Soil and fine roots ecological stoichiometry in different vegetation restoration stages in a karst area, southwest China.

The cyclic process of carbon (C), nitrogen (N), and phosphorus (P) elements is an important factor affecting the function of the forest ecosystem. However, the relation between soil and root stoichiometric ratios, especially in karst areas with extremely fragile geology and intensive human disturbance has rarely been investigated. In the current study the concentrations of C, N, and P and their stoichiometric characteristics were investigated using sequential soil coring under different stages of vegetation restoration (primary forest, secondary forest, shrubland and grassland) and soil layer (0-10 cm, 10-20 cm, 20-30 cm) in fine root and soil samples. The results showed that total C concentration had no significant change in all four vegetation types and three soils layer in the fine root, whereas total N and P concentration reached the maximum value in secondary forest and the minimum in grassland. In addition, soil organic C (SOC) and total N increased continuously with natural succession and decreased with soil depth. Secondary forest showed the largest total P concentration in soil, with the smallest corresponding to grassland. Furthermore, both vegetation type and soil layer significantly affected soil C, N, and P stoichiometric ratios. There was a positive correlation among C, N and P in the fine roots, as well as in the soil. While fine root C:N and C:P ratios were negatively related to soil C:N and C:P, fine root N:P was significantly related to soil N:P. This study can provide a scientific basis for the restoration of fragile ecosystem vegetation and for comprehensive treatment of rocky desertification in karst.

Spatial heterogeneity of soil available medium- and micro-elements in evergreen-deciduous broadleaved forest in karst.

Understanding the spatial heterogeneity of soil available medium- and micro-elements in karst area can provide a valuable theoretical guideline for soil nutrient management of karst ecosystem. We collected soil samples at a soil depth of 0-10 cm using grid sampling (20 m×20 m) in a 25 hm2 (500 m×500 m) dynamic monitoring plot. We further analyzed the spatial variability of soil medium- and micro-elements and their drivers, with classic statistics analysis and geo-statistics analysis. The results showed that the average contents of exchangeable Ca and Mg and available Fe, Mn, Cu, Zn, and B were 7870, 1490, 30.24, 149.12, 1.77, 13.54, and 0.65 mg·kg-1, respectively. The coefficient of variation of the nutrients ranged from 34.5% to 68.8%, showing a medium degree of their spatial variation. The coefficient of determination of the best-fit semi-variogram models of each nutrient was higher than 0.90, except for available Zn (0.78), indicating a strong predictive power for the spatial variation of the nutrients. The nugget coefficients for all the nutrients were less than 50%, showing a moderate spatial correlation, and the structural factors played a pivotal role. The spatially autocorrelated variation was within the range of 60.3-485.1 m, among which available Zn showed the lowest range and the deepest fragmentation degree. The spatial distribution of exchangeable Ca, Mg, and available B were consistent, with contents in the depression being significantly lower than that in other habitats. The contents of available Fe, Mn, and Cu declined with the increases of altitude and were significantly lower on the hilltop than in other habitats. The spatial variation of soil medium- and micro-elements was closely related to topographic factors in karst forest. Elevation, slope, soil thickness, and rock exposure rate were the primary drivers of spatial variation of soil elements and need to be considered in soil nutrient management of karst forestlands.

[Effects of tree mortality on the spatial patterns and interspecific associations of individuals in karst evergreen deciduous broad-leaved mixed forests]. / å–€æ–¯ç‰¹å¸¸ç»¿è½å¶é˜”å¶æž—ä¸ªä½“æ­»äº¡å¯¹ç©ºé—´æ ¼å±€åŠç§é—´å ³è”æ€§çš„å½±å“.

