David M. Eissenstat - US grants

Natural ecosystems are dynamic, not static. For instance, plants themselves alter properties of soils and ecosystems. Thus, the characteristics of different plant species influence important ecosystem functions such as soil fertility, soil development and plant productivity, and thus in part control ecosystem functioning. The specifics of these controls, however, are very poorly understood due to difficulties in separating effects of climate or soils from those of vegetation. To explore the way in which plants can influence their own environment, we will utilize a unique common-garden experiment of 32-year old monoculture stands with 14 temperate tree species in Poland. This is the only such experiment in the world. The proposed research will compare and contrast leaf and fine root traits and their effects on ecosystem by examining: above- and belowground tissue physiology, structure and productivity, litter decomposition and soil chemistry and development.

Temperature is a major constraint on mycorrhizal root metabolism in many environments. In cold climates, temperatures in the spring restrict root metabolism and nutrient acquisition. In the summer in temperate and tropical climates, unshaded soils may reach temperatures that cause excessive carbohydrate metabolism unless root acclimation occurs. The central objective of this proposal is to examine how latitude of origin affects plant root and mycorrhizal fungal respiratory responses to soil temperature. These investigators will use phylogenetically independent contrasts (contrasts using distinct evolutionary lineages) to permit general inferences on plant and mycorrhizal fungal responses to temperature as a function of latitude of origin. The research will focus on four, interrelated hypotheses associated with organism response to temperature. Does diurnal temperature variation affect an organism's ability to acclimate to temperature? Under conditions of no acclimation, do plants and mycorrhizal fungi from higher latitudes exhibit higher respiration than those from lower latitudes when measured at the same temperature? Under conditions where acclimation occurs, do plants & mycorrhizal fungi from high latitudes exhibit less acclimation to high temperature (i.e., excessively metabolize carbohydrates) than those from lower latitudes? Are the independent mycorrhizal fungal or plants respiratory responses to temperature the same when the organisms are measured in symbiosis? The use of multiple, distinct evolutionary lineages of both fungi and plants will provide new insight into how organisms respond globally to both average temperatures and temperature variation.
This work has several opportunities for broader scientific impacts. Global climate change is an area of intense interest to both scientists and government policy makers. The Intergovernmental Panel on Climate Change predicts a 1.4-5.8 degree C increase in global surface temperature by 2100, using atmospheric models that assume increases in atmospheric CO2 will lead to increases in ambient temperature, which increases soil respiration, causing a positive feedback. Mycorrhizal root respiration represents the dominant source of soil respiration in many soils. If mycorrhizal roots acclimate to increases in temperature, than predicted increases in surface temperatures may be overestimated.
There will also be several opportunities to enhance scientific training. At the undergraduate level, students will be involved in the project in several meaningful ways, including learning how to culture mycorrhizal fungi and assess their colonization on roots, growing plants and measuring the respiration of roots and fungi using a gas-exchange system that requires an understanding of data loggers, gas analyzers and gas flow meters and controllers. The postdoctoral fellow will also have opportunities to become trained both in root and mycorrhizal fungal physiology and participate in a field project with a foreign graduate student in Poland.

