Studying the vegetation response to simulated leakage of sequestered CO2 using spectral vegetation indices

Measurement of spectral reflectance provides a fast and nondestructive method of stress detection in vegetation. In this shallow subsurface CO₂ release experiment to simulate CO₂ leakage of geologically sequestered CO₂, the radiometric responses of plants to elevated soil CO₂ concentration were monitored using a spectroradiometer. Spectral responses included increased reflectance in the visible spectral region and decreased reflectance in the near-infrared region and thus an altered spectral pattern of vegetation. Visible responses of vegetation include purple discoloration and eventual death of leaves at sites where the soil CO₂ concentration was very high. Derivative analysis identified two features (minimum and maximum) in the 575–580 nm and 720–723 nm spectral regions. The normalized difference first derivative index (NFDI) was defined based on the spectral derivative at the two bands. Four vegetation indices were analyzed with the accumulated soil CO₂ concentration to assess the accumulated impact of high soil CO₂ concentration on vegetation. Results show that with increased soil CO₂ concentration due to the surface CO₂ leakage, (1) the structural independent pigment index (SIPI) increased, indicating a high carotenoid to chlorophyll ratio; (2) the chlorophyll normalized difference vegetation index (Chl NDI) decreased, suggesting a decrease in chlorophyll content with time; (3) pigment specific simple ratios (both PSSRa and PSSRb) were reduced for stressed vegetation compared to that at the control site, indicating a reduction in both chlorophyll a and chlorophyll b; and (4) NFDI was low where plants were stressed. Changes in NFDI during the experiment were 36% and 1% for stressed and control plants, respectively. All four indices were found to be sensitive to stress in vegetation induced by high soil CO₂ concentration.     

Detecting <Emphasis Type="Italic">Suaeda salsa</Emphasis> L<Emphasis Type="Italic">.</Emphasis> chlorophyll fluorescence response to salinity stress by using hyperspectral reflectance

Measurements of chlorophyll fluorescence and hyperspectral reflectance were used to detect salinity stress in Suaeda salsa L., beach of Dongtai, Jiangsu Province, China. Three experimental sites were used in our study, which belong to low salinity, middle salinity and high salinity. The results showed that leaf chlorophyll fluorescence changed along salinity gradient. To select the sensitive hyperspectral ranges of leaf chlorophyll fluorescence, the correlationship between leaf chlorophyll fluorescence and hyperspectral reflectance was regressed and analyzed. Statistical results indicated that the 680 and 935 nm were the most sensitive hyperspectral bands for estimating leaf chlorophyll fluorescence. Then, 11 relative hyperspectral indices were selected based on the sensitive bands and previous literature. (R ₆₈₀ − R ₉₃₅)/(R ₆₈₀ + R ₉₃₅) and R ₆₈₀/R ₉₃₅ have higher correlationship coefficient (R) and lower root mean square error, may be used for detecting chlorophyll fluorescence, such as F _o, F _m, F _v/F _m, qP, and ΦPSII, while NPQ may be detected by (R ₇₈₀ − R ₇₁₀)/(R ₇₈₀ − R ₆₈₀). These results suggest that chlorophyll fluorescence of halophyte response to salinity stress could be identified by remote sensing.     

Stress tolerance and stress-induced injury in crop plants measured by chlorophyll fluorescence in vivo: chilling, freezing, ice cover, heat, and high light

The proposition is examined that measurements of chlorophyll fluorescence in vivo can be used to monitor cellular injury caused by environmental stresses rapidly and nondestructively and to determine the relative stress tolerances of different species. Stress responses of leaf tissue were measured by F_R, the maximal rate of the induced rise in chlorophyll fluorescence. The time taken for F_R to decrease by 50% in leaves at 0°C was used as a measure of chilling tolerance. This value was 4.3 hours for chilling-sensitive cucumber. In contrast, F_R decreased very slowly in cucumber leaves at 10°C or in chilling-tolerant cabbage leaves at 0°C. Long-term changes in F_R of barley, wheat, and rye leaves kept at 0°C were different in frost-hardened and unhardened material and in the latter appeared to be correlated to plant frost tolerance. To simulate damage caused by a thick ice cover, wheat leaves were placed at 0°C under N₂. Kharkov wheat, a variety tolerant of ice encapsulation, showed a slower decrease in F_R than Gatcher, a spring wheat. Relative heat tolerance was also indicated by the decrease in F_R in heated leaves while changes in vivo resulting from photoinhibition, ultraviolet radiation, and photobleaching can also be measured.     

