紫茎泽兰(Eupatorium adenophorum)对光强的生态适应性

紫茎泽兰(Eupatorium adenophorum)是我国主要外来入侵植物之一,在我国西南地区迅速传播,引起了巨大的经济损失。本文比较研究了不同光强下生长14个月的(透光率RI分别为10%、20%、30%、55%、100%)紫茎泽兰幼苗的生物量分配、叶片形态和生长反应特性。结果表明:紫茎泽兰在不同的光强条件下显示出极强的叶生态适应性。植株总生物量随光强升高而增加(RI从10%到55%),但在全光照下总生物量反而有所下降。株高也随光强增大(RI从10%到30%)而增大,但到达一定程度(RI30%)后,株高反而下降。在弱光照条件下,从比叶面积(SLA),叶面积比(LAR)和比茎长(SSL)等指标表明,植物通过叶片变薄、变大增加单位生物量的叶面积来捕获光能。随着光强的升高,平均相对生长速率增加,在本试验尺度下,RI在55%左右达到平均相对生长速率最大值。植株在RI为30%–55%下生长状况好于全光照条件下的幼苗。在高遮荫条件下能阻止其它生物的生存和生长,这可能是紫茎泽兰强入侵性的一种生态适应策略。结论:紫荆泽兰对光照强度拥有极强的生态适应性,可能是紫荆泽兰入侵性比较强的重要原因之一。图3参26。     

Genetic analysis of crossing effects for growth traits of Pinus massoniana and selection of cross combinations

Two groups of filial generations derived from two different Pinus massoniana complete-diallel crosses were analyzed. Results show that the general combining ability (GCA), specific combining ability (SCA) and reciprocal effects were significant for some growth traits, including height, DBH and volume index. The heredity of these growth traits was controlled by additive and non-additive genes, of which the additive genes played a dominant role. The epistatic effect was greater for group I (cross in 1992) than group II (cross in 1993). The SCA of P. massoniana growth traits was significantly greater than GCA, which may be related to different geographical provenance for parents and the indirect selection by GCA. Inbreeding depression was commonly observed for P. massoniana growth traits. The extent of inbreeding depression was −17.8%–−18.4%, −23.3%–−27.7% and −44.3%–−50.6% for height, DBH and volume index, respectively. It was observed that parents with small GCA values exhibited a greater extent of inbreeding depression. Large differences in hybrid vigor of different crosses were observed and the difference between original cross and reciprocal cross was not significant. Based on the volume index, 10 fine crosses were selected for two groups respectively, and the average increment of volume index was 59.41% and 41.76%, respectively, in comparison with the average of the testing groups, and was 100.58% and 74.61% in comparison with the local commercial variety. __________ Translated from Scientia Silvae Sinicae, 2008, 44(6): 28–33 [译自: 林业科学]     

Genotypic variation in wood properties and growth traits of <Emphasis Type="Italic">Eucalyptus</Emphasis> hybrid clones in southern China

Growth traits, wood properties and bark percentage were assessed for 19 hybrid eucalypt clones at three sites in southern China sampled at age 51 months. Analysis of variance showed that there were significant differences in growth traits and wood properties between clones and sites, and that the clone × site interactions were also significant except for basic density. Coefficients of variation ranged from 8.4 to 27.9% for growth traits, 2.7–11.1% for wood properties and 14.0–23.3% for bark percentage. Repeatability ranged from 0.73 to 0.96 for growth traits, 0.32–0.93 for wood properties and 0.77–0.88 for bark percentage. Strong genotypic correlations between the same traits in clones at pairs of sites indicated that the traits were rather stable across sites. The genotypic correlations between growth traits and basic density ranged from −0.67 to 0.43, and generally favorable negative genotypic correlations between growth traits and bark percentage were also found. The correlations between growth traits and Pilodyn pin penetration were positive, ranging from 0.28 to 0.65 and therefore unfavorable as lower wood density will be associated with higher values of Pilodyn pin penetration and improved growth rate. The correlations between traits assessed using non-destructive field methods and wood property assessment results indicated that Pilodyn and Fakopp microsecond timer tools can be confidently used to indirectly select for fiber width and basic density.     

