Climate Change Hastens Invasional Interference Between Two Notorious Invasive Plants, Common Ragweed (Ambrosia Artemisiifolia) and Redroot Pigweed (Amaranthus Retroflexus), in China

As multiple invaders co-occur in similar habitats, understanding the interactions between different invasive species is very important. Invasional meltdown and neutral and interference relationships have been reported. However, interspecific interactions may vary with environmental change due to the different responses of various invaders. To better understand the interaction of notorious invasive alien plants under global climate change, the growth characters of common ragweed (Ambrosia artemisiifolia) and redroot pigweed (Amaranthus retroflexus) were compared when they were planted in monoculture or mixed culture under four environmental treatments: elevated CO2, enriched N, elevated CO2 + enriched N and a control. The results showed that 1) the plant height, basal stem diameter, and shoot, root, and total biomass of common ragweed all consistently increased in response to the treatments, while the growth traits of redroot pigweed were all inhibited. A significant CO2×N interaction was found only for the shoot and total biomass of common ragweed. 2) Invasional interference between these two notorious alien invasive plants was discovered. Common ragweed consistently displayed an obvious competitive advantage over redroot pigweed regardless of treatment. 3) Elevated CO2 and enriched N obviously changed the seed mass frequency distribution of common ragweed: elevated CO2 increased the proportion of small seeds, while enriched N increased the proportion of large seeds. We conclude that common ragweed can outcompete redroot pigweed; moreover, elevated CO2 and N addition hasten this competitive advantage.

Inhibitory Effects of Redroot Pigweed and Crabgrass on Germination and Growth----From Lab To Field

Interactions between weeds and crops often occur by resource competition or allelopathy. However, it is still unknown how local weed species influence artificially introduced switchgrass. In this study, four experiments were conducted to evaluate the inhibitory effects of redroot pigweed (Amaranthus retroflexus) and crabgrass (Digitaria sanguinalis) on germination and growth of switchgrass, the lowland tetraploid cultivar ‘Alamo’ (Panicum virgatum cv. Alamo). Switchgrass germination was inhibited significantly in Petri dishes, with 48.1% and 33.9% inhibition on germination rate by redroot pigweed and crabgrass root aqueous extracts at 0.1 g·mL− 1 concentration, respectively. Significant inhibitory effects on switchgrass seedling biomass were observed at 5:5 proportion with redroot pigweed and crabgrass in glass jars, with 61.6% and 53.4% inhibition on plant biomass, respectively. Under the same root segregation, redroot pigweed had a stronger inhibitory effect on switchgrass seedling growth than crabgrass. Growth of transplanted switchgrass seedlings was inhibited significantly by local weeds in the field, with 46.2% and 11.7% inhibition on shoot biomass during the first and second growing seasons, respectively. However, no significant growth reduction in switchgrass was detected in the third growing season.

Improving weed control in sustainable agro-ecosystems: role of cultivar and termination timing of rye cover crop

Highlights - One month after rye termination, the weed biomass under mulching is reduced by 4 times, compared with the control. - When rye is terminated early, the weed biomass production is reduced by the allelochemical content in rye tissues. - When rye is terminated late, the weed biomass production is reduced by the amount of rye biomass. - Lambsquarters, redroot pigweed, and purslane growth is inhibited by rye mulching, while velvetleaf is not affected. Abstract Alternative strategies to control weeds are required at field level to reduce herbicides and derived pollution. Rye (Secale cereale L.) cultivation as cover crop is adopted mainly because of its allelopathic weed control, which takes place throughout a strong inhibition of germination and seedling growth in several grass and broad-leaved weeds. The present study consisted of: i) a field trial, focused on evaluation of biomass production and allelochemical concentration in the biomass, and in situ weed control at 30 days after termination (with two termination timings: T1 - heading phase and T2 - 10 days later) of 8 rye varieties; ii) a pot experiment, focused on the inhibition effect of mulches derived by those 8 rye varieties on four summer weeds: velvetleaf (Abutilon theophrasti Med.), lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and common purslane (Portulaca oleracea L). Results showed that biomass production was the highest with Protector, closely followed by Primizia, Sito 70, Hellvus, Forestal, and Hymonta. In any case, rye mulching always reduced the weed biomass, especially with Fasto and Forestal. The allelochemical concentration in the biomass was the highest with Fasto and Forestal, and decreased on average from T1 to T2 (-38% for total BX and -57% for isovitexin). Conversely, the rye biomass production increased (on average + 77%) passing from T1 to T2. We found also that the reduction of weed biomass, compared with the control, is highly correlated with the allelochemical content in rye biomass in the case of T1 termination, while with the biomass production in the case of T2. In pots, a strong inhibitory effect on seedling growth due to rye mulching was observed for C. album (-76%), A. retroflexus (-56%), and P. olearcea (-84%), while not for A. theophrasti. We concluded that, whatever the variety, adopting rye as cover crop may be considered as a suitable practice to reduce weed pressure at the field level. Among all the varieties tested, Forestal and Protector showed the greatest weed suppression potential, as a consequence of high amount of allelochemicals production for Forestal, and high biomass production for Protector.