Distinguishing natural from anthropogenic stress in plants: physiology, fluorescence and hyperspectral reflectance

Background and Aims

Explosives released into the environment from munitions production, processing facilities, or buried unexploded ordnances can be absorbed by surrounding roots and induce toxic effects in leaves and stems. Research into the mechanisms with which explosives disrupt physiological processes could provide methods for discrimination of anthropogenic and natural stresses. Our objectives were to experimentally evaluate the effects of natural stress and explosives on plant physiology and to link differences among treatments to changes in hyperspectral reflectance for possible remote detection.

Methods

Photosynthesis, water relations, chlorophyll fluorescence, and hyperspectral reflectance were measured following four experimental treatments (drought, salinity, trinitrotoluene and hexahydro-1,3,5-trinitro-l,3,5-triazine) on two woody species. Principal Components Analyses of physiological and hyperspectral results were used to evaluate the differences among treatments.

Results

Explosives induced different physiological responses compared to natural stress responses. Stomatal regulation over photosynthesis occurred due to natural stress, influencing energy dissipation pathways of excess light. Photosynthetic declines in explosives were likely the result of metabolic dysfunction. Select hyperspectral indices could discriminate natural stressors from explosives using changes in the red and near-infrared spectral region.

Conclusions

These results show the possibility of using variations in energy dissipation and hyperspectral reflectance to detect plants exposed to explosives in a laboratory setting and are promising for field application using plants as phytosensors to detect explosives contamination in soil.     

Chlorophyll fluorescence upper-to-lower-leaf ratio for determination of irrigation time for Pentas lanceolata

The objective of this study was to use nondestructive measurements as the precise irrigation indices for potted star cluster (Pentas lanceolata). Drought stress was imposed on plants for 0, 3, 5, 7, 12, and 16 d by withholding water. Measurements were conducted on the third leaf counted from the apex (upper leaves) and on the third leaf from the bottom (lower leaves). Within the range of soil water content (SWC) from 10 to 45%, leaf water potential (WP), SWC, and soil matric potential (SMP), chlorophyll fluorescence, photochemical reflectance index (PRI), adjusted normalized difference vegetation index (aNDVI), and the reflectance (R) at 1950 nm (R₁₉₅₀) were measured. The plants reached the temporary wilting point at ?3.87 MPa of leaf WP; the maximal fluorescence yield of the light-adapted state (F_m′) ratio of upper-to-lower leaves was 1.7. When the F_m′ ratio was 1.3, it corresponded to lower-leaf WP < ?2.27 MPa, SWC < 21%, SMP < ?20 kPa, PRI < 0.0443, aNDVI < 0.0301, and R₁₉₅₀ > 8.904; it was the time to irrigate. In conclusion, the F_m′ ratio of upper-to-lower leaves was shown to be a nondestructive predictor of leaf WP and can be used to estimate irrigation timing.     

Effect of drought stress on chlorophyll a fluorescence and electrical admittance of shoots in Norway spruce seedlings

Effects of mild and severe soil drought on the water status of needles, chlorophyll a fluorescence, shoot electrical admittance, and concentrations of photosynthetic pigments in needles of seedlings of Picea abies (L.) Karst. were examined under controlled greenhouse conditions. Drought stress reduced shoot admittance linearly with a decrease in shoot water potential (_w) and increase in water deficit (WD) and led to a decrease in concentrations of chlorophyll a, b and carotenoids. Severe water stress (shoot _w=–2.4 MPa) had a negative effect on chlorophyll a fluorescence parameters including PSII activity (F_v/F_m), and the vitality index (R_fd). Variations in these parameters suggest an inhibition of the photosynthetic electron transport in spruce needles. Water stress led to a decrease in the mobility of electrolytes in tissues, which was reflected by decreased shoot electrical admittance. After re-watering for 21 days the WD in needles decreased and the shoot water potential increased. In the re-watered plants, the chloroplast function was restored and chlorophyll a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in the seedlings triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. We conclude that the shoot electrical admittance and photosynthetic electron transport in leaves are closely linked to changes in water status and their decrease is among the initial responses of seedlings to water stress.     

