Drought manipulation and its direct and legacy effects on productivity of a monodominant and mixed-species semi-arid grassland

• A small annual variation for leaf water potential suggests geological water sources.
• ANPP decreased under extreme drought but only for the species mixed condition.
• Only a marginal legacy effect of annual precipitation was observed on ANPP.
• Previous winter/spring precipitation had the largest legacy effect on ANPP.

Future precipitation changes in the semiarid grassland region in Central Mexico are expected to be larger for winter rainfall (−20%) than for summer rain (−10%). Winter rainfall however comprises a small proportion of annual precipitation (5–6%), therefore the potential effects on productivity are expected to be negligible. We are realizing however, that winter rain events are important controls of tiller population and consequently of grassland productivity. To attest its influence we examined rain legacy effects using rainout shelters, by reducing rainfall by 42% (2011) and 20% (2012) relative to unmanipulated rainfall on monodominant Bouteloua gracilis and mixed-species disturbed grasslands. In 2013 rainout shelters were removed to allow all incoming rain into the plots. Plant cover type was a significant predictor of aboveground productivity with monodominant B. gracilis consistently producing 50–80 g/m2 more than mixed stands. Decreased rainfall did not have negative effects on aboveground productivity except in an extreme drought year for the mixed-species grassland. We also observed a significant legacy effect of winter precipitation on summer aboveground productivity in both grassland types, but not to previous-year total precipitation. In spite of the large annual variability of soil ψ, leaf ψ fluctuated between −0.5 and −1.5 MPa most of the year suggesting a geologic source of water.