Short-term effects of wildfire on soil arthropods in a semi-arid grassland on the Loess Plateau.

Fires lead to dramatic shifts in ecosystems and have a large impact on the biota. Soil organisms, especially soil fauna, are often used as indicators of environmental change. At present, minimal attention has been paid to using soil fauna as an indicator of environmental change after a fire. Here, a field survey of burnt herbaceous vegetation in semi-arid areas was conducted to determine the response of soil arthropods to fire and their short-term recovery after fire. Overall, the abundance and biomass of soil arthropods was more sensitive to fire than the number of groups. The number of soil arthropod groups, especially the dominant groups (mites and springtails), was not significantly affected by wildfires. At the unburned site, soil arthropod abundance showed significant seasonal shifts that may be related to the vegetation properties, temperature, and precipitation caused by seasonal changes. In contrast, soil arthropods at the burnt sites showed a delayed recovery and had only reached 56%-82%, 17%-54%, and 91%-190% of the biomass in the unburnt forest at the 3, 6, and 9 months after the burning event. Our findings of soil arthropod abundance changes in the present study suggest that fire-induced changes in soil and vegetation properties (e.g., AN, LT, and VC) were crucial factors for the changes in soil arthropod abundance in this semi-arid grassland. We conclude that fire disturbance reduces the seasonal sensitivity of soil arthropods by altering their habitat. This study furthers our understanding of wildfire impact recovery by documenting the short-term temporal dynamics of soil arthropods.

[Distribution of soil organic carbon, total nitrogen, total phosphorus and water stable aggregates of cropland with different soil textures on the Loess Plateau, Northwest China]. / 黄土高原不同土壤质地农田土壤碳、氮、磷及团聚体分布特征.

In this study, combined with field investigation and laboratory analyses, we assessed the distribution of soil organic carbon, nitrogen, phosphorous contents and their stoichiometric ratios, and the distribution of soil water stable aggregates along a soil texture gradient in the cropland of the Loess Plateau to understand the effect of soil texture and the regulation of soil aggregates on soil fertility in cropland. The results showed that, with the change from fine soils to coarse soils along the texture gradient (loam clay→ clay loam→ sandy loam), the contents of macroaggregates, organic carbon, nitrogen, phosphorous and their stoichiometric ratios decreased, while pH value and microaggregates content showed an opposite changing pattern. The contents of macroaggregates, organic carbon, nitrogen, phosphorous, and C/P and N/P were significantly increased, but pH value and microaggregates content were significantly decreased with increasing the soil clay content. Furthermore, the contents of organic carbon, nitrogen, phosphorous, and C/P and N/P increased with the increase of macroaggregates content. These results indicated that soil fertility in croplands at a regional scale was mainly determined by soil texture, and was regulated by soil macroaggregates.

[Effects of different re-vegetation patterns on soil organic carbon and total nitrogen in the wind-water erosion crisscross region, China].

This study was conducted to analyze the responses of soil organic carbon (SOC) and total nitrogen (TN) to three typical re-vegetation patterns, i.e., grassland, alfalfa land and peashrub land on the Loess Plateau of China, and also to assess the dynamics of SOC and TN with re-vegetation age. The results showed that all the three re-vegetation practices increased the concentrations of SOC and TN in the 0-10 cm soil layer, but their effects differed with re-vegetation age. Compared with adjacent croplands, the concentrations of SOC and TN in the 0-10 cm soil layer in grassland did not change within 10 years of succession, but increased after 20 years of succession. In alfalfa land, the concentrations of SOC and TN increased by 51.6%-82.9% and 43.4%-67.0% in the 0-10 cm soil layer, with the increasing rates of stocks of SOC and TN being 0.17-0.46 and 0.015-0.043 t · hm⁻² · a⁻¹, respectively. However, SOC and TN were not affected by re-vegetation age in alfalfa land. The increases of concentrations of SOC and TN remained high in the first 20 years after conversion of cropland to peashrub land, but decreased after 40 years of conversion. In conclusion, the conversion of croplands to peashrub or alfalfa land could be better in contributing to high stocks of SOC and TN than natural succession of grassland. However, their positive effects on the enrichment of SOC and TN may not be sustainable due to the scarcity of soil moisture and high water consumption of these two re-vegetation plants.

[Stem biomass estimation models for dominant shrubs on the northern Loess Plateau of China]. / é»„åœŸé«˜åŽŸåŒ—éƒ¨å ¸åž‹çŒä¸›æžæ¡ç”Ÿç‰©é‡ä¼°ç®—æ¨¡åž‹.

