About

Dr. Kristin Mercer is a professor in the Department of Horticulture and Crop Science at The Ohio State University, where she directs the Plant Evolutionary Ecology Lab. Her research focuses on plant evolutionary ecology within agricultural systems, specifically examining how ecological processes and evolutionary forces influence issues related to agricultural sustainability. Her primary interests include the conservation of crop genetic resources in centers of origin, the biosafety of genetically modified crops, and the impacts of climate change on agriculture. Dr. Mercer earned her B.A. in Biology from Wesleyan University, followed by an M.S. and Ph.D. in Applied Plant Sciences from the University of Minnesota. She also completed a postdoctoral fellowship in Evolution, Ecology, and Organismal Biology at Ohio State University and was a Fulbright Fellow in southern Mexico. Since joining Ohio State in 2006, she has contributed to understanding plant evolutionary ecology, with a particular emphasis on agricultural systems and the dynamics that influence crop sustainability and biodiversity.

Research topics

• Biology
• Genetics
• Agronomy
• Demography
• Horticulture
• Agroforestry
• Environmental science
• Botany

Selected publications

• Heat Stress Affects Plant Morphology, Leaf Chlorophyll Content, and Photosynthetic Characteristics in Pelargonium

  HortScience · 2026-01-13

  articleOpen access

  Pelargonium is a globally cultivated ornamental plant; however, its ornamental and commercial values are severely threatened by heat stress. To identify heat-tolerant Pelargonium , we evaluated plant morphological traits, leaf color, chlorophyll content, and photosynthetic characteristics of six Pelargonium wild species and three commercial cultivars under heat stress. The results showed that heat stress significantly increased leaf color hue ( h °), chlorophyll concentration indices (CCIs), and chlorophyll a content in P. sidoides and Pelargonium ‘Chocolate Mint’. In addition, the net assimilation rate ( P n ) was remarkably improved in P. sidoides under heat stress. Conversely, heat stress dramatically reduced whole plant dry weight and CCIs of new leaves, induced leaf chlorosis, and enhanced the heat damage index of P. stenopetalum and Pelargonium ‘Madame Thibault’. Moreover, heat stress caused significant reductions in P n , chlorophyll a, and soluble sugar contents in P. stenopetalum . In conclusion, among nine Pelargonium genotypes evaluated, P. sidoides and Pelargonium ‘Chocolate Mint’ exhibited heat tolerance, whereas P. stenopetalum and Pelargonium ‘Madame Thibault’ were identified as heat susceptible. Thus, these heat-tolerant genotypes offer important genetic materials and contribute to breeding efforts aimed at developing new heat-tolerant Pelargonium cultivars.

  PublisherDOI

• Agrestal Environments and Maternal Genetic Effects Weaken the Ecological Barriers for Crop to Wild Introgression in Sunflower

  Ecology and Evolution · 2026-02-01

  articleOpen accessCorresponding

  Admixture between crops and their wild relatives may lead to the evolution of aggressive weeds in agricultural and natural habitat. As many crops and their wild relatives belong to the same species, admixture is common, and the low fitness of crop-wild hybrids is the main ecological barrier for introgression. However, fitness of hybrids can vary between environmental conditions, genetic background of recipient and donor populations, and maternal genetic effects. Here, we study how these three factors influence the phenotypic variation of crop-wild sunflower hybrids in the field. To this end, we measured seven variables related to fitness throughout the life cycle in eight populations (including reciprocal crop-wild hybrids and their parents) in two agrestal (wheat and maize plantings) and one ruderal (natural vegetation in a human-disturbed area) environments over 2 years. Overall, high out-of-season germination was observed in the first year but declined in the second across all environments. In ruderal habitats, flowering was delayed, and fitness was lower compared to agrestal ones. Hybrids exhibited similar or lower fitness than wild plants in agrestal habitats, but the differences were larger in ruderal habitats. Hybrids with maternal crop parents displayed higher fitness than their reciprocal crosses across all environments in the first year, but differences disappeared the second year. Our findings suggest that agrestal conditions and crop maternal parent favor the establishment of crop-wild hybrids, weakening the ecological barriers for crop introgression.

  PublisherOA PDFDOI

• A comprehensive rhizobox pipeline for analyzing pepper root system architecture under well-watered and water deficit conditions

