Abstract
Both spiny and edible amaranths (Amaranthus spinosus and A. tricolor) are exotic annuals in China that produce numerous small seeds every year. Spiny amaranth has become a successful invader and a troublesome weed in Xishuangbanna, but edible amaranth has not, although it is widely grown as a vegetable there. As seed germination is one of the most important life-stages contributing to the ability of a plant to become invasive, we conducted experiments to compare the effects of high temperature and water stress on seed germination in two varieties each of spiny amaranth and edible amaranth. Overall, the seeds of both amaranth species exhibited adaptation to high temperature and water stress, including tolerance to ground temperatures of 70°C for air-dried seeds, which is consistent with their behavior in their native ranges in the tropics. As expected, the invasive spiny amaranth seeds exhibited higher tolerance to both continuous and daily periodic high-temperature treatment at 45°C, and to imbibition-desiccation treatment, compared to edible amaranth seeds. Unexpectedly, edible amaranth seeds exhibited higher germination at extreme temperatures (10°C, 15°C, and 40°C), and at lower water potential (below -0.6 MPa). It is likely that cultivation of edible amaranth has selected seed traits that include rapid germination and germination under stressful conditions, either of which, under natural conditions, may result in the death of most germinating edible amaranth seeds and prevent them from becoming invasive weeds in Xishuangbanna. This study suggests that rapid germination and high germination under stress conditions—excellent seed traits for crops and for many invasive species—might be a disadvantage under natural conditions if these traits are asynchronous with natural local conditions that support successful germination.
Highlights
Biological invasion is a serious threat to native agriculture and natural ecosystems worldwide [1,2,3]
This study investigated the germination requirements and seed germination of two congeneric species, spiny and edible amaranths, under high-temperature and water stress
Seeds of both species germinated across a wide temperature range, from 10 ̊C to 40 ̊C, with their maximum germination occurring at 35 ̊C, and they exhibited strong tolerance to extreme high temperature of 70 ̊C in air-dried seeds, and to continuous and daily periodic heat treatment at 45 ̊C
Summary
Biological invasion is a serious threat to native agriculture and natural ecosystems worldwide [1,2,3]. Spiny amaranth is native to tropical America, but now is considered an invasive plant worldwide [10,11]; in China, it is abundant in the tropical, subtropical, and warm temperate regions [12,13], with its first appearance documented in Macao in the 1930s [13]. It is a common invasive weed in Xishuangbanna [4,12], where it often grows in abandoned areas and cornfields. A comparative study of the spiny and edible amaranths will help to increase our knowledge of plant invasiveness
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