Growth and Root-Shoot Partitioning in Eighteen British Grasses

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Abstract
In this paper we propose a simplification of a published ''hyperbolic'' model concerning the coarse control of growth and root-shoot partitioning. This allows the model''s input and output variables to be more legitimately related to ''independent'' factors from Plant Strategy Theory, such as environmental stress, environmental disturbance and innate growth potential. New experimental measurements are presented encompassing an ecologically diverse diverse selection of eighteen British grasses [Agrostis capillaris, Agrostis stolonifera, Arrhenatherum elatius, Bromus erectus, Briza media, Cynosurus cristatus, Deschampsia caespitosa, Deschampsia flexuosa, Dactylis glomerata, Festuca ovina, Festuca rubra, Holcus lanatus, Koeleria macrantha, Lolium perenne .times. multiflorum, Lolium perenne, Nardus stricta, Poa annua, Poa trivialis.] experiencing both above- and below-ground stresses. The percentage attainments of optimal growth rate in this material range from 24 to 94, according to species and treatment. Allometric (root/shoot) coefficient range from 49% below to 27% above those of optimally-grown material. The simplified model is evaluated in relation to these new data. The mean effects of environmental stress, environmental disturbances and innate growth potential are subtle, but the predicted directions of response are confirmed: species associated with low environmental stress or with high disturbance in the field attained a few percent less of their growth potential than species associated with the opposite set of conditions; species associated with high disturbance ''perceived'' an average of 38% more stress in the eperiment that those associated with low disturbance. Of the significant effects, degree of disturbance was particularly influential on the ''perception'' of shoot stress (P < 0.001), and both environmental stress and environmental disturbance had a consdierable influence upon partitioning. On average, species from little-stressed or from highly-disturbed environments ''perceived'' the need for partitioning coefficients which were respectively 6 and 12% different from those exhibited by species of the opposite contingency.