Morphological plasticity of cotton roots in response to interspecific competition with pecan in an alleycropping system in the southern United States

A study was conducted in northwest Florida, USA, to investigate root development and morphology of cotton (Gossypium hirsutum L.) under pecan (Carya illinoensis K. Koch) trees in an alleycropping experiment. Root:shoot ratio, root biomass, total root length and root length density were examined under three treatments: (1) barrier (separating belowground interspecific competition by trenching to a depth of 120 cm and installing polyethylene barrier), (2) non-barrier (root systems were free to interact), and (3) monoculture of cotton (without above and belowground interspecific competition with trees). Results indicated that plants in the barrier and non-barrier treatments had lower root:shoot ratios compared to the monoculture treatment. Belowground competition for resources between pecan and cotton in the non-barrier treatment resulted in 25 and 33% reduction of total root length (359 cm) when compared to that of the barrier (477 cm) and monoculture (539 cm) treatments, respectively. The non-barrier plants also exhibited the lowest root length density. Specific root length was highest for the monoculture (179 cm g⁻¹) and lowest for the non-barrier treatment (146 cm g⁻¹) with the barrier treatment being intermediate (165 cm g⁻¹). Interspecific competition with pecan significantly altered root development and morphology of cotton plants. Research in agroforestry should take into account the developmental differences in root systems of the associated crop species so that better models incorporating nutrient and water uptake can be developed.     

Ailanthus triphysa at different density and fertiliser levels in Kerala, India: tree growth, light transmittance and understorey ginger yield

Ailanthus triphysa (Family – Simaroubaceae) growth is known to vary in response to different stocking and fertiliser levels. Understorey productivity related to these differences remain elusive, yet are important for optimising the combined production of tree and crop components. A split plot experiment to evaluate the effect of different stocking levels and fertiliser regimes on ailanthus growth, stand leaf area index (LAI) and understorey PAR (photosynthetically active radiation) transmittance was started at Vellanikkara, India in June 1991. Main plot treatments included four densities (3,333, 2,500, 1,660 and 1,111 trees ha⁻¹), replicated thrice. Four fertiliser levels (0:0:0, 50:25:25, 100:50:50 and 150:75:75 kg N:P₂O₅:K₂O ha⁻¹) formed the sub plot treatments. Ginger (Zingiber officinale) was planted as an understorey crop in May 1994 with contiguous treeless control plots. Soil nutrient availability before and after ginger was assessed. Higher densities stimulated ailanthus growth modestly, while fertiliser response of tree and ginger was inconsistent. PAR transmittance below the canopy was related to tree density, LAI and time of measurement. Midday PAR flux having low standard deviations is ideal for evaluating canopy effects on understorey light availability. Ginger in the interspaces exhibited better growth compared to sole crop. Highest rhizome yield was observed in the 2,500 trees ha⁻¹ stocking level, which is optimum for below five year-old ailanthus stands on good sites. It represents 52% mean daily PAR flux or 73% midday PAR flux. Ailanthus+ginger combinations improved the site nutrient capital when ginger was adequately fertilised, despite treeless controls having relatively higher initial soil nutrient availability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Competition for water in a pecan (Carya illinoensis K. Koch) – cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Understanding the belowground interactions between trees and crops is critical to successful management of agroforestry systems. In a study of competition for water in an alley cropping system consisting of pecan (Carya illinoensis) and cotton (Gossypium hirsutum) in a sandy loam soil (Rhodic Paleudult) in Jay, Florida, root systems of the two species were separated by trenching to 120 cm depth. A polyethylene barrier was installed in half of the plots. Spatial and temporal variations in soil water content, root distribution and water uptake by both species, and leaf area development and height of cotton were measured. Interspecific competition for water was greater in the non-barrier treatment near tree rows than at the alley center. Competition became evident 3 to 4 weeks after emergence of cotton and increased during the following 7 to 8 weeks. Compared with the non-barrier treatment, the barrier treatment had higher soil water content and better growth of cotton (height, leaf area, and fine root biomass). Cotton lint yield in the barrier treatment (677 kg ha^–1) was similar to that in a sole-crop stand, but higher than in the non-barrier (502 kg ha^–1) treatment. Lint production efficiency of plants was higher in the interior rows in the non-barrier treatment (0.197 kg lint per square meter of leaf area, compared to 0.117 kg in the barrier treatment). The results suggest that trenching or even deep disking parallel to the tree row may reduce competition for water, but the impact on tree growth cannot be established from this study. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dry matter production,morphology and nutritive value of <Emphasis Type="Italic">Dactylis glomerata</Emphasis> growing under different light regimes

