Variations in daytime net carbon and water exchange in a montane shrubland ecosystem in southeast Spain

Carbon and water fluxes in a semiarid shrubland ecosystem located in the southeast of Spain (province of Almería) were measured continuously over one year using the eddy covariance technique. We examined the influence of environmental variables on daytime (photosynthetically active photons, F _P >10 μmol m⁻² s⁻¹) ecosystem gas exchange and tested the ability of an empirical eco-physiological model based on F _P to estimate carbon fluxes over the whole year. The daytime ecosystem fluxes showed strong seasonality. During two solstitial periods, summer with warm temperatures (>15 °C) and sufficient soil moisture (>10 % vol.) and winter with mild temperatures (>5 °C) and high soil moisture contents (>15 % vol.), the photosynthetic rate was higher than the daytime respiration rate and mean daytime CO₂ fluxes were ca. −1.75 and −0.60 μmol m⁻² s⁻¹, respectively. Daytime evapotranspiration fluxes averaged ca. 2.20 and 0.24 mmol m⁻² s⁻¹, respectively. By contrast, in summer and early autumn with warm daytime temperatures (>10 °C) and dry soil (<10 % vol.), and also in mid-winter with near-freezing daytime temperatures the shrubland behaved as a net carbon source (mean daytime CO₂ release of ca. 0.60 and 0.20 μmol m⁻² s⁻¹, respectively). Furthermore, the comparison of water and carbon fluxes over a week in June 2004 and June 2005 suggests that the timing—rather than amount—of spring rainfall may be crucial in determining growing season water and carbon exchange. Due to strongly limiting environmental variables other than F _P, the model applied here failed to describe daytime carbon exchange only as a function of F _P and could not be used over most of the year to fill gaps in the data.     

盐度、温度和光照强度对针叶蕨藻的生长及光合活性的影响

为探究环境因子对针叶蕨藻（Caulerpa sertularioides）生长的影响,对不同盐度、温度和光照强度下针叶蕨藻的生长和叶绿素荧光参数进行了研究。结果表明：藻体日特定生长率（SGR）、最大光量子产量（F_v/F_m）、实际光合效率（Yield）、电子传递速率（ETR）和光化学淬灭（qP）随盐度升高呈先上升后下降的变化趋势,非光化学淬灭（qN）则呈相反的变化趋势,藻体光合活性和固碳效率在盐度27.5‰时达到最高,且与25‰和30‰盐度的差异显著（P<0.05,n=3）。藻体SGR、F_v/F_m、Yield、ETR和qP随温度升高而下降,qN则相反,藻体光合活性和固碳效率在26℃下达到最高,且与28℃和30℃的差异显著（P<0.05,n=3）。藻体的SGR、F_v/F_m、Yield、ETR和qP随光照强度升高呈先上升后下降的变化趋势,qN则相反,且在18.75 μmol/（m²·s）弱光照下出现轻微光抑制,藻体生长、光合活性及固碳效率在光照强度25.00 μmol/（m²·s）时达到最高,但与18.75和31.25 μmol/（m²·s）的差异不显著（P>0.05,n=3）。因此,针叶蕨藻在27.5‰盐度、26℃和25.00 μmol/（m²·s）光照强度下生长最快且光合作用能力最高。     

