Interacting effects of irradiance and water stress on dry weight and biomass partitioning in Fagus sylvatica seedlings

Abstract

Actual climate models for central Europe predict prolonged summer droughts. Knowledge on how the interaction between light and water availability affects regeneration will hence be of major importance. In an experiment carried out under controlled conditions, newly emerged beech seedlings were grown in pots with sand during 54 days. Three treatments applying three different light levels (2, 9 and 43% relative light intensity) were combined with two soil water treatments (control and drought). At the end of the experiment, seedlings were separated into leaves, stem and root and the seedlings’ dry mass, leaf area and stem length was determined. Low irradiance (2%) had a strong negative effect on dry weights of seedling components, leaf area and specific leaf mass. Drought clearly affected biomass partitioning for seedlings at high irradiance levels (43%). An interaction between irradiance and drought on biomass partitioning in beech seedlings was observed at medium irradiance level (9%). Within a wide range of light levels in the forests, both light and drought may affect biomass partitioning in young seedlings.     

Morphological response of Vitex negundo var. heterophylla and Ziziphus jujuba var. spinosa to the combined impact of drought and shade

Light and soil moisture availability are two important abiotic factors influencing plant growth in an agroforestry system. Different soil moisture and light treatments were applied to examine the combined impact of drought and shade on the morphological plasticity of Vitex negundo var. heterophylla (Chinese chastetree) and Ziziphus jujuba var. spinosa (Spine jujube). We found that the interaction of light and soil moisture was orthogonal in the two species. V. negundo captured irradiance efficiently with relatively long petiole and petiolule, while Z. jujuba maintained higher branches to absorb light than V. negundo. Compared to the seedlings under full sunlight, the palmately compound leaves of V. negundo under low light showed larger specific leaf area (SLA), lower ratio of leaflet length to width and higher leaf mass ratio (leaf biomass to total biomass); in contrast, the simple leaves of Z. jujuba under low light showed larger SLA and ratio of leaf length to petiole length. In both species, drought reduced the branch number, mean internode length of stem, and increased root mass ratio (root biomass to total biomass), but leaf morphology showed little variation to the decreased soil moisture. Between the two species, V. negundo is more shade-tolerant, while Z. jujuba is more drought-tolerant. In an alley cropping system, the spacing can be smaller in the V. negundo-crop system than the Z. jujuba-crop system when soil moisture is adequate. However, the V. negundo-crop system should be managed with more caution under the soil moisture limited conditions.     

Growth and photosynthetic responses of Gallesia integrifolia (Spreng.) Harms and Schinus terebinthifolius Raddi seedlings in dense shade

We analyzed the growth and photosynthetic behavior of Gallesia integrifolia (‘pau-d’alho’) and Schinus terebinthifolius (‘aroeirinha’) under shade, seeking to obtain ecophysiological information for introducing seedlings of those species in previously established cacao agroforestry systems. Considering that light intensity under the shade of cacao trees varied between 5 and 10% daylight, 5 months old seedlings were exposed to four irradiance levels (25, 17, 10 and 5% daylight) for 92 days. With shade increase both species displayed trends of decrease leaf mass per unit leaf area, leaf area per plant (LA), relative growth rate (RGR) and net assimilation rate (NAR), and increase leaf area ratio (LAR). The mean values of light-saturated net photosynthetic rate (P _nmax) in 25 and 5% daylight were 12.8 and 8.0 μmol CO₂ m⁻² s⁻¹ for G. integrifolia and 17.9 and 7.4 μmol CO₂ m⁻² s⁻¹, respectively, for S. terebinthifolius. Based on the measurements of photosynthetic photon flux density and estimated values of photosynthetic saturated irradiance (Is) we concluded that, in all shaded conditions, the leaves of both species were under sub optimal light conditions to reach P _nmax. In spite of the lowest P _nmax values, RGR and NAR were significantly higher for G. integrifolia in all irradiance levels. Differences in growth rates can be explained by the higher values of LA, LAR and leaf mass ratio (LMR), as well as by the lower values of Is, photosynthetic compensation irradiance and dark respiration rates observed for G. integrifolia. Even though seedlings of G. integrifolia presented higher capacity to adapt under conditions of dense shade, we concluded that both species were under stress conditions induced by shade in light environments below 25% daylight. On a practical point of view it is possible to conclude that seedlings of both species should be introduced in light gaps, formed after the fall of big trees, or in places in which cacao trees are cultivated using large plant spacing.     

