Lesson 32 Mineral Cycling - Alaska Geobotany Center

Lesson 32
Mineral Cycling
• Essential plant nutrients
• Gaseous and sedimentary cycles
• Compartments of nutrients
• Transfer of nutrients into and out of ecosystems
• Time scales of cycles
• Abiotic vs. biotic factors in nutrient cycling
• Examples from grassland and forest ecosystems
• Greenhouse gases
– CO 2
flux
– Nitrogen saturation
• Homeostatic mechanisms for nutrient retention
– Resorption
– Nutrient Use Efficiency (NUE)
• Hubbard Brook LTER site: example of acid rain and potassium
cycles
• Focus on nitrogen and CO 2 fluxes with examples from major
watershed studies.

Essential plant nutrients
• Nutrients can be
deficient,
adequate, or
toxic.
Micronutrients

Micronutrients

Biogeochemistry
• Refers to the transfer or flux of materials back and forth between living
and nonliving components of the biosphere.
• Nutrient Cycling is the movement of the materials that are essential
to organisms.
• Cycling within the system is often an order of magnitude faster than
movement into or out of the system.
• Others (P, K, Ca, Mg, Fe, micronutrients) move in sedimentary
cycles.
• Gaseous materials (N, O, C, H) are involved in gaseous cycles.
Some, such as S, have both sedimentary and gaseous cycles.
• Much of the current focus in plant ecology is on the nitrogen cycle
and flux of greenhouse gases to the atmosphere.

A sedimentary cycle: the phosphorus cycle
• Marine sediments and
volcanic apatite are the
source of P in phosphate
rocks and soils.
• P is taken up by plants as
H 2 PO - 4 or HPO -2 4 , where it
becomes a component of
energy-carrying phosphate
compounds (ATP and ADP),
nucleic acids, several
essential coenzymes, and
phospholipids.
http://arnica.csustan.edu/carosella
/Biol4050W03/figures/phosphoru
s_cycle.htm
• Chemical erosion has
reduced P 2 O 5 content of
midwest soils by 36% in the
last 50 y.
Odum and Odum 1959

Ecosystem pools and fluxes of potassium at
Hubbard Brook
• In the 1960s and 1970s Bormann and
Likens worked out the biogeochemistry
of potassium, a very easily leached
element in forests at Hubbard Brook.
• K is the most abundant cation in
throughfall at HBEF, representing 33%
of the total during the growing season.
• K is added to the system through wet
and dry deposition, where it enters the
available pool directly or is washed into
the soils through the forest canopy.
Weathering is another important input.
• K is moved within the system
(intrasystem cycling) by throughfall,
stemflow, nutrient uptake, plant
assimilariotn and use, resorption and
biological decomposition.
• K departs the system through the
dissolved fraction and particulate
fraction in streams.
• The ecosystem is thus connected to
the larger biogeochemical cycles by
meteorologic, geologic, and biologic
vectors that move nutrients across
ecosystem boundaries.
Modified from Likens et al. 1977. Biogeochemistry of a Forested Ecosystem.

Hubbard Brook LTER site: whole
watershed manipulations
Watershed 2 (lower photo, foreground) was clear
felled (no vegetation was removed) and treated
with herbicide. This first watershed manipulation
at Hubbard Brook was undertaken to evaluate
the role of forest vegetation in regulating the
hydrologic and element output of a northern
hardwood forest.
Watershed 4 (lower photo, background) was
harvested in three successive 25m strips from
1970 to 1974 to assess the effects of strip
cutting on water yield and nutrient input-output
budgets.
Watershed 5 (right photo) was whole-tree clear-cut
during the autumn of 1983 through the spring of
1984. This watershed manipulation was
designed to assess the effects of a commercial
whole-tree harvest on nutrient cycles.
Courtesy of LTER web site: http://lternet-183.lternet.edu/

Monitoring stream flow at Hubbard Brook
Stream discharge is monitored at nine
watersheds throughout the the Hubbard
Brook Valley. At the bottom of each
watershed, the stream flows into a
concrete stilling basin and over a V-notch
weir, where the stage height is measured
continuously. This is the weir at
Watershed 1.

