[Influencing mechanism of stand age to the accumulation of microbial residue carbon in the Pinus masso-niana plantations]. / 林龄对马尾松人工林微生物残体碳积累的影响机制.

Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.

[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.

Comparison of species composition and community characteristics of Quercus forests on south and north slopes of Taibai Mountain, China.

We examined species composition, community characteristics, diversity, and community similarity of five Quercus communities composed of three Quercus species (Q. variabilis, Q. aliena var. acutiserrata, Q. wutaishanica) on the altitudinal gradient on the south and north slopes of Taibai Mountain. The results showed that there was an altitudinal transition pattern from Q. variabilis pure forest to Q. variabilis-Q. aliena var. acutiserrata mixed forest, Q. aliena var. acutiserrata pure forest, Q. aliena var. acutiserrata-Q. wutaishanica mixed forest and Q. wutaishanica pure forest on the south and north slopes of Taibai Mountain. The main companion species of Quercus community on the north slope were Pinus armandii, Castanea seguinii, and Sorbus alnifolia, and were Pinus tabuliformis, C. seguinii, Carpinus cordata, and Q. spinosa on the south slope. Species richness, woody plant density, and Quercus species dominance on the north slope of Taibai Mountain were higher than those on the south slope. α diversity of tree layer in Quercus community on the south and north slopes of Taibai Mountain increased first, then decreased and then increased with altitude. α diversity of tree layer was higher in mixed forests than pure forests. α diversity of shrub layer was higher than that of tree layer and herb layer in Quercus community on south and north slopes. ß diversity fluctuated greatly along the altitudinal gradient on the south and north slopes, indicating that species composition changed greatly with altitude. Results of redundancy analysis showed that mean warmest month temperature, altitude and tree height accounted for 79.0% of the community diversity on the north slope, and that soil water content, tree height, canopy density and mean annual temperature accounted for 79.6% of the community diversity on the south slope. Overall, Quercus dominance was higher on the north slope of Taibai Mountain, and the substitution distribution pattern of Quercus species was clearer than that on the south slope. Environmental factors related to temperature and precipitation jointly affected α diversity of Quercus communities.

Effects of gravel on the evaluation of soil organic carbon density in Pinus massoniana plantations.

Gravel (>2 mm) is one of the main parameters for estimating soil carbon pool. To assess the effects of gravel on soil bulk density (BD) and organic carbon density (SOCD) in Pinus massoniana plantations, we estimated the BD and SOCD at the 0-10, 10-20 and 20-40 cm soil depths of 131 plots under two different conditions, with and without removing gravel. The BD of each soil layer after removing gravel was 0.58-1.57, 0.60-1.67, and 0.59-1.75 g·cm-3, respectively, which was significantly lower than that before removing gravel. Gravel increased the BD by 6.5%-6.8%. The SOCD of each soil layer before removing gravel was 8.93-65.97, 7.63-59.08, and 8.79-94.53 t·hm-2, respectively, which was higher than that after removing gravel. Overall, by neglecting the effect of gravel, SOCD was overestimated by 4.9%-11.8%. As gravel content increased, the relative deviation in the estimated BD and SOCD among different methods increased. When the gravel content was higher than 20%, the estimated SOCD at soil layer of 0-40 cm showed a significant difference between neglecting gravel and removing gravel, with the former being 29.7%-47.4% higher than the latter. In conclusion, gravel markedly affected the estimations of BD and SOCD. It was recommended that SOCD should be estimated by the method that not only uses the BD after removing gravel but also considers gravel as a correction factor (especially when gravel content is above 20.0%) to avoid overestimation of soil carbon pool.

[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.

Ecosystem service value effects of the Three Gorges Reservoir Area land use transformation under the perspective of "production-living-ecological" space.

In the context of rapid socio-economic development, eliciting "production-living-ecological" space (PLES) changes with corresponding ecosystem service benefits is critical for national land optimization and regional sustainability. Based on land use data obtained via remote sensing of 1980, 2000, 2018, and from a PLES perspective, we applied geo-information Tupu to depict land use transformations in the Three Gorges Reservoir Area (TGRA) from 1980 to 2018. The ecological/environmental effects of land use transformation were also explored based on the contribution value of ecosystem service. The results showed that both industrial production space and living space had increased from 1980 to 2018, while agricultural production space and ecological space displayed a decreasing trend. From the perspective of Tupu transformation, land use transformation pattern was relatively stable from 1980 to 2000, with the untransformed Tupu unit being dominant. However, with the complex land use transformation from 2000 to 2018, mutual transformation of agricultural production space and forest and grassland ecological space became dominant. Urbanization and industrialization were the main factors contributing to the decreased agricultural production space and ecological space. The ecosystem service value of TGRA initially decreased, then increased temporally, with greater change in the east than in the west. In the study period, ecological protection and restoration projects had positive effects on ecosystem service values, while rapid socio-economic development negatively impacted agricultural production space and ecological space. Combined with second ploughing, socio-economic development negatively impacted ecosystem ser-vice values.

