Decrease In Leaf Area Index Research Articles

Effects of urea mixed with nitrapyrin on leaf photosynthetic and senescence characteristics of summer maize (Zea mays L.) waterlogged in the field

Waterlogging is one of the major abiotic stresses in agricultural crop production. However, the application of 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) can effectually mitigate the losses of nitrogen efficiency and grain yield of summer maize induced by waterlogging. In order to explore its role to alleviate waterlogging stress on leaf antioxidative system and photosynthetic characteristics of summer maize, a field experiment was executed to research effects of nitrapyrin application on leaf photosynthetic and senescent characteristics of waterlogged summer maize Denghai 605 (DH605) and Zhengdan 958 (ZD958). Experimental treatments consisted of waterlogging treatment that was applying only urea (WL), waterlogging treatment that was applying urea mixing with nitrapyrin (WL-N), and no waterlogging treatment that was only applying urea (NWL). Results showed that WL significantly decreased leaf area index (LAI), SPAD, photosynthetic rate (Pn), and protective enzyme activities, accelerated leaf aging, eventually led to a remarkable yield reduction by 38 and 42% for DH605 and ZD958, respectively, compared to NWL. However, the application of nitrapyrin was useful for relieving waterlogging damages on leaf photosynthetic ability. LAI, SPAD and Pn of WL-N for DH605 were 10, 19 and 12–24% higher, and for ZD958 were 12, 23 and 7–25% higher, compared to those of WL, respectively. Moreover, application of nitrapyrin effectually relieved waterlogging losses on antioxidative enzyme activities. Leaf superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities of WL-N were averagely increased by 24, 15 and 30%, respectively, while malondialdehyde (MDA) content was averagely decreased by 13%, compared to those of WL. Visibly, nitrapyrin application could improve leaf photosynthetic characteristics and retard leaf aging induced by waterlogging, thereby leading to a yield increase of waterlogged maize.

Salinity stress effects on transpiration and plant growth under different salinity soil levels based on thermal infrared remote (TIR) technique

Soil salinization is a serious land degradation issue in Northwest China and significantly threatens food security; thus, a comprehensive understanding of plant response to salinity stress is desirable. The objective was to detect the effect of salinity stress on alfalfa transpiration rate and plant growth under four salinity levels. The thermal infrared remote (TIR) technique was used to acquire the canopy temperature of plants exposed to four salinities (no salinity, S0; slight salinity, S3; moderate salinity, S5; and severe salinity, S7), while transpiration was evaluated based on the three temperature (3 T) model. Results indicated that the 3 T model and TIR technique successfully simulated transpiration with a high coefficient determination of R2 above 0.8. The general pattern is that canopy temperature values correspond well with salinity values. With the increase of soil salinity for the treatment of S3, S5, and S7, the canopy temperature increased by 0.88 °C, 0.98 °C, and 1.19 °C, respectively. Moreover, the growth of alfalfa was inhibited, resulting in a corresponding decrease in leaf area index by 19.3%, 31.2%, and 54.2%, respectively. Transpiration reduced by 1.2%, 6.7%, and 20.0%, correspondingly, because of stunted growth and less canopy cover. Salinity stress on agricultural crops was extremely negative; the higher the soil salinity was, the lower the canopy cover, so salinity reduced the growth rate and resulted in reduced plants growing due to osmotic effects. Where salt accumulation occurs in a horizontally nonuniform way, transpiration may be presented by spatial heterogeneity; however, there remains limited research on this issue. This research will provide a scientific basis for ecological construction programs.

