Control of climate and litter quality on leaf litter decomposition in different climatic zones

Gut microbial communities and their potential roles in cellulose digestion and thermal adaptation of earthworms

Adaptations to temperature and food resources, which can be affected by gut microbiota, are two main adaptive strategies allowing soil fauna to survive in their habitats, especially for cold-blooded animals. Earthworms are often referred to as ecosystem engineers because they make up the biggest component of the animal biomass found in the soil. They are considered as an important indicator in the triangle of soil quality, health and functions. However, the roles of gut microbiota in the environmental adaptation of earthworms at a large scale remain obscure. We explored the gut bacterial communities and their functions in the environmental adaptation of two widespread earthworm species (Eisenia nordenskioldi Eisen and Drawida ghilarovi Gates) in Northeast China (1661 km). Based on our findings, the alpha diversity of gut bacterial communities decreased with the increase of latitude, and the gut bacterial community composition was shaped by both mean annual temperature (MAT) and cellulose. Actinobacteria, Proteobacteria, Firmicutes, and Planctomycetes, recognized as the predominant cellulose degraders, were keystone taxa driving gut bacterial interactions. Actinobacteria, Firmicutes, and Planctomycetes were influenced by MAT and cellulose, and had higher contributions to gut total cellulase activity. The optimal temperature for total cellulase in the gut of E. nordenskioldi (25-30 °C) was lower than that of D ghilarovi (40 °C). The gut microbiota-deleted earthworms had the lowest cellulose degradation rate (1.07 %). The cellulose was degraded faster by gut bacteria from the host they were derived, indicating the presence of home field advantage of cellulose decomposition. This study provides a foundation for understanding the biotic strategies adopted by earthworms when they enter a new habitat, with gut microbiota being central to food digestion and environmental adaptability.

Field performance of sweet sorghum in salt-affected soils in China: A quantitative synthesis

Sweet sorghum is a high-yield crop with strong resistance, which has the potential to support the development of the forage farming industry in China where vast salt-affected lands are potentially arable. Nutrient management is imperative for sweet sorghum growing on salt-affected lands. Although nitrogen (N) synthetic fertilizers have long been recognized as a key factor for increasing crop yields, their effects on sweet sorghum cultivation are under debate. Consequently, this study integrated the current available observations of yield (n = 255) and partial factor productivity of nitrogen (NPFP, n = 242) of sweet sorghum in salt-affected lands, which included both inland (n = 189) and coastal (n = 66) areas. We quantitatively analyzed the effects of climatic, soil properties and management measures on biomass yield and NPFP of sweet sorghum, comparing the differences between inland and coastal salt-affected lands. We found that average biomass yield and NPFP of sweet sorghum in coastal areas were 19,082.48 ± 8262.75 kg/ha and 107.29 ± 51.44 kg/kg respectively, both significantly lower than that in inland areas (p < 0.05). The N application rate did not have significant promoting effect on the biomass yield of sweet sorghum in inland salt-affected areas (p > 0.05), whereas in coastal salt-affected areas, N application significantly increased the biomass yield of sweet sorghum. Increasing soil organic matter content could promote NPFP in inland areas. The recommended N application rate for inland salt-affected and coastal salt-affected areas were 100 kg/ha and 150 kg/ha respectively. The results indicate that it is crucial to apply nutrient management measures based on the local climatic and soil conditions, since the causes of salinity differ in coastal and inland salt-affected lands. More systematic field studies are required in the future to optimize the management of water and nutrients for sweet sorghum planting in salt-affected lands.

Microbial community composition controls carbon flux across litter types in early phase of litter decomposition

Leaf litter decomposition is a major carbon input to soil, making it a target for increasing soil carbon storage through microbiome engineering. We expand upon previous findings to show with multiple leaf litter types that microbial composition can drive variation in carbon flow from litter decomposition and specific microbial community features are associated with synonymous patterns of carbon flow among litter types. Although plant litter type selects for different decomposer communities, within a litter type, microbial composition drives variation in the quantity of dissolved organic carbon (DOC) measured at the end of the decomposition period. Bacterial richness was negatively correlated with DOC quantity, supporting our hypothesis that across multiple litter types there are common microbial traits linked to carbon flow patterns. Variation in DOC abundance (i.e. high versus low DOC) driven by microbial composition is tentatively due to differences in bacterial metabolism of labile compounds, rather than catabolism of non-labile substrates such as lignin. The temporal asynchrony of metabolic processes across litter types may be a substantial impediment to discovering more microbial features common to synonymous patterns of carbon flow among litters. Overall, our findings support the concept that carbon flow may be programmed by manipulating microbial community composition.

Phytolith-Occluded Carbon Storages in Forest Litter Layers in Southern China: Implications for Evaluation of Long-Term Forest Carbon Budget

Phytolith-occluded carbon (PhytOC) can be preserved in soils or sediments for thousands of years and might be a promising potential mechanism for long-term terrestrial carbon (C) sequestration. As the principal pathway for the return of organic matters to soils, the forest litter layers make a considerable contribution to terrestrial C sequestration. Although previous studies have estimated the phytolith production fluxes in the above-ground vegetations of various terrestrial ecosystems, the storages of phytoliths and PhytOC in litter layers have not been thoroughly investigated, especially in forest ecosystems. Using analytical data of silica, phytoliths, return fluxes and storages of forest litter, this study estimated the phytolith and PhytOC storages in litter layers in different forest types in southern China. The results indicated that the total phytolith storage in forest litter layers in southern China was 24.34 ± 8.72 Tg. Among the different forest types, the phytolith storage in bamboo forest litter layers (15.40 ± 3.40 Tg) was much higher than that in other forests. At the same time, the total PhytOC storage reached up to 2.68 ± 0.96 Tg CO2 in forest litter layers in southern China, of which approximately 60% was contributed by bamboo forest litter layers. Based on the current litter turnover time of different forest types in southern China, a total of 1.01 ± 0.32 Tg of PhytOC per year would be released into soil profiles as a stable C pool during litter decomposition, which would make an important contribution to the global terrestrial long-term biogeochemical C sink. Therefore, the important role of PhytOC storage in forest litter layers should be taken into account in evaluating long-term forest C budgets.

Contribution of Harvest Residues to Nutrient Cycling in a Tropical Acacia mangium Willd. Plantation

Harvest residues can play a crucial role in conserving nutrients for recycling in forests, but little is known about the rates of decomposition and nutrient release from these residues following logging in tropical acacia plantations. In this study, we examined the biomass and nutrient content of harvest residue components (bark, leaves, and branches) using the litterbag technique for a 1.5-year-period following harvest of a seven-year-old Acacia mangium plantation in Northern Vietnam. At harvest, the total dry biomass of harvest residues was 18 t ha−1 comprising bark (8.9 t ha−1), branches (6.6 t ha−1), and leaves (2.5 t ha−1). The retained bark on site conserved 51% N, 29% P, 32% K, 64% Ca, and 24% Mg content from harvest residues for recycling. Decomposition rate of the leaves was the most rapid (k = 1.47 year−1; t0.5 = 0.47 year), then branches (k = 0.54 year−1; t0.5 = 1.29 year), and bark (k = 0.22 year−1; t0.5 = 3.09 year). During decomposition, the loss of nutrients from harvest residues was K ≈ Ca > N > P> Mg. Decomposition of harvest residues and the associated rate of nutrient release can potentially supply a significant amount of nutrients required for stand development in the next rotation.