Review of the Invasive Forage Grass, Guinea Grass (Megathyrsus maximus): Ecology and Potential Impacts in Arid and Semi-Arid Regions

Several introduced African grasses are known to present recurring patterns of invasiveness and cause a severe impact on the diversity and functioning of ecosystems worldwide. Megathyrsus maximus (Guinea grass), a forage grass species native to South Africa, is reported to be highly invasive and pose a serious threat to native biodiversity in the introduced range. Despite the severe ecological threats posed by M. maximus worldwide, there is a dearth of information on the ecological and agroecological impact of M. maximus when growing in unintended areas. In this review, we present general information on M. maximus, its distribution and ecological threats it poses, particularly in arid and semi-arid regions. We highlight the gaps in current knowledge on the impact on recipient communities, challenges in effective management, and potential impacts due to climate change, particularly changes in rainfall patterns. We also stress the need for public awareness about the threats posed by M. maximus to prevent its invasion in unintended areas

Effect of exotic invasive old world climbing fern (lygodium microphyllum) on soil properties

Old World climbing fern (Lygodium microphyllum) has become one of the most serious ecological threats to the integrity of the greater Everglades ecosystem of south Florida. In this study, we analyzed the effects of Old World climbing fern on surfacesoil characteristics at invaded sites in Florida. We compared soil characteristics of six invaded and adjacent uninvaded plots at three different locations. Our results show that the fern can grow and thrive in a wide range of soil types and the impact on the soil was site specific with effects being more prominent in sites with low nutrient status. Additionally, there were significant differences in the soil nutrient status and microbial population in the invaded and uninvaded sites. Sites with Old World climbing fern had significantly higher nutrient concentrations that correlated with higher soil organic matter. Overall our results indicate that this exotic pest plant can potentially alter its below ground environment to its own benefit by enhancing the soil nutrient status by adding soil organic matter

Soil biotic and abiotic conditions negate invasive species performance in native habitat

Background: Most studies on plant invasion consider the enemy release hypothesis when analyzing native habitats. However, the lower performance of invasive species in the native habitats can be the result of unfavorable soil conditions in the native habitats. While soil biotic and abiotic factors have a potential to restrict the growth of invasive species in their native habitats, our understanding of belowground environment of invasive species in their native habitats is very limited. In this study, we analyzed soil characteristics associated with an exotic invasive plant, Old World Climbing Fern (Lygodium microphyllum), in its native habitat in Australia and the recipient habitat in South Florida. Rhizosphere soil samples from both habitats were analyzed for soil physical, chemical and biological characteristics. Results: Soil characteristics in the recipient habitats were significantly different compared to those in the native habitats. Soil samples from the native habitat had low soil pH, and high concentrations of elements such as aluminum and zinc which are phytotoxic in acidic soil environments. Additionally, mycorrhizal fungi spores were more diverse in the recipient habitat in Florida compared to the native habitat in Australia. Conclusion: Overall, our results indicate that growth of an invasive plant in its native habitats could be restricted by the toxic effects associated with strong soil acidity. Results from this study indicate that invasive plants not only escape from their natural herbivores but also from toxic soil environment in their native habitats

Data on foliar nutrient concentration of invasive plants in the recipient habitat and their native habitat

Higher foliar nitrogen concentration in plants is often attributed to higher biomass assimilation and subsequently higher plant growth rate. To understand the underlying mechanism of extensive growth rate of an invasive plant, Old World climbing fern (Lygodium microphyllum), we analyzed the leaf tissue samples from the native and invaded habitats. In each habitat we selected 3 different locations with varying habitat characteristics (soil type, land use history and coexisting vegetation). Plant aboveground tissue collected from each site were analyzed for macro and micro nutrients. Total C and N were measured with a Truspec CN Analyzer. Total Ca, Fe, Mg, K, Mn, and P in plant tissue samples were measured using inductively coupled plasma mass spectrometry (ICP eMS). Here we present the difference in foliar nutrient concentration of invasive plant species in their native habitats and invaded habitats

Influence of Soil Biogeochemical Properties on the Invasiveness of Old World Climbing Fern (Lygodium microphyllum)

