CONICET | Buscador de Institutos y Recursos Humanos

The high productivity of sandy groundwater-coupled woodlands in the Monte Desert is exploited by local pastoralist communities for fuel, domestic use, and manure accumulation and export to irrigated oases. We explored processes and species that could replenish C and N losses from the ecosystem using stable isotopes of plants and nutrient analysis of soils. Foliar 15N natural abundances, which were lower in Prosopis ﬂexuosa plants and C4 grasses from dune ﬂanks, indicate that these plants may ﬁx atmospheric N2. Groundwater availability did not decrease water use efﬁciency (indicated by similar foliar d13C in dune ﬂanks and interdune valleys), suggesting that the higher stomatal conductance allowed by the additional water source and reported in previous studies is coupled with higher photosynthetic rates, increasing productivity in interdune valleys. Water use efﬁciency and N stable isotopes of P. ﬂexuosa responded to temporal changes in precipitations, suggesting rapid shifts of N sources, to uptake of recently mineralized soil N (higher d15N and lower d13C after rain events). Soil heterogeneity was low, except for ammonium and moisture in interdune valley soils. This study allows us to hypothesize that carbon is replenished in interdune valleys by increasing photosynthetic rates, and N is replenished by N2 ﬁxation done by young P. ﬂexuosa plants and grasses from dune ﬂanks.