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A Radioisotope Based Methodology for Plant-Fungal Interactions in the Rhizosphere

A.G. Weisenberger, G. Bonito, S. Lee, J.E. McKisson, A. Gryganskyi, C.D. Reid, M.F. Smith, G. Vaidyanathan and B. Welch

Abstract- In plant ecophysiology research there is interest in studying the biology of the rhizosphere because of its importance in plant nutrient-interactions. The rhizosphere is the zone of soil surrounding a plant's root system where microbes (such as fungi)are influenced by the root and the roots by the microbes. We are investigating a methodology for imaging the distribution of molecular compounds of interest in the rhizosphere without disturbing the root or soil habitat. Our intention is to develop a single photon emission computed tomography (SPECT) system (PhytoSPECT) to image the bio-distribution of fungi in association with a host plant's roots. The technique we are exploring makes use of radioactive isotopes as tracers to label molecules that bind to fungal-specific compounds of interest and to image the fungi distribution in the plant and/or soil. We report on initial experiments designed to test the ability of fungal-specific compounds labeled with an iodine radioisotope that binds to chitin monomers (N-acetylglucosamine). Chitin is a compound not found in roots but in fungal cell walls. We will test the ability to label the compound with radioactive isotopes of iodine (125I, and 123I).

I. INTRODUCTION ECENTLY in plant ecophysiology research much attention has been focused on studying the biology of the rhizophere.

The rhizosphere is the zone of soil surrounding a plant’s root system where soil microbes are influenced by the root and the roots by the microbes. In this zone biological and chemical activity is driven by compounds exuded by or present in the root and consumed by specialized guilds of fungi and bacteria that inhabit or surround the roots. Root inhabiting fungi include mycorrhizal and endophytic species. Arbuscular mycorrhizal fungi and many root fungal endophytes grow intercellularly, while ectomycorrhizal fungi do not penetrate root cortical cells (see Fig. 1). These different modes of fungal-root structure are the product of independent origins of plant-fungal symbioses that began with the co-colonization of land by plants and fungi, and are integral to terrestrial carbon cycling. As important as the rhizosphere is to the functioning of terrestrial ecosystems it is still poorly characterized and understood. One of the main challenges to studying the

Manuscript received November 22, 2013. This work was supported in part

by the U.S. Department of Energy under contract DE-AC05-06OR23177.Support for this research came from, the DOE Office of Biological and Environmental Research.

A. G. Weisenberger, S. Lee, and J. McKisson are with the Thomas Jefferson National Accelerator Facility, Newport News, VA 23606 USA (telephone: 757-260-7090, e-mail: drew@jlab.org).

G. Bonito, A. Gryganskyi C.D. Reid and G. Vaidyanathan are with Duke University, Durham, NC, 27704 USA (telephone: 919-660-7363, e-mail: gmb2@duke.edu).

M. F. Smith is with University of Maryland School of Medicine, Baltimore, MD, 21201 USA (telephone: 410-328-1320, e-mail: msmith7@umm.edu).

B. Welch is with Dilon Diagnostics Inc., Newport News, VA, 23606 USA(telephone: 757-269-4910, e-mail: bwelch@dilon.com).

rhizosphere is the 3-D opaque nature of the soil environment. Another major challenge is that specific interactions occur at the micro-scale but individual fungi and roots can occupy large and irregular physical space in the soil (which is still poorly mapped).

Fig. 1. Fungi mycelium of Mortierella elongata (stained blue) surrounds and penetrates the roots of Arabidopsis (photo courtesy of Khalid Hameed).

Presently methods for visualizing microbe-root interactions involve removing the roots from the soil for inspection, using limited optical techniques that introduce transparent tubes into the soil (i.e. mini-rhizotrons) or growing plants in narrow transparent boxes [1]. A method is needed to quantify and image the biological interaction of plant root-fungal associations without disturbing the plant or soil so longitudinal studies can occur on the same plant and soil/microbe biological system. The method should interfere as little as possible with the status and functioning of the fungi and plant.

