Biological Invasion Influences the Outcome of Plant-Soil Feedback in the Invasive Plant Species from the Brazilian Semi-arid

Plant-soil feedback and plant invasion: effect of soil conditioning on native and invasive Prosopis species using the plant functional trait approach

Introduction

Invasive species have been identified as a major threat to native biodiversity and ecosystem functioning worldwide due to their superiority in spread and growth. Such superiority is explained by the invasional meltdown phenomena, which suggests that invasive species facilitate the establishment of more invasive species rather than native species by modifying the plant-soil feedback (PSF).

Methods

We conducted a two-phase plant-soil feedback experiment using the native Prosopis cineraria and the invasive Prosopis juliflora in Oman. Firstly, we conditioned the soil by planting seedlings of native species, invasive species, native and invasive species "mixed", and unconditioned soil served as a control. Secondly, we tested the feedback of these four conditioned soil on the two species separately by measuring the productivity (total biomass) and the performance in the form of plant functional traits (plant height, specific leaf area (SLA), leaf nitrogen content (Nmass), leaf carbon content (Cmass) and specific root length (SRL) of native and invasive species as well as the nutrient availability in soil (soil organic carbon (SOC) and soil total nitrogen (STN)).

Results and discussion

We found that the native species produced more biomass, best performance, and higher SOC and STN when grown in soil conditioned by native species, additionally, it gave lower biomass, reduced performance, and lower SOC and STN when grown in the soil conditioned by invasive and mixed species. These results suggest negative PSF for native species and positive PSF for invasive species in the soil conditioned by invasive species, which can be considered as red flag concerning the restoration of P. cineraria as an important native species in Oman, as such positive PSF of the invasive species P. juliflora will inhibit the regeneration of P. cineraria.

Biochemical characterization and mycorrhizal fungal community of plant species in the Brazilian seasonal dry forest

Invasive alien plant species (IAPS) have the ability to change the biochemical properties and the arbuscular mycorrhizal fungal (AMF) community structure in their rhizosphere. Organic acids, microbial activity, and AMF play a key role in the invader's spread and also has interactions with the soil chemical factors. Our aim here was to assess the rhizosphere's biochemical factors, AMF community composition, and soil chemical properties associated with Cryptostegia madagascariensis (IAPS) and Mimosa tenuiflora (endemic plant species) from the Brazilian Seasonal Dry Forest. The highest values of total glomalin (5.87 mg g-1 soil), root colonization (54.5%), oxalic and malic acids (84.21 and 3.01 μmol g-1 , respectively), microbial biomass C (mg kg-1 ), Na+ (0.080 cmolc  kg-1 ), Ca2+ (7.04 cmolc  kg-1 ), and soil organic carbon (4.59 g kg-1 ) were found in the rhizosphere of C. madagascariensis. We found dissimilarities on AMF community structure considering the studied plant species: (i) Racocetra coralloidea, Dentiscutata heterogama, Dentiscutata cerradensis, Gigaspora decipiens, and AMF's richness were highly correlated with the rhizosphere of M. tenuiflora; and (ii). The rhizosphere of C. madagascariensis was highly correlated with the abundance of Claroideoglomus etunicatum, Rhizoglomus aggregatum, Funneliformis mosseae, and Funneliformis geosporum. The results of our study highlight the importance of considering C. madagascariensis as potential hosts for AMF species from Glomerales, and a potential plant species that increase the bioavailability of exchangeable Na and Ca at semi-arid conditions.

Litter Deposition and Nutrient Cycling of Invaded Environments by Cryptostegia madagascariensis at Tropical Cambisols from Northeastern Brazil

Cryptostegia madagascariensis is an invasive plant species that covers 11% of the Brazilian northeastern territory, but its role on the litter trait in tropical ecosystems remains unclear. Here, we analyzed and compared the litter deposition, litter nutrient content, soil organic matter, and the litter decay rate from invaded and non-invaded environments by C. madagascariensis at a tropical Cambisol. The PCA analysis revealed that litter deposition, litter quality, and soil organic matter were correlated with the invaded environment. We grew plant species in greenhouse conditions to obtain a standard litter material to use in our litter bags in field conditions. We found that litter decay rate was higher in the invaded environment than in the non-invaded one. Our results suggest that C. madagascariensis changes litter traits in tropical ecosystems that in turn create negative plant–soil feedback to the native species by creating a physical barrier on soil surface and to promote its own rhizosphere.

