Ecological causality between vegetation construction and habitat drought in arid areas.

The core of scientific greening in arid areas is 'greening based on water'. One of its preconditions is the potential causal relationship between vegetation construction and habitat drought. However, the causal relationship between factors or processes in ecology is generally difficult to accurately define and describe, especially for complex ecosystems. To scientifically carry out 'greening based on water', it is necessary to clarify the relationship between vegetation construction and hydrological cycle in drylands, and clarify the basis and conditions for habitat drought. Taking the construction of scientific greening pilot demonstration province in Ningxia as an example, we started with the theoretical connotation and application model of ecological causality of 'greening based on water', and empirically analyzed the causal relationship between vegetation construction and habitat drought at the regional, landscape, and ecosystem scale, respectively. The contradictions and problems in relevant understanding and practice were pointed out, and the principles and suggestions of scientific practice of 'greening based on water' were put forward.

[Village-level landscape succession and its driving mechanism in the agro-pastoral ecotone of Ningxia, China]. / 宁夏农牧交错带村域景观演替及驱动机制.

The relationship between human activities and landscape patterns and its regulation are one of the core fields in landscape ecology. The ecological conditions and local cultures of agro-pastoral ecotone are gradually wea-kening due to environmental fluctuations, land-use characteristics (suitable for both farming and grazing), and unstable policy. Therefore, protecting and restoring this semi-natural landscape and the resulting biological, ecolo-gical and cultural functions are becoming increasingly urgent. Here, by combing remote sensing data with interview survey and geographic investigation, we characterized the landscape changes (1964 to 2019) of Wanjigou Village in Yanchi County of Ningxia Hui Autonomous Region, which lay within the agro-pastoral ecotone. We further explored the rules of landscape succession and the underlying natural and social mechanism, as well as the interactions between landscape types. Results showed that Wanjigou Village had been subjected to a succession from the landscape characterized by grassland, arable land and sandy land to that characterized by grassland, shrub land, sandy land and arable land. The change from the competition of landscape function separation to the preliminary integration had formed a definite succession path for grassland-arable land-sandy land-shrub land. The main driving factors were a synthesis of policy, human needs, and environment. Policy often promoted landscape change through large-scale and intensified human activities, while environment promoted landscape succession through internal driving force of ecosystem toward a mutual adaption between landscape and the innate conditions. The driving factors of landscape succession were soil moisture variations caused by the change of soil physical structure, and vegetation change in adapting to new environment. In agro-pastoral ecotone with low resource density, the separation of landscape functions was one of the main reasons for land desertification. The integration and coordination of landscape functions greatly alleviated the situation of ecological deterioration. The critical path to maintain sustainable development of agro-pastoral ecotone was to achieve complementation among landscape types and even integrating with external resources by transforming landscape separation competition into landscape symbiosis.

Trade-off between soil moisture and species diversity in semi-arid steppes in the Loess Plateau of China.

Effectively balancing soil moisture and biodiversity restoration remains a contentious issue for managers and researchers in the Loess Plateau region of China, even after many years of restoration efforts. We conducted a regional study on the trade-off between soil moisture and species diversity using spatial grid sampling in a semi-arid steppe (200-300 mm annual precipitation) in the northwest Loess Plateau. Results reveal that only soil moisture between 20 and 60 cm depth was significantly correlated with diversity indexes. Root-mean-square deviation (RSMD, the index of the soil water-biodiversity relationship) increased by monotonous linear trends with soil moisture in 20-60 cm depth. The linear relationship for Shannon Wiener diversity index (SD) was stronger than for species richness index (SR). When soil moisture in 20-60 cm depth was lower than 6-8%, RSMD often was less than zero, representing the trade-off relationship. However, synergism was more common as the soil moisture increased beyond 6-8%. The overall trends and the soil moisture threshold (6-8%) did not differ significantly between sites with different vegetation cover and aspect, though there were differences in the relative ratio of trade-off and synergism samples. Comparing results from sampling at different scales in the Loess Plateau suggests 6-8% soil moisture in 200-300 mm precipitation gradient, consistent with 370 mm rainfall depth in 250-550 mm precipitation gradient, might be a scale-independent threshold driving the soil moisture-biodiversity relationship from trade-off to synergism in the region.

[Comparison on moisture dynamics of two different soil types in desert steppe]. / è’æ¼ è‰åŽŸä¸¤ç§ç±»åž‹åœŸå£¤çš„æ°´åˆ†åŠ¨æ€å¯¹æ¯”.