3种无脊椎动物对近江牡蛎Crassostrea ariakensis和熊本牡蛎C. sikamea的捕食研究

捕食是影响牡蛎种群建立和牡蛎礁发育的重要生物因子之一。通过室内受控实验测定了日本蟳（Charybdis japonica）、脉红螺（Rapana venosa）和黄口荔枝螺（Thais luteostoma）对4组规格（W1：壳高10-20mm;W2：壳高20-30mm;W3：壳高30-40mm;W4：壳高>40mm）近江牡蛎（Crassostrea ariakensis）和熊本牡蛎（C.sikamea）的捕食偏好性和捕食效率。双因子方差分析结果表明,日本蟳对2种牡蛎的捕食效率没有显著性差异（P>0.05）,但牡蛎规格大小显著影响着日本蟳的捕食效率（P<0.05）,即日本蟳对W1组近江牡蛎的捕食效率显著高于W2和W4组（P<0.05）,W3组的被捕食效率介于中间（P>0.05）;日本蟳对W1组熊本牡蛎的捕食效率显著高于W2和W3组（P<0.05）,W4组的被捕食效率与其他处理组均没有显著性差异（P>0.05）。牡蛎种类（P=0.590）和规格大小（P=0.357）对脉红螺的捕食效率均无显著性影响,不同规格的两种牡蛎均呈现较低的被捕食效率。黄口荔枝螺对2种牡蛎的捕食效率无显著性差异（P=0.917）,但牡蛎规格大小显著影响其捕食效率（P=0.035）,即对W1组熊本牡蛎捕食效率显著高于其他3个规格组（P<0.05）,但其对不同规格近江牡蛎的捕食效率没有显著性差异（P>0.05）。2种牡蛎的壳厚与其壳高之间均存在极显著的正相关关系（P<0.001）。研究结果表明,3种无脊椎动物捕食者对近江牡蛎和熊本牡蛎并未表现出差异性的捕食偏好,但对不同规格牡蛎的捕食效率具有种间差异。     

Phytoplankton primary production in a mesotrophic pond in sub-tropical Bangladesh

Annual gross primary productivity in mesotrophic Shahidullah Hall pond (Dhaka, Bangladesh) was 1383.35 g C m⁻² y⁻¹ (arithmetic mean). Daily primary productivity (between 1.6 and 6.8 g C m⁻² d⁻¹ was correlated with chlorophylla, day length and dissolved silica. Chlorophylla related significantly withk, incident light, SRP, alkalinity and conductivity. A negative correlation existed between biomass and rainfall. Productivity, biomass, conductivity, alkalinity, and SRP increased after mid-winter.k, I _k andZ _eu varied according seasonally.P _max related directly with temperature. Seasonal variation of ∝ ^B was 0.0049–0.0258 mg C (mg chla mmol PAR)⁻¹ m⁻². Q₁₀ was 2.12, community respiration 1334.99 g C m⁻² y⁻¹, and the underwater light climate 186.43μE m⁻² s⁻¹.     

川西平原小流域不同水体N2O排放特征及驱动因素

氧化亚氮（N₂O）是一种潜在的、强大的温室气体,应该根据京都议定书规定开展监测和削减。河流、水库、鱼塘和沟渠等受人类影响的小流域水生生态系统是氮素生物地球化学循环的活跃区域,更是N₂O重要的源和汇。然而,同一流域不同水体N₂O的排放特征差异及其驱动因素尚不清楚。因此,选择川西平原西河流域作为研究区,于2016年6月到2017年5月连续监测不同水体水气界面的N₂O排放强度,并结合聚类分析解析N₂O排放特征的驱动因素。结果显示,不同水体的N₂O年排放通量差异显著,沟渠的N₂O年排放通量最高（（52.68±36.09）μg m^-2 h^-1）,城市段河流和鱼塘次之（（34.16±23.97）μg m^-2 h^-1和（29.03±31.41）μg m^-2 h^-1）,乡镇段和农区段河流再次（（8.32±28.60）μg m^-2 h^-1和（8.52±9.43）μg m^-2 h^-1）,水库最低（（-16.45±29.76）μg m^-2 h^-1）。除水库表现为N₂O的汇,其他水体均表现为N₂O的排放源。另外,不同水体N₂O排放的季节特征差异显著,农区段河流和农业沟渠表现为夏天最高,冬春最低（P<0.05）,而其他水体均表现为冬春显著高于夏秋（P<0.05）。根据N₂O排放季节特征及其驱动因素可将西河流域水体分为四类：第一类农业类水体的N₂O排放季节特征受气象因素和农业活动的联合驱动;第二类城乡类河流和第三类鱼塘分别受控于人类活动和养殖活动,与降雨温度等气象指标关系较弱;第四类水库主要受控于气象因素。并且,第一类农业类水体已成为大气N₂O排放的重要源,农业氮素管控是区域控制N₂O排放的重点。     

