Amount Of Photosynthetically Active Radiation Research Articles

Calculations of Arctic Ice‐Ocean Interface Photosynthetically Active Radiation (PAR) Transmittance Values

AbstractSea ice algae play an important role in the Arctic Ocean ecosystem, driving primary production in the spring and sequestering carbon to the deep ocean. Up to 45% of Arctic Ocean primary production occurs in ice‐covered areas; photosynthetically active radiation (PAR) is fundamental to driving this production. Sea ice, and particularly snow, strongly scatter and reflect light, reducing the amount of PAR transmitted to the ice‐ocean interface. The effect that varying thicknesses of sea ice (0.2–3.5 m) and snow (0.01–1 m) have on the value of PAR transmittance at the ice‐ocean interface are considered for a Winter, Spring, and Summer scenario. When characteristic Arctic Ocean conditions (2 m sea ice and ∼0.2 m snowpack) are modeled, there is roughly a two‐fold difference in PAR transmittance at the ice‐ocean interface between the Winter (0.003) and Spring (0.007) scenarios and an order of magnitude difference with the Summer scenario (0.04). The modeled values correlate within one standard deviation of measured values and show good agreement with extended pan‐Arctic Ocean field campaign measurements. The results also indicate that simple exponential decay methods may lead to inaccurate results, and radiative‐transfer modeling is required to accurately predict PAR transmittance at the ice‐ocean interface. Therefore, this study offers a novel mathematical technique to predict the value of PAR transmittance at the ice‐ocean interface. Coupled with year‐round near‐real‐time sea ice and snow thickness remote sensing data, this technique may improve understanding of primary production and carbon budgets in the changing Arctic Ocean.

Use of data-driven models to analyse the habitat preferences of the leaping grey mullet (Chelon saliens, Risso, 1810) in the Caspian Sea

Identifying the most important independent environmental variables affecting the habitat preferences of marine fish species is very important for a proper and effective fisheries management in marine ecosystems. Classification tree (CT) and support vector machine (SVM) were implemented to examine the habitat preferences of the leaping grey mullet (Chelon saliens) in various sampling locations situated in the southern part of the Caspian Sea. The CT model (with the highest level of pruning) confirmed that the deepest part of the sea may not provide a favourite place to the fish population, while the probability of fish presence may increase with high photosynthetically active radiation (PAR). Based on the model’s decision, increasing the sand percentage (SP) may lead to the decrease of the presence of suitable conditions for the mullet population. The outcomes of SVM model (in terms of the attribute weight) also demonstrated that the deepest part of sea and high SP may restrict the potential area of the fish population. On the contrary, an increase in the amount of PAR, sea surface temperature (SST) and sea level anomaly (SLA) may lead to an increase in the presence of fish. The attribute weight of SVM model also showed that total organic matter (TOM), sediment type, sea surface chlorophyll-a (chla) and benthic biomass had a low contribution to the mullet’s prediction. Both models, thus, identified the most important variables influencing the habitat preferences of the mullet. Determining the key variables influencing the habitat preferences of the fish allows to identify the mullet’s feeding behaviour in the sea. The identified variables can be valuable for evaluating the habitat preferences of the mullet species in other coastal tropical and temperate ecosystems worldwide with similar and comparable ecological patterns as the Caspian Sea.

Light interception and radiation use efficiency in quinoa (Chenopodium quinoa Willd.)

AbstractQuinoa (Chenopodium quinoa Willd.) is an annual plant belonging to the Amaranthaceae family. The total accumulated incident photosynthetic active radiation (PAR) in a plant is a function of the site, year, sowing date, and phenology, whereas the amount of PAR intercepted by the plant is dependent on its leaf area index (LAI) and light extinction coefficient (KPAR). This study investigated changes in KPAR and radiation use efficiency (RUE) levels in quinoa before and after inflorescence (fruit set) color change under various temperature and light conditions through the sowing date. This study was conducted in the Jihad Keshavarzi allocated field of Khalilabad city in Khorasan Razavi province, Iran, using a randomized complete block design with three replications over two seasons, 2017–2018 and 2018–2019. Treatments included eight and seven sowing dates in the first and second season years, respectively. The results showed that the mean of KPAR was 0.66 and 0.31 in the first and second years, respectively. Also RUE in vegetative stages of development was higher than during the grain‐filling period. The mean of RUE was 2.60 ± 0.06 and 0.78 ± 0.17g/MJ in the first year before and after changing the color of the inflorescence (fruit set), respectively; these values were 2.12 ± 0.04 and 1.01 ± 0.61 g/MJ in the second year. The results indicated the base (TBRUE), lower optimum (TP1RUE), upper optimum, and ceiling temperatures of quinoa for RUE were determined to be 3, 18.8, 25.5, and 35°C, respectively.

