Biodiversity-Mediated Effects of Environmental Change on Decomposition

Root-specific and leaf-specific biomarkers have been used for decades to identify the origin of organic materials in soils and sediments. However, quantitative approaches require appropriate knowledge about the fate of these indicator molecules during degradation. To clarify this issue, we performed a 1-year incubation experiment with fine root and leaf material of six temperate tree species: European ash (Fraxinus excelsior), European beech (Fagus sylvatica), Oak spec. (Quercus spec.), Linden spec. (Tilia spec.), Norway spruce (Picea abies) and Scots pine (Pinus sylvatica). Only one molecule, x,16-dihydroxy hexadecanoic acid (x,16-C16), could be validated as a general leaf-specific biomarker for the set of all species. For roots, no general root biomarker was found. Ester-bound tricosanol (C23-OH) could be validated for five out of six species; 20-hydroxy eicosanoic acid (ωC20) could be validated for four out of six species, leaving Norway spruce without a suitable root biomarker. The results of this study suggest that the validity of leaf- and root-derived ester-bound lipids as biomarkers is highly species dependent and does not always coincide with previous findings. Concentrations of root- and leaf-derived ester-bound lipids did not stay constant within 1 year of degradation and changed without a linear trend. The change of concentrations seems to be highly species dependent. This might be due to a different structure and arrangement of the individual monomers in cutin and suberin per species, and, therefore, a different accessibility of bond cleaving enzymes. The usefulness of root and leaf biomarkers is context dependent. Our results suggest that general assumptions about litter input to forest soils solely based on biomarker analysis have to be considered carefully. Full article

Soil organic carbon (SOC) is the largest terrestrial organic carbon pool. Plant litter is an important source of SOC, but the knowledge gap between SOC fractions and plant litter input remains inconsistent. Here, a litter input control experiment was conducted at three subalpine forest types (coniferous forest, mixed forest, and broadleaved forest). We assessed the variations of total organic C, active organic C (easily oxidizable C, labile organic C), recalcitrant organic C, and microbial biomass C under litter input or removal. The results showed that soil total organic C decreased greatly under litter input. It was mainly caused by the change of easily oxidizable C and labile C, while the influence of recalcitrant C was small. At the same time, this effect varied among different forest types. Among them, the effect of litter input on SOC was weak and slow in the coniferous forest with low-quality litter input, while a quick effect was observed in the mixed and broadleaved forests with high-quality litter input. Microbial biomass C declined under litter input in most cases, and its variation was strongly controlled by soil temperature and freeze-thaw events. Overall, our results provide new evidence that forest type would strongly control SOC dynamics, in concert with litter quality shifts, with potential consequences for long-term C sequestration. We highlighted that litter input could reduce microbial biomass carbon which might limit the native SOC decomposition, but the loss of active C ultimately changed the SOC in the subalpine forests. It suggested that the interaction of multiple mechanisms should be considered in the study of SOC in this region. Full article

Litter decomposition is a vital link between material circulation and energy flow in forest ecosystems and is intensely affected by global change factors, such as increased nitrogen (N) deposition and altered precipitation regimes. As essential nutrients, calcium (Ca), magnesium (Mg), and manganese (Mn) play crucial roles in plant energy metabolism, photosynthesis, and membrane transport of plants, and the major source of these nutrients is litter decomposition. However, the dynamics of Ca, Mg, and Mn during decomposition have been largely ignored. Thus, to better understand Ca, Mg, and Mn dynamics during leaf litter decomposition in the scenario of increasing N deposition and decreasing precipitation, we carried out a two-year field litterbag experiment in a natural evergreen broad-leaved forest in the central area of the rainy area of Western China. Two levels of N deposition (ambient N deposition and 150 kg·N·ha⁻¹·y⁻¹) and precipitation reduction (no throughfall reduction and 10% throughfall reduction) were set, i.e., control (Ctr: without nitrogen deposition or throughfall reduction), N deposition (N, 150 kg·N·ha⁻¹·y⁻¹), throughfall reduction (T, 10% throughfall reduction), and N deposition and throughfall reduction (NT, 150 kg·N·ha⁻¹·y⁻¹ and 10% throughfall reduction). We found that leaf litter Ca concentration increased in the early decomposition stage and then decreased, while Mg and Mn concentrations generally decreased during the whole period of decomposition. The amount of Ca showed an accumulation pattern, while Mg and Mn generally showed a release pattern. N deposition and throughfall reduction affected the Ca, Mg, and Mn dynamics, varying with different decomposition stages; i.e., N deposition significantly affected the concentration and amount of Ca, regardless of the decomposition stages, while throughfall reduction significantly affected the Ca concentration in the whole and early decomposition stages. N deposition significantly affected the concentration and amount of Mg in the whole and early decomposition stages, while throughfall reduction had no significant effects. Throughfall reduction significantly affected the concentration and amount of Mn in the whole and late decomposition stages, while N deposition had no significant effects. Ca concentration generally showed a significant positive linear relationship with mass loss in the early decomposition stage; Mg concentration showed a significant positive linear relationship with mass loss in the Ctr and N treatments in the early and late decomposition stages; Mn generally showed a significant negative linear relationship with mass loss, regardless of the decomposition stage. Overall, the results suggest that Ca accumulation is more likely affected by N deposition, while Mg and Mn releases are more likely affected by N deposition combined with throughfall reduction, particularly in the early decomposition stage. Full article