Based on the positioning monitoring data from 2017 to 2018, we analyzed the spatial-temporal dynamic characteristics of moisture in two different soil types (sierozem and aeolian sandy soil) in the Yanchi desert steppe in the eastern Ningxia. The results showed that the rainfall in the study area was 208.2 and 274.8 mm in the growing season of 2017 and 2018 (May-October), respectively. The distribution of rainfall varied across different months. Except for the extreme rainfall event (129.6 mm) in May in 2018, rainfall in other months was lower than that in 2017. The seasonal dynamics of soil water content was roughly divided into two phases: compensation period (early May to early June) and fluctuation period (mid June to late September). The soil moisture of 0-20 cm layer had a pulse characteristic of rapid increase and decrease after rainfall, while that of the deep soil was relatively stable. The soil water content of sierozem showed a "rise-fall-liter" change with increasing soil depth. The saeolian sandy soil increased sharply from 0 to 60 cm then increased slowly, whereas soil water content gradually increased with increasing soil depth. In 2017, soil moisture in the soil profile (0-100 cm) of the sierozem was accumulated, and the aeo-lian sand soil was in the consumption type. In 2018, both soil water across the full profile in both soil types were the consumption type. The temporal stability of soil moisture of two soil types increased with increasing soil depth. The average soil water content of the whole sections of sierozem and aeolian sandy soil were 80-100 and 40-60 cm, respectively. The two soil types had different spatial and temporal distributions of soil moisture. Aeolian sandy soil was more affected by precipitation than sierozem. Precipitation would reduce the variability of soil moisture and change its temporal stability.

[Population dynamics of Artemisia scoparia in heterogeneous habitats in the desert steppe]. / è’æ¼ è‰åŽŸå¼‚è´¨ç”Ÿå¢ƒä¸‹çŒªæ¯›è’¿ç§ç¾¤åŠ¨æ€.

To understand the intra- and inter-annual population dynamics of Artemisia scoparia in the desert steppe, we set up three treatments, i.e., increasing the precipitation by 30%, reducing the precipitation by 30%, and the control (CK) in each soil habitat of aeolian sandy soil, sierozem soil, and bedrock weathered sedimentary soil. We drew up the dynamic life table to produce population survival and death curves and analyzed the population dynamics of A. scoparia in different habitats. Results showed that the survival curve of A. scoparia was approached to Deevey-1type. The survival rate was high in the early growth stage and tended to be relatively stable. The mortality rate maintained at a low level, but rose fast at the end of the growth stage. The individual survival number of A. scoparia in all habitats fluctuated at the early stage and declined at the later stage. The mortality rates of A. scoparia in habitats of both aeolian sandy soil and sierozem soil fluctuated greatly. There was no significant difference in the effects of increased and decreased precipitation treatments on the mortality rate of A. scoparia. Soil types had significant effects on all parameters, including the plant height, crown width, density, cover, and biomass of A. scoparia. Precipitation treatments had significant impacts on plant height, crown width and coverage of A. scoparia, and had no significant effect on plant density and biomass. The interactions between soil type and precipitation treatments had only a significant impact on plant height and crown width. The plasticity index of biomass in the habitat of bedrock weathered sedimentary soil was significantly higher than that in habitats of aeolian sandy soil and sierozem soil, while the plasticity index of plant coverage in the habitats of both sierozem soil and bedrock weathered sedimentary soil were significantly higher than that in the habitat of aeolian sandy soil. The density plasticity index of increased precipitation treatment was significantly higher than those of CK and the decreased precipitation treatments. The plasticity index of plant height and crown width were higher than other parameters, indicating that A. scoparia could respond to habitat changes by giving priority to these two parameters under different habitat pressures.

[Effects of cutting and reseeding on the ground-dwelling arthropod community in Caragana intermedia forest in desert steppe].

Taking a 25-year-old Caragana intermedia forest in desert steppe as test object, an investigation was conducted on the ground-dwelling arthropod community in cutting and no-cutting stands with and without reseeding, aimed to understand the effects of cutting, reseeding and their interaction on the individual number and group richness of ground-dwelling arthropod in C. intermedia forest. There were significantly lower number and richness of ground-dwelling arthropod in the open spaces than under the shrubs in the no-cutting and no-reseeding stands. Cutting, reseeding and both of them could significantly increase the number and richness of ground-dwelling arthropod in the open spaces, but not under the shrubs, compared with no cutting or reseeding. Consequently, there were no significant differences in the distribution of ground-dwelling arthropod in the open spaces and under the shrubs in the cutting, reseeding, or cutting and reseeding stands. Further, there was a similar buffer effect between cutting and reseeding on the ground-dwelling arthropod. No significant differences were observed in the ground-dwelling arthropod distribution, between cutting stand and reseeding stand, between cutting stand and cutting and reseeding stand, and between reseeding stand and cutting and reseeding stand. It was suggested that cutting, reseeding, or both of them could significantly improve the ground-dwelling arthropod diversity especially in the open spaces, being beneficial for the restoration of degraded grassland ecosystem and the rational management on artificial C. intermedia forest in desert steppe.

