Canopy Openness Enhances Diversity of Ant–Plant Interactions in the Brazilian Amazon Rain Forest

In closed‐canopy tropical forest understory, light availability is a significant determinant of habitat diversity because canopy structure is highly variable in most tropical forests. Consequently, variation in canopy cover affects the composition and distribution of plant species via creating variable light environments. Nevertheless, little is known about how variation in canopy openness structures patterns of plant–animal interactions. Because of the great diversity and dominance of ants in tropical environments, we used ant–plant interactions as a focal network to evaluate how variation in canopy cover influences patterns of plant–insect interactions in the Brazilian Amazon rain forest. We observed that small increases in canopy openness are associated with increased diversity of ant–plant interactions in our study area, and this change is independent of plant or ant species richness. Additionally, we found smaller niche overlap for both ants and plants associated with greater canopy openness. We hypothesize that enhanced light availability increases the breadth of ant foraging sources because variation in light availability gives rise to plant resources of different quality and amounts. Moreover, greater light availability promotes vegetative growth in plants, creating ant foraging ‘bridges’ between plants. In sum, our results highlight the importance of environmental heterogeneity as a determinant of ant–plant interaction diversity in tropical environments.     

Abundance of Gall Midges on Poulsenia armata (Moraceae): Importance of Host Plant Size and Light Environment in Tropical Rain Forests1

We studied the effects of contrasting light environments on the relationship between the host plant size of Poulsenia armata and the abundance of two gall midges in a tropical rain forest in Veracruz, Mexico. The number and density of two gall morphs (i.e., laminar and vein‐petiole galls) were positively correlated with plant size only in trees found in the forest but not in gaps. The availability of foliar area of P. armata trees was greater in forest gaps than in the forest. The foliar area was positively correlated with the abundance of laminar galls in trees in forest sites, but not with vein‐petiole galls. We concluded that the abundance of two morphs of gall midges on P. armata was associated with host plant size only in the forest trees. Larger plants had more galls than small plants, although this relationship was affected by local light environments.     

A tropical epiphytic orchid uses a low‐light interception strategy in a spatially heterogeneous light environment

Light is considered a non‐limiting factor for vascular epiphytes. Nevertheless, an epiphyte's access to light may be limited by phorophyte shading and the spatio‐temporal environmental patchiness characteristic of epiphytic habitats. We assessed the extent to which potential light interception in Rodriguezia granadensis, an epiphytic orchid, is determined by individual factors (plant size traits and leaf traits), or environmental heterogeneity (light patchiness) within the crown of the phorophyte, or both. We studied 104 adult plants growing on Psidium guajava trees in two habitats with contrasting canopy cover: a dry tropical forest edge, and isolated trees in a pasture. We recorded the number of leaves and the leaf area, the leaf position angles, and the potential exposure of the leaf surface to direct irradiance (silhouette area of the leaf blade), and the potential irradiance incident on each plant. We found the epiphytes experience a highly heterogeneous light environment in the crowns of P. guajava. Nonetheless, R. granadensis plants displayed a common light interception strategy typical of low‐light environments, resembling terrestrial, forest understory plants. Potential exposure of the total leaf surface to direct irradiance correlated positively with plant size and within‐plant variation in leaf orientation. In many‐leaved individuals, within‐plant variation in leaf angles produced complementary leaf positions that enhanced potential light interception. This light interception strategy suggests that, in contrast to current wisdom, enhancing light capture is important for vascular epiphytes in canopies with high spatio‐temporal heterogeneity in light environments.     

Rain forest promotes trophic interactions and diversity of trap-nesting Hymenoptera in adjacent agroforestry