II. MATERIALS AND METHODS We are proposing to image the dynamic translocation and bio-distribution of plant and fungi molecular compounds of interest without disturbing the soil containing the root and fungi. Our method will make use of radioactive isotopes as tracers to label molecules that will bind to a fungal specific compound called chitin. We then intend to image their distribution in the plant and/or soil through the use of a gamma camera and ultimately with a SPECT system designed specifically for plant imaging (PhytoSPECT). The ability to detect the emissions of radioactive isotopes used as tracers or labels through radioactive decay (e.g. beta particles, x-rays and gamma-rays) has been used for over 80 years as a tracer method for studying natural phenomena. [2, 3 & 4]

Radioisotope-labeled compounds have been used to identify fungal infections in animal models and several papers have been published primarily from the same group [5, 6, 7 & 8]. Lupetti et al [9] reviews the use of nuclear imaging of fungal infections in mice and humans. The agents coupled to 99mTc were primarily antifungal agents that bind to fungi.

We are investigating the development of radioisotope labeled compounds which could be imaged through the soil. We made

R

use of a gamma camera manufactured by Dilon Diagnostics Inc., which manufactures a gamma-ray breast imager using technologies developed by the group and under license from 1Thomas Jefferson National Accelerator Facility. Though the Dilon detector was designed for breast imaging we were able to establish feasibility and practices that would be applicable to imaging single photon emitter radiotracers in plants. Currently, we are developing a gamma imager that is more adapted to plant biological studies than current gamma cameras. To explore the use of a gamma camera we imaged the uptake of 99mTc pertechnetate (TcO4) in phantom studies and in live plants similar to methods reported by others [10, 11 & 12]. Preliminary scattering and attenuation tests with different growth media were performed using capillary phantoms filled with 99mTc pertechnetate. The attenuation and scattering of the140 keV gamma rays through 10 cm of dry soil, water and wet (saturation) soil were compared to air. To obtain wet soil dry soil was placed in a container then fully saturated with water. By using a strainer, excess water was drained from the soil until no more water dripped that is, soil water saturation. In Fig. 2 are shown photographs of the experimental setup using five 99mTc filled capillary tubes (1 mm OD and .75 mm ID) arranged at separations of 8, 12, 20 and 24 mm. A 10 cm thick container was placed between the gamma camera face and the capillaries such that different soils could be tested.

Fig. 2: Photograph of 10 cm thick soil container and capillary phantom. Tests were performed with a Dilon Diagnostics Inc gamma camera constructed with high sensitivity, low-resolution parallel hole collimators (15 cm x 20 cm) mounted to a NaI(Tl) scintillator pixellated into 2.9 mm square pixels with 3.2 mm pitch. Nominal resolution for these detectors is 3.2 mm FWHM at the surface of the detector face. 99mTc was introduced as anaqueous solution to the soil surface in two studies involving an ivy plant and a tomato seedling. To test our fungal imaging methodology our plan is first to conduct a number of in vitro experiments to test the binding ability and fungal impact of a radioactively labeled compound that will bind to chitin. Chitin is a long-chain polymer [(C8H13O5N)n] found in fungi cell walls but not present in plants. In a paper by Siaens et al [13] chitin is described as a target molecule for ChiB_E144Q, a variant of chitinase B. They tagged ChiB_E144Q with 123I and determined its biodistribution in live mice by imaging. The paper by Brurberg [14] describes how they formulated ChiB_E144Q. The company Sigma-Aldrich (www.sigmaaldrich.com) supplies compounds that could be used to indicate the presence of chitin. For instance Sigma-Aldrich sells wheat germ agglutinin lectin

that binds to N-acetylglucosamine chitin monomers. Deshmukh et al [15] report use of this lectin to stain chitin.

We are undertaking several in vitro studies with and without fungi prior to performing an imaging study. The planned in vitro studies include: labeling lectin with 125I, binding studies of [125I]-lectin to chitin, soil [125I]-lectin interaction studies and [125I]-lectin binding to soil and rhizosphere fungi. We report here on our initial results with labeling lectin with 125I.

III. RESULTS Phantom TestsImages, count rates and energy spectra were measured for 99mTc passing through a 10 cm thickness of air, water, dry soil and wet soil. With the photopeak amplitude at 140 keV normalized to one for air, photopeak amplitude was 0.91 for dry soil, 0.58 for wet soil and 0.47 for water. Energy spectra for the four cases are shown in Fig. 3.

