Effects of floral diversification on beneficial arthropods and ecosystem services in an edamame agroecosystem

Progress report for GNE21-254

Project Type: Graduate Student
Funds awarded in 2021: $14,998.00
Projected End Date: 08/31/2023
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
Anahi Espindola
University of Maryland, College Park
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Project Information

Project Objectives:

This proposal seeks to understand how floral diversification practices (i.e., the addition of wildflower strips and floral intercropping) within and bordering the crop, affect (1) the diversity and density of beneficial arthropod communities (natural enemies and pollinators), within the crop and in the surrounding habitat, and (2) pest control and the reproductive output of wild plant communities and crops. Specific objectives and sub-objectives are to:

Objective 1. Quantify the effect of floral additions (i.e., wildflower strips and floral intercropping) on the abundance and diversity of beneficial arthropods in designated croplands and in neighboring wild plant communities. I hypothesize that arthropod diversity and abundance will increase in plots with higher combined flower density (intercropping and wildflower strip).

Objective 2a. Assess how floral additions affect pest control and the reproductive output of crops and non-target (i.e., non-crop) wild plants in the neighboring landscape. I hypothesize that both pest control and the reproductive output of crops and wild plants will increase with proximity to floral additions.

Objective 2b. Evaluate the spatial scale (e.g. distance) at which the floral additions affect beneficial arthropod diversity and abundance, and translate to direct ecosystem services (i.e., pest control, plant reproduction) by measuring the limits of the spillover effect of floral additions on the crop and the natural habitat. I hypothesize that increases in the diversity and abundance of arthropods is local and will decrease with increasing distance from the wildflower strips. I also hypothesize that the addition of wildflower strips and floral intercropping will lead to increased competition for ecosystem services between plants in natural and managed lands, leading to a reduction of ecosystem services in those plants that are the furthest away from the wildflower strips.

Introduction:

The purpose of this project is to quantify the beneficial effects of enhanced floral diversification on ecosystem services within a crop and the surrounding habitat. The loss of natural and seminatural habitats associated with expanded agricultural acreage and an associated increase in monocultural plantings has resulted in reduced floral diversity in landscapes1, which has been shown to negatively affect beneficial arthropods2. Indeed, pollinators and natural enemies of crop pests require plant-derived resources which are often limited in monoculture cropping systems and may only be present for a finite period. Two practices that may be used to enhance these resources in agricultural fields include adding wildflower strips along the crop border and intercropping flowering plants within the crop field. These practices are known to help with weed suppression, and enhance biological control and pollination activity in the crop fields3,4. Flowering plants situated around the perimeter of a crop enhance and support natural enemies and pollinators by providing them food and refuge throughout the season2. Further, intercropping (i.e., growing different plant species between cultivated crop rows) has been shown to improve soil quality, suppress weeds and attract natural enemies4. Some of these intercropped plants (e.g., clover) can also attract pollinators and natural enemies, enhancing crop pollination, pest suppression, and crop yield3,5,6.

Although increasing floral resources could restore ecosystem services within a crop, little research attention has been directed at determining how these newly-added resources can affect ecosystem services in neighboring plant habitats. For example, pollinator visitation increases with increased floral density and diversity7,8. However, it is unclear as to what extent such an increase in pollinator visitation from the floral additions along crop borders and within crop rows will spillover into target crops and native plants in the surrounding habitat9

Further, floral strips may also act as pollinator sinks, concentrating pollinators and pollination services from the surrounding habitats within the floral strip8–10. This could result in competition for pollinators between crops and wild plants, negatively impact the reproductive output of plant communities in neighboring habitats10, and indirectly affect food webs11. Ultimately, natural areas are sources of pollinators and biological control agents, and changes in resource availability and floral diversity could affect this spillover from natural to managed systems9. This, in turn, could have lasting implications on pest populations and ecosystem services in cropping systems. However, to date little research has been conducted on spillover effects in agroecosystems from managed to natural areas9.