[Effects of Fertilization on the Nitrogen Residual Amounts and Leaching from Citrus Orchard Soil in the Three Gorges Reservoir Area].

This experiment has the citrus orchard soil in the basin of the Zigui County Ecological Station in the Three Gorges Reservoir Area as its research object. Leaching tests of an undisturbed soil column at 0-20, 0-40, and 0-60 cm depth were performed in a citrus orchard. The effects of nitrogen leaching and residual amounts in the soil were studied. Four kinds of fertilization treatments were set up in the experiment:no fertilization treatment (CK), low nitrogen fertilization treatment (T1:250kg·hm-2), medium nitrogen fertilization treatment (T2:500kg·hm-2), and high nitrogen fertilization treatment (T3:750kg·hm-2). The results showed that:① The main form of nitrogen leaching in citrus orchard soil was nitrate nitrogen (NO3--N), accounting for 36.93%-60.07% of total nitrogen (TN) leaching. The ratio of TN to ammonium nitrogen (NH4+-N) was 4.40% to 5.79%. The ratio of NO3--N residues in soil to TN residues was 11.31‰-45.66‰, and the ratio of NH4+-N residues to TN residues was 1.051‰-2.07‰. ② Nitrogen leaching and residual amounts in citrus orchards at the same depth showed significant positive correlation with the amount of fertilizer applied. The leaching losses and residual amounts of TN in soil at different fertilization rates were 11.35-30.11 kg·hm-2and 0.30-1.86 g·kg-1, respectively. Among them, the ratio of leaching losses of NO3--N and NH4+-N to TN leaching amounts peaked under T2 treatment, and the peaks of NO3--N and NH4+-N residues in TN residual amounts appeared in T1 and T2 treatment, respectively. ③ Given the same fertilization amounts, the leaching amounts and residual amounts of different forms of nitrogen in the soil were greatly affected by soil depth. After fertilization, the peaks of NO3--N leaching and residual amounts appeared at 20 cm and 40 cm, respectively, and the peaks of NH4+-N leaching and residual amounts mainly appeared at 20 cm depth. Inferred from the results of the experiment, the neutral nitrogen treatment in the 0-40 cm soil column is more conducive to the conversion of fertilizer nitrogen to inorganic nitrogen for plant absorption, and reduces the risk of nitrogen leaching after fertilization.

The Concentration of Non-structural Carbohydrates, N, and P in Quercus variabilis Does Not Decline Toward Its Northernmost Distribution Range Along a 1500 km Transect in China.

Understanding the mechanisms that determine plant distribution range is crucial for predicting climate-driven range shifts. Compared to altitudinal gradients, less attention has been paid to the mechanisms that determine latitudinal range limit. To test whether intrinsic resource limitation contributes to latitudinal range limits of woody species, we investigated the latitudinal variation in non-structural carbohydrates (NSC; i.e., total soluble sugar plus starch) and nutrients (nitrogen and phosphorus) in mature and juvenile Chinese cork oak (Quercus variabilis Blume) along a 1500 km north-south transect in China. During the growing season and dormant season, leaves, branches, and fine roots were collected from both mature and juvenile oaks in seven sites along the transect. Tissue concentration of NSCs, N, and P did not decrease with increasing latitude irrespective of sampling season and ontogenetic stage. Furthermore, higher levels of NSCs and N in tissues of juveniles relative to mature trees were found during the dormant season. Partial correlation analysis also revealed that during the dormant season, soluble sugar, NSC, the ratio of soluble sugar to starch, and tissue nitrogen concentration were correlated positively with latitude but negatively with precipitation and mean temperature of dormant season. Our results suggest that carbon or nutrient availability may not be the driving factors of the latitudinal range limit of the studied species. Further studies should be carried out at the community or ecosystem level with multiple species to additionally test the roles of factors such as regeneration, competition, and disturbance in determining a species' northern distribution limit.

[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.

