| The yellow river irrigation areas of middle Gansu Province is one of the main processing potato and seed potatoes growing regions in China. Potato is often grown continuously by planting enterprises eager to maximize profit. This practice results in the severe decline in plant productivity,which greatly impairs the healthy development of the potato industry locally. It is necessary to increase the understanding of continuous potato monoculture barrier in the region,and then develop new controlling approaches. Field experiments were conducted at Jingtai county of Gansu province from 2011 to 2014 to investigate the effects of continuous potato monoculture on plant eco-physiological characteristics and soil biological processes. Moreover,we evaluated the effectiveness of combination application of pre-plant soil fumigation and post-plant bio-organic fertilizer amendment in the control of continuous monoculture barrier. Key results were as follows: 1?Effects of continuous monoculture on dry matter accumulation and distribution of potato plantsThere were no statistical differences in tuber yield under the short-term continuous monoculture compared with control. Whereas the significant decline by 21.7%~75.7% occurred after three years of continuous monoculture,which was mainly derived from the decline in the average fresh-weight of individual tuber. Dynamics of dry matter accumulation in the whole plant and tuber both showed the “S” curve feature,continuous monoculture decreased the average rate and the duration in dry matter accumulation during rapid accumulative period of potato plants compared with the control. Continuous monoculture also affected dry matter distribution process of potato plants,showing that increased dry matter distribution proportion within root system compared with the control. Long-term continuous monoculture increased the contribution of translocation of dry matter stored in vegetative organs during pre-anthesis,whereas decreased the contribution of direct assimilate accumulation filled into tuber during post-anthesis. 2?Effects of continuous monoculture on sink-source relationship of potato plantsLong-term continuous potato monoculture significantly decreased sink size by 38.4%~53.0% compared to control,which was associated with the reduction in tuber number per plant during early growing stage and dry matter accumulation content per tuber during later growing stage. There was no significant difference in sink activity of potato plants between Control and all of continuous monoculture treatments. Moreover,continuous monoculture significantly restrained the source activity of potato plants, representing that growth and development as well as physiological characteristics of plants under long-term continuous monoculture were significantly lower than the control and short-time continuous monoculture,which directly contributed to the decline in production capacity of source during post-anthesis,and inhibited the enlargement of sink size of potato plants. Long-term continuous monoculture delayed the building of sink-source relationship of potato plants,caused the imbalance of sink-source relationship during middle and later growing stage,which were involved in the reduction of tuber yield in continuous potato monoculture system. The restriction derived from source played a more important role in the devastating reduction of plant productivity of potato subjected to long-term continuous monoculture practice. 3?Effects of continuous potato monoculture on soil physico-chemical and bio-chemical propertiesAlkaline hydrolyzable N and NH4 OAc extractable K as well as Ec increased linearly with the duration of continuous monoculture,whereas soil organic carbon decreased linearly. Similar trend was also observed for the activities of soil sucrase,urease,and dehydrogenase. Results of selected microbial properties including soil microbial biomass carbon,soil basal respiration and FDA hydrolysis activity were also similar. Biolog Eco measurement showed that the overall activities and function diversity of soil microbial significantly decreased with increasing continuous potato monoculture. The structure of soil microbial community showed highly positive correlation with productivity of potato in continuous monoculture system. Changes in soil microbial activities affects soil biological processes, which were associated with the decline in potato plant productivity in continuous monoculture system. 4?Effects of continuous potato monoculture on soil fungal community structureContinuous potato monoculture significantly affected soil fungal community structure. Potato monoculture practice increased populations of Fusarium sp. and Fusarium solani as well as Verticillium dahliae within rhizosphere soils,which induced a lot of soil-borne diseases involved in potato plants in continuous monoculture system. There were significantly positive linear correlation among Fusarium sp. population and tuber yield and plant incidence rate. The results suggested that the decline of tuber yield and plant biomass in continuous potato monoculture system might be associated with the change in fungal community structure of rhizosphere soils,especially the increase in fungal soil-borne. 5?Field evaluation of the controlling effectivity of obstacles to continuous potato monoculture viacombination application of soil fumigation and bio-organic fertilizer amendmentOn the plots which had taken on heavy continuous potato monoculture barrier,combination application of pre-plant soil fumigation and post-plant bio-organic fertilizer amendment significantly increased tuber yield and the ratio of marketable tuber by 71.1%~152.1% and 39.2%~53.3% compared to control,respectively. In terms of physiological characteristics of potato plants,combination application significantly increased chlorophyll content and root vigor compared to the control,whereas MDA contents both in leaf and root significantly decreased. Based on PCR-DGGE technique,it was observed that combination application significantly affected soil fungal community structure,showing diversity index of fungal community under combination application significantly lower than the control. In addition,combination application could effectively suppress soil-borne diseases,exhibiting both the incidence of diseased plant and the ratio of diseased tuber significantly declined by 67.2%~82.2% and 69.1%~70.5% relative to Control,respectively. Results from Real-time PCR confirmed that populations of Rhizoctonia solani, Fusarinm solani and Fusarium sambucinum under combination application were significantly lower than the control during potato growing stage.On the plot which had taken on mild continuous potato monoculture barrier,combination application of pre-plant soil fumigation and post-plant bio-organic fertilizer amendment significantly increased tuber yield by 10.4%~21.2% compared to the control. Pre-plant soil fumigation using aqueous ammonia was better than that of lime plus ammonium bicarbonate. Combination application significantly decreased the incidence of diseased plant and the ratio of diseased tuber by 54.9%~72.8% and 66.2%~64.8%,respectively. Combination application also significantly increased chlorophyll content and improved morphological characteristics of potato root system. Compared with control,combination application increased populations of bacteria and actinomycetes,and decreased the population of fungi,maintained the greater ratio of bacteria to fungi in the testing soil samples collected from potato later growing stage. Combination application also greatly decreased the population of Fusarium sp. during the whole growing stage compared with the control. The findings confirmed that combination application of pre-plant soil fumigation and post-plant bio-organic fertilizer amendment is a potential approach for the control of continuous potato monoculture barrier in Yellow River Irrigation Areas of Middle Gansu Province. |
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