27 research outputs found
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JULES-crop: a parametrisation of crops in the Joint UK Land Environment Simulator
Studies of climate change impacts on the terrestrial biosphere have been completed without recognition of the integrated nature of the biosphere. Improved assessment of the impacts of climate change on food and water security requires the development and use of models not only representing each component but also their interactions. To meet this requirement the Joint UK Land Environment Simulator (JULES) land surface model has been modified to include a generic parametrisation of annual crops. The new model, JULES-crop, is described and evaluation at global and site levels for the four globally important crops; wheat, soybean, maize and rice. JULES-crop demonstrates skill in simulating the inter-annual variations of yield for maize and soybean at the global and country levels, and for wheat for major spring wheat producing countries. The impact of the new parametrisation, compared to the standard configuration, on the simulation of surface heat fluxes is largely an alteration of the partitioning between latent and sensible heat fluxes during the later part of the growing season. Further evaluation at the site level shows the model captures the seasonality of leaf area index, gross primary production and canopy height better than in the standard JULES. However, this does not lead to an improvement in the simulation of sensible and latent heat fluxes. The performance of JULES-crop from both an Earth system and crop yield model perspective is encouraging. However, more effort is needed to develop the parametrisation of the model for specific applications. Key future model developments identified include the introduction of processes such as irrigation and nitrogen limitation which will enable better representation of the spatial variability in yield
Sodium chloride added to transport water and physiological responses of Matrinxã Brycon amazonicus (Teleost: Characidae)
Photosynthesis and productivity in heterogeneous arctic tundra: consequences for ecosystem function of mixing vegetation types at stand edges
1. Arctic vegetation tends to be spatially heterogeneous and can have large areas of mixed transition zone vegetation between stands dominated by a single or few species. If plant photosynthesis and growth within these transition zones differs significantly from main vegetation stands, and if transition zones are not considered when extrapolating stand-level findings to larger scales in space, then transition zones will provide considerable error to landscape-level estimates of gross primary productivity (GPP). 2. In a heterogeneous sub-Arctic tundra landscape, we undertook a detailed assessment of plant and ecosystem photosynthesis and plant growth in stands dominated by the short-stature evergreen dwarf shrub Empetrum hermaphroditum, the deciduous dwarf shrub Betula nana, the taller deciduous shrub Salix glauca and also the transition zones between them. 3. Our findings show that plants in transition zones towards taller and more productive vegetation types frequently showed reduced shoot growth, equal or reduced light-saturated photosynthesis (P-max) and other typical shade responses (e. g. increased leaf chlorophyll and leaf area per mass) when compared with conspecific plants in main stands where the species is dominant. Critically, whole-ecosystem GPP per leaf area was 20-40% lower in transition zones than in main vegetation stands as a consequence. A modelling analysis suggests that the under-productivity of some transition zones results fromthe lack of a clear 'winner' in the competition for light, such that active leaves of some species are shaded by relatively inactive leaves of others. 4. These findings highlight how biotic interactions can considerably influence plant performance to the extent that productivity of mixed vegetation (transition zones) cannot be predicted from their main stands either side. How the consequences of mixing vegetation relate to mechanisms in biodiversity-function theory is discussed. 5. Synthesis: Our work shows that the productivity of transition zones of arctic vegetation is considerably lower than may be estimated fromthe main stands on either side. This reduced GPP in transition zones, therefore, must be considered when modelling carbon fluxes at the landscape scale and suggests that the impact of transition zones on ecosystem function needs further investigation in heterogeneous landscapes, where they make up a significant proportion of the land cover