ISSN 1673-3517
ISSN 1673-3630(Online)
CN 11-5728/S
In order to make clear the relationships between photosynthesis and leaf N, leaf P and SLA of tropical trees, and test the differences in the relationships among life-form groups (trees, shrub-like trees and shrubs), seedlings and saplings of 101 species from a tropical montane rain forest, located in the Diaoluo Mountain of Hainan Island, were selected. The net photosynthesis based on area and mass (Aarea and Amass), leaf nitrogen content based on area and mass (Narea and Nmass), leaf phosphorus content based on area and mass (Parea and Pmass) and specific leaf area (SLA) were measured and/or calculated. The results showed that Aarea and Amass tended to follow the order of shrubs>trees>shrub-like trees. One-way ANOVA showed that the difference in Aarea between shrubs and shrub-like trees was significant (p<0.05), and for Amass there were significant differences between shrubs and shrub-like trees and between shrubs and tree species (p<0.05). The relationships between Aarea and Nmass were highly significant in all three life-form groups and for all species (p<0.0001). The correlation between Aarea and Pmass was highly significant in shrubs (p=0.0038), shrub-like trees (p=0.0002) and for all species (p<0.0001), but not significant in trees (p>0.05). The relationship between Aarea and SLA was highly significant in shrubs (p=0.0006), trees (p<0.0001) and for all species (p<0.0001), however this relation was not significant in shrub-like trees (p>0.05). The relationships between Amass and leaf N and SLA were highly significant in all three life-form groups and for all species (p<0.0001). For Amass and leaf P, there were significant correlations in tree groups (p=0.0377) and highly significant correlations in shrub groups (p=0.0004), shrub-like tree groups (p=0.0018) and for all species (p<0.0001). Stepwise regression showed that predicted Amass values were closer to the observed values than those for predicted Aarea values. Thus, it can be concluded that the relationships obtained from seedling and sapling measurements are close to those from mature individuals; correlations between photosynthesis and Nmass, Pmass and SLA traits are significant and the relationships are stronger and more stable for Amass than for Aarea.
Using the PMS pressure chamber and isotope mass spectrometer (MAT-252), the leaf juice of Acacia mangium was obtained, and the carbon isotope discrimination (D) representing the most recently fixed carbon in the juice was determined. At the same time, the water-use efficiency of A. mangium was estimated. The results indicated that the carbon isotope ratio in the air of forest canopy (da), 10 m high above ground averaged -7.57±1.41‰ in cloudy days, and -8.54±0.67‰ in sunny days, respectively. The diurnal change of the carbon isotope ratio in the photosynthetic products of the leaf juice (dp) was of saddle type in cloudy days, but dropped down from morning to later afternoon in sunny days. A strong negative correlation between dp and leaf-to-air vapor pressure deficit (D) was observed in sunny days, but a slight change in dp was found in cloudy days. The dp also decreased with decreasing leaf water potential (Ψ), reflecting that water stress could cause the decrease of dp. The carbon isotope discrimination of the leaf juice was positively correlated with the ratio between intercellular (Pi) and atmospheric (Pa) partial pressure of CO2. For A. mangium, the isotope effect on diffusion of atmospheric CO2 via stomata was denoted by a = 4.6‰, and that in net C3 diffusion with respect to Pi was indicated by b = 28.2‰. The results were in reasonable accord with the theoretically diffusive and biochemical fractionation of carbon isotope. It was defined that carbon isotope discrimination of photosynthetic products in A. mangium leaf juice was in proportion to that from photosynthetic products in dry material. The water-use efficiency estimated by the carbon isotope discrimination in leaf juice, fit well with that measured by gas exchange system (R2 = 0.86, p< 0.0001). The application of leaf juice in measuring the stable carbon isotope discrimination would reduce the effects of fluctuating environmental factors during the synthesis of dry matter, and improve the eco-physiological studies on carbon and water balance when scaling from the plant to canopy in the fields.
We tested the dynamics of nine enzymes during leaf litter decomposition in Xishuangbanna tropical rainforest both in the field and laboratory to explore the response of enzyme dynamics to decomposition under different food-web structures. We used coarse and fine (1 mm and 100 μm mesh size, respectively) litterbags in the field to create different food-web structures during litter decomposition. Most soil macrofauna such as nematodes could access only the coarse mesh litterbags, leaving only microbiota, such as mites, in the fine mesh litterbags. In the laboratory, sterilization and inoculation were adopted to investigate different enzyme dynamics with nematodes or only microbiota participating in litter decomposition. Invertase and amylase increased more for shorter food webs at the early stages of decomposition, while activities of endocellulase, β-glucosidase, xylanase and polyphenoloxydase increased to their maximum at the later stages, but greater increase occurred with extended food webs. Invertase and amylase had negative relationships and endocellulase, β-glucosidase, xylanase and polyphenoloxydase had positive relationships with litter decomposition (mass loss). The activities of enzymes responded to the process of litter decomposition. Invertase and amylase played key roles for microbiota utilizing the substrates at early stages of decomposition, while endocellulase, β-glucosidase, xylanase and polyphenoloxydase worked on the further decay of recalcitrant compounds at later stages. All enzymes related to carbon decay acted as effective indicators of litter decomposition. The decomposition of plant organic matter was essentially an enzymatic process.
Landslides, which develop in the Three Gorges Reservoir area, are related to many factors. Lithology is one of the indispensable internal factors, besides relative height differences, slope gradients and slope profiles. We used an information value model with geographical information system (GIS) technology to study how lithology contributes to the development of landslides from the Yunyang to Wushan segment in the Three Gorges Reservoir area and we quantify the relationship between lithology and development of landslides. Via an investigation of 205 examples of past landslides, we found that the lithology of J3s, J3p and T2b contributes most. Our research results can provide a valid basis for future construction in the Three Gorges Reservoir area.
