Plant Ecology 139: 247–258, 1998. © 1998 Kluwer Academic Publishers. Printed in the Netherlands. 247 Effects of pollution on the nutrient return via litterfall for Pinus radiata plantations in the Basque Country A. Gonz´ alez-Arias 1 , I. Amezaga 1 , A. Echeand´ ıa 1 , M. Domingo 2 & M. Onaindia 1 1 Dep. Biolog´ ıa Vegetal y Ecolog´ ıa, Universidad del Pa´ ıs Vasco/EHU, Apdo. 644, 48080 Bilbao, Spain; 2 Servicio de Investigaci´ on y Mejora Agraria (SIMA), Derio, Bizkaia, Spain Received 10 July 1997; accepted in revised form 31 July 1998 Key words: Cycling of nutrients, Litterfall, Nutrient return, Nutrient Use Efficiencies, Pinus radiata, Pollution Abstract The effects of atmospheric pollution on two 10 year old Pinus radiata D. Don forests (Manzanal and Posadero) was studied in the Basque country, analysing the concentration of different nutrients and nutrient input via litterfall. Litterfall production peaked in autumn, and 97.5% of the litterfall consisted of pine needles at Posadero (the less-polluted area), whereas this figure was found to be 88.6% at Manzanal (the polluted area). Posadero had a higher production of litterfall than Manzanal due to the higher tree density. Nutrient concentration showed a similar seasonal variation over the year at both sites. Pine litterfall in the polluted area, Manzanal, had significantly higher concentrations of iron, copper, zinc, sulphur, calcium, sodium and magnesium than in Posadero, while the concentrations of nitrogen, phosphorous and potassium did not differ between sites. Calcium, sodium, magnesium, sulphur, iron and copper input to the forest via litterfall was significantly higher for the polluted area, but the inputs of nitrogen, phosphorous, potassium and zinc did not significantly differ between sites. Both sites showed high nutrient use efficiencies for phosphorous and calcium compared with other coniferous forests. The highest efficiency was for phosphorous, possibly due to the low availability of this ion in the soil. Trees at Posadero were consistently more efficient for calcium than at Manzanal due to the effect of pollution on the latter site. Molar ratios between aluminium and the basic cation nutrients calcium and magnesium in soil were higher at the polluted area, as a result of the increased inputs of anions to the forest soil (Al:Ca = 1.9:1 and Al:Mg = 6.9:1 at Posadero and Al:Ca = 5.7:1 and Al:Mg = 14:1 at Manzanal). The current pollution level of Manzanal is leading to a loss of cations that may cause future changes in the functioning of this forest. Introduction Due to the death of forests in industrialised countries during the last 2 decades, numerous studies have been carried out to evaluate the effect that acidic ion deposi- tion has on nutrient cycling in forest ecosystems (e.g., Rehfuess 1981; Ulrich 1984; Bredemeier 1988; Mu- rach & Matzner 1988; Smith 1990; Tomlinson 1990; Kratz 1991; Capellato et al. 1993; Onaindia et al. 1995; Gjengedal 1996; Amezaga et al. 1997). There are two main groups of air pollutants, those emitted directly into the atmosphere such as sulphur dioxide, carbon monoxide, nitrogen oxides and hydrocarbons and those produced through reactions between pri- mary pollutants and normal atmospheric compounds. Sulphur oxides, mainly sulphur dioxide, and nitrogen dioxide are the main pollutants derived from human activities. Sulphur dioxide is emitted primarily from station- ary sources, such as power plants that burn fossil fuels, whereas nitrogen oxides are emitted from both station- ary and transport-related sources. In the atmosphere, sulphur dioxide and nitrogen oxide are transformed by reactions with oxygen and water vapour to form sulphuric and nitric acids (Botkin & Keller 1995). During the 1960’s monitoring stations for the collec- tion and analysis of rain and snow were established in North America and Europe. It was apparent that sul- phuric and nitric acids were present in the precipitation falling over large areas (Tomlinson 1990).