Despite its importance, variation in root lifespan among species and in response to changes in the environment is poorly understood. Relatively few species have been examined and rarely have multiple species been compared in a common environment. The work proposed will examine the root lifespan of 12 tree species that vary widely in root diameter, root tissue density and potential growth rate using state-of-the-art approaches. Trees were transplanted as 1-yr-old seedlings in replicated plots in a common garden approximately nine years ago. Variation in root lifespan will be related to plant potential growth rate, root structure (specific root length, diameter, tissue density) and root N concentration. Do roots and leaves share parallel suites of traits commonly associated with their lifespan? Three hypotheses are proposed that attempt to explain what controls and constrains root lifespan: the "Starch depletion hypothesis" (SDH), the "Resource optimization hypothesis" (ROH) and a new hypothesis proposed here, the "Metabolic activity hypothesis" (MAH). The Starch depletion hypothesis assumes that a finite amount of stored carbohydrates (starch) is deposited at root formation and that the rate the carbohydrates are depleted by root respiration determines the lifespan of the root. The Resource optimization hypothesis assumes that root lifespan is optimized to provide the greatest benefit in terms of water and nutrients for the least cost (usually measured in carbon) over the lifespan of the root or cluster of roots. The Metabolic activity hypothesis suggests that root lifespan is mainly governed by metabolic rate; roots with higher respiratory activity live shorter lives than those with lower respiratory activity.
Three experiments are proposed to distinguish which hypothesis best explains patterns of root lifespan. One experiment involves creating fertile patches which do not become depleted. These patches should increase the efficiency of nitrogen acquisition and also increase metabolic rate. If root lifespan is increased in the patch, then ROH is supported. If root lifespan is decreased then either SDH or MAH is supported, depending on how quickly the roots die in relation to their starch reserves. Respiration and nonstructural carbohydrates (including starch) of the roots of the different species will be examined as a function of root age in another experiment. A final experiment examines the importance of current photosynthate on root lifespan of 1st-order roots by pulse-labeling carbohydrates with 13C.
This study will have several broader impacts. A better understanding of root lifespan will be valuable to those attempting to model ecosystem carbon cycles. Many of the trees examined in this study are forest dominants in eastern hardwood forests. Better understanding of their root lifespan will be useful to forest managers as well as investigators of climate change. This study will provide strong support for the training of two graduate students and several undergraduates each year. In addition, the Eissenstat lab has a track record of attracting under-representative minorities to conduct summer research, partly because of the generous support and well-defined programs at Penn State provide a quality summer research experience, including payment of 75% of program costs for the students enrolled in this 8-week summer research program.

Abstract
OISE-0754731
David Eissenstat, Penn State

Forests are substantial reservoirs of soil organic matter and are globally significant in the absorption of Carbon; yet changes taking place in forests today and in the future threaten to perturb the Carbon balance of these ecosystems. For example, the identity of dominant tree species in temperate forests is being altered by human-driven changes in climate, fire regimes, and pest or pathogen outbreaks. Very little is known about how these alterations in tree species composition will impact the dynamics of soil organic matter.

This proposal addresses fundamental questions and hypotheses regarding soil organic matter formation and recalcitrance. In combination with on-going, complementary analyses of soil organic matter properties at the Polish common garden, this proposal?s Carbon-13 nuclear magnetic resonance studies are well positioned to provide new insights regarding the impacts of chemical diversity of plant litter on soil organic matter sources and dynamics.

Broader impacts: One application of the results of the work would be to use variation in litter chemistry among tree species to predict the impacts of shifts in tree species composition on soil organic matter dynamics in forests. Accurate estimates of forest Carbon budgets are critical to efforts in the U.S. and abroad to manage Carbon, including trading of Carbon credits and sales of Carbon offsets. By conducting this research with Dr. Ingrid Kögel-Knabner (Technical University of Munich), the U.S. research group will establish new relationships between U.S. and European institutions and enable the utilization of two highly specialized techniques, including physical soil fractionation and Carbon-13 nuclear magnetic resonance spectroscopy.

Forest soils contain more carbon than the entire atmosphere and thus the exchange of carbon dioxide between forest soils and the atmosphere can influence the global carbon cycle and climate change. Changes taking place in forests today, including shifts in the identity of dominant tree species and exotic earthworm species invasions, threaten to perturb the carbon balance of these ecosystems. Unfortunately, the effect of these two disturbances on forest soil carbon storage is largely unknown. The intent of this proposal is to study the influence of tree species and earthworms on soil carbon storage at a unique field experiment in Poland, where 14 different tree species were planted more than 35 years ago. At this site, tree species are known to differ with respect to the earthworm populations they support and other qualities that could influence soil carbon, including leaf and fine root characteristics. The research put forth in this proposal will relate these known species differences to new studies of soil carbon dynamics using advanced molecular and isotopic analytical tools.

