The Response of Critical Microbial Taxa to Litter Micro-Nutrients and Macro-Chemistry Determined the Agricultural Soil Priming Intensity After Afforestation

Afforestation with trees and shrubs around cropland can effectively decrease soil degradation and avoid sand storms, but subsequent modification of litter quality accelerates the degradation of native organic matter via the soil priming effect (PE). Although carbon accumulation in agricultural soils after afforestation was widely studied, little is known about the extent to which soil organic carbon (SOC) mineralization is induced by complex residue input in agro-forest-grass composite ecosystems. Here, we mixed corn field soil and litter of afforestation tree and shrub species together in a micro-environment to quantify the effects of litter-mixture input on farmland soil priming associated with afforestation. Additionally, we studied the responses of bacterial and fungal species to litter chemistry, with the aim to identify the litter and microbial driver of soil priming. The results showed that soil priming was accelerated by different litter addition which varied from 24 to 74% of SOC mineralization, suggesting that priming intensity was relatively flexible and highly affected by litter quality. We also find that the macro-chemistry (including litter carbon, nitrogen, lignin, and cellulose) directly affects priming intensity, while micro-chemistry (including litter soluble sugar, water-soluble phenol, methanol-soluble phenol, and condensed tannin) indirectly influences priming via alteration to dominant bacterial taxa. The stepwise regression analysis suggested that litter nitrogen and cellulose were the critical litter drivers to soil priming (r2 = 0.279), and the combination of bacterial phylum Proteobacteria, Firmicutes, Bacteroidetes, Acidobacteria, and fungal taxa Eurotiomycetes was a great model to explain the priming intensity (r2 = 0.407).

Litter mixing effect on decomposition rate and nutrient release to water: low quality leaves of coastal species

Non-additive effect on litter decomposition often occurs in mixed terrestrial communities but little investigated on coastal ecosystems. We selected three common mangrove species and one alien saltmarsh species from a coastal wetland stand to test whether non-additive effect occurs when the litters of these coastal species mixed together. To avoid the heterogeneity of soil conditions and to detect nutrient release into water, we conducted an in vitro litter-bag experiment in a glasshouse. Among three litter mixtures, the non-additive effect was observed in the litter mixture composed of mangrove species Aegiceras corniculatum vs. Kandelia obovata (antagonistic) and A. corniculatum vs. Avicennia marina (synergistic), but not in the litter mixture of A. corniculatum vs. Spartina alterniflora (the alien saltmarsh species). The strength of non-additive effect was unrelated to litter initial trait dissimilarity. Instead, litter decomposition rate and mass remaining of litter mixtures were strongly related to the community-weighted mean of leaf carbon. The nutrients and carbon released into water were more likely controlled by litter decomposition rate rather than by litter initial nutrient concentrations. These findings would lead to the expectations on ecosystem scale that the mangrove stand mixed with A. corniculatum and K. obovata accumulates more organic carbon in the sediment and releases less nutrients into water column than the stand composed of A. corniculatum and A. marina . It is also implying that the alien species S. alterniflora invasion may not reduce soil carbon stock of mangrove forests. These hypotheses need to be further tested and which will be suggestive for the protection or reconstruction of coastal wetlands.

Diversity-decomposition relationships in forests worldwide

Plant species diversity affects carbon and nutrient cycling during litter decomposition, yet the generality of the direction of this effect and its magnitude remains uncertain. With a meta-analysis including 65 field studies across the Earth’s major forest ecosystems, we show here that decomposition was faster when litter was composed of more than one species. These positive biodiversity effects were mostly driven by temperate forests but were more variable in other forests. Litter mixture effects emerged most strongly in early decomposition stages and were related to divergence in litter quality. Litter diversity also accelerated nitrogen, but not phosphorus release, potentially indicating a decoupling of nitrogen and phosphorus cycling and perhaps a shift in ecosystem nutrient limitation with changing biodiversity. Our findings demonstrate the importance of litter diversity effects for carbon and nutrient dynamics during decomposition, and show how these effects vary with litter traits, decomposer complexity and forest characteristics.

Establishment of mixed plantations of Pinus sylvestris var. mongolica and Populus × xiaozhuanica may not be appropriate: evidence from litter decomposition

Aims Mongolian pine (Pinus sylvestris var. mongolica) and Xiaozhuan poplar (Populus × xiaozhuanica) are two predominant afforestation tree species in the semi-arid sandy lands of northeast China, which are characterized by poor soil nutrients. Plant litter decomposition plays a critical role in regulating nutrient cycling in terrestrial ecosystems. Admixture of broadleaf litter to conifer litter is expected to improve litter decomposition and soil fertility, and thus productivity. However, the effects on the decomposition of litter mixture of the above two tree species are not well understood. Therefore, it is essential to assess the decomposition performance of litter mixture with the aim of improving forest nutrient management and the establishment of mixed plantation. Appropriate forest management practice is critical for the sustainability of site productivity in plantation forests. Methods We conducted a field litterbag decomposition transplant experiment for single pine litter, single poplar litter and their mixture in a pine stand, a poplar stand and an adjacent grassland for 16 months in the Keerqin Sandy Lands, northeast China. Important Findings After 16 months of incubation, there remained significantly more litter mass of pine (73.8%) than of poplar (67.2%). The mass remaining was positively correlated with litter carbon (C):nitrogen (N), C:phosphorus (P) and lignin:N ratios, and negatively with litter N and P concentrations, which suggests that initial litter chemical properties were an important factor affecting litter decay. Generally, net N and P immobilizations were observed during decomposition. This indicates that litter decomposition in this area was N-limited as N was progressively immobilized, and then tended to induce P limitation. Thus, we strongly recommend prohibiting litter harvesting by local residents to maintain soil fertility in this nutrient-poor area. Our results do not support the home-field advantage hypothesis, as illustrated by the fact that, in most cases, mass loss of litter from native habitat was comparable to that in transplanted habitats during decomposition. Furthermore, a dominant additive effect was detected, indicating that the establishment of mixed plantation may not be appropriate for these two species.