Structural characteristics and eco-adaptability of heteromorphic leaves of <Emphasis Type="Italic">Populus euphratica</Emphasis>

The microstructural and ultrastructural traits of three kinds of typical leaves ofPopulus euphratica Olive, including lanceolate, broad-ovate and dentate broad-ovate leaves, were studied by using electron microscope and optical microscope. The resuits showed that with the leaves changing from lanceolate shape to dentate broad-ovate shape, their structure obviously tended to be xeromorph: developed palisade tissue, undeveloped spongy tissue, thick cutin layer and sunken stomas. The amount of mitochondria tended to be increased, and the shape of chloroplasts varied from regular spindle to irregular rotundity or oval. The leaves were covered with wax without cilium, and the stomas on the upper and lower epidermis of the leaves opened unevenly. The stomas on the lower epidermis were deeper than those on the upper epidermis under the scanning electron microscope. The results implied that the structural characteristics of the diversiform-leaves ofP euphratica are related to its eco-adaptability.     

Structural Characteristics and Eco-adaptability of Heteromorphic Leaves of Populus euphratica

The microstructural and ultrastructural traits of three kinds of typical leaves of Populus euphratica Olive, including lanceolate, broad-ovate and dentate broad-ovate leaves, were studied by using electron microscope and optical microscope. The re- sults showed that with the leaves changing from lanceolate shape to dentate broad-ovate shape, their structure obviously tended to be xeromorph: developed palisade tissue, undeveloped spongy tissue, thick cutin layer and sunken stomas. The amount of mitochondria tended to be increased, and the shape of chloroplasts varied from regular spindle to irregular rotundity or oval. The leaves were cov- ered with wax without cilium, and the stomas on the upper and lower epidermis of the leaves opened unevenly. The stomas on the lower epidermis were deeper than those on the upper epidermis under the scanning electron microscope. The results implied that the structural characteristics of the diversiform-leaves of P. euphratica are related to its eco-adaptability.     

Diurnal Course of Gas Exchange and Water Use Efficiency of Platycladus orientalis in the Semiarid Region of the Loess Plateau

The daily gas exchange, stomatal conductance, and water use efficiency of Platycladus orientalis in the test field of Fangshan county of Shanxi Province in the semiarid region of the Loess Plateau were measured with portable Li-6200 gas analysis system in natural conditions. The results showed that the diurnal course of net photosynthetic rate displayed a two-peak pattern, that of stomatal conductance displayed a hollow pattern, and that of transpiration rate displayed a signal-peak pattern. Water use efficiency culminated in the early morning. On the basis of two criteria of stomatal limitation of photosynthesis suggested by Farquhar and Sharkey, the predominant limiting factor of photosynthesis was the stomatal conductance of stomatal limitation in the morning (10:00–12:00). However, the midday depression of photosynthesis at noon (12:00–14:00) and the decrease in photosynthesis in the afternoon (16:00–18:00) were the results of nonstomatal limitation, such as low carboxylation capacity of the leaf mesophyll.     

Nitrate reductase activity and its diurnal variation rhythm for Camptotheca acuminata seedlings

Nitrate reductase activity (NRA) in different plant organs and leaves in different positions of Camptotheca acuminata seedlings was determined by an In vivo assay, the diurnal variation rhythm of NRA in leaves of different positions was observed,and the correlations between leaf NRA, leaf area and lamina mass per unit area (LMA) were also examined. The results showed that NRA in the leaf was significantly highest, compared with that in other organs such as roots, stems and leaves. In this experiment, the 10 leaves were selected from the apex to the base of the seedlings in order. The different NRA occurred obviously in leaves of different positions of C. acuminata seedlings from the apex to the base, and NRA was higher in the 4th-6th leaves.The diurnal change rhythm of leaf NRA showed a one peak curve, and maximum NRA value appeared at about midday (at 12:30 or so). No obvious correlations between NRA and leaf area or lamina mass per unit area were observed. This study offered scientific foundation for the further research on nitrogen metabolism of C. acuminata.     

