Mechanism Of Water Competition And Niche Differentiation Between Intercropped Wheat(triticum Aestivum) And Maize(zea Mays)

Intercropping has been regarded as an effective way to solving the contradiction between supply and demand of global grain, for its high yie ld and land use efficiency. Recent years, however, the application of intercropping has become big challenge due to the serious shortage of water resources, interspecies interactions was the intrinsic factors to coordinating water use in intercropping systems. To further improving the water use efficiency, coordination the relationship between interspecies competition and facilitation and utilization the spatial-temporal niche differentiation was current problem to be solve. Therefore, a study took the wheat and maize intercropping system as simple, with different densities and row arrangements, was carried out on Oasis arid land. Our works reported here are aiming at investigating the spatial-temporal distribution, migration characteristics and consumption structure of soil moisture, determining water physiological characteristics, dry matter accumulation and translocation, interspecific competition dynamics and niche differentiation characteristics, clarifying the water saving mechanism of intercropping. Main results were summarized as the following:1. In wheat/maize intercropping system, soil water potential of two crop strips was varied in growth period, crop density and row arrangement had signif icant effect on it, which formed the hydrodynamics basis of spatial and temporal using water with competitive and complementary way. During the co-growth period of wheat and maize, water potential of maize strip was 13.5% higher than that of wheat strip, of which the treatment with high wheat density was 18.5%, th e treatment with 6:3 row arrangement was 18.5%. During the period of wheat harvest, water potential of wheat strip was 21.8% higher than that of maize strip, of which the treatment with low maize density was 27.9%, the treatment with 6:4 row arrangement was 28.0%. Soil water potential difference between the two strips is the result of spatial and temporal niche separation for water requirement. The absolute values of water potential difference between wheat and maize strips were decreased with the density increases, low maize density treatment was 12.1% higher than high maize density, low wheat density treatment was 16.5% higher than high wheat density, indicating that the magnitude of complementary use of water was been strengthened by the increase of interspecific. During the co-growth period of wheat and maize, the absolute values of water potential difference were increased with the row increases, 6:4 treatment was 3.2% higher than 6:2, while, during the period after wheat harvest, the values were decreas ed with the density increases, 6:2 treatment was 2.7% higher than 6:4, indicating that the complementary in using water was been weaken during the co-growth period, however, it was been strengthen during the period after wheat harvest with the increase of maize row, this was beneficial to the compensation effect of maize.2. Moisture migration between intercropping strips at different growth stages leaded to efficient and complementary use of water at different spatial and temporal niche. Wheat competed for 16 to 55 mm soil water from neighboring maize strip during co-growth period, while wheat strip recharged for 20 to 60 mm soil water to maize after wheat harvest. Increasing density could significant increase soil water transfer, the water transfer in treatment with high wheat and maize density was, respectively, 101 mm and 74 mm, which was, respectively, 136% and 68% higher than low density treatment. Row arrangement had no significant effect on water transfer of whole growth stage with an averaged value of 74 mm, however, row arrangement had signif icant effect on water transfer during wheat harvest. Water transfer after wheat harvest(averaged 46mm) was 61% higher than during co-growth(averaged 28mm). Density was better than row arrangement in the regulation of soil water use, increasing intraspecific competition of wheat lead to great water niche differentiation, which could greatly promote the complementary use of resources in intercropping.3. Intercropped wheat and maize had different water critical stage and soil water uptake area,which weakened interspecific competition for water and strengthen the complementary, this effect was varied as crop density and row arrangement. During the co-growth period, water consumption of wheat accounted for 65% of whole growth stage water consumption, while maize accounted for 42%, correspondingly, water consumption of wheat accounted for 35% of whole growth stage water consumption, maize accounted for 58% after wheat harvest. Higher WUE of intercropping than monoculture was due to mismatch of water consumption in different growth period. To some extent, water consumption decreased with density increase, water consumption in low wheat density was 3.8% high than that high wheat density treatment, but the difference was not significant. During the co-growth period, water consumption was increased with the increase of maize rows, which in 6:4 treatment was 1.7% higher than 6:2 treatment. After wheat harvest, water consumption was decreased with the increase of maize rows, whic h in 6:2 treatment was 2.3% higher than 6:4 treatment. There was a negative correlation between water consumption and water transfer, indicating that complementary use of water had significant effect on reducing water consumption.4. During the co-growth period of wheat and maize, the interspecific competition of wheat was great than maize(b11/b12> b22/b21), wheat in a dominant position when competitive resources. Niche differentiation index(NDI) was varied as the crop growth stages, and was been signif icantly affected by the density and row arrangement. The NDI of additive wheat density treatment was 19.6% higher than that of additive maize dens ity treatment. The NDI of increasing maize row treatment was, respectively, 20.4% and 44.1% than that of additive wheat and maize density treatment. The ratio b11/b12 that surpasses the inverse of b22/b21, indicating that the species was not only competing but was also complementary for some of resources during the co-growth period of wheat and maize. The change of NDI was well matched the water complementary characteristic. Soil moisture migration increased linearly with NDI increase, and the correlation coefficient was significant at p<0.05, density and row arrangement signif icantly affect their relationship. Wheat density had greater influence on NDI than maize density, increasing wheat density can lead to great complementary when using soil water. Moisture migration occurs need a certain degree of NDI when additive maize row, if niche separation is further increas ed, the rate of moisture migration was higher than the additive density treatment(slope: 10.458 vs 3.68 and 5.771).5. Spatial and temporal separation of water niche was the main reason for yield advantage and efficient water production in intercropping system. There was a positive correlation between NDI, water transport, yield and WUE.LER of treatment w ith wheat density of 900 plants m-2 and maize density of 4.5 plants m-2 was 1.39 and the WUE was 23.6 kg hm-2 mm-1, which shows signif icant intercropping advantage. Wheat yield was reduced while maize yield was increased as the increasing of maize rows in row arrangement intercropping system. NDI increased with the increasing of maize row, however, considering the truth that the demand for NDI values was increased with the increasing of maize row, the yield was decreased with the increasing of maize row can be explained by the NDI was decreased after wheat harvest.