Amaranthus retroflexus L. (Redroot Pigweed): Effects of Elevated CO2 and Soil Moisture on Growth and Biomass and the Effect of Radiant Heat on Seed Germination

Amaranthus retroflexus L. (Amaranthaceae), Redroot pigweed, is native to North America, but has become a weed of agriculture worldwide. Previous research into competition with food crops found it significantly reduces yields. Additionally, taxonomy, biomass allocation, physiological responses to light intensity, water stress, elevated CO2, and herbicide resistance have been investigated. To extend other research findings, we investigated growth and biomass yield in response to (i) soil moisture stress, and (ii) drought and elevated CO2. Additionally, we investigated seed germination rates following exposure to three elevated temperatures for two different time periods. Overall, moisture stress reduced plant height, stem diameter, and number of leaves. Elevated CO2 (700 ppm) appeared to reduce negative impacts of drought on biomass productivity. Heating seeds at 120 °C and above for either 180 or 300 s significantly reduced germination rate. These results inform an understanding of potential responses of A. retroflexus to future climate change and will be used to predict future occurrence of this weed. The finding that exposing seeds to high temperatures retards germination suggests fire could be used to prevent seed germination from soil seed banks, particularly in no-till situations, and therefore may be used to address infestations or prevent further spread of this weed.

Results of Studying the Efficiency of Chemical Measures Against Weed Vegetation in Sunflower Crops

This study identified the most effective methods for protecting sunflowers from weeds through the treatment of crops with the herbicides Euro Lightning, Euro Lightning Plus and Express. These options provided substantial protection of sunflowers from weeds such as the cursed thistle, field bindweed, yellow bristle grass, field mustard, frost blite and redroot pigweed. In the fight against ragweed, the herbicides Euro Lightning and Euro Lightning Plus provided excellent action and the herbicide Express provided good results. Variants with the use of the soil herbicides Gezagard and Gardo Gold suppressed yellow bristle grass, field mustard and frost blite, and satisfactorily protected against redroot pigweed. However, they were ineffective against perennial species of weeds (cursed thistle and field bindweed) and ragweed growing in the experimental area. The application of soil herbicides did not influence the growth of sunflower broomrape and plots. The use of the herbicides Euro Lightning and Express helped to reduce the contamination of crops with this type of weed. When processing crops with the herbicide Euro-Lightning Plus, this type of weed was completely absent. Statistical processing of crop data showed a difference in yield in the studied variants. Carrying out weed control measures significantly increased the yield of sunflowers in comparison to control options (without treatment). There was a significant difference in the yield of oilseeds when herbicides intended for application on vegetating plants (Euro Lightning and Express) were used, compared to when the variants of soil herbicides Gezagard and Gardo Gold were used. Keywords: sunflower, weed plants, herbicides, oilseed productivity

Target-site Basis for Fomesafen Resistance in Redroot Pigweed (Amaranthus retroflexus) from China

Redroot pigweed (Amaranthus retroflexus L.) is a dominant weed in soybean [Glycine max (L.) Merr.] fields in Heilongjiang Province, China. High selective pressure caused by the extensive application of the protoporphyrinogen oxidase (PPO)-inhibiting herbicide fomesafen has caused A. retroflexus to evolve resistance to this herbicide. Two susceptible and two resistant populations (S1, S2, R1 and R2) were selected in this study to illustrate the target-site resistance mechanism in resistant A. retroflexus. Whole-plant bioassays indicated that R1 and R2 had evolved high-level resistance to fomesafen, with resistance factors of 27.0-27.9. Sequence alignment of the PPO gene showed an Arg128Gly substitution in PPX2. The basal expression differences of PPX1 and PPX2 between the S1 and R1 plants were essentially nonsignificant, whereas the basal expression of PPX2 in R2 plants was slightly lower than that in S1 plants. Compared to the PPX1 gene, the PPX2 gene maintained higher expression in the resistant plants after treatment with fomesafen. ELISA showed a similar basal PPO content between the susceptible and resistant plants without treatment. After fomesafen treatment, the PPO content decreased sharply in the susceptible plants compared with that in the resistant plants. Furthermore, after 24 h of treatment, the resistant plants showed an increased PPO content, whereas the susceptible plants had died. PPO2 mutation resulted in high extractable PPO activity and low sensitivity to fomesafen along with changes in the PPO enzyme kinetics. Although the mutant PPO2 exhibited increased Km values in the resistant plants, the Vmax values in these plants were also increased. Changes in the properties of the PPO enzyme due to an Arg128Gly substitution in PPX2, including changes in enzyme sensitivity and enzyme kinetics, are the target-site mechanism of resistance in A. retroflexus.