Influence of Canopy Management Practices on Canopy Architecture and Reproductive Performance of Semillon and Shiraz Grapevines in a Hot Climate

Canopy management techniques can be beneficial to grapevine reproduction because they improve canopy structure and microclimate. In this study, the influence of different canopy management practices—cluster thinning, leaf removal, shoot-thinning, and light pruning—on reproductive performance was studied for the varieties Semillon and Shiraz grown under field conditions in a hot climate in South Australia. Canopy architecture, canopy light interception, and reproductive parameters for different management practices were measured. Results showed that the applied practices modified canopy architecture and influenced reproductive performance and the berry ripening process. Specifically, shoot-thinning and leaf removal decreased leaf area index and increased canopy porosity and light interception. Berry ripening was positively affected by cluster thinning and shoot-thinning, while leaf removal and light pruning delayed the process. For reproductive parameters, leaf removal had a relatively minor effect; shoot-thinning and cluster thinning reduced cluster number but showed compensation effects in other yield components, and light pruning decreased berry weight. In addition, cluster compactness was found to be significantly correlated with bunch rot (Botrytis cinerea) incidence for Semillon.

Distinct characteristics of canopy gaps in the subtropical mangroves of Moreton Bay, Australia

Mangroves often form extensive closed forests characterised by the occurrence of canopy gaps consisting of a group of standing dead trees. This article describes the physical characteristics, micro-environmental changes and the regrowth pattern of the naturally created unique circular canopy gaps in the subtropical Avicennia marina mangroves of Moreton Bay, Southeast Queensland, Australia. A survey on 52 canopy gaps was carried out to quantify the size and shape of canopy openings. We found that gap size ranged from a minimum area of 27 m2 to a maximum area of 474 m2 with an average (±standard deviation) of 134 ± 102 m2. All of the gaps surveyed were circular in shape with the eccentricity of length and width between 0.7 and 1.3. Once a canopy gap is created, the forest physical and biological processes are altered compared with the surrounding forest, such as in an increase in the potential photosynthetic active radiation (PPAR) and canopy openness, and a decrease in leaf area index (LAI). We found that canopy openings also had a significant effect on sediment pore water temperature but not on salinity and pH. The sudden increase in the amount of light following canopy opening stimulated rapid growth of seedlings which were available for the opportunity to take the place of the dead trees. Gap Closure Index (GCI) is introduced to illustrate surveyed gaps in the context of vertical growth of seedlings to fill up gap space to reach the site maximal canopy height, thus demonstrating the phases of gap dynamics in the natural regeneration of the subtropical monospecific mangrove forest.

Source-sink optimization and morpho-physiological response of soybean [Glycine max] to detopping and mepiquat chloride application

Effect of detopping and mepiquat chloride on morphological, physiological and yield attributes of soybean cultivar ‘SL 544’ was studied. A two year investigation was conducted at Punjab Agricultural University, Ludhiana, during kharif seasons of 2014 and 2015. The experiment was laid-out in randomized complete block design (RCBD) with eight treatments viz. control, detopping (removal of 4-5 cm apical portion of main stem) at 50-55 days after sowing (DAS), mepiquat chloride @ 200 ppm (50-55 DAS), mepiquat chloride @ 200 ppm (50-55 + 65-70 DAS), mepiquat chloride 250 ppm (50-55 DAS), mepiquat chloride @ 250 ppm (50-55 + 65-70 DAS), mepiquat chloride @ 300 ppm (50-55 DAS) and mepiquat chloride @ 300 ppm (50-55 + 65-70 DAS) with four replications. Detopping had a non-significant effect on leaf area index, SPAD value, PAR interception, abscission of reproductive parts, seeds per pod, 100-seed weight, pod length and stover yield of soybean. It significantly decreased plant height, increased total dry matter accumulation/plant, number of flowers and pods/plant, pod setting percentage and seed yield over control during 2014 and 2015. At crop harvest, detopping developed optimized source-sink relationship by means of distribution of total dry matter between stem, foliage and pods by 20.4, 14.9 and 64.6 % during 2014 while 22.6, 20.1 and 57.4 % during 2015, respectively. Mepiquat chloride posed a non-significant effect on plant height, PAR interception, number of flowers/plant, number of seeds/pod, pod length and stover yield of soybean but it significantly decreased leaf area index, abscission of reproductive parts while increased the dry matter accumulation/plant, number of pods/plant, 100-seed weight and seed yield relative to control. At harvest, two foliar applications of mepiquat chloride @ 250 ppm resulted in optimized source-sink relationship by the distribution of total dry matter among stem, foliage and pods by 20.6, 10.9 and 68.5 % during 2014 while 19.5, 7.6 and 72.9 % during 2015, respectively. Occurrence of more rainfall during 2015 as compared to 2014 caused mepiquat chloride to hike seed yield as compared to detopping which is clearly witnessed by increase in pod dry weight per plant during 2015 than 2014. Conclusively, both detopping and mepiquat chloride resulted in enhancement in source-sink relationship and seed yield of soybean.

