树种及多样性组配对南亚热带人工林早期树木生长的影响

为科学筛选提升南亚热带人工林生产力的树种配置模式,选择南亚热带8个乡土树种,采用随机区组的试验设计,建立了树种多样性梯度(1、2、4、6个树种)人工新造林试验平台,研究树种多样性及不同功能特性树种混交对人工林早期树木生长的影响。结果表明: 在树木生长第5年,树木生长并没有随树种多样性增加而增加;速生树种马尾松和米老排纯林生长量是珍贵树种红椎和格木纯林的2.5～4.5倍;2个树种混交和4个树种混交情况下,针阔树种混交、速生树种与固氮树种混交显著提高树木生长量51.5%～132.8%,而当6个树种混交时,不同树种组配对生长量没有显著影响。不同树种配置模式下土壤氮、磷养分是影响树木早期生长的主要因素。针阔树种混交、速生和固氮树种混交能显著提高南亚热带人工林树木的早期生长。     

Effect of strictly plant-related factors on the response ofHevea brasiliensis andTheobroma Cacao nodal explants culturedIn vitro

Summary Nodal cuttings (primary nodal explants) were used to initiate microcutting cultures ofHevea brasiliensis andTheobroma cacao. The physiological stage of growth reached by the branches from which the explants were taken had a considerable influence on culture initiation and response. In both species, the buds of the nodal explants taken from dormant branches (stages 11, 12 and 13 inTheobroma; stage D inHevea) revealed greater opening abilityin vitro and shoot elongation than buds taken from branches in a phase of active meristem growth inTheobroma (stages F1 and F2) or during a foliar growth phase inHevea (stage C). InHevea, the branch growth phase effect persisted into the multiplication phase when shoots developedin vitro were used as the source of secondary nodal explants. However, it disappeared during subcultures of primary nodal explants. In both species, the position of the nodes on the branch with respect to the apex also had an effect on culture initiation. The buds of nodes furthest from the apex were more likely to develop into shoots. InHevea, the position of secondary nodal explants obtained from the primary shoot was seen to vary in effect depending on growth regulator applications during primary culture. These results are analyzed in terms of variations in the balance between endogenous growth promoters/inhibitors in the buds, depending on morphogenic stages and the bud position on the branch.     

No evidence for consistent long‐term growth stimulation of 13 tropical tree species: results from tree‐ring analysis

The important role of tropical forests in the global carbon cycle makes it imperative to assess changes in their carbon dynamics for accurate projections of future climate–vegetation feedbacks. Forest monitoring studies conducted over the past decades have found evidence for both increasing and decreasing growth rates of tropical forest trees. The limited duration of these studies restrained analyses to decadal scales, and it is still unclear whether growth changes occurred over longer time scales, as would be expected if CO₂‐fertilization stimulated tree growth. Furthermore, studies have so far dealt with changes in biomass gain at forest‐stand level, but insights into species‐specific growth changes – that ultimately determine community‐level responses – are lacking. Here, we analyse species‐specific growth changes on a centennial scale, using growth data from tree‐ring analysis for 13 tree species (~1300 trees), from three sites distributed across the tropics. We used an established (regional curve standardization) and a new (size‐class isolation) growth‐trend detection method and explicitly assessed the influence of biases on the trend detection. In addition, we assessed whether aggregated trends were present within and across study sites. We found evidence for decreasing growth rates over time for 8–10 species, whereas increases were noted for two species and one showed no trend. Additionally, we found evidence for weak aggregated growth decreases at the site in Thailand and when analysing all sites simultaneously. The observed growth reductions suggest deteriorating growth conditions, perhaps due to warming. However, other causes cannot be excluded, such as recovery from large‐scale disturbances or changing forest dynamics. Our findings contrast growth patterns that would be expected if elevated CO₂ would stimulate tree growth. These results suggest that commonly assumed growth increases of tropical forests may not occur, which could lead to erroneous predictions of carbon dynamics of tropical forest under climate change.     

