Abstract
Ambrosia artemisiifolia L. (Asteraceae), known as common ragweed, is an annual herbaceous species native to North America that has become one of the most economically important weeds in arable fields throughout Central Europe. Its large ecological amplitude enables the species to become established in several types of environments, and management options to effectively contain its spread are limited due to a lack of efficacy, high cost, or lack of awareness. In the last decade, in particular, soybean fields have been severely affected by common ragweed invasion. However, until now, information on the yield-decreasing effects of the plant has been scarce. Therefore, the aim of this study was to evaluate the competition effects of common ragweed on (1) soybean growth (aboveground/belowground), (2) the yield of two different soybean cultivars, and (3) the nodulation potential. Based on a greenhouse and biennial field trial, we found that in plots with the highest common ragweed biomass, the soybean yield loss accounted for 84% compared to the weed-free control, on average. The number of nodules, in addition to the mean nodule weight, which are tightly correlated with soybean yield, were significantly reduced by the presence of common ragweed. Just one common ragweed plant per square meter reduced the number of nodules by 56%, and consequently led to a decrease in yield of 18%. Although it has been reported that the genus Ambrosia produces and releases several types of secondary metabolites, little is known about the influence of these chemical compounds on soybean growth and nodulation. Thus, there is substantial need for research to understand the mechanisms behind the interaction between common ragweed and soybean, with a view to finding new approaches for improved common ragweed control, thereby protecting soybean and other crops against substantial yield losses.
Highlights
Soybean (Glycine max (L.) Merr.) is one of the world’s most important oilseed and protein crops, constituting the second largest source of vegetable oil and the largest source of animal protein feed at a global scale [1]
Significant differences in the aboveground dry matter (AGDM), between the control plants grown without ragweed (R0) and the soybean plants grown at the highest ragweed density of five plants per pot (R5), were detected
We found significant linear correlations between the number of nodules and the yield (Mentor: r = 0.6, p < 0.001; Albenga: r = 0.6, p < 0.001), and the ragweed root dry matter and the number of nodules (ES Mentor: r = −0.6; Albenga: r = −0.6, p < 0.001), generalized linear mixed model (GLMM) analysis revealed that the most parsimonious model explaining the yield of soybean was the interaction of the factors of mean weight of nodules and the amount of ragweed AGDM present (Table 3)
Summary
Soybean (Glycine max (L.) Merr.) is one of the world’s most important oilseed and protein crops, constituting the second largest source of vegetable oil and the largest source of animal protein feed at a global scale [1]. The spread of ragweed has been promoted by a combination of three factors: (1) the steady extension of the cultivation area of soybean, (2) climate change (warmer and drier), and (3) a lack of efficacy in management options to effectively contain the spread of the plant [7,8,9]. In recent years, this annual herbaceous species, native to North America, has become an economically important and troublesome agronomic weed in Central Europe, but is one of the most dominant inducers of pollen allergy [10,11,12]. It was first observed in Europe in the mid-19th century, its main naturalization and establishment has been accelerated since the beginning of the new millennium, through changing climatic conditions related to climate warming [9,13]
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