Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    The fertilization effect of global dimming on crop yields is not attributed to an improved light interception
    Shao, Liping ; Li, Gang ; Zhao, Qiannan ; Li, Yabing ; Sun, Yutong ; Wang, Weinan ; Cai, Chuang ; Chen, Weiping ; Liu, Ronghua ; Luo, Weihong ; Yin, Xinyou ; Lee, Xuhui - \ 2020
    Global Change Biology 26 (2020)3. - ISSN 1354-1013 - p. 1697 - 1713.
    acclimation - diffuse radiation - fertilization effect - global dimming - radiation use efficiency - rice - wheat - yield

    Global dimming, a decadal decrease in incident global radiation, is often accompanied with an increase in the diffuse radiation fraction, and, therefore, the impact of global dimming on crop production is hard to predict. A popular approach to quantify this impact is the statistical analysis of historical climate and crop data, or use of dynamic crop simulation modelling approach. Here, we show that statistical analysis of historical data did not provide plausible values for the effect of diffuse radiation versus direct radiation on rice or wheat yield. In contrast, our field experimental study of 3 years demonstrated a fertilization effect of increased diffuse radiation fraction, which partly offset yield losses caused by decreased global radiation, in both crops. The fertilization effect was not attributed to any improved canopy light interception but mainly to the increased radiation use efficiency (RUE). The increased RUE was explained not only by the saturating shape of photosynthetic light response curves but also by plant acclimation to dimming that gradually increased leaf nitrogen concentration. Crop harvest index slightly decreased under dimming, thereby discounting the fertilization effect on crop yields. These results challenge existing modelling paradigms, which assume that the fertilization effect on crop yields is mainly attributed to an improved light interception. Further studies on the physiological mechanism of plant acclimation are required to better quantify the global dimming impact on agroecosystem productivity under future climate change.

    Narrow-wide-row planting pattern increases the radiation use efficiency and seed yield of intercrop species in relay-intercropping system
    Raza, Muhammad Ali ; Feng, Ling Yang ; Werf, Wopke van der; Cai, Gao Ren ; Khalid, Muhammad Hayder Bin ; Iqbal, Nasir ; Hassan, Muhammad Jawad ; Meraj, Tehseen Ahmad ; Naeem, Muhammd ; Khan, Imran ; Ur Rehman, Sana ; Ansar, Muhammad ; Ahmed, Mukhtar ; Yang, Feng ; Yang, Wenyu - \ 2019
    Food and Energy Security 8 (2019)3. - ISSN 2048-3694
    competition - intercropping - land equivalent ratio - radiation use efficiency

    Planting arrangements affect radiation use efficiency (RUE) and competitiveness of intercrop species in intercropping systems. Here, we reveal that narrow-wide-row planting arrangement in maize-soybean relay-intercropping system increases the dry matter and competitiveness of soybean, increased the RUE of maize and soybean, and compensates the yield loss of maize by substantially increasing the yield of soybean. In this field study, maize was planted with soybean in different planting arrangements (P1, 20:180, P2, 40:160; P3, 60:140, and P4, 80:120) of relay intercropping, all the relay-intercropping treatments were compared with sole crops of maize (SM) and soybean (SS). Results showed that P1 improved the total RUE 3.26 g/MJ (maize RUE + soybean RUE) of maize and soybean in relay-intercropping system. Compared to P4, treatment P1 increased the soybean competition ratio (CR) values (by 55%) but reduced the maize CR values (by 29%), which in turn significantly improved the yield of soybean by maintaining the maize yield. Generally, in P1, soybean produced 82% of SS yield, and maize produced 88% of SM yield, and it achieved the land equivalent ratio of 1.7. These results suggest that by maintaining the appropriate planting distances between maize and soybean we can improve the competitiveness and yield of intercrop species in relay-intercropping system.