1. Human alteration of natural ecosystems to agroecosystems continues to accelerate in tropical countries. The resulting world-wide decline of rain forest causes a mosaic landscape, comprising simple and complex agroecosystems and patchily distributed rain forest fragments of different quality. Landscape context and agricultural management can be expected to affect both species diversity and ecosystem services by trophic interactions. 2. In Central Sulawesi, Indonesia, 24 agroforestry systems, differing in the distance to the nearest natural forest (0-1415 m), light intensity (37.5-899.6 W/m(-2)) and number of vascular plant species (7-40 species) were studied. Ten standardized trap nests for bees and wasps, made from reed and knotweed internodes, were exposed in each study site. Occupied nests were collected every month, over a period totalling 15 months. 3. A total of 13,617 brood cells were reared to produce adults of 14 trap-nesting species and 25 natural enemy species, which were mostly parasitoids. The total number of species was affected negatively by increasing distance from forest and increased with light intensity of agroforestry systems. The parasitoids in particular appeared to benefit from nearby forests. Over a 500-m distance, the number of parasitoid species decreased from eight to five, and parasitism rates from 12% to 4%. 4. The results show that diversity and parasitism, as a higher trophic interaction and ecosystem service, are enhanced by (i) improved connectivity of agroecosystems with natural habitats such as agroforestry adjacent to rain forest and (ii) management practices to increase light availability in agroforestry, which also enhances richness of flowering plants in the understorey.     

光强因子对少花桂幼苗形态和生理指标及精油含量的影响

光是影响植物生长的重要因子之一。它不仅能够影响植物的光合作用,同时,光还以环境信号的形式作用于植物,通过光敏色素等作用途径调节植物生长、发育和形态建成,使植物更好地适应外界环境。除此之外,光还可以影响植物的初生代谢过程和次生代谢。因此提高植物体内重要次生代谢产物,光的因素不可忽视。少花桂(Cinnamomum pauciflorum)是樟科樟属多年生常绿小乔木,其体内含有精油,鲜叶含油量可达3．5％,比黄樟树根含油量高出1倍左右,精油中黄樟油素纯度高达95％以上。以少花桂为材料,采用人工模拟不同生境的光照条件,探讨光强因子对少花桂生长及精油含量的影响,以求对其生产提供理论指导。通过窗纱遮荫实现对其生境光的控制,研究了光强因子对少花桂幼苗形态结构、水分状况、光合指标、生物量、香桂油含量和纯度的影响。结果表明：随生境相对光照强度的减弱,叶片厚度、叶片上表皮厚度、下表皮厚度、栅栏组织、海绵组织厚度、根冠比等都呈现降低的趋势;而平均单叶面积却呈现出增加的趋势;株叶面积在61．5％的全光照下有所增加,而在33．8％和15．4％全光照条件下大幅度减小;遮荫条件下生长的少花桂幼苗根系相对不发达,根冠比小;生境的光照强度会影响植株的水分蒸腾,从而影响含水量。在同样光照下,全光照条件下生长的少花桂幼苗保水能力最强,其次是61．5％全光照,最差的是15．4％全光照。少花桂幼苗的光饱和点、光补偿点随生境中的光强减弱而降低。过度遮荫条件下生长的少花桂幼苗CO2补偿点明显高于自然条件下生长的少花桂幼苗;随生境中的光强度的减弱其光呼吸速率升高,单位叶面积的叶绿素含量增加．Chla／Chlb值减小。遮荫处理后,不同光照条件下生长的少花桂幼苗的质量增加存在显著差异。遮荫过程中61．5％、33．8％和15．4％全光照条件下生长的少花桂幼苗叶片鲜质量的增长速率分别为全光照的1．6倍、1．2倍和0．77倍。香桂油含量以61．5％和33．8％全光照为多,均比全光照高出5％左右,而15．4％全光照叶片含油量又较全光照少5％左右。香桂油中黄樟油素纯度,以33．8％、15．4％全光照生境下的少花桂幼苗叶片为高。少花桂幼苗轻微遮荫(61．5％全光照)栽培．能获得较高的枝叶产量和香桂油产率．重度遮荫(33．8％、15．4％全光照)能获得纯度较高的黄樟油素。     

Leaf traits determine the growth-survival trade-off across rain forest tree species

A dominant hypothesis explaining tree species coexistence in tropical forest is that trade-offs in characters allow species to adapt to different light environments, but tests for this hypothesis are scarce. This study is the first that uses a theoretical plant growth model to link leaf trade-offs to whole-plant performances and to differential performances across species in different light environments. Using data of 50 sympatric tree species from a Bolivian rain forest, we observed that specific leaf area and photosynthetic capacity codetermined interspecific height growth variation in a forest gap; that leaf survival rate determined the variation in plant survival rate under a closed canopy; that predicted height growth and plant survival rate matched field observations; and that fast-growing species had low survival rates for both field and predicted values. These results show how leaf trade-offs influence differential tree performance and tree species' coexistence in a heterogeneous light environment.     

