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1.
A proposal for universal formulas for estimating leaf water status of herbaceous and woody plants based on spectral reflectance properties 总被引:3,自引:0,他引:3
Yu Gui-Rui Miwa Takuji Nakayama Keiichi Matsuoka Nobuhiro Kon Hisashi 《Plant and Soil》2000,227(1-2):47-58
The present study deals with the relationships between water status parameters of plant leaves and reflectances (Rλ) at characteristic wavelengths, between 522 and 2450 nm, as well as reflectance ratios, Rλ/R1430, Rλ/R1650, Rλ/R1850, Rλ/R1920, and Rλ/R1950, based on the air-drying experimental results of soybean (Glycine max Merr.), maize (Zea mays L.), tuliptree (Liriodendron tulipifera L.) and viburnum (Viburnum awabuki K. Koch.) plants. The water status parameters include leaf water content per unit leaf area (LWC), specific leaf water content
(SWC), leaf moisture percentage of fresh weight (LMP), relative leaf water content (RWC) and relative leaf moisture percentage
on fresh weight basis (RMP). Effective spectral reflectances and reflectance ratios for estimating the LWC, SWC, LMP, RWC
and RMP were identified. With these spectral indices, approaches to estimating LWC, RWC and RMP were discussed. Eventually,
an attempt on universal formulas was made for estimating the leaf moisture conditions of both herbaceous and woody plants
as mentioned above. Moreover, applicability of these formulas was checked with the field experimental results of soybean and
maize grown under water and nutrient stresses.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
Nam Jin Noh Yowhan Son Sue Kyoung Lee Tae Kyung Yoon Kyung Won Seo Choonsig Kim Woo-Kyun Lee Sang Won Bae Jaehong Hwang 《Journal of plant research》2010,123(4):411-419
We investigated the influence of stand density [938 tree ha−1 for high stand density (HD), 600 tree ha−1 for medium stand density (MD), and 375 tree ha−1 for low stand density (LD)] on soil CO2 efflux (R
S) in a 70-year-old natural Pinus densiflora S. et Z. forest in central Korea. Concurrent with R
S measurements, we measured litterfall, total belowground carbon allocation (TBCA), leaf area index (LAI), soil temperature
(ST), soil water content (SWC), and soil nitrogen (N) concentration over a 2-year period. The R
S (t C ha−1 year−1) and leaf litterfall (t C ha−1 year−1) values varied with stand density: 6.21 and 2.03 for HD, 7.45 and 2.37 for MD, and 6.96 and 2.23 for LD, respectively. In
addition, R
S was correlated with ST (R
2 = 0.77–0.80, P < 0.001) and SWC (R
2 = 0.31–0.35, P < 0.001). It appeared that stand density influenced R
S via changes in leaf litterfall, LAI and SWC. Leaf litterfall (R
2 = 0.71), TBCA (R
2 = 0.64–0.87), and total soil N contents in 2007 (R
2 = 0.94) explained a significant amount of the variance in R
S (P < 0.01). The current study showed that stand density is one of the key factors influencing R
S due to the changing biophysical and environmental factors in P. densiflora. 相似文献
3.
Leaf water status information is highly needed for monitoring plant physiological processes and assessing drought stress. Retrieval of leaf water status based on hyperspectral indices has been shown to be easy and rapid. However, a universal index that is applicable to various plants remains a considerable challenge, primarily due to the limited range of field-measured datasets. In this study, a leaf dehydration experiment was designed to obtain a relatively comprehensive dataset with ranges that are difficult to obtain in field measurements. The relative water content (RWC) and equivalent water thickness (EWT) were chosen as the surrogates of leaf water status. Moreover, five common types of hyperspectral indices including: single reflectance (R), wavelength difference (D), simple ratio (SR), normalized ratio (ND) and double difference (DDn) were applied to determine the best indices. The results indicate that values of original reflectance, reflectance difference and reflectance sensitivity increased significantly, particularly within the 350–700 nm and 1300–2500 nm domains, with a decrease in leaf water. The identified best indices for RWC and EWT, when all the species were considered together, were the first derivative reflectance based ND type index of dND (1415, 1530) and SR type index of dSR (1530, 1895), with R2 values of 0.95 (p < 0.001) and 0.97 (p < 0.001), respectively, better than previously published indices. Even so, different best indices for different species were identified, most probably due to the differences in leaf anatomy and physiological processes during leaf dehydration. Although more plant species and field-measured datasets are still needed in future studies, the recommend indices based on derivative spectra provide a means to monitor drought-induced plant mortality in temperate climate regions. 相似文献
4.