    Understanding the productivity of cassava in West Africa
    Ezui, Kodjovi Senam - \ 2017
    Wageningen University. Promotor(en): Ken Giller, co-promotor(en): Linus Franke; A. Mando. - Wageningen : Wageningen University - ISBN 9789463430470 - 183
    manihot esculenta - cassava - crop production - rainfed agriculture - drought - crop yield - water use efficiency - radiation use efficiency - fertilizers - togo - ghana - west africa - manihot esculenta - cassave - gewasproductie - regenafhankelijke landbouw - droogte - gewasopbrengst - watergebruiksrendement - stralingsbenuttigingsefficiëntie - kunstmeststoffen - togo - ghana - west-afrika

    Drought stress and sub-optimal soil fertility management are major constraints to crop production in general and to cassava (Manihot esculenta Crantz) in particular in the rain-fed cropping systems in West Africa. Cassava is an important source of calories for millions of smallholder households in sub-Sahara Africa. The prime aim of this research was to understand cassava productivity in order to contribute to improving yields, food security and farm incomes in rain-fed cassava production systems in West Africa. A long-term goal was to contribute to a decision support tool for site-specific crop and nutrient management recommendations. Firstly, we studied farmers’ perception of cassava production constraints, assessed drivers of diversity among households and analysed the suitability of farmers’ resource endowment groups to the intensification of cassava production. The results indicate that farmers perceived erratic rainfall and poor soil fertility to be prime constraints to cassava production. The agricultural potential of the area and the proximity to regional markets were major drivers for the adoption of crop intensification options including the use of mineral and organic fertilizers. While the use of mineral and organic fertilizers was common in the Maritime zone that had a low agricultural potential, storage roots yields were below the national average of 2.2 Mg dry matter per hectare, and average incomes of 0.62, 0.46 and 0.46 US$ per capita per day for the high, medium and low farmer resource groups (REGs – HRE, MRE and LRE, respectively) were below the poverty line requirement of 1.25 US$. In the high agricultural potential Plateaux zone, HRE and MRE households passed this poverty line by earning 2.58 and 2.59 US$ per capita per day, respectively, unlike the LRE households with 0.89 US$ per capita per day. Secondly, we investigated the effects of mineral fertilizer on nutrient uptake, nutrient physiological use efficiency and storage roots yields of cassava since soil fertility was a major issue across the zones. We used an approach based on the model for the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS). This model was successfully adapted for cassava and it appropriately assessed the response of cassava to N, P and K applications, especially in years with good rainfall. Under high drought stress, the model overestimated cassava yields. Thirdly, we investigated the impact of balanced nutrition on nutrient use efficiency, yield and return on investment compared to blanket fertilizer use as commonly practiced in cassava production systems in Southern Togo, and in Southern and Northern Ghana. The balanced nutrition approach of the QUEFTS model aimed to maximize simultaneously nutrient use efficiency of N, P and K in accordance with the plant’s needs. Larger nutrient use efficiencies of 20.5 to 23.9 kg storage root dry matter (DM) per kilo crop nutrient equivalent (1kCNE of a nutrient is the quantity of that nutrient that has the same effect on yield as 1 kg of N under balanced nutrition conditions) were achieved at balanced nutrition at harvest index (HI) of 0.50 compared to 20.0 to 20.5 kg storage root DM per kilo CNE for the blanket rates recommended by national research services for cassava production. Lower benefit:cost ratios of 2.4±0.9 were obtained for the blanket fertilizer rates versus 3.8±1.1 for the balanced fertilizer rates. Our study revealed that potassium (K) was a major yield limiting factor for cassava production, especially on the Ferralsols in Southern Togo. Hence, we fourthly studied the effect of K and its interaction with nitrogen (N), phosphorus (P), and the timing of harvest on the productivity of cassava in relation to the effects of K on radiation use efficiency (RUE), light interception, water use efficiency (WUE) and water transpiration. The results suggest that K plays a leading role in RUE and WUE, while N is the leading nutrient for light interception and water transpiration. Potassium effects on RUE and WUE depended on the availability of N and harvest time. Values of RUE and WUE declined with harvest at 4, 8 and 11 months after planting. Thus, enhanced K management with sufficient supply of N during the early stage of development of cassava is needed to maximize RUE and WUE, and consequently attain larger storage root yields. Given that erratic rainfall was another major constraint to cassava production according to the results of the farm survey, and due to the inability of QUEFTS modelling to assess drought effects on cassava yield successfully, another modelling approach based on light interception and utilization (LINTUL) was used. We quantified drought impacts on yields and explored strategies to improve yields through evaluation of planting dates in Southern Togo. The evaluation of the model indicated good agreement between simulated and observed leaf area index (Normalised Root Mean Square Error - NRMSE - 17% of the average observed LAI), storage roots yields (NRMSE 5.8% of the average observed yield) and total biomass yield (NRMSE 5.8% of the average observed). Simulated yield losses due to drought ranged from 9-60% of the water-limited yields. The evaluation of planting dates from mid-January to mid-July indicated that the best planting window is around mid-February. Higher amount of cropping season rainfall was also achieved with early planting. These results contradict current practices of starting planting around mid-March to mid-April. However, the results indicate the possibility to increase cassava yields with early planting, which led to less yield losses due to drought. By contrast, late planting around June-July gave larger potential yields, and suggested these periods to be the best planting window for cassava under irrigated conditions in Southern Togo. This shows that appropriate water control and planting periods can contribute to attaining larger yields in Southern Togo. Further improvement of the LINTUL model is required towards using it to assess water-limited yield, which can be used as boundary constraint in QUEFTS to derive site-specific fertilizer requirements for enhanced cassava yield and returns on investments in West Africa.