Effect of two natural light regimes and nutrient addition on the forest herb Begonia decandra (Begoniaceae)

The effect of two natural light-growing conditions (understory versus light gaps) and the interaction with nutrient availability (through fertilization) were studied in the understory herb Begonia decandra, in the Luquillo Experimental Forest in Puerto Rico. Sixteen potted plants obtained from cuttings were randomly chosen and distributed in each of eighth forest environments (four light gaps and four understories), for a total of 128 plants. Fertilizer was applied to half of the plants in each site. After seven months in the two given microenvironments, increased light and fertilization resulted in greater growth and some changes in the biomass allocation patterns. All measured variables responded similarly to reported changes for tree seedlings and saplings from other tropical and subtropical regions. Total growth parameters (height, biomass and leaf area) were very sensitive to increases in the main resource (light). The addition of nutrients was less important in producing changes in the allocation variables (root to shoot ratio, leaf area ratio, and specific leaf mass) under conditions of high light availability. Changes due to nutrient levels were relatively greater on plants grown under under-story conditions. Also, small light differences among sites can cause significant changes in the variables related to total growth. Lastly, plant mortality in the nutrient treatments was found to be independent of mortality in two forest light environments. Some hypotheses about resource acquisition and plant growth are not supported by this data.     

Effect of agricultural land‐use change on the structure of a temperate forest ant–plant interaction network

Studies on the responses of ant–plant interactions to land‐use change have mainly focused on tropical habitats, usually without considering the impacts on the structure of interaction networks. Here we show that land‐use modifies the structure of the ant–plant interaction networks in a temperate habitat. Ant–plant interactions and plant diversity were recorded in an oak forest and agricultural land in central Mexico. We registered five ant species in the oak forest, and four ant species in the agricultural land. Plant diversity was higher in the agricultural land than in the oak forest. In the ant–plant networks of both sites, our results showed a higher dependence of ants on the plants on which they feed than vice versa, and the ants Formica spp. and the plants Barkleyanthus salicifolius were the species with the most strength and greatest influence in the network structure. The ant–plant network in the oak forest showed a nested structure. However, the network at the agricultural land site showed non‐nestedness; the identity of both ants and plants with the highest values of specialization was different and the number of ant species in the network was decreased, but the number of plant species with which they interacted significantly increased. Both ant–plant networks were equally tolerant to simulated extinction of individual species. We conclude that temperate forest ant–plant networks can be inherently fragile and susceptible to the effects of agricultural land‐use change, not on the number of interacting species but on their identity.     

飞机草对热带珊瑚岛的生理生态适应性

入侵植物对环境的适应性是探究其入侵性的基础.西沙群岛为热带珊瑚岛,具有高盐、强碱、高温、强光、干旱等恶劣环境特点.近年来,西沙群岛的一些原生植物群落中出现了飞机草(Chromolaena odorata)入侵现象,可能会对当地脆弱的生态系统造成严重的危害.该文研究了西沙群岛原生植物群落林窗中和文昌市郊飞机草的叶片形态解...     

西双版纳热带雨林林窗空间分布格局及其特征数与林窗下植物多样性的相关性

林窗作为森林群落中一种重要的干扰方式, 对林下物种构成有着重要的影响。开展林窗空间格局及其特征指数与林下植物多样性关系研究对于探讨林窗对林下生物多样性的影响有重要意义, 有助于进一步了解群落动态, 在物种多样性保护方面也具有指导作用。本研究在西双版纳热带雨林地区随机选取3块大小为1 ha的热带雨林为研究样地, 采用轻小型六旋翼无人机搭载Sony ILCE-A7r可见光传感器, 分别获取各个样地的高清数字影像, 结合数字表面高程模型以及各个样地的地形数据用以确定各样区的林窗分布格局, 并进一步提取出各林窗的景观格局指数。结合地面样方基础调查数据, 对各样地各林窗下植物多样性情况进行统计, 旨在分析热带雨林林窗空间分布格局以及林窗下植物多样性对各林窗空间格局特征的响应情况。研究表明, 西双版纳州热带雨林林窗呈大而分散的空间分布, 林窗空间格局特征指数如林窗形状复杂性指数、林窗面积都与林下植物多样性呈显著正相关关系。在面积小的林窗下, 较之林窗形状复杂性因子, 林窗面积大小对林下植物多样性影响更显著; 在面积达到一定程度后, 相对于面积因子, 林窗形状复杂性指数对林下植物多样性影响更显著, 各样地林窗皆趋于向各自所处样地顶极群落发展。     

