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Author: Leslie Goldman
© 2013 National Ecological Observatory Network, Inc. All rights reserved. The National Ecological Observatory Network is a project sponsored by the National Science Foundation and managed under cooperative agreement by NEON, Inc. This material is based upon work supported by the National Science Foundation under the following grants: EF-1029808, EF-1138160, EF-1150319 and DBI-0752017. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
For data, protocols, and more, visit www.neoninc.org
Integration of below-ground measurements in the NEON terrestrial observation system LF Stanish, CL Meier, E L-Hinckley, A Hoek-Spaans, C Flagg [email protected]
1 2 3
Coordinated Measurements of Critical Belowground Processes
Ø Belowground processes play a major role in nutrient storage and cycling in ecosystems and belowground biomass is a significant fraction of net primary productivity (NPP). Factors such as climate, ecological factors such as land use, and plant-microbe interactions mediate belowground processes in complex ways.
Ø The National Ecological Observatory Network (NEON) aims at quantifying belowground biomass across its continent-scale monitoring network by coordinating measurements through space and time, with the goals of improving models of belowground nutrient cycling and predicting long-term responses to climate and land use change.
At each site, NEON will measure: 1. Fine root biomass 2. Microbial biomass 3. N-transformation rates
Ø These measurements will complement more frequent measurements of plant and soil microbial community properties that are part of NEON’s Terrestrial Observation System.
Fine roots amount to an estimated 33% of global annual net primary productivity (Jackson 1997). Fine roots exhibit 1) fast turnover rates; 2) high surface area: volume ratios; and 3) relatively rapid decomposition rates. Complex feedbacks exist between fine roots, N availability, and microbial composition and abundances.
Methodologies Core sampling During NEON operation, fine root biomass will be measured from soil cores to a depth of 30cm. Currently, NEON is complementing this approach by characterizing fine root biomass distribution with depth at a large soil pit located at each site. The cumulative root proportion as a function of depth is determined (Fig 2). These data are used to constrain model estimates of belowground biomass. Soil pit sampling Ø A soil pit (2m deep and ~1.5m wide), is dug adjacent to the NEON instrument tower in the site’s dominant vegetation type. Ø Soil samples of a known volume are taken from three vertical profiles down the face at 10 cm intervals down to 1m and at 20cm intervals from 1 m to the final pit depth.
Fine Root Biomass
50 cm
Left, Sampling for fine roots from a 2 meter
deep “megapit” as part of the initial site
characterization at TREE, Wisconsin.
Right, root-washing station for separating fine root biomass from
soil particles.
photo by Avalon Hoek-Spaans
A Continental Scale Dataset
Beginning in 2017, NEON will operate an ecological monitoring network consisting of approximately 47 terrestrial and 34 aquatic sites for 30 years across the United States (Fig 2). Within a site, soil sampling plots are selected in the dominant vegetation type/s based on NLCD designations and field verification. Plots are located within the airshed of an instrument tower and soil instrument array (Fig 3), and are distributed across the site to capture spatial heterogeneity.
Ø In addition to informing NEON’s sampling design, all data will be available to the public.
Estimating Rooting Depth
Fig 2. Variability in soil rooting profiles as shown for 3 NEON sites. The cumulative proportion of root biomass as a function of soil depth is shown. Lower ß (beta) values indicate shallower rooting profiles, while higher ß values indicate deeper rooting profiles. The ß value is the non-linear least squares fit for ß using the equation Y=1-ßd (Gale and Grigal, 1987) where Y = cumulative root proportion, d = depth from the soil surface, and ß is the fitted parameter (Jackson et al., 1996).
Ø The rooting depth at each site helps determine what proportion of roots will be captured by NEON’s long-term monitoring protocol.
Ø A major goal of this initial effort is to develop a robust predictive model of ß as a function of independent state factors (Fig 5). The ability to accurately model the contribution of fine root biomass to NPP will reduce the need for costly excavations, and can aid in reducing uncertainty in modeled C stocks and fluxes.
