Contrasting species responses to continued nitrogen and phosphorus addition in tropical montane forest tree seedlings

Global changes in nutrient deposition rates are likely to have profound effects on plant communities, particularly in the nutrient‐limited systems of the tropics. We studied the effects of increased nutrient availability on the seedlings of six tree species in montane forests of southern Ecuador in situ. After five years of continued N, P, or N+P addition, naturally grown seedlings of each of the two most common species at each elevation (1000, 2000, and 3000 m asl) were harvested for analyses of leaf morphology, nutrient content, herbivory, and tissue biomass allocation. Most species showed increased foliar N and P concentrations after addition of each respective element. Leaf tissue N:P ratios of >20 in the control plants of all species suggest that P is more growth‐limiting in these forests than N. Leaf morphological responses to nutrient addition were species and nutrient specific, with some species (Hedyosmum purparescens, Graffenrieda emarginata) exhibiting increased specific leaf area (SLA), and others (Graffenrieda harlingii) increased leaf area ratios (LAR). Pouteria torta (1000 m) had lower SLA and LAR after P addition. Increased herbivory was only evident in G. emarginata (after N and N+P addition). Only the species from 3000 m asl modified biomass allocation after nutrient addition. In general, N and N+P addition more strongly affected the species studied at the upper elevations, whereas P addition had a similar range of effects on the species at all elevations. We conclude that the responses of the studied tropical montane forest tree seedlings to chronic N and P addition are highly species‐specific and that successful adaptation to increased nutrient availability will depend on species‐specific morphological and physiological plasticity.     

Growth and phenotypic plasticity of two tropical tree species under low light availability

两种热带树种在弱光条件下的生长和表型可塑性 根据耐荫性筛选热带雨林树种,对于在次生林富集区域中更有效地管理具有经济意义的本土树种非常重要。本研究旨在确定全株的光补偿点,比较弱光条件下Cariniana legalis和Gallesia integrifolia 幼苗生长和碳分配有关的表型可塑性。实验所用幼苗在5种光合有效辐射条件下(0.02、1.1、2.3、4.5 和5.9 mol photons m⁻² day⁻¹)培养77天,设置3个重复,并分析了生长和碳分配变量指标。结果显示,在 1.1 mol photons m⁻² day⁻¹ 条件下,C. legalis 的生长速率高于G. integrifolia,而在5.9 mol photons m⁻² day⁻¹ 条件下,C. legalis的生长速率低于G. integrifolia。不同物种间的光补偿点差异显著。根据耐阴分类标准对这两种热带树种进行分类,我们的研究结果表明,C. legalis相对较低的光补偿点和表型可塑性与生长速率有关,比G. integrifolia具有更强的耐荫性。从实际的角度来看,我们证明了两种树种之间生长和光合有效辐射变化的不同关系可以成为在森林丰富工程中比较和选择种植树种的可行工具     

Contrasting responses to ectomycorrhizal inoculation in seedlings of six tropical African tree species

Five caesalpinioid legumes, Afzelia africana, Afzelia bella, Anthonotha macrophylla, Cryptosepalum tetraphylum and Paramacrolobium coeruleum, and one Euphorbiaceae species, Uapaca somon, with a considerable range in seed sizes, exhibited different responses to inoculation by four species of ectomycorrhizal (ECM) fungi, Scleroderma dictyosporum, S. verrucosum, Pisolithus sp. and one thelephoroid sp. in greenhouse conditions. Thelephoroid sp. efficiently colonized seedlings of all of the five caesalpinioid legumes except U. somon, but provided no more growth benefit than the other fungi. Thelephoroid sp. and S. dictyosporum colonized seedlings of U. somon poorly, but stimulated plant growth more than the other fungi. The relative mycorrhizal dependency (RMD) values of the caesalpinioid legumes were never higher than 50%, whilst U. somon had RMD values ranging from 84.6 to 88.6%, irrespective of the fungal species. The RMD values were negatively related to seed mass for all plant species. Potassium concentrations in leaves were more closely related than phosphorus to the stimulation of seedling biomass production by the ECM fungi. Our data support the hypothesis that African caesalpinioid legumes and euphorbe tree species with smaller seeds show higher RMD values than those with the larger seeds.     