  Research Square · 2025-10-06

  preprintOpen accessSenior author
  PublisherOA PDFDOI

• Nitrogen fixation rates and aerial root production among maize landraces

  Frontiers in Plant Science · 2025-01-28 · 2 citations

  articleOpen accessSenior authorCorresponding

  In Mexico, the center of maize origin ( Zea mays ssp. mays ), there are landraces from the highlands that develop extensive aerial root systems which secrete a carbohydrate-rich mucilage. This mucilage produces a favorable environment for nitrogenase activity by diazotrophs. This plant-microbial interaction enables the fixation of nitrogen (N) from the atmosphere, reducing the required N that otherwise must come from the soil and/or fertilizers. The objective of this research was to investigate the degree to which other landraces of maize and nutrient management affect aerial root growth and the ability of maize to perform and benefit from N 2 fixation. In two replicated field experiments in Columbus, Ohio, USA in 2019 and 2020, we planted 21 maize landraces and three improved varieties with and without fertilizer to measure their growth, production of aerial roots, and rate of atmospheric N 2 fixation using the 15 N natural abundance method. Maize accessions varied in the growth rate and number of nodes with aerial roots. Up to 36% of plant N was derived from the atmosphere, with values varying by accession, the reference plant used, and the fertilizer level. Moreover, there was a positive relationship between early growth parameters and numbers of nodes with aerial roots, which, in turn, predicted the amount of N derived from the atmosphere. Thus, larger seedlings may experience enhanced root growth and thereby benefit more from N fixation. By phenotyping a diverse set of maize accessions with and without fertilizer, this study explores both environmental and quantitative genetic variation in the traits involved in N fixation capacity, clarifying that N fixation found in the Sierra Mixe landrace is more broadly distributed than previously thought. In sum, farmers stewarding genetic diversity in a crop center of origin have preserved traits essential for biological symbioses that contribute to maize's nutrient requirements. These traits may enable maize crops grown by Mexican farmers, and farmers globally, to benefit from N fixation from the atmosphere.

  PublisherOA PDFDOI

• Evolution Under Domestication: The Intersection of Genes, Organism and Management in Mexican Chili Pepper

  2025-01-01 · 1 citations

  book-chapter
  PublisherDOI

• Physiological traits contribute to growth and adaptation of Mexican maize landraces

  PLoS ONE · 2024-02-01 · 10 citations

  articleOpen accessSenior authorCorresponding

  Local adaptation of populations results from an interplay between their environment and genetics. If functional trait variation influences plant performance, populations can adapt to their local environment. However, populations may also respond plastically to environmental challenges, altering phenotype without shifting allele frequencies. The level of local adaptation in crop landraces and their capacity for plasticity in response to environmental change may predict their continued utility to farmers facing climate change. Yet we understand little about how physiological traits potentially underlying local adaptation of cultivars influence fitness. Farmers in Mexico-the crop center of origin for maize-manage and rely upon a high diversity of landraces. We studied maize grown in Chiapas, Mexico, where strong elevational gradients cover a relatively small geographic area. We reciprocally transplanted 12 populations sourced from three elevational zones (600, 1550 and 2150 m) back into those elevations for two years using a modified split-split plot design to model effects of environment, genetics, and their interaction. We studied physiological and growth traits, including photosynthetic rate, stomatal conductance, stomatal density, relative growth rate (RGR), and seed production. Maize fitness showed indications of local adaptation with highland and midland types performing poorly at warmer lowland locations, though patterns depended on the year. Several physiological traits, including stomatal conductance, were affected by G x E interactions, some of which indicated non-adaptive plastic responses with potential fitness implications. We discerned a significant positive relationship between fitness and relative growth rate. Growth rates in highland landraces were outperformed by midland and lowland landraces grown in high temperature, lowland garden. Lowland landrace stomatal conductance was diminished compared to that of highland landraces in the cooler highland garden. Thus, both adaptive and non-adaptive physiological responses of maize landraces in southern Mexico may have implications for fitness, as well as responses to climate change.

  PublisherOA PDFDOI

• Natural genetic variation in dynamic photosynthesis is correlated with stomatal anatomical traits in diverse tomato species across geographical habitats

  Journal of Experimental Botany · 2024-04-12 · 25 citations

  articleOpen access

  Plants grown under field conditions experience fluctuating light. Understanding the natural genetic variations for a similarly dynamic photosynthetic response among untapped germplasm resources, as well as the underlying mechanisms, may offer breeding strategies to improve production using molecular approaches. Here, we measured gas exchange under fluctuating light, along with stomatal density and size, in eight wild tomato species and two tomato cultivars. The photosynthetic induction response showed significant diversity, with some wild species having faster induction rates than the two cultivars. Species with faster photosynthetic induction rates had higher daily integrated photosynthesis, but lower average water use efficiency because of high stomatal conductance under natural fluctuating light. The variation in photosynthetic induction was closely associated with the speed of stomatal responses, highlighting its critical role in maximizing photosynthesis under fluctuating light conditions. Moreover, stomatal size was negatively correlated with stomatal density within a species, and plants with smaller stomata at a higher density had a quicker photosynthetic response than those with larger stomata at lower density. Our findings show that the response of stomatal conductance plays a pivotal role in photosynthetic induction, with smaller stomata at higher density proving advantageous for photosynthesis under fluctuating light in tomato species. The interspecific variation in the rate of stomatal responses could offer an untapped resource for optimizing dynamic photosynthetic responses under field conditions.

