Fractionation and solubility of cadmium in paddy soils amended with porous hydrated calcium silicate

Previous studies have shown that porous hydrated calcium silicate （PS） is very effective in decreasing cadmium （Cd） content in brown rice. However, it is unclear whether the PS influences cadmium transformation in soil. The present study examined the effect of PS on pH, cadmium transformation and cadmium solubility in Andosol and Alluvial soil, and also compared its effects with CaCO3, acidic porous hydrated calcium silicate （APS） and silica gel. Soil cadmium was operationally fractionationed into exchangeable （Exch）, bound to carbonates （Carb）, bound to iron and manganese oxides （FeMnOx）, bound to organic matters （OM） and residual （Res） fraction. Application of PS and CaCO3 at hig rates enhanced soil pH, while APS and silica gel did not obviously change soil pH. PS and CaCO3 also increased the FeMnOx-Cd in Andosol and Carb-Cd in Alluvial soil, thus reducing the Exch-Cd in the tested soils. However, PS was less effective than CaCO3 at the same application rate. Cadmium fractions in the two soils were not changed by the treatments of APS and silica gel. There were no obvious differences in the solubility of cadmium in soils treated with PS, APS, silica gel and CaCO3 except Andosol treated 2.0% CaCO3 at the same pH of soil-CaC12 suspensions. These findings suggested that the decrease of cadmium availability in soil was mainly attributed to the increase of soil pH caused by PS.     

Vertical zonation of endosymbiotic zooxanthellae within a population of the intertidal sea anemone,Anthopleura uchidai

Intertidal organisms commonly form zonation bands along the shore. Environmental stressors often determine the vertical position of each zonation band. These stressors may similarly affect the distribution pattern of endogenous species in their intertidal hosts. To evaluate this possibility, we investigated the distribution pattern of endosymbiotic zooxanthellae in the genus Symbiodinium in a population of the intertidal sea anemone Anthopleura uchidai. We used molecular genetics to identify the Symbiodinium clades and found that A. uchidai has two clades of Symbiodinium, clades A and F. These Symbiodinium clades were disproportionally distributed along the vertical gradient of the intertidal shore. Anemones on the upper shore exclusively possessed clade F Symbiodinium while clade A Symbiodinium became dominant in the sea anemones on the lower shore. Photosynthesis activity assays showed that these Symbiodinium clades had similar net productivities at 23.3 and 31.8 °C at all irradiance levels. At 35 °C, however, clade A Symbiodinium exhibited substantially lower net productivities than clade F Symbiodinium, demonstrating that these Symbiodinium clades have distinct tolerances to thermal stress. These results suggest that the thermal gradient across tidal height is a major factor shaping the zonation pattern of Symbiodinium clades in A. uchidai.     

Rhythmic patterns of abundance in small sublittoral crustaceans: variety in the synchrony with day/night and tidal cycles

Temporal fluctuations of abundance (or emergence) in small benthic and planktonic crustaceans were studied in shallow subtidal waters (1.5 to 3.5 m in tide height). The abundances were more or less rhythmic, and showed wide diversity ranging from very clear nocturnal patterns to patterns in sychrony with the tidal cycle alone. These abundance patterns were classified into categories relating to the degree of synchrony with day/night and tidal cycles. Nocturnal patterns were especially strong in benthic crustaceans, which would be inactive during the daytime, being attached to algae and stones or disappearing into rock crevices, and actively swim in the water at night. Mysis larvae also showed a clear nocturnal pattern. Their lifestyle might be similar to that of many benthic animals. Other planktonic crustaceans drifting in the water showed weak nocturnal patterns. In some planktonic crustaceans (e.g., Calanoida), the ratio of abundance in the surface and bottom samples was reversed between day and night. Their pattern might be a manifestation of weak diel vertical movement between day and night. Furthermore, most patterns of zooplankton and benthos were modified in synchrony with tides to various degrees. Small crustaceans may respond to changes of hydrologic variables fluctuating with the tides, which may exogenously produce a weak tidal component in their emergence patterns. Received: 12 January 1998 / Accepted: 29 August 1998     

Circatidal rhythm of an intertidal crab, Hemigrapsus sanguineus : synchrony with unequal tide height and involvement of a light-response mechanism

