Xinping Liu

Effects of rainfall patterns on annual plants in Horqin Sandy Land, Inner Mongolia of China

Growth of annual plants in arid environments depends largely on rainfall pulses. An increased understanding of the effects of different rainfall patterns on plant growth is critical to predicting the potential responses of plants to the changes in rainfall regimes, such as rainfall intensity and duration, and length of dry intervals. In this study, we investigated the effects of different rainfall patterns (e.g. small rainfall event with high frequency and large rainfall event with low frequency) on biomass, growth characteristics and vertical distribution of root biomass of annual plants in Horqin Sandy Land, Inner Mongolia of China during the growing season (from May to August) of 2014. Our results showed that the rainfall patterns, independent of total rainfall amount, exerted strong effects on biomass, characteristics of plant growth and vertical distribution of root biomass. Under a constant amount of total rainfall, the aboveground biomass (AGB), belowground biomass (BGB), plant cover, plant height, and plant individual and species number increased with an increase in rainfall intensity. Changes in rainfall patterns also altered the percentage contribution of species biomass to the total AGB, and the percentage of BGB at different soil layers to the total BGB. Consequently, our results indicated that increased rainfall intensity in future may increase biomass significantly, and also affect the growth characteristics of annual plants.

Shrub Effects on Herbaceous Vegetation Vary with Growth Stages and Herb Relative Location

ABSTRACT: In arid and semi-arid ecosystems, shrubs have an important effect on neighboring plants. However, little is known about the interaction of herb growth stages and shrub location on herb performance. We selected Reaumuria soongorica, (Pall.) Maxim a shrub dominant in the semiarid region of northwest China, to determine whether (1) shrubs facilitate or have negative effects on neighbouring herbaceous vegetation, and (2) such effects vary with herb growth stage and with shrub orientation relative to herbs. The presence of herbaceous plant species, plant density, plant height, and percent cover were determined along 2 m long transects spreading in four directions from the base of shrub — east (transect E), west (transect W), south (transect S), and north (transect N); this was repeated for three growth stages (in May, June and July). Results indicated that the effects of R. soongorica on neighboring herbs in different growth stages were similar. Species number of herb-layer plants tended to increase from beneath the canopy to the opening, but plant density, cover and plant height decreased with distance away from shrub base. The presence of R. soongorica had positive effects on density, cover, and plant height, and negative on the number of herbaceous species during the entire growing season. Herbaceous plants growing on transect N under the shrub canopy had significantly higher density and percent cover than those growing in other directions. Biomass of herbs on transect N grown under the shrub canopy was higher than that of herbs on other transects. We concluded that shrub effects on neighbouring herbaceous vegetation were closely related to the shrub orientation relative to the herbs. Therefore, using shrubs as nurse plants for grass-growing must consider the relative placement of shrubs.

Desertification Effects on Calorific Value, Biomass and Energy Allocation in Horqin Sandy Land, Inner Mongolia, North China

The Horqin Sandy Land is one of the most seriously desertified regions of China. In this paper, we measured the aboveground and belowground biomass, caloric value in biomass components, and biomass energy allocation at three distinct land-cover types of habitat along a desertification gradient in Horqin Sandy Land: non-desertification land (ND), light desertification land (LD), and severe desertification land (SD). The results indicated that not only plant biomass decreased significantly but plant life-form and proportion of biomass components changed with desertification development. The more serious desertification of sandy land, the higher proportion of living biomass accounted for the total aboveground and belowground biomass, and the lower surface litter and belowground litter accumulated. Plant communities of sandy land have the lower ability to convert solar energy into organic matter. The worse was that desertification limited the amount of energy inputting and resulted in producer’s function weakening or bankrupting in ecosystem.

Characteristics of deep drainage and soil water in the mobile sandy lands of Inner Mongolia, northern China

Quantification of deep drainage and the response of soil water content to rainfall patterns are critical for an effective management strategy of soil water conservation and groundwater utilization. However, there has been little information on how rainfall characteristics influence soil water dynamics and deep drainage in mobile sandy lands. We used an underground chamber to examine the responses of deep drainage and soil water content in mobile sandy lands to rainfall characteristics in Inner Mongolia during the growing seasons of 2010, 2011 and 2012. Results showed that rainfall in this area was dominated by small events (≤5 mm), which increased soil water content in the surface soil layers (0–40 cm), but did not increase soil water content in the deeper soil layers (greater than 40 cm). Soil water content at the 0–100 cm depth increased significantly when the total amount of rain was >20 mm. Rainfall amount, intensity and the duration of dry intervals were significantly related to the soil water content in different soil layers. Deep drainage was significantly correlated with rainfall amount and intensity, but not with the duration of dry intervals. The coefficients of deep drainage in the mobile sandy lands ranged from 61.30% to 67.94% during the growing seasons. Our results suggested that rainfall infiltration in the mobile sandy lands had considerable potential to increase soil water storage while recharging the groundwater in this region.

