STUDIES ON THE POLLINATION ECOLOGY OF TIPULARIA DISCOLOR (ORCHIDACEAE)

Tipularia discolor, a woodland orchid, flowers in mid-summer when reproductive activity is minimal within the herb synusia. Tipularia is insect-pollinated, and artificial crosses showed that seeds are produced after self-pollination, intra-inflorescence pollination, and outcrossing. The single nocturnal pollinator, Pseudaletia unipuncta (Noctuidae), located Tipularia populations within a day or two of anthesis. Pollinators were shown to be capable of utilizing portions of the inflorescences that contained the most nectar. After total nectar resources declined, pollinators were no longer active on the inflorescences, even though flowers and nectar were still available. The mode of pollinator activity seems to be closely related to floral morphology, although the moths are able, early in the flowering phenophase, to successfully obtain nectar without effecting any change in the reproductive status of flowers.     

RELATIONS BETWEEN SUNFLECK SEQUENCES AND PHOTOINHIBITION OF PHOTOSYNTHESIS IN A TROPICAL RAIN FOREST UNDERSTORY HERB

We report the photosynthetic characteristics of a C₃ shade plant native to the tropical rain forest understory. It was shown that Elatostema repens Lour. (Hall) f. (Urticaceae) presents a large light adjustment capacity. The effects of several lightfleck sequences on photoinhibition of photosynthesis and carbon gain are analyzed. Photoinhibition is measured both as a decrease in leaf net CO₂ uptake in limiting light (shown to be linearly correlated to quantum yield of O₂ evolution measured at saturating CO₂) and as a decrease of the ratio of variable fluorescence (Fv) to maximum fluorescence (Fmax) measured in liquid nitrogen. It is shown that lightflecks (from 10 to 30 min in duration) of 700 μmol m^–2 s^–1 (high light) induce photoinhibition, and that the effects of those successive high light periods are additive; there is apparently no recovery from photoinhibition during the low light periods (from 10 to 45 min in duration). In contrast, the Fv/Fmax ratio, though decreasing similarly to quantum yield of net CO₂ uptake on leaves submitted to a continuous illumination of 700 μmol m^–2 s^–1, is only decreased a little on leaves submitted to lightfleck sequences of the same photon flux density. Lightflecks of 250 μmol m^–2 s^–1 are not photoinhibitory. Compared to the control maintained under light growth condition (40 μmol m^–2 s^–1) carbon gain is increased on leaves submitted to lightflecks; this gain remains high throughout the light cycles on leaves submitted to nonphotoinhibitory lightflecks and to the photoinhibitory lightflecks followed by the shortest low light period. In the other cases, carbon gain, higher than that of the control at the beginning of the treatments, decreases and becomes lower than the control carbon gain. Finally, the relevance of photoinhibition in the tropical rain forest understory environment is discussed.     

COMPARISON OF INTRASPECIFIC VARIATIONS IN THE REPRODUCTION AND PHOTOSYNTHESIS OF AN UNDERSTORY HERB,ARNICA CORDIFOLIA

Intraspecific variations in the reproduction of individual ramets and monospecific patches of the understory herb Arnica cordifolia Hook. were compared with variations in photosynthesis and understory light conditions. Ramets and patches were compared from three microhabitats (open, intermediate, and shaded) that differed in daily integrated irradiance. Individual ramets from open microhabitats (> 12 MJ m⁻² d⁻¹) had 23% more total dry wt and produced twice as many seeds, when compared to ramets from shaded locations (< 5 MJ m⁻² d⁻¹). In addition, monospecific patches from open locations were 63% more dense, and estimates of seed and vegetative patch reproductive effort were 4 and 2 times greater, respectively, when compared to shaded plant patches. For all measurements, ramets and patches from intermediate understory locations (6–10 MJ m⁻² d⁻¹) were intermediate in reproductive capacity between those of open and shaded locations. In addition, A. cordifolia seeds from open microhabitats germinated significantly better (45%) than either intermediate or shaded location seeds under high light and only seeds from shaded microhabitats germinated (14%) in the dark. Compared to shaded location plants, the greater total dry weight and seed production of individual ramets and the greater estimated reproductive effort of patches from open locations corresponded to a greater maximum photosynthetic rate (16.9 μmoles m⁻² s⁻¹) and daily carbon gain (12.2 g m⁻² d⁻¹). Possibly, a greater photosynthetic capacity may make more photosynthetic resources available for reproduction by A. cordifolia plants in open locations. Thus, intraspecific variation in physiology may contribute to intraspecific variation in reproduction.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

