Effects of irrigation on water use and water use efficiency in two fast growing Eucalyptus plantations

Eucalyptus plantations occupy almost 20 million ha worldwide and exceed 3.7 million ha in Brazil alone. Improved genetics and silviculture have led to as much as a three-fold increase in productivity in Eucalyptus plantations in Brazil and the large land area occupied by these highly productive ecosystems raises concern over their effect on local water supplies. As part of the Brazil Potential Productivity Project, we measured water use of Eucalyptus grandis × urophylla clones in rainfed and irrigated stands in two plantations differing in productivity. The Aracruz (lower productivity) site is located in the state of Espirito Santo and the Veracel (higher productivity) site in Bahia state. At each plantation, we measured stand water use using homemade sap flow sensors and a calibration curve using the clones and probes we utilized in the study. We also quantified changes in growth, leaf area and water use efficiency (the amount of wood produced per unit of water transpired). Measurements were conducted for 1 year during 2005 at Aracruz and from August through December 2005 at Veracel. Transpiration at both sites was high compared to other studies but annual estimates at Aracruz for the rainfed treatment compared well with a process model calibrated for the Aracruz site (within 10%). Annual water use at Aracruz was 1394 mm in rainfed treatments versus 1779 mm in irrigated treatments and accounted for approximately 67% and 58% of annual precipitation and irrigation inputs respectively. Increased water use in the irrigated stands at Aracruz was associated with higher sapwood area, leaf area index and transpiration per unit leaf area but there was no difference in the response of canopy conductance with air saturation deficit between treatments. Water use efficiency at the Aracruz site was also not influenced by irrigation and was similar to the rainfed treatment. During the period of overlapping measurements, the response to irrigation treatments at the more productive Veracel site was similar to Aracruz. Stand water use at the Veracel site totaled 975 mm and 1102 mm in rainfed and irrigated treatments during the 5-month measurement period respectively. Irrigated stands at Veracel also had higher leaf area with no difference in the response of canopy conductance with air saturation deficit between treatments. Water use efficiency was also unaffected by irrigation at Veracel. Results from this and other studies suggest that improved resource availability does not negatively impact water use efficiency but increased productivity of these plantations is associated with higher water use and should be given consideration during plantation management decision making processes aimed at increasing productivity.     

Long-term effect of an ectomycorrhizal inoculum and other treatments on survival and growth of Populus hopeiensis Hu et Chow

We evaluated the effects of direct use of an ectomycorrhiza fungal inoculum (Boletusedulis) mixed with indolebutyric acid (IBA), super-absorbent polymers (SAP) and organic compound fertilizer on the survival and growth of Populus hopeiensis saplings on a semiarid site in Inner Mongolia, China, during the first 5 years after planting, and the practical feasibility of using this inoculum mixture over large semiarid areas in North China.     

Mycorrhizas and secondary succession in aspen-conifer forests: Light limitation differentially affects a dominant early and late successional species

Plant succession and mycorrhizal fungi both play crucial roles in shaping the development of forest ecosystems. However, despite the strong potential for interactions between them, few studies have examined how patterns of forest succession affect mycorrhizal associations that a majority of plant species depend on to alleviate soil resource constraints. Fire suppression in subalpine forests over the last century has changed successional patterns in ways that may have important implications for mycorrhizal associations of forest tree species. To better understand these relationships we conducted a field and greenhouse study in which we examined mycorrhizal infection along gradients of light intensity and soil nutrient availability that develop as aspen becomes seral to conifers under longer fire return intervals. We examined whether ectomycorrhizal associations of quaking aspen (Populus tremuloides), a shade intolerant, early succession species, were more sensitive to light and soil resource limitations than subalpine fir (Abies lasiocarpa), a shade tolerant, late succession species. In the field study, ectomycorrhizal infection of aspen roots was reduced by 50% in conifer dominated stands relative to aspen stands. In contrast, subalpine fir maintained its EM associations regardless of the successional status of the stand. The greenhouse results were consistent with field results and indicated that light limitation was the driving force behind reductions in EM infection of aspen roots in later stages of succession. These results suggest that nutrient limitations constraining early successional species may be exacerbated by losses in EM associations via light limitations created by late successional species. This is one potential mechanism by which climax forest species create a competitive advantage over early successional species and these results suggest that it is likely exacerbated by longer fire return intervals.     

