紫胶虫四种寄主树次生韧皮部与周皮的解剖学观察

紫胶虫的4种寄主树钝叶黄檀、南岭黄檀、木豆和苏门答腊金合欢的次生韧皮部轴向系统均由筛管、伴胞、韧皮薄壁细胞、纤维组成,径向系统由射线组成。木豆、苏门答腊金合欢中尚有少量石细胞。苏门答腊金合欢筛管分子端壁较倾斜,具复筛板,无明显的 P-蛋白质。其余3种筛管分子端壁均为横向,具单筛板,具 P-蛋白质。根据观察结果分析,4种寄主树2—3年生枝条或具表皮,或木栓层很薄;次生韧皮部的筛管看来均具相对较长的寿命;4种寄主中有3种筛管与伴胞均属特化程度高的类型。     

降香黄檀着叶期和无叶期次生韧皮部筛分子的超微结构

利用透射电镜技术研究了生长在海南岛的热带落叶树降香黄檀(Dalbegia odorifera T.Chen)1—2年生枝条着叶期和无叶期次生韧皮部筛分子的超微结构,并就这两个时期的筛分子进行了比较。着叶期每个成熟筛分子内有一个带尾的纺锤形P-蛋白质体,主体由稠密而散乱的P-蛋白质细纤维组成,尾部呈结晶状;筛分子具有横向端壁和单筛板,在邻近筛板处,细胞壁向筛分子腔内形成明显的突起。无叶期仍然保持着与着叶期大致相同厚度的有功能韧皮部,筛分子具有正常的原生质体,P-蛋白质和筛板孔的结构也与着叶期的相同,但筛分子内有较多的淀粉粒和囊泡。     

Net nitrogen mineralization in soils under six indigenous tree species,an abandoned pasture and a secondary forest in the atlantic lowlands of costa rica

Nitrogen mineralization, nitrification potentials, pH, total N, C, extractable P and cations were measured in soils under 4-year-old, mono-specific stands of six fast-growing, native tree species, an abandoned pasture, and a 20-year-old secondary forest, as part of a study on the use of indigenous tree species for rehabilitation of soil fertility on degraded pastures at the La Selva Biological Station in the Atlantic humid lowlands of Costa Rica. Soil net nitrification potential rates were higher under two N-fixing, leguminous species,Stryphnodendron microstachyum Poepp. et Endl. (1.1–1.9 mg kg^–1 day^–1) andDalbergia tucurensis Donn. Smith (0.7–1.5 mg kg^–1 day^–1), than under the non-N-fixing trees in the plantation,Vochysia guatemalesis Don. Sm.,Vochysia ferruginea Mart,Dipteryx panamensis (Pittier) Record and Mell andHyeronima alchorneoides Fr. Allemao (0.2–0.8 mg kg^–1 day^–1). Values under the N-fixing trees were comparable to those found in secondary forest. There were no statistically significant differences in soil total N or in other nurtients between the species. Results of pH measurements done before and after incubation did not show any clear evidence of a pH drop attributable to nitrification.     

A new species of <Emphasis Type="Italic">Brasiliomyces</Emphasis> (Erysiphaceae) on <Emphasis Type="Italic">Dalbergia cultrata</Emphasis> var. <Emphasis Type="Italic">cultrata</Emphasis> from Thailand

A powdery mildew fungus on leaves of Dalbergia cultrata var. cultrata (Fabaceae) collected at the Queen Sirikit Botanical Garden in northern Thailand is proven to be a new species of the genus Brasiliomyces and is described as B. chiangmaiensis sp. nov. with light and SEM micrographs. Differences in known Brasiliomyces species are discussed, and a key to species of this genus is provided.     

Manganese and zinc toxicity thresholds for mountain and Geyer willow

Information on the heavy metal toxicity thresholds of woody species endemic to the western United States is lacking but critical for successful restoration of contaminated riparian areas. Manganese (Mn, 50-10,000 mg l(-1)) and zinc (Zn, 100-1000 mg l(-1)) toxicity thresholds were determined for Geyer (Salix geyeriana Anderss.) and mountain (S. monticola Bebb) willow using a sand-culture technique. The lethal concentration (50%) values were 3117 and 2791 mg Mn l(-1) and 556 and 623 mg Zn l(-1) for Geyer and mountain willow, respectively. The effective concentration (50%) values for shoots were 2263 and 1027 mg Mn l(-1) and 436 and 356 mg Zn l(-1) for Geyer and mountain willow, respectively. Shoot tissue values did not increase with increasing treatment concentrations. However, metals in the roots did increase consistently in response to the treatments. Metal levels in the shoot tissues were low for Zn (65-139 mg kg(-1)) and moderate for Mn (1300-2700 mg kg(-1)). Geyer and mountain willow have good resistance to Mn, possibly due to evolution in hydric soils with increased Mn availability, and may be useful for phytostabilization of soils with high levels of available Mn. Both species were affected to a greater degree by Zn as compared to Mn, but still exhibited good resistance and should be useful in remediating sites with at least moderate levels of available Zn. Based on the thresholds evaluated, Geyer willow had greater resistance to both Mn and Zn as compared to mountain willow, especially at lower concentrations in which growth of Geyer willow was actually stimulated.     

