Early growth and photosynthetic responses to light in seedlings of three tropical species differing in successional strategies

Containerized seedlings of three commercially important tropical species were grown under four different light treatments [i.e., 100 (open site), 45, 22 and 10% sunlight] for 130 days. Light-saturated photosynthesis (A _max) and light saturation estimates (LSE) reflected the species successional status with Terminalia superba Engl. and Diels, the pioneer species showing largest mean A _max and LSE at 100% sunlight, whereas at 10% sunlight, it showed the lowest A _max and LSE. At 22% sunlight, Cedrela odorata L., an intermediate successional species had greater A _max and LSE than Mansonia altissima A. Chev., a non-pioneer light demander and T. superba. T. superba had the lowest relative growth rate (RGR) at 10% sunlight and greatest net assimilation rate (NAR) at 100% sunlight; although a higher RGR at this light level was not seen for this species. Strong and positive linear mean A _max–mean NAR relationship of C. odorata and T. superba indicated that differences in leaf photosynthetic rates of the two species were reflected in their NAR, which increased with increasing light. At final harvest, superior biomass production was found at 45% sunlight for all the species. Seedling responses in specific leaf area, leaf area ratio, leaf mass ratio and root mass ratio were typically those found along a light gradient. At the 100% sunlight, intrinsic water-use efficiency (WUE), F _v/F _m and final root system of the plants was generally superior in T. superba but at 10% sunlight, WUE was inferior in T. superba when compared to C. odorata and M. altissima, reflecting the respective species’ short-term acclimation to high or low light. Results of this study may have practical use in screening tropical tree species for use in plantation forestry.     

Low light acclimation in five temperate broad-leaved tree species of different successional status: the significance of a shade canopy

?Context

Tree species differ largely in their capability to produce characteristic shade leaves with effective morphological and physiological acclimation to low light.

?Aims

By examining the sun/shade leaf differentiation in leaf morphology, foliar nitrogen and photosynthetic capacity in five temperate tree species of different successional status, we aimed at identifying those leaf traits that determine the development of a typical shade crown with low light-acclimated leaves.

?Methods

Leaf morphology, foliar N content, photosynthetic capacity (V _cmax, J _max and A _max) and leaf dark respiration (R _d) were measured in the canopies of 26 adult trees of Fraxinus, Acer, Carpinus, Tilia and Fagus species.

?Results

Six traits (the sun/shade leaf differentiation in specific leaf area, leaf size, A _max per leaf area or per mass, photosynthetic N use efficiency and R _d) were found to characterise best the degree of low light acclimation in shade leaves. All five species exhibited certain modifications in leaf morphology and/or physiology in response to low light; Fagus sylvatica showed the highest and Fraxinus excelsior the lowest shade leaf acclimation.

?Conclusions

Our results indicate that the five early/mid- to late-successional species have developed species-specific low light acclimation strategies in their shade crowns which differ in terms of the relative importance of leaf morphological and physiological acclimation.     

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]     

Photosynthetic response to green crown pruning in young plantation-grown Eucalyptus pilularis and E. cloeziana

The loss of foliage through pruning of live branches may reduce tree growth or it may be compensated by photosynthetic up-regulation of the remaining crown. Here, the changes in light-saturated photosynthesis following pruning to remove 50% of green crown length were examined in 4-year-old Eucalyptus pilularis Sm. and Eucalyptus cloeziana F. Muell. trees. The objectives of the study were to: (1) compare leaf-level physiological (light-saturated photosynthesis (A_max), stomatal conductance (g), transpiration (T), dark respiration (R_d), quantum yield (Φ), light compensation point (Γ), water-use efficiency (WUE), nitrogen-use efficiency (NUE)) traits in species with contrasting crown dynamics and structure, (2) examine the effect of crown position on these traits, and (3) examine the effect of pruning on A_max, g, T, WUE, NUE, leaf N and P concentrations and specific leaf area (SLA). Prior to pruning there were no differences in R_d, Γ and Φ between E. pilularis and E. cloeziana but differences in A_max, T, g, leaf N, leaf P, WUE, NUE and SLA. Whereas the rate of physiological processes (A_max, T, and g) and leaf N and P concentrations increased with crown height, R_d, Γ, Φ and SLA declined along this vertical gradient, except in the upper crown of E. cloeziana where A_max, T and g were not different to the lower crown. No up-regulation of photosynthesis or changes in leaf physiology occurred between 6 and 13 months after pruning in either species. The results provide an important basis for modelling pruning effects in process-based tree growth models.     