Trends and variations in the activity of global vegetation in response to climate variability between 1987 and 1997

Eleven-year (1987-1997) time series data of remotely sensed vegetation index (NDVI) and meteorological observations (temperature, precipitation, cloud cover and relative humidity) provided a powerful tool to illuminate the response of global terrestrial vegetation to short-and long-term climate variability. NDVI being a sensitive estimator of the amount of photosynthetic active radiation intercepted by the canopy has been treated as a proxy for above ground net primary production (ANPP). Analyses of trends, multiple regression and correlation analyses were employed. The main result indicates a considerable increase (0.7~1.9%/year) of monthly vegetation production in all ecosystems over the investigated period, allied with an analogous increase (0.9~15%/year) in precipitation. Additionally, several direct relationships were also observed on the intra- and inter-annual time scales suggesting that the increase and variation of ANPP in most biomes could be mainly linked to the corresponding increase and variation in precipitation. Overall, the four climate variables play a considerable role in the inter-annual variability of ANPP of global vegetation.

High density orcharding and canopy management of some tropical and subtropical fruits

High density planting (HDP) is a highly efficient and advanced production system of fruit cultivation. In most of the temperate tree and nut crops it is now commercially followed all over the world because of availability of suitable dwarfing rootstock to control tree vigor. Major tropical fruit crops are either propagated by suckers (banana, pineapple), seed (papaya) or by layering (guava) and grafting (mango). The use of dwarfing rootstocks, as in many temperate tree fruits, is not possible/available in most of the commercial tropical fruits for high density planting. High density planting is one of the novel methods to achieve high productivity per unit area both in short duration and perennial horticultural crops. High yield and high fruit quality can be achieved with a high-density orchard when the orchard has good light distribution throughout the tree canopy and there is a balance between vegetative growth and cropping. Many variables must be included in making a decision about spacing. Tree vigor and growth habit as influenced by cultivar and rootstock (where it could be utilized) are important. The ultimate limit on productivity of any crop is the amount of photosynthetically-active radiation (PAR) intercepted. Much of the planning that goes into the design of HDP orchards is actually based on average light interception over the life of the planting. This involves both minimizing the amount of light which strikes the ground and providing canopy structures in which the largest amount of canopy receives optimum light intensity. A tree with a large portion of its volume devoted to bearing has a greater potential for productivity than one with most of its volume devoted to tree support, middles or other functions. In India, HDP has been proved useful in many tropical and subtropical fruit crops e.g., mango, citrus, pineapple, banana, guava litchi, and papaya. The productivity of fruit crops depends on several factors, poor management of canopy architecture being the most important one. The fruiting potential of the trees is largely governed by their architecture, canopy density and photosynthetic efficiency. Canopy in a fruit tree refers to its physical composition comprising of the stem, branches, shoots and leaves. While, the canopy density is determined by the number, length and orientation of stem, branches and shoots. Tree canopy management, especially size control has become a priority for reducing production cost and increasing fruit yield and quality. The objective of canopy management is to optimize the plant model in such a way so that it may intercept maximum light by tree training, pruning, branch and tree orientation. Some of the basic principles in canopy management are: maximum utilization of the light, avoidance of the buildup of micro-climate congenial for the diseases and pests, convenience in carrying out the cultural operations, maximizing the productivity and quality and economy in obtaining the required canopy architecture.