    Improving radiation use efficiency in greenhouse production systems
    Li, Tao - \ 2015
    Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Ep Heuvelink. - Wageningen : Wageningen University - ISBN 9789462572577 - 156
    glastuinbouw - kassen - gewasfysiologie - agrarische productiesystemen - gewasproductie - stralingsbenuttigingsefficiëntie - straling - fotosynthese - licht - gebruiksefficiëntie - greenhouse horticulture - greenhouses - crop physiology - agricultural production systems - crop production - radiation use efficiency - radiation - photosynthesis - light - use efficiency

    SUMMARY

    A large increase in agricultural production is needed to feed the increasing world population with their increasing demand per capita. However, growing competition for arable land, water, energy, and the degradation of the environment impose challenges to improve crop production. Hence agricultural production efficiency needs to increase. Greenhouses provide the possibility to create optimal growth conditions for crops, thereby improving production and product quality. Light is the driving force for plant photosynthesis and in greenhouse horticulture, light is often the most limiting factor for plant growth. Therefore, improving radiation use efficiency (RUE) in greenhouse production systems is imperative in order to improve plant growth and production. The objective of this thesis is to obtain insight in improving RUE in greenhouse production systems through better understanding of crop physiology. Three aspects related to RUE have been studied in this thesis, 1) improving light distribution in the crop canopy; 2) allowing more light in the greenhouse during summer; and 3) balancing the source and sink strength during plant growth.

    Light is heterogeneously distributed in the crop canopy. Due to the saturating response of leaf photosynthesis rate to light, a more homogeneous light distribution in the canopy will result in a higher crop photosynthesis. In Chapter 2, the effect of diffuse glass on spatial light distribution in a fully developed tomato canopy and its direct and indirect effects on crop photosynthesis were explored. Diffuse glass, which transforms a portion of direct solar light into diffuse light without influencing the light transmissivity of the glass, was applied as greenhouse cover. Under diffuse glass cover, light was more evenly distributed (in both horizontal and vertical direction) within the canopy compared with plants grown under conventional clear glass cover. Besides a more uniform light distribution, diffuse glass also resulted in higher leaf photosynthetic capacity in the middle of the crop canopy and in a higher leaf area index (LAI). The higher leaf photosynthetic capacity was positively correlated with a higher leaf total nitrogen and chlorophyll content. Moreover, lower leaf temperature and less photo-inhibition of top canopy leaves were observed under diffuse glass cover when global radiation was high. Total crop photosynthesis between 1st April and 1st October was enhanced by 7.2 % under diffuse glass. This enhancement mainly resulted from four factors (in order of decreasing importance): a more homogeneous horizontal light distribution, a higher leaf photosynthetic capacity, a more uniform vertical light distribution and a higher LAI.

