Chloroplast position and photosynthetic characteristics in two monostromatic species,Monostroma angicava and Protomonostroma undulatum (Ulvophyceae), having a shared ecological niche

Monostroma angicava and Protomonostroma undulatum are monostromatic green benthic algae (Ulvophyceae), which grow together in the same intertidal habitat of Muroran, Hokkaido, Japan, during the spring season. Commonly, both species have a single chloroplast with one pyrenoid per cell. The parietal chloroplast is located on the periphery of the thallus in both species, although the location of the chloroplast differs in the two. In M. angicava , the chloroplast was observed to be arranged on one‐side of the thallus surface, whereas, in P. undulatum , it was dispersed and randomly located on either side of the thallus or on the lateral face. The density of chlorophylls (Chls) assessed from the absorption spectra of the thallus and its solvent extract was higher in M. angicava , which appeared dark‐green in color, than in the light‐green colored P. undulatum . The maximum photosynthetic rate per thallus area (μmol O₂ m^?2 s^?1) was higher in M. angicava , whereas, per total chlorophyll content (μmol O₂ g Chl a + Chl b ^?1 s^?1) was higher in P. undulatum . Both species showed similar efficiency of photosynthesis at light‐limiting conditions. The efficiency of light absorption by photosystem II (PSII ) in P. undulatum was higher than M. angicava , whereas the photoprotective response was higher in M. angicava . This indicates that more energy is utilized in M. angicava to protect its PSII due to the chloroplast position, which has more direct exposure to light and, therefore, lowers the efficiency of light absorption by PSII . The higher density of chlorophylls in M. angicava could explain higher photosynthesis per thallus area, whereas, higher efficiency of light absorption by PSII in P. undulatum could explain higher photosynthesis per total chlorophyll content. The differences in light absorption efficiency and quantum efficiency of PSII might be an important ecological strategy in these two species for their coexistence in the intertidal area.     

Intra- and inter-specific variation in canopy photosynthesis in a mixed deciduous forest

 Within the same forest, photosynthesis can vary greatly among species and within an individual tree. Quantifying the magnitude of variation in leaf-level photosynthesis in a forest canopy will improve our understanding of and ability to model forest carbon cycling. This information requires extensive sampling of photosynthesis in the canopy. We used a 22-m-tall, four-wheel-drive aerial lift to reach five to ten leaves from the tops of numerous individuals of several species of temperate deciduous trees in central Massachusetts. The goals of this study were to measure light-saturated photosynthesis in co-occurring canopy tree species under field conditions, and to identify sampling schemes appropriate for canopy tree studies with challenging logistics. Photosynthesis differed significantly among species. Even though all leaves measured were canopy-top, sun-acclimated foliage, the more shade-tolerant species tended to have lower light-saturated photosynthetic rates (P _max) than the shade-intolerant species. Likewise, leaf mass per area (LMA) and nitrogen content (N) varied significantly between species. With only one exception, the shade-tolerant species tended to have lower nitrogen content on an area basis than the intolerant species, although the LMA did not differ systematically between these ecological types. Light-saturated P _max rates and nitrogen content, both calculated on either an area or a mass basis, and the leaf mass to area ratio, significantly differed not only among species, but also among individuals within species (P<0.0001 for both). Differences among species accounted for a greater proportion of variance in the P _max rates and the nitrogen content than the differences among individuals within a species (58.5–78.8% of the total variance for the measured parameters was attributed to species-level differences versus 5.5–17.4% of the variance was attributed to differences between individual trees of a given species). Furthermore, more variation is accounted for by differences among leaves in a single individual tree, than by differences among individual trees of a given species (10.7–30.4% versus 5.5–17.4%). This result allows us to compare species-level photosynthesis, even if the sample size of the number of trees is low. This is important because studies of canopy-level photosynthesis are often limited by the difficulty of canopy access. As an alternative to direct canopy access measurements of photosynthesis, it would be useful to find an ”easy-to-measure” proxy for light-saturated photosynthetic rates to facilitate modeling forest carbon cycling. Across all species in this study, the strongest correlation was between nitrogen content expressed on an area basis (mmol m^–2, N _area) and light-saturated P _max rate (μmol m^–2 s^–1, P _maxarea) (r ²=0.511). However, within a given species, leaf nitrogen was not tightly correlated with photosynthesis. Our sampling design minimized intra-specific leaf-level variation (i.e., leaves were taken only from the top of the canopy and at only one point in the season). This implies that easy-to-measure trends in nitrogen content of leaves may be used to predict the species-specific light-saturated P _max rates. Received: 16 March 1996 / Accepted: 16 August 1996     

基于流速梯度的河流生境多样性分析——以长江湖北宜昌中华鲟自然保护区核心区江段为例

选取量化断面沿水平方向和沿测流垂线方向流速变化的8个流速梯度指标,并根据这8个指标和2005年12月2-10日采用声学多普勒流速剖面仪(ADCP)在长江葛洲坝至红花套江段走航观测所获得的285个断面的原型数据,对长江葛洲坝至红花套江段生境多样性进行了分析.结果表明:葛洲坝至红花套江段水深以4.71～12.04 m居多;据断面平均流速和8个流速梯度指标采用k均值分类法分析,整个江段以第7类、第8类和第2类区域占主要优势,这3类区域面积共占整个江段面积的88.66%,葛洲坝至庙咀江段为整个研究江段各类区域相间分布最多样化的江段;采用尺型聚类方法分析,断面平均流速与断面8个流速梯度指标之间没有显著的相关性,即具有相同流速的区域不一定具有相似的流速梯度特征,有必要用这些流速梯度指标描绘水流的特性.ADCP在河流水流生境多样性评估、河流生态修复等方面具有较大的潜能,但在数据采集规范、后期数据处理等方面还需作进二步探讨.     

SEASONAL PHOTOSYNTHETIC PERFORMANCE OF MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1

The seasonal photosynthetic performances of three age classes of blades of Macrocystis integrifolia Bory were estimated by studying their photosynthetic rate vs. irradiance curves and pigment contents for 15 months. All blade types were irradiance-saturated between 25 and 70 μE · m^?2· S^?1. Young and mature blade tissues had higher photosynthetic maxima and initial slopes on an area basis than older blade tissue. The latter, however, had pigment concentrations similar to those in mature blade tissues. All these parameters varied on a seasonal basis. The photosynthetic maxima ranged from 0.1–0.8 μmol · C · cm^?2· h^?t and showed two peaks, one in late summer-early fall and the other in late winter. Changes in initial slope and pigment concentrations in the blade tissues suggest that, changes in the size or efficiency of electron transfer in the photosynthetic unit occur. These data are discussed in relation to changes in seawater temperature and nitrate concentrations.