Tree species identity determines wood decomposition via microclimatic effects

Abstract

Empirical evidence suggests that the rich set of ecosystem functions and nature's contributions to people provided by forests depends on tree diversity. Biodiversity–ecosystem functioning research revealed that not only species richness per se but also other facets of tree diversity, such as tree identity, have to be considered to understand the underlying mechanisms. One important ecosystem function in forests is the decomposition of deadwood that plays a vital role in carbon and nutrient cycling and is assumed to be determined by above‐ and belowground interactions. However, the actual influence of tree diversity on wood decay in forests remains inconclusive. Recent studies suggest an important role of microclimate and advocate a systematical consideration of small‐scale environmental conditions. We studied the influence of tree species richness, tree species identity, and microclimatic conditions on wood decomposition in a 12‐year‐old tree diversity experiment in Germany, containing six native species within a tree species richness gradient. We assessed wood mass loss, soil microbial properties, and soil surface temperature in high temporal resolution. Our study shows a significant influence of tree species identity on all three variables. The presence of Scots pine strongly increased wood mass loss, while the presence of Norway spruce decreased it. This could be attributed to structural differences in the litter layer that were modifying the capability of plots to hold the soil surface temperature at night, consequently leading to enhanced decomposition rates in plots with higher nighttime surface temperatures. Therefore, our study confirmed the critical role of microclimate for wood decomposition in forests and showed that soil microbial properties alone were not sufficient to predict wood decay. We conclude that tree diversity effects on ecosystem functions may include different biodiversity facets, such as tree identity, tree traits, and functional and structural diversity, in influencing the abiotic and biotic soil properties.

Biotic and abiotic drivers of soil microbial functions across tree diversity experiments

“…By contrast, soil microbial biomass and the respiratory quotient were not affected by tree diversity at all. None or weak tree diversity effects on soil microorganisms have been shown in many previous studies, highlighting that tree species identity may be a more important driver of soil microorganisms and soil functions (e.g., Khlifa et al, 2017;Gottschall et al, 2019). Our study suggests that soil microorganisms are mainly influenced by abiotic drivers, which are also important in modulating tree diversity effects.…”

“…evergreen coniferous species, may explain more variation (Reich et al, 2005). For instance, single tree species can affect the structure of the litter layer with significant influence on microclimatic conditions that drive soil microbial functions (Gottschall et al, 2019). Therefore, improved data on litter and root traits as well as their influence on soil quality and microclimate are required to improve the mechanistic understanding of tree effects on soil functions (Laliberté, 2017).…”

SoilTemp: A global database of near‐surface temperature

“…The latter requires both a good understanding of what defines current microclimates and of how climate change will interact with the drivers of microclimatic conditions (Maclean, 2019). Additionally, it is the soil temperature rather than the air temperature that defines many ecosystem functions in and close to the soil, like evapotranspiration, decomposition, root growth, biogeochemical cycling and soil respiration (Gottschall et al., 2019; Hursh et al., 2017; Medinets, Gasche, Kiese, Rennenberg, & Butterbach‐Bahl, 2019; Pleim & Gilliam, 2009; Portillo‐Estrada et al., 2016). Given the repeatedly proven sensitivity of many of these processes to temperatures (Coûteaux, Bottner, & Berg, 1995; Rosenberg, Kimball, Martin, & Cooper, 1990; Schimel et al., 1996), here again having accurate measurements will be of utmost importance.…”

Island size affects wood decomposition by changing decomposer distribution

“…from tree species other than L. chinense ) may increase with increasing island size, resulting in higher termite feeding activity. Second, tree species identity alters the understory microclimate, thereby changing both decomposer community and decomposition rates (Augusto et al 2015, Gottschall et al 2019). In the islands of TIL, where forests were once clear‐cut, the unshaded conditions exposed fungi to dryness, thus selecting for dry‐adapted species in this region (Peay et al 2016).…”

“…These changes may alter decomposer communities and decomposition, thus hampering an appreciation of the generality of relationships between island size, island isolation and decomposition. Decomposers differ in their habitat preferences, including with respect to litter type (Austin et al 2014) and microclimate (Bässler et al 2010, Seibold et al 2016), both of which are shaped by forest composition (Vivanco and Austin 2008, Gottschall et al 2019), which itself is affected by island size and isolation. For instance, larger islands harbor a higher tree species diversity and more late‐successional tree species than do smaller islands (Liu et al 2019, 2020).…”