Seasonal patterns of reproductive and vegetative sink activity in early and late maturing peach (Prunus persica) cultivars

Weekly measurements of fruit growth, fruit respiration and shoot extension growth were made in the field on early (June Lady) and late (O'Henry) maturing cultivars of peach ( Prunus persica L. Batsch). The seasonal patterns of fruit growth and respiration for the two cultivars were very similar except that the early maturing cultivar bloomed a few days earlier than the late cultivar and had a shorter intermediate stage (Stage II) of fruit growth. Maximum rates of fruit respiration per unit weight at 20°C were similar for both cultivars during the first two stages of fruit growth but higher for the early cultivar during the final stage of fruit growth. Maximum fruit growth rates within any particular stage of fruit growth were similar for both cultivars, but the mean fruit weight of the late cultivar was greater at the end of Stage II, because of the extended length of this stage compared to the early cultivar. The final stage of most rapid fruit growth and respiration coincided with the period of most rapid shoot extension growth in the early maturing cultivar but occurred after this period in the late maturing cultivar. Genetic selection for early fruit maturity in peach has apparently had little effect on timing of shoot growth and this may result in increased competition between vegetative and reproductive sinks during peak periods of fruit growth in early maturing cultivars.     

Growth Rates of Tree Height Six Years after Hurricane Damage at Four Localities in Eastern Nicaragua1

Growth rates for 44 species of trees in a posthurricane forest in Nicaragua were measured. The pattern is consistent with the interpretation of succession as a two stage process: an initial building phase after the hurricane followed by a thinning phase. Localities that were damaged less from the hurricane are now entering the thinning phase of postdisturbance succession, while those subjected to the most severe damage appear to remain in the building phase.     

Climate‐driven speedup of alpine treeline forest growth in the Tianshan Mountains,Northwestern China

Forest growth is sensitive to interannual climatic change in the alpine treeline ecotone (ATE). Whether the alpine treeline ecotone shares a similar pattern of forest growth with lower elevational closed forest belt (CFB) under changing climate remains unclear. Here, we reported an unprecedented acceleration of Picea schrenkiana forest growth since 1960s in the ATE of Tianshan Mountains, northwestern China by a stand‐total sampling along six altitudinal transects with three plots in each transect: one from the ATE between the treeline and the forest line, and the other two from the CFB. All the sampled P. schrenkiana forest patches show a higher growth speed after 1960 and, comparatively, forest growth in the CFB has sped up much slower than that in the ATE. The speedup of forest growth at the ATE is mainly accounted for by climate factors, with increasing temperature suggested to be the primary driver. Stronger water deficit as well as more competition within the CFB might have restricted forest growth there more than that within the ATE, implying biotic factors were also significant for the accelerated forest growth in the ATE, which should be excluded from simulations and predictions of warming‐induced treeline dynamics.     

马尾松直径生长与气候的非线性响应函数

 在Fritts响应函数基础上,提出一种树木生长对各气候变量的非线性响应函数。该响应函数把气候变量的交互作用(各气候变量乘积)之和进行合并,不仅防止了自由度的显著下降,而且还有助于了解各气候变量交互作用对树木生长的平均效应。一组马尾松芯样(15株树,30个芯样,位于马尾松分布带北端)经定年和除趋势后得到的年轮年表与各月平均气温、降水量的关系,经该非线性响应函数分析,表明所取马尾松对前1年11月、当年2、5、8、9、11月的降水量的平方有显著正响应;对前1年12月、当年3、8、12月的平均气温之平方有显著正响应,而对当年2月的平均气温的平方有显著负响应。     

High-altitude tree growth responses to climate change across the Hindu Kush Himalaya

兴都库什喜马拉雅地区高海拔树木生长对气候变化的响应 高海拔地区快速升温可能导致树木对温度响应更为敏感,而限制高海拔地区树木生长的关键气候因子以及气候变化对树木生长产生多大程度的影响尚不清楚。本研究在兴都库什喜马拉雅地区收集了73 个样点的树轮数据,包括3个优势属的树种(Abies属、Juniperus属和Picea属),样点海拔均在3000 m以上。 将时间动态规整(dynamic time warping)的方法用于建立亚区域年表,以考虑不同站点年表之间变化的同步 性。同时,定量分析了气候因子对树木生长的贡献以及树木生长与气候因子关系的时空动态。研究结果发现,73个站点年表可以聚为3类,且与其所处的生物气候区相对应,即西喜马拉雅地区,中东喜马拉雅地区和藏东南地区。在干旱的西喜马拉雅地区,树木生长与冬、春两季的降水呈正相关关系,而在湿润的藏东南地区,树木生长与冬季温度和春季降水呈正相关关系。树木生长受最低温度的影响最大,特别是冬季温度,其重要性从西到东呈现递增趋势。滑动窗口相关分析表明,在中西喜马拉雅地区,影响树木生长的冬季温度信号在减弱,然而在藏东南地区该信号随着1980年以来的快速升温而增强。本研究结果表明,若该地区升温持续,在西喜马拉雅地区可能会因变暖引起的水分亏缺而造成森林衰退,而在藏东南地区因树木生长得益于变暖而使得森林扩张。     