Interspecific variation in leaf water use associated with drought tolerance in four emergent dipterocarp species of a tropical rain forest in Borneo

By use of tree-tower and canopy-crane systems we studied variations in the water use, including transpiration, stomatal conductance, and leaf water potential, of the uppermost sun-exposed canopy leaves of four emergent dipterocarp species in an aseasonal tropical rain forest in Sarawak, Malaysia. Midday depression in stomatal conductance and leaf water potential was observed in all the species studied. Interspecific differences were clearly observed in the maxima of transpiration rates and stomatal conductance and the minima of leaf water potential among the four dipterocarp species. These interspecific variations were closely related to wood density and to factors affecting ecological patterns of distribution. Specifically, Shorea parvifolia and S. smithiana, both of which have a relatively low wood density for Dipterocarpaceae and are found on clay-rich soil, had a high transpiration rate in the daytime but had a large midday depression and a low leaf water potential. In contrast, Dryobalanops aromatica, which has a high wood density and is found in sandy soil areas, consumed less water even during the daytime. Dipterocarpus pachyphyllus, which has a high wood density and is found on clay-rich soil, stood intermediate between Shorea and D. aromatica in leaf water use. The two Shorea species had higher mortality than the others during the severe drought associated with El Ni?o in 1998, so daily pattern of leaf water use in each dipterocarp species might be correlated with its susceptibility to unusual drought events.     

An integrated model for predicting maximum net photosynthetic rate of cocksfoot (Dactylis glomerata) leaves in silvopastoral systems

Net light-saturated photosynthetic rate (A_max) of field grown cocksfoot (Dactylis glomerata L.) leaves in a radiata pine (Pinus radiata D. Don) silvopastoral system (Canterbury, New Zealand) was measured at different times under severe shade (85–95 μmol m^–2 s^–1 photosynthetic photon flux density, PPFD) and in full sunlight (1900 μmol m^–2 s^–1 PPFD). The aim was to integrate individual functions for A_max against air temperature (2 to 37 oC), water status, expressed as pre-dawn leaf water potential (ψ_lp) (-0.01 to −1.6 MPa), herbage nitrogen (N) (1.5 to 5.9%), regrowth duration (20 to 60 days) and time under shade (1 to 180 min) into a multiplicative model. The highest A_max value obtained was 27.4 μmol CO₂ m^–2 s^–1 in non-limiting conditions with full sunlight. This value was defined as standardised dimensionless A_maxs = 1 for comparison of factor effects. The canopy temperature of the cocksfoot sward was up to 7.4 oC cooler than air temperature for plants under shade. Therefore, canopy temperature was used to predict A_max. The only interaction was between time under severe shade (5% of the open PPFD) and water stress (ψ_lp = −0.4 to −1.3 MPa) and this was included in the model. Validation of this model indicated 78% of the variation in A_max could be accounted for using these five factors by the addition of the interaction function. This model could be used to assist the prediction of pasture growth in silvopastoral systems through incorporation into a canopy photosynthesis model. This revised version was published online in June 2006 with corrections to the Cover Date.     

Review on Leaf Water Use Efficiency of Major Trees Species in Arid and Semi-Arid Area

The tree specie selection is the critical part in the process of vegetation restoration and reconstruction in arid and semi-arid areas.As a reliable indicator of drought resistance and water use characteristics of tree species,water use efficiency（WUE） has become a hotspot in the research on tree specie selection.This paper introduced the concept and correspondingly research method of leaf WUE and summarized the research progress of leaf WUE in terms of the variation in leaf WUE between species,positions in the canopy,and characteristics of temporal and spatial variation,its influence on environmental factors like illumination,moisture,temperature, CO₂ and O₃ concentrations.Furthermore,it put forward the problems currently existing in the research and prospected the trend of future research on leaf WUE.     

