Study On Ecological Responses Of Artificial Mangrove To Key Environmental Factors In Zhejiang Province

A large number of afforestation practices showed that temperature, salinity and intertidal position are the major limiting factors for mangrove forestation success. Therefore, study on the ecological responses of mangroves to temperature, salinity and intertidal position would provide theoretical basis and technical support to mangrove forestation in species and habitat selection. It has important location values in academic research on the study that ecological response of artificial mangroves to key environmental factors in Zhejiang Province, north area of mangrove introduction of China. In this study, field and greenhouse experiments were carried out to investigate to changes in plant growth, adaptation, survival, chilling injury index, photosynthesis and physiological parameters of 10 mangrove species, such as Kandelia obovata etc., in responding to key environmental factors, temperature, salinity and intertidal position, in order to clarify the adaptability of these mangroves to environmental factors though the methods of qualitative and quantitative analyses, the single index and the comprehensive analyses. Moreover, population structure and biomass were also investigated to provide theoretical basis for assessment of mangrove population dynamics and biomass of different ages in responding to intertidal position. The main results are as follows:(1) Under the background of global climate change, the present paper forecasts for the introduction of artificial mangrove species in Zhejiang province:if the average temperature increased by 1.8℃, mangrove plants will achieve 3 species, K. obovata, Aegiceras corniculatum, distributed to Zhejiang Province. If the average temperature increased by 4℃, twelve mangrove species including to K. obovata, Avicennia marina, A. corniculatum, Sonneratia apetala etc, can be distributed to Zhejiang. It has important theoretical values on forecasts of Zhejiang artificial mangrove species selection. (2) Response of Zhejiang artificial mangrove species to temperature: low temperature, especially extreme low temperature affected growth of mangroves. Relative electrolyte conductance (RE), malondiadehyde (MDA), proline (PRO) and superoxide dismutase (SOD) of experimental plants leaves increased with a decreasing temperature. After winter, plants of L. racemosa and A. marina were all dead (chilling injury index, Cii>3), some individuals of S. apetala were dead (Cii=2.76), while A. corniculatum, K. obovata and native species Ficuas concinna var. subsessilis were survival, with the similar values of Cii (1.08-1.14). After extreme low temperature (-4℃), the survival rate were K. obovata (77%)> A. corniculatum (73%)> E. agallocha (70%)> S. apetala (25%), whereas the other six mangrove species, including L. racemosa, B. gymnorhiza, B. sexangula var. rhynchopetala, R. stylosa, A. ilicifolius and A. marina, were all dead. As a result, cold tolerance of the experimental mangrove species as follows: K. obovata> A. corniculatum> E. agallocha> S. apetala > the other six mangrove species. Therefore, K. obovata, A. corniculatum, E. agallocha and S. apetala can be used as the main mangrove species in the artificial mangrove forestation in Zhejiang province, confirmed the context of mangrove species selection of Zhejiang artificial mangrove introduction.(3) The effects of salinity on growth and photosynthesis were investigated in the two mangroves, S. apetala and K. obovata, under cultured conditions. The results showed that salinity affected plant photosynthesis by pigment synthesize, stomata changes, the values of the maximum rate of carboxylation by Rubisco and the PAR saturated electron transport rate, and the effective quantum yield etc. Kandelia obovata had a wider range of suitable salinity than S. apetala, which could grow well in≦340 Mm NaCl salinity habitats, with the optimum salinity of 170 Mm NaCl; whereas S. apetala had a strong low salinity preferences, with the salinity of its habitat should be less than 170 Mm NaCl.(4) The effects of intertidal position on growth of K. obovata, S. apetala and A. corniculatum were tested, and the results were as followed: the three mangroves had the highest survival rate in middle intertidal position. The survival rate was higher in high than low intertidal position for K. obovata and S. apetala, and A. corniculatum opposite. The value of adaptation (adp) was estimated by the parameters of SOD, PRO and RE. The value of adp of K. obovata and A. corniculatum decreased,-0.8204 and -0.7050 for K. obovata and A. corniculatum, respectively, but increased for S. apetala (adp=0.4795) in high intertidal position compared to the adp value in middle intertidal position (adp =0). The adp values of K. obovata (adp=3.4776) and S. apetala (adp=-3.3934) in low intertidal position significantly decreased in comparison to middle intertidal position, while adp value did not change for A. corniculatum (adp=-0.0988). Therefore, K. obovata and S. apetala adapted to be planted in relative higher intertidal position, while A. corniculatum adapted to be planted in relative lower intertidal position.(5) An experiment was conducted to investigate the population characteristics and biomass in artificial K. obovata mangrove in different intertidal position. The results showed that population characteristics such as height, canopy, and size structure positive relative to population age, but negative to intertidal position (tide-flooding time). Population density was negative to population age, while positive to tide-flooding time. Diameters of stems were used as variable for estimate plant biomass (leaf, WL; stem, Ws; belowground parts, WB; and total dry weight, WT). Allometric equations as followed: WL=0.187D1.855; Ws=0.267D1.906; WB=4.6D1.136; WT=3.614D1.446. Population biomass of 3-,5- and 10-year K. obovata was estimated at 7.13,11.32 and 24.35 t hm-2, with an average of 43.7% corresponding to belowground biomass.