遮荫对13种盆栽棕榈植物生长的影响

研究13种盆栽棕榈植物在不同遮荫处理条件下的生长、叶片叶绿素含量、含水量及比叶重的变化,并通过系统聚类分析及主分量分析,将13种棕榈植物的耐阴性分为三类,其中缨络椰子、散尾葵和小琼棕较耐阴,国王椰子、假槟榔、金帝葵和美丽针葵耐阴性较差,短穗鱼尾葵、袖珍椰子、雪佛里椰子、穗花轴榈、蒲葵和棕竹等棕榈植物耐阴性居中.     

Monitoring individual tree‐based change with airborne lidar

Understanding the carbon flux of forests is critical for constraining the global carbon cycle and managing forests to mitigate climate change. Monitoring forest growth and mortality rates is critical to this effort, but has been limited in the past, with estimates relying primarily on field surveys. Advances in remote sensing enable the potential to monitor tree growth and mortality across landscapes. This work presents an approach to measure tree growth and loss using multidate lidar campaigns in a high‐biomass forest in California, USA. Individual tree crowns were delineated in 2008 and again in 2013 using a 3D crown segmentation algorithm, with derived heights and crown radii extracted and used to estimate individual tree aboveground biomass. Tree growth, loss, and aboveground biomass were analyzed with respect to tree height and crown radius. Both tree growth and loss rates decrease with increasing tree height, following the expectation that trees slow in growth rate as they age. Additionally, our aboveground biomass analysis suggests that, while the system is a net source of aboveground carbon, these carbon dynamics are governed by size class with the largest sources coming from the loss of a relatively small number of large individuals. This study demonstrates that monitoring individual tree‐based growth and loss can be conducted with multidate airborne lidar, but these methods remain relatively immature. Disparities between lidar acquisitions were particularly difficult to overcome and decreased the sample of trees analyzed for growth rate in this study to 21% of the full number of delineated crowns. However, this study illuminates the potential of airborne remote sensing for ecologically meaningful forest monitoring at an individual tree level. As methods continue to improve, airborne multidate lidar will enable a richer understanding of the drivers of tree growth, loss, and aboveground carbon flux.     

Tree rings provide no evidence of a CO2 fertilization effect in old‐growth subalpine forests of western Canada

Atmospheric CO₂ concentrations are now 1.7 times higher than the preindustrial values. Although photosynthetic rates are hypothesized to increase in response to rising atmospheric CO₂ concentrations, results from in situ experiments are inconsistent in supporting a CO₂ fertilization effect of tree growth. Tree‐ring data provide a historical record of tree‐level productivity that can be used to evaluate long‐term responses of tree growth. We use tree‐ring data from old‐growth, subalpine forests of western Canada that have not had a stand‐replacing disturbance for hundreds of years to determine if growth has increased over 19th and 20th centuries. Our sample consisted of 5,858 trees belonging to five species distributed over two sites in the coastal zone and two in the continental climate of the interior. We calculated annual increments in tree basal area, adjusted these increments for tree size and age, and tested whether there was a detectable temporal trend in tree growth over the 19th and 20th centuries. We found a similar pattern in 20th century growth trends among all species at all sites. Growth during the 19th century was mostly stable or increasing, with the exception of one of the coastal sites, where tree growth was slightly decreasing; whereas growth during the 20th century consistently decreased. The unexpected decrease in growth during the 20th century indicates that there was no CO₂ fertilization effect on photosynthesis. We compared the growth trends from our four sites to the trends simulated by seven Earth System Models, and saw that most of the models did not predict these growth declines. Overall, our results indicate that these old‐growth forests are unlikely to increase their carbon storage capacity in response to rising atmospheric CO₂, and thus are unlikely to contribute substantially to offsetting future carbon emissions.     