Modeling cotton production response to shading in a pecan alleycropping system using CROPGRO

Light optimization assessment in alleycropping systems through model application is becoming an integral part of agroforestry research. The objective of this study was to use CROPGRO-cotton, a process-based model, to simulate cotton (Gossypium hirsutum L.) production under different levels of light in a pecan (Carya illinoensis K. Koch) alleycropping system in Jay, Florida, USA. Soil classification in the area was Red Bay sandy loam soil (Rhodic Paleudult). To separate roots of cotton and pecan, polyethylene-lined trenches were installed parallel to tree rows, thus competition for water and nutrients was assumed to be non-existent. Four treatments were set up in the CROPGRO-cotton model, as follows: (1) control (full amount of light transmittance), (2) Row 1 (50% light transmittance), (3) Row 4 (55% light transmittance), and (4) Row 8 (70% light transmittance). Cotton model parameters affecting specific leaf area (SLA), leaf area index (LAI), maximum leaf photosynthetic rate (FLMAX) and carbon partitioning were calibrated using the full sun treatment. Measurements of SLA, LAI, and aboveground biomass were made on the different shaded treatments and compared with simulated values. Simulation results showed that aboveground mechanisms affecting production in shaded environment (i.e., SLA, LAI, LFMAX, and carbon partitioning) influence model behavior. After calibration, the model predicted SLA of cotton in all treatments with reasonable precision. However, LAI was underestimated in the more shaded treatment rows 4 and 8. Generally, the model provided a close agreement between measured and simulated biomass both in 2001 and 2002 (R ² = 0.95 and R ² = 0.92, respectively). In 2001, predicted biomass for the control was 5,401 kg ha⁻¹ compared to the measured value of 5,393 kg ha⁻¹. A similar trend was also observed in 2002. The CROPGRO-Cotton model was able to describe variations in growth among the shaded treatments well across both growing seasons. However, it was found that additional research is needed to improve the model’s ability to simulate LAI under shading conditions. Parameters associated with photosynthesis and dry matter partitioning were reasonably stable across shading treatments and years but those associated with leaf area growth varied.     

改良式V形架对设施葡萄光照的影响

葡萄是喜光植物,设施葡萄栽培中最难克服的是光照不足问题。除改进农膜透光性之外,通过合理的架式,改善设施葡萄的光照条件成为设施葡萄栽培中的重要技术措施。通过对改良式＂V＂形架不同叶幕层次、不同生育时期光照强度的测量和分析研究,以期探知最有利于葡萄生长发育的架式结构。试验结果表明,与直立篱架相比,改良式＂V＂形篱架能有效改善设施葡萄的光照条件,有利于设施葡萄的生长发育。     

Soil water regime under rotational fallow and alternating hedgerows on an Ultisol in southern Cameroon

Soil moisture depletion during dry seasons by planted hedgerows to lower levels than under natural fallow, would reduce drainage and nutrient losses in the following rainy season when food crops are grown. The volumetric water content of the 0–150 cm soil profile was measured under planted hedgerows (alternating Leucaena leucocephala and Gliricidia sepium) and natural fallow, both either annually cropped to sole maize or in a two-year crop/two-year fallow rotation, in the humid forest zone (annual rainfall 1700 mm) of southern Cameroon during the 1995–1996 and 1996–1997 dry seasons. Hedgerows were cut to 0.05 m height, largely eliminating trees’ water consumption during cropping phases. Differences in total soil water content at 0–150 cm depth, between systems, occurred only in the early phases of the 1996–1997 dry season. In both dry seasons, differences between systems in water content were found in some soil layers, all within 0–60 cm depth, yet, without consistent advantage of any system in exploiting the topsoil water resources. Soil water content was lower under L. leucocephala than G. sepium at 20–40 cm depth only. Below 60 cm depth, no differences in water regimes between systems were found. Under southern Cameroonian conditions it is unlikely that any of the systems has an advantage in accessing or recovering water and thus, if available, nutrients from the sub-soil. None of the systems examined was capable of delaying drainage and thus it appears unlikely that downward displacement of nutrients is delayed after the start of the rains.     