    In summer growers of shade tolerant pot-plants often apply shading screens in the greenhouse or white wash on the greenhouse cover in order to avoid leaf or flower damage caused by high light. Shading carries a penalty on potential crop growth which is positively related to the amount of light that can be captured. Considering the advantageous properties of diffuse glass cover, i.e. a more homogeneous light distribution, a lower leaf temperature and less photo-inhibition when global radiation is high, in Chapter 3 we tested the feasibility of allowing more light (i.e. less shading) via diffuse glass cover for cultivation of shade tolerant pot-plants during summer. Two Anthurium andreanum cultivars (Pink Champion and Royal Champion) were grown in 3 greenhouse compartments. Under similar DLI [7.5 mol m-2 d-1 PAR (photosynthetic active radiation)], diffuse glass cover resulted in 8 % higher crop RUE (i.e. dry mass production per unit intercepted light) in ‘Royal Champion’ compared with clear glass cover treatment, which consequently resulted in higher total biomass production. This effect was not observed in ‘Pink Champion’. Under diffuse glass cover, high DLI (10 mol m-2 d-1 PAR) resulted in 20-23 % higher total biomass production in both cultivars compared with low DLI (7.5 mol m-2 d-1 PAR), this mainly resulted from the higher cumulative intercepted light. No flower or leaf damage was observed in these treatments. High DLI even resulted in more compact plants as indicated by a higher ratio of aboveground fresh mass to plant height.

    In Chapter 4, we addressed a question resulting from Chapter 3, i.e. why the stimulating effect of diffuse light on crop RUE in anthurium pot-plants is cultivar specific? We excluded the fraction of canopy light interception and steady-state leaf photosynthesis as potential explanations, and explained it from instantaneous leaf photosynthesis which closely correlates with the temporal light distribution. Diffuse glass cover smoothed the variation of temporal light distribution at a given point on a leaf during a clear day, which consequently resulted in less temporal variation of stomatal conductance in ‘Royal Champion’ which had stomata showing a fast-response to the variation in light intensity. As stomata are the gateway for CO2 uptake, less variation in stomatal conductance imposed less limitation for leaf photosynthesis under diffuse glass cover, thereby resulting in a higher crop RUE. For ‘Pink Champion’, however, stomata were less responding to variations in light intensity. Therefore, stomata imposed only a marginal limitation on leaf photosynthesis even under clear glass cover where the temporal incident light intensity varied substantially due to the shadow cast by the greenhouse construction parts and equipment.

    Application of supplementary assimilation light in greenhouses is rapidly increasing. The beneficial effect of supplementary assimilation light is determined by the balance between assimilate production in source leaves and the overall capacity of the plant to use these assimilates. Therefore, it is important to identify the source-sink balance during plant growth. In Chapter 5, three tomato cultivars with different potential fruit size [‘Komeett’ (large size); ‘Capricia’ (medium size); ‘Sunstream’ (small size, cherry tomato)] were grown under commercial crop management. We estimated the source-sink ratio from the early growth stage to fully fruiting stage through experimentation and model simulation. Carbohydrate content of leaves and stems were periodically determined. Tomato plants showed a period of sink limitation (‘Komeett’ and ‘Capricia’) or came close to sink limitation (‘Sunstream’) during the early growth stage under ample natural irradiance (early September) as indicated by a source-sink ratio higher than or close to 1. Fruiting tomato plants were source-limited as indicated by an extremely low source-sink ratio (average source-sink ratio from 50 days after planting onwards was 0.17, 0.22 and 0.33 for ‘Komeett’, ‘Capricia’ and ‘Sunstream’, respectively). During the fully fruiting stage, the source-sink ratio was negatively correlated with the potential fruit size when commercial fruit load was maintained. Carbohydrate content in tomato stems and leaves increased linearly with plant source-sink ratio.

