The allelopathy of horseweed with different invasion degrees in three provinces along the Yangtze River in China.

The effect of allelopathy from invasive alien plants (IAPs) on native species is one of the main factors for their adaptation and diffusion. IAPs can have different degrees of invasion under natural succession and are distributed in numerous regions. Seed germination and seedling growth (SGe-SGr) play a crucial role in population recruitment. Thus, it is critical to illustrate the differences in the allelopathy caused by an IAP with different degrees of invasion in numerous regions on SGe-SGr of native species to describe the primary force behind their adaptation and diffusion. This study assessed the allelopathy of the notorious IAP horseweed (Conyza canadensis (L.) Cronq.) on SGe-SGr of the native lettuce species (Lactuca sativa L.) under different degrees of invasion (light degree of invasion and heavy degree of invasion) in three provinces (Jiangsu, Anhui, and Hubei) along the Yangtze River in China. The allelopathy of horseweed leaf extract on lettuce SGe-SGr remarkably increased with the increased degree of invasion, which may be due to the buildup of allelochemicals generated by horseweed with a heavy degree of invasion compared with a light degree of invasion. A high concentration of horseweed leaf extract resulted in noticeably stronger allelopathy on lettuce SGe-SGr compared to the extract with a low concentration. There are noticeable differences in the allelopathy of the extract of horseweed leaves from different provinces on lettuce SGe-SGr with the following order i.e. Jiangsu > Hubei > Anhui. This may be due to the high latitudes for the three sampling sites in Jiangsu compared with the latitudes for the collection sites in Hubei and Anhui. There are certain differences in the environments among the three provinces. Thus, the allelopathy of horseweed on SGe-SGr of lettuce may have a greater negative impact in Jiangsu compared to the other two provinces. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00962-y.

Nitrogen application and osmotic stress antagonistically affect wheat seed germination and seedling growth.

Atmospheric nitrogen (N) deposition (AtNiDe) and drought stress (DS) have strongly affected plant growth. However, previous research has primarily focused on the effects of AtNiDe with various levels and DS on plant growth (especially seed germination and seedling growth). This study aimed to evaluate the single and combined effects of AtNiDe with four types (compounds: NH4-N, NO3-N, CO(NH2)2-N, and a mixture of the three types of N) and DS (three levels: control, low, and high) on wheat seed germination and seedling growth. The AtNiDe treatment increased wheat seed germination and seedling growth. Mixed N exerted a greater positive effect on wheat seed germination and seedling growth than single N forms. Organic N also had a greater positive effect on wheat seed germination and seedling growth than reduced inorganic N. The DS treatment decreased wheat seed germination and seedling growth. The AtNiDe treatment alleviated the adverse effects of DS on wheat seed germination and seedling growth. Mixed N had the greatest effect on alleviating the adverse effects of DS on wheat seed germination and seedling growth. Thus, AtNiDe and DS antagonistically affected wheat seed germination and seedling growth. NOVELTY STATEMENT This study assessed the single and combined effects of atmospheric nitrogen deposition with four types and drought stress at three levels on wheat seed germination and seedling growth. Generally, nitrogen and drought antagonistically affected wheat seed germination and seedling growth.

Changes in community structure and metabolic function of soil bacteria depending on the type restoration processing in the degraded alpine grassland ecosystems in Northern Tibet.

The alpine grassland ecosystems in Northern Tibet is seriously degraded. The condition of the degraded alpine grassland ecosystems in Northern Tibet (DAGENT) triggers a serious threat to environmental health and ecological safety of the local society. Thus, restoring DAGENT is a pressing task presently to sustain social stability and sustainable development. Soil microorganisms act a vital role in the structure and function execution of ecosystems. Further, bacteria are sensitive to external disturbances. This study purposes to evaluate the effects of the three types of restoration processing (i.e., the separated plant sowing, the separated water-soluble polyurethane fertilization, and the combined plant sowing and water-soluble polyurethane fertilization) on soil bacterial communities in DAGENT by using high-throughput sequencing with Illumina Novaseq 6000. The separated plant sowing significantly elevations soil pH, and soil nitrogen and phosphorus contents in DAGENT. Additionally, the combined plant sowing and water-soluble polyurethane fertilization markedly improves soil nitrogen content in DAGENT. The combined plant sowing and water-soluble polyurethane fertilization antagonistically affect soil pH and soil phosphorus content in DAGENT. The three types of restoration processing have no obvious effects on the alpha diversity of soil bacteria in DAGENT. But the three types of restoration processing create obvious alterations in the beta diversity of soil bacteria and the relative abundance of soil bacterial proportions in DAGENT. The three types of restoration processing also cause significant modifications in metabolic function of soil bacteria in DAGENT. The leading reason for the altered community structure and metabolic function of soil bacteria may be attributed to the changes in plant growing condition as well as soil pH and nutrient contents in DAGENT. Consequently, the three types of restoration processing are mainly changed the community structure and metabolic function of soil bacteria, rather than the alpha diversity of soil bacteria, in DAGENT.

