Abstract
This study aimed to investigate the correlation of carbon and nitrogen in soil and leaves with the altitude, vegetation type, herbaceous biomass (HB), litter mass (LM) and with each other. Soil and leaf samples collected from different forest types along altitudinal gradients in the Karakoram Mountains. Dry and gas law methods were used for the chemical analysis. Regression models used for correlation analysis and T test for comparison. The correlation of soil total carbon (STC) and soil total nitrogen (STN) along altitudinal gradients and correlation between soil organic carbon (SOC) and STN was significantly positive with the values R2 = 0.1684, p = 0.01, R2 = 0.1537, p = 0.009 and R2 = 0.856, p = 7.31E−10 respectively, while it was non-significant between soil inorganic carbon (SIC) and altitude and also between SIC and STN. The concentration of SOC and STN was highest in the broad leaved Betula utilis forest (22.31, 1.6 %) and least in the mixed (Pinus, Juniper, Betula) forest soil (0.85, 0.09 %) respectively. In the tree species leaf total carbon (LTC) and leaf total nitrogen (LTN) were highest in the Pinus wallichiana (PW) (632.54, 19.77), and least in the Populus alba (87.59, 4.06). In the shrub species LTC and LTN nitrogen were highest in the Rosa webiana (235.64, 7.45) and least in the Astragalus gilgitensis (43.45, 1.60) respectively. Total carbon and total nitrogen showed a slightly decreasing and increasing trend with altitude in the leaf and soil samples, respectively. The mean nitrogen and carbon was higher in the leaves of trees (3, 97.95) than in the shrubs (2.725, 74.24) and conifers (2.26, 76.46) than in the leaves of the deciduous (2, 46.36) trees. The correlation between LTC and STN was non-significant. Strong significant (R2 = 0.608, p = 0.003) and weak non-significant (R2 = 0.04, p = 0.32) relationships were found in STN and STC with LM and HB respectively. SOC (75.15 %) was found to be the main contributor to the STC (76.20 %) as compared to the SIC (1.05 %). Furthermore, SOC (75.15 %) was the major constituent to the soil organic matter (SOM) as compared to the STN (5.85 %). The vegetation type and litter both showed high impact on STN and STC, while altitude and HB showed very little or no impact on carbon and nitrogen concentrations. However, altitude puts great impact on shaping vegetation structure due to decreasing temperature along the elevation and other climatic factors which are further responsible in controlling the carbon and nitrogen concentration.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-1935-9) contains supplementary material, which is available to authorized users.
Highlights
Carbon and nitrogen are the two chemical elements in organic matter which are the most important, especially in their relation and proportion to each other
Over all soil total carbon (STC) was found to be highest along the altitudinal gradients 76 % followed by soil organic carbon (SOC) 75.15 %, soil total nitrogen (STN) 5.85 % and soil inorganic carbon (SIC) 1.05 %
There was a strong significant positive correlation found between the SOC and STN, while there was a non-significant correlation observed between SIC and STN (Fig. 5)
Summary
Carbon and nitrogen are the two chemical elements in organic matter which are the most important, especially in their relation and proportion to each other. Carbon sequestration in nondisturbed ecosystems are the best sinks of carbon and mitigate global climate change (Parras-Alcántara et al 2015). Nitrogen process is biologically influenced and which is further influenced by the climatic conditions, physical and chemical properties of the soil. Interactions between the terrestrial nitrogen (N) and carbon (C) cycles shape the response of ecosystems to global change (Zaehle 2013). The concentration of CO2 has increased from 280 ppm in preindustrial times to 392 ppm in the early twenty-first century (Tans 2012), highlighting that a reduction in the concentration of both gases would aid in the mitigation of climate change (Nguyen et al 2014). Nitrous oxide is produced from nitrification and denitrification processes (Davidson et al 1986) and are influenced by pH (Law et al 2011), soil moisture, and availability of C and N substrates (Beare et al 2009; Nguyen et al 2014)
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