Net photosynthesis, root respiration, and regrowth of Bouteloua gracilis following simulated grazing

Abstract

Net photosynthesis (P), root respiration (R), and regrowth of Bouteloua gracilis (H.B.K.) Lag. were examined in the laboratory over a 10-day period following clipping to a 4-cm height to simulate grazing by large herbivores. Net photosynthesis rates of tissue remaining immediately following defoliation were only about 40% as great as preclipping rates. Three days after clipping, P rates of defoliated plants had increased to values about 21% greater (per unit leaf area) than those of unclipped controls and remained at that level through Day 10. No statistically significant changes in R occurred following defoliation. Biomass of unclipped plants nearly doubled during the 10-day study period, while that of defoliated plants increased 67%. Over half the new growth of defoliated plants was allocated to new leaf blades and only 18% to new roots, while only 33% of the new growth of control plants was allocated to new leaf blades but 29% went to new roots. As a consequence of increased P rates and increased carbon allocation to synthesis of additional photosynthetic tissue following defoliation, net CO uptake per plant increased from 9% to 80% of that of the controls from Day 0 through Day 10.

Influence of Management on Soil Organic Carbon Dynamics in Northern Mixed-Grass Rangeland

“…The CER T measurements were taken from 1000 to 1300 h (Mountain Standard Time) about every 3 wk during the growing seasons of 1995 through 1997. Measurements made on the treatment sites showed that maximum daily CER T occurred during 1000-to 1300-h period of the day, which agrees with Detling et al (1979). Each time CER T measurements were made, a point frame was used to determine the green vegetation index (GVI) within each of the CER frames (Warren-Wilson, 1963).…”

“…Studies have shown that grazing affects SOC levels, either through changes in plant community (Coupland et al, 1960;Dormaar and Willms, 1990;Coupland, 1992) or by other more subtle and less discernable responses such as litter accumulation and decomposition rates, changes in chemical composition of soil organic matter (SOM), amount and quality of root exudates, increased root biomass, and more rapid cycling of C (Schuster, 1964;Smoliak et al, 1972;Dyer and Bokhari, 1976;Davidson, 1978;Christie, 1979;Detling et al, 1979;Holland and Detling, 1990;Naeth et al, 1991;Shariff et al, 1994;Ganjegunte et al, 2005). The quantity and chemical composition of SOM is important to C and N cycling, as N is often the limiting factor to productivity in rangeland ecosystems (Power, 1994).…”

Bottom-up effects of host plant nutritional quality on Plutella xylostella (Lepidoptera: Plutellidae) and top-down effects of herbivore attack on plant compensatory ability

“…Plants can also increase their net aboveground productivity when infested (Belsky, 1986 and references therein) and various mechanisms have been identified that could contribute to such compensatory growth. They include intrinsic mechanisms such as photosynthetic enhancement and reallocation of available assimilates (Delting et al, 1979;Oesterheld & McNaughton, 1988;Trumble et al, 1993) and extrinsic mechanisms such as nutrient recycling (Floate, 1981;Holland et al, 1992). Therefore, increased shoot growth could lead to increased root growth (McNaughton et al, 1998) and well nourished plants have a higher capability of compensating (and even overcompensating) than when nutrients are limiting.…”

Réaction à un composé salivaire et tolérance à la coupe de génotypes de Dactylis glomerata L issus de populations ayant une expérience contrastée du pâturage

“…Les (Balent et Duru, 1984 Soulas, 1981). Ces modalités de coupe ont été choisies aussi d'après la bibliographie (McNaughton, 1979;Detling et al, 1979;Detling et al, 1980); -le facteur «thiamine» : la quantité de thiamine apportée est très faible : 0,2 ml d'une solution à 10 ppb (partie pour billion). Elle correspond à la quantité déposée par un animal selon Reardon et al (1974) et McNaughton (1985).…”