Nitrogen, Phosphorus Seasonal Variation In Needles, Stems And Fine Roots Of Larix Principis-rupprechtii Mayr Of Different Stand Age

This study adopts a wild woodlands sampling test, we set up a total of five forest agegradient, which is5a,10a,20a,30a and40a. Through studying the nitrogen, phosphoruscontent and seasonal variation in needles, stem and fine roots of Larix principis-rupprechtii,soil nutrition content, and moisture content, we find that:(1) The N, P content of Larix principis-rupprechtii Mayr in needles is very high when theneedles are expanding, which decreased rapidly after that. Then the nitrogen contentfluctuates according to the change of season changes, while the phosphorus content decreasedstably and maintains at a low level (0.135%) after august. The nitrogen content in needles ofmature forest (40a) is a bit higher than near-mature forest (30a), and half-mature forest (20a)is higher than young forest (10a,5a). While the phosphorus content in needles is just oppositeas nitrogen.(2) The nitrogen and phosphorus contents of Larix principis-rupprechtii Mayr in stems areentirely different with that in needles. The N, P contents are very low in May, and then thenitrogen content fluctuates just opposite to it in needles. The phosphorus content in stemsincreased rapidly during May and July, then decreased stably and maintains at a middle level(0.064%).(3) The variation trend of nitrogen content in fine root of Larix principis-rupprechtii Mayris similar to that in needles. It decreased then increased during May to September, and thendecreased rapidly in October before the leaves fallen. The phosphorus content in fine rootschanges just opposite to that in needles. It increased steadily during May and July, and thenmaintains at a middle level after July. The nitrogen and phosphorus content in fine roots ofmature forest (40a) are very high. That’s because of the root system of mature forest is higherdeveloped and has a better absorbing ability.(4) The nutrition contents in needles, stems and fine roots of Larix principis-rupprechtiiMayr are fluctuating according to the change of season changes. Nutrient content distributionis shown as: needles> fine roots> stems and the dynamic change in needles is the most severely. Nutrient element content in stability is shown as:40a>30a>20a>(10a,5a).(5) The nitrogen content variation coefficient of5a,10a,20a,30a,40a Larixprincipis-rupprechtii Mayr are25.86%,32.07%,32.75%,16.21%,11.11%, and thephosphorus content variation coefficient are33.70%,34.55%,40.49%,34.39%,30.21%. Thephosphorus content has a significant negative correlation with N:P in needles of differentstand age of Larix principis-rupprechtii Mayr. The nitrogen content has a positive correlationwith N:P in needles of20a,10a,5a Larix principis-rupprechtii Mayr. In a word, the variabilityof phosphorus contends has a leading role in the dynamic changes of N:P in growing seasonof Larix principis-rupprechtii Mayr.(6) The nitrogen content has a positive correlation with phosphorus content in needles of30a and20a Larix principis-rupprechtii Mayr, while it is not notable in40a needles. The N:Pis more stable than N, P contents of Larix principis-rupprechtii Mayr, which reflects the leaf N,P content relative consistency, but leaves ecological stoichiometry characteristics changingwith the season and phenology of the replacement. One-time sampling and analysis is not ableto plant ecological stoichiometry characteristics truly reflected, comprehensive, across timeand space sampling will be more scientific and reasonable.