Effects of Rising Temperature and Elevated CO2 on Rhizoshere Microbial Community Structure in Three Crop Species.

Elevated CO₂ accompanying increasing temperature has great effects on crop productivity and stability. While the responses of aboveground plants to temperature and CO₂ have been extensively examined, it is not well understood how belowground rhizosphere microbial community is affected by the environmental changes. We examined responses of rhizophsere microbial community structure to rising temperature, elevated CO₂ concentration and different soil fertility in three crops: soybean(Glycine max), wheat(Triticum aestivum), and canola(Brassica napus).
Plants were raised in environmentally controlled greenhouses(“Gradiotron”), where air temperature within a house is gradually increased by 5℃. Two glasshouses were used. One was set at same as atmospheric CO₂ and the other was 200ppm higher than atmospheric CO₂. Planting soil had two nutrient conditions. One was added 300mg of fertilizer(N:12%, P;18%, K:16%), and the other received no fertilizer. Plants were harvested at five weeks after seeding, and shoot and leaf dry weight(dw) and leaf area were measured. Microbial biomass was estimated by DNA content extracted from rhizophere soils, and fungal community structure was analyzed by PCR-DGGE method.
Soil nutrients greatly affected plant growth(shoot and leaf dw and leaf area)in three crops. High temperature inhibited growth of wheat and soybean, but canola wasn’t largely affected by the temperature. Despite the large difference in aboveground growth, the rhizosphere microbial biomass wasn’t affected by temperature, CO₂ concentration and soil nutrient in three crops. But the microbial biomass significantly differed among crop species. Similarly, rhizoshere microbial community structure measured by DGGE method wasn’t affected by environments, but largely differed among crop species.
These results indicate that although plant growth are largely affected by environmental conditions such as temperature and soil nutrient condition, rhizosphere microbial community was less affected by environments.　Rhizosphere fungal community structure showed distinctive difference among the three crop species irrespective of different environmental conditions.