Abstract
High planting density and nitrogen shortage are two important limiting factors for crop yield. Phytohormones, abscisic acid (ABA), and jasmonic acid (JA), play important roles in plant growth. A pot experiment was conducted to reveal the role of ABA and JA in regulating leaf gas exchange and growth in response to the neighborhood of plants under different nitrogen regimes. The experiment included two factors: two planting densities per pot (a single plant or four competing plants) and two N application levels per pot (1 and 15 mmol·L−1). Compared to when a single plant was grown per pot, neighboring competition decreased stomatal conductance (gs), transpiration (Tr) and net photosynthesis (Pn). Shoot ABA and JA and the shoot-to-root ratio increased in response to neighbors. Both gs and Pn were negatively related to shoot ABA and JA. In addition, N shortage stimulated the accumulation of ABA in roots, especially for competing plants, whereas root JA in competing plants did not increase in N15. Pearson’s correlation coefficient (R2) of gs to ABA and gs to JA was higher in N1 than in N15. As compared to the absolute value of slope of gs to shoot ABA in N15, it increased in N1. Furthermore, the stomatal limitation and non-stomatal limitation of competing plants in N1 were much higher than in other treatments. It was concluded that the accumulations of ABA and JA in shoots play a coordinating role in regulating gs and Pn in response to neighbors; N shortage could intensify the impact of competition on limiting carbon fixation and plant growth directly.
Highlights
Neighboring plant competition and soil mineral shortages resulting from an increasing planting density are common biotic and abiotic stresses, limiting crop growth and production [1,2]
Two-way analysis of variance (ANOVA) results showed that competition, nitrogen, and their interaction did not affect ψshoot, suggesting that the plant water status was unaffected by these two factors in this study
These results suggested that plants might suffer from neighboring competition under an elevated planting density
Summary
Neighboring plant competition and soil mineral shortages resulting from an increasing planting density are common biotic and abiotic stresses, limiting crop growth and production [1,2]. Nitrogen (N), as one of the most essential macronutrients for plant growth and development, plays a significant role in carbon metabolism, protein synthesis, and plant hormone synthesis [3]. Plants may detect and interact with neighbors in different manners [4]. Recent data argue that phytohormones, such as ethylene and abscisic acid (ABA), play a crucial role in the modulation of many processes of plant development, including response to neighbors [5,6]. The combined effects of the two factors on endogenous hormones remain unclear, on ABA.
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