@article {KNZ001657, title = {The effects of genotype richness and genomic dissimilarity of Andropogon gerardii on invasion resistance and productivity}, journal = {Plant Ecology and Diversity}, volume = {8}, year = {2015}, pages = {61 -71}, abstract = {

Background: The genetic diversity within populations has been shown to affect ecosystem functions, including productivity and invasion resistance. To date most experiments have focused on manipulation of genotypic richness and have ignored other measures of genetic diversity. Aims: In the present study we aimed to establish whether manipulated genotypic richness and genomic dissimilarity of Andropogon gerardii affect productivity and invasion resistance. Methods: We created experimental mesocosms with three levels of genotypic richness: one-, three-, and nine-genotypes. In the three-genotype treatment, we manipulated a range of genomic dissimilarity values (genetic relatedness among individuals). At the end of one growing season we measured above-ground, below-ground and total biomass of the mesocosms, and invasion resistance to Andropogon bladhii. Results: Overall, we found no significant effect of genotypic richness on any measure of ecosystem function, although there tended to be more root biomass (due to complementarity) and invasive seedling biomass with higher levels of genotypic richness. Within the three-genotype treatment we found a significant positive relationship between genomic dissimilarity and above-ground biomass, which was caused by a selection effect. We also found a positive relationship between genomic dissimilarity and biomass of A. bladhii. Conclusions: Using these two measures of genetic diversity we detected differences in the strength and mechanism of positive diversity effects within the same experiment, demonstrating the value of manipulating multiple measures of diversity when performing biodiversity\–ecosystem function experiments.

}, keywords = {LTER-KNZ, Andropogon bladhii, biodiversity ecosystem function, complementarity, dominant species, genomic dissimilarity, genotypic richness, invasion resistance, productivity, tallgrass prairie}, doi = {10.1080/17550874.2013.866990}, url = {https://www.tandfonline.com/doi/abs/10.1080/17550874.2013.866990}, author = {M.L. Avolio and Chang, C.C. and Weis, J.J. and M.D. Smith} } @article {KNZ001701, title = {Invasibility of a mesic grassland depends on the time-scale of fluctuating resources}, journal = {Journal of Ecology}, volume = {103}, year = {2015}, pages = {1538 - 1546}, abstract = {

1. Global change is increasing the frequency and magnitude of resource fluctuations (pulses) at multiple time-scales. According to the fluctuating resource availability hypothesis (FRAH), susceptibility of an ecosystem to invasion (i.e. invasibility) is expected to increase whenever resource supply exceeds that which is utilized by native communities. Thus, global change has the potential to increase invasibility around the world. 2. Here, we test the FRAH by adding seeds of a target invader grass species to a long-term climate change experiment manipulating precipitation pulse size in tallgrass prairie in Kansas, USA. 3. Our experimental work yielded three important findings. First, contrary to predictions of the FRAH, invasibility was reduced with short time-scale resource pulses (intra-annual time-scale). Secondly, we found evidence to suggest that at inter-annual time-scales, the FRAH is supported. Wet years resulted in an increase in the number of established seedlings as well as the number of seedlings that persisted to the end of the season. Finally, we found that invasibility was positively related to native community richness and the density of individuals in the community suggesting that native communities facilitate establishment of invader species. Perhaps more importantly, results from this 10-year invasion study also show that resource availability drives invasion and that the biotic filters of plant community structure and diversity are secondary. 4. Synthesis. Our findings suggest that intensification of precipitation regimes may enhance resistance to invasion at intra-annual time-scales, but will have opposing effects if precipitation regimes include more wet years.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.12479}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12479}, author = {Koerner, S.E. and M.L. Avolio and Chang, C.C. and Grey, J. and D.L. Hoover and M.D. Smith} } @article {KNZ001639, title = {Direct and indirect relationships between genetic diversity of a dominant grass, community diversity and above-ground productivity in tallgrass prairie}, journal = {Journal of Vegetation Science}, volume = {25}, year = {2014}, pages = {470 -480}, abstract = {