植被叶片及冠层层次含水量估算模型的建立 总被引:12,自引:2,他引:10
利用LOPEX'93数据库中7个鲜叶片含水量(Cw)和光谱反射率实测数据,基于光谱指数法,在叶片层次,用47个随机样本建立Cw与不同光谱指数的统计模型,并用另外20个样本验证.结果表明,Cw的两种表征形式相对含水量FMC和等价水深EWT在提取叶片Cw时差异较大,EWT与各光谱指数的相关性较FMC高,但FMC对叶片Cw的反演精度高于EWT.而反演精度更高的是基于最优子集回归建立的光谱指数线性模型.Ratio975是叶片层次提取Cw的普适光谱指数.冠层层次,利用PROSPECT+SAILH耦合模型,模拟在不同叶面积指数LAI和Cw下的冠层光谱.为了剔除背景影响,更好地提取冠层Cw,提出用近红外和短波红外波段反射率构造土壤可调节水分指数(SAWI),该指数与其他光谱指数的比值能明显地剔除土壤背景影响,更准确地提取冠层Cw.Ratio975的改进型光谱指数(Ratio975-0.9)/(SAWI+0.2)能用来提取叶面积指数LAI从0.3到8.0,Cw从0.0001cm到0.07cm的冠层Cw,研究表明精度较高. 相似文献
5.
A broad regional understanding of tropical forest leaf photosynthesis has long been a goal for tropical forest ecologists,
but it has remained elusive due to difficult canopy access and high species diversity. Here we develop an empirical model
to predict sunlit, light-saturated, tropical leaf photosynthesis using leaf and simulated canopy spectra. To develop this
model, we used partial least squares (PLS) analysis on three tropical forest datasets (159 species), two in Hawaii and one
at the biosphere 2 laboratory (B2L). For each species, we measured light-saturated photosynthesis (A), light and CO2 saturated photosynthesis (A
max), respiration (R), leaf transmittance and reflectance spectra (400–2,500 nm), leaf nitrogen, chlorophyll a and b, carotenoids, and leaf mass per area (LMA). The model best predicted A [r
2
= 0.74, root mean square error (RMSE) = 2.9 μmol m−2 s−1)] followed by R (r
2
= 0.48), and A
max (r
2
= 0.47). We combined leaf reflectance and transmittance with a canopy radiative transfer model to simulate top-of-canopy
reflectance and found that canopy spectra are a better predictor of A (RMSE = 2.5 ± 0.07 μmol m−2 s−1) than are leaf spectra. The results indicate the potential for this technique to be used with high-fidelity imaging spectrometers
to remotely sense tropical forest canopy photosynthesis. 相似文献
6.
Sedimentation in Boreal Lakes—The Role of Flocculation of Allochthonous Dissolved Organic Matter in the Water Column 总被引:1,自引:0,他引:1
We quantified sedimentation of organic carbon in 12 Swedish small boreal lakes (<0.48 km2), which ranged in dissolved organic carbon (DOC) from 4.4 to 21.4 mg C l−1. Stable isotope analysis suggests that most of the settling organic matter is of allochthonous origin. Annual sedimentation
of allochthonous matter per m2 lake area was correlated to DOC concentration in the water (R
2 = 0.41), and the relationship was improved when sedimentation data were normalized to water depth (R
2 = 0.58). The net efflux of C as CO2 from the water to the atmosphere was likewise correlated to DOC concentration (R
2 = 0.52). The losses of organic carbon from the water column via mineralization to CO2 and via sedimentation were approximately of equal importance throughout the year. Our results imply that DOC is a precursor
of the settling matter, resulting in an important pathway in the carbon cycle of boreal lakes. Thus, flocculation of DOC of
terrestrial origin and subsequent sedimentation could lead to carbon sequestration by burial in lake sediments. 相似文献
7.
