Responses of soil organic carbon, soil respiration, and associated soil properties to long‐term thinning in a semiarid spruce plantation in northwestern China

Abstract

Silvicultural thinning using whole‐tree harvesting (WTH) has been an important and common forest management practice for Picea crassifolia plantations in the Qilian Mountains of China. However, consequences of this silvicultural practice are still not well known. We examined the influence of three thinning levels on long‐term soil carbon storage, soil respiration (Rs), and soil properties. Our results showed that soil carbon stocks decreased significantly with increasing thinning intensity at a soil depth of 0–70 cm, whereas soil water storage increased, especially in the deep soil layers (30–70 cm). Mean Rs rates during the growing season increased significantly with increasing thinning intensity, and the dynamics of Rs coincided with that of soil temperature. Generally, 65% to 73% of the variation in Rs rates in three thinning levels was explained by the changes in soil temperature. WTH significantly increased soil bulk density at the 0‐ to 30‐cm and soil pH at the 0‐ to 20‐cm depths and significantly decreased soil nitrogen and C:N ratio in the 0‐ to 20‐cm layers. As no significant effect of WTH was detected on fine root biomass, we attributed the elevated soil respiration to accelerated decomposition of organic matter as a result of elevated soil temperature and substrate quality. Our results demonstrate the potential for WTH to relieve water deficits in spruce plantations in semiarid regions but suggest that WTH has a negative impact on carbon sequestration.

Soil Salinity and Moisture Control the Processes of Soil Nitrification and Denitrification in a Riparian Wetlands in an Extremely Arid Regions in Northwestern China

“…In our study, the average value of soil denitrification rates (308.9 µg kg −1 h −1 ) was higher than nitrification rates (144.11 µg kg −1 h −1 ), indicating that the function of removing NO 3 − -N was strong in the riparian wetland in this extremely arid region. Similar results have been previously reported in other riparian wetlands from different climatic zones [29][30][31]. High denitrification rates are due mainly to the high soil water content in riparian wetlands resulting in the relatively low soil oxygen (O 2 ) concentration, which is conducive to the anaerobic process of denitrification [11].…”

Aboveground litter inputs determine carbon storage across soil profiles: a meta-analysis

“…We demonstrate that litter manipulation treatments and land management such as thinning in forest (He et al 2018;Lull et al 2020), mowing in grassland (Belay-Tedla et al 2009;Kitchen et al 2009;Ma et al 2013), and bare fallow in cropland (Barré et al 2010;Meyer et al 2017), can alter soil C storage, but the depth to which changes were apparent depended on the treatment or management practice. Our comparison of changes across depth increments was somewhat hampered by the lack of standard sampling depths among ecosystems.…”

“…Changes in plant litter inputs have motivated numerous litter manipulation experiments in different ecosystems using litter removal and litter addition treatments (Leff et al 2012;Bowden et al 2014;Lajtha et al 2014a, b;Sayer and Tanner 2010). In addition, human disturbance or management in different ecosystems often alters aboveground plant litter inputs to soils, such as thinning and clear cutting in forests (He et al 2018;Lull et al 2020), mowing in grasslands (Belay-Tedla et al 2009;Kitchen et al 2009;Ma et al 2013), residue removal or mulching and bare fallow periods in croplands (Barré et al 2010;Meyer et al 2017). However, such management practices not only differ in the quality and quantity of organic matter added or removed from the ecosystem but can also entail substantial soil disturbance.…”

Effects of thinning and understory removal on the soil water-holding capacity in Pinus massoniana plantations

“…Thinning and understory removal are commonly adopted forest management practices 15 – 17 . Reasonable thinning intensity and proper understory vegetation management reduce water and nutrient competition between tree species, which enhances forest resistance and resilience to global changes and human disturbances 16 , 18 , 19 .…”