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Studying the changes and linkages between dissolved organic matter (DOM) and microorganisms in soils during vegetation restoration will help to understand the role of vegetation restoration in soil carbon sequestration and thus improve the understanding of the global soil carbon cycle. Soil DOM molecules were characterized by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the results showed that the soil DOM consisted mainly of lignin/carboxylic rich alicyclic molecule (CRAM)-like structures, while the ratios of lipids and aliphatic/protein decreased in sequence with recovery time. Lipids and aliphatic/proteins with high H/C DOM (labile DOM) degrade preferentially, while lignin/CRAM-like structures and tannins with low H/C DOM (recalcitrant DOM) are recalcitrant during vegetation restoration. With the restoration of vegetation, DOM molecules tend to be diversified and complicated, and DOM compounds with low double bond equivalent (DBE), low aromatic, and low alkyl structures will be converted into persistent organic matter with high carbon numbers and high DBE. The diversity of soil microorganisms was determined by high-throughput sequencing. The results showed that the abundance and diversity of soil bacteria increased significantly after revegetation, while the abundance and diversity of soil fungi began to increase when the ecosystem became a more mature coniferous forest. The soil microbial community exhibited complex connectivity and strong interaction with DOM molecules during vegetation restoration. As most of the DOM molecules are recalcitrant, vegetation restoration facilitates C sequestration in the soil, thereby contributing to climate change mitigation.

Background Under natural conditions, soil nutrients are heterogeneously distributed, and plants have developed adaptation strategies to efficiently forage patchily distributed nutrient. Most previous studies examined either patch strength or patch size separately and focused mainly on root morphological plasticity (increased root proliferation in nutrient-rich patch), thus the effects of both patch strength and size on morphological and physiological plasticity are not well understood. In this study, we examined the foraging strategy of Neyraudia reynaudiana (Kunth) Keng ex Hithc, a pioneer grass colonizing degraded sites, with respect to patch strength and size in heterogeneously distributed phosphorus (P), and how foraging patchily distributed P affects total plant biomass production. Plants were grown in sand-culture pots divided into ½, ¼, 1/6 compartments and full size and supplied with 0 + 0/30, 0 + 7.5/30 and 7.5 + 0/30 mg P/kg dry soil as KH2PO4 or 0 + 15/15, 0 + 18.5/ 18.5, 7.5 + 15/15 mg kg − 1 in the homogenous treatment. The first amount was the P concentration in the central region, and that the second amount was the P concentration in the outer parts of the pot. Results After 3 months of growth under experimental conditions, significantly (p Conclusion The result demonstrates that root morphological and physiological plasticity are important adaptive strategies for foraging patchily distributed P and the former is largely determined by patch strength and size. The results also establish that foraging patchily distributed P resulted in increased total plant biomass production compared to homogeneous P distribution.

Dissolved Organic Matter (DOM) affects the fundamental biogeochemical processes in soil including circulation and distribution of carbon and nutrients. Likewise, soils are hotspots of microbial diversity, supporting their ability to provide key soil functions and ecosystem services. Detailed understanding of the interaction between DOM chemical diversity and soil microbial community is essential to predict the direction of C in soil after vegetation restoration. In this study we have characterized the chemical diversity of soil DOM, evaluated the associated changes of the soil microbial community composition and determined the specific relationship between DOM and microbial community composition. The results indicated that the unsaturated degree, obstinacy, oxidation degree, and average molecular mass of soil DOM increased with the duration of vegetation restoration. DOM with low double-bond equivalents (DBE) was less stable and was more likely to undergo transformation reactions to produce persistent organic materials with high carbon and high double-bond equivalents. The relative abundance of soil bacteria and fungi showed different trends in response to vegetation restoration efforts which may be related to the change of soil chemical composition as suggested by redundancy analysis. In addition, network analysis identified complex connectivity and strong interaction between the soil microbial community and DOM. Overall, this study has important guiding and prediction significance for the relationship between DOM and soil microbial community during vegetation restoration. Moreover, it provides a theoretical basis for the quantitative evaluation of the ecological restoration effect to alleviate soil and water loss on the Loess Plateau.

Additional file 1. Supplementary material.

