Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. Don tree

Abstract

The three dimensional distribution of intercepted radiation, intercellular CO 2 concentration (C i ) and late summer needle nitrogen (N) concentration were determined at the tips of all 54 branches in a 6·2-m-tall Pinus radiata D. Don tree growing in a New Zealand plantation. Measurements included above-and below-canopy irradiance, leaf stable carbon isotopic composition (δ 13 C) and tree canopy architecture. The radiation absorption component of the model, MAESTRO, was tested on site and then used to determine the branch tip distribution of intercepted radiation. We hypothesized that in branch tip needles: (i) the allocation of nitrogen and other nutrients would be closely associated with the distribution of intercepted radiation, reflecting carbon gain optimization theory, and (ii) C i would predominantly reflect changes in photosynthetic rate (A) rather than stomatal conductance (g s ), indicating that the increase in A for a given increase in N concentration was larger than the corresponding increase in g s . Needle nitrogen concentration was poorly related to intercepted radiation, regardless of the period over which the latter was calculated. At a given height, there was a large azimuthal variation in intercepted radiation but N concentration was remarkably uniform around the tree canopy. There was, however, a linear and positive correspondence between N concentration and δ 13 C and needle height above ground (r 2 = 0·73 and 0·68, respectively). The very strong linear correspondence between N concentration and C i (r 2 = 0·71) was interpreted, using gas exchange measurements, as supporting our second hypothesis. Recognizing the strong apical control in P. radiata and possible effects of leaf nitrogen storage in an evergreen species, we propose that the tree leader must have constituted a very strong carbon sink throughout the growing season, and that the proximity of branch tip needles to the leader affected their photosynthetic capacity and nutrient concentration, independent of intercepted radiation. This implies an integrated internal determination of resource allocation within the tree and challenges the current convention that resources are optimally distributed according to the profile of intercepted radiation.

Foliage physiology and biochemistry in response to light gradients in conifers with varying shade tolerance

“…For our measurements of R D , variance was high and the values small, so it is possible that we did not detect real relationships. In our study, as in many other studies of both angiosperms and gymnosperms (Gulmon and Chu 1981;Kull and Koppel 1987;Hollinger 1989;Weinbaum et al 1989;Ellsworth and Reich 1993; but see also Barker and Booth 1996;Livingston et al 1998), N and A max expressed on a leaf mass basis were relatively constant within canopies and showed little response to light gradients (slopes were signi®cantly dierent from but close to 0). Therefore, with increased LMA of foliage in highlight environments, N area and A max-area also increased.…”

“…Numerous studies have shown that variations in leaf structure, nitrogen content, and A max within canopies correspond to variations in light (e.g., Field 1983;DeJong and Doyle 1985;Hirose and Werger 1987;Hollinger 1989Hollinger , 1996Ellsworth and Reich 1993;Brooks et al 1996;Livingston et al 1998;Schoettle and Smith 1999), and these variations generally mimic the responses that occur when whole plants are grown in controlled experiments at dierent light levels (Boardman 1977;BjoÈ rkman 1981). Several investigators (e.g., Gutschick and Wiegel 1988;Takenaka 1989;Field 1991;Jarvis 1993) have proposed that carbon and/or nitrogen are allocated within canopies to optimize use of solar energy.…”

Correlations between net primary productivity and foliar carbon isotope ratio across a Tibetan ecosystem transect

“…The model predictions generally integrate previous knowledge from the literature, indicating that: 1) in water-limited conditions, water availability has greater effects on NPP than N mass (Macfarlane et al 2004, Klein et al 2005), leading to a negative correlation between NPP and d 13 C (Condon et al 1987, Roux et al 1996; and 2) when water is not limiting, NPP increases with increasing N mass (Field and Mooney 1986, Wright et al 1988, Sun et al 1996, Livingston et al 1998). Equation 5 further suggests a threshold of water limitation of E/E m B0.85.…”

Productivity, carbon isotope discrimination and leaf traits of trees of Eucalyptus globulus Labill. in relation to water availability

“…However, in three other eucalypt species, Anderson et al (2000) also found no correlation between rainfall and physical leaf traits. These results suggest that variation of SLA is a more important adaptation to aridity between genotypes than within a genotype but that the opposite is the case for leaf N. Numerous other studies have found either negative correlations between leaf N and D, positive correlations between SLA and D or both (Korner, Farquhar & Wong 1991;Anderson et al 1996;Sparks & Ehleringer 1997;Livingston et al 1998). The correlations between D, and SLA and leaf N found in this and other studies are consistent with the theory that larger leaf N content and smaller SLA are associ-ated with increased photosynthetic capacity and increased leaf-scale water-use-efficiency (Mooney, Ferrar & Slatyer 1978).…”