The effects of ontogeny and soil nutrient supply on aboveground biomass accumulation, allocation, and stemwood growth efficiency of loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliottii) were investigated in north-central Florida over 16 years using a 2 × 2 × 2 factorial experiment (species, fertilization, weed control). Aboveground biomass growth responses to the combined fertilizer and weed control treatments (FW) averaged ~2- and 2.8-fold for slash and loblolly pine, respectively. In the same treatment, annual needlefall (NF) production for slash pine approached a "steady state" of 6 Mg·ha-1 at ages 8-14 years, while loblolly pine NF production peaked at 7 Mg·ha-1 at age 10 years, and then declined 17% following curtailment of the fertilizer treatment. Periodic stemwood biomass increment (PAI) for the FW treatment for both species culminated at about 15 Mg·ha-1·year-1 at age 8 years and then declined rapidly (~275%) to <4 Mg·ha-1·year-1 at 15 years; reductions for the untreated control were considerably slower. The progressive decline in PAI following peak leaf area development was closely associated with a decrease in stemwood production per unit leaf area (growth efficiency). A unit increase in leaf area index in the 7- to 9-year-old stands produced about 3.0 and 3.1 times more stemwood biomass per year than in the 14- to 16-year-old stands for loblolly and slash pine, respectively.

We used three methods to measure boundary layer conductance to heat transfer (g(bH)) and water vapor transfer (g(bV)) in foliated branches of Abies amabilis Dougl. ex J. Forbes, a subalpine forest tree that produces clumped shoot morphology on sun-formed branches. Boundary layer conductances estimated in the field from energy balance measurements increased linearly from approximately 10 mm s(-1) at low wind speeds (< 0.1 m s(-1)) to over 150 mm s(-1) at wind speeds of 2.0 m s(-1). Boundary layer conductances measured on shoot models in a wind tunnel were consistently higher than field measurements. The difference between wind tunnel values and field measurements was attributable to variation in path length between the two experimental environments. Boundary layer conductance estimated by subtracting stomatal resistance (r(sV)) measured with a porometer from the total branch vapor phase resistance were unusually small. Sensitivity analysis demonstrated that this method is not suitable for coniferous foliage or when stomatal conductance (g(sV)) is small compared with g(bV). Analysis of the relative magnitudes of g(sV) and g(bV) revealed that, under most conditions, A. amabilis branches are well coupled (i.e., g(sV) is the dominant controller of transpiration). The boundary layer conductance to heat transfer is small enough that leaf temperature can become substantially higher than air temperature when radiation is high and wind speed is low. Over a two-month period, the maximum difference between leaf and air temperatures exceeded 6 degrees C. Leaf temperature exceeded air temperature by more than 2 degrees C on 10% of the daylight hours during this period. Consideration of both the photosynthetic temperature response of A. amabilis foliage as well as the summer air temperature conditions in its habitat suggests that these elevated leaf temperatures do not have a significant impact on carbon gain during the growing season.

Temperature-independent fluctuations in stem CO(2) efflux were measured in Pinus taeda L. seedlings. Stem CO(2) efflux was measured during high and low transpiration rates, high and low net photosynthesis rates, and normal and interrupted substrate supply conditions. Stem CO(2) efflux rates were an average of 6.7% lower during periods of high transpiration compared to periods of low transpiration. This difference in stem CO(2) efflux rates was not due to water stress. The most likely cause was movement of respiratory CO(2) in the transpiration stream. Interruption of substrate supply to the stem by phloem girdling reduced stem CO(2) efflux rates. Increasing net photosynthesis rates from low to high had no effect on stem CO(2) efflux, but decreasing net photosynthesis from high to low caused relatively small reductions in stem CO(2) efflux. These results indicate that diurnal changes in net photosynthesis rate may play a small role in temperature-independent afternoon depressions of stem CO(2) efflux. The transport of respiratory CO(2) by the transpiration stream compromises measurements of woody tissue respiration obtained by commonly accepted gas exchange techniques. This phenomenon could also affect measurement of leaf net photosynthesis and branch woody tissue respiration.

Increased prevalence of Alzheimer's disease‐like β‐amyloid deposits in the neuropil and within neurons occurs in the brains of non‐demented individuals with heart disease. Heart disease is a prevalent finding in Alzheimer's disease, and may be a forerunner to the dementing disorder. In the cholesterol‐fed rabbit model of human coronary heart disease there is production and accumulation of β‐amyloid in the brain. This accumulation of β‐amyloid can be reversed by removing cholesterol from the rabbits' diet. In culture cells, a cholesterol challenge has been shown to increase production of β‐amyloid, and dramatic reductions of cholesterol produced by HMG Co‐A reductase inhibitors decrease production of β‐amyloid. Increased β‐amyloid production is also produced by dietary cholesterol in a number of transgenic mouse models of Alzheimer's disease. Administration of HMG Co‐A reductase inhibitors may block β‐amyloid production caused by dietary cholesterol in rabbits. Clinical trials testing the benefit of HMG Co‐A reductase inhibitors in the treatment of Alzheimer's disease are underway. Microsc. Res. Tech. 50:287–290, 2000. © 2000 Wiley‐Liss, Inc.

Abstract. Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

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Crown structure, absorbed photosynthetically active radiation (APAR) and growth were analyzed in 300 replicated loblolly (Pinus taeda L.) and slash pine (Pinus elliottii Engelm. var. elliotti) clones to: (1) quantify genetic variation in crown structural traits, growth and APAR at the species, family and clonal levels; and (2) estimate within-family genetic and environmental influences on measured variables. Species and family-within-species differences were found in some growth traits, crown size, leaf area, APAR and branch angle. Loblolly pine developed larger crowns, exposed more leaf area with an acute angle, and intercepted more radiation than slash pine. Significant differences among clones within-family were found for stem volume and crown architecture. Loblolly pine and slash pine within-family, individual-tree broad-sense heritabilities ranged from 0.00 to 0.41 for growth and crown structural traits and most were between 0.10 and 0.25 when estimated from a combined analysis across families. Genetic correlations of crown size, leaf area and APAR with volume increment generally ranged from 0.60 to 0.75. This knowledge of the genetic interactions among growth and crown structural traits improves our understanding of how crown morphology affects light interception and stand development, and ultimately how these attributes can be incorporated in the selection of families or clones for the development of new crop tree ideotypes.