Factors affecting potential for Palmer amaranth (Amaranthus palmeri) suppression by winter rye in Georgia, USA

Herbicide resistant Palmer amaranth (Amaranthus palmeri) has rapidly become a dominant weed management issue in agronomic crops of the Southeast US. The small size of Palmer amaranth seeds, relative to other common weeds, provides an opportunity to use physical weed control through high-biomass, rolled cover crop mulches, in conjunction with herbicide tools. Experiments were conducted to characterize Palmer amaranth suppression and light permeability from a range of rye biomass levels. There was an inverse relationship between Palmer amaranth emergence and rye biomass that was described by a log-logistic regression model. In the absence of rye, there was approximately 80% Palmer amaranth emergence, while the highest rate of rye biomass prevented Palmer amaranth emergence. A log-logistic regression model also described the amount of photosynthetic active radiation transmitted through rye mulch in a green house experiment. The highest level of rye biomass reduced the amount of light to 13% of full sunlight, while 5370kgha−1 of rye caused a 50% reduction of light transmission; a similar level of rye biomass (P=0.93) reduced Palmer amaranth emergence by 50%. Effective suppression of Palmer amaranth will depend upon the ability to produce high-biomass rye. Field experiments evaluated changes in planting date, seeding rate, and nitrogen application on rye biomass production. Maximum rye biomass in April occurred when rye was planted prior to middle-November. However, a 50% reduction in rye biomass resulted from middle-December planting of rye, providing growers with a short planting interval for high-biomass rye production. Additionally, rye seeding rate did not increase rye biomass accumulation indicating that delays in autumn sowing cannot be overcome with plant density. Finally, nitrogen fertilizer applied at planting consistently increased rye biomass production 23–33% relative to non-fertilized controls averaged over all planting dates. Additional research is needed to evaluate how repeated high-biomass cover crop systems affect weed management systems, other pest complexes, and soil moisture status in the sandy soils of the southeast Coastal Plain.

Obnova lesa pod výstavky dubu letního (Quercus robur L.)

Work objective was to establish reasons to the impaired vitality of woody and herbaceous vegetation growing under standards of pedunculate oak (Quercus robur L.). The paper analyzes the influence of insolation, root competition, soil moisture content and chemical composition of soil on the growth of pedunculate oak seedlings under standards. The analyses included three standards of pedunculate oak aged over 150 years, growing at an altitude of 160 m a.s.l. Controls were plots occurring at a distance of 20 m from the standards. Conclusions following out from the analyses are as follows: The number of seedlings emerged under the standards was lower than the number of seedlings emerged in the open area. Shoot height as well as root collar diameter of seedlings under the standards were lower than in the control seedlings. Total cover of herbaceous layer and height of herbs under the standards were lower than in the open area. The impaired vitality of woody and herbaceous vegetation resulted from a great amount of the fine roots of pedunculate oak standards, withdrawing water up to the wilting point. The amount of photosynthetic active radiation (PAR) under the standards was sufficient for the growth of plants.

Hail net cover, cultivar and pod size influence the chemical composition of dwarf French bean