新疆额尔齐斯河流域白杨派植物居群遗传多样性分析

应用SSR标记技术,对新疆齐斯河流域河谷分布的白杨派树种银白杨、银灰杨和欧洲山杨天然居群的克隆结构、克隆多样性和遗传多样性进行研究。结果表明:欧洲山杨、银白杨和银灰杨均有很强的克隆繁殖特性。欧洲山杨、银白杨居群的克隆多样性均比较高,Simpson指数分别为0.987和0.983。与欧洲山杨相比较,银白杨居群具有较低的遗传多样性,Shannon信息指数分别为1.068 9和0.324 9,Nei多样性指数平均为0.505 6和0.211 2。欧洲山杨和银白杨居群间的遗传一致度均较高,变幅分别为0.778 1 0.954 4和0.975 1 0.994 6,反映出其超长距离的基因流特性,超强的基因流阻止了银白杨和欧洲山杨居群的遗传分化。研究发现,银白杨和欧洲山杨分别有95%和89.98%的遗传变异存在于居群内。     

Predisposition to bark beetle attack by root herbivores and associated pathogens: Roles in forest decline,gap formation,and persistence of endemic bark beetle populations

Bark beetles are largely known for their ability to undergo intermittent population eruptions that transform entire landscapes and pose significant economic hardships. However, most species do not undergo outbreaks, and eruptive species usually exert only minor disturbances. Understanding the dynamics of tree-killing noneruptive species can provide insights into how beetles persist at low densities, and how some spatiotemporal patterns of host predisposition may more likely favor breaching eruptive thresholds than others. Elucidating mechanisms behind low-density populations is challenging, however, due to the requirement of long-term monitoring and high degrees of spatial and temporal covariance. We censused more than 2700 trees annually over 7 years, and at the end of 17 years, in a mature red pine plantation. Trees were measured for the presence of bark beetles and wood borers that breed within the primary stem, root weevils that breed in root collars, and bark beetles that breed in basal stems. We quantify the sequence of events that drive this decline syndrome, with the primary emergent pattern being an interaction between below- and above-ground herbivores and their fungal symbionts. This interaction results in an expanding forest gap, with subsequent colonization by early-successional vegetation. Spatial position strongly affects the likelihood of tree mortality. A red pine is initially very likely to avoid attack by tree-killing Ips beetles, but attack becomes increasingly likely as the belowground complex spreads to neighboring trees and eventually make trees susceptible. This system is largely internally driven, as there are strong gap edge, but not stand-edge, effects. Additional stressors, such as drought, can provide an intermittent source of susceptible trees to Ips beetles, and elevated temperature slightly accentuates this effect. New gaps can arise from such trees as they subsequently become epicenters for the full complex of organisms associated with this decline, but this is not common. As Ips populations rise, there is some element of positive feedback, in that the proportion of killed trees that were not first colonized by root organisms increases. This positive feedback is very weak, however, and we propose the slope between beetle population density and reliance on host stress as a quantitative distinction along a gradient from noneruptive through eruptive species. Almost all trees colonized by Ips were subsequently colonized by wood borers, likely a source of negative feedback. We discuss implications to our overall understanding of cross-scale interactions, between-guild interactions, forest declines, and eruptive thresholds.     

Persistent effects of fire severity on early successional forests in interior Alaska