Fig. 3. Energy spectra for 99mTc for four different media demonstrating attenuation and scattering effect.

The qualitative effect of scattering on images of the capillary phantom for the four cases is clearly shown in Fig. 4

Fig. 4. Profiles of the images obtained of the 99mTc filled capillaries.

Plant Studies In two separate manipulations, the uptake of 99mTc was measured on seedlings of ivy and tomato. The initial activity of 99mTc was 185 MBq and 370 MBq for the seedlings of ivy and tomato, respectively. Through water uptake from the soil medium and water transport along a water potential gradient in the plant, 99mTc moves upwards to leaves as shown in Fig. 5.

Fig. 5. Projection image showing uptake of 99mTc and co-registered with a photograph of the ivy seedling (left). Photograph of a tomato seedling in front of the gamma detector with parallel hole collimator (middle). A montage of the tomato seedling projection images in time slices of 20 minutes in length is shown at the right. The translocation of 99mTc from the soil to the plant by water flow during the first 160 minutes is shown. Most of the activity remained in the pot.

Fig. 5 shows the results from a 2-hr uptake study. On the left is shown an overlay of an optical photograph and the image of radiotracer activity in the stem of ivy. The center image shows the tomato seedling and in the rightmost frame a montage of the tomato seedling projected images in 20-minute time slices is shown, confirming the ability of this non-optimized system to measure the uptake rate due to water transport. Fig. 6 shows the results for a tomato seedling after 24-hr.

Fig. 6. Photograph of tomato seedling in soil in front of the gamma camera while being imaged, an image showing uptake of 99mTc and the same images co-registered. Resulting image shown is after completion of a 24-hour study. In Fig. 6 the potted tomato seedling is shown positioned in front of the Dilon 15 cm x 20 cm camera. The photograph and image of the radiotracer are shown separately at the left and center, while the rightmost frame shows a co-registered image. During the first 2 hours, most of the activity is in the container and the soil as shown in Fig. 5 however the distribution of the radioactive label throughout the plant shown in Fig. 6 is clearer 24-hr after activity administration and shows well the transport of ions from the soil into the plant through the soil-plant-atmosphere continuum. The root ball is imaged through the soil and pot. Lectin Labeling From preliminary experiments, 200 µl of a 1 mg/ml solution of wheat agglutinin lectin was labeled with 125I using Iodogen. Radiochemical yield was 65% and radiochemical purity 94%. The 125I –labeled lectin will be used for in vitro binding assays as a function of purified chitin concentration

IV. DISCUSSION We have outlined our strategy to develop a non-destructive methodology to allow the imaging of plant-fungal interactions in the rhizosphere in natural soils. We have obtained gamma-ray attenuation and scattering imaging results. Once we understand the in vitro binding performance through basic scintillation counting we can move to imaging studies using 125I

and/or 123I with a prototype gamma camera. The higher energy emissions and shorter half life of 123I (159 keV, t1/2 = 13.3 hours) compared with 125I (~28-35 keV, t1/2 = 59.4 days) may be more appropriate for dense soils such as sand. We intend to experiment with different in vivo (in soil) protocols to facilitate the non-destructive visualization of fungal activity in the rhizosphere.

REFERENCES [1] Plant Physiology, Fifth Edition by Lincoln Taiz and Eduardo

Zeige, 2010. [2] G. Hevesy and F. Paneth, “The solubility of lead sulphide and lead

chromate,” Z. Anorg. Chem. 82: 322; 1913. [3] G. Hevesy, “The absorption and translocation of lead by plants,”

Biochemical Journal 17:439–445. 1923. [4] A. Benson and M. Calvin, “The Dark Reductions of

Photosynthesis,” Science, vol. 105, no. 2738, pp. 648 –649, Jun. 1947.

[5] A. Lupetti, E. K. J. Pauwels, P. H. Nibbering, and M. M. Welling, “99mTc-antimicrobial peptides: promising candidates for infection imaging,” Q J Nucl Med, vol. 47, no. 4, pp. 238-245, Dec. 2003.