Dwarf French bean is cultivated in the open field, where unpredictable extreme weather events decreased crop yield quality. Hail net protection is therefore desirable. The pods are a rich source of sugars, organic acids and phenolic compounds and, as such, are an important nutritional vegetable. Due to consumer demand for half-sized pods in some traditional cuisines, the chemical profile of both pod sizes are desired. The aim of the study was to determine the effect of hail net covering on microclimatic conditions, specifically on light interception and temperature modification and, consequently, on the chemical profile of bean pods harvested in two sizes. The experiment was treated as a split–split plot designed three factorial experiment in four randomized replications. The main factor ‘covering’, had two levels, (hail net covered and uncovered plots); the sub-factor ‘cultivar’ had four levels, (‘Berggold’, ‘Re dei burri’ ‘Paulista’, ‘Top crop’) and the sub–sub-factor ‘pod size’, had two levels (half-size and full-size pods). Individual sugars and organic acids were analyzed, using high-performance liquid chromatography (HPLC). Total phenolic content was determined by spectrometry. Lighting was measured as the amount of photosynthetic active radiation (PAR). PAR under the hail net was reduced by 30–75% and mean daily temperature by 2.4°C in comparison with the control. Significant genotypic effect was confirmed for vitamin C, while sugars, organic acids and total phenolics are affected mostly by interaction of two or three factors. Higher vitamin C content was found in cultivars classified as anthracnose resistant (‘Berggold’ and ‘Paulista’) compared to not resistant cultivars (‘Re dei burri’ and ‘Top crop’). Covering decreased fructose, glucose and vitamin C contents. Total phenolics were decreased under hail net only in pods of green pod cultivar. Hail net also influenced the composition of individual sugars in yellow pod cultivars (‘Berggold’ and ‘Re dei burri’), with which sweeter pods were harvested, with a higher fructose/glucose ratio. Pod size also significantly affected all chemical compounds analyzed bean pods. Younger half-sized pods had higher fructose and glucose content, as well as malic and citric acids and also total phenolic content, compared to full-sized pods. On the other side, younger pods contain significant lower amount of vitamin C and sucrose compared to older pods. Significant genotypic variation connected with hail net covering observed within yellow pod cultivars, provides opportunities for the plant breeders to develop special genotypes for maximizing the nutraceutical value of bean pods under hail net production.

Estimating hourly variation in photosynthetically active radiation across the UK using MSG SEVIRI data

The amount of photosynthetically active radiation (PAR) reaching the Earth's surface is a key input variable in most gross primary productivity models. However, poor representation of PAR due to large pixel size or limited temporal sampling is one of the main sources of uncertainty in such models. This paper presents a method to estimate PAR at up to 1 km spatial resolution at a regional to global scale. The method uses broadband radiance data (400–1100nm) and per-pixel estimates of relative cloud cover from a geostationary satellite to estimate the amount of PAR reaching the Earth's surface at high spatial and temporal resolution (1–2 km and hourly). The method was validated using data from 54 pyranometers located at sites across the UK. Hourly averaged PAR over the range 400–1400 μmol m−2 s−1 was estimated with a mean bias error = 5.01 μmol m−2 s−1 (R2 = 0.87), providing a source of accurate data for high resolution models of gross primary productivity.

Radiation capture and radiation use efficiency in response to N supply for crop species with contrasting canopies

Nitrogen (N) is a key determinant of plant productivity. A shortage of N can give three responses: (1) reduce leaf area (light capture) and maintain leaf N content (photosynthetic capacity); (2) maintain leaf area and reduce leaf N content; or (3) a combination of these responses. We examined these responses in contrasting crop canopies. Forage rape (C3 dicotyledons), wheat (C3 monocotyledons) and forage sorghum (C4 monocotyledons) were grown with fertiliser N supplies of 0, 50, 100 or 200kgN/ha. Crop biomass, leaf area index (LAI) and photosynthetically active radiation (PAR) interception were measured regularly, while accumulated intercepted PAR and radiation use efficiency (RUE) were calculated. Each crop exhibited distinct functional responses of biomass production to N shortage. For all crops specific leaf N (SLN), RUE, LAI and PAR capture were reduced in response to N shortage. However, the extent of the response differed between species. The SLN and RUE were reduced to a greater extent in forage rape than in wheat. In contrast, the LAI and PAR capture were reduced to a greater extent in wheat than in forage rape. Sorghum was intermediate between these two crops. Leaf inclination could account for these distinct responses – with forage rape's more horizontally inclined leaves, a change in LAI has a much smaller effect on PAR interception compared with wheat and sorghum. Under N shortage the amount of PAR intercepted per unit leaf N increased in forage rape but not in the other two crops. Alternatively leaf structure could account for these distinct responses – forage rape has larger petioles and midribs than wheat. Petioles and midribs have a large N content but only a small area, therefore to achieve given RUE, forage rape requires an extra 1.2gN/m2 leaf than wheat. Therefore the functional response that maximised growth under limited N supply was to reduce SLN and RUE to a greater extent than LAI and PAR interception for forage rape; reduce LAI and PAR interception to a greater extent than SLN and RUE for wheat; and reduce both RUE and LAI for sorghum to a similar extent. These were the observed responses for each species.