There has been a recent increase in the frequency and extent of wildfires in interior Alaska, and this trend is predicted to continue under a warming climate. Although less well documented, corresponding increases in fire severity are expected. Previous research from boreal forests in Alaska and western Canada indicate that severe fire promotes the recruitment of deciduous tree species and decreases the relative abundance of black spruce (Picea mariana) immediately after fire. Here we extend these observations by (1) examining changes in patterns of aspen and spruce density and biomass that occurred during the first two decades of post-fire succession, and (2) comparing patterns of tree composition in relation to variations in post-fire organic layer depth in four burned black spruce forests in interior Alaska after 10-20 years of succession. We found that initial effects of fire severity on recruitment and establishment of aspen and black spruce were maintained by subsequent effects of organic layer depth and initial plant biomass on plant growth during post-fire succession. The proportional contribution of aspen (Populus tremuloides) to total stand biomass remained above 90% during the first and second decades of succession in severely burned sites, while in lightly burned sites the proportional contribution of aspen was reduced due to a 40-fold increase in spruce biomass in these sites. Relationships between organic layer depth and stem density and biomass were consistently negative for aspen, and positive or neutral for black spruce in all four burns. Our results suggest that initial effects of post-fire organic layer depths on deciduous recruitment are likely to translate into a prolonged phase of deciduous dominance during post-fire succession in severely burned stands. This shift in vegetation distribution has important implications for climate-albedo feedbacks, future fire regime, wildlife habitat quality and natural resources for indigenous subsistence activities in interior Alaska.     

旱柳无性系在富营养化水体中的生长及去除氮磷能力

【目的】比较旱柳无性系的生长以及对水体中氮、磷去除效果,以筛选出处理富营养化水体效果较好的无性系。【方法】利用8个旱柳无性系在富营养化水体中进行静态培养试验,研究各无性系的形态特征、叶绿素相对含量指数、对营养元素的吸收以及对废水中氮、磷的去除效率。【结果】旱柳无性系在整个试验期间生长良好,无死亡现象。各无性系最终生物量、苗高和相对生长率有显著差异,其中,旱59和旱97整体表现最好。旱柳无性系对富营养化水体中氮、磷吸收较好,地上部分营养元素浓度较高。旱柳各无性系对总氮、氨氮和硝态氮的去除效率分别为87.17%96.94%、90.35%99.33%和66.66%88.19%,对总磷的去除效率为76.59%83.15%,无性系旱13总的去除效率最高。【结论】参试8个旱柳无性系均能在富营养化水体中正常生长,但各无性系在富营养化水体中的生长响应有较大差异。综合多个指标并结合长期野外试验观察,旱13、旱59、旱97是适合修复富营养化水体的较好材料。     

抗虫转基因欧洲黑杨多重PCR技术检测体系构建

根据抗虫转基因欧洲黑杨中的CaMV 35S启动子、NOS终止子、NPTⅡ标记基因以及Bt目的基因序列,设计合成了相应引物,采用单重PCR和多重PCR技术对启动子、终止子、选择标记基因以及目的基因等多个外源基因进行检测,并对各引物的退火温度及引物之间的浓度配比进行优化,建立了适用于抗虫转基因欧洲黑杨检测的Bt、NPTⅡ和NOS基因的三重PCR分析的技术体系。结果表明:当各组引物的终浓度配比为1.0∶ 0.5∶ 0.5,退火温度为59 ℃时,所建立的三重PCR检测体系能够有效地检测出抗虫转基因欧洲黑杨中的转基因成分,实现了对抗虫转基因欧洲黑杨的快速、高效、准确的鉴定。     

欧洲黑杨PnEXPA1基因多态性与稳定碳同位素比率的关联分析

对欧洲黑杨α-expansin基因PnEXPA1的SNP多态性与水分利用效率相关性状稳定碳同位素比率(δ13C)进行了关联分析。利用SNaPshot技术对PnEXPA1基因内11个SNP位点进行了基因型分型,发现各SNP位点优势基因型均为纯合,且其频率高于杂合基因型。关联分析显示:SNP8和SNP12在采用单因素方差分析(ANOVA)和一般线性模型(GLM)2种方法时均与δ13C值显著关联。SNP8为exon 1内的无义突变,可解释6.620%的表型变异;而SNP12位于intron 1中,遗传贡献率为6.613%;这2个SNP位点与SNP9、SNP13共同位于一个高连锁不平衡(LD)的单倍型块中。SNP8与SNP12的TT基因型无性系均具有较高的δ13C值,为优势基因型。     

