Ecological consequences of shifting the timing of burning tallgrass prairie

Citation: Towne EG, Craine JM (2014) Ecological Consequences of Shifting the Timing of Burning Tallgrass Prairie. PLoS ONE 9(7): e103423. doi:10.1371/journal.pone.0103423In the Kansas Flint Hills, grassland burning is conducted during a relatively narrow window because management recommendations for the past 40 years have been to burn only in late spring. Widespread prescribed burning within this restricted time frame frequently creates smoke management issues downwind. A potential remedy for the concentrated smoke production in late spring is to expand burning to times earlier in the year. Yet, previous research suggested that burning in winter or early spring reduces plant productivity and cattle weight gain while increasing the proportion of undesirable plant species. In order to better understand the ecological consequences of burning at different times of the year, plant production and species abundance were measured for 20 years on ungrazed watersheds burned annually in autumn, winter, or spring. We found that there were no significant differences in total grass production among the burns on either upland or lowland topographic positions, although spring burned watersheds had higher grass culm production and lower forb biomass than autumn and winter burned watersheds. Burning in autumn or winter broadened the window of grass productivity response to precipitation, which reduces susceptibility to mid-season drought. Burning in autumn or winter also increased the phenological range of species by promoting cool-season graminoids without a concomitant decrease in warm-season grasses, potentially widening the seasonal window of high-quality forage. Incorporating autumn and winter burns into the overall portfolio of tallgrass prairie management should increase the flexibility in managing grasslands, promote biodiversity, and minimize air quality issues caused by en masse late-spring burning with little negative consequences for cattle production

Increased C3 productivity in Midwestern lawns since 1982 revealed by carbon isotopes in Amanita thiersii

How climate and rising carbon dioxide concentrations (pCO2) have influenced competition between C3 and C4 plants over the last 50 years is a critical uncertainty in climate change research. Here we used carbon isotope (δ13C) values of the saprotrophic lawn fungus Amanita thiersii to integrate the signal of C3 and C4 carbon in samples collected between 1982 and 2009 from the Midwestern USA. We then calculated 13C fractionation (Δ) to assess the balance between C3 and C4 photosynthesis as influenced by mean annual temperature (MAT), mean annual precipitation over a 30 year period (MAP‐30), and pCO2. Sporocarp Δ correlated negatively with MAT (−1.74‰ °C−1, 79% of variance) and positively with MAP (9.52‰ m−1, 15% of variance), reflecting the relative productivity of C3 and C4 grasses in lawns. In addition, Δ values correlated positively with pCO2 (0.072‰ ppm−1, 5% of variance). Reduced photorespiration with rising pCO2 accounted for 20% of this increased Δ, but the remaining 80% is consistent with increased assimilation of C3‐derived carbon by Amanita thiersii resulting from increased productivity of C3 grasses with rising pCO2. Between 1982 and 2009, pCO2 rose by 46 ppm and the relative contribution of C3 photosynthesis to Amanita thiersii carbon increased 18.5%. The δ13C value of Amanita thiersii may integrate both lawn maintenance practices and the physiological responses of turf grasses to rising CO2 concentrations

Microbial Nitrogen Limitation Increases Decomposition

With anthropogenic nutrient inputs to ecosystems increasing globally, there are long-standing, fundamental questions about the role of nutrients in the decomposition of organic matter. We tested the effects of exogenous nitrogen and phosphorus inputs on litter decomposition across a broad suite of litter and soil types. In one experiment, C mineralization was compared across a wide array of plants individually added to a single soil, while in the second, C mineralization from a single substrate was compared across 50 soils. Counter to basic stoichiometric decomposition theory, low N availability can increase litter decomposition as microbes use labile substrates to acquire N from recalcitrant organic matter. This “microbial nitrogen mining” is consistently suppressed by high soil N supply or substrate N concentrations. There is no evidence for phosphorus mining as P fertilization increases short- and long-term mineralization. These results suggest that basic stoichiometric decomposition theory needs to be revised and ecosystem models restructured accordingly in order to predict ecosystem carbon storage responses to anthropogenic changes in nutrient availability

Lack of eutrophication in a tallgrass prairie ecosystem over 27 years

Many North American grasslands are receiving atmospheric nitrogen (N) deposition at rates above what are considered critical eutrophication thresholds. Yet, potential changes in grassland function due to anthropogenic N deposition are poorly resolved, especially considering that other dynamic factors such as land use and precipitation can also affect N availability. To better understand whether elevated N deposition has altered ecosystem structure or function in North American grasslands, we analyzed a 27-year record of ecophysiological, community, and ecosystem metrics for an annually burned Kansas tallgrass prairie. Over this time, despite increasing rates of N deposition that are within the range of critical loads for grasslands, there was no evidence of eutrophication. Plant N concentrations did not increase, soil moisture did not decline, forb diversity did not decline, and the relative abundance of dominant grasses did not shift toward more eutrophic species. Neither aboveground primary productivity nor N availability to plants increased. The fates of deposited N in grasslands are still uncertain, and could include management losses through burning and grazing. However, evidence from this grassland indicates that eutrophication of North American grassland ecosystems is not an inevitable consequence of current levels of N deposition

The role of plant species in biomass production and response to elevated CO 2 and N

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72902/1/j.1461-0248.2003.00467.x.pd