Indigenous plant species and invasive alien species tend to diverge functionally under heavy metal pollution and drought stress.

The functional similarity between indigenous plant species (IPS) and invasive alien species (IAS) governs the invasion process of successful IAS because IPS and coexisting IAS suffer alike or even same ecological selection pressures. The aggravated condition created by heavy metal pollution (HMP) and drought stress may generate a noticeable impact on the invasive competitiveness and invasion process of IAS possibly via the variations in the functional similarity between IPS and IAS. Consequently, it is necessary to illumine the functional similarity between IPS and IAS under HMP and drought stress to clarify the mechanisms underlying the successful invasion of IAS. This study aims to estimate the functional similarity between IPS Amaranthus tricolor L. and IAS A. retroflexus L. under the condition with the alone and combined effects of HMP with different kinds (e.g., Cu and Pb) and drought stress [simulated by polyethylene glycol-6000 (PEG) solution]. HMP notably declines A. tricolor growth but has no remarkable effect on A. retroflexus growth. A. retroflexus displays a strong competitive intensity than A. tricolor under HMP. Further, HMP makes a greater stress intensity on A. tricolor growth than A. retroflexus growth. Therefore, HMP can accelerate A. retroflexus invasion. A. retroflexus displays a poor competitive intensity under drought stress. Thus, drought stress can hinder A. retroflexus invasion. However, drought stress causes a greater stress intensity on A. tricolor growth than A. retroflexus growth. Thus, the continued drought stress may converse the adverse effects of drought stress on A. retroflexus invasion potentially. The two Amaranthus species tend to diverge functionally under the combined HMP and drought stress. Further, A. retroflexus shows a strong competitive intensity than A. tricolor under the combined HMP and drought stress. Moreover, the combined HMP and drought stress induces a greater stress intensity on A. tricolor growth than A. retroflexus growth. Thus, the combined HMP and drought stress can facilitate A. retroflexus invasion. Meanwhile, the competitiveness for sunlight acquisition and leaf photosynthetic capacity may play a key role in the successful invasion of A. retroflexus under the combined HMP and drought stress.

The mixed silicon and cadmium synergistically impact the allelopathy of Solidago canadensis L. on native plant species Lactuca sativa L.

Several invasive alien plants (IAP) can trigger evidently allelopathy on the seed germination and seedling growth (SgSg) of native plant species (NPS). The getting worse condition with heavy metal pollution (e.g., cadmium) can significantly impact SgSg of plant species. Silicon can offset the adverse effects of environmental pressure on the growth and development of plant species. Thus, it is important to evaluate the influences of silicon on the allelopathy of IAP on SgSg of NPS under cadmium stress to better understand the mechanism driving the successful colonization of IAP. This study focuses on the allelopathy of the infamous IAP Solidago canadensis L. (Canada goldenrod; by using leaf extracts) on SgSg of NPS Lactuca sativa L. under the separated and mixed silicon and cadmium addition. S. canadensis triggers notably allelopathy on SgSg of L. sativa and gradually upsurges with increasing leaf extract concentration. Thus, the growth performance of NPS will be gradually reduced with an increasing degree of S. canadensis invasion. Cadmium evidently declines SgSg of L. sativa due to the broken balance of plant species for nutrient absorption. The mixed S. canadensis leaf extracts and cadmium synergistically impact seed germination of L. sativa but antagonistically affect seedling growth of L. sativa. The mixed silicon and cadmium intensify the allelopathy of S. canadensis on SgSg of L. sativa probably due to the increased effective content of cadmium in plant roots under silicon addition. Thus, the mixed silicon and cadmium will be advantageous to the following invasion process of IAP largely via the depressed SgSg of NPS.

