Pesquisa Agropecuária Brasileira (1999) 34, 952-961

Moacyr Bernardino Dias-Filho (1999)
Physiological responses of two tropical weeds to shade: II. Leaf gas exchange and nitrogen content
Pesquisa Agropecuária Brasileira 34 (6), 952-961
Abstract: Ipomoea asarifolia (Desr.) Roem. and Schultz (Convolvulaceae) and Stachytarpheta cayennensis (Rich) Vahl. (Verbenaceae), two weeds found in pastures and crop areas in the Brazilian Amazonia, Brazil, were grown in controlled environment cabinets under high (800-1000 µmol m^-² s^-¹) and low (200-350 µmol m^-² s^-¹) light regimes during a 40-day period. The objective was to determine the effect of shade on photosynthetic features and leaf nitrogen content of I. asarifolia and S. cayennensis. High-irradiance grown I. asarifolia leaves had significantly higher dark respiration and light saturated rates of photosynthesis than low-irradiance leaves. No significant differences for these traits, between treatments, were observed in S. cayennensis. Low-irradiance leaves of both species displayed higher CO₂ assimilation rates under low irradiance. High-irradiance grown leaves of both species had less nitrogen per unit of weight. Low-irradiance S. cayennensis had more nitrogen per unit of leaf area than high-irradiance plants; however, I. asarifolia showed no consistent pattern for this variable through time. For S. cayennensis, leaf nitrogen content and CO₂ assimilation were inversely correlated to the amount of biomass allocated to developing reproductive structures. These results are discussed in relation to their ecological and weed management implications.
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Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Stachytarpheta cayennensis (weed)	Grasses/turf/rangeland	Brazil (NE)
	Ipomoea asarifolia (weed)	Grasses/turf/rangeland	Brazil (NE)