Atmospheric inputs of nutrients and
pollutants
Rain gauge and dry and wet deposition collectors
at Hubbard Brook LTER site.
Courtesy of Hubbard Brook web site: www.hubbardbrook.org/yale/,
• Cloud chemistry of various sites.
• Sites in the East show elevated
concentrations of hydrogen ion,
nitrate, sulfate.
From Gilliam, F.S. 1989. Enviornment in Appalachia
Proceedings, 4th Annual Conference on Appalachia

Acid rain at
Hubbard Brook
• Precipitation chemistry has been monitored
since the late 1960s, when scientists noticed the
unusually low pH, between 4.0 and 4.2 (5.6 is
normal for rain).
• Since 1965 rain water has been collected in
containers which are located throughout the
watersheds. The samples are collected weekly
and brought back to the lab where pH values
are measured and then entered into the longterm
database.
• Although pH has been rising steadily since the
Clean Air Act was passed in 1970, the
precipitation is still quite acid, and has effects on
other components of the ecosystem, such as
calcium levels.
Courtesy of Hubbard Brook web page: www.hubbardbrook.org/education/SubjectPages/AcidRainPage.htm

Calcium addition experiment
at Hubbard Brook
• In October 1999, calcium silicate - in a
mineral form known as "wollastonite" was
applied to all of Watershed 1 in an
experiment designed to replace the
calcium that has been washed out of the
soil by acid rain.
• A helicopter was used to apply forty-five
tons of wollastonite to the watershed,
increasing the levels of soil calcium to
those believed to exist before acid
precipitation began falling on the forest.
• Over the next 50 years (this is a VERY
long experiment!) scientists will
investigate the response of major
ecosystem processes, including stream,
soil, and soil water chemistry; forest floor
mass and chemistry; composition and
structure of the forest, aquatic ecology;
leaf chemistry; soil microorganism activity,
and ultimately tree growth
Courtesy of Hubbard Brook web page: www.hubbardbrook.org/education/SubjectPages/AcidRainPage.htm

Adding ground
glacial rocks to
remineralize soils
• John Hamaker, a farmer in Michigan,
started a movement to remineralize
the Earth by spreading glacial dust
over declining forests and croplands.
What started as a “fringe”
movement has gained scientific
support through large programs in
Europe to spray ground rock over
forests declining from acid rain.
http://www.remineralize.org/about/context.html

Soil lysimeter to collect water for chemical
analysis
• Open pit containing partially installed
zero-tension lysimeters.
• Researchers dig a large whole in the
ground and install lysimeter cups into the
uphill side of the pit, as shown here.
Eventually, all the tubing is connected
and the pit is filled back in.
• When it rains, water filters through the
soil (uphill of the pit), enters the cup, and
travels through a tube (dotted line) to a
buried (barely visible) "reservoir," which
collects the sample.
• Approximately once a month technicians
visit these sites and, using a hand pump,
empty the reservoirs using the "sampling
tube." The end of the sampling tube is
the only part of the lysimeter that is
above ground.
Courtesy of Hubbard Brook web page: www.hubbardbrook.org/education/SubjectPages/AcidRainPage.htm

Trends in aboveground nutrient pools and biomass following
disturbance at HBEF
Watershed 2*
recovery following
treatment
* clearcut and herbicide treatment
** control 55-yr old
W.A. Reiners. 1992. Ecol. Monogr. 62: 503-523
Percent compared to
Watershed 6**
• Once suppression of vegetation with
herbicideds ceased, W2 displayed
vigorous recovery.
• Ca, N, S, K, Mg, and P all increased
along with biomass.
• Ca increased linearly, and had the
greatest absolute increase in any element.
This reflects the structural nature of Ca in
plants.
• Rates of N and K increase declined over
time.
• S, P, Mg showed slow asymptotic growth.
• Comparison with Watershed 6 (control),
shows that K, P, and Mg have much
higher relative rates of accumulation,
probably because they are needed first in
regenerating canopies, while S, Ca, and
N are more important for the woody
trunks and branches and will likely play a
larger role later in the succession.

