| Intercropping has the advantages of improving yield and water use efficiency compared with single cropping.However,due to the lack of water resources,the intercropping application is confronted with great challenges of water supply,and it is imperative to study the theory and technology of intercropping water use efficiency.Interspecific interaction is an important ecological basis for intercropping advantages.However,existing studies have focused on underground interaction or jade-ground interaction,and few studies have been made on the cooperative interaction effect between above-and below-ground,which leads to the lack of theoretical basis for improving intercropping yield and water use efficiency through cooperative optimization of underground and above-ground tissues in production practice.From 2015 to 2017,this study took wheat-maize intercropping as the research object,created different belowground interaction intensities in intercropping by root separation technology,set different maize planting densities to form different aboveground interaction intensities,and explored the mechanism of interaction between aboveground and underground to improve water use efficiency.The main conclusions are as follows:1.The positive effect of above and below-ground interaction on dense planting is one of the reasons to improve the grain yield and water use efficiency of intercropping.Compared with partial below-ground interaction and intercropping without belowground interaction,the advantages of above-and below-ground complete interaction are increased by 10.1% and 23.0%;among them,the contribution rate of above-and below-ground complete interaction to grain yield is 23.7%;the increase of density makes it increase by 7.3%.For intercropping water use efficiency,the water use efficiency of complete below-ground interaction treatment is increased by 11.6% and 24.6% respectively compared with that of partial underground interaction treatment and non-belowground interaction treatment,and the difference between partial underground interaction treatment and non-belowground interaction treatment is not significant,and the increase of corn density promotes the maximum increase of water use efficiency of complete underground interaction,increasing by 12.0 %.2.Complete interaction belowground interaction in intercropping significantly reduced evapotranspiration ratio in key growth stages of intercropping,and optimized water consumption ratio in stages.The evapotranspiration ratio of above-and below-ground interactions decreased significantly by 37.1% and 16.1% from jointing to silking and from grouting to harvest,and decreased with the increase of corn density.In addition,compared with partial belowground interaction treatment and without belowground interaction treatment,the complete belowgrpund interaction treatment increased the water consumption ratio from jointing to bell mouth stage,but decreased the water consumption ratio before jointing and after grouting,so that the water consumption in the whole growth period was reasonably distributed and the effective utilization of water was promoted.3.In wheat-maize intercropping system,the soil water potential in maize strip is higher than that in wheat strip in symbiosis period,and after wheat harvest,the soil water potential in wheat strip is higher than that in maize strip,which forms the potential transport and migration potential of water between strips in symbiosis period and maize independent growth period,thus realizing the possibility of complementary utilization of soil water in time and space.Complete interaction between the above-and below-ground of intercropping promoted the positive effect of close planting on the aboveground,optimized the difference of soil water content between strips in key growth periods of intercropping,promoted the increase of water transport volume between strips,and promoted the increase of density on the above-ground parts.During the co-growth period,the water transport volume between complete belowground interaction was 14.2 mm,which increased by 43.8% with the increase of maize density.The complete belowground water transport capacity of maize in independent growth period was 28.0 mm,and the density increased by 47.4 %.Complete interaction between the above-and below-ground has good characteristics of point water control.Increasing the amount of water transport between strips in co-growth period effectively reduces the water competition between strips,and maize independent growth period enhances the compensation of water from wheat empty strips to maize strips,which lays a foundation for the high-efficiency utilization of water in intercropping.4.The root growth of intercropping in wheat flowering stage is significantly lower than that of single cropping,but after wheat harvest,the root growth of intercropping is significantly larger than that of single cropping,which has stronger ability of recovering growth.Complete interaction between above-and below-ground and increasing maize density promote the enhancement of root recovery effect.During the flowering period of wheat,the total root weight density(TRWD),total root length density(TRLD)and total root surface area density(TRSAD)of intercropping were 25.2%,31.8% and 36.9% lower than those of single cropping wheat respectively,and were 26.4%,20.9% and 32.7% lower than those of single cropping maize respectively.During the maize filling stage,the above three root parameters in intercropping increased by 43.9%,35.6% and 8.8% respectively compared with single maize,among which the percentage of total underground interaction increased the most,and the root quantity increased with the increase of maize density.After wheat harvest,the root system recovered and grew the strongest by completely underground interaction,which showed that RWD,RLD and RSAD recovered and grew stronger,among which RLD recovered effect increased with the increase of maize density.Complete belowground interaction promotes the root system to recovery growth and strengthen,making up for the inhibition of crop root system growth caused by the population during co-growth period,making full use of sufficient belowground space and resources in the late growth stage of maize after wheat harvest,promoting the growth and development of root system,improving the ecological niche of compensation and utilization of soil water,and thus improving the water use efficiency of intercropping.5.Complete belowground interaction can promote the positive effect of close planting to play,improve the photosynthetic rate and reduce the transpiration rate of wheat and maize in the filling stage,and show relatively higher leaf water use efficiency and lower leaf water potential.During the filling stage,the photosynthetic rate of wheat and maize treated with complete underground interaction increased by 23.9% and 19.4% respectively compared with those treated without underground interaction,but there was no significant difference compared with those treated with partial underground interaction and without underground interaction.Compared with partial underground interaction and without underground interaction,the complete belowground interaction had increased water use efficiency of wheat leaves by 10.3% and 26.6% respectively,and that of maize leaves increased by 17.9% and 23.6%.With the increase of maize density,the water use efficiency of leaves increased.Higher leaf water use efficiency and lower leaf water potential can enhance the ability of intercropping crops leaf to absorb and utilize water,which plays an important role in improving intercropping water use efficiency.6.Complete belowground interaction significantly increased dry matter accumulation during jointing and filling of wheat.Before wheat harvest,belowground interaction had no significant effect on dry matter accumulation of maize.After wheat harvest,the recovery and growth of intercropping maize accelerated,and complete belowground interaction was beneficial to increase dry matter quality.Complete belowground interaction enhanced the interspecific competitiveness of wheat and maize during the co-growth period and the recovery effect of maize after wheat harvest,which increased with the increase of density.Therefore,the complete belowground interaction strengthens the competitiveness of intercropping during the symbiotic period,and strengthens the recovery effect of maize after wheat harvest,making full use of soil water and promoting the improvement of water use efficiency in intercropping system. |
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