The influence of organic and inorganic nutrient inputs on soil organic carbon functional groups content and maize yields

Locally available organic inputs to soil, solely or in combination with inorganic fertilizers, are used to reverse declining soil fertility and improve soil organic matter content (SOM) in smallholder farms of most Sub-Saharan Africa (SSA) countries. Soil organic matter characterization can indicate soil organic input, carbon (C) sequestration potential, or even an authentication tool for soil C dynamics in C stocks accounting. This study determined the effects of the long-term application of selected integrated soil fertility management (ISFM) technologies on SOM functional group composition and maize yields. The study was carried out on an ongoing long-term soil fertility field experiment established in 2004 in Mbeere South sub-county, the drier part of upper Eastern Kenya. The experimental design was a randomized complete block design. The ISFM treatments were 60 kg ha-1 nitrogen (N) from goat manure (GM60); 30 kg ha-1 inorganic N fertilizer (IF30); 60 kg ha-1 inorganic N fertilizer (IF60); GM30+IF30; 90 kg ha-1 inorganic N fertilizer (IF90); 60 kg ha-1 N from lantana (Lantana camara) (LC60); LC30+IF30; 60 kg ha-1 N from mucuna beans (Mucuna pruriens) (MP60); MP30+IF30; 60 kg ha-1 N from Mexican sunflower (Tithonia diversifolia) (TD60); TD30+IF30, and a control with no inputs. The C compositions of ground soil samples and organic amendments were analyzed using 13C solid-state NMR. The GM60, GM30+IF30, LC60, and TD60 treatments had much higher Alkyl and O-Alkyl C SOM functional groups than the control and other treatments. The average soil C for the control was 7.47 mg kg-1 and ranged from 5.03 to 7.37, 9.57 to 18.77, and 7.03-14.50 mg kg-1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. The mean grain yield for the control was 0.56 Mg ha-1 and ranged from 1.51 to 1.99, 1.94 to 4.16, and 2.98-4.60 Mg ha-1 for inorganic fertilizers, organic fertilizers, and organic + inorganic fertilizers, respectively. The results showed that a long-term application of sole organic fertilizers or combined with inorganic fertilizers increases maize yield and soil C sequestration potential. The increase was attributed to high Alkyl and O-Alkyl C SOM functional groups. Hence, knowing the C fraction content of organic inputs is vital in determining the best-fit management technologies for ameliorating soil fertility and sustaining and/or improving crop yields.

Loss of capillary pericytes and the blood-brain barrier in white matter in poststroke and vascular dementias and Alzheimer's disease

White matter (WM) disease is associated with disruption of the gliovascular unit, which involves breach of the blood–brain barrier (BBB). We quantified pericytes as components of the gliovascular unit and assessed their status in vascular and other common dementias. Immunohistochemical and immunofluorescent methods were developed to assess the distribution and quantification of pericytes connected to the frontal lobe WM capillaries. Pericytes with a nucleus were identified by collagen 4 (COL4) and platelet‐derived growth factor receptor‐β (PDGFR‐β) antibodies with further verification using PDGFR‐β‐specific ELISA. We evaluated a total of 124 post‐mortem brains from subjects with post‐stroke dementia (PSD), vascular dementia (VaD), Alzheimer’s disease (AD), AD‐VaD (Mixed) and post‐stroke non‐demented (PSND) stroke survivors as well as normal aging controls. COL4 and PDGFR‐β reactive pericytes adopted the characteristic “crescent” or nodule‐like shapes around capillary walls. We estimated densities of pericyte somata to be 225 ±38 and 200 ±13 (SEM) per COL4 mm² area or 2.0 ± 0.1 and 1.7 ± 0.1 per mm capillary length in young and older aging controls. Remarkably, WM pericytes were reduced by ~35%–45% in the frontal lobe of PSD, VaD, Mixed and AD subjects compared to PSND and controls subjects (P < 0.001). We also found pericyte numbers were correlated with PDGFR‐β reactivity in the WM. Our results first demonstrate a reliable method to quantify COL4‐positive pericytes and then, indicate that deep WM pericytes are decreased across different dementias including PSD, VaD, Mixed and AD. Our findings suggest that downregulation of pericytes is associated with the disruption of the BBB in the deep WM in several aging‐related dementias.

Comparative responses of ovipositing Anopheles gambiae and Culex quinquefasciatus females to the presence of Culex egg rafts and larvae

Field observations have demonstrated that gravid Anopheles gambiae Giles s.s. (Diptera: Culicidae) are selective in their choice of oviposition sites. For example, immature stages of An. gambiae s.s. are rarely found in water that contains Culex quinquefasciatus Say immatures. The possibility that this may, in part at least, reflect a response by ovipositing An. gambiae s.s. females to volatile signals associated with Culex juveniles was evaluated by testing the response of An. gambiae s.s. females to varying densities of Cx. quinquefasciatus egg rafts and/or larvae in oviposition choice assays. For comparison, the oviposition choices of Cx. quinquefasciatus to conspecific egg rafts and/or larvae were similarly assayed. At a low density of Cx. quinquefasciatus egg rafts (1-15 egg rafts/100 mL water), An. gambiae s.s. females laid more eggs in the treatment water than in the control, with a maximum of twice as many in the treatment water at 5 egg rafts/100 mL water. At higher egg raft densities and in all treatments that included Cx. quinquefasciatus larvae, oviposition decreased significantly in the treatment dishes in a density-dependent manner. As previous studies have indicated, ovipositing Cx. quinquefasciatus females were attracted to and laid egg rafts in dishes containing conspecific egg rafts and, interestingly, also in dishes containing larvae.