Measuring the immeasurable: A structural equation modeling approach to assessing soil health

Soil health is recognized as an important ecosystem property sensitive to human impact. As a concept, soil health cannot be directly measured, and so assessment and modeling efforts largely rely upon key biological, chemical, and physical indicators. Efforts to develop an overall soil health index are largely lacking due to significant statistical challenges and the necessity for regional calibration. Taken from the field of educational research, structural equation modeling (SEM) is an attractive approach to enhance the reliability and validity of soil health scoring. Therefore, SEM may be utilized to advance research efforts to understand management practices impacts on soil health. Our objectives were to develop a robust scoring function that (i) captures the concept of soil health and latent variables, (ii) adjusts scores by inherent soil properties and legacy of intensive land use to adequately reflect our regional conditions and contemporary land management, and (iii) meets the diverse practitioner needs. Through this process, we refined our minimum dataset of soil health indicators and reconceptualized soil health indicators into functional properties. Our results support the development of a robust single level or a multilevel SEM model-depending on the practitioner's goals-that accounts for repeated sampling or pseudoreplication. While the SEM scoring functions were highly related to the conventional scoring approach, SEM outperformed the conventional methods in terms of its wider distribution of scores-and thus enhanced discriminatory power on the lower and higher range of scores. We also confirmed that the SEM scoring function that includes adjustments for mineralogy and legacy of intensive land use successfully differentiates among contemporary management practices and land use. Therefore, we have confidence that the tool is reliable and appropriate to further examine more nuanced impacts of land use change and management practices within a given land use across time and space covering a diversity of soils. (300 words).

Edaphic controls of soil organic carbon in tropical agricultural landscapes

Predicting soil organic carbon (SOC) is problematic in tropical soils because mechanisms of SOC (de)stabilization are not resolved. We aimed to identify such storage mechanisms in a tropical soil landscape constrained by 100 years of similar soil inputs and agricultural disturbance under the production of sugarcane, a C₄ grass and bioenergy feedstock. We measured soil physicochemical parameters, SOC concentration, and SOC dynamics by soil horizon to one meter to identify soil parameters that can predict SOC outcomes. Applying correlative analyses, linear mixed model (LMM) regression, model selection by AICc, and hierarchical clustering we found that slow moving SOC was related to many soil parameters, while the fastest moving SOC was only related to soil surface charge. Our models explained 78-79%, 51-57%, 7-8% of variance in SOC concentration, slow pool decay, and fast pool decay, respectively. Top SOC predictors were roots, the ratio of organo-complexed iron (Fe) to aluminum (Al), water stable aggregates (WS_agg), and cation exchange capacity (CEC). Using hierarchical clustering we also assessed SOC predictors across gradients of depth and rainfall with strong reductions in Roots, SOC, and slow pool decay associated with increasing depth, while increased rainfall was associated with increased Clay and WS_agg and reduced CEC in surface soils. Increased negative surface charge, water stable aggregation, organo-Fe complexation, and root inputs were key SOC protection mechanisms despite high soil disturbance. Further development of these relationships is expected to improve understanding of SOC storage mechanisms and outcomes in similar tropical agricultural soils globally.

Beyond bulk: Density fractions explain heterogeneity in global soil carbon abundance and persistence

Understanding the controls on the amount and persistence of soil organic carbon (C) is essential for predicting its sensitivity to global change. The response may depend on whether C is unprotected, isolated within aggregates, or protected from decomposition by mineral associations. Here, we present a global synthesis of the relative influence of environmental factors on soil organic C partitioning among pools, abundance in each pool (mg C g^-1  soil), and persistence (as approximated by radiocarbon abundance) in relatively unprotected particulate and protected mineral-bound pools. We show that C within particulate and mineral-associated pools consistently differed from one another in degree of persistence and relationship to environmental factors. Soil depth was the best predictor of C abundance and persistence, though it accounted for more variance in persistence. Persistence of all C pools decreased with increasing mean annual temperature (MAT) throughout the soil profile, whereas persistence increased with increasing wetness index (MAP/PET) in subsurface soils (30-176 cm). The relationship of C abundance (mg C g^-1  soil) to climate varied among pools and with depth. Mineral-associated C in surface soils (<30 cm) increased more strongly with increasing wetness index than the free particulate C, but both pools showed attenuated responses to the wetness index at depth. Overall, these relationships suggest a strong influence of climate on soil C properties, and a potential loss of soil C from protected pools in areas with decreasing wetness. Relative persistence and abundance of C pools varied significantly among land cover types and soil parent material lithologies. This variability in each pool's relationship to environmental factors suggests that not all soil organic C is equally vulnerable to global change. Therefore, projections of future soil organic C based on patterns and responses of bulk soil organic C may be misleading.