Effects of shade on arbuscular mycorrhizal colonization and growth of crops and tree seedlings in Central India

The study was conducted to investigate the effects of different light intensities (25, 50, 67, and 100% of full sun [open]) on arbuscular mycorrhizal (AM) colonization and growth of two intercrops (a rainy season crop, Phaseolus mungo Roxb. var. PU-35 and a winter crop, Triticum aestivum L. var. WH-147) and seedlings of two multipurpose tree species (Eucalyptus tereticornis Sm. [Clone C-7, ITC, Bhadrachalam] and Albizia procera Benth.) of Central India. The results showed that various plant growth parameters viz., shoot length, dry weight and phosphorus (P) uptake were adversely affected by low light intensity. Inoculations with AM fungi (Acaulospora scrobiculata Trappe, Glomus intraradix Schenck & Smith and an unidentified Glomus species) increased the plant growth on account of all measured parameters under tested light conditions. Mycorrhizal efficiency of different AM fungi varied in narrow range. AM inoculants were more efficient at higher light intensity in above mentioned plant species, except wheat. Data on colonization of P. mungo, T. aestivum, E. tereticornis and A. procera showed that formation of arbuscules, vesicles and sporocarp was delayed by lower light intensity. Colonization index of host roots and spore counts increased with increase in light intensity during successive months after inoculation. Data on effect of light regimes on microclimate of net house showed that lux meter reading decreased as per grades of shading nets used during both rainy and winter seasons. With increase in light intensity, ambient temperature, soil surface temperature and sub surface temperature at 15 cm depth increased, except that the ambient and soil surface temperature in control (open) were slightly lower than net house observations during January and February. Value of ambient temperature varied in narrow range, with in treatments as compared to soil surface and sub soil surface temperature at 15 cm depth. Soil surface temperature at 25% of full sunlight was less than respective control values by 2–11°C and sub soil temperature at 15 cm depth was less by 4–12°C. The values of different microclimate parameters varied in narrower range during winter season as compared to rainy season. While ranking the importance of two factors studied—light and AM fungi—for their effect on the growth and P uptake by different plant species, inoculations with AM fungi came in the first place (explained 50–82% variation) and light substantially increased the values of R ² in stepwise regression analysis (forward selection). The results suggest that AM inoculation may enhance the growth and P uptake of intercrops under tree shade and the tree canopy management is likely to increase the efficiency of AM inoculants in agroforestry systems. Use of excessive shading (25% of full sun or more) in nurseries may be avoided and PAR (photosynthetically active radiation) lamps may be used to increase growth and colonization index of tree seedlings.     

