2006-2011 mission kearney foundation of soil science

2006-2011 Mission Kearney Foundation of Soil Science: Understanding and Managing Soil-Ecosystem

Functions Across Spatial and Temporal Scales Final Report: 2007033, 1/1/2009-12/31/2009

1University of California, Davis

2Michigan State University

3University of Texas, Austin

*Principal Investigator

For more information contact Dr. Valerie Eviner ([email protected])

Spatial and Temporal Dependence of Plant Effects on Soils across Multiple Scales: Building Mechanistic Understanding to Enhance Management Options

Valerie Eviner*1, Kevin Rice1, Carolyn Malmstrom2, Mary Cadenasso*1 and Christine Hawkes3

Project Background

A comprehensive understanding of vegetation impacts on soil properties and processes, and how

these vary over spatial and temporal scales, is a critical tool for ecosystem management.

Management-induced shifts in plant community composition can have marked impacts on almost

every soil process and property (reviewed in Wardle 2002, Eviner and Chapin 2003).

Furthermore, manipulations of vegetation composition are one of the most effective approaches

for managing multiple soil properties and functions (e.g. resistance to erosion, the capacity to

absorb and retain water, storage and cycling of carbon (C) and nutrients) (Lavelle 2000, Eviner

and Chapin 2001, Drinkwater 1999, Rhoades 1997, Coleman et al. 2001). Documenting the

multiple effects of plant species on soils provides an “ecological toolbox” (Sarrantonio 1994,

Ingels et al. 1998, Eviner and Chapin 2001), allowing managers to select species based on the

multiple services they provide, and to understand the consequences of management-induced

shifts in vegetation. This toolbox can be invaluable in sustainable agriculture, restoration, and

bioremediation.

Existing species toolboxes are based on the average effect of species on soil properties and

processes. Scientific focus on broad-scale generalizations provides a “one size fits all” solution

which is at odds with a manager’s need to provide key soil functions under variable conditions

across space and through time. The effects of a given plant species or community on soils can

vary greatly depending on landscape context (e.g. environmental conditions, management

practices, time, neighboring communities, interaction with other organisms). Ecological

management needs a framework that allows for decision making based on site-specific

conditions—shifting the focus from the average towards incorporating spatial and temporal

variability.

Spatial and Temporal Dependence of Plant Effects on Soils Across Multiple Scales: Building Mechanistic Understanding to Enhance Management Options—Eviner

2

Project Objectives Addressed

This project focuses on understanding the ecosystem effects of the prevalent species in

California grasslands, particularly focusing on:

- “Annuals”- invasive annual species that have dominated California grasslands for the

past two to three centuries and are now naturalized (e.g. Avena sp., Bromus sp.,

Lolium multiflorum)

- “Natives”- native grassland species, including short-lived species (e.g. Vulpia

microstachys, Bromus carinatus, Lupinus bicolor), and long-lived perennial

bunchgrasses (e.g. Nassella pulchra, Elymus glaucus, Leymus triticoides)

- Invasive “Weeds”- more recent annual grass invasions that are noxious weeds and are

currently displacing the previous invasive “annuals” in many areas. These species

Aegilops triuncialis, Taeniatherum caput-medusae) can decrease range productivity

50-80%.

Within and across these groups of species, our objectives included:

1. Determine the impacts of California grassland species on multiple soil processes and

properties. To what extent are species effects on different soil processes related or independent?

Are there likely tradeoffs and synergies in using plant species to provide multiple ecosystem

services?

Soil properties and processes include:

1. Carbon

- plant net primary productivity (aboveground and belowground)

- soil C by depth

- soil organic matter by depth

2. Soil cohesion (an indicator of surface erosion control)

3. Nitrogen

- total soil N

- net N mineralization and nitrification rates

- seasonal resin available N

- N leaching loss (on a subset of plots)

4. Soil water

- infiltration

- water holding capacity

- leaching loss (on a subset of plots)

- soil water content and/or potential

- potential of hydraulic lift

2. Determine how plant species effects on multiple soil processes and properties change over

space and time.

a. Spatial variation

- by soil depth

- across sites (differing in soil, aspect, microclimate, management history,

etc.)


3

b. Temporal variation

- daily (hydraulic lift)

- seasonal

- annual (fluctuations due to weather, etc.)