UV-B as a Photoacclimatory Enhancer of the Hermatypic Coral <i>Stylophora pistillata</i>

Photoacclimation processes are crucial for the survival of all photosynthetic organisms in the photic zone. Changes in photosynthetic active radiation (PAR) are however simultaneous to changes in UV-B radiation. The influence of UV-B levels on bio-optical and physiological parameters of deep (30 m) corals from the species Stylophora pistillata and their symbiotic algae, zooxanthellae, was examined during their gradual, stepwise acclimation to a shallow depth (3 m). Drastic exposure of deeper corals to higher UV-B levels in shallower depths is usually fatal. Hence, the acclimation process lasted 118 days and included 10 intermediate stations with an addition of similar amount of PAR at each depth transfer. Concomitantly, in an on-shore experiment, fragments from the same colonies were acclimated by changing shading nets corresponding in PAR levels to each in situ station. Since UV-B is attenuated more efficiently than PAR in seawater, the PAR: UV-B ratio changes in the depth experiment while remaining constant under the neutral density nets. This provided the opportunity to evaluate the importance of UV-B to photoacclimation. In both experiments all fragments survived, in spite of a four-fold difference in levels of PAR and a 140-fold difference in UV-B flux between the initial and final conditions. Both experimental designs resulted in reduction of zooxanthellae density, photosynthesis rates, and quantum yields of PSII, while cellular chlorophyll content remained unaffected. Zooxanthellae density and maximal photosynthetic rate was found decreased in correlation with UV-B radiation, whether it was elevated logarithmically with reducing depths or linearly with reducing shades. Conversely, quantum yields of PSII were adjusted according to the enhancement of PAR rather than UV-B. We conclude that UV-B enhances the magnitude of photoacclimation to higher PAR. This novel aspect of photoacclimation can provide the basis for our understanding of the underlying mechanisms that result in UV-related bleaching.

LIGHT TRANSMISSION THROUGH GREENHOUSE COVERS

The selection of the greenhouse covering material is essential for the success of the protected horticultural production, and among the properties of a material (optical, chemical, physical, etc…) the most important for the growers are the optical properties, as they define the amount and quality of solar radiation entering the greenhouse and thus the amount of photosynthetic active radiation (PAR) that will be intercepted by the crop, determining the production of dry biomass. However, there is no such a material that can be considered optimum, in terms of optical properties. Therefore, the grower has to choose a suitable covering material, with the optimum optical properties for its specific growing conditions. The most important covering materials used in horticulture in terms of covered surface in the world are flexible plastic films, glass and different types of screens. The industry is continuously incorporating new optical properties to these materials that may be of interest for the growers depending on their specific growing conditions. In the case of glass recent developments tested in The Netherlands include anti-reflection coatings, to increase the global radiation transmission at low sun radiation incident angles; new glasses have also been tested with different levels of light diffusion with none of minimum loss of global transmission, with very promising results in terms of light use efficiency by the crops, and thus, interesting yield increases. Other types of filters being tested are near infrared filters (absorption or reflection) both in glass and in plastic films, with results that suggest that reflection is preferable and that few materials are available that do not affect PAR transmission too. UV filters have provided very remarkable results in limiting the infestation by pests in plastic films. In the case of screens, a large variability of materials are available (in terms of porosity, colour of the threads, photoselective filters, etc.), and recently have been subject of different studies to understand better the combination of direct transmission of light through the pores and the interaction with the threads of the incoming radiation.

Simulated effects of changes in direct and diffuse radiation on canopy scale isoprene emissions from vegetation following volcanic eruptions