Spatial and temporal distribution of chloroplast DNA polymorphism in a tropical tree species

The level and the spatial organization of chloroplast DNA polymorphism were investigated in Dicorynia guianensis Hamshoff (Caesalpiniaceae) at different spatial and temporal scales. D. guianensis is a canopy tree of the rain forest that is distributed throughout the Guiana plateau in small aggregates. Twelve different haplotypes were identified using restriction analysis of polymerase chain reaction (PCR) amplified fragments of the chloroplast genome. When populations from different areas of French Guiana were compared, a clear geographical pattern of haplotype frequencies was identified along the Atlantic coast. This pattern is most likely the result of the restriction-expansion dynamics of the tropical forest during the Quaternary. At the local level, D. guianensis was characterized by a high level of within population diversity. Maintenance of within population diversity results from the dynamics of the aggregates; stochastic demography associated with the turnover of aggregates generates genetic differentiation among them. At the stand level, a strong spatial aggregation of haplotypes persisted from the adult to the seedling cohort indicating limited seed flow. There was also a strong difference in levels of diversity between the cohorts which suggested that recruitment over several years is needed in order to maintain genetic diversity during regeneration.     

海南热带山地雨林幼苗幼树的光合能力与水分利用效率

应用Li-6400光合测定系统研究了海南岛热带山地雨林林内幼苗、幼树的最大光合能力及其水分利用效率.结果表明:150个树种中,大戟科中平树的最大光合速率(Pmax)和山毛榉科竹叶栎的水分利用效率(WUE)最高,分别为13.27μmol.m-2.s-1和5.99mmol.mol-1;桃金娘科柬埔寨子楝树的Pmax和大戟科山乌桕的WUE最低,分别为1.35μmol.m-2.s-1和2.4mmol.mol-1.其中,Pmax以桑科的平均值最高,桃金娘科最低;WUE以山矾科的平均值最高,桑科最低;但各科间的差异均不显著(P>0.05).乔木和灌木之间的Pmax和WUE也无显著差异(P>0.05).Pmax随着科分布区的扩大而增大,为宽分布科>中分布科>窄分布科,且差异显著(P<0.05);WUE无显著差异.在种的层次上,随着物种分布区的扩大,植物Pmax逐渐增大,为热带亚热带温带种>热带亚热带种>热带种>海南特有种.而WUE则相反,为海南特有种>热带亚热带种>热带种>热带亚热带温带种.     

Soil phosphorus heterogeneity promotes tree species diversity and phylogenetic clustering in a tropical seasonal rainforest

The niche theory predicts that environmental heterogeneity and species diversity are positively correlated in tropical forests, whereas the neutral theory suggests that stochastic processes are more important in determining species diversity. This study sought to investigate the effects of soil nutrient (nitrogen and phosphorus) heterogeneity on tree species diversity in the Xishuangbanna tropical seasonal rainforest in southwestern China. Thirty‐nine plots of 400 m² (20 × 20 m) were randomly located in the Xishuangbanna tropical seasonal rainforest. Within each plot, soil nutrient (nitrogen and phosphorus) availability and heterogeneity, tree species diversity, and community phylogenetic structure were measured. Soil phosphorus heterogeneity and tree species diversity in each plot were positively correlated, while phosphorus availability and tree species diversity were not. The trees in plots with low soil phosphorus heterogeneity were phylogenetically overdispersed, while the phylogenetic structure of trees within the plots became clustered as heterogeneity increased. Neither nitrogen availability nor its heterogeneity was correlated to tree species diversity or the phylogenetic structure of trees within the plots. The interspecific competition in the forest plots with low soil phosphorus heterogeneity could lead to an overdispersed community. However, as heterogeneity increase, more closely related species may be able to coexist together and lead to a clustered community. Our results indicate that soil phosphorus heterogeneity significantly affects tree diversity in the Xishuangbanna tropical seasonal rainforest, suggesting that deterministic processes are dominant in this tropical forest assembly.     

