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

Abstract To examine the predictability of leaf physiology and biochemistry from light gradients within canopies, we measured photosynthetic light-response curves, leaf mass per area (LMA) and concentrations of nitrogen, phosphorus and chlorophyll at 15–20 positions within canopies of three conifer species with increasing shade tolerance, ponderosa pine [Pinus ponderosa (Laws.)], Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and western hemlock [Tsuga heterophylla (Raf.) Sarg.]. Adjacent to each sampling position, we continuously monitored photosynthetically active photon flux density (PPFD) over a 5-week period using quantum sensors. From these measurements we calculated FPAR: integrated PPFD at each sampling point as a fraction of full sun. From the shadiest to the brightest canopy positions, LMA increased by about 50% in ponderosa pine and 100% in western hemlock; Douglas fir was intermediate. Canopy-average LMA increased with decreasing shade tolerance. Most foliage properties showed more variability within and between canopies when expressed on a leaf area basis than on a leaf mass basis, although the reverse was true for chlorophyll. Where foliage biochemistry or physiology was correlated with FPAR, the relationships were non-linear, tending to reach a plateau at about 50% of full sunlight. Slopes of response functions relating physiology and biochemistry to ln(FPAR) were not significantly different among species except for the light compensation point, which did not vary in response to light in ponderosa pine, but did in the other two species. We used the physiological measurements for Douglas fir in a model to simulate canopy photosynthetic potential (daily net carbon gain limited only by PPFD) and tested the hypothesis that allocation of carbon and nitrogen is optimized relative to PPFD gradients. Simulated photosynthetic potential for the whole canopy was slightly higher (<10%) using the measured allocation of C and N within the canopy compared with no stratification (i.e., all foliage identical). However, there was no evidence that the actual allocation pattern was optimized on the basis of PPFD gradients alone; simulated net carbon assimilation increased still further when even more N and C were allocated to high-light environments at the canopy top.

[1]  Han Y. H. Chen,et al.  Effects of light on growth, crown architecture, and specific leaf area for naturally established Pinuscontorta var. latifolia and Pseudotsugamenziesii var. glauca saplings , 1996 .

[2]  K. Pregitzer,et al.  Effects of elevated CO(2) and light availability on the photosynthetic light response of trees of contrasting shade tolerance. , 1996, Tree physiology.

[3]  P. Jarvis,et al.  Photosynthesis in Sitka spruce (Picea sitchensis (Bong.) Carr.) IX. The relative contribution made by needles at various positions on the shoot. , 1980 .

[4]  Richard H. Waring,et al.  Evidence of Reduced Photosynthetic Rates in Old Trees , 1994, Forest Science.

[5]  Dennis D. Baldocchi,et al.  5 – Scaling Water Vapor and Carbon Dioxide Exchange from Leaves to a Canopy: Rules and Tools , 1993 .

[6]  R. K. Dixon,et al.  An optimal sampling strategy for determining CO2 exchange rate as a function of photosynthetic photon flux density , 1987 .

[7]  Christopher B. Field,et al.  2 – Ecological Scaling of Carbon Gain to Stress and Resource Availability , 1991 .

[8]  C. Field,et al.  A reanalysis using improved leaf models and a new canopy integration scheme , 1992 .

[9]  S. Kellomäki,et al.  Effect of angular distribution of foliage on light absorption and photosynthesis in the plant canopy: Theoretical computations , 1982 .

[10]  Peter Millard,et al.  Nitrogen allocation and carbon isotope fractionation in relation to intercepted radiation and position in a young Pinus radiata D. don tree , 1998 .

[11]  Ülo Niinemets,et al.  Effects of light availability and tree size on the architecture of assimilative surface in the canopy of Picea abies: variation in shoot structure , 1995 .

[12]  Ruiliang Pu,et al.  Seasonal Patterns and Remote Spectral Estimation of Canopy Chemistry Across the Oregon Transect , 1994 .

[13]  W. Smith,et al.  Interrelationships among light, photosynthesis and nitrogen in the crown of mature Pinus contorta ssp. latifolia. , 1999, Tree physiology.

[14]  Harold A. Mooney,et al.  Response of Plants to Multiple Stresses , 1993 .

[15]  D. Hollinger.  Optimality and nitrogen allocation in a tree canopy. , 1996, Tree physiology.

[16]  Richard H. Waring,et al.  Environmental Limits on Net Primary Production and Light‐Use Efficiency Across the Oregon Transect , 1994 .

[17]  T. Dejong,et al.  Seasonal relationships between leaf nitrogen content (photosynthetic capacity) and leaf canopy light exposure in peach (Prunus persica) , 1985 .

[18]  Tadaki Hirose,et al.  Canopy Development and Leaf Nitrogen Distribution in a Stand of Carex Acutiformis , 1989 .

[19]  Christopher B. Field,et al.  photosynthesis--nitrogen relationship in wild plants , 1986 .

[20]  D. Hollinger.  Canopy organization and foliage photosynthetic capacity in a broad-leaved evergreen montane forest , 1989 .

[21]  Richard H. Waring,et al.  Forest Ecosystems: Analysis at Multiple Scales , 1985 .

[22]  R. Waring,et al.  The normalized difference vegetation index of small Douglas-fir canopies with varying chlorophyll concentrations , 1994 .

[23]  Photosynthetic Electron Transport in Shoots of Sitka Spruce from Different Levels in a Forest Canopy , 1977 .

[24]  Optimal leaf photosynthetic capacity in terms of utilizing a natural light environment , 1989 .

[25]  G. Carter,et al.  Influence of shoot structure on light interception and photosynthesis in conifers. , 1985, Plant physiology.

[26]  J. Leverenz.  Shade-shoot structure, photosynthetic performance in the field, and photosynthetic capacity of evergreen conifers. , 1996, Tree physiology.

[27]  N. Boardman.  Comparative photosynthesis of sun and shade plants. , 1977 .

[28]  R. Teskey,et al.  A relationship between carbon dioxide, photosynthetic efficiency and shade tolerance , 1985 .

[29]  F. W. Wiegel,et al.  Optimizing the Canopy Photosynthetic Rate by Patterns of Investment in Specific Leaf Mass , 1988, The American Naturalist.

[30]  A. Koppel,et al.  Net photosynthetic response to light intensity of shoots from different crown positions and age in picea abies (L.) karst , 1987 .

[31]  Paul G. Jarvis,et al.  6 – Prospects for Bottom-Up Models , 1993 .

[32]  P. Stenberg.  Implications of shoot structure on the rate of photosynthesis at different levels in a coniferous canopy using a model incorporating grouping and penumbra , 1998 .

[33]  T. Hinckley,et al.  Shoot structure, leaf area index and productivity of evergreen conifer stands. , 1990, Tree physiology.

[34]  Pauline Stenberg,et al.  Simulations of the effects of shoot structure and orientation on vertical gradients in intercepted light by conifer canopies. , 1996, Tree physiology.

[35]  D. Sprugel,et al.  Effects of light on shoot geometry and needle morphology in Abies amabilis. , 1996, Tree physiology.

[36]  P. Jarvis,et al.  CHANGES IN CHLOROPHYLL AND CAROTENOID CONTENT, SPECIFIC LEAF AREA AND DRY WEIGHT FRACTION IN SITKA SPRUCE, IN RESPONSE TO SHADING AND SEASON , 1977 .