Invasive Plant Conyza canadensis Exacerbates Wheat Susceptibility to Aphids and Disease Under Drought and Nitrogen...

Biological invasion and environmental stress such as drought and nitrogen (N) deposition can affect crop plant-insect interactions, threatening the stability of agricultural ecosystems. However, the combined effects of invasive plants and environmental stressors on crop and associated pest/disease performance remain poorly understood. Here, we conducted a controlled common garden experiment to examine how the invasive Conyza canadensis, versus native Artemisia annua, influences wheat (Triticum aestivum) growth, biochemical defenses, and associated aphid/disease pressure under drought and N enrichment conditions. Results revealed that C. canadensis significantly reduced wheat growth (height, biomass) and key defense chemicals (cellulose, 2,4-dihydroxy-7-methoxy-2H,1,4-benzoxazin-3(4H)-one (DIMBOA), phenolics) compared to A. annua, resulting in increased aphid abundance and greater disease severity. Drought further suppressed wheat defenses (e.g., lower DIMBOA) and increased malondialdehyde (MDA) content and activities of antioxidant enzymes (SOD, POD, CAT), while N addition enhanced wheat growth but reduced phenolic contents, exacerbating wheat's susceptibility to disease when grown with C. canadensis. Regression analyses confirmed negative correlations between wheat leaf carbon (C), cellulose, and DIMBOA levels and aphid/disease pressure. These findings demonstrate that invasive plants can enhance wheat pest/disease susceptibility by reducing plant defensive chemicals under drought and nitrogen addition, highlighting the cascading impacts of plant invasions on agroecosystems and calls for adaptive practices to mitigate multitrophic disruptions.