Carbon and nitrogen allocation to male and female reproduction in Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca, Pinaceae)

We measured carbon (respiration, photosynthesis, and production) and nitrogen allocation to male and female cones of Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) to quantify gender-specific: (1) resource allocation to reproduction, and (2) contribution to carbon costs of reproduction via photosynthesis. We also measured foliar photosynthesis and nitrogen concentration ([N]) near and far from female cones to examine the relationship between reproduction and foliar physiology. Over one growing season, male cones required only 8% of all carbon allocated to reproduction, with females consuming the remaining 92%. Female cones, however, had maximum instantaneous refixation rates of 54%, which, integrated over the season, offset 6% of their total carbon requirements, while male cones were completely dependent on vegetative tissues for carbon. Male cones received 22% of all nitrogen allocated to reproduction and female cones received the remaining 78%. Foliage near female cones had elevated photosynthesis during the early stages of cone development and consistently lower [N] than foliage far from cones. Although female cones may photosynthesize, the annual sum of carbon fixed by reproductive structures is minor in comparison to the total carbon allocated to production and respiration.     

Ethanol synthesis, nitrogen, carbohydrates, and growth in tissues from nitrogen fertilized Pseudotsuga menziesii (Mirb.) Franco and Pinus ponderosa Dougl. ex Laws. seedlings

 Seedlings of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, and ponderosa pine, Pinus ponderosa Dougl. ex Laws., were grown in a controlled environment and fertilized with nutrient solutions containing 150 ppm (+N), or 0 ppm nitrogen (−N). These treatments greatly altered seedling growth, and the concentrations of N and carbohydrates in their tissues. Metabolically active tissues, such as roots, incubated with a limited supply of O₂ became hypoxic faster and synthesized more ethanol than less active tissues, such as needles. All tissues that were incubated for 4 h in N₂ synthesized ethanol. Needles incubated in N₂ and light had much lower quantities of ethanol than needles in N₂ and dark, suggesting that O₂ from photosynthetsis limited internal anoxia. Most tissues from +N seedlings synthesized greater quantities of ethanol in N₂ anoxia than tissues from −N seedlings, probably because they were able to produce more enzymes with a greater availability of N. However, this increase in ethanol synthesis between N treatments was most pronounced in the phloem. Ethanol and soluble sugar concentrations were negatively related in needles and positively related in roots of N+ seedlings, but not −N seedlings. Starch concentrations had no effect on the amount of ethanol produced by any tissue. Regardless of N treatments, all tissues from ponderosa pine produced more N₂-induced ethanol than Douglas-fir, in part because its tissues contained different concentrations of soluble sugars and N as a consequence of phenological differences between the species. However, ponderosa pine tissues may also maintain greater quantities of anaerobic enzymes, or their isozymes than Douglas-fir. Received: 22 February 1998 / Accepted 23 June 1998     

The role of sugars in western spruce budworm nutritional ecology

Abstract.

• 1 The western spruce budworm, Choristoneura occidentalis Freeman, and Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, have been used to test the hypothesis that variation in levels of foliar sugars form part of the basis for plant resistance to herbivore attack.
• 2 Budworm population growth was evaluated on artificial diets with 2–45% sucrose using a three generation bioassay. Diets with 1.2% and 3.9% N were tested to determine if responses to sugar were dependent on levels of protein. The 3.9% N diets were supplemented with a mineral salt mixture, so they had high levels of N and minerals.
• 3 The response of budworm population growth to sucrose concentrations ≤20% was convex at 1.2% N and flat for 3.9% N. Population growth on the 1.2% N diet, which had levels of N and minerals similar to host foliage, was good with only 2% sugar, but optimal at the 6% sucrose level; the number of F₁, F₂ and F₃ larvae produced declined substantially when sugar was increased to 11% and 20%. On the 3.9% N diets, population growth was equivalent for diets with 2% and 11% sucrose. Sucrose concentrations ≥29% were detrimental to the budworm at both N levels.
• 4 Sugar concentrations in Douglas-fir foliage varied between 5.7% and 18.4%. Thus, results from the 1.2% N experiment indicated that budworm performance was best on diets with sugar concentrations near the lower limit observed for host foliage. This implies that plants with higher foliar sugar may be inferior hosts for the budworm. Field observations supported this conclusion, as putatively resistant Douglas-fir trees had significantly higher levels of sugars in their foliage than nearby paired susceptible trees. Variation in foliar sugars among individual trees may be part of the mechanism in Douglas-fir resistance to C.occidentalis damage.

     

THE RED ALGAL EPIPHYTES MICROCLADIA COULTERI AND M. CALIFORNICA (RHODOPHYCEAE,CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytes Microcladia californica Farl. and M. coulteri Harv. was examined by studying the interface with their respective basiphytes and by cross-inoculation experiments. Microcladia californica attaches only to the surface of its single basiphyte Egregia menziesii (Aresch.) Turn. whereas M. coulteri penetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross-inoculation experiments show that Microcladia californica is not able to colonize the basiphytes of M. coulteri, Iridaea and Prionitis, or Ulva. The mechanisms by which these algae restrict the growth of epiphytes include short life-span, “cuticle peeling” and chemical defense. Microcladia coulteri, which naturally colonizes Iridaea and Prionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of why Egregia is the exclusive substratum for M. californica remains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive to M. californica spore settlement and growth.     

Genetic maladaptation of coastal Douglas-fir seedlings to future climates

Climates are expected to warm considerably over the next century, resulting in expectations that plant populations will not be adapted to future climates. We estimated the risk of maladaptation of current populations of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii) to future climates as the proportion of nonoverlap between two normal distributions where the means and genetic variances of current and future populations are determined from genecological models derived from seedling common garden studies. The risk of maladaptation was large for most traits when compared with the risk associated with current transfers within seed zones, particularly for the more drastic climate change scenario. For example, the proportion of nonoverlap for a composite trait representing bud set, emergence, growth, and root : shoot ratio was as high as 0.90. We recommend augmenting within-population variation by mixing local populations with some proportion of populations from lower elevations and further south. Populations expected to be adapted to climates a century from now come from locations as far down in elevation as 450–1130 m and as far south in latitude as 1.8–4.9°.