23 research outputs found
Measuring plant nitrogen availability in forest soils with lab incubations and phytometer growth assays: a power analysis
As the most commonly-limiting nutrient in terrestrial ecosystems,
nitrogen plays a critical role in carbon sequestration and other
ecosystem services. However, it is notoriously difficult to measure
the availability of nitrogen in the forms that plants are able to take
up. We conducted a combined lab and greenhouse experiment to
determine the sampling sizes required to reliably measure plant
nitrogen availability in forest soils collected from two plots at The
Morton Arboretum, one angiosperm-dominated and the second
gymnosperm-dominated. We used two methods to measure plant
nitrogen availability in our forest soil samples: lab incubations and
phytometer growth. Lab incubations measure mineral nitrogen
concentration before and after a two-week incubation period to
determine net nitrogen mineralization. Phytometer growth indexes
nitrogen availability via height and biomass of seedlings grown in
the soil. Using 40 soil cores per plot, we will determine how
many samples are required to have an 80% chance of detecting
significant results between plots with a two-fold increase or
decrease in nitrogen availability. By determining minimum
sample sizes required, this pilot study will aid in the efficient
design of an upcoming larger study comparing soil nitrogen
availability across 18 plots at The Morton Arboretum
Managing for Resilience: Lessons from Ecology
Understanding and developing resilience is becoming increasingly important in business for both leaders and organizations. Resilient organizations can successfully navigate uncertainty and change. Resilience, however, is a poorly understood attribute. We thus turn to ecosystem resilience theory to understand the concept of resilience. We identify four lessons that can be adapted from management for ecological resilience to management for business resilience: 1) resilience can be positive or negative depending on the nature of the function it supports, 2) diversity of individuals, departments, flows of information, perspective, and other attributes contributes to resilience, 3) because we have imperfect knowledge about the timing and nature of a given disturbance and thus imperfect knowledge about the exact components of diversity that will promote resilience in the face of it, there is a benefit to preserving diversity, even if it reduces efficiency under static conditions, and 4) to the extent that disturbances are unavoidable, emphasis should be placed on low-level adaptability to support high-level resilience of function. In managing for resilience, the leader can apply these lessons both by promoting diversity (of functional redundancy and response diversity) throughout all levels of the organization and by focusing on development of flexibility, nimbleness, and adaptability. This work has led us to develop seven theoretical propositions on leadership for resilience that can spur further research to integrate ecology and business leadership perspectives
Managing for Resilience: Lessons from Ecology
Understanding and developing resilience is becoming increasingly important in business for both leaders and organizations. Resilient organizations can successfully navigate uncertainty and change. Resilience, however, is a poorly understood attribute. We thus turn to ecosystem resilience theory to understand the concept of resilience. We identify four lessons that can be adapted from management for ecological resilience to management for business resilience: 1) resilience can be positive or negative depending on the nature of the function it supports, 2) diversity of individuals, departments, flows of information, perspective, and other attributes contributes to resilience, 3) because we have imperfect knowledge about the timing and nature of a given disturbance and thus imperfect knowledge about the exact components of diversity that will promote resilience in the face of it, there is a benefit to preserving diversity, even if it reduces efficiency under static conditions, and 4) to the extent that disturbances are unavoidable, emphasis should be placed on low-level adaptability to support high-level resilience of function. In managing for resilience, the leader can apply these lessons both by promoting diversity (of functional redundancy and response diversity) throughout all levels of the organization and by focusing on development of flexibility, nimbleness, and adaptability. This work has led us to develop seven theoretical propositions on leadership for resilience that can spur further research to integrate ecology and business leadership perspectives
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Competition alters predicted forest carbon cycle responses to nitrogen availability and elevated CO2: simulations using an explicitly competitive, game-theoretic vegetation demographic model