    The experiments and results described in this thesis provide insights for improving RUE in greenhouse production systems. The main achievements and limitations as well as practical applications are discussed in Chapter 6.

    Brandstof kweken biedt zicht op schone toekomst
    Klein Lankhorst, R.M. - \ 2013
    Milieu : opinieblad van de Vereniging van Milieuprofessionals 2013 (2013)sept. - ISSN 1873-5436 - p. 11 - 13.
    zonne-energie - biobrandstoffen - biobased economy - duurzame energie - fotosynthese - stralingsbenuttigingsefficiëntie - cyanobacteriën - solar energy - biofuels - biobased economy - sustainable energy - photosynthesis - radiation use efficiency - cyanobacteria
    De zon is onze perfecte duurzame energiebron die we kunnen aftappen via fotosynthese. Planten doen dit al van nature, maar lang niet efficiënt genoeg. Daarom werkt het bedrijf BioSolar Cells aan de ontwikkeling van Solar Fuels: brandstoffen die rechtstreeks, zonder eerst biomassa te maken, worden gemaakt uit zonlicht, water en CO2. Dit kan met hoge efficiëntie en ondervangt bovendien een aantal knellende problemen met het gebruik van biomassa.
    Modeling the productivity of energy crops in different agro-ecological environments
    Jing, Q. ; Conijn, J.G. ; Jongschaap, R.E.E. ; Bindraban, P.S. - \ 2012
    Biomass and Bioenergy 46 (2012). - ISSN 0961-9534 - p. 618 - 633.
    miscanthus-x-giganteus - light-use efficiency - short-rotation coppice - reed canary grass - woody biomass production - phalaris-arundinacea l. - morphologically diverse varieties - radiation use efficiency - net primary production - dry-matter production
    A relatively stable biomass productivity of perennial crop after plantation establishment makes it possible to calculate their total biomass yield through predicting the annual biomass yield. The generic model LINPAC (LINTUL model for Perennial and Annual Crops) is presented to predict annual biomass yield of energy crops on large spatial scales by adding new modules to LINTUL: (1) Leaf Area Index (LAI) is simulated independent of specific leaf area; (2) a species specific daily Light Use Efficiency (LUE, g MJ-1) is modified by temperature and light intensity; (3) crop base temperature is generated by local weather conditions within crop physiological ranges. LINPAC is driven either by site-specific input data or by globally gridded weather and soil data. LINPAC was calibrated on the basis of a model sensitivity analysis of the input parameters and validated against different agro-ecological experimental data sets for two grass species Miscanthus (Miscanthus spp.) and Reed canary grass (Phalaris arundinacea L.), and for two woody species Willow (Salix spp.) and Eucalyptus (Eucalyptus spp.). LINPAC reproduced the biomass yields with a normalized root mean square error (RMSE) of 17%, comparable to the coefficient of variation (CV = 12%) of the experimental data. In the model photosynthetic pathways were differentiated by assigning higher LUE values for the C4 crop (Miscanthus) compared with the C3 crops (others), leading to higher simulated biomass yield of Miscanthus (18.8 ± 1.5 t ha-1) over Reed canary grass (10.5 ± 1.6 t ha-1) in comparable environments. LINPAC is applicable for local, regional and global estimations of biomass yield of energy crops.
    Exploring the potential of MODIS EVI for modeling gross primary production across African ecosystems
    Sjöström, M. ; Ardö, J. ; Arneth, A. ; Veenendaal, E.M. - \ 2011
    Remote Sensing of Environment 115 (2011)4. - ISSN 0034-4257 - p. 1081 - 1089.
    leaf-area index - eddy covariance technique - radiation use efficiency - carbon-dioxide exchange - satellite sensor data - southern africa - time-series - seasonal-variation - solar-radiation - energy fluxes
