Interactive effects of water supply and defoliation on photosynthesis, plant water status and growth of Eucalyptus globulus Labill

Increased climatic variability, including extended periods of drought stress, may compromise on the health of forest ecosystems. The effects of defoliating pests on plantations may also impact on forest productivity. Interactions between climate signals and pest activity are poorly understood. In this study, we examined the combined effects of reduced water availability and defoliation on maximum photosynthetic rate (A(sat)), stomatal conductance (g(s)), plant water status and growth of Eucalyptus globulus Labill. Field-grown plants were subjected to two water-availability regimes, rain-fed (W-) and irrigated (W+). In the summer of the second year of growth, leaves from 75% of crown length removed from trees in both watering treatments and physiological responses within the canopies were examined. We hypothesized that defoliation would result in improved plant water status providing a mechanistic insight into leaf- and canopy-scale gas-exchange responses. Defoliated trees in the W+ treatment exhibited higher A(sat) and g(s) compared with non-defoliated trees, but these responses were not observed in the W- treatment. In contrast, at the whole-plant scale, maximum rates of transpiration (E(max)) and canopy conductance (G(Cmax)) and soil-to-leaf hydraulic conductance (K(P)) increased in both treatments following defoliation. As a result, plant water status was unaffected by defoliation and trees in the defoliated treatments exhibited homeostasis in this respect. Whole-plant soil-to-leaf hydraulic conductance was strongly correlated with leaf scale g(s) and A(sat) following the defoliation, providing a mechanistic insight into compensatory up-regulation of photosynthesis. Above-ground height and diameter growth were unaffected by defoliation in both water availability treatments, suggesting that plants use a range of responses to compensate for the impacts of defoliation.     

Gas exchange characteristics of Populus trichocarpa, Populus deltoides and Populus trichocarpa x P. deltoides clones

Responses of net photosynthesis, dark respiration, photorespiration, transpiration, and stomatal conductance to irradiance, temperature, leaf-to-air vapor density difference (VDD), and plant water stress were examined in two Populus trichocarpa clones (one from a moist, coastal climate in western Washington and one from a dry, continental climate in eastern Washington), one P. deltoides clone, and two P. trichocarpa x P. deltoides clones. Light saturation of photosynthesis in greenhouse-grown trees occurred at about 800 micromol m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern Washington ecotype of P. trichocarpa, but at about 600 micromol m(-2) s(-1) for the western Washington ecotype of P. trichocarpa. Average net photosynthesis (at saturating irradiance and the optimum temperature of 25 degrees C) was 20.7, 18.8, 18.2 and 13.4 micromol CO(2) m(-2) s(-1) for P. deltoides, P. trichocarpa x P. deltoides, and the eastern and western Washington clones of P. trichocarpa, respectively. In all clones, net photosynthesis decreased about 14% as VDD increased from 3 to 18 g H(2)O m(-3). Stomatal conductance decreased sharply with decreasing xylem pressure potential (XPP) in all clones except the western Washington clone of P. trichocarpa. Stomata in this clone were insensitive to changes in XPP and did not control water loss. Complete stomatal closure (stomatal conductance < 0.05 cm s(-1)) occurred at about -2.0 MPa in the eastern Washington clone of P. trichocarpa and around -1.25 MPa in the P. deltoides and P. trichocarpa x P. deltoides clones. Transpiration rates were highest in the P. trichocarpa x P. deltoides clone and lowest in the western Washington clone of P. trichocarpa. The P. deltoides clone and eastern Washington clone of P. trichocarpa had the highest water use efficiency (WUE) and the western Washington clone of P. trichocarpa had the lowest WUE. The hybrids were intermediate. It was concluded that: (1) gas exchange characteristics of eastern and western Washington clones of P. trichocarpa reflected adaptation to their native environment; (2) crossing the western Washington clone of P. trichocarpa with the more drought resistant P. deltoides clone produced plants better adapted to the interior Pacific Northwest climate, although the stomatal response to soil water deficits in the hybrid was conservative compared with that of the eastern Washington clone of P. trichocarpa; and (3) introducing eastern Washington clones of black cottonwood into breeding programs is likely to yield lines with favorable growth characteristics combined with enhanced WUE and adaptation to soil water deficits.     

