A relatively simple procedure is presented for computation of kinetic energy of a rainstorm from information on a recording-raingage chart. An equation is developed de scribing rainfall energy as a function of rainfall intensity. The effects of rainfall energy and its interaction with other variables are evaluated in multiple regression analyses based on data representing four soil types. Application of this information to separate the effects of rainfall from those of physical and management characteristics in plot data is discussed briefly.Soil erosion is a mechanical process that requires energy. Much of this energy is supplied by falling raindrops. The tremendous magnitude of the kinetic energy of rainfall is readily apparent from a few simple calculations. The dead weight of the water falling in 30 min. of a common thunderstorm in the cornbelt states may well exceed 100 tons on each acre. The billions of drops which comprise this 100-ton volume of water strike the soil, if unprotected, at an average velocity of nearly 20 mi/hr. The rainfall energy to be expended during the 30 minutes may well exceed two million foot pounds per acre. If the rain is driven by violent winds, the energy of impact may be even greater.In 1954, the Soil and Water Conservation Re search Division of the Agricultural Research Ser vice initiated a program to summarize all available runoff and soil-loss data on a national basis for further analyses. Studies on the project have pointed out that the accuracy of soil-loss prediction equations on an individual storm basis is consider ably enhanced when a measure of rainfall energy is included as a variable, and that both the ef ficiency and the simplicity of such equations are further improved by terms measuring the inter action effects between variables. In this paper, a relatively simple procedure for computation of the approximate rainfall-energy value of a storm is presented, and the application of this information in more efficient estimates of expected soil loss is discussed.Drop me-Studies of drop-size distribution of natural rainfall have shown a high degree of cor relation between drop size and rainfall intensity. Size distributions of raindrops as a per cent of total volume were published by Laws and Parsons [1943] for intensities ranging from 0.01 to 6.0 inches per Hour. These data are briefly summarized in Figure 1. The mean drop sizes, weighted by per cent of total volume, lie along the solid-line curve. The broken lines in the graph represent the boundaries of the 25-75 percentile and the 5-95 percentile ranges of drop size, respectively.

Forest ecosystems store approximately 45% of the carbon found in terrestrial ecosystems, but they are sensitive to climate-induced dieback. Forest die-off constitutes a large uncertainty in projections of climate impacts on terrestrial ecosystems, climate-ecosystem interactions, and carbon-cycle feedbacks. Current understanding of the physiological mechanisms mediating climate-induced forest mortality limits the ability to model or project these threshold events. We report here a direct and in situ study of the mechanisms underlying recent widespread and climate-induced trembling aspen (Populus tremuloides) forest mortality in western North America. We find substantial evidence of hydraulic failure of roots and branches linked to landscape patterns of canopy and root mortality in this species. On the contrary, we find no evidence that drought stress led to depletion of carbohydrate reserves. Our results illuminate proximate mechanisms underpinning recent aspen forest mortality and provide guidance for understanding and projecting forest die-offs under climate change.carbon starvation | ecosystem shift | biosphere-atmosphere feedbacks | drought impacts | global change ecology

