Abstract
Macropores are an important part of soil structure. However, in alpine regions, the effects of soil macropores on soil properties and vegetation growth are not clear. We used the X-ray computed tomography (CT) method to obtain 3D images and visualize the distribution and morphology of soil macropores. By combining principal component analysis (PCA) and stepwise regression methods, we studied the relationships between soil macropores and both soil properties and vegetation growth in three types of grassland [alpine degraded steppe (ADS), alpine typical steppe (ATS), and alpine meadow steppe (AMS)] on the Tibetan Plateau. More tubular and continuous macropores occurred in the soil profiles of the AMS and ATS than in that of the ADS. In addition, the AMS soil had the highest macropore number (925 ± 189), while the ADS soil had the lowest macropore number (537 ± 137). PCA and correlation analysis suggested that macroporosity (MP) has significant positive correlations with the contents of soil organic matter, total nitrogen (TN), available phosphorus (AP) and total phosphorus (TP) (p < 0.05). The two parameters with the greatest influence on aboveground and belowground biomass were the shape factor (p < 0.05) and MP (p < 0.05), respectively. However, there was no significant correlation between plant diversity and soil macropores. We conclude that the irregularity of soil macropores restricts the growth space of roots and causes plants to sacrifice the accumulation of aboveground biomass for that of roots to find suitable sites for nutrient and water absorption.
Highlights
Soil structure can regulate biophysical and chemical processes and properties in soil that are associated with soil function and plant growth, such as water retention and infiltration, gas exchange, soil organic matter and nutrient dynamics, root penetration and sensitivity to erosion (Bronick and Lal, 2005; Guimarães et al, 2017; Rabot et al, 2018)
The total phosphorus (TP) content of alpine meadow steppe (AMS) was much higher than that of alpine degraded steppe (ADS) and alpine typical steppe (ATS), but there was no significant difference in the distribution of TK in the soil at 20∼30 cm among the sites, whereas the TK contents in the 0∼10 and 10∼20 cm soil layers were much higher in ATS than in ADS and AMS
The results of the 3D visualization of the soil macropore network showed that the soil MP in the AMS was larger than that in the ATS and that the macropore content was smallest in the ADS (Figure 3 and Table 3), which may be related to the location of the northeastern Tibetan Plateau in an arid area of northern China and the limited precipitation received by degraded grasslands
Summary
Soil structure can regulate biophysical and chemical processes and properties in soil that are associated with soil function and plant growth, such as water retention and infiltration, gas exchange, soil organic matter and nutrient dynamics, root penetration and sensitivity to erosion (Bronick and Lal, 2005; Guimarães et al, 2017; Rabot et al, 2018). Soil structure and its effects on soil function deserve further research because soil structure affects soil water dynamics and nutrient cycling and is of great significance for understanding the relationship between soil and plant growth (Kuka et al, 2013). Soil Macropores Affect Plant Biomass the pore wall (Pierret et al, 2002; Jarvis, 2007; Colombi et al, 2017; Rabot et al, 2018). Due to inconsistent classification criteria for macropores, the definitions of the equivalent pore size of macropores are somewhat vague in the literature, with some being greater than 1 mm and some greater than 3 mm (Iversen et al, 2012), macropores are usually defined as pores having an equivalent diameter greater than 0.5 mm (Hlaváciková et al, 2019)
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