Foliar Mass Research Articles

Comportamento do NDVI obtido por sensor ótico ativo em cereais

O objetivo deste trabalho foi avaliar, com um sensor ótico ativo, o comportamento do índice de vegetação por diferença normalizada (NDVI - "normalized difference vegetation index"), nas culturas de trigo, triticale, cevada e milho. Cinco experimentos foram conduzidos no Paraná e São Paulo, com variação de classes de solo, doses e fontes de N, e variedades de trigo. As seguintes variáveis foram avaliadas: NDVI, teor de N foliar, matéria seca e produtividade das culturas. Análises de regressões foram realizadas entre as doses de N aplicadas e NDVI, teor de N foliar, matéria seca e produtividade. Análises de correlação entre as variáveis foram realizadas. O trigo, triticale e cevada apresentaram resposta às aplicações de doses crescentes de N, pelo aumento nas leituras do NDVI, no teor de N foliar e na produtividade. Medido pelo sensor ótico ativo utilizado, o NDVI apresenta alto potencial para manejo do N nas culturas do trigo, triticale e cevada, e baixo potencial para a cultura do milho. Há interferência das variedades de trigo nas leituras do sensor ótico ativo.

Adubação foliar com macro e micronutrientes no crescimento de mudas micropropagadas do abacaxizeiro cv. Gold [Ananas comosus (L.) Merrill] em diferentes recipientes

Objetivou-se com este trabalho avaliar o efeito da adubação foliar com macro e micronutrientes no crescimento das mudas micropropagadas do abacaxizeiro cv. Gold [Ananas comosus (L.) Merrill], em diferentes recipientes. O experimento foi em esquema fatorial 8x3, adubação foliar em 8 níveis e recipientes em 3 níveis, através de um delineamento inteiramente casualizado com 5 repetições. As mudas foram padronizadas com altura média de 7,12 cm. As adubações foliares foram feitas com uréia, cloreto de potássio, ácido bórico, um formulado comercial com macro e micronutrientes e testemunha (pulverização com água) e os recipientes: bandeja de isopor com 200 células; tubete pequeno de 115 cm³; e tubete grande com 300 cm³. O substrato utilizado foi o plantmax hortaliças®. Avaliaram-se as características área foliar, altura de planta e massa seca da parte aérea e da raiz, aos 140 dias do transplantio. Os adubos foliares proporcionaram maior crescimento em área foliar, altura e massa seca da parte aérea às mudas do abacaxizeiro, embora com resultados diferentes. Os adubos foliares não aumentaram a massa seca do sistema radicular. A bandeja de isopor apresentou as menores médias, com todos os adubos foliares para área foliar, altura e massa seca da parte aérea das mudas do abacaxizeiro. O tubete pequeno e o tubete grande apresentaram resultados semelhantes com a maioria dos adubos foliares utilizados.

Foliar Nutrient Dynamics and Foliar Resorption in Quercus brantii Lindley along an Elevational Gradient

Foliar mass per area (mg dm(-2)) -based nitrogen and phosphorus concentrations, specific leaf mass (mg dm(-2)) and absolute and proportional resorption in Quercus brantii was investigated along a topographic gradient from 450 to 850 m altitude. Foliar N and P concentrations in Q. brantii exhibited significant differences with respect to topographic position and sampling dates in all of the studied parameters. A sharp decrease was observed from April to September in terms of Specific Leaf Mass (SLM) values. However, mass per area-based absolute and proportional N resorption was lowest at 450 m, while absolute and proportional P resorption was lowest at 850 m. Significant correlations were found between mass per area-based leaf nutrient concentration and foliar resorption except for the correlations between absolute P resorption and foliar P concentrations at 450, 650 and 750 m during full-leaf expansion and 850 m during senescence, respectively.

