Nutrient content and resorption efficiency of leaves of broad-leaved trees along altitudes in Wuyi Mountains, China.

To reveal the variation of leaf nutrient utilization strategies with altitude gradient in subtropical mountain broadleaved trees, 44 species of broadleaved trees at different altitudes (1400, 1600 and 1800 m) in Wuyi Mountains were selected to measure nutrient content, stoichiometric ratio, and nutrient resorption efficiency of green and senescent leaves, and analyzed their allometric growth relationships. The results showed that nitrogen (N) and phosphorus (P) contents in green leaves were significantly higher than those in senescent leaves, which increased with the increases of altitude. The average values of phosphorus resorption efficiency (PRE) and nitrogen resorption efficiency (NRE) were 48.3% and 34.9%, respectively. PRE was significantly higher than NRE. There was no significant difference in nutrient resorption efficiency with altitude. NRE had positive isokinetic growth with and mature leaf N content at low altitude (1400 m) and negative allometry growth with senescent leaf N content at high altitude (1800 m). PRE and N and P contents of senescent leaves had negative isokinetic growth at low altitude (1400 m) and negative allometry growth at high altitudes (1600 and 1800 m). PRE-NRE allometric growth index was 0.95 at each altitude. The nutrient contents of green and senescent leaves increased with the increases of altitude, but altitude did not affect nutrient resorption efficiency. Plants preferred to re-absorbed P from senescent leaves. Nutrient resorption efficiency of leaves at high altitude affected the nutrient status of senescent leaves.

[Identification of the potential distribution area of Cunninghamia lanceolata in China under climate change based on the MaxEnt model]. / 基于MaxEnt模型预测气候变化下杉木在中国的潜在地理分布.

Based on the distribution records of Cunninghamia lanceolata, we used the maximum Entropy (MaxEnt) model and geographic information system (GIS) methods, combined with environmental factors such as climate and terrain, to predict the potential distribution areas suitable for C. lanceolata under current and future climate scenarios. The results showed that annual precipitation was the most important factor driving the distribution of C. lanceolata. Under the current climate scenario, the total area of suitable for C. lanceolata growth was about 3.28 million km2, accounting for about 34.5% of the total land area of China. Among all the suitable areas, the lowly, intermediately, and highly suitable areas accounted for 18.3%, 29.7% and 52.0% of the total, respectively. Under future climate scenarios, the suitable area of C. lanceolata would increase, showing a clear trend of northward expansion in China. A concentrated and contiguous distribution region highly suitable for C. lanceolata would appear in the humid subtropical areas of southern China. The model was tested by the receiver operating characteristic curve (ROC). The average area under the curve of ROC of the training set was 0.91, showing high reliability.

[Effects of combined nitrogen and phosphorus addition on fine root traits of young Machilus pauhoi forest]. / æ°®ç£·é æ–½å¯¹åˆ¨èŠ±æ¥ å¹¼æž—ç»†æ ¹æ€§çŠ¶çš„å½±å“.

Both nitrogen (N) and phosphorus (P) are the main limiting elements for plant growth in terrestrial ecosystems. Fine roots play a critical role in plant growth. To reveal the effects of combined N and P addition on fine root traits of Machilus pauhoi, we performed a field N and P addition experiment in the midmonth from April to September in 2016 and 2017 in a 3-year M. pauhoi forest (N and P supply ratios were 8:1, 10:1, 12:1, 15:1). Both fine root morphological traits (specific root length, specific root area, average diameter, root tissue density) and stoichiometric traits (total carbon content, total nitogen content and carbon-nitrogen ratio) were analyzed. The results showed that the effects of combined application of N and P on fine root raits varied with seasons. In June, fertilization significantly increased specific root area, total nitrogen content and specific root length of 0-1 mm fine root, but decreased root tissuse density, carbon-nitrogen ratio and average diameter of 0-1 mm root. The most obvious change of fine root traits in June was found under the treatment with a N and P supply ratio of 12:1. In December, combined N and P addition significantly increased root tissue density, total nitrogen content, carbon-nitrogen ratio as well as fine root biomass with the diameter of 0-1 mm. The results of principal component analysis showed that different N and P supply ratios exerted different effects on the relationships among fine root traits. Fine root traits were distributed at both ends of Axis 1 when treated with 12:1 N:P, while distributed at Axis 1 and Axis 2 under other treaments. There was a significant negative correlation between fine root average diameter variation and the relative plant growh rate. The relationship among fine root traits, and between fine root traits and the relative growth rate of plant biomass were optimally coordinated at the treament with a N:P ratio of 12:1.

