Reforestation and slope-position effects on nitrogen, phosphorus pools, and carbon stability of various soil aggregates in a red soil hilly land of subtropical China

Abstract

Abstract:The impact of slope position on forest restoration processes may dominate the interaction among topsoil aggregates, nutrients, and organic carbon (C) stability following reforestation on degraded hilly land. Six paired plots of shrubland and Masson pine (Pinus massoniana Lamb.) plantation reforested on shrubland were selected at different positions along a 25°slope in subtropical China. Soil and ecosystem nitrogen (N), phosphorus (P), and organic C stocks were quantified using a combination of excavation, harvest, and modeling methods. Carbon stability in differently sized soil aggregates was measured using dry sieving and closed-jar alkali-absorption methods. Reforestation increased total ecosystem C, N, and P stocks, but did not alter soil C and P stocks, and decreased N stocks at 0-75 cm soil depth by 18%. The shift from shrubland to forests increased organic C stability for various soil aggregates, particularly with a mean increase of 34% and 30% at lower and middle slope positions, respectively. The slope-position effect was largely attributable to the increased mean mass diameter of soil aggregates and the reduced organic C mineralization potential in larger soil aggregates relative to smaller soil aggregates. Soil aggregates had more stable organic C in forests than in shrubland due to increase in the carbon to nitrogen (C/N) and carbon to phosphorus (C/P) ratios with reforestation. Slope position influenced restoration effectiveness in the red soil hilly region.Key words: biogeochemistry, ecosystem function, land-use change, organic carbon mineralization, soil property.Résumé : L'impact de la position dans la pente sur les processus associés à la restauration de la forêt pourrait dominer l'interaction parmi les agrégats des horizons superficiels, les nutriments et la stabilité du C organique à la suite du reboisement en terrain accidenté et dégradé. Six placettes appariées contenant des arbustes ou une plantation de pin rouge chinois (Pinus massoniana Lamb.) reboisé dans une zone arbustive ont été établies à différents endroits le long d'une pente de 25°dans la partie subtropicale de la Chine. Les stocks de N, P et C organique ont été quantifiés dans le sol et l'écosystème en combinant excavation, récolte et modélisation. La stabilité de C dans les agrégats de sol de différentes tailles a été mesurée en utilisant le tamisage à sec et l'absorption de bases en contenant fermé. Le reboisement a augmenté les stocks totaux de C, N et P dans l'écosystème mais n'a pas modifié les stocks de C et P dans le sol et a diminué les stocks de N de 18 % à une profondeur de 0-75 cm dans le sol. Le fait de passer d'une formation arbustive à la forêt a augmenté la stabilité du C organique pour une variété d'agrégats de sol, particulièrement avec une moyenne de 34 % et 30 % respectivement au bas et au milieu de la pente. L'effet de la position sur la pente était en grande partie attribuable à l'augmentation du diamètre moyen des agrégats de sol et à la réduction de la capacité de minéralisation du C organique dans ...

Exogenous nutrients and carbon resource change the responses of soil organic matter decomposition and nitrogen immobilization to nitrogen deposition

“…The region has a subtropical moist monsoon climate, with a warm, dry summer and a cool, wet winter. The soil is Typic Hapludult Ultisols (locally “red soil”), which develops from Quaternary Red Clay and covers over 60% of 1.14 million km 2 of total land area in the southern China 48 . The average stand density, diameter at breast height and height of the selected Chinese fir plantation are approximately 1950 tree/ha, 10 cm and 9 m, respectively.…”

“…The quantity of CO 2 produced was measured by titrating NaOH to pH 8.3 with 0.5 M HCl in the presence of BaCl 2 . The net amount of CO 2 produced from the soil or litter was calculated as the difference between the treatments and control jars 48 50 . Three replicates were applied for each treatment per incubation temperature.…”

Topsoil and Deep Soil Organic Carbon Concentration and Stability Vary with Aggregate Size and Vegetation Type in Subtropical China

“…In China alone, reforested plantations covered 69.33 million ha in 2014, becoming the largest around the world [27]. Although the influence of reforestation on deep soil OC is still poorly understood [22], deep soil carbon may be influenced by changes in land-use and/or management [28].…”

“…Globally, roughly 140 million hectares of land had been reforested before 2005, and reforestation has the potential to create more than 34 million hectares of forest by 2020 [ 4 ]. In China alone, reforested plantations covered 69.33 million ha in 2014, becoming the largest around the world [ 27 ]. Although the influence of reforestation on deep soil OC is still poorly understood [ 22 ], deep soil carbon may be influenced by changes in land-use and/or management [ 28 ].…”

The interactions among herbaceous diversity, edaphic factors, and topography under typical afforestation in the transition zone between the qinghai–Tibet Plateau and Loess Plateau

“…in the altitude, slope position, and slope exposure in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau is responsible for the heterogeneity of the microenvironment due to changing the light and water conditions, and affecting the soil texture, nutrient, vegetation diversity, and distribution (Xu et al 2020). Forests might be more prone to nutrition loss from hilltops (Zou et al 2014). The results of previous studies have suggested using strategies according to different topographic conditions of the Loess Plateau to maximize the benefits of afforestation, such as mitigating soil degradation and improving biodiversity (Taye et al 2013;X.…”