Christmas Tree Response to N Fertilization and the Development of Critical Foliar N Levels in New York

Abstract The effectiveness of fertilization as a tool to increase growth rate and quality of Christmas trees depends on the ability to identify trees that are limited by nutrition. Foliar analysis is one approach to identify nutrition-limited trees, but it requires pre-established diagnostic criteria for application. The objective of this study was to assess growth response of Christmas trees to N fertilizer, and to develop critical foliar N levels for species commonly grown in New York. We evaluated diameter growth and foliar N concentration response of balsam fir (Abies balsamea [L.] Mill.), Canaan fir (Abies balsamea var. phanerolepis [Fern.]), Fraser fir (Abies fraseri [Pursh] Poir.), concolor fir (Abies concolor [Gord. and Glend.] Lindl.), and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) midrotation Christmas trees to N fertilization on 11 sites distributed across central New York. Two fertilizer treatments were applied: 1 oz N tree−1 as ammonium nitrate (AN) and chicken manure compost (CMC) applied at 0.6 oz N tree−1. Current annual diameter increment (CAI) for Canaan fir, Fraser fir, and Douglas-fir increased in response to AN. Two-year CAI for AN-treated trees was greater than control trees for all species with the exception of Canaan fir. Application of CMC had no effect on CAI the first year after application but did increase 2-year CAI for concolor and Fraser fir. Vector analysis, which simultaneously displays foliar mass, N concentration, and N content, indicated that all species responded positively to AN in more than 50% of the cases (with the exception of Canaan fir). Foliar response to CMC was weak, exhibiting a positive response in only 38% of the cases. Based on the foliar response of trees to AN, the following critical foliar N concentrations are proposed for Christmas trees in New York: balsam fir, 1.65%; concolor fir, 1.75%; Canaan fir, 1.60%; Douglas-fir, 1.45%; and Fraser fir, 1.60%.

Effect of 2,4-D and CPPU on Triploid Watermelon Production and Quality

Pollination is one problem with intensive seedless watermelon (Citrullus lanatus Thunb.) production under unfavorable environmental conditions (low solar radiation and temperature) due to the lowered activity of pollinating insects, such as the bee (Apis mellifera L.). An alternative to overcome these problems is the use of plant growth regulators. For this reason, experiments were conducted for 2 years in plastic greenhouses in the fields of Almeria, southwestern Spain, to evaluate the production and quality of ‘Reina de corazones’ triploid watermelon grafted onto RS841 rootstock (Cucurbita maxima × Cucurbita moschata). Two phytoregulators were used for the development of the ovary: 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) and 2,4-dichlorophenoxyacetic acid (2,4-D). Concentrations of CPPU evaluated were 50, 100, 150, and 200 mg·L−1. An application of 0.6 mL was applied to each ovary in addition to 4, 6, 8, or 12 mg·L−1 of 2,4-D to the foliar mass at a proportion of 1000 L·ha−1. Results showed that the production and number of fruit obtained with CPPU treatments were similar to what is obtained by using bees for fruit pollination. Maximum production was reached at concentrations of 100–200 mg·L−1. Average production was 32% to 83% higher than results from 2,4-D at 8 mg·L−1. The number of fruit per plant was 33% to 35% higher as well. In the first assay, a positive correlation was also observed between production and CPPU concentration. CPPU treatments had a lower accumulation of sugars than those with 2,4-D; nevertheless, both treatments showed values of commercially acceptable soluble solids.

Efeito do pré-plantio com plantas medicinais e aromáticas no controle de Plasmodiophora brassicae

A "hérnia das crucíferas" é a principal doença na produção de brássicas na Região Metropolitana de Curitiba-PR. Fatores ambientais favoráveis, ausência de cultivares resistentes e de controle químico eficiente, aliados ao plantio sucessivo de espécies da mesma família, têm colaborado para sua disseminação. Com o objetivo de controlar a doença com menor impacto ambiental, o presente estudo verificou o efeito do pré-plantio de plantas medicinais e aromáticas na redução de inóculo de Plasmodiophora brassicae. Dois experimentos foram conduzidos em casa de vegetação no Setor de Ciências Agrárias da Universidade Federal do Paraná, nos períodos de junho a novembro de 2003 e julho a dezembro de 2004. O delineamento foi inteiramente casualizado com nove tratamentos e seis repetições. As plantas utilizadas nos tratamentos foram: menta (Mentha piperita L.); alfavaca (Ocimum basilicum L.); bardana (Arctium minus Hill); calêndula (Calendula officinalis L.); cebolinha (Allium fistulosum L.); salsa (Petroselinum hortense Hoffm) e sálvia (Salvia officinalis L.), e como testemunhas foram utilizados solos sem patógeno e solo infestado, ambos em pousio. Utilizaram-se vasos contendo 3 Kg de solo esterilizado via vapor e como inóculo de P. brassicae foram utilizados 2,5 g de galhas por vaso. A rúcula (Eruca sativa Mill) foi o hospedeiro suscetível utilizado. Após 45 dias do plantio da rúcula foram determinadas a massa aérea fresca, incidência de galhas galhas e o índice de severidade. A maior massa aérea fresca e as menores severidades foram obtidas no experimento de 2003, nos tratamentos com o pré-plantio das medicinais bardana, salsa, menta, alfavaca e cebolinha.

