独叶草的光合生理生态特性

应用CI-301PS便携式光合测定仪对独叶草(Kingdonia uniflora)营养叶的光合生理生态特征进行了研究.结果表明:独叶草的净光合速率(Pn)日变化曲线呈双峰型,峰值出现在13:30和16:30左右,具有明显的光合"午休"现象;其叶片的蒸腾速率(Tr),水分利用率(WUE)的变化也呈双峰型.自然条件下,独叶草叶片净光合速率与光合有效辐射(PAR)、蒸腾速率、气孔导度(Gs)之间都具有多项式回归关系,R2分别为0.2082、0.2016和0.0582(n=129,P＜0.05),但独叶草叶片净光合速率与空气温度(Ta)相关性不显著(P＞0.05).独叶草叶片的光补偿点(LCP)、光饱和点(LSP)分别为14.93和215.76 μmol·m-2·s-1,只能适应较窄的光照环境.     

南海主要珊瑚礁水域的鱼类物种多样性研究

根据2004年5–7月和2005年3–4月采用深水三重刺网在南海的羚羊礁、华光礁、银砾滩、东岛、滨湄滩、排洪滩、本固暗沙、比微暗沙、武勇暗沙、海鸠暗沙、双子群礁、中业群礁、鲎藤礁、美济礁、仁爱礁、仙宾礁、南方浅滩、棕滩、大渊滩、永署礁、南薰礁、牛轭礁、道明群礁等23座主要珊瑚礁过渡性水域进行的2个航次专业调查资料, 分析了南海主要珊瑚礁水域的鱼类种类组成和群落特征。结果表明, 在珊瑚礁水域软骨鱼类以真鲨目和鲼目的种类数占优势, 硬骨鱼类以鲈形目和鲀形目的种类数占优势。相对重要指数(IRI)大于500的鱼类定为优势种, 西沙群岛有5种, 分别为迈氏条尾魟(Taeniura meyeni)、长吻裸颊鲷(Lethrinus miniatus)、胡椒鲷(Plectorhinchus pictus)、黄斑胡椒鲷(P. flavomaculatus)和灰六鳃鲨(Hexanchus griseus); 中沙群岛有6种, 分别为黄斑胡椒鲷、迈氏条尾魟、圆燕鱼(Platax orbicularis)、密斑刺鲀(Dioson hystrix)、红裸颊鲷(Lethrinus rubrioperculatus)和胡椒鲷; 南沙群岛有3种, 分别为黑梢真鲨(Carcharhinus limbatus)、灰三齿鲨(Triaenodon obesus)和星点鲹(Caranx stellatus)。针对南海珊瑚礁水域鱼类个体大小悬殊的特点, 本文分别以个体数和生物量为基础计算该水域的Margalef丰富度指数、Shannon-Wiener多样性指数、Simpson多样性指数和Pielou均匀度指数。物种组成的区域差异分析结果表明, 各珊瑚礁水域的鱼类物种无论与南海北部陆架海域还是与南沙西南陆架区相比都有明显的差异, 而属于相同生境类型水域的鱼类物种相似性较高。     

Cross validation of open-top chamber and eddy covariance measurements of ecosystem CO2 exchange in a Florida scrub-oak ecosystem

Simultaneous measurements of net ecosystem CO₂ exchange (NEE) were made in a Florida scrub‐oak ecosystem in August 1997 and then every month between April 2000 to July 2001, using open top chambers (NEE_O) and eddy covariance (NEE_E). This study provided a cross validation of these two different techniques for measuring NEE. Unique characteristics of the comparison were that the measurements were made simultaneously, in the same stand, with large replicated chambers enclosing a representative portion of the ecosystem (75 m², compared to approximately 1–2 ha measured by the eddy covariance system). The value of the comparison was greatest at night, when the microclimate was minimally affected by the chambers. For six of the 12 measurement periods, night NEE_O was not significantly different to night NEE_E, and for the other periods the maximum difference was 1.1 µ mol m ^{? 2}s ^{? 1}, with an average of 0.72 ± 0.09 µ mol m ^{? 2}s ^{? 1}. The comparison was more difficult during the photoperiod, because of differences between the microclimate inside and outside the chambers. During the photoperiod, air temperature (T_air) and air vapour pressure deficits (VPD) became progressively higher inside the chambers until mid‐afternoon. In the morning NEE_O was higher than NEE_E by about 26%, consistent with increased temperature inside the chambers. Over the mid‐day period and the afternoon, NEE_O was 8% higher that NEE_E, regardless of the large differences in microclimate. This study demonstrates both the uses and difficulties associated with attempting to cross validate NEE measurements made in chambers and using eddy covariance. The exercise was most useful at night when the chamber had a minimal effect on microclimate, and when the measurement of NEE is most difficult.     