Litter decomposition process dramatically declines the allelopathy of Solidago canadensis L. on the seed germination and seedling growth of Lactuca sativa L.

A variety of invasive alien species (IAS) can trigger distinct allelopathy on the seed germination and seedling growth (SGeSGr) of native plant species (NPS) mainly through the released allelochemicals. However, the decomposition process of IAS litters may affect their allelopathy on SGeSGr of NPS because part of the allelochemicals will be released during the litter decomposition process, especially under heavy metal pollution. This study focuses on the impacts of the litter decomposition process of the notorious IAS Solidago canadensis L. on its allelopathy on SGeSGr of NPS Lactuca sativa L. under cadmium (Cd) pollution. The decomposition process signally declines the allelopathy of S. canadensis litters on SGeSGr of L. sativa likely because partial allelochemicals in S. canadensis litters discharged during the decomposition process. Cd addition noticeably rises the allelopathy of S. canadensis litters on SGeSGr of L. sativa probably because Cd can reduce plant growth largely via the improved lipid membrane permeability and the induced reactive oxygen molecules which is unfavorable to plant cell metabolism. This phenomenon may also be attributed to the weak acid properties of one of the most abundant allelochemicals in S. canadensis litters, i.e., phenolics (particularly polyphenols), can improve the solubility and the toxicity of Cd.

Erigeron annuus (L.) Pers. and Solidago canadensis L. antagonistically affect community stability and community invasibility under the co-invasion condition.

The successful invasion of one invasive alien plant (IAP) can generate a favorable habitat in the invaded communities that beneficial to the successful invasion of the subsequent IAP. Advanced variations in the species number of IAP have the potential to alter the functional similarity and dissimilarity between IAP and co-existing native plant species (NPS), plant taxonomic diversity, plant functional diversity, community stability, and community invasibility. This study aims to evaluate the effects of the co-invasion of two notorious IAP, Erigeron annuus (L.) Pers. and Solidago canadensis L., on the functional similarity and dissimilarity between IAP and co-existing NPS, plant taxonomic diversity, plant functional diversity, community stability, and community invasibility in East China by using a comparative study. Results presented that: (I) IAP and co-existing NPS tend to converge functionally under E. annuus invasion and the functional similarity between IAP and co-existing NPS under E. annuus invasion supports the habitat filtering; (II) IAP and co-existing NPS tend to diverge functionally under S. canadensis invasion and the co-invasion condition and the functional dissimilarity between IAP and co-existing NPS under S. canadensis invasion and the co-invasion condition supports the niche differentiation; (III) plant taxonomic diversity was dramatically reduced under invasion condition, especially under S. canadensis invasion; (IV) Mason's α functional diversity was remarkably elevated under S. canadensis invasion and the co-invasion condition; (V) E. annuus and S. canadensis antagonistically affect community stability and community invasibility under the co-invasion condition compared with their independent invasion.

Cadmium influences the litter decomposition of Solidago canadensis L. and soil N-fixing bacterial communities.

It is important to illuminate the effects of litter decomposition of invasive alien species on soil N-fixing bacterial communities (SoNiBa), especially under heavy metal pollution to better outline the mechanisms for invasion success of invasive alien species. This study attempts to identify the effects of litter decomposition of Solidago canadensis L. on SoNiBa under cadmium (Cd) pollution with different concentrations (i.e., low concentration, 7.5 mg/kg soil; high concentration, 15 mg/kg soil) via a polyethylene litterbags-experiment. Electrical conductivity and total N of soil were the most important environmental factors for determining the variations of SoNiBa composition. S. canadensis did not significantly affect the alpha diversity of SoNiBa but significantly affect the beta diversity of SoNiBa and SoNiBa composition. Thus, SoNiBa composition, rather than alpha diversity of SoNiBa, was the most important determinant of the invasion success of S. canadensis. Cd with 15 mg/kg soil did not address distinct effects on alpha diversity of SoNiBa, but Cd with 7.5 mg/kg soil noticeably raised the number of species and species richness of SoNiBa mainly due to the hormonal effects. The combined S. canadensis and Cd with 15 mg/kg soil obviously decreased cumulative mass losses and the rate of litter decomposition (k) of S. canadensis, but the combined S. canadensis and Cd with 7.5 mg/kg soil evidently accelerated cumulative mass losses and k of S. canadensis. Thus, Cd with 7.5 mg/kg soil can accelerate litter decomposition of S. canadensis, but Cd with 15 mg/kg soil can decline litter decomposition of S. canadensis.