Foliar and shoot allometry of pollarded black locust, Robinia pseudoacacia L.

Browse of multipurpose tree species such as black locust could be used to broaden grazing options, but the temporal distribution of foliage has not been adequately studied. Our objective was to determine effects of harvest date, P fertilization (0 and 600 kg ha 1 yr 1 ), and pollard height (shoots clipped at 5-, 50-, and 100cm above ground) on foliar and shoot allometry of black locust. The experiment was conducted on a naturally regenerated 2-yr-old black locust stand (15,000 trees ha 1 ). Basal shoot diameter and foliar mass were measured monthly in June to October 2002 and 2003. Foliar and shoot dry mass (Y) was estimated from basal shoot diameter (D) by the function Y = aD b , with regression explaining ‡95% of variance. Allometry of foliar mass was affected by harvest date, increasing at a greater rate with D in September than in June or July, but not by P fertilization or pollard height. Foliar mass was predicted best by monthspecific equations for the June to October growth interval. Allometry of shoot dry mass was unaffected by harvest date, P fertilization, or pollard height. These equations could be used as a first approximation of foliar and shoot mass for pollarded black locust.

Competitive strategies in adult beech and spruce: space-related foliar carbon investment versus carbon gain

In Central Europe, Fagus sylvatica and Picea abies represent contrasting extremes in foliage type, crown structure and length of growing season. In order to examine the competitive strategies of these two co-occurring species, we tested the following hypotheses: (1) the space occupied by the foliage of sun branches is characterized by greater foliar mass investment compared to shade branches, (2) the carbon (C) gain per unit of occupied space is greater in sun than in shade branches, and (3) annual C and water costs of the foliage for sustaining the occupied space are low, wherever C gain per unit of occupied space is low. These were investigated in a mature forest in Southern Germany. The examination was based on the annual assessment of space-related resource investments and gains of the foliage. The foliated space around branches was regarded as the relevant volume with respect to aboveground resource availability. Occupied crown space per standing foliage mass was higher in shade compared to sun branches of beech, whereas no difference existed in crown volume per foliage mass between sun and shade branches of spruce (hypothesis 1 accepted for beech but rejected for spruce). However, beech occupied more space per foliage mass than spruce. The C gain per occupied crown volume was greater in sun than in shade branches (hypothesis 2 accepted) but did not differ between species. The amount of occupied space per respiratory and transpiratory costs did not differ between species or between sun and shade branches. In beech and spruce, the proportion of foliage investment in the annual C balance of sun and shade branches remained rather stable, whereas respiratory costs distinctly increased in shade foliage. Hence, shade branches were costly structures to occupy space, achieving only low and even negative C balances (rejection of hypothesis 3), which conflicts with the claimed C autonomy of branches. Our findings suggest that competitiveness is determined by the standing foliage mass and the annual branch volume increment rather than annual investments in foliage. Expressing competitiveness in terms of space-related resource investments versus returns, as demonstrated here, has the potential of promoting mechanistic understanding of plant-plant interactions.