A total of 200 stems of Caragana korshinskii and 210 stems of Salix psammophila were collected in the late August of 2015 in the Liudaogou catchment of Shenmu County, Shaanxi Pro-vince, China. Basal diameter (D), length (H), water content (W0), fresh mass (WF) and dry mass (W) were measured for each stem of the two species. Exponential and allometric equations were used to establish relationship models relating stem biomass to its morphological parameters. Altogether four models were established for each species, and their accuracy of estimation was also validated. The results showed that, the allometric model that used D2H as input variable was optimal in estimating stem biomass for C. korshinskii and S. psammophila, after transformed into its linear form. Meanwhile, the heteroscedasticity of the biomass data was greatly eliminated. This model had a maximum value of coefficient of determination (R2), and meanwhile minimum values of mean error (ME), mean absolute error (MAE), total relative error (TRE), mean systematic error (MSE), and mean absolute percentage error (MPSE), thus basically meeting the requirement of the accuracy in ecological study.

[Distribution of micronutrients in soils as affected by landforms in a loessial gully watershed].

Landform is the most important environmental factor influencing the distribution of soil micronutrients in the Loess Plateau and the well understanding of the effects is an important prerequisite for the estimation of soil micronutrients' availability and geochemistry in the Loess Plateau. This study was therefore conducted in a watershed of the loessial gully region to reveal the effects of landforms on profile distribution of soil micronutrients. Soil samples from 37 profiles were collected and total, available and adsorbed iron, manganese, zinc and copper were determined. The results showed that total micronutrients varied slightly with covariance coefficients lower than 15%, while available and adsorbed micronutrients varied greatly in the studied area. Total contents of iron, manganese and copper were higher in gully bottom soils, while total zinc, available and adsorbed micronutrients were higher in plateau land soils compared with soils in other landforms. The soil-forming process and land use conditions in each landform are the major reasons for the differences in soil total micronutrients. Landform induced changes of soil organic matter is the major factor controlling profile distribution of available and adsorbed micronutrients.

[Distribution characteristics of soil pH, CEC and organic matter in a small watershed of the Loess Plateau].

Soil chemical properties play important roles in soil ecological functioning. In this study, 207 surface soil (0-20 cm) samples were collected from different representative landscape units in a gully watershed of the Loess Plateau to examine the distribution characteristics of soil pH, cation exchange capacity (CEC) and organic matter, and their relations to land use type, landform, and soil type. The soil pH, CEC and organic matter content ranged from 7.7 to 8.6, 11.9 to 28.7 cmol x kg(-1), and 3.0 to 27.9 g x kg(-1), and followed normal distribution, log-normal distribution, and negative binomial distribution, respectively. These three properties were significantly affected by land use type, landform, and soil type. Soil CEC and organic matter content were higher in forestland, grassland and farmland than in orchard land, and soil pH was lower in forestland than in other three land use types. Soil pH, CEC and organic matter content were higher in plateau land and sloping land than in gully bottom and terrace land. Soil CEC and organic matter content were higher in dark loessial soil and rebified soil, while soil pH was higher in yellow loessial soil. Across all the three landscape factors, soil CEC and organic matter content showed the similar distribution pattern, but an opposite distribution pattern was observed for soil pH.

[Relationships between soil organic carbon and environmental factors in gully watershed of the Loess Plateau].

Understanding the distribution of organic carbon fractions in soils and their relationships with environmental factors are very important for appraising soil organic carbon status and assessing carbon cycling in the Loess Plateau. In this research, through field investigation and laboratory analysis, we studied the relationships between soil organic carbon and environmental factors in a gully watershed of the Loess Plateau. The environmental factors are landforms, land use conditions and soil types. The results showed that total soil organic carbon presented less variance, while high labile organic carbon presented greater variance. The variation coefficients of them are 34% and 43%, respectively, indicating that the variability of organic carbon in soils increased with the increasing of their activities. Total soil organic carbon, labile organic carbon, middle and high labile organic carbon were highly interrelated and presented similar distribution trend with environmental factors. Among different landforms, land uses, and soil types, the highest contents of organic carbon in different fractions were observed in plateau land, forest and farm lands, and black loessial soils, while the lowest contents of them were observed in gully bottom, grass land, and rubified soils, respectively. The relationships between organic carbon and environmental factors indicate that environmental factors not only directly influence the distribution of soil organic carbon, but also indirectly influence them through affecting the relationships among organic carbon fractions. The relationship between total organic carbon and labile organic carbon responses rapidly to environmental factors, while that between middle labile organic carbon and high labile organic carbon responses slowly to environmental factors.