Essential plant nutrients
• Nutrients can be
deficient,
adequate, or
toxic.
Micronutrients

Trends in potassium storage in plants and
resorption of K over time at Hubbard Brook
Rate of storage of K in living and dead biomass
(mol ha -1 yr -1 ) and net soil release of K in
Watershed 6 (control watershed at HBEF)
Estimate of resorption of K in Watershed 6.
• Potassium is a very mobile ion that is
lost from the system through leaching
if it is not captured by biomass.
• Net soil release of K and storage of K
in biomass declined markedly over 27
years in Watershed 6 (control). In
1987-1992 biomass assimilation of K
was less than 17% of that in 1965-
1977.
• Concomitant with decline in rates of
biomass assimilation, K in throughfall
and biomass storage of K declined.
• More of the available K was resorbed
from leaves before they senesced and
leaching of K declined.
Likens, et al. 1994. Biogeochemisty 25: 61-125. Kluwer Academic Publishers

Nutrient supply in a coastal dune community
Bulk deposition and rainfall
• Primary nutrient source is from salt spray (8 times the
mineral ions of rain water.) Note the differences in the
salt-spray input of the fore dunes vs. lee side (e.g., for Ca,
80 vs 19 kg ha -1 yr -1 ).
• Calcium input is 35 kg ha -1 yr -1 , compared to 10.5 kg ha -1
yr -1 for an inland forested site.
• Much more Ca is retained in the more dense vegetation
on the lee side of the dune.
• In the sandy soils of the dunes, much of the calcium is
quickly leached away. (Note: more calcium is leached out
than arrived in the salt spray, indicating that CaCO 3
is
leaching from the sea-shell fragments in the dune.
• Turnover times are very short, 11-37 days for K, Na, and
Mg, and 32-206 days for Ca, reflecting the input from the
dissolved shells.
• There is no storage of nutrients in the sandy soils of the
dunes.

The carbon cycle: example of a gaseous cycle
Drawing by Terry Chapin
• 100% of carbon comes
from the atmosphere.
• Enters the system
through carbon fixation
in autotrophs (plants,
algae, cyanobacteria,
green and purple
photosynthetic bacteria).
• Portion of Gross Primary
Production (GPP) is
converted back to the
atmosphere through
respiration leaving Net
Primary Production
(NPP).
• Part of organic carbon
that is not respired is
available to heterotrophic
consumers.
• Part becomes
incorporated in the soil.

Soil respiration for mixed hardwood forest at
Harvard Forest, MA
Soil carbon flux rate, g m -2 yr -1 (%)
• Soil respiration
accounts for most
of the CO 2
released to the
atmosphere.
• Respiration is
from living roots,
and
decomposition of
aboveground and
belowground litter.
• The total
respiration for the
forest is 371 gm -2
yr -1 . Nearly two
thirds of this is
from root activity
(belowground
litter and root
respiration).
From Bowden et al. (1993)

Recalcitrant organic substances: Two-phase
decomposition model of John Aber et al.
(1990)
Mass
N-concentration
• Decomposition of organic material involves easily decomposed nitrogen-rich
materials (Phase 1) and recalcitrant lignin-rich material (Phase 2). Phase 1
includes about 80% of the total mass.
• Data above are from a paper birch foliage decomposing in a hardwood forest at the
Harvard forest LTER site.
J. Aber, 1990.

Decomposition of litter material by soil invertebrates and
evolution of forest mull soils
Brauns 1968. Cited in Walter, H. and Breckle, S.W. 1986. Ecological Systems of the Geobiosphere. Springer-Verlag.

Reasons for focus on greenhouse gases
Courtesy EPA website
• CO 2 ,CH 4 ,andN 2 O are all greenhouse
gases that trap long-wave radiation (heat)
emitted from the surface of the Earth. This
energy would otherwise be radiated to
space. The added heat affects the global
energy budget, and global climate.
• Anthropogenic influence has increased
both N and C to the level of atmospheric
pollutants.
• Nitrogen is the primary growth limiting
nutrient in many if not most plant
communities. It also limits recovery
following disturbance. It is, therefore,
important to study N in conjunction with C
(see slide of Terrestrial Ecosytem Model).
• Nitrogen-saturated ecosystems can
become sources (not sinks) of nitrogen,
causing:
– Nitrous oxide (a greenhouse gas) flux to
the atmosphere and
– Nitrate eutrophication of streams.