Influence of dose and molecular weight on foliar mass uptake of surfactant

Foliar uptake of model xenobiotics and active ingredients on a unit area basis can be related to the initial dose of compound applied per unit area Current concepts propose that ideally surfactants and active ingredients copenetrate into plants Other evidence has shown that this is not always the case with pesticides and surfactants influencing each others behaviour Hence it is relevant to determine whether surfactants follow a similar mass uptake relationship This study determined the uptake of five surfactants differing in structure and molecular weight (2901350) into two plant species (fathen and wheat) The results showed that surfactants follow the same mass uptake relationship found previously for model compounds and active ingredients ie the initial dose (nmol/mm2) of surfactant applied to plant foliage is a strong positive determinant of uptake per unit area However at the constant concentration () studied surfactant molecular weight also played a role in uptake

Ten-year postharvest effects of silviculture systems on soil-resource availability and conifer nutrition in a northern temperate forest

Silviculture systems (clear-cut, partial-cut, and unharvested forest) were compared 9–10 years after harvesting to determine their effects on conifer nutrition and the availability of soil resources, especially nitrogen. These results were used to discuss the effects of silviculture systems on tree growth in relation to the more commonly described effects of light. Differences in soil properties across the silviculture treatments were most apparent in the forest floor. Depth and C/N ratio of the forest floor had decreased slightly in clearcuts, and forest-floor moisture was highest under partial-cut forest. Despite these differences in soil chemistry and soil moisture, no differences were detected in mineralizable N (anaerobic incubation) or in situ net N mineralization among treatments. Height growth and foliar mass were reduced under the low-light conditions of the partial-cut forest, but there were no differences in foliar N concentrations of hybrid white spruce (Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carrière), western redcedar (Thuja plicata Dougl. ex D. Don), or western hemlock (Tsuga heterophylla (Raf.) Sarg.) saplings. Mature western hemlock trees in partial-cut forest also had concentrations of foliar N equal to that of mature trees in the unharvested forest. Overall, we detected only minor effects of silviculture systems on soils after 10 years, and we conclude that light availability is likely more responsible for the current differences in tree growth.

Patterns of canopy interception and throughfall along a topographic sequence for black spruce dominated forest ecosystems in northwestern Ontario

A 3-year (1993–1995) study was conducted to describe both the spatial (within- and between-site) and temporal (monthly) patterns associated with canopy interception, throughfall, and net forest water along a black spruce (Picea mariana (Mill.) BSP) topo-sequence situated in northwestern Ontario. This site array included (1) an upland, well-drained, mineral soil site; (2) a poorly drained, midslope, wet mineral site; and (3) a treed wetland on organic (peat) soil. Bulk precipitation (BP) and throughfall (TF) were collected, on an event basis (63 events, over 4800 samples analyzed), using standard collecting devices and analyzed for total Kjeldahl nitrogen (TKN), ammonium (NH4+), nitrate (NO3–), total phosphorus (TP), potassium (K), calcium (Ca), and magnesium (Mg). Comparison of BP and TF data suggested that an enrichment of K (190%), Mg (115%), and Ca (70%) occurred during canopy interactions. On the other hand, inorganic nitrogen (NH4+: –73%; NO3–: –47%), and to a lesser extent TP (–35%), rates declined. TKN, however, remained the same, suggesting that inorganic N reductions were offset by organic N inputs. Downward shifts in pH were also detected for TF (4.45–4.48), as compared with the pH of BP (4.52–4.80). Although all study sites received similar rainfall amounts, the more productive sites (i.e., carrying greater foliar mass, higher leaf area index) had lower TF volumes (i.e., higher interception rates) but higher macronutrient returns to the forest floor. This increase in macronutrient deposition was directly related to substantial increases in nutrient concentrations, which, in turn, suggested a greater degree of canopy interaction and (or) leaching on these sites. Throughfall pH, however, was not significantly different across the three study sites. With respect to temporal patterns, the major cations (K+, Ca2+, Mg2+) demonstrated an increasing trend in concentration levels in TF as the season progressed to a maximum in October. TKN and TP concentrations, on the other hand, maintained relatively stable levels throughout the summer, peaking in September, but dropping substantially in October as metabolic processes slowed and the supply of these nutrients to the foliage was reduced. Even with the increase in base cation concentration, throughfall pH shifted downward to 4.3 or below by late fall.

