This material is based upon work supported by the National Science Foundation under Cooperative Agreement #DEB-9806438. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Current knowledge of the relationship between soil biodiversity and ecosystem functioning is primarily restricted to soil biotic functional groups, and this project aims to examine the relationship at the much finer taxonomic resolution of species. This means bringing together soil ecologists, ecosystem scientists, modellers and sytematists to work towards a common goal. The project has been undertaken in conjunction with a program in the UK, including regular joint meetings and a protocol workshops.
The US field research for this project was be carried out at the Konza PrairieResearch Natural Area, near Manhattan, Kansas. This is the site of the Konza Long Term Ecological Research (LTER) program. Manipulations to plots on an area of this tallgrass prairie have been carried out for over a decade, and these will provide the basis for our investigations. Soil samples will be taken and split between the investigators for an intensive analysis of soil organisms to the species level, plus analyses of soil chemical and physical characteristics. All species identified will be photographed and made available on a World Wide Web site (see below). Data will be incorporated in to a simulation model which will allow us to compare the relative importance of plant species diversity, plant functional group and primary production on the community composition of the soil organisms.
For information on this program, please visit:
The US Program
The UK NERC Soil Biodiversity Programme
The Publications and Graduate Thesises for the Programme
and, to see the developing species list of nematodes, please visit:
and, to visit Konza Prairie's web site, please see
Two sites, the Native Plants Site (NPS) and the Invasive Plant Site (IPS) in two separate watersheds, were selected for soil sampling. The NPS has a 4-year burn regime and the last burn of the watershed occurred one year prior to sampling. Four blocks (~ 20 m x 20 m) as units of replication were established on the upper side of the watershed's slope. Plant species pairs in 12 different combinations as a "treatment" were marked with a marking flag within each block. The chosen plant species are all native or naturalized grasses and belong to photosynthetic pathways characterized as C4 and C3. The selected plant species were: big bluestem (Andropogon gerardii) (C4), little bluestem (Schizachyrium scoparium (Michx)) (C4), Scribner's panicum (Dichanthelium oligosanthes) (C3), Kentucky bluegrass (Poa pratensis) (C3), prairie dropseed (Sporobolus heterolepis) (C4), and prairie junegrass (Koeleria pyramidata) (C3). Soil samples were taken from soil between tillers (with distance between plants no more than the diameter of the sampling core) belonging to either 1 or 2 target grass species (e.g. samples from big bluestem alone, little bluestem alone, and big bluestem and little bluestem together) and away from non-target plant species. Roots belonged to targeted species only.
Knowing that plant roots extend far beyond the sampling core (both in diameter and depth), the experimental design enabled us to investigate not only the importance of plant species identity and plant richness (1 vs. 2 species), but also the importance of resource quality (photosynthetic pathway) (C4 vs. C3 vs. C4C3), and resource heterogeneity (C4 or C3 vs. C4C3) on selected soil biological properties. Photosynthetic pathway is assumed to represent quality of plant resources (including roots) with C3 plants characterized by lower C to N ratio and lignin content than C4 plants (Wedin and Tilman, 1990; Tilman et al., 1997). We recognize that any results would be specific only to the plant species chosen for our study.
On 18 May 1999 three replicates of every plant species combinations within each block were sampled with a soil corer (5.5 cm in diameter) to a depth of 10 cm. The three soil cores of a particular plant combination were combined in one plastic bag. Root samples from separately flagged plant species combinations were collected the following day with the same soil corer at locations described above.
At the Invasive Plants Site, which has been burned annually in recent years, four blocks were established, and soil samples collected from two plant species combinations: 1) big bluestem - big bluestem and 2) Caucasian bluestem (Andropogon bladhii) - Caucasian bluestem. Caucasian bluestem, unlike big bluestem, is a nonnative (first observation at the site was made in the mid 1980's) and could be considered a functional equivalent to big bluestem. Both species are C4 plants and appear identical in physiological and morphological traits except for growth form (Smith and Knapp, 2001). In contrast to big bluestem, Caucasian bluestem is a bunchgrass and forms vegetated and bare soil patches. The C:N ratio of soil and tissue of the Caucasian bluestem is greater than that of big bluestem (Heather Reed, University of Colorado, personal communication) and thus might out-compete the dominant grasses by lowering soil N availability. An assumption for both Native and Invasive Plant Sites is that the plant species (relatively long-lived in comparison to soil biota cycles) have been present on these soils for sufficient time such that their impact on soil biota and processes have been imposed.