湖北省农村地区住院服务利用的家庭聚集性分析

目的 了解湖北省农村地区住院服务利用的家庭聚集性大小及其分布。方法 以湖北省麻城市2014年新农合住院数据库为基础，利用Excel 2010中的“IF”“LOOKUP”等函数获取样本县区所有农村家庭的住院利用情况；利用面积图和散点图绘出洛伦兹曲线并计算出基尼系数；采用IBM SPSS Statistic 22.0对数据进行描述性统计和方差分析等。结果 3%的家庭利用了19%的住院服务，农村家庭住院服务利用的基尼系数为0.366；高住院服务利用家庭门诊服务利用量（29.2±26.9）低于中等住院服务利用家庭（31.7±23.5）；除低住院服务利用个体外，高住院服务利用家庭中住院服务利用成员的住院量都大于其他家庭（N_高高9.2>N_中高4, N_高中2.4>N_中中2.2>N_低中1.7）；高住院服务利用家庭到县医院的驾车时间最短（t_高44.3<t_中44.9<t_低45.2），家庭住院人数最多（N_中>4.5>N_高4.4>N_低3.9）。结论 农村地区住院服务利用存在较大的家庭聚集性，存在一定不合理；门诊服务利用的提高可能会降低住院服务的利用。     

Transpiration and whole-tree conductance in ponderosa pine trees of different heights

Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine if transpiration (E) and whole-tree conductance (g _t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m^–2 (leaf area, projected) s^–1 for the 12-m trees and 0.57 mmol m^–2 (leaf area) s^–1 for the 36-m trees. When photosynthetically active radiation (I _P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m^–2 (ground) s^–1), differences in E were more pronounced: 2.4 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 1.2 mmol m^–2 s^–1 for the 36-m trees, yielding g _t of 140 mmol m^–2 (leaf area) s^–1 for the 12-m trees and 72 mmol m^–2 s^–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g _t in the taller trees also likely lowers photosynthesis during the growing season. Received: 19 April 1999 / Accepted: 23 March 2000     

不同恢复方式下大兴安岭重度火烧迹地林地土壤温室气体通量

为研究大兴安岭重度火烧迹地在不同恢复方式下林地土壤CO₂、CH₄和N₂O排放特征及其影响因素,采用静态箱/气相色谱法,在2017年生长季（6月-9月）对3种恢复方式（人工更新、天然更新和人工促进天然更新）林地土壤温室气体CO₂、CH₄、N₂O通量进行了原位观测。研究结果表明：（1）3种恢复方式林地土壤在生长季均为大气CO₂、N₂O的源,CH₄的汇;生长季林地土壤CO₂排放通量大小关系为人工促进天然更新（（634.40±246.52）mg m^-2 h^-1） > 人工更新（（603.63±213.22）mg m^-2 h^-1） > 天然更新（（575.81±244.12）mg m^-2 h^-1）,3种恢复方式间无显著差异;人工更新林地土壤CH₄吸收通量显著高于人工促进天然更新;天然更新林地土壤N₂O排放通量显著高于其他两种恢复方式。（2）土壤温度是影响3种恢复方式林地土壤温室气体通量的关键因素;土壤水分仅对人工更新林地土壤N₂O通量有极显著影响（P < 0.01）;3种恢复方式林地土壤CO₂通量与大气湿度具有极显著的响应（P < 0.01）;土壤pH仅与天然更新林地土壤CO₂通量显著相关（P < 0.05）;土壤全氮含量仅与人工促进天然更新林地土壤CH₄通量显著相关（P < 0.05）。（3）基于100年尺度,由3种温室气体计算全球增温潜势得出,人工促进天然更新（1.83×10⁴ kg CO₂/hm²） > 人工更新（1.74×10⁴ kg CO₂/hm²） > 天然更新（1.67×10⁴ kg CO₂/hm²）。（4）阿木尔地区林地土壤年生长季CO₂和N₂O排放量为8.85×10⁶ t和1.88×10² t,CH₄吸收量为1.05×10³ t。     