美洲黑杨生长变异与无性系选择

从美洲黑杨原产地密西西比州、得克萨斯州和路易斯安娜州等地引种了104个无性系,并于1998年春在江苏省泗洪县陈圩林场开展无性系对比试验造林。12年生试验结果表明,来自于密西西比州和得克萨斯州7个产地89个无性系长势较好,路易斯安娜州的15个无性系长势较差。树高、胸径和材积等3个生长性状在无性系间差异极显著,性状遗传力(0.552 3~0.658 7)较高,遗传变异系数(8.26%~31.61%)较大。在入选率为5%,选择强度为2.02条件下,材积生长量的选择增益为50.82%。选择的S3412等5个速生无性系12年平均单株材积生长量为1.021 1 m3,超过对照(CK)品种I-69杨15.05%。     

地膜覆盖边缘效应对土壤水分及杨树苗生长的影响

针对杨树地膜覆盖扦插苗在苗床不同部位的生长差异现象,应用美洲黑杨湘林-75无性系1年生苗,采取不同苗木及苗床部位双因子试验设计方法,进行扦插育苗试验.结果显示:种苗不同部位扦插育苗的保存率、地径和苗高年生长量均无显著差异.在地膜仅覆盖苗床上面而裸露侧面情况下,由于地膜的边缘效应,边行土壤在8月中旬的土壤含水率比苗床中部...     

Organic solute accumulation and dehydration tolerance in three water-stressed Populus deltoides clones

The relationship between osmotic potential, water-soluble organic solutes and electrolyte leakage was investigated in three greenhouse-grown eastern cottonwood (Populus deltoides Bartr.) clones. The Ohio Red (from southern Ohio) and Platte (from eastern Nebraska) clones were selected because they differ in dehydration tolerance, gas exchange and osmotic potential. A third clone, Wildcat (from western Nebraska) was included because of its origin in a very dry area. Plants were either watered daily (control) or watered every 4-6 days (preconditioned). A third group of plants was watered daily until it was water-stressed at the end of the experiment (nonconditioned). Leaves for osmotic potential and water-soluble solute determinations were sampled at predawn after plants were rewatered. All clones showed osmotic adjustment ranging from 0.23 to 0.48 MPa. Organic solutes contributed up to 48% of the total osmotic adjustment. The solutes that contributed at least -0.05 MPa each to leaf osmotic potential in any clone were sucrose, malic acid, glucose, fructose, myoinositol and salicin. Fructose and glucose concentrations were unchanged or declined in preconditioned Ohio Red and Platte but increased in Wildcat. The Ohio Red clone had the highest sucrose concentration in both well-watered and preconditioned plants, and a lower injury index (more membrane stability) than Wildcat in the preconditioned plants, whereas nonconditioned Platte displayed the greatest electrolyte leakage of all clones and treatments. Cell membrane stability was correlated to osmotic potential and sucrose concentration only in Ohio Red.     

Influence of rewatering and time of sampling on solute accumulation of two Populus deltoides clones

We investigated effects of rehydration and time of sampling on solute accumulation in plants of two greenhouse-grown Populus deltoides Bartr. clones (Ohio Red and Platte) subjected to multiple cycles of water stress. Osmotic potential of leaves at full turgor was measured at predawn on well-watered (control) and water-stressed (conditioned) plants that had been rewatered the previous afternoon. Water-soluble organic solutes (carbohydrates, phenolic glucosides and organic acids) were determined at both predawn and midday, before and after rewatering. Conditioning resulted in solute accumulation; however, rewatering of conditioned plants decreased the predawn concentration of glucose by 19-35% and the total solute concentration by 14-15%, relative to values before rewatering. There was a 52% increase in salicin concentration in response to rewatering in conditioned plants of the Platte clone. In conditioned plants of both clones, the concentration of glucose was generally lower at midday than at predawn (16-47%), whereas the concentration of sucrose was higher at midday than at predawn (46-133%). Time of sampling was an important factor in determining whether conditioning resulted in accumulation of glucose and fructose. Compared with control plants, there was a significant accumulation of glucose and fructose at predawn and either no accumulation or a significant reduction of these solutes at midday both before and after rewatering of conditioned plants. Sampling time also affected the amount of solute that accumulated in response to conditioning.     

