Unraveling the Influence of Land-Use Change on δ13C, δ15N, and Soil Nutritional Status in Coniferous, Broadleaved, and Mixed Forests in Southern China: A Field Investigation.

Taimoor Farooq,Uttam Kumar,Xiaoyong Chen,Jun Wang,Wende Yan,Yong Li,Awais Shakoor,Muhammad Rashid

doi:10.3390/plants10081499

Abstract

Natural isotopic abundance in soil and foliar can provide integrated information related to the long-term alterations of carbon (C) and nitrogen (N) cycles in forest ecosystems. We evaluated total carbon (TC), total nitrogen (TN), and isotopic natural abundance of C (δ13C) and N (δ15N) in soil and foliar of coniferous plantation (CPF), natural broadleaved forest (NBF), and mixed forest stands at three different soil depths (i.e., 0–10, 10–20, and 20–40 cm). This study also explored how soil available nutrients are affected by different forest types. Lutou forest research station, located in Hunan Province, central China, was used as the study area. Results demonstrated that the topsoil layer had higher TC and TN content in the mixed forest stand, resulting in a better quality of organic materials in the topsoil layer in the mixed forest than NBF and CPF. In general, soil TC, TN, and δ15N varied significantly in different soil depths and forest types. However, the forest type did not exhibit any significant effect on δ13C. Overall, soil δ13C was significantly enriched in CPF, and δ15N values were enriched in mixed forest. Foliar C content varied significantly among forest types, whereas foliar N content was not significantly different. No big differences were observed for foliar δ15N and δ13C across forest types. However, foliar δ13C and δ15N were positively related to soil δ13C and δ15N, respectively. Foliar N, soil and foliar C:N ratio, soil moisture content (SMC), and forest type were observed as the major influential factors affecting isotopic natural abundance, whereas soil pH was not significantly correlated. In addition, forest type change and soil depth increment had a significant effect on soil nutrient availability. In general, soil nutrient availability was higher in mixed forest. Our findings implied that forest type and soil depth alter TC, TN, and soil δ15N, whereas δ13C was only driven by soil depth. Moreover, plantations led to a decline in soil available nutrient content compared with NBF and mixed forest stands.

Highlights

Human activities and different natural environmental factors produce abrupt, large scale, irreversible changes and alter forest structure and composition, resulting in the changes of biogeochemical cycles [1,2]
In the topmost soil layer, total carbon (TC), total nitrogen (TN), and soil C:N ratio was higher in the mixed forest stand, while for the remaining two soil layers, it was greater in coniferous plantation forest (CPF) (Table 2)
This study explored how δ13 C, δ15 N, TC, and TN content of soil and foliage and soil nutrient availability is affected by different forest types

Summary

Introduction

Human activities and different natural environmental factors produce abrupt, large scale, irreversible changes and alter forest structure and composition, resulting in the changes of biogeochemical cycles [1,2]. Species composition significantly affects the quality and quantity of carbon (C) and nitrogen (N) input by controlling surface soil and vegetation layer C and N contents and their turnover rates [3,4,5]. N is the essential element in the natural ecosystem, and is a vital limiting resource for plant growth [5]. The. 13 C and 15 N natural abundance in the soils is a dynamic function of the rate and isotopic composition and the C and N transformations in the forest ecosystem as it provides cohesive insights into C and N cycles [6,7,8].

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