Estimating soil respiration using spectral vegetation indices and abiotic factors in irrigated and rainfed agroecosystems

Aims

Our aims were to identify the primary factors involved in soil respiration (R_s) variability and the role that spectral vegetation indices played in R_s estimation in irrigated and rainfed agroecosystems during the growing season.

Methods

We employed three vegetation indices [i.e., normalized difference vegetation index (NDVI), green edge chlorophyll index (CI_{green edge}) and enhanced vegetation index (EVI)] derived from the Moderate-resolution Imaging Spectroradiometer (MODIS) surface reflectance product as approximations of crop gross primary production (GPP) for R_s estimation. Different statistical models were used to analyze the dependencies of R_s on soil temperature, soil water content and plant photosynthesis, and accuracy of these models were compared in the irrigated and rainfed agroecosystems.

Results

The results demonstrated that a model based only on abiotic factors (e.g., soil temperature and soil water content) failed to describe part of the growing-season variability in R_s. Residual analysis indicated that R_s was influenced by a short-term gross primary production (GPP) and a longer-term (≥3 days) accumulated GPP in the irrigated and rainfed agroecosystems. Therefore, photosynthesis dependency of R_s should be included in the R_s model to describe the growing-season dynamics of R_s. Among the three VIs, CI_{green edge} showed generally better correlations with GPP at different cumulative times and canopy green leaf area index than EVI and NDVI. Adding the CI_{green edge} into the model considering only soil temperature and soil water content significantly improved the simulation accuracy of R_s.

Conclusions

Our results suggest that spectral vegetation index from remote sensing could be used to estimate R_s, which will be helpful for the development of a future R_s model over a large spatial scale.     

An approach to develop a model for describing the influence of fluoride-contaminated irrigation water on physiological responses in poplar (Populus deltoides clone S7C15)

The physiological responses pertaining to influence of fluoride-contaminated irrigation water (100–500 ppm) on 6-week-old seedlings of Populus deltoides, a fast growing tree crop in northern India are investigated. It is observed that the various fluoride concentrations in irrigation water are directly proportional to the changes in the physiological responses. The reduction in stomatal conductance is found higher (~57 %) in relation to photosynthetic CO₂ assimilation (~38 %) and chlorophyll fluorescence yield (~12 %) in fluoride-contaminated (100 ppm) irrigation. Similarly, impaired values for g _s (75 %), P _N (55 %), and F _v/F _m (18 %) are also triggered by higher level of fluoride-contaminated (200 ppm) irrigation. Further higher dose of fluoride (500 ppm) contaminated irrigation water could severely minimize the physiological responses viz., g _s, P _N and F _v/F _m ca. 86, 65, and 36 %. A mathematical model developed based on the changes in rates of stomatal conductance (Δg _s/ΔC), photosynthetic CO₂ assimilation (ΔP _N/ΔC) and chlorophyll fluorescence yield (ΔF _v/F _m/ΔC), which has shown straight line relationship, and was verified with average deviations from 1.86 to 5.87 %. The calculated physiological responses influenced by fluoride irrigation on poplar seedlings are also verified with developed model. The governing equation suggests the existence of functional relationship between physiological responses and applied fluoride treatment doses. Hence, the cultivation of poplar crop may be designed precisely in fluoride affected areas to boost and sustain agro-socio economy.     

Chemical and hydraulic signals regulate stomatal behavior and photosynthetic activity in maize during progressive drought