A new model for relationship between irradiance and the rate of photosynthesis in <Emphasis Type="Italic">Oryza sativa</Emphasis>

The calculated maximum net photosynthetic rate (P _N) at saturation irradiance (I _m) of 1 314.13 μmol m⁻² s⁻¹ was 25.49 μmol(CO₂) m⁻² s⁻¹, and intrinsic quantum yield at zero irradiance was 0.103. The results fitted by nonrectangular hyperbolic model, rectangular hyperbolic method, binomial regression method, and the new model were compared. The maximum P _N values calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were higher than the measured values, and the I _m calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were less than measured values. Results fitted by new model showed that the response curve of P _N to I was nonlinear at low I for Oryza sativa, P _N increased nonlinearly with I below saturation value. Above this value, P _N decreased nonlinearly with I.     

林下植被和凋落物对寒温带森林生长季土壤CH4通量的影响

为进一步探究林下植被和凋落物管理对我国寒温带森林生长季土壤CH₄通量的影响,采用静态箱-气相色谱法对大兴安岭北部4种林型（白桦林、山杨林、樟子松林和兴安落叶松林）4种处理（自然状态、去除凋落物、去除林下植被以及去除林下植被和凋落物）的土壤CH₄通量排放特征进行观测研究。结果表明：该地区森林生长季土壤均表现为CH₄的汇,4种林型不同处理后土壤CH₄通量表现为单峰变化趋势,吸收峰值出现在7月或8月。自然状态4种林型土壤CH₄平均吸收通量表现为白桦林（-79.23±14.92）μg m^-2 h^-1>山杨林（-64.27±9.60）μg m^-2 h^-1>樟子松林（-62.54±15.48）μg m^-2 h^-1>兴安落叶松林（-48.73±12.26）μg m^-2 h^-1,兴安落叶松土壤CH₄平均吸收通量显著小于其他三种林型（P<0.05）。相比于自然状态,4种林型在去除凋落物后土壤CH₄吸收通量提高了2.12%-12.15%,但变化幅度均没有达到显著水平（P>0.05）。去除林下植被后4种林型CH₄吸收通量提高了0.84%-20.55%,且只有山杨林吸收增加达到显著水平（P<0.05）。同时去除林下植被和凋落物后,对白桦林和樟子松土壤CH₄通量影响不显著（P>0.05）,但对山杨林和兴安落叶松林影响显著（P<0.05）。总之,去除凋落物或林下植被均会提高土壤对CH₄吸收,去除林下植被对土壤CH₄通量的影响要大于去除凋落物的影响,但不同林型不同处理之间还存在差异。     

Effects of different irradiances on the photosynthetic process during ex-vitro acclimation of Anoectochilus plantlets

Six months old in vitro-grown Anoectochilus formosanus plantlets were transferred to ex-vitro acclimation under low irradiance, LI [60 μmol(photon) m⁻² s⁻¹], intermediate irradiance, II [180 μmol(photon) m⁻² s⁻¹], and high irradiance, HI [300 μmol(photon) m⁻² s⁻¹] for 30 d. Imposition of II led to a significant increase of chlorophyll (Chl) b content, rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), electron transfer rate (ETR), quantum yield of electron transport from water through photosystem 2 (Φ_PS2), and activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBPCO, EC 4.1.1.39). This indicates that Anoectochilus was better acclimated at II compared to LI treatment. On the other hand, HI acclimation led to a significant reduction of Chl a and b, P _N, E, g _s, photochemical quenching, dark-adapted quantum efficiency of open PS2 centres (F_v/F_m), probability of an absorbed photon reaching an open PS2 reaction centre (F_v′/F_m′), ETR, Φ_PS2, and energy efficiency of CO₂ fixation (Φ_CO2/Φ_PS2). This indicates that HI treatment considerably exceeded the photo-protective capacity and Anoectochilus suffered HI induced damage to the photosynthetic apparatus. Imposition of HI significantly increased the contents of antheraxanthin and zeaxanthin (ZEA), non-photochemical quenching, and conversion of violaxanthin to ZEA. Thus Anoectochilus modifies its system to dissipate excess excitation energy and to protect the photosynthetic machinery.     