[Effect of litterfall input on soil respiration and its temperature sensitivity in moso bamboo forest under simulated drought.] / æ¨¡æ‹Ÿå¹²æ—±ä¸‹å‡‹è½ç‰©è¾“å ¥å¯¹æ¯›ç«¹æž—åœŸå£¤å‘¼å¸åŠæ¸©åº¦æ•æ„Ÿæ€§çš„å½±å“.

Increases in drought frequency and intensity under climate change will have great impacts on the carbon cycle of forest ecosystems. Understanding the responses of soil respiration and its temperature sensitivity to drought is necessary, when we assess whether soil is a carbon sink or source. The effects of litterfall input on soil respiration, temperature sensitivity and its lagging effect were studied in moso bamboo forests under simulated drought by ceiling method in the field with three litterfall treatments, i.e., ambient litterfall (unchanged, LU), litter addition (LA) and litter removal (LR). The results showed that LU decreased annual soil respiration rate in drought treatment (2.34 Μmol·m-2·s-1), compared with that in the control (3.15 Μmol·m-2·s-1) with ambient natural rainfall. LR showed stronger effect on soil respiration than LA. Compared with LU, LR decreased soil respiration rate by 21.0% in ambient condition and by 20.9% in drought treatment, while LA led to 5.3% increase only in drought treatment. Such a result indicated that the effects of LA and LR on soil respiration rate were stronger than LU in the drought condition. Drought decreased the temperature sensitivity of soil respiration by 8.4%, while LA and LR reduced that by 15.4% and 7.6%, respectively. The cumulative CO2 emissions during the whole 18 months were 7.35 and 5.40 kg CO2·m-2 in the control and drought treatment. Compared with LU, LA increased the cumulative CO2 emissions by 1.8% and 10.7%, and LR decreased that by 19.9% and 18.0% in the control and drought treatments. Our results indicated that the relationship between the litterfall amount (addition or removal) and soil respiration rate was nonlinear. The significant lagging effect may be caused by the decrease in root growth and microbial activity due to decreased soil water availability in drought treatment. Litterfall played a more important role in soil CO2 emission under drought, and thus litterfall was a crucial factor in soil carbon emission in the context of climate change.

[Characteristics of Nitrogen and Phosphorus Output in Runoff and Rainfall Runoff in Lanlingxi Watershed, Three Gorges Reservoir Area].

The small watershed of an agroforestry system in the Lanlingxi watershed in the Three Gorges Reservoir area was studied by performing continuous monitoring of nitrogen and phosphorus output and concentrations and analyzing the changes in the output of nitrogen and phosphorus in runoff and its response to different rainfall conditions. The results showed that:①The total runoff loss was 50.92×104 m3 in this watershed during the rainy season, with 52.43 kg·hm-2 lost by total nitrogen, including nitrate nitrogen (30.26 kg·hm-2) and particulate nitrogen (21.61 kg·hm-2), and 0.06 kg·hm-2 and 0.10 kg·hm-2 lost by ammonium nitrogen and total phosphorus; ②The distribution of rainfall has the characteristics of stage and strong rainfall during the wet season was the main driving force of soil nutrient output. Rainfall runoff contributed to 88% of total nitrogen loss and 90% of total phosphorus loss in the rainy season; ③The main path of nitrogen and phosphorus loss in the rainy season was the surface runoff caused by rainfall, accounting for 68% of total nitrogen loss and 74% of total phosphorus loss; ④Nitrate nitrogen concentrations showed a negative correlation with rainfall runoff and the output was mainly distributed in the later runoff process. Ammonium nitrogen and total phosphorus concentrations were positively correlated with rainfall and both were mainly distributed in the early stage of the runoff process; ⑤The concentrations of total nitrogen in this watershed exceeded the standard values. The water quality in the rainfall and the non-rainfall period was worse than Grade Ⅴ.

[Long-term changes of land use/cover in the Three Gorges Reservoir Area of the Yangtze River, China.] / 长江三峡库区土地利用/覆盖的长期变化.