- with time since establishment of a community (trajectory of change over

years)

c. Environmental variation- manipulation of key variables that aid in

understanding fluctuations across space and time

- amount and timing of grazing/clipping

- N additions

- precipitation manipulations

Approach and Procedures

A suite of experimental and observational plots were studied to assess the impacts of vegetation

composition on multiple soil processes and properties. These include:

1. Experimental plantings of a native grass, dominant annual grasses (naturalized exotics)

and a mix of the two groups. At Hopland Research and Extension Center’s lysimeter facility,

we planted lysimeter tanks (38cm dia x 70 cm depth) with: Nassella pulchra (native perennial

bunchgrass), two dominant annual exotic grasses (Aegilops triuncialis, Taeniatherum caput-

medusae), and a mix of the native and exotics (8 replicates of each).

2. Experimental plantings of monocultures and mixtures of natives, exotic annual grasses,

and newer invasive annual weeds. On the campus agricultural fields, we planted 1.5 x 1.5 m

plots with:

Monocultures of the following species:

Exotic annuals (naturalized):

- Avena fatua

- Bromus hordeaceus

- Lolium multiflorum

- Trifolium subterraneum

Invasive weeds:

- Aegilops triuncialis

- Taeniatherum caput-medusae

Natives:

- Bromus carinatus

- Elymus glaucus

- Leymus triticoides

- Lotus purshianus

- Lupinus bicolor

- Nassella pulchra

- Vulpia microstachys


4

In addition, we planted each of the above groups as monotypic mixes, and in all 2- and 3-way

combinations. These group plantings were exposed to clipping treatments (none, fall, spring) and

N fertilization (none, 45 kg N/ha/yr). (All plots- monocultures and mixtures will be exposed to

precipitation manipulations—but these treatments were delayed during this project’s duration,

due to rain shelter damage in a storm). There are 8 replicates of each treatment.

3. Observational studies across the landscape of areas restored with native species vs. adjacent

unrestored areas (dominated by annual exotic grasses). Across Yolo County, we sampled 11

native grassland restoration sites of varying ages, and adjacent unrestored areas.

4. Observational studies across the landscape of areas dominated by invasive weeds vs. those

dominated by naturalized annual exotics. Across the Willow Slough Watershed in Winters,

CA, we sampled 30 sites that were invaded by Aegilops and/or Taeniatherum, and adjacent

sites dominated by long-term annual exotics (e.g. Avena, Bromus, Lolium).

Measurements

1. Carbon

- Net primary productivity (aboveground and belowground) - clipping from

aboveground rings, and root cores down to 30 cm (experimental plots) and 100

cm (observational plots)

- Soil C by depth- Incremental soil sampling (0-15 cm, 15-30, 30-45, 45-60, 60-

90 depths) for bulk density and soil %C

- Soil organic matter by depth- combustion method

2. Soil cohesion (an indicator of surface erosion control)- using a torsional sheer vein tester on

the soil surface (and for experimental approach #1, with depth)

3. Nitrogen

- total soil N- %N and bulk density by depth (see depth increments for C)

- net N mineralization and nitrification rates- week-long aerobic incubations (0-

15 cm depth for all plots, additional samples at 15-30 cm depths in

experimental plots)

- seasonal resin available N- in experimental approach #2, placed at 5-10cm

depth

- N leaching loss- in plots from experimental approach #1—lysimeter leachate was

collected after each rainfall and analyzed for N

4. Soil water

- infiltration- disk infiltrometer for experimental approach #1, double-ring

infiltrometer for others

- water holding capacity- lab assay for soil at same depth increments as for C


5

(above)

- leaching loss in plots from experimental approach #1—lysimeter leachate

was collected after each rainfall

- soil water content and/or potential- in experimental approach #2, TDR was

used to determine water content, psychrometers to determine water potential.

Gravimetric methods were used for other experimental approaches

- potential of hydraulic lift- in experimental approach #2- psychrometers at 30 cm

and 80 cm depths

Results

1. Experimental plantings of a native grass, dominant annual grasses (naturalized exotics)

and a mix of the two groups.

a. Soil Carbon

Compared with the native Nassella pulchra, exotic annuals had higher percent soil organic matter

(SOM) in the top 15 cm, and lower SOM at the 15-30 cm depth, leading to no difference in total

SOM content in the top 30 cm of soil (Figure 1). The mix of exotics and natives was not

significantly different from the exotics alone. Soil %C in the top 15 cm mirrors the results from

SOM (data not shown).


