Physiological interactions along resource gradients in a tallgrass prairie

TitlePhysiological interactions along resource gradients in a tallgrass prairie
Publication TypeJournal Article
Year of Publication1991
AuthorsSchimel, DS, Kittel, TGF, Knapp, AK, Seastedt, TR, Parton, WJ, Brown, VB
Pagination672 -684
Accession NumberKNZ00335
Keywordstallgrass prairie

Spatial variability in availability of resources that limit photosynthesis (water and N) leads to variation in rates of atmosphere- biosphere exchange. N content and allocation are canopy properties that link ecosystem, physiological, and biophysical processes and that vary in space at scales relevant to atmosphere-biosphere interaction. We studied landscape-scale variation in these and related canopy properties in Kansas Tallgrass Prairie (USA). The tallgrass ecosystem was suited to this investigation because primary production in the prairie is constrained by N availability. This work was designed to aid in interpertation and spatial extrapolation of gas exchange measurements made using aerodynamic techniques as part of FIFE (First ISLSCP Field Experiment), a NASA- supported study. We collected data on spatial disrtibution of biomass, leaf area index (LAI), canopy N mass. N concentration ([N]), and gas exchange along topographic and management gradients. We also measured height distribution of N, light interception, and gas exchange within canopies as a function of position in the landscape. Substantial variation in biomass, LAI, N accumulation, and N allocation occurred over time, with topography, and as a result of previous burning. The verticle gradient of [N] and photosynthetic capacity within canopies were correlated, in space and time, with biomass and canopy light interception. The gradients were steper in high biomass sites than in low biomass sites. In addition, proportional N allocation to the upper layer increased with time (12% in June, 32% in August) as biomass increased. As nutrient uptake increased within the tallgrass landscape, biomass increased and light limitation in the lower canopy was induced. As this light limitation increased with increasing biomass, or with accumulation of dead vegetation, allocation of N to the upper canopy increased. Height distribution of photosyntheticd capicity paralleled within-canopy N allocation and light interception. As resource ratios (light, water and nitrogen) varied in the landscape, so did rates of gas exchange. This work suggests that in interactions between light extinction, N allocation, and photosynthesis that have been proposed for monospecific stands apply to the multispecies, but structurally simple, canopy of the tallgrass prairie. Models of plant performance based on evolutionary arguments may provide a powerful basis for spatial extarapolation of atmosphere-ecosystem exchange rates from sites to landscape and larger regions. Key words: atmosphere-ecosystem exchange, FIFE; Konza Prairie Long-Term Ecological Research site; leaf area index; light interception; nitrogen allocation; photosynthetic capacity; photosynthetically active radiation; remote sensing; toposequences