Given the current pollinator crisis12, it is important that the effects of these practices are quantified beyond the crop-field. To date, virtually no research has been done to quantify the combined effects of using wildflower strips and intercropping to enhance natural enemy efficacy and pollination within crop fields and surrounding habitats. This project proposes to address these knowledge gaps and concomitantly develop pest suppression practices that are more congenial to pollinators and natural enemies (predators and parasitoids) within and outside the crop field, thus enhancing the sustainability of the entire agroecosystem.

Research

Materials and methods:

Project Objectives This proposal seeks to understand how floral diversification practices (i.e., the addition of wildflower strips and floral intercropping) within and bordering the crop, affect (1) the diversity and density of beneficial arthropod communities (natural enemies and pollinators), within the crop (edamame) and in the surrounding natural habitat, (2) pest populations and (3) the reproductive output of wild plant communities and crops.

Research and Results This is a two-year project, with the first-year sampling completed. Our research is being conducted at the University of Maryland Beltsville Agricultural Research Center starting in April and lasting through October. The 2022 sampling is currently being processed (weighed, insects identified, first statistics analyses performed) and, therefore, we do not have full results from the 2022 field season. Data was collected biweekly, April-October, and included (1) hand-netting floral visitors of edamame, wildflower strip and wild plants, (2) sweep samples, (3) sticky cards, (4) passive trapping of potential pollinators with bee bowls, and (5) harvesting edamame pods and wild plant seeds to estimate plant reproductive output and yield. The field set-up consisted of two treatments (mowed strip without intercropping (control) or floral strip with floral intercropping (floral treatment)), each replicated six times (12 plots/year). In our study, the wild plant communities were represented by three species native to the Mid-Atlantic: harebells (Campanula rotundifolia), Culver’s root (Veronicastrum virginicum) and partridge pea (Chamaecrista fasciculata). On either side of the (mowed/floral) strip, we placed each of these three plant species at three distances from the strip (10m, 30m, 50m). The floral supplements included a (1) wildflower strip composed of 17 locally-sourced flowering plants that are mostly native to the Mid-Atlantic region and (2) clover intercropping.

Field set-up
Two treatments, each replicated six times (12 plots/year), will consist of either (a) a mowed strip adjacent to an edamame plot or (b) a wildflower strip adjacent to an edamame plot which is also inter-planted with clover (Figure 1). In both cases, on the other side of the strip, we will place four pots per three plant species of wild plants native to Maryland at three distances from the strip (10m, 30m, 50m).
On the farm, each treatment will be separated by a minimum of 500m.
Research results and discussion:

Project outcomes During 2021 and 2022, we investigated the effects of wildflower strips on the reproductive output of edamame. Through a controlled pollination experiment, we recorded edamame seed set, floral abortion rate and pod weight for three treatments (pollinator-excluded, open-pollination and hand-pollination) at varying distances from a floral supplemented border. We found that edamame benefited from cross-pollination, with greater weights and reductions in floral abortions in rows closer to the flower strip, indicating edamame benefits from increased insect biodiversity associated with floral additions. Through our controlled experiment, we also likely identified the optimal timing of stigma receptivity to be late morning and provide new insights into interplay between pollination, floral herbivory and floral abortion in soybean. The most common edamame floral visitors were Hymenoptera and Coleoptera. This work is currently in review: Evans KC, El-Hifnawi J, Hooks C, Espíndola A. (In review for Pollination Ecology). Benefits of Cross-Pollination in Vegetable Soybean Edamame.

Participation Summary

Education & Outreach Activities and Participation Summary

1 Journal articles

Participation Summary:

Education/outreach description:

Education and outreach summary We presented our research at the Entomological Society of America Eastern Branch in March 2022. We also presented aspects of our work at a MOFFA (Maryland Organic Food and Farming Association) farm tour on the MD Eastern Shore in summer 2022 and will present at a Master Gardener meeting in Montgomery County, MD in August 2023. Through this project, we are providing ample research opportunities for undergraduate students, with one student conducting an Honor’s thesis on the effects of floral diversity on parasitoid richness in an edamame agroecosystem.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.