Fate of the soil seed bank of giant ragweed and its significance in preventing and controlling its invasion in grasslands

Abstract

Giant ragweed (Ambrosia trifida, L. henceforth referred to as GR), an annual non‐native invasive weed, may cause health problems and can reduce agricultural productivity. Chemical control of GR in grasslands may have irreversible side effects on herbs and livestock. In an attempt to propose a solution to the harmful effects of GR on grasslands, this study explores the fate of its soil seed bank (SSB) and considers the physical control of its SSB reduction. By studying GR distributed in grasslands of the Yili Valley, Xinjiang, China, we measured the spatial and temporal changes in seed density, seed germination, dormancy, and death. We analyzed seed germination, dormancy, and death following different storage periods. The study analyzed population characteristics over time, including seed fate, and examined physical control methods for reducing the SSB density. The SSB of GR occurs in the upper 0–15 cm of soil in grasslands. Seed density in the SSB decreased by 68.1% to 82.01% from the reproductive growth period to the senescence period. More than 98.7% of the seeds were rotten, eaten, germinated, dispersed, or died within one year after being produced. The seed germination rate of the SSB decreased with the number of years after invasion. When stored for 0.5 or 3.5 years, seed germination rates fell by 40%, during which time seed death rate increased by almost 40%. When GR was completely eradicated for two consecutive years, the SSB and population densities decreased by >99%. The vast majority of GR seeds germinated or died within one year; the germination rate decreased significantly if the seeds were stored dry at room temperature for a long time. Newly produced seeds are the main source of seeds in the SSB. Therefore, thoroughly eradicating GR plants for several years before the seeds can mature provides an effective control method in grasslands.

The Changes of Soil Seed Banks In Time Series Before And After The Invasive Artemisia Trifida Was Removed From Grassland

“…It is newly recorded that giant ragweed invades grassland and causes serious damage. Through previous studies (Dong et al 2020) and this study, it was found that a large number of seeds are produced every year, which is an important reason why giant ragweed can cause damage to the grassland. With the increase in invasion years, a dense forest population was formed in the aboveground portion of the studied ecosystem.…”

“…However, more than 98.66% of its seeds are consumed in one year, and a few of them are actually used for germination (Dong et al 2020). Therefore, it can be said that the high seed bank density generated in that year is the basis for the formation of a dense population of giant ragweed in the following year.…”

“…Giant ragweed grows mostly in the grasslands of this region, a diverse grazing area with rich chestnut soil, regarded as the source of the 'Chinese wild fruit gene pool'. Large distribution areas and high densities of giant ragweed pose a serious threat to native seedling regeneration (Dong et al 2020).…”

“…A special phenomenon occurs when giant ragweed invades grasslands (Montagnani et al 2017), which poses a great threat to forage yield (Dong et al 2020). It was first discovered in the Yili Valley, Xinjiang, China in 2010, and its distribution area had expanded to 2150-fold its original size by 2016 (Dong et al 2017).…”

“…By 2020, this distribution area has expanded 3113-fold, reaching 37900 ha. After 4-5 years of invasion with no external control, a single dense stand had formed over the area with nearly 100% population coverage, leading to a seed bank with certain characteristics (Dong et al 2020). However, the effect of giant ragweed on the native seed banks in the process of forming a high coverage population remains unclear.…”