Search results for "canopy"
showing 10 items of 221 documents
Expression of PIP1 and PIP2 aquaporins is enhanced in olive dwarf genotypes and is related to root and leaf hydraulic conductance
2007
The expression of OePIP1.1 and OePIP2.1 aquaporins in root, stem and leaf was higher in Olea europaea L. (olive) plants carrying a dwarfing (D) clone as rootstock, than in plants carrying a vigorous (M) clone as rootstock. The highest difference of expression between plants with D and M rootstocks was detected in the root and for the PIP2 gene, the transcripts of which show a high water channel activity in oocytes. Compared with plants with M rootstock, plants with D rootstock showed reduced root and canopy biomass and reduced hydraulic conductance of the bulk root system (Kroot). Hydraulic conductance of D roots was higher than that of M roots when Kroot was scaled by root DW, in agreemen…
Simplified Interception/Evaporation Model
2021
It is known that at the event scale, evaporation losses of rainfall intercepted by canopy are a few millimeters, which is often not much in comparison to other stocks in the water balance. Nevertheless, at yearly scale, the number of times that the canopy is filled by rainfall and then depleted can be so large that the interception flux may become an important fraction of rainfall. Many accurate interception models and models that describe evaporation by wet canopy have been proposed. However, they often require parameters that are difficult to obtain, especially for large-scale applications. In this paper, a simplified interception/evaporation model is proposed, which considers a modified …
Estimation of vegetation loss coefficients and canopy penetration depths from SMAP radiometer and IceSAT lidar data
2017
In this study the framework of the τ — ω model is used to derive vegetation loss coefficients and canopy penetration depths from SMAP multi-temporal retrievals of vegetation optical depth, single scattering albedo and ICESat lidar vegetation heights. The vegetation loss coefficients serve as a global indicator of how strong absorption and scattering processes attenuate L-band microwave radiation. By inverting the vegetation loss coefficients, penetration depths into the canopy can be obtained, which are displayed for the global forest reservoirs. A simple penetration index is formed combining vegetation heights and penetration depth estimates. The distribution and level of this index reveal…
Solar angle and sky light effects on ground reflectance measurements in a citrus canopy
1993
Abstract Ground radiometry was used to gather spectral data from different targets of a citrus canopy, in order to analyze the effect of solar zenith angle and proportion of diffuse radiation on spectral reflectance. Results have shown that the variation in solar angle causes significant changes in nadirsensed reflectance from vegetation, which exhibits a marked diurnal pattern with a minimum slightly shifted from the solar noon. This fact is more noticeable in the near-infrared and middle-infrared regions of the spectrum. Furthermore, the visible part of the spectrum has resulted in being highly influenced by the diffuse radiation incident on the canopy, which has been quantified by two di…
Global sensitivity analysis of the SCOPE model : what drives simulated canopy - leaving sun - induced fluorescence?
2015
This study provides insight into the key variables that drive sun-induced chlorophyll fluorescence (SIF) emanating from vegetation canopies, based on a global sensitivity analysis (GSA) of the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) balance model. An updated version of the SCOPE model was used here (v1.53) which contains novel leaf physiological modules for determination of the steady state fluorescence yield: a photosynthesis model coupled with (a) submodels having empirically derived relationships, identified as TB12 for unstressed and TB12-D for drought conditions and (b) a mechanistic (MD12) submodel based on theoretical relationships. By inspecting Sobol's total or…
Dry matter accumulation and seasonal partitioning in mature Opuntia ficus-indica (L.) Mill. fruiting trees
2014
Aim of this study was to understand the allocation of biomass into different canopy and root components and to measure the stem area index and its partitioning by cladode functionality (age), for fruiting Opuntia ficus-indica (OFI) Gialla trees, spaced 6x5 m apart and trained to a globe. The net primary productivity (NPP), calculated taking into account dry weight gain for above-ground vegetative components of OFI trees was 3.6 t C ha –1 . Including the fruit component and 1 st flush current-year cladodes, NPP of above-ground components becomes 12 t ha –1 , equivalent to 5.4 t C ha –1 . Current-year cladodes were the highest C sink (49% of total annual C fixed in the canopy), secondary grow…
Comparison of Crop Trait Retrieval Strategies Using UAV-Based VNIR Hyperspectral Imaging.
2021
Hyperspectral cameras onboard unmanned aerial vehicles (UAVs) have recently emerged for monitoring crop traits at the sub-field scale. Different physical, statistical, and hybrid methods for crop trait retrieval have been developed. However, spectra collected from UAVs can be confounded by various issues, including illumination variation throughout the crop growing season, the effect of which on the retrieval performance is not well understood at present. In this study, four retrieval methods are compared, in terms of retrieving the leaf area index (LAI), fractional vegetation cover (fCover), and canopy chlorophyll content (CCC) of potato plants over an agricultural field for six dates duri…
WITHIN TREE AND ORCHARD VARIABILITY OF SILVER KING PEACH (PRUNUS PERSICA (L.) BATSCH) FRUIT QUALITY
2012
The variability of crop quality accounts for most of seasonal variation of farmers’ incomes, since fruit value mostlydepends on its size and overall quality. Canopy architecture and orchard lay-out are mainly responsible for within tree environment and allocation, which in turn, account for fruit quality and its variability. Little is known about within tree and between trees variability resulting from different planting and training systems. A positive relationship has been measured in peach between PAR and TEAC (Motisi et al., 2005; Scalzo et al., 2005; Motisi et al., 2008). This study was carried out to measure within tree and orchard variability of fruits of the early ripening ‘Silver K…
Relating Hyperspectral Airborne Data to Ground Measurements in a Complex and Discontinuous Canopy
2015
The work described in this paper is aimed at validating hyperspectral airborne reflectance data collected during the Regional Experiments For Land-atmosphere EXchanges (REFLEX) campaign. Ground reflectance data measured in a vineyard were compared with airborne reflectance data. A sampling strategy and subsequent ground data processing had to be devised so as to capture a representative spectral sample of this complex crop. A linear model between airborne and ground data was tried and statistically tested. Results reveal a sound correspondence between ground and airborne reflectance data (R2 > 0.97), validating the atmospheric correction of the latter.
Plant chlorophyll fluorescence: active and passive measurements at canopy and leaf scales with different nitrogen treatments
2015
Highlight We studied for the first time the temporal and spatial limits within which active and passive chlorophyll fluorescence measurements are comparable.