Root zone calcium modulates the response of potato plants to heat stress

Potato plant growth and development are known to be severely impacted by heat stress. Here plants grown in a chemically inert medium of 1 : 1 quartzite : perlite (v : v) were subjected to either 35/25 degrees C (stress) or 20/15 degrees C (control) day/night air temperatures and four concentrations of root zone calcium (5, 25, 125 and 600 &mgr;M Ca) for 3 weeks. We report for the first time that potato plant growth under heat stress can persist at specific levels of Ca2+ in the root zone and that the Ca2+ level required for growth under heat stress exceeds that required for growth under normal temperatures. We also provide strong, initial evidence that the ability of high Ca2+ levels to mitigate heat stress effects results from shifts in meristematic activity. Total foliar mass and leaf area were essentially unaffected by Ca2+ level under control temperatures. Under heat stress, leaf area was reduced to about 5% of the control at 5 and 25 &mgr;M Ca but to only 70% of the control at 125 and 600 &mgr;M Ca. Likewise, total foliar mass was reduced under heat stress to about 30% of the control at 5 and 25 &mgr;M Ca but total foliar mass was greater under heat stress than control conditions at 125 and 600 &mgr;M Ca. This increase at higher Ca2+ concentrations was due primarily to axillary shoot growth. Anatomical studies of leaves grown under heat stress show that cell expansion was impaired by heat stress and this impairment was overcome by increasing root zone calcium levels. These results provide insight into the mechanism by which root zone Ca2+ may modulate plant response to heat stress.

Influence of different levels of aluminum on the development of citrus rootstock swingle citrumelo (Citrus paradisi mcf. x Poncirus trifoliata raf.) in nutrient solution

This work aimed at evaluating the influence of different levels of aluminum on the physiological parameters of the citrus rootstock Swingle Citrumelo in hydroponic solution. The experiment was carried out with a completely randomized design with three replications, subdivided in several lots. The levels of aluminum used were: 0, 7.5, 15, 22.5 and 30 mg L-1 in form of AlCl3.6H2O in nutrient solution. Following physiological parameters were evaluated: specific and relative foliar area, relative foliar mass, and the ratio of aerial part dry matter/root system dry matter. The results showed that aluminum did not influence the parameters evaluated except the specific foliar area, which decreased starting at the 7.5 mg L-1 level.

Effects of fertilization on seasonal patterns of foliar mass and nutrients of tamarack and black spruce on undrained and drained minerotrophic peatland sites

We investigated seasonal patterns of needle mass and foliar N, P and K of tamarack (Larix laricina (Du Roi) K. Koch.) and black spruce (Picea mariana (Mill.) B.S.P.) as affected by fertilization of undrained and drained minerotrophic peatland sites. The drained site was ditched in fall 1987. Four N‐P‐K fertilization treatments, i.e. 0‐0‐0, 0‐80‐120, 200‐80‐120, and 400‐

Distance-dependence in herbivory and foliar condition for juvenile Shorea trees in Bornean dipterocarp rain forest.

We assessed density- and distance-dependence in herbivore effects and juvenile condition for four species of Shorea, the most speciose genus in the dominant canopy family of southeast Asian rain forest trees (Dipterocarpaceae). Herbivore damage was quantified as partial leaf loss on young leaves, and whole plant foliar condition as the product of the fraction of leaf nodes containing leaves and the fraction of tissue remaining on extant leaves. Adults of the four species were centers of high total, as well as conspecific, density of juveniles (<1 m tall). For two species, S. hopeifolia and S. pinanga, herbivore damage declined significantly with distance, decreasing by 40% and 51% respectively, between 5 m and 35 m from the parent. For the same two species, foliar condition improved significantly between 5 m and 35 m, increasing by 45% for S. hopeifolia and 24% for S. pinanga. If foliar condition influences juvenile survival and growth, more widely dispersed seeds of these species are more likely to recruit to the canopy. In contrast, there was no significant distance-dependence for S. parvifolia or S. longisperma. Among species, herbivore damage was greatest in those species with greatest local juvenile abundances, i.e., those with highest densities, leaf size, juvenile foliar mass and/ or foliar mass/m2 ground area, but was unrelated to the toughness of mature leaves. However, distance was a better predictor of herbivore damage than was conspecific juvenile density, as evaluated by backward elimination regressions, for both S. hopeifolia and S. pinanga. For foliar condition, the best predictor was distance for S. pinanga, but conspecific density for S. hopeifolia, whose juveniles were smallest and occurred at the highest densities. Total juvenile density (all woody plants) was eliminated as a factor in all cases. The species-specificity of effects (i.e., their dependence on conspecific distance or density), together with the marked differences among congeneric species, caution against generalizations regarding distance-dependent effects in diverse forests.

