Studying root decomposition in situ using the minirhizotron approach

Background/Question/Methods

The pool of dead and decomposing finest roots can be similar or higher than the pool of living finest roots in temperate forest ecosystems. The minirhizotron technique (MR) allows for the nondestructive investigation of seasonal fine root dynamics, including the dead and living root fractions. The primary objective of this work was to examine the influence of root order on rates of decomposition in situ, while a secondary objective was to compare the persistence of severed roots (decomposition) with the persistence of intact roots (survivorship).

            I tracked the persistence of roots severed by trenching around minirhizotron tubes (root disappearance = total decomposition) as well as roots of untrenched MR tubes (root disappearance = mortality, including decomposition) among 10 temperate tree species in a 33-year-old common garden planting in central Poland. Vital staining was used to determine longevity of severed roots, while root diameter was used to categorize roots into two classes: lower, 1^st and 2^nd order roots, and higher, 3^rd and higher order roots. 

Results/Conclusions

Across species, all severed roots died within three months after trenching. From the time of death, severed root persistence was significantly shorter for 1^st and 2^nd order roots than 3^rd and higher order roots of angiosperms, while gymnosperms showed a similar rate of persistence for both root categories. Within root order classifications, root age significantly affected persistence, with older 1^st and 2^nd order roots showing longer persistence than younger roots. When comparing the persistence of 1^st & 2^nd order roots (untrenched MR) with the persistence of 1^st & 2^nd order roots (trenched MR), untrenched root persistence was in general twice as long as the persistence of 1^st & 2^nd order roots, using 25% failure estimates (1^st quartile).

            This work reveals another approach to understanding root decomposition that compared to the more commonly used litterbag approach. The advantages and disadvantages of minirhizotron technique to understand root decomposition will be discussed.