马占相思人工林净二氧化碳交换和碳同位素通量

应用稳定碳同位素技术,对马占相思人工林冠层受光和遮荫叶片的碳同化率(A_net)和叶面积指数(L)进行加权,将叶片水平的¹³C甄别率(Δ_i)扩展至冠层光合甄别率(Δ_canopy),测定光合固定和呼吸释放的碳同位素通量及其净交换通量.结果表明：Δ_canopy的日变化明显,日出前和中午出现较低值(18.47‰和19.87‰),而日落前达到最大(21.21‰);秋季末期(11月)至翌年夏季,Δ_canopy逐步升高,年平均为(20.37±0.29)‰.不同季节自养呼吸(日间叶片呼吸除外)和异养呼吸释放CO₂的碳同位素比率(δ¹³C)平均值分别为(-28.70±0.75)‰和(-26.75±1.3)‰,春季林冠夜间呼吸CO₂的δ¹³C最低(-30.14‰),秋季末期最高(-28.01‰).马占相思林与大气的CO₂碳同位素通量在春季和夏季中午时峰值分别为178.5和217 μmol·m^-2 ·s^-1·‰,日均值分别为638.4 和873.2 μmol·m^-2·s^-1·‰.冠层叶片吸收CO₂的碳同位素通量较呼吸释出CO₂的碳同位素通量高1.6～2.5倍,表明马占相思林日间吸收大量CO₂,降低空气CO₂浓度,具有改善环境的良好生态服务功能.     

滨海沙地不同树种人工林叶片和土壤表层稳定碳氮同位素及水分利用效率研究

以福州市滨海后沿沙地人工营造的湿地松、木麻黄、尾巨桉、肯氏相思和纹荚相思防护林为研究对象,测定不同年龄(新叶、老叶)叶片、表层土壤(0~10cm)天然稳定碳、氮同位素丰度值(δ~(13) C、δ~(15)N),研究稳定碳、氮同位素丰度值与水分利用效率和土壤氮饱和程度的相互关系,以揭示不同树种水分利用效率、氮饱和程度和碳氮循环速率差异的机理。结果表明:(1)滨海沙地不同树种叶片δ~(13) C变化范围为-31.682‰~-29.323‰,其δ~(13) C大小为:湿地松肯氏相思木麻黄纹荚相思尾巨桉,除尾巨桉外各树种δ~(13) C均表现为新叶老叶;各树种叶片δ~(15)N变化范围为-5.548‰~-2.167‰,其δ~(15)N大小为:肯氏相思纹荚相思木麻黄湿地松尾巨桉,且各树种均表现为新叶老叶。(2)不同树种表层土壤δ~(15)N变化范围为-4.675‰~-2.975‰,表层土壤δ~(15)N大小为:纹荚相思肯氏相思木麻黄尾巨桉湿地松,但不同树种表层土壤C含量无显著差异。(3)滨海沙地湿地松、木麻黄、肯氏相思和纹荚相思的水分利用效率随叶龄增加均呈显著递减趋势;不同树种新叶的水分利用效率变化范围为39.09~76.57μmol·mol~(-1),其大小依次为:湿地松肯氏相思木麻黄纹荚相思尾巨桉;老叶的水分利用效率变化范围为38.56~62.59μmol·mol~(-1),其大小依次为:湿地松木麻黄肯氏相思尾巨桉纹荚相思。(4)不同树种人工林水分利用效率与其新叶水分利用效率呈显著正相关关系,说明林分水分利用效率主要体现在新叶的水分利用效率上,同时林分水分利用效率受林分类型的影响。     

干旱胁迫下四倍体刺槐幼苗水分利用效率及稳定碳同位素组成的研究

在模拟自然干旱的条件下,测定2个四倍体刺槐品种(K2、K3)和普通二倍体刺槐(K1)一年生组培苗的长期和瞬时水分利用效率(WUE)及其稳定碳同位素组成(δ13C),以探讨四倍体刺槐的抗旱机理.结果表明,K2、K3的长期水分利用效率(WUEL)在不同水分胁迫条件下都显著高于K1,它们在同等供水条件下比K1具有更大的生物量产出;3个材料叶片的瞬时水分利用效率(WUEI)均随干旱胁迫的加剧表现先升后降的趋势,且胁迫处理均高于适宜水分处理.随水分胁迫的加剧,各品种刺槐苗木叶片的δ13C显著升高;K2、K3的δ13C在各水分条件下均高于K1;各材料叶片的δ13C与其WUEL有良好的正相关性,可以作为筛选高WUE刺槐品种的指标.     

