| Orchidaceae is one of the largest families of flowering seed plants,and most species are perennial herbs.Cypripedium is an important genus in subfamily of Cypripediodeae.Due to the peculiar flower appearance and high economical,ornamental and medicinal values,all Cypripedium species have been recognized as global hot spots.However,overcollection and severe destruction of their original habitat result in the sharp decline of the population of Cypripedium,making this genus as an endangered group.The establishment of protection strategy of Cypripedium plants requires the detailed basic biology of Cypripedium and population monitoring,such information will be helpful to reveal the mechanism of endangered status of Cypripedium.In this study,we intended to study the different patterns in population structure and individual functional traits of Cypripedium at different spatial and temporal scales,to explore the response patterns of Cypripedium populations and individuals to environmental changes.This study investigated the change patterns of functional traits of the above-and belowground organs of both Cypripedium macranthos and C.guttatum along the large-scale geographical gradient in Northeast China.The distribution of populations of two Cypripedium species in Northeast China were assessed,as well as in Nenjiang in a four-years' monitoring.In Northeast China,the annual dynamics of population age structure and individual growth characteristics of C.macranthos and C.guttatum were also assessed,as well as their static life table,fecundity and numeric.In Northeast China,compared with the understory plants,the leaf and root functional traits variation of C.macranthos,C.guttatum,C.×ventricosum and C.calceolus plants after 3 years of cultivation in nursery were measured.These studies would not only help us to understand the response patterns of root,stem and leaf functional traits to environmental changes,but also help us to figure out the adaptation mechanisms and survival strategies of Cypripedium to environmental changes.The main findings are as follows:1.Along the large-scale gradient in Northeast China,significant changes of the aboveground leaves and stems and underground roots of C.macranthos and C.guttatum were observed,as well as the coordinated variations to long-term environmental changes.With the increasing of latitude,the annual average temperature and annual precipitation decrease,but the aridity index increases.Thicker leaf,higher stomatal density,lower specific leaf area(SLA),thicker root and lower specific root length(SRL)were more general in high latitude areas for both Cypripedium species.This pattern was mainly related to the tough environment condition in the north.Both thicker leaf and root were more resistant to adverse environments,ensuring plants could adapt to relatively cold habitats.Even though,the specific stem length(SSL)and stem tissue density were relatively independent of the climate factors in both Cypripedium,the proportion of the stem vascular bundles in the stem cross-section decreased with the increase of latitude,which might be related to the continuity of the vascular system within plant.Because the environmental condition in the south was relatively adaptable,warm and wet,which would improve plant growth.Thus,relatively more fixed carbohydrates in leaves and more absorbed water and nutrients in root would be transported in southern Cypripedium plants than the northern ones.It was necessary to construct stem with high efficient transportation tissue.Besides,there was a close relationship between SLA and SRL for C.macranthos,but not for C.guttatum.Such close relationships were also found in other anatomical and morphological traits.These patterns reflected the species specific,as well as the different survival strategies of Cypripedium in adapting to long-term environmental changes,which was of great significance for maintaining plant survival and population stability.2.We conducted a four-years dynamic monitoring of the population of C.macranthos and C.guttatum in Nenjiang region,including the plant morphological growth indicators,age structure,which showed obvious annual dynamics.About the population distribution patterns in two Cypripedium species,14 sites were also selected in Northeast China.Both populations were clustered,which was general in northeastern.The plant growth characteristics showed significant intra-and inter-specific variations.Compared with C.guttatum plants,C.macranthos ones were taller and thicker,but similar in seed setting.In the four years' consecutive observations,strong plants and high seed setting were found in the year with a high temperature and rainfall.Although the higher seed setting rate in both Cypripedium,the mature seed setting rate was lower.In addition,within the populations of both Cypripedium,the proportion of seedlings was the similar to the breeding ones,which was conducive to maintaining the stability and development of the populations.This was mainly due to the both efficient sexual and asexual reproduction ways.3.In the four-years dynamic monitoring in the Northeast China,the individual plant within population were divided into different age classes,the static life table and population fecundity table were compiled,the numeric dynamics of both Cypripedium populations were also predicted by the Leslie matrix and density-dependent growth model.The proportion of seedling of both Cypripedium were relatively high.The mortality rate of young plants and older ones were also high,indicating the expanding population.The important fecundity indicators were similar in two Cypripedium,net growth rate Ro>1,intrinsic growth rate rm>0,and population growth rate ?>1,which also directly confirmed that the Cypripedium population was stable and expanding.This was related to the effective sexual and asexual reproduction ways.According to the results of the density-dependent growth model,the populations of C.macranthos and C.guttatum would reach saturation after a long period.These results meant that biological traits of two Cypripedium population account for their continuous and successful development,man-made commercial activity and original habitat destruction were the main reason for them being endangered.Therefore,protecting the natural habitat,in-situ conservation is an effective way to maintain the Cypripedium population.4.In the ex-situ cultivation of Cypripedium in Northeast China,the increased of light density in the short-term altered environmental condition reduced the significant variations in leaf and root functional traits,including morphology,anatomy and physiology among C.macranthos,C.guttatum,C.×ventricosum and C.calceolus.Compared with the understory,the light radiation was higher in nursery,generally,leaf tended to be thicker,due to the thickening of the mesophyll cells,and stomatal density increased,but the SLA decreased.In the nursery,the photosynthetic rate increased significantly,but leaf dark respiration rate increased significantly,consequently the maximum net photosynthetic rate was decreased by 13.6%,11.5%,5.3%and 15.9%in four Cypripedium species,respectively,decreasing the carbohydrate accumulation,resulting in a decline in the growth for all Cypripedium species.These patterns were mainly manifested by the thinning and dwarfing plants in nursery.Besides,only vegetative growth was found in C.guttatum,reproductive growth disappeared.Contrary to the leaf,the root of four Cypripedium species did not show significant changes after transplanting,which may be related to the small changes in soil biology and microbial factors and the long root lifespan.The stems and leaves were short in lifespan,but high in traits plasticity,which could complete the life history in growth season with relatively low cost.Compared with the root,the changes in leaf functional traits would enable plants to adapt to the change of short-term environmental conditions quickly.It is important to supply an adaptive growing environmental conditions for Cypripedium species in the ex-situ conservation in the future,especially the light condition.Our research results showed that in order to adapt to long-and short-term environmental conditions,Cypripedium would show significant changes in population structure and plant characteristics,in terms of morphology,anatomy and physiology.In the wild,the Cypripedium populations is in the stable development,which is not at risk of being endangered.However,in the context of global climate change,the increasingly tense relationship between humans and terrestrial ecosystems will profoundly change the survival status of Cypripedium in their natural habitats.From below-ground to above-ground,from roots to leaves and stems,the coordinated responses of Cypripedium to environmental conditions would facilitate the individuals and populations to adapt to different conditions.These findings help us to understand the mechanisms of the endangerment of Cypripedium,and also provide important theoretical basis and reference for the conservation of Cypripedium in the future. |
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