The rhizosphere priming effect (RPE) is the change in decomposition of soil organic matter caused by root activity, and it can be affected by plant species, nutrient availability, and by many other factors. Although plant and soil nitrogen (N) are likely to greatly influence RPE and vice-versa, not much is known about these relationships. There is a need for more research, particularly in N-fertilized cropping systems. We examined the RPE on soil N mineralization in a 42-day greenhouse experiment. The experiment included three vegetable crops (broccoli, lettuce, and spinach) and two grain crops (sunflower and maize) and an unplanted control. These plantings were crossed with two fertilization treatments: fertilized (100 kg ha−1 of N) and unfertilized. We evaluated NO3−, NH4+, microbial N, and mobilized N, plant biomass, plant tissue N, and %RPE by planting treatment. We found that vegetables almost completely depleted NO3− in both fertilized and unfertilized soils, whereas grain crops did not. Further, vegetables took up more than twice as much N in their aboveground tissue compared to grain crops under N fertilization. Both vegetables and crops produced RPEs on N mineralization. Nitrogen fertilization significantly enhanced the RPE for vegetable crops but not for grain crops. This result corroborates the assertion that plants with higher N concentration in their tissues tend to produce a higher RPE than plants with lower N concentration. The RPE of vegetable crops were significantly enhanced with N fertilization. Our data strongly rejects the “N-mining” hypothesis which would predict a much reduced RPE with N fertilization, and suggest that this hypothesis is not a universal explanation for the observed priming phenomena.

Rhizosphere priming effect on N mineralization in vegetable and grain crop systems

Soil respiration plays a key role in the carbon budget and carbon cycle of terrestrial ecosystems. To examine soil respiration response to fertilizer application and water addition, soil respiration was measured in a semiarid region of northeast China. We examined the effects of fertilizer application, water addition, and their interactions on soil respiration in a randomized block experiment, analyzed by repeated-measures ANOVA. The results indicated that the effects of fertilization on soil respiration were dependent on water addition, in 2010. However, soil respiration after fertilizer application was not significantly different from the control, in 2011, under the same water conditions. Soil temperature clearly affected soil respiration, and explained 9.8-22.5% of the variation in soil respiration of 2010, and 25.8-48.3% in 2011. However, soil water dynamics has an overriding influence on soil respiration in Horqin Sandy Land. A simple empirical model indicated that soil water content explained 22.7-86.1% of the soil respiration dynamics under water and fertilization treatments. Compared to temperature, we found that soil moisture has an overriding effect on soil respiration in Horqin Sandy Land.

Responses of soil respiration to simulated precipitation and nitrogen, phosphorus additions in horqin sandy land of northeastern china (sci)

Soil respiration and N-mineralization processes in the Patagonian steppe are more responsive to fertilization than to experimental precipitation increase

Amino sugars are key microbial biomarkers for determining the contribution of microbial residues in soil organic matter (SOM). However, it remains largely unclear as to what extent inorganic nitrogen (N) fertilization can lead to the significant degradation of SOM in alkaline agricultural soils. A six-year field experiment was conducted from 2013 to 2018 to evaluate the effects of chronic N enrichment on microbial residues, amino sugars, and soil biochemical properties under four nitrogen (urea, 46% N) fertilization scenarios: 0 (no-N, control), 75 (low-N), 225 (medium-N), and 375 (high-N) kg N ha−1. The results showed that chronic N enrichment stimulated microbial residues and amino sugar accumulation over time. The medium-N treatment increased the concentration of muramic acid (15.77%), glucosamine (13.55%), galactosamine (18.84%), bacterial residues (16.88%), fungal residues (11.31%), and total microbial residues (12.57%) compared to the control in 2018; however, these concentrations were comparable to the high-N treatment concentrations. The ratio of glucosamine to galactosamine and of glucosamine to muramic acid decreased over time due to a larger increase in bacterial residues as compared to fungal residues. Microbial biomass, soil organic carbon, and aboveground plant biomass positively correlated with microbial residues and amino sugar components. Chronic N enrichment improved the soil biochemical properties and aboveground plant biomass, which stimulated microbial residues and amino sugar accumulation over time.