Long-distance pollen flow and tolerance to selfing in a neotropical tree species

Outcrossing rates, pollen dispersal and male mating success were assessed in Dicorynia guianensis Amshoff, a neotropical tree endemic to the Guiana shield. All adult trees within a continuous area of 40 ha (n = 157) were mapped, and were genotyped with six microsatellite loci. In addition, progenies were genotyped from 22 mature trees. At the population level, the species was mostly outcrossing (tm = 0.89) but there was marked variation among individuals. One tree exhibited mixed mating, confirming earlier results obtained with isozymes that D. guianensis can tolerate selfing. A Bayesian extension of the fractional paternity method was used for paternity analysis, and was compared with the neighbourhood method used widely for forest trees. Both methods indicated that pollen dispersal was only weakly related to distance between trees within the study area, and that the majority (62%) of pollen came from outside the study stand. Using maximum likelihood, male potential population size was estimated to be 1119, corresponding to a neighbourhood size of 560 hectares. Male mating success was, however, related to the diameter of the stem and to flowering intensity assessed visually. The mating behaviour of D. guianensis is a combination of long-distance pollen flow and occasional selfing. The species can still reproduce when it is extremely rare, either by selfing or by dispersing pollen at long distances. These results, together with the observation that male mating success was correlated with the size of the trees, could be implemented in management procedures aiming at regenerating the species.     

Growth,biomass allocation and plant nitrogen concentration in Chilean temperate rainforest tree seedlings: effects of nutrient availability

Seedlings of nine southern Chilean trees were grown at three nutrient supply rates, to examine the roles of growth rate, biomass distribution and nutrient use traits in determining species natural distributions on resource gradients. Relative growth rate (RGR) showed no overall relationship with species site requirements, although RGR of fertile-site species tended to be more responsive to nutrient supply. In the low-nutrient treatment, infertility-tolerant Fitzroya cupressoides showed a higher RGR rank than a fertility-demanding species (Laurelia philippiana) which outgrew it substantially at the highest supply rate. This reversal of RGR ranks was associated with divergent nutrient use responses: at high nutrient supply both spp. had similar plant nitrogen concentrations (PNC), whereas at the low supply rate Fitzroya’s production of biomass per unit of assimilated N was twice that of Laurelia’s. However, this pattern does not appear to serve as a general explanation of the respective distributions of the study species, as RGR ranks of most species were unaltered by nutrient supply. At low nutrient availability, no clear differences in shoot:root ratio (SRR) were apparent between poor-site and fertile-site species. However, at high nutrient availability, SRR was markedly higher in the latter, resulting from differences in biomass allocation to stems (not leaves). Leaf area ratios (LAR) were higher in fertile-site species than in those tolerant of low fertility, because of differences in specific leaf area rather than leaf weight ratio. Very high LAR at high nutrient supply was characteristic of most shade-tolerant angiosperms, but not of shade-tolerant conifers. Although PNC showed no overall differences between poor- and fertile-site species, sensitivity of PNC to external supply rate was greatest in two infertility-tolerant conifers. In contrast, the angiosperm Weinmannia trichosperma, although tolerant of low fertility, responded to increased nutrient supply with greatly increased RGR and little change in PNC. Results show little trait convergence between conifers and angiosperms in adaptation both to shade and to infertile soils; i.e. fitness of different taxa in a given environment may hinge on different trait combinations. Received: 12 September 1995 /Accepted: 14 June 1996     

