Soil Moisture Variations with Land Use along the Precipitation Gradient in the North–South Transect of the Loess Plateau

Abstract

Knowledge of soil moisture spatial variation with land use along the precipitation gradient is necessary to improve land management and guide restoration practice in the water‐limited Chinese Loess Plateau. This study selected 45 sampling points at 11 sites across the north–south transect of the Loess Plateau based on the precipitation gradient and land use. Results showed that the vertical profiles of soil moisture revealed large variations with the precipitation gradient changing, especially in the surface layer (0–100 cm). Significant linear correlation existed between the average soil moisture of the profile and the mean annual precipitation (MAP) for each land use type (p < 0·05). Hereinto, the soil moisture under the grassland was affected more greatly by precipitation. The soil moisture under each land use commonly revealed the trend as farmland > grassland > shrubland > woodland, while it might be higher under the woodland than the shrubland in the surface layer in regions with MAP <500 mm. The soil moisture of woodland or shrubland at the selected points was below or approximate to the permanent wilting point in regions with MAP <520 mm. Covariance analysis confirmed the effects of land use and MAP on the soil moisture in depth of 100–300 cm, and it showed land use did not pose significant effects in the surface layer. In addition, our study indicated that it is necessary to reconsider and re‐evaluate the current vegetation restoration strategy in the perspective of vegetation sustainability and soil water availability, in which woodland and shrubland were selected on a large scale in the arid and semi‐arid regions. Copyright © 2016 John Wiley & Sons, Ltd.

The Joint Effects of Precipitation Gradient and Afforestation on Soil Moisture across the Loess Plateau of China

“…On the other hand, the moisture in the upper soil layer (0-1.4 m) for the three plantations was not obviously lower than that in the control grassland (Figure 2), which was consistent with recent studies on the spatial variations of soil moisture under different land uses in the Loess Plateau [18]. Moisture in the upper soil layer might be more susceptible to additional hydro-geographical factors in contrast to the deep soil layer, such as rain throughfall, canopy interception, and soil evaporation [39].…”

“…The results of redundancy analyses indicated that afforested vegetation types had a weak influence on the degree of soil moisture decline following afforestation (Figure 3). Comparisons of soil moisture under different land uses has been well investigated [7,18,45]. However, such species-dependent impacts on the degree of soil moisture alterations following afforestation across a precipitation gradient has rarely been explored previously.…”

“…This implies that one potential limiting factor is the precipitation gradient. Furthermore, the soil-vegetation-atmosphere system indicated that the influences of afforestation on soil moisture also depended on afforested vegetation types [17,18]. Given that dominant vegetation types inevitably vary greatly along extensive precipitation gradients, there remains considerable uncertainty at the regional scale.…”

Soil water content and temporal stability in an arid area with natural and planted grasslands

“…Grasslands are one of the largest ecosystems in the world and play an important role in vegetation restoration (Zhang, Zhao, Liu, Fang, & Feng, 2016). Besides, recent studies have suggested that grasslands have higher values of soil water content (SWC), whereas scrublands and forests present drier conditions at deeper soil layers in dry lands (Wang, Wang, Fu, Yang, & Li, 2017). Precipitation is the sole source of soil water replenishment in arid and semiarid regions; improper planting patterns can aggravate water scarcity and strongly influence the growth and natural succession of vegetation (Porporato, D'odorico, Laio, Ridolfi, & Rodriguez-Iturbe, 2002;Wilcox & Newman, 2005;Shangguan & Zheng, 2006;Chen et al, 2008;Feng et al, 2016).…”

黄土高原草地土壤水分和物种多样性沿降水梯度的分布格局

“…式中：SMi和 [37] 。一般认为，降水是干旱、半干 旱地区土壤水分补充的主要来源，在较大的尺度上与蒸散发共同控制着土壤水分含量及 其时空动态格局 [38][39] 。黄土高原具有典型的大陆性季风气候，水分输送受距离、地形、地 貌的影响，降水自东南向西北递减，这种降水格局控制着多数生态过程 [40] 。受降水梯度 影响，本研究中草地 0~3 m 各层土壤水分自东南向西北均呈相应递减趋势 (图 1、图 3) 。各个土层土壤水分与年均降水量均呈极显著正相关 (P<0.01) ，说明区域尺度上 0~3 m 土壤水分空间异质性主要受降水格局主导 [41] 。此外，本研究中土壤水分和年均降水量 的相关系数在浅层 (0~1 m) 最大，随着深度的增加而减小，这是由于黄土高原地区地 下水埋藏深，使得天然降水成为土壤水分补给的唯一来源，降水对土壤水分的补充随着 土层深度的增加而减少 [42] 。 在水分限制地区，陆地生态系统对气候变化的敏感性很大程度上源于降水时空格局 的变化 [4] 。降水减少不仅可以直接降低土壤有效水分，还可以限制根际微生物的正常活 动，进而影响植物对水分、养分的吸收、运输和利用 [43] 。在黄土高原地区，降水格局通 过调控中生、旱生草本种类、多度和高度，进而影响群落的分布、结构和生态功能 [7,23] 。 图 4 物种多样性与年均降水量之间的关系 Key words: soil moisture; species diversity; precipitation gradient; tradeoff analysis; Loess Plateau…”