Geographical variation of ecological stoichiometry and nutrient resorption in leaves of Pinus koraiensis and Fraxinus mandshurica.

In this study, we sampled leaves of coniferous species Pinus koraiensis and broad-leaved tree species Fraxinus mandshurica from four latitudes in northeastern China to investigate the carbon (C), nitrogen (N), phosphorus (P) stoichiometric characteristics and nutrient resorption efficiency and their potential relationships, as well as their responses to climatic and edaphic factors. The results showed that stoichiometric characteristics were species-specific, and that the C and N contents in leaves of F. mandshurica significantly increased with increasing latitude. The C:N of F. mandshurica and N:P of P. koraiensis were negatively correlated with latitude, but an inverse relationship was found for N:P of F. mandshurica. P resorption efficiency was significantly correlated with latitude in P. koraiensis. The spatial variation of ecological stoichiometry of these two species was mainly affected by climatic factors such as mean annual temperature and precipitation, while that of nutrient resorption was influenced by several soil factors such as soil pH and nitrogen content. Principal component analysis showed that P resorption efficiency of P. koraiensis and F. mandshurica was significantly negatively correlated with N:P, but positively correlated with P content. N resorption efficiency showed significantly positive correlation with P content but negative correlation with N:P in P. koraiensis. Compared with P. koraiensis, F. mandshurica was more inclined to fast investment and return in terms of leaf traits.

[Effects of defoliation on the allocation of non-structural carbohydrates in roots of Fraxinus mandshurica seedlings.] / åŽ»å¶å¯¹æ°´æ›²æŸ³è‹—æœ¨æ ¹ç³»éžç»“æž„æ€§ç¢³æ°´åŒ–åˆç‰©åˆ†é çš„å½±å“.

Global climate changes would lead to outbreaks of leaf-feeding insects. Leaf loss could reduce photosynthate production, with consequences on non-structural carbohydrates (NSC) storage and allocation in trees. In this study, the responses of NSC and its compartment concentrations in tap-, coarse- and the first to fifth order fine roots of 2-year-old seedlings of Fraxinus mandshurica to defoliation (40% loss of leaf area) were measured from June to October. The results showed that NSC and its compartment concentrations in roots exhibited distinct seasonal dynamics in both control and defoliation treatments. Following defoliation, NSC concentration decreased in tap- and coarse roots by 3.8% and 30.7%, respectively, while increased in the first five order roots by 1.2%-23.5%, to which starch contributed majorly for each root compartment. Soluble sugar concentration was enhanced by defoliation in tap- and coarse roots by 7.1% and 62.3%, respectively, but decreased in the first to fifth order roots by 2.7%-42.8%. Defoliation had different influences on starch and soluble sugar, with positive effects on the ratio of soluble sugar to starch concentrations in tap- and coarse roots but negative effects on the first to fifth order roots. Overall, defoliation decreased photosynthate production in leaves, leading to the remobilization of starch in tap- and coarse roots and the transportation as soluble sugar to fine roots, as well as the following storage in these roots, which would facilitate the resistance of fine roots to the low temperature in winter.

[Effects of elevated N availability on anatomy, morphology and mycorrhizal colonization of fine roots: A review.] / æ°®æœ‰æ•ˆæ€§å¢žåŠ å¯¹ç»†æ ¹è§£å‰–ã€å½¢æ€ç‰¹å¾å’ŒèŒæ ¹ä¾µæŸ“çš„å½±å“.

Increase of nitrogen (N) availability can greatly affect the structure and function of forest ecosystems. Fine root is critical to belowground ecological processes, thus its response to elevated N availability has become a focus of ecological researches. This article reviewed the trend and under-lying mechanism of fine root response to elevated N availability, including root anatomy, morphology and mycorrhizal colonization. We found that cross-sectional areas of root stele and xylem and the diameter, number and wall thickness of xylem vessel (tracheid) all increased, however, cortex thickness, the number of cortical cell layer, diameter of cortical cell and number of passage cell in exodermis decreased with higher N availability. The response of root anatomy was closely related to plant hormones. In addition, mycorrhiza colonization rate decreased after N fertilization, while specific root length (root length per unit root mass) generally decreased in arbuscular mycorrhizal species, while increased in ectomycorrhizal species. By contrast, the root diameter and tissue density varied widely among species under higher N status. These findings based on individual roots and species provided deeper understanding of carbon and nutrient cycles in terrestrial ecosystems. In addition, we discussed some knowledge gaps and proposed several research outlooks for guiding future researches.

[Seasonal dynamics of carbon and nitrogen concentrations in Phellodendron amurense fine roots].