Question Both genetic diversity within a dominant species and species diversity have been shown to affect productivity. However, these two levels of diversity have the potential to affect productivity in similar or opposing ways. Our study assessed direct and indirect relationships between genetic diversity of a dominant grass species and plant community diversity on productivity within a mesic grassland with naturally co-occurring genotypes and species. Location Konza Prairie Biological Station, Kansas, USA (39\°05\′35\″ N, 96\°33\′31\″ W). Methods We conducted a study at two sites (~65 plots per site) in intact tallgrass prairie that have been subjected to frequent (burned 14 times) and infrequent (burned nine times) fire treatments for ~30 yrs. With frequent burning, the dominant C4 grass, Andropogon gerardii, typically has higher abundance; in contrast, infrequently burned sites typically have higher species diversity but lower abundance of A. gerardii. Therefore, we hypothesized that genetic diversity within A. gerardii would have a significant direct relationship with productivity for the frequently burned site due to higher population abundances of A. gerardii overall, whereas species diversity would have a significant direct relationship with productivity for the infrequently burned site. Results Contrary to our predictions, genetic diversity of A. gerardii was not related to above-ground productivity either directly or indirectly via traits, while diversity at the community level had a negative indirect relationship with productivity via a negative effect of A. gerardii abundance on community diversity for both frequently and infrequently burned sites. Conclusions While much of the focus of diversity\–productivity research has been on direct relationships between diversity at the community or population level separately, future studies should examine the indirect and potentially interactive effects of both levels of diversity in natural communities.

}, keywords = {LTER-KNZ, Community diversity, disturbance, dominant species, Fire;Grassland, Phylogenetic diversity, Plant trait, Productivity{\textendash}diversity relationship, Structural equation modelling}, doi = {10.1111/jvs.12108}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12108}, author = {Chang, C.C. and M.D. Smith} } @article {KNZ001661, title = {Resource availability modulates above and belowground competitive interactions between genotypes of a dominant C4 grass}, journal = {Functional Ecology}, volume = {28}, year = {2014}, pages = {1041 -1051}, abstract = {

The well-described pattern of a few common and many rare species in plant communities (dominance-diversity curves) also has been documented within populations of dominant plant species. Understanding how these common genotypes coexist has implications for how genotype richness of a dominant species may impact community and ecosystem processes. Some studies have shown that increased genotype richness of a dominant species leads to an increase in above-ground productivity, suggesting niche complementarity between genotypes. However, mechanistic understanding of how genotypes may complement one another is lacking. We conducted a pairwise competition experiment between four common and naturally co-occurring genotypes of a dominant C4 grass species, Andropogon gerardii, in tallgrass prairie of the central United States. The genotypes were grown under both intra- and intergenotypic competition with different combinations of resources (low and high light, water, and nitrogen) in the greenhouse. We determined that there were above- and below-ground phenotypic differences between genotypes which results in altered competitive interactions depending on resource conditions. Different genotypes were competitively dominant under low- and high-light conditions and low and high N and water availability. Moreover, relative yield total values (RYT) for each genotype pairwise combination indicated that all four genotypes make demands on different resources, providing evidence for niche complementarity. Finally, we found that differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success of the genotypes, which has implications for the population dynamics of this primarily asexually reproducing perennial grass. Our results suggest that naturally co-occurring genotypes coexist because they are competitively dominant under different environmental conditions, providing insight into how genetic diversity within dominant plant species is maintained and may potentially affect important ecosystem processes.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2435.12227}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.12227}, author = {Chang, C.C. and M.D. Smith} } @article {KNZ001658, title = {Genotypic diversity of a dominant C4 grass across a long-term fire frequency gradient}, journal = {Journal of Plant Ecology}, volume = {6}, year = {2013}, pages = {448 -458}, abstract = {

Aims and Methods Diversity-disturbance research has focused on community diversity, but disturbance frequency could impact diversity within species as well, with important consequences for community diversity and ecosystem function. We examined patterns of genetic diversity of a dominant grass species, Andropogon gerardii, in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments (burned every 1, 2, 4 or 20 years) since the 1970s. In addition, we were able to assess the relationships between genetic diversity of A. gerardii, species diversity and productivity across this range of fire frequencies. Important Findings We found no significant relationships between genetic diversity of A. gerardii at the local scale (1 m2 plot level) and disturbance frequency (burned 2 to 32 times over a 38-year period). However, at the site level (i.e. across all plots sampled within a site, ~100 m2) there were differences in genotype richness and composition, as well as genomic dissimilarity among individuals of A. gerardii. Genotype richness was greatest for the site burned at an intermediate (4-year) frequency and lowest for the infrequently (20-year) burned site. In addition, genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites. Genotype composition of A. gerardii was not significantly different between the frequently burned sites (annual vs. 2 year) but did differ between frequently burned and infrequently burned sites (1 and 2 year vs. 4 and 20 year, etc.). Together, these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies, likely driven by alterations in environmental conditions. Frequent fire promotes the abundance of dominant grass species, reduces plant community diversity and impacts ecosystem processes such as productivity. Our study suggests that genetic diversity within dominant grass species also may be affected by disturbance frequency, which could have important implications for how species are able to respond to disturbance.

