Budget of Plant Litter and Litter Carbon in the Subalpine Forest Streams

Investigations on the budget of plant litter and litter carbon in forest streams can provide a key scientific basis for understanding the biogeochemical linkages of terrestrial–aquatic ecosystems and managing forest catchments. To understand the biogeochemical linkages among mountain forests, riparian vegetation, and aquatic ecosystems, the changes in litter input and output from the subalpine streams with stream characteristics and critical periods were investigated in an ecologically important subalpine coniferous forest catchment in the upper reaches of the Yangtze River. The annual litter input to the stream was 20.14 g m−2 and ranged from 2.47 to 103.13 g m−2 for 15 streams during the one-year investigation. Simultaneously, the litter carbon input to the stream was 8.61 mg m−2 and ranged from 0.11 to 40.57 mg m−2. Meanwhile, the annual litter output varied from 0.02 to 22.30 g m−2, and the average value was 0.56 g m−2. Correspondingly, the litter carbon output varied from 0.01 to 1.51 mg m−2, and the average value was 0.16 mg m−2. Furthermore, the average ratio of litter carbon input to output was 270.01. The maximum and minimum values were observed in the late growing season and the snowmelt season, respectively. Additionally, seasonal variations in temperature, together with the stream length, dominated the input of litter and litter carbon to the stream, while the precipitation, temperature, water level, and sediment depth largely determined their output. Briefly, the seasonal dynamics of litter and litter carbon were dominated by stream characteristics and precipitation as well as temperature patterns.

Dynamics of Leaf- and Root-Specific Biomarkers during 1-Year of Litter Decomposition

Root-specific and leaf-specific biomarkers have been used for decades to identify the origin of organic materials in soils and sediments. However, quantitative approaches require appropriate knowledge about the fate of these indicator molecules during degradation. To clarify this issue, we performed a 1-year incubation experiment with fine root and leaf material of six temperate tree species: European ash (Fraxinus excelsior), European beech (Fagus sylvatica), Oak spec. (Quercus spec.), Linden spec. (Tilia spec.), Norway spruce (Picea abies) and Scots pine (Pinus sylvatica). Only one molecule, x,16-dihydroxy hexadecanoic acid (x,16-C16), could be validated as a general leaf-specific biomarker for the set of all species. For roots, no general root biomarker was found. Ester-bound tricosanol (C23-OH) could be validated for five out of six species; 20-hydroxy eicosanoic acid (ωC20) could be validated for four out of six species, leaving Norway spruce without a suitable root biomarker. The results of this study suggest that the validity of leaf- and root-derived ester-bound lipids as biomarkers is highly species dependent and does not always coincide with previous findings. Concentrations of root- and leaf-derived ester-bound lipids did not stay constant within 1 year of degradation and changed without a linear trend. The change of concentrations seems to be highly species dependent. This might be due to a different structure and arrangement of the individual monomers in cutin and suberin per species, and, therefore, a different accessibility of bond cleaving enzymes. The usefulness of root and leaf biomarkers is context dependent. Our results suggest that general assumptions about litter input to forest soils solely based on biomarker analysis have to be considered carefully.

Litterfall and Element Return in an Abies faxoniana Forest in Tibet—A Five-Year Study

Forest litter is the main contributor to soil fertility and the main carrier of circulating material and energy in forest ecosystems. Abies faxoniana (Minjiang fir) is one of the dominant species in alpine forest ecosystems. Its litter input plays important roles in soil organic matter formation and biogeochemical cycles in these ecosystems, but the annual litterfall pattern and its components remain largely unknown. To determine the litter input and nutrient return of A. faxoniana, we measured the litterfall and element (carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), aluminium (Al), iron (Fe), and manganese (Mn)) contents of different litter components (branches, leaves and epiphytes) from 2016 to 2020. The results showed that the annual litterfall in the A. faxoniana forest ranged from 2055.96 to 5384.15 kg·ha−1·a−1, and the average mass proportions of branches, leaves and epiphytes were 30.12%, 62.18% and 7.7%, respectively. The litterfall yield varied significantly with time and component; not only was the yield of litter in the nongrowing season higher than that in the growing season, but it also exhibited dramatic interannual variations. We also found that time had significant effects on the contents of all elements except for Ca in the litter. The return and input amounts of each element followed the same dynamics, which closely resembled a bimodal pattern. Moreover, there was significant interannual variability in the returned amounts of each element. The ranges of annual returns of C, N and P were 744.80~2275.12, 19.80~59.00 and 1.03~2.81 kg·ha−1·a−1, respectively. The ranges of annual returns of K, Ca, Na, Mg, Al, Fe and Mn were 0.91~2.00, 7.04~18.88, 0.13~0.58, 0.33~1.20, 0.55~2.29, 0.41~1.37 and 0.16~0.48 kg·ha−1·a−1, respectively, reflecting a seasonal double-peak pattern. These results have important implications for understanding the biogeochemical cycles and material migration processes in alpine forest ecosystems.

