Takayoshi Koike

Variations in leaf β13C along a vertical profile of irradiance in a temperate Japanese forest

Abstract The vertical profile of stable carbon isotope ratios (δ13C) of leaves was analyzed for 13 tree species in a cool-temperate deciduous forest in Japan. The vertical distribution of long-term averaged δ13C in atmospheric CO2 (δa) was estimated from δ13C of dry matter from NADP-malic enzyme type C4 plant (Zea mays L. var. saccharata Sturt.) grown at a tower in the forest for 32␣days, assuming constant Δ value (3.3‰) in Z. mays against height. The δa value obtained from δ13C in Z.␣mays was lowest at the forest floor (−9.30 ± 0.03‰), increased with height, and was almost constant above 10␣m (−7.14 ± 0.14‰). Then leaf Δ values for the tree species were calculated from tree leaf δ13 C andδa. Mean leaf Δ values for the three tall deciduous species (Fraxinus mandshurica, Ulmus davidiana, and Alnus hirsuta) were significantly different among three height levels in the forest: 23.1 ± 0.7‰ at the forest floor (understory), 21.4 ± 0.5‰ in lower canopy, and 20.5 ± 0.3‰ in upper canopy. The true difference in tree leaf Δ among the forest height levels might be even greater, because Δ in Z. mays probably increased with shading by up to ∼‰. The difference in tree leaf Δ among the forest height levels would be mainly due to decreasing intercellular CO2 (Ci) with the increase in irradiance. Potential assimilation rate for the three tree species probably increased with height, since leaf nitrogen content on an area basis for these species also increased with height. However, the increase in stomatal conductance for these tree species would fail to meet the increase in potential assimilation rate, which might lead to increasing the degree of stomatal limitation in photosynthesis with height.

Molecular and physiological evaluation of transgenic tobacco plants expressing a maize phosphoenolpyruvate carboxylase gene under the control of the cauliflower mosaic virus 35S promoter

The expression of maize (Zea mays) phosphoenolpyruvate carboxylase (PEPC) gene constructs in transgenic tobacco plants (Nicotiana tabacum) was studied. Where transcription was under the control of a CaMV 35S promoter, maize PEPC transcripts of the correct size were detected. Western blot analysis indicated that the transgenic plants contained about twice as much PEPC as non-transformed plants. Furthermore, the enzymatic activity of PEPC in the leaves of these transgenic plants was up to twice as high as that in non-transformed plants. Two forms of PEPC with different kinetic properties were identified in leaf extracts of the transgenic plants: one form (the maize isoform) gave a high apparentKm value for phosphoenolpyruvate (PEP) and a high maximum activity, and the other (the tobacco isoform) exhibited a low apparentKm value for PEP and a low maximum activity. These biochemical differences resulted in several significant physiological changes in the transgenic plants: (1) the growth rate of the transgenic plants was lower than that of non-transgenic plants: (2) chlorophyll content per leaf area was relatively lower in the transgenic plants; and (3) the quantum yield of photosynthesis in the transgenic plants was not affected by changes in leaf temperature.

Increased susceptibility to photoinhibition in leaves of Japanese elm (Ulmus davidiana var. japonica) with high manganese concentrations

The effects of Mn toxicity on photoinhibition was studied in leaves of Japanese elm (Ulmus davidiana var. japonica) grown hydroponically in three Mn concentrations (1, 10, 50 mg L-1). The degree of photoinhibition was evaluated by measuring the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) using a portable fluorometer. Even after overnight dark acclimation, sustained reduction of Fv/Fm was observed in several high Mn leaves. An exposure to 1 hour of photoinhibitory irradiance (2000 μmol m-2 s-1 PFD) caused an increase in the fast-recovery component of photoinhibition but had little effect on the slow-recovery component suggesting that in leaves grown at high Mn concentrations there are increased photoinhibitory effects that appear to be associated with xanthophyll cycle.

Photosynthetic and Photosynthesis-Related Responses of Japanese Native Trees to CO2: Results from Phytotrons, Open-Top Chambers, Natural CO2 Springs, and Free-Air CO2 Enrichment

We explore the effects of elevated CO2, in relation to other environmental factors, on leaf photosynthesis, the functioning of other organs, and the plant as a unit, primarily in tree species and herbs common to cool temperate forests in northeast Asia. First, results of a series of chlorophyll fluorescence and gas exchange studies using white birch as a model tree species are discussed. Excess energy appears to be suppressed by enhancing photosynthetic capacity or thermal dissipation, depending on the availability of nitrogen in both current and elevated CO2 levels. Next, evidence suggests adaptation of wild plants to CO2 near springs. If some adaptation occurs, plants will not necessarily respond like current plants to future environmental change. Finally, physiological ecology of woody plants grown in open top chambers and Free-Air CO2 Enrichment (FACE) is summarized in relation to the changing environment. This summary emphasizes that effects of future environments on plants should be examined by paying attention not only to CO2 but also to various environmental components, such as soil types, nutrient availability, herbivores, mycorrhizae, ground level O3, and methane emission.