Divergent Accumulation of Microbial Residues and Amino Sugars in Loess Soil after Six Years of Different Inorganic Nitrogen Enrichment Scenarios

The responses of soil respiration to water and nitrogen inStipa breviflorasteppe

The mechanisms underlying the response of soil respiration (Rs) to nitrogen (N) addition remain to be explored in semiarid ecosystems. This study was conducted to determine the effect of N addition on soil microbial composition, Rs and the temperature sensitivity of Rs (Q10). The N addition experiment was carried out in a semiarid grassland in China, with N fertilizer application rates of 0, 2, 4, 8, 16, or 32 g N m–2 yr–1. Microbial phospholipid fatty acids (PLFAs), Rs and Q10 were measured, and their relationships with soil properties were determined for three growing seasons. The results showed that N addition significantly increased the content of soil dissolved organic carbon (DOC) and inorganic nitrogen (IN), and decreased soil pH. With respect to soil microbes, N addition reduced soil PLFAs, reduced the fungi to bacteria ratio (F:B) and increased the gram-positive bacteria to gram-negative bacteria ratio (G+:G–). Rs under the N2, N4, N8, N16 and N32 treatments decreased by 2.58%, 14.86%, 22.62%, 23.97% and 19.87%, respectively, compared to the N0 (control) treatment. The results of structural equation models showed that N addition reduced Rs by lowering soil PLFAs and altering the microbial composition. However, N addition had no significant effect on either Q10, soil total organic carbon (TOC) or total nitrogen (TN), indicating that N addition alleviated soil carbon loss and was unlikely to change the potential for a bigger loss under global warming.

https://bioone.org/journals/journal-of-resources-and-ecology/volume-11/issue-2/j.issn.1674-764x.2020.02.001/Nitrogen-Addition-Decreases-Soil-Respiration-without-Changing-the-Temperature-Sensitivity/10.5814/j.issn.1674-764x.2020.02.001.pdf

Nitrogen Addition Decreases Soil Respiration without Changing the Temperature Sensitivity in a Semiarid Grassland

We investigated soil respiration (Rs) dynamics and influencing factors under different nitrogen (N) addition levels (0, 2, 4, 8, 16, 32 g m–2 yr–1) on typical grassland plots in Inner Mongolia. We measured soil respiration, temperature, moisture and nutrients. We found that N addition did not change dynamic characteristics of Rs; daily and seasonal dynamics followed a single peak curve. N addition reduced Rs during the growing season. Rs under N2, N4, N8, N16 and N32 treatments decreased by 24.00%, 21.93%, 23.49%, 30.78% and 28.20% in the growing season, respectively, compared to the N0 treatment. However, Rs in the non-growing season was not different across treatments. Rs was significantly positively correlated with soil temperature and moisture and these two factors accounted for 72%–97% and 74%–82% of variation in Rs, respectively. The soil respiration temperature sensitivity (Q10) was between 2.27 and 4.16 and N addition reduced Q10 except in the N8 treatment.

Soil Respiration Dynamics and Influencing Factors in Typical Steppe of Inner Mongolia Under Long-term Nitrogen Addition

The priming effect is well acknowledged in soil systems but the effect of nitrogen (N) fertilization remains elusive. To explore how N modifies the priming effect in soil organic matter (SOM), one in situ experiment with 13C labeled glucose addition (0.4 mg C g-1 soil, 3.4 atom % 13C) was conducted on soil plots fertilized with three gradients of urea (0, 4 and 16 g N m-2 yr-1). After glucose addition, the soil CO2 concentration and phospholipid fatty acid (PLFA) were measured on day 3, 7, 21 and 35. The study found that N fertilization decreased soil CO2, PLFA and the fungi to bacteria ratio. Glucose triggered the strongest positive priming in soil at 0 g N m-2 yr-2, meanwhile N fertilization decreased SOM-derived CO2. Soil at 4 g N m-2 yr-2 released the largest amount of glucose-derived carbon (C), likely due to favorable nutrient stoichiometry between C and N. Stable microbial community biomass and composition during early sampling suggests “apparent priming” in this grassland. This study concludes that N fertilization inhibited soil priming in semi-arid grassland, and shifted microbial utilization of C substrate from SOM to added labile C. Diverse microbial functions might be playing a crucial role in soil priming and requires attention in future N fertilization studies.

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China

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Nitrogen Addition Decreases Soil Respiration without Changing the Temperature Sensitivity in a Semiarid Grassland

Soil Respiration Dynamics and Influencing Factors in Typical Steppe of Inner Mongolia Under Long-term Nitrogen Addition

Soil Priming Effect Mediated by Nitrogen Fertilization Gradients in a Semi-arid Grassland, China