[Stoichiometric Imbalance of Abandoned Grassland Under Precipitation Changes Regulate Soil Respiration].

As a key factor of global climate change, precipitation can affect soil respiration. Microorganisms are the key drivers of soil respiration, but the relationship between microbial stoichiometry and respiration in vulnerable habitat areas under different precipitation gradients is unclear. In this study, five precipitation gradients were simulated on a typical abandoned grassland in the loess hilly region. Soil respiration, nutrients, microbial biomass, and extracellular enzymes were measured, and the microbial measurement characteristics were calculated. The results showed that:①soil respiration (SR) increased significantly under rainfed treatment but decreased significantly under D50 treatment. ②Precipitation changes affected the stoichiometric imbalance, and the N:P imbalance of the active resource pool presented a u-shaped trend, whereas the C:P imbalance changed significantly only in 2019, with a trend of P50>P25>CK>D25>D50. Additionally, the stoichiometric imbalance was caused by the soil stoichiometry. In 2019, the C:P imbalance of the active resource pool showed a trend of P50>P25>CK>D25>D50, whereas the N:P imbalance of the active resource pool showed a u-shaped trend, and the stoichiometric imbalance was caused by soil stoichiometry changes. ③Soil ß-1,4-glucosidase (BG) enzyme decreased with increasing precipitation, and the sum activities of ß-1,4-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP) significantly decreased during two years of rainfall reduction treatment. The activity of alkaline phosphatase (ALP) significantly increased under increasing rainfall but significantly decreased under decreasing rainfall. BG:(NAG+LAP) and BG:ALP were significantly decreased under increasing precipitation conditions but significantly increased under decreasing precipitation conditions. ④The partial least squares path model (PLS-PM) showed that precipitation had an impact on soil respiration through influencing C:P stoichiometric imbalance and soil enzyme stoichiometric ratio. These results highlight the importance of stoichiometric imbalances in regulating soil respiration and may help predict how they are caused by precipitation change control carbon cycling and nutrient flow in terrestrial ecosystems.

[Mineralization Characteristics of Soil Organic Carbon and Its Relationship with Organic Carbon Components in Artificial Robinia pseudoacacia Forest in Loess Hilly Region].

In order to explore the characteristics of organic carbon mineralization and the variation law of organic carbon components of an artificial forest in a loess hilly area, an artificial Robinia pseudoacacia forest restored for 13 years and the adjacent slope farmland were selected as the research objects, and indoor culture experiments under three different temperature treatments (15, 25, and 35℃) were carried out. The results indicated that the mineralization rate of soil organic carbon decreased sharply at first and then stabilized. The cumulative release of organic carbon increased rapidly in the initial stage of culture and gradually slowed in the later stage. Soil organic carbon mineralization in sloping farmland was more sensitive to temperature change, and its temperature sensitivity coefficient Q10 was 1.52, whereas that in R. pseudoacacia forest land was only 1.38. According to the fitting of the single reservoir first-order dynamic equation, the soil mineralization potential Cp of R. pseudoacacia forest land and slope farmland was between 2.02-4.32 g·kg-1 and 1.25-3.17 g·kg-1, respectively, that is, the mineralization potential of the R. pseudoacacia forest was higher. During the cultivation period, the content of various active organic carbon components decreased with time, and that in the R. pseudoacacia forest land was greater than that in the slope land. The cumulative carbon release of soil was significantly positively correlated with the contents of MBC and DOC (P<0.05), and Q10 (15-25℃) was negatively correlated with the contents of SOC, EOC, and SWC (P<0.05). These results could provide some reference for the study of soil carbon sequestration in loess hilly regions under climate change.

[Effects of Warming and Increased Precipitation on Soil Respiration of Abandoned Grassland in the Loess-Hilly Regions].