模拟干旱和磷添加对热带低地雨林叶凋落物分解的影响

凋落物是植物在其生长发育过程中新陈代谢的产物,是土壤有机质输入的重要途径,凋落物分解是生态系统养分循环的关键过程之一。在全球气候变化背景下,热带地区干旱事件发生的频率和强度均在增加,同时,普遍认为热带地区受磷(P)限制,所以探讨干旱胁迫和土壤磷可用性对热带地区叶凋落物分解的影响及两者是否存在交互效应十分必要,有助于了解干旱对该区叶凋落物分解的影响机制以及是否受土壤磷调控。依据植物多度、碳固持类型、叶质地,以海南三亚甘什岭热带低地雨林的4个树种叶凋落物(铁凌 Hopea exalata、白茶树 Koilodepas bainanense、黑叶谷木 Memecylon nigrescens、山油柑 Acronychia pedunculata)为实验材料,依托2019年在该区建成的热带低地雨林模拟穿透雨减少、磷(P)添加双因素交互控制实验平台,包括干旱(D -50%穿透雨)、P添加(P +50Kg P hm^-2a^-1)、模拟干旱×P添加(DP -50%穿透雨×+50Kg P hm^-2a^-1)、对照(CK)4个处理,且4种处理随机分布于3个区组,即设置了3个重复。使用常规的凋落物分解袋法探究实验处理对4个树种叶凋落物的分解系数、碳(C)、氮(N)元素动态变化的影响。结果表明:不同树种的叶凋落物因基质质量不同分解存在差异。模拟干旱处理对叶凋落物C、N损失产生抑制作用,但是对不同树种叶凋落物的抑制作用不同,原因是干旱处理通过抑制土壤分解者活动、减弱凋落物的物理破碎作用,间接抑制凋落物分解,并且由于高质量(含N量高)凋落物受微生物分解者影响较大,所以该凋落物分解受干旱抑制程度较大;P添加处理对叶凋落物C损失存在促进作用、N损失存在抑制作用,原因是土壤中P含量的升高,提高了微生物分解高C物质的能力,以及当土壤中P含量较高时,间接抑制微生物通过分解凋落物获取养分或者促进微生物优先完成自身生长代谢需要而不是合成分解凋落物所需要的酶,导致叶凋落物N损失下降;模拟干旱与P添加处理存在显著交互效应,P添加处理缓解或反转了干旱胁迫对叶凋落物分解的抑制作用。以上结果表明,不同基质质量的凋落物分解存在差异,对干旱胁迫的响应不同;在叶凋落物分解过程中,P添加促进C损失、抑制N损失;此外,在热带低地雨林,土壤中P可用性变化可调节干旱对凋落物分解的影响。     

Contrasting response of seedlings of two tropical species Clusia minor and Clusia multiflora to mycorrhizal inoculation in two soils with different pH

Differences in mycotrophic growth and response to phosphorus (P) fertilization were studied in seedlings of two woody native species: Clusia minor L. and Clusia multiflora H.B.K. from a cloud montane forest of tropical America. Greenhouse investigation was undertaken to determine the relationships between mycorrhizal dependency of host species associated with P utilization and growth in two different soils contrasting in pH (acidic and neutral) and nutrient content. Four treatments were performed: sterilized soil; sterilized soil plus 375 mg/kg of triple superphosphate (TSP); sterilized soil inoculated with Scutellospora fulgida (20 g/pot); and sterilized soil plus S. fulgida and TSP, with 10 replications per treatment for the two species. Results showed that both Clusia species presented high growth response to increasing P availability, which indicates that the root morphology (magnolioid roots) of these species is not a limiting factor for the incorporation of P from soils. Plants inoculated with arbuscular mycorrhizal fungi (AMF) in acidic soil had significantly increased shoot and root biomass, leaf area and height, in comparison to the biomass of P-fertilized plants and nonmycorrhizal plants. In neutral soil, seedlings of C. minor and C. multiflora were negatively affected by inoculation with AMF. In contrast, a significant decrease in growth was observed when inoculated plants were compared with noninoculated plants on neutral soil. Results indicate that an increase in the availability of a limiting nutrient (P) can turn a balanced mutualistic relationship into a less balanced nonmutualistic one.     

