Carbon limitation leads to suppression of first year oak seedlings beneath evergreen understory shrubs in Southern Appalachian hardwood forests

Inhibition of canopy tree recruitment beneath thickets of the evergreen shrubs Rhododendron maximum L. and Kalmia latifolia L. has long been observed in Southern Appalachian forests, yet the mechanisms of this process remain unresolved. We present a first-year account of suppression of oak seedlings in relation to Rhododendron and Kalmia basal area, light and resource availability, seedling performance and the rates of seedling damage (i.e., herbivory). We found no evidence of first-year seedling suppression or significant resource deficiencies beneath thickets of K. latifolia in mature mixed hardwood stands. Suppression beneath R. maximum was apparent during the first growing season. We found that seedling biomass, light availability prior to canopy closure, and seedling tissue C:N ratios were negatively correlated with R. maximum basal area. Basal area of R. maximum was positively correlated with seedling mortality rates, soil [Al], and early-growing season leaf herbivory rates. Seedling growth was positively correlated with light and tissue C:N, while negatively correlated with soil [Al]. Overall, our results support the inhibition model of shade-mediated carbon limitation beneath dense understory shrubs and indicate the potential importance of herbivory and aluminum toxicity as components of a suppression mechanism beneath R. maximum thickets. We present a causal model of first year inhibition beneath R. maximum in the context of our findings and the results of prior studies.     

桃叶杜鹃组织培养技术研究

选用桃叶杜鹃试管苗的芽苗、叶片进行离体培养,通过正交试验设计并结合方差分析、多重比较从中选出了不同中间繁殖体的最佳培养基配方.试验结果表明:改良MS和6-BA及KT不适合桃叶杜鹃的组织培养,相对较低浓度的TDZ却能诱导植株分化,建立起桃叶杜鹃的离体培养体系,达到保护名贵杜鹃的种质资源,加速繁殖的目的.     

Kinship between parents reduces offspring fitness in a natural population of Rhododendron brachycarpum

Background and Aims

A reduction in offspring fitness resulting from mating between neighbours is interpreted as biparental inbreeding depression. However, little is known about the relationship between the parents'' genetic relatedness and biparental inbreeding depression in their progeny in natural populations. This study assesses the effect of kinship between parents on the fitness of their progeny and the extent of spatial genetic structure in a natural population of Rhododendron brachycarpum.

Methods

Kinship coefficients between 11 858 pairs of plants among a natural population of 154 R. brachycarpum plants were estimated a priori using six microsatellite markers. Plants were genotyped, and pairs were selected from among 60 plants to vary the kinship from full-sib to unrelated. After a hand-pollination experiment among the 60 plants, offspring fitness was measured at the stages of seed maturation (i.e. ripening) under natural conditions, and seed germination and seedling survival under greenhouse conditions. In addition, spatial autocorrelation was used to assess the population''s genetic structure.

Key Results

Offspring fitness decreased significantly with increasing kinship between parents. However, the magnitude and timing of this effect differed among the life-cycle stages. Measures of inbreeding depression were 0·891 at seed maturation, 0·122 (but not significant) at seed germination and 0·506 at seedling survival. The local population spatial structure was significant, and the physical distance between parents mediated the level of inbreeding between them.

Conclusions

The level of inbreeding between individuals determines offspring fitness in R. brachycarpum, especially during seed maturation. Genetic relatedness between parents caused inbreeding depression in their progeny. Therefore, biparental inbreeding contributes little to reproduction and instead acts as a selection force that promotes outcrossing, as offspring of more distant (less related) parents survive better.     

