Soil extracellular enzyme stoichiometry reveals the nutrient limitations in soil microbial metabolism under different carbon input manipulations.

Changes in the quality and quantity of litter and root inputs due to climate change and human activities can influence below-ground biogeochemical processes in forest ecosystems. However, it is unclear whether and how much aboveground litter and root inputs affect soil microbial metabolism and nutrient limitation mechanisms. In this study, according to a 4-years field manipulation experiment, litter and root manipulations (control (CK), double litter input (DL), no litter (NL), no root (NR), and no inputs (NI)) were set up to analyze the extracellular enzyme activities and stoichiometric ratios characteristics of 0-10 cm and 10-20 cm soils, explore the metabolic limitations of microorganisms, and clarify the main driving factors restricting nutrient limitation. The results showed that the enzyme activities associated with the C cycling (ß-1,4-glucosidase (BG), cellulose disaccharide hydrolase (CBH)) and N cycling (ß-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP)) in DL treatment were significantly higher than those in NR treatment. Moreover, enzyme activities related to P cycling are significantly higher in comparison to other treatments. The acid phosphatase (AP), which is related to the P cycle, showed the highest activity under NR treatment. In addition, there was no significant difference in soil microbial metabolic limitation by the different carbon inputs, which did not change the original nutrient limitation pattern. The main drivers of microbial nutrient metabolic limitation included soil physicochemical properties, soil total nutrients, and available nutrients, among which soil SWC and pH presented the greatest influence on microbial C limitation and soil total nutrients showed the greatest influence on microbial N limitation. Changes in soil carbon input altered soil extracellular enzyme activities and their stoichiometric ratios by affecting soil physicochemical properties, total nutrients. This study provides data for the understanding of material cycling in forest ecosystems under environmental change.

[Characteristics of Soil Organic Carbon Components and Their Correlation with Other Soil Physical and Chemical Factors in Cotton Fields with Different Continuous Cropping Years in the Oasis on the Northern Edge of Tarim Basin].

The study of soil organic carbon components in continuous cropping cotton fields in oases is helpful to reveal the change characteristics of the soil organic carbon stability mechanism in arid areas under the effects of man-land relationships. In this study, the contents of soil organic carbon, easily oxidized organic carbon, dissolved organic carbon, and microbial biomass carbon in cotton fields with different continuous cropping years (2 a, 5 a, 12 a, 20 a, and 35 a) were collected and analyzed by using space instead of the time series method. Through redundancy analysis, the relationship between soil organic carbon components and other soil physical and chemical factors was discussed. The results showed that:① continuous cropping for different years had a significant impact on the content of soil organic carbon components in the study area. The contents of soil organic carbon, easily oxidized organic carbon, dissolved organic carbon, and microbial biomass carbon in continuous cropping cotton fields for 12 a, 20 a, and 35 a were higher than those in continuous cropping cotton fields and wasteland for 2 a and 5 a. ω(soil organic carbon) reached the peak value (7.06 g·kg-1) in the cotton field in 20 a, which was 76.91% higher than that in the wasteland. The content of soil organic carbon decreased with the deepening of the soil layer. ② Based on the redundancy analysis of soil organic carbon content and soil environmental factors, the results showed that the content of soil organic carbon was positively correlated with total nitrogen, available phosphorus, and water content and negatively correlated with pH value and bulk density. The importance of soil environmental factors on the interpretation of soil organic carbon content was as follows:total N>available P>pH value>bulk density>water content>available K>total salt.