[Effects of short-term combined application of ammonium nitrogen and nitrate nitrogen on the growth and leaf traits of Machilus pauhoi seedlings]. / çŸ­æœŸé“µæ€æ°®ä¸Žç¡æ€æ°®é æ–½å¯¹åˆ¨èŠ±æ¥ å¹¼è‹—ç”Ÿé•¿åŠå¶ç‰‡æ€§çŠ¶çš„å½±å“.

Trees are characterized with selective absorption of different forms of nitrogen. Ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) are the main forms of nitrogen for plant absorption. We examined the differences of absorption between NH4+-N and NO3--N for 1-year-old Machilus pauhoi seedlings planted in local hilly red soil in a pot experiment. A controlled experiment with 7 different NH4+-N/NO3--N treatments was conducted, to study the effects of nitrogen forms and different NH4+-N/NO3--N ratios on the growth and leaf traits of M. pauhoi seedlings. The results showed that there were no significant differences in the relative growth rate of ground diameter (GD), plant height (TH), and biomass (RGR) of M. pauhoi seedlings with different NH4+-N/NO3--N ratios for four months, but these parameters were relatively high under the treatment of NH4+-N:NO3--N=5:5. The seedlings of M. pauhoi didn't show obvious preference for NH4+-N and NO3--N in short term. The extremely low NH4+-N/NO3--N ratio application was unsuitable for their growth. Different NH4+-N/NO3--N application had significant effects on leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf relative water content (LRWC), net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), water use efficiency (WUE), and photosynthetic nitrogen use efficiency (PNUE). M. pauhoi seedlings under the treatment of NH4+-N:NO3--N=1:9 had the highest LA, SLA, Pn, WUE and PNUE. However, the seedlings under the treatment of NH4+-N:NO3--N=9:1 had the lowest LDMC, leaf tissue density (LTD), LRWC and Ci. Different NH4+-N/NO3--N combined application did not affect leaf nitrogen content (LN) and leaf phosphorus content (LP), which were highest under the treatment of NH4+-N:NO3--N=5:5. Across different NH4+-N/NO3--N combined treatments, GD, TH, and RGR were significantly negatively correlated with SLA, while both GD and RGR were significantly negatively correlated with PNUE. Our results could provide theoretical basis for precise nutrient management and high-efficiency cultivation techniques during the seedling stage of the M. pauhoi.

[Nitrogen and phosphorus contents and resorption efficiency of thirty broadleaved woody plants in Yangjifeng, Jiangxi, China.] / æ±Ÿè¥¿é˜³é™ å³°30ç§é˜”å¶æ ‘å¶ç‰‡æ°®ç£·å«é‡åŠå†å¸æ”¶æ•ˆçŽ‡.

Nutrient resorption is an important strategy of nutrient conservation, which reflecting the ability of plants to conserve and utilize nutrients and adapt to environment. To explore the relationship between nutrient content and nutrient resorption of broadleaved woody species of different life forms (i.e., evergreen vs. deciduous), we sampled 30 broadleaved woody species in subtropical region of China located in Yangjifeng National Nature Reserve, Jiangxi Province. The nitrogen (N) and phosphorus (P) concentrations in green and senescent leaves of each species were measured to calculate nutrient resorption efficiency. Furthermore, we analyzed the relationship of leaf nutrient concentration and resorption efficiency for the different life forms. The results showed that N and P concentrations in green leaves were significantly higher in deciduous trees than those in evergreen trees. The P concentrations of senescent leaves in deciduous woody species was significantly higher than that in evergreen woody species. There was no significant difference of N concentration in senescent leaves between evergreen and deciduous species. Nitrogen resorption efficiency (NRE) and phosphorus resorption efficiency (PRE) of the 30 broadleaved woody species were 49.6% and 50.9%, respectively. There were no significant differences between the NRE and PRE of evergreen and deciduous species. NRE and PRE negatively correlated with N and P concentrations in senescent leaves, respectively. Additionally, evergreen and deciduous species showed similar relationships between nutrient resorption efficiency and nutrient concentration in senescent leaves. The sca-ling exponent of allometric relationship between NRE and PRE was 1.18 across all the species. The nutrient resorption efficiency of all the species were affected by the nutrient status of the senesced leaves. Plants examined in this study generally re-absorbed P from senescing leaves than N.

