Nitrogen-phosphorus Stoichiometry In Potentilla Fruticosa Linn, In Gannan Sub-alpine Meadow

Ecological stoichiometry is a new tool to study ecological process from genes to the biosphere. It has been successfully applied in many ecological studies in recent years. Stoichiometric homeostasis, the degree to which an organism maintains its elements ratios despite variation in the relative availabilities of elements in its resource supplies, is a key parameter in ecological stoichiometry. However, the ecology stoichiometry dynamics showed convergence and variation in studies at different levels. Nitrogen (N) and phosphorus (P) are essential for plant growth and their cyclings and play a key role in ecosystem processes. Organism level of ecological stoichiometry can connect to the three dimensions of the living system:the molecular level, the organism level and large scale ecosystem processes. Therefore, the studies in this area are very important for ecological development. Environment (including light, temperature, soil temperature and soil water content, etc) and internal factors (including growth, reproduction, aging, etc) interact to produce the observed patterns of internal plant nutrient stoichiometry, but we do not know much about such interactions. We studied the dynamics of nutrient stoichiometry in Potentilla fruticosa L. in relation to both two environmental (fertilization, slope) and two internal factors (reproduction, age)in a field experiment.We studied the effect of (a) four levels fertilization, (b) with and without flower removal, (c) 6 plant ages, (d) different slopes, on the N and P stoichiometry of naturally-occurring Potentilla fruticosa L. individuals.The main results and conclusions:1, Fertilization significantly increased the leaf N and P concentration; however N:P ratio was not significant affected by fertilization(range [8.81,9.36], P>0.05). CVs of leaf N and P were bigger than that of soil N and P. The results of fertilization experiments suggested that P. fruticosa L. showed a higher degree of homeostasis in N:P than N and P, maintaining internal nutrient stoichiometry under variation in external nutrient levels.Flower P was significantly higher than leaf P; there was no significant difference between flower N and leaf N. Flowers need more phosphorus to synthesize DNA, RNA etc for reproduction.2, Reproduction decreased leaf N and N:P significantly, whereas there was no significant effect on plant leaf P. It suggested that reproduction leads to lower leaf N and N:P. The physiological mechanism may be the re-allocation of N and P between flowers and leaves by caused by reproduction. Leaves to the reproductive organs of the transport of phosphorus, and phosphorus content of the flower than leaf phosphorus content. Flower P was more than leaf P which did not significantly decrease. That may be due to plants can absorb enough phosphorus to ensure the reproduction.N:P showed convergence and variation under internal(reproduction) and external (fertilization)factor respectively. The mechanisms may be Homeostatic mechanism and Reproduction mechanism respectively. Reproduction should have a relatively independent mechanism with the effects of nitrogen and phosphorus in plants: reproduction lead to reduce leaf N:P.3, Plant leaf P was generally stable through 1-6 ages. Plant leaf N appeared to fluctuate later in development when plants were reproducing. The dynamics of N:P are basically the same with leaf N, which can explained by Reproduction mechanism but can not explained by Growth rate hypothesis. The low N:P can also predict that the limited element is N not P.4, The research on the environmental factors from South-facing slope to North-facing slope showed that:The average value of soil temperature was that: South-facing slope>West-facing slope>North-facing slope (P＜0.05); Soil water content increased from South-facing slope to North-facing slope(P<0.05); Daily light intensity decreased from South-facing slope to North-facing slope (P＜0.05).The results of slopes experiments suggested that Daily light intensity, soil temperature and soil water content should be the key factors that affect the distribution of Potentilla fruticosa L. upward slope. Leaf N was significantly negative correlated in soil temperature. With the increase of light intensity, leaf N and N:P ratios decreased. The physiological mechanism of leaf nitrogen content decreases with soil temperature increases may be the adaptation of physiological and temperature in plant.