VINE PHOTOSYNTHESIS AND RELATIONSHIPS TO CLIMBING MECHANICS IN A FOREST UNDERSTORY

Photosynthesis in a deciduous forest understory was studied for three exotic vine species (Pueraria lobata, Lonicera japonica, and Hedem helix) and five common native species (Rhus radicans, Clematis virginiana, Smilax rotundifolia, Vitis vulpina, and Parthenocissus quinquefolid) possessing a variety of climbing mechanisms. The adventitious-root climbers (H. helix and R. radicans) had the lowest maximum photosynthetic rates of all species (5.5 and 6.4 μmol m^–2 s^–1, respectively). The twining vine P. lobata was the most poorly adapted to the understory with a high light-compensation point (43 μmol m^–2 s^–1), low photosynthesis under low light (0.5 μmol m² s^–1 at 50 μmol m^–2 s^–1), and the highest light requirement for obtaining 90% of maximum photosynthesis (860 μmol m^–2 s^–1). Lonicera japonica, another twining vine, was better-adapted to low light conditions, but vines with tendril climbing mechanics were physiologically the best adapted to low light. The adhesive-tendril climber P. quinquefolia was the most highly adapted to shade, with a low light compensation point (20 μmol m^–2 s^–1), a high photosynthetic rate under low light (3.5 μmol m^–2 s^–1), and a low light saturation point (160 μmol m^–2 s^–1). Results suggest that physiological adaptability of vines to low-light environments may be related to climbing mechanics.     

杉木苗木光合作用及其产物分配对水分胁迫的响应

 使用LI-6400红外CO2气体分析仪并应用13C 稳定性同位素脉冲标记方法,研究了两年生杉木(Cunninghamia lanceolata)苗木在水分胁迫下的光合特性及光合产物的分配规律和分配格局的变化。干旱处理没有明显抑制苗木在饱和光强以下的净光合速率。干旱处理各器官13C自然丰度略高于正常的对照处理。从标记后1～21 d苗木光合产物分配的动态过程来看,干旱处理全株稳定性碳同位素比值（δ13C值）和单位质量碳的净增加比率（N13CR）的平均值均低于对照,即水分胁迫限制了苗木对13C的吸收,而且对地上部分的影响大于地下部分。生长季结束时对苗木干重的测定结果表明,水分胁迫对苗木地上部分生物量影响较大,而对地下部分生物量的影响不明显。在苗木各器官中,水分胁迫对当年生针叶的影响最大。水分亏缺条件下当年生针叶的δ13C值、N13CR和生物量均明显低于对照,标记后21 d内其N13CR降幅最大,表明水分胁迫使苗木当年生针叶的碳输出增加。当年生针叶生长的降低使苗木光合总面积减少,因而净初级生产的总量减少。另外,水分胁迫下苗木全株的平均N13CR降幅大于对照,即13C的流失增加。水分胁迫下光合产物向地下部分尤其是细根迁移,使地下部分的分配比例增加,最终改变了苗木光合产物的分配格局,使根冠比增加。     