Abstract. Volcanic eruptions can alter the quality of incoming solar irradiance reaching the Earth's surface thereby influencing the interactions between vegetation and the Earth system. Isoprene (C5H8) is a biogenic volatile organic compound emitted from leaves at a rate that is strongly dependent on the received flux of photosynthetically active radiation (PAR). We used a theoretical approach to investigate the potential for volcanic eruptions to change the isoprene flux from terrestrial forests using canopy-scale isoprene emission simulations that vary either the relative or absolute amount of diffuse (Idiff) and direct (Idir) PAR. According to our simulations for a northern hardwood deciduous forest, if the total amount of PAR during summer remains constant while the proportion of Idiff increases, canopy-scale isoprene emissions increase. This effect increases as leaf area index (LAI) increases. Simulating a decrease in the total amount of PAR, and a corresponding increase in Idiff fraction, as measured during the 1992 Pinatubo eruption, changes daily total canopy-scale isoprene emissions from terrestrial vegetation in summertime by +2.8% and −1.4% for LAI of 6 and 2, respectively. These effects have not previously been realized or quantified. Better capturing the effects of volcanic eruptions (and other major perturbations to the atmospheric aerosol content) on isoprene emissions from the terrestrial biosphere, and hence on the chemistry of the atmosphere, therefore may require inclusion of the effects of aerosols they produce on climate and the quality of PAR.

Effect of shading by baobab (Adansonia digitata) and néré (Parkia biglobosa) on yields of millet (Pennisetum glaucum) and taro (Colocasia esculenta) in parkland systems in Burkina Faso, West Africa

An experiment was conducted in Nobere, Burkina Faso to assess the effect of shade of two indigenous fruit trees, Adansonia digitata (Baobab) and Parkia biglobosa (Nere), on a shade-tolerant crop called taro (Colocasia esculenta) in comparison with millet (Pennisetum glaucum) a shade-intolerant crop. Photosynthetically active radiation (PAR) and performance of crops under trees and in the open field were assessed during three cropping seasons. Millet performed better under baobab (806.1 ± 121.48 kg ha−1) compared to the control plot (595.8 ± 83.43 kg ha−1) and nere (320.2 ± 59.91 kg ha−1). In contrast, the yield of taro was higher under nere (4124.0 ± 469.05 kg ha−1) compared to the control plot (2336.9 ± 617.04 kg ha−1) and baobab (2738.3 ± 595.61 kg ha−1). There was a strong relationship between the amount of PAR intercepted by trees and crop yields under trees. As PAR decreased the yield of millet decreased whereas the yield of taro increased. Hence, it was concluded that parkland productivity could be enhanced by cropping taro under nere where light reduction was 83, 56 and 18% in zones A, B and C, respectively. An efficient association of baobab with crops could be the production of taro in zone A and millet in zones B and C where PAR reduction was 62, 38 and 15%, respectively.

Modeling Net Ecosystem Exchange for Grassland in Central Kazakhstan by Combining Remote Sensing and Field Data

Carbon sequestration was estimated in a semi-arid grassland region in Central Kazakhstan using an approach that integrates remote sensing, field measurements and meteorological data. Carbon fluxes for each pixel of 1 × 1 km were calculated as a product of photosynthetically active radiation (PAR) and its fraction absorbed by vegetation (fPAR), the light use efficiency (LUE) and ecosystem respiration (Re). The PAR is obtained from a mathematical model incorporating Earth-Sun distance, solar inclination, solar elevation angle, geographical position and cloudiness information of localities. The fPAR was measured in field using hemispherical photography and was extrapolated to each pixel by combination with the Normalized Difference Vegetation Index (NDVI) obtained by the Vegetation instrument on board the Satellite Pour l’Observation de la Terra (SPOT) satellite. Gross Primary Production (GPP) of the aboveground and belowground vegetation of 14 sites along a 230 km west-east transect within the study region were determined at the peak of growing season in different land cover types and linearly related to the amount of PAR absorbed by vegetation (APAR). The product of this relationship is LUE = 0.61 and 0.97 g C/MJ APAR for short grassland and steppe, respectively. The Re is estimated using complex models driven by climatic data. Growing season carbon sequestration was calculated for the modelling year of 2004. Overall, the short grassland was a net carbon sink, whereas the steppe was carbon neutral. The evaluation of the modelled carbon sequestration against independent reference data sets proved high accuracy of the estimations.