Exotic tree leaf litter accumulation and mass loss dynamics compared with two sympatric native species in south Florida,USA

The exotic tree Melaleuca quinquenervia (melaleuca) forms dense forests usually characterized by low plant diversities and dense litter biomass accumulations on forest floors of ecologically sensitive ecosystems, including portions of the Florida Everglades. We quantified litter accumulation in mature melaleuca stands and compared decomposition rates of melaleuca leaves with a sympatric native plant, either Cladium jamaicense (sawgrass) in sawgrass marshes or Pinus elliottii (slash pine) in pine flatwoods habitats that varied in soil types. Total litter accumulation in mature melaleuca forests prior to June 1997 ranged from 12.27 to 25.63 Mg ha⁻¹. Overall, melaleuca leaves decomposed faster in organically rich versus arenaceous soils. Decomposition rates were lower for melaleuca leaves than for sawgrass in both melaleuca-invaded and uninvaded sawgrass marshes. In arenaceous soils of pine flatwoods, melaleuca leaf and pine needle decomposition rates were similar. Complete mineralization of sawgrass leaves occurred after 258 weeks, whereas melaleuca leaves had up to 14% and pine foliage had up to 19% of the original biomass remaining after 322 weeks. Total carbon (C) in intact decomposing leaves varied slightly, but total nitrogen (N) steadily increased for all three species; the greatest being a fourfold in sawgrass. Increases in N concentrations caused decreases in the C/N ratios of all species but remained within an optimal range (20–30) in sawgrass resulting in higher decomposition rates compared to melaleuca leaves and pine needles (C/N ratio >30). Slower decomposition of melaleuca leaves results in denser litter layers that may negatively affect recruitment of other plant species and impede their establishment in invaded communities.     

Screening agroforestry tree mulches for corn growth: a combined soil test,pot trial and plant analysis approach

The response of corn (Zea mays) to incorporated leaf and twig mulches ofLeucaena leucophala, Gliricidia sepium andCassia siamea, andGrevillea robusta as a non-legume comparison was investigated in a 10-week pot trial and a concurrent soil incubation study to evaluate the suitability of various agroforestry trees as mulch sources.Leucaena contributed to the highest N uptake and biomass production of these corn plants, reflecting the benefits of organic mulching.Cassia-treated plants also performed better than the unmulched controls, butGrevillea incorporation suppressed corn growth probably because of the relatively high Mn status of this mulch. Manganese toxicity was confirmed by comparative vector diagnosis of plant nutrient status.Cliricidia mulching resulted in seedling mortality after germination possibly from high soil pH and ammonium toxicity. Mineral N production in mulched soils during the laboratory incubation was well correlated with N uptake in corn shoots. The results suggest that the nutritional effects of agroforestry tree mulches on growth of companion crops may be effectively screened by a combined soil test, pot trial, and plant analysis approach.     

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.     

Soil biological properties under different tree based traditional agroforestry systems in a semi-arid region of Rajasthan,India

An investigation was carried out in an Entisol at farmers’ field in Jaipur district, Rajasthan, India during 2002–2004 to evaluate the effect of traditionally grown trees on soil biological characteristics. Traditionally grown trees in farm lands for study consisted of Prosopis cineraria (L.), Dalbergia sissoo (Roxb.) ex DC, Acacia leucophloea (Roxb.) and Acacia nilotica (L.) Del. having a canopy diameter of 8 m. Results revealed significant and substantial improvement in soil biological activity in terms of microbial biomass C, N and P, dehydrogenase and alkaline phosphatase activity under different tree based agroforestry systems as compared to a no tree control (cropping alone). Soil microbial biomass C, N and P under agroforestry varied between 262–320, 32.1–42.4 and 11.6–15.6 μg g⁻¹ soil, respectively, with corresponding microbial biomass C, N and P of 186, 23.2 and 8.4 μg g⁻¹ soil under a no tree control. Fluxes of C, N and P through microbial biomass were also significantly higher in P. cineraria based land use system followed by D. sissoo, A. leucophloea and Acacia nilotica in comparison to a no tree control. Thus, it is concluded that agroforestry system at farmers’ field enhance soil biological activity and amongst trees, P. cineraria based system brought maximum and significant improvement in soil biological activity.     