  PublisherOA PDFDOI

• Fluctuation of ecological niches and geographic range shifts along chile pepper's domestication gradient

  Ecology and Evolution · 2023-11-01 · 8 citations

  articleOpen access

  Abstract Domestication is an ongoing well‐described process. However, while many have studied the changes domestication causes in plant genetics, few have explored its impact on the portion of the geographic landscape in which the plants exist. Therefore, the goal of this study was to understand how the process of domestication changed the geographic space suitable for chile pepper ( Capsicum annuum ) in its center of origin (domestication). C. annuum is a major crop species globally whose center of domestication, Mexico, has been well‐studied. It provides a unique opportunity to explore the degree to which ranges of different domestication classes diverged and how these ranges might be altered by climate change. To this end, we created ecological niche models for four domestication classes (wild, semiwild, landrace, modern cultivar) based on present climate and future climate scenarios for 2050, 2070, and 2090. Considering present environment, we found substantial overlap in the geographic niches of all the domestication classes. Yet, environmental and geographic aspects of the current ranges did vary among classes. Wild and commercial varieties could grow in desert conditions, while landraces could not. With projections into the future, habitat was lost asymmetrically, with wild, semiwild, and landraces at greater risk of territorial declines than modern cultivars. Further, we identified areas where future suitability overlap between landraces and wilds is expected to be lost. While range expansion is widely associated with domestication, we found little support of a constant niche expansion (either in environmental or geographical space) throughout the domestication gradient in chile peppers in Mexico. Instead, particular domestication transitions resulted in loss, followed by capturing or recapturing environmental or geographic space. The differences in environmental characterization among domestication gradient classes and their future potential range shifts increase the need for conservation efforts to preserve landraces and semiwild genotypes.

  PublisherOA PDFDOI

• The Effect of Altered Soil Moisture on Hybridization Rate in a Crop-Wild System (Raphanus spp.)

  2023-09-13

  preprintOpen accessSenior authorCorresponding

  <p>Since plant mating choices are flexible and responsive to the environment, rates of spontaneous hybridization may vary across ecological clines. Developing a robust and predictive framework for rates of plant gene flow requires assessing the role of environmental sensitivity on plant reproductive traits, relative abundance, and pollen vectors. Therefore, across a soil moisture gradient, we quantified pollinator movement, life-history trait variation, and unidirectional hybridization rates from crop (<em>Raphanus sativus</em>) to wild (<em>Raphanus raphanistrum</em>) radish populations. Both radish species were grown together in relatively dry (no rain), relatively wet (double rain), or control soil moisture conditions in Ohio, USA. We measured wild and crop radish life-history, phenology and pollinator visitation patterns. To quantify hybridization rates from crop-to-wild species, we used a simply inherited morphological marker to detect F1 hybrid progeny. Although crop-to-wild hybridization did not respond to watering treatments, the abundance of hybrid offspring was higher in fruits produced late in the period of phenological overlap, when both species had roughly equal numbers of open flowers. Therefore, the timing of fruit production and its relationship to flowering overlap may be more important to hybrid zone formation in <em>Raphanus</em> spp. than soil moisture or pollen vector movements.</p> <p> </p>

  PublisherOA PDFDOI

• The Effect of Altered Soil Moisture on Hybridization Rate in a Crop-Wild System (Raphanus spp.)

  2023-09-13 · 5 citations

  preprintOpen accessSenior authorCorresponding

  <p>Since plant mating choices are flexible and responsive to the environment, rates of spontaneous hybridization may vary across ecological clines. Developing a robust and predictive framework for rates of plant gene flow requires assessing the role of environmental sensitivity on plant reproductive traits, relative abundance, and pollen vectors. Therefore, across a soil moisture gradient, we quantified pollinator movement, life-history trait variation, and unidirectional hybridization rates from crop (<em>Raphanus sativus</em>) to wild (<em>Raphanus raphanistrum</em>) radish populations. Both radish species were grown together in relatively dry (no rain), relatively wet (double rain), or control soil moisture conditions in Ohio, USA. We measured wild and crop radish life-history, phenology and pollinator visitation patterns. To quantify hybridization rates from crop-to-wild species, we used a simply inherited morphological marker to detect F1 hybrid progeny. Although crop-to-wild hybridization did not respond to watering treatments, the abundance of hybrid offspring was higher in fruits produced late in the period of phenological overlap, when both species had roughly equal numbers of open flowers. Therefore, the timing of fruit production and its relationship to flowering overlap may be more important to hybrid zone formation in <em>Raphanus</em> spp. than soil moisture or pollen vector movements.</p> <p> </p>

  PublisherDOI

Frequent coauthors

• Michael B. Kantar

  University of Hawaiʻi at Mānoa

  19 shared

• Vivian Bernau

  Iowa State University

  18 shared

• Lev Jardón‐Barbolla

  Universidad Nacional Autónoma de México

  16 shared

• Colin K. Khoury

  15 shared

• Leah K. McHale

  The Ohio State University

  14 shared

• Hugo Perales

  El Colegio de la Frontera Sur

  13 shared

• Gloria E. Barboza

  Centre Hospitalier Compiègne-Noyon

  11 shared

• Stephanie L. Greene

  United States Department of Agriculture

  10 shared