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P A Schultz

Publications and source records attributed to P A Schultz.

6 recordsLinked to original sources
PubMed2005

Variable responses of old-field perennials to arbuscular mycorrhizal fungi and phosphorus source.

If arbuscular mycorrhizal fungi (AMF) promote phosphorus partitioning of plant hosts, they could provide one mechanism for the maintenance of plant community diversity. We investigated whether AMF improved the ability of old field perennials to grow on a range of phosphorus sources and whether AMF facilitated differential performance of plant species on different phosphorus sources (phosphorus niche partitioning). We manipulated form of phosphorus (control versus different inorganic and organic sources) and AM fungal species (control versus four individual AMF species or an AMF community) for five old field perennials grown in a greenhouse in individual culture. Based on biomass after four months of growth, we found no evidence for phosphorus niche partitioning. Rather, we found that effects of AMF varied from parasitic to mutualistic depending on plant species, AMF species, and phosphorus source (significant Plant x Fungus x Phosphorus interaction). Our results suggest that the degree of AMF benefit to a plant host depends not only on AMF species, plant species, and soil phosphorus availability (as has also been found in other work), but can also depend on the form of soil phosphorus. Thus, the position of any AMF species along the mutualism to parasitism continuum may be a complex function of local conditions, and this has implications for understanding plant competitive balance in the field.

Biomass↗
PubMed2005

Arbuscular mycorrhizal fungi do not enhance nitrogen acquisition and growth of old-field perennials under low nitrogen supply in glasshouse culture.

Arbuscular mycorrhizal fungi (AMF) are known to promote plant growth when phosphorus is limiting, but the role of AMF in plant growth under nitrogen (N) limiting conditions is unclear. Here, we manipulated N (control vs inorganic and organic forms) and AMF species (control vs four AMF species) for five old-field perennials grown individually in a glasshouse under N-limiting conditions. We found that AMF were at best neutral and that some AMF species depressed growth for some plant species (significant plant-fungus interaction). Native plant species growth was strongly depressed by all but one AMF species; exotic plant species were less sensitive to AMF. We found no evidence of plant N preferences. Both natives and exotics were able to acquire more N with N addition, but only exotics grew more with added N. Our results suggest that AMF do not promote plant N acquisition at low N supply, and our results are consistent with other research showing that AMF can act as a parasitic carbon drain when phosphorus availability is relatively high.

Agriculture↗
PubMed1997

Optimal reductions in CO2 emissions.

Current optimizing climate-economy models use CO2 uptake functions that greatly underestimate both peak atmospheric CO2 concentrations and the time horizon of elevated CO2. As a result these models underestimate potential global warming damages. Here, a more realistic, but practical, carbon cycle parameterization is developed that can be incorporated within an optimizing climate-economy model framework. This method is utilized in conjunction with the DICE model (Nordhaus, 1994) to estimate optimal reductions in CO2 emissions. The results are shown to be extremely sensitive to the pore rate of time preference, rho. For rho=3% (Nordhaus' preferred value), our model predicts an optimal CO2 emission reduction of 13% by the year 2045, as compared to 11% in the original DICE model. But, for rho=0% the optimal emissions reduction rises to 79% in the year 2045 and to 97% by the year 2200. We argue that energy policy should be guided by the rho=0% results for both economic and ethical reasons. A steady-state analysis performed using the DICE model supports the argument that large fractional reductions in CO2 emissions should be undertaken.

Atmosphere↗
PubMed1995

Tissue specific changes in acyl-CoA: cholesterol acyltransferase (ACAT) mRNA levels in rabbits.

A human cDNA clone (K1) was recently isolated that encodes functional acyl-CoA:cholesterol acyltransferase (ACAT) protein (Chang et al. J. Biol. Chem. 1993. 268: 20747-20755). We used the K1 clone to screen a rabbit liver cDNA library and isolated a 919 base pair partial rabbit cDNA (ACAT14b) that was greater than 90% homologous with the human nucleotide sequence. Northern blotting using the rabbit ACAT cDNA14b revealed the existence of at least six related mRNA species (ranging from 6.2 to 1.7 kb) in various rabbit tissues. Using an RNAse protection assay, ACAT mRNA14b was detected in twelve separate rabbit organs. Adrenal gland contained the highest concentrations of ACAT mRNA14b (per microgram of total RNA) being 20-, 30-, and 50-fold higher than small intestine, aorta, and liver, respectively. Additional studies with isolated liver cell populations revealed that rabbit hepatic nonparenchymal cells contained 30-fold more ACAT mRNA14b (per microgram of total RNA) than parenchymal cells. To determine whether ACAT mRNA14b levels are regulated in vivo, rabbits were fed for 4 weeks a high fat/high cholesterol diet (HFHC; 0.5% cholesterol, 3% coconut oil, 3% peanut oil) at which point they were either kept for an additional 4 weeks on the HFHC-diet or switched to the HFHC-diet plus CI-976 (50 mg/kg), a potent and specific ACAT inhibitor; another group of rabbits was fed a chow diet for the entire 8 weeks. The HFHC-diet caused a 2- and 3-fold increase in hepatic and aortic ACAT mRNA14b levels, respectively, in comparison to chow-fed animals; there was no change in adrenal or small intestine levels. CI-976 treatment lowered ACAT mRNA14b levels by 60% and 40% in liver and aorta, respectively, in comparison to the HFHC controls; again there was no change in adrenal or small intestine levels. These data indicate that ACAT mRNA14b levels increase in a tissue specific manner in response to dietary fat and cholesterol.

Animals↗