Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate change

Abstract

Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (S E ) affected soil water content (SWC) and three aspects of ecosystem function: leaf photosynthetic carbon gain (A CO2 ), aboveground net primary productivity (ANPP), and soil respiration (J CO2 ). We utilized rainout shelter-covered mesocosms (2.6 m 3 ) containing assemblages of tallgrass prairie grasses and forbs. These were hand watered with 16 I Â Q treatment combinations, using event sizes from 4 to 53 mm. Increasing Q by 250% (400-1000 mm yr À1 ) increased mean soil moisture and all three processes as expected, but only by 20-55% (P 0.004), suggesting diminishing returns in ecosystem function as Q increased. Increasing I (from 3 to 15 days between rainfall inputs) caused both positive (A CO2 ) and negative (J CO2 ) changes in ecosystem processes (20-70%, P 0.01), within and across levels of Q, indicating that I strongly influenced the effects of Q, and shifted the system towards increased net carbon uptake. Variation in S E at shorter I produced greater response in soil moisture and ecosystem processes than did variation in S E at longer I, suggesting greater stability in ecosystem function at longer I and a priming effect at shorter I. Significant differences in ANPP and J CO 2 between treatments differing in I and Q but sharing the same S E showed that the prevailing pattern of rainfall influenced the responses to a given event size. Grassland ecosystem responses to extreme rainfall patterns expected with climate change are, therefore, likely to be variable, depending on how I, Q, and S E combine, but will likely result in changes in ecosystem carbon cycling.

Integrating plant ecological responses to climate extremes from individual to ecosystem levels

“…However, only drought impacts translated to changes in growth rates and propagated to impacts in higher order ecological processes to individuals that do not produce detectable impacts on plant population or community composition and ecosystem productivity [49,50]. For example, despite evidence of widespread tissue dieback in individuals, Kreyling et al [49] observed plant community productivity to be unaffected by both drought and heavy precipitation events.…”

How do variations in the temporal distribution of rainfall events affect ecosystem fluxes in seasonally water-limited Northern Hemisphere shrublands and forests?

“…Studies in a mesic grassland have previously observed a decrease in both leaf photosynthetic carbon gain and soil respiration as a result of more intermittent rainfall patterns Fay et al, 2002;Harper et al, 2005), while Fay et al (2008) reported increases in leaf-level photosynthesis and decreases in soil respiration due to increased rainfall event size for levels of total rainfall ranging from 400 to 1000 mm yr −1 . These studies did not provide information concerning the relative sensitivity of these individual processes to variations in rainfall pattern, so it is not possible to reconstruct the dependence of overall ecosystem carbon flux on precipitation frequency for these sites.…”

Species identity of biocrust-forming lichens drives the response of soil nitrogen cycle to altered precipitation frequency and nitrogen amendment

“…In parallel to climate change, environmental nitrogen (N) inputs resulting from anthropogenic activities is changing the N cycle in terrestrial ecosystems (Vitousek et al, 1997;Cui et al, 2013), affecting ecosystem processes (Phoenix et al, 2012;. Despite global change drivers are known to interact in their impacts on ecosystem services, we have limited knowledge on how the interaction between important factors such as decreasing rainfall frequency and increasing N inputs will affect ecosystem functioning in drylands (e. g. N cycle) and influence microbial communities; which carry out vital ecosystem functions (Fay et al, 2008;Delgado-Baquerizo et al, 2014). In drylands, water and N are the most important factors limiting resources for plant and microbial activity (Hooper and Johnson, 1999;Austin, 2011).…”