Abstract
A positive interaction between plant populations is a type of population relationship formed during long-term evolution. This interaction can alleviate population competition, improve resource utilization in populations, and promote population harmony and community stability. However, cultivated plant populations may have insufficient time to establish a positive interaction, thereby hindering the formation of the positive interaction. As current studies have not fully addressed these issues, our study established soybean/wheat intercropping populations beneficial for growth and explored the effects of nutrient level and planting density on the positive interaction between the two crops. Changes across population modules in both sole cropping and intercropping populations of soybean and wheat were analyzed. Results using nutrient levels of ½- or ¼-strength Hoagland solution indicated that soybean/wheat intercropping population modules significantly increased at low planting densities (D20 and D26) and significantly decreased at high planting densities (D32 and D60). Therefore, as planting density increased, the modules of both intercropping populations initially increased before decreasing. Similarly, positive interaction initially strengthened before weakening. Moreover, at an intermediate planting density, the population modules reached their maxima, and the positive interaction was the strongest. Under the same planting density, ¼-strength Hoagland solution recorded better growth for the soybean/wheat intercropping population modules compared to results using the ½-strength Hoagland solution. These findings indicated that low nutrient level can increase the positive interaction of intercropping populations at a given planting density, and that environmental nutrient level and population planting densities constrain the positive interaction between soybean and wheat populations in the intercropping system. This study highlights issues that need to be addressed when constructing intercropping populations.
Highlights
In nature, populations form the basic unit of existence, reproduction and species evolution [1]; species present today are the result of evolution and preservation of populations over millions of years
Our results indicated that D26, recording a stronger positive interaction compared to other planting densities (D20, D32, and D60), was a suitable planting density for soybean/wheat intercropping populations
As planting density increased in both populations, the restriction of nutrient level on population modules increased and the positive interaction between the two populations weakened
Summary
Populations form the basic unit of existence, reproduction and species evolution [1]; species present today are the result of evolution and preservation of populations over millions of years. In soybean/wheat intercropping populations, roots from both plants absorb and utilize the greatest amount of nutrients and water [8]. The positive interaction between populations is the result of long-term environmental selection and adaptation. In an artificial environment, such as an agricultural plantation, long-term natural selection has either not occurred, or the time to establish positive interaction between populations may not be sufficient. In such a system, it is unknown whether the positive interaction between intercropping populations is stable or weak. It is unknown if changes to environmental nutrient level and population planting density affect positive interaction on intercropping populations
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