Greenhouse Gases
Total Greenhouse Gas
Emissions (ppm) in 1995
Courtesy EPA website
• CO 2 in the atmosphere is increasing at
rate of 1.78 ppm per year. Preindustrial
CO 2 concentrations were 276 ppm and
are now 360 ppm.
• Methane (CH 4 ) is increasing at an
annual rate of 0.9%, and has nearly
doubled in the past century from 0.9 to
1.72 ppm. CH 4 traps 21 times more
heat per molecule than CO 2 .
• Nitrous oxide (N 2 O) also participates in
the destruction of stratospheric ozone,
which is affecting the increase in UV
radiation. NO 2 is increasing at the rate
of 2.5% per year. NO 2 traps 270 times
more heat per molecule than CO 2 .
• Potential benefits of rising CO 2
concentrations include stimulation of
photosynthesis, crop growth and water
use efficiency.
• Improved biomass production may not
be experienced by all natural
ecosystems. Limitations of soil nitrogen
and increases in soil respiration may
offset or restrict biomass gains
stimulated by additional carbon dioxide
(see earlier slide).

Estimated current and future carbon fluxes
in the terrestrial biosphere
Sampson et al. (1993)
• Tundra and boreal forests appear to be a
net sink of carbon to the atmosphere
(absorbing carbon in biomass and peat
formation).
• Tropical forests are strong source
(releasing C in respiration and forest
burning).
• Currently, it is unclear whether the
terrestrial biosphere is a net sink or
source of carbon to the atmosphere.
• Doubling of CO 2 will most likely result in
the biosphere being a larger net source.
• The Kyoto accord and other international
efforts are aiming at reducing the flux of
carbon to the atmosphere, partly through
vegetation management or vegetation and
energy management (Columns C and D).

Monitoring Greenhouse Gas Fluxes: First ISLSCP (International Satellite Land
Surface Climatology Project) Field Experiment (FIFE): Konza Prairie LTER site
The Konza tall-grass prairie site near Manhatten, Kansas.
• The FIFE project was a large-scale climatology project conducted
from 1987 through 1989 at the Konza Prairie LTER site to
understand the biophysical processes controlling the fluxes of
radiation, moisture, and carbon dioxide between the land surface
and the atmosphere and to develop remote-sensing
methodologies for observing these processes.
• The remote-sensing data were used to determine surface energy
budgets, soil moisture and vegetation parameters, surfaceatmosphere
fluxes, and atmosphere properties. Surfaceatmosphere
exchanges and atmospheric boundary layer models
were used to more completely understand the dynamics
measured in the FIFE study.
• Numerous flux experiments have followed FIFE including several
in Alaska (e.g., FLUX and ATLAS in the Arctic)
• The scaling up of measurement involves measuring fluxes with
small chambers, eddy correlation flux towers, and aircraft.
Measurements of the spectral properties of the earth surface are
made with hand-held, aircraft-mounted, and satellite-mounted
spectrometers.

• Carbon balance models, despite
their flaws, provide us with the
capacity to interpolate and
extrapolate measurements in time
and space. Hence, they are and
will be a key tool for making
regional and global assessments of
the carbon balance.
• Most data for testing ecosystem,
regional and global carbon models
stems from long term monitoring of
carbon dioxide concentrations and
biomass .
• The Ameriflux network was
established in 1996 to provide
continuous observations of
ecosystem level exchanges of CO 2 ,
water, and energy, spanning diurnal,
synopitc seasonal and intrannual
time scales.Continuous monitoring
of large areas with towers is the
primary method. Chambers are
used for detailed studies of small
patches.
• At present, 40 to 60% of the
anthropogenically-released CO 2
remains in the atmosphere. We do
not know, with confidence, whether
the missing half of emitted CO 2 is
being sequestered in the deep
oceans, in soils or in plant biomass.

AmeriFlux Objectives
Generally:
• Establish an infrastructure for guiding, collecting,
synthesizing, and disseminating long-term
measurements of CO 2 , water, and energy exchange
from a variety of ecosystems.
• Collect critical new information to help define the
current global CO 2 budget
• Enable improved predictions of future
concentrations of atmospheric CO 2
• Enhance understanding of carbon fluxes, Net
Ecosystem Production (NEP), and carbon
sequestration in the terrestrial biosphere.
Specifically:
• Share data and the science plan.
• Quantify magnitude of net annual CO 2 exchange in
major ecosystem/biome types (natural and
managed)
• Determine response of CO 2 fluxes to changes in
environmental factors and climate changes
• Provide information on processes controlling CO 2
flux and net ecosystem productivity
• Provide site-specific calibration and verification data
for process-based CO 2 flux models.
• Address scaling issues (spatial and temporal).
• Quality control and quality assure data collection.