Effects of drought stress at different growth stages on photosynthetic efficiency and water consumption characteristics in sweet potato.

To investigate the effects of drought stress on the growth of sweet potato, photosynthesis, yield, and water consumption characteristics were investigated in field-grown sweet potato plants (Jishu 21, a drought-tolerant cultivar) at different growth stages in 2014-2015. There were five drought treatments, including the whole growth period (DS), the early stage of growth (rooting and branching period, DS1), the middle stage of growth (storage root initiation period, DS2), and the late stage of growth (storage root bulking period, DS3), and a normal irrigation treatment (WW) as control. The results showed that sweet potato plants in DS significantly decreased in dry mass, biomass, and harvest index during two years. The biomass of sweet potato under DS, DS1, DS2 and DS3 was decreased by 31.3%, 21.2%, 19.6% and 7.7%; the harvest index was decreased by 19.9%, 14.5%, 14.1% and 6.5%, and the dry mass was decreased by 45.3%, 33.1%, 31.3% and 14.2%, respectively. The leaf area index in DS, DS1, DS2 and DS3 was decreased by 77.1%, 60.1%, 39.2% and 17.1% at 100 days after transplanting (DAT), and the net photosynthesis was decreased by 56.7%, 26.6%, 18.7% and 9.5% at 90 DAT, respectively. Plants under drought stress reduced diurnal evaporation, transpiration rate, water consumption, daily water consumption, and soil water use efficiency, but increased irrigation water use efficiency. Drought stress decreased leaf area index, Pn, biomass and the allocation of biomass to storage root, resulting in a significant reduction of yield. The early drought and the long stress duration had significant impacts on leaf area index, Pn, biomass and harvest index, leading to a greater reduction in yield and water use efficiency. Therefore, drought stress at the early growth stages of sweet potato should be avoided during cultivation.

Grafting of watermelon (Citrullus lanatus cv. Mahbubi) onto different squash rootstocks as a means to minimize cadmium toxicity

ABSTRACTTo test the possibility that using appropriate rootstocks could improve the tolerance of watermelon to cadmium (Cd) toxicity, a greenhouse experiment was conducted to determine growth and antioxidant activities of watermelons, either nongrafted or grafted onto summer squash and winter squash. We provided nutrient solutions having four levels (0, 50, 100, and 200 μM) of cadmium to treat the plants. Shoot and root biomass reduction were significantly lower in summer squash rootstock-grafted watermelon than winter squash rootstock-grafted and nongrafted watermelons. Cadmium induced a smaller decrease in leaf area index in grafted watermelons compared with nongrafted plants. The Cd- related reductions in chlorophyll content and efficiency of photosynthesis were more severe in nongrafted watermelons compared with dose grafted onto summer squash. Cd accumulation in shoot at the highest dose (200 µM) of CdCl2 was significantly lower (19.76 mg/kg) in summer squash rootstock-grafted watermelon compared with winter squash rootstock-grafted (37.58 mg/kg) and nongrafted watermelon (72.12 mg/kg). H2O2, MDA production and electrolyte leakage of summer squash rootstock-grafted watermelon showed less increase, which was associated with a significant increase in the activities of antioxidant. The improved crop performance of grafted watermelons was attributed to their strong capacity to inhibit Cd accumulation in the aerial parts.

