Influences of the bark economics spectrum and positive termite feedback on bark and xylem decomposition

Abstract

The plant economics spectrum integrates trade‐offs and covariation in resource economic traits of different plant organs and their consequences for pivotal ecosystem processes, such as decomposition. However, in this concept stems are often considered as one unit ignoring the important functional differences between wood (xylem) and bark. These differences may not only affect the performance of woody plants during their lifetime, but may also have important “afterlife effects.” Specifically, bark quality may strongly affect deadwood decomposition of different woody species. We hypothesized that (1) bark quality strongly influences bark decomposability to microbial decomposers, and possibly amplifies the interspecific variation in decomposition by invertebrate consumption, especially termites; and (2) bark decomposition has secondary effects on xylem mass loss by providing access to decomposers including invertebrates such as termites. We tested these hypotheses across 34 subtropical woody species representing five common plant functional types, by conducting an in situ deadwood decomposition experiment over 12‐month in two sites in subtropical evergreen broad‐leaved forest in China. We employed visual examination and surface density measurement to quantify termite consumption to both bark and the underlying xylem, respectively. Using principal component analysis, we synthesized seven bark traits to provide the first empirical evidence for a bark economics spectrum (BES), with high BES values (i.e., bark thickness, nitrogen, phosphorus, and cellulose contents) indicating a resource acquisitive strategy and low BES values (i.e., carbon, lignin, and dry matter contents) indicating a resource conservative strategy. The BES affected interspecific variation in bark mass loss and this relationship was strongly amplified by termites. The BES also explained nearly half of the interspecific variation in termite consumption to xylem, making it an important contributor to deadwood decomposition overall. Moreover, the above across‐species relationships manifested also within plant functional types, highlighting the value of using continuous variation in bark traits rather than categorical plant functional types in carbon cycle modeling. Our findings demonstrate the potent role of the BES in influencing deadwood decomposition including positive invertebrate feedback thereon in warm‐climate forests, with implications for the role of bark quality in carbon cycling in other woody biomes.

A whole‐plant economics spectrum including bark functional traits for 59 subtropical woody plant species

“…As an essential part of woody species, the bark includes all tissues external to the vascular cambium, including the phloem (Esau, 1963;Rosell et al, 2014). It serves as a complex protective, mechanically supportive and hydraulic tissue system that accounts for a significant carbon investment (Niklas, 1999a(Niklas, , 1999bRosell, 2016;Rosell et al, 2015;Staver et al, 2020;Tuo et al, 2021). In addition, it often participates in photosynthesis as well as nutrient storage and transport (Aschan & Pfanz, 2003;Scholz et al, 2007).…”

Size matters for linking traits to ecosystem multifunctionality

“…For example N, P, DMC, lignin content, and C:N ratio indicate the litter substrate quality, and determine the composition and activity of the decomposer community and the animals feeding on them [31,35,55] and, thereby, the associated rates of carbon and nutrient cycling and soil fertility [45]. Along the RES spectrum, larger stems with denser tissues (higher DMC) will decompose slowly [28,56] and thereby provide a long-term habitat, while in low DMC, more decomposable dead stems will provide a good albeit transient habitat to invertebrates [31,57] (cf. [55] for leaves).…”

Stem Trait Spectra Underpin Multiple Functions of Temperate Tree Species

“…The sapwood transports water and nutrients from roots to leaves, whereas the heartwood (i.e., inner wood), which is no longer functional in terms of transport but chemically protected against pathogens by accumulation of antifungal substances (e.g., phenols and tannins) ( Hillis, 1987 ; Domec et al, 2005 ). The bark fulfills multiple functions, such as storage, transportation, photosynthesis, and protection ( Franceschi et al, 2005 ; Rosell et al, 2014 ; Tuo et al, 2021 ). The inner bark and outer bark have different traits and show little coordination because they fulfill different functions.…”