Do branch and root of trees grow in harmony or independently?

Submitted by editor on 30 March 2020.Get the paper!

Beautiful autumn forest in northern Japan with a variety of tree species.

Study: "Synchronous and asynchronous root and shoot phenology in temperate woody seedlings" by Makoto et al. (2020)

Bud burst, leafing, flowering, autumn coloring…. it is interesting to enjoy the changing trees across the seasons in your garden, nearby forest, commuter path. “When and how long do the trees growth?” is closely linked to temporal resource use strategy because the timing and duration of growth directly links to the amount of resource that trees can get. Clarifying differences in growth phenology among species may contribute to understanding mechanisms of temporal niche differentiation among the species, and consequently those of the maintenance of biodiversity

It is obvious that trees need not only light and CO2 (aboveground resources) but also water and nutrients (belowground resources). But this fact means, to understand the resource use strategy of tree and its variation among species, we should know how the growth phenology vary both for aboveground and belowground organs. However, mostly due to the methodological difficulty, the growth phenology of roots are less understood as compared to that of shoot. Root growth are solely investigated without linking with shoot phenology, often for a limited number of species.

In this paper, we examined fine root and shoot phenology of 42 seedlings representing a variety of woody species in northern Japan. Our forest is ecotone between temperate forests and boreal forests, so the tree diversity is high.

Based on the analysis, we found the trees which ended the shoot growth later also stopped the root growth later. As the result, the trees whose shoot grew longer also grew the roots longer. Interestingly, there was no relationship between the timing of the start of shoot and root growth.  

Another finding is that the growth phenology differed with functional traits but the growth phenology was predictable with different trait between shoot and root (for the details, please read the paper). This fact indicates that different environmental factors drive the evolution of growth phenology in fine roots and shoots.

Plant root in soil via the transparent box.

Together, our results suggest that niche differentiation may be promoted by differences in growth phenology between root and shoots in complex, likely contributing to the co-existence of various woody species in our diverse forests.

Important history of this study is that the data used in this paper is obtained by Dr. Takao Sato (one of the co-authors) about 35 years ago (almost same timing with my own birth!). He investigated the phenology every one tor two weeks over two years! When I found this data in his Ph.D thesis of Hokkaido University written in Japanese, I was extremely impressed. At the same time, even after 35 years of the investigation, we thought that the data provide us the important information about the shoot-root phenological linkage for trees by conducting the additional analysis.

In Japan, outstanding root research has been conducted by many scientists including Drs. Takao Sato and Noboru Karizumi from 1970s and 1980s. Now, woody root scientists including Drs. Mizue Ohashi, Yasuhiro Hirano, Kyotaro Noguchi and Naoki Makita are very active in Japan. For example, they organize a session of woody roots in the Annual Meeting of Japanese Forest Society every year. I was really happy to be able to appeal the traditional and latent power of Japan’s woody root study by publishing this paper. Still we have many hypotheses to be tested with this dataset. Don’t miss the coming outcome!

By Kobayashi Makoto 


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