}, keywords = {LTER-KNZ, Andropogon gerardii, disturbance frequency, genetic relatedness, genetic-species diversity relationship, genotype richness, intermediate disturbance hypothesis, productivity, tallgrass prairie}, doi = {10.1093/jpe/rtt006}, url = {https://academic.oup.com/jpe/article/6/6/448/980977}, author = {Chang, C.C. and M.D. Smith} } @phdthesis {KNZ001466, title = {Dimensions of diversity and their direct and indirect effects on tallgrass prairie ecosystem functioning}, volume = {PhD Dissertation}, year = {2012}, pages = {1 -165}, school = {Yale University}, type = {Ph.D. Thesis}, address = {New Haven, CT}, abstract = {

Understanding the role of biological diversity to ecosystem function in ecological communities is particularly important now in the face of unprecedented, human-driven global change. Anthropogenic impacts such as climate change, nitrogen deposition, and land-use changes that modify natural disturbance regimes and promote the introduction of invasive species are all altering environmental conditions in such a way as to impact both diversity and ecosystem functioning. Diversity can be described in several ways and until recently, most research has focused on the relationship between the number and diversity of species and ecosystem function. Recently however, there has been a growing focus on the importance of genetic diversity within a dominant species and its impact on community and ecosystem processes. In this dissertation, I examine the relationship between community and population diversity, evaluate how diversity at both levels is maintained under varying environmental conditions, and test the relative effects of population and community level diversity on ecosystem function. First, I utilized a long-term experimental burn manipulation to examine the impact of fire frequency on genetic diversity of the dominant species and assessed the relationship between genetic diversity of the dominant species, species diversity, and productivity across the entire fire gradient. Genetic diversity of the dominant species was highest in a four year burn cycle and lowest in an annual and two year burn cycle. However, there was not a significant relationship between genetic and species diversity or between genetic diversity of the dominant species and productivity across the disturbance Gradient. In the second and third study, I explored in further detail the relationship between genetic diversity of the dominant species, species diversity, and evaluate the direct and indirect effects of both levels of diversity on productivity and invasion resistance. Contrary to expectations, genetic diversity of the dominant species did not have a direct effect on invasion resistance or productivity. Rather the effects of diversity at both the community and population level are primarily indirect via traits. Genetic differences between naturally co-occurring genotypes of the perennial dominant grass species were more subtle, and thus also highlighted the necessity of conducting studies in intact communities with naturally co-occurring individuals. Finally, to tease apart the possible mechanisms for how diversity within the population is maintained and subsequently impacts community and ecosystem processes, I conducted a pairwise competition experiment with the four most common genotypes of the dominant species and manipulated light, water, and nitrogen resources. Phenotypic differences between genotypes resulted in different competitive successes depending on resource conditions. Some genotypes were able to take advantage of increased water or nitrogen resources under low and high light conditions, providing evidence for niche complementarity. There was evidence that some genotypes were more antagonistic under low versus high resource conditions while other genotypes were more synergistic. This differential success in resource acquisition, biomass accumulation, and subsequent competitive ability translated to variation in vegetative reproductive success, which has implications for the population dynamics of this perennial, primarily asexually reproductive, dominant C4 grass. Together the results from these four studies suggest that the roles of population and community level diversity are complex in intact, natural tallgrass prairie where diversity effects on ecosystem function may be primarily indirect via traits.

}, keywords = {LTER-KNZ}, url = {http://search.proquest.com/docview/1039554547}, author = {Chang, C.C.} } @article {KNZ001467, title = {Invasion of an intact plant community: the role of population vs. community level diversity}, journal = {Oecologia}, volume = {168}, year = {2012}, pages = {1091 -1102}, abstract = {