Effect of tree-crop intercropping on a young Populus tomentosa plantation

In order to study the effect of tree crop intercropping on a young plantation of Populus tomentosa in the plains along the Yellow River, field experiments were conducted by observing the growth of the plantation, the nutrient content in leaves, the nutrient and water content in the soil, and the output of crops. The relationship between forest growth and nutrient content in the tree leaves and the soil were analyzed. Results show that tree crop intercropping in young plantations can not only improve soil water content, but also enhance the contents of organic matter and the available nitrogen, phosphorus and potassium in soil resulting in the vigorous growth of the individual trees. Diameter at breast height (DBH) was positively related to the contents of organic matter in the soil, and the contents of N, P and K in the tree leaves had correlation coefficients of 0.967, 0.955, 0.988 and 0.972, respectively. Whole tree leaf area, crown width, number of branches and the mean length of branches in the intercropped plantation (intercropped with watermelon and vegetables, peanut and winter wheat, and soybean) were, respectively, 1.70–3.0 times, 2.22–2.47 times, 1.0–1.41 times and 1.70–2.32 times of those of CK (without intercropping). Diameter at breast height (DBH) and tree height in the intercropped plantation were 50.5%–136.7% and 27%–59.5% higher than those of the CK, respectively. The study also showed that intercropping with watermelon and vegetables proved to have the highest economic return among the treatments adopted. Tree crop intercropping in young plantations is an effective measure to increase forest growth and economic benefit. __________ Translated from Journal of Beijing Forestry University, 2006, 28(3): 81–85 [译自: 北京林业大学学报]     

A study on the shade tolerance ofMuehlewbeckia complera

Muehlewbeckia complera was introduced to China in 2002 as indoor-hanging ornamental foliage plant. The experiment of the shade tolerance for this species was carried out in different light intensities (0.14–946.00 μmol·m⁻²·s⁻¹). After 40 days in experimental areas, leaf photosynthentic characteristics indexes ofM. complera in different photosynthesis active radiation (PAR) were measured with LI-COR6400 apparatus, such as the light compensation point, light saturation point, and maximum net photosynthesis rate, at the same time, the increments of total leaf area and leaf amount were measured. The results showed that the optimum light intensity range forM. complera was from 9.26 μmol·m⁻²·s⁻¹ to 569.00 μmol·m⁻²·s⁻¹ (463–28150 lx, relative humidity (RH) for 46–60%, temperature at 16–22°C). Under this condition, leaf photosynthetic efficiency was tiptop. AlthoughM. complera belonged to the moderate sun-adaptation plant species, the plant growth was inhibited when PAR increased to the level of 569.000 μmol·m⁻²·s⁻¹ or above.M. complera could sprout new leaves in photosynthesis active radiation of 0.16–19.22 μmol·m⁻²·s⁻¹ (8–961 lx), or 10 μmol·m⁻²·s⁻¹ for above 6 h. Foundation item: This study was supported by the Research Foundation of Northeast Forestry University. Biography: YUE Hua (1962-), female, Associate professor in Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Zhu Hong     

栽培密度与施肥对雷州半岛桉树大径材培育效果的中期研究

摘要：针对桉树大径材培育,对试验地设置5种栽培密度作主区,5种施肥量作副区。18个月和66个月生的试验调查结果表明：栽培密度与密度×施肥的交互效应对66个月生桉树生长特征影响的差异性达到显著至极显著;木材基本密度和弹性模量在栽培密度各水平之间的差异性也达到显著至极显著。综合密度处理和施肥处理对桉树生长和材性的影响以及经济效益分析,4 m×3.5 m的栽培密度配合施用雷林1号肥800克,桉树大径材的培育效果较理想。     

Rapid changes of induced volatile organic compounds in Pinus massoniana

Using the thermal-desorption cold trap gas chromatography/mass spectrometer (TCT-GC-MS) technique, the composition and relative contents of volatile compounds were analyzed in undamaged (control), insect-damaged (ID) and artificially-damaged (AD) leaves of Pinus massoniana in field at different times and levels of damage. Results showed that although volatile substances were highly released earlier in AD leaves plants, they were significantly less abundant in AD than in ID leaves treatments. Also, the damage level considerably influenced the changes of induced volatile products from leaves. Compared with the control, the emission rate of camphene, β-pinene, phellandrene, caryophyllene and (E)-farnesene was high after 1 h in 25%–40% ID-affected leaves, whereas that of tricyclene, myrcene, camphene, β-Pinene, phellandrene and caryophyllene reached its maximum after 24 h in 60%–75% ID-affected leaves. In the same manner, some volatile compounds in the AD leaves treatment displayed their peaks just after 1 h, but others after 24 h. The AD and ID leaves at the damage level of 25%–40% did not exhibit an obvious regularity with time; however, in 60%–75% AD leaves, peaks of volatile substances were attained after 1 or 2 h. Our results also showed that the relative content of β-pinene increased and was higher in damaged than control plants. β-pinene plays an important role in inducing the insect resistance of P. massoniana trees. __________ Translated from Scientia Silvae Sinicae, 2006, 42(4): 65–70 [译自: 林业科学]     

