| Wheat/maize intercropping has been widely applied in the Hexi Oasis Area due to more effective use of resources and high productivity. However, the planting pattern is facing enormous challenges because water shortage, intercropping- saving mechanism and technology research further study is necessarily. Given significant effect of interspecies relations and coordination of intercropping root and shoot on efficient use of resources, a field experiment was carried out in typical oasis area for this study. In order to investigate the synergies of aboveground and belowground interspecies interactions on the yield and water use efficiency of intercrops, different plant densities were designed to study interactions of root and canopy, and three root-barrier treatments were designed to research interactions of belowground water and root. This study objective is to provides a theoretical basis for forming intercrops with synergistic interaction of belowground and aboveground. The main results were obtained as the following:1. There are significant effect of canopy and interaction of root on interspecies water competition and complementation in intercrop system, and that was varying follow the time. During the symbiotic period of wheat and maize, wheat had stronger competition to absorb moisture from maize strips, water competition of no root barrier(W//C)、nylon mesh barrier(NW//C) and plastic sheet barrier(PW//C) respectively were 36.8 mm, 29.4 mm and 0.5 mm; after wheat harvest, maize had stronger competition to absorb the moisture of the wheat strips, water competition of three root barrier treatments respectively were 37.4mm, 28.5mm and 2.5mm. The mean complementary effect on underground moisture migration was 36.6mm, and the effect of root on the moisture use of belowground spatial overlay was 9.2mm. Moreover, with same kind of root barrier, moisture migration of high density treatment were higher than the low density treatment, respectively as 27.5%, 27.5%, 35%.2. Intercropping and density makes significant effected on the temporal and spatial distribution of the root of wheat/maize intercropping, and makes a superposition use of underground space in different periods. During the symbiotic period of wheat and maize, equivalence lines of root weight density as 0.02 in wheat sole-cropping(g/500cm3) reached 68 cm, that of wheat in intercropping with no root barrier(W//C) occupies all of the root zone of the two intercropping crops, and vertical distribution area of 0.02 root weight density reached more than 90 cm, root vertical distribution of intercropped maize in W//C was more shallow compared to that of the maize standing sole. Root weight densities in three root barrier treatments were PW//C>NW//C>W//C. three treatments, wheat and maize equivalence lines of 0.02 root weight density of high-density treatment in W//C, NW//C, PW//C compared with that of the low-density treatment were increased by 6.7%, 5.1%, 4.7% and 16.3%, 15.2%, 14%, respectively.When the wheat harvest, single maize occupies and makes use of all the space of the underground part of the two intercropping plants, W//C root distribution in the longitudinal reach of a single horizontally, the sidelong distribution occupies and makes use of all the space of the underground part of the wheat, three kinds of intercropping maize treatments root weight density size: W//C>NW//C>PW//C, three intercropping treatments, maize root weight density of 0.4, high-density compared with low-density increased by 23.3%, 8.3% and 11.1%.compensation underground part of the maize root contribution is 14.5cm, superimposed on the direct contribution of root soil space utilization is 8.5cm, the contribution of water and nutrient exchange between the role of wheat and maize belt 6cm.3. Intercropping and planting density could affect photosynthetically active radiation and leaf area index in wheat-maize intercropping. During the symbiotic period of wheat and maize, the photosynthetically active radiation of sole wheat was increased by 8.2%, 17.6% and 42.1% as compared to intercropped wheat. After wheat harvesting, the photosynthetically active radiation of sole maize was decreased by 30.8%, 21.9% and 15.1 % than intercropped maize. The contribution of compensation from underground part of wheat-maize intercropping to photosynthetically active radiation was 22.8%, of roots directly superimposed on soil space utilization was 12.9%, and of compensation from water and nutrient exchange between intercropped wheat and maize strip was 9.9%. The photosynthetically active radiation of three intercropped maize treatments under low density was increased by 5.4%, 4.2% and 6.3% than under high density.The dynamic of leaf area index for sole crops were revealed a "single peak" tendency with the peak appeared at maximal leaf area of sole wheat and sole maize, respectively. However, dynamics of leaf area index of intercropping was revealed a "bimodal peak" with the peaks appeared alternatively at maximal leaf area of sole wheat and sole maize. Consequently, high leaf area of intercropping maintained even longer. Leaf area index of W//C, NW//C and PW//C under high density was 7%, 16% and 13% greater than under low-density. The contribution of compensation from underground part of wheat-maize intercropping to improved leaf area of was 22%, of roots directly superimposed on soil space utilization was 7%, and of compensation from water and nutrient exchange between intercropped wheat and maize strip was 14%.4. Compared with the monoculture, wheat-maize intercropping had an advantage on increasing yield and water use efficiency, moreover, density and root partition had significant influence on intercropped yield and water use efficiency. The grain yield and biological yield of W//C, NW//C, PW//C were higher 44%, 28%, 7%, and 29%, 18%, 3% than that of monoculture wheat, respectively, and higher 55.5%, 50.4%, 43.6%, and 63.9%, 57.4%, 49% than that of monoculture maize. The average yield advantage of W//C were greater 16% and 6% than that of PW//C, NW//C, which demonstrates that 16 % of yield advantage in wheat-maize intercropping from compensation of the underground, and 6% comes from the direct superposition of root system on soil space utilization; the average yield advantage of NW//C higher 9% than that of PW//C, which demonstrates that the compensation effect of water and nutrient exchange was 9% between wheat and maize strip 9%. Moreover, high-density significantly increased grain yield by 14%, 13% and 8% than low-density in W//C, NW//C, PW//C, respectively.A positive correlation was observed among yield and soil water content, LAI, WUE, LAI and yield, WUE. LAI of high-density was averaged higher 12% than that of low-density in intercropping system. WUE of W//C、NW//C、PW//C were greater 19.5%、11.1%、7.2% than that of the weighted average in corresponding monoculture. Moreover, high-density increased WUE by 19.4%, 15.2%, 4.9% than low-density in the same root partition, respectively. |
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