Fast seedling root growth leads to competitive superiority of invasive plants

Soil nutrient limitation and natural enemies promote the establishment of alien species in native communities

The invasion of alien plant species threatens the composition and diversity of native communities. However, the invasiveness of alien plants and the resilience of native communities are dependent on the interactions between biotic and abiotic factors, such as natural enemies and nutrient availability. In our study, we simulated the invasion of nine invasive plant species into native plant communities using two levels of nutrient availability and suppression of natural enemies. We evaluated the effect of biotic and abiotic factors on the response of alien target species and the resistance of native communities to invasion. The results showed that the presence of enemies (enemy release) increased the biomass proportion of alien plants while decreasing that of native communities in the absence of nutrient addition. Furthermore, we also found that the negative effect of enemy suppression on the evenness of the native community and the root-to-shoot ratio of alien target species was greatest under nutrient addition. Therefore, nutrient-poor and natural enemies might promote the invasive success of alien species in native communities, whereas nutrient addition and enemy suppression can better enhance the resistance of native plant communities to invasion.

High temperature can improve the performance of invasive plants by facilitating root growth

PREMISE

The ever-increasing temperatures of the Anthropocene may facilitate plant invasions. To date, studies of temperature effects on alien plants have mainly focused on aboveground plant traits but ignored belowground traits, which may confound predictions of plant invasion risks.

METHODS

The temperature effects on the root growth dynamics of two alien shrubs, invasive Mimosa sepiaria and naturalized Corchorus capsulari, were studied using a 3D, transparent growth system under five temperature treatments (day/night: 18°C/13°C to 34°C/29°C) that cover the present and future warming temperature scenarios in China. We measured root depth and width growth in response to temperature treatments over 84 days. We also investigated intra- and interspecific competition of paired plants of the two species grown together at the five temperatures.

RESULTS

Shoot growth of M. sepiaria and C. capsularis was optimal at the mid-range temperature. Root growth, however, was faster at the highest temperature (34°C/29°C) for M. sepiaria, but decreased for C. capsularis as temperatures increased. Root depth growth was more sensitive than root width for both species during neighbor competition. Compared to C. capsularis, M. sepiaria had relatively greater advantage during intra- and interspecific competition with increasing temperature, possibly because of its better root growth at high temperatures.

CONCLUSIONS

These results suggest that temperature increases can improve the performance of some alien plants by facilitating width and depth growth of their roots. This enhancement requires serious attention when managing and predicting invasion risk.

Effects of Clipping an Invasive Plant Species on the Growth of Planted Plants of Two Co-Occurring Species in a Greenhouse Study

The restoration of native plants in invaded habitats is constrained with the presence of highly competitive exotic species. Aboveground removal, such as clipping or mowing, of invasive plants is required for successful restoration. The effects of clipping an invasive plant species, Solidago canadensis, grown at five densities (1-5 plants per pot), and planting two co-occurring and competitive species, Sesbania cannabina and Imperata cylindrica, on the growth of both the invasive species and the co-occurring species were investigated in a greenhouse experiment. The established S. canadensis suppressed the growth of planted seedlings with 47.8-94.4% reduction in biomass, with stronger effects at higher densities; clipping significantly reduced 97.5-97.4% of biomass of S. canadensis and ameliorated the suppression effects (with only 8.7-52.7% reduction in biomass of the co-occurring plants), irrespective of density. Both the aboveground and belowground part of S. canadensis contributed to its suppression effects on planted co-occurring species. Seed sowing of co-occurring species reduced the belowground growth, but not the underground growth of S. canadensis. S. cannabina appeared to be more effective at reducing the growth of S. canadensis than I. cylindrica. Therefore, clipping together with planting competitive species that can overcome the belowground priority effects of S. canadensis could be a promising strategy for controlling S. canadensis invasion and restoring native plant communities.

