The Effects of Varying Nitrogen Amounts on the Growth and Leaf Morphology of Cattail Species

In Iowa, there are three types of cattails (Typha spp.): Typha latifolia (broadleaf), Typha angustifolia (narrow leaf), and Typha x glauca. T. latifolia is native to Iowa, while T. angustifolia and T. x glauca are not native. Cattails are found in wetlands, highly productive ecosystems that provide many services such as water filtration and flood control. However, Typha are opportunistic and invasive: if left uncontrolled, Typha grows rapidly by clonal reproduction, quickly dominating the ecosystem, lowering overall diversity and hurting the wetland’s conservation value. Being able to easily identify these taxa will improve the pace of future research. The purpose of this study is to understand the effects of different nitrogen amounts on the growth and morphology of each Typha taxon. In order to achieve this, Typha was grown in 1.75-m mesocosms and in 25-cm pots with different amounts of fertilizer. Leaf length and width were measured, and a taxon was assigned based on those measurements. Leaves from these individuals were sampled, ground up for DNA extraction, purified, amplified by PCR, and sequenced. The data show how each taxon’s leaf height and width responds to differing nitrogen amounts

Evaluating vegetation response subsequent to CRP mid-contract management across the western United States: Draft Project Report

It is impossible to explicitly state the degree to which mid-contract management (MCM) impacts the benefits that CRP enrollments provide due to the size of the program and variety of management prescriptions. But it is well documented that all native grasslands evolved with some type of ecological disturbance and the relatively good health of the grassland correlates with its disturbance regime. Concomitantly, all grassland bird communities have habitat requirements that evolved in conjunction with disturbance (primarily grazing). While natural-disturbance regimes may be desirable from an ecological prospective, dependence on natural disturbances to meet specific conservation objectives is unrealistic. Management policies are needed to encourage efforts to preserve and enhance grassland habitat by managing for heterogeneity while offsetting principal threats such as invasion of noxious plant species and woody vegetation. The accumulation of dead vegetation (litter), in the absence of management, greatly retards growth in the spring, prevents the emergence of some plants, reduces flowering, decreases productivity and promotes monocultures. Perpetuation of diversity in grass-species composition is a fundamental goal for trying to sustain desirable habitat for grassland-dependent wildlife. In the absence of natural disturbance, this goal is only accomplished through some form of prescribed management. And while some types of management are superior at replicating historic disturbances (grazing, burning), other forms of management (haying, mowing, disking) accomplish at least some level of necessary disturbance

Soil Organic Carbon Accumulation in Restored Native Prairies Over Time

With the recent focus on the causes and effects of climate change, the relationship between agriculture and climate change has become an important concern. Conventional farming maximizes crop production at the expense of ecosystem services like soil carbon storage. As the human population grows, it is vital to develop practices that balance crop production and ecosystem services. We investigated organic carbon accumulation in restored prairie soil over the course of a decade. Our goal was to determine how organic carbon levels and soil bulk density changed over time, and how that change was influenced by species diversity and soil depth. We hypothesized that more organic carbon would be stored in soil over time, and bulk density would decrease, both of which we found to be true. We also hypothesized that the amount of organic carbon stored would increase with greater species diversity (1-species, and 5-, 16-, and 32-species mixes) and it would decrease with soil depth. Our results showed us that species diversity has no noticeable effect on organic carbon levels, with the 5-species mix being the exception, as it stored very low levels of organic carbon. In both soil depths (0-7.5 cm and 7.5-15.0 cm), bulk density increased the first 5 years, then decreased drastically over the next 6 years, but when we compared 0-7.5 cm and 7.5-15.0 cm depths with each other, we found an overall decrease. We concluded that organic carbon accumulation increases over time in restored prairie soil regardless of species diversity or soil depth

Effectiveness of cattail (Typha spp.) management techniques depends on exogenous nitrogen inputs