Tree mortality is an important ecological process in forests. It is crucial to understand how tree mortality affects spatial patterns and interspecific associations for revealing the mechanisms of tree mortality and community dynamics. We employed the correlation method of spatial point pattern analysis to analyse the variations in spatial patterns and interspecific relations before and after mortality using data obtained from two surveys of a 25 hm2 plot in the Mulun National Natural Reserve, China. The results showed that most species had an aggregated distribution both pre- and post-mortality. The proportion of species with aggregated distribution reduced slightly post-mortality compared with that for pre-mortality. Increases in the number of species with random distribution at small scale indicated that tree death was not random. At the species level, there were significant positive associations between dead and live trees of the 13 common species at different levels of 0-30 m range, suggesting weak intraspecific and interspecific competition among dominant species. Pre- and post-mortality interspecific associations were mostly positive, which remained stable during the period of two surveys for most species, indicating that the community had reached a rather stable stage. Following tree mortality, the number of species with positive associations increased at 1-30 m scales, whereas the number of species with negative and no associations decreased at most scales. These results indicated that the pressure of interspecific competition was relieved to some extent after individual death.

[Changes of soil microbial biomass carbon, nitrogen, and enzyme activities in East Dongting Lake wetlands at different water levels]. / ä¸åŒæ°´ä½æ—¶æœŸä¸œæ´žåº­æ¹–æ¹¿åœ°åœŸå£¤å¾®ç”Ÿç‰©ç”Ÿç‰©é‡ç¢³æ°®å’Œé ¶æ´»æ€§å˜åŒ–.

We analyzed soil quality based on soil microbial characteristics of three different vegetation types in the wetlands of East Dongting Lake, including Carex tristachya wetland (CTW), Phragmites australis wetland (PAW), and Salix babylonica wetland (SBW). The soil microbial biomass carbon (MBC), nitrogen (MBN) and enzyme activities were measured and the key influen-cing factors were analyzed during the normal, flood, and dry periods. The results showed that: 1) The amounts of MBC, MBN, and the activities of invertase and cellulase (except cellulase of dry season) in 0-10 cm were higher than those in 10-20 cm for all wetlands, while the catalase activity showed an opposite pattern. 2) The amounts of MBC and MBN and the values of MBC/TOC and MBN/TN for the 0-20 cm soil layer of each vegetation type wetland were the lowest in flood period. 3) Soil invertase activity for each vegetation type wetland in the 0-20 cm soil layer peaked in the dry period, while soil cellulase activity peaked in the normal period. The seasonal fluctuation of soil catalase activities in all wetlands were small, with activities being slightly higher in flood period than the other two periods. 4) Among different vegetation types, soil invertase activity of PAW was significantly higher than that of other vegetation types, and cellulase activity of which was the lowest in both normal and flood periods. There was no difference in these two enzymes activities among wetlands during the dry period. The highest soil catalase activity was found in CTW during normal period and in SBW during dry period, respectively, while its lowest value was in PAW during flood period. 5) Soil MBC, MBN and invertase activity were correlated positively with soil TOC, TN and TP, and negatively correlated with soil pH. The activities of soil cellulase and catalase were significantly negatively correlated with TOC, TN, TP and positively correlated with pH. It suggested that the seasonal fluctuation of water level affected soil C, N, P contents and pH values, with consequences on soil MBC, MBN and enzyme activities.

Effect of Different Grain for Green Approaches on Soil Bacterial Community in a Karst Region.

Soil bacteria participate in nutrient cycling above and below ground to promote ecosystem stability and health. However, the relationship of soil bacteria and environmental factors following the Grain for Green (GfG) program remains poorly understood in southwest China. Soil samples were collected from seven Grain for Green sites that had been revegetated for 15 years. Four of these sites were afforested with a different tree species: Zenia insignis (ZI), Toona sinensis (TS), Castanea mollissima (CM), and Citrus reticulate (CR). One site was revegetated with Zenia insignis and Guimu-1 elephant grass (ZG), and one with only Guimu-1 elephant grass (GM). The remaining site, abandoned cropland (AC), was left to regenerate naturally. Here, we used Illumina sequencing of 16S rRNA genes to explore how the Grain for Green project affected soil bacterial community. We found that Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the dominant phyla in these soils. The dominant genera at each revegetation site were also different. The CM, ZI, TS, and AC sites were dominated by Micromonospora, ZG was dominated by Streptomyces, and CR and GM were dominated by Subgroup 6. The bacterial structure was most similar in AC and TS. Correlation analysis showed that the ratio of C:P had positive effects on KD4-96, Intrasporangiaceae, and Gaiella. The ratio of soil N:P was significantly positively correlated with Cupriavidus and Kribbella. The combination of planting Zenia insignis and Guimu-1 elephant grass had the best edaphic benefits, and the approach of planting Citrus reticulate and Toona sinensis needs to be improved. Redundancy analysis (RDA) revealed that plant Simpson index, and soil N:P contributed to 16 and 15.7% of the total variations in the soil bacterial community composition, respectively. Our results suggested that plant diversity (Simpson index) and soil stoichiometric ratio (N:P) were the important factors affecting the bacterial community, and phosphorus was the limiting factor of the bacterial community in the Grain for Green karst region. In the future, revegetation should be accompanied with phosphorus fertilizer and polycultures should be considered.