Manipulating nutrient and water availability in a maritime pine plantation: effects on growth, production, and biomass allocation at canopy closure

? We present here the results of a water and nutrient manipulation experiment in a five-year-old plantation of maritime pine in south-western France.

? Water and nutrient levels were manipulated in a factorial design with two levels of irrigation (control receiving only rainfall (C) and irrigated (I)) and three levels of fertilisation (control with no added nutrients (C), P-only (P) and annual addition of a complete nutrient mix (F)) in order to quantify growth limitations of plantation forest in this particular area.

? The treatments applied during five years increased aboveground biomass annual increment by 4% (I) to 58% (IF) with respect to the control (C). The fertilised plots had a slightly non-significant lower root-to-shoot ratio. The effect of irrigation was maximal in 2002, resulting in 6%, 7% and 12% higher growth rate on the F, C and P plots, respectively. A windstorm disturbed the experiment in 1999 and has affected preferentially the fertilised plots, with IF plots displaying 60% damage.

? The higher growth rate of fertilised and irrigated plots was attributed to both an increase (estimated at 5 to 15%) in the amount of light absorbed by the canopy, and an increase (estimated at 26% for IF plots) in the amount of above-ground biomass produced annually per unit leaf area.

     

Influence of soil water on the physiological and morphological components of plant water balance in Populus trichocarpa, Populus deltoides and their F(1) hybrids

Patterns of leaf growth, transpiration and whole-plant water balance in Populus trichocarpa, P. deltoides and their F(1) hybrids were studied during a soil drying cycle. Plant responses were analyzed during three distinct stages of dehydration. In stage I, the transpiration rate of drought-stressed plants remained constant and equal to that of well-watered plants even though soil water content declined by more than 40%. Stage II began as soil and plant water deficits induced stomatal closure. When soil water was expressed as a fraction of transpirable soil water, the transition from stage I to stage II occurred at soil water fractions of 0.35, 0.45 and 0.60 for P. trichocarpa, P. deltoides and their F(1) hybrids, respectively. Reductions in leaf growth coincided with the shift from stage I to stage II. As soil water declined further, decreases in relative transpiration and whole-plant leaf area were significantly greater in parental species than in F(1) hybrids. Inherent feedbacks controlling stomatal water loss and the maintenance and growth of leaf tissue appeared to differ between F(1) and parental genotypes in a pattern characteristic of an overdominant mode of inheritance.Stage III began once the ability of stomata to compensate for water loss had been exhausted. Substantial differences were found in plant survival during stage III, with F(1) hybrids surviving longer than parental species. Survival was more strongly correlated with the hydraulic conductivity of xylem tissues than with the dehydration tolerance of leaf tissues. Collectively, these responses suggest that F(1) hybrids were more drought resistant than either parental species and highlight the importance of whole-plant studies of functional relationships between plant growth, water balance and hydraulic conductivity.     

Effect of Poplar (Populus deltoides) shelterbelt on the growth and yield of wheat in Punjab, India

A study was conducted around Chandigarh (Punjab), India to assess the effect of Populus deltoides shelterbelt on wheat. Crop density, root and shoot length, biomass and grain yield of wheat at crop maturity were significantly lower, up to 12 ± 1 m in the fields sheltered by P. deltoides than in unsheltered plots. The reduction of biomass and grain yield of wheat were comparatively more than that of other parameters. The observed reduction in the growth and yield of wheat could be attributed to phytotoxic interference of the phenolics from the tree with the crop. This revised version was published online in August 2006 with corrections to the Cover Date.     

南方型黑杨种质资源表型及生长性状遗传多样性分析

为了解南方型黑杨种质材料的表型及生长性状遗传多样性,丰富黑杨种质资源遗传基础,并进一步为南方地区黑杨种质资源定向选育提供参考,选取地径、苗高、叶面积、叶长、叶宽、叶柄长、叶绿素、侧枝数、叶厚、单株总叶片、叶片干质量共11个树体性状及生理指标,同时观测记录了每个无性系的生长期和抗性,对62份南方型黑杨种质资源的13个性状进行了遗传多样性分析。结果表明:62份黑杨资源分成7个类群,各类群材料根据不同性状的相似性进行聚类,整体比较分散,具有较高的分化强度。13个性状的多样性指数H′变化范围介于0.587~1.550之间,平均值为1.098,叶片相关性状以及生长期遗传多样性较丰富。主成分分析将相关变量转化为叶片形态、单株叶片数量、抗性及生长期、侧枝数4个主成分,涵盖了13个测定性状80.953%的遗传信息。本研究首次从表型及生长相关性状等方面探明了南方型黑杨的遗传多样性,对于充分发掘黑杨资源优良基因型,进一步开展南方型黑杨遗传改良工作具有重要意义。     