植物警戒色的研究进展

植物为适应植食动物的取食压力而进化出物理、化学等多种防御机制,以把植食伤害降到最低程度,但动物不断的抽样尝试行为还是让有防御行为的植物受到伤害。因此,向潜在的植食动物传达自己的防御信号对植物是有益的。颜色作为一种稳定有效的视觉信号通常是花和果实的诱惑信号,某些情况下也是一种警戒防御信号,植食动物经过抽样学习后能识别这种防御信号并主动回避,从而形成了植物的警戒色。起源于猎物-捕食者关系的警戒色理论在动物界得到了充分研究,但植物警戒色却不为人所知,直到2001年Hamilton关于秋季树叶颜色的信号假说公开发表后,才引起人们对植物警戒色的初步研究。如今在早秋变色树种、幼叶、多剌植物、植物繁殖器官都发现了警戒色的一些例证,尽管有些还不太明确甚至存在争议,但至少为植物警戒色的进一步研究奠定了基础。植物营养体颜色在时空上的多态性变化值得人们更深入地研究,防御权衡假说也预示了防御有害植食动物的警戒作用存在于繁殖器官的可能性,研究它们生理和生态适应意义有利于人们更深程度地理解植物-动物之间的复杂关系。     

A pre‐adaptive approach for tropical forest restoration during climate change using naturally occurring genetic variation in response to water limitation

Effective reforestation of degraded tropical forests depends on selecting planting material suited to the stressful environments typical at restoration sites that can be exacerbated by increased duration and intensity of dry spells expected with climate change. While reforestation efforts in nontropical systems are incorporating drought‐adapted genotypes into restoration programs to cope with drier conditions, such approaches have not been tested or implemented in tropical forests. As the first effort to examine genetic variation in plant response to drought in a tropical wet forest, we established a watering experiment using five replicated maternal lines (i.e. seedlings from different maternal trees) of five dipterocarp species native to Borneo. Apart from the expected species level variation in growth and herbivory (3‐fold variation in both cases), we also found intraspecific variation so that growth in some cases varied 2‐fold, and herbivory 3‐fold, among genetically different maternal lines. In two species we found that among‐maternal line variation in growth rate was negatively correlated with tolerance to water limitation, that is, the maternal lines that performed the best in the high water treatment lost proportionally more of their growth during water limitation. We argue that selection for tolerance to future drier conditions is not only likely to impact population genetics of entire forests, but likely extends from forest trees to the communities of canopy arthropods associated with these trees. In tropical reforestation efforts where increased drought is predicted from climate change, including plant material resilient to drier conditions may improve restoration effectiveness.     

Elevation‐dependent effects of forest fragmentation on plant–bird interaction networks in the tropical Andes

Tropical forests harbor diverse ecological communities of plants and animals that are organized in complex interaction networks. The diversity and structure of plant–animal interaction networks may change along elevational gradients and in response to human‐induced habitat fragmentation. While previous studies have analyzed the effects of elevation and forest fragmentation on species interaction networks in isolation, to our knowledge no study has investigated whether the effects of forest fragmentation on species interactions may differ along elevational gradients. In this study, we analyzed main and interaction effects of elevation and forest fragmentation on plant–frugivore interaction networks at plant and bird species level. Over a period spanning two years, we recorded plant–frugivore interactions at three elevations (1000, 2000 and 3000 m a.s.l.) and in two habitat types (continuous and fragmented forest) in tropical montane forests in southern Ecuador. We found a consistent effect of elevation on the structure of plant–frugivore networks. We observed a decrease in the number of effective bird partners of plants and, thus, a decline in the redundancy of bird species with increasing elevation. Furthermore, bird specialization on specific plant partners increased towards high elevations. Fragmentation had a relatively weak effect on the interaction networks for both plant and bird species, but resulted in a significant increase in bird specialization in fragmented forests at high elevations. Our results indicate that forest fragmentation may have stronger effects on plant–frugivore interaction networks at high compared to low elevations because bird species richness declined more steeply towards high elevations than plant species richness. We conclude that conservation efforts should prioritize the maintenance of consumer diversity, for instance by maintaining stretches of continuous forest. This applies in particular to species‐poor communities, such as those at high elevations, as the ecological processes in these communities seem most sensitive towards forest fragmentation.     