Radiation use efficiency and yield of winter wheat under deficit irrigation in North Chin

Water stress is a frequent and critical limit to wheat (<I>Triticum aestivum</I> L.) production in North China. It has been shown that photosynthetic active radiation (PAR) is closely related to crop production. An experiment was conducted to investigate the effects of deficit irrigation and winter wheat varieties on the PAR capture ration, PAR utilization and grain yield. Field experiments involved Jimai 20 (J; high yield variety) and Lainong 0153 (L; dryland variety) with non-irrigation and irrigated at jointing stage. The results showed that whether irrigated at jointing stage or not, there was no significant difference between J and L with respect to the amount of PAR intercepted by the winter wheat canopies. However, significant differences were observed between the varieties with respect to the amount of PAR intercepted by plants that were 60–80 cm above the ground surface. This result was mainly caused by the changes in the vertical distributions of leaf area index (LAI). As a result, the effects of the varieties and deficit irrigation on the radiation use efficiency (RUE) and grain yield of winter wheat were due to the vertical distribution of PAR in the winter wheat canopies. During the late growing season of winter wheat, irrespective of the irrigation regime, the RUE and grain yield of J were significantly (LSD, <I>P</I> < 0.05) higher than those of L. These results suggest that a combination of deficit irrigation and a suitable winter wheat variety should be applied in North China.

Light distribution, photosynthetic rate and yield in a Paulownia-wheat intercropping system in China

Measurements of photosynthetically active radiation (PAR), leaf photosynthesis, canopy leaf area index (LAI) and crop yield were carried from flowering to maturity to study the effects of tree shading on crop yield in a Paulownia-wheat intercropping system in China. We found that the tree shading reduced the amount of incoming PAR within the intercropping system by 22%, 44% and 56% during flowering, grain-filling and maturing, respectively. The amount of PAR intercepted by the wheat crop inside the intercropping system was 34%, 55% and 68% less than the crop outside the intercropping system during flowering, grain-filling and maturing. Estimates of PAR-saturated leaf photosynthetic rate were not affected by tree shading, and the differences between the wheat yield inside the intercropping system and outside the intercropping system can be explained by the difference in the amount of PAR intercepted. Total grain numbers and grain dry weight per 1000 grains were linearly correlated with the amount of PAR intercepted during 7 days prior to anthesis and during anthesis and grain-filling, respectively. As compared with the wheat crop outside the intercropping system, grain numbers and grain dry weight were reduced by 36% and 25%, respectively. As a result wheat yield inside the intercropping system was 51% lower than that outside the intercropping system. Our results suggest a much higher reduction in crop yield and much smaller economic gain of the Paulownia-wheat intercropping system than previous studies on the similar Paulownia-wheat intercropping systems in China.

Effects of irrigation and planting patterns on radiation use efficiency and yield of winter wheat in North China

The factor limiting the increase in winter wheat yield was not the deficiency of light radiation but the low radiation use efficiency (RUE). In 2004–2005 and 2005–2006, an experiment was conducted at the Agronomy Station of Shandong Agricultural University to study the effects of irrigation and different planting patterns on the photosynthetic active radiation (PAR) capture ratio, PAR utilization, and winter wheat yield. In this experiment, winter wheat was planted in four patterns as follows: uniform row planting (U; row spacing, 30 cm), “20 + 40” wide-narrow row planting (W), “20 + 40” furrow planting (F), and “20 + 40” bed planting (B), which are very popular in North China. The results showed that under different irrigation regimes, there was no significant difference (less than 15.93%) between any of the planting patterns with respect to the amount of PAR intercepted by the winter wheat canopies. However, significant differences were observed between different planting patterns with respect to the amount of PAR intercepted by plants that were 60–80 cm above the ground surface (53.35–225.16%). This result was mainly due to the changes in the vertical distributions of leaf area index (LAI). As a result, the effects of the planting patterns on RUE and the winter wheat yield were due the vertical distribution of PAR in the winter wheat canopies. During the late winter wheat growing season, irrespective of the applied irrigation, the RUE in case of F was higher than that in case of U, W, and B by 0.05–0.09, 0.04–0.08, and 0.02–0.12 g/mol, respectively, and the yield was higher by 238.39–693.46, 160.02–685.96, and 308.98–699.06 kg/ha, respectively. Only under the fully irrigated conditions, the RUE and winter wheat yield significantly (LSD; P < 0.05) increased in case of B. This experiment showed that in North China, where the water shortage is the highest, application of planting pattern B should be restricted. Instead, F should be used in combination with deficit irrigation to increase the RUE and grain yield of winter wheat.

