| In recent decades, climate warming as the main feature of the global climate change has occurred and has a significant impact on the natural environment and economic development, threating the survival of human environment. The global surface temperature has increased by 0.74 degrees in recent 100 years (1996-2005) and is expected to increase 1.1-6.4 degrees in the end of the century; and the concentration of atmospheric CO2 will likely increase to 550-970 ppm by 2100. Global climate change has caused the problem of melting glaciers, rising sea levels, frequency of extreme climate events and precipitation change. Agricultural production has very strong dependence on climatic conditions and soil properties. Therefore, climate change will affect agricultural production and national food security. Soil microbial community is an important biological indicators of soil fertility, which play a decisive role in the biological elements cycle of farmland ecosystem. Investigating the impacts of global climate change in microbial community structure, diversity and soil biochemical process of farmland soil, can help us to understand the mechanism of climate change on soil properties, greenhouse gas emission and soil carbon pool, and provide a scientific basis for the development of agricultural production in the global climate change measures.This research is an open platform of simulating climate change field condition, which for all-weather simulation system of future climate change on rice-wheat rotation process and crop productivity cycles, including atmospheric CO2 enrichment to 500 ppm, increment of canopy air temperature by 2 degrees and simultaneous CO2 enrichment and warming. We sampled the rhizosphere soil of rice and wheat in this study, and measured soil basic properties and soil microbial biomass carbon. We also measured the gene abundance and community diversity of soil fungi, bacteria, archaea, ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and denitrifier by microbial molecular technoligies. This study was conducted to address how elevated CO2, warming and their combination affect the abundance, community structure and activity of soil microorganisms in rice-wheat rotation system. The main results obtained are as follows:1. Changes in soil microbial diversity and function in paddy field under simulated climate changeElevated atmospheric CO2 concentration and temperature alone had no effect on soil pH, but their combination significantly reduced the pH value in rice heading and ripening stages. Soil microbial biomass carbon (SMBC) ranged from 0.24 g kg-1 to 0.77 g kg-1 for the rice season. CE (atmospheric CO2 enrichment) and the CW (interactive CO2 enrichment and warming) treatment increased SMBC by 71%-104% comparing to CK treatment, but WA (warming of canopy air) treatment has no effect on SMBC. Moreover, CE and CW treatment significantly increased soil basal respiration in rice heading and ripening stages, and WA treatment showed no effect on soil basal respiration. Elevated CO2, warming and their combination increased urease activity, but showed no effect on invertase activity.With a variability across the stages and treatments, the copy number ranged from 1.1×109 g-1 dry soil weight to 1.3×1010 g-1 dry soil weight of bacteiral, from 3.2×108 to 2.3×109 g-1 dry soil weight of fungal and from 2.0×109 to 4.6×109 g-1 dry soil weight for archaeal. The gene abundance and diversity of bacteria, fungi and archaea respond differently to rice growth stages and climate change factors. CE treatment significantly increased the soil fungal and bacterial abundance, and CW treatment had no effect on fungal and bacterial abundance. Archaea gene copy number is relatively stable in rice season, elevated atmospheric CO2 concentration and temperature had no effect on soil archaeal abundance. PCA analysis of T-RFLP profiles showed that CE, CW and WA treatment changed fungal community structure in a certain extent, but had no significant effect on bacterial and archaeal community struture. By clone library, sequencing and sequence alignment, we found that both Proteobacteria and Acidobacteria is the dominant bacteria in this paddy field. CE treatment reduced the relative abundance of Betaproteobacteria, but WA treatment increased the Betaproteobacteria. Elevated CO2, warming and their combination had no effect on the relative abundance of Acidobacteria, Crenarchaeota and Euryarchaeota.2. Changes in soil microorganism and activity of nitrogen cycle in paddy field under simulated climate changeSoil NH4+-N ranged from 2.72 mg kg-1 to 10.16 mg kg-1 and soil NO3=-N ranged from 6.45 mg kg=1 to 17.79 mg kg=1 in the rice season. Elevated atmospheric CO2 concentration and warming had no effect on soil NH4+-N and NO3--N concentration. In rice tillering, heading and ripening stages, CE and CW treatment significantly increased nitrifying rate, WA only significantly increased nitrifying rate at the heading stage. CE and CW treatment has an inhibitory effect on the denitrifying