| Most of the methods currently used to measure root respiration introduce various disturbances which may lead to biased results, and require destruction of roots which does not permit repeated measurements of root growth and respiration. A root box method was developed for measurement of root respiration, as well as root growth. Roots grew in the root box in two dimensions between a glass and a fabric sheet, and shoots grew in normal atmosphere. This method allowed simultaneous and repeated measurements of root growth and respiration over a three to four month period on undisturbed intact roots. With this method, the effects of the disturbances associated with some of the methods currently used, and effects of some of the controlling factors on root respiration were examined with three to six-month-old Douglas-fir and ten to twelve-month-old western hemlock seedlings. Root injury should be avoided for root respiration measurements because root respiration increased immediately after root injury. The time elapsed from root injury to respiration recovery varied from species to species. For both species, root respiration decreased as soil water content decreased. Root respiration varied from day to day throughout the entire experimental period, and root respiration response to root temperature could be described as a regression of the logarithm of root respiration rate on the reciprocal of the absolute root temperature. The slope of these regressions did not vary under the various conditions tested. The determination coefficients of these regressions ranged between 0.3 and 0.5 for a group of seedlings grown at the same treatment, but ranged between 0.7 and 1.0 for individual seedlings. We can predict the root respiration rates of individual roots at other temperatures very well if we know the rate at a specific temperature. For Douglas-fir seedlings, the respiration rate of roots grown at 0.36 mM N (NH{dollar}sb4{dollar}NO{dollar}sb3{dollar}) was significantly lower than that of roots grown at 1.8 and 7.2 mM N level. Root respiration of western hemlock seedlings did not respond to nitrogen treatments. Root temperature, nitrogen level, soil water potential, root to root variation, and day to day variation need to be considered for prediction of root respiration for forest trees. |
