[Effects of radiation changes on net ecosystem exchange of carbon dioxide in a middle subtropical Chinese fir plantation]. / 辐射变化对中亚热带杉木人工林净CO2交换的影响.

Total solar radiation is an important factor affecting carbon exchange in forest ecosystem. In order to understand the effects of radiation change on carbon exchange in Chinese fir plantation, long-term monitoring data of carbon dioxide flux and meteorological factors measured by open eddy covariance system and meteorological gradient observation system were used in this study. The clearness index (kt) was used to represent the condition of solar radiation. We analyzed the effects of kt on net ecosystem exchange of carbon dioxide (NEE) in the central subtropical Chinese fir plantation during the growing season (from April to October). The results showed that total solar radiation in clear sky was usually higher in the morning than that in the afternoon, and that NEE was lower in the morning than in the afternoon. Such difference in NEE reached the maximum when the solar elevation angle was about 50°. At the medium kt(0.42-0.52), carbon absorption of Chinese fir plantation was the strongest. The ave-rage maximum relative change of NEE in 10 years in different solar elevation angles ranged from 11.0% to 29.4%, while the minimum and maximum critical values appeared at 35°-40° and 45°-50°, respectively. When kt was at the moderate degree due to the existence of clouds, carbon absorption and diffuse photosynthetically active radiation of Chinese fir plantation reached the maximum, and the latter might be the main reason for the former. Moderate radiation condition with the presence of cloud clould promote NEE of Chinese fir plantation and lead to largest carbon absorption.

[Leaf nitrogen and phosphorus stoichiometry of shrubland plants in the rocky desertification area of Southwestern Hunan, China.] / æ¹˜è¥¿å—çŸ³æ¼ åŒ–åœ°åŒºçŒä¸›æ¤ç‰©å¶N、P化学计量特征.

In this paper, we took the leaves of shrubland plants in rocky desertification area in Southwestern Hunan as the research object to analyze the nitrogen (N) and phosphorus (P) stoichiometry characteristics for different functional groups and different grades of rocky desertification, i.e., light rocky desertification (LRD), moderate rocky desertification (MRD) and intense rocky desertification (IRD). The results showed that the average contents of N and P were 12.89 and 1.19 g·kg-1, respectively, and N/P was 11.24 in common shrubland plants in the study area, which indicated that the growth of most plants were mainly limited by N. The content of N was declined in order of deciduous shrubs > evergreen shrubs > annual herbs > perennial herbs. The content of P and N/P were higher in deciduous shrubs than in perennial herbs. Significant differences were found among the main families of plants in terms of the contents of N, P and N/P in the study sites. The plants of Gramineae had the lowest contents of N and P, andtheir growth was mostly restricted by N, while Leguminosae had the highest content of N and N/P, and their productivity was majorly controlled by P. The contents of N and P in the leaves were significantly higher in dicotyledon plants and C3 plants than in monocotyledon plants and C4 plants, but the N/P was not significantly diffe-rent between these two plant categories. The nitrogen-fixing plants had higher content of N and N/P than the non-nitrogen-fixing plants, but the P content was not significantly different between these two plant groups. There were significant correlations between contents of N and P, N/P and N in all study plots. No significant correlation was found between N/P and P content in the examined rocky desertification sites, except for that in MRD. There were no significant differences of the contents of N, P and N/P under different grades of rocky desertification.

[Spatial heterogeneity and influencing factors of soil phosphorus concentration in a mid-subtropical Choerospondias axillaris deciduous broad-leaved forest, China.] / ä¸­äºšçƒ­å¸¦å—é ¸æž£è½å¶é˜”å¶æž—åœŸå£¤ç£·ç´ ç©ºé—´å˜å¼‚åŠå ¶å½±å“å› ç´ .

In order to investigate spatial variations in soil phosphorus (P) concentration and the influencing factors, one permanent plot of 1 hm2 was established and stand structure was surveyed in Choerospondias axillaries deciduous broadleaved forest in Dashanchong Forest Park in Changsha County, Hunan Province, China. Soil samples were collected with equidistant grid point sampling method and soil P concentration and its spatial variation were analyzed by using geo-statistics and geographical information system (GIS) techniques. The results showed that the variations of total P and available P concentrations in humus layer and in the soil profile at depth of 0-10, 10-20 and 20-30 cm were moderate and the available P showed higher variability in a specific soil layer compared with total P. Concentrations of total P and available P in soil decreased, while the variations increased with the increase in soil depth. The total P and available P showed high spatial autocorrelation, primarily resulted from the structural factors. The spatial heterogeneity of available P was stronger than that of total P, and the spatial autocorrelation ranges of total P and available P varied from 92.80 to 168.90 m and from 79.43 to 106.20 m in different soil layers, respectively. At the same soil depth, fractal dimensions of total P were higher than that of available P, with more complex spatial pattern, while available P showed stronger spatial correlation with stronger spatial structure. In humus layer and soil depths of 0-10, 10-20 and 20-30 cm, the spatial variation pattern of total P and available P concentrations showed an apparent belt-shaped and spot massive gradient change. The high value appeared at low elevation and valley position, and the low value appeared in the high elevation and ridge area. The total P and available P concentrations showed significantly negative correlation with elevation and litter, but the relationship with convexity, species, numbers and soil pH was not significant. The total P and available P exhibited significant positive correlations with soil organic carbon (SOC), total nitrogen concentration, indicating the leaching characteristics of soil P. Its spatial variability was affected by many interactive factors.

