Verification of a threshold concept of ecologically effective precipitation pulse: From plant individuals to ecosystem

Abstract In water-limited ecosystems, an ecologically significant rainfall pulse was defined as a rainfall event that altered both soil water status and plant physiological activity. We developed a new threshold concept of an ecologically effective precipitation pulse (EEPP) applicable to both plant individual and ecosystem scales. The concept was tested in a typical steppe on Inner Mongolia plateau. Two EEPPs, single 3-mm rainfall and 5-mm rainfall, were applied to investigate their effects on soil and plant water status, CO 2 assimilation of five species (four C 3 plants and one C 4 plant), whole-plot soil respiration ( R s ), and net ecosystem CO 2 exchange (NEE) on 1 June and 28 July 2009, respectively. Both EEPPs increased leaf water potential ( Ψ l ) of all the species, which peaked 1–3 days after rainfall pulses. Soil water content ( SWC ) in two depths (5 cm and 20 cm) significantly increased after the two EEPPs for 1–3 days. Soil water potential ( Ψ s ) within 20‐cm soil layer in EEPP treatments significantly differed ( p A net ) of all C 3 plants had a slight increase at the next day after two EEPPs, in contrast to the C 4 species. R s elevated and peaked 1–3 days later after water supply. Ecosystem net CO 2 absorption rate rose to maximum value 3 days after the 5-mm pulse on 28 July, higher than the response to 3-mm pulse on June 1. The grassland turned to net emission of CO 2 after 3-mm pulse on 28 July. The results supported that there was an ecosystem level threshold for EEPP, and the threshold was temporally variable. It also highlighted the necessity of considering the response threshold of EEPP in rainfall manipulative experiment. In addition, effective rainfall amount was more approriate than total rainfall amount in modeling ecosystem carbon balance.