| The pecan [Carya illinoensis(Wagenh.) K. Koch], a deciduous tree native to North America, belongs to the Juglandaceae family, which is widely known for nuts, superior woody oil, excellent hardwood and lumber. As it has economic, social and ecological benefits, it has been developed rapidly in recent years. However, trees were grown mainly with bare-rooted seedlings in recent afforestation and plantations, which led to lower survival rates and slow tree growth. As a result, planters lost confidence in pecan. This dissertation studied seed dormancy, seedling growth, subirrigation and controlled release fertilizer, with the aim of developing a production system for containerized pecan seedlings.The main conclusions were as follows:1. The shell was physically restricting, released endogenous inhibitory substances and had physical physiological characteristics which were shown to be the causes of seed dormancy. The effects of soaking days, GA3 soaking and incubating temperature on seed germination were also studied. Results showed that:Complete excision of the embryo as well as the removal of the shell from around the radicle resulted in rapid germination. The two treatments decreased the time for maximum germination from 20 to about 12 days, which indicated that the shell physically restricted radicle elongation. Scarified nuts imbibed water rapidly with 85 percent of final water absorbed on third day, while intact nuts needed 8 days. The result proved that the shell restricted water uptake to some extent. Oxygen uptake of pecan nuts was also studied, results showed that respiratory rate of notched nuts was higher than that of intact nuts. Respiratory rate of nuts incubated at 30 °C enhanced rapidly and was higher than nuts incubated at 20 °C, which indicated that pecan nuts were not freely permeable to oxygen. However, respiratory rate of nuts may be improved or eliminated at higher temperatures. The shell of the pecan nut was scanned under scanning electron microscope. The shell was composed of lignification stone cells and had quantities of holes on the surface which were channels for water and oxygen exchange with the outside. Different pecan nut cultivars had holes which varied in quantity and shape, resulting in different patterns of water uptake and oxygen exchange.Shell extracts and decomposition liquids demonstrated strongly allelopathic effects on the stem growth of young seedlings of hybrid penisetum, which also inhibited seed germination of pecan nuts. However, the inhibiting effects were related to concentration and could be eliminated by regular water changing. Increasing soaking days from 0 to 9 days, GA3 concentration from 50 to 200 mg/L and incubating temperature from 20 °C to 30 °C could accelerate development, but had no effect on final germination rate.There was no evidence that the embryos were dormant or required an after-ripening period. Mature nuts which were collected direct from trees, dry stored at room temperature, or stratified germinated equally well if incubated under favorable temperatures. The germination rate could reach 90 percent in 8 days when incubated at 37 °C.2. Growth conditions for containerized pecan seedlings in different container types and sizes were studied. Results showed all growth parameters had significant or extremely significant correlations and single parameters did not reflect seedling growth. Growers could choose Planting Green Bag of thinner materials according to research results.Container size, substrate composition and root cutting ratio had interaction effects on growth of containerized pecan seedlings by multi factor analysis of variance. To cultivate good seedlings, nurseryman could choose 15 cm×25 cm or 10 cm×30 cm containers, 3:1 peat:perlite(v/v) medium, and 1/2 radicle cutting(radicle length 6 cm).3. The 1-year-old containerized seedling height and root collar diameter had the same growth pattern with double S-Curves. Two growth peaks occurred in one year. Seedlings grew in height mainly in early stage and root collar diameter mainly in later stage. Root growth also had two peaks with taproot growth in early stage and lateral root growth in the later stage. Root growth was closely allied to above-ground growth which appeared to alternate.Leaf spray and stem smear KT and GA3 both improved RCD and leaf area of containerized pecan seedlings. Leaf spray with 200 mg/L GA3 and 50 mg/LKT appeared best. Stem smear showed lower growth stimulus than leaf spray and resulted lateral bud elongation and deformity.4. Water tolerance mechanism of pecan containerized seedling was investigated and the results showed that pecan seedlings had high water tolerance. After 30-days flooding stress, a few spots appeared on leaves and chloroplast lamellae gradually became less loose, whereas the number of osmophores increased. However, chloroplast structures were completely destroyed and most organelles disintegrated after 30-days drying.Compared with overhead irrigation, subirrigation conserved at least 62% of irrigation water and improved water use efficency(WUE) by at least 193%. Seedling growth, photosynthesis and nutrient status were improved significantly with seedling height increasing 11.7% and RCD 41.5%. N and K content of roots increased 53.8% and 100%, N and P content of stems increased 35.3% and 48.3%, N, P and K content of leaves increased 48.7%, 117.2% and 28.7% respectively. Roots of containerized pecan seedlings maintained a higher level of activity under subirrigation. Along with the seedling growth, root SOD、POD and CAT activity first rose then declined, which indicated that seedlings avoided damage by increasing protective enzymes activity in order to adapt to new circumstances.5. Effect of different controlled release fertilizer(CRF) on vegetative growth of pecan containerized seedlings was analyzed by correlation analysis and subordinate function value. APEX 19-6-12 at 6 g/L showed the best response. Content of soluble sugar, soluble protein, starch and leaf SPAD value promoted by CRF application. As increasing of CRF rate, the nutrient accumulation increased with APEX 19-6-12 at the 6 g/L rate produced the highest value.Mineral content and distribution differed with various CRF applications. N and Ca content were affected by both rate and formulation. Mineral content was higher under APEX 19-6-12 application than APEX 14-14-14 at the same rate. K content was significantly affected by formulation, while Mg content showed no relationship with the two factors. With the exception of K, distribution of other mineral elements was not affected by CRF formulation. |
PDF Full Text Request