Understanding the temporal and spatial dynamics of land use/cover (LUC) can contri-bute to reveal the impacts of climate change and human activities on ecosystems and thus be an important prerequisite for ecosystem management. As an ecologically vulnerable area in China, the Three Gorges Reservoir Area (TGRA) of the Yangtze River presented significant complexity in the response to environmental changes. However, there is a general lack of understanding in the underlying mechanism. In this study, we interpreted the time series remote sensing images derived from the Landsat sensors to map the LUC of the TGRA, and aimed to analyze the long-term changes in the distribution and structure of LUC and elucidate the evolution process of LUC, which could provide a scientific basis to understand the complexity of ecosystem changes and regional ecosystem management in ecologically fragile regions. The results showed that the TGRA presented the significant changes in spatial heterogeneity of LUC structure from 1990 to 2015. Meanwhile, the landscape changed from farmland to woodland (forest and shrubland). Farmland decreased from 66.2% to 40.4%, but woodland increased from 31.3% to 53.5%, buildings and water area increased gradually. Forest gradually spread to the middle of the TGRA, while the buildings presented a scattered expansion. In the altitude zone of 500-1000 m and slope zone of 15°-25°, woodland increased noticeably, and the coniferous forest, mixed forest and shrubland had a higher growth rate. In the study period, due to the urban construction and the various ecological restoration projects in the TGRA, the LUC structure varied with the dam's impoundment and was characterized by the ecosystem restoration. Ecological restoration projects were helpful to reduce the negative impacts of urban construction and economic development on the environment.

[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.

[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.

[Land Use Structure Change and Its Control Effect of Nitrogen Output in a Small Watershed of Three Gorges Reservoir Area: A Case Study of Lanlingxi Watershed].

The nitrogen (N) output in Lanlingxi watershed of Three Gorges Reservoir Area in 2015 was monitored and the current land use map was investigated. Cluster analysis and correlation analysis were used to identify the major sources of pollutants and to discriminate the source and the sink land use types. The effects of land use on N exports were quantitatively analyzed by stepwise regression analysis. The results showed that: ① After the returning farmland to forest project the land use structure of this area changed dramatically. The area proportions of forest land and garden plot increased to 76.85% and 13.87% respectively, and the proportion of cultivated land dropped to 1.16%. Cultivated lands were stellate distributed and garden plots in some catchments were flake distributed. ② The content of TN in some monitoring points surpassed the Class V standard of the national groundwater environmental quality. The ammonium-N (NH4+-N) concentrations ranged 0.089-0.214 mg·L-1, 2.925-13.203 mg·L-1 for nitrate-N (NO3--N) and 3.561-14.572 mg·L-1 for total-N (TN). And NO3--N accounted for more than 80% of TN. ③ There were significant positive correlations between garden plot, residential land and N loss, and negative correlations between forest land, unutilized land and N export, which indicated that the former were N sources and the latter were sinks. ④ Forest land area should be increased and garden plot should be controlled, and the area ratio of residential land should be kept below 5% when adjusting land use structure of this watershed. Moreover, forest-tea and forest-fruits modes should be applied to change single land use type of garden plot in some catchments.

[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.

[Control of Soil Nutrient Loss of Typical Reforestation Patterns Along the Three Gorges Reservoir Area].

Annual soil nutrient loss characteristics on typical reforestation patterns in watershed along the Three Gorges Reservoir Area were studied based on runoff plot experiment. Runoff and sediment nutrition content from May to October 2014 of typical reforestation patterns including garden plot (tea garden), forest land (Chinese chestnut) and the original slope farmland were determined and then analyzed. The results showed that: (1) After the Returning Farmland to Forest Project the quantity of annual soil nutrient (nitrogen and phosphorus, the sum of them in sediment and runoff) loss decreased. The output of total nitrogen (TN) was in the order of slope farmland (2 444.27 g x hm(-2)) > tea garden (998.70 g x hm(-2)) > Chinese chestnut forest (532.61 g x hm(-2)), and for total phosphorus (TP) loss was slope farmland (1 690.48 g x hm(-2)) > tea garden (488.06 g x hm(-2)) > Chinese chestnut forest (129.00 g x hm(-2)) . Compared with slope farmland, the load of TN and TP output of reforestation patterns decreased 68.68% and 81.75%, respectively. (2) Compared with slope farmland, available nitrogen loss decreased in reforestation patterns. Total nitrate nitrogen (NO3(-)-N) loss ranked in the order of slope farmland (113.79 g x hm(-2)) > tea garden (73.75 g x hm(-2)) > Chinese chestnut forest (56.06 g x hm(-2)) The largest amount of ammonium nitrogen (NH4(+)-N) was found in tea garden (69.34 g x hm(-2)), then in farmland (52.45 g x hm(-2)), and the least in Chinese chestnut forest (47.23 g x hm(-2)). (3) The main route of NO3(-)-N and NH4(+)-N loss was both through runoff, the quantity of NO3(-)-N and NH4(+)-N output in which accounted for 91.4% and 92.2% of the total, respectively. The quantity of TN and TP in sediment accounted for 86.6% and 98.4% of the total. TN and TP loss showed an extremely significant correlation with sediments, which showed that sediment output was the main approach of TN and TP loss.