六种杜鹃花属植物花粉活力测定方法的比较研究

选取睫毛杜鹃(Rhododendron ciliatum)、多鳞杜鹃(Rhododendron polylepis)、薄皮杜鹃(Rhdodenron taronense)、映山红(Rhododendron simsii)、马银花(Rhododendron ovatum)和比利时杜鹃(Rhododendron hybridum)为研究对象,通过蔗糖、H3BO3、CaCl2单因子及L25( 53)正交试验对它们进行花粉萌发试验研究,比较I2-Kl染色法、TTC染色法、联苯胺染色法、MTT染色法4种花粉活力测定方法的不同.结果表明:蔗糖、H3BO3、CaCl2及3因子交互效应对杜鹃花花粉萌发有显著影响.适宜的离体培养基配方依杜鹃花种类不同而不同,睫毛杜鹃为:蔗糖150 g/L +H3BO3 0 mg/L +CaCl2 50 mg/L;映山红为:蔗糖100 g/L +H3BO3 100 mg/L +CaCl20 mg/L;马银花为:蔗糖50 g/L+ H3BO3 200 mg/L +CaCl2 0 mg/L;比利时杜鹃为:蔗糖150 g/L+ H3BO3100 mg/L +CaCl2 0 mg/L.MTT染色法是简单快速测定杜鹃花花粉活力的最适染色法.     

Monilinia jezoensis sp. nov. in the Sclerotiniaceae, causing leaf blight and mummy fruit disease of Rhododendron kaempferi in Hokkaido, northern Japan

A new leaf blight and mummy fruit disease caused by a species of Monilinia was first found on Rhododendron kaempferi at the lakeside of Shikotsu-ko, Hokkaido, northern Japan, in 2002. Studies on morphology, life cycle, cultural characters, and gene analyses of the causal fungus enabled us to conclude that it is a new species of the genus. It is named M. jezoensis. Rhododendron is a new host genus for Monilinia fungi in Japan.     

四川杜鹃花属三个新异名

将我国四川杜鹃花属Rhododendron L.植物2个种和1个亚种（R.decorum Franch. ssp.cordatum Hu,R.xichangense Z.J.Zhao及R.davidsonianum Rehd.&Wils.）处理为新异名,并作了相应的讨论。     

云南马先蒿属植物的生物地理及物种多样性

马先蒿属(Pedicularis)是被子植物中最大的属之一,在云南植物区系中占有重要地位.按照钟补求系统,该属植物在云南有151种分属于13个群72个系.马先蒿属在云南的地理分布体现了下列特点:(1)种类十分丰富,占整个属总种数的25%,占中国的42.6%.(2)包括了该属全部花冠类型,即无齿、有齿的原始类型各为24种、短管具喙的中间过渡类型87种,较进化的长管类型16种.(3)马先蒿属植物分布在云南的11个地理分布区域中,但该属植物在康藏高原区最为丰富,有108个种在本区有分布,占云南种数的71.5%;横断山植物区和东喜马拉雅植物区是本属的现代分布中心和多样化中心.(4)特有现象十分明显,其中8个系、52个种为云南特有,横断山和东喜马拉雅的特有种最为丰富,也是本属的特有中心.(5)云南马先蒿植物与邻近的四川(西南部)和西藏(东南部)在区系上联系密切,与缅甸和不丹有一定的联系.     

Thermotolerance of Photosystem 2 of Three Alpine Plant Species Under Field Conditions

The species specific response of photosystem 2 (PS2) efficiency and its thermotolerance to diurnal and seasonal alterations in leaf temperature, irradiance, and water relations were investigated under alpine field conditions (1 950 m) and in response to an in situ long-term heat treatment (+3 K). Three plant species were compared using the naturally occurring microstratification of alpine environments, i.e. under contrasting leaf temperatures but under similar macroclimatic conditions. Thermotolerance of PS2 showed a high variability in all three species of up to 9.6 K. Diumal changes (increases or even decreases) in PS2 thermotolerance occurred frequently with a maximum increase of +4.8 K in Loiseleuria procumbens. Increasing leaf temperatures and photosynthetic photon flux density influenced thermotolerance adjustments. Under long-term heating (+3 K) of L. procumbens canopies with infra-red lamps, the maxima of the critical (T_c) and the lethal (T_p) temperature of PS2 increased by at least 1 K. Thermotolerance of the leaf tissue (LT₅₀) increased significantly by +0.6 K. The effects of slight water stress on thermotolerance of PS2 were species specific. High temperature thresholds for photoinhibition were significantly different between species and increased by 9 K from the species in the coldest microhabitat to the species in the warmest. Experimental heating of L. procumbens canopies by +3 K caused a significant (p>0.01) upward shift of the high temperature threshold for photoinhibition by +3 K. Each species appeared to be very well adapted to the thermal conditions of its microhabitat as under the most frequently experienced daytime leaf temperatures no photoinhibition occurred. The observed fine scale thermal adjustment of PS2 in response to increased leaf temperatures shows the potential to optimise photosynthesis under varying environmental conditions as long as the upper thermal limits are not exceeded.     