Long-term declines in dietary nutritional quality for North American cattle

With over 1 billion cattle in the world as well as over 2 billion sheep, goats and buffalo, these animals contribute approximately 15% of the global human protein supply while producing a significant proportion of anthropogenic emissions of greenhouse gases and global nutrient fluxes. Despite increasing reliance on grazers for protein production globally, the future of grazers in a changing world is uncertain. Factors such as increased prevalence of drought, rising atmospheric CO2 concentrations, and sustained nutrient export all have the potential to reduce cattle performance by reducing the nutritional quality of forage. However, there are no analyses to quantify changes in diet quality, subsequent impact on cattle performance and cost of supplementation necessary to mitigate any predicted protein deficiency. To quantify the trajectory of nutritional stress in cattle, we examined more than 36 000 measurements of dietary quality taken over 22 yr for US cattle. Here, we show that standardizing for spatial and temporal variation in drought and its effects on forage quality, cattle have been becoming increasingly stressed for protein over the past two decades, likely reducing cattle weight gain. In economic terms, the replacement costs of reduced protein provision to US cattle are estimated to be the equivalent of $1.9 B annually. Given these trends, nitrogen enrichment of grasslands might be necessary if further reduction in protein content of forages is to be prevented

Evolutionary relationships in Panicoid grasses based on plastome phylogenomics (Panicoideae; Poaceae)

Background: Panicoideae are the second largest subfamily in Poaceae (grass family), with 212 genera and approximately 3316 species. Previous studies have begun to reveal relationships within the subfamily, but largely lack resolution and/or robust support for certain tribal and subtribal groups. This study aims to resolve these relationships, as well as characterize a putative mitochondrial insert in one linage. Results: 35 newly sequenced Panicoideae plastomes were combined in a phylogenomic study with 37 other species: 15 Panicoideae and 22 from outgroups. A robust Panicoideae topology largely congruent with previous studies was obtained, but with some incongruences with previously reported subtribal relationships. A mitochondrial DNA (mtDNA) to plastid DNA (ptDNA) transfer was discovered in the Paspalum lineage. Conclusions: The phylogenomic analysis returned a topology that largely supports previous studies. Five previously recognized subtribes appear on the topology to be non-monophyletic. Additionally, evidence for mtDNA to ptDNA transfer was identified in both Paspalum fimbriatum and P. dilatatum, and suggests a single rare event that took place in a common progenitor. Finally, the framework from this study can guide larger whole plastome sampling to discern the relationships in Cyperochloeae, Steyermarkochloeae, Gynerieae, and other incertae sedis taxa that are weakly supported or unresolved.Fil: Burke, Sean V.. Northern Illinois University; Estados UnidosFil: Wysocki, William P.. Northern Illinois University; Estados UnidosFil: Zuloaga, Fernando Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Craine, Joseph M.. Jonah Ventures; Estados UnidosFil: Pires, J. Chris. University of Missouri; Estados UnidosFil: Edger, Patrick P.. Michigan State University; Estados UnidosFil: Mayfield Jones, Dustin. Donald Danforth Plant Science Center; Estados UnidosFil: Clark, Lynn G.. Iowa State University; Estados UnidosFil: Kelchner, Scot A.. University of Idaho; Estados UnidosFil: Duvall, Melvin R.. Northern Illinois University; Estados Unido

Ecological interpretations of nitrogen isotope ratios of terrestrial plants and soils

Background Knowledge of biological and climatic controls in terrestrial nitrogen (N) cycling within and across ecosystems is central to understanding global patterns of key ecosystem processes. The ratios of 15N:14N in plants and soils have been used as indirect indices of N cycling parameters, yet our understanding of controls over N isotope ratios in plants and soils is still developing. Scope In this review, we provide background on the main processes that affect plant and soil N isotope ratios. In a similar manner to partitioning the roles of state factors and interactive controls in determining ecosystem traits, we review N isotopes patterns in plants and soils across a number of proximal factors that influence ecosystem properties as well as mechanisms that affect these patterns. Lastly, some remaining questions that would improve our understanding of N isotopes in terrestrial ecosystems are highlighted. Conclusion Compared to a decade ago, the global patterns of plant and soil N isotope ratios are more resolved. Additionally, we better understand how plant and soil N isotope ratios are affected by such factors as mycorrhizal fungi, climate, and microbial processing. A comprehensive understanding of the N cycle that ascribes different degrees of isotopic fractionation for each step under different conditions is closer to being realized, but a number of process-level questions still remain

Climatic warming and the future of bison as grazers

Climatic warming is likely to exacerbate nutritional stress and reduce weight gain in large mammalian herbivores by reducing plant nutritional quality. Yet accurate predictions of the effects of climatic warming on herbivores are limited by a poor understanding of how herbivore diet varies along climate gradients. We utilized DNA metabarcoding to reconstruct seasonal variation in the diet of North American bison (Bison bison) in two grasslands that differ in mean annual temperature by 6&thinsp;&deg;C. Here, we show that associated with greater nutritional stress in warmer climates, bison consistently consumed fewer graminoids and more shrubs and forbs, i.e. eudicots. Bison in the warmer grassland consumed a lower proportion of C3 grass, but not a greater proportion of C4 grass. Instead, bison diet in the warmer grassland had a greater proportion of N2-fixing eudicots, regularly comprising &gt;60% of their protein intake in spring and fall. Although bison have been considered strict grazers, as climatic warming reduces grass protein concentrations, bison may have to attempt to compensate by grazing less and browsing more. Promotion of high-protein, palatable eudicots or increasing the protein concentrations of grasses will be critical to minimizing warming-imposed nutritional stress for bison and perhaps other large mammalian herbivores. </div