Ecophysiological Responses Of Different Maple Seedlings To Water, Light And Nitrogen Deposition

Global environmental change, such as regional drought and nitrogen deposition, has becoming more serious and urgent than ever before. Global change also increases the frequency of environmental heterogeneity such as drought and illumination heterogeneity, which has become hot issues in ecology. The plants living in this chaning world are therefore supposed to take steps to adapt to the new environment in prospective climate change scenario, which ecologists also pay close attention to. In this study, we choose several maple trees as the research objects and investigated the effects of various moisture, illuminations and nitrogen depositions on these maples in terms of growth morphology, leaf traits, gas exchange characteristics, chlorophyll contents and fluorescence characteristics and biomass parametrs.As native species, Acer buergerianum Miq.(Trident maple) and Acer davidii Franch (David maple) have large distributions in China. Both species play crucial roles in the forest ecosystem and has high ornamental values. Among all those environmental factors, water and light are two important factors of them, which can limit plant growth and are crucial in sylvicultural practises and in the framework of forest regeneration. Understanding their combined effects on species is fundamental for predicting the effects of global change on forest habitats since environmental factors will change concomitantly. Nevertheless, there is no consensus on how drought interacts with shade. It is variously predicted that shade may have a stronger, weaker or equal impact on seedlings at drought condition by four hypotheses in the recent literature.We performed a potted growth experiment with a wide range of water supply regime [15%,35%,55%,75%and95%of soil field capacity (FC)] combined with two illumination levels (10and66%of full sunlight) to investigate the interactive responses of A. buergerianum and A. davidii to light and water in terms of seedling growth, leaf traits, biomass parameters and partitioning patterns. The experiment was run for123days following the initial acclimation stage. In respect of A. buergerianum, the results showed that shade reduced growth, biomass and leaf size of A. buergerianum to a large extent, but enhanced the chlorophyll content, leaf water content and specific leaf area. Regarding A. davidii seedlings, shade decreased growth, biomass and increased leaf water content, specific leaf area and chlorophyll content, but did not change the size of the leaves. Drought decreased growth, biomass and leaf size of both tree species.For both species, most biomass characteristics partitioning patterns had strong interactions in their responses to illumination and moisture treatments. Leaf traits of A. buergerianum displayed strong interactions in responses to illumination and moisture treatments but not of A. davidii. A. buergerianum owns a higher plasticity than A. davidii. Allometric analysis demonstrated that illumination and moisture influenced stem mass ratio and leaf mass ratio of A. buergerianum and stem mass ratio of A. davidii but had no effects on root mass ratios and root to shoot ratios of both species. The combined effects of light and water differ from simple sum of either factor alone. Shade mitigated the negative effects of drought for both species. In order to keep the seedlings vigorous under various illumination conditions, we recommend a water supply above15%of soil fild capacity. Regulations of forest canopy density would facilitate seedlings growth and accelerate regeneration.In order to uncover the impact of canopy opening in the forest ecosystem, a simulated potted experiment was conducted. We investigated responses of the mid-successional species Acer truncatum Bunge and the late-successional species Quercus variabilis Blume to three solar illumination conditions:(1) low light and low light (LL),(2) high light and high light (HH) and (3) low light to high light (LH). The last treatment was used to simulate canopy opening process. Morphological and physiological acclimations at whole plant and leaf levels were recorded. Both species exhibited increases in biomass, totally and in partly, and decreases in leaf water content, specific leaf area and chlorophyll concentrations when moved to LH treatment. In A. truncatum, sudden exposure to high light conditions (LH) increased crown, and decreased root to shoot ratio, leaf size. However, in Q. variabilis, LH treatment increased stem diameter at ground height, effective quantum yield, photochemical quenching and decreased maximum photosystem II quantum yield. The biomass allocation pattern did not change in Q. variabilis among three conditions. Maximum photosystem II quantum yield underwent a sharp decline and then recovery for both species after sudden exposure to high light, with A. truncatum recovering more quickly than Q. variabilis. In both species, effective quantum yield decreased over time upon LL or HH treatment. Newly developed maple leaves from the LH saplings remained significantly smaller than HH leaves when developing under high light whereas no difference was found in all chlorophyll fluorescence parameters between LH and HH environment. However, the newly developed oak leaves did not display significant difference for mean leaf area and mean leaf perimeter and increased all chlorophyll fluorescence parameters. A. truncatum displayed a greater overall plasticity than Q. variabilis although the oak seedlings have a greater plasticity with respect to chlorophyll content and chlorophyll fluorescence parameters. The two tree species have similar acclimation mechanisms to different light conditions in respect to light absorbing and utilizing, but different strategies in respect to resource allocation.Increasing levels of atmospheric nitrogen deposition have greatly affected forest trees. Acer truncatum Bunge has a large distribution in northern China, Korea and Japan and plays an important ecological role in forest ecosystems. We investigated the responses of A. truncatum to a broad range of nitrogen addition regime with a focus on seedling growth, biomass partitioning, leaf morphology, gas exchange physiology and chlorophyll fluorescence physiology. After the initial acclimation period, the experiment was run from June to September2011. Moderate nitrogen addition promoted shoot height, stem diameter at ground height, total biomass, bulk of leaves and chlorophyll fluorescence and gas exchange performance, whereas extreme level of nitrogen addition did not result in such facilitation. Chlorophyll content, pattern of biomass partitioning, ratio of leaf length to width, leaf water content, and specific leaf area did not change among the addition regimes. The critical amount of nitrogen deposition should be defined in the context of a certain time period in a particular region for a certain species at a special developmental stage. The critical amount of N deposition that weakens total biomass facilitation in A. truncatum planted in mixed soil of yellow cinnamon soil and humic soil is approximately10gNm-2y-1during its first growing season.In summary, all these maple species displayed certain phenotypic plasticity in response to different climate fators, in the level of leaf and the whole plant. Results of this study will provide fundamental and theoretical data to vegetation recovery, forest administration and management and help to predict the responses of forest vegetation in a prosective climate change scenario.