Afforestation with an age-sequence of Mongolian pine plantation promotes soil microbial residue accumulation in the Horqin Sandy Land, China

Land use change affects the balance of organic carbon(C)reserves and the global C cycle.Microbial residues are essential constituents of stable soil organic C(SOC).However,it remains unclear how microbial residue changes over time following afforestation.In this study,16-,23-,52-,and 62-year-old Mongolian pine stands and 16-year-old cropland were studied in the Horqin Sandy Land,China.We analyzed changes in SOC,amino sugar content,and microbial parameters to assess how microbial communities influence soil C transformation and preservation.The results showed that SOC storage increased with stand age in the early stage of afforestation but remained unchanged at about 1.27-1.29 kg/m2 after 52 a.Moreover,there were consistent increases in amino sugars and microbial residues with increasing stand age.As stand age increased from 16 to 62 a,soil pH decreased from 6.84 to 5.71,and the concentration of total amino sugars increased from 178.53 to 509.99 mg/kg.A significant negative correlation between soil pH and the concentration of specific and total amino sugars was observed,indicating that the effects of soil acidification promote amino sugar stabilization during afforestation.In contrast to the Mongolian pine plantation of the same age,the cropland accumulated more SOC and microbial residues because of fertilizer application.Across Mongolian pine plantation with different ages,there was no significant change in calculated contribution of bacterial or fungal residues to SOC,suggesting that fungi were consistently the dominant contributors to SOC with increasing time.Our results indicate that afforestation in the Horqin Sandy Land promotes efficient microbial growth and residue accumulation in SOC stocks and has a consistent positive impact on SOC persistence.

Linkage of microbial living communities and residues to soil organic carbon accumulation along a forest restoration gradient in southern China

Background:Forest restoration has been considered an effective method to increase soil organic carbon(SOC),whereas it remains unclear whether long-term forest restoration will continuously increase SOC.Such large uncertainties may be mainly due to the limited knowledge on how soil microorganisms will contribute to SOC accumulation over time.Methods:We simultaneously documented SOC,total phospholipid fatty acids(PLFAs),and amino sugars(AS)content across a forest restoration gradient with average stand ages of 14,49,70,and>90 years in southern China.Results:The SOC and AS continuously increased with stand age.The ratio of fungal PLFAs to bacterial PLFAs showed no change with stand age,while the ratio of fungal AS to bacterial AS significantly increased.The total microbial residue-carbon(AS-C)accounted for 0.95-1.66% in SOC across all forest restoration stages,with significantly higher in fungal residue-C(0.68-1.19%)than bacterial residue-C(0.05-0.11%).Furthermore,the contribution of total AS-C to SOC was positively correlated with clay content at 0-10 cm soil layer but negatively related to clay content at 10-20 cm soil layer.Conclusions:These findings highlight the significant contribution of AS-C to SOC accumulation along forest restoration stages,with divergent contributions from fungal residues and bacterial residues.Soil clay content with stand age significantly affects the divergent contributions of AS-C to SOC at two different soil layers.

Effect of Kelp Residue Microbial Fertilizer on Eco-Control Peanut Pathogenic Fungus Aspergillus Parasiticus 1

Ecological prevention and control of plant disease is very important in sustainable agriculture.Adjusting soil p H value and fertilizing organic microbial fertilizer are two effective measures in this process.Kelp residue contains a large amount of organic compounds and alkaline metal ions.The bio-control Bacillus amyloliquefaciens strain Hitwh-BA2 was inoculated into kelp residue medium to produce kelp residue microbial fertilizer.Acidic soil and alkaline soil were used to study the effect of kelp residue microbial fertilizer on soil p H and soil suppressive activity.Tip-culture method was used to determine soil leachate suppressive activity,which characterized the soil suppressive activity.Results showed that fertilizing kelp residue microbial fertilizer had increased the soil p H and soil suppressive ability significantly,which was verified by peanut validation experiments as well.Peanut potting experiments proved that fertilizing kelp residue microbial fertilizer not only improved the yield of peanuts obviously,but also reduced the amount of Aspergillus parasiticus 95 in peanut geocarposphere soil significantly.Results also showed that fertilizing kelp residue microbial fertilizer was effective in reducing A.parasiticus 95 infection rate.So the kelp residue microbial fertilizer has good potential application prospect on ecological prevention and control of plant disease.

