Measurement of root respiration according to root thickness

1.Introduction<BR>The separation of root respiration from soil respiration is important at the carbon cycle in the forest ecosystem. However, the technique has not been established yet. In this research, the root was dug out, classified according to the size, and the respiration rate was measured. <BR>2.Material and method<BR> Measurements were conducted at Yamashiro experimental forest located in the Kyoto Pref.. Annual mean temperature is 15.5 degrees, and precipitation is 1449.1mm a year. It is secondary forest of the broad leaf tree including some conifer. <BR>2-1 Difference of carbon dioxide burst size by difference of diameter of root<BR>Root systems of Quercus serrata and Ilex pedunculosa were carved, and the samples were cut out. The samples measured the respiration rate separately for the class based on the diameter. The respiration rate was measured by the closed-chamber method consisted of IRGA, the pump, and the acryl chamber (Jomura,2004). The temperature in the chamber was measured by using thermo couple. <BR>2-2 Correspondence with soil respiration<BR> The plot was installed on the examination ground as soil respiration measurement place, and seven cylinders made of vinyl chloride of 20cm in the diameter were set up in that. Soil temperature was measured by using thermo couple and soil water content was measured by using TDR. The measurement was done from September to October, 2002 three times. After the soil respiration was measured, the soil block of right under measurement part was dug and taken. The root included in the soil was divided into 2mm<=D, 2mm<D<=5mm, and 5mm<D<=20mm by each diameter. Root respiration of each class was calculated from the relational expression of the diameter of the root and its respiration rate. <BR>2-3 Estimation of root respiration of the experimental forest<BR>To presume the amount of root of the experimental forest, the root system was dug, and the diameter of those roots was measured every 5cm. The relational expression of DBH and root biomass of each class (5mm<D<=20mm, 20mm<D<=50mm, 50mm<D, and rootstock) was made. For the estimation of fine root biomass (2mm<=D,2mm<D<=5mm), the soil block in ten places was sampled and root biomass per unit area was estimated. The soil respiration rate in the experimental forest was presumed by using this result and root respiration rate of each diameter class. <BR>3..Result and discussion<BR>3-1<BR>Root respiration rate per surface area has grown by growing of the diameter of the root. As for the respiration rate per weight, the smaller the diameter of root, the higher root respiration per unit weight. In the fine root, an especially big value was indicated. <BR>3-2<BR>There was a positive correlation between the soil respiration rate and root biomass. There are a lot of soil respiration rates in the place where a lot of amount of roots exist. Root biomass will be an important factor of a spatial change of the soil respiration rate. The relation becomes clearer if paying attention to the fine root. This suggests that fine root respiration plays an important role in a total root respiration. Root respiration of measurement area was calculated by using the root biomass and root respiration rate of each diameter. The proportion of the respiration rate of the root in the soil respiration was 43.4(24.8-65.4) %. <BR>3-3<BR>Root respiration of each class of root diameter in the experimental forest was calculated. Respiration from fine root shows more than the half of the entire root respiration in all.