Ecophysiological Responses Of Five Common Shrubs To Water And Light In The Warm Temperate Zone

Drought is becoming more serious as global climate change in the world, coupled with light environmental heterogeneity and disturbance because of natural and man-made factor, forest ecosystems is suffering growing pressure to survive. The relationship of plants and environment, especially the changing environment, is foucused by ecologists once again. Plants adapt different environment according to the harmonization of root, stem and leaf. With the modern controlled experimental method and instrument analysis method to study the ecophysiological adaption mechanism to environment, is the important research aspect of global changing ecology. In this study, we chose Vitex negundo var. heterophylla as the main research objects. The species is the widely distributed in the shrub layer of north China. We explained why this species is so dominative of shrub layer in warm temperate zone from the growth characteristics and the response mechanism to water and light. We compared the leaf traits and biomass partitioning of Vitex negundo var. heterophylla, Ziziphus jujuba var. spinosa, Grewia biloba var. parviflora, Amorpha fruticosa, and Rhus typhina. There was difference among the five shrub species from the ecophysiological aspect. The results will help to understand the mechanisms of adaptation and niche differentiation of coexisting species and the likely species variation trend with the succession and climate change in the future. It may also provide evidences for vegetation restoration and establishing the blueprints for local ecological environment and sustainable development.A potted experiment was carried out in the greenhouse to study the physiological and morphological adaptation of Vitex negundo var. heterophylla seedlings to different soil water content. With the aggravation of drought, net photosynthetic rate, transpiration rate, stomatal conductance and maximum quantum yield of PS2 became smaller, but the degressive degree was not consistent between photosynthetic rate and transpiration rate, stomatal closure was the dominant limitation at mild to moderate drought, while metabolic impairment became dominant at severe drought. Plant growth was inhibited under water stress, and consequently, all parts of the biomass decreased markedly with drought, but the relative growth rate was not affected under mild and moderate drought. Seedling growth was nearly stagnant, metabolism was affected, seedlings were withered and more was invested in leaf to photosynthesis at severe water stress. Water supply above 15% Field Capacity is recommended for the seedlings for vegetation restoration.Vitex negundo var. heterophylla seedlings were subjected to different light conditions which were carried out with woven black nylon nets. The adaption to the irradiance variation was also investigated to simulate gap formation. There was good adjustment to different light conditions:light absorbed efficiency was improved under low light while photoinhibition was avoided under high light. The lower LMA, higher chlorophyll content, lower chlorophyll a/b and lower root to shoot ratio were all the strategys to ensure the light absorbing adequately. It showed excellent heat dissipation ability in high irradiance, which was used to avoide damage to the leaf. After gap formation, the old leaves and new leaves adapted the new environment together. Fot old leaves, the physiological index recovered completely, while LMA only recovered partially. For new leaves, leaf water content became higher, LMA became lower, chlorophyll content became higher, and there were higher maximum quantum yield and lower non-photochemical quenching in low light (LL)-high light (HL) treatment, which means that the leaves were healthier. There will be heavy photoinhibition after transformation from low light to high light, so the elevation of physiological activity is the adaption at individual level. The biomass increase was not the most which was also caused by the heavy photoinhibition in LL-HL treatment. The elevation of physiological activity and the steady investment to leaves were very important to adapt new environment.Five typical habitats of V. negundo var. heterophylla were selected on the hill, i.e. open forest, edge of deciduous broadleaved forest, understory of deciduous broadleaved forest, gap of evergreen coniferous forest, and understory of evergreen coniferous forest. Leaf traits were analysed from different months. Temporal and spatial variation of leaf traits of the shrub were studied in the regional scale. We found that all the leaf traits, including specific leaf area (SLA), leaf nitrogen (N) and phosphorus (P) content, chlorophyll (Ch1) content, and chlorophyll fluorescence, showed both temporal and spatial variation. The seasonal variation was consistent in different habitats. Light condition was the determinative factor in spatial difference. Plants under shade developed light-capturing behavior at