Sheep manure application increases soil exchangeable base cations in a semi-arid steppe of Inner Mongolia

The long-term productivity of a soil is greatly influenced by cation exchange capacity（CEC）.Moreover,interactions between dominant base cations and other nutrients are important for the health and stability of grassland ecosystems.Soil exchangeable base cations and cation ratios were examined in a 11-year experiment with sheep manure application rates 0–1,500 g/（m2？a） in a semi-arid steppe in Inner Mongolia of China,aiming to clarify the relationships of base cations with soil p H,buffer capacity and fertility.Results showed that CEC and contents of exchangeable calcium（Ca2＋）,magnesium（Mg2＋）,potassium（K＋） and sodium（Na＋） were significantly increased,and Ca2＋ saturation tended to decrease,while K＋ saturation tended to increase with the increases of sheep manure application rates.The Ca2＋/Mg2＋ and Ca2＋/K＋ ratios decreased,while Mg2＋,K＋ and Na＋ saturations increased with increasing manure application rates.Both base cations and CEC were significantly and positively correlated with soil organic carbon（SOC） and soil p H.The increases of SOC and soil p H would be the dominant factors that contribute to the increase of cations in soil.On a comparison with the initial soil p H before the experiment,we deduced that sheep manure application could partly buffer soil p H decrease potentially induced by atmospheric deposition of nitrogen and sulfur.Our results indicate that sheep manure application is beneficial to the maintenance of base cations and the buffering of soil acidification,and therefore can improve soil fertility in the semi-arid steppes of northeastern China.

Enhanced carbon acquisition and use efficiency alleviate microbial carbon relative to nitrogen limitation under soil acidification

Background:Soil microbial communities cope with an imbalanced supply of resources by adjusting their element acquisition and utilization strategies.Although soil pH has long been considered an essential driver of microbial growth and community composition,little is known about how soil acidification affects microbial acquisition and utilization of carbon(C)and nitrogen(N).To close the knowledge gap,we simulated soil acidification and created a pH gradient by adding eight levels of elemental sulfur(S)to the soil in a meadow steppe.Results:We found that S-induced soil acidification strongly enhanced the ratio of fungi to bacteria(F:B)and microbial biomass C to N(MBC:MBN)and subsequently decreased the C:N imbalance between microbial biomass and their resources.The linear decrease in the C:N imbalance with decreasing soil pH implied a conversion from N limitation to C limitation.To cope with enhanced C versus N limitation,soil microbial communities regulated the relative production of enzymes by increasing the ratio ofβ-glucosidase(BG,C-acquiring enzyme)to leucine aminopeptidase(LAP,N-acquiring enzyme),even though both enzymatic activities decreased with S addition.Structural equation modeling(SEM)suggested that higher C limitation and C:N-acquiring enzyme stimulated microbial carbon-use efficiency(CUE),which counteracted the negative effect of metal stress(i.e.,aluminum and manganese)under soil acidification.Conclusions:Overall,these results highlight the importance of stoichiometric controls in microbial adaption to soil acidification,which may help predict soil microbial responses to future acid deposition.