Clarifying the changing trends and driving factors of soil respiration in fragile habitats under the background of climate change is of great significance for understanding the regional carbon cycle and the conversion of ecosystem carbon source and sink functions. This research focused on grasslands that had been naturally abandoned and restored for 12 years in the loess hilly region of northern Shaanxi, using an open top chamber (OTC) and artificially increased natural rainfall to simulate climate warming and precipitation increase and their interaction. Furthermore, we used a combination of field monitoring and indoor analysis to explore soil water content, temperature, and nutrient characteristics and the response characteristics of soil respiration rate to warming and increased precipitation and further analyzed the key factors driving changes in soil respiration. The results showed that:① warming (W) significantly increased the 5 cm soil temperature, with an average increase of 1.34℃ throughout the sampling year, whereas the increased precipitation (P50%) treatment significantly reduced the 5 cm soil temperature, reducing the average 5 cm soil temperature during the entire sampling year by 0.88℃ and increasing the soil water content (SWC) at the same time. The SWC was 13.12% and 16.45% higher than that in the control (CK), respectively. In addition, compared with that in the CK, the treatment of warming and increased precipitation (WP50%) not only increased soil temperature but also increased SWC; in general, the increase in temperature and precipitation played an antagonistic effect on the influence of soil temperature and humidity. ② P50% significantly increased the content of soil organic carbon, dissolved organic carbon, and labile organic carbon, causing changes in the soil stoichiometric ratio and the distribution characteristics of labile-recalcitrant carbon components, whereas W did not have a significant impact on organic carbon. In addition, soil total nitrogen and phosphorus and available nitrogen and phosphorus nutrients were not significantly different between treatments. ③ P50% significantly increased the Rs rate, and the effect of W on the soil respiration rate mainly depended on the seasonal precipitation and temperature. It was demonstrated that warming in winter and seasons with abundant rainfall had a significant promotion effect on the soil respiration rate. The exponential fitting of soil respiration rate and 5 cm soil temperature found that the soil respiration temperature sensitivity (Q10) was the highest under the precipitation treatment, reaching 1.68, whereas the Q10 was the lowest under the warming treatment (1.50). ④ Linear regression analysis showed that soil organic carbon, dissolved organic carbon, and labile organic carbon were all significantly positively correlated with soil respiration rate. Variation partitioning analysis showed that soil temperature, SWC, and nutrient characteristics explained 64.43% of the variation in soil respiration rate. The soil temperature and SWC were the main controlling factors of the change in soil respiration rate, with an explanation degree of 31.16%. Correlation analysis also showed that there was a significant correlation between SWC, soil temperature and respiration rate, soil organic carbon, dissolved organic carbon, labile organic carbon, C:N, and C:P. In summary, the climate prediction of abandoned grassland tending toward warm temperatures and high humidity in the loess hilly region will significantly affect the regional hydrothermal environment and nutrient characteristics, change the distribution ratio of soil labile and recalcitrant carbon, and promote regional soil carbon emissions. The analysis results showed that the key factor driving the change in soil respiration rate of abandoned grassland in the loess hilly region was soil temperature and SWC characteristics.

[Changes in Soil Microbial Carbon-Degrading Enzymes and Their Relationships with Carbon Pool Components During the Restoration Process of Robinia pseudoacacia].

To reveal the change in the characteristics of soil microbial C-degrading enzyme activities and the response to the components of C during the restoration process of Robinia pseudoacacia forests in the Loess Plateau, the components of the soil C pool, C-degrading enzyme activities, and microbial metabolic entropy of R. pseudoacacia in different restoration stages were studied, and the response relationship between C-degrading enzymes and soil C components was explored. The results showed that the microbial respiration (MR) first increased and then decreased with the restored years. We found that the microbial metabolic entropy (qCO2) decreased significantly with the restored years, but the microbial entropy (qMB) increased. Soil C-degrading enzymes increased significantly in the early-stage restoration of R. pseudoacacia; however, oxidizing enzymes (PO and PER) and cellobiohydrolase (CBH) decreased in the late stage of restoration. The soil organic C and recalcitrant organic C increased significantly with the restored years; however, there was no significant difference for the labile organic C. Correlation analysis and the partial least squares-path model (PLS-PM) showed that soil C-degrading enzymes and C components were significantly correlated with microbial respiration and entropy (qCO2 and qMB), respectively. The hydrolytic enzyme (BG+CBH) was significantly positively correlated with SOC, microbial biomass C, qMB, and recalcitrant and labile organic C. The oxidizing enzyme (PO+PER) was significantly positively correlated with the soil clay and qCO2. In addition, the recalcitrant organic C was the key driver of soil microbial metabolism affected by vegetation restoration. Overall, the ecosystem of R. pseudoacacia plantations would gradually stabilize with the increase in restored years and significantly increase the sequestration effect of soil C. These results will be helpful to understand the transformation rule and regulation mechanism of the soil C pool in vulnerable habitats and provide scientific basis for the restoration and management of vegetation in the Loess Plateau.

