Ichiro Terashima

Is photosynthesis suppressed at higher elevations due to low CO2 pressure

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Photosynthetic properties of leaves of Eupatorium makinoi infected by a geminivirus

We examined photosynthetic properties of Eupatorium makinoi leaves infected by a geminivirus. Since a major symptom of the geminivirus infection is variegation or yellowing of leaves, Chl content was used as an index of disease severity. As leaf Chl content was lowered, leaf absorptance, maximal quantum yield of photosynthesis on an absorbed quantum basis (φo2,max) and light-saturated rate of photosynthesis (Pmax) decreased. The share of energy allocated to PS II, which can be estimated from fluorescence parameters and oxygen evolution rate, was about 30% lower in the infected yellow leaves than in uninfected leaves. Analyses of the composition of thylakoid polypeptides by gel electrophoresis showed preferential loss of LHC II. The lower φo2,maxin the infected leaves was, thus, attributed to the decreased energy allocation to PS II. These features were largely consistent with those of b-less mutants, but lowered Pmaxhas been never reported for b-less mutants. Possible mechanisms causing these changes in photosynthetic properties to the infected leaves are discussed.

Effects of virus infection and light environment on population dynamics of Eupatorium makinoi (Asteraceae).

We studied the effects of virus infection on dynamics of three Eupatorium makinoi populations in contrasting light environments, Gora-dani (a shaded population) and Minou 1 and Minou 2 (open-site populations). Censuses of the plants were taken for 8 yr in Gora-dani and 4 yr in Minou 1 and Minou 2. After the epidemics of virus infection, most plants were virus infected at both sites. The number of plants and the proportion of flowering individuals decreased rapidly and simultaneously in the shaded population in Gora-dani. By contrast, in the open-site populations of Minou, the proportion of flowering plants decreased first, and then the number of plants decreased gradually. Growth analysis of the plants in the Gora-dani population revealed that stem growth was significantly suppressed by infection and that flowering and survivorship of the infected plants decreased with reducing plant height. Since light availability affected plant growth and thereby flowering and survivorship, the differences in population dynamics between the two field sites could be caused by the differences in light environments. Although populations in open sites may persist for considerable periods after virus epidemics, the individual local populations of E. makinoi would eventually become extinct irrespective of light environments.

Differential Analyses of the Effects of the Light Environment on Development of Deciduous Trees: Basic Studies for Tree Growth Modeling

One of the tasks of the ecophysiology team of the Ogawa Forest Reserve (OFR) project was to provide physiological bases for modeling the growth of individual trees, for incorporation into the individual-based model (IBM) of forest dynamics (see Chapter 14).

Leaf Anatomy and Function

Plant leaves provide the following main functions: (1) light interception and utilization of light energy for photosynthesis. This includes efficient light absorption under low and moderate light, while reducing excess light absorption under high light. (2) Incorporating CO2 as the substrate of photosynthesis, while limiting the amount of water lost. (3) Maintaining a stable internal environment for physiological processes by modulating leaf temperature. (4) Maintaining structural integrity that allows leaves to photosynthesize under various mechanical stresses such as gravity, wind, rainfall and herbivory. (5) Transporting water, photosynthates, and nutrients to realize efficient functioning of the plant and the leaf.