不同基因型冬小麦旗叶的稳定碳同位素比值及其与产量和水分利用效率的关系

以我国北方12个冬小麦(Triticum aestivum)品种(系)和美国德克萨斯州3个冬小麦品种(系)为供试材料, 在甘肃陇东黄土高原旱作和拔节期有限补灌条件下, 比较研究了不同基因型冬小麦之间产量、水分利用效率(WUE)和灌浆期旗叶稳定碳同位素比值(δ¹³C)的差异, 以及δ¹³C值与产量和WUE的关系。旨在通过分析δ¹³C值与产量和WUE的关系, 明确δ¹³C值在评价植物WUE方面的可靠性, 为抗旱节水品种的筛选提供理论依据。结果表明: 不论旱作还是有限补灌, 不同基因型冬小麦之间产量、WUE、旗叶δ¹³C值存在显著差异, 随着灌浆过程的进行, 旗叶δ¹³C值呈缓慢增大的趋势, 而且旗叶δ¹³C值旱作高于有限补灌。不论旱作还是补灌条件, 旗叶δ¹³C值在4个测定时期的平均值与籽粒产量、WUE呈显著正相关关系(R²= 0.527 3-0.691 3)。小麦拔节期补灌100 mm水分后, 不同基因型小麦表现出明显的水分超补偿效应。说明冬小麦灌浆期旗叶δ¹³C值在旱作条件下和在补灌条件下均可较好地评价WUE, 可将冬小麦灌浆期旗叶δ¹³C值作为筛选高效用水品种的参考指标之一。     

水分条件对红砂叶片碳同位素组成与光合特性和分枝生长的影响

在盆栽条件下,研究了不同水分处理对红砂(Reaumuria soongorica)叶碳同位素组成、光合特性和分枝生长的影响,并进一步调查了自然条件下不同退化程度红砂草地的土壤含水量,分枝生长、叶碳同位素及其关系。结果表明:(1)在盆栽条件下,随土壤含水量的降低,红砂当年生分枝生物量、一级分枝长、二级分枝数及其叶片净光合速率、气孔导度和蒸腾速率均显著减小,而叶片碳同位素组成(δ~(13) C)和水分利用效率则随土壤含水量降低而显著增加;且叶片δ~(13) C与当年生分枝生物量、一级分枝长、二级分枝数、叶片净光合速率、气孔导度和蒸腾速率呈显著负相关关系。(2)在田间自然条件下,红砂叶片δ~(13) C与立地30~60cm及60~100cm土层的土壤含水量、单位冠幅面积生物量、单位冠幅面积分枝数呈显著负相关关系。研究认为,在盆栽和田间条件下,红砂叶片δ~(13) C是指示其生境水分状况的良好指标;红砂主要利用土壤的深层水分,其在土壤含水量相对较低的轻度退化区水分利用效率比土壤含水量相对较高的重度退化区更高。这一结论对于理解干旱生境中红砂的水分利用策略以及红砂草地的管理和恢复具有一定的指导意义。     

生长光强对亚热带自然林两种木本植物稳定碳同位素比、细胞间CO2浓度和水分利用效率的影响

生长于１００％、４０％和１６％自然光下的荷木和黧蒴幼苗叶片稳定碳同位素比（δ１３Ｃ,－‰）,细胞间ＣＯ２浓度（Ｃｉ）和水分利用效率（ＷＵＥ）有一定的差别。１６％和４０％弱光下,δ１３Ｃ的负值增加－０．５４Ｊ‰到－０．８９‰。Ｃｉ增大８．１－１３．２μｉＬ－１,ＷＵＥ则下降６－２４％。结果表明,叶片的水分和气体交换特性受生长光强的调节,叶片的δ１３Ｃ值可反映其生长过程中受光的强弱状况。     

蒙古裸腹溞与褶皱臂尾轮虫的种间关系

在实验室内将蒙古裸腹溞按0．06、0．10、0．30、0．60个·ml^-1的密度与褶皱臂尾轮虫(密度为0．3个·ml。)进行}昆合培养,同时按上述密度分别单种培养了蒙古裸腹溞和褶皱臂尾轮虫作为对照．结果表明,蒙古裸腹溞与褶皱臂尾轮虫之间存在种间竞争,当二者共存时,褶皱臂尾轮虫对蒙古裸腹溞种群产生压制作用,使蒙古裸腹溞在混合培养体系中以很低的密度存在,而褶皱臂尾轮虫种群受蒙古裸腹溞影响不大．通过进一步的饥饿实验发现90％的褶皱臂尾轮虫经过144h饥饿后仍然存活,而经过120h饥饿后的蒙古裸腹溞100％死亡,褶皱臂尾轮虫耐饥饿能力较强是其在与蒙古裸腹溞竞争中获胜的原因之一。     