Insect herbivory declines with forest fragmentation and covaries with plant regeneration mode: evidence from a Mexican tropical rain forest

The consequences of tropical forest fragmentation on herbivory are poorly understood. The limited evidence suggests that forest fragmentation can have positive, negative or neutral effects on herbivory. Inconsistencies may be partly explained by plant interspecific variation and differential responses related to plant life history. In this study we examined the effects of forest fragmentation and plant regeneration mode (shade‐tolerant and light‐demanding species) on sapling herbivory using a large sample of the community (97 species, representing 25% of the woody flora of the study site), and a subset of species shared by forest fragments and continuous forest. For the latter, we also analyzed the effects of species identity on variation in herbivory. Also, for the shared species we used two techniques to measure herbivory: standing herbivory (i.e. instantaneous, actual damage) and cumulative herbivory (i.e. damage, accumulated over time, on initially intact leaves). Insect herbivory was the predominant type of damage in the two forest types, and standing herbivory at both the community and the shared species level was significantly higher in continuous forest than in fragments. Considering shared species, both standing and cumulative herbivory were significantly higher in light‐demanding than in shade‐tolerant species. Cumulative herbivory also showed a significant interaction between forest fragmentation and plant regeneration mode, whereby a significant decline in herbivory in fragments was driven by reduced herbivory in shade‐tolerant species, whereas for light‐demanding species herbivory did not change significantly, due to contrasting species‐specific responses. We conclude that tropical forest fragmentation reduces insect herbivory, but this depends on plant regeneration mode and species identity. These changes could have effects on plant regeneration and diversity in forest fragments via long‐term demographic consequences.     

Special ecological effects of ravines in Danxia Landform, China

Danxia Mountain in Guangdong Province was investigated on the special ecological effects of ravines in Danxia Landform. The results showed that its geomorphologic ecological effects could be manifested in the following two aspects. Firstly, multitudinous ridgy stone peaks and hollow ravines were shaped in the forming process of Danxia Landform. Ecological factors were different between the ravines and other open regions. Relatively close microclimate and high moisture condition in ravines could provide suitable living environment for tropical species which preferred hot and humid environment. Geomorphologic environment in ravines, like smooth degree of surrounding cliffs, would affect intensity of light reflected into ravines. All the aspects had influence on the temperature and humidity in ravines. Secondly, the special ecological effects of ravines in Danxia Landform provided a possibility to gestate a group of taxa with greater tropical characteristics. There, tropical plant flora was markedly increased in comparison with other vegetations at similar latitude. Tropical plant distributions were obvious in most ravines of Danxia Landform. Its proportion was 10% more than that of other regions at the similar latitude. The ravines in Danxia Landform were rich in liana, ferns and other plants with high water-logging resistance. Collectively, the phenomena that some typical species in south subtropical regions appeared in mid-subtropical regions revealed latitudinal shift of plant distribution. This kind of climax communities, which were coordinated and balanced with their geomorphologic environments due to the special ecological effects of ravines in Danxia Landform, could be called geo-climax communities.     

丹霞地貌沟谷生态效应

以广东省丹霞山为研究实例,探讨丹霞地貌特殊的沟谷生态效应.结果表明,丹霞地貌的特殊沟谷生态效应体现在以下两个方面:第一是丹霞地貌演变过程中形成了众多石峰隆起和沟谷凹陷,特殊的地貌环境使得沟谷中的生态因子与其它非丹霞地貌开阔区域产生差异,小气候相对封闭,水湿条件极好,为喜高温高湿的热带物种提供了较好的生存环境;沟谷所处位置的地理环境,如四周崖壁的光滑程度会影响到太阳光反射到沟谷的光强,这些都会对沟谷中的温湿度产生影响.第二是丹霞地貌特殊的生态条件,为沟谷地带孕育出一批热带性较强的分类群提供了可能,与相近纬度的诸多植被相比,丹霞地貌植物区系热带性明显增强,热带分布区类型所占比重比同纬度区域要大10%以上,大多数沟谷中热带性物种分布现象比较明显,藤本分布较多,蕨类植物也较丰富,耐水湿的植物区系发育良好;这实际上造成了植物水平分布上的移位,使中亚热带区域中分布有南亚热带甚至热带区域的物种,出现了由于其特殊的沟谷地貌效应而形成的与其地貌条件保持协调和平衡的演替顶级群落类型,称为地貌顶级群落.     