Temporal change in carbon stocks of cocoa–gliricidia agroforests in Central Sulawesi,Indonesia

In a false-time series, the temporal development of cocoa–gliricidia carbon (C) stocks and soil organic carbon (SOC) were investigated in Napu and Palolo Valleys of Central Sulawesi, Indonesia. As a first step, the Functional Branch Analysis (FBA) method was used to develop allometric equations for the above- and below-ground growth of cocoa and gliricidia. FBA resulted in shoot–root ratios of 2.54 and 2.05 for cocoa and gliricidia, respectively. In Napu and Palolo, the trunk diameter and carbon levels per gliricidia tree were always much greater than that of cocoa. The highest aerial carbon levels were attained at year four in Napu (aerial cocoa–gliricidia = 20,745.2 kg C ha⁻¹) and at year five in Palolo (aerial cocoa–gliricidia = 38,857.0 kg C ha⁻¹). After years four or five, however, the reduced stocking density of gliricidia attributed to a loss of aerial C. During the time spans in question, SOC remained fairly stable though slightly decreasing in Napu and slightly increasing in Palolo. The SOC harbored a vastly greater amount of system C (one-half and one-third of SOC in the 0–15 cm stratum in Napu and Palolo, respectively) relative to tree components. Eight years (Napu) or 15 years (Palolo) after conversion of a rainforest to cocoa–gliricidia agroforestry caused an 88% and 87% reduction of aerial C-stocks in Napu and Palolo, respectively.     

Tree and crop productivity in gliricidia/maize/pigeonpea cropping systems in southern Malawi

This study examined the hypothesis that incorporation of Gliricidia sepium (Jacq.) Walp.) (gliricidia), a fast-growing, nitrogen-fixing tree, into agroforestry systems in southern Malawi may be used to increase the input of organic fertilizer and reduce the need for expensive inorganic fertilizers. The productivity of maize (Zea mays L.), pigeonpea (Cajanus cajan L.) and gliricidia grown as sole stands or in mixed cropping systems was examined at Makoka Research Station (latitude 15° 30′ S, longitude 35° 15′ E) and a nearby farm site at Nazombe between 1996 and 2000. Treatments included gliricidia intercropped with maize, with or without pigeonpea, and sole stands of gliricidia, maize and pigeonpea. Trees in the agroforestry systems were pruned before and during the cropping season to provide green leaf manure. Maize yields and biomass production by each component were determined and fractional light interception was measured during the reproductive stage of maize. Substantial quantities of green leaf manure (2.4 to 9.0 Mg ha⁻¹ year⁻¹) were produced from the second or third year after tree establishment. Green leaf manure and fuelwood production were greatest when gliricidia was grown as unpruned sole woodlots (c. 8.0 and 22 Mg ha⁻¹ year⁻¹ respectively). Improvements in maize yield in the tree-based systems also became significant in the third year, when c. 3.0 Mg ha⁻¹ of grain was obtained. Tree-based cropping systems were most productive and exhibited greater fractional light interception (c. 0.6 to 0.7) than cropping systems without trees (0.1 to 0.4). No beneficial influence of pigeonpea on maize performance was apparent either in the presence or absence of gliricidia at either site in most seasons. However, as unpruned gliricidia provided the greatest interception of incident solar radiation (>0.9), coppicing may be required to reduce shading when gliricidia is grown together with maize. As pigeonpea production was unaffected by the presence of gliricidia, agroforestry systems containing gliricidia might be used to replace traditional maize + pigeonpea systems in southern Malawi. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preliminary study of application effect of bamboo vinegar on vegetable growth