[Stoichiometry of carbon, nitrogen and phosphorus and their allometric relationship between leaves and fine roots of three functional tree seedlings.] / 3ç§åŠŸèƒ½åž‹æž—æœ¨å¹¼è‹—å¶ç‰‡ä¸Žç»†æ ¹ç¢³æ°®ç£·åŒ–å­¦è®¡é‡ç‰¹å¾åŠå ¶å¼‚é€Ÿå ³ç³».

We analyzed the contents and stoichiometric ratios of carbon (C), nitrogen (N) and phosphorus (P) in leaves and fine roots of Machilus pauhoi (an evergreen broad-leaved species), Cerasus campanulata (a deciduous broad-leaved species) and Fokienia hodginsii (an evergreen coniferous species) to compare the leaf and root stoichiometry and allometric relationship between different functional groups of trees. There were significant difference in the contents and stoichiometry of C, N and P in the leaves and fine roots among different functional groups. C content, C/N and C/P of the leaves and roots were the highest in M. pauhoi. N content and N/P of the leaves and roots were the highest in C. campanulata, whereas P content of the leaves and roots was the highest in F. hodginsii. The allometric relationship of C, N and P contents as well as their stoichiometric ratios between the leaves and fine roots showed significant difference, which was affected by functional difference. The allometric relationship between C/P and N/P with significantly different allometric indexes in leaves in seedlings of those three tree species, while the isometric relationship between the contents of N and P was found in fine roots. There were significant difference in the C, N and P stoichiometry between the leaves and fine roots. The allometric relationship between leaf C content and root P content in M. pauhoi was detected. C and N contents and C/N, N/P in leaves generally had the allometric or isokinetic relationships with C/N, N/P of fine roots. There were allometric relationships between the leaf C content and the root C, N and P contents in F. hodginsii. It was concluded that nutrient allocation between leaves and fine roots of C. campanulata was more strongly coordinated. The investment strategy of P for leaves and fine roots across those three tree species was similar. The results provided scientific reference for accurate nutrient management at seedling stage and efficient cultivation technique.

[Relationship between the main functional traits of fine root and the rhizosphere soil nutrients of different diameter classes in Zenia insignis plantation.] / ç¿ èšæœ¨äººå·¥æž—ä¸åŒå¾„é˜¶é—´ç»†æ ¹ä¸»è¦åŠŸèƒ½æ€§çŠ¶ä¸Žæ ¹é™ åœŸå£¤å »åˆ†çš„å ³ç³».

Fine roots are sensitive to changes in the soil environment, and play an important role in plant growth and development. To clarify the relationship between fine root traits and rhizosphere soil nutrient characteristics, fine roots of trees belonging to different diameter classes in six-year-old Zenia insignis plantation were sampled. The results showed that root biomass, root length density and root volume density increased with the increases of diameter class. Specific root length and specific root area showed the trend of first rising and then falling and rising again with the increases of diameter class. Root tissue density did not change with diameter class. There were significant diffe-rences in soil pH, water content, total carbon, total phosphorus, ammonium nitrogen, nitrate nitrogen and total available nitrogen contents of rhizosphere soil belonging to different diameter classes. The concentrations of soil total carbon, total nitrogen, nitrate nitrogen and total available nitrogen in the rhizosphere soil of large diameter trees were relatively higher, while the soil water content, total phosphorus and ammonium nitrogen contents of small diameter trees were relatively higher. The concentrations of soil total nitrogen, total carbon, nitrate nitrogen and total available nitrogen were significantly positively correlated with root biomass, root length density and root volume density. The concentrations of soil total phosphorus was significantly positively correlated with root tissue density of fine roots, but negatively correlated with specific root length and specific root area. Soil water content was significantly positively correlated with root biomass and root volume density. Soil pH was significantly positively correlated with the specific root length and specific root area of fine roots, but negatively correlated with root tissue density. Our results provide scientific basis for the selection of excellent germplasm resources of Z. insignis.

