Photosynthetic responses to carbon dioxide concentration can provide data on a number of important parameters related to leaf physiology. Methods for fitting a model to such data are briefly described. The method will fit the following parameters: V_cmax, J, TPU, R_d and g_m[maximum carboxylation rate allowed by ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco), rate of photosynthetic electron transport (based on NADPH requirement), triose phosphate use, day respiration and mesophyll conductance, respectively]. The method requires at least five data pairs of net CO₂ assimilation (A) and [CO₂] in the intercellular airspaces of the leaf (C_i) and requires users to indicate the presumed limiting factor. The output is (1) calculated CO₂ partial pressure at the sites of carboxylation, C_c, (2) values for the five parameters at the measurement temperature and (3) values adjusted to 25 °C to facilitate comparisons. Fitting this model is a way of exploring leaf level photosynthesis. However, interpreting leaf level photosynthesis in terms of underlying biochemistry and biophysics is subject to assumptions that hold to a greater or lesser degree, a major assumption being that all parts of the leaf are behaving in the same way at each instant.

Isoprene-emitting plants lose a large portion of their assimilated C as isoprene. Because isoprene synthesis can be regulated, it has been assumed that isoprene benefits the plant. Since the rate of isoprene emission from leaves is highly responsive to temperature, we hypothesized that isoprene benefits plants by increasing their thermotolerance. We used three methods to measure isopreneinduced thermotolerance in leaves. Each technique assayed thermotolerance under conditions that suppressed endogenous isoprene synthesis. When measured by chlorophyll fluorescence, thermotolerance of kudzu (Pueraria lobata [Willd.] Ohwi.) leaves increased as much as 4[deg]C in very low light. With higher light, isoprene increased thermotolerance of kudzu leaves by as much as 10[deg]C. When measured as the temperature at which photosynthesis declined to zero, thermotolerance increased with added isoprene by 2.5[deg]C. All three measures of thermotolerance were dose dependent. Both fluorescence techniques also showed isoprene-induced thermotolerance in white oak (Quercus alba L.). Thermotolerance was not observed in bean (Phaseolus vulgaris var Linden), a species that does not emit isoprene. None of the experiments was designed to determine the mechanism of thermotolerance, but we theorize that isoprene functions by enhancing hydrophobic interactions in membranes.

The resorption protection hypothesis, which states that anthocyanins protect foliar nutrient resorption during senescence by shielding photosynthetic tissues from excess light, was tested using wild-type (WT) and anthocyanin-deficient mutants of three deciduous woody species, Cornus sericea, Vaccinium elliottii (Chapmn.), and Viburnum sargentii (Koehne). WT Betula papyrifera (Marsh) was included to compare the senescence performance of a species that does not produce anthocyanins in autumn. Plants were subjected to three environmental regimes during senescence: an outdoor treatment; a 5-d high-stress (high light and low temperature) treatment followed by transfer to a low-stress environment and a low-stress treatment that served as control. In the outdoor treatment, the appearance of anthocyanins in senescing leaves of WT plants was concomitant with the development of photo-inhibition in mutant plants of all three anthocyanin-producing species. In the high-stress environment, WT plants maintained higher photochemical efficiencies than mutants and were able to recover when transferred to the low-stress environment, whereas mutant leaves dropped while still green and displayed signs of irreversible photooxidative damage. Nitrogen resorption efficiencies and proficiencies of all mutants in both stressful treatments were significantly lower than the WT counterparts. B. papyrifera displayed photochemical efficiencies and nitrogen resorption performance comparable with the highest of the anthocyanin-producing species in all three senescing environments, indicating a photoprotective strategy divergent from the other species studied. These results strongly support the resorption protection hypothesis of anthocyanins in senescing leaves.

Norway spruce (Picea abies (L.) Karst.) seedlings growing in a growth pouch system were used to investigate the effects of the ectomycorrhizal fungus Hebeloma crustuliniforme (Bull. ex St. Amans) Quél. and various Cs/K ratios on the uptake of ¹³⁴Cs, expressed as a percentage of the total amount of ¹³⁴Cs supplied. The amount of ¹³⁴Cs taken up by seedlings increased with increasing Cs/K ratio. At a Cs/K ratio of 0.1, uptake of ¹³⁴Cs ranged between 7.2 and 7.3% and was independent of ectomycorrhizal status, whereas at Cs/K ratios ≥ 1 uptake of ¹³⁴Cs varied from 8.1 to 11.1% for ectomycorrhizal and from 10.4 to 14.4% for non-inoculated plants. Ectomycorrhizal seedlings contained a lower concentration of ¹³⁴Cs than non-inoculated seedlings. Among plant parts, the amount of ¹³⁴Cs was significantly lower in needles and lateral roots of ectomycorrhizal seedlings compared with non-inoculated seedlings. Among fungal and seedling tissues, highest X-ray net counts of ¹³³Cs were measured in fungal hyphae of ectomycorrhizal mantles. X-Ray net counts of ¹³³Cs in lateral roots of ectomycorrhizal and non-inoculated plants were similar, but 5 to 10 times higher than in main roots and needles, suggesting an accumulation of ¹³³Cs in lateral roots and slow translocation to other plant parts. In contrast, X-ray net counts of K indicated that K was readily mobilized from lateral roots to main roots and needles. Elemental mapping showed a relatively homogeneous distribution of ¹³³Cs within the root.