Biomedical subjects

C van Kessel

Publications and source records attributed to C van Kessel.

6 recordsLinked to original sources

PubMed2005

Quantifying the impact of regular cutting on vegetative buffer efficacy for nitrogen-15 sequestration.

This study used the stable 15N isotope to quantitatively examine the effects of cutting on vegetative buffer uptake of NO3(-)-N based on the theory that regular cutting would increase N demand and sequestration by encouraging new plant growth. During the summer of 2002, 10 buffer plots were established within a flood-irrigated pasture. In 2003, 15N-labeled KNO3 was applied to the pasture area at a rate of 5 kg N ha(-1) and 99.7 atom % 15N. One-half of the buffer plots were trimmed monthly. In the buffers, the cutting effect was not significant in the first few weeks following 15N application, with both the cut and uncut buffers sequestering 15N. Over the irrigation season, however, cut buffers sequestered 2.3 times the 15N of uncut buffers, corresponding to an increase in aboveground biomass following cutting. Cutting and removing vegetation allowed the standing biomass to take advantage of soil 15N as it was released by microbial mineralization. In contrast, the uncut buffers showed very little change in 15N sequestration or biomass, suggesting senescence and a corresponding decrease in N demand. Overall, cutting significantly improved 15N attenuation from both surface and subsurface water. However, the effect was temporally related, and only became significant 21 to 42 d after 15N application. The dominant influence on runoff water quality from irrigated pasture remains irrigation rate, as reducing the rate by 75% relative to the typical rate resulted in a 50% decrease in total runoff losses and a sevenfold decrease in 15N concentration.

Biomass↗

PubMed2002

What is the Revised Fear Survey Schedule for Children measuring?

The Fear Survey Schedule for Children-Revised (FSSC-R) is a widely used self-report questionnaire that purports to measure the number of fears and the overall level of fearfulness in children. A number of studies have shown that the ten most common childhood fears can be found on the Danger and Death subscale of the FSSC-R, with upwards of 50% of children endorsing such fears. However, some researchers (e.g., H. McCathie & S.H. Spence, 1991; Behaviour Research and Therapy, 29, 495-502) have questioned the validity of these findings, suggesting that these items do not reflect actual childhood fears that children have or experience on a daily or regular basis. Rather, they suggest that children are responding to these fear items as if they were actually occurring to them in the here and now. The current study examined the occurrence of five Danger and Death fears from the FSSC-R (i.e., "Not being able to breathe", "Being hit by a car or truck", "Falling from high places", "Bombing attacks or being invaded", and "Fire or getting burned") in a sample of normal school children aged eight to 12 years (N=102). More specifically, we used three different methods to asses these fears: (1). prevalence as determined by the standard FSSC-R procedure, (2). prevalence as determined by a fear list procedure, and (3). actual occurrence or prevalence of these fears in the past week, as determined by a diary method. Results indicated that while these fears ranked high when using the standard FSSC-R procedure, they were considerably less common when using the fear list procedure, and had a low probability of actual occurrence on a daily basis, as well as possessing a short duration and low intensity. Implications for the assessment of fears and the use of self-report measures like the FSSC-R are briefly discussed.

Child↗

PubMed1987

Effect of localized nitrogen availability to soybean half-root systems on photosynthate partitioning to roots and nodules.