纤维蛋白对尿激酶原激活纤溶酶原反应动力学的影响

反应体系中存在的纤维蛋白（fibrin）对尿激酶（UK）、scu-PA以及组织型纤溶酶原激活剂（t-PA）激活纤溶酶原（plasminogen）的反应有不同的作用：UK、t-PA激活plasminogen的反应可被反应体系中存在的fibrin所加强;fibrin对scu-PA激活plasminogen反应的动力学常数无明显影响;但对小分子质量scu-PA与单链抗体的嵌合分子激活plasminogen的反应起明显的抑制作用.为确定反应体系中存在的fibrin对scu-PA的K区插入突变体-InB激活plasminogen反应的影响,测定了在反应体系中存在fibrin的情况下的InB激活plasminogen反应的K_m^fibrin以及k_cat^fibrin.K_m^fibrin＝4.2 μmol·L^-1,远远大于无fibrin时的K_m＝0.379 μmol·L^-1,说明有fibrin存在时突变体InB与天然底物plasminogen的亲和性降低了.k_cat^fibrin＝0.107 s^-1,也远远大于无fibrin时k_cat＝0.0165 s^-1,说明有fibrin存在时突变体InB对plasminogen的反应活性增强了.原因可能是：与fibrin结合的plasminogen的构象发生了有利于被纤溶酶原激活剂水解的变化.     

深圳市前海桂湾公园土壤蒸发及植被蒸腾模拟

蒸散发（ET）是连接水文循环和地表能量平衡的重要组成部分,准确的估算土壤蒸发（LE_s）和植被蒸腾（LE_v）对城市水资源分配和管理具有重要意义。针对城市林地蒸散发双源模型的缺失,本研究基于MOD16模型提出了应用于城市林地区域改进的MOD16双源模型。改进的MOD16双源模型更加准确的描述城市林地区域复杂下垫面的能量分配过程。结合高时空分辨率的Sentinel-2遥感卫星影像,对2020年深圳市前海桂湾公园20个无云日的LE_s和LE_v进行反演研究。用Shuttleworth-Wallace （S-W）模型和双作物系数法（FAO dual-K_c）验证模型性能,同时分析改进的MOD16模型对输入变量的敏感度,结果表明：改进的MOD16模型与S-W模型和FAO dual-K_c之间的均方根误差（RMSE）分别为21.39 W/m²和20.41 W/m²,平均绝对误差（MAE）分别为18.81 W/m²和19.05 W/m²,R²分别为0.801和0.634。改进的MOD16模型可以应用在城市林地LE_s和LE_v估算中。桂湾公园地区总蒸散月均值在85-165 W/m²之间。研究区域的LE_s和LE_v呈现出明显的季节变化,春夏季蒸散量升高,秋冬季蒸散量降低,LE_s的变化范围为0-50 W/m²,LE_v的变化范围为0-120 W/m²。LE_v高值在研究区呈现零散分布,多集中在前海桂湾沿岸,LE_s高值集中在研究区的西北、东北和东南部。敏感性分析结果表明,改进后的MOD16模型对植被覆盖、太阳辐射和湿度更敏感。其中,LE_v模拟结果受净辐射和植被覆盖影响最大,LE_s的模拟结果受湿度和植被覆盖的影响最大。因此,应用改进的MOD16模型时需要优先确保这些参数的准确输入。修正后的MOD16模型极大地提高了高分辨率、小尺度区域城市林地LE_s和LE_v模拟的准确性,为准确获取植被耗水量信息从而科学指导城市林地灌溉、解决城市水资源分配与管理提供有力工具。     