Fractal dimension ofPopulus davidiana leaf surface rough extent

The rough extent of leaf surface may be described by protruding of waxes which like as wart and of stomatal aperture and of width of the cuticular ledge around guard cells. Because the morphology of the leaf surface has obviously similar itself, so one can use the theory of the fractal dimension to deal with the problems of leaf surface rough. The paper studied the rough extent and the result showed: with the leaf growing up, the waxes accumulate more and more, the leaf surface is more rough and the dimension is larger. The dimension D _w ^p which indicates the rough extent of warts protruding is about 2.10–2.20 on the above epidermis; On the beneath epidermis the dimension D _s ^p of stomatal opening protruding is about 2.00–2.24; Maximum widthL of cuticular ledge is about 1.0–7.4μm. The project supported by Natural Science Foundation of China     

Effects of enhanced ultraviolet-B radiation on water use efficiency, stomatal conductance, leaf nitrogen content and morphological characteristics of Spiraea pubescens in a warm-temperate deciduous broad-leaved forest

Spiraea pubescens, a common shrub in the warm-temperate deciduous forest zone which is distributed in the Dongling Mountain area of Beijing, was exposed to ambient and enhanced ultraviolet-B (UV-B, 280–320 nm) radiation by artificially supplying a daily dose of 9.4 kJ/m² for three growing seasons, a level that simulated a 17% depletion in stratospheric ozone. The objective of this study was to explore the effects of long-term UV-B enhancement on stomatal conductance, leaf tissue δ ¹³C, leaf water content, and leaf area. Particular attention was paid to the effects of UV-B radiation on water use efficiency (WUE) and leaf total nitrogen content. Enhanced UV-B radiation significantly reduced leaf area (50.1%) but increased leaf total nitrogen content (102%). These changes were associated with a decrease in stomatal conductance (16.1%) and intercellular CO₂ concentration/ air CO₂ concentration (C _i /C _a) (4.0%), and an increase in leaf tissue δ ¹³C (20.5‰), leaf water content (3.1%), specific leaf weight (SLW) (5.2%) and WUE (4.1%). The effects of UV-B on the plant were greatly affected by the water content of the deep soil (30–40 cm). During the dry season, differences in the stomatal conductance, δ ¹³C, and WUE between the control and UV-B treated shrubs were very small; whereas, differences became much greater when soil water stress disappeared. Furthermore, the effects of UV-B became much less significant as the treatment period progressed over the three growing seasons. Correlation analysis showed that enhanced UV-B radiation decreased the strength of the correlation between soil water content and leaf water content, δ ¹³C, C _i/C _a, stomatal conductance, with the exception of WUE that had a significant correlation coefficient with soil water content. These results suggest that WUE would become more sensitive to soil water variation due to UV-B radiation. Based on this experiment, it was found that enhanced UV-B radiation had much more significant effects on morphological traits and growth of S. pubescens than hydro-physiological characteristics. __________ Translated from Journal of Plant Ecology, 2006, 30(1): 47–56 [译自: 植物生态学报]     

Spatial and seasonal variations in photosynthetic properties within a beech (Fagus crenata Blume) crown