Plant growth, morphology and nutritive value under shade can differ between temperate grasses. Therefore, the aim of this study was to quantify the dry matter (DM) production, sward morphology, crude protein (CP%), organic matter digestibility (OMD) and macro-nutrient concentrations (P, K, Mg, Ca and S) in a grazed cocksfoot (Dactylis glomerata L.) pasture under 10-year-old Pinus radiata D. Don forest. Four levels of light intensity were compared: full sunlight (100% photosynthetic photon flux density-PPFD), open + wooden slats (∼43% PPFD), trees (∼58% PPFD) and tree + slats (∼24% PPFD). The mean total DM production was 8.2 t DM ha⁻¹ yr⁻¹ in the open and 3.8 t DM ha⁻¹ yr⁻¹ in the trees + slats treatment. The changes in cocksfoot leaf area index (LAI) were related to variations in morphological aspects of the sward such as canopy height and tiller population. CP% increased as PPFD declined with mean values of 18.6% in open and 22.5% in the trees + slats treatment. In contrast, the intensity of fluctuating shade had little effect on OMD with a mean value of 79 ± 3.2%. The mean annual macro-nutrient concentrations in leaves increased as the PPFD level declined mainly between the open and the trees + slats treatments. It therefore appears that heavily shaded dominant temperate pastures in silvopastoral systems limit animal production per hectare through lower DM production rates and per animal through reduced pre-grazing pasture mass of lower bulk density from the etiolated pasture.     

Biomass production potential of three short rotation woody crop species under varying nitrogen and water availability

A study was conducted in an agricultural field to examine the biomass production of three fast-growing short rotation woody crop (SRWC) species, Populus deltoides, Quercus pagoda, and Platanus occidentalis using fertilization and irrigation (fertigation). The study included a randomized complete block (RCB) with five treatments; control, irrigated, and irrigated with 56, 112, and 224 kg nitrogen (N) ha⁻¹ year⁻¹. We quantified survival, basal area, standing biomass, aboveground net primary productivity (ANPP), leaf area index (LAI), and growth efficiency (GE) for each species along the soil nitrogen and water gradient. P. deltoides had low rates of survival (83, 82, and 77% years six, seven, and eight, respectively), but had production values greater than Q. pagoda and P. occidentalis. Standing biomass reached its peak for P. deltoides and P. occidentalis (17.56 and 10.36 Mg ha¹, respectively) in the irrigation treatment, and in the 112 kg N treatment for Q. pagoda (5.42 Mg ha⁻¹). P. deltoides and P. occidentalis ANPP peaked in the irrigation treatment (6.66 and 6.31 Mg ha⁻¹ year⁻¹, respectively) and in the 112 kg N (4.43 Mg ha⁻¹ year⁻¹) for Q. pagoda. ANPP was correlated with LAI; however, the relationship was species specific. Maximum ANPP was reached below the maximum LAI for Q. pagoda and P. occidentalis. P. deltoides ANPP was highest at the maximum LAI, which was achieved with IRR. These results suggest that species-specific cultural practices producing optimum LAI and maximum ANPP should be identified before fertigation techniques are adopted widely for SRWC production on agricultural fields.     

Dynamics of coast redwood sprout clump development in variable light environments

Post-thinning stump sprout response was assessed in a coast redwood [Sequoia sempervirens (D. Don) Endl.] stand from 5 to 9 years after five treatments were initiated. Nine years after treatment, leaf area index (LAI) ranged from 5.9 to 14.1 and the percent above canopy light (PACL) ranged from 0.8 to 3.9. Sprout responses included rapid self-thinning in all treatments with complete sprout mortality at low light regimes. Self-thinning of clumps increased with greater overstory LAI and poorer light regimes. Leaf area of individual sprout clumps also declined in low light regimes. The probability of sprout survival declined rapidly below 10 PACL and coincided with declining leaf area in sprout clumps. A conceptual model is presented that shows the sensitivity of redwood sprouts to light regime. Results have implications for management of multiaged stands and indicate these redwood coppice systems require relatively severe overstory treatments to provide sufficient light for sprout vigor and growth.     