Seed limitation,not soil legacy effects,prevents native understorey from establishing in oak woodlands in Scotland after removal of Rhododendron ponticum

Following removal of the invasive species Rhododendron ponticum, the native understorey plant community typically fails to reestablish itself. Potential explanations for this failure include (1) lack of an appropriate native seed source; (2) inability of seed to penetrate a dense bryophyte layer; and (3) persistence of chemical “legacy effects” in the soil. We established an experiment to test these competing hypotheses in an Atlantic oak woodland where R. ponticum had been removed. The following experimental treatments were applied singly and in combination: (1) addition of a native seed mix to test for seed limitation; (2) removal of the established ground vegetation at the start of the experiment (which principally consisted of bryophytes) to test for the impact of a barrier layer; (3) addition of activated carbon to test for chemical legacy effects in the soil; and (4) fertilization as an additional measure to promote the establishment of native vascular plants. Application of the native seed mix was revealed to be an effective way to increase the cover of native vascular plants and was particularly effective when applied after the removal of the bryophyte layer. The application of activated carbon and/or fertilizer, however, had no effect on the cover of native vegetation. We conclude that reports of R. ponticum exerting chemical legacy effects long after its removal may have been overstated and that seed limitation and inability to successfully establish in a dense bryophyte layer provided the strongest barriers to natural recolonization by the native plant community following R. ponticum removal.     

Validation of criteria for the selection of AFLP markers to assess the genetic variation of a breeders’ collection of evergreen azaleas

Fluorescent AFLP and automated data analysis were employed to assess the genetic conformity within a breeders’ collection of evergreen azaleas. The study included 75 genotypes of Belgian pot azaleas (Rhododendron simsii Planch. hybrids), Kurume and Hirado azaleas and wild ancestor species from the Tsutsusi subgenus. Fluorescent detection and addition of an internal size standard to each lane enabled the automated scoring of each fragment arising from a single AFLP primer combination (PC). The use of three PCs generated an initial data set with a total of 648 fragments ranging from 70 bp to 450 bp. Different marker selection thresholds for average fluorescent signal intensity and marker frequency were used to create eight extra restricted data subsets. Pairwise plant genetic similarity was calculated for the nine data sets using the Simple Matching coefficient (symmetrical, including double-zeros) and Jaccard coefficient (asymmetrical, excluding double zeros). The averages, the ranges and the correlation to one other (Mantel analysis) were compared for the obtained similarity matrices. This revealed the sensitivity of ordinations obtained by both similarity coefficients for the presence of weak or intensive markers or for the degree of polymorphism of the markers. For 34 cultivars, pedigree information (at maximum to the fifth ancestor generation) was available. Genetic similarity by descent (kinship coefficient) was turned into a genetic distance and correlated to the genetic conformity, as revealed by the different selections of AFLP markers (Mantel analysis). Use of a Simple Matching coefficient with no or moderate selection to signal intensity and excluding rare and abundant markers gave the best correlation with pedigree. Finally, the ordination of the studied genotypes by means of dendrograms and principal co-ordinate analysis was confronted with known or accepted relationships based on geographical origin, parentage and morphological characters. Genotypes could be assigned to three distinct groups: pot azaleas, Kurume azaleas and Hirado azaleas. Wild ancestor species appeared to be more related to the Japanese azaleas. Intermediate cultivars could be typified as crossings with Kurume or Hirado azaleas or with wild species. Received: 3 September 1998 / Accepted: 25 March 1999