02989nas a2200241   4500008004100000245012400041210006900165300001300234490000800247520216100255653001202416653002502428653002702453653001802480653001802498100002002516700001602536700001702552700001802569700001702587700001602604856012702620       2006                        eng d00aConvergence and contingency in production-precipitation relationships in North American and South African C4 grasslands0 aConvergence and contingency in productionprecipitation relations  a456 -4640 v1493 aMesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C4 grasses and had similar growing season climates; thus, we expected convergence in precipitation–ANPP relationships. Lack of convergence, however, would support an alternative hypothesis—that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m2 respectively) and growing season precipitation–ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.10aclimate10aEvolutionary history10aNet primary production10aPrecipitation10asoil moisture1 aKnapp, Alan, K.1 aBurns, C.E.1 aFynn, R.W.S.1 aKirkman, K.P.1 aMorris, C.D.1 aSmith, M.D.  uhttp://knz.lternet.edu/content/convergence-and-contingency-production-precipitation-relationships-north-american-and-south