Phosphorus,nitrogen and potassium nutrition on Calonectria leaf blight in eucalypt plants

Calonectria pteridis causes Calonectria leaf blight (CLB), and consequently severe defoliation in eucalypt plantations, which results in losses in wood volume. To reduce the negative impacts of this disease in eucalypt, this study aimed to assess the application of different doses and combinations of the macronutrients N, P and K on the percentage of symptomatic leaf area (SLA) and defoliation induced by the pathogen. Cuttings of a clone of Eucalyptus grandis were transplanted to pots containing soil that received different dose combinations of N, P and K, according to an incomplete factorial design. At 200 days after transplanting, leaf samples were analysed for N, P and K contents, and then, the plants were inoculated. Forty‐five days post‐inoculation, SLA and percentage of defoliation were quantified. Potassium doses above 75 mg/dm³ of soil significantly reduced SLA and defoliation. The influence of N and P on defoliation was dependent on K doses, but both reduced symptomatic leaf area. The best control of the disease, expressed by decreased defoliation and symptomatic leaf area, was achieved with leaf content of N, P and K of 9.8, 0.8 and 10.4 g per kg leaf, respectively, obtained with doses of 55, 82.5 and 143 mg/dm³of soil, respectively. Therefore, N, P and K nutrition can be a component of an integrated management programme for the control of CLB in eucalypts.     

Characteristics of leaf areas of plantations in semiarid hills and gully loess regions

The objectives of our study were to explore the relationship of leaf area and stand density and to find a convenient way to measure stand leaf areas. During the 2004 growing season, from May to October, we used direct and indirect methods to measure the seasonal variation of the leaf areas of tree and shrub species. The trees were from Robinia pseudoacacia stands of four densities (3333 plants/hm², 1666 plants/hm², 1111 plants/hm², and 833 plants/hm²) and Platycladus orientalis stands of three densities (3333 plants/hm², 1666 plants/hm², and 1111 plants/hm²). The shrub species were Caragana korshinskii, Hippophae rhamnoides, and Amorpha fruticosa. Based on our survey data, empirical formulas for calculating leaf area were obtained by correlating leaf fresh weight, diameter of base branches, and leaf areas. Our results show the following: 1) in September, the leaf area and leaf area index (LAI) of trees (R. pseudoacacia and P. orientalis) reached their maximum values, with LAI peak values of 10.5 and 3.2, respectively. In August, the leaf area and LAI of shrubs (C. korshinskii, H. rhamnoides, and A. fruticosa) reached their maximum values, with LAI peak values of 1.195, 1.123, and 1.882, respectively. 2) There is a statistically significant power relation between leaf area and leaf fresh weight for R. pseudoacacia. There are significant linear relationships between leaf area and leaf fresh weight for P. orientalis, C. korshinskii, H. rhamnoides, and A. fruticosa. Moreover, there is also a significant power relation between leaf area and diameter of base branches for C. korshinskii. There are significant linear relations between leaf area and diameter of base branches of H. rhamnoides and A. fruticosa. 3) In the hills and gully regions of the Loess Plateau, the LAIs of R. pseudoacacia stand at different densities converged after the planted stands entered their fast growth stage. Their LAI do not seem to be affected by its initial and current density. The same is true for P. orientalis stands. However, the leaf area of individual trees is negatively and linearly related with stand density. We conclude that, in the hills and gully regions of the Loess Plateau, the bearing capacity of R. pseudoacacia and P. orientalis stands we studied have reached their maximum limitation, owing to restricted access to soil water. Therefore, in consideration of improving the quality of single trees, a stand density not exceeding 833 and 1111 plants/hm² is recommended for R. pseudoacacia and P. orientalis, respectively. In consideration of improving the quality of the entire stands, the density can be reduced even a little more. __________ Translated from Journal of Plant Ecology (Chinese Version), 2008, 32 (2): 440–447 [译自: 植物生态学报]     

Soil respiration and microbial biomass in a pecan — cotton alley cropping system in Southern USA

