Values Of Photosynthetic Capacity Research Articles

Decadal trends in photosynthetic capacity and leaf area index inferred from satellite remote sensing for global vegetation types

In the face of a mounting diversity of experimental, satellite and ground-based observations, it is becoming necessary to simulate all changes associated with vegetation (phenological, structural, physiological and biochemical) and to understand the links between them. In this respect, global land-surface models are an indispensible tool. These models require, above all, a temporally and spatially explicit parameterisation of light- and Rubisco-limited photosynthetic capacity in order to simulate photosynthesis accurately. The current study carries out a novel retrieval of these quantities by combining the standard satellite products of Leaf Area Index (LAI), from the Moderate Resolution Imaging Spectroradiometer (MODIS), with a hyperspectral index of total canopy chlorophyll concentration from the MEdium Resolution Imaging Spectrometer (MERIS). Monthly values of photosynthetic capacity are retrieved for the period 2002–2012 for global 0.5° landpoints and made available to the community. We examine the decadal trends in both photosynthetic capacity and LAI in order to ascertain biochemical and structural responses of vegetation to environmental change. The main conclusion is that these trends, if sustained, are of a sufficient magnitude to vie in importance with other environmental factors which affect vegetation productivity and carbon uptake (e.g. CO2 fertilisation and climate). The decadal trends for Rubisco-limited photosynthetic capacity, which tend to be negative, depend more on plant functional type than latitude, suggesting that biochemical change, like physiological response (e.g. owing to CO2 fertilisation), might best be monitored in terms of vegetation type rather than climate zone. We record an LAI trend which, globally, is flat (−0.2±0.4% per decade) and, for the (mid-)northern latitudes, is much smaller (1.5–2.7% per decade) than that inferred by previous authors for Normalised Difference Vegetation Index (NDVI) during the 1980s (9–13%).

Comparative study of growth and carbon uptake inFagus sylvatica L. trees growing under different light conditions

Growth, carbon uptake and carbon utilization in leaves of various growing phase shoots (GPS) on beech trees(Fagus sylvatica L.) growing under different light conditions were compared. The values of photosynthetic capacity (maximum daily net photosynthetic rate, Pn max) were used as comparable parameters. Daily time and irradiance (I, PhAR), when PN max was attained, were investigated similarly. Statistically significant differences were found in growth, Pn max and SLM (specific leaf mass) between different GPS and within the same stand, as well as within the same GPS and different stands. Pn max and SLM increased in the leaves of GPS I (spring - plagiotropic shoots) on trees from a sun stand from May till September. At the end of the growing season, the spring leaves exhibited, in comparison with the summer ones, intensive senescence, but leaves of the GPS II and III (summer -orthotropic shoots) evidently attained higher values of Px max and SLM at higher I (PhAR). The correlation of growth, PN max and SLM in relation to environmental conditions, as well as the importance of transport, distribution and utilization of assimilates for annual carbon gain and biomass production are discussed in detail.

Photosynthesis in leaf disks as a measure of photosynthetic capacity in crop plants

In a previous communication (Bartoš, Kubín andŠetlík 1960) a method was reported, which makes it possible to measure the average rate of photosynthesis in a representative sample of a large number of leaves. The sampling is made by cutting out disks of leaf tissue, following a definite pattern. Isolated leaf disks are then illuminated under controlled conditions and the rate of photosynthesis is estimated by weighing the increment of dry matter in a given time interval. Data published in the present paper demonstrate that this method can be successfully used for a characterisation of photosynthetic capacity (specific rate of photosynthesis, seeBartoš, Kubín andŠetlík 1960). Both specific values for individual plants and average values for homogenous plant populations may be estimated with very good accuracy. One of the chief factors which render this possible is obviously the surprising homogeneity of the photosynthetic tissue of leaves. Samples of very small size may serve as representative of a large total leaf area, e.g. of a population under field conditions. Preliminary results of comparative investigations suggest that, with the plant varieties examined, differences in photosynthetic capacity are not very great, both between and within populations of diverse varieties. Differences as large as 50% have been encountered so far solely between values of photosynthetic capacity estimated for individual plants in a population. On the other hand, values of average photosynthetic capacity in populations of crop plant varieties within one species or genus are, as a rule, not very distinct and quite often no statistically significant difference can be demonstrated in such cases. Even if the varieties belong to different genera, differences in photosynthetic capacity in their populations greater than some 50% have been found only as an exception. In considering all these results one important fact must be taken into account, i.e. the intensity of illumination in the apparatus. Contrary to what was intended and awaited, the radiation intensity used was not high enough to saturate photosynthesis in leaf disks. The light dependence of photosynthesis in isolated portions of leaf tissue apparently has a somewhat different character from that usually assumed for intact leaves of higher plants.