Browsing by Subject "nitrogen deposition"

Now showing 1 - 6 of 6
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    CO2, nitrogen, and diversity differentially affect seed production of prairie plants
    (2009) Hillerislambers, J; Harpole, W S; Schnitzer, S; Tilman, D; Reich, Peter B
    Plant species composition and diversity is often influenced by early life history stages; thus, global change could dramatically affect plant community structure by altering seed production. Unfortunately, plant reproductive responses to global change are rarely studied in field settings, making it difficult to assess this possibility. To address this issue, we quantified the effects of elevated CO2, nitrogen deposition, and declining diversity on inflorescence production and inflorescence mass of 11 perennial grassland species in central Minnesota, USA. We analyzed these data to ask whether (1) global change differentially affects seed production of co-occurring species; (2) seed production responses to global change are similar for species within the same functional group (defined by ecophysiology and growth form); and (3) seed production responses to global change match productivity responses. We found that, on average, allocation to seed production decreased under elevated CO2, although individual species responses were rarely significant due to low power (CO2 treatment df = 2). The effects of nitrogen deposition on seed production were similar within functional groups: C4 grasses tended to increase while C3 grasses tended to decrease allocation to seed production. Responses to nitrogen deposition were negatively correlated to productivity responses, suggesting a trade-off. Allocation to seed production of some species responded to a diversity gradient, but responses were uncorrelated to productivity responses and not similar within functional groups. Presumably, species richness has complex effects on the biotic and abiotic variables that influence seed production. In total, our results suggest that seed production of co-occurring species will be altered by global change, which may affect plant communities in unpredictable ways. Although functional groups could be used to generalize seed production responses to nitrogen deposition in Minnesota prairies, we caution against relying on them for predictive purposes without a mechanistic understanding of how resource availability and biotic interactions affect seed production.
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    Direct and indirect effects of CO2, nitrogen, and community diversity on plant–enemy interactions
    (Ecological Society of America, 2008) Lau, Jennifer A; Strengbom, Joachim; Stone, Laurie R; Reich, Peter B; Tiffin, Peter
    Resource abundance and plant diversity are two predominant factors hypothesized to influence the amount of damage plants receive from natural enemies. Many impacts of these environmental variables on plant damage are likely indirect and result because both resource availability and diversity can influence plant traits associated with attractiveness to herbivores or susceptibility to pathogens. We used a long-term, manipulative field experiment to investigate how carbon dioxide (CO2) enrichment, nitrogen (N) fertilization, and plant community diversity affect plant traits and the amount of herbivore and pathogen damage experienced by the common prairie legume Lespedeza capitata. We detected little evidence that CO2 or N affected plant traits; however, plants growing in high-diversity treatments (polycultures) were taller, were less pubescent, and produced thinner leaves (higher specific leaf area). Interestingly, we also detected little evidence that CO2 or N affect damage. Plants growing in polycultures compared to monocultures, however, experienced a fivefold increase in damage from generalist herbivores, 64% less damage from specialist herbivores, and 91% less damage from pathogens. Moreover, within diversity treatments, damage by generalist herbivores was negatively correlated with pubescence and often was positively correlated with plant height, while damage by specialist herbivores typically was positively correlated with pubescence and negatively associated with height. These patterns are consistent with changes in plant traits driving differences in herbivory between diversity treatments. In contrast, changes in measured plant traits did not explain the difference in disease incidence between monocultures and polycultures. In summary, our data provide little evidence that CO2 or N supply alter damage from natural enemies. By contrast, plants grown in monocultures experienced greater specialist herbivore and pathogen damage but less generalist herbivore damage than plants grown in diverse communities. Part of this diversity effect was mediated by changes in plant traits, many of which likely are plastic responses to diversity treatments, but some of which may be the result of evolutionary changes in response to these long-term experimental manipulations.
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    Effects Of Nitrogen And Nutrient Co-Limitation On Carbon Dynamics And Plant Community Composition
    (2023) Wilcots, Megan
    Despite its necessity in all life forms, nitrogen (N) is a limiting nutrient in many ecosystems. However, N availability is increasing through human-derived inputs, in particular through deposition of reactive N as a result of fossil fuel emissions and fertilizer volatilization. Anthropogenic N deposition currently represents a relatively small, but continuous, addition of N into ecosystems; but, because N is frequently limiting to plant growth, particularly in terrestrial systems, this small flux can have substantial effects on ecosystem diversity, productivity, and function. Grasslands, covering 40% of Earth’s land surface, are a particularly important biome in which to study the effects of N deposition because of their high biodiversity as well as agricultural and environmental value. In my dissertation, I studied how small rate of N inputs, similar to rates of N deposition, affect plant community composition, productivity, and carbon fluxes. I also investigated how the effects of N were contingent on the supply of other commonly limiting nutrients, such as phosphorus (P), potassium (K), and micronutrients (µ). I found consistent nonlinear responses to N addition, with plant biomass and carbon fluxes peaking at low rates of N addition. Additionally, I found that the effects of high rates of N were contingent on the supply of PKµ, and that plant community composition only changed when all three nutrients were added together. Overall, my work indicates that plant community response to nitrogen is dependent on both rate of N supply and supply of nutrients other than N.
