Abstract:

Chemical analysis of plant tissues, such as in pine trees, is a frequently used method to evaluate the changes of forest health caused by air pollution. Pine needles also have been used widely as bioindicators of atmospheric pollution due to their wide distribution and easy identification. However, the results of whole needle analysis may ignore differences in elemental concentrations in particular needle parts. To date, only limited research has described the concentrations of different elements in various parts of needles injured by pollutants.
Masson pine (Pinus massoniana) is a pioneer species widely spread throughout Southern China. Six separate trees were selected from Dinghushan, Guangdong Province and cut down. The healthy looking current year (C) and previous year (C+1) needles were separated from branches at the upper, middle and lower crown. The needles were cut into three sections, defined as tip section (T), middle section (M) and base section (B), proportional to the needle length. The sheath (S) of each needle-age group also was collected. All parts of the different-aged needles were dried and ground for chemical analysis of the elements, total S, total P, K, Mg, Na, Ca, Al, Mn, Zn, Cu, Fe, Pb, Cr, Cd and Ni. The Ca/Al ratios of each needle component were calculated.
The mean concentrations of the elements in the C+1 needles were higher than in the C needles, except for total S, total P, K and Cd which were not significantly different, whereas the Ca/Al ratios were lower. The elements were unevenly distributed along the length of the needles. The total S, Na, Ca, Al and Mn did not show significant differences among the different needle sections whereas K, Mg, Zn, Fe, Cr, Ni and the Ca/Al ratios differed statistically among the different sections of the C and C+1 needles. The total P, Cu, Cd and Pb were significantly different among the sections in the C+1 needles only. The element patterns along the needles were mainly caused by air pollution. The needles were under Al stress as determined by the Al concentrations and Al/Ca ratios, especially in the base section. Values of Al and/or Ca/Al ratios in the base of the needle potentially can be used as an early diagnostic index of Al toxicity. Concentrations of Cu and Pb in the area were far above background values for Masson Pine needles implying that excessive heavy metals might damage the needles. Concentrations of Fe, Cu, Pb, Zn, Cd, Ni and Cr in the needle sheath were significantly higher than in the other three sections of the needle suggesting that the needle sheath might be a better bioindicator of those elements than other needle parts. The results of this study and the techniques employed constitute a new contribution to the development of biogeochemical methods for environmental monitoring. These methods may be of value for follow up studies aimed at the assessment of municipal and industrial pollution.

Key words: Chemical analysis, Element distribution, Needle parts, Dinghushan, Pinus massoniana