| Effects of surface ozone pollution (O3) on the terrestrial ecosystem and plant growth have drawn great attention. In this present study, the effects of elevated atmospheric O3on wheat biomass matter and distribution to root, root activity (i.e. fresh root respiration, apparent root respiration and nutrient utilization intensity of root), root morphology (i.e. root length, root surface area, etc.), and soil environment (i.e. soil structure, soil enzyme) were studied, with the monitoring of root system and soil-air interface CO2emission, during the wheat growth period in an agro-ecosystem with rice/wheat rotation. Two winter wheat cultivars (Y15and YN19) with different sensitivities to O3, split-root growth-gas collection chamber, and field monitoring, had been applied. In order to provide theoretical support for the selection of resistance varieties and the regulation and management of existing varieties in the future, the field experiment was conducted in the China rice/wheat O3FACE (free-air ozone enrichment) platform where the elevated atmospheric O3was50%higher than the ambient atmospheric O3. The main results were as follows:(1) Elevated O3decreased the total biomass accumulation and root to shoot ratio of wheat at key growth stages, and reduced the proportion of photosynthetic product transplant to the underground; it significantly reduced the grain yield of YN19, and slightly increased that of Y15. Thus, YN19was sensitive to O3, and the tolerance ability of Y15in response to O3was stronger.(2) The effect of elevated O3on root morphology of wheat differentiated with the different cultivars and growth period. Elevated O3significantly reduced the root length, root surface area, root diameter, root volume and root length density of wheat at jointing stage, and most of the root morphology index showed an increasing trend at booting-heading stage, but obviously decreased at milk-ripe stage. Root morphology index of wheat was more sensitive to O3at vegetative growth period compared with at late growth stage. (3) Elevated O3affected root activity and the absorption and distribution of nutrients in root system. Elevated O3decreased and increased apparent root respiration rate of Y15in early and later growth period, respectively, but kept increasing that of YN19during the whole wheat growth period. Elevated O3increased accumulative CO2emission of apparent root respiration during the whole growth period of wheat, which suggested that O3pollution may increase the total root activity of wheat from wheat turning-green stage to mature period. Elevated O3significantly decreased the contents of nitrogen and potassium in roots, and decreased the distributive proportion of nitrogen and potassium in roots. Elevated O3increased the phosphorus accumulation in Y15, and significantly decreased it in root of Y15. On the contrary, elevated O3decreased phosphorus accumulation in YN19, and significantly increased it in root of YN19. The effects of ozone pollution on root absorption and distribution of N, P and K were different with related to the differences of cultivars, nutrient element type and development stage of wheat.(4) Elevated O3influenced soil environment that the root grew. Elevated O3significantly increased the content of0.25-0.053mm aggregates in the0-10cm soil depth, and significantly decreased the content of <0.053mm aggregates in the0-5cm depth and the content of>0.25mm aggregates in the5-10cm soil layer, but had no remarkable effect on the10-20cm depth aggregates at all levels. Elevated O3significantly decreased topsoil (0-20cm) gas porosity and significantly increased the soil capillary porosity in10-20cm soil layer. Elevated O3increased the activity of urease and catalase in Y15cropland soil, promoted the activity of catalase but inhibited the activity of urease in YN19cropland soil, and the effects were related to soil depth and crop planted. |
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