DNA-Stable Isotope Probing Shotgun Metagenomics Reveals the Resilience of Active Microbial Communities to Biochar Amendment in Oxisol Soil

The functions and interactions of individual microbial populations and their genes in agricultural soils amended with biochar remain elusive but are crucial for a deeper understanding of nutrient cycling and carbon (C) sequestration. In this study, we coupled DNA stable isotope probing (SIP) with shotgun metagenomics in order to target the active community in microcosms which contained soil collected from biochar-amended and control plots under napiergrass cultivation. Our analyses revealed that the active community was composed of high-abundant and low-abundant populations, including Actinobacteria, Proteobacteria, Gemmatimonadetes, and Acidobacteria. Although biochar did not significantly shift the active taxonomic and functional communities, we found that the narG (nitrate reductase) gene was significantly more abundant in the control metagenomes. Interestingly, putative denitrifier genomes generally encoded one gene or a partial denitrification pathway, suggesting denitrification is typically carried out by an assembly of different populations within this Oxisol soil. Altogether, these findings indicate that the impact of biochar on the active soil microbial community are transient in nature. As such, the addition of biochar to soils appears to be a promising strategy for the long-term C sequestration in agricultural soils, does not impart lasting effects on the microbial functional community, and thus mitigates un-intended microbial community shifts that may lead to fertilizer loss through increased N cycling.

Carbon budgets of potential tropical perennial grass cropping scenarios for bioenergy feedstock production

BACKGROUND

The environmental costs of fossil fuel consumption are globally recognized, opening many pathways for the development of regional portfolio solutions for sustainable replacement fuel and energy options. The purpose of this study was to create a baseline carbon (C) budget of a conventionally managed sugarcane (Saccharum officinarum) production system on Maui, Hawaii, and compare it to three different future energy cropping scenarios: (1) conventional sugarcane with a 50% deficit irrigation (sugarcane 50%), (2) ratoon harvested napiergrass (Pennisetum purpureum Schumach.) with 100% irrigation (napier 100%), and (3) ratoon harvested napiergrass with a 50% deficit irrigation (napier 50%).

RESULTS

The differences among cropping scenarios for the fossil fuel-based emissions associated with agricultural inputs and field operations were small compared to the differences associated with pre-harvest burn emissions and soil C stock under ratoon harvest and zero-tillage management. Burn emissions were nearly 2000 kg C_eq ha^-1 year^-1 in the conventional sugarcane; whereas soil C gains were approximately 4500 kg C_eq ha^-1 year^-1 in the surface layer of the soil profile for napiergrass. Further, gains in deep soil profile C were nearly three times greater than in the surface layer. Therefore, net global warming potential was greatest for conventional sugarcane and least for napier 50% when deep profile soil C was included. Per unit of biomass yield, the most greenhouse gas (GHG) intensive scenario was sugarcane 50% with a GHG Index (GHGI, positive values imply a climate impact, so a more negative value is preferable for climate change mitigation) of 0.11 and the least intensive was napiergrass 50% when a deep soil profile was included (GHGI = - 0.77).

CONCLUSION

Future scenarios for energy or fuel production on former sugarcane land across the Pacific Basin or other volcanic islands should concentrate on ratoon-harvested crops that maintain yields under zero-tillage management for long intervals between kill harvest and reduce costs of field operations and agricultural input requirements. For napiergrass on Maui and elsewhere, deficit irrigation maximized climate change mitigation of the system and reduced water use should be part of planning a sustainable, diversified agricultural landscape.