Water potential (ψw) and water saturation deficit (WSD), and several reflectance (R) indexes were assessed in an aerophytic lichen Umbilicaria hirsuta (Sw. ex Westr.) Hoffm. The water index (WI, R900/R970) and normalized difference vegetation index, NDVI [(R900-R680)/(R900+R680)] were strongly correlated both with the ψw and the WSD of lichen thalli. No significant changes during desiccation were found in structural independent pigment index,
SIPI [(R800-R445)/(R800-R680)]. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or ψw > −1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually
inhibited at much lower values of ψw than in leaves of vascular plants. 相似文献
8.
Looming water scarcity and climate change pose big challenges for China's food security. Previous studies have focus on the impacts of climate change either on agriculture or on water resources. Few studies have linked water and agriculture together in the context of climate change, and demonstrated how climate change will affect the amount of water used to produce per unit of crop, or virtual water content (VWC). We used a GIS-based Environmental Policy Integrated Climate (GEPIC) model to analyze the current spatial distribution of VWC of various crops in China and the impacts of climate change on VWC in different future scenarios. The results show that C4 crops (e.g. irrigated maize with a VWC of 0.73 m3 kg− 1 in baseline) generally have a lower VWC than C3 crops (e.g. irrigated wheat with a VWC of 1.1 m3 kg− 1 in baseline), and the VWC of C4 crops responds less sensitively to the CO2 concentration change in future climate scenarios. Three general change trends exist for future VWC of crops: continuous decline (for soybean and rice without considering CO2 concentration changes) and continuous increase (for rice with considering CO2 concentration changes) and first-decline-then-increase (other crop-scenario combinations). The trends reflect the responses of different crops to changes in precipitation, temperature as well as CO2 concentration. From south to north along the latitude, there is a high-low-high distribution trend of the aggregated VWC of the crops. Precipitation and temperature changes combined can lead to negative effects on crop yield and higher VWC particularly in the far future e.g. the 2090s, but when CO2 concentration change is taken into consideration, it is likely that crop yield will increase and crop VWC will decrease for the whole China. Integrated effects of precipitation, temperature and CO2 concentration changes will benefit agricultural productivity and crop water productivity through all the future periods till the end of the century. Hence, climate change is likely to benefit food security and help alleviate water scarcity in China. 相似文献
9.
Leaf gas exchange in a clonal eucalypt plantation as related to soil moisture, leaf water potential and microclimate variables 总被引:7,自引:0,他引:7
M. S. Mielke M. A. Oliva N.F. de Barros R. M. Penchel C. A. Martinez S. da Fonseca A.C. de Almeida 《Trees - Structure and Function》2000,14(5):263-270
In order to determine how environmental and physiological factors affect leaf gas exchange in a 9-year-old clonal eucalypt
plantation (Eucalyptus grandis Hill ex. Maiden hybrids) in the State of Espirito Santo, Brazil, the diurnal patterns of predawn leaf water potential (Ψpd), and leaf gas exchange were monitored from November 1995 to August 1996. Soil water content (Θ) and microclimatic variables
were also recorded. Most of the rainfall during the experimental period occurred from October to December 1995 and from March
to April 1996, causing a significant variation in Θ and Ψpd. A high positive correlation (r
2=0.92) was observed between Ψpd and Θ measured at 0.3 m depth from the soil surface. During conditions of high soil water availability, the maximum values
of stomatal conductance for water vapor (g
s) and net photosynthetic rate (A) were over 0.4 mol m–2 s–2 and l5 μmol m–2 s–1, respectively. The results showed that Ψpd and leaf gas exchange of the examined trees were susceptible to changes in the water content of the upper soil layers, where
the major concentration of active roots occur. Multiple linear regression analysis indicated that photosynthetic active radiation
(Q), vapor pressure deficit (VPD), atmospheric CO2 molar fraction (C
a), and Ψpd were the most important factors controlling g
s whereas Q and VPD were the main microclimatic variables controlling A.
Received: 5 November 1998 / Accepted: 10 November 1999 相似文献
10.