我国不同季节陆地植被NPP对气候变化的响应

阐明不同季节陆地植被净第一性生产力（NPP）对全球变化的响应将有助于理解陆地生态系统和气候系统之间的相互作用以及NPP变化机制。本文使用1982－1999年间的AVHRR／NDVI、气温、降水以及太阳辐射等资料,结合植被分布图和土壤质地图,利用生态过程模型,研究不同季节我国陆地植被NPP的年际变化及其地理分异。结果表明,在1982－1999年的18年间,4个季节的NPP都呈显著增加趋势。其中,春季是NPP增加速率最快的季节,夏季是NPP增加量最大的季节,不同植被类型对全球变化的响应有很大差异。常绿阔叶林,常绿针叶林和落叶针叶林NPP的增加主要由生长季节的提前所致。而落叶阔叶林、针阔混交林、矮林灌丛,温带草原及草甸,稀树草原、高寒植被,荒漠以及人工植被NPP的增加主要来自生长季生长加速的贡献。从区域分布看,在四季中春季NPP增加量最大的地区主要集中在东部季风区域;夏季NPP增量最大的地区包括西北干旱区域和青藏高原的大部分地区,小兴安岭－长白山区,三江平原,松辽平原,四川盆地,雷州半岛,长江中下游部分地区以及江南山地东部;而秋季植被NPP增加量最大的地区主要有云南高原－西藏东部和呼伦湖的周围等地区。不同植被和地理区域NPP的这些响应方式与区域气候特征及其变化趋势有关。     

Effects of phosphorus and chilling under low irradiance on photosynthesis and growth of tomato plants

To determine the effects of phosphorus nutrition on chilling tolerance of photosynthetic apparatus, tomato (Lycopersicon esculentum Mill. cv. Kenfengxin 2002) plants were raised under different P contents and subjected to 7 d of chilling at 9/7 °C. After chilling (2 h or 7 d) plant growth, P content in tissue, gas exchange and chlorophyll fluorescence were measured. Decreasing P concentration [P] in the nutrient solution markedly reduced plant growth and the chilled plants exhibiting higher optimum [P] than the unchilled plants. Decreasing [P] significantly decreased light saturated net photosynthetic rate (P_Nsat), maximum carboxylation velocity of Rubisco (V_cmax), maximum potential rate of electron transport contributed to Rubisco regeneration (J_max), quantum efficiency of photosystem (PS) 2 (ΠPS2) and O₂ sensitivity of P_Nsat (PS_O2) and this trend was especially apparent in chilled plants.     

The biomass and aboveground net primary productivity of <Emphasis Type="Italic">Schima superba-Castanopsis carlesii</Emphasis> forests in east China

The biomass and productivity of Schima superba-Castanopsis carlesii forests in Tiantong, Zhejiang Province, were determined using overlapping quadrants and stem analyses. The total community biomass was (225.3±30.1) t hm⁻², of which the aboveground parts accounted for 72.0% and the underground parts accounted for 28.0%. About 87.2% of biomass existed in the tree layer. The resprouting biomass was small, of which over 95.0% occurred in the shrub layer. The productivity of the aboveground parts of the community was (386.8±98.9) g m⁻²a⁻¹, in which more than 96.0% was present at the tree level. The trunk’s contribution to productivity was the greatest, while that of leaves was the smallest. In China, the community biomass of subtropical evergreen broadleaved forests differs significantly with the age of the forest. The community biomass of the 52-year-old S. superba-C. carlesii forests in this study was lower than the average biomass of subtropical evergreen broadleaved forests in China, and was lower than the biomass of other subtropical evergreen broadleaved forests elsewhere in the world. Moreover, its productivity was lower than the model estimate, indicating that without disturbance, this community has great developmental potential in terms of community biomass and productivity.     

Relationship between δ13C and photosynthetic parameters and their responses to leaf nitrogen content in six broadleaf tree species