Biogenic isoprene emission: Model evaluation in a southeastern United States bottomland deciduous forest

Isoprene is usually the dominant natural volatile organic compound emission from forest ecosystems, especially those with a major broadleaf deciduous component. Here we report isoprene emission model performance versus leaf and canopy level isoprene emission measurements made at the Duke University Research Forest near Chapel Hill, North Carolina. Emission factors, light and temperature response, canopy environment models, foliar mass, leaf area, and canopy level isoprene emission were evaluated in the field and compared with model estimates. Model components performed reasonably well and generally yielded estimates within 20% of values measured at the site. However, measured emission factors were much higher in early summer following an unusually dry spring. These decreased later in the summer but remained higher than values currently used in emission models. There was also a pronounced decline in basal emission rates in lower portions of the canopy which could not be entirely explained by decreasing specific leaf weight. Foliar biomass estimates by genera using basal area ratios adjusted for crown form were in excellent agreement with values measured by litterfall. Overall, the stand level isoprene emissions determined by relaxed eddy accumulation techniques agreed reasonably well with those predicted by the model, although there is some evidence for underprediction at ambient temperatures approaching 30°C, and overprediction during October as the canopy foliage senesced. A “Big Leaf” model considers the canopy as a single multispecies layer and expresses isoprene emission as a function of leaf area rather than mass. This simple model performs nearly as well as the other biomass‐based models. We speculate that seasonal water balance may impact isoprene emission. Possible improvements to the canopy environment model and other components are discussed.

UNITED STATES LAND USE INVENTORY FOR ESTIMATING BIOGENIC OZONE PRECURSOR EMISSIONS

The U.S. Geological Survey’s (USGS) EROS (Earth Resources Observation System) Data Center’s (EDC) 1-km classified land cover data are combined with other land use data using a Geographic Information System (GIS) to create the Biogenic Emissions Landcover Database (BELD). The land cover data are being used to estimate biogenic emissions in the contiguous United States. These emissions include volatile organic compound (VOC) emissions from vegetation and nitric oxide (NO) from soils. The EDC data are used predominately in the western United States, while other sources, such as the U.S. Department of Agriculture’s Census of Agriculture and the U.S. Forest Service Eastwide Forest Inventory and Analysis Database (EWDB), are used in the eastern United States. The EROS Data Center land cover classifications must be used with caution in heterogenous areas. Emission factors vary drastically by specific crop and tree genera, and mixed classes in the EDC scheme may not always accurately reflect the actual crop/genus mix. However, future use of satellite-derived vegetation indices and other land cover characteristics may prove useful in understanding geographic distributions of foliar mass and seasonal variation in Leaf Area Index (LAI), which are important drivers in biogenic emission models.

Extrapolating leaf CO2 exchange to the canopy: a generalized model of forest photosynthesis compared with measurements by eddy correlation.

Over the last 4 years, two data sets have emerged which allow increased accuracy and resolution in the definition and validation of a photosynthesis model for whole forest canopies. The first is a greatly expanded set of data on the nitrogen-photosynthesis relationship for temperate and tropical woody species. The second is a unique set of long-term (4 year) daily carbon balance measurements at the Harvard Forest, Petersham, Massachusetts, collected by the eddy-correlation technique. A model (PhET-Day) is presented which is derived directly from, and validated against, these data sets. The PnET-Day model uses foliar nitrogen concentration to calculate maximum instantaneous rates of gross and net photosynthesis which are then reduced for suboptimal temperature, photosynthetically active radiation (PAR), and vapor pressure deficit (VPD). Predicted daily gross photosynthesis is closely related to gross carbon exchange at the Harvard Forest as determined by eddy-correlation measurements. Predictions made by the full canopy model were significantly better than those produced by a multiple linear regression model. Sensitivity analyses for this model for a deciduous broad-leaved forest showed results to be much more sensitive to parameters related to maximum leaf-level photosynthetic rate (A max) than to those related to light, temperature, VPD or total foliar mass. Aggregation analyses suggest that using monthly mean climatic data to drive the canopy model will give results similar to those achieved by averaging daily eddy correlation measurements of gross carbon exchange (GCE).