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    A novel soil manganese mechanism drives plant species loss with increased nitrogen deposition in a temperate steppe
    (Wiley, 2016) Tian, Qiuying; Liu, Nana; Bai, Wenming; Li, Linghao; Chen, Jiquan; Reich, Peter B; Yu, Qiang; Guo, Dali; Smith, Melinda D; Knapp, Alan K; Cheng, Weixin; Lu, Peng; Gao, Yan; Yang, An; Wang, Tianzuo; Li, Xin; Wang, Zhengwen; Ma, Yibing; Han, Xingguo; Zhang, Wen‐Hao
    Loss of plant diversity with increased anthropogenic nitrogen (N) deposition in grasslands has occurred globally. In most cases, competitive exclusion driven by preemption of light or space is invoked as a key mechanism. Here, we provide evidence from a 9-yr N-addition experiment for an alternative mechanism: differential sensitivity of forbs and grasses to increased soil manganese (Mn) levels. In Inner Mongolia steppes, increasing the N supply shifted plant community composition from grass–forb codominance (primarily Stipa krylovii and Artemisia frigida, respectively) to exclusive dominance by grass, with associated declines in overall species richness. Reduced abundance of forbs was linked to soil acidification that increased mobilization of soil Mn, with a 10-fold greater accumulation of Mn in forbs than in grasses. The enhanced accumulation of Mn in forbs was correlated with reduced photosynthetic rates and growth, and is consistent with the loss of forb species. Differential accumulation of Mn between forbs and grasses can be linked to fundamental differences between dicots and monocots in the biochemical pathways regulating metal transport. These findings provide a mechanistic explanation for N-induced species loss in temperate grasslands by linking metal mobilization in soil to differential metal acquisition and impacts on key functional groups in these ecosystems.
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    Plant diversity, CO2 and N influence inorganic and organic N leaching in grasslands
    (2007) Dijkstra, Feike A; West, Jason B; Hobbie, Sarah E; Reich, Peter B; Trost, Jared
    In nitrogen (N)-limited systems, the potential to sequester carbon depends on the balance between N inputs and losses as well as on how efficiently N is used, yet little is known about responses of these processes to changes in plant species richness, atmospheric CO2 concentration ([CO2]), and N deposition. We examined how plant species richness (1 or 16 species), elevated [CO2] (ambient or 560 ppm), and inorganic N addition (0 or 4 g·m−2·yr−1) affected ecosystem N losses, specifically leaching of dissolved inorganic N (DIN) and organic N (DON) in a grassland field experiment in Minnesota, USA. We observed greater DIN leaching below 60 cm soil depth in the monoculture plots (on average 1.8 and 3.1 g N·m−2·yr−1 for ambient N and N-fertilized plots respectively) than in the 16-species plots (0.2 g N·m−2·yr−1 for both ambient N and N-fertilized plots), particularly when inorganic N was added. Most likely, loss of complementary resource use and reduced biological N demand in the monoculture plots caused the increase in DIN leaching relative to the high-diversity plots. Elevated [CO2] reduced DIN concentrations under conditions when DIN concentrations were high (i.e., in N-fertilized and monoculture plots). Contrary to the results for DIN, DON leaching was greater in the 16-species plots than in the monoculture plots (on average 0.4 g N·m−2·yr−1 in 16-species plots and 0.2 g N·m−2·yr−1 in monoculture plots). In fact, DON dominated N leaching in the 16-species plots (64% of total N leaching as DON), suggesting that, even with high biological demand for N, substantial amounts of N can be lost as DON. We found no significant main effects of elevated [CO2] on DIN or DON leaching; however, elevated [CO2] reduced the positive effect of inorganic N addition on DON leaching, especially during the second year of observation. Our results suggest that plant species richness, elevated [CO2], and N deposition alter DIN loss primarily through changes in biological N demand. DON losses can be as large as DIN loss but are more sensitive to organic matter production and turnover.
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    Stepping N-to the Past: Plant Responses to Anthropogenic Nitrogen Deposition
    (2017-04) Tang, Alex D; Cline, Lauren C; Kennedy, Peter G
    Anthropogenic nitrogen (N) deposition has doubled the amount of N entering the biosphere. To quantify the historical effect of N deposition on plant N uptake, we sampled long-term herbaria collections from the Bell Museum of Natural History. We expected that plants would increase leaf N and 15N:14N ratios as a result of increasing soil N availability. Contrary to our hypothesis, the 15N:14N ratios decreased over the last 120 years for both Acer and Betula. Betula leaf N content decreased through time; Acer leaf N had no response. These results suggest that anthropogenic N deposition may not be the only factor to influence soil N availability over the last century.