leaf level (lower SLA) and cellular level (higher Ch1/N ratio and lower Ch1 a/b). Soil condition related to climate was the determinative factor in temporal difference. We should pay more attention to analysis when collecting leaves from different months, in order to prevent inaccurate conclusions appearing. Ontogenetic impact to leaf traits also existed over the entire growth season, such as the smaller SLA with growth and higher Chl/N in June. The smaller SLA with age could ascribe to an overall increase in leaf density, which is also associated with accumulation of carbon-rich chemicals and the enhanced lignification of cell walls. The distinct N-allocation pattern enables higher maximum photosynthetic nitrogen-use efficiency in flcwer-leaves to compensate the N allocation to flowers.The combined impact of drought and shade on Vitex negundo var. heterophylla and Ziziphus jujuba var. spinosa, in terms of morphological plasticity, was studied. The interaction of light and water was orthogonal in V. negundo var. heterophylla, but it remained inconclusive in Z. jujuba var. spinosa. Effects of drought and shade on biomass allocation were orthogonal, while effects on biomass production were not orthogonal in Z. jujuba var. spirosa. V. negundo var. heterophylla captured irradiance efficiently with relatively long common petiole and petiolule, while Z. jujuba var. spinosa maintained higher branches to absorb light. Under deep shade, V. negundo var. heterophylla showed larger specific leaf area (SLA), lower ratio of leaf length to width and higher leaf dry mass ratio; while Z. jujuba var. spinosa showed larger SLA and ratio of leaf length to petiole length. In both species, the branch number became smaller, mean leaf space of stem was lower, and root dry mass ratio was higher under drought, but leaf morphology showed little variance to water deficit. The short petiole and waxen leaves are the important characters to enhance drought tolerance in Z. jujuba var. spinosa. Different morphological characters and different responses to light and water endowed the two species with different ecological characteristics. V. negundo var. heterophylla appears to be more shade-tolerant, while Z. jujuba var. spinosa is more drought-tolerant. The species-specific adaptation of drought and shade may be an important mechanism driving forest community dynamics in temperate forests.In order to compare the ecophysiological difference among the five common shrubs in the warm temperate zone, potted seedlings of Vitex negundo var. heterophylla, Ziziphus jujuba var. spinosa, Grewia biloba var. parviflora, Amorpha fruticosa, and Rhus typhina were cultured in the greenhouse. We found that the five species showed different ecophysiological characters. From the leaf physiological aspect, Amorpha fruticosa and Rhus typhina showed a photosynthetic superiority and strong ability to adapt variable irradiance, which is benefit to use the sunfleck. Vitex negundo var. heterophylla and Ziziphus jujuba var. spinosa had conservative resource use strategy; it is the advantage to use irradiance at noon for the former species. The gas exchange ability was higher in Grewia biloba var. parviflora, but the leaves showed somewhat shade-grown character. According to fluorescence analysis, the maximal electron transport rate is the lowest and the recovery of effective quantum yield is the slowest. There is always corresponding relation between leaf structural traits and leaf physiological trais. Grewia biloba var. parviflora showed the lowest LMA and chlorophyll a/b, which verified the shade grown character. Amorpha fruticosa showed the highest supporting structure ratio, corresponding to the moveable leaves. The higher photosynthetic ability and well drought tolerance are the important reasons that the two alien species could settle down. There is no risk of Amorpha fruticosa to the native ecosystem while Rhus typhina showed the strong invasive ability. We should pay more attention when we introduce the alien species to the native ecosystem. Vitex negundo var. heterophylla is the widely distributed shrub species in the warm temperate zone because of the well diffusivity, conservative resource use strategy, and good recovery ability after disturbance.In conclusion, the ecophysiological characters from leaf scale to whole plant scale and well adaption mechanism to light and water enable Vitex negundo var. heterophylla becoming the widely distributed shrub species in the warm temperate zone. The temporal and spatial variation of leaf traits are also the adaption to different environment. The different responses to water and light are the reason of niche differentiation between Vitex negundo var. heterophylla and Ziziphus jujuba var. spinosa. Vitex negundo var. heterophylla, Ziziphus jujuba var. spinosa, Amorpha fruticosa, Rhus typhina, and Grewia biloba var. parviflora show different ecophysiological characters, which is very important to species selection for vegetation restoration and succession of shrub layer.