Response of Ecoenzymatic Stoichiometry to Soil Physicochemical Properties after Afforestation on Loess Hilly Region
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EGRADATION, REHABILITATION, AND CONSERVATION OF SOILS
Response of Ecoenzymatic Stoichiometry to Soil Physicochemical Properties after Afforestation on Loess Hilly Region Sheng-Ji Yana, Bo-Yong Lia, De-Xin Gaoa, b, Shu-Yue Fua, b, Yun-Fei Lua, Miao-Ping Xua, b, Cheng-Jie Rena, b, *, and Xin-Hui Hana, b, * aCollege
b
of Agronomy, Northwest A&F University, Yangling, Shaanxi 712100, China Research Center of Recycle Agricultural Engineering and Technology of Shaanxi Province, Yangling, Shaanxi 712100, China *e-mail: [email protected] Received March 14, 2019; revised April 20, 2020; accepted April 24, 2020
Abstract—Afforestation has significantly affected interactions between soil nutrients and microbial enzymes. To understand the detailed variations in extracellular enzyme activity and their link with soil nutrient availability after returning farmland (FL) to forest, soil samples were collected from FL and three afforested lands, Robinia pseudoacacia L. forest (RP), Caragana korshinskii Kom. forest (CK), and abandoned land (AL) in the Loess Hilly Region of northern China. The soil enzymes: β-glucosidase (BG), N-acetylglucosaminidase (NAG), alkaline phosphatase (AP), and leucine aminopeptidase (LAP); their stoichiometric ratios; and soil properties such as soil organic carbon, total nitrogen (TN), total phosphorus (TP), dissolved organic carbon, dissolved organic nitrogen, available phosphorus, soil moisture content (SMC), soil bulk density, and pH were measured. The BG activity showed similar trends as AP activity during afforestation, reaching the highest level in CK and showing a value 205% higher than that in FL. The NAG and LAP activities were not altered by afforestation; only the (NAG + LAP) : AP ratio decreased significantly by 44 to 60%. The BG : AP and (NAG + LAP) : AP ratios were strongly correlated with pH. Compared with other soil physicochemical properties, the soil moisture content greatly affected soil enzyme activity. The most relevant nutrients for the enzymes and stoichiometry were TN and TN : TP. Thus, our results suggest that soil enzyme activity and its stoichiometry are sensitive to changes in soil physical and chemical properties and total soil nutrients content, particularly pH, SMC, TN, and TN : TP. Keywords: forestation, C : N : P stoichiometry, ecoenzymatic stoichiometry, Loess Region, soil nutrients DOI: 10.1134/S1064229320110125
INTRODUCTION Afforestation is one of most effective land use approaches for improving soil nutrient accumulation [13, 19] and the growth status of above-ground vegetation [6, 35]. The circulation of underground soil nutrition in afforestation ecosystems is greatly affected by soil enzymes produced by soil microbes. Soil enzymes are sensitive to changes in ecosystems and land use types [9]. Recent studies have shown that soil enzymes play a vital role in nutrient cycling processes in organic matter degradation, transformation, and mineralization [21]. Especially, β-glucosidase (BG), N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline ph
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