Herbaceous layer development during spring does not deplete soil nitrogen in the Portuguese montado

Nitrogen (N) content in the soil and in the herbaceous biomass were monitored during spring of 2004-2006 to determine how the herbaceous layer development influences soil N availability in the montado ecosystem of southern Portugal. Highest (246.6 ± 52.7 g m-2) and lowest (123.2 ± 89.5 g m-2) peak biomass occurred in 2006 and 2005 respectively. Total soilNwithin the top 20 cmsoil profile ranged between 0.2 0.1% in February and 0.41 0.2% inMay,while available soil N was lowest (5 ± 2 μg g-1soil) in February but increased three-to-five fold in March and was >17.5 μg g-1 soil at senescence in May. Significant (p < 0.001) increase in total N in the aboveground pool occurred between February and May. There was however, no decay in soil N content. Instead, the herbaceous vegetation enhanced soil N input and N retention in the ecosystem. Most of the herbaceous plants were annuals with large reserves of organic N at senescence, which returned to the soil as detritus. The herbaceous vegetation is a critical component of the montado that contributes to N recharge and cycling within the ecosystem.