To improve the understanding of how native plant diversity influences invasion, we examined how population and community diversity may directly and indirectly be related to invasion in a natural field setting. Due to the large impact of the dominant C4 grass species (Andropogon gerardii) on invasion resistance of tallgrass prairie, we hypothesized that genetic diversity and associated traits within a population of this species would be more strongly related to invasion than diversity or traits of the rest of the community. We added seeds of the exotic invasive C4 grass, A. bladhii, to 1-m2 plots in intact tallgrass prairie that varied in genetic diversity of A. gerardii and plant community diversity, but not species richness. We assessed relationships among genetic diversity and traits of A. gerardii, community diversity, community aggregated traits, resource availability, and early season establishment and late-season persistence of the invader using structural equation modeling (SEM). SEM models suggested that community diversity likely enhanced invasion indirectly through increasing community aggregated specific leaf area as a consequence of more favorable microclimatic conditions for seedling establishment. In contrast, neither population nor community diversity was directly or indirectly related to late season survival of invasive seedlings. Our research suggests that while much of diversity\–invasion research has separately focused on the direct effects of genetic and species diversity, when taken together, we find that the role of both levels of diversity on invasion resistance may be more complex, whereby effects of diversity may be primarily indirect via traits and vary depending on the stage of invasion.

}, keywords = {LTER-KNZ, Andropogon bladhii, dominant species, genetic diversity, grassland, tallgrass prairie}, doi = {10.1007/s00442-011-2157-z}, url = {https://link.springer.com/article/10.1007\%2Fs00442-011-2157-z}, author = {Chang, C.C. and M.D. Smith} } @article {KNZ001420, title = {Assessing fine-scale genotypic structure of a dominant species in native grasslands}, journal = {The American Midland Naturalist}, volume = {165}, year = {2011}, pages = {211 -224}, abstract = {

Genotypic diversity of dominant species has been shown to have important consequences for community and ecosystem processes at a fine spatial scale. We examined the fine-scale (i.e., plant neighborhood scale, \<1 m2) genotypic structure of Andropogon gerardii, a dominant species in the tallgrass prairie, which is a productive and endangered grassland ecosystem, employing the commonly used amplified fragment length polymorphism (AFLP) technique. In this paper we used two methods to assess the fine-scale genetic spatial structure of a dominant perennial grass, (1) we determined how many tillers to sample in a 1 m2 area and (2) we developed AFLP markers that would differentiate between genotypes. By determining appropriate sampling and molecular techniques, our findings can be applied to questions addressing how genetic diversity of dominant species affect ecosystem processes in the tallgrass prairie.

}, keywords = {LTER-KNZ}, doi = {10.1674/0003-0031-165.2.211}, url = {https://doi.org/10.1674/0003-0031-165.2.211}, author = {M.L. Avolio and Chang, C.C. and M.D. Smith} } @article {KNZ001411, title = {Explaining temporal variation in above-ground productivity in a mesic grassland: the role of climate and flowering}, journal = {Journal of Ecology}, volume = {99}, year = {2011}, pages = {1250 -1262}, abstract = {

1. Annual above-ground net primary productivity (ANPP) in mesic grasslands is known to be highly temporally variable. While yearly precipitation or average yearly temperature can explain some of this temporal variability, much of the variation in ANPP remains unexplained. 2. Here we address the heretofore unexplained variation in 25 years of productivity data from a mesic grassland at Konza Prairie (north-eastern Kansas) by examining the effects of precipitation and temperature during periods relevant to the phenology and growth cycle of the dominant C4 grasses and the flowering stalk production of these species. We assessed both the direct effects and indirect effects via flowering of phenologically relevant climate periods on ANPP using structural equation modelling (SEM). 3. We found ANPP to be strongly positively influenced by flowering stalk production of the dominant C4 grasses, precipitation during periods relevant to vegetative growth (15 April\–14 July) and flowering stalk elongation (15 July\–14 August) of the dominant grasses, and fire. In addition, flowering stalk production was negatively influenced by high temperatures during the flowering stalk elongation period, which therefore resulted in a negative indirect effect on ANPP. We found little evidence for the effects of the previous year\’s total annual precipitation or mean annual temperature on ANPP. 4. By including flowering stalk production and separating climate variables into phenologically relevant periods we were able to increase the percentage of observed variance in ANPP explained by six models, relating to different topographic positions and burn regimes, from an average of 22\% to 48\%, with the best model explaining 61\% of variation in ANPP. 5.Synthesis. The link between climatic periods relevant to the phenology and growth of dominant C4 grasses, flowering stalk production of these grasses and ANPP shown here improves our ability to predict productivity in mesic grasslands, an ecologically and economically important ecosystem.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2745.2011.01844.x}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2745.2011.01844.x}, author = {Kimberly J. La Pierre and Yuan, S.H. and Chang, C.C. and M.L. Avolio and Hallett, L.M. and Schreck, T. and M.D. Smith} }