Accumulation of residual soil microbial carbon in Chinese fir plantation soils after nitrogen and phosphorus additions

Nitrogen （N） and phosphorus （P） additions can affect soil microbial carbon （C） accumulation. However, the mechanisms that drive the changes in residual microbial C that occur after N and P additions have not been well-defined for Chinese fir plantations in subtropical China. We set up six different treatments, viz. a control （CK）, two N treatments （NI： 50kgha-1 a-1; N2： 100 kg ha-1 a-1）, one P treatment （P： 50 kg ha-1 a-1）, and two combined N and P treatments （NIP： 50kgha-1a-1 of N ＋50kgha-1a-1 of P; N2P：100 kg ha-1 a-1 of N ＋ 50 kg ha-1 a-1 of P）. We then investigated the influences of N and P additions on residual microbial C. The results showed that soil pH and microbial biomass decreased after N additions, while microbial biomass increased after P additions. Soil organic carbon （SOC） and residual microbial C contents increased in the N and P treatments but not in the control. Residual microbial C accumulation varied according to treatment and declined in the order： N2P 〉 N1P 〉 N2 〉 N1 〉 P 〉 CK. Residual microbial C contents were positively correlated with available N, P, and SOC contents, but were negatively correlated with soil pH. The ratio of residual fungal C to residual bacterial C increased under P additions, but declined under combined N1P additions. The ratio of residual microbial C to SOC increased from 11 to 14% under the N1P and N2P treatments, respectively. Our results suggest that the concentrations of residual microbial C and the stability of SOC would increase under combined applications of N and P fertilizers in subtropical Chinese fir plantation soils.

Fungal residues were more sensitive to nitrogen addition than bacterial residues in a meadow grassland soil

Nitrogen(N)addition can significantly affect the amount of soil carbon(C)pools through biological routes,and microbial residues are important components of soil carbon pools.However,it remains unclear how N addition affects the accumulation of soil microbial residues in meadow grasslands.This study analyzed the effects of N addition on microbial residues in a meadow grassland soil,and the key factors affecting the accumulation of microbial residues under N addition were analyzed in combination with soil physicochemical properties and microbial community structure.The results showed that N addition significantly changed the structure of the microbial communities and the accumulation of microbial residues,mainly manifested by a significant decrease in fungal biomass and the fungal/bacterial ratio(F/B),but had no significant effect on bacterial or total microbial biomass(PLFAs).N addition significantly increased the accumulation of fungal residues(7.45%),but had no significant effect on the accumulation of bacterial residues or total amino sugar(TAS).We found that fungal residues were more affected by soil environmental factors than bacterial residues.The results of the random forest analysis showed that bacterial biomass under N addition was the most important predictor of soil bacterial residues,whereas total N(TN),pH and F/B were the most important predictors of soil fungal residue.In summary,our results indicate that fungal communities and residues accumulation play important roles in regulating the response of grassland soil C to N addition,further enhancing our understanding of the mechanisms of soil carbon pool to N addition.

Linking microbial carbon pump capacity and efficacy to soil organic carbon storage and stability under heavy metal pollution

Heavy metal pollution can lead to a great loss of soil organic carbon(SOC).However,the microbial mechanisms that link heavy metal pollution to SOC remain poorly understood.Here,we investigated five apple-orchard soils at different distances from a Pb-Zn smelter.After assessing the heavy metal pollution level based on Grade Ⅱ of the national soil environmental quality standard(China),we found SOC stocks and microbial carbon pump(MCP)capacity(i.e.,microbial residue carbon)under medium and heavy pollution levels were significantly lower than those under safe,cordon and light pollution levels.The structural equation model showed causality in the SOC variations linked to pollution level through MCP capacity,which could contribute 77.8% of the variance in SOC storage.This verified MCP capacity can serve as a key parameter for evaluation of SOC storage under heavy metal pollution.Soil MCP efficacy,i.e.,the proportion of microbial residue carbon to SOC,also decreased under medium and heavy pollution.This suggested that,with a heavier pollution level,there was a higher rate of reduction of microbial residue carbon in soil than the rate of reduction of SOC.As MCP efficacy can be a useful assessment of SOC stability,the significantly positive relationship between MCP efficacy and clay content in correlation analysis implied that lower MCP efficacy was correlated with SOC stability under the heavier pollution level.Our study provides valuable insights to identify the mechanisms of microbially mediated C transformation processes that are influenced by heavy metal pollution in agroecosystems.

The soil Microbial Carbon Pump as a new concept for terrestrial carbon sequestration

Soil is a huge terrestrial carbon pool, which has higher carbon storage than the sum of atmospheric and terrestrial vegetation carbon. Small fluctuations in soil carbon pool can affect regional carbon flux and global climate change. As soil organic carbon plays key roles in soil carbon storage and sequestration, studying its composition, sources and stability mechanism is a key to deeply understand the functions of terrestrial ecosystem and how it will respond to climate changes. The recently-proposed concept of soil Microbial Carbon Pump(MCP) emphasizes the importance of soil microbial anabolism and its contributions to soil carbon formation and stabilization, which can be applied for elucidating the source, formation and sequestration of soil organic carbon. This article elaborates MCP-mediated soil carbon sequestration mechanism and its influencing factors, as well as representative scientific questions we may explore with the soil MCP conceptual framework.