| Phosphorus is the second major essential nutrient element for plant growth.However,due to the poor availability and easy accumulation characteristic of phosphorus,there is a general lack of available phosphorus in soil,which seriously restricts the development of agricultural production in China and even all around the world.At present,the application of phosphorus fertilizer is an important way to solve the limitation of phosphorus in farmland soil.However,the application of excessive phosphorus fertilizer results in a series of environmental pollution problems.Therefore,how to improve the utilization efficiency of phosphorus fertilizer and fully excavate soil phosphorus pool have become the hotspot of current research.Intercropping is one of the most effective ways to improve the utilization efficiency of phosphorus.In northeast cropping-pastoral interlacing region of China,maize(Zea mays L.)is an important food crop and alfalfa(Medicago sativa L.)is a leguminous forb,their intercropping has a great significance to the agricultural development in this area.Although former studies have focused on the mechanism of intercropping dominance from root architecture,root exudates and mycorrhizal formation,root dynamic plays an important role in plant nutrient uptake and it is often neglected.Therefore,field experiment was carried out to explore the relationship between root dynamics,P uptake and utilization in maize/alfalfa intercropping system to improve the underground ecological mechanism of intercropping advantage.Our experiment was conducted in a split-plot design with three replications form 2015 to 2017.The main plots included no P application(P0)and P application(P1).Subplots included three cropping patterns: four maize rows intercropped with six alfalfa rows with a spacing of 30 cm(IMA43),monoculture maize(MM),and monoculture alfalfa(MA).It aimed to explore the effects of intercropping and phosphorus application levels on the root productivity,mortality,standing crop,lifespan and turnover,and the relationship between root productivity,mortality,standing crop,lifespan and turnover and phosphorus uptake and utilization in maize/alfalfa intercropping system.The main results are presented as follows:(1)The productivity,mortality,standing crop of root were not significantly affected by the interaction between phosphorus levels and cropping patterns.Maize/alfalfa intercropping could accelerate the production and mortality of root system,increase the standing crop of the root system,and promote the uptake and utilization of phosphorus in crops.Compared with MM and MA,IMA43 intercropping improved standing crop,productivity and mortality of crop roots in 0-20 cm soil layer.The productivity,mortality,standing crop of root were not significantly affected by phosphorus levels.Meanwhile,the root dynamics were obviously changed with the seasons,the timing of root dynamics peak was not affected by phosphorus levels and cropping patterns.Root productivity,mortality and standing crop with different treatments in the topsoil had peaked in July-August yearly.(2)Intercropping of maize and alfalfa significantly reduced the root survival rate,mean lifespan,and increased root turnover.Regardless of the phosphorus levels,in the 0-20 cm soil layer,the root survival rate of IMA43 was reduced by 17.74% and 23.09%,the average root lifespan was reduced by 12.14% and 17.32%,and the root turnover was increased by 12.90% and 0.86%,respectively,compared with MM and MA.Regardless of cropping patterns,compared with no phosphorus application,phosphorus application increased root survival rate and mean lifespan by 3.68% and 19.35%,respectively,and reduced root turnover by 7.42% in soil layer 0-20 cm.(3)The phosphorus content,phosphorus uptake,and yield of the crop were significantly increased by phosphorus application and intercropping.Compared with that no P application,the P content,P uptake and yield of maize were significantly increased by 17.99%,57.04% and 32.6%,respectively;and the phosphorus content,phosphorus uptake and yield of alfalfa were significantly increased by 59.55%,60.47% and 9.06%,respectively.Without considering the phosphorus application level,maize/alfalfa intercropping significantly increased the phosphorus content and phosphorus uptake of maize by 26.58% and 13.90%,respectively,and the phosphorus content,phosphorus uptake and yield of alfalfa were significantly increased by 8.12%,63.80% and 76.31%,respectively.(4)In the maize/alfalfa intercropping system,the annual turnover rate of crop root was significantly and positively correlated with phosphorus utilization efficiency,phosphorus uptake and total yield,but there is no correlation between annual turnover rate of crop root and phosphorus content.Therefore,the improvement of root turnover caused by maize/alfalfa intercropping is closely related to the efficient uptake and utilization of plant phosphorus and the increase of yield.In conclusion,intercropping maize/alfalfa increased root productivity,root mortality,root standing crop,reduced the root lifespan,survival rates and speed up the root turnover,promoted the efficient uptake and utilization of phosphorus,and thus improved crop yield.The dynamics change of root system caused by maize/alfalfa intercropping is one of the important reasons for improving phosphorus uptake and utilization. |
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