Little information is available on soil respiration and microbial biomass in soils under agroforestry systems. We measured soil respiration rate and microbial biomass under two age classes (young and old) of a pecan (Carya illinoinensis) — cotton (Gossypium hirsutum) alley cropping system, two age classes of pecan orchards, and a cotton monoculture on a well-drained, Redbay sandy loam (a fine-loamy, siliceous, thermic Rhodic Paleudult) in southern USA. Soil respiration was quantified monthly during the growing season from May to November 2001 using the soda-lime technique and was corrected based on infrared gas analyzer (IRGA) measurements. The overall soil respiration rates ranged from 177 to 776 mg CO₂ m^–2 h^–1. During the growing season, soil respiration was higher in the old alley cropping system than in the young alley cropping system, the old pecan orchard, the young pecan orchard, and the monoculture. Microbial biomass C was higher in the old alley cropping system (375 mg C kg^–1) and in the old pecan orchard (376 mg C kg^–1) compared to the young alley cropping system (118 mg C kg^–1), young pecan orchard (88 mg C kg^–1), and the cotton monoculture (163 mg C kg^–1). Soil respiration was correlated positively with soil temperature, microbial biomass, organic matter, and fine root biomass. The effect of alley cropping on soil properties during the brief history of alley cropping was not significant except in the old systems, where there was a trend of increasing soil respiration with short-term alley cropping. Over time, different land use and management practices influenced soil properties such as soil temperature, moisture, microbial biomass, organic matter, and fine root biomass, which in turn affected the magnitude of soil respiration. Our results suggest that trees in agroforestry systems have the potential to enhance soil fertility and sustainability of farmlands by improving soil microbial activity and accreting residual soil carbon.This revised version was published online in November 2005 with corrections to the Cover Date.     

Leaf photosynthetic properties in a willow (Salix viminalis and Salix dasyclados) plantation in response to fertilization

Specific leaf area (SLA), nitrogen and chlorophyll concentrations and photosynthetic characteristics were studied in upper and lower canopy leaves of Salix viminalis and S. dasyclados grown at two nutrition levels. Fertilization increased SLA and leaf mass-based nitrogen concentration in most cases. Positive effects of fertilization on leaf light-saturated photosynthetic rate (A _max ^A ) and maximum carboxylation rate (V _cmax) were not detected. Significant differences between the leaves from upper and lower canopy layers in area-based nitrogen, A _max ^A , SLA, mass-based chlorophyll, V _cmax and stomatal conductance were found for most plots. We attempted to estimate the fraction of non-photosynthetic nitrogen and found that it tended to be higher due to fertilization. Thus, the insensitivity of leaf photosynthesis to fertilization could be caused by higher proportion of non-photosynthetic nitrogen in the leaves of fertilized plots. Though leaf-level photosynthesis was not increased by fertilization, considerably higher leaf area index of fertilized plots still resulted in increased canopy carbon gain.     

Seedling biomass allocation and vital rates of cloud forest tree species: Responses to light in shade house conditions

Patterns of above- and below-ground biomass allocation in seedlings of nine common cloud forest (CF) tree species of western Mexico were examined under varying controlled light conditions using artificial shade houses. We analysed the relationships between vital rates (growth and survival) and four morphological traits (SLA, biomass allocation to stems, leaves and roots). We hypothesised that these traits represent differentiation axes in the way seedlings face the heterogeneous light regime typical of the CF understorey. For all species, traits between the different light levels, i.e. allocation to leaves, roots and stems differed among light levels. Five species had the largest SLA in the lowest light levels at the end of the experiment (Citharexylum, Dendropanax, Fraxinus, Quercus and Magnolia). Juglans was the only species with a large SLA at the highest light level (377.47 cm² g⁻¹). In contrast, light levels did not cause any significant variation in SLA of Persea and Simplococarpon at the end of the experiment. The relative height growth rates (RHGR) of the seedlings of five species were significantly different between light levels (P < 0.05). Overall, all species grew better in the highest light levels. The RHGR of three species were correlated positively with SLA. In turn, allocation to stem, leaves and root biomass were strongly correlated with the RHGR of five species (e.g. Citharexylum, Dendropanax and Fraxinus). Survival did not vary significantly between treatments in any species, only in the case of Simplococarpon (P < 0.05) and was correlated with all morphological variables. For this species, Peto and Peto's test showed a significantly larger survival of seedlings in the highest light level. The mean responses of these species based on all traits to the controlled light variation did not differed significantly. Our results show that these species display a wide range of resource allocation patterns when exposed to the varying light conditions that may be found in the forest understorey and highlight the role of morphological traits in this variation.     

