Altitude trends in conifer leaf morphology and stable carbon isotope composition

Abstract

The natural ratio of stable carbon isotopes (δC) was compared to leaf structural and chemical characteristics in evergreen conifers in the north-central Rockies, United States. We sought a general model that would explain variation in δC across altitudinal gradients. Because variation in δC is attributed to the shifts between supply and demand for carbon dioxide within the leaf, we measured structural and chemical variables related to supply and demand. We measured stomatal density, which is related to CO supply to the chloroplasts, and leaf nitrogen content, which is related to CO demand. Leaf mass per area was measured as an intermediate between supply and demand. Models were tested on four evergreen conifers: Pseudotsuga menziesii, Abies lasiocarpa, Picea engelmannii, and Pinus contorta, which were sampled across 1800 m of altitude. We found significant variation among species in the rate of δC increase with altitude, ranging from 0.91‰ km for A. lasiocarpa to 2.68‰ km for Pinus contorta. Leaf structure and chemistry also varied with altitude: stomatal density decreased, leaf mass per area increased, but leaf nitrogen content (per unit area) was constant. The regressions on altitude were particularly robust in Pinus contorta. Variables were derived to describe the balance between supply and demand; these variables were stomata per gram of nitrogen and stomata per gram of leaf mass. Both derived variables should be positively related to internal CO supply and thus negatively related to δC. As expected, both derived variables were negatively correlated with δC. In fact, the regression on stomatal density per gram was the best fit in the study (r =0.72, P<0.0001); however, the relationships were species specific. The only general relationship observed was between δC and LMA: δC (‰)=-32.972+ 0.0173×LMA (r =0.45, P<0.0001). We conclude that species specificity of the isotopic shift indicates that evergreen conifers demonstrate varying degrees of functional plasticity across environmental gradients, while the observed convergence of δC with LMA suggests that internal resistance may be the key to understanding inter-specific isotopic variation across altitude.

Adaptive characteristics of grassland community structure and leaf traits along an altitudinal gradient on a subtropical mountain in Chongqing, China

“…This mechanism could effectively reduce the ''loss'' of nutrients, demonstrating that a deficit of soil nutrition does not limit the growth of species at higher altitudes. Previous studies have reported similar increase in foliar d 13 C with altitude (Körner et al 1988(Körner et al , 1991Morecroft et al 1992;Harshall and Zhang 1994;Hultine and Marshall 2000) and this is shown in our results averaged for all species (Fig. 8).…”

“…6, 7a) are similar to the trends shown by other studies (Woodward 1986;Körner et al 1986Körner et al , 1989Vitousek et al 1990;Hultine and Marshall 2000;Luo et al 2005;Milla et al 2009). Nevertheless, our results varied from other studies in showing that N mass was not significantly related to increased altitude (Fig.…”

Relationships Between Tree Height and Carbon Isotope Discrimination

“…We corrected the isotopic results for elevation impacts on CO 2 partial pressure (Hultine and Marshall 2000;Warren et al 2001;Körner 2007;McDowell et al 2010). Though this effect is minor, it is relatively straightforward to correct for when elevation and temperature are known.…”

“…These processes are captured in Eq. 10.1 where p c and p a are the chloroplast and atmospheric partial pressures of CO 2 , respectively (Hultine and Marshall 2000;Seibt et al 2008). Thus, anything that affects p c affects D. This is a simplified representation of the processes that influence D but it provides an initial hypothesis framework.…”

Soil n‐alkane δ13C along a mountain slope as an integrator of altitude effect on plant species δ13C

“…[2] Investigations on C 3 plants at the species level have shown that plant carbon isotope composition (d 13 C) increases with altitude in humid areas [Körner et al, 1988[Körner et al, , 1991Friend et al, 1989;Morecroft and Woodward, 1990], meaning that the ratio of carbon gained to water lost in leaf gas exchange increases with altitude [Farquhar et al, 1989;Hultine and Marshall, 2000]. This phenomenon has been attributed to decreasing temperature and atmospheric partial pressure of CO 2 and O 2 with altitude [e.g., Körner et al, 1991;Kelly and Woodward, 1995].…”