No-tillage is commonly used as a sustainable and environmentally friendly cropland management practice in intensive agricultural ecosystems. However, the impact of no-tillage practices on soil multifunctionality and microbial metabolic entropy, as well as their interconnection, remains largely uninvestigated. Consequently, we performed a meta-analysis using 96 scholarly articles, encompassing 390 global studies on the impact of notillage on soil multifunctionality and microbial metabolic entropy. The results showed that no-tillage significantly improved soil multifunctionality compared with conventional tillage. At the same time, no-tillage significantly reduced microbial metabolic entropy by 12.6 % and improved carbon use efficiency. On a global scale, pH was the main factor regulating microbial metabolic entropy and soil multifunctionality, and there was a negative link between them, particularly in soils with a pH above 7. Meanwhile, the increase in the duration of no-tillage can effectively reduce the soil microbial metabolic entropy of soil microbics and reduce carbon emissions. Straw returning in no-tillage systems is a key management measure to improve soil multifunctionality and microbial carbon utilization efficiency (CUE). In summary, our findings emphasize the significance of notillage as a sustainable agricultural technique for enhancing soil multifunctionality and microbial CUE, which is conducive to the reduction of soil carbon emissions.

Artificial forest restoration is widely recognized as a crucial approach to enhance the potential of soil carbon sequestration. Nevertheless, there is still limited understanding regarding the dynamics of aggregate organic carbon (OC) and the underlying mechanisms driving these dynamics after artificial forest restoration. To address this gap, we studied Pinus tabuliformis forests and adjacent farmland in three recovery periods (13, 24 and 33 years) in the Loess Plateau region. Samples of undisturbed soil from the surface layer were collected and divided into three aggregate sizes: >2 mm (large aggregate), 0.25-2 mm (medium aggregate), and <0.25 mm (small aggregate). The aim was to examine the distribution of OC and changes in enzyme activity within each aggregate size. The findings revealed a significant increase in OC content for all aggregate sizes following the restoration of Pinus tabuliformis forests. After 33 years of recovery, the OC of large aggregates, medium aggregates and micro-aggregates increased by (30.23 ± 9.85)%, (36.71 ± 21.60)% and (37.88 ± 16.07)% respectively compared with that of farmland. Moreover, the restoration of Pinus tabuliformis forests lead to increased activity of hydrolytic enzymes and decreased activity of oxidative enzymes. It is noteworthy that the regulation of carbon in all aggregates is influenced by soil P-limitation. In large aggregates, P-limitation promotes the enhancement of hydrolytic enzyme activity, thereby facilitate OC accumulation. Conversely, in medium and small aggregates, P-limitation inhibits the increase in oxidative enzyme activity, resulting in OC accumulation. The results emphasize the importance of P restriction in regulating OC accumulation during the restoration of Pinus tabulaeformis forest, in which large aggregates play a leading role.

Understanding the distribution and transfer of photosynthetic carbon (PC) in ecosystems is important to determine the fate of soil carbon (C). However, the allocation on plants of newly fixed PC during secondary succession is unknown. Using in-situ (CO2)-C-13 pulse labeling we report characteristics of PC turnover and driving factors that drive it in plants and soils at different successional stages on the Loess Plateau, China. Within 30 d of labeling, C-13 abundance significantly decreased in plant leaves and stems, and significantly increased in roots, especially on farmland abandoned for 30a (from 114.67 mg center dot m(-2) to 225.08 mg center dot m(-1)). The abundance of C-13 in soils significantly increases over time, with C-13 abundances in bulk soil 8a after abandonment being 8.17 % higher than those after 30a and 9.34 % after 15a. The contribution of newly fixed PC to soil organic carbon (SOC) was also significantly higher in soil 8a after abandonment than after 15a and 30a. Plant diversity and nutrients are the main factors to drive PC fixation and transfer. Because farmland abandoned for 8a has low plant diversity, high species evenness, and high plant nutrient contents, its plant-soil system fixes more PC. Plant diversity is a key predictor of PC fixation, and plant nutrients have an important influence on the transfer of PC. These results provide improve our understanding of vegetation restoration and terrestrial carbon sequestration in abandoned farmlands.

Plant nutrient requirements and acquisition strategies are critical to understand the net primary productivity and community stability in terrestrial ecosystems. However, the current knowledge regarding this subject is limited, especially in the case of afforestation. Therefore, we selected four Robinia pseudoacacia (RP) forests (15-, 21-, 31-, and 46-year-old forests) in the Loess Plateau, and analyzed the nutrients in the plant organs, litter, and soil, along with the extracellular enzyme activities (EEAs), microbial biomass, and mineralization rate. In addition, the biomass of RP was determined using an allometric growth model. The results showed that during afforestation, the nitrogen and phosphorus requirement of RP increased significantly, from 3.97 to 18.14 g & BULL;m  2 & BULL;year  1 and 0.17 to 0.71 g & BULL;m  2 & BULL;year  1, respectively, while the nutrient resorption efficiency and the contributions of nutrient resorption to the total nutrient requirements significantly decreased. Meanwhile, the ratio of nitrogen to phosphorus resorption efficiency (NRE:PRE) significantly increased with afforestation, but were less than 1 which may indicate the phosphorus limitation of RP decreased. In addition, the vector angle significantly increased form 44.80 degrees to 49.51 degrees after afforestation, which may indicate the phosphorus limitation of soil microorganisms increased. Meanwhile, the vector angle was significantly positive with phosphorus mineralization rate and NRE: PRE, which may show that soil microorganisms activity alleviate the phosphorus limitation of plants. Collectively, our study contributes to a better understanding of nutrient cycling above and below the ground.