[Effects of land use and landscape pattern on nitrogen and phosphorus exports in Lanlingxi Watershed of the Three Gorges Reservoir Area, China].

The temporal and spatial characteristics of N, P exports and effects of land use and landscape pattern on N, P exports were analyzed in the Lanlingxi Watershed of the Three Gorges Reservoir Area. The results showed that the TN, TP and NO3(-) -N were mainly generated by non-wood forest, the N, P exports in flood period (June to September) were significantly higher than the non-flood period (January to May). The NH4(+) -N export was derived from the residential area in the non-flood period, while from non-wood forest in the flood period. In addition, the performance of samples N, P exports with forest distributed were lower in both two periods. Also, the proportion of forest significantly negatively correlated with NO3(-) -N, TP in the non-flood period and TN, TP in the flood period. The residential area proportion notably positively correlated with NO3(-) -N, TN in non-flood period and NO3(-) -N, TN, TP in the flood period. The non-wood forest proportion also significantly positively correlated with NH4(+) -N, TN in the flood period. Moreover, PD closely positively correlated with N exports in non-flood period, with NO3(-) -N, NH4(+) -N in flood period. The CONT index strongly negatively correlated with N exports in flood period and TP in non-flood period. However, the proportions of farmland, unused land and the indices of ED were relatively weakened with N, P exports in both periods, while SHMN and water proportion did not show any positive or negative correlation. Moreover, the regression fitting degree of NH4(+)-N was superior to NO3(-) -N, TN and TP with the adjust R2 of 0.885 and 0.969 in two periods, while the regression relation was better than that of non-flood period. The result of redundancy analysis further demonstrated that the landscape fragmentation caused by patches types of different land uses could better explain impacts on the exports of nitrogen and phosphorus. The two canonical axes accumulated explained the 90% proportion of the variables and the highest contribution was PD, which was an important indicator for watershed water quality assessment and prediction.

[Eco-physiological response of Quercus variabilis seedlings to increased atmospheric CO2 and N supply].

The effect of CO2 enhancement, nitrogen deposition and their interaction on the northern boundary (Zhuanghe in Liaoning Province) of Quercus variabilis seedlings was studied by controlling the CO2 concentration (700 micromol x mol(-1); 400 micromol x mol(-1)) and nitrogen level (non nitrogen fertilizer: CK; nitrogen fertilizer: 120 kg N x hm(-2)). The results showed that under elevated CO2 the Q. variabilis seedlings' leaf morphology, photosynthetic pigments and leaf nitrogen content tended to decrease, and the dark respiration rate decreased 63. 3% and soluble sugar increased 2.6%. Nitrogen deposition significantly promoted the Q. variabilis seedlings' leaf morphology and photosynthetic pigments, leading to increased leaf nitrogen content, decreased potassium content, and 26.7% of increase in nitrogen to potassium ratio. CO2 and N interaction played a significant role on promoting the Q. variabilis seedlings' leaf morphology and photosynthetic. The maximum net photosynthetic and light saturation point were 1.4 and 2.6 times of the control, while dark respiration and light compensation point decreased 65.9% and 50.0%, respectively. Elevated CO2 and nitrogen deposition had a positive effect on Q. variabilis seedlings to some degree, which might result in the movement of distribution boundary of Q. variabilis to north.

[Research progress on remote sensing of ecological and environmental changes in the Three Gorges Reservoir area, China].

The Three Gorges Reservoir area (TGR area) , one of the most sensitive ecological zones in China, has dramatically changes in ecosystem configurations and services driven by the Three Gorges Engineering Project and its related human activities. Thus, understanding the dynamics of ecosystem configurations, ecological processes and ecosystem services is an attractive and critical issue to promote regional ecological security of the TGR area. The remote sensing of environment is a promising approach to the target and is thus increasingly applied to and ecosystem dynamics of the TGR area on mid- and macro-scales. However, current researches often showed controversial results in ecological and environmental changes in the TGR area due to the differences in remote sensing data, scale, and land-use/cover classification. Due to the complexity of ecological configurations and human activities, challenges still exist in the remote-sensing based research of ecological and environmental changes in the TGR area. The purpose of this review was to summarize the research advances in remote sensing of ecological and environmental changes in the TGR area. The status, challenges and trends of ecological and environmental remote-sensing in the TGR area were further discussed and concluded in the aspect of land-use/land-cover, vegetation dynamics, soil and water security, ecosystem services, ecosystem health and its management. The further researches on the remote sensing of ecological and environmental changes were proposed to improve the ecosystem management of the TGR area.