ABSTRACT
Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.
Subject(s)
Ferric Compounds , Pinus , Soil , Soil/chemistry , Carbon/analysis , Leucyl Aminopeptidase , China , Nitrogen/analysis , Soil Microbiology , BacteriaABSTRACT
BACKGROUND: Karst tiankengs serve as a reservoir of biodiversity in the degraded karst landscape areas. However, the microbial diversity of karst tiankengs is poorly understood. Here, we investigated the composition and function of the microbial community in a karst tiankeng. RESULTS: We found that habitat differences inside and outside the karst tiankeng changed the composition and structure of the soil microbial communities, and the dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria. The Shannon-Wiener diversity of microbial communities inside and outside the tiankeng was significantly different, and it was higher inside the tiankeng (IT). Venn and LEfSe analysis found that the soil microbial communities inside the tiankeng had 640 more endemic species and 39 more biomarker microbial clades than those identified outside of the tiankeng (OT)..Functional prediction indicated that soil microorganisms in outside the tiankeng had a high potential for carbohydrate metabolism, translation and amino acid metabolism. There were biomarker pathways associated with several of human diseases at both IT and OT sites. Except for auxiliary activities (AA), other CAZy classes had higher abundance at IT sites, which can readily convert litter and fix carbon and nitrogen, thereby supporting the development of underground forests. The differences in microbial communities were mainly related to the soil water content and soil total nitrogen. CONCLUSIONS: Our results provide a metagenomic overview of the karst tiankeng system and provide new insights into habitat conservation and biodiversity restoration in the area.
Subject(s)
Microbiota , Soil Microbiology , Humans , Metagenome , Nitrogen , Soil/chemistryABSTRACT
In the negative terrain habitat of the karst degraded tiankeng, the shady and sunny slopes are dramatically different, which results in substantial variations in plant communities. With the degraded tiankeng Shenxiantang in Zhanyi, Yunnan as an example, we explored the functional traits of Fagaceae plants in the shady and sunny slopes, which would help reveal the value of tiankeng as species diversity conservation pool. The results showed that soil nutrients in the shady slope were more than those in the sunny slope. Leaf area, specific leaf area and leaf dry weight of Faga-ceae plants in the shady slope were significantly larger than those in the sunny slope. Leaf thickness was significantly lower than that in the sunny slope. Dry matter content of leaves was less than that of the sunny slope. The main environmental factors affecting functional traits of Fagaceae plants in the shady slope were soil total potassium concentration and soil moisture, while soil total phosphorus concentration was the key factor in the sunny slope. The extent of variation of leaf functional traits in shady slope was less than that in the sunny slope. Fagaceae plants mainly adapted to the shady slope habitat by changing the leaf dry weight to increase photosynthetic rate and carbon accumulation abi-lity. Sunny slope obtained more resource by keeping smaller specific leaf area and increasing the extent of variation of the leaf area. The succession rate of plant community in the shady slope of the degraded tiankeng Shenxiantang was significantly faster than that in the sunny slope. The dominance of Fagaceae plants gradually decreased in the shady slope, but remained to be the constructive species in the sunny slope.
Subject(s)
Fagaceae , China , Ecosystem , Plant Leaves , Plants , SoilABSTRACT
The underground forests developed on inverted stone slopes in degraded karst tiankengs are important areas for biodiversity conservation, but the microbial community profiles have not been sufficiently characterized. Thus, we investigated the soil microbial communities at four sites (at the bottom of the slope (BS), in the middle of the slope (MS), in the upper part of the slope (US) and outside the tiankeng (OT)) in the Shenxiantang tiankeng. The dominant phyla in the inverted stone slope were Proteobacteria, Actinobacteria, and Acidobacteria, and the relative abundance were different in different slope positions. The Shannon-Wiener diversity index of the microbial community was significantly greater for the US site than for the MS or BS sites. The metabolism functional pathways (including C/N cycle) were more abundant at the BS site. Total nitrogen and pH were the dominant factors in determining the distribution of the microbial community along an inverted stone slope. These results suggest that topographic heterogeneity can influence the variations in the soil microbial structure, diversity, and function in degraded karst tiankengs and emphasized the ecological value of inverted stone slopes within karst tiankengs.
ABSTRACT
We investigated the characteristics of plant species diversity in tree and shurb layers and the main influencing factors in different slope positions of a shady slope of degraded tiankeng talus. The results showed that there were 21 species in 17 genera and 13 families in the tree layer, and 20 species in 20 genera and 14 families in shrub layer in the south side of the Shenxiantang. Plant communities were subtropical moist coniferous and broad-leaved mixed forest. Micro-climate led to obvious vegetation variation between the pit and the pit slope at the tiankeng. The secondary collapse over the talus with mid-slope could conserve more water, which supported the water-demanding species in a high-quality niche. All the α diversity indices including Margalef (3.58), Shannon (2.47), Simpson (0.79) and Pielou (0.86) reached the maximum at the pit bottom edge with slight variability, and the maximum coefficient of variation was only 0.226. The ß diversity index fluctuated greatly among the pit-pit, slope-pit, bottom edge. The Routledge and Whilson-Shmida indices showed the trends of decrease-increase-decrease, with the maximum values of 15.95 and 1.20, respectively. Species turnover demonstrated the upward trend overall, and the number of co-species was decreased. Plant diversity on each slope position was mainly related to the contents of total nitrogen, total phosphorus, available phosphorus and organic carbon in soil. Soil was the most important factor leading to the difference among slope positions.
Subject(s)
Ecosystem , Talus , China , Forests , Plants , SoilABSTRACT
We carried out niche monitoring and analysis of plant populations under the forest community in the talus slope ecotone of a typical moderate-degraded Bajiaxiantang tiankeng to provide scientific references for biodiversity conservation and vegetation restoration in degraded tiankeng area. The results showed that soil ammonium, available potassium, and available phosphorus signifi-cantly affected species distribution, which explained 37.4%, 32.8%, 29.3% of the total variation, respectively. With the change of talus slope of tiankeng (pit, uphill, mid-slope, downhill and pit bottom), life form of understory plants changed from evergreen and xerophytes to evergreen and hygro-mesophytes, with the niche overlap of herbs being larger than that of shrubs. Shrubs of Viburnum congestum and Campylotropis polyantha, and herbs of Arisaema erubescens and Arthraxon hispidus had wide ecological amplitude and strong resistance, which occupied the upper layer of the shrub and herb layers. Shrub Cornus oblonga and herb Geranium nepalense, Agrimonia pilosa lost the competitiveness with increasing soil alkalinity. Niche characteristics of understory dominant species in Bajiaxiantang were closely related to the canopy structure of mixed trees, ecological strategies of shrub and herb species, unique habitat of tiankeng, and the importance value of dominant species.