干旱半干旱地区主要树种叶片水分利用效率研究综述

树种选择是干旱、半干旱地区森林植被恢复与重建的关键环节, 而水分利用效率(WUE)是表征树种抗旱性和水分利用特征的基本生理参数, 是目前树种选择研究中的一个热点和难点问题。文中在介绍树木叶片WUE概念和研究方法的基础上, 从树木叶片WUE在树种和生活型之间的差异和时空变化规律及其对光照、水分、温度、CO₂和O₃浓度等环境因子的响应等方面阐述了干旱、半干旱地区主要树种叶片WUE研究的进展情况, 指出目前树木叶片WUE研究中存在的问题及今后研究展望。     

Leaf-level responses to light in two co-occurring <Emphasis Type="Italic">Quercus</Emphasis> (<Emphasis Type="Italic">Quercus ilex</Emphasis> and <Emphasis Type="Italic">Quercus suber</Emphasis>): leaf structure,chemical composition and photosynthesis

We studied morphological, biochemical and physiological leaf acclimation to incident Photon-Photosynthetic-Flux-Density (PPFD) in Quercus ilex (holm oak) and Quercus suber (cork oak) at Mediterranean evergreen oak woodlands of southern Portugal. Specific leaf area (SLA) decreased exponentially with increasing PPFD in both species. Q. ilex had lower SLA values than Q. suber. Leaf nitrogen, cellulose and lignin concentration (leaf area-based) scaled positively with PPFD. Maximum rate of carboxylation (V_cmax), capacity for maximum photosynthetic electron transport (J_max), rate of triose-P utilization (V_TPU) and the rate of nonphotorespiratory light respiration (Rd) were also positively correlated with PPFD in both Quercus species, when expressed in leaf area but not on leaf mass basis. Q suber showed to have higher photosynthetic potential (V_cmax, J_max^m and V_TPU^m) and a higher nitrogen efficient nitrogen use than Q.ilex. Leaf chlorophyll concentration increased with decreasing PPFD, improving apparent quantum use efficiency (Φ) in both Quercus species. We concluded that, in Q.ilex and Q.suber, leaf structural plasticity is a stronger determinant for leaf acclimation to PPFD than biochemical and physiological plasticity.     

Growth,biomass partitioning,and water-use efficiency of a leguminous shrub (<Emphasis Type="Italic">Bauhinia faberi</Emphasis> var. <Emphasis Type="Italic">microphylla</Emphasis>) in response to various water availabilities

Responses of the endemic leguminous shrub Bauhinia faberi var. microphylla, to various soil water supply regimes were studied in order to assess water stress tolerance of seedlings. Two-month-old seedlings were grown under water supply regimes of 100, 80, 60, 40, and 20% water field capacity (FC), respectively, in a temperature and light-controlled greenhouse. Plant height and leaf number were measured monthly over a 4-month period, while water use (WU), water-use efficiency (WUE), leaf relative water content (RWC), biomass production and its partitioning were recorded at the end of the experiment. Seedlings exhibited the greatest biomass production, height, basal diameter, branch number, leaf number, and leaf area when soil content was at 100% FC, and slightly declined at 80% FC. These parameters declined significantly under 60% FC water supply, and severely reduced under 40 and 20% FC. RWC, WU and WUE decreased, while the ratio of root mass to stem mass (R:S) increased in response to decreasing water supply. Water stress caused leaf shedding, but not plant death. The results demonstrated that B. faberi var. microphylla seedlings could tolerate drought by reducing branching and leaf area while maintaining a high R:S ratio. However, low dry mass and WUE at 40 and 20% FC suggested that the seedlings did not produce significant biomass under prolonged severe water deficit. Therefore, before introducing B. faberi var. microphylla in vegetation restoration efforts, water supply above 40% FC is recommended for seedlings to maintain growth.     

Gas exchange characteristics of a Canarian laurel forest tree species (Laurus azorica) in relation to environmental conditions and leaf canopy position

Diurnal courses of gas exchange were measured over a 1-year period in fully expanded current-year leaves in the upper (sun-exposed, 18 m above ground) and the lower (shaded, 12 m above ground) canopy of Laurus azorica (Seub.) Franco, a major canopy species of the Canarian laurel forest in Tenerife, Canary Islands, Spain. Laurus azorica exhibited high leaf plasticity in gas exchange characteristics, with a maximum carbon assimilation rate (Amax) of shade leaves about 50% that of sun leaves. This difference reflects the high leaf area index (LAI) of the stand and the correspondingly sharp light attenuation with increasing canopy depth. In sun leaves, Amax peaked at about 11 micromol m-2 s-1 and maximum transpiration (E) was about 8 mmol m-2 s-1, which corresponded with a maximum stomatal conductance (gs) of about 650 mmol m-2 s-1. Mean maximum instantaneous water-use efficiency (WUE) was 1.5 mmol mol-1 and the mean maximum A/gs was 20-35 micromol mol-1. Mean minimum internal CO2 concentration (Ci) was 225 micromol mol-1. Although high air vapor pressure deficit (VPD) caused a small decrease in gs, it remained high enough to maintain relatively high A and E. These gas exchange characteristics indicate a non-conservative use of water, which is appropriate for a species subject to droughts that are mild or of short duration. In this respect, Laurus azorica differs from its congener, L. nobilis L., of the Mediterranean region and other shrubs growing in Mediterranean-type climates in California and Chile that have to withstand more severe or more prolonged droughts.     

