Carbon and Water Fluxes in an Exotic Buffelgrass Savanna

摘要

Buffelgrass savanna is becoming widespread in aridland ecosystems around the world following invasion or deliberate land conversion for cattle forage. There is still a gap of information regarding functional and ecohydrological aspects such as carbon, water, and greenhouse gas exchanges in these highly productive novel ecosystems where buffelgrass is an exotic species. We measured net ecosystem CO2 exchange (NEE), ecosystem respiration (Rego), gross primary production (GPP), and evapotranspiration (ET) with eddy covariance techniques over a buffelgrass savanna established for cattle grazing, approximately 30 yr ago within the Sonoran Desert. The savanna was a net carbon sink (NEE 230 g C/m(2)/yr) during both a year with above average and one with below-average precipitation (NEE 84 g C/m(2)/yr). Water loss through evapotranspiration (ET) was similar to total annual rainfall input. Up to 62% of the annual fixed carbon and 75% of ET occurred during the summer monsoon season, when 72 86% of annual rainfall occurred and buffelgrass was active. ET from summer months explained 73% of variation in NEE, with an average ET of 50 mm H2O/month needed to turn the ecosystem into a net carbon sink during this season. Other seasons in the year, when buffelgrass was dormant, contributed with up to 48% of annual fixed carbon but with higher water use efficiency (-NEE/ET). We discuss the importance of the seasonal variability in R-eco, GPP, and ET processes and the phenology of native plant species for the net carbon uptake through the year for this managed novel ecosystem. (C) 2016 The Society for Range Management. Published by Elsevier Inc. All rights reserved