Allelopathic effects of <Emphasis Type="Italic">Pinus halepensis</Emphasis> and <Emphasis Type="Italic">Quercus coccifera</Emphasis> on the germination of Mediterranean crop seeds

Agroforestry is a leading alternative for food security and forest conservation. A full understanding of positive and negative, i.e. allelopathic, interactions between crops and forest trees is necessary for producing crops and conserving forests especially within the threatened Mediterranean forest ecosystems. The present study explored the allelopathic effects of green and senescent leaf and soil extracts of two agroforestry trees—Pinus halepensis and Quercus coccifera—on the germination of wheat, barley, lentil, chickpea, and fababean as the major grain crops of Jordan. Results revealed that allelopathic effects reduced seed germination of these crops. Germination reduction reached a maximum of 75% in fababean treated with green extracts of Q. coccifera and differed among crops and extract sources, but not between tree species. Comparing between green and senescent leaf and soil extract, regarding their effect on germination percentage, it was noticed that these effects were similar in some crops and were different in others. Germination responses were generally different between cereals and legumes where cereals tend to be less affected by allelopathic influences than legumes, especially fababean. We suggest using cereals such as wheat and barley in agroforestry practices in the Mediterranean region of Jordan.     

Leaf nitrogen productivity is the major factor behind the growth reduction induced by long-term salt stress

Plant growth response to salinity on a scale of years has not been studied in terms of growth analysis. To gain insights into this topic, 2-year-old Mediterranean Fan Palm (Chamaerops humilis L.) and Mexican Fan Palm (Washingtonia robusta H. Wendl) seedlings, each with its own distinct plant morphology, were grown for 2 years in a peat soil and irrigated with water of 2 dS m(-1) (control) or 8 dS m(-1) (saline). Plants were harvested on seven occasions and the time trends in relative growth rate (RGR, the rate of increase of biomass per unit of biomass already existing) and its components were analysed. In the long term, salinity produced a slight reduction in the mean RGR, values in both species. In the short term, salinity caused a reduction in RGR. However, during the second year, plants irrigated with 8 dS m(-1) grew somewhat more quickly than the control plants, probably as a result of delay in the growth kinetics due to salinity. Regarding RGR components, leaf nitrogen productivity (the rate of biomass gain per unit leaf N and time) was the major factor causing the differences in RGR resulting from salinity. Washingtonia robusta showed a relatively high plasticity in plant morphology by increasing root and decreasing stem biomass allocation in the presence of salinity. However, the long-term response of W. robusta to salinity, based to a great extent, on this morphological plasticity, was less effective than that of C. humilis, which is based mainly on the contribution of leaf N to RGR values.     

Growth and yield of coffee plants in agroforestry and monoculture systems in Minas Gerais, Brazil

This research compared coffee plants (Coffea arabica L.) grown in an agroforestry and monoculture systems. Data were collected during two years, on vegetative growth, reproductive development, nutritional status and yield of coffee, besides monitoring air temperature and the tree growth. All trees in agroforestry system increased in growth, resulting in a reduction in the magnitude of the diurnal temperature variation and also maximum temperature. Coffee plants in agroforestry system had less branch growth and leaf production, more persistent and larger leaves, and presented earlier flowering, with a smaller number of productive nodes and flower buds, leading to smaller berry yield than plants in monoculture system. In both systems, the coffee plants showed adequate leaf nutrient levels, except for P and K. The yield of 2443 kg ha^-1 of coffee from the monoculture was greater than 515 kg ha^-1 of coffee from the agroforestry system.     

Response of five dry tropical tree seedlings to elevated CO2: Impact of seed size and successional status

