Spatial Heterogeneity of Soil Nutrients after the Establishment of Caragana intermedia Plantation on Sand Dunes in Alpine Sandy Land of the Tibet Plateau.

Qingxue Li,Defu Yang,Hong Li,Zhiqing Jia,Xuebin Zhao,Yongsheng Wang,Yajuan Zhu,Sergio R Roiloa

doi:10.1371/journal.pone.0124456

Abstract

The Gonghe Basin region of the Tibet Plateau is severely affected by desertification. Compared with other desertified land, the main features of this region is windy, cold and short growing season, resulting in relatively difficult for vegetation restoration. In this harsh environment, identification the spatial distribution of soil nutrients and analysis its impact factors after vegetation establishment will be helpful for understanding the ecological relationship between soil and environment. Therefore, in this study, the 12-year-old C. intermedia plantation on sand dunes was selected as the experimental site. Soil samples were collected under and between shrubs on the windward slopes, dune tops and leeward slopes with different soil depth. Then analyzed soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP) and available potassium (AK). The results showed that the spatial heterogeneity of soil nutrients was existed in C. intermedia plantation on sand dunes. (1) Depth was the most important impact factor, soil nutrients were decreased with greater soil depth. One of the possible reasons is that windblown fine materials and litters were accumulated on surface soil, when they were decomposed, more nutrients were aggregated on surface soil. (2) Topography also affected the distribution of soil nutrients, more soil nutrients distributed on windward slopes. The herbaceous coverage were higher and C. intermedia ground diameter were larger on windward slopes, both of them probably related to the high soil nutrients level for windward slopes. (3) Soil “fertile islands” were formed, and the “fertile islands” were more marked on lower soil nutrients level topography positions, while it decreased towards higher soil nutrients level topography positions. The enrichment ratio (E) for TN and AN were higher than other nutrients, most likely because C. intermedia is a leguminous shrub.

Highlights

Desertification is one of the main types of land degradation in arid, semi-arid and dry subhumid areas and results from various factors, including climatic variability and human activities [1]
(2) Topography affected the distribution of soil nutrients, more soil nutrients distributed on windward slopes
When the impaired sand flow reached the dune tops and leeward slopes, less wind erosion materials, dust and litter were trapped by C. intermedia, and this may be another reason for more soil nutrients distributed on windward slopes, further study is needed for clarification

Summary

Introduction

Desertification is one of the main types of land degradation in arid, semi-arid and dry subhumid areas and results from various factors, including climatic variability and human activities [1]. Sand mobility and wind erosion result in coarse, poor soil and low land productivity, which can degrade the human living environment and impede socioeconomic development. Previous studies have shown that the existed of leguminous shrub resulted in spatial heterogeneity of soil properties. Some studies have shown that after the establishment of Caragana microphylla plantation on sand dunes, soil nutrient concentrations were higher under the shrubs than outside the canopies [9,10]. The studies of Caragana tibetica nebkhas on the Inner Mongolia Plateau have shown that the “fertile islands” are formed inside and underneath C. tibetica nebkhas [14]. Formation of “fertile islands” increases spatial heterogeneity in soil resources [15], and affects seedling establishment [16], and the spatial distribution of plant productivity and diversity [17,18]

Methods

Results

Discussion

Conclusion