Foliar plasticity of hybrid spruce in relation to crown position and stand age

Abstract

This study examined the foliar response of putative hybrid Engelmann × white × Sitka spruce (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr) needles in relation to crown position and across three stages of development (15, 55, and 145 years). We focused on the morphological and anatomical response, and used physiological measures (photosynthesis and stomatal conductance) to emphasize the important relationship between structure and function. We found that needles from the upper outer crown position were adaptated to reduce stress from evapotranspiration. Trees from the 15- and 55-year-old stands generally responded the most, and trees from the 145-year-old stand responded the least. As they mature, these spruce trees may have reduced ability to adapt to their environment. Some of our results contradict what the literature considers "typical" for sun-shade dimorphism in temperate forests. For example, in all stands, sun needles were broader than shade needles and, in the two younger stands, sun needles were larger in area, not smaller, than shade needles. Also, in the youngest stand, stomatal pores were longer on sun needles than on shade needles. There were no definite patterns in stomatal spacing with regard to crown position. Our results are indicative of the strategies adopted to increase competitiveness in a resource-limited environment. We suggest that, in the 15-year-old stand, neither water nor light is limiting; in the 55-year-old stand, both water and light are highly limiting; and in the 145-year-old stand, water is most limiting.Key words: drought, foliar plasticity, needle anatomy, photosynthesis, Picea, stand development, sun-shade.

How strong is intracanopy leaf plasticity in temperate deciduous trees?

“…Species also differed significantly in the intracanopy plasticity of leaf mass (0.8-1.6), LA : SA (1.2-2.3), and SPI gcl (1.1-1.8); whether these differences scale up to species differences in whole canopy performance requires further study. Our findings are consistent with previous reports of invariance in guard cell length (Bongers and Popma, 1988;Carr, 2000;Richardson et al, 2000Richardson et al, , 2001 and of a maximum intracanopy plasticity in LMA of '1.5-2 times as reported for Populus tremula and Tilia cordata and for three species of conifers (Bond et al, 1999). The observed boundedness of intracanopy plasticity for all the traits, up to '2 times the maximum, implies a general convergence across species due to general optimization and/or to similar developmental constraints operating during primordia formation and leaf expansion, as discussed in the following section.…”

“…The R 2 and slope are for values predicted by the model plotted against observed values; AIC ¼ Akaike information criterion, corrected for low N (values lowest by more than 2, in boldface type, indicate best-supported models). Kull, 1994;Richardson et al, 2000). It is possible that in those previous studies the particular species, conditions, or sampling protocols led to findings that did not represent the general patterns of intracanopy plasticity shown here for the six species.…”

“…Despite the wealth of studies on intracanopy plasticity, our understanding remains fragmentary. Reports for a number of species even conflict with the general trends, including shade leaves smaller than sun leaves, lower-canopy leaves with higher LMA than upper-canopy leaves, and invariant stomatal density across the canopy (Wylie, 1949;Talbert and Holch, 1957;Niinemets and Kull, 1994;Carr, 2000;Richardson et al, 2000). In fact, in our literature review, we found that intracanopy plasticity has rarely been quantified systematically.…”

Age-Dependent Tree-Ring Growth Responses to Climate in Larix Decidua and Pinus Cembra

“…For example, observed a shift of carbon resources to different parts of the plant with ageing. Reductions in foliar efficiency, leaf size, and gas exchange attributes have been observed in trees of increasing age (Kull and Koppel 1987, Richardson et al 2000, Day et al 2001). Lower photosynthetic rates in older trees have been measured in various conifer species (see Bond 2000 for a review).…”

Post-fire fuel succession in a rare California, USA, closed-cone conifer

“…We chose a smaller area for live fuel sampling because we wanted to limit potential differences in climate conditions over time across sites. Live foliage samples were collected within 2 m from the ground on the south side of each tree to minimize variation associated with crown position (Richardson et al 2000). All sampling occurred between 1200 and 1600 hours to limit variation caused by daily moisture fluctuations (Zahn and Henson 2011).…”