By defining clear relationships between tree species, earthworms, and soil carbon storage, the consequences of changing tree species composition and earthworm invasions on the carbon balance of forests can be better understood. This information could be used to manage the species composition of U.S. forests for the purpose of carbon sequestration, facilitating participation in economic and political pursuits aimed at carbon management and climate change mitigation.

Linking Belowground Phenology and Ecosystem Function in a Warming Arctic ? Non-technical abstract (E. Post, PI)
This project comprises a four-year, passive warming experiment of low-Arctic tundra vegetation at a long-term study site in Greenland, with the primary aim of measuring the response of plant roots to warming, and the role of this response in ecosystem carbon exchange. Phenology, the annual timing and progression of events such as aboveground plant growth, is a well-studied an important component of the ecology of climate change, but remains under-studied belowground. This study will estimate and compare above- and belowground responses of plant phenology to warming and their respective contributions to ecosystem function, specifically the exchange of carbon between the atmosphere and tundra. It will furthermore determine which plant types, e.g., shrubs or grasses, show the greater belowground response to warming and contribution to ecosystem carbon exchange.
Novel insights into the expected response of the Arctic to climate change will emerge from this experiment, which will also expand the infrastructure for field-based experimental and observational research in the Arctic. This research will promote the involvement of under-represented groups by recruitment of students through Penn State?s Minority Undergraduate Research Experience program, and promote education and dissemination of its results through a summer field ecology module at the study site and in courses at Penn State and the University of Alaska-Anchorage. Results will also be published in peer-reviewed journals and presented at international conferences by participating students and the Principal Investigators.

Root traits that influence nutrient foraging in different plants are poorly understood. In most plants, roots form a symbiotic association with mycorrhizal fungi that may improve the ability of the plant to forage for nutrients. However, species differ in the extent that mycorrhizae can benefit nutrient uptake, and this is likely related to root morphology, including root diameter and root hair abundance. The PIs hypothesize that tree species with coarse roots with few or short root hairs forage in nutrient-rich patches by relying heavily on mycorrhizal fungi, while tree species with more rapidly growing roots that produce many long root hairs forage for nutrients by proliferating their roots, increasing root hair development and altering the rate of nutrient uptake. The project will be primarily conducted in a 14-year-old planting of 16 different tree species that vary widely in root morphology, although additional studies will be conducted in natural forest stands and in growth chambers. This study will improve the theoretical basis by which plant roots can be used for calculating the influence of vegetation on elemental cycles, improve predictions of vegetation responses and feedbacks to climate change, and increase the understanding of roots needed for better management of crops and trees for food and fiber. There will be a strong educational component to this research, including the training of three graduate students, undergraduate training in research and international exchanges of students and scientists.

An Accomplishment-Based Request for Renewal of the Susquehanna - Shale Hills Critical Zone Observatory (SSHO)

With funding from the NSF Critical Zone Observatory (CZO) program, CZO workers led by PI Susan Brantley and coInvestigator Chris Duffy (Pennsylvania State University) will focus on cross-disciplinary synthesis, data sharing, and outreach at the Susquehanna Shale Hills CZO. Established originally in the 1970s as a site to study water flow in forested catchments, the 8-hectare Shale Hills watershed was expanded in 2007 as a CZO to understand broader questions targeting the interplay of water, energy, atmospheric gases, biota, soils, and the land surface. In addition to the small Shale Hills catchment, the CZO includes a suite of satellite sites that overly the same bedrock type (shale) but which are situated in different climate regimes. One additional satellite site is located on organic-rich Marcellus shale. These satellites allow researchers to understand how climate and organic content control water flow and soil formation while working with minority-and undergrad-serving institutions. CZO researchers are investigating i) new methodologies to model the age and chemistry of water as it moves from the atmosphere to groundwater; ii) new techniques to synthesize measurements of soil moisture for incorporation into land-atmosphere models; iii) observations that constrain water, energy, and solute fluxes related to trees; iv) models that quantify how soil grows on shale; v) new uses of isotopes to measure soil formation; and vi) observations concerning how variables describing characteristics at depth such as the fracture distribution in bedrock combine with features at Earth's surface such as the sunniness of hillslopes to control the evolution of soils and hillslopes over time. Datasets of isotopes, chemistry, soil moisture, CO2 and energy flux, LiDAR, sapflux, and other observables collected at high spatial and temporal resolution are published online. Outreach activities include community education about natural gas development on shale and K-12 educational opportunities.