Does strategy of resource acquisition in tropical woody species vary with life form,leaf texture,and canopy gradient?

In order to test whether the strategy of resource acquisition varies with life form, leaf texture and canopy gradient, we measured light-saturated net photosynthetic capacity (A _max-mass) and leaf nitrogen and phosphorus concentrations (N _mass and P _mass) for 127 woody species of understory (small shrubs and tree seedlings) and 47 woody species of canopy (large shrubs and tree adults) in a tropical montane rain forest of Hainan Island, South China. Photosynthetic nitrogen use efficiency (PNUE) and photosynthetic phosphorus use efficiency (PPUE) were studied by taking into account functional groups, which classified by either life form (FG1) or leaf texture (FG2). For FG1, there were significant (P < 0.05) differences between trees and shrubs in A _mass, N _mass and P _mass, but not in PNUE and PPUE; whereas for FG2, there were significant (P < 0.05) differences between the papery-leaved species and those with leathery leaves in the measured leaf traits inclusive of PNUE and PPUE. Within the same classification systems, significant allometric scaling relationships were found in the leaf trait pairs of A _mass-N _mass and A _mass-P _mass. Considered separately, the slope and y-intercept of the linear regression between A _mass and N _mass did not differ among functional groups nor between understory and canopy, but those for the linear regression between A _mass and P _mass differed significantly (P = 0.001) between understory and canopy species regardless of functional groups. The results of phylogenetic comparative analyses were in accordance with the observed positive scaling relationships. The overall results indicate that there are no fundamentally different nitrogen capture strategies in tropical woody species regardless of their life form, leaf texture and canopy gradient. However, the strategies of phosphorus acquisition of tropical woody species differ with canopy layer increases. This variation may correspond to the special soil conditions in this ecosystem, as phosphorus is an element limiting plant growth in tropical areas.     

华山松、油松不同叶龄针叶光合特性对林窗式疏伐的响应

[目的]通过对比研究华山松和油松不同叶龄针叶形态、光合速率、叶绿素和叶氮含量对林窗式疏伐的响应,探讨林窗大小、叶龄和树种对林窗式疏伐后叶光合特性响应的影响。[方法]2008年在30年生华山松和油松混交人工林中,设置对照、小林窗(80 m2)和中林窗(110 m2)处理,2013年以对照样地内和林窗边缘华山松和油松为研究对象,测定其当年生、1年生和2年生叶比叶重(LMA)、单位叶面积叶绿素a(Chl a)、叶绿素b含量(Chl b)、氮含量(N)、最大净光合速率(Amax)、光合氮利用效率(PNUE)等指标。[结果]小林窗和中林窗疏伐对叶光合特性影响一致,均对当年生叶影响不显著,但显著改变了1年生和2年生叶绿素含量、N和PNUE,提高了其Amax。华山松叶LMA、叶绿素含量、N、Amax均低于油松,两树种多年生叶对林窗式疏伐的响应也明显不同:林窗边缘华山松1年生和2年生叶LMA和N与对照差异不显著,但叶绿素含量低于对照,PNUE和Amax显著高于对照;林窗边缘油松1年生和2年生叶LMA和PNUE与对照差异不显著,但N和Amax显著高于对照。[结论]80 110 m2林窗疏伐显著改变叶光合特性,提高其光合潜力;林窗疏伐影响1年生和2年生叶光合特性,对当年生叶影响不显著;华山松和油松对林窗式疏伐的响应特征存在差异。     

Growth of Festuca pallescens in Silvopastoral Systems in Patagonia, Part 2: Parameterization of Models of Stomatal Conductance and Leaf Photosynthesis

