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1. A comparison of lodgepole and spruce needle chemistry impacts on terrestrial biogeochemical processes during isolated decomposition

Author

Laura T. Leonard, Kristin Mikkelson, Zhao Hao, Eoin L. Brodie, Kenneth H. Williams, and Jonathan O. Sharp

Subjects
Soil biogeochemistry, Needle Decomposition, Nutrient Cycling, Soil Respiration, Bark Beetle Disturbance, Lodgepole, Medicine, Biology (General), QH301-705.5
Abstract

This study investigates the isolated decomposition of spruce and lodgepole conifer needles to enhance our understanding of how needle litter impacts near-surface terrestrial biogeochemical processes. Harvested needles were exported to a subalpine meadow to enable a discrete analysis of the decomposition processes over 2 years. Initial chemistry revealed the lodgepole needles to be less recalcitrant with a lower carbon to nitrogen (C:N) ratio. Total C and N fundamentally shifted within needle species over time with decreased C:N ratios for spruce and increased ratios for lodgepole. Differences in chemistry correlated with CO2 production and soil microbial communities. The most pronounced trends were associated with lodgepole needles in comparison to the spruce and needle-free controls. Increased organic carbon and nitrogen concentrations associated with needle presence in soil extractions further corroborate the results with clear biogeochemical signatures in association with needle chemistry. Interestingly, no clear differentiation was observed as a function of bark beetle impacted spruce needles vs those derived from healthy spruce trees despite initial differences in needle chemistry. These results reveal that the inherent chemistry associated with tree species has a greater impact on soil biogeochemical signatures during isolated needle decomposition. By extension, biogeochemical shifts associated with bark beetle infestation are likely driven more by changes such as the cessation of rhizospheric processes than by needle litter decomposition.

Published
2020
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2. Secretory Event in Intestinal Grafts during Preservation Ischemia

Author

Joanna Arcuni, Roberta E. Sonnino, Kabir Yousef, Steven Chiu, Richard D. Franson, Li Wang, and Kristin Mikkelson

Subjects
Male, Adenosine, Allopurinol, Organ Preservation Solutions, Phospholipases A, Acetylglucosamine, Andrology, chemistry.chemical_compound, Raffinose, Phospholipase A2, Ischemia, Lactate dehydrogenase, Animals, Insulin, Viaspan, Secretion, Intestinal Mucosa, Cryopreservation, chemistry.chemical_classification, Phospholipase A, L-Lactate Dehydrogenase, biology, Proteins, Glutathione, Rats, Intestines, Transplantation, Phospholipases A2, Enzyme, chemistry, Biochemistry, Rats, Inbred Lew, biology.protein, Muramidase, Surgery, Lysozyme
Abstract

Background. Ischemia triggers secretion of proteins from the intestine, including type II secretory phospholipase A2 (sPLA2). This “secretory event” was studied in intestinal grafts during the first few hours of preservation by measuring total protein, sPLA2, and other enzymes in the UW preservation solution over time. The effect of PX-13, a PLA2 inhibitor, was also studied. Materials and methods. Twenty-five centimeter intestinal grafts were harvested from Lewis rats, flushed, and preserved in UW solution ± PX-13 at 4°C. UW samples from 0 to 48 h (n = 5 each) were analyzed for total protein, sPLA2, lactate dehydrogenase (LDH), N-acetylglucosamine (NAGA), and lysozyme. Nonpreserved grafts were homogenized in PBS as tissue controls. Standard biochemical methods were used for all assays. Results. Total protein increased rapidly by 5 min, continued to rise more slowly until 30 min, and then stabilized. The most significant increase in sPLA2 activity occurred between 90 and 180 min. NAGA increased most markedly between 30 and 180 min, while LDH increased in the first 30 min, although the level of both enzymes was negligible compared to tissue enzyme. Lysozyme levels were minimal at all times. PX-13 decreased sPLA2 activity markedly at all time points. Conclusion. Total protein levels increased before sPLA2, suggesting that sPLA2 may be secreted in response to other proteins or enzymes released even earlier during preservation (e.g., cytokines). These elevations do not appear to be caused by cell death. Phospholipase A2 secretion may be blocked, and this may greatly improve the outcome of intestinal preservation.

Published
1999

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