Purification of an isoflavonoid 7-O-beta-apiosyl-glucoside beta-glycosidase and its substrates from Dalbergia nigrescens Kurz

A beta-glycosidase was purified from the seeds of Dalbergia nigescens Kurz based on its ability to hydrolyse p-nitrophenyl beta-glucoside and beta-fucoside. This enzyme did not hydrolyze various glycosidic substrates efficiently, so it was used to identify its own natural substrates. Two substrates were identified, isolated and their structures determined as: compound 1, dalpatein 7-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside and compound 2, 6,2',4',5'-tetramethoxy-7-hydroxy-7-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside (dalnigrein7-O-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside). The beta-glycosidase removes the sugar from these glycosides as a disaccharide, despite its initial identification as a beta-glucosidase and beta-fucosidase.     

Fine-scale spatial genetic structure of Dalbergia nigra (Fabaceae), a threatened and endemic tree of the Brazilian Atlantic Forest

The Atlantic Forest is one of the most diverse ecosystems in the world and considered a hotspot of biodiversity conservation. Dalbergia nigra (Fabaceae) is a tree endemic to the Brazilian Atlantic Forest, and has become threatened due to overexploitation of its valuable timber. In the present study, we analyzed the genetic diversity and fine-scale spatial genetic structure of D. nigra in an area of primary forest of a large reserve. All adult individuals (N = 112) were sampled in a 9.3 ha plot, and genotyped for microsatellite loci. Our results indicated high diversity with a mean of 8.6 alleles per locus, and expected heterozygosity equal to 0.74. The co-ancestry coefficients were significant for distances among trees up to 80 m. The Sp value was equal to 0.017 and indirect estimates of gene dispersal distances ranged from 89 to 144 m. No strong evidence of bottleneck or effects of human-disturbance was found. This study highlights that long-term efforts to protect a large area of Atlantic Forest have been effective towards maintaining the genetic diversity of D. nigra. The results of this study are important towards providing a guide for seed collection for ex-situ conservation and reforestation programmes of this threatened species.     

Phenotypic plasticity to light of two congeneric trees from contrasting habitats: Brazilian Atlantic Forest versus cerrado (savanna)

The Brazilian Atlantic Forest is a typically multi-layer tropical forest, while cerrado (savanna) is a patchy habitat with different physiognomy. Despite these differences, both habitats have high light heterogeneity. Functional traits of Dalbergia nigra and D. miscolobium from the Atlantic Forest and cerrado, respectively, were evaluated under shade (25% of full sunlight) and full sunlight in a nursery experiment. We hypothesised that both species should benefit from high phenotypic plasticity in relation to light. Plasticity was estimated using the relative distance phenotypic index (RDPI). D. miscolobium had lower shoot growth under both light conditions, suggesting it has low competitive capacity in the forest environment, which could explain its limited ability to expand over areas of Atlantic Forest. The studied species exhibited photoprotection strategies under high light and improved light capture under low light. Stomatal conductance, ETR(max) (maximum electron transport rate), PPFD(sat) (saturating photosynthetically active photon flux density), chlorophyll and carotenoid content had higher RDPI than stem morphological traits. Although both species showed considerable phenotypic plasticity, D. miscolobium had higher RDPI for eight of 11 evaluated traits. This high plasticity could be one of the factors that explain the occurrence of this species in a wide range of environmental conditions, from open grassland to dense woodlands, and it could also reflect its adaptation to high light. D. nigra also had considerable plasticity and good growth performance in both shade and full sunlight, but its absence in areas of cerrado suggests that factors other than light limit its occurrence in these habitats.     

豆科黄檀属的二个新异名

在比较研究标本馆馆藏标本的基础上,确认Dalbergia esquirolii H. L関. 与滇黔黄檀(D. yunnanensis Franch.); 西盟黄檀(D. ximengensis Y. Y. Qian)与多裂黄檀(D.rimosa Roxb.)分别为同种植物,因此予以归并。     

Long‐term in situ persistence of biodiversity in tropical sky islands revealed by landscape genomics

Tropical mountains are areas of high species richness and endemism. Two historical phenomena may have contributed to this: (i) fragmentation and isolation of habitats may have promoted the genetic differentiation of populations and increased the possibility of allopatric divergence and speciation and (ii) the mountain areas may have allowed long‐term population persistence during global climate fluctuations. These two phenomena have been studied using either species occurrence data or estimating species divergence times. However, only few studies have used intraspecific genetic data to analyse the mechanisms by which endemism may emerge at the microevolutionary scale. Here, we use landscape analysis of genomic SNP data sampled from two high‐elevation plant species from an archipelago of tropical sky islands (the Trans‐Mexican Volcanic Belt) to test for population genetic differentiation, synchronous demographic changes and habitat persistence. We show that genetic differentiation can be explained by the degree of glacial habitat connectivity among mountains and that mountains have facilitated the persistence of populations throughout glacial/interglacial cycles. Our results support the ongoing role of tropical mountains as cradles for biodiversity by uncovering cryptic differentiation and limits to gene flow.