A combined model of stomatal conductance and photosynthesis was developed for Festuca pallescens (St. Ives) Parodi, a forage species in Patagonia. Curves showing the relationship between photosynthesis and photosynthetic photon flux density (PPFD) were constructed for plants grown under differing levels of water availability, relative humidity (RH) and air temperature (T). Stomatal conductance (g_s) was related to these variables and pre-dawn leaf water potential (ψ_pd) using an empirical multiplicative submodel. Parameters of the photosynthesis-PPFD curves were related to the average g_s values for each curve to introduce stomatal limitation on photosynthesis. Considering the simplicity of the models, estimated stomatal conductance and photosynthesis agree satisfactorily with independent measured values in the field and in the glasshouse, particularly in the range of low and medium values of both variables (R² = 0.84 and 0.87 for g_s and photosynthesis models, respectively). Photosynthesis–PPFD curves were also determined under field conditions for plants growing under shade and in the open, in a silvopastoral trial in northwestern Patagonia. No significant differences in the photosynthetic light response curves were found between these locations, but slight increases in maximum assimilation rate and quantum yield (light use efficiency) were found for leaves grown under shade. This study of environmental influences on photosynthesis in F. pallescens may help to predict its capacity to grow under trees in silvopastoral systems. In addition, this simple model may be easily parameterised for other species to predict photosynthetic responses under different environmental conditions.     

Carbon isotope discrimination in leaf juice of Acacia mangium and its relationship to water-use efficiency

Using the PMS pressure chamber and isotope mass spectrometer (MAT-252), the leaf juice of Acacia mangium was obtained, and the carbon isotope discrimination (D) representing the most recently fixed carbon in the juice was determined. At the same time, the water-use efficiency of A. mangium was estimated. The results indicated that the carbon isotope ratio in the air of forest canopy (δ _a), 10 m high a bove ground averaged − 7.57 ± 1.41 ‰ in cloudy days, and − 8.54±0.67‰ in sunny days, respectively. The diurnal change of the carbon isotope ratio in the photosynthetic products of the leaf juice (δ _p) was of saddle type in cloudy days, but dropped down from morning to later afternoon in sunny days. A strong negative correlation between δ _p and leaf-to-air vapor pressure deficit (D) was observed in sunny days, but a slight change in δ _p was found in cloudy days. The δ _p also decreased with decreasing leaf water potential (Ψ), reflecting that water stress could cause the decrease of δ _p. The carbon isotope discrimination of the leaf juice was positively correlated with the ratio between intercellular (P _i) and atmospheric (P _a) partial pressure of CO₂. For A. mangium, the isotope effect on diffusion of atmospheric CO₂ via stomata was denoted by a = 4.6‰, and that in net C₃ diffusion with respect to P _i was indicated by b = 28.2‰. The results were in reasonable accord with the theoretically diffusive and biochemical fractionation of carbon isotope. It was defined that carbon isotope discrimination of photosynthetic products in A. mangium leaf juice was in proportion to that from photosynthetic products in dry material. The water-use efficiency estimated by the carbon isotope discrimination in leaf juice, fit well with that measured by gas exchange system (R ² = 0.86, p < 0.0001). The application of leaf juice in measuring the stable carbon isotope discrimination would reduce the effects of fluctuating environmental factors during the synthesis of dry matter, and improve the ecophysiological studies on carbon and water balance when scaling from the plant to canopy in the fields. __________ Translated from Chinese Journal of Ecology, 2008, 27(4): 497–503 [译自: 生态学杂志]     

Effects of water stress on growth,dry matter allocation and water-use efficiency of a leguminous species, <Emphasis Type="Italic">Sophora davidii</Emphasis>

The adaptation responses to different water conditions and the drought tolerance of Sophora davidii seedlings were assessed in a greenhouse experiment. Two-month-old seedlings were subjected to the following water supplies for 95 days: 100, 80, 60, 40 and 20% of field water capacity. The seedlings at 100% FC had the greatest productivity, height, basal diameter, branch number, leaf number and leaf area. Water supply <80% FC was the threshold of drought-initiated negative effects on seedling growth, yield and physiological processes; these parameters were severely reduced at 20% FC, however, there was no plant death during the experiment. Moreover, water stress decreased leaf relative water content, specific leaf area, leaf area ratio, and water-use efficiency (WUE), whereas it increased the biomass allocation to roots, which resulted in a higher root:stem mass ratio under drought. The S. davidii seedlings tolerated drought by maintaining high leaf relative water content and by reducing branching and leaf expansion. However, low productivity and WUE at 20% FC suggested that seedlings did not produce high biomass under severe drought. Therefore, prior to introducing S. davidii in forestation efforts, a water supply >40% FC is recommended for seedlings to maintain growth and productivity. These results provide insights into limitations and opportunities for establishment of S. davidii in arid regions.     