Spatial Patterns and Drivers of Microbial Taxa in a Karst Broadleaf Forest.

Spatial patterns and drivers of soil microbial communities have not yet been well documented. Here, we used geostatistical modeling and Illumina sequencing of 16S rRNA genes to explore how the main microbial taxa at the phyla level are spatially distributed in a 25-ha karst broadleaf forest in southwest China. Proteobacteria, dominated by Alpha- and Deltaproteobacteria, was the most abundant phylum (34.51%) in the karst forest soils. Other dominating phyla were Actinobacteria (30.73%), and Acidobacteria (12.24%). Soil microbial taxa showed spatial dependence with an autocorrelation range of 44.4-883.0 m, most of them within the scope of the study plots (500 m). An increasing trend was observed for Alphaproteobacteria, Deltaproteobacteria, and Chloroflexi from north to south in the study area, but an opposite trend for Actinobacteria, Acidobacteira, and Firmicutes was observed. Thaumarchaeota, Bacteroidetes, Gemmatimonadetes, and Verrucomicrobia had patchy patterns, Nitrospirae had a unimodal pattern, and Latescibacteria had an intermittent pattern with low and high value strips. Location, soil total phosphorus, elevation, and plant density were significantly correlated with main soil bacterial taxa in the karst forest. Moreover, the total variation in soil microbial communities better explained by spatial factors than environmental variables. Furthermore, a large part of variation (76.8%) was unexplained in the study. Therefore, our results suggested that dispersal limitation was the primary driver of spatial pattern of soil microbial taxa in broadleaved forest in karst areas, and other environmental variables (i.e., soil porosity and temperature) should be taken into consideration.

Seasonal Changes and Vertical Distribution of Fine Root Biomass During Vegetation Restoration in a Karst Area, Southwest China.

In karst ecosystems, plants absorbing smaller amounts of nutrients, owing to shallow soil, show limited growth. In addition, fine roots (diameter < 2 mm) contribute to the regulation of nutrient cycles in terrestrial ecosystems. However, the spatial and temporal variations of fine root biomass in different vegetation types of the karst region remains poorly understood. In this study, we investigated the seasonal and vertical variation in biomass, necromass, and total mass of fine roots using sequential soil coring under different stages of vegetation restoration (grassland, shrubland, secondary forest, and primary forest) in Southwest China. The results showed that the fine root biomass and necromass ranged from 136.99 to 216.18 g m-2 and 47.34 to 86.94 g m-2, respectively. The total mass of fine roots and their production ranged from 187.00 to 303.11 g m-2 and 55.74 to 100.84 g m-2 year-1, respectively. They showed a single peak across the vegetation restoration gradient. The fine root biomass and total fine root mass also showed a single peak with seasonal change. In autumn, the fine root biomass was high, whereas the necromass was low. Most of the fine roots were concentrated in the surface soil layer (0-10 cm), which accounted more than 57% root biomass, and decreased with increasing soil depth. In addition, fine root production showed a similar vertical pattern of variation with biomass. Overall, our results suggested that fine roots show clear seasonal and vertical changes with vegetation succession. Moreover, there was a higher seasonal fluctuation and a greater vertical decreasing trend in late-successional stages than in the early-successional stages. The conversion of degraded land to forest could improve the productivity of underground ecosystems and vegetation restoration projects in the fragile karst region should, therefore, continue.

Spatial distribution of tree species in evergreen-deciduous broadleaf karst forests in southwest China.