The impact of seed size and successional status on seedling growth under elevated CO₂ was studied for five dry tropical tree species viz. Albizia procera, Acacia nilotica, Phyllanthus emblica, Terminalia arjuna and Terminalia chebula. Seedlings from large (LS) and small seeds (SS) were grown at two CO₂ levels (ambient and elevated, 700–750 ppm). CO₂ assimilation rate, stomatal conductance, water use efficiency and foliar N were determined after 30 d exposure to elevated CO₂. Seedlings were harvested after 30 d and 60 d exposure periods. Height, diameter, leaf area, biomass and other growth traits (RGR, NAR, SLA, R:S) were determined. Seedling biomass across species was positively related with seed mass. Within species, LS seedlings exhibited greater biomass than SS seedlings. Elevated CO₂ enhanced plant biomass for all the species. The relative growth rate (RGR), net assimilation rate (NAR), CO₂ assimilation rate, R:S ratio and water use efficiency increased under elevated CO₂. However, the positive impact of elevated CO₂ was down regulated beyond 30 d exposure. Specific leaf area (SLA), transpiration rate, stomatal conductance declined due to exposure to elevated CO₂. Fast growing, early successional species exhibited greater RGR, NAR and CO₂ assimilation rate. Per cent enhancement in such traits was greater for slow growing species. The responses of individual species did not follow functional types (viz. legumes, non-legumes). The enhancement in biomass and RGR was greater for large-seeded species and LS seedlings within species. This study revealed that elevated CO₂ could cause large seeded, slow growing and late successional species to grow more vigorously.     

Decomposition of Erythrina poeppigiana leaves in 3-, 9-, and 18-year-old alleycropping systems in Costa Rica

Timing the application of organic residues and therefore the release of nutrients during decomposition may be critical to the growing crop in tropical alleycropping agroforestry systems. Field experiments were carried out in Turrialba, Costa Rica, to determine differences in Erythrina poeppigiana (Walp.) O.F. Cook leaf decomposition in 3, 9 and 18-year alleycropped agroforestry systems. Treatments consisted of mulch-only, and mulch plus Arachis pintoi Krapov. and W. Gregory var. CIAT 18347 in 3 and 9-year old alleycrops under no-till cultivation. The 18-year old site consisted of treatments with mulch-only and mulch plus chicken manure under disk plow cultivation. Litterbags, filled with E. poeppigiana leaves from 3, 9 and 18-year old trees, were placed on the soil surface and collected over a period of 84 days. Results showed no significant differences in the amount of plant residues remaining after 84 days in the 3-, 9-, and 18-year-old systems, or between the manure and mulch-only treatments. Comparing mulch-only treatments, leaves in the 18-year old system decomposed most rapidly which may be due to disk-plow cultivation practices where litterbags were in direct contact with the soil as opposed to the no-till system in the younger alleycrops.     

Soil acidity, and the growth, biomass partitioning and leaf mineral composition of honeylocust (Gleditsia triacanthos L.) seedlings

Honeylocust seedlings (Gleditsia triacanthos L.) were grown in cylinders containing soil adjusted to pH 4, 5 or 6, and harvested every 10 days for 40 days for dry weight and leaf mineral analysis. Total weight of plants grown at pH 4 was less than that of plants grown at pH 5 or 6. Root weight accounted for a greater proportion of total weight in plants grown at pH 4 than in plants grown at pH 5 or 6. Root growth as a function of total plant growth was higher in plants grown at pH 4 than in plants grown at pH 5 or 6, whereas leaf growth as a function of total plant growth was less in plants grown at pH 4 than in plants grown at pH 5 or 6. However, the relationships between root biomass and root length and between leaf biomass and leaf area were the same in all treatments. An analysis of total leaf concentrations of Ca, P, K, Mg, Mn and Al indicated that Al accumulation in leaves was significantly related to a decrease in plant growth at pH 5. A leaf tissue aluminum concentration of 35 microg g(-1) was associated with toxicity symptoms and a 25% reduction in total plant weight.     

Effects of drought on isolates of <Emphasis Type="Italic">Bradyrhizobium elkanii</Emphasis> cultured from <Emphasis Type="Italic">Albizia adianthifolia</Emphasis> seedlings of different provenances

Albizia adianthifolia (Schumach) W. F. Wright, a N-fixing legume tree, has a wide distribution in Africa, in Ghana occurring in high rainfall forests and in seasonally droughted forests, and is associated in the Ghanaian forest zone with dry, infertile sites. We hypothesised that A. adianthifolia hosted different rhizobial strains in different forest types, and that these different strains would show different growth responses to moisture stress and different motility and mortality in droughted soil. Three isolates, extracted from seedlings of A. adianthifolia growing in three forest types differing in seasonal drought, were identified as Bradyrhizobium elkanii and exposed to varying levels of osmotic stress. Growth responses varied between the three strains, one of which displayed clear signs of drought tolerance. A novel approach using soil leaching columns was used to test the effects of soil pore water (in terms of neck diameter) on both the survival and movement of wet and dry forest rhizobial isolates through soil columns. The responses of the isolates were significantly different, the pore neck diameter, marginally insignificant and the drought treatment insignificant. Thus the dry forest isolate survived better in all treatments, and showed less response to the treatments, than the isolate from the wet forest. The results offer preliminary evidence that Bradyrhizobium elkanii strains from A. adianthifolia in Ghana have evolved in response to local differences in seasonal water availability. These differences could assist the selection of A. adianthifolia provenances for agroforestry or land rehabilitation.     