[6] A. Lupetti, M. M. Welling, E. K. J. Pauwels, and P. H. Nibbering, “Detection of fungal infections using radiolabeled antifungal agents,” Curr Drug Targets, vol. 6, no. 8, pp. 945-954, Dec. 2005.

[7] A. Lupetti, M. M. Welling, U. Mazzi, P. H. Nibbering, and E. K. J. Pauwels, “Technetium-99m labelled fluconazole and antimicrobial peptides for imaging of Candida albicans and Aspergillus fumigatus infections,” Eur. J. Nucl. Med. Mol. Imaging, vol. 29, no. 5, pp. 674-679, May 2002.

[8] M. M. Welling, R. Visentin, H. I. J. Feitsma, A. Lupetti, E. K. J. Pauwels, and P. H. Nibbering, “Infection detection in mice using 99mTc-labeled HYNIC and N2S2 chelate conjugated to the antimicrobial peptide UBI 29-41,” Nucl. Med. Biol., vol. 31, no. 4, pp. 503-509, May 2004.

[9] A. Lupetti, M. G. J. de Boer, P. Erba, M. Campa, and P. H. Nibbering, “Radiotracers for fungal infection imaging,” Med. Mycol., vol. 49 Suppl 1, pp. S62-69, Apr. 2011.

[10] G. C. Krijger, A. V. Harms, R. Leen, T. G. Verburg and B. Wolterbeek, “Chemical forms of technetium in tomato plants; TcO4−, Tc–cysteine, Tc–glutathione and Tc–proteins, Environmental and Experimental Botany, vol. 42, no 1, pp 69-81, August 1999.

[11] Keiko Tagami, Shigeo Uchida, “Comparison of transfer and distribution of technetium and rhenium in radish plants from nutrient solution,” Applied Radiation and Isotopes, vol. 61, no. 6, Pages 1203-1210, December 2004.

[12] M. Simonoff, T. V. Khijniak, C. Sergeant, M. H. Vesvres, M. S. Pravikoff, E. Leclerc-Cessac, G. Echevarria, S. Denys, “Technetium species induced in maize as measured by phosphorimager,” Journal of Environmental Radioactivity, vol. 70, nos.1-2, Pages 139-154, 2003.

[13] R. Siaens, V. G. H. Eijsink, R. Dierckx, and G. Slegers, “(123)I-Labeled chitinase as specific radioligand for in vivo detection of fungal infections in mice,” J. Nucl. Med., vol. 45, no. 7, pp. 1209-1216, Jul. 2004.

[14] M. B. Brurberg, I. F. Nes, and V. G. Eijsink, “Comparative studies of chitinases A and B from Serratia marcescens,” Microbiology (Reading, Engl.), vol. 142 ( Pt 7), pp. 1581–1589, Jul. 1996

[15] S. Deshmukh, R. Hückelhoven, P. Schäfer, J. Imani, M. Sharma, M. Weiss, F. Waller, and K.-H. Kogel, “The root endophytic fungus Piriformospora indica requires host cell death for proliferation during mutualistic symbiosis with barley,” PNAS, vol. 103, no. 49, pp. 18450-18457, Dec. 2006

A Method for Characterization of PhytoPET in Plant Growth Media

S. Lee, A. G. Weisenberger, and M. F. Smith

Abstract–A positron emission tomography (PET) system (PhytoPET) designed specifically for plant biology imaging is being developed for use at the Duke University Biology Department Phytotron. The system has a modular design to accommodate various shapes and sizes of plants and plant structures. The target isotope, 11C in 11CO2 gas, is absorbed by the leaf through photosynthesis then converted to sugars, and translocated to other parts of the plant. A large fraction of positrons from 11C can escape from thin leaves without annihilation, while in the root a large fraction of positrons annihilate because of surrounding materials such as water or soil. Since the PhytoPET system can be used for imaging both leaves and roots, it is required to characterize system performance with various surrounding materials. A capillary tube phantom was designed and fabricated to allow placement within different absorbing media such as air, water, and soil. We report on sensitivity and spatial resolution measurements of the PhytoPET system using this phantom.