Morpho-anatomical and physiological leaf traits of two alpine herbs, Podophyllum hexandrum and Rheum emodi in the Western Himalaya under different irradiances

Morpho-anatomical leaf traits and photosynthetic activity of two alpine herbs, Podophyllum hexandrum (shade-tolerant) and Rheum emodi (light-requiring), were studied under field (PAR>2 000 μmol m⁻² s⁻¹) and greenhouse (PAR 500 μmol m⁻² s⁻¹) conditions. Mesophyll thickness, surface area of mesophyll cells facing intercellular spaces (S_mes), surface area of chloroplasts facing intercellular spaces (S_c), intercellular spaces of mesophyll cells (porosity), photon-saturated rate of photosynthesis per unit leaf area (P _Nmax), and ribulose-1,5-bisphosphate carboxylase/oxygenase activity decreased in the greenhouse with respect to the field and the decreases were significantly higher in R. emodi than in P. hexandrum. P. hexandrum had lower intercellular CO₂ concentration than R. emodi under both irradiances. The differences in acclimation of the two alpine herbs to low irradiance were due to their highly unlikely changes in leaf morphology, anatomy, and P _Nmax which indicated that the difference in radiant energy requirement related to leaf acclimation had greater impact under low than high irradiance.     

The effect of benthic sediments on dissolved nutrient concentrations and fluxes

The Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment–seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 μmol l⁻¹) and effluxes (123 ± 14 μmol m⁻² h⁻¹) were greater from sand than mud (37 ± 10 μmol m⁻² h⁻¹), possibly due to the binding of P with the <63 μm fraction. NH₄⁺ effluxes were high outside the Anc?o Basin (821 ± 106 μmol m⁻² h⁻¹) and were associated with Enteromorpha sp. mats. The greatest NO₃⁻ efflux was from sediments near a salt marsh (170 ± 67 μmol m⁻² h⁻¹). These sediment fluxes of P were not sufficient to account for elevated P concentrations seen by other workers on the ebb tide from the Anc?o Basin. Intertidal pools were sinks for Dissolved Inorganic Nitrogen (DIN) and DIP over the 6 h exposure period. Thus, tidepools may be an important route of nutrients into sediments that enhances the effects of sediments on seawater nutrient concentrations.     

Environmental induced variations in leaf dark respiration and net photosynthesis of <Emphasis Type="Italic">Quercus ilex</Emphasis> L.

The relationships between dark respiration rate (R _D) and net photosynthetic rate (P _N) in Quercus ilex L. shrubs growing at the Botanical Garden in Rome were analysed. Correlation analysis of the data sets collected in the year 2006 confirmed the dependence among the considered leaf traits, in particular, R _D was significantly (p<0.05) correlated with P _N (r = 0.40). R _D and P _N increased from March to May [1.40±0.10 and 10.1±1.8 μmol(CO₂) m⁻² s⁻¹ mean values of the period, respectively], when air temperature was in the range 14.8–25.2 °C, underlining the highest metabolic activity in the period of the maximum vegetative activity that favoured biomass accumulation. On the contrary, the highest R _D [1.60±0.02 μmol(CO₂) m⁻² s⁻¹], associated to the lowest P _N rates (44 % of the maximum) and carbon use efficiency (CUE) in July underlined the mobilization of stored material during drought stress by a higher air temperature (32.7 °C).     

