Figure 4: Patterns of 13C discrimination (Δ) across treatments and plant functional groups.
From: Long-term decline in grassland productivity driven by increasing dryness
(a–c) Response of Δ in grass (green points and 95% confidence region of linear regression) and forbs (orange points and 95% confidence region of linear regression) to variation in the palmer Drought Severity Index (PDSI) and (d–f) late-summer rain. Across all treatments Δ by forbs decreased significantly (P<0.01, linear regression, n=27) with decreasing PDSI values (that is, increasing PDSI drought), indicating increasing water use efficiency. The Δ by grass also decreased significantly with increasing PDSI drought in control plots (a). The Δ by forbs and grasses decreased significantly with decreasing late-summer rain only in × 2 treatments (e).
