根际土中,不同施肥处理的基础呼吸速率和CUE均无显著差异. MicroResp^(TM)结果显示,非根际土中微生物对外源碳源代谢能力高于根际土.施用有机物料(秸秆或有机肥)均能提高微生物对羧酸类、氨基酸、碳水化合物的代谢速率,且土壤微生物利用羧酸类碳源的活性最高,其次为氨基酸类和碳水化合物类碳源,对复杂化合物的代谢速率较低. RDA分析表明,微生物对不同碳源代谢情况的聚类总体以根际土与非根际土分开,CK与施肥处理分开,且NPK与NPKS相对聚集,LOM与HOM相对聚集,NPK、NPKS与LOM、HOM分开,即不同施肥处理显著改变土壤微生物对外源碳源代谢特征.结果表明,施肥未改变微生物CUE和基础呼吸速率,但有外源碳源输入(如根系分泌物)的情况下,施用有机物料增加基础呼吸、降低CUE.

Rhizosphere and non-rhizosphere soil samples under different long-term fertilization treatments including control without fertilizer(CK),chemical fertilization alone(NPK),rice residues combined with NPK(NPKS),30%manure plus 70%chemical fertilizers(LOM),and 60%manure plus 40%chemical fertilizers(HOM)were collected from a paddy field in a red soil hilly area in Ningxiang City,Hunan Province,China.The characteristics of microbial carbon utilization in the soils were studied.Results of18OH2 O tracer analysis showed that both soil microbial biomass carbon content(MBC)and microbial growth rate(CGrowth)were highest in the HOM treatment,whereas they were lowest in CK.In the rhizosphere soil,the highest basal respiration was observed in HOM,and the lowest values were in CK and NPK.Microbial carbon utilization efficiency(CUE)was highest in NPK but lowest in the LOM and HOM treatments.In non-rhizosphere soil,no significant differences between basal respiration and CUE were observed among the fertilization treatments.Results from MicroRespTMshowed that the ability of microorganisms to metabolize exogenous carbon sources was higher in non-rhizosphere soil than in rhizosphere soil.The application of organic materials(rice residues or manure)increased the microbial metabolic rate of carboxylic acids,amino acids,and carbohydrates in the order carboxylic acids>amino acids and carbohydrates>complex compounds.Redundancy analysis of the microbial metabolism patterns of various carbon substrates showed that:①CK was well separated from the fertilization treatments;②NPK was grouped with NPKS,whereas LOM and HOM were grouped together and were separate from NPK and NPKS.This indicates that the fertilization treatments changed the microbial carbon metabolism patterns.The above-mentioned results indicated that the fertilization treatments did not affect microbial CUE and basal respiration.However,exogenous carbon source input(such as root exudates)and the application of organic materials can increase microbial basal respiration,and thus,reduce microbial CUE.