Simulating damage for wind storms in the land surface model ORCHIDEE-CAN (revision 4262)

Abstract. Earth system models (ESMs) are currently the most advanced tools with which to study the interactions among humans, ecosystem productivity, and the climate. The inclusion of storm damage in ESMs has long been hampered by their big-leaf approach, which ignores the canopy structure information that is required for process-based wind-throw modelling. Recently the big-leaf assumptions in the large-scale land surface model ORCHIDEE-CAN were replaced by a three-dimensional description of the canopy structure. This opened the way to the integration of the processes from the small-scale wind damage risk model ForestGALES into ORCHIDEE-CAN. The integration of ForestGALES into ORCHIDEE-CAN required, however, developing numerically efficient solutions to deal with (1) landscape heterogeneity, i.e. account for newly established forest edges for the parameterization of gusts; (2) downscaling spatially and temporally aggregated wind fields to obtain more realistic wind speeds that would represents gusts; and (3) downscaling storm damage within the 2500 km2 pixels of ORCHIDEE-CAN. This new version of ORCHIDEE-CAN was parameterized over Sweden. Subsequently, the performance of the model was tested against data for historical storms in southern Sweden between 1951 and 2010 and south-western France in 2009. In years without big storms, here defined as a storm damaging less than 15 × 106 m3 of wood in Sweden, the model error is 1.62 × 106 m3, which is about 100 % of the observed damage. For years with big storms, such as Gudrun in 2005, the model error increased to 5.05 × 106 m3, which is between 10 and 50 % of the observed damage. When the same model parameters were used over France, the model reproduced a decrease in leaf area index and an increase in albedo, in accordance with SPOT-VGT and MODIS records following the passing of Cyclone Klaus in 2009. The current version of ORCHIDEE-CAN (revision 4262) is therefore expected to have the capability to capture the dynamics of forest structure due to storm disturbance on both regional and global scales, although the empirical parameters calculating gustiness from the gridded wind fields and storm damage from critical wind speeds may benefit from regional fitting.

Responses of maize ecosystem to warming based on WATDPED experiment under near-field condition

By using the standard climate in Beijing during 2000–2010 as baseline, a current and warming contrast experiment was conducted with the Water Transformation Dynamical Processes Experimental Device (WATDPED) to quantify the responses of a maize system to warming in terms of growth and water consumption. Under 2°C warming, the maize growth period was shortened by 8days. Chlorophyll content and N content of leaves were enhanced but C content and C/N ratio were decreased. Similarly, there were slight decreases in plant height and stem diameter. The stalk biomass component decreased in leaf and stem ratio, whenever increase in ear ratio over the total biomass. The 100-seed weight and yield were enhanced slightly as a result of the increase of net photosynthesis rate and the decrease of leaf area index. Although the daily evapotranspiration was increased, the total water consumption over the entire growth period was decreased mainly due to the shortened growth period. The values of water use efficiency leaf scale, ecosystem scale (irrigation water use efficiency), and ecosystem scale (evapotranspiration efficiency) were boosted to 28.88%, 6.78% and 5.38%, respectively. It was concluded from the experiments that under 2°C warming at the p=0.05 significant level, maize’s yield did not change but the size of maize became smaller in terms of stalk diameter and biomass was higher on the ear. It showed a stronger physiological vigor (higher N content and chlorophyll content) plus a lower total water consumption. Maize’s responses to warming were shown diversified and ensemble assessment by using multiple indicators including yield, biomass component, nutrient and water consumption among others is recommended.

Ridge tillage improves plant growth and grain yield of waterlogged summer maize

Regulation of ridge tillage on yield and growth of waterlogged summer maize hybrids Denghai 605 (DH605) and Zhengdan 958 (ZD958) were investigated in field conditions. Results showed that waterlogging significantly decreased leaf area index (LAI), SPAD value, and biomass, resulting in the reduction of photosynthetic rate, thereby decreased grain yield of summer maize. Grain yields of DH605 and ZD958 were decreased by 38% and 42% respectively, compared to no waterlogging treatment. However, ridge tillage was conducive to alleviate the adverse effects of waterlogging on photosynthetic performance and photosynthetic effective radiation by increasing LAI and SPAD value, and improving canopy structure. At tasseling stage (VT), the light transmittance of ear layer in ridge tillage treatment for DH605 and ZD958 was decreased by 12% and 19%, respectively, compared to that of waterlogging treatment. Visibly, ridge tillage effectively alleviated leaf senescence and the decrease of LAI and chlorophyll content induced by waterlogging, and improved canopy structure, photosynthetic effective radiation, and photosynthesis of waterlogged summer maize, and thus increasing grain yield by 39% and 50% for DH605 and ZD958, respectively, compared to waterlogging treatments.