黑杨DNA甲基转移酶基因片段的分离及表达分析

利用同源序列克隆技术,分离了三倍体黑杨中4类(MET、CMT、DRM、DNMT2)8个特异甲基转移酶片段,其中,5个片段与二倍体同源性达到100%,3个片段发生了剪切变化。通过实时定量PCR技术检测8个甲基转移酶在不同倍性、不同部位、不同生长时期间表达模式的差异,通过对5个不同部位基因表达的检测,表明不同倍性黑杨在相同的部位可能由不同种类的甲基转移酶参与主要的甲基化调控。通过分析植株从分化早期的茎尖到分化晚期的叶和茎整个生长过程中基因表达的情况,发现随着时间的推移,MET家族 (PnD1和PnD2) 基因可能是拮抗调节,CMT (PnD3和PnD4) 家族基因可能是协同调节;而隶属于DNMT2家族的PnD6基因在各部位的表达都比较弱,唯独三倍体茎尖有很高的表达。由于茎尖是生长旺盛的部位,PnD6有可能是影响三倍体速生的重要基因。这些结果可能暗示,DNA甲基转移酶基因可能参与了黑杨发育过程中叶片形态发生的过程。     

Effects of moisture limitation on tree growth in upland and floodplain forest ecosystems in interior Alaska

The objective of this study was to examine the impact of summer throughfall on the growth of trees, at upland and floodplain locations, in the vicinity of Fairbanks, Alaska. Corrugated clear plastic covers were installed under the canopy of floodplain balsam poplar/white spruce stands and upland hardwood/white spruce stands to control soil moisture recharge as a result of summer precipitation. The covers were installed in 1989 and tree growth measurements were conducted through 2005. Soil moisture dynamics were measured using TDR techniques. Tree basal area growth at dbh in the control plots was approximately twice as high on the floodplain compared to the upland. Summer throughfall exclusion significantly decreased white spruce growth on the floodplain sites but not in the upland sites. In upland sites the melting snow pack is a major moisture resource for tree growth although it is not clear if moisture limitation occurs during the summer in the control plots. However in the floodplain stands white spruce growth was highly dependent on seasonal throughfall even though the ground water table was within the rooting zone and the soils were supplied with a spring recharge due to snowmelt. A number of factors were suggested as a foundation for this strong relationship. These include rooting distribution, soil texture, and the electrical conductivity of the ground water.     

Predicting productivity of trembling aspen in the Boreal Shield ecozone of Quebec using different sources of soil and site information

Site quality index (SQI) of trembling aspen (Populus tremuloides Michx) in the Boreal Shield of Quebec was predicted using two sources of information: (1) mappable permanent site variables derived from permanent sampling plots and other sources and (2) measured soil and site properties including both biological and permanent site variables. General mappable information did not produce reasonable relationships (R² < 0.25) with SQI while measured variables were able to explain much of trembling aspen SQI variability. For the two parent material types found in our study, i.e. fluvial and till, there was no difference between median SQI values between groups. However, different soil and site variables were better at predicting trembling aspen productivity for the individual parent material types. As much as 60% of the variability in trembling aspen productivity was explained when both biological and permanent site variables were considered in stepwise regression models. When treated individually, models developed for fluvial sites better explained trembling aspen productivity compared to models developed for till sites. Moreover, the ability of the model to predict trembling aspen productivity on till sites when using permanent site variables alone, e.g. soil texture, elemental chemistry and elevation was decreased (R² < 0.3). This indicates that the inclusion of biological site variables such as overstory species composition and forest floor properties provide a major contribution to SQI prediction and are necessary to yield high R². Overall, the data indicate that the traditional mapping of landscape attributes such as drainage and deposit as well as inferred soil geochemistry do not contribute much to explaining SQI. At present, field measurements are needed to predict SQI with a reasonable degree of precision within a forest management unit.     