The circatidal rhythm of intertidal animals may reflect the inequality of the tides. In addition, a light-sensitive mechanism may be involved in their internal timing systems. To test these hypotheses, the larval release activity of the intertidal crab Hemigrapsus sanguineus was monitored under different light conditions in the laboratory. Under a 24-h light–dark (LD) cycle with the phase similar to the field, the activity coincided with the times of high tide in the field and showed a tidal rhythm. This rhythm free-ran in constant, dim-light conditions, suggesting that the timing is controlled by an endogenous clock. When the population was exposed to a 24-h LD cycle with the phase changed from that in the field, the tidal rhythm was phase-shifted; while the light cycle advanced in phase from the field caused a phase-advance of the rhythm, that delayed in phase induced a phase-delay of the rhythm. Thus, a light-response mechanism is definitely involved in circatidal timing systems. But the population rhythm showed a large variability among individuals, associated with the phase-shift, and the magnitude of the phase-shift did not accurately correspond to that of the light cycle. These results suggest that the light-response system can control the phase of the rhythm less stronger than that in estuarine crabs. Most releases occurred at higher high tides, but the release of some females obviously occurred at lower high tides. The larval release pattern thus could not be accounted for by a simple synchrony with higher high tides. Hatching of H. sanguineus occurred after a “hatching program” of 49.5 to 52.5 h. This program is initiated by some factor (hatching-program inducing stumuli: HPIS) transmitted from the female to the embryos. We speculated that this factor is effectively transmitted to the embryos when the habitat is exposed to air, i.e., at lower low-tide periods, and that once each embryo is stimulated, hatching occurs synchronously 2 d later during high tide. The release of HPIS is probably controlled by the circatidal clock of the female, and the 24-h LD cycle may participate in shifting this timing to the opposite low tide. Received: 14 January 1997 / Accepted: 18 February 1997     

Net ecosystem CO2 exchange over a larch forest in Hokkaido, Japan

Larch forests are distributed extensively in the east Eurasian continent and are expected to play a significant role in the terrestrial ecosystem carbon cycling process. In view of the fact that studies on carbon exchange for this important biome have been very limited, we have initiated a long-term flux observation in a larch forest ecosystem in Hokkaido in northern Japan since 2000. The net ecosystem CO₂ exchange (NEE) showed large seasonal and diurnal variation. Generally, the larch forest ecosystem released CO₂ in nighttime and assimilated CO₂ in daytime during the growing season from May to October. The ecosystem started to become a net carbon sink in May, reaching a maximum carbon uptake as high as 186 g C m⁻² month⁻¹ in June. With the yellowing, senescing and leaf fall, the ecosystem turned into a carbon source in November. During the non-growing season, the larch forest ecosystem became a net source of CO₂, releasing an average of 16.7 g C m⁻² month⁻¹. Overall, the ecosystem sequestered 141–240 g C m⁻² yr⁻¹ in 2001. The NEE was significantly influenced by environmental factors. Respiration of the ecosystem, for example, was exponentially dependent on air temperature, while photosynthesis was related to the incident PAR in a manner consistent with the Michaelis–Menten model. Although the vapor pressure deficit (VPD) was scarcely higher than 15 hPa, the CO₂ uptake rate was also depressed when VPD surpassed 10 hPa.     

PnET-CN模型对东亚森林生态系统碳通量模拟的适用性和不确定性分析

东亚地区森林类型多样,开展区域生态系统碳循环模拟时应考虑森林类型的差异。论文利用基于叶氮浓度-最大净光合作用速率关系的PnET-CN模型,对东亚地区8 个森林生态系统通量观测站点的总生态系统碳交换（GEE）和生态系统呼吸（RE）进行模拟,以探讨模型的适用性并对不确定性来源进行分析。研究结果表明：①PnET-CN模型能较为准确地模拟东亚地区大部分森林生态系统站点的GEE和RE;②模型的适用性排序依次为温带、寒温带、亚热带、 热带,模型未能很好地模拟热带湿地森林GEE和RE 的季节与年际变异;③在同一气候区中,PnET-CN模型更加适用于针叶林碳交换的模拟;④PnET-CN模型比较准确地反映了东亚森林生态系统GEE、RE对气候因子（例如,温度或辐射）的响应,但在低温、较弱辐射条件下模型低估了GEE,在高温或较强辐射条件下高估了GEE;在低温条件下模型低估了RE,在高温条件下模型高估了RE。针对东亚多个森林通量站点的模拟情况,论文提出模型应在以下方面进行改进：①PnET-CN模型计算物候时除了考虑温度之外还应加入土壤湿度的影响,并对不同气候区森林生态系统赋予不同叶片凋落时长;②PnET-CN模型中温度对GEE的限制以及光合最适温度应该根据不同站点设置;③PnET-CN模型应该考虑森林生态系统对环境胁迫的适应性,加强对干旱等干扰的模拟;④同时对于拥有复杂水文条件的森林生态系统应该改进土壤含水量的算法,以准确反映该类型森林生态系统GEE和RE的季节变化。