[Effects of short-term fencing on organic carbon fractions and physical stability of sandy sierozem in desert steppe of Northwest China].

In order to explore the change patterns of organic carbon fractions and physical stability of sandy sierozem in desert steppe at the early stage of fencing, 0-40 cm soil samples were collected from a 5-year fenced desert steppe (inside the fence) and a free grazing steppe (outside the fence) in Yanchi County of Ningxia, Northwest China, with the soil organic carbon, labile organic carbon, and particulate organic carbon contents and soil particle composition analyzed. No significant differences were observed in the soil organic carbon content and soil particle composition inside and outside the fence. The average soil organic carbon inside and outside the fences was 3.25 g x kg(-1), the percentages of sand, silt, and clay were averagely 72%, 16%, and 12%, respectively, and the soil physical stability index was 1.30% -1.31%. The soil active organic carbon showed a significant change in 10-20 cm layer. The soil labile organic carbon content was 0.80 g x kg(-1) inside the fence, which was significantly higher than that outside the fence (0.62 g x kg(-1)). The percentage of soil particulate organic carbon was 50.9% inside the fence, which was also significantly higher than that outside the fence (31.7%). The soil texture inside the fence changed from sandy to loam, and the soil labile organic carbon content increased gradually; while the soil texture outside the fence was sandy, and its vertical change was relatively smooth. The organic carbon of sandy si- erozem in the desert steppe under the conditions of short-term fencing was still in a balance between consumption and accumulation, the soil texture was relatively stable, and the soil physical stability changed little. It was suggested that the soil active organic carbon content and its relative percentage in 10-20 cm layer could be used as the indicators of early soil quality change of desert steppe.

[Soil sandy desertification and salinization and their interrelationships in Yanghuang irrigated area of Hongsipu, Ningxia of northwest China].

By the methods of controlled and typical sampling, this paper analyzed the texture, salinization characteristics, cation exchange capacity (CEC), and their correlations in the 0-40 cm soil profiles of corn land, medlar land, and non-utilized land in Yanghuang irrigated area of Hongsipu, Northwest China. Under controlled sampling, the salt content in the soil profiles was 0.69-1.30 g x kg(-1) (except in non-utilized land where the 0-10 cm soil salt content was up to 1.74 g x kg(-1)), with no obvious salinization. The sodium adsorption ratio and exchangeable sodium percentage in the 20-40 cm soil layer of medlar land were 12.18 and 14.1%, respectively, and the total content of clay and silt in the 0-40 cm soil profile of medlar land was up to 37.3% whereas that in the 0-20 cm soil layer of corn land was only 13.5%. In the 20-40 cm soil layer of corn land, the indices of sandy desertification and salinization had significant correlations under controlled sampling but no correlations under typical sampling, while the CEC and the sandy desertification and salinization indices had significant correlations under typical sampling. In different land use types in the study area, soil sandy desertification and salinization had complicated interrelationships, and CEC could be used as the indicator for the changes in soil environmental quality.

[Changes of plant community biomass and soil nutrients during the vegetation succession on abandoned cultivated land in desert steppe region].

By the method of substituting temporal serial with spatial serial, and taking five abandoned cultivated lands with different ages (1, 4, 9, 12, and 20 years) in desert steppe region as test objects, this paper studied the change characteristics of plant community biomass and soil nutrients during vegetation succession. With the increasing abandoned years, the plant community aboveground biomass on the abandoned lands increased after an initial decrease, whereas the total nitrogen, total phosphorus, organic carbon contents, and carbon density in 0-60 cm soil layer increased first, decreased then, and increased again, with the maximum values of soil total nitrogen and phosphorus contents appeared on the abandoned lands with the ages 4 and 20 years. During vegetation succession, the effects of soil total nitrogen and organic carbon on plant community biomass were greater than those of soil total phosphorus and soil bulk density.