Effect of shade on biomass accumulation and partitioning for Eucalyptus camaldulensis sprouts

ABSTRACT

Eucalyptus is widely cultivated in homogeneous monocultures throughout the world alongside plants of the same age. Furthermore, the productivity of forest stands is highly dependent on how solar radiation is intercepted and used. Meanwhile, it is possible to consider cultivating trees of different ages in the same area, and thus under different regimes of available solar radiation, creating a sequence of plantings and harvestings and to develop Eucalyptus-based agroforestry systems. We have examined biomass accumulation of Eucalyptus camaldulensis along a shade gradient. Eucalyptus trees presented power-law responses to increasing irradiance for biomass, indicating it has low plasticity and is unable to maintain growth under lower irradiance levels. Biomass partitioning showed no dependence on available irradiation. Leaf density presented very little increase toward sunnier places meaning that an increment in Eucalyptus biomass would be mostly due to its increase in size and thus higher radiation interception. Careful management of shade will be a key consideration for the integration of Eucalyptus into agroforestry. With knowledge of the growth habits of different species, we will have the potential to propose more perennial ways in which to manage land and reduce anthropogenic disturbances by avoiding clear-cuts of areas that removes all plant structures.     

Response of cocoa trees (<Emphasis Type="Italic">Theobroma cacao</Emphasis>) to a 13-month desiccation period in Sulawesi,Indonesia

In South-east Asia, ENSO-related droughts represent irregularly occurring hazards for agroforestry systems containing cocoa which are predicted to increase in severity with expected climate warming. To characterize the drought response of mature cocoa trees, we conducted the Sulawesi Throughfall Displacement Experiment in a shaded (Gliricidia sepium) cocoa agroforestry system in Central Sulawesi, Indonesia. Three large sub-canopy roofs were installed to reduce throughfall by about 80% over a 13-month period to test the hypotheses that (i) cocoa trees are sensitive to drought due to their shallow fine root system, and (ii) bean yield is more sensitive to drought than leaf or stem growth. As 83% of fine root (diameter <2 mm) and 86% of coarse root biomass (>2 mm) was located in the upper 40 cm of the soil, the cocoa trees examined had a very shallow root system. Cocoa and Gliricidia differed in their vertical rooting patterns, thereby reducing competition for water. Despite being exposed for several months to soil water contents close to the conventional wilting point, cocoa trees showed no significant decreases in leaf biomass, stem and branch wood production or fine root biomass. Possible causes are active osmotic adjustment in roots, mitigation of drought stress by shading from Gliricidia or other factors. By contrast, production of cocoa beans was significantly reduced in the roof plots, supporting reports of substantial reductions in bean yields during ENSO-related drought events in the region. We conclude that cocoa possesses traits related to drought tolerance which enable it to maintain biomass production during extended dry periods, whereas bean yield appears to be particularly drought sensitive.     

Seasonal variation of soil respiration rates in a secondary forest and agroforestry systems

Agroforestry systems are widely practiced in tropical forests to recover degraded and deforested areas and also to balance the global carbon budget. However, our understanding of difference in soil respiration rates between agroforestry and natural forest systems is very limited. This study compared the seasonal variations in soil respiration rates in relation to fine root biomass, microbial biomass, and soil organic carbon between a secondary forest and two agroforestry systems dominated by Gmelina arborea and Dipterocarps in the Philippines during the dry and the wet seasons. The secondary forest had significantly higher (p < 0.05) soil respiration rate, fine root biomass and soil organic matter than the agroforestry systems in the dry season. However, in the wet season, soil respiration and soil organic matter in the G. arborea dominated agroforestry system were as high as in the secondary forest. Whereas soil respiration was generally higher in the wet than in the dry season, there were no differences in fine root biomass, microbial biomass and soil organic matter between the two seasons. Soil respiration rate correlated positively and significantly with fine root biomass, microbial biomass, and soil organic C in all three sites. The results of this study indicate, to some degree, that different land use management practices have different effects on fine root biomass, microbial biomass and soil organic C which may affect soil respiration as well. Therefore, when introducing agroforestry system, a proper choice of species and management techniques which are similar to natural forest is recommended.     

