Effects of deicing salt on the vitality and health of two spruce species, Picea abies Karst., and Picea glehnii Masters planted along roadsides in northern Japan
Introduction
Spruce and fir have been planted along roadsides because of their dense foliage canopy and capacity for fast growth. In northern Japan, however, the health of the spruce trees planted along highways has begun to deteriorate. Most plantation trees were coniferous species, such as Picea abies, Picea glehnii, and Abies sachalinensis. One third of the P. abies and P. glehnii planted near the highway have experienced suppressed growth (Kayama et al., 2002a).
P. abies was introduced in the early 1900s because of its promising traits for timber production (Kubota and Fukuchi, 1981) and has been widely planted in the northern part of Japan to serve as windbreaks. P. glehnii is a dominant species at infertile sites in northern Japan (Tatewaki, 1943, Tatewaki, 1958, Kayama, 2002), and also had been planted along roadsides.
A decline in the number of conifers along roadsides has been reported in various countries located in cold regions (Hofstra and Hall, 1970, Hall et al., 1972, Sucoff, 1975, Sucoff et al., 1975, Hautala et al., 1992, Viskari and Karenlampi, 2000). To ascertain the cause of the forests’ decline, researchers have had to examine various factors. According to previous studies, air pollutants are one of the main reasons for the declining number of P. abies growing to maturity in Europe (e.g. Cowling et al., 1988, Schulze, 1989, Izuta, 1998). A particular factor, nitrogen deposition, is known to lead to soil acidification and cause a nutrient imbalance in the soil. This indirectly suppresses tree growth (Aber et al., 1989, Aber et al., 1998, Wilson and Skeffington, 1994). Another adverse factor is acid sulfate penneated soil, a condition that occurs as a result of the oxidation of pyrite (FeS2) being accidentally brought to the surface during road construction (Kitao et al., 1997, Kitao et al., 2001). For the past 10 years in northern Japan, nitrogen oxide measurements have revealed low concentrations of no more than 0.008 mg l−1 h−1 (Hokkaido prefecture, 2000). As NO2 contamination in spruce trees has only been slight, the effects of NO2 and pyrite seem to have had little effect on the decline in tree health (Kayama et al, 2002a). Soil samples near the highway have continued to register high pH levels.
A more apparent and probable cause of tree decline seems to be deicing salt (Sucoff, 1975, Larcher, 1995). To maintain safety during winter, deicing salt (sodium chloride) is sprinkled over the roads. The snow, mixed with highway salt, is then cleared by snowplows and usually ends up on the roadside where trees have been planted. On conifers adversely affected by deicing salt, needle shedding is accelerated (Sucoff, 1975). Spruce species are known to have a high sensitivity to salt compared to other woody species (Zulauf, 1966, Buschbom, 1968, Sucoff, 1975, Bogemans et al., 1989, Larcher, 1995).
When sodium chloride is absorbed into plants, various physiological traits are depressed due to the toxicity of sodium and chloride (Marschner, 1995, Larcher, 1995). Moreover, salt stressed plants also experience a decrease in the rate of mycorrhizal colonization (Duke et al., 1986). To date physiological traits of salt stress have been mainly confined to studies involving the salt tolerance capacity of horticulture plants (e.g. Lloyd et al., 1987a, Lloyd et al., 1987b, Lloyd et al., 1990). Few studies concerning salt-damaged conifers grown in cold regions have been carried out (e.g. Kayama et al., 2002a). Moreover, there is no information about P. abies and P. glehnii and the level of sodium chloride concentration in the needles that leads to suppress physiological activity.
The objective of this research was to examine the physiological traits of two declining spruce species planted along highways, which have been adversely affected by road salt. The physiological traits examined were: (1) needle life span as an indicator of the degree of needle vitality and health of spruce (Kayama et al., 2002b), (2) concentration of trace elements in needles, and (3) photosynthesis, water potential, and transpiration. In addition, because mycorrhizal symbiosis is essential for the growth of spruce species (Smith and Read, 1997), the effect of road salts on the mycorrhizal infection of spruce roots was also examined. Based on the results of these analyses, we discussed the plausible factors affecting vitality and health, and physiological activities of the two spruce species.
Section snippets
Study sites
Study sites were located along a highway, in the central part of Hokkaido Island in Japan (43°07′ N, 141°46′ E, 60 m a.s.l.). The mean annual precipitation is 1200 mm year−1, and the mean snow depth in the middle of the winter is 107 cm. The mean, maximum and minimum temperatures are 7.2, 34.7 and −24.3 °C, respectively. These measurements were taken by a thermo recorder over a span of 30 years (Hokkaido Branch of Japan Weather Association, 1991). Trees were planted along this highway for
Soil chemical properties
The concentration of sodium and chlorine from the soil samples of both sites are shown in Table 1. The concentration of sodium and chlorine in the soil of the damaged site, for both species, was significantly higher than that of the healthy site (P<0.01). Soil pH in the damaged site, for both species, was also significantly higher than that of the healthy site (P<0.05). In contrast, the concentration of phosphorus and magnesium in the soil in the damaged site was significantly lower than that
Discussion
Based on field survey data, the growth of P. abies and P. glehnii at the damaged site was suppressed markedly. Tree height and DBH decreased, and survivorship of needles was also reduced because of early shedding of the needles (Fig. 2). Moreover, mycorrhizal symbiosis of the two species at the damaged site was very poor (Fig. 3). At the damaged sites, high concentrations of sodium and chlorine in the soil and snow were detected (Table 1, Fig. 1). Furthermore, nutrients in the soil at the
Conclusion
When comparing the growth characteristics of P. abies and P. glenhii at the damaged and healthy sites in northern Japan we discovered, tree height and DBH of P. abies and P. glenhii in the damaged site were smaller than those of the healthy site. In the damaged site, large amounts of sodium and chlorine in both the soil and snow were detected, and these elements had also accumulated in the needles of P. abies and P. glenhii. Moreover, needle shedding of P. abies and P. glenhii at the damaged
Acknowledgements
We appreciated the financial support of JSPS, MEXT and the Japan Highway Landscape Association. We also thank Dr. I. Burner of the WSL for his helpful advice on the early draft.
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