Autotrophic and heterotrophic respiration in needle fir and Quercus-dominated stands in a cool-temperate forest, central Korea 总被引:3,自引:0,他引:3
Na-yeon Lee Jin-Woo Koo Nam Jin Noh Joon Kim Yowhan Son 《Journal of plant research》2010,123(4):485-495
To investigate annual variation in soil respiration (R
S) and its components [autotrophic (R
A) and heterotrophic (R
H)] in relation to seasonal changes in soil temperature (ST) and soil water content (SWC) in an Abies holophylla stand (stand A) and a Quercus-dominated stand (stand Q), we set up trenched plots and measured R
S, ST and SWC for 2 years. The mean annual rate of R
S was 436 mg CO2 m−2 h−1, ranging from 76 to 1,170 mg CO2 m−2 h−1, in stand A and 376 mg CO2 m−2 h−1, ranging from 82 to 1,133 mg CO2 m−2 h−1, in stand Q. A significant relationship between R
S and its components and ST was observed over the 2 years in both stands, whereas a significant correlation between R
A and SWC was detected only in stand Q. On average over the 2 years, R
A accounted for approximately 34% (range 17–67%) and 31% (15–82%) of the variation in R
S in stands A and Q, respectively. Our results suggested that vegetation type did not significantly affect the annual mean
contributions of R
A or R
H, but did affect the pattern of seasonal change in the contribution of R
A to R
S. 相似文献
11.
Chlorophyll fluorescence and landscape-level reflectance imagery were used to evaluate spatial variations in stress in Myrica cerifera and Iva frutescens during a severe drought and compared to an extremely wet year. Measurements of relative water content and the water band
index (WBI970) indicated that the water stress did not vary across the island. In contrast, there were significant differences in tissue
chlorides across sites for both species. Using the physiological reflectance index (PRI), we were able to detect salinity
stress across the landscape. For M. cerifera, PRI did not differ between wet and dry years, while for I. frutescens, there were differences in PRI during the 2 years, possibly related to flooding during the wet year. There was a positive
relationship between PRI and for M. cerifera (r
2 = 0.79) and I. frutescens (r
2 = 0.72). The normalized difference vegetation index (NDVI), the chlorophyll index (CI), and WBI970 were higher during the wet summer for M. cerifera, but varied little across the island. CI and WBI970 were higher during 2004 for I. frutescens, while there were no differences in NDVI during the 2 years. PRI was not significantly related to NDVI, suggesting that the
indices are spatially independent. These results suggest that PRI may be used for early identification of salt stress that
may lead to changes in plant distributions at the landscape level, as a result of rising sea level. Comparsions between the
two species indicate that variations in PRI and other indices may be species specific. 相似文献
12.
Encapsulated cocoa (Theobroma cacao L.) somatic embryos subjected to 0.08–1.25 M sucrose treatments were analyzed for embryo soluble sugar content, non-freezable
water content, moisture level after desiccation and viability after desiccation and freezing. Results indicated that the higher
the sucrose concentration in the treatment medium, the greater was the extent of sucrose accumulation in the embryos. Sucrose
treatment greatly assisted embryo post-desiccation recovery since only 40% of the control embryos survived desiccation, whereas
a survival rate of 60–95% was recorded for embryos exposed to 0.5–1.25 M sucrose. The non-freezable water content of the embryos
was estimated at between 0.26 and 0.61 g H2O g−1dw depending on the sucrose treatment, and no obvious relationship could be found between the endogenous sucrose level and
the amount of non-freezable water in the embryos. Cocoa somatic embryos could withstand the loss of a fraction of their non-freezable
water without losing viability following desiccation. Nevertheless, the complete removal of potentially freezable water was
not sufficient for most embryos to survive freezing. 相似文献
13.
Abdel-monem Mohamed Amer 《Biologia》2009,64(3):516-521
Six calcareous and alluvial soil profiles differing in their texture, CaCO3 and salinity were chosen from west and middle Nile Delta for the present study. The 1st and 2nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO3, while the 3rd and 4th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO3. The 2nd and 4th profiles were taken from cultivated area with maize. The 5th profile from Epshan area was non-saline clay alluvial soil and the 6th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content (W%) and water vapour pressure (P/P
o) was established for the mentioned soils. Data showed that the specific surface area (S) values were 34–53 and 44–60 m2/g for calcareous soils of Borg El-Arab and Nubaria areas, 206–219 and 206–249 m2/g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of
the external specific surface area (S
e) were 16–21, 14–22, 72–86 and 92–112 m2/g. Submitting W
m+W
me as an adsorption boundary of moisture films (W
c) (where W
m is mono-adsorbed layer of water vapour on soil particles and W
me is the external mono-adsorbed layer), the maximum water adsorption capacity (W
a) was found to be W
c + W
me or W
m + 2W
me. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70–10.70% and 10.80 to 13.12% while the maximum hygroscopic water (M
H) values were 2.43–3.78%, 2.91–4.65%, 16–17% and 18.30–21.9% for the studied soil profiles respectively. The residual moisture
content (θ
r) at pF 7 and P/P
o = 0 was ranged from 0.0005–0.0010%, 0.0007–0.0019% and 0.0043–0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles,
respectively.