Phenological responses of juvenile pecan and white oak on an upland site

Pecan (Carya illinoiensis) and white oak (Quercus alba) produce multiple products and wildlife values, but their phenological responses to N fertilization have not been well characterized. We compared tree growth at planting and for six consecutive growing seasons during establishment (2003–2008, Test 1), and determined if phenology of budburst, leaf area index (LAI), quantum yield of photosystem II (Fv/Fm), radial growth, and total chlorophyll concentration (a, b) responded to poultry litter fertilization supplying 0, 50, and 100 kg ha^?1 N (2010–2012, Test 2) in a mixed-species orchard on an upland site near Booneville, Arkansas. Species did not differ significantly in height in Test 1. Budburst was 9 days earlier for white oak than pecan in 2010. Budburst for both species could be predicted by accumulating chilling and forcing units throughout the dormant season. Maximum predicted radial growth was comparable for pecan (2.19 mm) and white oak (2.26 mm), and peaked 28 days earlier for white oak (3 June) than pecan (1 July). White oak LAI generally exceeded that of pecan during the growing season. Senescence began about 27 October regardless of species, and was better characterized by decreasing Fv/Fm or total chlorophyll concentration than LAI. Phenology was generally not responsive to N fertilization, perhaps because of adequate soil and foliar N. The study provides additional information on growth responses of these high-valued species to supplemental fertilization on an upland site.     

Foliar carbon isotope discrimination and related traits along light gradients in two different functional-type tree species

To understand how different plant functional types respond to light intensities, foliar carbon isotope discrimination (Δ¹³C) and related traits, i.e., specific leaf area (SLA), mass- and area-based nitrogen concentrations (N_mass and N_area), leaf dry mass content (LDMC) of two evergreen coniferous and three deciduous broad-leaved species, were measured under four light intensities. Foliar Δ¹³C and SLA increased significantly from full- to low-light conditions for all species. These indicate that species studied could increase their light capture capacity under low-light conditions, leading to lower water-use efficiency (higher ¹³C discrimination). There were significant differences in the responses of foliar N_mass or N_area to light variations in the two functional types, indicating that different functional-type tree species may have different N-use strategies to adapt to the light variations. It was found that there were large functional-type-dependent differences with regard to the relationships between foliar Δ¹³C and other leaf traits. Our findings suggest that all tree species could change foliar morphology to increase their light-harvesting ability under low-light conditions at the expense of decreasing their water-use efficiency. However, large differences in N-use strategy may exist between deciduous and evergreen species, which may be vital for the survival of these two functional-type tree species in a shaded understory. More important, our findings reveal that changes in Δ¹³C are not directly related to foliar N if N investment does not proportionally increase the photosynthetic capacity; this should be considered when exploring the relationships of nitrogen concentrations with Δ¹³C.     

Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography

The slope effect and correction methods for estimation of canopy gap fraction, leaf area index (LAI), mean leaf angle and clumping index using hemispherical photography, were investigated. The evaluation was carried out in tropical cloud forest and plantations in South-East Kenya in order to consider a range of canopy architecture and slopes up to 65%. The aim was to compare two acquisition techniques and various correction procedures. All estimates assume uniform slope, canopy parallel to ground and homogeneous canopy structure at the photo site level.

(1) Photographs oriented to local zenith (levelled acquisition). Calculation and removal of sky parts of the hemisphere obstructed by topography. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model). (i) Fixed path lengths over azimuths. Zenith reference axis. LAI referred to horizontal and corrected for topographic shading. (ii) Variable path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine.

(2) Photographs oriented parallel to slope (tilted acquisition). Fixed path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model).

Gap fractions present a stronger upslope/downslope asymmetry if retrieved from levelled acquisition. As a result, gap dispersion index and clumping index proved to be significantly higher for levelled acquisition (P < 0.001). LAI estimates adjusted to horizontal are not significantly different, whether retrieved from levelled or tilted acquisitions, up to 30% slopes. From levelled acquisition, fixed and variable path length do not yield significantly different LAI estimates along the whole slope gradient. From tilted acquisition, LAI values were systematically higher than from levelled acquisitions, the stronger the slope, the higher the difference. Mean leaf angles do not differ significantly (P > 0.05) for fixed vs. variable path lengths along the slope gradient up to 30%. For more severe slopes, variable path lengths yield lower mean leaf angle values. The interpretation of results from tilted acquisition remains uncertain. As a preliminary study, no preference is suggested for the levelled or tilted acquisition technique. Further investigation is needed and indirect optical derived estimates should be checked against direct reference measures, which are almost entirely lacking for mountainous areas.     

