[Effects of nitrogen addition on acidolyzable organic nitrogen components and nitrogen mineralization in aggregates of Pinus massoniana plantations in the Three Gorges Reservoir area, China]. / æ°®æ·»åŠ å¯¹ä¸‰å³¡åº“åŒºé©¬å°¾æ¾äººå·¥æž—åœŸå£¤å›¢èšä½“æœ‰æœºæ°®ç»„åˆ†å’Œæ°®çŸ¿åŒ–çš„å½±å“.

We sieved soils from a Pinus massoniana plantation in the Three Gorges Reservoir area into four aggregate sizes, including aggregates of 2000-8000 µm (large macroaggregates), 1000-2000 µm (coarse aggregates), 250-1000 µm (small macroaggregates), and <250 µm (microaggregates). We analyzed the differences in the acidolyzable organic N components and net N mineralization of the aggregates under different N addition levels (30, 60, and 90 kg N·hm-2·a-1, representing by N30, N60 and N90, respectively). The results showed that net nitrification rate of the aggregates ranged from 0.30-3.42 mg N·kg-1 and accounted for more than 80% of net nitrogen mineralization. Compared with the control, addition of 30, 60, and 90 kg N·hm-2·a-1 increased total N by 24.1%-45.5%, 6.4%-34.3%, and 7.9%-42.4% in the large aggregates, coarse aggregate, small macroaggregates, and microaggregates, increased net N mineralization rate by 1.3-7.2, 1.4-6.6, and 1.8-12.9 times, but decreased the contents of available phosphorus by 9.3%-36.9%, 12.2%-56.7%, and 19.2%-61.9%, respectively. The contents of total acidolyzable N, soil organic matter, and rates of net ammonification, net nitrification, and net N mineralization increased as the aggregate size decreased, while available phosphorus contents showed an opposite trend. The levels of acid-hydrolyzable N components were ranked as acidolyzable amino acid N > acidolyzable ammonia N > acidolyzable unknown N> acidolyzable amino sugar N. Total N was the dominant contributor to the increases in acid-hydrolyzable N components. Results of stepwise multiple regression analyses showed that acidoly-zable amino acid N and acidolyzable amino sugar N were predictors of net ammonification rate. Acidolyzable amino sugar N, acidolyzable amino acid N, and acidolyzable ammonia N were predictors of net nitrification, net nitrogen mineralization rate, and net nitrogen mineralization accumulation. The physical structure of aggregates was associa-ted with soil net N mineralization. Addition of N increased the contents and bioavailability of acidolyzable organic N, a large amount of which contributed to soil organic matter levels and the decrease in available phosphorus.

[Effects of nitrogen addition on soil microbial biomass and enzyme activities of Pinus massoniana-Quercus variabilis mixed plantations in the Three Gorges Reservoir Area]. / æ°®æ·»åŠ å¯¹ä¸‰å³¡åº“åŒºé©¬å°¾æ¾-æ “çš®æ Žæ··äº¤æž—åœŸå£¤å¾®ç”Ÿç‰©ç”Ÿç‰©é‡å’Œé ¶æ´»æ€§çš„å½±å“.

We examined the effects of nitrogen addition (0, 30, 60, and 90 kg N·hm-2·a-1) to soil microbial biomass, enzyme activities, and nutrient contents of the Pinus massoniana-Quercus variabilis mixed plantations in the Three Gorges Reservoir Area, with the aim to provide a theoretical basis for predicting soil carbon dynamics under the background of continuously increasing atmospheric nitrogen deposition in this area. The results showed that nitrogen addition at all levels led to a significant increase of the contents of organic carbon, total nitrogen, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) in the forest soil, while a decrease of soil pH-value, and no significant effect on the total phosphorus content. Nitrogen addition increased the activities of ß-1-4 glucosidase (BG), cellobiose hydrolase (CB), acid phosphatase (AP), N-acetylglucosaminosidase (NAG) and peroxidase (POD), while inhibited that of polyphenol oxidase (PPO). There was a significant seasonal variation in soil oxidase activities, in which the peroxidase activity was higher in May and August, and the polyphenol oxidase activity was the highest in August. Soil enzyme activities were significantly correlated with soil moisture and the contents of soil nutrients, MBC, MBN, and MBP. The variation of soil enzyme activities was caused by the comprehensive effects of multiple factors. The redundancy analysis (RDA) showed that the contents of total soil nitrogen and MBC were the main environmental factors driving soil enzyme activities. The continuous increase of atmosphere nitrogen deposition would lead to soil acidification and promote the turnover of soil organic carbon and nutrient cycling in the Pinus massoniana-Quercus variabilis mixed plantations of the study area.

