Pine needle growth and fine structure after prolonged acid rain treatment in the subarctic

Abstract

The growth and morphology of Scots pine needles were studied in a long‐term acid rain experiment in the far north of Finnish Lapland. Pine trees 5 m tall of age 50–70 years were exposed, by spraying the foliage and soil from a height of 2 m, to either clean water (IC) or acidified water over the period 1985–1992, the acidification site being divided into sub‐areas in which the precipitation contained two levels of either sulphuric (Sm, Sh) or nitric (Nm, Nh) acid, or both (SNm, SNh). The treatments with medium and high sulphate‐S over eight consecutive years yielded a total sulphur deposition of 3·4 and 17·1 gm−2, respectively, and those with medium and high nitrate‐N a total nitrogen deposition of 1·1 and 5·9 g m−2. Needles were collected for light and electron microscopy, growth measurements and morphometry. Growth in branch height had decreased by about 40% after 6 years of SNm or SNh treatment, and needle growth by 15% in the SNh trees as compared with the irrigated control trees (IC), although decreases were statistically significant only with respect to the non‐irrigated control trees (DC). Growth of branches and needles was slightly better in the Nh treatment than in the IC group. The areas of the whole needle, the mesophyll and the phloem decreased in response to SNh treatment as compared with IC or DC, and a statistically significant decrease of about 30–40% was seen in the area of the xylem in comparison with DC. Cellular damage was observed following the acid treatments, especially with a high acid load. The damage was manifested in collapse of the cellular compartments, increases in lipid accumulations and swelling or disorganization of the protoplast. Increased vacuolization of the cytoplasm, plasmalemma irregularities and chilling‐type damage to the mitochondria were also observed.

Responses of ground vegetation to prolonged simulated acid rain in sub‐arctic pine—birch forest

“…Weather data for the study period, as well as long-term averages, were obtained from the meteorological station at Kevo and are shown in Figure 1. The mean pH of the precipitation ranged from 4'6 to 4-8 and the annual ambient loads of SOj^^-S and NO-j^-N varied from 78 to 193 and from 29 to 57 mg m^^, respectively, during the study years (Back et al, 1994).…”

“…In addition to natural precipitation, artificial rain amounted to c.180 mm per growing season ( Fig. 1), depending on the period of irrigation (Back et al, 1994). From 1985 to 1988, the water for the SAR4 and SAR3 treatments was prepared by adding both sulphuric and nitric acid (with a sulphate to nitrate ratio 1-9:1 by weight) to spring water.…”

“…soilmediated) effects, depending on the plant species, type of substrate, weather conditions, time period, doses and anion composition of acid application (e.g. Evans, 1984;Jacobson et al, 1990;Back, Neuvonen & Huttunen, 1994). For example, long-term detrimental effects of acid deposition on plant growth have been reported, especially when sulphuric acid is applied and when rain has been allowed to reach the soil (Leith et al, 1989;Jacobson et al, 1990;Back et al, 1994), with a likely delayed negative growth response to acid application (Abrahamsen, 1984;Back et al, 1994).…”

“…Evans, 1984;Jacobson et al, 1990;Back, Neuvonen & Huttunen, 1994). For example, long-term detrimental effects of acid deposition on plant growth have been reported, especially when sulphuric acid is applied and when rain has been allowed to reach the soil (Leith et al, 1989;Jacobson et al, 1990;Back et al, 1994), with a likely delayed negative growth response to acid application (Abrahamsen, 1984;Back et al, 1994). On the other hand, enhanced tree \igour and increased biomass growth observed, for instance, in Scandinavian trees (Kenttamies, 1991) are usually related to a possible fertilizing effect of nitrogen deposition during the earlier stages of acidification (Wood & Bormann, H 7;Kauppi, Mielikainen & Kuusela, 1992).…”

Chemodiversity of a Scots pine stand and implications for terpene air concentrations

“…A light micrograph of a Scots pine needle cross section. The sectioning was done from a resin-embedded needle and the 2 µm thick section was stained with Toluidine blue according to Bäck et al (1994). RD = resin duct; ME = mesophyll cell; S = stoma; * = epithelial cell.…”