Image_1_Nitrogen Limitations on Microbial Degradation of Plant Substrates Are Controlled by Soil Structure and Moisture Content.PDF

<p>Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO₂ emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one.</p

Renal function during the follow-up.

<p>Summary of the renal function evaluation parameters during the follow-up including plasma creatinine levels (μmol/L), urinary fractional excretion of sodium and magnesium, urinary protein excretion (mg/mmol creatinine), and osmolarity ratio (blood/urine). Values are expressed as the mean ± SEM (* p < 0.05 or ** p < 0.01 <i>vs</i>. the uni-nephrectomized kidney group).</p

Analysis of vascular segments and vascular network complexity in kidneys three months after autotransplantation.

<p>Analysis of vascular segments and vascular network complexity in kidneys three months after autotransplantation.</p

Histogram of vascular volume fractions.

<p>Coronal maximum intensity projection of the vascular network from renal cortex samples: A) Uni-nephrectomized kidney and (B) grafted kidney. Histogram of vascular volume fraction as the ratio between vascular network volume and total sample volume expressed as the percentage in samples of (C) total renal cortex, (D) the outer cortex, (E) middle cortex, and (F) inner cortex from the uni-nephrectomized and grafted kidney groups. Values are expressed as the mean ± SEM.</p

Ischemia reduces microcirculation in kidney grafts within three months.

<p>(A) Histogram of vessel density computed by vascular segment diameter expressed as a percentage of total vessels in the outer cortex, (B) middle cortex, (C) and inner cortex. Values (mean ± SEM) that differ significantly from those of the uni-nephrectomized kidney group are represented by **p < 0.01.</p

Renal transplantation induces vascular remodeling and interstitial fibrosis.

<p>(A-B) Media-to-lumen ratio of renal cortex samples of uni-nephrectomized and grafted kidneys. (C) Evaluation of fibrosis by Red Sirius or αSMA staining (Magnification x20; C). (D) CD31 and aminopeptidase P-positive blood microvessels from renal cortex samples from uni-nephrectomized and grafted kidneys three months after surgery (Magnification x40; C). Values (mean ± SEM) significantly different from those of the uni-nephrectomized kidney group are represented by **p < 0.01.</p

Summary table of semi-quantification of total cortex staining from kidneys three months after auto-transplantation.

<p>Summary table of semi-quantification of total cortex staining from kidneys three months after auto-transplantation.</p

Renal transplantation induces profibrotic and antiangiogenic pathways associated with decreased NO production.

<p>Western blot analysis of proteins involved in profibrotic and antiangiogenic pathways in cortex samples from uni-nephrectomized and grafted kidneys. (B) Evaluation of NO production by quantification of nitrite + nitrate. Values (mean ± SEM) significantly different from those of the uni-nephrectomized kidney group are represented by **p < 0.01; *p < 0.05.</p

Vascular network analysis.

<p>(A) Subdivision of the renal cortex structure in the outer, middle, and inner cortex. (B) Volume rendering of the vascular network from the renal cortex. (C) Centerline skeletonization showing the nodes (spheres) and vascular segments (lines). (D) Example of a vascular segment between two nodes (N1 and N2). Tortuosity is the ratio between the curvilinear distance between N1- N2 and the respective chord linear distance.</p