Taking a 23 years old Phellodendron amurense plantation as test object, the first five order roots of P. amurense were sampled to study the seasonal dynamics of their total carbon (TC), total nitrogen (TN), total non-structural carbohydrates (TNC), and soluble N concentrations, with the correlations among these parameters analyzed. In the first five order roots, the TNC occupied 49% of TC, and the soluble N accounted for 26% of TN. Within the growth season, the rate of TNC to TC increased from 42% in the first order roots to 52% in the fifth order roots, and the rate of soluble N to TN decreased from 28% to 21% correspondingly. All the first five order roots had the lowest concentration of TC but the highest concentration of TN in spring, and the lowest concentrations of TNC and soluble N in summer. The increase of the TC concentration in the roots decreased the concentrations of TNC and soluble N, whereas the increase of the TN concentration decreased the TNC concentration significantly and increased the concentration of soluble N. From the first to the fifth order roots, the TC and TN had an increasing correlation with TNC but a decreasing correlation with soluble N, suggesting the close correlations of TNC and soluble N with TC and TN in P. amurense fine roots.

[Seasonal variations of fine root production and mortality in Larix gmelinii plantation in 2004-2008].

Minirhizotron approach was employed to investigate the seasonal variations of fine root production and mortality in Larix gmelinii plantation in 2004-2008. At the same time, air temperature, precipitation, and soil temperature and moisture at 10 cm depth were recorded. The overall aim of this study was to determine the seasonal patterns of fine root production and mortality in the plantation, and their relationships with the four environmental factors. On an annual basis, the fine root length production ranged from 0.20 to 0.78 mm x cm(-2), while the mortality varied from 0.26 to 0.72 mm x cm(-2). The mean fine root production and mortality in 2004-2006 were 0.67 mm x cm(-2) and 0.59 mm x cm(-2), respectively, being greater than the corresponding values (0.37 mm x cm(-2) and 0.39 mm x cm(-2)) in 2007-2008. During growth season (from May to October), the fine root production in late spring and early summer (June and July) occupied 51% -68% of total, while that in late autumn (October) only occupied 1% -4%. The root mortality in late summer (August) and autumn (September and October) ranged from 59% to 70%, but that in early spring (May) only ranged from 1% to 5%. Correlation analysis indicated that 66% of the variation in fine root production could be explained by air temperature, and only 24% and 27% could be explained by the soil temperature at 10 cm depth and precipitation, respectively. Fine root mortality only showed an exponential positive correlation with the soil temperature at 10 cm depth.

[Carbon and nitrogen storages and allocation in tree layers of Fraxinus mandshurica and Larix gmelinii plantations].

By the methods of wood analysis and sequential soil core, the biomass and productivity of the tree layers in 20-year old Fraxiuns mandshurica and Larix gmelinii plantations, as well as the carbon (C) and nitrogen (N) storages in the above- and below-ground organs of the stands, were estimated. The biomass of F. mandshurica and L. gmelinii was 6815.10 g x m(-2) and 9295.95 g x m(-2), in which, stem occupied 57.32% and 58.01%, and fine roots occupied 2.67% and 1.80%, respectively. The annual productivity of F. mandshurica and L. gmelinii was 1618.16 and 2102.45 g x m(-2) x a(-1), in which, stem accounted for 39.34% and 46.70%, and fine roots accounted for 12.06% and 5.25%, respectively. The C content in the organs of F. mandshurica was lower than that of L. gmelinii, while the N content was in adverse. The C storage of F. mandshurica was lower than that of L. gmelinii, while the N storage had no significant difference between the two tree species. The biomass, productivity, and C and N storages of aboveground organs were lower for F. mandshurica than for L. gmelinii, indicating the higher construction efficiency of the aboveground part of L. gmelinii. Due to the significant differences in the C and N contents between tree species and between the organs of same tree species, the measurement should be made on different tree species and different organs to have an accurate estimation of forest C and N storages.

[Effects of nitrogen fertilization on ectomycorrhizal infection of first order roots and root morphology of Larix gmelinii plantation].

In this paper, the first order roots of Larix gmelinii plantation under N fertilization were sampled from different soil depths in different seasons to study their morphology under effects of ectomycorrhizal fungi. The results showed that the infection rate of ectomycorrhizal fungi on the first order roots was significantly affected by soil N availability, soil depth, and season. N fertilization induced a decrease of the infection rate, and the decrement varied with soil depth and season. In comparing with the control, the infected first order roots had an obvious variation of their morphology, e. g., averagely, root diameter increased by 18.7%, root length decreased by 23.7%, and specific root length decreased by 16.3%, which differed significantly with N application rate, soil depth, and season. The infection of ectomycorrhizal fungi changed the first order root morphology of L. gmelinii, which might substantially affect the physiological and ecological processes of host plant fine roots.