Soil carbon stocks of inceptisols under different land use in the Northern tropical humid region of Honduras

Soil organic carbon (SOC) is important in the carbon cycle and studies in the field are gaining relevance because of its relation to global climate change. In this paper, we report a study of SOC stock (0-200 cm) from a 50 years old secondary forest and a pasture under inceptisols in a floodplain in the tropical humid Caribbean coast of Honduras. Samples were collected at the depths 0-20, 20-40, 40-80, 80-120, 120-160, and 160-200 cm. Total SOC stocks were 89.2±10.9 Mg ha−1, and 72.5±10.0 Mg ha−1 for the secondary forest and pasture respectively. The estimated annual increase of SOC stock in the forest is 0.34 Mg C ha-1 year-1. SOC stock values were 50.3% and 47.9% of the total (0-200 cm) in the 0-20 cm layer for forest and pasture respectively. SOC distribution at a depth of 0-20 cm were 21.26 g kg-1 and 12.09 g kg-1 for forest and pasture respectively. Soil texture at the 0-20 cm depth were clay loam, and sandy clay loam, in the forest and pasture respectively. SOC stock in these ecosystems would be reduced if they were converted back to conventional agriculture, particularly in the forest. The forest had higher SOC values because of higher litter input as compared to the pasture, particularly in the upper soil layers, at deeper layers there are no significant differences (p <0.05) and SOC values are low. Compared to most other studies in tropical regions, SOC stock in our study were lower in both ecosystems, this may be due to high precipitation (ca. 3200 mm year-1) and high temperatures, rate of decomposition of litter input, general low clay content, and possibly priming effects which we have not addressed. More studies on the SOC stock in Central America with a similar climate are needed to improve our understanding of SOC dynamics and help reducing uncertainty in SOC models.

Increased Litter Greatly Enhancing Soil Respiration in Betula platyphylla Forests of Permafrost Region, Northeast China

The change of litter input can affect soil respiration (Rs) by influencing the availability of soil organic carbon and nutrients, regulating soil microenvironments, thus resulting in a profound influence on soil carbon cycle of the forest ecosystem. We conducted an aboveground litterfall manipulation experiment in different-aged Betula platyphylla forests (25-, 40- and 61-year-old) of the permafrost region, located in the northeast of China, during May to October in 2018, with each stand treated with doubling litter (litter addition, DL), litter exclusion (no-litter, NL) and control litter (CK). Our results indicated that Rs decreased under NL treatment compared with CK treatment. The effect size lessened with the increase in the stand age; the greatest reduction was found for young Betula platyphylla forest (24.46% for 25-year-old stand) and tended to stabilize with the growth of forest with the reduction of 15.65% and 15.23% for 40-and 61- year-old stands, respectively. Meanwhile, under DL treatment, Rs increased by 27.38%, 23.83% and 23.58% on 25-, 40- and 61-year-old stands, respectively. Our results also showed that the increase caused by DL treatment was larger than the reduction caused by NL treatment, leading to a priming effect, especially on 40- and 61-year-old stands. The change in litter input was the principal factor affecting the change of Rs under litter manipulation. The soil temperature was also a main factor affecting the contribution rate of litter to Rs of different-aged stands, which had a significant positive exponential correlation with Rs. This suggests that there is a significant relationship between litter and Rs, which consequently influences the soil carbon cycle in Betula platyphylla forests of the permafrost region, Northeast China. Our finding indicated the increased litter enhanced the Rs in Betula platyphylla forest, which may consequently increase the carbon emission in a warming climate in the future. It is of great importance for future forest management in the permafrost region, Northeast China.

Factors controlling <i>Carex brevicuspis</i> leaf litter decomposition and its contribution to surface soil organic carbon pool at different water levels

Litter decomposition plays a vital role in wetland carbon cycling. However, the contribution of aboveground litter decomposition to the wetland soil organic carbon (SOC) pool has not yet been quantified. Here, we conducted a Carex brevicuspis leaf litter input experiment to clarify the intrinsic factors controlling litter decomposition and quantify its contribution to the SOC pool at different water levels. The Carex genus is ubiquitous in global freshwater wetlands. We sampled this plant leaf litter at −25, 0, and +25 cm relative to the soil surface over 280 d and analysed leaf litter decomposition and its contribution to the SOC pool. The percentage litter dry weight loss and the instantaneous litter dry weight decomposition rate were the highest at +25 cm water level (61.8 %, 0.01307 d−1), followed by the 0 cm water level (49.8 %, 0.00908 d−1), and the lowest at −25 cm water level (32.4 %, 0.00527 d−1). Significant amounts of litter carbon, nitrogen, and phosphorus were released at all three water levels. Litter input significantly increased the soil microbial biomass and fungal density but had nonsignificant impacts on soil bacteria, actinomycetes, and the fungal∕bacterial concentrations at all three water levels. Compared with litter removal, litter addition increased the SOC by 16.93 %, 9.44 %, and 2.51 % at the +25, 0, and −25 cm water levels, respectively. Hence, higher water levels facilitate the release of organic carbon from leaf litter into the soil via water leaching. In this way, they increase the soil carbon pool. At lower water levels, soil carbon is lost due to the slower litter decomposition rate and active microbial (actinomycete) respiration. Our results revealed that the water level in natural wetlands influenced litter decomposition mainly by leaching and microbial activity, by extension, and affected the wetland surface carbon pool.