Photosynthetic Comparison of Carex planostachys (C3) and Aristida purpurea (C4) to Light and Water Manipulations

摘要

In some southwestern Juniperus woodlands, Carex planostachys (C3 sedge) occurs at high coverbelow the canopy and Aristida purpurea (C4 grass) has high cover in associated grasslands or gaps.Availability of light or water are often suggested causing this variation. Photosynthetic measurementswere made as light and water were manipulated in a transplant field study. Monocultures of potted plantswere placed below canopy and in an associated gap for three summer months. There were significantmain experimental effects on photosynthetic and transpiration rates including location, shade, water leveland species. Both species were capable of photosynthetic gain in either location, but CO2 uptake was threeand one-half times greater for the grass in full light. Transpiration rates for both species mostly trackedphotosynthetic rates. Examining means plots of three-way interactions showed that no supplemental waterhad a small effect on A. purpurea photosynthetic rates below the canopy, but a large reduction in thegaps. Rates were opposite indicating an interaction. For C. planostachys in either location non-wateringhad limited negative effects. Aristida purpurea could carry out photosynthesis at intermediate light levelsbelow the canopy but at reduced rates with no interaction. Carex planostachys photosynthesis increasedbelow the canopy when shaded, but decreased without shade in the gaps, an interaction. Water additionimpacted photosynthetic rates of both species, but the greatest effect was on A. purpurea in the gaps.Light levels and water levels interact to regulate the presence of these two species in Juniperus woodlandsand associated canopy gaps, they do not act independently. Published on-line www.phytologia.orgPhytologia 100(1): 91-103 (Mar 16, 2018). ISSN 030319430.