Kinetics of urea uptake by Melosira italica (Ehr.) Kütz at different luminosity conditions

The kinetic parameters K_m and V_max for urea uptake by Melosira italica were determined at 160 μeinsteins m⁻² s⁻¹ and in the dark. The transport systems showed an affinity for the substrate and a storing capacity in the dark (K_m = 65.07 μM; V_max = 2.18 nmoles 10⁵ cells ⁻¹ h⁻¹) greater than under 160 μE m⁻² s ⁻¹ (K_m = 111.2 μM; V_max = 1.11 nmoles 105 cells⁻¹ h⁻¹). Similarly, a reduction in consumption rate of urea under increasing photon flux densities was observed. The use of an inhibitor (potassium cyanide) indicated that the uptake process requires metabolic energy. That urea transport is more important in darkness, may constitute a survival strategy in which this compound is utilized by cells mainly during heterotrophic growth.     

Avocado shoot culture, plantlet development and net CO2 assimilation in an ambient and CO2 enhanced environment

Summary The proliferation and survival of avocado nodal cultures of juvenile origin were affected by the form and concentration of nitrogen. Optimum growth was achieved on modified Murashige and Skoog medium containing 67% KNO₃ and 33% NH₄NO₃ with total N of 40 mM supplemented with 100 mg l⁻¹ myo-inositol, 1 mg l⁻¹ thiamine HCl, 30 g l⁻¹ sucrose, and 4.44 μM BA with a 16-h photoperiod (120–150 μmol m⁻² s⁻¹). Proliferating shoots and plantlets were photosynthetically active. Better shoot growth and accumulation of higher biomass occurred in a CO₂-enriched environment than under ambient CO₂ conditions. CO₂ assimilation efficiency, however, was higher under the latter conditions than in a CO₂-enhanced environment, e.g., 31±7 and 17±2 μmol CO₂ m⁻² s⁻¹, respectively. The net CO₂ assimilation rates of in vitro grown plantlets were comparable to those of seedlings ex vitro.     

Photosystem 2 photochemistry and pigment composition of a yellow mutant of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under different irradiances

A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents. At weak irradiance [50 μmol(photon) m⁻² s⁻¹], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (Φ_PS2), photochemical quenching (q_P), and the efficiency of excitation capture by open PS2 centres 1 (F_v′/F_m′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (F_v/F_m). With progress in irradiance [100 and 200 μmol(photon) m⁻² s⁻¹], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. Φ_PS2, q_P, and F_v′/F_m′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio [(Z+A)/(V+A+Z)] associated with non-photochemical quenching (q_N) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance.     

不同CO2浓度升高和氮肥水平对水稻叶绿素荧光特性的影响

为研究不同CO₂浓度升高和氮肥水平对水稻叶绿素荧光特性的影响,利用由开顶式气室（OTC）组成的CO₂浓度自动调控平台开展田间试验。以粳稻9108为试验材料,CO₂浓度设置CK（对照,环境大气CO₂浓度）、C₁（CO₂浓度比CK增加160 μmol/mol）和C₂（CO₂浓度比CK增加200 μmol/mol）3个水平;氮肥设置低氮（N₁：10 g/m²）、中氮（N₂：20 g/m²）和高氮（N₃：30 g/m²）3个水平。结果表明,在低氮条件下,与CK相比,C₁处理使拔节期的F_o上升4.8%（P=0.031）;C₂处理使拔节期的F_o上升6.3%（P=0.015）,F_v/F_m下降4.8%（P=0.003）,使孕穗期的F_o上升12.7%（P=0.039）,F_v/F_o下降18.2%（P=0.039）。在高氮条件下,与CK相比,C₂处理使灌浆期的F_m、F_v和F_v/F_m分别下降3.6%（P=0.039）、4.9%（P=0.013）和1.3%（P=0.039）。在中氮条件下,与CK相比,C₁和C₂处理的影响不明显。在整个生育期内,CO₂浓度升高与施氮处理交互作用对水稻叶绿素荧光特性的影响未到达显著水平。研究表明,大气CO₂浓度升高使水稻叶片光系统Ⅱ受损,抑制其电子传递能力、电子受体Q_A氧化还原情况、最大光化学效率和潜在活性,通过适量施氮可以有效地缓解其负面效应。