Soil organic carbon in deep profiles under Chinese continental monsoon climate and its relations with land uses

Abstract

The selection of tree species is critical for soil organic carbon (SOC) stock and dynamics under afforestation. Exotic tree species were widely introduced and have been considered as a form of human-induced global change. However, how exotic tree species, as compared with native ones, affect SOC storage and soil respiration (R s ) has not been sufficiently investigated. Here we studied this issue in an even-aged (22 years) plantation composed by native Masson pine (Pinus massoniana Lamb.) (MP) and exotic slash pine (Pinus elliottii Engelm.) (SP) in subtropical China. A trenching method was used to partition R s into heterotrophic (R h ) and autotrophic respiration (R a ). R s and R h were measured approximately biweekly during August 2007 to December 2009. Our results showed that seasonal patterns of R s and R h in both pine forests were mainly affected by soil temperature and moisture (R 2 = 0.56-0.78, P b 0.001). There was no difference in SOC stock (forest floor + mineral soil of 0-40 cm), R h and turnover rate (R h /SOC stock) between MP and SP forests. However, annual R s , R a and R a /R s of MP were significantly 24%, 119% and 74% higher than those of SP, respectively. In contrast, even though MP and SP had similar fine and coarse root biomass, MP had significant higher ratios of R a /fine root biomass and R a /coarse root biomass than SP, suggesting a higher respiration rate in native pine species on a root biomass basis. We concluded that the exotic SP, as compared with indigenous MP, did not alter SOC stock, R h and turnover rate but depressed R a and R s . Therefore, both pine species were recommended in case of reforestation in terms of SOC sequestration.

A State‐Space Analysis of Soil Organic Carbon in China's Loess Plateau

“…Guo & Gifford () noted that roots are critical in terms of the response of SOC to changes in land use. This observation was consistent with the findings of Wang et al () who found the SOC distribution in deep soil layers to be significantly affected by land use, probably by the differences in root characteristics. Generally, crops have the shallowest root profile in CLP, followed by grasses (moderate deep root profile) and the trees and shrubs (the deepest root profile).…”

“…Second, dry soil layer develops in the soil layers below 100‐cm soil depth under forestlands and grasslands due to deep root water uptake (Jia et al, ). The dry soil conditions in the deep soil layers are difficult to reclaim in the CLP study area due to limited precipitation, deep water table and high vegetation water demand, influencing organic matter flow from shallow soil to deep soil layers (Zhang et al, ; Wang et al, ). In contrast, shallow soil layers (<200‐cm deep) are recharged by precipitation, while recharge depth hardly exceeds 200 cm in the CLP study area, even during extremely wet years (Liu & Shao, ).…”

“…There have been many studies on the spatial distribution of SOC, e.g. at local (Jimenez et al, 2008;Jia et al, 2012;Zhang et al, 2013;Wu et al, 2016), regional (Liu et al, 2011;Wang et al, 2015b;Deng & Shangguan, 2016;Willaarts et al, 2016) and global (Jobbágy & Jackson, 2000;Lal, 2004a;Van et al, 2009) scales. However, measurements of SOC in most of these studies are generally limited to the upper 100-cm soil depth, where most SOC is stored (Shi et al, 2013).…”

“…However, measurements of SOC in most of these studies are generally limited to the upper 100-cm soil depth, where most SOC is stored (Shi et al, 2013). The scarcity of SOC data below 100-cm soil depth has limited the estimation of deep soil C pools (Jobbágy & Jackson, 2000;Wang et al, 2015b;Wang et al, 2016). For example, Batjes (1996) reported a 60% increase in global SOC budget when data for the 100-200 cm soil layer were included.…”

Rooting Depth and Extreme Precipitation Regulate Groundwater Recharge in the Thick Unsaturated Zone: A Case Study

“…Woody species in water-limited environments often root into the deep soil to take advantage of the water reserves located there due to insufficient water in shallower soil [8]. For example, roots can be as deep as 25 m in apple orchards over 20 years old [5,9], and the cloned root fronts of eucalyptus can reach a depth of 11.5 m [10]. These deep roots can substantially alter ecohydrological processes.…”