Increasing precipitation event size increases aboveground net primary productivity in a semi-arid grassland

Abstract

Water availability is the primary constraint to aboveground net primary productivity (ANPP) in many terrestrial biomes, and it is an ecosystem driver that will be strongly altered by future climate change. Global circulation models predict a shift in precipitation patterns to growing season rainfall events that are larger in size but fewer in number. This "repackaging" of rainfall into large events with long intervening dry intervals could be particularly important in semi-arid grasslands because it is in marked contrast to the frequent but small events that have historically defined this ecosystem. We investigated the effect of more extreme rainfall patterns on ANPP via the use of rainout shelters and paired this experimental manipulation with an investigation of long-term data for ANPP and precipitation. Experimental plots (n = 15) received the long-term (30-year) mean growing season precipitation quantity; however, this amount was distributed as 12, six, or four events applied manually according to seasonal patterns for May-September. The long-term mean (1940-2005) number of rain events in this shortgrass steppe was 14 events, with a minimum of nine events in years of average precipitation. Thus, our experimental treatments pushed this system beyond its recent historical range of variability. Plots receiving fewer, but larger rain events had the highest rates of ANPP (184 +/- 38 g m(-2)), compared to plots receiving more frequent rainfall (105 +/- 24 g m(-2)). ANPP in all experimental plots was greater than long-term mean ANPP for this system (97 g m(-2)), which may be explained in part by the more even distribution of applied rain events. Soil moisture data indicated that larger events led to greater soil water content and likely permitted moisture penetration to deeper in the soil profile. These results indicate that semi-arid grasslands are capable of responding immediately and substantially to forecast shifts to more extreme precipitation patterns.

Decreased water limitation under elevated CO 2 amplifies potential for forest carbon sinks

“…Responses of aboveground net primary productivity (ANPP) to experimental repackaging of ambient rainfall into fewer, larger rainfall events depend on site productivity (37). At a less productive experimental site, ANPP increased in response to such an experimental repackaging (38), whereas at a more productive site, ANPP decreased in response to the manipulation (39). These contrasting responses align with our model predictions for allocation to leaves with decreasing λ at low and high total annual rainfall, respectively.…”

Water controls on nitrogen transformations and stocks in an arid ecosystem

“…Similar rainout shelters are being used in many studies from the Patagonian Steppe, the Arctic Tundra, the short grass steppe, the Mediterranean and Californian grasslands to the southwestern rangelands of the US (Heisler-White et al 2008, Adler et al 2009, Fiala et al 2009, Levine et al 2010, Rao and Allen 2010, Matías et al 2011, Talmon et al 2011. The shelter design consists of a metal structure that supports V-shaped clear acrylic bands ('shingles').…”

Organic and inorganic carbon in the topsoil of the Mongolian and Tibetan grasslands: pattern, control and implications

“…Although high temperature may stimulate plant production as temperature is an important limiting factor for vegetation growth in the alpine meadow , temperature-induced higher SOC decomposition overrides the resulting increase in C inputs, thus leading to a decrease of SOC. On the other hand, in steppe ecosystems, water conditions are the primary constraint to vegetation productivity (Heisler-White et al, 2008;Jobbagy et al, 2002;Sala et al, 1988). High GSP could stimulate plant production and increase soil C accumulation, thus precipitation is the most important variable in controlling SOC patterns in steppe ecosystems.…”