Flux towers used by Walt Oechel at Barrow
and La Paz
Photos courtesy of Walt Oechel

FLUXNET: Integrating worldwide
CO 2 measurements
FLUXNET builds on regional networks of
tower sites:
• South and North America (AmeriFlux);
• Europe (CarboEurope);
• Asia (AsiaFlux);
• Australia and New Zealand (OzFlux);
• Korea and Thailand (KoFLux);
• Canada (Fluxnet-Canada);
• Independent tower sites.

Another gaseous cycle: the nitrogen cycle
5
N 2
1
4
7
6
Nitrogen
fixation
3
2
1. Nitrogen is taken up from the soil by plants in
theformofNH 4 + or NO 3 - , where it is used to
form organic compounds (amino acids,
proteins, nucleic acids).
2. It returns to the soil via litter, which is
decomposed to form ammonia. This process
of decomposition is also called nitrogen
mineralization.
3,4. The ammonia is oxidized in a two step
nitrification process to form nitrates
(NO 3 - ),which are an available form of N for
plant uptake.
5. NO 3 - -N can also be converted back to the
gaseous NO, N 2 O, and N 2 , through the
process of denitrification. The atmospheric
store of N is about 1 million times larger than
the total N in living organisms.
6. Nitrogen-fixation transforms atmospheric
N 2 into ammonia (NH 3 ) , which is also an
available form of N for plant uptake.
7. NO 3 - is also easily leached from the soil.
Courtesy of Michael Pidwirny and Jim Deacon web sites
http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm
http://www.physicalgeography.net/fundamentals/9s.html

Carbon and nitrogen cycling in terrestrial ecosystems are
tightly linked: Terrestrial Ecosystem Model
From McGuire, Melilllo, and Joyce 1995
Carbon
• C enters the vegetation pool (C v ). as
gross primary production (GPP).
• Transfers either to the atmosphere as
autotrophic plant respiration (R A )orto
the soil pool ( C S ) as litter (L C ).
• Leaves the soil pool as soil
heterotrophic respiration (R H ).
Nitrogen
• N enters the vegetation pool (N V )from
the inorganic N pool of the soil (N AV )as
NUPTAKE.
• Transfers from the vegetation to the
organic soil pool (N S ) in litter production
as the flux (L N ).
• Net nitrogen mineralization (NETNMIN)
accounts for nitrogen exchanged
between the organic and inorganic
nitrogen pool of the soil through
decomposition.
• NINPUT and NLOST are the inputs
and outputs of N to and from the
system.
Other nutrients are linked to this cycle as
they become needed for
photosynthesis, metabolism, or
structural plant tissues.

Relationship between production and N
uptake in temperate and boreal forests
• Strong linear relationship
between N-uptake and total
production.
From Cole and Rapp (1981)

Litter bags and dowels for measuring decomposition rates
Litter bag data containing Andropogon gerardii from Konza Prairie, (Seastedt 1988).
Litter bags as part of the LIDET experiment.
• Litter bags are mesh bags that allow entry of decomposers. The bags contain a known weight
of a plant.
• The LIDET (Long-term Intersite Decomposition Experiment Team) is examining long-term
Carbon and Nitrogen, and Phosphorus Dynamics of Leaf and Fine Root Litter in North
American ecosystems.
• The experiment involves 28 sites, 10 types of standard litter (leaves, stems, roots), 10
replicates each, and wide array of biomes, and will last 10 years.
• Data above from Konza Prairie shows rapid loss of mass during first 203 days, leaving the
more recalcitrant material. The apparent increase in N is due to microbial and fungal
additions.
Litterbags
Wooden dowels placed as part of the LIDET
experiment. Photos courtesy of
http://www.fsl.orst.edu/lter/research/intersite/lidet/lidet_met
h/lidet.htm
Litter bags in High Arctic on Banks Island.
Photo courtesy of G. Gonzalez