The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were
as follows
Calcareous soils; W
m = 0.40 M
H, W
c = 0.55 M
H, W
a = 0.70 M
H, S = 14 M
H
Non-saline soil; W
m = 0.35 M
H, W
c = 0.49 M
H, W
a = 0.63 M
H, S = 13 M
H
Saline soil; W
m = 031 M
H, W
c = 0.45 M
H, W
a = 0.59 M
H, S = 12 M
H
These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic
water, which can be obtained through the experimental determination of water vapor adsorption isotherms. 相似文献
14.
Three-dimensional quantitative structure–activity relationship studies were performed on a series of 88 histamine receptor
4 (H4R) antagonists in an attempt to elucidate the 3D structural features required for activity. Several in silico modeling
approaches, including comparative molecular field analysis (CoMFA), comparative similarity indices analysis (CoMSIA), molecular
docking, and molecular dynamics (MD), were carried out. The results show that both the ligand-based CoMFA model (Q
2 = 0.548, R
ncv2 = 0.870, R
pre2 = 0.879, SEE = 0.410, SEP = 0.386) and the CoMSIA model (Q
2 = 0.526, R
ncv2 =0.866, R
pre2 = 0.848, SEE = 0.416, SEP = 0.413) are acceptable, as they show good predictive capabilities. Furthermore, a combined analysis
incorporating CoMFA, CoMSIA contour maps and MD results shows that (1) compounds with bulky or hydrophobic substituents at
positions 4–6 in ring A (R2 substituent), positively charged or hydrogen-bonding (HB) donor groups in the R1 substituent,
and hydrophilic or HB acceptor groups in ring C show enhanced biological activities, and (2) the key amino acids in the binding
pocket are TRP67, LEU71, ASP94, TYR95, PHE263 and GLN266. To our best knowledge, this work is the first to report the 3D-QSAR
modeling of these H4R antagonists. The conclusions of this work may lead to a better understanding of the mechanism of antagonism
and aid in the design of new, more potent H4R antagonists. 相似文献
15.
Nocturnal increases in water potential (ψ) and water content (θ) in the upper soil profile are often attributed to root water efflux, a process termed hydraulic redistribution
(HR). However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the
daily recovery in θ (Δθ), confounding efforts to determine the actual magnitude of HR. We estimated liquid (J
l) and vapor (J
v) soil water fluxes and their impacts on quantifying HR in a seasonally dry ponderosa pine (Pinus ponderosa) forest by applying existing datasets of ψ, θ and temperature (T) to soil water transport equations. As soil drying progressed, unsaturated hydraulic conductivity declined rapidly such that
J
l was irrelevant (<2E−05 mm h−1 at 0–60 cm depths) to total water flux by early August. Vapor flux was estimated to be the highest in upper soil (0–15 cm),
driven by large T fluctuations, and confounded the role of HR, if any, in nocturnal θ dynamics. Within the 15–35 cm layer, J
v contributed up to 40% of hourly increases in nocturnal soil moisture. While both HR and net soil water flux between adjacent
layers contribute to θ in the 15–65 cm soil layer, HR was the dominant process and accounted for at least 80% of the daily
recovery in θ. The absolute magnitude of HR is not easily quantified, yet total diurnal fluctuations in upper soil water content
can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total
ecosystem water flux. 相似文献
16.