Silver nanoparticles reduced the invasiveness of redroot pigweed.

The differences in the growth performance between invasive species and native species might paly a key role in the effective invasion. The extensive use of silver nanoparticles (AgNPs) has created the concern of their release into environment. Thus, the possible effects of AgNPs on the growth performance of invading agents are critical to better illustrate the underlying mechanisms for effective invasion. This study aimed to assess the impacts of AgNPs with different concentrations [200 and 400 mg kg (soil)-1] and particle sizes (30 and 70 nm) on the growth performance and competitive ability of well known invasive Amaranthus retroflexus L. (redroot pigweed) and native A. tricolor L. (red amaranth). It was observed that the growth characteristics and supporting ability of redroot pigweed were significantly lower than those of amaranth. Results of the relative competitive intensity index and the relative dominance index also revealed that redroot pigweed exhibited lower competitive ability compared to red amaranth, especially under AgNPs. It can be assumed that the poor growth performance and competitive ability of redroot pigweed might prevent its invasiveness under AgNPs. The supporting ability, leaf photosynthetic area, leaf growing ability, leaf resource use efficiency and acquisition capability, and growth competitiveness of the two plant species were found to be significantly reduced under AgNPs. AgNPs with 30 nm at 400 mg kg (soil)-1 triggered more toxicity on the supporting ability and growth competitiveness of the two plant species than AgNPs with 30 nm at 200 mg kg (soil)-1. In addition, AgNPs with 30 nm imparted high toxicity on the leaf growing ability of red amaranth than AgNPs with 70 nm. However, the particle size of AgNPs did not address significant effects on the growth performance of redroot pigweed. Ag+ solution exhibited stronger toxicity on the supporting ability and leaf growing ability of the two plant species than AgNPs.

Allelopathic effects of Canada goldenrod leaf extracts on the seed germination and seedling growth of lettuce reinforced under salt stress.

Allelopathic effects on the seed germination and seedling growth of the natives play a crucial role in the successful invasion of numerous invaders. Meanwhile, soil salinity is an emerging driver of the spread of many invaders, especially in the colonization of saline habitats. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be altered or even reinforced under salt stress. This study aims to address the allelopathic effects of the notorious invader Canada goldenrod (Solidago canadensis L.; goldenrod hereafter) on the seed germination and seedling growth of the native lettuce (Lactuca sativa L.; lettuce hereafter) under a gradient of salt stress. Goldenrod leaf extracts with high concentration significantly decreased root length, leaf shape index, germination percentage, germination potential, germination index, germination vigor index, and germination rate index of lettuce. However, goldenrod leaf extracts with low concentration significantly increased root length and leaf width of lettuce. Goldenrod leaf extracts with high concentration display more serious allelopathic effects on the seed germination and seedling growth of lettuce than those with low concentration. Salt stress regardless of concentration significantly decreased seedling height, root length, leaf shape index, and seedling biomass (fresh weight) of lettuce. The combined goldenrod leaf extracts and salt stress have a synergistic effect on seedling height, root length, leaf shape index, germination percentage, germination potential, germination index, and germination rate index of lettuce. Thus, the allelopathic effects of the invaders on the seed germination and seedling growth of the natives may be reinforced under salt stress. Accordingly, salt stress may be beneficial to the further invasion of the invaders mainly via the reduced growth performance of the natives.

Ecotoxicological effects of metals with different concentrations and types on the morphological and physiological performance of wheat.