Increased pollinator service and reduced pollen limitation in the fixed dune populations of a desert shrub

Evaluations of restoration success usually focus on the structural aspects of ecosystems. Pollination, as an important functional aspect, is often overlooked. Here, the shifts in pollinator assemblage and pollen limitation in the desert shrub Caragana microphylla were examined along a restoration gradient in Horqin Sand Land, northern China. We identified seven species of bees; however, only four bee species were found to be effective pollinators, with Xanthosaurus remota dominating in the fixed dunes, and with no bee species or only a single species, X. remota, being observed in the semi-fixed and mobile dunes. Flower visitation rate was nearly ten times higher in the fixed dunes than in the mobile and semi-fixed dunes. Experimental floral manipulations revealed that the fixed dune populations experienced less pollen limitation, along with the increase in pollinator availability. Between the mobile and semi-fixed dune populations, pollen limitation was severe and at similar levels. The intensity of pollen limitation was negatively related to pollinator abundance and richness. Overall, the dependence on pollinators for reproduction may be an important constraint that limits persistence in this system. Increased pollinator service during the restoration process may ameliorate pollen limitation, benefiting the restoration of vegetation in this semiarid sandy area.

Variations of Leaf Economic Spectrum of Eight Dominant Plant Species in Two Successional Stages Under Contrasting Nutrient Supply

ABSTRACT Leaf functional traits are indicators of both plant community and ecosystem responses to environmental factors and can thus increase our capacity to understand ecosystem processes and community assembly due to climate change. The variation in leaf functional traits between succession stages in Horqin Sandy Land is caused by soil nutrient content and by intrinsic biological characteristic of species, but the effects are different. Leaf economic spectra were assessed for seven leaf traits of eight species from early and advanced stages of succession. Species from early succession stages are Agriophyllum squarrosum (L.) Moq., Corispermum macrocarpum Bge., Setaria viridis (L.) Beauv. and Pennisetum centrasiaticum Tzvel., and species from advanced successional stages are Chenopodium acuminatum Willd., Chloris virgate Swartz, Digitaria sanguinalis (L.) Scop. and Leymus secalinus (Georgi) Tzvel. All these species were grown in a greenhouse experiment under two contrasting nutrient supplies including high nutrient level (N+, with 20 g of nutrient addition) and low nutrient level (N-, with no added nutrients). As expected, the resource uptake strategies of the species were affected by soil fertilization addition. Leaf nitrogen content (LNC), leaf phosphorus content (LPC), and photosynthetic capacity per unit leaf area (Aarea) significantly increased at high nutrient level but LPC is more dramatically changed than others leaf traits. Leaf life span (LLS) and specific leaf area (SLA) did not show similar tendency with succession stage. At the same nutrient level, LES still shows different pattern between the early and the advanced succession stages. Species from early succession stages have higher LPC and Aarea, compared to species from advanced stages. Species from early succession stage also tend to have higher SLA and higher LNC than at the advanced succession stage. The LLS did not show any clear changes with succession process. These results provide evidence that LES shift along the succession process is mainly caused by intrinsic biological characteristic of species.

Effects of Sand Burial Depth on Seedling Growth of Caragana microphylla

Caragana microphylla is a pioneer leguminous shrub species, and plays an important role in sand fixing and desertification control in the Horqin Sandy Land of Northern China. In this study, seedlings were buried by sand to depths of 0 (control), 1/3, 2/3, 1 and 4/3 of their mean height, and the effects of sand burial depth on seedling growth of Caragana microphylla were tested. Results show that with increasing burial depth, biomass allocation to leaves decrease, while stem biomass allocation increase, and both shoot and root growth of C. microphylla are stimulated and seedling biomass is the highest when burial depth is 2/3 of seedling height. Therefore, moderate burial could facilitate seedlings growth of C. microphylla

Impact of Grazing Excluding and Grazing on Soil Properties in Sandy Grassland in Horqin Sand Land, China

The restoration of degraded grassland which caused by overgrazing is directly related to land sustainable and economical development in North China. However, it is not well know that the impact of grazing excluding and continuous free grazing on soil properties in this region. In this paper, Soil physical and chemical properties under grazing excluded for 5 and 11 years and free grazing were examined in representative degraded sandy grassland. Results showed that continuous free grazing cause soil compaction, soil structure degradation, and loss of soil organic C and total N. Different period exclusion contribute to soil structure improvement, bulk density decreased, and soil fertility improvement through area protection. In addition, soil organic C and total N stocks showed a significant increasing trend from FG to 11GE. It indicated grazing excluding has important significance in soil restoration. So there is a need to develop sustainable grassland management and exclusion practices to combat the ongoing grassland degradation in the region.

Water Diffusivity of Sandy Soil of Different Particle Sizes in Typical Sandy Cropland

A laboratory experiment was conducted in May 2006 to measure water diffusivity (Dθ) of sandy soil of different particle sizes. The method of cobalt chloride test paper (CCTP) was made to observe moving position of wetting front. Results showed that the rate of wetting front advancement (RWFA) is in the order: 0.50-0.25 mm soil¿ 0.25-0.10 mm soil¿ undisturbed soil¿ the soil of less than 0.10 mm. The relationship between infiltration distance and the RWFA was expressed as a power function. With decrease in the sand particle sizes, Dθ was decreased gradually. The Dθ change was most obvious in the soil of 0.50-0.25 mm, the least obvious one was the soil of less than 0.10mm. There existed significant correlation between Dθ and soil water content which met an exponential curve and was in accordance with the empirical equation. As a new attempt, CCTP was reliable to measure the position of wetting front and decrease the subjective error of visual method.