Da-Chun Zhuang Yi-Guang Chen Yu-Qin Zhang Shu-Kun Tang Xiao-Lei Wu Zhou-Cai Tan Wen-Jun Li Xiao-Long Cui 《Antonie van Leeuwenhoek》2009,96(3):295-301
A novel Gram-negative, catalase- and oxidase-positive, non-sporulating, rod-shaped, aerobic bacterium, designated strain JSM
078120T, was isolated from sea water collected from a tidal flat of Naozhou Island, South China Sea. Growth occurred with 1–15% (w/v)
total salts (optimum, 2–4%), at pH 6.0–10.0 (optimum, pH 7.5) and at 4–35°C (optimum, 25–30°C). The major cellular fatty acids
were C18:1
ω9c, C16:0, C12:0 3-OH and C16:1
ω7c. The predominant respiratory quinone was ubiquinone Q-9, and the genomic DNA G + C content was 60.6 mol%. Phylogenetic analysis
based on 16S rRNA gene sequences indicated that strain JSM 078120T should be assigned to the genus Marinobacter, being related most closely to the type strains of Marinobacter segnicrescens (sequence similarity 98.2%), Marinobacter bryozoorum (97.9%) and Marinobacter gudaonensis (97.6%). The sequence similarities between the novel isolate and the type strains of other recognized Marinobacter species ranged from 96.7 (with Marinobacter salsuginis) to 93.3% (with Marinobacter litoralis). The levels of DNA–DNA relatedness between strain JSM 078120T and the type strains of M. segnicrescens, M. bryozoorum and M. gudaonensis were 25.3, 20.6 and 18.8%, respectively. The combination of phylogenetic analysis, DNA–DNA relatedness, phenotypic characteristics
and chemotaxonomic data supported the view that strain JSM 078120T represents a novel species of the genus Marinobacter, for which the name Marinobacter zhanjiangensis sp. nov. is proposed. The type strain is JSM 078120T (= CCTCC AB 208029T = DSM 21077T = KCTC 22280T).
The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain JSM 078120T is FJ425903. 相似文献
17.
Junichi Imanishi Yukihiro Morimoto Ayumi Imanishi Kayoko Sugimoto Kazutaka Isoda 《Landscape and Ecological Engineering》2007,3(1):55-65
Measurement of vegetation drought stress or leaf density is essential in ecosystem and agronomic studies. The normalized differential
vegetation index (NDVI), a widely used vegetation index in remote sensing, seems to have some limitations as it is known to
be affected by both drought stress and leaf density. A field experiment was conducted, using two-year-old potted Quercus serrata (a deciduous tree) and Q. glauca (an evergreen tree), to determine the optimal indices of vegetation drought stress or leaf density that have the least a
simultaneous effect, and to test if the existing vegetation indices are useful for independently detecting drought stress
or leaf density. The results showed that NDVI and similar indices, which utilize the difference or ratio between the reflectance
of red and near infrared bands, such as the ratio vegetation index (RVI), the difference vegetation index (DVI), the atmospherically
resistant vegetation index (ARVI), the renormalized difference vegetation index (RDVI), the enhanced vegetation index (EVI),
the perpendicular vegetation index (PVI), soil-adjusted vegetation index (SAVI) and the improved variants of SAVI, were effective
for the independent detection of leaf density but relatively ineffective for drought stress because they were significantly
affected by leaf area index (LAI). Similarly, vegetation indices developed as detectors of vegetation stress, such as the
water index (WI), the stress index (SI) and the derivative chlorophyll index (DCI), showed weak correlation (r) and partial correlation (r
p) with leaf water content (LWC). The optimal hyperspectral indices were proposed as (F
502.8 − F
852.0)/(F
502.8 + F
852.0) for LWC (r = 0.847, r
p = 0.849) and R
750/R
550 (R750R550; Lichtenthaler et al. in J Plant Physiol 148:483–493, 1996) for LAI (r = 0.926, r
p = 0.940) where R
λ
and F
λ
represent reflectance and first derivatives at wavelength λ nm, respectively. A simulation of lower spectral sampling intervals (ca. 3-nm intervals of original to 10-nm intervals) indicated
that it will be necessary to check the appropriateness of the derivative indices approximate to the proposed indices before
application because derivative spectra are less smooth as a function of wavelength than reflectance spectra. 相似文献
18.