6

Figure 1. Soil organic matter after 10 years of lysimeters planted to exotic grasses, the native Nassella pulchra, and a mix of exotics and the native. Percent soil organic matter in the top 15 cm (top panel) and 15-30 cm depth (middle panel), and SOM content from 0-30 cm (bottom panel).


7

b. Soil cohesion

Vegetation type had no significant effect on soil cohesion at any soil depth (Figure 2).

Figure 2. Soil cohesion, by depth, after 10 years of soils being affected by the planting of exotic grasses, the native Nassella pulchra, and a mix of exotics and the natives.

c. Nitrogen

Soil percent nitrogen was higher for exotics than for natives, or natives + exotic mixes in the top

15 cm of soil (Figure 3). We are currently analyzing deeper soil depths.

Rates of net N mineralization were not significant (p=0.06), but soils in Nassella plots tended to

have higher rates than the mixtures and exotics (Figure 4). Net nitrification rates did significantly

differ (p=0.003), with Nassella having higher rates than exotics or the mix (Figure 4). We are

currently analyzing more samples to determine how these vegetation effects vary by depth, and

season, and to see how they relate to seasonal leaching loss patterns of N.

Figure 3. Soil %N in the top 15 cm of soil.


8

Figure 4. Rates of net N mineralization (top panel) and nitrification (bottom panel) in top 15 cm of soil.


9

d. Water

Early in the growing season, water leaching losses were consistently lower in the native Nassella

plots than in the exotics, and even the unvegetated plots. There were no, or only small

differences in water leached from vegetation treatments over the rest of the growing season

(Figure 5). Infiltration rates were also slower for Nassella plots than for the exotics at the soil

surface, but not over the rest of the soil depth profile (Figure 6).

2. Experimental plantings of monocultures and mixtures of natives, exotic annual grasses,

and newer invasive annual weeds. a. Carbon- Samples are currently being processed for aboveground and belowground

biomass, and soil C with depth .

b. Soil cohesion- Soil cohesion is currently being analyzed, and there were no significant

differences in vegetation type on soil compaction with depth (data not shown).

c. Nitrogen- Seasonal plant N, net mineralization and nitrification rates, and resin-

available N are currently being analyzed.

d. Water- Infiltration rates differed across species, and were relatively high in Lolium

plots and low in Aegilops and Elymus plots. There were no significant differences across broad

groups (weeds vs. annuals vs. natives) or their mixtures (Figure 7).

Figure 5. Amount and timing of leachates from lysimeters planted with different vegetation types. Top panel is 2005-6 growing season bottom panel is 2006-7 growing season

Figure 6.


10

Infiltration rates, by soil depth, from lysimeters planted with different vegetation types. Sampling occurred in 2008, by sequential excavation of the lysimeters by depth

Figure 7. Infiltration rates in early spring 2010 across vegetation types. Species significantly differ in their effects on infiltration (p=0.04), but there are no differences across broad vegetation groups and their mixes (p= 0.79).


11

Infiltration rates of annual and weed treatments are higher with spring clipping than in the no

clipping and fall clipping treatments (Figure 8).

Figure 8. Effects of timing of clipping on infiltration rates.


12

Potential for hydraulic lift was assessed only in the native plots, since these species are the most

active during the dry summers. Psychrometer readings at 30 vs. 80 cm depths were compared at

different times of the day, indicating significant increases in water potential as soon as plants are

exposed to shade (1830 to 1945 hours), with significant drawdown at dawn, particularly at the 30

cm depth (Figure 9). Currently, in the summer of 2010, we are assessing how these daily

moisture fluctuations impact N cycling rates across vegetation treatments.

Figure 9. % change in psychrometer readings between daily time points indicate likely hydraulic lift in native plots.


13

3. Observational studies across the landscape of areas restored with native species vs. adjacent

unrestored areas (dominated by annual exotic grasses).

