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

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 fruit–frugivore 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 fruit–frugivore 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

Scaling from individual trees to forests in an Earth system modeling framework using a mathematically tractable model of height-structured competition

The long-term and large-scale dynamics of ecosystems are in large part determined by the performances of individual plants in competition with one another for light, water, and nutrients. Woody biomass, a pool of carbon (C) larger than 50% of atmospheric CO2, exists because of height-structured competition for light. However, most of the current Earth system models that predict climate change and C cycle feedbacks lack both a mechanistic formulation for height-structured competition for light and an explicit scaling from individual plants to the globe. In this study, we incorporate height-structured competition for light, competition for water, and explicit scaling from individuals to ecosystems into the land model version 3 (LM3) currently used in the Earth system models developed by the Geophysical Fluid Dynamics Laboratory (GFDL). The height-structured formulation is based on the perfect plasticity approximation (PPA), which has been shown to accurately scale from individual-level plant competition for light, water, and nutrients to the dynamics of whole communities. Because of the tractability of the PPA, the coupled LM3-PPA model is able to include a large number of phenomena across a range of spatial and temporal scales and still retain computational tractability, as well as close linkages to mathematically tractable forms of the model. We test a range of predictions against data from temperate broadleaved forests in the northern USA. The results show the model predictions agree with diurnal and annual C fluxes, growth rates of individual trees in the canopy and understory, tree size distributions, and species-level population dynamics during succession. We also show how the competitively optimal allocation strategy - the strategy that can competitively exclude all others - shifts as a function of the atmospheric CO2 concentration. This strategy is referred to as an evolutionarily stable strategy (ESS) in the ecological literature and is typically not the same as a productivity-or growth-maximizing strategy. Model simulations predict that C sinks caused by CO2 fertilization in forests limited by light and water will be down-regulated if allocation tracks changes in the competitive optimum. The implementation of the model in this paper is for temperate broadleaved forest trees, but the formulation of the model is general. It can be expanded to include other growth forms and physiologies simply by altering parameter values