Global budget of N 2 O–N (Tg)
• Estimated annual increase in
nitrous oxide (N 2
O) is about 3.5 x
10 12 g (3.5 Tg).
• Note the discrepancy between total
sources and total sinks and
accumulation, which is due mostly
to the large uncertainty factors.
• Major causes of increased N 2
O are
tropical forest clear-cutting.
• Tropical forests circulate more
nitrogen at higher concentrations
than do most boreal or temperature
forests and exhibit high N 2
O fluxes.
• Deforestation in the Amazon basin
has cleared at least 230,000 km 2 of
tropical forest by 1990.
Matson and Vitousek 1990

Summary of effects of nitrogen saturation in
forested ecosystems
• Even though Clean Air Bill intended to
improve air quality, total N deposited in NE
US will remain high for many years,
exceeding forest outputs, resulting in N
saturation, i.e. a net export of N from the
system into streams and the atmosphere.
• Diagram is a summary of forest nitrogen
biogeochemistry trends along a gradient of
increasing N saturation.
• Foliar N content increases across the full
gradient.
• N-mineralization and NPP increase and then
decline.
• Ca:Al and Mg:N ratios decline along the full
gradient.
Increasing N saturation
HFHW: Harvard forest hardwood
HFP: Harvard forest pine
BBW: Bear Brook stand
Ascutney: Mount Ascutney transect
Transect: 161 spruce-fir stands across NE US.
• Nitrification and N-leaching increase from 0
to high values along the gradient.
• Consequences include increased emission
of N 2 O, stream eutrophication, declining tree
vigor, and potential loss of frost hardiness in
conifers.

Summary
Aspects of nutrient cycling
– Gaseous (e.g., Carbon and Nitrogen cycles) and sedimentary cycles (e.g., Potassium
cycle).
– Nutrients are compartmentalized into (a) rocks and soils, (b) soil solution, ( c) the
atmosphere, and (d) biomass.
– Transfer into or out of the system can be via meteorologic, geologic, or biologic
events.
– Time scales of cycles can require minutes, decades, or millennia to revolve. Biological
cycling within systems is much more rapid than abiotic cycling.
– Abiotic factors include fire, earth movement, and aspects of the hydrologic cycle
(deposition, leaching, evapotranspiration, runoff, infiltration).
– Biotic factors include litter production, organic matter accumulation, decomposition,
ingestion and digestion, gas flux, root exudation, and retrieval of nutrients from deep
soil layers through roots.
– Stability of systems often depend on a variety of homeostatic mechanisms to retain
nutrients in the sytem, including resorption (ability to withdraw nutrients from plant
parts that senesce to avoid loss of nutrients in litterfall), high nutrient use efficiency
(high rate of production per unit of nutrient), large storage pools within the system
(such as large standing crop of trees), and immobilization of nutrients (e.g., in
decomposer microorganisms, and plants to prevent leaching.
– The carbon and nitrogen cycles are tightly linked because plant tissues have high
demand for nitrogen. Production is often limited by the availability of nitrogen.
– Acid rain affects mineral cycles through lower soil water pH, which leaches nutrients
from the soil. Nitrogen saturation occurs from enhanced inputs of N in rain water and
dry deposition and leads to stream eutrophication.
– Increases in greenhouses gases including CO 2
, NH 4
,N 2
O, and water vapor are of
major concern because of possible effects on global climate.

Summary (cont )
Measurement of nutrient pools and fluxes
– Measurement of nutrient pools and fluxes requires a great variety of tools including
wiers to measure quantity and chemistry of stream waters, dry and wet deposition
collectors to measure atmospheric inputs, lysimeters to measure chemistry of soil
water, litter collectors to measure quantity of litter, litter bags and buried wooden
dowels to measure decomposition rates, and harvest and mineral analysis of
biomass to determine the nutrients in the vegetation.
– Measurement of CO 2
, NH 4
, and N 2
O fluxes requires large coordinated efforts to
simultaneously study climate, fluxes of trace gases at multiple scales, and monitor
ground-surface changes through remote sensing studies.
– The Hubbard Brook studies are an excellent example that has fully studied the biotic
and abiotic aspects of nutrient cycling, focusing on potassium, calcium, and nitrogen
cycles.
– AmeriFlux and FIFE are examples of the large interdisciplinary efforts to study
greenhouse gases.