Wetlands occupy a position in the landscape that makes them vulnerable to the effects of current land use and the legacies of past land use. Many wetlands in agricultural regions like the North American Midwest are strongly affected by elevated nutrient inputs as well as high rates of invasion by the hybrid cattail Typha × glauca. These two stressors also exacerbate each other: increased nutrients increase invasion success, and invasions increase nutrient retention and nutrient loads in the wetland. This interaction could create a positive feedback that would inhibit efforts to manage and control invasions, but little is known about the effects of past or present nutrient inputs on wetland invasive plant management. We augmented a previously-published community-ecosystem model (MONDRIAN) to simulate the most common invasive plant management tools: burning, mowing, and herbicide application. We then simulated different management strategies and 3 different durations in low and high nutrient input conditions, and found that the most effective management strategy and duration depends strongly on the amount of nutrients entering the wetland. In high-nutrient wetlands where invasions were most successful, a combination of herbicide and fire was most effective at reducing invasion. However, in low-nutrient wetlands this approach did little to reduce invasion. A longer treatment duration (6 years) was generally better than a 1-year treatment in high-nutrient wetlands, but was generally worse than the 1-year treatment in low-nutrient wetlands. At the ecosystem level, we found that management effects were relatively modest: there was little effect of management on ecosystem C storage, and while some management strategies decreased wetland nitrogen retention, this effect was transient and disappeared shortly after management ceased. Our results suggest that considering nutrient inputs in invaded wetlands can inform and improve management, and reducing nutrient inputs is an important component of an effective management strateg

Plant Size and Competitive Dynamics along Nutrient Gradients

Resource competition theory in plants has focused largely on resource acquisition traits that are independent of size, such as traits of individual leaves or roots or proportional allocation to different functions. However, plants also differ in maximum potential size, which could outweigh differences in module-level traits. We used a community ecosystem model called mondrian to investigate whether larger size inevitably increases competitive ability and how size interacts with nitrogen supply. Contrary to the conventional wisdom that bigger is better, we found that invader success and competitive ability are unimodal functions of maximum potential size, such that plants that are too large (or too small) are disproportionately suppressed by competition. Optimal size increases with nitrogen supply, even when plants compete for nitrogen only in a size-symmetric manner, although adding size-asymmetric competition for light does substantially increase the advantage of larger size at high nitrogen. These complex interactions of plant size and nitrogen supply lead to strong nonlinearities such that small differences in nitrogen can result in large differences in plant invasion success and the influence of competition along productivity gradients

Density and Diversity of Bees in the Midwestern Agricultural Landscape: Influence of Surrounding Agricultural Land Use and Biofuel Candidate Crops

Recent trends in land management practices have led to dramatic population decline in bees and other insect pollinators (Cameron et al. 2011). Concerns about “Colony Collapse Disorder” in domestic honeybees, for example, have received widespread high-profile attention in the scientific community. While concerns have centered mainly on the domestic honeybee, native bees also provide indispensable, cost-free pollination services to crops production. Despite the value of native bee species, little is known about them in the Midwest region, and recent studies suggest their populations may be in decline specifically due to a lack of native vegetation in this highly agricultural landscape. Vegetable farms and lands managed for cellulosic biofuels have the potential to provide usable habitat, but their utility is not well understood

Nitrogen loading leads to increased carbon accretion in both invaded and uninvaded coastal wetlands

Gaining a better understanding of carbon (C) dynamics across the terrestrial and aquatic landscapes has become a major research initiative in ecosystem ecology. Wetlands store a large portion of the global soil C, but are also highly dynamic ecosystems in terms of hydrology and N cycling, and are one of the most invaded habitats worldwide. The interactions between these factors are likely to determine wetland C cycling, and specifically C accretion rates. We investigated these interactions using MONDRIAN, an individual-based model simulating plant growth and competition and linking these processes to N and C cycling. We simulated the effects of different levels of (1) N loading, (2) hydroperiod, and (3) plant community (natives only vs. invasion scenarios) and their interactions on C accretion outcomes in freshwater coastal wetlands of the Great Lakes region of North America. Results showed that N loading contributed to substantial rates of C accretion by increasing NPP (net primary productivity). By mediating anaerobic conditions and slowing decomposition, hydroperiod also exerted considerable control on C accretion. Invasion success occurred with higher N loading and contributed to higher NPP, while also interacting with hydroperiod via ecosystem-internal N cycling. Invasion success by both Typha × glauca and Phragmites australis showed a strong nonlinear relationship with N loading in which an invasion threshold occurred at moderate N inputs. This threshold was in turn influenced by duration of flooding, which reduced invasion success for P. australis but not for T. × glauca. The greatest simulated C accretion rates occurred in wetlands invaded by P. australis at the highest N loading in constant anaerobic conditions. These model results suggest that while plant invasion may increase C storage in freshwater coastal wetlands, increased plant productivity (both native and invasive) due to increased N loading is the main driver of increased C accretion