Survivorship and growth of seedlings of four dipterocarp species in a tropical rainforest of Sarawak,East Malaysia

Survivorship and growth of seedlings of four dipterocarp species (Dipterocarpus actangulus, D. globosus, Dryobalanops aromatica, Dryobalanops lanceolata) were studied for 2.5 years in a mixed dipterocarp forest in Sarawak, East Malaysia. Predispersal seed predation rates were larger forD. globosus (75%) thanD. lanceolata (27–34%) andD. aromatica (18–26%). Less than 20% of the twoDryobalanops seeds were damaged by vertebrates after seed dispersal. During the period from seed dispersal to the time when the seedlings had shed cotyledons, more dispersed seeds died in the twoDipterocarpus (ca 90%) than the twoDryobalanops (ca 60–70%). The major mortality factors during this period were uprooted and seed/seedling predation by insects or vertebrates. After the seedlings shed cotyledons, all species showed constant mortality rates of 34, 15–16, 17 and 6%/year forD. actangulus, D. lanceolata, D. aromatica andD. globosus, respectively, in the forest understorey. Mortality was lower in less shaded conditions than in more shaded ones forD. aromatica andD. actangulus, but not significantly different forD. lanceolata andD. globosus. A majority of dead seedlings were killed by fallen branches or were found standing with wilted leaves, probably due to water stress. No significant correlation was found between seed/seedling mortality and distance from mother trees or the initial density of seeds/seedings for all species. The mean leaf production was positively correlated with the estimated diffuse light factor of their habitats for each species.     

五指山常见热带树种的丛枝菌根真菌多样性

采用野外调查的方法,分析了五指山不同海拔高度7个科10种常见热带树种形成丛枝菌根(Arbuscular Mycorrhizal,AM)的状况及其根际土壤中AM真菌的多样性。结果表明,所调查的10种热带常见树种都能形成AM共生体,其菌根侵染率随寄主植物的不同,从21.8%～90.5%变化不等,同时,在10种常见植物的根系中也都观察到了AM真菌的典型结构——丛枝和泡囊。从10种植物的根际土壤中共分离到36种AM真菌,隶属于Acaulospora,Glomus,Gigaspora和Scutellospora4个属,其中,Glomus属的真菌是该地区的优势类群,其出现频度和相对多度分别为84%和56%。在所调查的10种热带常见树种中,Swietenia macrophylla根际AM真菌的孢子最丰富,密度高达7.32;Machilus namu根际的AM真菌种类则最为丰富,多样性指数达到1.6548。通过对不同海拔高度Swietenia macrophylla根际AM真菌分布的分析表明,海拔高度显著影响着AM真菌的分布,Gigaspora属的真菌随海拔高度的增加显著升高,Scutellospora属的真菌则显著降低。     

Photosynthetic responses to temperature of two tropical rainforest tree species from Costa Rica

Annual mean temperature increases will cause alterations in many ecosystem processes, which affect plants given their physiological sensitivity to temperature. That is closely related with plant growing conditions, genotype and plasticity. We studied the photosynthetic responses to instantaneous temperature changes and functional leaf traits in two tropical tree species associated with different successional positions, Zygia longifolia (early successional) and Dipteryx oleifera (late successional), in the northern lowlands of Costa Rica. We found that D. oleifera had thicker leaves and lower stomatal density, but similar specific leaf area to Z. longifolia. Maximum photosynthetic rate (A _max) and maximum RuBP saturate rate of carboxylation were higher in Z. longifolia than in D. oleifera. At 37 °C, only Z. longifolia reduced A _max and water use efficiency (WUE). But D. panamensis presented more severe effects on the quantum yield, respiration and light compensation points. The temperature response curves showed a similar optimum temperature near 27 °C for both species. On the other hand, the low and high temperature compensation points were different, with D. oleifera showing a narrower range than Z. longifolia. As a whole, we found two different strategies to avoid temperature stress: one reducing WUE (Z. longifolia), and the other one increasing metabolic rates (D. oleifera). However, the ability to withstand stressful situations may, in a larger context, negatively affect ecosystem water and carbon fluxes. Also, functional plasticity in response to temperature changes may relatively affect the ecosystem by causing long-term variations in their representation within the complex diversity mosaic of their forest habitats.     