The Qinghai–Tibetan Plateau is the highest plateau in the world and is sensitive to climate change. The dynamics of soil enzyme activities and microbial communities are good indicators of alpine biochemical processes during warming. We collected topsoil (0–10 cm) and subsoil (10–20 cm) samples at altitudes of 3200–4000 m; determined the activities of β-1,4-glucosidase (BG), cellobiohydrolase (CBH), β-1,4-N-acetyl-glucosaminidase (NAG) and acid phosphomonoesterase (PME); and performed Illumina 16S rRNA high-throughput sequencing. We found that the soil carbon (total organic carbon and dissolved organic carbon) and nitrogen (total nitrogen and dissolved organic nitrogen) fluctuated with altitude in both the topsoil and subsoil, whereas the dissolved phosphorus continuously decreased with the increasing altitude. BG and CBH decreased from 3200 to 3600 m and increased from 3800 to 4000 m, with the lowest levels occurring at 3600 m (topsoil) and 3800 m (subsoil). NAG and PME showed similar fluctuations with altitude, with the highest levels occurring at 3400 m and 4000 m in both the topsoil and subsoil. Generally, the altitudes from 3600 to 3800 m were an ecological transition belt where most of the nutrients and enzyme activities reached their lowest levels. All of the alpine soils shared similar dominant phyla, including Proteobacteria (32.7%), Acidobacteria (30.2%), Actinobacteria (7.7%), Bacteroidetes (4.4%), Planctomycetes (2.9%), Firmicutes (2.3%), Gemmatimonadetes (2.0%), Chloroflexi, (1.2%) and Nitrospirae (1.2%); Gemmatimonadetes and Verrucomicrobia were significantly affected by soil depth and Planctomycetes, Firmicutes, Gemmatimonadetes, Nitrospirae, Latescibacteria and Armatimonadetes were significantly affected by altitude. In addition, nutrient availability, enzyme activity and microbial diversity were higher in the topsoil than in the subsoil, and they had more significant correlations in the subsoil than in the topsoil. Our results provide useful insights into the close linkages between soil nutrient cycling and microbial activities on the eastern Qinghai–Tibetan Plateau, and are of great significance for further assessing the long-term impact of environmental changes in the alpine ecosystems. Full article

Atmospheric nitrogen (N) and sulfur (S) deposition in subtropical forests has increased rapidly and the current level is very high, thus seriously affecting nutrient (e.g., N and phosphorus (P)) release from litter. However, the specific effects of S addition and its interaction with N on the release of carbon (C), N, and P from litter in subtropical evergreen broadleaved forests are unclear. Therefore, a two-year field experiment was performed using a litterbag method in a subtropical evergreen broadleaved forest in western China to examine the responses of litter decomposition and nutrient release to the control (CK), added N (+N), added S (+S), and added N and S (+NS) treatments. The results showed that the remaining litter mass, lignin, cellulose, C, N, P, and litter N/P ratio were higher, whereas the litter C/N ratio and soil pH were lower in the fertilization treatments than in CK. The annual decomposition coefficients (k-values) in the +N, +S, and +NS treatments were 0.384 ± 0.002, 0.378 ± 0.002, and 0.374 ± 0.001 year⁻¹, respectively, which were significantly lower than the k-values in CK (0.452 ± 0.005 year⁻¹, p < 0.05). The remaining mass, lignin, cellulose, C, and litter N/P ratio were higher, whereas the soil pH was lower in the +NS treatment than in the +N and +S. The interactive effects of N addition and S addition on the remaining litter lignin, cellulose, C, N, and P; the litter C/N, C/P, and N/P ratios; and the soil pH were significant (p < 0.05). In conclusion, the addition of N and S synergistically decreased the degradation of lignin and cellulose and the release of C and N and increased the litter N/P ratio, suggesting that external N and S inputs synergistically slowed the release of C and N from litter and exacerbated litter P limitation during decomposition in this forest. Full article

Whether decomposition can be affected by the biodiversity of soil organisms is an important question. Biodiversity is commonly expressed through indices that are based on species richness and abundances. Soil processes tend to saturate at low levels of species richness. A component of biodiversity is functional diversity, and we have shown that the absence of the influence of species richness on decomposition switched into a positive relationship between fauna diversity and decomposition when we expressed biodiversity in terms of interspecific functional dissimilarity. Communities with functionally dissimilar species are characterized by complementary resource use and facilitative interactions among species. It is suggested that the effects of environmental changes on ecosystem functions such as decomposition can be better understood if we have more knowledge about the selective effect of these changes on specific facets of soil biodiversity, such as functional diversity. Full article