Dynamic, Intermediate Soil Carbon Pools May Drive Future Responsiveness to Environmental Change

Accurately capturing dynamic soil response to disturbance effects in agroecosystem models remains elusive, thereby limiting projections of climate change mitigation potential. Perennial grasses cultivated in zero-tillage management systems hold promise as sustainable agroecosystems. High-yielding tropical C grasses often have extensive rooting systems, and the belowground processes of root turnover, aggregate formation, and mineral stabilization drove rapid C accumulation after cultivation in a recent study. We sought (i) to understand and constrain the size and responsiveness of dynamic, intermediate-cycling C pools contributing to the observed C accrual rates, and (ii) to simulate C stocks over time under the disturbance of elevated temperature using soil incubation at multiple temperatures and physical fractionation via density and sonication. Three-pool transfer modeling of soil incubations revealed small pools of readily available (i.e., days to months) microbial substrate that were responsive to temperature, time since cultivation, and inputs. Larger, kinetically slow-cycling pools were more indicative of long-term (i.e., years to decades) changes in C stock and strongly connected to measured changes in physical fractions. Combining the sensitivity of readily available microbial substrate with three-pool transfer modeling of the physical fractions over time since cultivation revealed that dynamic transfers of inputs occurred between the free organic and aggregate-protected fractions, and from these fractions to the mineral-associated dense fraction. Under 5°C temperature elevation, increased transfer rates outweighed elevated decomposition losses to sustain soil C accrual into the future. To effectively plan managed landscapes and monitor sustainable agroecosystems for climate change mitigation, tools must incorporate the complexity of soil response to change.

Networking our science to characterize the state, vulnerabilities, and management opportunities of soil organic matter

Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.

Allometric Models for Predicting Aboveground Biomass and Carbon Stock of Tropical Perennial C4 Grasses in Hawaii

Biomass is a promising renewable energy option that provides a more environmentally sustainable alternative to fossil resources by reducing the net flux of greenhouse gasses to the atmosphere. Yet, allometric models that allow the prediction of aboveground biomass (AGB), biomass carbon (C) stock non-destructively have not yet been developed for tropical perennial C₄ grasses currently under consideration as potential bioenergy feedstock in Hawaii and other subtropical and tropical locations. The objectives of this study were to develop optimal allometric relationships and site-specific models to predict AGB, biomass C stock of napiergrass, energycane, and sugarcane under cultivation practices for renewable energy and validate these site-specific models against independent data sets generated from sites with widely different environments. Several allometric models were developed for each species from data at a low elevation field on the island of Maui, Hawaii. A simple power model with stalk diameter (D) was best related to AGB and biomass C stock for napiergrass, energycane, and sugarcane, (R² = 0.98, 0.96, and 0.97, respectively). The models were then tested against data collected from independent fields across an environmental gradient. For all crops, the models over-predicted AGB in plants with lower stalk D, but AGB was under-predicted in plants with higher stalk D. The models using stalk D were better for biomass prediction compared to dewlap H (Height from the base cut to most recently exposed leaf dewlap) models, which showed weak validation performance. Although stalk D model performed better, however, the mean square error (MSE)-systematic was ranged from 23 to 43 % of MSE for all crops. A strong relationship between model coefficient and rainfall was existed, although these were irrigated systems; suggesting a simple site-specific coefficient modulator for rainfall to reduce systematic errors in water-limited areas. These allometric equations provide a tool for farmers in the tropics to estimate perennial C₄ grass biomass and C stock during decision-making for land management and as an environmental sustainability indicator within a renewable energy system.