Protection of spruce from colonization by the bark beetle, Ips perturbatus, in Alaska

Field bioassays were conducted in south-central Alaska in a stand of Lutz spruce, Picea × lutzii, to determine whether a semiochemical interruptant (verbenone and trans-conophthorin) and/or a defense-inducing plant hormone (methyl jasmonate, MJ) could be used to protect individual standing trees from bark beetle attack. During two experiments (initiated in May 2004 and 2005, respectively), attacks by Ips perturbatus on standing trees were induced by using a three-component aggregation pheromone (ipsenol, cis-verbenol, and ipsdienol) and prevented by using the interruptant. In 2005, treatments from 2004 were repeated and additional treatments were evaluated by using MJ spray or injection with and without the interruptant. Aggregation began before 3 or 7 June, and attack density was monitored through 3 or 16 August. During both years, tree mortality caused by I. perturbatus was recorded twice (in August, and in May of the following year). In both experiments, attack density was greatest on trees baited with the three-component attractive pheromone, but was significantly reduced by addition of the semiochemical interruptant to trees baited with the attractant. There were no significant differences in attack density between attractant + interruptant-treated trees and unbaited trees. In 2004, mortality was highest among attractant-baited trees, whereas addition of the interruptant significantly reduced the level of initial (10 week post-treatment) and final (54 week post-treatment) mortality. In 2005, no significant reduction in attack density occurred on trees baited with the attractant when MJ was sprayed or injected. The highest initial (10.6 week post-treatment) and final (49.4 week post-treatment) mortality was observed among trees that had been injected with MJ and baited with the attractant. Mortality at the final assessment was significantly lower in all other treatment groups. As in 2004, addition of the interruptant to attractant-baited trees significantly reduced the level of final mortality compared to attractant-baited trees. MJ was not attractive or interruptive to I. perturbatus or associated bark beetles in a flight trapping study. However, MJ-treated trees (sprayed or injected) exuded copious amounts of resin on the bark surface. Anatomical analyses of felled trees from four treatment groups [Tween (solvent)-sprayed, MJ-sprayed, Tween-injected, and MJ-injected + attractant baited] showed that treatment with MJ increased the number and size of resin ducts produced following treatment. These analyses also revealed a reduction in radial growth in MJ-treated trees. Our results show that during both years, treatment with a simple, two-component interruptant system of verbenone and trans-conophthorin significantly reduced I. perturbatus attack density and tree mortality on attractant-baited trees and provided a full year of protection from bark beetle attack.     

Characteristics of aspen infected with heartrot: Implications for cavity-nesting birds

Phellinus tremulae is an important fungal decay agent common to aspen and a critical component to the cavity-nesting bird complex found in western aspen stands. Little information exists on the conditions that facilitate infection and spread of P. tremulae in aspen forests. I used Forest Inventory and Analysis (FIA) data to explore the relationships of several tree and stand characteristics to the presence and frequency of P. tremulae in aspen measured across several western states of the United States. Results suggest a strong relationship between tree age, tree diameter, and compacted crown ratio with infection frequency in trees while stand purity, canopy cover and stand age had a positive relationship with the occurrence of P. tremulae in forest stands containing aspen. Logistic regression modeling identified stand age as the only variable that increased the odds of predicting infection at the stand-level while all tree-level variables were included in the tree model. Data also show that infection rates in the study area were lower than in other parts of aspen's range, and that average size of infected trees was smaller in the study area than those reported elsewhere. These results have important implications to management of aspen for wildlife, especially for birds that use decayed aspen for nesting.     

荒漠河岸林2种典型植物的耐盐性比较

在新疆尉犁县的天然荒漠河岸林里,选择了3个土壤盐度不同的样地,测定了胡杨和柽柳叶片的脯氨酸含量、K+/Na+、氯离子(Cl-)含量、超氧化物歧化酶(SOD)活性和丙二醛(MDA)含量等5个生理指标,并利用模糊数学隶属函数法对二者的耐盐性进行了综合评价.结果表明:随着土壤盐胁迫的增强,胡杨叶片的脯氨酸含量总体上呈增加趋势...     

Short term effects of alternative silvicultural treatments on stand attributes in irregular balsam fir-black spruce stands

The eastern Canadian boreal forest exhibits a specific disturbance regime where forest fires are less frequent than in the western part. This particularity may explain the abundance of irregular stands with distinct ecological features. To ensure sustainable forest management, these characteristics require the implementation of an adapted silviculture regime. In this context, two selection cutting methods were developed and compared with more conventional techniques, initially designed for cutting more regular stands of the boreal forest (cutting leaving small merchantable stems, careful logging preserving advance regeneration). The comparison focused on the capacity of treatments to maintain the primary attributes of irregular boreal forests, including complex vertical structure, abundant tree cover, species composition, and an abundance of dead wood. Mortality and regeneration processes were also compared.     