Understanding the spatial distribution of tree species in subtropical evergreen-deciduous broadleaf karst forest is fundamental to studying species coexistence and karst species diversity. Here, complete spatial randomness and heterogeneous Poisson process models were used to analyze the spatial distribution patterns of 146 species with at least one individual per ha in a 25-ha plot in southwest China. We used canonical correspondence analysis (CCA) and the torus-translation test (TTT) to explain the distributions of observed species. Our results show that an aggregated distribution was the dominant pattern in Mulun karst forests; the percentage and intensity of aggregated decreased with increasing spatial scale, abundance, mean diameter at breast height (DBH), and maximum DBH. Rare species were more aggregated than intermediately abundant and abundant species. However, functional traits (e.g., growth form and phenological guild) had no significant effects on the distributions of species. The CCA revealed that the four analyzed topographic variables (elevation, slope, aspect, and convexity) had significant influences on species distributions. The TTT showed that not all species have habitat preferences and that 68.5% (100 out of 146 species) show a strongly positive or negative association with at least one habitat. Most species were inclined to grow on slopes and hilltops.

[Soil fertility characteristics under different land use patterns in depressions between karst hills].

Soil samples were collected from the depressions between karst hills by grid sampling method (5 m x 5 m), soil pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) in surface layer (0-20 cm) under different land use patterns (burning, cutting, cutting plus root removal, enclosure, maize plantation, and pasture plantation) were measured, the main factors of influencing the soil fertility was identified by principal component analysis (PCA), and the relationships between soil nutrients and microorganisms were demonstrated by canonical correlation analysis (CCA). The results showed that the soil was slightly alkaline (pH 7.83-7.98), and the soil fertility differed under the different land use patterns, with 76.78-116.05 g x kg(-1) of SOC, 4.29-6.23 g x kg(-1) of TN, 1.15-1.47 g x kg(-1) of TP, 3.59-6.05 g x kg(-1) of TK, 331.49-505.49 mg x kg(-1) of AN), 3.92-10.91 mg x kg(-1) of AP, and 136.28-198.10 mg x kg(-1) of AK. These soil indexes except pH showed moderate or strong variation. Different land use patterns had various impacts on soil fertility: Soil nutrients such as SOC, TN, TP, and AN were most significantly influenced by land use patterns in the depressions between karst hills; Followed by soil microorganisms, especially soil actinomycetes, and the effect decreased with the increasing gradient of human disturbance from enclosure, burning, cutting, cutting plus root removal, pasture plantation, and maize plantation. CCA elucidated that considerable interactions existed in soil TP with MBP (microbial biomass phosphorus), TK with MBC (microbial biomass carbon), TN with actinomycetes in the burned area, while TN and MBC in the cutting treatment, AP and MBN (microbial biomass nitrogen) in the treatment of cutting plus root removal, pH with MBC and fungus in the enclosure treatment, TN and TK with MBP in the maize plantation, pH with fungi and actinomycetes in the pasture plantation. Land use patterns changed the soil fertility in the depressions between karst hills; therefore, in the ecological restoration and reconstruction of karst region with fragmented landforms and shallow soil, rational land use patterns should be adopted to improve the soil quality of degraded ecosystems.

[Stoichiometric characteristics of plant and soil C, N and P in different forest types in depressions between karst hills, southwest China].

The stoichiometric properties of plant carbon (C), nitrogen (N) and phosphorus (P) and their relationships with soil were studied in six dominant plant communities in three forest types, i.e., plantation forest, secondary forest and primary forest in depressions between karst hills, southwest China. The C, N and P contents of both plant and soil had significant differences among the different forest types. Soil C and N contents were the highest in the secondary forest and the lowest in the plantation forest. Soil P content was the highest in the plantation forest and the lowest in the primary forest. Plant C and P contents were in the order of plantation forest > primary forest > secondary forest, and plant N content was the highest in the plantation forest and the lowest in the primary forest. Soil N:P,C:P and plant C:P ratios were significantly higher in the primary forest than in the other two forest types. There were no significant difference for the soil C:N ratio among the three forest types. Plant N:P ratio was the highest in the secondary forest and the lowest in the plantation forest. Plant C:N ratio was in the order of primary forest > plantation forest > secondary forest. There were significantly positive linear correlations between N and P contents, C:N and C:P ratios, C:P and N:P ratios of arbor leaves in the different forest types, and significant negative linear correlations between plant C:N and N:P ratios, and between soil C:N and N:P ratios. There were no significant correlations between plant and soil C, N, P contents and C:P ratio, suggesting that the supply of C, N and P from soil had little influence on plant C, N and P contents.