The state of Florida has one of the most severe exotic species invasion problems in the United States, but little is known about their influence on soil biogeochemistry. My dissertation research includes a cross-continental field study in Australia, Florida, and greenhouse and growth chamber experiments, focused on the soil-plant interactions of one of the most problematic weeds introduced in south Florida, Lygodium microphyllum (Old World climbing fern). Analysis of field samples from the ferns introduced and their native range indicate that L microphyllum is highly dependent on arbuscular mycorrhizal fungi (AMF) for phosphorus uptake and biomass accumulation. Relationship with AMF is stronger in relatively dry conditions, which are commonly found in some Florida sites, compared to more common wet sites where the fern is found in its native Australia. In the field, L. microphyllum is found to thrive in a wide range of soil pH, texture, and nutrient conditions, with strongly acidic soils in Australia and slightly acidic soils in Florida. Soils with pH 5.5 - 6.5 provide the most optimal growth conditions for L. microphyllum, and the growth declines significantly at soil pH 8.0, indicating that further reduction could happen in more alkaline soils. Comparison of invaded and uninvaded soil characteristics demonstrates that L. microphyllum can change the belowground soil environment, with more conspicuous impact on nutrient-poor sandy soils, to its own benefit by enhancing the soil nutrient status. Additionally, the nitrogen concentration in the leaves, which has a significant influence in the relative growth rate and photosynthesis, was significantly higher in Florida plants compared to Australian plants. Given that L. microphyllum allocates up to 40% of the total biomass to rhizomes, which aid in rapid regeneration after burning, cutting or chemical spray, hence management techniques targeting the rhizomes look promising. Over all, my results reveal for the first time that soil pH, texture, and AMF are major factors facilitating the invasive success of L. mcirophyllum. Finally, herbicide treatments targeting rhizomes will most likely become the widely used technique to control invasiveness of L. microphyllum in the future. However, a complete understanding of the soil ecosystem is necessary before adding any chemicals to the soil to achieve a successful long-term invasive species management strategy

Agricultural and Environmental Weeds of South Texas and their Management

The Lower Rio Grande Valley (LRGV) in south Texas is one of the most productive agricultural regions in southern United States. With subtropical climate and highly fertile soils, this region provides a year-round growing condition for crops. Along with citrus, major crops grown in the region are sorghum cotton and corn in the summer and vegetables in winter. Thus, a fallow period of 3-6 months between successive crops is common in the re-gion. Growers in this region report weeds as their number one economic and agronomic problem affecting crop yield and quality and increasing the cost of production and weeds account for the largest annual loss agricultural produce. In addition to the agronomic weeds, South Texas also has invasive non-native plants which result in eco-nomic or environmental consequences. Traditionally, land managers and farmers have depended on chemical and cultural (mowing/cultivation) methods for weed management. These methods are costly, labor intensive and might potentially pose environmental problems. With additional challenges posed by herbicide resistance in weeds and changing weather patterns, weed management is an important consideration for the growers in this region. Under-standing the weed ecology and biology should be part of developing and maintaining an effective weed manage-ment strategy for the LRGV. Here we present a review on the most economically and agronomically important weeds and their management options in the LRGV region

Laboratory Evaluation of Efficacy of Entomopathogenic Nematodes on Texas Leaf-cutting Ants, Atta texana

Entomopathogenic nematodes, a large group of nematodes specialized for parasitism of insects, have been used as classical biological control agents. The nematodes have potential to be used for insect pest management in organic gardening. We studied the potential impact of two entomopathogenic nematodes Steinerneima carpocapsae Weiser and Heterohabditis bacteriophora Poinar on the Texas leaf-cutting ant, Atta texana Buckley, that is considered a problematic agricultural pest in the southern US. We used a relatively large exposure rate of 250,000 nematodes per 10 ants in Petri dishes and monitored ant activity during a 96-hour time period. Results showed no significant differences among the two nematodes and check in numbers of ants killed after 12, 24, 48, 72, or even 96 hours of exposure

Abiotic and Biotic Limitations to Nodulation by Leguminous Cover Crops in South Texas