[Effects of the current-year shoot stem configuration on leaf biomass in different canopy heights of woody plants in evergreen broad-leaved forest in Jiangxi Province, China.] / æ±Ÿè¥¿å¸¸ç»¿é˜”å¶æž—æœ¨æœ¬æ¤ç‰©ä¸åŒå† å±‚é«˜åº¦å½“å¹´ç”Ÿå°æžèŒŽæž„åž‹å¯¹å¶ç”Ÿç‰©é‡çš„å½±å“.

To investigate the effects of stem configuration on leaf biomass allocation in different organs of the current-year shoots at different canopy heights, relationships of biomass in different organs (i.e., leaves, stems, and twigs) and stem configuration (i.e., stem diameter, length, width/length, stem volume and stem density) were analyzed using the data of 69 woody species from the Yangjifeng Natural Reserve, Jiangxi Provence. Standardized major axis (SMA) was used to explore the regression between biomass and stem configuration. The results showed that there was no significant difference in leaf biomass, stem biomass, twig biomass, stem diameter, stem length, stem width/length and stem volume of current year shoots from upper and lower canopy heights and life forms (i.e., evergreen and deciduous woody plants). Stem density differed significantly in the current year shoots at different heights for both evergreen and deciduous woody species. There were isometric relationships among leaf, stem and total biomass of shoots in different canopy heights and in different life forms. Leaf biomass scaled allometrically with stem diameter and volume, with the scaling exponents being not different significantly among different canopy heights. With respect to the stem configuration of the twigs, stem length, stem width/length and stem density contributed less than 24% to the leaf biomass variation in the current-year shoots. On the contrary, stem diameter and volume had greater effects on leaf biomass of the current-year shoots than stem length, stem width/length and stem density. Canopy heights did not significantly affect the allometric scaling relationships between the stem configuration and leaf biomass of the current-year shoots.

[Allometry between twig size and leaf size of typical bamboo species along an altitudinal gradient]. / ä¸åŒæµ·æ‹”å ¸åž‹ç«¹ç§æžå¶å¤§å°å¼‚é€Ÿç”Ÿé•¿å ³ç³».

To investigate the trade-off between the twig size and leaf size, we measured the total leaf mass, stem mass, individual leaf mass and leafing intensity of typical bamboo’s (Phyllostachys edulis, Indocalamus tessellatus, Oligostachyum oedogonatume, Yushania hirticaulis and Yushania wuyishanensis) twigs at different altitudes in Wuyi Mountain. The results showed that the exponents of the scaling between total leaf mass and stem mass on twigs significantly decreased with increasing altitude for all the five bamboo species. The common scaling exponents of total leaf mass vs. stem mass for P. edulis, I. tessellatus and O. oedogonatum were 0.94, 0.85 and 0.84, respectively. A common slope of 0.79 was observed in total leaf mass vs. stem mass in Y. hirticaulis and Y. wuyishanensis. There was significant negative correlation between individual leaf mass and leafing intensity among bamboo species, except Y. wuyishanensis. A common slope of -1.12 existed between individual leaf mass and leafing intensity for five bamboo species. In conclusion, bamboos at low altitudes tended to support more leaf biomass while preferring to invest more to stem biomass at high altitudes. Although the stem mass investment of different bamboo’s twig increased with altitude, the leafing intensity strategies based on stem mass were determined by the leaf size construction rather than altitude.

[Short-term effects of nitrogen and water treatments on fine root order morphology of Machilus pauhoi seedlings.] / 短期氮-æ°´å¤„ç†å¯¹åˆ¨èŠ±æ¥ å¹¼è‹—ç»†æ ¹æ ¹åºå½¢æ€çš„å½±å“.

