Optical LAI

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Dire

ct L

AI

0

1

2

3

4

5

6

7

6 4

15

7 11

12

19

16

13

910

8

14

17

5

18

1 2

3

Y = 1.40 X + 0.59

R2 = 0.86

Height (cm)

0 20 40 60 80

Ab

ove

grou

nd

Bio

ma

ss (

g)

0

5

10

15

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25

30

35

40

15

6 4

7

16

8

9

10

18

111

14

19

1712

13

3

2

5

Y = 0.41 X + 6.28

R2 = 0.91

Non-destructive Estimation of Net Primary Production in Urban Rain GardensNon-destructive Estimation of Net Primary Production in Urban Rain Gardens

Design

Plastic pots (open cylinders, diameter 36 cm and height 92 cm) were filled with a mix of topsoil, sand, and compost. Planting took place in late June, 2006. There are three replicate pots per species of prairie (Table 1) and shrub (Table 2).

Prairie monocultures were planted with four individuals per pot, using second-year plugs (Prairie Nursery, Brodhead, WI).

Shrubs were planted one individual per pot, using mature potted plants (Watts Landscaping Service, Madison, WI).

All plants are growing under field conditions with minimal irrigation. The pots are located near experimental rain gardens on the west side of Madison, WI.

Rain gardens installed within the urban landscape have included various vegetation types, such as a wet-mesic prairie or typical landscaping shrubs. We evaluate the performance of rain gardens by estimating plant productivity and light interception for each vegetation type. We seek simple predictors of biomass for each vegetation type using dimensional analyses.

Most of the species of shrub planted in the rain gardens have allometric equations derived from physical dimensions such as stem diameter and crown area. These allometries estimate aboveground biomass (Smith and Brand, 1983; Golubiewski, 2006), whereas estimates of belowground biomass are lacking. Similarly, the 19 species of prairie plants included in this study are commonly planted within raingardens, yet these species lack allometric equations for estimating biomass. In the past, studies have approximated belowground production beneath prairie vegetation from aboveground growth (Reich et al., 2003), or have emphasized differences in productivity at a landscape scale (Knapp et al., 1993). By destructive sampling, we will establish allometric equations between total, aboveground, and belowground biomass for each species of shrub and wet-mesic prairie vegetation. Moreover, we will regress plant biomass to a suite of physical measurements, including stem diameter, plant height, crown area, and canopy height.

Since we can easily measure indirect leaf area index (LAI) in the rain gardens (with a light attenuation probe), we will measure LAI as another possible predictor of biomass. For each species of prairie and shrub, we will relate plant aboveground biomass to indirect LAI (Turner et al., 2004), asking also whether indirect LAI correlates best with leaf biomass or total aboveground biomass (i.e., some of the prairie species have photosynthetic stems). Through these species-specific allometries, we will be able to estimate aboveground, and thus belowground, biomass for a community of species.

Prairie plants one month after planting, in July 2006. The fourth pot of each species was harvested for biomass.

Shrubs one month after planting, in July 2006.

Hand-sorting belowground biomass one month after planting.

Harvest

We will harvest all shrubs at the end of the growing season (October, 2007). Each species of prairie vegetation will be considered independently to account for the seasonal range in peak productivity (harvested before, during, and after flowering).

Clip aboveground biomass and separate into leaves, stems, fruit, flowers. Hand sort and rinse live roots from soil carefully excavated from pot. Hand sort roots and separate them into two groups: roots which were part of the original plug and roots new since planting.

Dropped leaves from all pots will be collected every week and factored into the biomass summations.

Measuring aboveground biomass one month after planting, Aster sp.

Table 1. Prairie Mix Species List

No. Scientific Name Common Name 1 Andropogon geradii Big bluestem2 Asclepias incarnata Red milkweed3 Aster novae-angliae New England aster4 Baptisia bracteata Cream indigo5 Boltonia asteroides False aster6 Carex vulpinoidea Fox sedge7 Echinacea pallida Pale purple coneflower8 Echinacea purpurea Purple coneflower9 Eupatorium perfoliatum Boneset10 Helianthus occidentalis Ox-eye sunflower11 Liatris pycnostachya Prairie blazing star12 Monarda fistulosa Bergamot13 Panicum virgatum Switch grass14 Parthenium integrifolium Wild quinine15 Penstemon calycosus Longsepal beardtongue16 Ratibida pinnata Yellow coneflower17 Rudbeckia hirta Black-eyed susan18 Solidago rigida Stiff goldenrod19 Veronicastrum virginicum Culver's root

Measurement

Record physical plant measurements, including heights, canopy volume, and basal stem diameters.