The objectives of this study were to investigate stomatal regulation in maize seedlings during progressive soil drying and to determine the impact of stomatal movement on photosynthetic activity. In well-watered and drought-stressed plants, leaf water potential (Ψ _leaf), relative water content (RWC), stomatal conductance (g _s), photosynthesis, chlorophyll fluorescence, leaf instantaneous water use efficiency (iWUE_leaf), and abscisic acid (ABA) and zeatin-riboside (ZR) accumulation were measured. Results showed that g _s decreased significantly with progressive drought and stomatal limitations were responsible for inhibiting photosynthesis in the initial stages of short-term drought. However, after 5 days of withholding water, non-stomatal limitations, such as damage to the PSII reaction center, became the main limiting factor. Stomatal behavior was correlated with changes in both hydraulic and chemical signals; however, changes in ABA and ZR occurred prior to any change in leaf water status. ABA in leaf and root tissue increased progressively during soil drying, and further analysis found that leaf ABA was negatively correlated with g _s (R ² = 0.907, p < 0.05). In contrast, leaf and root ZR decreased gradually. ZR in leaf tissue was positively correlated with g _s (R ² = 0.859, p < 0.05). These results indicate that ABA could induce stomatal closure, and ZR works antagonistically against ABA in stomatal behavior. In addition, the ABA/ZR ratio also had a strong correlation with g _s, suggesting that the combined chemical signal (the interaction between ABA and cytokinin) plays a role in coordinating stomatal behavior. In addition, Ψ _leaf and RWC decreased significantly after only 3 days of drought stress, also affecting stomatal behavior.     

Impact of flooding and drought conditions on the emission of volatile organic compounds of Quercus robur and Prunus serotina

We conducted measurements with oak (Quercus robur L.) and black cherry (Prunus serotina Ehrh.) seedlings to investigate their volatile organic compound (VOC) emission behavior to flooding and drought conditions. A novel cuvette enclosure approach was applied on 18 individuals and emission rates were derived using proton transfer reaction-mass spectrometry (PTR-MS) and gas chromatography–mass spectrometry (GC–MS) techniques. Complementary chlorophyll fluorescence and CO₂ uptake measurements were performed for all of the samples. Q. robur seedlings remained unaffected by flood. On the contrary, P. serotina seedlings reduced their chlorophyll fluorescence yield by 34.5 ± 4.1 % and their CO₂ uptake by 67.5 ± 10.5 %. These observations along with the highest acetaldehyde emissions recorded indicate strong susceptibility to water stress. Drought had a similar impact on both species that reduced chlorophyll fluorescence yield, CO₂ uptake, and the emission rates of most VOC. Nevertheless, isoprene was found to be emitted more than 20 times stronger by Q. robur seedlings under all treatments. In general, most VOC emissions increased with soil water availability displaying an exponential trend for acetaldehyde and methanol and a linear one for the sum of mono- and sesquiterpenes. Only methyl salicylate was released about two times stronger from oaks under drought conditions in comparison to wet conditions. Considering their VOC emission behavior, Q. robur seedlings appear to tolerate flood much better than P. serotina and thus it is likely to have a competing advantage under these conditions.     

Effects of nitrogen and phosphorus imbalance on photosynthetic traits of poplar Oxford clone under ozone pollution

Ozone (O₃) pollution and the availability of nitrogen (N) and phosphorus (P) in the soil both affect plant photosynthesis and chlorophyll (Chl) content, but the interaction of O₃ and nutrition is unclear. We postulated that the nutritional condition changes plant photosynthetic responses to O₃. An O₃-sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha^??1; N80, 80 kg N ha^??1), two P levels (P0, 0 kg P ha^??1; P80, 80 kg P ha^??1) and three levels of O₃ exposure (ambient concentration, AA; 1.5?×?AA; 2.0?×?AA) over a growing season in an O₃ free air controlled exposure (FACE) facility. The daily change of leaf gas exchange and dark respiration (R_d) were investigated at mid-summer (August). Chl a fluorescence was measured three times in July, August and September. At the end of the growing season, Chl content was measured. It was found that Chl content, the maximum quantum yield (F_v/F_m), Chl a fluorescence performance index (PI) and gas exchange were negatively affected by elevated O₃. Phosphorus may mitigate the O₃-induced reduction of the ratio of photosynthesis to stomatal conductance, while it exacerbated the O₃-induced loss of F_v/F_m. Nitrogen alleviated negative effects of O₃ on F_v/F_m and PI in July. Ozone-induced loss of net photosynthetic rate was mitigated by N in medium O₃ exposure (1.5?×?AA). However, such a mitigation effect was not observed in the higher O₃ level (2.0?×?AA). Nitrogen addition exacerbated O₃-induced increase of R_d suggesting an increased respiratory carbon loss in the presence of O₃ and N. This may result in a further reduction of the net carbon gain for poplars exposed to O₃.     