Optimizing nursery and plantation methods to grow <Emphasis Type="Italic">Cedrela odorata</Emphasis> seedlings in tropical dry agroecosystems

Cedrela odorata (Spanish cedar) is a valuable multi-purpose tree which Central American rural communities and farmers give priority to introducing in pastures and home gardens. In order to propose realistic methods for C. odorata production in local nurseries in the dry tropical region of Nicaragua, we studied: (a) the ability of locally collected C. odorata seeds to germinate, (b) seed response to storage under ambient conditions or under cold storage, (c) the effects of irradiance and watering during cultivation on seedling morphology and post-transplantation survival, and (d) the effects of competition from grasses on C. odorata seedlings transplanted to pastures. Seed germination ranged from 55 to 66% and remained constant after 6 months of storage under ambient conditions or cold storage. C. odorata seedling morphology was sensitive to irradiation and watering in the nursery growing period. Deep shade reduced seedling biomass and leafiness and increased specific leaf area and root-to-shoot ratio. Water shortage increased root mass ratio and root-to-shoot ratio and decreased leaf mass ratio. Post-transplantation success was favored by weeding, and was the highest for seedlings grown under deep shade and water restrictions.     

不同土壤水分胁迫格局对印度沙漠中的黄檀种苗营养吸收和生物量的影响

1998年7月,利用非称重式蒸渗池种植单一种源的一年生黄檀种苗,研究在印度沙漠地区培养黄檀种苗的合理灌水技术参数。当各处理（W1、W2、W3、W4）的土壤水分含量分别降低到7.56%、5.79%、4.44%和3.23%时,通过灌溉使苗木生长保持在一定的土壤的水分状况,如36.2mm（W1）、26.5mm（W2）、20.2mm（W3）和18.1mm（W4）。结果表明,在36.2mm（W1）水平时,种苗的株高、冠径、叶数和叶面积达到最大值（p〈0.01）。在W1和W2处理中,虽然上述参数没有明显差异,但在W2处理中,种苗的每升水分利用率的生物量最大。在W3、W4和W5灌溉水平下,不利于提高种苗的株高、生物量和营养积累。在W2水平以下（5.79%）,土壤水分有效率能提高根系生物量占总生物量的百分比。但在W3和W4处理中,叶干生物量百分比下降,同时在W5处理中,茎干生物量百分比下降。在W5处理中,土壤水势达到-196Mpa,种苗才可以成活。在W3和W4处理中,土壤水分有效率的限额影响黄檀种苗的生长和生物量。在W2处理中,土壤水分有效利用率最高,种苗的生长和生物量达到最高值。因此,在壤砂土条件下,通过灌溉维持幼苗土壤水分含量在5.79%以上时,可获得较好的黄檀种苗的生长和生物量产量。     

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.     

Growth of <Emphasis Type="Italic">Dactylis glomerata</Emphasis> along a light gradient in the central Appalachian region of the eastern USA: II. Mechanisms of leaf dry matter production

Microsite influences development and resource allocation of Dactylis glomerata L. (orchardgrass), a traditional pasture species with potential as an understory crop in silvopasture of humid temperate regions. An experiment using container-grown orchardgrass was conducted under field conditions to determine how open (O), shaded woodland (W) and open-to-shaded woodland transition zone (E _O, E _W) microsites influenced leaf DM production. Plants established in spring (SP) and late summer (LS) were clipped each time mean canopy height reached 20 cm. Dry matter production and allocation among structures differed, as a function of light attenuation. Specific leaf area (SLA) and photosynthetic nitrogen-use efficiency (PNUE) were associated with leaf DM production, whereas leaf N, net assimilation rate and shoot total nonstructural carbohydrates (TNC), were not. Specific leaf area was related to leaf DM of LS plants, whereas PNUE influenced leaf DM of SP plants. Stembase TNC was inversely related to relative regrowth rate (RG_RR) with RG_RR greatest and TNC the least at W. The relationship for RG_RR and TNC for SP plants growing at O and LS plants growing at W was similar. Regardless of how indices of growth are related, SP and LS plantings responded as separate populations (representing young and established plants respectively) that have different leaf DM production efficiencies. Orchardgrass was able to sustain leaf production when subjected to simultaneous stresses of shade and repeated defoliation. The LS plants growing at W respond in a manner similar to SP plants and may require management practices attuned to establishing or immature plants. The US Government’s right to retain a royalty-free, non-exclusive copyright is achnowledged.