Plant Growth Modelling and Applications: The Increasing Importance of Plant Architecture in Growth Models

Background Modelling plant growth allows us to test hypotheses and carry out virtual experiments concerning plant growth processes that could otherwise take years in field conditions. The visualization of growth simulations allows us to see directly and vividly the outcome of a given model and provides us with an instructive tool useful for agronomists and foresters, as well as for teaching. Functional-structural (FS) plant growth models are nowadays particularly important for integrating biological processes with environmental conditions in 3-D virtual plants, and provide the basis for more advanced research in plant sciences. Scope In this viewpoint paper, we ask the following questions. Are we modelling the correct processes that drive plant growth, and is growth driven mostly by sink or source activity? In current models, is the importance of soil resources (nutrients, water, temperature and their interaction with meristematic activity) considered adequately? Do classic models account for architectural adjustment as well as integrating the fundamental principles of development? Whilst answering these questions with the available data in the literature, we put forward the opinion that plant architecture and sink activity must be pushed to the centre of plant growth models. In natural conditions, sinks will more often drive growth than source activity, because sink activity is often controlled by finite soil resources or developmental constraints. PMA06 This viewpoint paper also serves as an introduction to this Special Issue devoted to plant growth modelling, which includes new research covering areas stretching from cell growth to biomechanics. All papers were presented at the Second International Symposium on Plant Growth Modeling, Simulation, Visualization and Applications (PMA06), held in Beijing, China, from 13-17 November, 2006. Although a large number of papers are devoted to FS models of agricultural and forest crop species, physiological and genetic processes have recently been included and point the way to a new direction in plant modelling researc

The rise and fall of arbuscular mycorrhizal fungal diversity during ecosystem retrogression

(P) limitation of primary productivity. Arbuscular mycorrhizal fungi (AMF) enhance P acquisition for most terrestrial plants, but it has been suggested that this strategy becomes less effective in strongly weathered soils with extremely low P availability. Using next generation sequencing of the large subunit ribosomal RNA gene in roots and soil, we compared the composition and diversity of AMF communities in three contrasting stages of a retrogressive >2-million-year dune chronosequence in a global biodiversity hotspot. This chronosequence shows a ~60-fold decline in total soil P concentration,with the oldest stage representing some of the most severely P-impoverishedsoils found in any terrestrial ecosystem. The richness of AMF operationaltaxonomic units was low on young (1000?s of years), moderately P-rich soils, greatest on relatively old (~120 000 years) low-P soils, and low again on the oldest (>2 000 000 years) soils that were lowest in P availability. A similar decline in AMF phylogenetic diversity on the oldest soils occurred, despite invariant host plant diversity and only small declines in host cover along the chronosequence. Differences in AMF community composition were greatest between the youngest and the two oldest soils, and this was best explained by differences in soil P concentrations. Our results point to a threshold in soil P availability during ecosystem regression below which AMF diversity declines, suggesting environmental filtering of AMF insufficiently adapted to extremely low P availability.Fil: Kruger, Manuela. Academy of Sciences of the Czech Republic; República ChecaFil: Teste, Francois. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico San Luis; Argentina. University of Western Australia; Australia. Universidad Nacional de San Luis; ArgentinaFil: Laliberté, Etienne. University of Western Australia; Australia. Universit e de Montr eal; CanadáFil: Lambers, Hans. University of Western Australia; AustraliaFil: Coghlan, Megan. Smithsonian Tropical Research Institute; PanamáFil: Zemunik, Graham. Smithsonian Tropical Research Institute; PanamáFil: Bunce, Michael. Curtin University; Australi

A survey of leaf phosphorus fractions and leaf economic traits among 12 co-occurring woody species on phosphorus-impoverished soils

Background and Aims: The leaf economic spectrum (LES) is related to dry mass and nutrient investments towards photosynthetic processes and leaf structures, and to the duration of returns on those investments (leaf lifespan, LL). Phosphorus (P) is a key limiting nutrient for plant growth, yet it is unclear how the allocation of leaf P among different functions is coordinated with the LES. We addressed this question among 12 evergreen woody species co-occurring on P-impoverished soils in south-eastern Australia. Methods: Leaf ‘economic’ traits, including LL, leaf mass per area (LMA), light-saturated net photosynthetic rate per mass (Amass), dark respiration rate, P concentration ([Ptotal]), nitrogen concentration, and P resorption, were measured for three pioneer and nine non-pioneer species. Leaf P was separated into five functional fractions: orthophosphate P (Pi), metabolite P (PM), nucleic acid P (PN), lipid P (PL), and residual P (PR; phosphorylated proteins and unidentified compounds that contain P). Results: LL was negatively correlated with Amass and positively correlated with LMA, representing the LES. Pioneers occurred towards the short-LL end of the spectrum and exhibited higher [Ptotal] than non-pioneer species, primarily associated with higher concentrations of Pi, PN and PL. There were no significant correlations between leaf P fractions and LL or LMA, while Amass was positively correlated with the concentration of PR. Conclusions: Allocation of leaf P to different fractions varied substantially among species. This variation was partially associated with the LES, which may provide a mechanism underlying co-occurrence of species with different ecological strategies under P limitation

Phosphorus-acquisition strategies of canola, wheat and barley in soil amended with sewage sludges

Crops have different strategies to acquire poorly-available soil phosphorus (P) which are dependent on their architectural, morphological, and physiological root traits, but their capacity to enhance P acquisition varies with the type of fertilizer applied. The objective of this study was to examine how P-acquisition strategies of three main crops are affected by the application of sewage sludges, compared with a mineral P fertilizer. We carried out a 3-months greenhouse pot experiment and compared the response of P-acquisition traits among wheat, barley and canola in a soil amended with three sludges or a mineral P fertilizer. Results showed that the P-acquisition strategy differed among crops. Compared with canola, wheat and barley had a higher specific root length and a greater root carboxylate release and they acquired as much P from sludge as from mineral P. By contrast, canola shoot P content was greater with sludge than with mineral P. This was attributed to a higher rootreleased acid phosphatase activity which promoted the mineralization of sludge-derived P-organic. This study showed that contrasted P-acquisition strategies of crops allows increased use of renewable P resources by optimizing combinations of crop and the type of P fertilizer applied within the cropping system

Hidden miners the roles of cover crops and soil microorganisms in phosphorus cycling through agroecosystems

Background Phosphorus (P) is a limiting nutrient in many agroecosystems and costly fertilizer inputs can cause negative environmental impacts. Cover crops constitute a promising management option for sustainable intensification of agriculture. However, their interactions with the soil microbial community, which is a key driver of P cycling, and their effects on the following crop, have not yet been systematically assessed. Scope We conducted a meta-analysis of published field studies on cover crops and P cycling, focusing on plant-microbe interactions. Conclusions We describe several distinct, simultaneous mechanisms of P benefits for the main crop. Decomposition dynamics, governed by P concentration, are critical for the transfer of P from cover crop residues to the main crop. Cover crops may enhance the soil microbial community by providing a legacy of increased mycorrhizal abundance, microbial biomass P, and phosphatase activity. Cover crops are generally most effective in systems low in available P, and may access unavailable P pools. However, their effects on P availability are difficult to detect by standard soil P tests, except for increases after the use of Lupinus sp. Agricultural management (i.e. cover crop species selection, tillage, fertilization) can improve cover crop effects. In summary, cover cropping has the potential to tighten nutrient cycling in agricultural systems under different conditions, increasing crop P nutrition and yield