Plant Biomass and Soil Nutrients Mainly Explain the Variation of Soil Microbial Communities During Secondary Succession on the Loess Plateau.

Soil microorganisms play an important role in the circulation of materials and nutrients between plants and soil ecosystems, but the drivers of microbial community composition and diversity remain uncertain in different vegetation restoration patterns. We studied soil physicochemical properties (i.e., soil moisture, bulk density, pH, soil nutrients, available nutrients), plant characteristics (i.e., Shannon index [HPlant] and Richness index [SPlant], litter biomass [LB], and fine root biomass [FRB]), and microbial variables (biomass, enzyme activity, diversity, and composition of bacterial and fungal communities) in different plant succession patterns (Robinia pseudoacacia [MF], Caragana korshinskii [SF], and grassland [GL]) on the Loess Plateau. The herb communities, soil microbial biomass, and enzyme activities were strongly affected by vegetation restoration, and soil bacterial and fungal communities were significantly different from each other at the sites. Correlation analysis showed that LB and FRB were significantly positively correlated with the Chao index of soil bacteria, soil microbial biomass, enzyme activities, Proteobacteria, Zygomycota, and Cercozoa, while negatively correlated with Actinobacteria and Basidiomycota. In addition, soil water content (SW), pH, and nutrients have important effects on the bacterial and fungal diversities, as well as Acidobacteria, Proteobacteria, Actinobacteria, Nitrospirae, Zygomycota, and microbial biomass. Furthermore, plant characteristics and soil properties modulated the composition and diversity of soil microorganisms, respectively. Overall, the relative contribution of vegetation and soil to the diversity and composition of soil bacterial and fungal communities illustrated that plant characteristics and soil properties may synergistically modulate soil microbial communities, and the composition and diversity of soil bacterial and fungal communities mainly depend on plant biomass and soil nutrients.

[Effects of Farmland Abandonment on Soil Enzymatic Activity and Enzymatic Stoichiometry in the Loess Hilly Region, China].

Clarifying the characteristic of soil enzymatic activity and stoichiometry variations as well as their influencing factors following farmland abandonment have important implications for understanding soil nutrient availability after revegetation and for illuminating the underlying mechanisms of soil nutrient cycling in ecosystems. To determine microbial nutrient limitations after farmland abandonment and to explore the driving factors of the variations in soil enzymatic activity and stoichiometry along a chronosequence of abandoned farmlands (0-, 10-, 20-, and 30-year-old) in the Loess Hilly Region, China, the potential activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzymes, soil physicochemical properties, and plant diversity and family composition were measured. The results showed that the activities of ß-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline phosphatase (ALP) increased significantly with the increasing years of land abandonment, whereas the activity of ß-1,4-glucosidase (BG) showed the opposite change trend. Additionally, the ratios of BG:(NAG+LAP) and BG:ALP had the same variation trend with BG activity, which decreased significantly with increasing time, but the ratio of (NAG+LAP):ALP showed an increasing trend and then decreased, with the highest values observed in the 20-year sites. Moreover, the vector length of soil enzymatic stoichiometry decreased significantly as the years of land abandonment inceased, suggesting a reduced microbial C limitation after farmland abandonment. The vector angles <45°were observed at farmlands (0-year sites) and 10-year sites, whereas angles >45°were detected at 20-and 30-year sites, indicating that soil microbial communities were N-limited in the first 10 years of land abandonment and thereafter were P-limited. The redundancy analysis (RDA) reveled that soil organic C content, total N content, the C:N and C:P ratios, soil pH values, and plant diversity had significant effects on soil enzymatic activity and stoichiometry. A variation partitioning analysis (VPA) further demonstrated that edaphic and vegetation factors explained 62.0% of the total variance of soil enzymatic activity and stoichiometry. It should be noted that the interaction between vegetation characteristics and soil physicochemical properties was the major factor affecting soil enzymatic activity and stoichiometry, which explained 37.1% of the variance of the soil enzyme characteristics. Collectively, the application of P fertilizer should be considered to mitigate the deficiency of available P in the ecosystem during farmland abandonment, and these findings may provide a theoretical basis for understanding the mechanisms underlying microbe-mediated biogeochemical cycles as well as guiding soil nutrient management and the sustainable development of the ecological environment.