This award will partially support students to participate in a workshop aimed at scaling belowground processes to larger spatial and temporal realms. The workshop is primarily supported by the Department of Energy and will include approximately 25 speakers from as far away as Australia, China and Europe. Speakers will address both empirical studies and modeling of roots and belowground processes and part of the goal is to bring these two groups together to improve terrestrial carbon cycle models in the context of climatic change. Moreover, the influence of climatic change on soil carbon fluxes, on which roots have a major influence, is one of the greatest uncertainties in terrestrial ecosystem models. Students will participate in several ways. In most sessions, slots are reserved for a graduate student to speak; invitations will result from a competition of abstract submissions. Strong abstracts not chosen for oral presentation and that help balance workshop subject areas will be chosen for posters. This proposal leverages other support by providing an opportunity for 10 graduate students to participate either in oral or poster presentations. Students also will be included in small breakout groups that will enable them to interact closely with leaders in the field and provide fresh perspectives to perplexing areas in
ecosystem ecology. The workshop opportunities will be advertised openly on listserves and also at the participating universities.

This workshop will provide opportunities for 10 students to interact with leaders in the fields of ecosystem, landscape and global modeling science, along with root, microbial and soil ecologists. Students will experience firsthand how interdisciplinary science is conducted and play key roles in discussions of new directions for scientific inquiry.

The Critical Zone (CZ) is the zone between the upper branches of trees and the depths of groundwater. Humans are changing this zone at geologically unprecedented rates. Maintaining ecosystems will require the ability to project the future of the CZ. Only with concerted efforts to measure and model the landscape will it be possible to make forward projections or "earthcasts" of the CZ.

In the Susquehanna Shale Hills Critical Zone Observatory (CZO), scientists are working to earthcast the CZ by modeling aspects of the atmosphere, land surface, biota, soil, rocks and water. In addition, the models will eventually incorporate impacts of human activity. These models for water, energy, sediment, and solute (WESS) fluxes will be used to project changes spanning from 10^-3 y (water) to 10^6 y (soil). For the sedimentary rocks underlying the CZO, the models will be used to explore how the geological past has impacted today?s land surface, and, in turn, how this structure contributes toward controlling today's water and gas fluxes.

The central focus of the CZO is the forested Shale Hills watershed (~0.1 km2) but investigations will include the multiple-landuse Shavers Creek watershed (165 km2). These nested watersheds will comprise the expanded Susquehanna Shale Hills Observatory (SSHO). This upscaling will force a transition from measuring "everything everywhere" to measuring "only what is needed" in a larger watershed with multiple rock types and land use. The CZO will be used to test the over-arching hypothesis: To project CZ evolution into the future requires knowledge of geological history, observations of CZ processes today, and scenarios of human activities tomorrow.

An important focus of the CZO will be to transfer knowledge to nonCZO scientists and to the public. For example, the CZO will develop hydrological models for two PA watersheds in the region of drilling and hydrofracking for shale gas in western and northern Pennsylvania. The public will also be engaged through a "CZO Four Seasons" music concert, where Penn State musicians will create a music score from many years of watershed data at the CZO.