Field-Based Estimates of Global Warming Potential in Bioenergy Systems of Hawaii: Crop Choice and Deficit Irrigation

Replacing fossil fuel with biofuel is environmentally viable from a climate change perspective only if the net greenhouse gas (GHG) footprint of the system is reduced. The effects of replacing annual arable crops with perennial bioenergy feedstocks on net GHG production and soil carbon (C) stock are critical to the system-level balance. Here, we compared GHG flux, crop yield, root biomass, and soil C stock under two potential tropical, perennial grass biofuel feedstocks: conventional sugarcane and ratoon-harvested, zero-tillage napiergrass. Evaluations were conducted at two irrigation levels, 100% of plantation application and at a 50% deficit. Peaks and troughs of GHG emission followed agronomic events such as ratoon harvest of napiergrass and fertilization. Yet, net GHG flux was dominated by carbon dioxide (CO2), as methane was oxidized and nitrous oxide (N2O) emission was very low even following fertilization. High N2O fluxes that frequently negate other greenhouse gas benefits that come from replacing fossil fuels with agronomic forms of bioenergy were mitigated by efficient water and fertilizer management, including direct injection of fertilizer into buried irrigation lines. From soil intensively cultivated for a century in sugarcane, soil C stock and root biomass increased rapidly following cultivation in grasses selected for robust root systems and drought tolerance. The net soil C increase over the two-year crop cycle was three-fold greater than the annualized soil surface CO2 flux. Deficit irrigation reduced yield, but increased soil C accumulation as proportionately more photosynthetic resources were allocated belowground. In the first two years of cultivation napiergrass did not increase net greenhouse warming potential (GWP) compared to sugarcane, and has the advantage of multiple ratoon harvests per year and less negative effects of deficit irrigation to yield.

Interactive biotic and abiotic regulators of soil carbon cycling: evidence from controlled climate experiments on peatland and boreal soils

Partially decomposed plant and animal remains have been accumulating in organic soils (i.e. >40% C content) for millennia, making them the largest terrestrial carbon store. There is growing concern that, in a warming world, soil biotic processing will accelerate and release greenhouse gases that further exacerbate climate change. However, the magnitude of this response remains uncertain as the constraints are abiotic, biotic and interactive. Here, we examined the influence of resource quality and biological activity on the temperature sensitivity of soil respiration under different soil moisture regimes. Organic soils were sampled from 13 boreal and peatland ecosystems located in the United Kingdom, Ireland, Spain, Finland and Sweden, representing a natural resource quality range of C, N and P. They were incubated at four temperatures (4, 10, 15 and 20 °C) at either 60% or 100% water holding capacity (WHC). Our results showed that chemical and biological properties play an important role in determining soil respiration responses to temperature and moisture changes. High soil C : P and C : N ratios were symptomatic of slow C turnover and long-term C accumulation. In boreal soils, low bacterial to fungal ratios were related to greater temperature sensitivity of respiration, which was amplified in drier conditions. This contrasted with peatland soils which were dominated by bacterial communities and enchytraeid grazing, resulting in a more rapid C turnover under warmer and wetter conditions. The unexpected acceleration of C mineralization under high moisture contents was possibly linked to the primarily role of fermented organic matter, instead of oxygen, in mediating microbial decomposition. We conclude that to improve C model simulations of soil respiration, a better resolution of the interactions occurring between climate, resource quality and the decomposer community will be required.

Clinical trials in veterinary oncology: a clinician's viewpoint

Review of the veterinary oncology literature is important for keeping up-to-date, but it can be time-consuming and sometimes frustrating. Results of clinical trials are published in a variety of formats, including case descriptions, review articles, retrospective studies, and prospective trials. They may be found as abstracts, which usually present preliminary data and interpretation, as interesting items or commentary in a newsletter, or as articles in referred journals. In this "clinician's viewpoint," a practical approach to sifting through the mountains of literature is offered.

Concurrent renal adenocarcinoma and polycythemia in a dog

Concurrent renal adenocarcinoma and polycythemia were diagnosed in a 19-month-old, female Rhodesian ridgeback. An unusually early presentation for this neoplasm, it is the second reported case of renal adenocarcinoma in a dog less than two years of age. Concurrent renal adenocarcinoma and polycythemia have been reported previously in four older dogs. In the dog of this report, clinical signs included brick-red mucous membranes, lethargy, a periodic systolic heart murmur, and engorged retinal vessels. A large retroperitoneal mass and pulmonary metastatic nodules were present at the time of diagnosis. Red blood cell count, packed cell volume, and hemoglobin concentration were greatly increased (12,940,000 red blood cells/microliter; 73.2%; and 26.6 g/dl, respectively). Histopathological diagnosis was renal adenocarcinoma. Polycythemia was the result of excessive erythropoietin production by the neoplasm.