Competition is a major driver of carbon allocation to different plant tissues (e.g., wood, leaves, fine roots), and allocation, in turn, shapes vegetation structure. To improve their modeling of the terrestrial carbon cycle, many Earth system models now incorporate vegetation demographic models (VDMs) that explicitly simulate the processes of individual-based competition for light and soil resources. Here, in order to understand how these competition processes affect predictions of the terrestrial carbon cycle, we simulate forest responses to elevated atmospheric CO2 concentration [CO2] along a nitrogen availability gradient, using a VDM that allows us to compare fixed allocation strategies vs. competitively optimal allocation strategies. Our results show that competitive and fixed strategies predict opposite fractional allocation to fine roots and wood, though they predict similar changes in total net primary production (NPP) along the nitrogen gradient. The competitively optimal allocation strategy predicts decreasing fine root and increasing wood allocation with increasing nitrogen, whereas the fixed strategy predicts the opposite. Although simulated plant biomass at equilibrium increases with nitrogen due to increases in photosynthesis for both allocation strategies, the increase in biomass with nitrogen is much steeper for competitively optimal allocation due to its increased allocation to wood. The qualitatively opposite fractional allocation to fine roots and wood of the two strategies also impacts the effects of elevated [CO2] on plant biomass. Whereas the fixed allocation strategy predicts an increase in plant biomass under elevated [CO2] that is approximately independent of nitrogen availability, competition leads to higher plant biomass response to elevated [CO2] with increasing nitrogen availability. Our results indicate that the VDMs that explicitly include the effects of competition for light and soil resources on allocation may generate significantly different ecosystem-level predictions of carbon storage than those that use fixed strategies
Modeling carbon allocation in trees: a search for principles
We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an individual's strategy on its environment (game-theoretical optimization, GTO). Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability
Fruits, Frugivores, and the Evolution of Phytochemical Diversity
Plants produce an enormous diversity of secondary metabolites, but the evolutionary mechanisms that maintain this diversity are still unclear. The interaction diversity hypothesis suggests that complex chemical phenotypes are maintained because different metabolites benefit plants in different pairwise interactions with a diversity of other organisms. In this synthesis, we extend the interaction diversity hypothesis to consider that fruits, as potential hotspots of interactions with both antagonists and mutualists, are likely important incubators of phytochemical diversity. We provide a case study focused on the Neotropical shrub Piper reticulatum that demonstrates: 1) secondary metabolites in fruits have complex and cascading effects for shaping the outcome of both mutualistic and antagonistic fruitāfrugivore interactions, and; 2) fruits can harbor substantially higher levels of phytochemical diversity than leaves, even though leaves have been the primary focus of plant chemical ecology research for decades. We then suggest a number of research priorities for integrating chemical ecology with fruitāfrugivore interaction research and make specific, testable predictions for patterns that should emerge if fruit interaction diversity has helped shape phytochemical diversity. Testing these predictions in a range of systems will provide new insight into the mechanisms driving frugivory and seed dispersal and shape an improved, whole-plant perspective on plant chemical trait evolution
How are nitrogen availability, fine-root mass, and nitrogen uptake related empirically? Implications for models and theory
We gratefully acknowledge funding from Loyola University Chicago; suggestions for improvement by David Robinson and anonymous peer reviewers; logistical support from K. Erickson; help with maintenance and harvests from O. Urbanski, L. Papaioannou, H. Roudebush, & V. Roudebush; and tissue and substrate analyses from Z. Zhu. The authors have no conflicts of interest to report.Peer reviewedPostprin
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Modeling demographic-driven vegetation dynamics and ecosystem biogeochemical cycling in NASA GISS's Earth system model (ModelE-BiomeE v.1.0)
We developed a demographic vegetation model, BiomeE, to improve the modeling of vegetation dynamics and ecosystem biogeochemical cycles in the NASA Goddard Institute of Space Studies' ModelE Earth system model. This model includes the processes of plant growth, mortality, reproduction, vegetation structural dynamics, and soil carbon and nitrogen storage and transformations. The model combines the plant physiological processes of ModelE's original vegetation model, Ent, with the plant demographic and ecosystem nitrogen processes that have been represented in the Geophysical Fluid Dynamics Laboratory's LM3-PPA. We used nine plant functional types to represent global natural vegetation functional diversity, including trees, shrubs, and grasses, and a new phenology model to simulate vegetation seasonal changes with temperature and precipitation fluctuations. Competition for light and soil resources is individual based, which makes the modeling of transient compositional dynamics and vegetation succession possible. Overall, the BiomeE model simulates, with fidelity comparable to other models, the dynamics of vegetation and soil biogeochemistry, including leaf area index, vegetation structure (e.g., height, tree density, size distribution, and crown organization), and ecosystem carbon and nitrogen storage and fluxes. This model allows ModelE to simulate transient and long-term biogeophysical and biogeochemical feedbacks between the climate system and land ecosystems. Furthermore, BiomeE also allows for the eco-evolutionary modeling of community assemblage in response to past and future climate changes with its individual-based competition and demographic processes