[Leaf nutrient resorption characteristics of Robinia pseudoacacia at different ages and their response to soil nutrient availability]. / ä¸åŒæž—é¾„åˆºæ§å¶ç‰‡å »åˆ†é‡å¸æ”¶ç‰¹å¾åŠå ¶å¯¹åœŸå£¤å »åˆ†æœ‰æ•ˆæ€§çš„å“åº”.

To reveal nutrient resorption characteristics of Robinia pseudoacacia and their driving factors in hilly and gully regions, we measured the concentration of total nitrogen and total phosphorus in leaves and the concentrations and stoichiometry of organic carbon, total nitrogen, total phospho-rus, ammonium, nitrate and available phosphorus in soils of R. pseudoacacia plantations with different stand ages. We analyzed the relationship between leaf nitrogen and phosphorus resorption efficiencies and soil nutrient characteristics. The nutrients in plants and soil changed significantly with stand ages. The total and available phosphorus concentrations were low in the soil. Nitrogen resorption efficiency first increased and then decreased with the increases of stand age, with a range of 48.2%-54.0% and a mean value of 48.5%. Phosphorus resorption efficiency increased significantly with stand age, with a range of 45.2%-49.4% and a mean value of 46.9%. Nitrogen resorption efficiency showed negative response to soil nitrogen and N:P. Phosphorus resorption efficiency was significantly positively correlated to soil N:P and negatively correlated to soil available phosphorus. Our results indicated that soil nutrient availability negatively drove nutrient resorption efficiency. The strategies of leaf nutrient resorption responded strongly to soil N:P due to the N2-fixing effect and P-limitation of R. pseudoacacia.

[Relationship Between the Composition of Soil Aggregates and the Distribution of Organic Carbon Under Long-Term Abandoned Restoration].

Soil aggregates are important carriers of soil organic carbon (SOC) accumulation, and play an important role in the evaluation of soil structure and quality. Natural recovery can promote change in soil aggregate structure and quantity via the redistribution of SOC in the aggregates. Natural restoration from farmland is an important vegetation restoration model on the Loess Plateau. The changes in soil aggregate structure and soil carbon stock after natural restoration have received extensive attention. However, little is known about the continuous study of soil changes on the abandoned grassland during the recovery process. Therefore, to understand how SOC accumulates in the process of natural recovery and quantitatively analyze the contribution of aggregates to the total soil carbon pool, we selected four abandoned grasslands of different restoration ages on the Loess Plateau, China, and studied the changes in soil structure, soil total organic carbon (TOC), soil C:N, soil aggregate distribution, soil aggregate stable index (mean weight diameter, MWD; geometric mean diameter, GMD), and aggregate-associated SOC changes as well as their correlations from 0-20 cm and 20-40 cm soil layers in abandoned grasslands. In addition, we calculated the contribution of aggregates with different sizes to soil TOC stock. The results showed that:① natural restoration increased the macroaggregate amount, MWD, and GMD, but decreased the amount of microaggregate and silt-and clay-sized fractions. There are significant differences in the distribution and stability of aggregates between different soil layers; the promotion effect of the surface was higher than that of the subsurface soils. ② In the 42 years after abandoning recovery, soil TOC stock, macaggregate-and mesaggregate-associated SOC stock increased significantly, and varied with soil depth and years of abandonment (1.92 times, 10.2 times, and 3.61 times). In contrast, micaggregate-associated SOC stock decreased significantly, and silt-and clay-sized fractions-associated SOC stock showed no distinct change. In addition, natural restoration promoted the ratio of C:N; nevertheless, the ratio of C:N under the surface showed a reduced phenomenon after 42 years of abandonment. ③ The improvement in soil TOC stock depends primarily on changes in the macaggregate-associated organic carbon stocks, which account for 80% of macaggregate, and the significant increase in the amount of macaggregate is the main reason for the high contribution.The results of our study suggest that natural restoration is conducive to the accumulation of soil organic carbon, and improvement in soil structure and stability. Macroaggregate is the key factor in soil organic carbon accumulation and soil structure improvement in the process of natural restoration.