Assessment of ecosystem CO2 efflux and its components in a Pinus canariensis forest at the treeline

We estimated respiratory fluxes in a treeline-associated Pinus canariensis forest in Tenerife, Canary Islands, an ecotone with strong seasonal changes in soil water availability. CO₂ efflux rates from the foliage, above ground woody tissue and the soil were measured by chamber techniques. Site-specific models obtained from these chamber measurements were then combined with half-hourly measurements of canopy, stem and soil temperature as well as with soil water potential, leaf area and stem sapwood volume data for scaling up component-specific CO₂ efflux to ecosystem respiration (R _ECO). Integrated over an entire year R _ECO was 550 g C m^?2 ground surface area (average of 2008 and 2009) and comprised the following component fluxes: 57 % from the soil, 10 % from above ground woody tissue and 33 % from the foliage. Between year differences in R _ECO and its components were <3 %. R _ECO varied markedly throughout an entire year generally following the seasonal trends in temperature during most of the year. During the dry summer, however, R _ECO was significantly reduced due to limited soil water availability in the rooting horizon. Thus, in treeline-associated forests under predicted scenarios of increasing aridity in Mediterranean regions, it is likely that there will be a shift in the contribution of CO₂ efflux from the soil (R _S), the foliage (R _F) and above ground woody tissue (R _W) to R _ECO from predominately below ground to increasingly above ground. Such changes should be taken into account for predicting the response of treeline forests to a changing climate at their upper distribution limit.     

Arbuscular mycorrhizae improves low temperature stress in maize via alterations in host water status and photosynthesis

The effect of arbuscular mycorrhizal (AM) fungus, Glomus etunicatum, on growth, water status, chlorophyll concentration and photosynthesis in maize (Zea mays L.) plants was investigated in pot culture under low temperature stress. The maize plants were placed in a sand and soil mixture at 25°C for 7 weeks, and then subjected to 5°C, 15°C and 25°C for 1 week. Low temperature stress decreased AM root colonization. AM symbiosis stimulated plant growth and had higher root dry weight at all temperature treatments. Mycorrhizal plants had better water status than corresponding non-mycorrhizal plants, and significant differences were found in water conservation (WC) and water use efficiency (WUE) regardless of temperature treatments. AM colonization increased the concentrations of chlorophyll a, chlorophyll b and chlorophyll a + b. The maximal fluorescence (Fm), maximum quantum efficiency of PSII primary photochemistry (Fv/Fm) and potential photochemical efficiency (Fv/Fo) were higher, but primary fluorescence (Fo) was lower in AM plants compared with non-AM plants. AM inoculation notably increased net photosynthetic rate (Pn) and transpiration rate (E) of maize plants. Mycorrhizal plants had higher stomatal conductance (g_s) than non-mycorrhizal plants with significant difference only at 5°C. Intercellular CO₂ concentration (Ci) was lower in mycorrhizal than that in non-mycorrhizal plants, especially under low temperature stress. The results indicated that AM symbiosis protect maize plants against low temperature stress through improving the water status and photosynthetic capacity.     

A comparative analysis of photosynthetic recovery from thermal stress: a desert plant case study

Our understanding of the effects of heat stress on plant photosynthesis has progressed rapidly in recent years through the use of chlorophyll a fluorescence techniques. These methods frequently involve the treatment of leaves for several hours in dark conditions to estimate declines in maximum quantum yield of photsystem II (F _V/F _M), rarely accounting for the recovery of effective quantum yield (ΔF/F _M′) after thermally induced damage occurs. Exposure to high temperature extremes, however, can occur over minutes, rather than hours, and recent studies suggest that light influences damage recovery. Also, the current focus on agriculturally important crops may lead to assumptions about average stress responses and a poor understanding about the variation among species’ thermal tolerance. We present a chlorophyll a fluorescence protocol incorporating subsaturating light to address whether species’ thermal tolerance thresholds (T ₅₀) are related to the ability to recover from short-term heat stress in 41 Australian desert species. We found that damage incurred by 15-min thermal stress events was most strongly negatively correlated with the capacity of species to recover after a stress event of 50 °C in summer. Phylogenetically independent contrast analyses revealed that basal divergences partially explain this relationship. Although T ₅₀ and recovery capacity were positively correlated, the relationship was weaker for species with high T ₅₀ values (>51 °C). Results highlight that, even within a single desert biome, species vary widely in their physiological response to high temperature stress and recovery metrics provide more comprehensive information than damage metrics alone.     