Quality and Field Growth Characteristics of Hydroponically Grown Long‐Mat Seedlings

Looming labor shortages and lower efficiency demand a shift from the cultivation of seedlings via the traditional nutritive soil method (CK) to hydroponically grown long‐mat seedlings (HLMS), a new method of raising rice (Oriza sativa L.) seedlings. This study was conducted to investigate the seedling quality and field growth characteristics of HLMS. We examined the effect of HLMS on seedling quality, mechanical transplantation quality, field growth characteristics, yield and benefit/cost ratio compared with those of CK (as a control). A widely grown conventional japonica rice cultivar (Wuyunjing24) and an indica hybrid rice cultivar (6Liangyou9368) were used as test material. The HLMS and CK showed no significant differences in weight/height ratio, seedling emergence rate, N content of leaves or antioxidant enzyme activities after transplantation; however, HLMS exhibited a more vigorous root system, a significantly decreased leaf area index and an extended transplantation period. The mechanical transplantation quality of HLMS was similar to that of CK but showed a significantly improved force of root entanglement. Compared with CK, the dry matter accumulation of HLMS differed quite low at the early field growth stage, whereas increased rapidly at the late growth stage. The yield and benefit/cost ratio of HLMS were equivalent or superior to those of CK. Briefly, the seedling quality of HLMS was better than that of the control, and its mechanical transplantation quality was comparable to that of the CK, enabling high‐yield and high‐efficiency rice production.Core Ideas Hydroponically grown long‐mat rice seedlings is a novel seedling cultivation method that reduces labor costs and improves efficiency. The force of root entanglement of hydroponically grown long‐mat rice seedlings was significantly improved. The yield and benefit/cost ratio of hydroponically grown long‐mat rice seedlings were equivalent or superior to those of the control.

Dano por Granizo na Cultura da Soja em Condições de Lavoura: Um Estudo de Caso

Resumo O objetivo deste trabalho foi quantificar os danos causados por um evento de granizo sobre uma lavoura comercial de soja. O evento de granizo ocorreu no município de Água Santa, no Estado do Rio Grande do Sul, durante o ano agrícola de 2013/2014. Foram realizadas avaliações da matéria seca do limbo foliar, pecíolo, legume e do índice de área foliar. Tais medições foram obtidas em data anterior e posterior ao evento de granizo que ocorreu no dia 08/02/2014. Com o auxílio de imagens de satélites e de radar foi possível identificar a intensidade do evento e a presença de granizo nas nuvens. Os danos provocados pelo granizo na cultura da soja foram: a redução da matéria seca nos limbos foliares (0,13 Mg ha−1), nos pecíolos (0,01 Mg ha−1) e nos legumes (0,002 Mg ha−1) das plantas da lavoura; o decréscimo no índice de área foliar de 7 a 34%; e a quebra do ápice de crescimento em 32% das plantas do experimento. Possivelmente, devido a esta redução na massa seca, houve diminuição na produtividade de soja da lavoura. As imagens de satélite e de radar podem ser ferramentas para auxiliar os extensionistas na determinação dos danos de granizo nas lavouras de soja.

Effects of spraying exogenous hormone 6-benzyladenine (6-BA) after waterlogging on grain yield and growth of summer maize