Effects of enhanced hydraulic supply for foliage on stomatal responses in little-leaf linden (<Emphasis Type="Italic">Tilia cordata</Emphasis> Mill.)

Responses of leaf conductance (g _L) to variation in environmental and plant hydraulic factors were examined on intact and detached shoots of little-leaf linden (Tilia cordata Mill.) with respect to branch position in the crown. Using detached shoots, we manipulated leaf water supply and light availability in order to separate the effects of insufficient hydraulic supply and low irradiance. The intact upper-crown leaves demonstrated 2.0–2.2 times higher (P < 0.001) daily maxima of g _L compared to the lower-crown leaves growing in the shadow of upper branches. Mean soil-to-leaf conductance (G _T) was 1.9 times higher (P < 0.001) for the upper-crown foliage compared to that of the lower crown. The total hydraulic resistance was distributed: soil to distal shoots—41–51%, 25-cm distal shoots—10–15% and leaves—39–44%. In lower branches, g _L was constrained by both low light availability and limited water supply; in upper branches, only by irradiance. Artificial reduction of hydraulic constraints raised bulk leaf water potential (Ψ _L) and made g _L less sensitive to changes in both atmospheric and plant factors. Stomatal responses to leaf-to-air vapour pressure difference (VPD) were significantly modified by leaf water status: high Ψ _L seemingly inverted the g _L versus VPD relationship. Enhanced water supply increased g _L and transpiration rate (E) in the lower-crown foliage, but not in the upper-crown foliage. The results support the idea that leaves in the lower canopy are hydraulically more constrained than those in the upper canopy.     

Biomass accumulation,allocation, and water-use efficiency in 10 <Emphasis Type="Italic">Malus</Emphasis> rootstocks under two watering regimes

Variations in biomass productivity, plant water-use efficiency (WUE_p), and carbon isotope composition (δ¹³C) were investigated among 10 Malus rootstocks. In the semi-controlled environmental of a greenhouse, plants were watered to either 75% or 50% of field capacity. For each treatment, significant differences were found in dry matter accumulation and allocation, δ¹³C, and WUE_p. Relative growth rate (RGR) was correlated with WUE_p but not with allocation pattern. Variations in whole-plant transpiration were a result of fluctuations in the rate of transpiration per unit leaf area rather than from differences in leaf area or root weight per plant. Values for transpiration per unit leaf area or root weight were lower when the proportion of either leaf area or root weight per unit plant weight was larger. Rootstock differences in δ¹³C were related to changes in stomatal conductance rather than in net photosynthesis. Finally, δ¹³C was significantly correlated with WUE_p and rootstock rankings based on both of those parameters were maintained regardless of watering treatment.     

Adaptive responses of<Emphasis Type="Italic">Acer ginnala,Pyrus ussuriensis and Prunus davidiana</Emphasis> seedlings to soil moisture stress

One-year-old seedlings of Amur maple (Acer ginnala Maxim), Ussurian pear (Pyrus ussuriensis Maxim) and David peach (Prunus davidiana Carr) were planted in pots in greenhouse and treated with four different soil moisture contents (75.0%,61.1%, 46.4% and 35.4%). The results showed that net photosynthesis rate (NPR), transpiration rate (TR) and stomatal conductance (Sc) of seedlings of the three species decreased with the decease of soil moisture content, and Amur maple seedlings had the greatest change in those physiological indices, followed by Ussurian pear, David peach. Amur maple and Ussurian pear seedlings also presented a decrease tendency in water use efficiency (WUE) under lower soil moisture content, whereas this was reversed for David peach. Under water stress the biomass allocation to seedling root had a significant increase for all the experimental species. As to root/shoot ratio, Amur maple seedlings had the biggest increase, while David peach had the smaliest increase. The leaf plasticity of Amur maple seedlings was greater, the leaf size and total leaf area decreased significantly as the stress was intensified. No significant change of leaf size and total leaf area was found in seedlings of Ussurian pear and David peach. It was concluded that Amur maple was more tolerant to soil moisture stress in comparison with David peach and Ussurian pear.