Deyeuxia angustifolia Kom. encroachment changes soil physicochemical properties and microbial community in the alpine tundra under climate change

Plant encroachment in alpine regions, caused by global changes and human activities, has been well documented. However, our knowledge of the effects of plant encroachment on belowground microbial communities is limited. Here, we investigated soil physicochemical properties and microbial community structures under the impact of plant encroachment along an elevation gradient in the alpine tundra of the Changbai Mountain, China. We found that plant encroachment had insignificant (P > 0.05) and inconsistent effects on the α-diversity (number of observed OTUs, Shannon, Chao1, Faith's PD) of soil microbial communities. Plant encroachment indirectly influenced soil microbial community structures by altering soil physicochemical properties, which differed between elevations and plant types (P < 0.05). In all, 40 bacterial indicator taxa and 57 fungal indicator taxa significantly shifted in response to plant encroachment, some of which were involved in soil biogeochemical cycle. Overall, our results documented the impacts of plant encroachment on soil microbial diversity and community composition, and provided a scientific basis for predicting future changes in alpine ecosystem structure and function and its subsequent feedbacks to global change.

Invasive plants in the Brazilian Caatinga: a scientometric analysis with prospects for conservation

Understanding the impacts caused by invasive plant species, especially in regions where studies are scarce, is of great importance to the development of management and conservation strategies. Amongst the biomes present in Brazil, the Caatinga (Dry Tropical Forest) stands out for having had few studies dealing with biological invasions by plants and animals. An evaluation of scientific production can provide a means by which the progress of invasion-related studies can be assessed, as well as identify research gaps and provide a broad overview of the importance of invasions in this biome. Thus, the objective of this study was to perform a scientometric analysis to evaluate the development of scientific research over the years on exotic and invasive plant species in the Caatinga. We found 46 papers dealing with invasive plants in the Caatinga published over a 14-year period. The main objectives of most of the papers focused on identifying the main strategies used by plants in the process of invasion and characterising the invaded environment. A total of 28 species were cited as invasive for the Caatinga, with Prosopis juliflora (Sw.) DC., Cryptostegia madagascariensis Bojer, Calotropis procera (Aiton) W.T.Aiton and Parkinsonia aculeata L. being the most cited species. Although studies on the subject are incipient, there is already important information about the dynamics of the invasiveness of plant species in the Caatinga, which can serve as a basis for new studies, as well as for the development of management policies, based on consistent information.

Biological invasion, dry forest, exotic species, northeast Brazil, scientometry, semi-arid

Characteristics of soil moisture under different vegetation coverage in Horqin Sandy Land, northern China

Vegetation restoration as an effective sand fixation measure has made great achievements in China. However, soil water conditions deteriorate with the development and maturity of sand-fixing vegetation. In this study, we investigated the relationship between soil water content (SWC) and vegetation coverage (VC) at different portion (top, middle and bottom) on ten sand dunes during the growing season (April to October) in Horqin Sandy Land, northern China. We analyzed the temporal and spatial variation characteristics of SWC under different VC. The results indicate that VC and soil water storage were negatively correlated. The effect of vegetation on soil water storage on the sand dunes was greater in the dry season than the wet season. The VC and coefficient of coefficient of SWC were positively correlated at the 20 to 140 cm soil depth. As VC increased, the effect of drought stress increased at the 20 to 200 cm soil depths. The VC and SWC were negatively correlated at all the three portions of the sand dunes. According to soil water conditions and the concept of wilting humidity at different VC, we found that the suitable VC values were less than 0.46, 0.52, and 0.71 at the top, middle and bottom of the sand dunes, respectively.