Invasive and Native Plants Differentially Respond to Exogenous Phosphorus Addition in Root Growth and Nutrition Regulated by Arbuscular Mycorrhizal Fungi

Plant invasion has severely damaged ecosystem stability and species diversity worldwide. The cooperation between arbuscular mycorrhizal fungi (AMF) and plant roots is often affected by changes in the external environment. Exogenous phosphorus (P) addition can alter the root absorption of soil resources, thus regulating the root growth and development of exotic and native plants. However, it remains unclear how exogenous P addition regulates the root growth and development of exotic and native plants mediated by AMF, affecting the exotic plant invasion. In this experiment, the invasive plant Eupatorium adenophorum and native plant Eupatorium lindleyanum were selected and cultured under intraspecific (Intra-) competition and interspecific (Inter-) competition conditions, involving inoculation with (M⁺) and without AMF (M^-) and three different levels of P addition including no addition (P₀), addition with 15 mg P kg^-1 soil (P₁₅), and addition with 25 mg P kg^-1 soil (P₂₅) for the two species. Root traits of the two species were analyzed to study the response of the two species' roots to AMF inoculation and P addition. The results showed that AMF significantly promoted the root biomass, length, surface area, volume, tips, branching points, and carbon (C), nitrogen (N), and P accumulation of the two species. Under M⁺ treatment, the Inter- competition decreased the root growth and nutrient accumulation of invasive E. adenophorum but increased the root growth and nutrient accumulation of native E. lindleyanum relative to the Intra- competition. Meanwhile, the exotic and native plants responded differently to P addition, exhibiting root growth and nutrient accumulation of invasive E. adenophorum increased with P addition, whereas native E. lindleyanum reduced with P addition. Further, the root growth and nutrition accumulation of native E. lindleyanum were higher than invasive E. adenophorum under Inter- competition. In conclusion, exogenous P addition promoted the invasive plant but reduced the native plant in root growth and nutrient accumulation regulated by AMF, although the native plant outcompeted the invasive plant when the two species competed. The findings provide a critical perspective that the anthropogenic P fertilizer addition might potentially contribute to the successful invasion of exotic plants.

Sex-specific outbreeding advantages and sexual dimorphism in the seedlings of dioecious trees

PREMISE

Dioecious trees are important components of many forest ecosystems. Outbreeding advantage and sexual dimorphism are two major mechanisms that explain the persistence of dioecious plants; however, they have rarely been studied in dioecious trees.

METHODS

We investigated the influence of sex and genetic distance between parental trees (GDPT) on the growth and functional traits of multiple seedlings of a dioecious tree, Diospyros morrisiana.

RESULTS

We found significant positive relationships between GDPT and seedling sizes and tissue density. However, the positive outbreeding effects on seedling growth mainly manifested in female seedlings, but were not prominent in males. Among seedlings, the male ones generally had higher biomass and leaf area than female seedlings, but such differences diminished as GDPT increased.

CONCLUSIONS

Our research highlights that outbreeding advantage in plants can be sex-specific and that sexual dimorphism begins from the seedling stage of dioecious trees.

The competitive strategies of poisonous weeds Elsholtzia densa Benth. on the Qinghai Tibet Plateau: Allelopathy and improving soil environment

Introduction

The competitive strategies of plants play a crucial role in their growth. Allelopathy is one of the weapons that plants use to improve their competitive advantage.

Methods

In order to explore the competitive strategy of a poisonous weed Elsholtzia densa Benth. (E. densa) on the Qinghai-Tibet Plateau (QTP), the effects of decomposing substances of E. densa on growth, root border cells (RBCs) characteristics of highland crop highland barley (Hordeum vulgare L.), and soil environment were determined.

Results

The decomposing allelopathic effect of E. densa on the germination and seedling growth of highland barley mainly occurred in the early stage of decomposing. The allelopathic effects were mainly on seed germination and root growth of highland barley. After treatment with its decomposing solution, the RBC's mucilage layer of highland barley thickened, and the RBC's activity decreased or even apoptosis compared with the control. However, only the above-ground part of the treatment group showed a significant difference. The effects of E. densa decomposed substances on the soil environment were evaluated from soil physicochemical properties and bacterial community. The results showed that soil bacteria varied greatly in the early stage of decomposion under different concentrations of E. densa. In addition, E. densa decomposing substances increased the soil nutrient content, extracellular enzyme activities, and bacterial community diversity. In the process of decomposition, the bacterial community structure changed constantly, but Actinobacteriota was always the dominant phylum.