[Characteristics of spatial variation of soil nutrients in sloping field in a gorge karst region, southwest China].

Based on a grid (20 m x 20 m) sampling, spatial heterogeneity and pattern of soil nutrients in sloping field in the gorge karst region, southwestern China, were explored by using classical statistics and geostatistics methods. The results showed that soil nutrient contents in slope field in the canyon karst region were more abundant, where pH value had a weak variation and the soil organic matter (SOM) had a moderate degree of variation. All the soil nutrients had moderate or strong variation with an order of available phosphorus (AP) > total potassium (TK) > SOM > alkaline nitrogen (AN) > total nitrogen (TN) > total phosphorus (TP) > available potassium (AK). All of the soil nutrients had a good spatial autocorrelation and the autocorrelation function performed in the same law of developing from positive to negative direction with the inflection point ranged from 80 to 100 m. In addition, the Moran's I was small for TK and AP while large for other nutrients. Characteristics of spatial variation differed among soil nutrients. Exponential model fitted best for TK and AP, in which the ratio of nugget to sill (C0/(C0 + C)) and the range (A) were small and the fractal dimension (D) was high, showed a strong spatial correlation. Spherical model fitted best for other soil nutrients, with C0/(C0 + C) , the range (A) and D showing a moderate autocorrelation. Kriging analysis clearly indicated that pH, SOM, TN, TP and AN were distributed in a concave pattern, while AP and AK had fragmented patch distribution. Therefore, vegetation, topography, human disturbance and strong heterogeneity of microhabitats are main factors leading to the differences in patterns of soil nutrients on the sloping land in the gorge karst region.

[Characteristics of soil microbial populations in depressions between karst hills under different land use patterns].

Based on the investigation and analysis of six soil microbial indices, eight soil conventional nutrient indices, six soil mineral nutrient indices, and 15 vegetation indices in the farmland, grassland, scrub, forest plantation, secondary forest, and primary forest in the depressions between karst hills, this paper analyzed the main soil microbial populations, soil microbial biomass carbon (MBC), nitrogen (MBN), and phosphorus (MBP) and their fractal characteristics, and the relationships of the soil microbes with vegetation, soil nutrients, and soil mineral components under different land use patterns. The soil microbial populations differed in their quantity and composition under different land use patterns. Primary forest and farmland had the highest quantity of soil microbial populations, while forest plantation had the lowest one. The three forests had a higher proportion of soil bacteria, the farmland, grassland, and scrub had a higher proportion of actinomycetes, and all the six land use patterns had a low proportion of soil fungi. Under the six land use patterns, the soil MBC, MBN, and MBP were all high, with the maximum in primary forest. There was a good fractal relationship between the soil MBC and microbial populations, but no fractal relationships between the soil MBN and MBP and the microbial populations. Significant relationships were observed between the soil microbes and the vegetation, soil nutrients, and soil mineral components, and the soil MBC had the closest relationships with the Shannon index of tree layer and the soil total nitrogen, Fe2O3, and CaO contents.

[Profile distribution of soil aggregates organic carbon in primary forests in Karst cluster-peak depression region].