Plant growth, biomass production and nutrient accumulation by slash/mulch agroforestry systems in tropical hillsides of Colombia

Planted fallow systems under ‘slash and mulch’ management were compared with natural fallow systems at two farms (BM1 and BM2) in the Colombian Andes. The BM1 site was relatively more fertile than the BM2 site. Planted fallow systems evaluated included Calliandra calothyrsus CIAT 20400 (CAL), Indigofera constricta (IND) or Tithonia diversifola (TTH). During each pruning event slashed biomass was weighed, surface-applied to the soil on the same plot and sub-samples taken for chemical analyses. While Indigofera trees consistently showed significantly greater (p < 0.05) plant height and collar diameter than Calliandra trees at both study sites, only collar diameter in Indigofera was significantly affected at all sampling times by differences between BM1 and BM2. After 27 months, TTH presented the greatest cumulative dry weight biomass (37 t ha^–1) and nutrient accumulation in biomass (417.5 kg N ha^–1, 85.3 kg P ha^–1, 928 kg K ha^–1, 299 kg Ca ha^–1 and 127.6 kg Mg ha^–1) among planted fallow systems studied at BM1. Leaf biomass was significantly greater (P < 0.05) for CAL than IND irrespective of site. However, CAL and IND biomass from other plant parts studied and nutrient accumulation were generally similar at BM1 and BM2. At both sites, NAT consistently presented the lowest biomass production and nutrient accumulation among fallow systems. Planted fallows using Calliandra and Indigofera trees had the additional benefit of producing considerable quantities of firewood for household use. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of induction treatments on flowering in Populus deltoides

Stimulation of early flowering is required to shorten breeding cycles of eastern cottonwood (Populus deltoides Bartr. ex Marsh. var. deltoides), a commercially important and fast-growing hardwood species. A series of experiments was conducted to evaluate the influence of various treatments on flowering in rooted cuttings from mature and juvenile trees. A combined treatment of water stress, root pruning and paclobutrazol was applied to 3-month-old rooted cuttings from mature trees. These cuttings had been subjected to root restriction and long days. All treated plants flowered, whereas no untreated plants formed flower buds. One-year-old rooted cuttings from juvenile trees did not flower when treated with either paclobutrazol, paclobutrazol plus water stress, paclobutrazol plus root pruning, or paclobutrazol plus girdling. This was true both under continuous or periodic growth. Assessment of the lack of flowering in juvenile trees may require an integrated approach that investigates environmental or physiological stimuli, assimilate shift, gibberellic acid type and concentration, and flowering-time gene activity in the new shoots of mature and juvenile cottonwood trees.     

武汉地区不同杨树品种扦插苗的物候与生长节律

以12个不同杨树品种的1年生扦插苗为试验材料,对其在武汉地区的物候期和生长规律进行了动态测定。结果表明:各品种的物候期存在较大差异,以变异系数来看其中以芽膨大期差异最大,落叶末期差异最小;杨树扦插苗的苗高、地径以及叶片数的生长规律呈递增的变化趋势,符合S型生长曲线,杨树苗木的速生期在6月中旬到8月中旬左右。     

杨树EST-SSR标记的开发

利用来自美洲黑杨及欧美杨的20 023条EST序列,进行EST-SSR标记开发研究.首先对这些EST序列进行序列拼接,然后在非重复序列中发现由二核苷酸至五核苷酸组成的SSR重复序列.共在10 816个非重复序列中发现1 604个序列含有SSR,占总非重复序列的14.8%.在发现的1 918个SSR重复序列中,二核苷酸重复是最丰富的重复类型,占总类型的62.3%.设计合成48对SSR引物,利用6个不同的杨树品种对其进行验证.结果约90%的引物获得扩增产物,58%的引物在6个不同杨树品种中产生多态性分离.另外,还对重复序列的数量及重复类型进行了讨论.     