Plant vascular networks are central to botanical form, function, and diversity. Here, we develop a theory for plant network scaling that is based on optimal space filling by the vascular system along with trade-offs between hydraulic safety and efficiency. Including these evolutionary drivers leads to predictions for sap flow, the taper of the radii of xylem conduits from trunk to terminal twig, and how the frequency of xylem conduits varies with conduit radius. To test our predictions, we use comprehensive empirical measurements of maple, oak, and pine trees and complementary literature data that we obtained for a wide range of tree species. This robust intra-and interspecific assessment of our botanical network model indicates that the central tendency of observed scaling properties supports our predictions much better than the West, Brown, and Enquist (WBE) or pipe models. Consequently, our model is a more accurate description of vascular architecture than what is given by existing network models and should be used as a baseline to understand and to predict the scaling of individual plants to whole forests. In addition, our model is flexible enough to allow the quantification of species variation around rules for network design. These results suggest that the evolutionary drivers that we propose have been fundamental in determining how physiological processes scale within and across plant species. U nderstanding the coevolution of plant internal vascular networks and external branching networks is essential to predict botanical form and function (1-4). Seminal studies have attempted to unite these internal and external networks (3,5,6). A decade ago West, Brown, and Enquist (3) proposed a model (WBE) that focuses on the primacy of vascular networks, predicts myriad aspects of plant form and function (3, 7), and has subsequently been tested by the collection of new data for vascular networks (8, 9) and analyses of fluxes through plants (10, 11), forests, and ecosystems (12, 13). Since the publication of the WBE model, several criticisms have been published that question its basic framework, assumptions, and generality (14-16). Indeed, focusing on plant models, several studies have: (i) highlighted how hydraulic safety and efficiency may have shaped the evolution of vascular networks (2, 17), (ii) questioned whether vascular safety and efficiency are adequately described by the WBE model (8,18,19), and (iii) revealed empirical patterns that contradict parts of the WBE model (9,(20)(21)(22)(23). For example, building on earlier work (24, 25), Sperry and colleagues (2) compiled data for the xylem conduits that transport water in plants, and they documented a general principle termed the "packing rule"-the frequency of xylem conduits varies approximately inversely with the square of conduit radius. This packing rule contradicts the WBE model's assumption that conduit frequency remains unchanged as conduit radii taper, decreasing in size from trunk to terminal twig. Safety and efficiency considerations have been pr...

The concept of iso- vs. anisohydry has been used to describe the stringency of stomatal regulation of plant water potential (ψ). However, metrics that accurately and consistently quantify species' operating ranges along a continuum of iso- to anisohydry have been elusive. Additionally, most approaches to quantifying iso/anisohydry require labour-intensive measurements during prolonged drought. We evaluated new and previously developed metrics of stringency of stomatal regulation of ψ during soil drying in eight woody species and determined whether easily-determined leaf pressure-volume traits could serve as proxies for their degree of iso- vs. anisohydry. Two metrics of stringency of stomatal control of ψ, (1) a 'hydroscape' incorporating the landscape of ψ over which stomata control ψ, and (2) the slope of the daily range of ψ as pre-dawn ψ declined, were strongly correlated with each other and with the leaf osmotic potential at full and zero turgor derived from pressure-volume curves.

Abstract. Scatchard analyses of the binding of transforming growth factor-beta (TGF-beta) to a wide variety of different cell types in culture revealed the universal presence of high affinity (Kd = 1-60 pM) receptors for TGF-beta on every cell type assayed, indicating a wide potential target range for TGF-beta action. There was a strong (r = +0.85) inverse relationship between the receptor affinity and the number of receptors expressed per cell, such that at low TGFbeta concentrations, essentially all cells bound a similar number of TGF-beta molecules per cell. The binding of TGF-beta to various cell types was not altered by many agents that affect the cellular response to TGF-beta, suggesting that modulation of TGF-beta binding to its receptor may not be a primary control mechanism in TGF-beta action. Similarly, in vitro transformation resulted in only relatively small changes in the cellular binding of TGF-beta, and for those cell types that exhibited ligand-induced downregulation of the receptor, down-regulation was not extensive. Thus the strong conservation of binding observed between cell types is also seen within a given cell type under a variety of conditions, and receptor expression appears to be essentially constitutive. Finally, the biologically inactive form of TGF-beta, which constitutes >98% of autocrine TGF-beta secreted by all of the twelve different cell types assayed, was shown to be unable to bind to the receptor without prior activation in vitro. It is proposed that this may prevent premature interaction of autocrine ligand and receptor in the Golgi apparatus.

This study examined the effects of acute administration of delta-9-tetrahydrocannabinol (delta 9-THC), the psychoactive ingredient in marijuana, on extracellular efflux of dopamine (DA) and its metabolites as measured by in vivo microdialysis in nucleus accumbens of conscious, freely-moving rats. delta 9-THC, at low doses (0.5-1.0 mg/kg), which significantly enhance brain stimulation reward (intracranial self-stimulation), significantly increased DA efflux in nucleus accumbens. Augmentation of DA efflux by delta 9-THC was abolished by removal of calcium (Ca++) ions from the perfusion fluid, indicating a Ca(++)-dependence of delta 9-THC's action. Augmentation of DA efflux by delta 9-THC was either totally blocked or significantly attenuated by doses of naloxone as low as 0.1 mg/kg. Given the postulated role of mesocorticolimbic DA circuits in mediating and/or modulating brain stimulation reward, the present data raise the possibility that marijuana's rewarding effects, and hence its euphorigenic effects and abuse potential, may be related to pharmacological augmentation of presynaptic DA mechanisms. Additionally, the DA mechanisms enhanced by marijuana appear to be modulated by an endogenous opioid peptide system.

