Abstract
Long-term afforestation strongly changes the soil’s physicochemical and biological properties. However, the underlying mechanism of different tree species driving change in soil nutrients is still unclear in the long-term dryland plantations of the Loess Plateau, China. In this study, samples of surface soil (0–20 cm) and woody litter were collected from five plantations (≥50 years) of Caragana korshinskii, Armeniaca sibirica, Populus hopeiensis, Platycladus orientalis, and Pinus tabulaeformis and a natural grassland, and tested for the carbon, nitrogen, phosphorus, and potassium contents, as well as the soil sucrase (SC), urease (UE), and alkaline phosphorus (ALP) activities. We found that soil nutrients, enzyme activities, and the litter’s chemical properties obviously varied among five tree species. C. korshinskii significantly increased the soil’s TC, organic carbon (OC), total nitrogen (TN), available nitrogen (AN), and available potassium (AK) by 28.42%, 56.08%, 57.41%, 107.25%, and 10.29%, respectively, and also increased the soil’s available phosphorus (AP) by 18.56%; while P. orientalis significantly decreased soil TN (38.89%), TP (30.58%), AP (76.39%), TK (8.25%), and AK (8.33%), and also decreased soil OC (18.01%) and AN (1.09%), compared with those in grassland. The C. korshinskii plantation had higher quality litter and soil enzyme activities than the P. orientalis plantation. Moreover, 62.2% of the total variation in soil nutrients was explained by the litter’s chemical properties and soil enzyme activities, and the litter phosphorus (LP) and soil ALP had a more significant and positive impact on soil nutrients. Therefore, tree species, LP, and soil ALP were key factors driving soil nutrient succession in dryland plantations. The significantly positive nitrogen–phosphorus coupling relationship in the “litter–enzyme–soil” system revealed that the improving nitrogen level promoted the phosphorus cycle of the plantation ecosystem. Our results suggest that leguminous tree species are more suitable for dryland afforestation through the regulation of litter quality and soil enzyme activities.
Highlights
The artificial forest area in the world has reached 2.78 × 106 km2 in 2015 [1], and afforestation is considered an effective measure to alleviate soil erosion and land degradation [2,3]
Our results showed that deciduous plantations (C. korshinskii and P. hopeiensis) had higher soil TC, organic carbon (OC), total nitrogen (TN), available nitrogen (AN), and AK contents than evergreen plantations (P. orientalis and P. tabuliformis) by 1.34–166.87%
Our results showed that the variations in soil nutrients following long-term afforestation with different tree species were caused by soil TC, OC, TN, AN, available phosphorus (AP), and AK, which were significantly positively affected by the LN, litter phosphorus (LP), UE, and alkaline phosphorus (ALP) (Table 3)
Summary
The artificial forest area in the world has reached 2.78 × 106 km in 2015 [1], and afforestation is considered an effective measure to alleviate soil erosion and land degradation [2,3]. The temporal dynamics of and differences in soil nutrients in plantations of different tree species along afforestation chronosequences have been extensively studied [6,7]. Plantations promote the accumulation of litter while stimulating soil biological activities and producing more enzymes [8,9]. The effects of litter as a supplementary source of soil nutrients and enzymes as indicators of soil fertility on the succession of soil nutrients in plantations have rarely been considered. Whether and how the litter of different tree species and soil enzyme activities drive soil nutrients in plantations remains to be studied
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