I. INTRODUCTION

HOMAS Jefferson National Accelerator Facility, Duke University, and the University of Maryland at Baltimore

are collaborating on the development of radionuclide imaging technologies to facilitate plant biology research. We have reported earlier on plant PET radiotracer studies utilizing a Duke University detector system and a small two-headed prototype PET system used for plant studies at the at Duke University Biology Department Phytotron [1]. By utilizing the Triangle Universities Nuclear Laboratory tandem Van de Graaff accelerator to generate 11C, plant researchers are able to have 11CO2 gas piped to a plant environmental growth chamber in the Phytotron. Presently, we have been developing a new PET detector system, PhytoPET, that utilizes a novel PET system arrangement to achieve plant PET imaging. Unlike an animal or human PET scan, in which there is usually sufficient electron density near the positron emission site for an annihilation event to occur, an appreciable fraction of emitted positrons may escape the plant tissue such as the leaf and stalk without annihilation. Near the root, water and soils are dense enough for gamma ray attenuation and scattering which may cause degradation of overall image quality and/or inaccurate quantification results. Since the PhytoPET system is designed for imaging the leaf, stalk, stem,

Manuscript received November 15, 2013. The Jefferson Science Associates (JSA) operates the Thomas Jefferson National Accelerator Facility for the United States Department of Energy under contract DE-AC05-06OR23177. Support for this research came from the DOE Office of Biological and Environmental Research, the DOE Office of Nuclear Physics grant DE-FG02-97ER41033.

S. J. Lee and A. G. Weisenberger are with Jefferson Lab, Newport News, VA, USA, (telephone: 757-269-5476, e-mail: sjlee@jlab.org).

M. F. Smith is with the University of Maryland, Baltimore, MD, USA, (telephone: 410-328-1320, e-mail: msmith7@umm.edu).

and root, imaging performance for each target region will be different. It is desirable to develop a methodology suitable for characterizing the imaging performance in each part of the plant.

II. METHODS To characterize imaging performance of the PhytoPET, we

designed a phantom with capillary tubes that is imaged while it is surrounded by air, water, or wet/dry soil. As depicted in Fig. 1, a cross shaped holder was designed and fabricated to hold capillary tubes at regularly spaced intervals. The separation between holes on each arm is 2, 3, 4, and 5 mm, respectively. The height of holder is 6 cm and the diameter of bottom plate is 5 cm which is similar to the size of a PhytoPET module field of view (FOV) of 4.8 x 4.8 cm2. The inner diameter of the capillary tube is 0.55 mm and the length is 75 mm. A 60 mm length of each capillary tube was filled with 18F-fluorodeoxyglucose (FDG) in an aqueous solution providing 0.014 ml total volume in each tube. The phantom has only upper and lower holders and the middle section empty so that there is no positron annihilation due to the plastic in this region. A total of 12 capillary tubes were filled with 18F solution, sealed at the ends and inserted into the phantom. The total activity was about 400 µCi at the start of each scan. The phantom was attached to the bottom of the container (10 cm diameter and 0.8 mm wall thickness) in which water, dry soil, or wet soil was poured. For the wet soil sample, soil was saturated with water and then excessive water was removed by draining. The volume of water in the container was about 65 % in volume after draining. The container was placed at the center of PhytoPET system then a 5 minute scan was performed for each sample.

Fig. 1. A photograph of the calibration phantom (left). Spacings between

holes are 2, 3, 4, and 5 mm, respectively. The phantom was attached to a plastic container (middle) to hold the growth media. The container with the phantom was filled with soil (right) then placed at the center of PhytoPET system for imaging.

Eight PhytoPET modules in a ring arrangement (45° apart) were used for the scans. As shown in Fig. 2, two Jefferson Lab field programmable gate array (FPGA) based 16 channel flash ADC (EFADC-16) data acquisition (DAQ) units were used to digitize gamma events from the detectors. Details of the DAQ

T

system are described in a previous report [2]. The field of view (FOV) of the setup is a cylinder approximately 48 mm in diameter and 48 mm tall. A maximum likelihood expectation maximization (MLEM) reconstruction method was performed with a voxel size of 0.5 mm3 and a 0.6 mm full width at half maximum (FWHM) Gaussian smoothing filter. FWHM was measured as a function of spatial position. System sensitivity for the different surrounding media was measured using both reconstructed image and count rate after energy thresholding (511 keV ± 5 %).