PHOTOSYNTHETIC RESPONSES TO LIGHT IN AN UNDERSTORY HERB,ASTER ACUMINATUS

Previous studies of the understory herb, Aster acuminatus, have shown that variation among natural patches in ramet growth, reproduction and population dynamics reflects environmentally induced responses to differences in patch light regimes. This set of experiments was undertaken to determine if photosynthetic responses to variation in light could provide a physiological explanation for the observed differences among patches. Ramets were raised in pots under different light regimes in either the field or growth chambers and then were taken to the lab for analyses of photosynthetic light responses. Ramets acclimated to the light conditions they experienced. Low-light plants had lower maximum photosynthetic rates, light saturation points and light compensation points compared to high-light plants. These differences were more pronounced for growth chamber-grown plants than for those from the field. Differences between ramets grown in deep shade and partial sun in the field were greatest early in the season and then became less as photosynthetic rates for all plants declined. Photosynthetic rates were strongly correlated with leaf nitrogen level, and there was no evidence that nitrogen was any more limiting for one treatment compared to others. These results demonstrate a physiological basis for patch differences in growth, reproduction and dynamics.     

SEX ALLOCATION IN THE MONOECIOUS HERB BEGONIA SEMIOVATA

Sex-allocation models predict that the evolution of self-fertilization should result in a reduced allocation to male function and pollinator attraction in plants. The evolution of sex allocation may be constrained by both functional and genetic factors, however. We studied sex allocation and genetic variation for floral sex ratio and other reproductive traits in a Costa Rica population of the monoecious, highly selfing annual Begonia semiovata. Data on biomass of floral structures, flower sex ratios, and fruit set in the source population were used to calculate the average proportion of reproductive allocation invested in male function. Genetic variation and genetic correlations for floral sex ratio and for floral traits related to male and female function were estimated from the greenhouse-grown progeny of field-collected maternal families. The proportion of reproductive biomass invested in male function was low (0.34 at flowering, and 0.07 for total reproductive allocation). Significant among-family variation was detected in the size (mass) of individual male and female flowers, in the proportion of male flowers produced, and in the proportion of total flower mass invested in male flowers. Significant among-family variation was also found in flower number per inflorescence, petal length of male and female flowers, and petal number of female flowers. Except for female petal length, we found no difference in the mean value of these characters between selfed and outcrossed progeny, indicating that, with the possible exception of female petal length, the among-family variation detected was not the result of variation among families in the level of inbreeding. Significant positive phenotypic and broad-sense genetic correlations were detected between the mass of individual male and female flowers, between male and female petal length, and between number of male and number of female flowers per inflorescence. The ratio of stamen-to-pistil mass (0.33) was low compared to published data for autogamous species with hermaphroditic flowers, suggesting that highly efficient selfing mechanisms may evolve in monoecious species. Our results indicate that the study population harbors substantial genetic variation for reproductive characters. The positive genetic correlation between investment in male and female flowers may reflect selection for maximum pollination efficiency, because in this self-pollinating species, each female flower requires a neighboring male flower to provide pollen.     

EFFECTS OF LIGHT AND DENSITY ON RESOURCE ALLOCATION IN A FOREST HERB,ASTER ACUMINATUS (COMPOSITAE)

Recent studies show that forest herbs have low sexual reproductive efforts (SRE) and high vegetative reproductive efforts (VRE) and that a variety of factors may affect the levels of reproduction and the distribution patterns of forest species. Aster acuminatus is a micro-successional forest herb common in northern New England. Resource allocation patterns were determined for seven aster patches varying in density and light level. Plant density affects neither plant size nor any aspect of resource allocation, and VRE remains constant over all density and light levels. Light level is, however, significantly correlated with patch location, average plant size and average patch SRE. Only large plants produce flowers suggesting that light affects sexual reproduction indirectly through effects on plant size. The high rhizome and low seed survivorship of this species may partly explain the constant VRE and varying SRE levels, although the resource allocation patterns observed do not correspond well with the predictions of certain theoretical models.     