The impact of black cottonwood on soil fertility in coastal western hemlock forest

Black cottonwood (Populus trichocarpa Torr. and Gray) is a deciduous tree species that extends from Alaska through coastal regions of western Canada into the northwestern United States and as far south as Baja California. We examined the influence of black cottonwood on soil fertility within a forest dominated by Douglas-fir [Pseudotsuga menziessi (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg], and western red cedar (Thuja plicata Donn ex. D. Don.). Six circular 0.008 ha plots with a single cottonwood tree in the center of conifers were paired with six conifer plots (of the same size) without cottonwood. Litterfall, litter decomposition, properties of forest floor and mineral soil, and N mineralization were compared between plot types. Cottonwood litter had higher concentrations of almost all elements relative to conifer litter. Mass loss did not differ between cottonwood and fir/hemlock litter on cottonwood sites. Twice the amount of mull-like humus form (vermimull and mullmoder, 56%) was found in cottonwood plots compared to 28% in conifer plots. Higher pH (4.4) was found in the forest floor under cottonwood compared to conifer (3.9). Total N concentration (3.33 g/kg) and base saturation (68%) were higher in the mineral soil under cottonwood compared to conifers (2.98 g/kg total N and 50% base saturation). Net ammonification and net mineralization were both lower under cottonwood. These results suggest a variable effect of cottonwood on soil fertility within coastal western hemlock forests with some soil variables changed in a favourable direction and some in an unfavourable direction.     

地理隔离对西南藏区山杨居群遗传结构影响的SRAP分析

采用SRAP分子标记技术,对分布于我国西南3个藏族地区山杨9个居群130个个体进行了遗传结构分析。结果表明,筛选出的7对引物组合共检测到多态性条带(AP)99条,多态性条带百分比(PPB)为59.28%。采用POPGENE软件分析,山杨9个居群平均多态位点百分率(PPB)为33.80%,Nei’s基因多样性指数(H)和Shannon’s信息指数(I)分别为0.130 9和0.213 7,较东北地区山杨具有偏低的遗传多样性。遗传分化系数Gst=0.325 5,表明遗传变异主要存在于居群内个体间。地理距离与遗传距离之间具有弱相关关系(r=0.349,P=94.5%),山脉阻隔效应是导致西南藏族地区山杨居群间遗传分化的主要因素。UPGMA聚类表明,甘孜地区4个居群与迪庆地区的维西居群具有较近的亲缘关系,迪庆地区的德钦、香格里拉居群和昌都地区2个居群的遗传相似度较高。基于西南藏族地区山杨遗传结构分析,建议实施就地保护的同时,建立山杨种质资源库,促进不同居群间的基因交流。     

滇杨侧芽不同季节内源激素含量变化动态

In order to understand the content changes of endogenous hormones in lateral buds of Populus yunnanensis during different seasons, the lateral buds collected from stems of three-year old cuttings of P. yunnanensis were used as materials, contents of ABA, IAA and ZR in the lateral buds in the autumn, winter and spring were detected by enzyme-linked immunosorbent assays (ELISA). The results indicated that the contents of ABA and IAA were first decreased and then increased while the contents of ZR increased gradually, and the values of the three kinds of endogenous hormones reached maximum in spring. The content of each endogenous hormone among different seasons was different significantly. However, the ratio changes of ZR/ABA, ZR/IAA and ZR/(ABA+IAA) were first increased and then decreased, and all reached the maximum in winter, which were significantly higher than that in autumn and srping.     

The lateral spread of tree root systems in boreal forests: Estimates based on N uptake and distribution of sporocarps of ectomycorrhizal fungi

In nutrient poor environments, such as boreal forests, many of the most important interactions between plants take place belowground. Here, we report the results of two approaches to obtain estimates of the lateral spread of tree roots.