Little information is available on the effect of root cutting by the collar pre-insertion technique on soil respiration. In this study, we found that soil respiration rates decreased with increasing depth of collar insertion in both the "with live roots intact" and "with live roots severed" treatments, but the rate of decrease was substantially higher in the former. The cutting of roots, especially fine roots, may be responsible for this result.

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A stem-girdling experiment was carried out on an evergreen conifer, the Korean pine (Pinus koraiensis Sieb. et Zucc.), in mid summer in Northeast China. A 50 % higher respiration rate at the upper part of the stem was observed 3 d after stem girdling, and a stable higher rate (1.2-2.8 times) one week later. However, no higher soluble sugar or starch contents were found in the upper bark of the girdled stems in measurements over three weeks. These findings indicate that most of the newly-formed photosynthates were consumed by the high respiratory activity; this is also implied by the strong correlation between the photosynthetic photon flux over the canopy (PPF) and respiration at the upper parts of girdled stems. Moreover, the maximum PPF and cumulative PPF one day before measurement (PPFmax-Y and CPPF-Y, respectively) were closely correlated with the respiratory difference between the upper and the lower parts, but no such correlation was found with the instantaneous PPF (PPF-I) and cumulative PPF on the current day from sunrise to measured time point (CPPF-C). This shows that photosynthates newly formed by canopy needles need at least one day for transportation in order to increase the stem respiration at tree breast height.Additional key words: long-distance transport; photosynthetic photon flux; seasonal course; soluble sugar; starch.--Photosynthates are utilized mainly for synthesis of new organs, maintenance of the plant body, defence, and supporting symbiotic micro-organisms (Chapin et al. 1990). An important effect of tree-girdling is to stop the flow of newly-formed photosynthates to the lower part of the girdled stem; girdling can therefore be used to distinguish between the roles of newly-formed and stored photosynthates in respiration from stems and roots (Högberg et al. 2001). The issues are: how much of the newly-formed photosynthates from canopy photosynthesis are consumed in the enhanced respiratory activity resulting from girdling; and what is the functional difference between stored and newly-formed photosynthates in respiratory activity? From the girdling technique together with gas exchange measurements and photosynthate analysis, these questions may be answered.Newly-formed photosynthates deriving from the canopy are determined by the total photosynthetic photon flux (PPF) impinging on a plant. If newly-formed photosynthates are more important for respiration (Högberg et al. 2001), the photosynthetic photon flux (PPF) will positively correlate with the respiratory differences between the upper and the lower parts of girdled stems. Moreover, long-distance transport of photosynthates from the canopy to low stems will take time, which will be observable in the processes of symplasmic and apoplasmic ---

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