[Effects of 40 Years of Fertilizer Application on the Characteristics of Soil Enzymatic Stoichiometry in Black Soil].

Microorganisms produce extracellular enzymes to meet elemental requirements and cope with stoichiometric imbalances of resources. To gain insights into the cycling of C, N, and P, the activities of the C∶N∶P acquisition enzymes have been extensively investigated. To detect the effects of long-term fertilization practices on soil nutrient balance and characteristics of soil enzymatic stoichiometry in black soil, four different fertilization treatments were selected： no fertilization （CK）, nitrogen fertilizer （N）, phosphorus fertilizer （P）, and combination of nitrogen and phosphorus fertilizers （NP）. Soil samples were collected in both April 2021 and April 2022 to determine soil enzyme activities and their stoichiometric characteristics. The results showed that soil acid phosphatase and ß-D-glucosidase activities were significantly higher in the N and NP treatments than in CK by 68%-158% and 26%-222%, respectively. Soil ß-N-acetylaminoglucosidase activities were significantly higher in the P and NP treatments, with the highest around 75.48 nmol·ï¼ˆg·h）-1 and 106.81 nmol·ï¼ˆg·h）-1, respectively. Two-way ANOVA analysis showed that N and P inputs had a great impact on soil enzyme activities. Redundancy analysis showed that the main factors controlling enzyme activities were soil pH, microbial biomass phosphorus, and soil available P content. It was found that N inputs significantly increased enzyme vector length, which was ranged from 1.32 to 1.52, and the enzyme vector angles were all larger than 45°, suggesting C and P co-limited in the black soils. These findings suggest that 40 years of fertilization have had a great impact on soil enzymes and the related resource use strategy, which provides great implications for assessing soil nutrients balance and soil sustainability.

Response of gene abundance of ammonia-oxidizing microorganisms and denitrifying microorganisms to nitrogen and phosphorus addition in subtropical forest.

We conducted a nitrogen (N) and phosphorus (P) addition experiment in Qianjiangyuan National Park in 2015, to investigate the response of ammonia-oxidizing microorganisms and denitrifying microorganisms. There were four treatments, including N addition (N), P addition (P), NP, and control (CK). Soil samples were collected in April (wet season) and November (dry season) of 2021. The abundance of amoA gene of ammonia-oxidizing microorganisms (i.e., ammonia-oxidizing archaea, AOA; ammonia-oxidizing bacteria, AOB; comammox) and denitrifying microbial genes (i.e., nirS, nirK, and nosZ) were determined using quantitative PCR approach. The results showed that soil pH was significantly decreased by long-term N addition, while soil ammonium and nitrate contents were significantly increased. Soil available P and total P contents were significantly increased with the long-term P addition. The addition of N (N and NP treatments) significantly increased the abundance of AOB-amoA gene in both seasons, and reached the highest in the N treatment around 8.30×107 copies·g-1 dry soil. The abundance of AOA-amoA gene was significantly higher in the NP treatment than that in CK, with the highest value around 1.17×109 copies·g-1 dry soil. There was no significant difference in N-related gene abundances between two seasons except for the abundance of comammox-amoA. Nitrogen addition exerted significant effect on the abundance of AOB-amoA, nirK and nosZ genes, especially in wet season. Phosphorus addition exerted significant effect on the abundance of AOA-amoA and AOB-amoA genes in both seasons, but did not affect denitrifying gene abundances. Soil pH, ammonium, nitrate, available P, and soil water contents were the main factors affecting the abundance of soil N-related functional genes. In summary, the response of soil ammonia-oxidizing microorganisms and denitrifying microorganisms was more sensitive to N addition than to P addition. These findings shed new light for evaluating soil nutrient availability as well as their response mechanism to global change in subtropical forests.