Phenology of tropical forests: patterns, causes, and consequences

Leaf phenology of tropical forests is distinct from other biomes. Unlike the marked temperature-related periodicity of temperate forests, development tends to be continuous in aseasonal lowland tropical rain forests and becomes more episodic in response to increasing annual drought in tropical dry forests. Hence, in tropical rain forests, foliar development (production, senescence, and longevity) is largely under internal rather than environmental control. In contrast, tropical forests with marked annual dry seasons display associated seasonality of leaf production and shedding. This developmental seasonality can be explained by overlaying the influence of seasonality on trees' internally regulated development and appears to be controlled by acclimative physiological processes and not by sensitivity to photo-, thermo-periodic, or direct environmental cues. Consequences of tropical phenology stem from both the variety of leaf and species ecophysiological types common to a given moisture regime and their relative synchrony of development, and include the following: larger diversity of ecophysiological species types in rain than dry forests; differential rates of herbivory in dry than wet seasons and for synchronous versus asynchronous leaf flushes; ecosystems with greater canopy foliar mass per hectare in rain than dry forests; and several leaf adaptations perhaps unique to tropical forests, such as delayed greening and seasonal leaf phenotypes. Tropical forests may vary in sensitivity to predicted climate change. Phenology of rain forests should change little unless water balance changes markedly, and developmental events in rain forests may be relatively insensitive to moderate changes in CO2 or temperature. Phenology of dry forests could be more sensitive, and in opposite directions, to elevated CO2 and temperatures. Elevated CO2 might delay the onset of leaf shedding and stimulate longer life span if stand level transpiration is reduced, whereas higher temperatures could lead to more rapid water depletion, longer leafless periods, and more strongly synchronized phenology. Key words: tropical forests, phenology, leaf life span, herbivory.

Natural volatile organic compound emission rate estimates for U.S. woodland landscapes

Volatile organic compound (VOC) emission rate factors are estimated for 49 tree genera based on a review of foliar emission rate measurements. Foliar VOC emissions are grouped into three categories: isoprene, monoterpenes and other VOCs. Typical emission rates at a leaf temperature of 30°C and a light intensity of 1000 μmol m −2 s −1 range from <0.1 to 70 μg C g −1 h −1 for isoprene, <0.1 to 3 μg C g −1 h −1 for monoterpenes, and < 0.5 to 5 μg C g −1 h −1 for other VOCs. Isoprene emission factors are given for biogenic emission models that incorporate canopy shading effects and thus require leaf-level emission rates and for emission models that do not include a canopy model and therefore require branch-level isoprene emission factors which already account for some shading. Landscape-level emission rates are estimated by combining emission rate factors determined for tree genera with species composition and foliar mass data. Landscape emission rate factors are determined for each of the 91 woodland landscapes in the high resolution (1.1 km) gridded land-cover database compiled by the EROS Data Center (EDC) from satellite and ancillary data. This database covers the entire contiguous United States of America. Landscape emission rates are also be determined using gridded tree distribution data, based on aerial photographs and ground measurements, such as that available in the U.S. Forest Service (USES) Easlwide Forest Inventory Database (EFID). Emission rates are reported for 41 of the 65 tree genera in the EFID including all of the most common genera. Total VOC emission rate factors for the 91 EDC woodland-cover types range from 0.8 to 11 mg C m −2 h −1 at a standard condition of 30°C and 1000 μmol m −2 s −1 . These landscape factors are based on branch-level emission factors and thus already incorporate canopy shading effects. The estimated fluxes of isoprene and monoterpenes are in relatively good agreement with field measurements of area-averaged fluxes if accurate species composition data (e.g. from the EFID) are available. Total VOC emission rate estimates range from 0.8 to 4.3 mg C m −2 h −1 for scrub woodlands and 2.2 to 11 mg C m −2 h −1 for mixed deciduous/coniferous woodlands. The chemical composition of the VOC flux ranges from 8 to 91 isoprene, 1 to 56% for monoterpenes and 8 to 73% for other VOC. On an area-weighted basis, the U.S. average total VOC emission rate factor of 5.1 mg m −2 h −1 for all woodlands is comprised of 58% isoprene, 18% monoterpenes and 24% other VOC. In comparison to previous estimates, these emission rates are generally higher for isoprene and lower for monoterpenes.