Assessing multiple limiting factors of seasonal biomass production and N content in a grassland with a year-round production

Abstract

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit grassland functioning in different seasons (i.e., more than one factor at a time), and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed by two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass and N content at species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. In grasslands, the multiple factors hypothesis was tested broadly only with nutrient manipulations. Our study expands our knowledge to limitations imposed by factors associated to disturbance and stress, as mowing, shading, water availability and warming in grasslands with year-round production.