    One of the most frequently applied methods for integrating controls on primary production through satellite data is the light use efficiency (LUE) approach, which links vegetation gross or net primary productivity (GPP or NPP) to remotely sensed estimates of absorbed photosynthetically active radiation (APAR). Eddy covariance towers provide continuous measurements of carbon flux, presenting an opportunity for evaluation of satellite estimates of GPP. Here we investigate relationships between eddy covariance estimated GPP, environmental variables derived from flux towers, Moderate Resolution Imaging Spectroradiometer (MODIS) enhanced vegetation index (EVI) and GPP across African savanna ecosystems. MODIS GPP was found to underestimate GPP at the majority of sites, particularly at sites in the Sahel. EVI was found to correlate well with estimated GPP on a site-by-site basis. Combining EVI with tower-measured PAR and evaporative fraction (EF, a measure of water sufficiency) improved the direct relationship between GPP and EVI at the majority of the sites. The slope of this relationship was strongly related to site peak leaf area index (LAI). These results are promising for the extension of GPP through the use of remote sensing data to a regional or even continental scale. Research Highlights ¿ We explore relationships between GPP and MODIS data for sites across Africa. ¿ We assess the MODIS GPP product and whether MODIS EVI can be used for GPP modelling. ¿ We find that MODIS GPP underestimates GPP and that EVI is correlated with GPP. ¿ Including PAR and a water index (EF) improved relationships between GPP and EVI. ¿ We conclude that EVI, PAR, EF and LAI can be used to accurately model GPP at sites. Keywords: Africa; Gross primary production (GPP); Moderate Resolution Imaging Spectroradiometer (MODIS); Enhanced vegetation index (EVI); Evaporative fraction (EF); Leaf area index (LAI)
    Effects of modelling detail on simulated potential crop yields under a wide range of climatic conditions
    Adam, M.Y.O. ; Bussel, L.G.J. van; Leffelaar, P.A. ; Keulen, H. van; Ewert, F. - \ 2011
    Ecological Modelling 222 (2011)1. - ISSN 0304-3800 - p. 131 - 143.
    radiation use efficiency - light-use efficiency - air co2 enrichment - leaf-area index - spring wheat - elevated co2 - terrestrial biosphere - stomatal conductance - growth simulation - carbon balance
    Crop simulation models are widely applied at large scale for climate change impact assessment or integrated assessment studies. However, often a mismatch exists between data availability and the level of detail in the model used. Good modelling practice dictates to keep models as simple as possible, but enough detail should be incorporated to capture the major processes that determine the system's behaviour. The objective of this study was to investigate the effect of the level of detail incorporated in process-based crop growth models on simulated potential yields under a wide range of climatic conditions. We conducted a multi-site analysis and identified that by using a constant radiation use efficiency (RUE) value under a wide range of climatic conditions, the description of the process of biomass production may be over-simplified, as the effects of high temperatures and high radiation intensities on this parameter are ignored. Further, we found that particular attention should be given to the choice of the light interception approach in a crop model as determined by leaf area index (LAI) dynamics. The two LAI dynamics approaches considered in this study gave different simulated yields irrespective of the characteristics of the location and the light interception approaches better explained the differences in yield sensitivity to climatic variability than the biomass production approaches. Further analysis showed that differences between the two LAI dynamics approaches for simulated yields were mainly due to different representations of leaf senescence in both approaches. We concluded that a better understanding and modelling of leaf senescence, particularly its onset, is needed to reduce model uncertainty in yield simulations.
    Physiological and Morphological Changes Over the Past 50 Years in Yield Components in Tomato
    Higashide, T. ; Heuvelink, E. - \ 2009
    Journal of the American Society for Horticultural Science 134 (2009)4. - ISSN 0003-1062 - p. 460 - 465.
    dry-matter production - single-leaf photosynthesis - radiation use efficiency - rice varieties - old - cultivars - difference - quality - crop