A factorial nitrogen and water addition experiment was carried out with one year-old Machilus pauhoi seedlings from Suichuan County, Jiangxi Province, with six treatments being established: two water levels with 80% and 40% of field moisture holding capacity and three nitrogen addition levels of 0, 50, 100 kg N·hm-2. Specific root length, specific root area, average diameter and tissue density of three fine root orders of M. pauhoi were measured to understand the main and interactive effects of short-term nitrogen addition and drought stress on root characters of M. pauhoi seedlings. The results showed that average fine root diameter and specific root length differed significantly among fine root orders. With the increases of root orders, the average root diameter increased, with the maximum being present in the third order (0.97 mm), but specific root length decreased, with the minimum being present in the third order (238.99 cm·g-1). No significant effects of nitrogen addition on specific root surface area, average fine root diameter, specific root length and root tissue density were observed. There were significant effects of water treatments on average fine root diameter, specific root length and root tissue density. Drought stress significantly increased average diameter of the third order fine roots of seedlings and decreased root tissue density of the first and second order fine roots. Specific root length of the third order fine roots in arid environments was significantly lower than that under the normal water supply condition. There was no interactive effects of nitrogen addition and drought stress on fine root morphology of M. pauhoi.

[Relationships between leaf functional traits of Machilus pauhoi understory seedlings from different provenances and geographical environmental factors.] / ä¸åŒç§æºåˆ¨èŠ±æ¥ æž—ä¸‹å¹¼è‹—å¶åŠŸèƒ½æ€§çŠ¶ä¸Žåœ°ç†çŽ¯å¢ƒçš„å ³ç³».

To understand the adaptation mechanism of Machilus pauhoi seedlings to environmental changes, leaf functional traits of M. pauhoi seedlings from nine provenances, as well as relationships between leaf traits and environmental factors were analyzed. The results showed that leaf functional traits of M. pauhoi seedlings from different provenances showed significant intraspecific variations, with the coefficient of variation ranging from 8.8% to 28.2%. Specific leaf area, leaf relative water content, leaf tissue density and leaf thickness differed significantly among seedlings from different provenances, implying high leaf morphological plasticity. Moreover, leaf tissue density was positively correlated to leaf dry matter content and leaf relative water content, but negatively correlated to specific leaf area and leaf thickness. Specific leaf area showed significantly negative correlations with leaf dry matter content and leaf area. The covariation among those traits examined here indicated that M. pauhoi seedlings could adjust and balance the combination of leaf traits in response to environmental changes. Longitude, latitude, >10 ℃ annual accumulated temperature and mean annual temperature contributed largely to the variation of leaf functional traits of M. pauhoi seedlings. Leaf thickness decreased with the increase of longitude, while leaf dry matter content and leaf relative water content increased with the increase of longitude. Leaf tissue density was positively correlated with longitude and mean annual temperature, suggesting that longitude rather than mean annual temperature had greater effects on it. Leaf area was positively correlated with >10 ℃ annual accumulated temperature and longitude, indicating that annual accumulated temperature rather than longitude had greater effects on the variation of leaf area.

[Scaling relationships between twig size and leaf size of Pinus hwangshanensis along an altitudinal gradient in Wuyi Mountains, China.] / æ­¦å¤·å±±ä¸åŒæµ·æ‹”é»„å±±æ¾æžå¶å¤§å°å ³ç³».

To analyze the tradeoff relationship between twigs and leaves, the traits of Pinus hwang-shanensis including leaf area, leaf number, twig length and twig diameter were investigated in Wuyi Mountains along an altitudinal gradient. The results indicated that leaf number, twig length, twig diameter, leafing intensity and twig stem cross-sectional area of P. hwangshanensis increased gra-dually with the increasing altitude, while individual leaf area decreased gradually. Leafing intensity of P. hwangshanensis at different altitudes had significant negative relationships with leaf area. The cross-sectional area of P. hwangshanensis had significant positive relationship with total leaf area. Twig length and twig diameter of P. hwangshanensis correlated negatively with leafing intensity, but positively with leaf area, leaf number and total leaf area. To enhance the competitiveness and resource utilization efficiency, P. hwangshanensis at low altitude tended to have relatively few large leaves on short twigs, and those at high altitude tended to have a large number of small leaves on long twigs. Such tradeoff between twigs and leaves reflected the strategy of resource utilization and the balance of biomass allocation mechanism of P. hwangshanensis responding to the altitudinal change.