Validation of a canopy photosynthesis model for cocksfoot pastures grown under different light regimes

Daily net canopy photosynthesis (P _n) was predicted for cocksfoot (Dactylis glomerata L.) canopies grown under different light regimes by integration of a leaf photosynthesis model developed for the light-saturated photosynthetic rate (P _max), photosynthetic efficiency (α) and the degree of curvature (θ) of the leaf light–response curve. When shade was the only limiting factor, the maximum P _n (P _nmax) was predicted to decrease approximately linearly from 33.4 g CO₂ m⁻² d⁻¹ to zero as photosynthetic photon flux density (PPFD) fell from full sunlight (1800 μmol m⁻² s⁻¹ PPFD) to 10% of this in a fluctuating light regime. It was also predicted that at 50% transmissivity P _nmax was higher for a continuous light regime (10.4 g CO₂ m⁻² d⁻¹) than for a fluctuating light regime with the same intensity (8.4 g CO₂ m⁻² d⁻¹). The canopy photosynthesis model was then used to predict dry matter (DM) production for cocksfoot field grown pastures under a diverse range of temperature, herbage nitrogen content and water status conditions in fluctuating light regimes. This prediction required inclusion of leaf area index and leaf canopy angle from field measurements. The model explained about 85% of the variation in observed cocksfoot DM production for a range from 6 to 118 kg DM ha⁻¹ d⁻¹. The proposed model improves understanding of pasture growth prediction through integration of relationships between shade limitations in fluctuating light regimes and other environmental factors that affect the canopy photosynthetic rate of cocksfoot pastures in silvopastoral systems.     

Growth of <Emphasis Type="Italic">Dactylis glomerata</Emphasis> along a light gradient in the central Appalachian region of the eastern USA: II. Mechanisms of leaf dry matter production

Microsite influences development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in silvopasture of humid temperate regions. An experiment using container-grown orchardgrass was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zone (E _O, E _W) microsites influenced leaf DM production. Plants established in spring (SP) and late summer (LS) were clipped each time mean canopy height reached 20 cm. Dry matter production and allocation among structures differed, as a function of light attenuation. Specific leaf area (SLA) and photosynthetic nitrogen-use efficiency (PNUE) were associated with leaf DM production, whereas leaf N, net assimilation rate and shoot total nonstructural carbohydrates (TNC), were not. Specific leaf area was related to leaf DM of LS plants, whereas PNUE influenced leaf DM of SP plants. Stembase TNC was inversely related to relative regrowth rate (RG_RR) with RG_RR greatest and TNC the least at W. The relationship for RG_RR and TNC for SP plants growing at O and LS plants growing at W was similar. Regardless of how indices of growth are related, SP and LS plantings responded as separate populations (representing young and established plants respectively) that have different leaf DM production efficiencies. Orchardgrass was able to sustain leaf production when subjected to simultaneous stresses of shade and repeated defoliation. The LS plants growing at W respond in a manner similar to SP plants and may require management practices attuned to establishing or immature plants. The US Government’s right to retain a royalty-free, non-exclusive copyright is achnowledged.     

Estimating vertical vegetation density through a SPOT5 imagery at multiple radiometric correction levels

There is growing concern about remote sensing of vertical vegetation density in rapidly expanding peri-urban interfaces.A widely used parameter for such density,i.e.,leaf area index (LAI),was measured in situ in Nanjing,China and then correlated with two vegetation indices (VI) derived from multiple radiometric correction levels of a SPOT5 imagery.The VIs were a normalized difference vegetation index (NDVI) and a ratio vegetation index (RVI),while the four radiometric correction levels were i) post atmospheric correction reflectance (PAC),ii) top of atmosphere reflectance (TOA),iii) satellite radiance (SR) and iv) digital number (DN).A total of 157 LAI-VI relationship models were established.The results showed that LAI is positively correlated with VI (r varies from 0.303 to 0.927,p < 0.001).The R 2 values of "pure" vegetation were generally higher than those of mixed vegetation.The average R 2 values of about 40 models based on DN data (0.688) were higher than that of the routinely used PAC (0.648).Independent variables of the optimal models for different vegetation quadrats included two vegetation indices at three radiometric correction levels,indicating the potential of vegetation indices at multiple radiometric correction levels in LAI inversion.The study demonstrates that taking heterogeneities of vegetation structures and uncertainties of radiometric corrections into account may help full mining of valuable information from remote sensing images,thus improving accuracies of LAI estimation.     