Soil C and N, by depth are currently being analyzed, as are water holding capacity and

infiltration rates. Surface soil cohesion is significantly higher in soils dominated by annual

exotics, compared with soils associated with native grass restoration (Figure 10).

Figure 10. Soil cohesion in areas restored to native perennial grasses, and adjacent unrestored areas dominated by exotic annuals.


14

4. Observational studies across the landscape of areas dominated by invasive weeds vs. those

dominated by naturalized annual exotics.

Soil C and N, by depth are currently being analyzed, as are water holding capacity and

infiltration rates. Surface soil cohesion is significantly higher in soils dominated by weeds,

compared with soils associated with naturalized annual exotics (Figure 11).

Figure 11. Soil cohesion in areas dominated by annual exotics vs. noxious exotic weeds.

Discussion

Exotics and Nassella have no effect on total SOM in the top 30 cm of soil, but do differ in the

distribution of SOM, with exotics having higher SOM concentrations in the top 15 cm, and

natives having higher SOM content at the 15-30 cm depth. Exotics also have higher

concentrations of total N in the top 15 cm of soil, but lower net N cycling rates. Exotics and

natives do not differ in resistance to potential erosion (sheer stress), but exotics may decrease

erosion potential through increased water infiltration rates. Exotics also show higher rates of

water leaching early in the growing season. We are currently analyzing deeper soil depths to see

if natives may differentially affect C and N dynamics deeper in the soil profile, due to their

deeper rooting depths.


15

Did not see some of these effects in experimental plots in Davis—likely due to the shorter

duration of the plantings (3 vs. 10 years), but also potentially due to differences in climate and

soils between sites.

While most of this work is on-going, the conclusions we can draw thus far highlight that

species effects on multiple soil processes and properties are independent, so that there are some

benefits and detriments associated with all vegetation groups. For example, while native

grassland species increase deeper soil carbon, they delay water leaching at the start of the

growing season, and have lower soil surface cohesion than the exotic annuals that have displaced

them. While the noxious invasives, Aegilops triuncialis and Taeniatherum caput-medusae

greatly decrease rangeland productivity, they also may decrease surface soil erosion.

Another key conclusion is that the impacts of species can vary depending on time since

establishment, site, and grazing patterns. Many other studies have demonstrated that the

ecosystem effects of a given species are not constant. Both the values and relative ranking of

species effects on various soil properties and processes change across sites (Lovett and Rueth

1999, Scheffer et al. 2001, Kalburtji and Mamolas 2000, Verchot et al. 2001, Bridgham and

Richardson 2003). These variations in the soil effects of a given species can be as great as the

variation across different species (Bridgham and Richardson 2003, Eviner et al. 2006, Eviner and

Hawkes 2008). As we wrap-up analyses of samples that we have collected in this project, we

will assess the relative importance of the following mechanisms in determining the context-

dependence of plant species effects on soils:

1. Plant traits change in response to changes in environmental conditions and time, and

these shifts in traits directly alter soil processes (can use current predictive frameworks

linking multiple traits with soil processes, just shifting the values of species traits). For

example, in California’s grasslands, seasonal changes in root C inputs and the chemistry of

remaining litter are partial drivers of seasonal changes in plant species effects (Eviner et al.

2006).

2. The relative importance of traits in determining soil processes changes with

environmental conditions and time (shifts in which traits are used to predict soil effects).

For example, in California’s grasslands, species effects on net N mineralization are driven by

species effects on soil temperature and litter C in the fall, by root C inputs in the winter, and

by litter chemistry and species effects on soil moisture in the spring (Eviner et al. 2006).

3. There is a fundamental change in how a trait affects a soil process over environmental

gradients and time (a shift in the relationship between a trait and a soil process). For

example, the relationship between decomposition and litter lignin differs at low versus high

actual evapotranspiration (AET) (Meetenmeyer 1978), while the relationship between litter

quality and decomposition varies with nutrient availability (Hobbie 2000, Vesterdal 1999).

Relevance to Kearney Mission/Land Management and Policies

Understanding the interaction of environmental heterogeneity and plant community impacts on

soil processes is a critical tool for management of ecosystem services, agricultural productivity


16

and control of noxious weeds. In this research, we address Kearney’s current mission by

developing a mechanistic understanding of plants impacts on multiple soil processes, and how

these impacts change across time (ranging from daily to decadal) and space (ranging from soil

depth profiles to broad landscape patterns). Our data will enable us to develop an ecological

toolbox.

