Fine root production and phenology: A study of 11 temperate tree species in a common garden in Poland

Background/Question/Methods

We examined the extent to which fine root growth patterns were similar across species and years as a means to understand belowground dynamics in a forest ecosystem.  A variety of hypotheses have been made about whether temporal patterns of fine root production should match or be opposite of those of shoots, and whether this relationship differs for evergreen and deciduous trees.  Our a priori prediction was that deciduous species would have season-specific root production, while the evergreen species would have more continuous fine root production.  We used minirhizotrons to collect 6 years of observations on fine roots (1st and 2nd - order roots; <1 mm diameter) of 11 tree species growing in monoculture plots within a common garden.  

Results/Conclusions

Our results indicate similar timing of fine root growth can occur across tree species of diverse phylogeny and leaf phenology.  Root production peaked between July and October for all species for six years.  The timing of the peaks of fine root production varied significantly for only 4 species; in other words, the peaks occurred at the same time for a given year in 7 species.  For example, in year 1 the peak fine root growth was in September/October for all species, while in year 2, the peak of fine root growth was in August for 6 species.  Total annual fine root length production was positively associated with total rainfall of both the current and previous year across species, and the relationship was not influenced by whether the plants were angiosperms or gymnosperms.  We concluded that the relatively synchronous fluctuation in peak periods of growth across multiple years for 11 species suggests a large influence of environmental conditions on root growth.  This was supported by the link of total root production to annual rainfall.  The linkage of actual year total root length production with previous-year rainfall underscores the importance of lags in biological responses and the importance of long-term studies.