准噶尔荒漠早春短命植物的光合特性及生物量分配特点

准噶尔荒漠分布的早春短命植物不仅具有十分独特的生物学特点,而且在荒漠植物群落演替、物种多样性维持及土壤改良与防治水土流失等方面具有重要的生态学价值。该文运用Li-6400开放式气体交换光合作用测定系统,对分布于准噶尔荒漠的16种早春短命植物生长盛期的净光合速率(P_n)、蒸腾速率(T_r)、水分利用效率(WUE)等特征进行了测定,并对其中7种植物与生长相关的生物量分配特征进行了分析。结果表明:1)16种植物的最大P_n、 最大T_r及WUE分别为8.07~35.96 μmol CO₂·m^-2·s^-1、3.16~29.64 mmol H₂O·m^-2·s^-1、0.54~4.26 μmol CO₂·mmol^-1H₂O;种间最大P_n与最大气孔导度(Stomatal conductance, G_s)之间存在正相关关系,其相关系数为0.77(p<0.05),线性回归斜率为26.36 μmol·mmol^-1;从光合速率对胞间CO₂浓度及光量子通量密度的响应曲线来看,这类植物的表观CO₂补偿点均在4~5 Pa之间(28~30 ℃),表观羧化效率为0.64~1.86 μmol CO₂·m^-2·s^-1·Pa^-1,表观量子效率为0.05~0.06。2)从生物量分配来看,所测植物的个体生物量为0.05~0.39 g;单株总叶面积为 3.24~51.40 cm²;单位叶面积干重为0.40~0.77 g·m^-2,根在总生物量中所占比例为5.72%~19.43%,单株叶面积比在2.92~9.00 m²·kg^-1之间。种间根所占生物量的比与对应的WUE之间的比较分析结果表明,二者之间存在显著的正相关关系,其相关系数r为0.93(p<0.01)。这些结果表明,所观测的早春短命植物具有典型的C₃植物特征,相比其它类型的荒漠植物具有较高的单位叶面积P_n、高T_r及低WUE,并且在生长发育过程中表现出很低的根/地上生物量比、较高的叶面积比和单位叶面积干重,说明它们具有相对高的生长速率,这与其生长发育节律相一致,反映了它们与准噶尔荒漠环境相适应的特点。     

SEASONAL PATTERNS OF PHOTOSYNTHESIS AND LIGHT-INDEPENDENT CARBON FIXATION IN MARINE MACROPHYTES1

The contribution of light-independent carbon fixation (LICF) to the overall carbon gain and the seasonal patterns of maximum photosynthesis (P_max and LICF were characterized in a broad taxonomic range of macrophytes from Monterey Bay, California. P_max and LICF rates (nmol C.g filtered seawater^?1.min^?1) varied among species and taxonomic groups examined, and as a function of tissue type in the phaeophyte Laminaria setchellii Silva (Phaeophyceae). On average, P_max values were higher in the Rhodophyta, whereas LICF rates were greater in the Phaeophyceae. LICF rates were generally less than 5% of P_max in the marine macrophytes studied and, as a consequence, cannot fully compensate for respiratory carbon losses, which usually are greater than 10% of P_max. All species studied possessed the highest P_max and LICF rates when irradiance levels were highest and decreased during periods of low incident irradiance. Seasonal patterns of P_max and LICF in most of the macrophytes from the stenothermal environment of Monterey Bay were strongly correlated with photosynthetic photon flux rather than seawater temperature. The concomitant decrease of LICF and P_max rates in all species examined argues against LICF playing a major role in carbon acquisition under light-limiting conditions as suggested previously. Rather, the strong positive correlation of P_max and LICF indicates the direct coupling of photosynthate (e.g. 3-phosphoglyceric acid) generation with production of substrates for LICF reactions. Our results also suggest that LICF might be a useful indicator of photosynthetic metabolism in marine macrophytes.     