Comparative analysis of 2,4,6-trinitrotoluene (TNT)-induced cellular responses and proteomes in <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. HK-6 in two types of media

TNT-induced cellular responses and proteomes in Pseudomonas sp. HK-6 were comparatively analyzed in two different media: basal salts (BS) and Luria broth (LB). HK-6 cells could not degrade more than 0.5 mM TNT with BS medium, while in LB medium, they exhibited the enhanced capability to degrade as much as 3.0 mM TNT. Analysis of total cellular fatty acids in HK-6 cells suggested that the relative abundance of several saturated or unsaturated fatty acids is altered under TNT-mediated stress conditions. Scanning electron microscopy showed the presence of perforations, irregular rod formations, and wrinkled extracellular surfaces in cells under TNT stress. Proteomic analysis of soluble protein fractions from HK-6 cultures grown with TNT as a substrate revealed 11 protein spots induced by TNT. Among these, seven proteins (including Alg8, AlgB, NirB, and the AhpC/Tsa family) were detected only in LB medium containing TNT. The proteins AspS, Tsf, and assimilatory nitrate reductase were increasingly expressed only in BS medium containing TNT. The protein dGTPase was found to be induced and expressed when cells were grown in either type of TNT-containing media. These results provide a better understanding of the cytotoxicity and survival mechanism used by Pseudomonas sp. HK-6 when placed under TNT stress conditions.     

Effects of arbuscular mycorrhizal fungus on photosynthesis and water status of maize under high temperature stress

The purpose of this study was to investigate the effects of arbuscular mycorrhizal (AM) symbiosis on gas exchange, chlorophyll fluorescence, pigment concentration and water status of maize plants in pot culture under high temperature stress. Zea mays L. genotype Zhengdan 958 were cultivated in soil at 26/22°C for 6 weeks, and later subjected to 25, 35 and 40°C for 1 week. The plants inoculated with the AM fungus Glomus etunicatum were compared with the non-inoculated plants. The results showed that high temperature stress decreased the biomass of the maize plants. AM symbiosis markedly enhanced the net photosynthetic rate, stomatal conductance and transpiration rate in the maize leaves. Compared with the non-mycorrhizal plants, mycorrhizal plants had lower intercellular CO₂ concentration under 40°C stress. The maximal fluorescence, maximum quantum efficiency of PSII photochemistry and potential photochemical efficiency of mycorrhizal plants were significantly higher than corresponding non-mycorrhizal plants under high temperature stress. AM-inoculated plants had higher concentrations of chlorophyll a, chlorophyll b and carotenoid than non-inoculated plants. Furthermore, AM colonization increased water use efficiency, water holding capacity and relative water content. In conclusion, maize roots inoculated with AM fungus may protect the plants against high temperature stress by improving photosynthesis and water status.     

Farm practices influence the photosynthetic performance and plant efficiency of Oryza sativa L.

The photosynthetic and physiological performances of Oryza sativa L. (rice) were evaluated in organic and conventional rice–rice agroecosystems for 120 days after transplantation by measuring net photosynthesis (P _N), transpiration (E), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), chlorophyll content (SPAD) and JIP fluorescence rise. The soil health was measured as soil bacterial and fungi density and activities of soil microbial enzymes (amylase, invertase, cellulase, protease, alkaline phosphatase and dehydrogenase). The conventionally managed fields showed lower microbial density and activity than of organic fields especially after 60 days of transplantation. The crop grown in the conventional fields has significantly low level of P _N and chlorophyll, but E, g _s and C _i did not differ significantly till 105 days after transplantation. The JIP rise was low in conventional fields than in organic fields during 90–120 days. The efficiency and plant performance parameters (φP ₀, Ψ ₀, φE ₀, PI_φ, PI _Ψ , PI_ABS, and PI_total) showed a rapid rate of decrease in the conventional than of organic fields. Significant positive correlation could be established between the performance and soil microbial activities, whereas the stress indicating fluorescence parameters (V _J, M ₀, φD ₀, DI₀/RC) showed significant negative correlation with the soil parameters in both the farming systems. The result showed that JIP analysis can be used as an early indicator of soil fertility and plant performance.     