[Composition and niche of the existing herbaceous plants in the water-level-fluctuating zone of the Three Gorges Reservoir Area, China]. / 三峡库区消落带现存草本植物组成与生态位.

To understand the usages of available resource by dominant plants, their niches and the mechanisms of inter-specific competition and co-existence in the water level fluctuation zone, we studied the spatial distributions and niche characteristics of existing dominant herbaceous species at a typical water-level-fluctuation site of the Three Gorges Reservoir Area, Zigui. The results showed that there were 39 herb species in total, which belonged to 18 families and 32 genera. Gramineae, Compositae, Polygonaceae and Euphorbiaceae were the dominant families. Cynodon dactylon, Setaria viridis, Bidentis tripartitae and Digitaria chrysoblephara were the dominant species, with high importance value and niche breadth. In addition, at 145-155 m, 155-165 m and 165-175 m altitude section, the three major species, expressing the highest ecological niche breadth, which were in order of C. dactylon ＞ Polygonum lapathifolium ＞ S. viridis, S. viridis ＞ D. chrysoblephara ＞ C. dactylon, and S. viridis ＞ B. tripartitae ＞ P. orientale, respectively. The niche overlap of the species between the different altitudes zone was relatively high. The species which had a broad niche could co-exist with those occupying narrow niche. The niche overlap could not be determined by niche breadth lonely. Furthermore, after seven times of water level fluctuations, most of the species were annual herbs, and the degree of niche differentiation was low in the area. Due to scarce resources and unstable habitats, the inter-specific competition was strong, and the vegetation was at the primary successional stage.

[Fine root production and turnover of Pinus massoniana and their influencing factors in the Three Gorges Reservoir Area, China]. / ä¸‰å³¡åº“åŒºé©¬å°¾æ¾ç»†æ ¹ç”Ÿäº§å’Œå‘¨è½¬åŠå ¶å½±å“å› å­.

In this study, the annual production and turnover rate of fine root of Pinus massoniana in Three Gorges Reservoir Area were calculated using sequential soil core,litterbag and compartment flux model methods, and the relationship between fine root production, turnover rate and factors was analyzed. The results showed that the annual mean biomass of <0.5, 0.5-1 and 1-2 mm fine root was 0.29, 0.59 and 0.76 t·hm-2, annual production was 0.13, 0.49, 0.37 t·hm-2, and annual turnover rate was 1.49, 1.01, 0.40 a-1, respectively. The effects of factors on production and turnover of fine roots with different diameters were different. Soil temperature and soil Ca content had significant effects on production and turnover of <0.5 mm fine roots, and soil temperature explained the variation of production and turnover by 32.8% and 25.0%, and soil Ca content explained by 65.6% and 73.1%, respectively. There was a positive relationship between fine root biomass and fine root production, and the biomass of fine root explained 41.0%, 41.1% and 54.5% of variation in fine root production for <0.5, 0.5-1 and 1-2 mm fine roots, respectively. P and K contents of fine roots correlated significantly with <0.5 mm fine root production, and explained 32.2% and 39.2% of the variation of <0.5 mm fine root production, respectively. The fine root with diameter <0.5 mm was most closely associated with soil factors, and soil temperature and soil Ca content were the main factors affecting fine root biomass.

