| Nitrogen and phosphorus are necessary important elements of tree growth, and are alsothe main restrictive element of plant growth. The content of nitrogen and phosphorus and thebalance between nitrogen and phosphorus affect the growth, development and succession oftrees and the decomposition of tree litter and the change of soil fertility. Therefore, processesin absorption, utilization and allocation of nitrogen and phosphorus have an importantsignificance on nutrient balance of tree. The research object was North China Larchplantation, and nitrogen and phosphorus fertilization was carried out under the lack of soilnitrogen and phosphorus in woodland. By gathering needles, stems and roots in differentperiods under different fertilization treatments and different age of stand, we measurednitrogen and phosphorus content of needles, stems and roots, analyzed the distributioncharacteristics of nitrogen and phosphorus content, the space-time change of nitrogen andphosphorus and N:P stoichiometry characteristics in different parts of North China Larch,cleared nitrogen and phosphorus nutrient resorption efficiency characteristics, explored theresponse on dynamic change of nitrogen and phosphorus content and N:P stoichiometrycharacteristics in different parts of North China Larch plantation for nitrogen and phosphorusfertilization and different age of stand, in order to provide theoretical basis for revealingnitrogen and phosphorus nutrient absorption, utilization and return mechanism of NorthChina Larch, and to provide theory basis for healthy growth of North China Larch plantation.The main results were as follows:(1) Applying nitrogen and phosphorus fertilization had great effects on nitrogen andphosphorus content of needles, stems and roots in North China Larch. The application ofnitrogen significantly increased nitrogen content of needles, stems and roots, and decreasedphosphorus content of needles and roots, but had no significant effect on phosphorus contentof stems. The application of phosphate fertilizer significantly decreased nitrogen content ofneedles and roots, and increased phosphorus content of needles, stems and roots. Nitrogenand phosphorus content of needles, stems and roots changes of a fluctuating with the seasons under different fertilization treatments. Nitrogen content of needles showed a trend of riseand fall after the first reduce, and reached maximum in July or August, but reached minimumin October. Phosphorus content of needles showed a trend of increased first and thendecreased under phosphorus fertilization supply, but under other fertilization treatments,phosphorus content of needles had little fluctuation, and showed slightly downward trend inthe early and middle period of the growing season, and decreased sharply at the last ofgrowing season. Nitrogen and phosphorus content of stems showed the overall trend of falland rise after the first increase under different fertilization treatments, had consistent trend,but just had not the same transition time. Under different fertilization treatments, nitrogencontent of roots showed a trend of fall and rise after the first increase, but phosphorus contentof roots increased gradually, and nitrogen and phosphorus content reached maximum in thelate growing season (October). Different fertilization treatments had an obvious influence onN/P ratio of needles, stems and roots. The application of nitrogen increased N/P ratio ofneedles, stems and roots, and applying phosphate fertilizer decreased N/P ratio of needles,stems and roots. This showed that applying nitrogenous fertilizer increased nitrogen contentof needles, stems and roots and application of phosphate fertilizer increased phosphoruscontent of needles, stems and roots. Therefore, growth of needles, stems and roots wasaffected by nitrogen or phosphorus levels. The N/P ratio of needles, stems and roots of NorthChina Larch reached maximum in July or August under different fertilization treatments.Rational fertilization could increase N resorption efficiency. The application of nitrogenousfertilizer had little effect on P resorption efficiency, and applying phosphate fertilizerdecreased greatly P resorption efficiency.(2) Nitrogen content of needles in North China Larch showed a consistent trend with theseasonal change in the different age class, and the content was increased at first anddecreased subsequently. A decreasing tendency of phosphorus content of needles was foundin each stand age, but the phosphorus content of needles of6year old trees was increasedsuddenly and then decreased in the falling process. Nitrogen and phosphorus content ofneedles did not appear regularly change with the stand age growth in North China Larch.Nitrogen content of stems in the11year old and21year old North China Larch showed thetrend of fall and rise after the first increase with the seasonal change. Nitrogen content ofstems in the31year old and41year old North China Larch increased first, and thendecreased. Overall, in North China Larch of each stand age, phosphorus content of stemsincreased first, and then decreased with the season. With the change of stand age, nitrogencontent of stems did not show any particular change. But phosphorus content of stemsdecreased with increasing stand age. Overall, nitrogen and phosphorus content of roots increased with the seasonal change in the different age class. Nitrogen content of rootsincreased with increasing stand age, but phosphorus content of roots did not appear obviouslychange with increasing stand age. N/P ratio of needles and roots increased gradually withincreasing stand age. This showed that N/P ratio of needles and roots appeared an adjustmentwith increasing stand age. This may be an important change that North China Larch adapts tothe change of nitrogen and phosphorus in the soil. N and P resorption efficiency of needlesachieved maximum in the middle-aged forest (21year old), and did not show any particularchange with the change of tree age.(3) Nitrogen and phosphorus content of needles, stems and roots was different underdifferent fertilization treatments and different age of stand, and appeared different change lawwith the season. The basic law of nitrogen and phosphorus content showed that needles werethe largest, and then roots, the last was stems. That is to say, needles＞roots＞stems. Thisshowed that nitrogen and phosphorus nutrition from plant absorption was mainly distributedto needles. Forest growth of North China Larch plantation reflected that N element was inshort supply. Forest growth restricted by N, but did not limit by P.(4) In the growing season, the range of nitrogen content of6a,11a,21a,31a,41a NorthChina Larch needles was respectively12.01~22.33g/kg,14.16~17.79g/kg,5.85~20.97g/kg,15.69~23.06g/kg,12.32~24.42g/kg, the range of phosphorus content was respectively1.70~2.76g/kg,1.82~2.72g/kg,0.44~2.17g/kg,1.58~2.10g/kg,1.22~2.42g/kg, the range ofN/P ratio was respectively7.05~9.64,6.30~9.63,8.22~12.94,8.41~13.41,7.68~10.16. Therange of nitrogen content of6a,11a,21a,31a,41a North China Larch roots was respectively3.04~8.83g/kg,1.60~7.42g/kg,3.65~8.88g/kg,6.74~13.49g/kg,7.76~14.13g/kg, the range ofphosphorus content was respectively0.93~1.21g/kg,0.50~1.50g/kg,0.92~1.22g/kg,0.76~1.62g/kg,1.11~1.31g/kg, the range of N/P ratio was respectively3.26~7.30,3.35~8.06,3.48~8.46,8.34~11.12,6.47~10.88. The range of nitrogen content of11a,21a,31a,41a NorthChina Larch stems was respectively0.93~2.63g/kg,0.47~1.38g/kg,0.70~2.35g/kg,0.70~2.33g/kg, the range of phosphorus content was respectively0.085~0.142g/kg,0.055~0.104g/kg,0.032~0.057g/kg,0.048~0.063g/kg, the range of N/P ratio was respectively9.23~23.16,6.34~19.68,10.54~23.68,13.08~19.69. |
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