Ecological stoichiometry provides a new method for understanding the characteristics, driving forces and mechanisms of C, N and P coupled cycles. However, there are few reports on the variation in ecological stoichiometry of plants during their growth. In this study, we fitted the total elemental mass of different module based on the size of Nitraria tangutorum, and derived the ecological stoichiometry models of different module and whole ramet by measuring the biomass and nutrient concentrations of the current-year stems in 2017, 2-year-old stems, more than 2-year-old stems, leaves, roots and layerings of N. tangutorum ramet. Our results showed that the derivation model could well reflect the changes in ecological stoichiometry during plant growth. The old stems and the layering had higher N:P and C:P, while leaves,current-year stems, and roots had lower N:P and C:P. The whole plant nutrient elements cumulative rate was P:N:C during the growth process. These results were consistent with the growth rate hypothesis and allometric theory, and provide evidence for nutrient reabsorption. This model could be used as an effective way to analyze the dynamic characteristics of elements in plant growth.

Aims The pattern of plant biomass allocation represents the plant response to the environment and is accompa-nied by every stage of plant life history. So it is closely related to the growth and development of plants. There have been reports on the size dependence of plant biomass allocation, but few studies have reported on its responses to different phenological phase. In this study, Nitraria tangutorum in Ulan Buh Desert was used as the research object. The biomass of different organs (root, layering, newborn stem, older stem, leaf and reproductive organ) in the flowering, fruiting and vegetative growth stages in two consecutive years of 2016 and 2017 were measured. The significant differ-ences of slope and intercept of the fitted equation with Standardized-major-axis were respectively used to discuss the varied size dependence and the biomass allocation in different phenological phase or ages, especially between the aboveground and belowground biomass and between the support and assimilation organs. The results showed that the effect of reproductive allocation on biomass allocation pattern of N. tangutorum is mainly reflected in the scale of relative biomass allocation (36.00%) rather than the extent of size dependence (16.67%). The reproductive growth has a greater impact on the biomass allocation pattern of newborn stems, which changes the size dependence extent among different phenological phases, but the trend is inconsistent. The reproductive growth increases the scale of relative biomass allocation to leaves and reduces that to older stems, but did not change their extent of size dependence. The biomass allocation rate in the belowground part of N. tangutorum increased with the accumulation of its biomass, but the reproductive allocation slightly de-creased this rate. Nitraria tangutorum exhibited a higher rate of biomass allocation to supporting organs as plant biomass increases. Over time it is more likely for biomass to be allocated to assimilating organs.

Cold hardiness evaluation is important for screening woody species in cold areas. We compared cold hardiness by estimating the 50% lethal temperature (LT50) using electrolyte leakage test (ELLT50) and triphenyltetrazolium chloride test (TTCLT50) for 26 woody species in the Bashang region of China. One-year-old shoots were collected in January and exposed to five subfreezing temperatures in a programmable temperature and humidity chamber. LT50 was estimated by fitting relative electrolyte leakage and percentage of dead tissue against test temperature. For all tested species, triphenyltetrazolium chloride (TTC) staining of the pith was weak and the cambium TTCLT50 was lower than the extreme minimum temperature (−37 °C) recorded in the region. The cambium TTCLT50 and the sd were lower than that for the phloem and xylem. The phloem TTCLT50 was lower than the xylem TTCLT50, and the two sds were similar. The ELLT50 showed no significant correlation with any TTCLT50. For most species, the ELLT50 was higher than the cambium and phloem TTCLT50 and was not significant different with the xylem TTCLT50. The ELLT50 showed higher sd than any tissue TTCLT50. Based on results obtained in this study, when choosing cold hardiness of single stem tissue as an indicator for screening woody species, the xylem should be considered first, followed by the phloem; the cambium and pith were unsuitable. The cold hardiness estimated by ELLT50 was more suitable as indicator for screening woody species than that of stem tissue in winter estimated by TTCLT50.

[Objective]To investigate the differences in the composition and spatial structure of bud bank of Nitrar-ia tangutorum seedling under the different nitrogen addition gradients,and nutrient limitation and nitrogen utiliza-tion,and to reveal the linkage between the quality of roots and cuttings and the bud bank,and finally elucidate the adaptation strategies of bud bank for the nitrogen availability.[Method]The bud bank traits of N.tangutorum seedlings under different nitrogen addition were studied using pot experiments.The N addition levels consist of 0, 12,24,36,48 and 60 mmol·L-1 .[Result]The nitrogen addition significantly increased the number of buds and vegetative shoots in bud bank,and significantly reduced the number of dormant buds and dormant shoots;mean-while,the nitrogen addition promoted the bud production of secondary shoots and tertiary shoots.With the increas-@ing of nitrogen addition,the relative position of vegetative shoots in bud bank had a tendency to move from base to tip.There was a quadratic nonlinear positive correlation between nitrogen balance index (NBI)and budding inten-sity,branching intensity,bud production of secondary and tertiary shoots of N.tangutorum seedling;The N con-tent,accumulation amount (NAA)and the morphological traits underground were positively related to the number of buds and vegetative shoots,and negatively related to the number of dormant buds and dormant shoots.[Conclu-sion]Among the six nitrogen addition gradients,most of the indicators reached their maximum values in either 36 mmol·L-1 or 48 mmol·L-1 N addition levels,which were the optimum N additions for N.tangutorum seedlings. Nitrogen addition has a significantly influence on the bud bank size and spatial distribution of N.tangutorum seed-lings,which also reflects a response to the changing nutrient availability.