In order to explore the characteristics of the soil organic carbon(SOC)pool and its chemical composition during the succession of secondary forests in the Loess Plateau, samples of the primary stage (Populus davidiana forest), transition stage (Populus davidiana and Quercus wutaishansea mixed forest), and top stage (Quercus wutaishansea forest) of secondary forest succession in the Huanglong Mountain forest area of the Loess Plateau in Northern Shaanxi were selected as the research object. The variation characteristics of SOC content, storage, and its chemical composition at different soil depths (0-10, 10-20, 20-30, 30-50, and 50-100 cm) were analyzed. The results showed that:① the contents and storage of SOC increased significantly with the secondary forest succession process (P<0.05). The content of SOC decreased significantly with the increase in soil depth, and the storage of SOC increased from 64.8 Mg·hm-2 in the primary stage to 129.2 Mg·hm-2 in the top stage, with an increase of 99%. ② During the succession of secondary forests, in the surface (0-30 cm) soil organic carbon, the relative content of aliphatic carbon components that have a simple structure and can be decomposed more easily decreased, and the relative content of aromatic carbon components that have a complex structure and cannot be decomposed easily increased, indicating that the chemical composition of organic carbon stability of surface-layer soil increased significantly with the process of secondary forest succession. However, the stability of the chemical composition of SOC in the deep layer (30-100 cm) first increased and then decreased, that is, the transition stage>the top stage>the primary stage. ③In the process of secondary forest succession, the stability of SOC chemical composition in the primary stage and transition stage increased significantly with the increase in soil depth. The top stage tended to be stable, and the deep soil carbon stability decreased slightly. ④ Pearson correlation analysis showed that during the secondary forest succession process, SOC storage and chemical composition stability were significantly negatively correlated with soil total phosphorus content. In general, the content and storage of SOC in the 0-100 cm soil increased significantly during the secondary forest succession, playing the role of a "carbon sink." The stability of the chemical composition of SOC in the surface layer (0-30 cm) increased significantly, but in the deep layer (30-100 cm), it increased first and then decreased.

Soil organic carbon (SOC) mineralization is a process driven by microorganisms and is considered to be one of the main forms of carbon loss in land restoration. However, the interaction of SOC structures and bacteria that drive SOC mineralization remain unclear. Therefore, four forest succession stages were investigated on the Loess Plateau of Northern China: (1) primary stage Betula platyphylla (BP); (2) transitional stage which were two mixed communities of Populus davidiana and Quercus wutaishanica with different proportions (PQ1); (3) (PQ2) and (4) the late stage was climax communities of Quercus wutaishanica (QW). The Illumina sequencing of the 16S rRNA gene and Fourier transformation infrared (FTIR‐ATR) spectroscopy were used to clarify the regulation mechanism of microbial activity on SOC mineralization during forest succession through the perspective of SOC structures. Our results indicated higher aromatics‐C in QW contributed to decreased SOC mineralization ratio (SMR). Redundancy analysis confirmed SOC structures–bacteria interaction and revealed the groups Acidobacteria correlated with recalcitrant SOC structures while Proteobacteria and Bacteroides correlated with labile SOC structures, respectively. Moreover, the partial least squares path model revealed that the SOC and C:N ratio act on soil bacteria community characteristics, and the higher abundance of Acidobacteria and the increase of aromatics‐C decreased SMR. Collectively, these findings highlight the importance of bacteria–SOC structures interaction in decreased SMR and contribute to an improved understanding of how forest succession regulates carbon mineralization.

Changes in the composition of organic carbon lead to shifts in the selective environment, which in turn contribute to changes in the composition and assembly process of soil bacterial communities at different suc-cessional stages. Deterministic and stochastic processes are expected to clarify bacterial community assembly process during long-term ecosystem recovery. Therefore, by studying the bacterial community of the organic horizon and mineral horizon during forest succession, the main role of organic carbon composition in deter-mining soil bacterial community structure and assembly process during forest succession in the arid regions of Loess Plateau, China was revealed. Stochastic assembly was predominant in the organic horizon (75.0%) and mineral horizon (71.6%), and its relative contribution of stochastic assembly was similar in two horizons. In addition, network analyses demonstrated that bacterial nodes (as individual taxa) and connectivity between them was higher in the organic horizon (nodes: 297 and edges: 5242) than mineral horizon (nodes: 251 and edges: 1694). During forest succession, the bacterial community gradually changed to a K-strategy, and the degree of bacterial network connection cross the organic horizon and mineral horizon gradually decreased. The taxon-organic carbon composition cooccurrence network aided in identifying the relationship between the composition of organic carbon and the bacterial community, and ploysaccharide, methyl and aliphatic carbon were the main reason for the differences in the bacterial community. Meanwhile, the relationship between the composition of organic carbon in bacterial assembly was different in the organic horizon and mineral horizon: ploysaccharide, methyl, aliphatic, aromatics and carboxylic carbon were the main factors driving bacterial as-sembly in the organic horizon, whereas the interaction of them with bacterial traits jointly participated the assembly process in the mineral horizon. Our results highlight the importance of resource availability, partic-ularly the composition of organic carbon, in determining how the microbial community composition assembles during forest succession.