Precipitation temporal repackaging into fewer, larger storms delayed seasonal timing of peak photosynthesis in a semi‐arid grassland

Abstract

1. Against a backdrop of rising temperature, large portions of the western United States are experiencing fewer, larger and less frequent precipitation events.How such temporal 'repackaging' of precipitation alters the magnitude and timing of seasonal maximum gross primary productivity (GPP max ) remains unknown.Addressing this knowledge gap is critical, since changes to GPP max magnitude and timing can impact a range of ecosystem services and management decisions.2. Here we used a field-based precipitation manipulation experiment in a semi-arid mixed annual/perennial bunchgrass ecosystem with mean annual precipitation ~384 mm to investigate how temporal repackaging of a fixed total seasonal precipitation amount impacts seasonal GPP max and its timing.3. We found that temporal repackaging of precipitation profoundly influenced the seasonal timing of GPP max . Many/small precipitation events advanced the seasonal timing of GPP max by ~13 days in comparison with climatic normal precipitation. Conversely, few/large events led to deeper soil water infiltration, which delayed the timing of GPP max by up to 16 days in comparison with climatic normal precipitation, and altered end-of-season community composition by increasing the diversity of shallow-rooted annual plants. While GPP max magnitude did not differ across precipitation treatments, it was positively correlated with the abundance and biomass of deeper-rooted perennial bunchgrasses. The sensitivity of plant growth, biomass accumulation and plant life histories to the timing and magnitude of precipitation events and the resulting temporal patterns of soil moisture regulated ecosystem responses to altered precipitation patterns. 4. Our results highlight the sensitivity of semi-arid grassland ecosystem to the temporal repackaging of precipitation. We find that already-observed and modelforecasted shifts toward few/large precipitation events could drive significant delays in the timing of peak productivity for this ecosystem. Adaptive land management frameworks should consider these findings since shifts in peak ecosystem productivity would have major implications for multiple land user communities. Additional research is needed to better understand the role of | 647 Functional Ecology ZHANG et Al.

Response of soil carbon dioxide efflux to temporal repackaging of rainfall into fewer, larger events in a semiarid grassland

“…Because microbial respiration responds more rapidly to soil wetting than plant-mediated respiration (Carbone et al, 2011), our finding that the F s -GCC relationship is conditional on θ suggests that microbial responses to wetting dominate F s immediately after rainfall, whereas plant activity modulates F s during interstorm periods by regulating substrate availability. Prior work in this system has shown that repackaging rainfall into larger, fewer events delays peak plant productivity (Zhang et al, 2022). In this study, we observed a delayed increase in GCC for the few/large regime that was accompanied by an increase in pulse duration Frontiers in Environmental Science frontiersin.org (quantified as τ) and a decrease in pulse magnitude (Δ; Figure 6).…”

“…Thereafter, irrigation treatments were imposed with the following combinations of mean event size and dry intervals: many/small (9 mm; 3.5 days); reference (34 mm; 7 days, which is the climatic normal precipitation frequency at this site), and few/large (51 mm; 21 days). For more details about the experimental design of RainManSR, Zhang et al (2022).…”

“…Moreover, decreased T s late in the season appeared to contribute to the reduction in the sensitivity of F s to θ for the few/large plots (Supplementary Figure S3). We next examined the relationship between F s and green chromatic coordinate (GCC), a measure of plot-scale canopy greenness, which is correlated with vegetation gross productivity in open-canopy ecosystems (Yan et al, 2019;Zhang et al, 2022). This decision was based on prior work in this system, which found that vegetation productivity (quantified using ecosystemscale photosynthesis) is a driver of F s (Roby et al, 2019), and our observation that peak GCC timing varied among treatments (Figure 1E; see also Zhang et al, 2022).…”

“…We next examined the relationship between F s and green chromatic coordinate (GCC), a measure of plot-scale canopy greenness, which is correlated with vegetation gross productivity in open-canopy ecosystems (Yan et al, 2019;Zhang et al, 2022). This decision was based on prior work in this system, which found that vegetation productivity (quantified using ecosystemscale photosynthesis) is a driver of F s (Roby et al, 2019), and our observation that peak GCC timing varied among treatments (Figure 1E; see also Zhang et al, 2022). Whereas the relationship between daily F s and GCC was unclear when θ was high, a positive relationship emerged during drier conditions (θ < 0.06), during which GCC explained 34%-47% of F s (Figure 5).…”

Simulating Global Dynamic Surface Reflectances for Imaging Spectroscopy Spaceborne Missions: LPJ‐PROSAIL

“…The semi‐arid grassland site is the Rainfall Manipulation in the Santa Rita Experimental Range experimental facility (RainManSR) near Tucson, Arizona (31.79°N, 110.90°W). The spectra used for comparison were obtained using a full spectrum ASD FieldSpec3 (Zhang et al., 2022). Measurements were pre‐season (a senescenced period during the driest June month before the monsoon), peak season (when NDVI peaks in early September), and post season (late September when NDVI has decreased to a winter minimum).…”