Fig. 2. A photograph of the experimental setup. Two EFADC-16 units were used to digitize 8 PhytoPET detector modules. Each module is based on a H8500 PSPMT coupled with a pixelated LYSO crystal.

III. RESULTS

Fig. 3 depicts a 3D reconstruction of the phantom surrounded by air. The image shows clear separation of all capillary tubes except tubes with 2 mm spacing. From the vertical slice image (c), however, we can identify tubes with 2 mm spacing even though there was overlapping. Images with water and dry/wet soil (not shown in here) showed similar results. The slice thickness of each image was 0.5 mm.

(a) (b) (c) (d)

Fig. 3. Three dimensional reconstruction image (a) and slice image (b) of the phantom in the air. Vertically sliced images of the phantom (c)(d) shows each capillary tube of the phantom. Spacing between tubes were 2, 3, 4, and 5 mm, respectively.

Fig. 4 shows 0.5 mm thickness slice image of the phantom in the air and vertical/horizontal line profile along with capillary tubes. Line profiles with 3 mm, 4 mm, and 5 mm spacing show clear identification of each tube. An averaged FWHM of the peak was about 3 mm for all media. The center capillary tube shows maximum activity mainly due to sensitivity modeling error. More accurate modeling such as depth of interaction, accurate detector geometric parameters, and flood correction is required to achieve uniform activity for all capillary tubes.

Fig. 4. Line profiles for horizontal-A (middle, with 2 mm and 4 mm spacing) and vertical-B (right, with 3 mm and 5 mm spacing) selection of phantom in the air. An averaged FWHM of each peak was about 3 mm.

Fig. 5 shows slice images of reconstruction for sensitivity

comparison with the same color scale. Due to attenuation/scattering by surrounding media, overall count rates were different. Maximum count rate was achieved with air and minimum count rate with water. The dry soil sample does not attenuate 511 keV gamma ray significantly but the wet soil sample attenuates gamma rays as much as water. This result confirms that though excessive water was removed from the soil after filling with water and draining, a large amount of water was held by the wet soil. Therefore, it is required to measure water concentration in the soil for accurate quantitative PET imaging of roots in the soil.

Fig. 5. Axial slices of reconstruction images surrounded by air, water, dry

soil, and wet soil (from left to right). Overall image qualities are similar while count rates are varying by surrounding media. Images are on the same color scale.

Fig. 6 shows raw and normalized energy spectra for each

sample. The 511 keV peak shows significant attenuation for water and wet-soil samples. Relative peak heights to the air sample were 0.85, 0.6, and 0.5 for dry soil, wet soil, and water, respectively. The raw energy spectra confirm similar attenuation effect from water and wet soil. Normalized energy spectra show scattering of 511 keV gamma ray which introduce broad spectral increase at lower energy region resulting peak down shift of about 5 keV.

Fig. 6. Comparison of energy histogram for samples is shown. Raw count

rate (left) shows attenuation due to dense media. Normalized count rate (right) indicates an increased count rate at lower energy region and resulting peak shift (about 5 keV).

IV. CONCLUSION We have tested the PhytoPET system with a capillary tube

phantom with various surrounding media: air, water, dry soil, and wet soil. The system with 8 detector modules shows clear 3D images of the phantom in all sample media without

noticeable image degradation. The estimated FWHM of capillary tube was 3 mm. There was significant attenuation by water and wet soil. The soil itself does not attenuate as much as water, but it can hold enough water to introduce attenuation. Since most of root imaging is performed without media/soil removal, attenuation correction for the reconstruction is required for accurate quantification imaging.

REFERENCES [1] M. R. Kiser, C. D. Reid, A. S. Crowell, R. P. Phillips, and C. R. Howell,

“Exploring the transport of plant metabolites using positron emitting radiotracers,” HFSP J, vol. 2, no. 4, pp. 189–204, Aug. 2008.

[2] S. Lee, H. Dong, J. McKisson, J. E. McKisson, A. G. Weisenberger, W. Xi, C. R. Howell, C. D. Reid, and M. F. Smith, “Ethernet-based flash ADC for a plant PET detector system,” in 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012, pp. 1320–1322.