Spatial distribution of leaf water-use efficiency and carbon isotope discrimination within an isolated tree crown

The spatial variations in the stable carbon isotope composition (δ¹³C) of air and leaves (total matter and soluble sugars) were quantified within the crown of a well‐watered, 20‐year‐old walnut tree growing in a low‐density orchard. The observed leaf carbon isotope discrimination (Δ) was compared with that computed by a three‐dimensional model simulating the intracanopy distribution of irradiance, transpiration and photosynthesis (previously parameterized and tested for the same tree canopy) coupled to a biophysically based model of carbon isotope discrimination. The importance of discrimination associated with CO₂ gradients encountered from the substomatal sites to the carboxylation sites was evaluated. We also assessed by simulation the effect of current irradiance on leaf gas exchange and the effect of long‐term acclimation of photosynthetic capacity and stomatal and internal conductances to light regime on intracanopy gradients in Δ. The main conclusions of this study are: (i) leaf Δ can exhibit important variations (5 and 8‰ in total leaf material and soluble sugars, respectively) along light gradients within the foliage of an isolated tree; (ii) internal conductance must be taken into account to adequately predict leaf Δ, and (iii) the spatial variations in Δ and water‐use efficiency resulted from the short‐term response of leaf gas exchange to variations in local irradiance and, to a much lesser extent, from the long‐term acclimation of leaf characteristics to the local light regime.     

Carbon isotope discrimination and water-use efficiency of six crops grown under wet and dryland conditions

Mustard (Sinapis alba L.), Argentine canola (Brassica napus L. cv. Westar), Polish canola (Brassica campestris L. cv. Tobin), pea (Pisum sativum L.), durum wheat (Triticum durum L. cv. Kyle) and soft wheat (Triticum aestivum L. cv. Fielder) were grown at Outlook, Saskatchewan, Canada, under irrigated and dryland conditions. Carbon isotope discrimination (Δ) and water-use efficiency (W), defined as grams of above ground dry matter produced per kilogram water used, were negatively correlated in the six field-grown crops. In irrigated plants Δ remained relatively constant (20–21‰) throughout the growing season. However, in dryland plants, Δ declined in response to the progressive depletion of stored soil water (Polish canola, 20-2-18-8‰; mustard, 19.9–18 5‰; pea, 19.9–17 2‰ durum wheat, 19.7–16.4‰; Argentine canola, 19.4–17.6‰; soft wheat, 19.0–17.4‰). Although there were genetic differences in Δ among the species, water availability was the major factor controlling Δ.     

Carbon isotope discrimination,water-use efficiency,growth, and mortality in a natural shrub population

In order to scale up from the ecophysiological characters of individual plants to population-level questions, we need to determine if character patterns in natural populations are stable through time, and if the characters are related to growth and survival. We investigated these questions in a 3-year study for one character, integrated water-use efficiency (WUE) as estimated by carbon isotope discrimination () in a population of the Great Basin shrub, Chrysothamnus nauseosus. WUE was a conservative character for a given plant within and across seasons, and a previously documented difference between two size classes (represented by juveniles and adults) was maintained; smaller juveniles had a lower WUE than larger adults. The lower WUE of juveniles was often accompanied by higher rates of photosynthesis and stomatal conductance as compared to adults even though juveniles generally had more negative xylem pressure potentials. Although many discussions of the role of WUE in natural populations have been based on the expectation that higher WUE (lower ) is generally associated with less growth, we found no such relation-ship for juvenile plants in this population (i.e was not positively correlated with height increase). In addition, juvenile plant mortality was not correlated with . Although there were stable patterns of WUE for plants in this population, the positive correlation between WUE and size, and the lack of a negative correlation between WUE and height growth, make it unlikely that the WUE of an individual plant will be related in a simple manner to its growth and survival in the population.     

Effects of soil strength on the relation of water-use efficiency and growth to carbon isotope discrimination in wheat seedlings

The ratio of carbon accumulation to transpiration, W, of wheat (Triticum aestivum L.) seedlings increased with increasing soil strength, measured as soil penetrometer resistance, and this was already apparent at the two leaf stage. The ratio was negatively correlated with carbon isotope discrimination, in accord with theory. This means that decrease in intercellular partial pressure of CO₂ accounted for an important part of the increase in W with increasing soil strength. Despite a lower CO₂ concentration in the leaves at high soil strength, assimilation rate per unit leaf area was enhanced. Greater ribulose 1,5-bisphosphate carboxylase activity confirmed that photosynthetic capacity was actually increased. This pattern of opposite variation of assimilation rate and of stomatal conductance is unusual. The ratio of plant carbon mass to leaf area increased markedly with increasing soil strength, mainly because of a greater investment of carbon into roots than into shoots. A strong negative correlation was found between this ratio and carbon isotope discrimination. For a given increase in discrimination, decrease in carbon mass per leaf area was proportionally larger than decrease in assimilation rate, so that relative growth rate was positively correlated to carbon isotope discrimination.     

