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Various climatic and hydrological variables such as precipitation, soil moisture, stream flow, and water level can be used to assess drought conditions, however, the response of ecosystem productivity to such metrics is not very clear. In this study, we examined the sensitivity of GPP anomalies to five drought indicators: the Standardized Precipitation Index (SPI), the Standardized Precipitation–Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI), deficit of soil moisture (DSM), and the difference between precipitation (P) and evapotranspiration (ET) (D(P-ET)). The global spatial distributions of drying and wetting trends from 2000 to 2014 determined by these five indices were similar. Additionally, the percent of drought-impacted areas decreased over the study period, indicating a reduction in drought conditions. GPP increased over the study period in the Northern Hemisphere (NH) but decreased in the Southern Hemisphere (SH), resulting in a net increase in global GPP. GPP anomalies were more sensitive to drought indices in the SH than in the NH. Among the five indices, GPP anomalies were most closely correlated with SPI in the NH (R = 0.60, P < 0.05) and SPEI in the SH (R = 0.93, P < 0.01). Regionally speaking, annual and seasonal GPP anomalies were most sensitive to DSM and PDSI, highlighting the importance of soil moisture observations to regional drought monitoring and assessment. The results of this study are important for evaluating the impacts of drought on ecosystem production and the global carbon cycle. [ABSTRACT FROM AUTHOR]

Conceptual model of climate change (ocean acidification [OA] and seawater warming) effects on coral reef mesocosms that either do (light blue) or do not (blue) feature seagrass beds. Solid lines denote abiotic effects (i.e., OA or OA + warming to 31C), whereas dotted lines depict effects of co-incubation with seagrass. CCM = carbon concentrating mechanism. ER=ecosystem respiration, GPP = gross primary production, NEP = net ecosystem metabolism, and P/R = photosynthesis/respiration ratio. • The combined effect of OA and rising temperatures stimulated the growth of macroalgae. • OA resulted in higher coral calcification rates when corals were co-incubated with seagrass. • Macroalgal growth was lower in seagrass-containing mesocosms. • Coral and macroalgal, but not seagrass, growth suffered at 31 °C under OA conditions. • Seagrass helped to stabilize the system's metabolism in response to projected climate change stressors. Ocean acidification (OA) and warming currently threaten coastal ecosystems across the globe. However, it is possible that the former process could actually benefit marine plants, such as seagrasses. The purpose of this study was to examine whether the effects of the seagrass Thalassia hemprichii can increase the resilience of OA-challenged coral reef mesocosms whose temperatures were gradually elevated. It was found that seagrass shoot density, photosynthetic efficiency, and leaf growth rate actually increased with rising temperatures under OA. Macroalgal growth rates were higher in the seagrass-free mesocosms, but the calcification rate of the model reef coral Pocillopora damicornis was higher in coral reef mesocosms featuring seagrasses under OA at 25 and 28 °C. Both the macroalgal growth rate and the coral calcification rate decreased in all mesocosms when the temperature was raised to 31 °C under OA. However, the variation in gross primary production, ecosystem respiration, and net ecosystem production in the seagrass mesocosms was lower than in seagrass-free controls, suggesting that the presence of seagrass in the mesocosms helped to stabilize the metabolism of the system in response to simulated climate change. [ABSTRACT FROM AUTHOR]