Species composition influences soil nutrient depletion and plantphysiology in prairie agroenergy feedstocks

High-diversity mixtures of perennial tallgrass prairie vegetation could be useful biomass feed-stocks for marginal farmland in the Midwestern United States. These agroenergy crops can help meet cel-lulosic agrofuel targets while also enhancing other ecosystem services on the landscape. One proposedadvantage of high-diversity prairie biomass feedstocks is that they should become nutrient limited at aslower rate than monoculture feedstocks. In this study, we examine rates of soil nutrient depletion and thephysiology and performance of a focal species (switchgrass,Panicum virgatumL.) in four prairie agroen-ergy feedstocks with different species composition and diversity. The feedstocks in this study were a1-species switchgrass monoculture, a 5-species mixture of C4grasses, a 16-species mixture of C3and C4grasses, forbs, and legumes, and a 32-species mixture of C3and C4grasses, forbs, legumes, and sedges. Toassess feedstock effects on soil, we measured changes in soil N/P/K over afive-year period. We also per-formed a greenhouse study, in which we grew switchgrass plants infield soil conditioned by each feed-stock. To assess feedstock effects on plant function, we measured four physiological traits (photosyntheticrate, chlorophyll concentration, leafflorescence, leaf N concentration) on switchgrass plants within eachfeedstock in thefield. In the soil analysis, we found that the 5-species feedstock displayed higher rates ofsoil N/P/K depletion than other feedstocks. In the greenhouse analysis, we found that switchgrass plantsgrown in soil conditioned by the 5-species feedstock were smaller than plants grown in soil conditionedby other feedstocks. In the physiological analysis, we found that switchgrass plants in the 5-species feed-stock had lower leaf N, photosynthesis, chlorophyll concentration, and higherflorescence than switchgrassplants growing in other feedstocks. Collectively, our results show that prairie agroenergy feedstocks withdifferent species composition and diversity have different rates of soil nutrient depletion, which influencesthe physiology and performance of plants within the feedstock. These differences would ultimately impactthe ecosystem services (e.g., biomass production, need for fertilizer) that these prairie agroenergyfeedstocks provide

Persistence and quality of vegetation cover in expired Conservation Reserve Program fields

For nearly 40 years, the Conservation Reserve Program (CRP) has implemented practices to reduce soil erosion, improve water quality, and provide habitat for wildlife and pollinators on highly erodible cropland in the United States. However, an approximately 40,470 ha (10 million acres) decline in enrolled CRP land over the last decade has greatly reduced the program\u27s environmental benefits. We sought to assess the program\u27s enduring benefits in the central and western United States by (1) determining the proportion of fields that persist in CRP cover after contracts expired, (2) identifying the type of agricultural production that CRP fields shift to after contract expiration, (3) comparing the vegetation characteristics of expired CRP fields that are persisting in CRP-type cover with enrolled CRP fields, and (4) identifying differences in management activities (e.g., haying, grazing) between expired and enrolled CRP fields. We conducted edge-of-field vegetation cover surveys in 1092 CRP fields with contracts that expired ≥3 years prior and 1786 currently enrolled CRP fields in 14 states. We found that 41% of expired CRP fields retained at least half of their area in CRP-type cover, with significant variation in persistence among regions ranging from 19% to 84%. When expired fields retained CRP vegetation, bare ground was low in all regions and grass cover was somewhat greater than in fields with current CRP contracts, but at the expense of forb cover in some regions. Evidence of more frequent management in expired CRP fields may explain differences between active and expired CRP fields. Overall, there is clear evidence that CRP-type cover frequently persists and provides benefits for more than three years after contract expiration. Retaining CRP-type cover, post-contract, is an under-recognized program benefit that persists across the central and western United States long after the initial retirement from cropland