Modeling leaf maximum net photosynthetic rate of <Emphasis Type="Italic">Festuca pallescens</Emphasis>, the dominant perennial grass of Patagonian pine-based silvopastoral systems

The integrated relationship in a simple mechanistic model between the critical environmental factors controlling leaf photosynthesis of understory species would be a useful tool to optimize the management of the silvopastoral systems. Individual effect of leaf temperature, water stress and light environment over net maximum photosynthetic rate (Pmax) was evaluated on Festuca pallescens leaves grown in a silvopastoral system of two Pinus ponderosa canopy covers (350 and 500 trees ha⁻¹) and natural grassland. The aim was to integrate individual functions for Pmax against these environmental factors into a multiplicative model. We measured pre-dawn water potential (ψ _pd), leaf temperature and net photosynthetic rate (Pn), stomatal conductance (gs) and intercellular CO₂ concentration (Ci) as a function of photosynthetic photon flux density (PPFD). The highest Pmax under non-limiting conditions was 20.4 μmol CO₂ m⁻² s⁻¹ and was defined as standardized dimensionless Pmax _s  = 1 for comparison of environmental factors. The leaf temperature function showed an optimum range between 20.2 and 21.8°C where Pmax _s  = 1. Then, Pmax _s declined by an average 1 μmol CO₂ m⁻² s⁻¹ C⁻¹ from the optimum to 4.7 and 38.5°C. Pmax _s decreased at a rate of 9.49 μmol CO₂ m⁻² s⁻¹ MPa⁻¹ as water potential reaches −1.9 MPa and showed a lower slope as water potential decreased down to −4.3 MPa. The light environment was estimated from hemispherical photograph analysis. Pmax _s was 20% higher in leaves of open control plants than under the maximum tree canopy cover. The simple multiplicative model accounted for 0.82 of the variation in Pmax. Such a simple mechanistic model is the first step towards a more effective decision support tool.     

The Potential of Albizia lebbeck as a Supplementary Feed for Goats in Tanzania

Forty growing goats (20 males and 20 females) were used in a 90-day growth and intake study to evaluate the potential of Albizia lebbeck (ABC) based concentrate as compared with Gliricidia sepium (GBC), Leucaena leucocephala (LBC), and Moringa oleifera (MBC) based concentrates with cotton seed cake (CSC) as a control. The animals were fed a basal diet of maize stover and supplemented daily with 30 g/kg W^0.75 of ABC, GBC, LBC, MBC, and CSC. They were compounded so as to formulate iso-protein diets. Treatment effects were significant (p<0.05) for growth rates in that with the exception of GBC, goats on CSC exhibited significantly higher gains compared to counterparts in other treatments. The total DM intake was between 50.6 and 52.6 g/kg W^0.75/day and there were no significant (p>0.05) differences among treatments. There were significant differences (p<0.05) among treatments for maize stover intake. CSC based treatment showed the highest intake with insignificant (p>0.05) differences amongst the leaf meal based concentrates. It can be concluded that Albizia lebbeck had similar potential to the other leaf meal based supplements studied but had lower potential compared to a cotton seed cake based supplement, as protein sources for growing goats fed a poor quality basal diet.     

Difference in shade tolerance affects foliage–sapwood response to thinning by two eucalypts

In eucalypt plantations in subtropical Australia, Eucalyptus dunnii exhibits greater diameter increment after thinning than more shade-tolerant Corymbia citriodora. To elucidate the mechanism underlying this difference, we investigated relationships between tree leaf area and sapwood area following thinning in 11-year-old E. dunnii and C. citriodora plantations. There was no significant difference in specific leaf area (SLA) between thinned and unthinned stands in E. dunnii and C. citriodora, whereas crown zone significantly affected SLA in the two eucalypts. At the whole-tree level non-linear leaf area (A_l)–sapwood area (A_s) relationships were measured in both eucalypts by thinning treatment. A significant increase in A_l/A_s ratio was only observed at the upper crown in thinned E. dunnii. The present results suggested the plastic nature of response of leaf characteristics in both eucalypts grown in different light environments and the species-specific pattern of crown-zone leaf responses to thinning in the two species, i.e. the top of the canopy appears to be driving greater growth response to thinning in the less shade tolerant E. dunnii compared with the more shade-tolerant C. citriodora. It is concluded that different thinning regimes should be applied in shade-tolerant and shade-intolerant eucalypt forests.