[Responses mechanism of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.] / åœŸå£¤å¾®ç”Ÿç‰©ç”Ÿç‰©é‡ç¢³æ°®ç£·ä¸ŽåœŸå£¤é ¶åŒ–å­¦è®¡é‡å¯¹æ°”å€™å˜åŒ–çš„å“åº”æœºåˆ¶.

Microorganisms and soil enzymes are important drivers for biogeochemical cycles in terrestrial ecosystems. Understanding the role of microorganisms in the regulation of ecosystems and the response mechanisms of microbial biomass and soil enzymes to climate change are important topic in ecology. From the perspective of climatic factors, this review introduced the roles of microorganisms and soil enzymes in the carbon, nitrogen and phosphorus cycles of terrestrial ecosystems based on the theory of ecological stoichiometry. Moreover, we synthesized the responses mechanisms of soil microbial and soil enzyme stoichiometry, i.e., changes of microbial metabolic rate, enzymatic acti-vity, microbial community structure, ecological stoichiometry of soil microbial biomass and soil enzymes, and nutrient use efficiency. Finally, we analyzed the current research inadequacies and proposed the scientific problems in this field, i.e., to comprehensively elucidate the response mecha-nism of soil microbes and soil enzymes to climate change; to examine the nutrient coupling mechanism of soil microbes and extracellular enzymes; and to explore the adaptive strategies of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.

[Population spatial patterns of grassland plant communities in different slope aspects in the loess hilly area, China.] / é»„åœŸä¸˜é™µæ²Ÿå£‘åŒºä¸åŒå¡å‘æ’‚è’è‰åœ°æ¤ç‰©ç¾¤è½ç§ç¾¤ç©ºé—´æ ¼å±€.

We investigated the species composition and diversity of four grassland communities with different slope aspects in the loess hilly area of China. The power law was used to analyze spatial heterogeneity of the community and spatial pattern of the population. The results showed that Artemisia sacrorum was the dominant species and occurred in each site. Other species had different status and contributed differently to the spatial pattern of communities. Moreover, the spatial patterns of communities responded differently to various slope aspects, with the degree of aggregation ranked as sunny > half-sunny > half-shady > shady. The spatial heterogeneity index of community was positively correlated with the Simpson diversity index, but was negatively correlated with Margalef richness, Shannon diversity and Pielou evenness. The relative spatial heterogeneity index of the dominant species (A. sacrorum), sub-dominant species (Lespedeza dahurica and Stipa bungeana), and a few associated species (Artemisia scoparia, Melica scabrosa) were larger than that of the community, which resulted in cluster distribution. However, the relative spatial heterogeneity index of most associated species (Phragmites communis, Sonchus arvensis, and Bothriochloa flaccidum) showed the similar trends with the distribution of the community. In contrast, the relative spatial heterogeneity index of Cephalanoplos segetum, Gueldenstaedtia multiflora and Artemisia giraldii was lower than that of the community. These differences reduced the aggregation degree of the community. In summary, the aggregation degree of community was determined by dominant species, sub-dominant species and occasional species. Specifically, the dominant species, sub-dominant species and some associated species could promote the aggregation of the community, but occasional species would reduce the cluster distribution.

[Relationship Between the Vegetation Community and Soil Nutrient and Enzyme Activity During the Restoration of Abandoned Land in the Loess Hilly Region].

