@article {KNZ00413,
	title = {Landscape patterns in soil-water relations and primary production in tallgrass prairie},
	journal = {Ecology},
	volume = {74},
	year = {1993},
	pages = {549 -560},
	abstract = {Landscape variation in soil water relations, leaf xylem pressure potential ({\textdegree}) and leaf{\textemdash}level net photosynthesis (A) in Andropogon gerardii, and net primary production (NPP) were evaluated during the 1989 and 1990 growing seasons in a northeast Kansas (USA) tallgrass prairie. Landscape patterns were assessed along transects that spanned upland and lowland topographic positions in an annually burned and a long{\textemdash}term unburned watershed. Landscape variability in volumetric soil water content ({\textdegree}) was significantly greater in the unburned watershed (coefficient of variation [CV] = 0.425 and 0.479 for 0{\textemdash}15 and 0{\textemdash}30 cm soil depths in unburned prairie vs. 0.285 and 0.330 for similar depths in the burned watershed). In both watersheds, significantly higher {\textdegree} and total soil water content (0{\textemdash}30 cm) were measured in lowlands compared to uplands. Topographic anomalies, such as a lowland ridge, resulted in local, small{\textemdash}scale variation in soil moisture that equaled watershed variation. Variation across landscapes in predawn {\textdegree}, which was expected to reflect soil water content, was similar in both watersheds (CV = 0.312). Variation in midday @j was significantly greater across the burned than the unburned watershed in 1990 (maximum range in @j from uplands to lowlands was 0.708 MPa at predawn and 0.662 MPa at midday in the burned watershed). In both watersheds, variation in midday @j was much lower relative to {\textdegree}. Landscape patterns in leaf{\textemdash}level A in A. gerardii, the dominant species in this tallgrass prairie, were inconsistent when upland and lowland sites were compared. During an extended period of drought, A was significantly higher in plants in the unburned watershed. In both watersheds, NPP was strongly correlated with {\textdegree}. However, variability in NPP across topographic gradients in the unburned watershed was much less pronounced (CV = 0.224{\textemdash}0.245) than in the annually burned watershed (CV = 0.364{\textemdash}0.430). Moreover, the slope of the relationship between NPP and {\textdegree} was significantly greater in the annually burned watershed. We propose that relatively uniform energy limitations across topographic gradients in unburned tallgass prairie, caused by detrital accumulation that absorbs/reflects sunlight, reduced topographic variability in NPP in unburned watersheds. This pattern occurred in unburned watersheds despite greater landscape variation in {\textdegree} relative to burned watersheds. Analysis of long{\textemdash}term records of NPP from several watersheds supported the hypothesis that variability in NPP associated with topographic position is lower in unburned vs. burned watersheds. Variability in @j across watersheds and between years was muted by negative feedback of canopy leaf area (transpiring surface) on plant{\textemdash}soil water relations. We concluded that patterns in landscape variability in A and @j which may vary significantly over short time intervals, were not good predictors of seasonal carbon dioxide exchange or productivity in this tallgrass prairie. Nonetheless, interactions between A and @j, when combined with nitrogen and energy limitations to A. provide the mechanisms for integrated responses measured across these landscapes.},
	keywords = {LTER-KNZ, tallgrass prairie},
	doi = {10.2307/1939315},
	author = {Alan K. Knapp and Fahnestock, J.T. and Hamburg, S.P. and Statland, L.J. and Seastedt, T.R. and Schimel, D.S.}
}
