Do you remember the first match of the football World Cup that was held in Russia this summer? The match was played between Saudi Arabia and the host country, Russia, and everyone now knows the result, that Russia finally won with a high score of 5:0. This is a typical "Home-field advantage" (HFA), i.e., the home team has both physiological advantages (the visiting team may have jet lag or be unfamiliar with the football field on which it is playing) and psychological advantages (the home team is more emboldened when playing on its home turf), and thus, the home team is more likely to win. In fact, in the study of ecology, there is also a similar HFA that describes the biochemistry of litter decomposition.

  
Decomposition: A fallen leaf with shining golden tones during the decomposition process. Credit: Karolos Trivizas

I think each one of us is familiar with “litter.” When autumn comes, the components of trees—leaves, branches, fruits and flowers, all of which have fallen from the mother trees—can be considered as litter. Litter plays a pivotal role in the global carbon cycle and nutrient cycling of forest ecosystems. Zizhen Gong (1792 - 1841), a poet of the Qing Dynasty of China, wrote a well-known poem, "the fallen are not ruthless, because they will turn to spring mud to nourish flowers" (in Chinese: 落红不是无情物, 化作春泥更护花). Gong’s famous poem underscores the ecological meaning of litter. Litter is important, but what factors affect its decomposition (the premise of "nourishing flowers ")? Knowing how litter decomposes is key to the better understanding of its exact role in forest nutrient cycling. Many years ago, scientists discovered that litter also has an HFA just as in the example mentioned earlier, i.e., litter decomposition is faster beneath the tree species (mother trees) it was derived from. Through years of research, scientists have confirmed that the HFA of litter decomposition has many influencing factors, including biological factors (tree species, soil microbial activity, etc.) and abiotic factors (climate factors, physical and chemical properties of soil, etc.). However, to our surprise, people ignore the most likely influence—the fine roots of the mother trees. Fine roots, the frontier of mother trees that come into contact with the fallen leaves on the ground, have been ignored for many years.

There are many functions of fine roots, and there should be one influencing the HFA. Credit: M. Luke McCormack

A simplified model depicting home-field advantage (HFA). Copyright © 2018 Jianguo Gao. All rights reserved.

The possible role of fine roots in the HFA of litter decomposition, i.e., the knowledge gap in such research, was keenly perceived by a PhD candidate—Kai Tian from Nanjing University. A recent paper “Local root status: a neglected bio-factor that regulates the home-field advantage of leaf litter decomposition” has been published in the prestigious journal Plant and Soil. The researchers did indeed find that the fine roots of mother trees have positive effects in HFA, especially for the medium-diameter roots (0.5 mm mesh), which have the strongest effect on litter decomposition compared with fine and coarse ones. In their further analysis, fine roots have both direct and indirect effects, whereas the mineralization mediated by microorganisms has direct effects. However, this is not where the story ends; more research is needed into the role of fine roots in decomposing litter.

The experimental design. Credit: Kai Tian

During a football tournament, two important factors influence HFA, i.e., physiology and psychology. The value of Tian’s work lies in verifying the key role of fine roots in litter decomposition through empirical research, which is an analogy of the direct certification of physiology of HFA in a football competition. Only if the litter decomposes normally through HFA and transforms into “spring mud,” can it contribute to the nutrient cycling of forest ecosystems.

The leading author—Kai Tian was setting a root in-growth core in a coniferous forest stand on a cold winter morning. Credit: Kai Tian.

Investigation of the broad-leaved forest stands on a shining spring day. Left: a visiting scholar, Stephan Hättenschwiler (not involved in this study) from the Centre d'Ecologie Fonctionnelle et Evolutive, CNRS; middle: the leading author—Kai Tian, a PhD Candidate; right: Professor Tian. Credit: Kai Tian.

Reference:

Tian K, Kong XS, Gao JG, Jia YY, Lin H, He ZH, Ji YL, Bei ZL & Tian XJ. 2018. Local root status: a neglected bio-factor that regulates the home-field advantage of leaf litter decomposition. Plant and Soil, doi: 10.1007/s11104-018-3757-8.