Discussion

These results indicated that E. densa might adopt the following two strategies to help it gain an advantage in the competition: 1. Release allelochemicals that interfere with the defense function of surrounding plants and directly inhibit the growth and development of surrounding plants. 2. By changing the physical and chemical properties of soil and extracellular enzyme activity, residual plant decomposition can stimulate soil microbial activity, improve soil nutrition status, and create a more suitable soil environment for growth.

Use of ammonium salts or binary mixtures derived from amino acids, glycine betaine, choline and indole-3-butyric acid as plant regulators

A simple, efficient, and environmentally friendly synthesis method for bioproducts based on indole-3-butyric acid and amino acids, glycine betaine or choline has been developed. Spectral analysis and molecular calculations were used to determine whether the products were ammonium salts or binary mixtures. Moreover, it was observed that the ammonium salts degraded more rapidly than the binary mixtures when exposed to light. The structures of the products significantly impacted their thermal stability and phase transitions. Biological studies clearly showed that the synthesized products were more effective than a reference commercial preparation as a rooting agent and have significant potential as new biologically active agents with low environmental impact.

Morphological and physiological factors contributing to early vigor in the elite rice cultivar 9,311

Huanghuazhan (HHZ) and 9,311 are two elite rice cultivars in China. They have achieved high yield through quite different mechanisms. One of the major features that gives high yield capacity to 9,311 is its strong early vigor, i.e., faster establishment of its seedling as well as its better growth in its early stages. To understand the mechanistic basis of early vigor in 9,311, as compared to HHZ the cultivar, we have examined, under controlled environmental conditions, different morphological and physiological traits that may contribute to its early vigor. Our results show that the fresh weight of the seeds, at germination, not only determined the seedling biomass at 10 days after germination (DAG), but was also responsible for ~ 80% of variations in plant biomass between the two cultivars even up to 30 DAG. Furthermore, the 9,311 cultivar had a larger root system, which led to its higher nitrogen uptake capacity. Other noteworthy observations about 9,311 being a better cultivar than HHZ are: (i) Ten out of 15 genes involved in nitrogen metabolism were much more highly expressed in its roots; (ii) it had a higher water uptake rate, promoting better root-to-shoot nitrogen transfer; and (iii) consistent with the above, it had higher leaf photosynthetic rate and stomatal conductance. All of the above identified features explain, to a large extent, why the 9,311, as compared to HHZ, exhibits much more vigorous early growth.

Similar Impacts of Alien and Native Tree Species on Understory Light Availability in a Temperate Forest

Research Highlights: We evaluated influence of alien and native trees and shrubs on stand leaf area index to basal area ratio, indicating that both groups provide similar amounts of foliage. Background and Objectives: Foliage traits determine tree species effect on understory light availability. Direct comparisons of understory light availability due to different foliage traits of tree species are conducted less often at the stand level. We hypothesized that light availability is driven by canopy leaf area, and alien species contribution to canopy foliage will be similar to native species due to analogous patterns of biomass allocation in tree species. Materials and Methods: We studied forests dominated by alien and native tree species in Wielkopolski National Park (Western Poland). We measured light availability using the LAI-2200 canopy analyzer (Li-Cor Inc., Lincoln, NE, USA) and we calculated leaf area index (LAI) in 170 stands using published models of foliage biomass and data on specific leaf area. Results: Our study confirmed an impact of LAI on light availability in the understory layer. Analyzing the proportion of contribution to stand LAI and basal area (BA) we found that most alien species did not differ in LAI to BA ratio from native species. The exception was Prunus serotina Ehrh., with a LAI to BA ratio higher than all native and alien trees. However, the highest LAI to BA ratios we found were for the alien shrub Cotoneaster lucidus Schltdl. and native shrubs of fertile broadleaved forests. Conclusions: Our study showed that alien species contribution to shading the understory is comparable to native species, with the exception of P. serotina due to its dominance in the higher shrub canopy strata where it exhibits different patterns of biomass allocation than native trees. Our study explained that invasive tree species impact on light availability in forest ecosystems is mainly mediated by the increased quantity of foliage, not by more effective LAI to BA ratio.