Stem girdling treatment inhibits the axial transport of carbohydrates through the phloem and affects resource allocation to different organs of trees. Previous studies indicated that starch and soluble sugar may accumulate in the upper part but diminish in the lower part of the girdled stem in the long run. However, few studies so far have examined the short-term dynamics of starch and soluble sugar after the girdling and this information is important for understanding the functioning of carbohydrates for plant growth. For example, how much time does it take for girdling treatment to induce the accumulation or reduction of different carbohydrates and does girdling treatment affect the phloem-xylem transport of sugars? How are the dynamics of carbohydrate reserves related to the respiratory consumption in stem? To answer these questions, we carried out a stem girdling study on trees of Korean pine (Pinus koraiensis Sieb.et Zucc.) (38-year-old). We measured respiratory consumption of sugars with a Li-6400 system at an interval of 1-2 days. We collected samples of xylem woods and phloem barks at the same interval for carbohydrate analysis with the colorimetric method (Anthrone-perchloric acid method). We found:
(1) During the 4 weeks of measurement, soluble sugar and starch in xylem and starch in phloem in the upper part of the girdled stems did not differ from those in the lower part(p>0.05).
(2) Differences in soluble sugar in phloem between the upper and lower parts were first observed in the second week and substantially higher values in the upper part were observed during the 4th week (p<0.05).
(3) Girdling treatment obstructed the axial transport of soluble sugar via phloem but did not affect the transport in xylem. Moreover, girdling treatment did not affect the correlation of soluble sugar between phloem and xylem.
(4) Girdling treatment strongly affected the respiratory consumption of carbohydrates in stems. During the first week, the sugar consumption rate in the upper part did not differ from that in the lower part (p>0.05). However, the consumption rate in the upper part of the girdled stem sharply increased in the second week and became significantly higher than that in the lower part (p<0.05). From the third week, the consumption rate in the lower part significantly decreased (p<0.05).
We conclude that the most recently formed carbohydrates from canopy leaves were consumed by the enhanced respiration sincewe observed only slight increase in soluble sugar and no change in starch in the upper part of the girdled stems. Moreover, the stored carbohyrates could supply substrates about 2 weeks for the high respiration in the lower part of the girlded stems.