The light response curve and the intercellular CO₂ concentration response curve of CO₂ assimilation rate were investigated together with the light conditions at the four different heights within the beech crown from 1995 to 1997 on Mt. Fuji in Japan. On the seasonal fluctuation, the CO₂ assimilation rate at light saturated condition increased rapidly in May, and attained to the maximum between the end of June and July, thereafter, slightly decreased until the middle of August and rapidly decreased in September and October. The daily sum of photosynthetic photon flux density attenuated with deeping within the crown, and particularly, the relative value on 2nd position dropped to only 30%. TheA _max decreased from 10 to 5μmol m⁻² s⁻¹, approximately, with deeping within the crown. The light saturation point, quantum yield, light compensation point and dark respiration rate also varied with deeping. These results suggest that the photosynthetic properties vary gradually from sun to shade leaves along the light attenuation within a beech crown. At light saturated condition, the stomatal conductance and mesophyll conductance were strongly correlated withA _max among the four different heights (r > 0.96, respectively). TheC _i/C _a ratio was around 0.8, and there were no remarkable differences among the four different heights. These results suggest that the vertical gradient ofA _max depends on the variation of mesophyll conductance. The stomatal conductance may be also one of the major factor in the vertical gradient ofA _max. However the intercellular CO₂ concentration doesn’t influence the vertical gradient ofA _max within the crown. This work is supported by the Sasagawa Scientific Research Grant from The Japan Science Society and Grant-in-Aid for Scientific Research (C).     

Patchy stomatal behavior during midday depression of leaf CO₂ exchange in tropical trees

We investigated effects of heterogeneous stomatal behavior on diurnal patterns of leaf gas exchange in 10 tree species. Observations were made in middle and upper canopy layers of potted tropical rainforest trees in a nursery at the Forest Research Institute Malaysia. Measurements were taken from 29 January to 3 February 2010. We measured in situ diurnal changes in net photosynthetic rate and stomatal conductance in three leaves of each species under natural light. In both top-canopy and sub-canopy species, midday depression of net assimilation rate occurred in late morning. Numerical analysis showed that patchy bimodal stomatal behavior occurred only during midday depression, suggesting that the distribution pattern of stomatal apertures (either uniform or non-uniform stomatal behavior) varies flexibly within single days. Direct observation of stomatal aperture using Suzuki's Universal Micro-Printing (SUMP) method demonstrated midday patchy stomatal closure that fits a bimodal pattern in Shorea leprosula Miq., Shorea macrantha Brandis. and Dipterocarpus tempehes V.Sl. Inhibition of net assimilation rate and stomatal conductance appears to be a response to changes in vapor pressure deficit (VPD). Variable stomatal closure with increasing VPD is a mechanism used by a range of species to prevent excess water loss from leaves through evapotranspiration (viz., inhibition of midday leaf gas exchange). Bimodal stomatal closure may occur among adjacent stomata within a single patch, rather than among patches on a single leaf. Our results suggest the?occurrence of patches at several scales within single leaves. Further analysis should consider variable spatial scales in heterogeneous stomatal behavior between and within patches and within single leaves.     

Carbon Isotope Discrimination, Gas Exchange and Stem Growth of Four Euramerican Hybrid Poplars under Different Watering Regimes

Seasonal changes in carbon isotope discrimination (Δ) and gas exchange traits were assessed in four Populus×euramericana clones differing in growth potential. Measurements were made during the second year after establishment in the field under two watering regimes, which were defined by the time-span between flood irrigations, hence resulting in different dry-down cycles: high irrigation (conservative schedule currently applied in the Ebro Valley, Spain) and low irrigation (equivalent to about a one-fourth reduction in water inputs). Net CO₂ assimilation rate (A), stomatal conductance (g_s), intrinsic water-use efficiency (A/g_s) and other related photosynthetic traits (leaf nitrogen concentration, leaf greenness and leaf mass per area) were measured prior to watering, and Δ was analysed in water-soluble leaf extracts (Δ_s) and bulk leaves (Δ_l). Stem growth was monitored over 3 years starting at the year of establishment (1998). Data were subjected to a repeated measures ANOVA over time for a randomised block split-plot design across watering regimes. Significant differences between watering regimes were detected using a long-term estimate of photosynthetic performance such as Δ_l, in agreement with changes in soil water status and evapotranspirative demand. However, the lack of significant genotype×watering regime interactions for gas exchange traits and Δ_s suggested that water shortage imposed by low irrigation was not sufficient to reveal physiological adaptations to drought. In this regard, the reduction in water inputs brought about by low irrigation did not reduce tree growth for any of the clones, suggesting that the current irrigation scheme employed in the region is superfluous to the water consumption needs of poplars. Genotypic variation was detected in gas exchange traits, Δ_s, Δ_l and stem growth under both watering treatments. Significant correlations with stem volume for Δ_s (r = −0.60, p<0.05) and A (r = + 0.61, p<0.05) suggested that growth was improved by higher water-use efficiency (the ratio of carbon fixed to water lost, as inferred by Δ_s) due to variation in A rather than in g_s. This observation corroborated the expectation derived from current theories that a lower Δ is related to higher stem volume, as a result of changes in net CO₂ assimilation rates.     