Assessing the poplar photochemical response to high zinc concentrations by image processing and statistical approach

Exposure of plants to high-heavy metals concentration inhibits multiple metabolic processes in plants and leads to an oxidative stress commonly referred as heavy metal ion toxicity. Chlorophyll a fluorescence has enhanced understanding of heavy metal ion action on the photosynthetic system. A rapid and non-invasive technique involving imaging of chlorophyll fluorescence is a useful tool for early detection of plant responses to heavy metal ion toxicity. In this work chlorophyll fluorescence emission and photochemical parameters in plants of Populus x euramericana clone I-214 were investigated by the portable Imaging PAM fluorometer at different days after soil treatment with zinc. Custom software for analysis of the photochemical parameters images has been developed in order to gain a better assessing of the plant performance in response of metal stress. The imaging analysis allowed visualizing heterogeneity in plant response to high zinc concentrations. The heterogeneity of images suggests spatial differences in photochemical activity and changes in the antenna down-regulation.     

Soil CO2 efflux and soil carbon balance of a tropical rubber plantation

Natural rubber is a valuable source of income in many tropical countries and rubber trees are increasingly planted in tropical areas, where they contribute to land-use changes that impact the global carbon cycle. However, little is known about the carbon balance of these plantations. We studied the soil carbon balance of a 15-year-old rubber plantation in Thailand and we specifically explored the seasonal dynamic of soil CO₂ efflux (F _S) in relation to seasonal changes in soil water content (W _S) and soil temperature (T _S), assessed the partitioning of F _S between autotrophic (R _A) and heterotrophic (R _H) sources in a root trenching experiment and estimated the contribution of aboveground and belowground carbon inputs to the soil carbon budget. A multiplicative model combining both T _S and W _S explained 58 % of the seasonal variation of F _S. Annual soil CO₂ efflux averaged 1.88 kg C m^?2 year^?1 between May 2009 and April 2011 and R _A and R _H accounted for respectively 63 and 37 % of F _S, after corrections of F _S measured on trenched plots for root decomposition and for difference in soil water content. The 4-year average annual aboveground litterfall was 0.53 kg C m^?2 year^?1 while a conservative estimate of belowground carbon input into the soil was much lower (0.17 kg C m^?2 year^?1). Our results highlighted that belowground processes (root and rhizomicrobial respiration and the heterotrophic respiration related to belowground carbon input into the soil) have a larger contribution to soil CO₂ efflux (72 %) than aboveground litter decomposition.     

Benthic macrophyte metrics as bioindicators of water quality: towards overcoming typological boundaries and methodological tradition in Mediterranean and Black Seas

Benthic macrophyte communities of different substratum types (soft, hard) were studied in eleven differently impacted sites belonging in two different water typologies (transitional waters: Lesina Lagoon, Varna Lake; coastal waters: Varna Bay) and two ecoregions (Mediterranean Sea, Black Sea). Species lists were compiled for each study site, 20 taxa were found at Lesina and Varna Lake and Bay, and the abundance of each taxon was determined at each site. The relationship between nine metrics related to community structure [species richness, % of total coverage, dry biomass (g/m^?2), and cluster and multi-dimensional scaling plot of Bray–Curtis similarity] and function [Ecological Status Group I % coverage, ESG II % coverage, Ecological Evaluation Index (EEI-c) and Ecological Index (EI_EEI)] and key abiotic factors and an anthropogenic stress index (EnII) were studied. A strong relationship (Spearman rank correlation coefficient ρ ≤ ?0.89; R ² ≥ 0.89) between anthropogenic stress and functional indices, EEI-c and EI_EEI, was found. The structural index ‘species richness’ correlated negatively with EnII and positively with salinity, demonstrating a freshwater and confinement influence on species diversity. EEI-c and EI_EEI indices classified the studied sites and locations in different Ecological Status Classes in accordance with the anthropogenic stress gradient.