References:

Bridgham, S. D. and C. J. Richardson. 2003. Endogenous versus exogenous nutrient control over

decomposition and mineralization in North Carolina peatlands. Biogeochemistry. 65:151-178.

Coleman, J., K. Hench, K. Garbutt, A. Sexstone, G. Bissonnette, and J. Skousen. 2001.

Treatment of domestic wastewater by three plant species in constructed wetlands.

Drinkwater, L. E. 1999. Using plant species composition to restore soil quality and ecosystem

function. In: Olesen, JE, MJ Gooding and J Kopke (eds) International Workshop on

Designing and Testing Crop Rotation for Organic Farming. Sponsored by the Danish

Institute of Agricultural Sciences. Borris Landbrugsskole. Danish Research Centre for

Organic Farming, Tjele. pp. 37-46.

Eviner, V. and F. Chapin III. 2001. Plant species provide vital ecosystem functions for

sustainable agriculture, rangeland management, and restoration. California Agriculture.

55:54-59.

Eviner V.T. and F.S. Chapin III 2003. Functional matrix: A conceptual framework for predicting

multiple plant effects on ecosystem processes. Annual Review Ecology and Systematics,

34:455-485.

Eviner V.T., Chapin III F.S. and Vaughn C.E. 2006. Seasonal variations in species effects on N

and P cycling. Ecology, 87:974-986.

Eviner, V.T. and C.V. Hawkes. 2008. Embracing variability in the application of plant-soil

interactions to the restoration of communities and ecosystems. Restoration Ecology 16:713-

729.

Hobbie, S. E. 2000. Interactions between litter lignin and soil nitrogen availability during leaf

litter decomposition in a Hawaiian Montane forest. Ecosystems. 3:484-494.

Kalburtji, K. L. and A. P. Mamolos. 2000. Maize, soybean and sunflower litter dynamics in two

physicochemically different soils. Nutrient Cycling in Agroecosystems. 57:195-206

Lavelle, P. 2000. Ecological challenges for soil science. Soil Science. 165:73-86.

Lovett, G. M. and H. Rueth. 1999. Soil nitrogen transformations in beech and maple stands along

a nitrogen deposition gradient. Ecological Applications. 9:1330-1344.

Meentemeyer, V. 1978. Macroclimate and lignin control of litter decomposition rates. Ecology.

59:465-472.

Rhoades, C. C., T. M. Nissen, and J. S. Kettler. 1997. Soil nitrogen dynamics in alley cropping

and no-till systems on Ultisols of the Georgia Piedmont, USA. Agroforestry Systems. 39:31-

44.

Sarrantonio, M. 1994. Northeast Cover Crop Handbook. Rodale Institute, Emmaus, PA.


17

Scheffer, R. A., R. S. P. van Logtestijn, and J. T. A. Verhoeven. 2001. Decomposition of Carex

and Sphagnum litter in two mesotrophic fens differing in dominant plant species. Oikos.

92:44-54.

Verchot, L. V., Z. Holmes, L. Mulon, P. M. Groffman, and G. M. Lovett. 2001. Gross vs. net

rates of N mineralization and nitrification as indicators of functional differences between

forest types. Soil Biology & Biochemistry. 33:1889-1901.

Vesterdal, L. 1999. Influence of soil type on mass loss and nutrient release from decomposing

foliage litter of beech and Norway spruce. Canadian Journal of Forest Research-Revue

Canadienne de Recherche Forestiere. 29:95-105.

Wardle, D. 2002. Communities and ecosystems: linking the aboveground and belowground

components: Princeton University Press Princeton.392.

This research was funded by the Kearney Foundation of Soil Science: Understanding and Managing Soil-Ecosystem Functions Across Spatial and Temporal Scales, 2006-2011 Mission (http://kearney.ucdavis.edu). The Kearney Foundation is an endowed research program created to encourage and support research in the fields of soil, plant nutrition, and water science within the Division of Agriculture and Natural Resources of the University of California.

http://kearney.ucdavis.edu/

2006-2011 mission kearney foundation of soil science

Documents