落叶松幼苗碳素和氮素的获取与分配对供氮水平的响应

落叶松(Larix gmelinii)是中国东北林区最重要的工业用材树种,而且在北温带森林中具有重要的生态学意义。落叶松的种植区域内气温低、冬季长,氮素矿化速度低,供氮不足常常成为落叶松生长的限制因素。为揭示落叶松生长与氮素营养的关系,采用沙培法设置了1、4、8和16 mmol·L^-1 4个供氮水平,研究了不同供氮条件下落叶松一年生幼苗对碳和氮的获取与分配的规律。结果显示,落叶松幼苗的生物量、全株氮浓度、氮含量、比氮吸收速率均随供氮水平的增加而升高,叶重比(LWR)、茎重比(SWR)及叶氮比(LNR)、茎氮比(SNR)亦随供氮水平的增加而增加,而根重比(RWR)和根氮比(RNR)则随供氮水平的增加而降低。当供氮水平从1 mmol·L^-1增加至8 mmol·L^-1时,落叶松幼苗相对生长速率呈线性增加,而全株氮生产力几乎未受供氮水平的影响;当供氮水平从8 mmol·L^-1增加至16 mmol·L^-1时,全株相对生长速率不再增加,全株氮生产力则显著下降。与全株氮生产力的变化不同,落叶松幼苗的叶氮生产力与供氮水平呈负相关。     

CO_2倍增对紫花苜蓿碳、氮同化与分配的影响

本文简要报道ＣＯ２倍增下紫花苜蓿碳素积累、氮素的吸收与生物固氮及其产物在地上、地下部分配的特性１　材料和方法在北京香山中国科学院植物研究所植物园试验区,建立了两个高２．８ｍ、直径２．２ｍ的钢管支撑的圆柱状开顶式薄膜培养室,由底部向室内连续通气,保证培养室内每分钟换气３次。对照室通入正常空气（３５０×１０－６,１×ＣＯ２）,处理室通入ＣＯ２加倍的空气（７００×１０－６,２×ＣＯ２）。室内ＣＯ２浓度经红外ＣＯ２分析仪（ＱＧＤ－０７型,北京分析仪器厂产品）测定,２４ｈ内均可保持在３５０×１０－６及７０…     

马占相思的日光合作用和日碳固定总量研究 (英文)

 马占相思（Acacia mangium）是一种具有较高经济价值和生态效益的热带速生树种。为了研究其光合作用对一天内光强、温度等环境因子变化的响应,揭示其迅速生长的生理生态机制,在叶片水平上测量了马占相思在24 h内的净光合速率(Pn)、蒸腾速率、气孔导度(Gs)、胞间CO2浓度(Ci)、每日固定碳的总量、夜间消耗碳的总量以及日间光合系统Ⅱ光化学效率(Fv/Fm)的变化。结果显示：其净光合速率在正午降低了14.5%;其较高的蒸腾速率和气孔导度有助于保持叶片日间较高的碳固定速率;光合系统Ⅱ对于高光强和高温有较强的忍受度;每日固定碳的总量为502 mmol CO2·m-2,夜间碳的损失为54 mmol CO2·m-2。研究结果在一定程度上揭示了马占相思在热带高光强和高温条件下迅速生长的生理机制。     

EFFECT OF LIGHT AND WATER-STRESS ON PHOTOSYNTHESIS AND BIOMASS PRODUCTION IN BOLTONIA DECURRENS (ASTERACEAE), A THREATENED SPECIES

Boltonia decurrens (Torrey & Gray) Wood, a perennial species endemic to the Illinois River Valley, is threatened with extinction. Construction of a system of dikes along the Illinois River has altered flood patterns during the last 100 years, converting wet prairies and natural marshes to cropland. Remaining shore habitats have been modified by heavy siltation and altered flooding regimes. Boltonia decurrens is now confined to areas that are disturbed by occasional cropping, disappearing from sites after 3 to 5 years of natural succession. This study was conducted to determine the role of light and water availability upon growth and reproduction. Our data indicate that under greenhouse conditions B. decurrens requires high levels of light for optimal photosynthesis and growth, and is more sensitive to reductions in growth light level than to moderate drought-stress. This sensitivity to light regime may help explain its disappearance from disturbed areas after several years of natural succession. If B. decurrens is overtopped by fast-growing species, it could be shaded to the extent that growth and seed production would be severely affected, increasing the likelihood of its extinction.