Nitrate reductase activity as an indicator of ponderosa pine response to atmospheric nitrogen deposition in the San Bernardino mountains

acid deposition air pollution arbre forestier azote biological indicators bosques branche branches california californie coniferous forests eua feuille foliage forest trees forests highlands hojas indicator organisms leaves methode methods nitrate nitrate reductase nitrates nitrato reductasa nitratos nitrogen organisme indicateur organismos indicadores pinus ponderosa ramas usa