Cytokinin is known to be involved in the regulation of plant responses to counteract the adverse effects of stress conditions. This work investigated the effects of exogenous spraying of 6-benzyladenine (6-BA) after water logging for 6 days at the third leaf stage (V-3WL+BA) and the sixth leaf stage (V-6WL+BA) on grain yield and growth of summer maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958), which are planted most popularly in China. Waterlogging under field conditions delayed the growth process, decreased leaf area index, chlorophyll content and dry matter accumulation, resulted in a significant reduction of grain yield with a decrease of 30.30% and 18.78% under V-3WL (water logging for 6 days at the third leaf stage) and V-6WL (waterlogging for 6 days at the sixth leaf stage) of DH605, 30.39% and 21.38% under V-3WL and V-6WL of ZD958, respectively, compared to the control (CK). By contrast, exogenous application of 6-BA effectively alleviated the adverse effects of waterlogging on summer maize by delaying leaf senescence, increasing chlorophyll content and improving photosynthetic performance. At tasseling stage, the Pn of V-3WL+BA and V-6WL+BA in DH605 increased by 9.57% and 8.38%, respectively, compared to that of V-3WL and V-6WL, while the corresponding values for ZD958 increased by 2.96% and 4.05%, respectively. Those responses are conducive to the accumulation of photosynthetic products, increasing grain filling rate, and improving ear character, and then leading to increase grain yield of summer maize. Grain yield of DH605 under V-3WL+BA and V-6WL+BA increased by 15.57% and 12.39%, respectively, compared to that of V-3WL and V-6WL, while the corresponding values for ZD958 increased by 20.05% and 15.32%, respectively. Clearly, spraying exogenous 6-BA could effectively improve grain-filling characteristics and photosynthesis of waterlogged summer maize, resulting in a significant increase of grain yield, compared to water logging treatments.

Water deficit stress tolerance in chickpea is mediated by the contribution of integrative defence systems in different tissues of the plant.

Drought induces heavy yield losses in chickpea (Cicer arietinum L.). Besides understanding the physiological and biochemical parameters contributing to drought tolerance, we need to understand the importance of one tissue in combatting drought stress-induced oxidative stress and influencing the antioxidative defence system in other tissues. The study was conducted to examine the influence of drought stress conditions on the antioxidative defence system and physiology in different tissues such as roots, leaves, nodules, pod walls and seeds at various vegetative and reproductive growth stages in two chickpea cultivars differing in rooting behaviour: ICC4958 (deep rooted) and ILC3279 (shallow rooted). The traits contributing to drought tolerance in ICC4958 were increased root area, decreased leaf area index or increase in root area, decreased leaf area; ILC3279 displayed a decrease in root area and an increase in LAI. The adaptation of ICC4958 was also accompanied by biochemical adjustments, like increases in antioxidative enzymes (superoxide dismutase, peroxidase, ascorbate peroxidase, glutathione reductase and catalase) and nonenzymatic antioxidants (ascorbic acid, proline and stress-induced proteins). However, increases in antioxidant enzymes, nonenzymatic antioxidants and proteins in ILC3279 were lower than in ICC4958. The lower malondialdehyde content and membrane permeability index in ICC4958 might be responsible for reduced damage under drought stress. Increased H2O2 content in ICC4958 was related to enhanced antioxidative defence, emphasising its role as a signalling molecule under stress. This is the first study conducted on drought stress-induced enzymatic and nonenzymatic antioxidative defence systems in underground, aboveground vegetative and reproductive tissues in chickpea cultivars differing in rooting behaviour.

Influence of seed priming and water stress on selected physiological traits of borage

Abstract Borage is a valuable medicinal plant with various constituents in leaves, flowers and seeds. Hence, it is important to improve the performance of this medicinal plant under different environmental conditions. Thus, two field experiments were arranged as split-plots based on a RCB design with three replications in 2012 and 2013, to evaluate the effects of seed priming and different irrigation intervals on selected physiological properties of borage leaves. Irrigation intervals (irrigation after 60, 90, 120, 150 mm evaporation from Class A pans, respectively) and priming treatments (control, water, KNO3 and KH2PO4) were allocated to the main and sub plots, respectively. The chlorophyll content index was enhanced under limited irrigation treatments, mainly due to a decrease in leaf area index and intercepting more radiation. However, the membrane stability index was stable under different irrigation intervals. Decreased relative water content and leaf area index and increased leaf temperature under lower water availability led to some reductions in the grain yield of borage. All of the priming techniques, particularly hydro-priming, enhanced the seedling emergence rate, leaf area index and consequently grain yield per unit area. Therefore, seed hydro-priming can be used to improve the field performance of borage, particularly when sufficient water is available.