Effect of soil water changes on photosynthetic characteristics of Taxodium distichum seedlings in the hydro-fluctuation belt of the Three Gorges Reservoir area

Four different kinds of water treatment were applied to examine the photosynthetic characteristics of baldcypress (Taxodium distichum) seedlings in the hydro-fluctuation belt of the Three Gorges Reservoir area. The aim was to shed light on the physio-ecological adaptation of this species to changing water levels for revegetation purposes. The water treatments were normal growth water condition (CK), light drought water stress (T1), growth under soil water saturation (T2) and growth with soil submersion (T3). T3 had the lowest content of photosynthetic pigment; T1 and T2 did not differ from CK in the content of chlorophyll and carotenoid. The ratio of chlorophyll a to b in the four groups ranged from 2.04 to 2.69 and the ratio of chlorophyll to carotenoid from 3.08 to 4.51. In group T1, the seedling of baldcypres had lower apparent light use efficiency, lower apparent CO₂ use efficiency and a lower net photosynthetic rate, with the net photosynthetic rate 24.9% lower than that of group CK. However, T2 and T3 did not differ from CK in apparent light use efficiency, apparent CO₂ use efficiency and net photosynthetic rate. Water use efficiency of the four treatments consistently increased as treatment was prolonged; the average water use efficiency of T3 was the lowest while that of CK was the highest. Correlation analysis showed that the net photosynthetic rate of baldcypress seedlings was positively related to transpiration rate, stomatal conductance, water use efficiency, apparent light use efficiency and apparent CO₂ use efficiency, but highly negatively related to the ratio of chlorophyll a to b. Net photosynthetic rate was not significantly related to the contents of chlorophyll and carotenoid, the ratio of chlorophyll to carotenoid, relative air humidity and intercellular CO₂ concentration. The transpiration rate was positively correlated with stomatal conductance and negatively related to water use efficiency. The results showed that different water treatments could effectively influence the baldcypress seedlings’ content of photosynthetic pigment, leaf gas exchange and apparent resources use efficiency. The results verified that the species T. distichum takes on the features of a water-tolerant and hydrophilic plant, which can be considered as one of the species for the building of a forest protection system for the hydro-fluctuation belt in the Three Gorges Reservoir area. Baldcypress should not be planted in drought-stricken soils. __________ Translated from Acta Ecologica Sinica, 2005, 25(8) [译自:生态学报, 2005, 25(8)]     

Physio-ecological response of Haloxylon persicum photosynthetic shoots to drought stress

This paper studied the seasonal characteristics to resist the drought stress of Haloxylon persicum Bge. Ex Boiss. et Buhse photosynthetic shoots at habitat. The results showed that the predominant drought resistance factors were varied at the different stage from growth to development. In the blooming season (from May 31 to June 29), endogenous ABA contents were rare; stomatal conductance and photosynthesis intensity were the highest at the whole stage from growth to development; soluble sugars contents had a decreasing trend and proline contents increased a little that made proline become the predominant factor to resist the drought under this light water stress. In the hot summer (from June 29 to July 26), ABA contents accumulated rapidly; stomatal conductance dropped to the lowest level of the growth and development; chlorophyll was also decomposed; both soluble sugars and proline contents showed the trend of quickly accumulating, but the former was faster than the latter. It was due to stomatal limitation and osmotic organic molecules accumulation that would affect the photosynthetic shoots to resist severe drought stress. At the late period of the development (from Aug 9 to Aug 22), ABA rapidly accumulated, its contents got to the highest level of whole life-span; stomatal conductance increased a little; proline and soluble sugars contents changed little at high level; while the ratios of ABA to CTK content and ABA to IAA content got up obviously, the effect to resist drought stress on high content ABA was inhibited by endogenous plant hormone CTK and IAA, then the continuing accumulation of proline and soluble sugars would be prevented. Osmosis of organic molecules was the most important factor to adjust leaves to severe water stress at this period. __________ Translated from Scientia Silvae Sinicae, 2005, 41(5) [译自, 林业科学 2005, 41(5)]     

