Stem CO2 efflux in six co‐occurring tree species: underlying factors and ecological implications

Stem respiration plays a role in species coexistence and forest dynamics. Here we examined the intra‐ and inter‐specific variability of stem CO₂ efflux (E) in dominant and suppressed trees of six deciduous species in a mixed forest stand: Fagus sylvatica L., Quercus petraea [Matt.] Liebl, Quercus pyrenaica Willd., Prunus avium L., Sorbus aucuparia L. and Crataegus monogyna Jacq. We conducted measurements in late autumn. Within species, dominants had higher E per unit stem surface area (E_s) mainly because sapwood depth was higher than in suppressed trees. Across species, however, differences in E_s corresponded with differences in the proportion of living parenchyma in sapwood and concentration of non‐structural carbohydrates (NSC). Across species, E_s was strongly and NSC marginally positively related with an index of drought tolerance, suggesting that slow growth of drought‐tolerant trees is related to higher NSC concentration and E_s. We conclude that, during the leafless period, E is indicative of maintenance respiration and is related with some ecological characteristics of the species, such as drought resistance; that sapwood depth is the main factor explaining variability in E_s within species; and that the proportion of NSC in the sapwood is the main factor behind variability in E_s among species.     

Comparisons of soil‐water content between a Moso bamboo (Phyllostachys pubescens) forest and an evergreen broadleaved forest in western Japan

In Japan, forests of Moso bamboo (Phyllostachys pubescens, an exotic invasive giant bamboo) have naturalized and expanded rapidly, replacing surrounding broadleaved and coniferous forests. To evaluate impacts caused by these forest‐type replacements on the hydrological cycle, soil‐water content and its spatial variability in a Moso bamboo forest were compared with those in an adjacent evergreen broadleaved forest, in a case study of a stand in western Japan (northern Kyushu). The volumetric soil‐water content averaged over depths between 0 and 60 cm was consistently higher in the bamboo stand than that in the broadleaved stand. These results contrast with previous studies comparing the soil‐water content in Moso bamboo forests with that in other forest types. The sum of canopy transpiration and soil evaporation (E) in the bamboo stand tended to be larger than that in the broadleaved stand. Small canopy interception loss was reported in the bamboo forest. Therefore, the large amount of E would counterbalance the small canopy interception loss in the bamboo forest. Differences in soil characteristics between the two stands may be the main factor causing differences in soil‐water content. Spatial variation in soil‐water content in the bamboo stand was larger than that in the broadleaved stand, confirming findings in a previous series of our study. This could happen because the well‐developed root‐system in the bamboo forest enhances preferential flow in the soil. To evaluate the effects of aggressive invasion of alien giant bamboo on the ecosystem functions, we recommend further studies measuring various hydrological components in various Moso bamboo forests.     

Age‐related Crown Thinning in Tropical Forest Trees

Gap dynamics theory proposes that treefall gaps provide high light levels needed for regeneration in the understory, and by increasing heterogeneity in the light environment allow light‐demanding tree species to persist in the community. Recent studies have demonstrated age‐related declines in leaf area index of individual temperate trees, highlighting a mechanism for gradual changes in the forest canopy that may also be an important, but less obvious, driver of forest dynamics. We assessed the prevalence of age‐related crown thinning among 12 tropical canopy tree species sampled in lowland forests in Panama and Puerto Rico (total N = 881). Canopy gap fraction of individual canopy tree crowns was positively related to stem diameter at 1.3 m (diameter at breast height) in a pooled analysis, with 10 of 12 species showing a positive trend. Considered individually, a positive correlation between stem diameter and canopy gap fraction was statistically significant in 4 of 12 species, all of which were large‐statured canopy to emergent species: Beilschmiedia pendula, Ceiba pentandra, Jacaranda copaia, and Prioria copaifera. Pooled analyses also showed a negative relationship between liana abundance and canopy gap fraction, suggesting that lianas could be partially obscuring age‐related crown thinning. We conclude that age‐related crown thinning occurs in tropical forests, and could thus influence patterns of tree regeneration and tropical forest community dynamics.     

Harnessing Genetic Variation in Leaf Angle to Increase Productivity of Sorghum bicolor

The efficiency with which a plant intercepts solar radiation is determined primarily by its architecture. Understanding the genetic regulation of plant architecture and how changes in architecture affect performance can be used to improve plant productivity. Leaf inclination angle, the angle at which a leaf emerges with respect to the stem, is a feature of plant architecture that influences how a plant canopy intercepts solar radiation. Here we identify extensive genetic variation for leaf inclination angle in the crop plant Sorghum bicolor, a C4 grass species used for the production of grain, forage, and bioenergy. Multiple genetic loci that regulate leaf inclination angle were identified in recombinant inbred line populations of grain and bioenergy sorghum. Alleles of sorghum dwarf-3, a gene encoding a P-glycoprotein involved in polar auxin transport, are shown to change leaf inclination angle by up to 34° (0.59 rad). The impact of heritable variation in leaf inclination angle on light interception in sorghum canopies was assessed using functional-structural plant models and field experiments. Smaller leaf inclination angles caused solar radiation to penetrate deeper into the canopy, and the resulting redistribution of light is predicted to increase the biomass yield potential of bioenergy sorghum by at least 3%. These results show that sorghum leaf angle is a heritable trait regulated by multiple loci and that genetic variation in leaf angle can be used to modify plant architecture to improve sorghum crop performance.     