    Greenhouse tomato (Solanum lycopersicum) yield in The Netherlands has increased tremendously over the past 50 years. The effects of breeding during this period were investigated. Eight Dutch cultivars and one typical current Japanese cultivar that were released over the past 50 years were compared in a short-term experiment conducted from summer to fall in The Netherlands. Fresh fruit yield of the Dutch cultivars significantly increased 0.9% per year with the year of release from 1950 to 2000. Dry weight fruit yield of the Dutch cultivars also increased with the year of release, whereas the fruit dry matter content was not correlated with the year of release. Total dry matter production of plants increased with the year of release, and the dry matter partitioning to fruit was not correlated with the year of release. An increase in dry matter production was caused not by an increase in fraction of intercepted light, but by light use efficiency based on correlations between each of them and the year of release. The light extinction coefficient in the plant canopy decreased, whereas leaf photosynthetic rate increased significantly with the year of release. Although fresh fruit yield of the Japanese cultivar was lower than that of the modern Dutch cultivars, fruit dry matter content of the Japanese cultivar was higher than that of the Dutch cultivars. An increase in yield over the past 50 years in Dutch tomato was caused by an increase in light use efficiency resulting from a decrease in light extinction coefficient (a morphological change) and an increase in leaf photosynthetic rate (a physiological change).
    Modelling plant responses to elevated CO2: how important is leaf area index?
    Ewert, F. - \ 2004
    Annals of Botany 93 (2004)2004. - ISSN 0305-7364 - p. 619 - 627.
    radiation use efficiency - crop simulation-models - rising atmospheric co2 - light-use efficiency - canopy photosynthesis - spring wheat - ecosystem dynamics - growth-response - carbon-dioxide - climate-change
    Background and Aims The problem of increasing CO2 concentration [CO2] and associated climate change has [CO2] on plants. While variation in growth and productivity is generated much interest in modelling effects of closely related to the amount of intercepted radiation, largely determined by leaf area index (LAI), effects of elevated [CO2] on growth are primarily via stimulation of leaf photosynthesis. Variability in LAI depends on climatic and growing conditions including [CO2] concentration and can be high, as is known for agricultural crops which are specifically emphasized in this report. However, modelling photosynthesis has received much attention and photosynthesis is often represented inadequately detailed in plant productivity models. Less emphasis has been placed on the modelling of leaf area dynamics, and relationships between plant growth, elevated [CO2] and LAI are not well understood. This Botanical Briefing aims at clarifying the relative importance of LAI for canopy assimilation and growth in biomass under conditions of rising [CO2] and discusses related implications for process-based modelling. Model A simulation exercise performed for a wheat crop demonstrates recent experimental findings about canopy assimilation as affected by LAI and elevation of [CO2]. While canopy assimilation largely increases with LAI below canopy light saturation, effects on canopy assimilation of [CO2] elevation are less pronounced and tend to decline as LAI increases. Results from selected model-testing studies indicate that simulation of LAI is often critical and forms an important source of uncertainty in plant productivity models, particularly under conditions of limited resource supply. Conclusions Progress in estimating plant growth and productivity under rising [CO2] is unlikely to be achieved without improving the modelling of LAI. This will depend on better understanding of the processes of substrate allocation, leaf area development and senescence, and the role of LAI in controlling plant adaptation to environmental changes. (C) 2004 Annals of Botany Company.
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