 

About The Ecological Society of America The Ecological Society of America (ESA) is a nonpartisan, nonprofit organization of scientists founded in 1915 to:

• promote ecological science by improving communication among ecologists; • raise the public’s level of awareness of the importance of ecological science; • increase the resources available for the conduct of ecological science; and • ensure the appropriate use of ecological science in environmental decision making by

enhancing communication between the ecological community and policy-makers.

Ecology is the scientific discipline that is concerned with the relationships between organisms and their past, present, and future environments. These relationships include physiological responses of individuals, structure and dynamics of populations, interactions among species, organization of biological communities, and processing of energy and matter in ecosystems.

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ESA’s over 10,000 members conduct research, teach, and use ecological science to address environmental issues that include:

• biotechnology • natural resource management • ecological restoration • ozone depletion and global climate change • ecosystem management • species extinction and loss of biological diversity • habitat alteration and destruction • sustainable ecological systems

ESA publishes a suite of publications, from peer-reviewed journals to newsletters, fact sheets and teaching resources.

 

“From Oceans to Mountains: It’s All Ecology” That’s right! Ecology is everywhere. Whether we are exploring the depths of the ocean, arid desert communities, or frigid mountaintops, we find abundant ecological interaction among organisms and environment. These fascinating relationships abound in every setting. California is an especially interesting setting for studying ecology. It has all these and more! Its 160,000 square miles is a center of extraordinary biodiversity and endemism, containing more plant and animal species and more endemic species than any other state in the United States. Its biological richness is a consequence of its physical complexity from the Pacific Ocean to the high Sierra Nevada Mountains, distributed along a 1000 mile distance from north to south that creates widely varying local bioclimatic conditions overlaid on the strong regional Mediterranean climate with mild wet winters and hot dry summers and its highly varied edaphic conditions. California may be seen as an ecological island separated from the rest of the continent by its high mountains and deserts. Our theme emphasizes the inherent ecological diversity of the state, fitting well between the theme of the 98th Annual Ecological Society of America Meeting’s emphasis on learning from the past and the 100th Annual Meeting in 2015 which will develop a blueprint to shape the future.

Numerous research programs of California universities have focused on soil and marine microbial communities in recent years. This complements the traditional studies of the mid-20th

century where growth responses were examined from sea level to the timberline by more traditional methods, leading to breakthroughs in our understanding of many principles of ecological adaptation. For decades, California has led the U.S. in water conservation and clean water and clean air initiatives, in promoting alternative energy use and in recent years promoting initiatives to reduce greenhouse gas emissions 80% by 2050. For ecologists, Sacramento is well located in the heart of California’s biodiversity in Central Valley, between the Pacific Ocean and the interior deserts, the Coast Ranges and the Sierra Nevada Mountains.California’s cultural diversity parallels its ecological and physical diversity. California is a true melting pot of global cultures, with waves of immigration from other states and countries, starting from the earliest history of Spanish exploration in 1535 by Hernando Cortes to its gold rush in the 1850s, and statehood in 1850. Today it is a state of 40 million people so ethnically diverse that no single group forms a majority of the population and it is the 8th largest economy in the world. California culture is exceedingly dynamic and known for its innovation, new technologies and

free spirits, but also for recombining ideas from its many cultures into creative new forms.Sacramento, a city of 175,000 people and the state capital of California, is an excellent venue for ecologists to address the challenges of preserving biota and diversity in the presence of land use changes and urban pressures. Founded 164 years ago, Sacramento had few trees, but today it is known as the “tree city” with the largest urban forest in the U.S., planting 30,000 new trees between March 2012 to March 2013 to

improve its urban climate by capturing carbon, stormwater and air pollution. Sacramento is the site where the 1850s gold rush began and lies at confluence of the Sacramento and American Rivers along the northern edge of the Sacramento-San Joaquin Delta, the largest estuary on the Pacific coast of North and South America. Sacramento is also at the hub of California’s extensive and diverse agricultural economy, the largest in the U.S.—home to at least 250 commercial crops that provide more than half of the fruits and vegetables for the country.