Leaf Optical Responses to Light and Soil Nutrient Availability in Temperature Deciduous Trees

Leaf optical parameters influence light availability at the cellular, leaf, and canopy scale of integration. While recent studies have focused on leaf optical responses to acute plant stress, the effects of changes in plant resources on leaf optics remain poorly characterized. We examined leaf optical and anatomical responses of five temperate deciduous tree species to moderate changes in nutrient and light availability. Spectral reflectance in the visible waveband generally increased at high light, but decreased with increased nutrient availability. Patterns of both spectral reflectance and absorptance were primarily determined by chlorophyll concentration although carotenoid concentration was also influential. While most anatomical features did not explain residual variation in reflectance, cuticle thickness was significantly related to reflectance at complementary angles compared to the angle of incidence. Absorptance did not change with light environment; however, absorption efficiency per unit biomass increased by approximately 40% under low light, due to reduced leaf mass per area. We conclude that changes in resource availability differentially influence leaf optical properties and that such changes are driven primarily by changes in pigment concentrations. The magnitude of leaf optical responses to moderate changes in resource availability was comparable to those of acute stress responses and varied among species

The role of formate in combatting oxidative stress.

As all aerobic organisms are exposed to oxidative stress, they are known to devise intricate mechanisms to counter reactive oxygen species (ROS). Metabolic networks contributing to the production of ketoacids are prominent in alleviating the oxidative burden. When glyoxylate detoxifies ROS, formate is the principal by-product generated. In this study the contribution of formate in enabling the survival of the microbe Pseudomonas fluorescens challenged by hydrogen peroxide (H2O2) has been elucidated. When grown in the presence of H2O2 (stressed culture), the levels of formate were higher in the spent fluid and the soluble cell-free extracts compared to the controls. Formate was subsequently utilized as a reducing factor to produce NADPH and succinate. The former is mediated by formate dehydrogenase (FDH-NADP), whose activity was enhanced in the stressed cells. Fumarate reductase (FRD) that catalyzes the conversion of fumarate into succinate was also markedly increased in the stressed cells. Metabolic adaptation is a pivotal tool in combatting oxidative stress. Formate, a by-product of glyoxylate- mediated detoxification of ROS is recuperated as a potent reductive fuel. It is becoming quite evident that this simple metabolite has other biological roles that have not been fully appreciated.Master of Science (M.Sc.) in Biolog

Biochar seed-coatings for precision aerial seeding in forest restoration

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Edaphic Specialization in Tropical Trees: Physiological Correlates and Responses to Reciprocal Transplantation

Recent research has documented the importance of edaphic factors in determining the habitat associations of tree species in many tropical rain forests, but the underlying mechanisms for edaphic associations are unclear. At Sepilok Forest Reserve, Sabah, Malaysian Borneo, two main soil types derived from sandstone (ridges) and alluvium (valleys) differ in nutrient and water availability and are characterized by forests differing markedly in species composition, structure, and understory light availability. We use both survey and reciprocal transplants to examine physiological adaptations to differences in light, nutrient, and water availability between these soil types, and test for the importance of resource-use efficiency in determining edaphic specialization. Photosynthetic surveys for congeneric and confamilial pairs (one species per soil type) of edaphic specialists and for generalists common to both soil types show that species specializing on sandstone derived soil had lower stomatal conductance at a given assimilation rate than those occurring on alluvial soil and also had greater instantaneous and integrated water-use efficiencies. Foliar dark respiration rates per unit photosynthesis were higher for sandstone ridge than alluvial lowland specialists. We suggest that these higher respiration rates are likely due to increases in photosynthetic enzyme concentrations to compensate for lower internal CO2 concentrations resulting from increased stomatal closure. This is supported by lower photosynthetic nitrogen-use efficiencies in the sandstone ridge specialists. Generalist species had lower water-use efficiencies than sandstone ridge specialists when growing on the drier, sandy ridgetops, but their nitrogen-use efficiencies did not differ from the species specialized to the more resource-rich alluvial valleys. We varied light environment and soil nutrient availability in a reciprocal transplant experiment involving two specialist species from each soil type. Edaphic specialist species, when grown on the soil type for which they were not specialized, were not capable of acclimatory shifts to achieve similar resource-use efficiencies as species specialized to that soil type. We conclude that divergent water-use strategies are an important mechanism underlying differences in edaphic associations and thus contributing to maintenance of high local tree species diversity in Bornean rain forests

Fully fault tolerant quantum computation with non-deterministic gates

In certain approaches to quantum computing the operations between qubits are non-deterministic and likely to fail. For example, a distributed quantum processor would achieve scalability by networking together many small components; operations between components should assumed to be failure prone. In the logical limit of this architecture each component contains only one qubit. Here we derive thresholds for fault tolerant quantum computation under such extreme paradigms. We find that computation is supported for remarkably high failure rates (exceeding 90%) providing that failures are heralded, meanwhile the rate of unknown errors should not exceed 2 in 10^4 operations.Comment: 5 pages, 3 fig

A critical review of the role of local excision in the treatment of early (T1 and T2) rectal tumors

The optimal treatment of early (T1 and T2) rectal adenocarcinomas remains controversial. Local excision and radical resection with total mesorectal excision are the two surgical techniques for excising early rectal cancer. Each has their respective benefits, with local excision allowing for decreased operative morbidity and mortality while radical resection provides an oncologically complete treatment through lymphadenectomy. Local excision can be accomplished via transanal endoscopic microsurgery or transanal excision. There is no significant difference in the recurrence rates (21% vs. 33%) or overall survival (80% vs. 66%) between the two local excision modalities; however, transanal endoscopic microsurgery does allow for a higher rate of R0 resection. Current selection criteria for local excision include well to moderately differentiated tumors without high-risk features such as lymphovascular invasion, perineural invasion, or mucinous components. In addition, tumors should ideally be \u3c3 cm in size, excised with a clear margin, occupy less than 1/3 of the circumference of the bowel and be mobile/nonfixed. Despite these stringent inclusion criteria, local excision continues to be plagued with a high recurrence rate in both T1 and T2 tumors due to a significant rate of occult locoregional metastases (20% to 33%). For both tumor groups, the recurrence rate in the local excision group is more than double compared to radical resection. However, the overall survival is not significantly different between those with and without metastases. With intense postoperative surveillance, these recurrences can be identified early while they are confined to the pelvis allowing for salvage surgical options. Recently, neoadjuvant therapy followed by local excision has shown favorable short and long-term oncological outcomes to radical resection in the treatment of T2 rectal cancer. Ultimately, the management of early rectal cancer must be individualized to each patient\u27s expectations of quality and quantity of life. With informed consent, patients may be willing to accept a higher failure rate and an increased post-operative surveillance regimen to preserve a perceived increased quality of life