美洲黑杨新无性系的海涂适应性试验研究

１９９２－１９９５年的试验结果表明，在含盐量０．２０８％的海涂上栽植的１１个黑杨无性系中，筛选出５个优良无性系，具有适应性强，生长迅速抗盐和抗病虫害，与Ｉ－６９杨相比，单株材积增长率为４．８６％－６４．６３％，每公倾蓄积增长率为３８．３８％－７４．１７％，增加收入７８００－１５７５元／ｈｍ＾２。     

基因库中21个美洲黑杨无性系的抗寒性

基因库中２１个美洲黑杨无性系的抗寒性徐红，张崎纹，陈一山，解荷峰关键词美洲黑杨无性系，抗寒性，电导率，膜脂脂肪酸不饱和度美洲黑杨（ＰｏｐｕｌｕｓｄｅｌｔｏｉｄｅｓＭａｒｓｈ）无性系具有生长迅速，抗病虫性较强等优良性状。历史上引种成功的几个美洲黑杨无性...     

Loss of hydraulic conductivity due to water stress in intact juveniles of Quercus rubra and Populus deltoides

Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.     

Influence of nutrient supply on shade-sun acclimation of Picea abies seedlings: effects on foliar morphology,photosynthetic performance and growth

Norway spruce seedlings (Picea abies Karst.) were grown in low light for one year, under conditions of adequate and limiting nutrition, then transferred to high light. Three months after transfer we measured photosynthesis, leaf nitrogen concentration, leaf chlorophyll concentration and leaf mass per area (LMA) of current-year and 1-year-old shoots; silhouette area ratio (SAR, the ratio of shoot silhouette area to projected needle area) was also measured in current-year shoots. At the foliage level, the effects of light and nutrient treatments differed markedly. Light availability during foliage expansion primarily affected LMA and SAR (morphological acclimation at the needle and shoot level, respectively). By contrast, nutrient supply in high light affected photosynthetic capacity per unit of leaf tissue (physiological acclimation at the cellular level) but did not affect LMA and SAR. The capacity for shade-sun acclimation in foliage formed before transfer to high light differed greatly from that of foliage formed following the transfer. The morphological inflexibility of mature needles (measured by LMA) limited their shade-sun acclimation potential. In contrast, at high nutrient supply, shoots that developed just after the change in photosynthetic photon flux density largely acclimated, both morphologically and physiologically, to the new light environment. The acclimation response of both current- and 1-year-old shoots was prevented by nutrient limitation. Analysis of growth at the whole-plant level largely confirmed the conclusions drawn at the shoot level. We conclude that nutrient shortage subsequent to the opening of a canopy gap may strongly limit the acclimation response of Norway spruce seedlings. Successful acclimation was largely related to the plant's ability to produce sun foliage and adjust whole-plant biomass allocation rapidly.     

Estimates of above-ground biomass and nutrient accumulation in Mimosa scabrella fallows in southern Brazil

Naturally regenerated stands of bracatinga (Mimosa scabrella Bentham) are harvested for firewood after six to eight years of unregulated growth, debris burnt and the area planted to one cycle of intercropped maize (Zea mays L.) and beans (Phaseoulus vulgaris L.). Burning breaks dormancy of bracatinga seed (> 80% germination) marking the onset of a new fallow-crop cycle. This production system has been practiced for nearly 100 years in Southern Brazil, covering some 60,000 ha in 3,000 small farms. An estimation of above-ground biomass and nutrient accumulation was made using literature data on stand age, population numbers, tree sizes, tree biomass partitioning and concentration of major nutrients in tree tissues. A simple simulation model, used to quantify above-ground nutrient pathways and their temporal dynamics, confirmed that six to eight years is the optimal rotation length. Biomass and nutrients deposited onto the soil, peak at stand age six years, which may result in significant soil fertility improvement prior to crop planting. At year six, estimated total above-ground biomass amounts to 83 Mg ha^–1; 44 Mg ha^–1 available as firewood and 39 Mg ha^–1 to be returned to the soil. Roughly half the amount of nutrients fixed in the above-ground bracatinga biomass would be exported in firewood and subsequent grain crops.