[Dynamics of fine root decomposition and its affecting factors of Pinus massoniana in the Three Gorges Reservoir Area, China.] / ä¸‰å³¡åº“åŒºé©¬å°¾æ¾ä¸åŒç›´å¾„ç»†æ ¹åˆ†è§£åŠ¨æ€åŠå ¶å½±å“å› ç´ .

A decomposition experiment for a year was conducted at Jiulingtou Forest Farm, Zigui County, Hubei Province, China to examine the decomposition dynamics of fine roots with different diameters (<0.5, 0.5-1 and 1-2 mm) and its main affecting factors for Pinus massoniana. The results showed that the decomposition rate decreased with the increasing root diameter. The annual decomposition rates for fine roots with diameters <0.5, 0.5-1 and 1-2 mm were 34.0%, 28.0% and 25.7%, respectively. The decomposition rate of <1 mm fine root decreased along time, and 1-2 mm fine root increased first and then decreased. In the fine root decomposition process, N, P and Ca concentrations increased along time, and K concentration decreased firstly, then increased, and then decreased along time. Fine root decomposition rate was significantly related to initial chemical composition (N, P, K, Ca, C/N and C/P) of fine roots. Ca concentration in fine root and soil temperature were the major factors affecting fine root decomposition.

[Light response characteristics of photosynthesis and model comparison of Distylium chinense in different flooding durations].

The light responses of photosynthesis of two-year-old Distytum chinense seedlings subjected to a simulated reservoir flooding environment in autumn and winter seasons were measured by using a Li-6400 XT portable photosynthesis system, and the light response curves were fitted and analyzed by three models of the rectangular hyperbola, non-rectangular hyperbola and modified rectangular hyperbola to investigate the applicability of different light response models for the D. chinense in different flooding durations and the adaption regulation of light response parameters to flooding stress. The results showed that the fitting effect of the non-rectangular hyperbola model for light response process of D. chinense under normal growth condition and under short-term flooding (15 days of flooding) was better than that of the other two models, while the fitting effect of the modified rectangular hyperbola model for light response process of D. chinense under longer-term flooding (30, 45 and 60 days of flooding) was better than that of the other two models. The modified rectangular hyperbola model gave the best fitted results of light compensation point (LCP) , maximum net photosynthetic rate (P(n max)) and light saturation point (LSP), and the non-rectangular hyperbola model gave the best fitted result of dark respiration rate (R(d)). The apparent quantum yield (Φ), P(n max) and LSP of D. chinense gradually decreased, and the LCP and R(d) of D. chinense gradually increased in early flooding (30 days), but D. chinense gradually produced adaptability for flooding as the flooding duration continued to increase, and various physiological indexes were gradually stabilized. Thus, this species has adaptability to some degree to the flooding environment.

[Effects of litterfall and root input on soil physical and chemical properties in Pinus massoniana plantations in Three Gorges Reservoir Area, China].

An investigation was made on the soil physical and chemical properties in different-aged Pinus massoniana plantations in Three Gorges Reservoir Area under effects of litterfall and roots. The annual litter production in mature stand was 19.4% and 65.7% higher than that in nearly mature and middle-aged stands, respectively. The litter standing amount was in the sequence of mature stand > middle-aged stand > nearly mature stand, while the litter turnover coefficient was in the order of nearly mature stand (0.51) > mature stand (0.40) > middle-aged stand (0.36). The total root biomass, live root biomass, and dead root biomass were the highest in middle-aged stand, and the lowest in nearly mature stand. In middle-aged stand, soil total porosity was the highest, and soil bulk density was the lowest. Soil organic matter and total nitrogen contents were in the order of mature stand > middle-aged stand > nearly mature stand, soil nitrate nitrogen occupied a larger proportion of soil mineral N in nearly mature stand, while ammonium nitrogen accounted more in middle-aged and mature stands. In nearly mature stand, litter production was moderate but turnover coefficient was the highest, and soil nutrient contents were the lowest. In middle-aged stand, root biomass and soil total porosity were the highest, and soil bulk density were the lowest. In mature stand, root biomass was lower while soil nutrient contents were the highest. The increase of root biomass could improve soil physical properties.