Soil profiles were collected from three primary forests (Itoa orientalis, Platycladus orientalis, and Radermachera sinica) in Karst cluster-peak depression region to study the composition of soil aggregates, their organic carbon contents, and the profile distribution of the organic carbon. In the three forests, >2 mm soil aggregates were dominant, occupying about 76% of the total. The content of soil total organic carbon ranged from 12.73 to 68.66 g x kg(-1), with a significant difference among the forests. The organic carbon content in <1 mm soil aggregates was slightly higher than that in >2 mm soil aggregates, but most of soil organic carbon was stored in the soil aggregates with greater particle sizes. About 70% of soil organic carbon came from >2 mm soil aggregates. There was a significant positive relationship between the contents of 2-5 and 5-8 mm soil aggregates and the content of soil organic carbon. To increase the contents of 2-8 mm soil aggregates could effectively improve the soil carbon sequestration in Karst region. In Itoa orientalis forest, 2-8 mm soil aggregates accounted for 46% of the total, and the content of soil total organic carbon reached to 37.62 g x kg(-1), which implied that Itoa orientalis could be the suitable tree species for the ecological restoration in Karst region.

[Compositional characteristics and roles of soil mineral substances in depressions between hills in karst region].

Based on the investigation and analysis of seven soil mineral substance variables, nine vegetation factors, four topographical factors, and ten soil physicochemical factors in the 200 m x 40 m dynamic monitoring plots in farmland, forest plantation, secondary forest, and primary forest in the depressions between hills in karst region, and by using traditional statistical analysis, principal component analysis (PCA), and canonical correlation analysis (CCA), this paper studied the compositional characteristics and roles of soil mineral substances as well as the coupling relationships between the mineral substances and the vegetation, topography, and other soil properties. In the depressions, soil mineral substances were mainly composed of SiO2, Al2O3, K2O, and Fe2O3, whose contents were obviously lower than the mean background values of the soils in the world and in the zonal red soils at the same latitudes. The soil CaO and MgO contents were at medium level, while the soil MnO content was very low. The composition of soil mineral substances and their variation degrees varied with the ecosystems, and the soil development degree also varied. There was a positive correlation between vegetation origin and soil origin, suggesting the potential risk of rock desertification. Due to the high landscape heterogeneity of the four ecosystems, PCA didn't show good effect in lowering dimension. In all of the four ecosystems, soil mineral substances were the main affecting factors, and had very close relationships with vegetation, topography, and other soil properties. Especially for SiO2, CaO, and MnO, they mainly affected the vegetation species diversity and the soil organic matter, total nitrogen, and total potassium. This study indicated that soil mineral substances were the one of the factors limiting the soil fertility and vegetation growth in the depressions between hills in karst region. To effectively use the soil mineral resources and rationally apply mineral nutrients would have significances in the restoration and reconstruction of karst degraded ecosystems.

[Spatial heterogeneity of soil nutrients in Karst area's Mulun National Nature Reserve].

Soil samples were collected from the depression (200 m x 100 m) in Karst area's Mulun National Nature Reserve by grid sampling method (20 m x 20 m), with the spatial heterogeneity of soil nutrients analyzed by the methods of classic statistics and geo-statistics. The soil pH showed small variation, while the soil nutrients showed moderate variation, being in the order of available phosphorus (AP) > available potassium (AK) > available nitrogen (AN) > organic matter (OM) > total potassium (TK) > total phosphorus (TP) > total nitrogen (TN). Spherical model fitted best for soil pH, exponential model fitted best for soil TK and AK, and Gaussian model fitted best for other variables. The variation range of soil pH and AK was smaller, being 58.1 m and 41.1 m, respectively, that of soil OM, TN, TP, AN, and AP was from 100 m to 150 m, and that of soil TK was the largest (463.5 m). Soil TK and TN showed moderate spatial autocorrelation, while other soil nutrients showed strong spatial autocorrelation. Soil pH and AK presented fragmented patch distribution, showing high heterogeneity, while soil OM, TP, and TK changed gently, high in the middle and low in two sides. The spatial patterns of soil AN and AP were similar, i.e., increased with landform slope. Soil TN had a distribution pattern of low in the middle and high in two sides. Vegetation, topography, and high heterogeneity of micro-habitat were the main factors caused the differences of the spatial distribution patterns of soil nutrients in the Reserve.

[A spatial heterogeneity of surface soil moisture content in dry season in Mulun National Natural Reserve in Karst area].