Radiative transfer, interception and scattering in coniferous forests: models and applications for production ecology and remote sensing

This work develops methods to account for shoot structure in models of coniferous canopy radiative transfer. Shoot structure, as it varies along the light gradient inside canopy, affects the efficiency of light interception per unit needle area, foliage biomass, or foliage nitrogen. The clumping of needles in the shoot volume also causes a notable amount of multiple scattering of light within coniferous shoots. The effect of shoot structure on light interception is treated in the context of canopy level photosynthesis and resource use models, and the phenomenon of within-shoot multiple scattering in the context of physical canopy reflectance models for remote sensing purposes. Light interception. A method for estimating the amount of PAR (Photosynthetically Active Radiation) intercepted by a conifer shoot is presented. The method combines modelling of the directional distribution of radiation above canopy, fish-eye photographs taken at shoot locations to measure canopy gap fraction, and geometrical measurements of shoot orientation and structure. Data on light availability, shoot and needle structure and nitrogen content has been collected from canopies of Pacific silver fir (Abies amabilis (Dougl.) Forbes) and Norway spruce (Picea abies (L.) Karst.). Shoot structure acclimated to light gradient inside canopy so that more shaded shoots have better light interception efficiency. Light interception efficiency of shoots varied about two-fold per needle area, about four-fold per needle dry mass, and about five-fold per nitrogen content. Comparison of fertilized and control stands of Norway spruce indicated that light interception efficiency is not greatly affected by fertilization. Light scattering. Structure of coniferous shoots gives rise to multiple scattering of light between the needles of the shoot. Using geometric models of shoots, multiple scattering was studied by photon tracing simulations. Based on simulation results, the dependence of the scattering coefficient of shoot from the scattering coefficient of needles is shown to follow a simple one-parameter model. The single parameter, termed the recollision probability, describes the level of clumping of the needles in the shoot, is wavelength independent, and can be connected to previously used clumping indices. By using the recollision probability to correct for the within-shoot multiple scattering, canopy radiative transfer models which have used leaves as basic elements can use shoots as basic elements, and thus be applied for coniferous forests. Preliminary testing of this approach seems to explain, at least partially, why coniferous forests appear darker than broadleaved forests in satellite data.

Impacts of aerosols and clouds on forest‐atmosphere carbon exchange

The impact of aerosols and clouds on CO2 uptake and water use efficiency at Harvard Forest has been studied by using collocated turbulent flux and radiation measurements. Measurements of a multifilter narrowband radiometer provide both direct and diffuse components of photosynthetically active radiation (PAR) by product integrals of synthesized spectra, with a normalized action spectrum for canopy photosynthesis. Optical properties of aerosols and clouds are also retrieved from the radiometer data. Optical properties of aerosols and clouds have significant impacts on photosynthesis not only through changes of the total amount of PAR but also through changes of its spectral distribution (or light quality) and its partitioning between direct and diffuse components. The diffuse PAR is much greater under patchy/thin cloud conditions than under aerosol conditions for a given optical depth. The “diffuse radiation use efficiency” coefficients are 3.40 and 1.95 for patchy/thin clouds and aerosols, respectively. Furthermore, the radiation use efficiency of CO2 uptake under clouds which completely block direct beam solar (optically thick clouds) is approximately 57 and 13% higher than under aerosol and patchy/thin clouds, respectively. The water use efficiency also showed significant enhancement as atmospheric conditions changed from aerosols, to patchy/thin clouds, and then to clouds opaque to direct solar radiation. Under optically thick cloud conditions the water use efficiency is almost 5 and 3 times greater than under aerosol and patchy/thin cloud conditions, respectively. These indicate that an increase of diffuse radiation may not be the only factor responsible for the enhancement of carbon assimilation under cloudy conditions. Changes in many other factors, such as temperature, moisture, latent heating, and precipitation, in the presence of clouds may have both direct and indirect influences on carbon assimilation.