Sowing date and weed competition effects on growth, phenology and yield of three white bean (Phaseolus vulgaris L.) cultivars

Suitable sowing date and weed management are the most important factors in crop production. In order to study the effect of sowing date and weed competition on some ecophysiological traits of different white bean cultivars a factorial experiment based on randomized complete block design with three replications was carried out in 2009 in Semirom, Iran. The treatments consisted of three sowing dates (May10, May 25 and June 9) and three white bean cultivars (Shekoofa, Pak and Daneshkade) and two levels of weed infestation (weedy and weed free). Result showed that earlier sowing date, due to longer growing season, increased height, number of branches, number of days from sowing to flowering and the flowering period. The most leaf area index, leaf area duration and crop growth rate was obtained in May 10 sowing date. Weed interference significantly decreased leaf area index (41.6%), leaf area duration (37.7%) and crop growth rate (37.3%). Yield loss due to weed competition was more in later sowing dates than others. Shekoofa cultivar had higher grain yield because of higher leaf area index, more leaf area duration and more crop growth rate.

Forest response to increased disturbance in the central Amazon and comparison to western Amazonian forests

Abstract. Uncertainties surrounding vegetation response to increased disturbance rates associated with climate change remains a major global change issue for Amazonian forests. Additionally, turnover rates computed as the average of mortality and recruitment rates in the western Amazon basin are doubled when compared to the central Amazon, and notable gradients currently exist in specific wood density and aboveground biomass (AGB) between these two regions. This study investigates the extent to which the variation in disturbance regimes contributes to these regional gradients. To address this issue, we evaluated disturbance–recovery processes in a central Amazonian forest under two scenarios of increased disturbance rates using first ZELIG-TROP, a dynamic vegetation gap model which we calibrated using long-term inventory data, and second using the Community Land Model (CLM), a global land surface model that is part of the Community Earth System Model (CESM). Upon doubling the mortality rate in the central Amazon to mirror the natural disturbance regime in the western Amazon of ∼2% mortality, the two regions continued to differ in multiple forest processes. With the inclusion of elevated natural disturbances, at steady state, AGB significantly decreased by 41.9% with no significant difference between modeled AGB and empirical AGB from the western Amazon data sets (104 vs. 107 Mg C ha−1, respectively). However, different processes were responsible for the reductions in AGB between the models and empirical data set. The empirical data set suggests that a decrease in wood density is a driver leading to the reduction in AGB. While decreased stand basal area was the driver of AGB loss in ZELIG-TROP, a forest attribute that does not significantly vary across the Amazon Basin. Further comparisons found that stem density, specific wood density, and basal area growth rates differed between the two Amazonian regions. Last, to help quantify the impacts of increased disturbances on the climate and earth system, we evaluated the fidelity of tree mortality and disturbance in CLM. Similar to ZELIG-TROP, CLM predicted a net carbon loss of 49.9%, with an insignificant effect on aboveground net primary productivity (ANPP). Decreased leaf area index (LAI) was the driver of AGB loss in CLM, another forest attribute that does not significantly vary across the Amazon Basin, and the temporal variability in carbon stock and fluxes was not replicated in CLM. Our results suggest that (1) the variability between regions cannot be entirely explained by the variability in disturbance regime, but rather potentially sensitive to intrinsic environmental factors; or (2) the models are not accurately simulating all tropical forest characteristics in response to increased disturbances.

Spectral anisotropy of subtropical deciduous forest using MISR and MODIS data acquired under large seasonal variation in solar zenith angle