[Fine root production and turnover in Pinus massoniana plantation in Three Gorges Reservoir area of China].

By the methods of sequential soil cores and buried bags, an investigation was conducted to study the seasonal dynamics of fine roots in a 20-year-old Pinus massoniana plantation in Three Gorges Reservoir Area from March to December 2011, with the annual production and turnover rate of the fine roots calculated. In the plantation, the annual mean biomass of <2 mm fine roots was 146.98 g x m(-2) x a(-1), in which, the living root biomass (102.92 g x m(-2) x a(-1)) was far greater than that of the dead root biomass (44.06 g x m(-2) x a(-1)). Among the fine roots with different sizes, <1 mm fine roots had an obvious seasonal dynamics in their biomass, showing a unimodal curve in the sampling period. The annual production and turnover rate of <2 mm fine roots were 104. 12 g x m(-2) x 1(-1) and 1.05 a(-1), respectively, in which, the annual production of <1 mm and 1-2 mm fine roots was 58.35 and 45.77 g x m(-2) x a(-1), and the turnover rate was 1.41 and 0.69 a(-1), respectively.

[Effects of altitudinal gradient on Salix atopantha foliar delta13C].

In 2010, measurements were conducted on the foliar delta13C, photosynthesis, CO2 diffusive conductivity, nitrogen content, photosynthetic nitrogen use efficiency (PNUE), and special leaf area (SLA) of Salix atopantha at different altitudes (2350 m, 2700 m, 3150 m, and 3530 m) in Wolong Natural Reserve. With the increase of altitude, the foliar nitrogen content (especially the nitrogen content per unit leaf area, N(area)) and the PNUE increased, and the foliar delta13C had a significant increase, with an increment of 1.4 per thousand per 1000 m altitude. The stomatal and mesophyll CO2 diffusion conductance also increased with increasing altitude, which had definite negative effect on the increase of foliar delta13C, but the effect was not strong enough. Comparing with CO2 diffusion conductance, carboxylation capacity was a more important factor limiting the P(c)/P(a), and even, the foliar delta13C. At altitude 2350-2700 m, air temperature was the main factor affecting the allocation of nitrogen in S. atopantha photosynthetic system, whereas at altitude 2700-3530 m, light could be the main affecting factor. No significant difference was observed in the SLA at different altitudes.

[Characteristics of soil seed banks in backwater area of Three Gorges Reservoir water-level-fluctuating zone at initial stage of river-flooding].

A germination test was made to study the characteristics of soil seed banks in the backwater area (including the flooded, non-flooded, and control areas of secondary bush and abandoned farmland) of Three Gorges Reservoir water-level-fluctuating zone. There existed significant differences in the soil seed banks between secondary bush and abandoned farmland, with an average seed density being 6991 +/- 954 seed per m2 and 26193 +/- 6928 seed per m2, respectively. Flooded area had the lowest seed density, while non-flooded area had the highest one. The seed density decreased with soil depth. A total of 118 species belonging to 45 families and 97 genera were detected in the soil seed banks of secondary bush and abandoned farmland, most of which were annual and perennial herbage species, belonging to Asteraceae, Poaceae, Scrophulariaceae, and Cruciferae. Among the 118 species, there were 34 species (occupying 28.8%) whose individuals accounted for less than 0.01% of the total. In the soil seed banks of secondary bush and abandoned farmland, the species number was similar, species diversity index and evenness index were relatively high, but the dominant species differed greatly, and the ecological dominance was relatively low. The species diversity in non-flooded area and the ecological dominance in flooded area were the highest, and the similarity index between the flooded and non-flooded areas was the highest.