1 Introduction Bamboo vinegar is a condensed acidic liquid obtained in the process of producing bamboo charcoal. It has a special smoky odor and its color is light-yellow to brown. There are over 200 kinds of chemical compo- nents involved and these components mainly include organic acids, phenolic, alkone, alcohol and ester compounds. Of these, acetic acids are the main com- ponents, accounting for about 50% of the organic chemicals. Bamboo vinegar has been found to have an effect on improvi…     

Regeneration growth in different light environments of mixed species, multiaged, mountainous forests of Romania

Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m²/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m²/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m²/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.     

Effects of opening size and stand characteristics on light transmittance and temperature under young trembling aspen stands

While aspen (Populus tremuloides Michx.) cover provides protection from growing season radiative frosts, reduced light levels can limit growth of understory white spruce (Picea glauca (Moench) Voss). The creation of openings around individual spruce can provide more light, but the chance of radiative frost damage increases as gaps become larger. We examined the relationship between opening size and light and temperature levels in the center of circular gaps created in young aspen stands ranging from 1.8 to 8 m tall. Models for predicting transmittance as a function of sky view factor and transmittance under intact stands are presented. Results indicated a strong relationship between light levels and opening size after considering pre-treatment light levels. The relationship between opening size and temperature was weak with minimum temperatures being more affected by the height and density of the surrounding stand than opening size.     

Ailanthus triphysa at different density and fertiliser levels in Kerala, India: tree growth, light transmittance and understorey ginger yield

Ailanthus triphysa (Family – Simaroubaceae) growth is known to vary in response to different stocking and fertiliser levels. Understorey productivity related to these differences remain elusive, yet are important for optimising the combined production of tree and crop components. A split plot experiment to evaluate the effect of different stocking levels and fertiliser regimes on ailanthus growth, stand leaf area index (LAI) and understorey PAR (photosynthetically active radiation) transmittance was started at Vellanikkara, India in June 1991. Main plot treatments included four densities (3,333, 2,500, 1,660 and 1,111 trees ha⁻¹), replicated thrice. Four fertiliser levels (0:0:0, 50:25:25, 100:50:50 and 150:75:75 kg N:P₂O₅:K₂O ha⁻¹) formed the sub plot treatments. Ginger (Zingiber officinale) was planted as an understorey crop in May 1994 with contiguous treeless control plots. Soil nutrient availability before and after ginger was assessed. Higher densities stimulated ailanthus growth modestly, while fertiliser response of tree and ginger was inconsistent. PAR transmittance below the canopy was related to tree density, LAI and time of measurement. Midday PAR flux having low standard deviations is ideal for evaluating canopy effects on understorey light availability. Ginger in the interspaces exhibited better growth compared to sole crop. Highest rhizome yield was observed in the 2,500 trees ha⁻¹ stocking level, which is optimum for below five year-old ailanthus stands on good sites. It represents 52% mean daily PAR flux or 73% midday PAR flux. Ailanthus+ginger combinations improved the site nutrient capital when ginger was adequately fertilised, despite treeless controls having relatively higher initial soil nutrient availability. This revised version was published online in June 2006 with corrections to the Cover Date.     

Variability and divergence in <Emphasis Type="Italic">Pongamia pinnata</Emphasis> for further use in tree improvement