Effect of arbuscular mycorrhizal fungi inoculation of rice seedlings at the nursery stage upon performance in the paddy field and greenhouse

We examined the effect of arbuscular mycorrhizal fungi inoculation at the nursery stage on the growth and nutrient acquisition of wetland rice (t Oryza sativa L.) under field and pot conditions. Seedlings were grown on -ray sterilized paddy soil in two types of nurseries, namely dry nursery and wet nursery, with or without arbuscular mycorrhizal fungi (AMF) inoculation which was a mixture of indigenous AMF (t Glomus spp.) spores collected from the paddy field. Five-to-six week old seedlings were transplanted to the unsterilized soil under field and pot, respectively. Mycorrhizal seedlings had higher shoot biomass under both nursery conditions 5 weeks after sowing. Mycorrhizal colonization and sporulation were 2 to 3 times higher in the dry nursery than the wet nursery at the transplanting stage. Mycorrhizal colonization of plants inoculated in the nursery remained higher than those not inoculated under both field and pot conditions. Sporulation after transplanting to field conditions was about 10 times higher than in the pot. Inoculated plants produced higher biomass at maturity under field conditions, and the grain yield was 14-21% higher than those not inoculated. Conversely, grain yield and shoot biomass were not significantly influenced by AMF colonization under pot conditions. For plants originating from the dry nursery, N, P, Zn and Cu concentrations of field-grown plants at harvest were significantly increased by preinoculation with AMF over those left uninoculated. We conclude that the AMF inoculation at the nursery stage under both dry and wet conditions increased growth, grain yield and nutrient acquisition of wetland rice under field conditions.     

Root characteristics of native plant species in relation to the benefit of mycorrhizal colonization for phosphorus uptake

We aimed to relate the root characteristics of native plants, with their benefit from mycorrhizal colonization, to assist in developing criteria for predicting plant response to mycorrhizal fungi in revegetated soils. The response of four plant species to VA mycorrhizal fungi was measured at increasing applications of phosphorus (P).The benefit of colonization for all species was large at low rates of P, but declined rapidly for some species at moderate P deficiency. Only then were length and fineness of roots and characteristics of root hairs useful in predicting relative benefit.     

海南霸王岭热带雨林常见植物丛枝菌根真菌调查

对海南霸王岭热带雨林的12科16种常见植物的丛枝菌根状况进行了调查,用碱解离-酸性品红染色法进行了真菌鉴定。结果表明,13种植物形成典型的丛枝菌根,占所调查植物的81%;3种植物没有形成丛枝菌根,占所调查植物的19%。用湿筛沉淀法从这些植物根际土壤中共分离鉴定出了3属11种丛枝菌根真菌(AMF),即无梗囊霉属(Acaulos-pora)3种,球囊霉属(Glomus)7种,巨孢囊霉属(Gigaspora)1种;其中,球囊霉属是样地的优势属。在AMF中,孔窝无梗囊霉(A.foveata)分离频率最高,在14种植物的根际土中都有发现;此外,大果球囊霉(G.macrocarpum)的相对多度最大,为59%,具有最强的产孢能力。同时,在11种植物的根中发现了深色有隔内生真菌(DSE),占调查植物的69%;其中,11种植物同时被DSE和AMF感染。     

Isolation and characterization of microsatellite markers in the tropical tree species Dicorynia guianensis (Caesalpinaceae)

Dicorynia guianensis is a canopy tree endemic to French Guyana and the first to be exploited as timber wood. To investigate levels of diversity and dynamics of gene flow in a 40‐ha study plot, highly polymorphic microsatellite markers were developed. An enriched microsatellite library was constructed and seven microsatellite primer pairs were developed. Total genomic DNA was extracted and amplified from cambium tissue from 172 adult individuals. The level of genetic diversity was found to be low. A large heterozygote deficiency was found at one locus. This was resolved by redesigning the primer set.