References 1. Burton, AJ, Pregitzer, KS & Hendrick, RL. 2000. Relationships between fine root dynamics and nitrogen availability in Michigan northern hardwood forests. Oecologia 125, 389–399. 2. De Vries, et al. 2015. Disentangling plant and soil microbial controls on carbon and nitrogen loss in grassland mesocosms. J Ecol 103, 629–640. 3. Helmisaari, HS et al. 2002. Below- and above-ground biomass, production and nitrogen use in Scots pine stands in eastern Finland. Forest Ecol and Management 165, 317–326. 4. Jackson, RB, Mooney, HA & Schulze, ED.1997. A global budget for fine root biomass, surface area, and nutrient contents. PNAS 94, 7362–7366. 5. Jia, S. et al.2010. N fertilization affects on soil respiration, microbial biomass and root respiration in Larix gmelinii and Fraxinus mandshurica plantations in China. Plant and Soil 333, 325–336. 6. Nadelhoffer, KJ, Aber, JD & Melillo, JM. 1985. Fine roots, net primary production, and soil nitrogen availability: a new hypothesis. Ecology 66, 1377–1390. 7. Zak, DR, et al. 2003, Plant diversity, soil microbial communities, and ecosystem function: are there any links? Ecology 84, 2042–2050.
Fig 6. Prototype results showing relationships between soil microbial biomass and vegetation type and bacterial:fungal ratios.
0.80 0.85 0.90 0.95 1.00
0.80
0.85
0.90
0.95
1.00
Actual vs Predicted Beta
Measured Beta Value
Pred
icte
d Be
ta V
alue
Fig 5. Actual vs. predicted ß values for each soil pit. Predicted values were based on a most parsimonious model that included NLCD class + Climate Ratio (mean
annual precipitation/mean annual potential evapotranspiration) (R2adj=0.45)
Many critical belowground biogeochemical processes are either mediated by or influenced by microbes, particularly N-fixation and decomposition. The abundances and diversity of microbiota affect standing stocks of carbon in soil as well as respiration and nutrient cycling rates. Microbial biomass samples will be collected simultaneously with samples for microbial diversity and composition to more thoroughly characterize the quantity and composition of soil microbiota.
Method prototyping In summer of 2013, soil samples were collected from 2 sites in the Pacific Southwest Domain (D17), SOAP and SJER. Microbial biomass C and N were measured using the chloroform fumigation method, while bacterial and fungal concentrations were determined using qPCR. Results from this small-scale effort revealed differences in microbial biomass related to vegetation type and soil temperature (Fig 6). Also, bacteria:fungi ratios also varied by vegetation type. This methodology can enable NEON to detect meaningful relationships between microbial biomass and relevant ecological and environmental factors.
Nitrogen transformation rates NEON will use the soil core incubation method to measure net nitrification and mineralization rates. Prototyping efforts are planned for 2016 to test a draft protocol and ensure it can be properly scaled across all NEON sites.
Microbial Biomass and N-transformations
Microbial)biomass) Fine)root)biomass)
N)transforma2on)
3x/yr during peak biomass and
transi5onal ‘hot spots’
Fig 1. Overview of coordinated, belowground sampling. Spatial extent: 10 plots distributed across each NEON site. Temporal extent: Every five years. The timing and methodology represent a balance between adding field work requirements and budget constraints.
3x/yr with other biological
sampling
1x during peak
biomass
Fig 2. Map of NEON site locations. Fig 3. Diagram
showing general layout
of plots for terrestrial sampling.
Proportion of Fine Root Biomass at Depth
Depth (cm)
Fine R
oot B
iomas
s Pro
portio
n
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150
D03OSBS
0 50 100 150D09WOOD
0 50 100 150
D15ONAQ
WOOD, D09 ß=0.908
ONAQ, D15 ß=0.978
OSBS, D03 ß=0.966
forest grassland shrub
050
100
150
200
250
Microbial C
mg
C/k
g dr
y so
il
forest grassland shrub
05
1015
2025
Microbial N
mg
N/k
g dr
y so
il
forest grassland shrub
1520
2530
3540
4550
Soil Temperature
Soil
tem
pera
ture
, °C
forest grassland shrub
1015
20
Bacterial:Fungal Ratio
Bact
eria
l:fun
gal r
atio