西天目山针叶树直径生长与气候变化的关系

利用树木年轮分析方法研究了西天目山的三种主要针叶树：柳杉、金钱松和黄山松在林分范围内的直径生长与气候因子的关系。用逐步回归分析建立生长指数与１３个气候因子的回归方程,然后将生长曲线加入回归方程获得估计胸高处直径生长量的模型。结果表明,显著影响柳杉直径生长指数的因素为前期生长和夏季气温;影响金钱松生长指数达显著水平的有前期生长和夏、秋两季降水量;显著影响黄山松生长指数的因素有前期生长、夏季气温和秋季降水量。如果未来气温比目前分别升高１℃、２℃和３℃,柳杉的直径生长量将增加３．２％、６．３％和１１．１％;金钱松的将增加３．７％、５．６％和７．４％;黄山松的将增加３．５％、７．１％和１１．８％。文中对影响直径生长的其他因素也进行了讨论。     

马尾松直径生长与气侯的非线性响应函数

在Ｆｒｉｔｔｓ响应函数基础上,提出一种树木生长对各气候变量的非线性响应函数。该响应函数把气候变量的交互作用（各气候变量乘积）之和进行合并,不仅防止了自由度的显著下降,而且还有助于了解各气候变量交互作用对树木生长的平均效应。一组马尾松芯样（１５株树,３０个芯样,位于马尾松分布带北端）经定年和除趋势后得到的年轮年表与各月平均气温、降水量的关系,经该非线性响应函数分析,表明所取马尾松对前１年１１月、当年２、５、８、９、１１月的降水量的平方有显著正响应;对前１年１２月、当年３、８、１２月的平均气温之平方有显著正响应,而对当年２月的平均气温的平方有显著负响应。     

Detecting long‐term growth trends using tree rings: a critical evaluation of methods

Tree‐ring analysis is often used to assess long‐term trends in tree growth. A variety of growth‐trend detection methods (GDMs) exist to disentangle age/size trends in growth from long‐term growth changes. However, these detrending methods strongly differ in approach, with possible implications for their output. Here, we critically evaluate the consistency, sensitivity, reliability and accuracy of four most widely used GDMs: conservative detrending (CD) applies mathematical functions to correct for decreasing ring widths with age; basal area correction (BAC) transforms diameter into basal area growth; regional curve standardization (RCS) detrends individual tree‐ring series using average age/size trends; and size class isolation (SCI) calculates growth trends within separate size classes. First, we evaluated whether these GDMs produce consistent results applied to an empirical tree‐ring data set of Melia azedarach, a tropical tree species from Thailand. Three GDMs yielded similar results – a growth decline over time – but the widely used CD method did not detect any change. Second, we assessed the sensitivity (probability of correct growth‐trend detection), reliability (100% minus probability of detecting false trends) and accuracy (whether the strength of imposed trends is correctly detected) of these GDMs, by applying them to simulated growth trajectories with different imposed trends: no trend, strong trends (?6% and +6% change per decade) and weak trends (?2%, +2%). All methods except CD, showed high sensitivity, reliability and accuracy to detect strong imposed trends. However, these were considerably lower in the weak or no‐trend scenarios. BAC showed good sensitivity and accuracy, but low reliability, indicating uncertainty of trend detection using this method. Our study reveals that the choice of GDM influences results of growth‐trend studies. We recommend applying multiple methods when analysing trends and encourage performing sensitivity and reliability analysis. Finally, we recommend SCI and RCS, as these methods showed highest reliability to detect long‐term growth trends.     