Carbon isotope discrimination indicates improving water-use efficiency of trees in northern Eurasia over the last 100 years

We investigated the response of conifer trees in northern Eurasia to climate change and increasing CO₂ over the last century by measuring the carbon isotope ratio in tree rings. Samples from Larix, Pinus and Picea trees growing at 26 high‐latitude sites (59–71°N) from Norway to Eastern Siberia were analysed. When comparing the periods 1861–1890 and 1961–1990, the isotope discrimination and the ratio of the intercellular to ambient CO₂ concentration (c_i/c_a) remained constant for trees growing in mild oceanic climate and under extremely cold and dry continental conditions. This shows a strong coordination of gas‐exchange processes, consisting in a biochemical acclimation and a reduction of the stomatal conductance. The correlation for c_i/c_a between the two investigated periods was particularly strong for Larix (r²=0.90) and Pinus (r²=0.94), but less pronounced for Picea (r²=0.47). Constant c_i/c_a under increasing CO₂ in the atmosphere resulted in improved intrinsic water‐use efficiency (W_i), the amount of water loss at the leaf level per unit carbon gain. We found that 125 out of 126 trees showed increasing W_i from 1861 to 1890 to 1961 to 1990, with an average improvement of 19.2±0.9% (mean±SE). The adaptation in gas exchange and reduced transpiration of trees growing in this region must have had a strong impact on the water and energy budget, resulting in a drier and warmer surface air layer today than would exist without this vegetation–climate feedback.     

成熟马占相思水力导度对水分利用和光合响应的季节性差异

通过测定成熟马占相思叶片的水势、气孔导度、蒸腾速率(Tr)、叶面积指数、边材面积等参数,研究了湿季(5月)和干季(11月)叶片的水力导度(K1)、水分和光合特性的关系.结果表明:高大植株(平均树高20 m、胸径0.26 m)的边材面积与叶面积的比率(Asp/Acl)比较小植株(平均树高14.5 m、胸径0.19m)高8.5％,前者的木质部水分通量大于后者,以支持冠层叶片的水分利用.对木质部易损曲线进行分析,K1降低50％时,湿、干季的叶片水势(Ψ1)分别为-1.41和-1.55 MPa,且干季的木质部空穴化的易损性高于湿季.湿、干季的K1峰值分别为5.5和4.5 mmol·m-2·s-1·MPa-1,最大蒸腾速率(Trmax)分别为3.6和1.8 mmol·m-2·s-1,且湿季的K1和Trmax明显大于干季.一天中K1和Tr的多次波动反映了木质部空穴化和修复的往复循环,叶片气孔在K降低超过50％或Ψ1达到-1.6MPa时关闭,气孔导度在K1达到50％前仍保持较高水平.干季的水力导度与光合速率的相关性较湿季明显.季节更迭导致叶片水力导度损失是Tr和CO2交换下降的原因.     

Population Growth of Six Iranian Brachionus Rotifer Strains in Response to Salinity and Food Type

Intrinsic rates of population increase (r) were evaluated as a measure of population dynamics of four strains of Brachionus plicatilis and two strains of B. urceolaris from Iran in response to different salinities and feeding algae. Each rotifer strain was cultured at four salinities: 5, 20, 25 and 30‰ and fed with two microalgal species: Chlorella vulgaris and Nannochloropsis oculata. Salinity of 5‰ was critical for all the examined strains, at which r was at minimum and was different from the other salinities (P < 0.05). For B. plicatilis strains, the maximum r was observed in those fed on Chlorella at salinities of 10 and 30‰ (64 ± 0.01 day⁻¹). While, in B. urceolaris, maximum r was for Nannochloropsis fed rotifers at salinity of 20‰ (0.69 ± 0.01 day⁻¹). Maximum final population density (FD) was obtained for a strain of B. urceolaris fed on Nannochloropsis at 20‰ (329.3 ± 10.9 ind.mL⁻¹). FD was relatively lower in B. plicatilis strains among all examined salinities. ANOVA showed the significant effect of salinity and rotifer strain, and algae × rotifer strain on both r and FD, and salinity × rotifer × algae on FD (P < 0.05). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.