| Chinese cork oak (Quercus variabilis L.) is valuable as an deciduous tree species for both economic and ecological importance. Unfortunately, as a result of over-exploitation in the past decades, Q. variabilis population has been decreasing sharply in China. Therefore, the Chinese reforestation with high-quality Q. variabilis seedlings is of vital importance in its conservation and regeneration program. In nursery cultivation regimes, fertilization and irrigation as nursery tools, have strong influence on the morphological and physiological characteristics of seedlings, and also, can largely determine their field performance under stressful conditions.In this paper, based on the one-year growth pattern of Quercus variabilis L. seedlings, the effect of various fertilization methods on seedlings'growing process was investigated, so did the different soil moisture conditions, the nitrogen supply levels and the couple effect of water and nitrogen. Finally, the optimal regime for irrigation and fertilization in one-year old Q. variabilis seedlings' cultivation was established. The main conclusions were introduced as follows:(1) Two fast-growing periods existed in Q. variabilis seedlings'first growth season. In the first fast-growing period, most of the mineral nutrition, which supported the seedlings'growth, was from the corns'storage, therefore, no fertilizer application was needed in this period. As a contrast, irrigation was very'important. However, in the second fast-growing period, due to the depletion of the mineral nutrition storage in seeds, fertilization and irrigation were both of vital importance.At the ealier stage (May to July), more biomass was distributed to overground parts of the. seedlings, thus, nitrogen supply was necessary for promoting the growth of stems and leaves. On the contrary, from the end of July on, more biomass of the whole seedlings was devoted in the roots, so that the phosphorus and potassium fertilizers were needed in this period.So far as the mineral nutrition contents were concerned, the nitrogen content was highest of all (140.6mg·seedling-1), potassium content (31.6mg·seedling-1) was in the next place, phosphorus content was minimum of all. Forasmuch, the amounts of the three fertilizers was:N>K>P.July and August, in which the water consumption of Q. variabilis seedlings was the highest in the whole growing season, were the crucial period for water-saving irrigation regime establishment.Diagnosis and Recommendation Integrated System (DRIS) was applied'for nutritional diagnosis of one-year old Q. variabilis seedling leaves, by which three parameters (N/P=17.0±1.31, N/K=5.8±0.65 and P/K=0.34±0.29) were used to evaluated whether the seedlings were in healthy condition.(2) Among the three different fertilizer application patterns (average pattern, linear pattern and exponential pattern), the growth condition was the best and the nutrient use efficiency (NUE) was the highest under the exponential pattern, so that, the exponential fertilizer application pattern was the best method to load mineral nutrition for Q. variabilis seedlings.(3) In terms of the influence of various soil moistrue conditions on the seedlings' growth, negative effects to seedlings were observed in the highest and the lowest soil moistrue treatments (the soil water-potential were -0.0560 to -0.0503 MPa and -0.2285 to -0.1834 MPa, respectively.). However, roots'growth and water absorbing capacity of Q. variabilis L. seedlings were motivated while the soil water-potential was decreased from -0.0707 MPa to -0.1262 MPa.Secondly, the net photosynthetic rates (Pn) of Q. variabilis seedlings'leaves descended with the decline of soil water-potiential from -0.0707 to -0.2285 MPa and increased when soil water-potiential decreased from -0.0503 to -0.0707 MPa. At the two soil moistrue conditions (soil water-potiential were-0.0560 to -0.0503 MPa and -0.1262 to -0.1073MPa, respectively.), the reduction of Pn was mainly as a result of the stomatal relational factors, otherwise, under the drought stress conditon (soil water-potiential were -0.2285 to -0.1834 MPa), non-stomatal relational factors took place as the primary ones in Pn decline.(4) With respect to the effect of different nitrogen supply levels on the seedlings'growth, positive exhibition on seedlings' growth was observed when nitrogen application level increased from 0.0 to 216.4 mg·seedling-1·year-1. However, the highest nitrogen application (329.2mg·seedling-1·year-1) had reached the luxury consumption level, in which the plant biomass (g·seedling-1) declined, compared with N2 level (216.4mg·seedling-1·year-1).So far as the photosynthesis capability was concerned, instead of improving the maximal net photosynthetic rate (Pmax) of the seedlings'leaves, nitrogen nutrition enhanced seedlings'carbon assimilation ability resorting to extend their photosynthetic period and increase the whole leaf area per seedling. Similarly, when the nitrogen supply reached the luxury consumption level (329.2 mg·seedling-1·year-1), some poor responses appeared in seedlings' photosynthetic capability, such as the decline of the maximal net photosynthetic rate (Pmax),quantum efficiency (a) and the light saturation point (Lsp), and the up-grading of light compensation point (Lcp).In addition, at the prosperous phase, the nitrogen concentration in all seedlings'organs increased along with the elevation of nitrogen application. At the same time, among the three organs, the nitrogen concentration was highest in leaves, in which physiological process was most active, and lowest in the roots.Different from the influence of nitrogen levels on the organs' nitrogen concentration, no significant differnces had been found in organs'phosphorus and potassium concentrations (p>0.05), which indicated that the reaction of phosphorus and potassium's absorption to nitrogen fertilizer could parallelled with the response of biomass. However, N/P and N/K ratios in Q. variabilis seedlings increased in pace with nitrogen application levels. At luxury level treatment (329.2 mg·seedling-1·year-1), the N/P ratio had exceeded the harmonious range according to the Diagnosis and Recommendation Integrated System (DRIS) for one-year old Q. variabilis seedlings, which induced the reduction of biomass production and photosynthetic capability.(5) In the case of the couple effect of water and nitrogen, it showed no pronounced function on seedlings'growth as the soil water potential changed between -0.1262 and -0.0560 MPa. In these soil moistrue condition range, the differences of seedlings'growth among the treatments were mainly owing to the two main effect (water or nitrogen). But, at the lowest water moistrue treatment (soil water-potiential were -0.2285 to -0.1834 MPa), drought stress had taken place as the primary limiting factor in seedlings'growth, and no significant differences had been exhibited among various nitrogen treatments in this condition (p>0.05). Because of that, while the soil water potential changed between -0.2285 and-0.0560 MPa, a remarkable couple effect of water and nitrogen on seedlings'growth occurred (P<0.01), and all the three factor (water, nitrogen and waterxnitrogen), acted on seedlings'growth (P<0.05).In conclusion, since no significant couple effect of water and nitrogen existed while the soil water potential changed between -0.1262 and -0.0560 MPa, the irrigation regime under W3 teatment (soil water potiential were -0.1262 to -0.1073MPa) and the nitrogen application regime under N2 tretment (nitrgen supply level 216.4 mg·seedling-1·year-1) could be combined as the optimal irrigation and fertilization regime, and the exponential pattern was chosen as the best fertilizer application pattern. |
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