Severe leaching of calcium ions from fir needles caused by acid fog Manabu Igawa*, Toshiyuki Kase, Kosuke Satake, Hiroshi Okochi Faculty of Engineering, Kanagawa University, Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan Received 26 April 2001; accepted 29 November 2001 ‘‘Capsule’’: Leaching of calcium from needles by acid fog may lead to decline of fir trees. Abstract We have measured the components of the throughfall under fir trees (Abies firma) in the field around Mt. Oyama, where the forest appears to be declining, for the period 1994–1998. Exposure experiments of a simulated acid fog to fir twigs were performed underfieldconditions.Therewasasimilaritybetweentheacidresponseinthefieldandthatinthelaboratory.Inbothstudies,the severeleachingofcalciumionsfromtheneedlesurfacewascausedbyexposuretoacidfog.Wealsoappliedacidfogtofirseedlings over 1 year and observed a decrease in the growth of the seedlings due to this application in the dormant season. These results suggest that the severe leaching of calcium ions due to acid fog may cause the deficiency of calcium and be responsible for the decline of the fir trees. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Abies firma; Acid fog; Calcium leaching; Forest decline; Throughfall 1. Introduction Forest decline has been one of the most important problemsinadvancedordevelopingcountriesandsome hypotheseshavebeenproposedastothecauseorcauses of the decline (Schutt et al., 1985). They include acid- ification aluminum toxicity, ozone, magnesium defi- ciency, general stress, and excess nutrients or excess nitrogen. Schulze et al. (1989) proposed that sulfur dioxide, ozone, and nitrogen oxides are the air pollu- tants causing forest decline. Sulfur dioxide has been the major pollutants and many countries have made an effort to decrease the concentration. However, forest decline remains an important environmental problem despite the downward trend in sulfur dioxide emission in advanced countries. In Japan, the average sulfur dioxide concentration throughout the country was a maximum of 59 ppb in 1967, but in recent years it decreased to 5 ppb. The decline in the virgin fir forest (Abies firma) around Mt. Oyama on the east end of the Tanzawa Mountains, southwestoftheKantoPlains,iswellknowninJapan.A highsulfurdioxideconcentrationwasassumedtobeone of causes of fir trees dying from 1960 to 1980 (Suzuki, 1992). The declining trend in the fir trees became low around1980,butthedeclinesymptomsdevelopedagain notonlyinthefirtreesaroundMt.Oyamabutalsointhe beech and fir trees around the Tanzawa Mountains (Kanagawa Prefecture, 1994) and is spreading to other speciesinothermountainoussitesinJapan.Itisdifficult to determine the most important factor producing the declinesymptoms.InthecaseoftheforestdeclineinMt. Oyama,itwasreportedthatsomefactorssuchasahigh level of sulfur dioxide and ozone, acid fog, insects, and natural death of trees caused the decline of fir trees aroundMt.Oyama(KanagawaPrefecture,1994). Recently, DeHayes et al. (1999) and Jiang and Jagels (1999)pointedouttheimportanceofthesevereleaching of calcium from the canopy induced by acid precipita- tion. The total calcium pools in foliage was not reduced by the treatment with simulated acid mist but proton uptake leads to a displacement of membrane-associated calcium. Acid-induced alteration of membrane- associated calcium leads to membrane destabilization and foliar injury in red spruce. For example, a 4–10  C reductioninfreezingtoleranceatpH3.0thanatpH5.0 was observed after acid mist exposure (DeHayes et al., 1999).However,thecalciumleachinginthefieldandits effectonthedeclinewerenotquantitativelystudied,and the investigated species were limited. 0269-7491/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(01)00342-6 Environmental Pollution 119 (2002) 375–382 www.elsevier.com/locate/envpol * Corresponding author. Tel.: +81-45-481-5661 ext. 3880; fax: +81-45-491-7915. E-mail address: igawam01@kanagawa-u.ac.jp (M. Igawa).