热带雨林剑叶凤尾蕨(Pteris ensiformis)对光强变化的适应

野外调查表明剑叶凤尾蕨能适应不同的光环境,本研究测定剑叶凤尾蕨在两种不同光环境下的适应能力,在热带雨林林下和林窗生长40d后,林下生长的剑叶凤尾蕨比林窗生长的植株有较多的叶片数,大的冠幅,高的叶绿素含量和表观量子效率。同时。林下生长的剑叶凤尾蕨有高的光化学效率和较低的非光化学耗散能力,这说明低光植物表现出有较高的能量转换能力,而两种光强生长的剑叶凤尾蕨最大光合放氧速率相似。这可能与在高光下的非辐射耗散的提高和光合机构的损伤有关,研究结果表明,剑叶凤尾蕨通过光合器官的调整对不同光强的适应。以促进剑叶凤尾蕨在不同光环境的生长能力。     

Effects of fire and agricultural practices on neotropical ant communities

Fire is extensively used in agricultural management in Mexico. There is little information on the effects of those practices on the abundance and diversity of animals that live within these forest soils. We studied the effect of slashing, burning and land use in a tropical deciduous forest on ant communities in the State of Jalisco, Mexico. The original vegetation (tropical deciduous forest) was modified into a corn field. Sampling was carried out in five stages: before slashing, after slashing, after burning, after seeding and after harvest. We found that very severe fires greatly reduced ant diversity. The most important effect of fire was the reduction of ant density, and the change of species composition and trophic guilds. These changes are relevant in the recycling process of energy in the ecosystem.     

Seedling interactions in a tropical forest in Panama

Competition is believed to be a central force limiting local diversity and controlling the structure of plant communities. However, it has been proposed that the stressed understory environment limits total understory plant density to such low levels that competitive exclusion cannot be an important factor limiting the local diversity of understory plants. To evaluate the importance of inter-seedling competition, we performed a seedling competition experiment with five shade-tolerant species in a tropical moist forest in Panama. Three-month-old seedlings were transplanted into the forest singly or with their roots intertwined with a single conspecific or heterospecific seedling in all pairwise species combinations. If competition is important, performance (survival, stem height, and number of leaves after one and six years) would be expected to be lowest with a conspecific neighbor and greatest without a neighbor. The experiment was replicated in five 0.24-m² plots at each of 20 sites in tall secondary forest. To test whether seedling performance differed among treatments we fitted linear mixed models (LMM) and generalized linear mixed models (GLMM), treating species identity and microsite (site and plot) as random effects. The five shade-tolerant study species all experienced good establishment with relatively high survival and growth rates. The neighbor treatment consistently affected seedling performance, but the effect was always very small, both in absolute terms and relative to the much stronger species and microsite effects. Seedlings with a conspecific neighbor consistently performed worse than seedlings with a heterospecific neighbor, but having no neighbor generally did not cause superior performance relative to the other treatments. We conclude that direct competitive interactions are relatively unimportant among understory plants in humid tropical forests.     

Phytochromes and photomorphogenesis in Arabidopsis.

Plants have evolved exquisite sensory systems for monitoring their light environment. The intensity, quality, direction and duration of light are continuously monitored by the plant and the information gained is used to modulate all aspects of plant development. Several classes of distinct photoreceptors, sensitive to different regions of the light spectrum, mediate the developmental responses of plants to light signals. The red-far-red light-absorbing, reversibly photochromic phytochromes are perhaps the best characterized of these. Higher plants possess a family of phytochromes, the apoproteins of which are encoded by a small, divergent gene family. Arabidopsis has five apophytochrome-encoding genes, PHYA-PHYE. Different phytochromes have discrete biochemical and physiological properties, are differentially expressed and are involved in the perception of different light signals. Photoreceptor and signal transduction mutants of Arabidopsis are proving to be valuable tools in the molecular dissection of photomorphogenesis. Mutants deficient in four of the five phytochromes have now been isolated. Their analysis indicates considerable overlap in the physiological functions of different phytochromes. In addition, mutants defining components acting downstream of the phytochromes have provided evidence that different members of the family use different signalling pathways.