Abstract
Background
Long-term afforestation of different tree species strongly changes the soil physicochemical and biological properties. However, how tree species through litter quality and soil enzyme activities affect the succession of soil nutrients is still unclear in the dryland plantations. In this study, samples of surface soil (0–20 cm) and woody litter were collected from 55 years Caragana korshinskii, and 50 years Armeniaca sibirica, Populus hopeiensis, Platycladus orientalis, and Pinus tabulaeformis, and the 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.
Results
We found that long-term dryland plantations increased soil total carbon (TC) by 1.69%-28.42%, but significantly decreased soil total phosphorus (TP) and total potassium (TK) by 11.87%-30.58% and 4.69%-8.25%. The C. korshinskii significantly increased soil TC, organic carbon (OC), total nitrogen (TN), available nitrogen (AN), available potassium (AK), UE, and ALP by 28.42%, 56.08%, 57.41%, 107.25%, 10.29%, 11.00%, and 107.81%, respectively, and also raised soil available phosphorus (AP) by 18.56%; while the P. orientalis significantly decreased soil TN, TP, AP, TK, AK, and UE by 38.89%, 30.58%, 76.39%, 8.25%, 8.33%, and 18.97%, respectively, and also reduced soil SC and ALP by 3.84% and 25.32%, compared to those in grassland. In addition, the C. korshinskii produced high-quality litter with lower carbon, the highest nitrogen and phosphorus, and higher potassium contents than those of P. orientalis. The litter chemical properties and soil enzyme activities together explained 62.2% of the total variation of soil nutrients, especially the litter phosphorus (LP) and soil ALP. Therefore, the tree species, LP, and soil ALP were key factors driving soil nutrient succession in dryland plantations. And the significantly positive coupling relationship between nitrogen and phosphorus in the "litter-enzyme-soil" system revealed that the improvement of nitrogen level promoted the phosphorus cycle of the ecosystem.
Conclusions
This study suggests choosing leguminous tree species with high-quality litter to establish plantations in the phosphorus-limited dryland, which will improve soil nutrients and alleviate nutrient limitations by adjusting soil enzyme activities.
Nitrogen and phosphorus regulation of soil enzyme activities in acid forest soils
