Document: WAY-3-34-3

Leaf traits of dominant grassland perennials along a subambient to superambient gradient in atmospheric carbon dioxide concentration.

POLLEY, H.W.*, H.B.JOHNSON and J.D.DERNER

USDA, Agricultural Research Service, Temple, TX, 76502 ¹

Abstract:
Atmospheric CO₂ enrichment often improves plant water status and growth, but reduces leaf N content with potentially negative feedbacks on N cycling and productivity. Few studies, however, have addressed how consistently these traits vary with CO₂ in plant communities. We measured leaf water potential and leaf C and N concentrations of the dominant C₄ grass (Bothriochola ischaemum) and of selected C₃ perennial forbs in grassland exposed for three years to a CO₂ gradient from 550 to 200 ppm. Responses of specific leaf area (SLA) and of leaf C and N concentrations to CO₂ varied among the six perennial species studied. Measured traits usually were linearly related to CO₂, but leaf N concentration of B. ischaemum and of the dominant forb, Solanum dimidiatum, declined by 20-26% from 200 to 350 ppm CO₂ and by only 10-12% from 350 to 550 ppm. Trends in leaf traits sometimes were opposite those expected. SLA of B. ischaemum increased, rather than decreased as expected, with increasing CO₂ during spring. Increasing CO₂ concentrations improved mid-day water potential of B. ischaemum throughout the growing season, but improved water potential of S. dimidiatum only during late-summer droughts. Carbon dioxide enrichment affected both plant water status and tissue quality in this grassland, but responses to CO₂ were highly species-specific. Results thus reinforce the view that community responses to CO₂ depend on plant species composition.

Keywords: carbon dioxide concentration, grassland, leaf nitrogen, water potential

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.