Best hyperspectral indices for assessing leaf chlorophyll content in a degraded temperate vegetation 总被引:1,自引:0,他引:1 下载免费PDF全文
Extensive studies have focused on assessing leaf chlorophyll content through spectral indices; however, the accuracy is weakened by limited wavebands and coarse resolution. With hundreds of wavebands, hyperspectral data can substantially capture the essential absorption features of leaf chlorophyll; however, few such studies have been conducted on same species in various degraded vegetations. In this investigation, complete combinations of either original reflectance or first‐order derivative spectra we conducted a complete combination on either original reflectance or its first‐order derivative value from 350 to 1000 nm to quantify leaf total chlorophyll (Chll), chlorophyll‐a (Chla), and chlorophyll‐b (Chlb) contents. This was performed using three hyperspectral datasets collected in situ from lightly, moderately, and severely degraded vegetations in temperate Helin County, China. Suitable combinations were selected by comparing the numbers of significant correlation coefficients with leaf Chll, Chla, and Chlb contents. The combinations of reflectance difference (Dij), normalized differences (ND), first‐order derivative (FD), and first‐order derivative difference (FD(D)) were found to be the most effective. These sensitive band‐based combinations were further optimized by means of a stepwise linear regression analysis and were compared with 43 empirical spectral indices, frequently used in the literature. These sensitive band‐based combinations on hyperspectral data proved to be the most effective indices for quantifying leaf chlorophyll content (R2 > 0.7, p < 0.01), demonstrating great potential for the use of hyperspectral data in monitoring degraded vegetation at a fine scale. 相似文献
19.
Imaging spectroscopy is a powerful technique for monitoring the biochemical constituents of vegetation and is critical for
understanding the fluxes of carbon and water between the land surface and the atmosphere. However, spectral observations are
subject to the sun–observer geometry and canopy structure which impose confounding effects on spectral estimates of leaf pigments.
For instance, the sun–observer geometry influences the spectral brightness measured by the sensor. Likewise, when considering
pigment distribution at the stand level scale, the pigment content observed from single view angles may not necessarily be
representative of stand-level conditions as some constituents vary as a function of the degree of leaf illumination and are
therefore not isotropic. As an alternative to mono-angle observations, multi-angular remote sensing can describe the anisotropy
of surface reflectance and yield accurate information on canopy structure. These observations can also be used to describe
the bi-directional reflectance distribution which then allows the modeling of reflectance independently of the observation
geometry. In this paper, we demonstrate a method for estimating pigment contents of chlorophyll and carotenoids continuously
over a year from tower-based, multi-angular spectro-radiometer observations. Estimates of chlorophyll and carotenoid content
were derived at two flux-tower sites in western Canada. Pigment contents derived from inversion of a CR model (PROSAIL) compared
well to those estimated using a semi-analytical approach (r
2 = 0.90 and r
2 = 0.69, P < 0.05 for both sites, respectively). Analysis of the seasonal dynamics indicated that net ecosystem productivity was strongly
related to total canopy chlorophyll content at the deciduous site (r
2 = 0.70, P < 0.001), but not at the coniferous site. Similarly, spectral estimates of photosynthetic light-use efficiency showed strong
seasonal patterns in the deciduous stand, but not in conifers. We conclude that multi-angular, spectral observations can play
a key role in explaining seasonal dynamics of fluxes of carbon and water and provide a valuable addition to flux-tower-based
networks. 相似文献
20.
Moisture sorption isotherms of figs with and without glucose syrup (at 20% and 40%, w/w) were determined at 5 °C, 25 °C, and 40 °C. A static gravimetric method was used under 0.11–0.84 water activity ranges for
the determination of sorption isotherms that were found to be typical type ΙΙΙ for control sample. The inclusion of glucose
syrup had significant effects on the sorption isotherms, and the moisture content of samples at each a
w decreased with increasing temperature. The experimental data were fitted well with two-parameter Brunauer–Emmet–Teller, three-parameter
Guggenheim–Anderson–de Boer, and four-parameter Peleg models that all had R
2 of greater than 0.99. The net isosteric heats of sorption were estimated using the Clausius–Clapeyron equation from the equilibrium
data at different temperatures. It was found that the addition of glucose syrup significantly increased the amount of monolayer
water and the isosteric heat of sorption. Both water activity and isosteric heat of sorption increased with glucose syrup
level and the shape and status of sorption isotherms tend to change toward the typical sigmoid shape of most food systems. 相似文献