Natural killer cell activity in untreated and treated dogs with lymphoma

Natural killer (NK) cell activity and function were determined for 11 untreated and treated dogs with lymphoma. Concurrent chromium release and single cell binding assays, methods used to measure overall cytotoxic activity and that from individual cells, respectively, were performed at effector-to-target cell ratios of 50:1 and 100:1, with incubation periods of 12 and 16 hours. Significant reduction was achieved in overall activity for untreated dogs, using a 16-hour incubation period and an effector-to-target ratio of 100:1 (P less than 0.05). Decreased activity (P less than 0.025) was also achieved for those dogs that were administered combination chemotherapy, consisting of such drugs as cyclophosphamide, vincristine, prednisone, and doxorubicin. There was no significant difference in binding or cytotoxic activity by individual cells in the untreated or treated dogs, compared with the healthy controls. Short- or long-term treatment with glucocorticoids did not influence overall NK cll activity or individual cell cytotoxicity. The overall cytotoxic activity in untreated dogs was reduced, but these dogs had relatively normal numbers of NK cells compared with paracontrols. This suggests that a defect in recycling or the ability to kill targets repetitively, may be involved. A similar defect was found in NK cells of dogs treated aggressively with combination chemotherapy.

Severe hypophosphatemia associated with diabetes mellitus in six dogs and one cat

Severe hypophosphatemia was found in 6 diabetic dogs and in one diabetic cat. The cat suffered from hemolysis, and one dog had seizures, both apparently as a result of the severe hypophosphatemia. Clinical signs were not determined solely by the serum concentration of phosphorus, as seen in 5 other patients that did not have signs of disease despite similar serum phosphorus concentrations.

Immunologic profiles of cats with persistent, naturally acquired feline leukemia virus infection

Several immunologic responses were measured in 13 healthy cats with naturally acquired, persistent feline leukemia virus (FeLV) viremia from 4 multiple-cat households and were compared with responses from 28 of their healthy, non-FeLV-viremic housemates. Significant differences (P = less than 0.05) were not observed between results of FeLV-viremic and nonviremic cats for peripheral blood leukocyte or lymphocyte count, percentage of peripheral blood mononuclear cells able to form rosettes with guinea pig RBC or with antibody- and complement-coated sheep RBC, lymphocyte proliferative response to concanavalin A or pokeweed mitogen, or serum immunoglobulin G concentration. Seemingly, persistent FeLV viremia, when naturally acquired, may exist for some time without lymphopenia or a marked loss of mitogen-induced lymphocyte proliferation.

Tumors of the alimentary tract

Neoplasms of the canine and feline alimentary tract represent diagnostic and therapeutic challenges for the veterinarian in practice. Careful attention to historical details and thorough and repeated examination are of paramount importance in evaluating animals with chronic digestive disturbances. By judicious use of ancillary studies such as plain and contrast radiography, endoscopy, and exploratory surgery, the clinician may arrive at a diagnosis earlier in the course of a neoplasm. This in turn may facilitate more efficacious treatment. A particularly interesting aspect of tumors of the gastrointestinal tract is their frequent association with environmental carcinogens. By being aware of these relationships, veterinarians stand a better chance of reaching the ultimate goal of cancer therapists--the prevention of malignant disease.

