根间相互作用对玉米与马铃薯响应异质氮的调控

近年研究表明养分异质促进植物多样性与群落生产力的正相关性。然而,相关的促进机制还很不清楚。以农田生态系统下作物多样性群体(玉米马铃薯间作体系)为例,在盆栽条件下采用控释性氮肥构建养分异质性,通过目标植物法设计根间作用处理,探讨根系的觅养行为,植株个体生长和总生产力对土壤氮空间分布和根间作用的响应特征。结果表明:根间作用提高作物的觅养精确度(F=3.017,P=0.094),在异质性条件下马铃薯的根冠比增加(P=0.001),而玉米的根冠比则不论在均质性还是异质性条件下均显著降低(F=4.781,P=0.039);氮异质性显著地提高在根间作用下两作物的生物量生产(P=0.021),明显增加总生产力LER(Land equivalent ratio)(F=4.171,P=0.064),显著地降低相对关系指数RII(Relative interaction index)值(F=5.636,P=0.026),显著降低玉米的根冠比(F=4.273,P=0.049),增加根间作用下马铃薯的根冠比,而在无竞争下则降低。上述结果说明,非资源性的根间作用激发玉米和马铃薯对异质性氮的觅养能力,这可能是为什么异质性养分环境促进植物多样性与群体生产力正向关系的重要原因;结果还表明觅养能力的激发主要来自非资源性的根间作用机制,因此本研究验证了植物对异质性养分和竞争者的协同响应理论。而有关的非资源性根间作用机制,例如种间识别作用等值得进一步深入探讨。

Effects of root interactions on the response of maize and potato to heterogeneous nitrogen

Soil nutrient distribution is highly heterogeneous at the plant root system level because of the diversity of soil composition. The heterogeneity of soil nutrients plays an important role in determining plant community structure and function. Recently, research has shown that soil nutrient heterogeneity increases the importance of plant diversity in community productivity. However, knowledge on the mechanism behind this phenomenon is currently lacking. Soil nutrient heterogeneity affects plant root foraging behavior and individual growth, which in turn affects the community structure and function. Therefore, for a better understanding of why there is a positive relationship between plant diversity and community productivity under soil nutrient heterogeneity conditions, it is very important to explore how plant root interactions affect root foraging behavior. Because of the application of fertilizer and the complex community composition, soil nutrient heterogeneity should be more typical in a multi-cropping system than in natural or monoculture systems. Therefore in this study, a typical intercropping system of maize and potato was chosen as a case study, and a pot experiment was conducted. The crops were planted in large pots with controlled-release nitrogen fertilizer applied homogeneously or heterogeneously, and with or without root interaction. Root interaction was achieved by the classical method of target design. At the flowering stage, plant biomass and yield were measured and the relative interaction index (RII), root foraging precision (the ratio of root biomass between higher and lower nitrogen patch), and land equivalent ratio (LER) were calculated to explore the response characteristics of crop growth to nitrogen heterogeneity and root interaction. The results showed that root interaction increased the foraging precision for both crops (F=3.017, P=0.094), and increased the root: shoot ratio for potato under nitrogen heterogeneity (P=0.001), but reduced the root: shoot ratio for maize regardless of nitrogen distribution (F=4.781, P=0.039). Nitrogen heterogeneity significantly improved biomass production for both crops (P=0.021), increased the LER (F=4.171, P=0.064), and significantly decreased the RII values (F=5.636, P=0.026) under root interaction conditions. Nitrogen heterogeneity significantly reduced the root: shoot ratio of maize (F=4.273, P=0.049), but increased the root: shoot ratio of potato in root interaction conditions, and decreased it in no root interaction conditions. This study suggested that root interaction can stimulate plant foraging behavior, which could be a key reason for the increase in the importance of plant diversity in community productivity under soil nutrient heterogeneity conditions. The data also showed that the non-resource root interaction, but not the resource root interaction, stimulates plant foraging behavior, which is in accordance with the theory that plants can integrate information about nutrients and neighbors, or is related to species-specific pathogenic microorganisms. Studies on more species and different environments are required to investigate this further. Further study is also required on the effects of root foraging behavior stimulated by plant root interactions on other community functions, such as structure or stability. Finally, it is necessary to investigate the non-resource mechanisms of root interactions such as recognition between plants, which stimulate plant root foraging behavior.