A total of 24 candidate plus trees (CPTs) of Pongamia pinnata (L.) Pierre. were selected to elucidate their variation and diversity based on thirteen quantitative traits (4 pod traits, 6 seed traits of parent trees and 3 progeny traits) at Forest Research Centre, Institute of Forest Productivity — Mandar, Ranchi district during 2005–2007. The results show that, CPT-19 had maximum for seven traits viz, pod length (65.6 mm), 100-pod weight (542.4 g), seed 2D (two dimension) area (351.2 mm²), seed length (27.9 mm), seed breadth (17.4 mm), 100-seed weight (217.9 g) and plant height (164.3 cm). The traits, 100-pod weight and 100-seed weight had a high heritability (98.4%, 96.9%) accompanied with high genetic advance (46.0%, 34.9%). There is a positive significant correlation between 100-pod weight and 100-seed weight traits at both genotypic and phenotypic levels with plant height, collar diameter and volume index at 30 MAS (months after sowing). Volume index expressed a moderate heritability (47.4%) accompanied with high genetic advance (48.4%), indicating that the character is governed by additive gene effects. In divergence study, 24 accessions were grouped into 6 clusters on the basis of non-hierarchical euclidian cluster analysis. The genotypes in cluster IV (CPT-5, CPT-6, CPT-7, CPT-12, CPT-16, CPT-18, CPT-22) and cluster III (CPT-4, CPT-8, CPT-9, CPT-20, CPT-21) were most heterogeneous and can be best used within group hybridization. The wide diversity exists between the cluster V and II, followed by cluster II and I and crosses between CPTs of these clusters may result in substantial segregates. It is revealed that the existence of substantial variation and diversity can be utilized for genetic resource conservation and further tree improvement programmers of the species.     

Steady-state nutrition of hybrid poplar grown from un-rooted cuttings

Fertilizing plantations of fast-growing tree crops, in manners which supply nutrients at rates that match plant demand and maintain stable internal plant nutrient ratios, can maximize biomass production and carbon sequestration while reducing fertilizer wastage and pollution. Our objectives were to determine nutrient ratios of common hybrid poplar (Populus trichocarpa Torr. and Gray × Populus deltoides Marsh.) (T × D) clones under steady-state nutrition, and to determine if incremental additions of fertilizer were more successful than conventional (evenly-split) fertilizer additions in maximizing biomass production and inducing stable nutrient ratios. Un-rooted cuttings of three T × D clones (49–177, DTAC-7, 15–29) were grown under a conventional regime and a modified-exponential fertilization regime at three application rates (1.8, 3.7 or 7.4 g N plant⁻¹). Above- and below-ground biomass and nutrient concentrations were measured after one growing season. There were few differences in total plant biomass between conventional and modified-exponential fertilization regimes, but for one clone, biomass accumulation equivalent to the highest rate under the conventional regime was achieved with the medium rate of the modified-exponential regime. Stable nutrient ratios (at conditions consistent with steady-state nutrition) were: 100N:14P:50K (49–177), 100N:13P:49K (DTAC-7) and 100N:12P:60K (15–29).     

Soil erosion under a successional agroforestry sequence: a case study from Idukki District,Kerala, India

The Western Ghats of Kerala have been settled over the past 40 years by landless immigrants. Natural forests and cardamom (planted under forest canopy) have been widely replaced by small-holder cultivation. Settlers plant cassava and other annuals in the initial 3–5 years following clearing of the forest canopy. These crops are gradually replaced by black pepper, the dominant crop 5–15 years after clearing. Finally, other perennial crops, planted during the period when pepper was dominant, mature. A highly mixed “home garden” cropping phase is most common on sites 15–20 years after the forest canopy was removed. Soil erosion on sites cleared 1–3 years previously averaged 120 t/ha in the 1988 monsoon season. Over the same period, soil erosion under mature cardamom, pepper and mixed cultivation averaged 0.65, 3.5, and 1.45 t/ha respectively. Erosion levels appear to be related to cover at ground and intermediate (1–4 m) heights above the surface. Soil organic matter is high in the cardamom areas, declines rapidly when the forest canopy is cleared, remains low in pepper, and appears to rebuild to levels as more mixed agroforestry systems become established. Overall, there appears to be a succession in which high erosion and declining organic matter levels are temporary features associated with the conversion of sites from forests and cardamom to other phases.