Rainfall Mesocosm Experiment

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Mesocosm Design

               

 

 

 

The mesocosm facility consists of 64 containers (also referred to as mesocosms) arranged in two banks of 32 (2 x 16).  The containers are 1.2 m x 1.2 m with a depth of 1.8 m (2.6 m3).  They are constructed of 12 mm plywood lined with 0.15 mm polyethylene. These dimensions provide a large soil volume for root development, and allow for a 1.0 x 1.0 m central sampling area where soil attributes and above- and belowground plant responses can be measured without edge effects from the mesocosm walls. The containers have a perforated floor lined with root cloth to allow drainage but contain long roots.  Each mesocosm has a bottom layer (1.5 m) of heavier clay soils and an upper soil layer consisting of  0.3 m of topsoil; soil was excavated in the respective locations in the surrounding prairie and emulates the soil organic matter, nutrient, and textural profiles found on deep-soiled lowlands (P. Fay, personal observation).  The containers were built 50 cm below grade to lessen unrealistic soil temperature variation.

            The containers are covered by a 14 m x 24 m open-sided rain-exclusion shelter (Rainbow Plus®, Stuppy Manufacturing, North Kansas City, MO, USA).  This is a larger version of the shelters used at the Rainfall Manipulation Plot experiment (RaMPs) at Konza Prairie. The mesocosm facility shelter uses an improved permanent roof material (DynaGlas Plusä polycarbonate, SPS International, San Jose, CA, USA) with higher light transmission in place of the polyethylene greenhouse film used at RaMPs. The field shelters at Konza have proven extremely effective at excluding natural rainfall, maintaining insolation above photosynthetic light saturation levels for both C3 and C4 plant species, and minimizing confounding microclimate influences (Fay et al. 2000). Similar performance has been achieved with the mesocosm facility shelter.

                                       Table1. Experimental Species

Grasses (C4)

Forbs (C3)

Andropogon gerardii

Asclepias tuberosa

Schizachyrium scoparium

Aster ericoides

Sorghastrum nutans

Echinacea angustifolia

 

Liatris punctata

 

Amorpha canescens

 

Lespedeza capitata

 

Psoralea tenuiflora

            The mesocosms were planted with three warm season C4 grasses and six forbs (Table 1).  These species are abundant components of the tallgrass prairie flora. The grasses are all warm season C4 dominants, strongly rhizomatous, with similar phenologies and rooting depths in the field (all 1.2 - 1.7 m). The forbs have a range of phenologies, but all have less fibrous root systems than the grasses. These species were grown from seed obtained from the USDA Plant Materials Center (Manhattan, KS) and commercial sources. Forbs were germinated in 50/50 peat/vermiculite at 22°C in a greenhouse and transplanted as single-seedling plugs. Grasses were seeded directly into the containers. Planting densities reflected natural relative abundances and densities (grasses: 240 m-2; forbs: 30 m-2).  Each container was planted in an identical spatial pattern, so that species interactions did not affect initial establishment and treatment responses. Plants were well watered during establishment.