The trends of and relationships among the plant community, soil nutrients, and four soil enzymes were investigated after being abandoned for 10, 15, 20, 30, and 45 years to reveal the soil properties during the restoration in the Loess Hilly Region. The results indicate the following ranking of dominant plant community species:Artemisia scoparia→Lespedeza dahurica+Artemisia sacrorum→Artemisia giraldii+irons Artemisia annua→Bothriochloa flaccidum+Artemisia selengensis. The ranking reflects an increase along the chronosequence of abandoned land. Moreover, the ratio of the total species of Compositae, Poaceae, and Leguminosae decreases from 66.67% to 50% and then increases up to 75%. The SOC, TN, TP, AN, AP, and four enzyme activity types (ALP, CAT, UE, and SC) increase but respond differently to restoration, while the stoichiometric ratio fluctuates. In contrast to the number of plant families, genus, species, and plant diversity, Compositae, Poaceae, and Leguminosae have major effects on the soil nutrient and enzyme activity, which explains the total variation of 72.8%, 69.1%, and 66.0%, respectively. The effects of these three families on the soil enzymes are greater than that on soil nutrients. Poaceae and Leguminosae have a positive effect on the nutrient and enzyme activity, while the family Compositae has a negative effect. Overall, the changes of dominant species of grassland communities during restoration significantly affect the soil enzyme and thereby are responsible for the soil nutrient dynamics.

[Variation in leaf functional traits of different-aged Robinia pseudoacacia communities and relationships with soil nutrients]. / ä¸åŒæž—é¾„åˆºæ§å¶åŠŸèƒ½æ€§çŠ¶å·®å¼‚åŠå ¶ä¸ŽåœŸå£¤å »åˆ†çš„å ³ç³».

On the basis of various leaf functional traits of different-aged Robinia pseudoacacia communities, as well as the relationships between the traits and soil nutrients, the adaptation strategy of R. pseudoacacia in relation to soil conditions was analyzed in Ansai County, the Loess Plateau, China. The results showed that specific leaf area, leaf area, leaf water content, leaf total nitrogen content and leaf organic carbon content first increased and then decreased with the increasing stand age. The peak values of specific leaf area (279.18 cm2·g-1), leaf area (12.33 cm2), leaf water content (0.09%), leaf total nitrogen content (33.01 g·kg-1) and leaf organic carbon content (523.08 g·kg-1) were obtained at 30 years old. With the increasing stand age, leaf tissue density, leaf total phosphorus content, leaf thickness and stomata density increased, and stomata length and stomata width decreased. Leaf area, specific leaf area, leaf total phosphorus content, leaf water content, leaf thicknessand stomata density were the main indexes based on principal component analysis (PCA), for R. pseudoacacia leaf functional traits responding to the increased stand age. The indexes were correlated with each other, indicating that R. pseudoacacia was capable of changing leaf morphological structure to adapt to environmental changes. Soil total nitrogen content was the main factor influencing leaf area, leaf water content, specific leaf area and stomata length, while soil organic carbon content mainly affected stomata width, leaf tissue density, leaf thickness, leaf total phosphorus content, leaf total nitrogen content and stomata density. Therefore, soil total nitrogen and organic carbon content were main factors that affected leaf functional traits of R. pseu-doacacia in different stand ages. Soil nutrients in R. pseudoacacia communities were improved with the increasing stand age, which eventually affected leaf functional traits. The flexibility of leaf functional traits indicated that R. pseudoacacia communities had great potential to adapt to environmental change in Loess Plateau hilly region.

[Emergy analysis on different planting patterns of typical watersheds in Loess Plateau.] / é»„åœŸé«˜åŽŸå ¸åž‹æµåŸŸç§æ¤ä¸šå‘å±•æ¨¡å¼çš„èƒ½å€¼åˆ†æž.

To objectively evaluate and compare the stability and sustainability of different planting patterns of typical watersheds in Loess Plateau of China after the Grain for Green Project, this paper used the emergy analysis method to quantify the emergy inputs and outputs of three watersheds with different planting patterns, i.e., both grains and fruit trees (Gaoxigou watershed), mainly grains (Wuliwan watershed) and mainly fruit trees (Miaozuigou watershed). In addition, an emergy analysis system was established to evaluate the suitability of the three patterns from the perspectives of natural resources pressure as well as social and economic development levels. More than 75% of the total emergy inputs of all the three watersheds were purchased, and nonrenewable emergy inputs had a much larger contribution than renewable emergy inputs, indicating the characteristic of low emergy self-sufficient ratio and considerable high environmental loading ratio. The pattern of planting grains had high emergy inputs but low emergy outputs, while the patterns of planting fruit trees and planting both had high emergy inputs and outputs. The energy densities of all three patterns reached two times of the average of agricultural systems in China. Especially, the net emergy of planting grains pattern was the lowest while that of planting both grains and fruit trees was the highest. The environmental sustainability index (ESI) of planting grains pattern was less than 1 and both emergy and ESI were much lower than national averages. The ESI of planting both grains and fruit trees pattern was the highest. In summary, comparison of the three patterns showed that planting both grains and fruit trees had better sustainability and high stability and the emergy production efficiency was high. Thus, it was suggested to change the agricultural development from watershed based units to multi-industry integrated mode.