Compute specific leaf area (SLA) from dry leaf mass (60 °C for 48 hours) and a leaf area meter with transparent conveyor belt (LiCor LI-3000).

Measure SLA by species three times over the season, using 6 leaves per prairie species and 9 leaves per shrub.

Measure indirect leaf area index (LAI) at the soil surface every two weeks (LiCor LI-2000) beneath prairie vegetation.

Table 2. Shrub Species List

Scientific Name Common Name  Cornus sericea ‘isanti’ Red-twig dogwoodIlex verticillata Winter berryPrunus aroniamelanocarpaBlack chokeberrySalix purpurea ‘gracilis’ Dwarf arctic willowViburnum trilobum American cranberryViburnum dentatum Arrowwood viburnum

Establish allometric equations for aboveground, belowground, and total biomass by species.

Apply these allometric equations for each species to prairie and shrub vegetative communities in rain gardens.

IntroductionIntroduction MethodsMethods

ObjectivesObjectives

M. R. Johnston and N. J. Balster, Department of Soil Science, University of WI, 1525 Observatory Drive, Madison, WI 53706

Preliminary ResultsPreliminary Results

Harvesting one replicate of each prairie species a month after planting plugs provided preliminary relationships among biomass, LAI, and canopy height. Here, we show initial data for the 19 species of prairie planted in experimental rain gardens, labeled as in Table 1. We harvested a sample plant for each shrub species at time of planting, but preliminary data on shrubs are not presented here.

Total aboveground biomass was positively related to indirect LAI (Figure 1). In general, aboveground biomass and canopy characteristics seemed to change LAI. For example, Baptisia and Carex (numbers 4 and 6) grew very little aboveground since planting, Monarda (12) developed a tall, open canopy, and Boltonia and Solidago (5 and 18) established dense canopies. Aboveground biomass also related well with canopy height for the 19 prairie species (Figure 2).

We checked whether LAI measured with an optical light attenuation probe represented actual LAI when calculated from leaf biomass (Figure 3). Although we will establish this relationship on a species-basis, combined data from all 19 species supports measuring indirect LAI in rain gardens as a surrogate for direct LAI. Note that direct LAI calculated for Solidago (number 18) is high because this species grew the most leaf biomass at time of harvest (Figure 2).

LAI

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Abo

vegr

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40Y = 8.62 X + 9.13

R2 = 0.87

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Figure 1. Total aboveground biomass (g) and optical leaf area index (LAI) for the 19 prairie species harvested one month after planting.

Figure 3. Leaf area index (LAI) by direct calculation and optical light attenuation probe for the 19 prairie species harvested one month after planting.

Figure 2. Aboveground biomass and canopy height for the 19 species of prairie harvested one month after planting.

The Next StepThe Next StepBeginning in the spring of 2007, we will monitor changes in the physical dimensions, LAI, and productivity for each species of prairie and shrub. We will harvest all plants to capture their peak productivity and build allometric equations for each species. These measurements, excepting harvest, will be repeated in the experimental rain gardens.

We will select the best predictors of biomass for each species by generating sets of equations. We will apply these relationships to approximate aboveground and belowground productivity in the experimental rain gardens, where destructive sampling is not preferable. Finally, rain garden performance may be evaluated as a function of differing vegetation types.

ReferencesKnapp, A. K., J. T. Fahnestock, S. P. Hamburg, L. B. Statland, T. R. Seastedt, and D. S. Schimel. 1993. Landscape patterns in soil-plant water relations and primary production in tallgrass prairie. Ecology 74:549-560.

Reich, P. B., C. Bushena, M. G. Tjoelker, K. Wrage, J. Knops, D. Tilman, and J. L. Machado. 2003. Variation in growth rate and ecophysiology among 34 grassland and savanna species under contrasting N supply: a test of functional group differences. New Phytologist 157:617-631.

Smith, W. B., and G. J. Brand. 1983. Allometric biomass equations for 98 species of herbs, shrubs, and small trees. Research Note NC-299, North Central Forest Experimental Station, USDA Forest Service, St. Paul, Minnesota, USA.

Turner, M. G., D. B. Tinker, W. H. Romme, D. M. Kashian, and C. M. Litton. 2004. Landscape patterns of sapling density, leaf area, and aboveground net primary production in postfire lodgepole pine forests, Yellowstone National Park (USA). Ecosystems 7: 751-775.