Somatic embryogenesis and plant regeneration in Acacia farnesiana and A. schaffneri

Summary Efficient plant regeneration systems via somatic embryogenesis have been developed for Acacia farnesiana and Acacia schaffneri [Leguminosae (Mimosoideae)]. The protocol used in this study consisted of placing immature, zygotic embryos of these species in Murashige and Skoog semi-solid basal medium supplemented with 9.05 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.65 μM kinetin to induce callus. Some parts of the callus were used for direct embryo differentiation and others for establishment of cell suspension cultures. In the first case, somatic embryos were produced on semi-solid differentiation media without growth regulators or with abscisic acid (ABA). The higher number of somatic embryos, 345 and 198 embryos per g callus in A. farnesiana and A. schaffneri, respectively was obtained in media without growth regulators, but adding ABA increased the percentage of embryos that reached more advanced differentiation stages. The production of somatic embryos was achieved starting from cell suspensions only when these suspensions were plated into the semi-solid differentiation medium. Somatic embryos germinated on medium containing 217 μM adenine sulfate with efficiencies of 69% in A. farnesiana and 47% in A. schaffneri. Some somatic embryos that developed into plantlets were acclimatized in the greenhouse, and they grew into normal plants.     

Uneven winter snow influence on tree growth across temperate China

Winter snow is an important driver of tree growth in regions where growing‐season precipitation is limited. However, observational evidence of this influence at larger spatial scales and across diverse bioclimatic regions is lacking. Here, we investigated the interannual effects of winter (here defined as previous October to current February) snow depth on tree growth across temperate China over the period of 1961–2015, using a regional network of tree ring records, in situ daily snow depth observations, and gridded climate data. We report uneven effects of winter snow depth on subsequent growing‐season tree growth across temperate China. There shows little effect on tree growth in drier regions that we attribute mainly to limited snow accumulation during winter. By contrast, winter snow exerts important positive influence on tree growth in stands with high winter snow accumulation (e.g., in parts of cold arid regions). The magnitude of this effect depends on the proportion of winter snow to pre‐growing‐season (previous October to current April) precipitation. We further observed that tree growth in drier regions tends to be increasingly limited by warmer growing‐season temperature and early growing‐season water availability. No compensatory effect of winter snow on the intensifying drought limitation of tree growth was observed across temperate China. Our findings point toward an increase in drought vulnerability of temperate forests in a warming climate.     

树种相互作用、林分密度和树木大小对华北落叶松生产力的影响

本研究以塞罕坝地区华北落叶松纯林、白桦纯林和华北落叶松与白桦混交林为对象,每种林分类型设置2个林分密度(200～340和880～1100株·hm^-2)。基于树木大小分层取样,采集树芯样本668条。运用线性混合模型,分析了树种相互作用、林分密度和树木大小对华北落叶松生产力的影响。结果表明: 华北落叶松断面积生长量不同程度地受竞争、胸径、年龄和邻体密度的影响;在林分密度较高的混交林中,由于白桦对华北落叶松生长的促进作用,落叶松生产力发生明显的增益效应;在林分密度较低的混交林中,落叶松和白桦之间不发生相互作用,2个树种的生产力均低于相应的纯林;种内竞争是影响华北落叶松生产力的主要因素;树木大小对华北落叶松生产力产生积极的影响,但影响程度因林分密度和树种组成而异。适当增加林分密度和选择白桦作为混交树种可以提高华北落叶松生产力。     

山西省长治市过去150年森林的生长抑制和释放历史

森林生长与气候变化有着紧密的关系,在全球变暖情形下了解树木的干扰历史对准确预测森林生长的变化具有促进作用。本文选择山西黄土高原东南部长治地区保存较好的一个油松(Pinus tabuliformis)和两个白皮松(Pinus bungeana)森林为研究对象,利用树木年轮学方法分析了其干扰历史。结果表明:黎城县、平顺县和屯留县研究地点中年龄最老的树木分别有227、185、102a;通过计算树木径向生长的变化幅度,发现该地区在过去150年中发生了3次大的生长抑制事件(分别发生在1873—1877、1925—1930和1994—1997年期间)和5次大的生长释放事件(分别发生在1867—1871、1878—1884、1930—1935、1980—1985和1999—2004年期间)。树木径向生长与气象观测资料的相关分析显示,该地区森林生长在年际尺度上主要与6月份温度呈负相关而与4—5月份水分条件呈正相关,揭示了由降水减少或高温下水分蒸散所带来的极端干旱事件是导致森林抑制现象的主要原因。这些森林历史研究结果对区域林业管理具有实践意义,营林建设更宜选择在森林生长释放时期;经历多次干扰而存留下来的老龄树具有较强的抗干扰能力和丰富的历史信息,加强对老龄树的鉴定与针对性保护可有效维护区域森林生态服务功能。