[Species composition and point pattern analysis of standing trees in secondary Betula albosinensis forest in Xiaolongshan of west Qinling Mountains].

An investigation was conducted on the species composition and population diameter-class structure of a typical secondary Betula albo-sinensis forest in Xiaolongshan of west Qinling Mountains, and the spatial distribution pattern and interspecific correlations of the main populations were analyzed at multiple scales by the O-ring functions of single variable and double variables. In the test forest, B. albo-sinensis was obviously dominant, but from the analysis of DBH class distribution, the B. albo-sinensis seedlings were short of, and the natural regeneration was very poor. O the contrary, the regeneration of Abies fargesii and Populus davidianas was fine. B. albo-sinensis and Salix matsudana had a random distribution at almost all scales, while A. fargesii and P. davidianas were significantly clumped at small scale. B. albo-sinensis had positive correlations with A. fargesii and P. davidianas at medium scale, whereas S. matsudana had negative correlations with B. albo-sinensis, A. fargesii, and P. davidianas at small scale. No significant correlations were observed between other species. The findings suggested that the spatial distribution patterns of the tree species depended on their biological characteristics at small scale, but on the environmental heterogeneity at larger scales. In a period of future time, B. albo-sinensis would still be dominant, but from a long-term view, it was necessary to take some artificial measures to improve the regeneratio of B. albo-sinensis.

[Effects of forest gap on herbaceous plant diversity in mixed birch-fir forest of Taibai Mountain].

To better understand the effects of forest gap on the herbaceous species community in a mixed birch-fir forest of Taibai Mountain in Qinling, CCA ordination and random permutation test were employed to analyze the distribution pattern of the species composition across a gradient of gap size, and the relationships between the distribution of 55 herbaceous species with > or = 5 individuals and the habitat variables (convexity, slope, and soil total N, total P, available N, available P, pH, and organic matter). In this forest, gap area occupied 19.8% of the total land area, gap density was 20.7 per hm2, and gap size varied from 25.6 to 279.1 m2, with a mean of 93.7 m2. The species richness in herbaceous layer in gaps was significantly positively correlated with gap size, but of the 69 herbaceous species identified in the gaps, most species were found across all gap sizes, and only eight species were found in larger gaps (>120 m2). No successional change was observed in the herbaceous species distribution with gap size. The CCA ordination and random permutation test also showed that 27.3% of the 55 species with abundance > or = 5 had significant association with the eight habitat variables. It was concluded that gap size contributed to the species richness, but determined the diversity constitution in random.

[Biogas yield and its relations with the duration and temperature of mixed anaerobic fermentation of livestock dungs and wheat straw].

To approach the relationships between the biogas yield ot mixed anaerobic termentation of livestock dungs and crop straw and the fermentation duration and temperature is the key of selecting fermentation materials for rural household biogas, determining optimal fermentation temperature, and improving the reuse efficiency of agricultural residues. In this paper, a batch of experiments under the condition of 8% mass fraction of total solid were conducted in a self-manufactured anaerobic fermentation reactor, with pig dung, cattle dung, and wheat straw as fermentation materials, and the substrate of constant temperature fermentation pool as inoculation substance. The biogas yield, fermentation duration, and optimal temperature were determined. It was shown that the cumulative biogas yield of mixed anaerobic fermentation of pig dung and wheat straw was 2.4 times higher than that of the fermentation of pig dung alone, but no significant difference was observed between the cumulative biogas yields of the mixed fermentation of cattle dung and wheat straw and the fermentation of cattle dung alone. The optimal fermentation temperature for the mixed anaerobic fermentation was above 30 degrees C, and the fermentation duration was about 60 days. The fermentation duration was not always shortened by increasing temperature, and it would be not feasible to only use temnerature to determine the duration of anaerobic fermentation.