A water control pot experiment was conducted in climate controlled chambers to study soil carbon, nitrogen and microbial community structure and their rhizosphere effects in the rhizosphere and non rhizosphere soil of Bothriochloa ischaemum at elevated CO2 concentrations (800 μmol·mol-1) under three water regimes, i.e., well watered (75%-80% of field capacity, FC), moderate drought stress (55%-60% of FC), and severe drought stress (35%-40% of FC). The results showed that elevated CO2 concentration and drought stress did not have significant impacts on the content of soil organic carbon, total nitrogen or dissolved organic carbon (DOC) in the rhizosphere and bulk soils or their rhizosphere effects. Elevated CO2 concentration significantly decreased dissolved organic nitrogen (DON) content in the rhizosphere soil under moderate drought stress, increased DOC/DON, and significantly increased the negative rhizosphere effect of DON and positive rhizosphere effect of DOC/DON. Drought stress and elevated CO2 concentration did not have significant impacts on the rhizosphere effect of total and bacterial phospholipid fatty acids (PLFA). Drought stress under elevated CO2 concentration significantly increased the G+/G- PLFA in the rhizosphere soil and decreased the G+/G- PLFA in the bulk soil, so its rhizosphere effect significantly increased, indicating that the soil microbial community changed from chemoautotroph microbes to heterotrophic microbes.
采用人工气候室和盆栽控水试验研究黄土丘陵区典型草本植物白羊草在倍增CO2浓度(800 μmol·mol-1)下和充分供水(75%～80%的田间持水量)、轻度干旱胁迫(55%～60%的田间持水量)和重度干旱胁迫(35%～40%的田间持水量)下根际和非根际土壤碳氮含量和微生物群落结构及其根际效应.结果表明：CO2浓度升高和干旱胁迫对白羊草根际和非根际土壤有机碳、全氮和水溶性有机碳(DOC)含量及其根际效应均无显著影响.轻度干旱胁迫下CO2浓度升高显著促进了根际土壤水溶性有机氮(DON)的消耗，导致DOC/DON升高，提高了DON的负根际效应和DOC/DON的正根际效应.干旱胁迫和CO2浓度升高对土壤总磷脂脂肪酸(总PLFA)和细菌PLFA的根际效应无显著影响.CO2浓度升高条件下干旱胁迫显著提高了根际土壤G+/G- PLFA，降低了非根际土壤G+/G- PLFA，导致其根际效应显著提高，表明根际微生物群落由自养微生物群落向异养微生物群落的转变.
Keywords: Bothriochloa ischaemum; PLFA; drought; elevated CO2 concentration; rhizosphere effect.