rate, the inhibition reached significant level at the heading stage, while WA had no effect on denitrifying rate. Multiple regression analysis showed that, nitrification was correlated with soil NH4+-N concentration and AOB abundance, and denitrification had a significant correlation with soil NO3--N.The results showed that copy numbers of nirK gene of the paddy soils ranged from 4.48× 107 to 4.56×108 g=1 soil, and approximately 5-10 fold greater than those of AOA and AOB amoA genes, which ranged from 6.58×106 to 5.72×107 and 4.28×106 to 2.02×107 g-1 soil, respectively. In different growth stages of rice, microbial communities of nitrogen cycle respond differently to climate change treatments. At the tillering stage, elevated CO2 concentration and temperature had no effect on AOA, AOB and denitrifying bacteria gene abundances; at the heading and ripening stages, CE treatment significantly increased AOA and AOB gene abundances. The T-RFLP profiles showed that, no obvious change in AOA, AOB and denitrifying bacteria community structure under climate change conditions comparing to CK. CE, CW and WA treatment significantly increased AOA diversity in the tillering and ripening stages and AOB diversity in the tillering and heading stages; CE and CW treatment significantly increased denitrifying bacteria diversity.3. Changes in soil microbial diversity and function in wheat field under climate changeCE and CW treatment significantly increased SMBC in wheat season, but resulted no impact on soil basal respiration; WA treatment had no effect on SMBC, but significantly increased soil basal respiration. In the tillering stage, urease activity under CW was higher than that of control; in the heading and ripening stages, invertase activity under CE, CW and WA were higher than that of control. Therefor, soil basal respiration, urease and invertase activity in wheat soils are sensitive to warming.With a variability across the stages and treatments, the copy number ranged from 3.96×1010 g-1 dry soil weight to 1.02×1011 g-1 dry soil weight of bacteiral, from 2.12×107 to 1.06×108 g-1 dry soil weight of fungal and from 3.02×108 to 6.36×108 g-1 dry soil weight for archaeal. In different growth period of wheat, the gene abundance of bacteria, fungi and archaea respond differently to elevated CO2 and warming. At the tillering stage, elevated CO2 concentration and temperature had no effect on soil fungal and bacterial abundance, but in the heading and ripening stages, CW and WA treatment significantly reduced fungal abundance, WA treatment also decreased the bacterial abundance in the ripening stage. Archaeal abundance showed significant increase under CE and CW treatments, while on change was found under WA treatment. The analysis of T-RFLP profiles showed that CE, CW and WA treatment had no obvious effect on fungal and bacterial community structure, but changed the archaeal community structure in a certain extent. Comparing to the control, CE treatment significantly increased fungal diversity of the wheat soils, but CW and WA treatment reduced fungal diversity; CE, CW and WA treatment increased bacterial diversity in wheat tillering and heading stages, but had no effect on bacterial diversity in the ripening stage.4. Changes in soil microorganism and activity of nitrogen cycle in wheat field under simulated climate changeElevated atmospheric CO2 concentration and temperature had no effect on soil NH4+-N concentration in wheat season, however, CE treatment significantly increased soil NO3--N concentration and nitrifying rate at the ripening stage.The results showed that copy numbers of nirK gene of the paddy soils ranged from 3.68×107 to 1.23 x 108 g"1 soil, and approximately 10 fold greater than those of AOA and AOB amoA genes, which ranged from 8.63×106 to 3.27×107 and 3.07×106 to 4.14×107 g-1 soil, respectively. CE and WA treatment significantly increased the abundance of AOA, while CW had no effect on AOA abundance. In the tillering stage, CE, CW and WA treatment had no effects on both AOB and denitrifier abundance; in the heading and ripening stage, CE treatment significantly increased both AOB and denitrier gene abundance. The analysis of T-RFLP data showed that, AOA and denitrifier community structure in the ripening stage were separated from that of the tillering and heading stages, while CE, CW and WA treatment had no effects on AOA, AOB and denitrifier community structure.In summary, effects of climate change on soil microorganism and activity were found different between rice and wheat soil by molecular biololgy techniques and soil analyses, and soil microorganism respnd differently to multiple climage change treatments. The change may be related to the variation of soil abiotic factors such as reduced pH, increased microbial biomass carbon and NO3-N concentration etc. The impact of climate change on soil microorganism and function in agricultural system is inconsistent, which still need more studies. |
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