Land use history, ecosystem type and species composition drive water use efficiency in annual maize and perennial grasslands in a humid temperate climate

Water use efficiency (WUE), carbon gained per unit water lost, is a fundamental plant and ecosystem function that regulates plant productivity, global hydrology and carbon cycles. We examined ecosystem(E) and intrinsic (i) WUEs derived from eddy covariance (EC)measurements and plant carbon isotope discrimination, respectively, to study how WUE is affected by land-use history, ecosystem type, and plants community composition. We measured EWUE and iWUE of three perennial grasslands planted to mixed-prairie, switchgrass and brome grass as compared to a fields planted to corn. Each of studied ecosystems was replicated on two fields with contrasting land-use histories: one field was managed under the USDA Conservation Reserve Program (CRP, planted to bromק grass) and another was in conventional agriculture (AGR) corn/soybean rotation for few decades before start of the experiment. In 2009, all but one CRP field were converted to no-till soybean. In 2010, the converted CRP and AGR fields were planted to mixed-prairie (C3 and C4 grasses), switchgrass (C4 grass), and no-till corn (C4 grass). During 2009-2013, we measured carbon and water exchange over each field using an EC technique and sampled plant tissue for 13Cisotopes analysis. Land-use history, ecosystem type, and species composition had large effects on EWUEs. Intrinsic WUE of individual C3grass species, however, was similar across the study period, despite drought in 2012. Corn and brome grass had the highest and lowest over allmean EWUE, 4.1 and 2.2 g C kg-1 H2O, respectively. Restored prairie on former AGR land had a mean EWUE of 3.0 g C kg-1 H2O, significantly greater than on former CRP land with a EWUE of 2.5 g C kg-1 H2O. Landuse history had no effect on inter annual variability of EWUE of corn. Prairie and switchgrass established on former CRP land exhibited no change of EWUE, as well. Same ecosystems established on former AGR land, oppositely, increased their WUEs over the study period from ~ 2.5 g Ckg-1 H2O in 2010 to ~3.7 in 2013. Shift in plant dominants from C3 to C4grasses and C3 to C4 plants ratio, despite identical species compositionat planting within all ecosystems explained ~40% of the observed EWUEchange.