Changes in photosynthesis and water status of developing leaves of Brachystegia spiciformis Benth

Changes in net carbon assimilation and water status were studied during leaf development in the deciduous, tropical species Brachystegia spiciformis Benth. In this upland savanna African tree, bud-burst and leaf development occur approximately two months before the rainy season. The newly formed leaves synthesize anthocyanin until the fully expanded leaves of the whole canopy are red. This foliage is referred to as "spring flush" foliage. Subsequently, the anthocyanins are metabolized and the pre-rain leaves become green. Carbon dioxide assimilation exhibited a bimodal diurnal pattern and was similar for pre-rain green leaves and fully expanded flushing leaves, although pre-rain green leaves showed a net uptake of carbon throughout the daylight period, whereas flushing leaves exhibited only brief periods of net photosynthesis in the morning and early afternoon. Measurements of leaf water potential and relative water content showed a diurnal pattern with considerable variation throughout the day. Leaf water potential and relative water content values decreased soon after sunrise reaching a minimum at a time corresponding to the afternoon peak in CO(2) assimilation. Stomatal conductance was closely related to transpiration rate in both flushing and pre-rain green leaves, although flushing leaves had lower stomatal conductances than pre-rain green leaves. Pre-rain green leaves exhibited a compensation irradiance of approximately 180 micro mol m(-2) s(-1), whereas flushing leaves had positive net photosynthesis only at PPFDs greater than 300 micro mol m(-2) s(-1). Rate of photosynthesis (expressed per leaf area or chlorophyll unit) increased as anthocyanin concentration decreased, although the photosynthetic rate continued to increase long after the leaf anthocyanins had been degraded to low, visually undetectable amounts. Post-rain green leaves had chlorophyll concentrations, transpiration rates and stomatal conductances similar to those of pre-rain green leaves; however, photosynthetic rates in post-rain leaves were more than three times higher. Thus, during the early stages of the spring flush, carbon asimilation rates of the flushing leaves were inversely related to leaf anthocyanin concentrations. In pre-rain green leaves, photosynthesis was limited by other non-stomatal factors.     

Critical tidal level for forestation with hypocotyl of Rhizophora stylosa Griff along the Guangxi coast of China

From August 2004 to August 2005, three replicate experimental platforms were constructed in a section of the tidal flats in Yingluo Bay, Guangxi Province to study the growth and physiological responses of Rhizophora stylosa Griff seedlings to tidal waterlogging stress in a diurnal tidal zone. A total of eight tidal flat elevation (TFE) treatments, i.e., 320, 330, 340, 350, 360, 370, 380 and 390 cm above Yellow Sea Datum (YSD), were created on each platform. The results showed that lower TFEs (320–330 cm YSD) slightly increased the seedling stem height of 1-year old seedlings, while higher TFEs (>340 cm YSD) increased the seedling growth significantly. Moderate TFEs (350–370 cm YSD) favored the development of knots. Number of leaves, leaf conservation rate and leaf area per seedling all decreased dramatically with decreasing TFE. Lower TFEs caused large damage to Chl a, but Chl b was less affected. The Chl a/b ratio decreased with decreasing TFE. Prolonged waterlogging induced higher SOD activity in roots, while moderate TFE inhibited the SOD activity in leaves. The POD activity in roots and leaves increased with decreasing TFE. Waterlogging stress decreased the biomass of individual organs and entire seedlings. With increasing waterlogging, the biomass partitioning in 1-year old seedlings increased from leaf to stem. The survival rate decreased sharply from 88.9% to 40.0% as TFE decreased, while more than 80% of the seedlings were able to survive at the TFE level of 370 cm YSD and above. We propose that the local mean sea level should be adopted as the critical tidal level for forestation with hypocotyls of R. stylosa along the Guangxi coast.     

