Abstract
The metabolic activity of water-limited ecosystems is strongly linked to the timing and magnitude of precipitation pulses that can trigger disproportionately high (i.e., hot-moments) ecosystem CO2 fluxes. We analyzed over 2-years of continuous measurements of soil CO2 efflux (Fs) under vegetation (Fsveg) and at bare soil (Fsbare) in a water-limited grassland. The continuous wavelet transform was used to: (a) describe the temporal variability of Fs; (b) test the performance of empirical models ranging in complexity; and (c) identify hot-moments of Fs. We used partial wavelet coherence (PWC) analysis to test the temporal correlation between Fs with temperature and soil moisture. The PWC analysis provided evidence that soil moisture overshadows the influence of soil temperature for Fs in this water limited ecosystem. Precipitation pulses triggered hot-moments that increased Fsveg (up to 9000%) and Fsbare (up to 17,000%) with respect to pre-pulse rates. Highly parameterized empirical models (using support vector machine (SVM) or an 8-day moving window) are good approaches for representing the daily temporal variability of Fs, but SVM is a promising approach to represent high temporal variability of Fs (i.e., hourly estimates). Our results have implications for the representation of hot-moments of ecosystem CO2 fluxes in these globally distributed ecosystems.
Highlights
Water-limited ecosystems cover over 30% of the land-area of the world and changes in their carbon dynamics could have important impacts on the global carbon budget [1,2]
There were no substantial differences in total precipitation between the hydrological years, but the distribution of the precipitation pulse (PP) resulted in different patterns of soil moisture along the years (Figure 1B)
Similar total precipitation but lower soil moisture variability resulted in 50% higher functions ofof soil efflux (Fs) emissions during the second hydrologic year
Summary
Water-limited ecosystems cover over 30% of the land-area of the world and changes in their carbon dynamics could have important impacts on the global carbon budget [1,2]. Climate models project an increase in precipitation variability, including more extreme rainfall events followed by longer dry periods in water-limited ecosystems [17]. These projections have motivated multiple experiments to better understand the role of changes in frequency and intensity of PPs on ecosystem processes [18,19,20,21]. Rapid changes in water availability after a PP could increase the entropy of water-limited ecosystems [25], especially after those initial PPs following a long dry period resulting in hot-moments with disproportionately high Fs [26]. The non-stationary nature of these events and the diversity of underlying mechanisms complicate measurement campaigns and modeling efforts [29]
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