Soybean (Glycine max [L.] Merr. cv Davis) was grown in a split-root growth system designed to maintain control of the root atmosphere. Two experiments were conducted to examine how 80% Ar:20% O(2) (Ar:O(2)) and air (Air) atmospheres affected N assimilation (NH(4)NO(3) and N(2) fixation) and the partitioning of photosynthate to roots and nodules. Application of NH(4)NO(3) to nonnodulated half-root systems enhanced root growth and root respiration at the site of application. A second experiment applied Ar:O(2) or air to the two sides of nodulated soybean half-root systems for 11 days in the following combinations: (a) Air to both sides (Air/Air); (b) Air to one side, Ar:O(2) to the other (Air/Ar:O(2)), and (c) Ar:O(2) to both sides (Ar:O(2)/Ar:O(2)). Results indicated that dry matter and current photosynthate ((14)C) were selectively partitioned to nodules and roots where N(2) was available. Both root and nodule growth on the Air side of Air/Ar:O(2) plants was significantly greater than the Ar:O(2) side. The relative partitioning of carbon and current photosynthate between roots and nodules on a half-root system was also affected by N(2) availability. The Ar:O(2) sides partitioned relatively more current photosynthate to roots (57%) than nodules (43%), while N(2)-fixing root systems partitioned 36 and 64% of the carbon to roots and nodules, respectively. The Ar:O(2) atmosphere decreased root and nodule respiration by 80% and nitrogenase activity by 85% compared to half-root systems in Air while specific nitrogenase activity of nodules in Ar:O(2) was 50% of nodules supplied Air. Results indicated that nitrogen assimilation, whether from N(2) fixation or inorganic sources, had a localized effect on root development. Nodule development accounted for the major decrease in total photosynthate partitioning to non-N(2)-fixing nodules. Soybean compensates for ineffective nodulation by controlling the flux of carbon to ineffective nodules and their associated roots.

Journal Article↗

PubMed1985

Enhanced N-Transfer from a Soybean to Maize by Vesicular Arbuscular Mycorrhizal (VAM) Fungi.

Using a split-root technique, roots of soybean plants were divided between two pots. In one of the two pots, two maize plants were grown and half of those pots were inoculated with the vesicular arbuscular mycorrhizal (VAM) fungus, Glomus fasciculatus. Fifty-two days after planting, (15)N-labeled ammonium sulfate was applied to the pots which contained only soybean roots. Forty-eight hours after application, significantly higher values for atom per cent (15)N excess were found in roots and leaves of VAM-infected maize plants as compared with the non-VAM-infected maize plants. Results indicated that VAM fungi did enhance N transfer from one plant to another.

Journal Article↗

PubMed1983

N(2) fixation and h(2) evolution by six species of tropical leguminous trees.

The C(2)H(4)/(15)N(2) and H(2)/(15)N(2) ratios for six species of tropical leguminous trees are reported. C(2)H(4)/(15)N(2) ratios ranged from 2.4 to 4.7; values for the H(2)/(15)N(2) ratios were between 0.6 and 1.4. Relative efficiency values, based on C(2)H(2) reduction, (15)N incorporation, and H(2) evolution during (15)N incorporation varied between 0.68 and 0.84 for the six species. Overall, approximately 30% of the electron flow through nitrogenase was used for H(2) evolution.

Journal Article↗

PubMedDate not supplied

Using nitrogen-15 to quantify vegetative buffer effectiveness for sequestering nitrogen in runoff.

Previous studies have observed higher levels of soluble nutrients leaving vegetative buffers than entering them, suggesting that the buffers themselves are acting as a source rather than a sink by releasing previously stored nutrients. This study used 98 atom % (15)N-labeled KNO(3) at a rate of 5 kg ha(-1) to quantify buffer efficiency for sequestering new inputs of NO(-)(3)-N in an extensively grazed irrigated pasture system. Buffer treatments consisted of an 8-m buffer, a 16-m buffer, and a nonbuffered control. Regardless of the form of runoff N (NO(-)(3), NH(+)(4), or dissolved organic nitrogen [DON]), more (15)N was lost from the nonbuffered treatments than from the buffered treatments. The majority of the N attenuation was by vegetative uptake. Over the course of the study, the 8-m buffer decreased NO(-)(3)-(15)N load by 28% and the 16-m buffer decreased load by 42%. For NH(+)(4)-(15)N, the decrease was 34 and 48%, and for DON-(15)N, the decrease was 21 and 9%. Although the buffers were effective overall, the majority of the buffer impact occurred in the first four weeks after (15)N application, with the buffered plots attenuating nearly twice as much (15)N as the nonbuffered plots. For the remainder of the study, buffer effect was not as marked; there was a steady release of (15)N, particularly NO(-)(3)- and DON-(15)N, from the buffers into the runoff. This suggests that for buffers to be sustainable for N sequestration there is a need to manage buffer vegetation to maximize N demand and retention.

Adsorption↗