A polypeptide transforming growth factor (TGF) that induces anchorage-dependent rat kidney fibroblasts to grow in soft agar has been isolated from human placenta and purified to homogeneity. This polypeptide is classified as a type (3 TGF because it does not compete with epidermal growth factor (EGF) for membrane receptor sites but does require EGF for induction of anchorage-independent growth of indicator cells. Purification of this peptide was achieved by acid/ethanol extraction of the placenta, followed by gel filtration, cation exchange, and HPLC of the acid-soluble proteins. Homogeneity of the TGF-.3 from the final column was shown by its constant specific activity and amino acid composition across the peak of soft agar colony-forming activity and by its migration as a single band at Mr 23,000-25,000 on NaDodSO4/polyacrylamide gel electrophoresis. Under reducing conditions, the protein migrated on a gel as a single band at Mr 13,000. The purified placental TGF-(8 caused half-maximal growth stimulation of indicator cells in soft agar at 64-72 pg/ml (3 pM) in the presence of EGF at 2 ng/ml (0.34 nM).Transforming growth factors (TGFs) have been operationally defined as low molecular weight acid-stable polypeptides that induce nonneoplastic anchorage-dependent rat kidney cells to form colonies that grow in soft agar (1, 2). These TGFs have been shown to have important functional interactions with epidermal growth factor (EGF) and can be subdivided into at least two groups based on these interactions (3-5). One group, defined as type a, is able to compete with EGF for membrane receptor binding sites and includes sarcoma growth factor (1), a TGF purified from human melanoma cells (6), and EGF itself (5). The second group, type ,B, does not bind to the EGF receptor. Type /3 TGFs were originally isolated from nonneoplastic tissues (3) but have recently been shown to occur in neoplastic cells as well (4, 5, 7). Both TGF-a and TGF-P must be present to induce the growth of nonneoplastic cells in soft agar (8). The normal physiological functions of these potent growth factors are not yet known. It has been suggested that they may be involved in embryological development (9, 10), wound healing (11), and tissue repair (11). In this report, the presence of a TGF-,B in human placenta is documented and the total purification to homogeneity of a TGF-P derived from a human organ is described. MATERIALS AND METHODSSoft Agar Assay. Soft agar colony-forming activity was determined as described (2) except that the cells were stained (12) at the end of 1 wk in assay and the numbers and sizes of the colonies were determined using a Bausch and Lomb Omnicon image analysis system (3).Extraction. Normal term human placentas were frozen on dry ice within 30 min after delivery and stored at -60'C until used. Placentas were extracted as described (2) except that the homogenized tissue (600-1,000 g) was stirred in the acid/ethanol solution at room temperature for 2 to 3 hr prior to centrifugation. The resulting supernatant was adj...

Vulnerability curves using the 'Cavitron' centrifuge rotor yield anomalous results when vessels extend from the end of the stem segment to the centre ('open-to-centre' vessels). Curves showing a decline in conductivity at modest xylem pressures ('r' shaped) have been attributed to this artefact. We determined whether the original centrifugal method with its different rotor is influenced by open-to-centre vessels. Increasing the proportion of open-to-centre vessels by shortening stems had no substantial effect in four species. Nor was there more embolism at the segment end versus centre as seen in the Cavitron. The dehydration method yielded an 'r' shaped curve in Quercus gambelii that was similar to centrifuged stems with 86% opento-centre vessels. Both 'r' and 's' (sigmoidal) curves from Cercocarpus intricatus were consistent with each other, differing only in whether native embolism had been removed. An 'r' shaped centrifuge curve in Olea europaea was indistinguishable from the loss of conductivity caused by forcing air directly across vessel end-walls. We conclude that centrifuge curves on long-vesselled material are not always prone to the open vessel artefact when the original rotor design is used, and 'r' shaped curves are not necessarily artefacts. Nevertheless, confirming curves with native embolism and dehydration data is recommended.