Large amounts of heavy metals end up in the environment as a result of ever-increasing anthropogenic activities and economic development. At least two specific types of heavy metals occur in the soil sub-ecosystem in most regions of China, especially in farmland. The morphological and physiological performance of wheat play a vital role in its growth and development, but heavy metals, both occurring independently and combined, may affect wheat growth. Thus, this study examined different concentrations of two types of heavy metals (copper (Cu), lead (Pb), and Cu and Pb combined) on the morphological and physiological performance of wheat. The number of tillers, plant height, ground diameter, single-leaf fresh and dry weights, leaf thickness, single-plant fresh and dry weights, leaf chlorophyll and N contents, and plant peroxidase and catalase activities of wheat significantly decreased when treated with two types of heavy metals. Thus, the two types of heavy metals significantly reduced the morphological and physiological performance of wheat; the ecotoxicological effects of heavy metals on the morphological and physiological performance of wheat increased with increasing heavy metal concentrations, especially on the leaf chlorophyll and N contents of wheat. The ground diameter and single-plant fresh weight of wheat in the Pb treatment were significantly lower than those under the independent Cu treatment with same concentration. Thus, the Pb treatment exerted more toxic effects on the morphological performance of wheat than the independent Cu treatment. The ground diameter, single-leaf dry weight, leaf thickness, single-plant fresh weight, and plant proline content of wheat under the combined Cu and Pb were significantly lower than those in the Cu and/or the Pb treatments. The combined Cu and Pb treatments addressed synergistic effects on the morphological and physiological performance of wheat. Accordingly, the growth performance of wheat will be significantly reduced in the combined Cu and Pb treatments compared with the independent Cu or Pb treatments.

Silver nanoparticles with different particle sizes enhance the allelopathic effects of Canada goldenrod on the seed germination and seedling development of lettuce.

Allelopathic effects on the seed germination and seedling development of co-occurring native plant species (natives hereafter) are regarded as an important driver facilitating invasion of many invasive plant species (invaders hereafter). The release of silver nanoparticles (AgNPs) into the environment may affect the allelopathic effects of the invaders on the seed germination and seedling development of natives. This study aims to assess the allelopathic effects (using leaf extracts) of Canada goldenrod (Solidago canadensis L.) on the seed germination and seedling development of native lettuce (Lactuca sativa L.) treated with AgNPs with different particle sizes. Canada goldenrod leaf extracts with high concentration exhibit stronger allelopathic effects on the seedling height and root length of lettuce than those treated with low concentration. AgNPs of all particle sizes significantly decreased seed germination and seedling development indices of lettuce. AgNPs with larger particle sizes exerted stronger toxicity on leaf length and width of lettuce than those with smaller particle sizes. Thus, nanoparticles with larger particle sizes might mediate the production of increased sizes of cell wall pore size and large absorption of such substances by plant roots can be harmful. AgNPs significantly enhanced the allelopathic effects of Canada goldenrod on the seed germination and seedling development of lettuce. Small particle size AgNPs may play a more essential role in the enhanced allelopathic effects of low concentrations of Canada goldenrod leaf extracts; however, large particle size AgNPs may play a more important role in the enhanced allelopathic effects of high concentrations of Canada goldenrod leaf extracts.

Solidago canadensis invasion affects soil N-fixing bacterial communities in heterogeneous landscapes in urban ecosystems in East China.

Soil nitrogen-fixing bacterial communities (SNB) can increase the level of available soil N via biological N-fixation to facilitate successful invasion of several invasive plant species (IPS). Meanwhile, landscape heterogeneity can greatly enhance regional invasibility and increase the chances of successful invasion of IPS. Thus, it is important to understand the soil micro-ecological mechanisms driving the successful invasion of IPS in heterogeneous landscapes. This study performed cross-site comparisons, via metagenomics, to comprehensively analyze the effects of Solidago canadensis invasion on SNB in heterogeneous landscapes in urban ecosystems. Rhizospheric soil samples of S. canadensis were obtained from nine urban ecosystems [Three replicate quadrats (including uninvaded sites and invaded sites) for each type of urban ecosystem]. S. canadensis invasion did not significantly affect soil physicochemical properties, the taxonomic diversity of plant communities, or the diversity and richness of SNB. However, some SNB taxa (i.e., f_Micromonosporaceae, f_Oscillatoriaceae, and f_Bacillaceae) changed significantly with S. canadensis invasion. Thus, S. canadensis invasion may alter the community structure, rather than the diversity and richness of SNB, to facilitate its invasion process. Of the nine urban ecosystems, the diversity and richness of SNB was highest in farmland wasteland. Accordingly, the community invasibility of farmland wasteland may be higher than that of the other types of urban ecosystem. In brief, landscape heterogeneity, rather than S. canadensis invasion, was the strongest controlling factor for the diversity and richness of SNB. One possible reason may be the differences in soil electrical conductivity and the taxonomic diversity of plant communities in the nine urban ecosystems, which can cause notable shifts in the diversity and richness of SNB.