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Konza Project

by Jordan Okie last modified 2008-03-26 23:58

Konza Project

Titles

Plant traits and species interactions mediate effect of increased precipitation on primary production in a tallgrass prairie?

Description

In tallgrass prairies at the Konza LTER site, plant production and species abundances in irrigated and control transects spanning lowland and upland areas have been monitored for twelve years. Treatment transects are irrigated to maintain higher than average levels of actual evapotranspiration and soil water content during the growing season. Annual spring burns are also performed on both irrigated and control transects, in contrast to the previously intermittent fire regime.

Knapp et al. (2001, Ecosystems) analyzed productivity data for 1991 to 1998 and found linear positive effects of precipitation input on annual net primary production (ANPP) in both control and irrigated plots. However, during the period of 1999 to 2003, ANPP increased substantially in irrigated plots, but not at all in control plots and without any concomitant increase in precipitation.  These recent ANPP changes suggest that changes in community structure or species interactions in the irrigation plots may be modifying the effects of precipitation on ANPP. However, no one has yet investigated community composition changes in the transects to help inform an understanding of these recent ANPP changes. Therefore we are interested in:  (1) how community structure and composition have responded to irrigation treatments under regular burning, and (2) the role of plant functional traits and species interactions in mediating these changes and influencing the relationship between ANPP and precipitation. We will also consider the influence of upland and lowland areas, because of the potential importance of their differing soil characteristics.

We are still working to refine our questions and welcome any ideas or advice you all may have. We are working at putting together functional traits for the plants species at Konza, processing data, and performing exploratory analyses. Here are some brainstorms. Please feel free to add or change at will.

Brainstorms

How does % cover of traits change in response to irrigation under annual burning?

a.       C3 plants increase

b.      Species in lower canopy will decrease

c.       Annual plants will increase

d.      SLA will increase?

e.       SRL will decrease

f.       N-fixers will increase

g.      Bloom period? Perhaps those with longer blooming periods will increase

h.      Large seeds will decrease (lose advantage)

2-      How do traits differ between upland and lowland?

ORIGINAL QUESTIONS (FROM SCOTT COLLIN'S PPT)

Can site productivity be maintained under an annual fire regime with net primary production maximized each year? Or will soil N limitations become more severe over time as predicted by Century model output (Ojima et al., 1990)?

Will reproductive effort of the dominant grasses be enhanced by long-term irrigation? Or will allocation to reproduction decline as belowground resources become limited?

Will significant plant species composition shifts occur? More specifically, is annual fire sufficient to keep woody species from increasing along these wet transects? Will increased competition for N and light reduce the abundance of forbs?

How will soil processes such as decomposition and N mineralization be affected by irrigation? Will readily mineralizable C and N pools decrease (Ojima et al., 1990)? How will the temporal dynamics of microbial biomass be affected?

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