Observation of the scale of patchy stomatal behavior in leaves of Quercus crispula using an Imaging-PAM chlorophyll fluorometer

Patchy stomatal closure occurs in plants with heterobaric leaves, in which vertical extensions of bundle sheath cells delimit the mesophyll and restrict the diffusion of CO(2). The scale of patchy stomatal behavior was investigated in this study. The distribution of PSII quantum yield (Φ(II)) obtained from chlorophyll fluorescence images was used to evaluate the scale of stomatal patchiness and its relationship with leaf photosynthesis in the sun leaves of 2-year-old saplings of Quercus crispula Blume. Fluorescent patches were observed only during the day with low stomatal conductance. Comparison of numerical simulation of leaf gas exchange and chlorophyll fluorescence images showed that heterogeneous distribution of electron transport rate through PSII (J) was observed following stomatal closure with a bimodal manner under both natural and saturated photosynthetic photon flux densities. Thus, fluorescence patterns can be interpreted in terms of patchy stomatal closure. The mapping of J from chlorophyll fluorescence images showed that the scale of stomatal patchiness was approximately 2.5-fold larger than that of anatomical patches (lamina areas bounded by bundle sheath extensions within lamina). Our results suggest the spatial scale of stomatal patches in Q. crispula leaves.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

油茶不同叶龄叶片形态与光合参数的测定

为了探讨油茶叶片形态特征、光合特性与叶龄的相关性,从而为油茶的生产经营提供理论参考,利用CI-203叶面积分析仪和LI-6400便携式光合仪测定了油茶新梢不同叶龄叶片的形态特征和光合参数。结果表明:油茶叶面积和叶片鲜质量,从第1到第3位叶逐渐变大,又从第3到第7位叶逐渐减小;叶片的叶绿素含量和净光合速率均随着叶龄的增大而增大;叶龄与蒸腾速率和气孔导度均呈极显著正相关,而与胞间CO2浓度呈极显著负相关;叶片比叶面积与胞间CO2浓度间呈极显著正相关,而与净光合速率、蒸腾速率和气孔导度间均呈极显著负相关;叶片干物质含量比值与其净光合速率、气孔导度和蒸腾速率间均呈极显著负相关;叶片生长20 d,叶面积等形态特征基本发育完全,经过60 d的生长后,基本成为主要功能叶。     

金森女贞光合生理特性的研究

研究了金森女贞光合生理日变化及其光补偿点和饱和点.结果表明:金森女贞的单日净光合速率(Pn)呈双峰曲线,出现"午休"现象,造成Pn下降的主要原因是非气孔因素.蒸腾速率(Tr)和气孔导度(Gs)的变化趋势与Pn相似,胞间CO2浓度(Ci)与之相反.Pn与Ci和PAR的相关性达到极显著水平,Tr与PAR、RH和VPD均达到极显著水平.金森女贞的光补偿点(LCP)为16.67 μmol/(m2·s),饱和点(ISP)约为1 000 μmol/(m2·s),属于阳性植物.     