[Plant and soil nutrient characteristics in the karst shrub ecosystem of southwest Hunan, China]. / æ¹˜è¥¿å—å–€æ–¯ç‰¹åœ°åŒºçŒä¸›ç”Ÿæ€ç³»ç»Ÿæ¤ç‰©å’ŒåœŸå£¤å »åˆ†ç‰¹å¾.

This research was conducted in light (LRD), moderate (MRD, abandoned land) and intense (IRD) rocky desertification shrub ecosystems in Shaoyang, Hunan Province. We collected plant samples and soil at 3 layers (0-15, 15-30, 30-45 cm), and analyzed the distribution patterns of soil and plant nutrients and the relationships among them. Our results showed that the contents of soil organic carbon (SOC) and total N in different soil layers were various and decreased with soil depth, while the contents of total P, K, Ca and Mg had no obvious variation among the different soil layers. The contents of total N, P, Ca and Mg in soil were significantly different among the 3 rocky desertification shrub ecosystems, and the SOC, total N and total P in MRD were relatively higher than in the others. The rank of macroelement contents in soils for LRD and IRD was SOC>total K>total Ca>total Mg>total N>total P, while it was SOC>total K>total Ca>total N>total Mg>total P for MRD. The rank of macroelement contents in plants from the 3 rocky desertification shrub ecosystems was Ca>N>K>Mg>P, and the contents of N and P in plants were significantly positively correlated with the corresponding contents of total N and total P in soils. Soil nutrients were closely related to vegetation growth. According to the soil nutrient status of desertification plots of different grades, we should integrate the forest reservation with artificial afforestation and targeted fertilization methods for managing karst rocky desertification.

Development and Evaluation of Models for the Relationship between Tree Height and Diameter at Breast Height for Chinese-Fir Plantations in Subtropical China.

Tree diameter at breast height (dbh) and height are the most important variables used in forest inventory and management as well as forest carbon-stock estimation. In order to identify the key stand variables that influence the tree height-dbh relationship and to develop and validate a suit of models for predicting tree height, data from 5961 tree samples aged from 6 years to 53 years and collected from 80 Chinese-fir plantation plots were used to fit 39 models, including 33 nonlinear models and 6 linear models, were developed and evaluated into two groups. The results showed that composite models performed better in height estimate than one-independent-variable models. Nonlinear composite Model 34 and linear composite Model 6 were recommended for predicting tree height in Chinese fir plantations with a dbh range between 4 cm and 40 cm when the dbh data for each tree and the quadratic mean dbh of the stand (Dq) and mean height of the stand (Hm) were available. Moreover, Hm could be estimated by using the formula Hm = 11.707 × l n(Dq)-18.032. Clearly, Dq was the primary stand variable that influenced the height-dbh relationship. The parameters of the models varied according to stand age and site. The inappropriate application of provincial or regional height-dbh models for predicting small tree height at local scale may result in larger uncertainties. The method and the recommended models developed in this study were statistically reliable for applications in growth and yield estimation for even-aged Chinese-fir plantation in Huitong and Changsha. The models could be extended to other regions and to other tree species only after verification in subtropical China.

[CO2 exchanges between mangrove- and shoal wetland ecosystems and atmosphere in Guangzhou].

Based on the investigation of biomass and the measurement of CO2 and CH4 fluxes, the CO2 exchanges between mangrove- and shoal wetland ecosystems and atmosphere in Guangzhou were studied, and the CO2 absorption capability of the wetlands vegetation net productivity as well as the carbon sink function of the wetlands under different waterlogged conditions (perennial, intermittent, and no water-logging) was analyzed. As for mangrove wetland ecosystem, its vegetation net productivity absorbed 33.74 t x hm(-2) x a(-1) of CO2, and soil emitted 12.26 t x hm(-2) x a(-1) of CO2 (including the greenhouse effect amount of CH4 converted into that of CO2,) illustrating that mangrove wetland had a 21.48 t x hm(-2) x a(-1) net absorption of CO2, being a strong carbon sink. For shoal wetland ecosystem, its vegetation net productivity absorbed 8.54 t x hm(-2) x a(-1) of CO2, and soil emitted 5.88 t x hm(-2) x a(-1) of CO2 and 0.19 t x hm(-2) x a(-1) of CH4. If converting into carbon, the wetland absorbed 2.33 t C x hm(-2) x a(-1), and soil emitted 1.74 t C x hm(-2) x a(-1) (including the carbon in CH4), illustrating that shoal wetland fixed 0.59 t C x hm(-2) x a(-1), being a weak carbon sink. If the greenhouse effect amount of CH4 was converted into that of CO2, the soil emitted 9.78 t x hm(-2) x a(-1) of CO2, which was 1.24 t x hm(-2) x a(-1) more than the absorption. As a result, shoal wetland was a weak carbon source. Between the two test greenhouse gases, CH4 was the main one emitted under perennial water-logging, while CO2 was that under no water-logging. Moreover, the wetland under perennial water-logging had the strongest carbon sink function, while that under no water-logging was in adverse.