By the methods of classical statistics and geostatistics, the spatial heterogeneity of surface soil (0-5 cm and 5-10 cm layers) moisture content in dry season in the typical sloping fields and depressions in Mulun National Natural Reserve in Karst area were studied. The results indicated that in study area, the surface soil moisture content in dry season was still higher, and showed a fine semivariogram structure as a whole. The spatial distribution of moisture content in 0-5 cm and 5-10 cm soil layers, both for sloping fields and for depressions, fitted exponential model well. Under the same stand conditions, the moisture content in the two soil layers had the similar spatial structure and distribution pattern; while under different stand conditions, there existed obvious difference in the same soil layer. The spatial pattern of surface soil moisture content in sloping fields was characterized by medium spatial autocorrelation, clear patches with well continuum, relatively slow variation of Moran's I index, while that in depressions was characterized by strong spatial autocorrelation, larger variation of Moran' s I index, and more fragmented patches. Therefore, topography, micro-physiognomy, precipitation, human disturbance, and especially vegetation were the most important factors affecting the spatial pattern of soil moisture content in the Mulun National Natural Reserve, and to preserve primary forest should have favorable effect on the regulation of the spatial heterogeneity of soil moisture content in the Reserve.

[Spatial heterogeneity of soil organic matter and its response to disturbance in karst peak cluster depressions].

By using geostatistic methods, this paper studied the spatial variation and distribution of soil organic matter as well as its ecological processes and related mechanisms in four typical disturbed areas (cropland, man-made forest, secondary forest, and primary forest) of karst peak cluster depressions in northwest Guangxi of China. Eighty soil samples (0-20 cm) were collected from an aligned grid of 10 m x 10 m for the analysis of soil organic matter. The soil organic matter content increased significantly (P < 0.05) with the decrease of disturbance and the vegetation succession from crop to man-made forest to secondary forest to primary forest. Soil organic matter content had good spatial autocorrelation in all of the four typical disturbed areas, but its spatial heterogeneity differed. Gaussian model fitted best to the semivariance functions of soil organic matter content in the study areas except secondary forest area where exponential model fitted well. In cropland area, the spatial autocorrelation of soil organic matter was at medium level, with the C0/(C0 + C) being 26.5%; while in the other three areas, the spatial autocorrelation was at high level, with the C0/(C0 + C) being 9.0%-22.6%. The range and scale of the spatial autocorrelation of soil organic matter in cropland and man-made forest areas were larger than those in the other two areas, possibly due to the strong human disturbance and the homogeneity of low energy. The range of the spatial autocorrelation of soil organic matter in primary forest area was large due to the high vegetation coverage, while that in secondary forest area was the lowest due to the diverse vegetation communities and their uneven distribution. The low fractal value (D) of semivariance functions of soil organic matter in man-made forest and primary forest areas suggested that a strong spatial dependence existed, while the high D in cropland and secondary forest areas suggested a great random variance of spatial distribution of soil organic matter occurred. The spatial pattern of soil organic matter presented a unimodal distribution in cropland and man-made forest areas, a concave distribution in secondary forest area, and a gibbous distribution in primary forest area. To reduce human disturbance would be helpful to the soil quality improvement, rapid vegetation restoration, and ecological reconstruction of karst degenerative ecosystems.

[Effects of mulching and intercropping on temporal-spatial variation of soil temperature in tea plantation in subtropical hilly region].

The study of four years straw mulching and white clover intercropping in a tea plantation in subtropical hilly region showed that the soil temperature in the plantation presented a distinct dynamic temporal-spatial variation and hysteresis, which was greatly accorded with the fittest temperature of tea growth. Straw mulching and white clover intercropping altered the nature of soil thermal exchanging layer (soil surface), decreased daily temperature difference, enhanced the temperature stability in the same soil layer, and had duplex effects of lowering temperature when it went up and increasing and keeping temperature when it went down. The effectiveness was in the order of white clover intercropping > straw mulching > control, 13:00 > 19:00 >7:00,and lowering temperature > increasing and keeping temperature, and decreased with soil depth. Straw mulching and white clover intercropping adjusted the switching point of the temporal-spatial variation of soil temperature, and evidently decreased the emergence of harmful high temperature. During the period of continual high temperature, these measures markedly lowered soil temperature, and effectively shortened the duration of this period.