Dissolved organic matter originating from the riparian shrub Salix gracilistyla

To estimate the importance of leaching of dissolved organic matter (DOM) as a pathway through which organic matter is supplied to stream ecosystems, we examined the amount of leachate over time and chemical properties of DOM leached from leaves in different conditions. The samples used were green leaves, yellow senescent leaves, and leaf litter of Salix gracilistyla Miq., which is the dominant riparian plant species in the middle reaches of rivers in western Japan. We analyzed dissolved organic carbon (DOC), total sugar, and polyphenol in the leachate of leaf samples collected from a fluvial bar in the middle reaches of the Ohtagawa River in Hiroshima Prefecture, Japan. Considerable leaching of DOC from senescent leaves [37.3 mg g⁻¹ dry weight (dw) leaf] and leaf litter (8.1 mg g⁻¹ dw leaf) occurred within 24 h after immersion. In contrast, DOC leached from green leaves was negligible until 1 week after leaf immersion. Carbon loss of leaves by leaching within 24 h after leaf immersion was estimated to be less than 8%, suggesting that leaching of DOC from S. gracilistyla leaves is a minor pathway through which organic matter is supplied to stream ecosystems. DOM leached from the leaves included sugar and polyphenol, which were among the major chemical forms of DOM leached from the leaves (based on the molecular mass). In a laboratory experiment in which the difference in the stability of DOM between the chemical forms was examined, sugar decomposed more rapidly than polyphenol.     

紫茎泽兰叶片气体交换的气孔调节特性:对其入侵能力的意义

紫茎泽兰是一个典型的外来入侵植物.利用便携式光合测定系统,对分布于四川省凉山州德昌市郊(27°28′36"N,102°12′28″E)的紫茎泽兰的气体交换特性进行测定,并与本地8个伴生种和其他12个分布于我国不同地区和日本的入侵种和本地种进行比较.目的是探讨气孔调节在日变化过程和长期干旱与湿润生境上的差异及其对紫茎泽兰入侵能力的影响.研究发现紫茎泽兰光合午休现象明显,气孔调节和非气孔调节共同控制了紫茎泽兰的光合日进程模式,而以气孔调节最为重要.非气孔调节主要是通过羧化效率的降低,从而影响表观量子效率或其他光合过程来实现的,而气孔调节主要是通过降低胞间CO2浓度,提高气孔限制值来实现的,这与其他种的差异不大.经过长期的野外不同湿度环境适应后,气孔调节出现了一定的弹性变化.在气孔导度相差不大的情况下,土壤有机质、土壤pH值和土壤有效氮含量差异不明显,湿生生境的光合速率和蒸腾速率显著高于干生生境,并导致了叶片含氮量显著提高.气孔在调节紫茎泽兰水分利用效率方面有别于所测定的其他20种植物,在湿生生境下随气孔导度下降,水分利用效率下降,而在干生生境下则显著升高.因此,紫茎泽兰同时兼有"省水"植物和"费水"植物的双重特点,这一灵活水分利用特点保证了它在不利环境中的生存和有利环境中的扩展,对于其在侵入区的生长发育有一定的意义.     

The ecological and functional correlates of nocturnal transpiration

Contrary to the conventional theory of optimal stomatal control, there is substantial transpiration at night in many tree species, but the functional significance of this phenomenon remains uncertain. To investigate the possible roles of nocturnal transpiration, we compared and contrasted the correlations of both nocturnal and diurnal sap flow with a range of traits in 21 temperate deciduous tree species. These traits included soil water affinity, shade tolerance, cold hardiness, nitrogen concentration of tissues, minimum transpiration rate of excised leaves, growth rate, photosynthetic capacity, stomatal length and density, and the water potential and relative water content of leaves at the wilting point. Nocturnal sap flow was higher in species with higher leaf nitrogen concentrations, higher rates of extension growth and lower shade tolerances. Diurnal sap flow was higher in species with higher leaf nitrogen concentrations and photosynthetic capacities on a leaf area basis. Because leaf metabolism and dark respiration, in particular, are strongly related to leaf nitrogen concentration, our findings suggest that nocturnal transpiration functions to sustain carbohydrate export and other processes driven by dark respiration, and that this function is most important in fast- growing shade-intolerant tree species.