Stable carbon isotope composition (δ¹³C), net photosynthetic rate (P _N), actual quantum yield of photosystem 2 (PS2) electron transport (ΦPS2), nitrogen content (N_c), and photosynthetic nitrogen use efficiency (PNUE) in the leaves of six broadleaf tree species were determined under field environmental conditions. The six tree species were Magnolia liliflora Desr., M. grandiflora Linn., M. denudata Desr., Prunus mume (Sieb.) Sieb. et Zucc. cv. Meiren Men, P. mume (Sieb.) Sieb. et Zucc. f. alphandii (Carr.) Rehd., and P. persica (L.) Batsch. var. rubro-plena. The relationships among δ¹³C, Φ_PS2, P _N, and PNUE, as well as their responses to N_c in the six species were also studied. Both P _N and δ¹³C negatively correlated with N_c, but Φ_PS2 positively correlated with N_c. This indicated that with N_c increase, P _N and δ¹³C decreased, while Φ_PS2 increased. There were weak negative correlations between δ¹³C and PNUE, and strong negative correlations (p<0.01) between Φ_PS2 and PNUE. According to the variance analysis of parameters, there existed significant interspecific differences (p<0.001) of δ¹³C, P _N, Φ_PS2, PNUE, and N_c among the tree seedlings of the six tree species, which suggests that the potential photosynthetic capacities depend on plant species, irradiance, and water use capacity under field conditions.     

Temperature and rainfall interact to control carbon cycling in tropical forests

Tropical forests dominate global terrestrial carbon (C) exchange, and recent droughts in the Amazon Basin have contributed to short‐term declines in terrestrial carbon dioxide uptake and storage. However, the effects of longer‐term climate variability on tropical forest carbon dynamics are still not well understood. We synthesised field data from more than 150 tropical forest sites to explore how climate regulates tropical forest aboveground net primary productivity (ANPP) and organic matter decomposition, and combined those data with two existing databases to explore climate – C relationships globally. While previous analyses have focused on the effects of either temperature or rainfall on ANPP, our results highlight the importance of interactions between temperature and rainfall on the C cycle. In cool forests (< 20 °C), high rainfall slowed rates of C cycling, but in warm tropical forests (> 20 °C) it consistently enhanced both ANPP and decomposition. At the global scale, our analysis showed an increase in ANPP with rainfall in relatively warm sites, inconsistent with declines in ANPP with rainfall reported previously. Overall, our results alter our understanding of climate – C cycle relationships, with high precipitation accelerating rates of C exchange with the atmosphere in the most productive biome on earth.     

Temperature–nutrient interactions exacerbate sensitivity to warming in phytoplankton

Temperature and nutrients are fundamental, highly nonlinear drivers of biological processes, but we know little about how they interact to influence growth. This has hampered attempts to model population growth and competition in dynamic environments, which is critical in forecasting species distributions, as well as the diversity and productivity of communities. To address this, we propose a model of population growth that includes a new formulation of the temperature–nutrient interaction and test a novel prediction: that a species’ optimum temperature for growth, T_opt, is a saturating function of nutrient concentration. We find strong support for this prediction in experiments with a marine diatom, Thalassiosira pseudonana: T_opt decreases by 3–6 °C at low nitrogen and phosphorus concentrations. This interaction implies that species are more vulnerable to hot, low‐nutrient conditions than previous models accounted for. Consequently the interaction dramatically alters species’ range limits in the ocean, projected based on current temperature and nitrate levels as well as those forecast for the future. Ranges are smaller not only than projections based on the individual variables, but also than those using a simpler model of temperature–nutrient interactions. Nutrient deprivation is therefore likely to exacerbate environmental warming's effects on communities.     

Pinus taeda forest growth predictions in the 21st century vary with site mean annual temperature and site quality

Climate projections from 20 downscaled global climate models (GCMs) were used with the 3‐PG model to predict the future productivity and water use of planted loblolly pine (Pinus taeda) growing across the southeastern United States. Predictions were made using Representative Concentration Pathways (RCP) 4.5 and 8.5. These represent scenarios in which total radiative forcing stabilizes before 2100 (RCP 4.5) or continues increasing throughout the century (RCP 8.5). Thirty‐six sites evenly distributed across the native range of the species were used in the analysis. These sites represent a range in current mean annual temperature (14.9–21.6°C) and precipitation (1,120–1,680 mm/year). The site index of each site, which is a measure of growth potential, was varied to represent different levels of management. The 3‐PG model predicted that aboveground biomass growth and net primary productivity will increase by 10%–40% in many parts of the region in the future. At cooler sites, the relative growth increase was greater than at warmer sites. By running the model with the baseline [CO₂] or the anticipated elevated [CO₂], the effect of CO₂ on growth was separated from that of other climate factors. The growth increase at warmer sites was due almost entirely to elevated [CO₂]. The growth increase at cooler sites was due to a combination of elevated [CO₂] and increased air temperature. Low site index stands had a greater relative increase in growth under the climate change scenarios than those with a high site index. Water use increased in proportion to increases in leaf area and productivity but precipitation was still adequate, based on the downscaled GCM climate projections. We conclude that an increase in productivity can be expected for a large majority of the planted loblolly pine stands in the southeastern United States during this century.