Uptake of exogenous aspartate into circumventricular organs but not other regions of adult mouse brain

Adult mice were treated intraperitoneally with aspartate (Asp) at one of several doses (0.47-3.75 mmol/kg) and 30 min later given a subcutaneous Asp injection at the same dose. This treatment regimen resulted in steady state blood Asp elevations, a given dose producing the same degree of elevation at both 30 and 60 min. The lowest and highest doses, respectively, produced four-fold and 55-fold elevations of serum Asp. In selected circumventricular organ (CVO) regions of brain which lack blood brain barriers, tissue Asp levels rose 1.5 and 3 times above control values following the lowest and highest doses, respectively, whereas tissue Asp remained unchanged in non-CVO brain regions. Thus, even very moderate Asp dosing causes marked increases in CVO Asp. In order to analyze the pattern of Asp uptake into CVO, Asp was assayed in numerous subdivisions of each CVO, and maps were constructed which reflected microregional concentration differences. The pattern of Asp distribution suggests that Asp enters brain via fenestrated capillaries serving certain portions of CVO and then spreads into adjacent brain tissue. In separate experiments, we administered a single high dose of Asp (15 mmol/kg) to both adult and infant mice and measured Asp in serum and select brain regions 60 min later. Asp concentrations in serum and CVO (but not other brain regions) rose markedly at both ages but the increases were greater in serum and therefore also in CVO of infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemoimmunotherapy for canine lymphosarcoma: a prospective evaluation of specific and nonspecific immunomodulation

Fifty-six dogs were given chemoimmunotherapy for spontaneous lymphosarcoma. The dogs had been given identical combination chemotherapy (8 weeks) for induction of remission, and after achieving complete clinical remission, they were randomly assigned to one of three treatment groups to evaluate immunotherapy as a method ancillary to chemotherapy to maintain or extend the remission. For immunostimulation, one-third of the dogs were given chemically modified autochthonous tumor cell extract in Freund's complete adjuvant (FCA), one-third were given nonmodified tumor cell extract in FCA, and one-third were given FCA alone. A historical control population of dogs given the same chemotherapy was used for comparison. Of the 56 dogs, 50 (89.3%) achieved initial remission, but 18 of the latter relapsed clinically during the initial 8-week-chemotherapy regimen. The remaining 32 dogs (or 57.1% of the original 56 dogs) were subsequently given immunotherapy. Duration of remission and survival time were recorded. The median remission duration and survival time for all dogs given immunotherapy following cytoreductive chemotherapy were significantly longer than the historical control population given chemotherapy alone. However, there was no significant difference in remission duration or survival among the three immunotherapy groups.

Infectious peritonitis in a cat that subsequently developed a myeloproliferative disorder

The effusive form of feline infectious peritonitis was diagnosed clinically and serologically in a 3-year-old male domestic cat. The cat responded to treatment for 9 months, then developed a myeloproliferative disorder with cytologic characteristics of reticuloendotheliosis.

Chemoimmunotherapy for canine lymphosarcoma

Thirty-two dogs with naturally occurring multicentric lymphosarcoma were randomly assigned to one of two treatment groups. One half of the animals received combination chemotherapy plus vitamin injections (controls) while the other half received indentical chemotherapy plus injections of chemically-modified tumor cell extract in Freund's complete adjuvant (vaccinates). Clinical staging revealed no bias between groups but showed that prognosis could be closely correlated with the severity of disease at initial presentation. Twenty dogs (62%), including 11 vaccinates and 9 controls, responded favorably to chemotherapy and were evaluated for length of first remission and total survival time. Both parameters were significantly longer in vaccinated dogs than in controls. These data suggest that immunological stimulation may be a helpful adjunct to conventional therapy in selected types of cancer when immunological principles are observed.

Treatment of feline myelogenous leukemia: four case reports

Of 4 cats with myelogenous leukemia, 3 had the neutrophilic type and 1 had the basophilic type. Partial remission was achieved with chemotherapy in 2 of the cats. Their survival times, however, were 77 and 31 days from time of diagnosis. The other 2 cats did not respond to treatment and died 16 days from time of diagnosis.

Monocytic leukemia in three cats

Of 3 cats with monocytic leukemia, 1 responded favorably to treatment with cytosine arabinoside. With supportive therapy, it lived 78 days from the time of diagnosis, at which time it developed dyspnea and signs of toxicosis and died. The other 2 cats did not respond to treatment and died 4 and 16 days from time of diagnosis. Prior to death, they were bleeding from injection sites, and their blood had greater than 200,000 WBC/mm3. Necropsy of those 2 cats revealed extensive perivascular hemorrhagic infarcts within the cerebellum, medulla, and cerebrum.