Vegetation restoration greatly alters soil phosphorus (P) fractions and microbial community diversity, but the response of soil P dynamics to microbial activity, particularly to that of phosphorus-solubilizing bacteria (PSB), remains unclear. This study aimed to evaluate the effect of vegetation restoration on the content of various P fractions and by extension on the diversity of PSB. We also attempted to discover the role of PSB in promoting the availability of P in vegetation restoration chronosequence. According to the vegetation restoration sequence, soil samples were collected from bare land and forests stands of 6, 10, 34, and 80 years old. The PSB was detected by phoD gene function and the soil P fractions were determined by the Hedley sequential fractionation method as modified by Tiessen and Moir. We found that vegetation restoration effectively improved soil available P content, but there was no significant difference in soil available P content in 80-year and 34-year stands. Residual-P accounted for the largest proportion in all stages of vegetation restoration, up to 55%. With stand development, the diversity of soil PSB increased and reached its maximum in R34. The rare PSB groups greatly promoted the increase of PSB abundance. Proteobacteria was the main soil PSB expressing a large amount of acid phosphatase in the whole vegetation restoration sequence, which played an important role in the mineralization of HCl-Po. Although the relative abundance of Ramlibacter and Lysobacter was relatively low, they also played important roles in the mineralization of Residual-P and NaHCO3-Po, respectively.

Depletion of soil nutrients is a major cause of decline in productivity of forest plantations in successive rotations. Biochar amendment in agricultural systems has been shown to yield various beneficial effects, including increasing soil phosphorus (P) availability. However, the direct and indirect effects of biochar addition on forest soil P dynamics have largely been unexplored. The objective of this study was to examine how biochar produced from harvest residue (leaves and woodchips) affect the P dynamics in second rotation Cunninghamia lanceolata (Chinese fir) plantation soil. An incubation experiment which involved mixing of forest soil with 1% or 3% w/w leaf or woodchip biochar, pyrolyzed at 300 °C or 600 °C, was conducted for 80 days at 20 °C. After 7, 40 and 80 days of incubation, soil samples were analyzed for total and available P, inorganic and organic P pools, and soil phosphatase activity. At the end of the incubation period, bacterial community composition and diversity were analyzed by 16S rDNA sequencing. The leaf biochar produced at both pyrolysis temperatures was more alkaline and had significantly higher soluble P, nitrogen and calcium contents than the woodchip biochar. Soil total and available P increased significantly in all leaf biochar treatments after 80 days incubation compared to the untreated control soil, but the woodchip biochar treatments had no significant effects. At the end of the experiment, Al-P content was significantly lower and Ca10-P content higher in soil amended with both biochar types compared to the control soil, and Fe-P content was significantly higher in the leaf biochar treatments. Contrary to expectations, acid and alkaline phosphatase enzyme activities were significantly lower in some of the biochar treatments after 80 days incubation compared to the control soil. Nevertheless, the diversity of the bacterial community was higher in leaf biochar-amended forest soil than the woodchip biochar-amended and untreated soil at the end of the experiment. In particular, the abundance increased in the leaf biochar soil treatments of P-solubilizing bacteria, such as Burkholderia-Paraburkholderia, Planctomyces, Sphingomonas and Singulisphaera, which can indirectly improve P availability in soil. Thus, conversion of tree harvest residues, particularly leaves, into biochar and recycling back into the soil could be a viable option to boost P availability and help to conserve nutrients or reduce nutrient losses for the next rotation. Before recommending plantation management with biochar, long-term studies are required assessing the life cycle of biochar under field conditions and its promoting effect on growth of C. lanceolata.

A greenhouse experiment was conducted to assay the bioaccumulation and tolerance characteristics of Rhus chinensis Mill. to lead (Pb). The effects of exposing R. chinensis Mill seedlings to increasing Pb concentrations (0, 250, 500, 100mgkg-1) in the soil were assessed by measuring Pb accumulation, subcellular distribution, ultrastructure, photosynthetic characteristics, antioxidative enzyme activity, malondialdehyde content, and phytochelatin content. The majority of Pb taken up by R. chinensis Mill was associated with the cell wall fraction in the roots, where the absorption of Ca increased to maintain cell wall stability, and Pb deposits were found in the intercellular space or in the cell wall structures. In leaves, Pb was primarily stored in the cell wall, while it was compartmentalized into the vacuolar structures in the stem. Pb concentrations adversely affected the morphology of Rhus chinensis Mill cellular substructures. Furthermore, increased Peroxidase (POD) and catalase (CAT) activity was observed in plants grown in Pb-amended soil, and this may have led to reduced ROS to maintain the function of the membrane. Changes in phytochelatin levels (PCs) that were observed in Pb treated plants suggest that PCs formed complexes with Pb in the cytoplasm to reduce Pb2+ toxicity in the metabolically active cellular compartment. This mechanism may allow for the plant to accumulate higher concentrations of toxic Pb and survive for a longer period of time. Our study provides a better understanding of how Rhus chinensis Mill detoxifies Pb.