Recent studies in Amazonian tropical evergreen forests using the Multi-angle Imaging SpectroRadiometer (MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS) have highlighted the importance of considering the view-illumination geometry in satellite data analysis. However, contrary to the observed for evergreen forests, bidirectional effects have not been evaluated in Brazilian subtropical deciduous forests. In this study, we used MISR data to characterize the reflectance and vegetation index anisotropies in subtropical deciduous forest from south Brazil under large seasonal solar zenith angle (SZA) variation and decreasing leaf area index (LAI) from the summer to winter. MODIS data were used to observe seasonal changes in the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI). Topographic effects on their determination were inspected by dividing data from the summer to winter and projecting results over a digital elevation model (DEM). By using the PROSAIL, we investigated the relative contribution of LAI and SZA to vegetation indices (VI) of deciduous forest. We also simulated and compared the MISR NDVI and EVI response of subtropical deciduous and tropical evergreen forests as a function of the large seasonal SZA amplitude of 33°. Results showed that the MODIS-MISR NDVI and EVI presented higher values in the summer and lower ones in the winter with decreasing LAI and increasing SZA or greater amounts of canopy shadows viewed by the sensors. In the winter, NDVI reduced local topographic effects due to the red-near infrared (NIR) band normalization. However, the contrary was observed for the three-band EVI that enhanced local variations in shaded and sunlit surfaces due to its strong dependence on the NIR band response. The reflectance anisotropy of the MISR bands increased from the summer to winter and was stronger in the backscattering direction at large view zenith angles (VZA). EVI was much more anisotropic than NDVI and the anisotropy increased from the summer to winter. It also increased from the forward scatter to the backscattering direction with the predominance of sunlit canopy components viewed by MISR, especially at large VZA. Modeling PROSAIL results confirmed the stronger anisotropy of EVI than NDVI for the subtropical deciduous and tropical evergreen forests. PROSAIL showed that LAI and SZA are coupled factors to decrease seasonally the VIs of deciduous forest with the first one having greater importance than the latter. However, PROSAIL seasonal variations in VIs were much smaller than those observed with MODIS data probably because the effects of shadows in heterogeneous canopy structures or/and cast by emergent trees and from local topography were not modeled.

English

Sunflower is one of the most cultivated oil crops in the world. In Middle East environments where water deficit frequently occurs, tolerant cultivars and irrigation are used to overcome environmental constraints due to water scarcity. Since, in the literature, the data on the effect of these techniques on morphological and physiological characteristics of sunflower are scarce and contrasting, the aim of this paper was to evaluate the effect of the water deficit stress on morphological and physiological characteristics of sunflower hybrids in a Middle East environment. For this purpose, four hybrids (Azargol, Alstar, Hysun 33 and Hysun 25) sowed under three water regimes [normal irrigation, mild water deficit stress (WD2) and intense water deficit stress (WD3)] in 2009. The results of this study indicated that the highest and least seed yield in normal irrigation was found on Azargol (3448 kg ha-1) and Hysun 25 (1688 kg ha-1), respectively. However, in the mild and intense water stress conditions the seed yield with cultivar Alstar having the highest value (2121 and 829 kg ha-1, respectively) and Azargol and Hysun 33 had the lowest value (893 and 263 kg ha-1, respectively). The result of this study indicated that application of WD2 and WD3 caused a decrease in leaf area index (LAI) and total dry weight (TDW) of all sunflower hybrids that are studied in this research.   Key words: Sunflower, morphology, physiology, leaf area index (LAI), water deficit stress.

Diversity decrease of ant (Formicidae, Hymenoptera) after a forest disturbance: different responses among functional guilds

Abstract Background Disturbance is one of the main causes for determining diversity of natural communities. A 3-year (2003 to 2005) monitoring of ant communities at a Long-Term Ecological Research (LTER) site in South Korea revealed a drop of ant diversity due to a forest disturbance which was evidenced by decrease of leaf area index (LAI) associated with the dropping of tree branches. In order to determine the process of the decrease in diversity, we compared the annual change of functional ant guilds, which are composed of forest ground foragers (FGF), forest vegetation foragers (FVF), soil and litter dwellers (SLD), and open-land foragers (OF). Results Four functional guilds of ants responded differently to the forest disturbance; FGF and SLD decreased, but OF and FVF increased. Species richness decreased, due to the decrease in SLD, and species evenness decreased mainly due to a sudden increase in an OF species, Formica japonica. Based on these findings, a mechanism is proposed for the decrease in ant diversity after the forest disturbance. Conclusions Ant communities responded significantly to even a slight forest disturbance of branch dropping with decrease in diversity and change in functional guild structures.