Interactions among litter chemical traits alter the non-additive effect of litter mixing

Litter decomposition is a fundamental nutrient cycling process, and litter diversity decreases induced by biodiversity loss have substantial effects on soil carbon cycling. However, few experimental studies have characterized the effect of litter diversity on and litter chemistry. Here, we used single-species and mixed litters to study the effects of litter chemical properties on the direction, intensity and drivers of non-additive litter-mixing effects. We found that 1) there was no significant effect of litter species richness on soil processes, and the litter chemistry of component species was more robust to soil respiration and non-additive effects. 2) The early-stage mixing effect was negative, ranging from -3.1 to -0.3, and its magnitude was strongest in chemically diverse litter mixtures; the late-stage mixing effect ranged from -2.3 to 1.3, and the non-additive effect of chemically similar species was positive. 3) Litter carbon, lignin, phenols and soluble sugar affected early-stage soil respiration, and litter carbon, nitrogen, phenols, and condensed tannins affected late-stage soil respiration, which accounted for 46% and 56% of the variation in early- and late-stage soil respiration, respectively. 4) Compared with plant species richness, litter chemistry altered the direction and magnitude of litter mixing, and litter chemical composition (including litter chemical traits and their interactions) had a stronger effect on non-additive effects than variation in single chemical compounds according to the R value (R=0.36). 5) Artemisia halodendron, as a key sand-fixing plant species, will accelerate nutrient cycling, but it has negative effects on carbon cycling when mixed with other plant species

Effects of gamma irradiation on instream leaf litter decomposition

Leaf litter decomposition is a key process in stream ecosystems, the rates of which can vary with changes in litter quality or its colonization by microorganisms. Decomposition in streams is increasingly used to compare ecosystem functioning globally, often requiring the distribution of litter across countries. It is important to understand whether litter sterilization, which is required by some countries, can alter the rates of decomposition and associated processes. We examined whether litter sterilization with gamma irradiation (25 kGy) influenced decomposition rates, litter stoichiometry, and colonization by invertebrates after weeks of instream incubation within coarse-mesh and fine-mesh litterbags. We used nine plant species from three families that varied widely in litter chemistry but found mostly consistent responses, with no differences in decomposition rates or numbers of invertebrates found at the end of the incubation period. However, litter stoichiometry differed between irradiated and control litter, with greater nutrient losses (mostly phosphorus) in the former. Therefore, the effects of irradiation on litter chemistry should be taken into account in studies focused on stoichiometry but not necessarily in those focused on decomposition rates, at least within the experimental timescale considered here.

Microbial inputs at the litter layer translate climate into altered organic matter properties

<p>Plant litter chemistry is altered during decomposition but it remains unknown if these alterations, and thus the composition of residual litter, will change in response to climate. Selective microbial mineralization of litter components and the accumulation of microbial necromass can drive litter compositional change, but the extent to which these mechanisms respond to climate remains poorly understood. We addressed this knowledge gap by studying needle litter decomposition along a boreal forest climate transect. Specifically, we investigated how the composition and/or metabolism of the decomposer community varies with climate, and if that variation is associated with distinct modifications of litter chemistry during decomposition. We analyzed the composition of microbial phospholipid fatty acids (PLFAs) in the litter layer and measured natural abundance δ<sup>13</sup>C<sub>PLFA</sub> values as an integrated measure of microbial metabolisms. Changes in litter chemistry and δ<sup>13</sup>C values were measured in litterbag experiments conducted at each transect site. A warmer climate was associated with higher litter nitrogen concentrations as well as altered microbial community structure (lower fungi:bacteria ratios) and microbial metabolism (higher δ<sup>13</sup>C<sub>PLFA</sub>). Litter in warmer transect regions accumulated less aliphatic‐C (lipids, waxes) and retained more O‐alkyl‐C (carbohydrates), consistent with enhanced <sup>13</sup>C‐enrichment in residual litter, than in colder regions. These results suggest that chemical changes during litter decomposition will change with climate, driven primarily by indirect climate effects (e.g., greater nitrogen availability and decreased fungi:bacteria ratios) rather than direct temperature effects. A positive correlation between microbial biomass δ<sup>13</sup>C values and <sup>13</sup>C‐enrichment during decomposition suggests that change in litter chemistry is driven more by distinct microbial necromass inputs than differences in the selective removal of litter components. Our study highlights the role that microbial inputs during early litter decomposition can play in shaping surface litter contribution to soil organic matter as it responds to climate warming effects such as greater nitrogen availability.</p>

Linking Foliar Traits to Belowground Processes

Above- and belowground systems are linked via plant chemistry. In forested systems, leaf litter chemistry and quality mirror that of green foliage and have important afterlife effects. In systems where belowground inputs dominate, such as grasslands, or in ecosystems where aboveground biomass is frequently removed by burning or harvesting, foliar traits may provide important information regarding belowground inputs via exudates and fine-root turnover. Many, if not most, of the plant traits that drive variation in belowground processes are also measurable via remote sensing technologies. The ability of remote sensing techniques to measure fine-scale biodiversity and plant chemistry over large spatial scales can help researchers address ecological questions that were previously prohibitively expensive to address. Key to these potential advances is the idea that remotely sensed vegetation spectra and plant chemistry can provide detailed information about the function of belowground processes beyond what traditional field sampling can provide.