Biomass, carbon content, carbon storage and spatial distribution in the 32-year-old Phoebe bournei artificial forest were measured. The mean biomass of the forest stand was 174.33 t/hm2, among which the arbor layer was 166.73 t/hm2, which accounted for 95.6%. Carbon contents of stems, barks, branches, leaves, root, shrub layer, herb layer, lichen layer and litter layer were 0.5769 g C/g, 0.4654 g C/g, 0.5232 g C/g, 0.4958 g C/g, 0.4931 g C/g, 0.4989 g C/g, 0.4733 g C/g, 0.4143 g C/g, 0.3882 g C/g, respectively. The mean carbon content of soil was 0.0139 g C/g, which reduced gradually along with soil depth. Total carbon storage of the P. bournei stand ecosystem was 227.59 t/hm2, among which the arbor layer accounted for 40.13% (91.33 t/hm2), the shrub layer accounted for 0.17% (0.38 t/hm2), the herb layer accounted for 0.76% (1.71 t/hm2), the lichen layer accounted for 0.28% (0.63 t/hm2), and the litter layer accounted for 0.29% (0.66 t/hm2). Carbon content (0-80 cm) of the forest soil was 58.40% (132.88 t/hm2). Spatial distribution ranking of carbon storage was: soil layer (0-80 cm)>arbor layer>herb layer>litter layer>lichen layer>shrub layer. Net production of the forest stand was 8.5706 t/(hm2·a), in which the arbor layer was 6.6691 t/(hm2·a), and it accounted for 77.82%. Net annual carbon sequestration of the P. bournei stand was 4.2536 t/(hm2·a), and the arbor layer was 3.5736 t/(hm2·a), which accounted for 84.01%.
In order to describe and compare intuitively the impact of different kinds of ground cover on temporal and spatial variation of soil moisture, an experiment was carried out by continuous observations to obtain soil potential data of different treatments. Based on the data, isogram maps were drawn by a regression isogram method. The results indicate that the isogram of treatment A (Paspalum notatum Flugge-covered) is the most complicated among the three treatments with its significant transverse levels, while the isograms of treatment B (mulching of P. notatum Flugge) and C (bare slope) are relatively simple but have clear vertical levels. The variation of soil moisture 30 cm deep in the A treatment is the largest, while that at 60 cm is the second largest and that of 90 cm is the smallest. The variation of soil moisture at all levels of B is fairly small, while that at 30 and 60 cm of C is greater than that 90 cm deep.
Dynamic changes of soil erosion affected by conversion of farmland to forest or grassland in the Yanhe River Basin were analyzed based on the revised universal soil loss equation (RUSLE). The RUSLE variables were selected and calculated reasonably using the GIS technique. Results show that: 1) After the conversion of farmland to forest or grassland, soil erosion decreased greatly. Compared with soil erosion in period of 1986 to 1997, the soil erosion amount had been reduced on the average by 30.6% by 2000; 2) Of the different land uses, slope farmland, especially the steep slope land had the greatest impact on soil erosion. The conversion of forest or grassland was the main driving force for the reduction of soil erosion; 3) In the short term, soil erosion was mainly controlled by C-factor, implying that the adjustment of land use structure might be an effective approach to reduce soil erosion.
The dynamic change of soil water as a function of leaf area index and the soil water deficit value, prerequisites for assuring the survival of plants, were simulated. We established a dynamic soil water model based on a theory of water balance, the characteristics of the environment, and the physiological ecology of the plants in the Ulan Buh Desert, northwestern China. We estimated the soil water carrying capacity of the vegetation in our study area of the desert. The results showed that the proportion of soil evaporation in the total amount of precipitation was greater than 60% in the wandering and semifixed sands and 44.8% in the fixed sand. When the leaf area index was less than 1.7 m2/m2, the soil water deficit was maintained at a low level, but when the leaf area index continued to increase, the soil water deficit increased rapidly as well. In consequence, we come to the conclusion that the leaf area index of the soil water carrying capacity of the vegetation is 1.7 m2/m2 in our study area.
The effects of elevated nitrogen deposition on soil microbial biomass carbon (C) and extractable dissolved organic carbon (DOC) in three types of forest of southern China were studied in November, 2004 and June, 2006. Plots were established in a pine forest (PF), a mixed pine and broad-leaved forest (MF) and monsoon evergreen broad-leaved forest (MEBF) in the Dinghushan Nature Reserve. Nitrogen treatments included a control (no N addition), low N (50 kg N/(hm2a)), medium N (100 kg N/(hm2·a)) and high N (150 kg N/(hm2·a)). Microbial biomass C and extractable DOC were determined using a chloroform fumigation-extraction method. Results indicate that microbial biomass C and extractable DOC were higher in June, 2006 than in November, 2004 and higher in the MEBF than in the PF or the MF. The response of soil microbial biomass C and extractable DOC to nitrogen deposition varied depending on the forest type and the level of nitrogen treatment. In the PF or MF forests, no significantly different effects of nitrogen addition were found on soil microbial biomass C and extractable DOC. In the MEBF, however, the soil microbial biomass C generally decreased with increased nitrogen levels and high nitrogen addition significantly reduced soil microbial biomass C. The response of soil extractable DOC to added nitrogen in the MEBF shows the opposite trend to soil microbial biomass C. These results suggest that nitrogen deposition may increase the accumulation of soil organic carbon in the MEBF in the study region.