夏季栾树群落冠层结构对其环境温湿度的调节作用

为探究栾树群落降温增湿作用与其冠层结构参数的相关性在一天中的变化趋势,于天气晴朗的夏季对北京奥林匹克森林公园栾树群落内部和对照点的温度、相对湿度、群落冠层结构参数进行了铡定.结果表明:栾树群落的郁闭度与叶面积指数、平均叶倾角呈显著相关,且叶面积指数与平均叶倾角呈显著相关;在夏季8:00-18:00,栾树群落可降低空气温度0.43～7.53℃,在12:00左右达到降温最大值,增加相对湿度1％ ～ 22％,且在10:00左右增湿作用最显著,而在18:00-次日8:00降温增湿效果不明显;9:00-12:00,郁闭度和叶面积指数显著影响栾树群落的降温增湿作用;12:00-14:00,仅郁闭度与降温增湿作用显著相关;直到18:00,郁闭度和叶面积指数共同决定了栾树群落的降温增湿作用.因此,影响栾树群落降温增湿作用的冠层结构参数在一天中随着时间的推移发生变化.     

Design and performance of combined infrared canopy and belowground warming in the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment

Conducting manipulative climate change experiments in complex vegetation is challenging, given considerable temporal and spatial heterogeneity. One specific challenge involves warming of both plants and soils to depth. We describe the design and performance of an open‐air warming experiment called Boreal Forest Warming at an Ecotone in Danger (B4WarmED) that addresses the potential for projected climate warming to alter tree function, species composition, and ecosystem processes at the boreal‐temperate ecotone. The experiment includes two forested sites in northern Minnesota, USA, with plots in both open (recently clear‐cut) and closed canopy habitats, where seedlings of 11 tree species were planted into native ground vegetation. Treatments include three target levels of plant canopy and soil warming (ambient, +1.7 °C, +3.4 °C). Warming was achieved by independent feedback control of voltage input to aboveground infrared heaters and belowground buried resistance heating cables in each of 72‐7.0 m² plots. The treatments emulated patterns of observed diurnal, seasonal, and annual temperatures but with superimposed warming. For the 2009 to 2011 field seasons, we achieved temperature elevations near our targets with growing season overall mean differences (?T_below) of +1.84 °C and +3.66 °C at 10 cm soil depth and (?T^above) of +1.82 °C and +3.45 °C for the plant canopies. We also achieved measured soil warming to at least 1 m depth. Aboveground treatment stability and control were better during nighttime than daytime and in closed vs. open canopy sites in part due to calmer conditions. Heating efficacy in open canopy areas was reduced with increasing canopy complexity and size. Results of this study suggest the warming approach is scalable: it should work well in small‐statured vegetation such as grasslands, desert, agricultural crops, and tree saplings (<5 m tall).     

河套灌区九排域农田排水沟植物物种多样性

2010年8-9月对河套灌区九排域农田排水沟植物进行了综合调查.分别在干沟、支沟、斗沟/农沟的上、中、下游布设断面,断面上设置0.5m×0.5m和5m×5m样方对草本和灌木的植物种类和数量进行调查.结果表明:河套灌区九排域农田排水沟植物由17个科、38个属、39个种组成,禾本科(n=10)、菊科(n=7)和藜科(n=4)植物种类最多,芦苇、羊草和盐地碱蓬是分布面积最广的物种.干沟、支沟和斗/农沟的多样性指数、丰富度指数、均匀度指数和优势度指数值分别为0.57、1.93、0.37和0.81,0.77、3.46、0.65和0.50,0.90、3.88、0.64和0.53.物种多样性表现为边坡的高于沟底,但排沟等级间的变化趋势不明显.水的存留时间及农业管理(清沟)是影响植物物种多样性最主要的因素.     

基于RAPD技术探讨黄精属部分药用植物系统位置

目的：从分子水平探讨黄精属部分药用植物间的系统位置。方法：采用RAPD分子标记方法,以同科万寿竹属植物宝铎草（Disporum sessile D．Don）为外类群,对百合科黄精属19批（6种）药用植物进行基因组DNA的多态性分析,通过聚类分析探讨黄精种属间亲缘关系。结果：筛选出7条随机引物,聚类结果表明,黄精属植物在属级分类上特征明显,但属内分类有交叉。结论：RAPD技术可以为黄精属的分类和种的鉴别提供一定的理论依据。     

‘长林4号’油茶树冠不同部位的果实性状差异

以5年生‘长林4号’油茶为试材,对树体冠层不同部位的油茶果实性状进行研究。结果表明,与树冠内层果实相比,树冠外层中上部的果实较大(29.5 g),籽粒数较多(4.8粒/果),鲜出籽率和果形指数相对较小(分别为46.8%和0.81);树冠外层果实的种仁含油率(41.2%)显著高于内层果实(α=0.05),而树冠外层不同部位的种仁含油率无显著差异;此外,树冠不同部位的果实茶油的脂肪酸组成无明显差异,果实着生部位对茶油品质的影响不大。