Forest Gaps Slow the Humification Process of Fir (Abies faxoniana Rehder & E.H.Wilson) Twig Litter during Eight Years of Decomposition in an Alpine Forest

Abstract

Litter humification plays a crucial role in organic matter formation and soil carbon sequestration in forest ecosystems. However, how forest gap formation and gap size variation affect the litter humification process remains poorly understood. An eight-year in situ decomposition experiment was conducted to evaluate humus accumulation (humic substances, humic and fulvic acid), humification degrees, humification ratios and optical properties (ΔlogK, E4/E6 and A600/C) of Minjiang fir (Abies faxoniana Rehder & E.H.Wilson) twig litter in four gap size treatments in an alpine primitive forest on the eastern Tibetan Plateau, including (1) closed canopies, (2) small gaps (38–46 m2 in size), (3) medium gaps (153–176 m2 in size),and (4) large gaps (255–290 m2 in size). The results indicated that the accumulation of humic substances and humic acid in the closed canopies was significantly higher than that in the large gaps during the first two years of decomposition. After eight years of decomposition, there were significant differences in the humic substance accumulations and the values of ΔlogK and A600/C among the different gap sizes. Furthermore, twig litter was humified in the first 2 years of incubation, and the net accumulation of humic substances was ranged from −23.46% to −44.04% of the initial level at the end of the experiment. The newly accumulated humus was young (mature (type Rp) humus) and transformed to mature (type A) humus after 4–6 years of decomposition. Partial least squares (PLS) suggested that gap-induced variations in twig litter chemistry (i.e., contents of cellulose, lignin, nitrogen (N) and phosphorus (P), and the ratios of C/N N/P) mainly drove the process of twig litter humification. Our results presented here denote that the formation of forest gaps retard twig litter humification process, which might be detrimental to carbon sequestration in the alpine forest ecosystems.

Autumn sunlight promotes aboveground carbon loss in a temperate mixed forest

“…However, the magnitude of N release was greater in the forest gap than that in the understorey, suggesting that canopy structure may modulate the effect of solar radiation on N dynamics during litter decomposition. Similar results have been detected in various litter types, such as leaves, twigs, and logs (Wang et al 2023(Wang et al , 2022bWu et al 2023).…”

“…The reduction in forest canopy closure is the dominant form of disturbance due to changes in land-use (e.g., deforestation and clear felling). Together with climatic drivers, the increase in sunlight exposure gaps facilitates the litter decomposition of leaves, twigs, and logs (Chen et al 2023;Wang et al 2022b), and slows litter humification process (Wu et al 2023), enhancing ecosystem C release. Our recent study has found that exposure to the full-spectrum when a forest gap opens can greatly increase litter decomposion rate by almost 120% across a wide range of species (Wang et al 2021).…”

How Land Use Transitions Contribute to the Soil Organic Carbon Accumulation from 1990 to 2020

“…Carex myosuroides Vill. and a variety of grass vegetation mostly grow in the dark felty soil, and it is an important area for livestock products [30]. The vegetation in the alpine meadows is mainly Kobresia humilis and Carex alatauensis S. R. Zhang, and the accompanying species include Carex tristachya Thunb.…”