Author
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Belesky, David |
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Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/4/2004 Publication Date: 1/18/2005 Citation: Belesky, D.P. 2005. Growth of dactylis glomerata along a light gradient in the central appalachian region of the eastern usa: ii. mechanisms of leaf dry matter production. Agroforestry Systems, 65:91-98. Interpretive Summary: Small farms in much of the eastern US are a mosaic of woodland and open pasture. Silvopastoral grazing systems, or forages produced as understory crops on wooded sites can increase land-use efficiency and biological diversity on small farms. Widely accepted management practices that link grazing management to forage height may not be applicable in the shaded component of silvopastoral systems because the influence of conditions within the shaded sites on response of defoliated plants are not well understood. Orchardgrass, a common forage grass in the central Appalachian region was grown in open, shaded and woodland-open edge environments to determine production patterns and persistence. Plants growing at the edge of wooded and open sites seemed to benefit from partial shade. Plants grown in the open experienced too much light and water stress whereas plants grown at the wooded sites had too little light to sustain regrowth of clipped plants. Older or mature plants growing in shaded sites responded in a manner similar to very young or immature plants growing with adequate light. Clipping plants based on criteria to optimize grazing animal performance on open pasture was not suitable for shade grown plants. Understanding how to manage forage plants adapted to open pasture when grown in shade can lead to improved forage availability and distribution across a growing season, greater persistence and quite likely increased farm income. Technical Abstract: Microsite influences plant development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in woodlots. An experiment using container-grown plants was conducted under field conditions to determine how microsite of open (O), shaded woodland (W) and the edge effect of transition from O (EO) to W (EW) influenced mechanisms of leaf dry matter (DM) production of orchardgrass. Plants established in spring (SP) and late summer (LS), were clipped each time mean extended leaf length reached 20 cm. Dry matter production and allocation differed between SP and LS plants, with light attenuation and with the number of harvests obtained at sites. Collinearity diagnostics showed that specific leaf area (SLA) and photosynthetic nitrogen-use efficiency (PNUE) were associated with leaf DM production, whereas leaf N, net assimilation rate and shoot total nonstructural carbohydrates (TNC) were not. Specific leaf area influenced leaf DM of LS plants, whereas PNUE influenced leaf DM of SP plants. Stembase TNC was inversely related to relative regrowth rate (RGRR) with RGRR greatest and TNC the least at the W microsite. The relationship for RGRR and TNC for SP plants growing in the O microsite and LS plants growing in the W microsite was similar. Regardless of how indices of growth are related, SP and LS plantings responded as separate populations (representing young and established plants respectively) that have different leaf DM production efficiencies. This reinforces our observation that LS plants growing in W microsites respond in a manner similar to SP plants. |