[Characteristics of leaf carbon, nitrogen and phosphorus stoichiometry in relation to plant size of Machilus pauhoi].

To explore the effects of stand age on variation patterns of leaf C, N, P stoichiometric characteristics of Machilus pauhoi, two stands, i.e., 9 and 13 years old, were selected. The relationships between leaf nutrient contents (C, N and P) and diameters at breast height (DBH) of individual plants were analyzed. The data revealed that the individual variations of seedlings in M. pauhoi stands were strengthened with the stand development. The stand age had significant effects on leaf C, N, P contents and C:N ratio but not on C:P and N: P ratios. Specifically, the mean values of leaf C, N, P contents and N:P ratio in the 9-year-old stand were lower than those in the 13-year-old stand, whereas, inverse pattern of C:N and C:P ratios were found in the two stands. Furthermore, leaf N and P stoichiometry varied significantly within the stand. Specifically, leaf N and P contents, as well as their stoichiometric ratios, linearly correlated with DBH in the 9-year-old stand. On the contrary, leaf N and P stoichiometry showed quadratic correlation in 13-year-old stand (except leaf C:N which linearly correlated with DBH). Lastly, nutrient transfer rates of leaf N and P in the 9-year-old stand were higher than that in 13-year-old stand, and the discrepancies of leaf nutrient transfer strategy between growing and non-growing seasons were caused by the different growth phases and environmental conditions.

Scaling relationship between tree respiration rates and biomass.

The WBE theory proposed by West, Brown and Enquist predicts that larger plant respiration rate, R, scales to the three-quarters power of body size, M. However, studies on the R versus M relationship for larger plants (i.e. trees larger than saplings) have not been reported. Published respiration rates of field-grown trees (saplings and larger trees) were examined to test this relationship. Our results showed that for larger trees, aboveground respiration rates RA scaled as the 0.82-power of aboveground biomass MA, and that total respiration rates RT scaled as the 0.85-power of total biomass MT, both of which significantly deviated from the three-quarters scaling law predicted by the WBE theory, and which agreed with 0.81-0.84-power scaling of biomass to respiration across the full range of measured tree sizes for an independent dataset reported by Reich et al. (Reich et al. 2006 Nature 439, 457-461). By contrast, R scaled nearly isometrically with M in saplings. We contend that the scaling exponent of plant metabolism is close to unity for saplings and decreases (but is significantly larger than three-quarters) as trees grow, implying that there is no universal metabolic scaling in plants.

[Chlorophyll content and net photosynthetic rate of Machilus pauhoi and M. leptophylla].

By using SPAD-502 chlorophyll meter, LI-6400 portable photosynthesis system, and spectrophotometer, the leaf SPAD value, net photosynthetic rate (Pn), and chlorophyll (a + b) content (Ct) of 3-year-old Machilus pauhoi and M. leptophylla seedlings were measured, and the relationships of SPAD value with Pn and Ct were analyzed. The M. pauhoi seedlings were grown from the seeds originated from Suichuan County of Jiangxi Province and Jian'ou County of Fujian Province, named as MPS and MPJ, respectively; while the M. leptophylla seedlings were grown from the seeds originated from Shangyou County of Jiangxi Province, named as MLG. There were significant differences in the mean chlorophyll content of MPS, MPJ, and MLG. The SPAD value and the contents of chlorophyll (a + b) (Ct), chlorophyll a (Ca) and chlorophyll b (Cb) were in the order of MPS < MLG < MPJ, with the mean SPAD value being 43.80, 45.12, and 50.67 and the Ct value being 1.944, 2.831, and 3.447 mg c g(-1), respectively. The chlorophyll content was influenced by the maturing degree of mesophyll tissues of M. pauhoi and M. leptophylla, being lower in current-year leaves than in 2-year-old leaves. The Ct of same age leaves at different crown layers of MPS and MPJ and of MLG was in the order of upper layer < middle layer < lower layer and of upper layer < lower layer < middle layer, respectively, and the SPAD value of the same lamina at different positions was in the order of apex < middle < base. SPAD value had a significant positive linear correlation with Ct, and a statistically not significant positive correlation with Pn.