Litterfall is an important part of the process of nutrient circulation and energy flow in forest ecosystems. Mountain forests are strongly eroded by running water in that the surface soil is thinner, and the terrain is complex and diverse. They are more sensitive to climate change, which will affect the ecological processes and carbon sink functions of forest ecosystems. Taking Lushan Mountain as an example, we studied the dynamic characteristics of litterfall components, seasonal changes in carbon input and the influencing factors of typical forest communities in the subtropics. The results showed that the total annual average litterfall components of evergreen broad-leaved forest (EBF) > artificial coniferous forest (ACF) > deciduous broad-leaved forest (DBF) > renew young forest (RYF), and that leaf litterfall is the first productivity in the litterfall components, and the peak of litterfall is mainly concentrated in spring and autumn, showing a single- or double-peaked change pattern. There was a linear relationship between the components of litterfall in the four forest communities and the stand factor, but the correlation degree R2 was small. Overall, the results showed that the total amount of litterfall in the four forest communities was affected by canopy density and stand density. Light, temperature and water at different altitudes had different effects on the amount of litterfall, with excessive temperatures at lower altitudes likely to limit forest growth and development under adequate light and water, and the opposite was true at higher altitudes. The results of Pearson correlation analysis showed that EBF and DBF were negatively correlated with rainfall, that ACF and RYF were negatively correlated with temperature and rainfall, and that wind speed was positively correlated. The average annual carbon input size of the four forest communities was EBF > ACF > RYF > DBF, which may be related to environmental conditions and vegetation types, and the seasonal differences were arranged in order of spring > autumn > summer > winter. It can be seen that, considering performance under future climate change, EBF is more conducive to nutrient input and has good soil fertility maintenance ability.
In this study, the evergreen plant Cryptomeria japonica (L.f.) D.Don, 1839 forest gap in the subtropical region of China were taken as the research object. The effects of different forest gap ages (<10 years, 10–20 years, >20 years) on soil physical properties and stoichiometric characteristics were analyzed in Lushan Mountain, China. With the increase of forest gap ages, the physical properties of soil surface layer in forest gap were improved, and the water holding capacity of soil was enhanced. The capillary porosity and total porosity of soil increased significantly, and the soil bulk density of 10–20 cm soil layer decreased. The increase of forest gap recovery years is beneficial to the increase of large particle size soil aggregates, and the increase of large particle size aggregates has a good effect on improving soil structure. The contents of carbon (C), nitrogen (N), and phosphorus (P) in soil showed an overall increasing trend with the increase of forest gap age and were significantly higher than those of Cryptomeria japonica pure forest (p < 0.05). The nutrient content of forest gap in 10–20 years was the highest, and the nutrient content of 0–10 cm soil layer was generally higher than that of 0–20 cm soil layer. The C:P and N:P in the soil showed an overall decreasing trend, while C:N was significantly smaller than other age gaps in 10–20 years. The results showed that soil physical properties and stoichiometric characteristics were improved with the increase of forest gap ages.
As one of the most serious soil erosion areas in China, red sandstone erosion areas in southern China have been seriously affected by abundant annual rainfall. To understand the effects of AM fungi and different grass strips on soil erosion characteristics in red sandstone erosion areas in southern China, we selected Cynodon dactylon, Lotus corniculatus, Zoysia japonica, and Astragalus sinicus. Two treatments were carried out for each grass: AM was the soil in its original state, and CK was the soil in which the original AM fungi were eliminated. Taking CK treatment as the control group, any changes of runoff and sediment yield and nutrient loss under different grass strip conditions were measured. The total yield of runoff and sediment in the four grass strips under CK treatment was greater than that of AM. The runoff ammonium nitrogen loss concentration in AM treatment was smaller than in CK treatment under continuous scouring. The ammonium nitrogen loss concentration of sediment during continuous scouring showed a decreasing trend. Under AM treatment, the loss concentration of sediment ammonium nitrogen showed a decreasing trend compared with the CK treatment. The percentage of sediment particles >2 mm in the four grass strips was significantly larger for CK treatment than AM treatment (p < 0.05), and except for Cynodon dactylon, the percentage of sediment particles in the size range of 1–2 mm for other grass strips was significantly larger for CK treatment than for AM treatment (p < 0.05); the percentage of sediment particles at 0.02–0.25 mm was significantly smaller for CK treatment than for AM treatment (p < 0.05). The mean weight diameter (MWD) of sediments produced by the four grass strips under simulated scouring showed an overall increasing trend with increased scouring time. The mean weight diameter (MWD) of sediments produced under CK treatment was larger than that of AM treatment. The fractal dimension (D) of sediments showed a decreasing trend with increased scouring time. These results showed that AM fungi can promote the growth of plant roots, strengthen soil anchoring, protect large particle aggregates in soil under rainfall scouring, and reduce soil erosion and nutrient loss in red sandstone erosion areas in southern China. Cynodon dactylon and Zoysia japonica were more prominent than Lotus corniculatus and Astragalus sinicus in inhibiting soil erosion in red sandstone erosion areas.
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