Does resource availability modulate shade avoidance responses to the ratio of red to far‐red irradiation? An assessment of radiation quantity and soil volume

Microsite influences on resource allocation related to silvopastoral swards undergoing repeated defoliation are unclear. Defoliating traditional pasture species according to canopy development criteria may not be appropriate when the plants grow as understory crops in woodlots. An experiment using container-grown plants was conducted under field conditions to determine how open (O), shaded woodland (W) and opento-shaded woodland transition zones (E O , E W ), representing the partial shade conditions found in silvopastoral settings, influenced productivity and dry matter allocation in Dactylis glomerata L. Plants established in spring (SP) and late summer (LS) were clipped each time mean sward height reached 20 cm. Dry matter production differed for SP and LS plantings, and was greater in O than W sites. Dry matter allocation to shoots of SP plants indicated some agronomic benefit associated with the E O and E W sites. Leaf mass did not vary with irradiance, but stembase mass did. The SP plants had numerous small tillers whereas LS plants were composed of comparatively fewer but more massive tillers. Plants growing at O, E O and E W were similar, whereas plants in the W site were smaller and had the fewest tillers regardless of planting time. Results suggest that defoliation management for shaded components of silvopastoral systems should be based on some index other than sward height, and that management criteria might change during the growing season. Less intensive removal (e.g., 10-cm rather that 5-cm residue) should be considered for defoliated, shade grown plants, since this could allow more stembase and nonstructural carbohydrate storage tissues to remain.

Section: Plant Culturementioning

confidence: 99%

“…Many grass species adjust to shade by increasing leaf length and specific leaf area to increase light acquisition, while at the same time slowing tiller production or vegetative propagation (Monaco and Briske 2000), compromising sward persistence. Defoliation (clipping or grazing) disrupts the light acquisition process.…”

Section: Introductionmentioning

confidence: 99%

Growth of Dactylis glomerata along a light gradient in the central Appalachian region of the eastern USA: I. Dry matter production and partitioning

Belesky¹

2005

“…Tree shade changes light intensity and quality depending on tree species, seasons of year, time of day, and cloud cover. Light quantity and associated quality induces various morphological adaptations in understory plants such as leaf elongation, reduced specific leaf weight, and altered rates of tiller production (Devkota and Kemp 1999;Monaco and Briske 2000;Belesky 2005).…”

Section: Introductionmentioning

confidence: 99%

Photosynthetically active radiation use efficiency of Dactylis glomerata and Schedonorus phoenix along a hardwood tree-induced light gradient

Feldhake¹,

Belesky²

2008

Photosynthetically active radiation use efficiency (PARUE) of orchardgrass (Dactylis glomerata L.) and tall fescue (Schedonorus phoenix (Scop.) Holub) was determined. Leaf mass was harvested for canopies at different shade levels when each reached 20 cm height with 5 cm residue for regrowth to simulate grazing. Total incident PAR at each site was summed for the growth period (S-PAR). Values for PARUE were calculated from dried leaf mass divided by S-PAR. The more highly shaded plants reached 20 cm at lower S-PAR. While overall leaf mass decreased linearly with shade induced decreases in S-PAR, PARUE increased exponentially. The coefficients for the equations representing this exponential increase vary for forage species and may represent a useful index for characterizing forage response to silvopastoral systems.

“…Container-grown plants (with the pot bottoms removed) were used to eliminate or minimize site and soil related effects on germination, growth and nutrient availability. [Monaco and Briske (2000) present rationale for using container-grown plants.] Lime and fertilizer application was based on soil test results.…”

Section: Methodsmentioning

confidence: 99%

Growth of Dactylis glomerata along a light gradient in the central Appalachian region of the eastern USA: II. Mechanisms of leaf dry matter production

Belesky¹

2005

Microsite influences development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in silvopasture of humid temperate regions. An experiment using container-grown orchardgrass was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zone (E O , E W ) microsites influenced leaf DM production. Plants established in spring (SP) and late summer (LS) were clipped each time mean canopy height reached 20 cm. Dry matter production and allocation among structures differed, as a function of light attenuation. 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 was related to leaf DM of LS plants, whereas PNUE influenced leaf DM of SP plants. Stembase TNC was inversely related to relative regrowth rate (RG R R) with RG R R greatest and TNC the least at W. The relationship for RG R R and TNC for SP plants growing at O and LS plants growing at W 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. Orchardgrass was able to sustain leaf production when subjected to simultaneous stresses of shade and repeated defoliation. The LS plants growing at W respond in a manner similar to SP plants and may require management practices attuned to establishing or immature plants.