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Sammanfattning

In this study, we employ a network of thermal dissipation probes (TDPs) monitoring sap flux density to estimate leaf-specific transpiration (E-L) and stomatal conductance (G(S)) in Pinus taeda (L.) and Liquidambar styraciflua L. exposed to +200 ppm atmospheric CO2 levels (eCO(2)) and nitrogen fertilization. Scaling half-hourly measurements from hundreds of sensors over 11 years, we found that P. taeda in eCO(2) intermittently (49% of monthly values) decreased stomatal conductance (G(S)) relative to the control, with a mean reduction of 13% in both total E-L and mean daytime G(S). This intermittent response was related to changes in a hydraulic allometry index (A(H)), defined as sapwood area per unit leaf area per unit canopy height, which decreased a mean of 15% with eCO(2) over the course of the study, due mostly to a mean 19% increase in leaf area (A(L)). In contrast, L. styraciflua showed a consistent (76% of monthly values) reduction in G(S) with eCO(2) with a total reduction of 32% E-L, 31% G(S) and 23% A(H) (due to increased A(L) per sapwood area). For L. styraciflua, like P. taeda, the relationship between A(H) and G(S) at reference conditions suggested a decrease in G(S) across the range of A(H). Our findings suggest an indirect structural effect of eCO(2) on G(S) in P. taeda and a direct leaf level effect in L. styraciflua. In the initial year of fertilization, P. taeda in both CO2 treatments, as well as L. styraciflua in eCO(2), exhibited higher G(S) with N-F than expected from shifts in A(H), suggesting a transient direct effect on G(S). Whether treatment effects on mean leaf-specific G(S) are direct or indirect, this paper highlights that long-term treatment effects on G(S) are generally reflected in A(H) as well.

Nyckelord

allometry; hierarchical Bayes; hydraulic architecture; Jarvis model; leaf area; Liquidambar styraciflua; photosynthetic active radiation; Pinus taeda; sapwood area; soil moisture; tree height; vapor pressure deficit

Publicerad i

Tree Physiology
2013, volym: 33, nummer: 2, sidor: 135-151
Utgivare: OXFORD UNIV PRESS

SLU författare

UKÄ forskningsämne

Skogsvetenskap

Publikationens identifierare

  • DOI: https://doi.org/10.1093/treephys/tps118

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/52807