Many farms use leguminous cover crops as a nutrient management strategy to reduce their need for nitrogen fertilizer. When they are effective, leguminous cover crops are a valuable tool for sustainable nutrient management. However, the symbiotic partnership between legumes and nitrogen fixing rhizobia is vulnerable to several abiotic and biotic stressors that reduce nitrogen fixation efficiency in real world contexts. Sometimes, despite inoculation with rhizobial strains, this symbiosis fails to form. Such failure was observed in a 14-acre winter cover crop trial in the Rio Grande Valley (RGV) of Texas when three legume species produced no signs of nodulation or nitrogen fixation. This study examined the role of nitrogen, phosphorus, moisture, micronutrients, and native microbial communities in the nodulation of cowpea (Vigna unguiculata L. Walp) and assessed arbuscular mycorrhizal fungi as an intervention to improve nodulation. Results from two controlled studies confirm moisture and native microbial communities as major factors in nodulation success. Micronutrients showed mixed impacts on nodulation depending on plant stress conditions. Nitrogen and phosphorus deficiencies, however, were not likely causes, nor was mycorrhizal inoculation an effective intervention to improve nodulation. Inoculation method also had a major impact on nodulation rates. Continued research on improved inoculation practices and other ways to maximize nitrogen fixation efficiency will be required to increase successful on-farm implementation

Influence of microbial priming and seeding depth on germination and growth of native wildflowers

Background: Using native wildflowers for restoring marginal lands has gained considerable popularity. Establishment of wildflowers can be challenging due to several environmental factors. Restoring the microbial community in degraded habitats can potentially result in the native plant performance and habitat restoration. This study was conducted to investigate the impact of native soil microbes and seeding depth on germination of south Texas native wildflowers. Two wildflower species, Ratibida columnifera (Nutt.) (Mexican Hat) and Verbesina encelioides (Cav.) (cowpen daisy), were treated with microbial wash extracted from native soils, and germination rate was recorded for 14-day period. We further analyzed the growth, biomass allocation, and root colonization by mycorrhizal fungi in these two plants growing them in a plant growth chamber for 6 weeks. To determine the impact of seeding depth, we planted the seeds of the two plant species at 2-cm, 6-cm, and 12-cm depth and monitored germination and plant growth. Results: The two species responded differently to the seeding depth and microbial wash treatments. Microbial wash treatment resulted in higher germination rate in R. columnifera compared to control, while it did not have any impact on V. encelioides seed germination. While microbial treatment did not influence the total biomass, it had a significant impact on the biomass allocation in both the plant species. R. columnifera seeds germinated at both 2- cm and 6-cm depth and did not germinate at 12 cm, while the V. encelioides seeds germinated only at 2 cm and did not germinate at 6-cm or 12-cm seeding depth. Conclusions: While our results are species specific, our results indicate that native soil microbes can potentially improve the seed germination and growth of wildflowers. Our results also indicate the importance of specific seeding depth when sowing wildflower seeds for habitat restoration

Native and non-native plant species differentially affect arthropod community dynamics with consequences for crop production in Lower Rio Grande Valley

In agricultural ecosystems, arthropods play critical roles- including biocontrol, pollination services, and as herbivores. While herbivory negatively affects crop production, the recent decline in beneficial insect numbers have created a global concern, and consequently have led into multiple lines of conservation strategies. Agroecological practices that can provide sustenance, nesting, and refuge for beneficial organisms are considered as some of them, except we lack a better understanding of how seasonal and crop specific variation can affect their community dynamics. In this study, we examined this by investigating how native and non-native plants, when incorporated into a vegetable agroecosystem in Lower Rio Grande Valley in south Texas can influence arthropod community over their life cycle. We used a combination of different trapping systems and the following species: four species native to Texas: Ratibidia columnifera, Helianthus anuus L., Desmanthus virgatus var. and Pappophorum bicolor. We then compared these results to the non-native species Lobularia maritima (L.) Desv. We found that among the arthropods trapped, pests accounted for 66.3%, and were significantly more prevalent than beneficials. More specifically, we found that sampling time and feeding guild, also affected arthropods, but not plant species or their native/ invasive status. Detailed analyses also revealed that Eulophidae was the most abundant parasitoids family, and Aleyrodidae was the most abundant herbivore family. We followed the experiment by also examining whether these differences had any consequences for eggplant, the cash crop planted post cover, although we found no significant effects. Collectively, we show that arthropod community response to vegetation is variable, and a single species may not create the interactive dynamics to meet the benefits desired in food production and needs to be examined further