Abstract The conversion of farmland to forest in China has been recognized for its positive impact on above-ground vegetation greening and carbon sequestration. However, the importance of soil functions in these conversion models, particularly in vulnerable karst areas, has received less attention. In this study conducted in a karst area of southwest China, eight different returning models (GM, GZ, ZI, TS, CM, AC, ZL) were investigated to assess soil carbon, nitrogen, and soil multi-functionality in the surface soil. The results showed significantly higher total carbon (TC), soil organic carbon (SOC), soil active organic carbon (AOC) and, ammonium nitrogen (AN) in afforestation land and abandonment land compared to grassland and maize crop area. Moreover, soluble organic carbon (DOC) was significantly higher in afforestation land and grassland compared to the maize crop area. Grassland and abandonment land exhibited significantly higher levels of NO 3 - -N compared to afforestation land and maize crop. However, no significant difference in concentration of NH 4 + -N was found in afforestation land (except ZI) than between grassland and abandonment land. Regardless of soil multi-functionality or carbon and nitrogen multi-functional, afforestation land consistently exhibited significantly higher values than grassland. Pearson correlation analysis indicated positive correlations between soil indices and ecosystem multi-functionality (EMF), except for NO 3 - -N.Random forest analysis, which explained 95% of the variation in soil EMF, identified the AOC L , SOC, TN, AN and TC as the main drivers of soil multi-functionality. In conclusion, different models of returning farmland have the potential to enhance soil nutrient accumulation and improve soil multi-functionality in karst areas. These findings highlight the effectiveness of such models for sustainable soil management and production.
Forest succession can change soil microbial community composition and structure. However, it is unclear how soil microbes respond to forest succession. Using high-throughput sequencing methods, we evaluated the dynamics of soil bacterial and fungal communities during forest succession from shrubland, to secondary forest, to primary forest in the karst region of Southwest China. We found no significant differences in fungal α-diversity with karst forest succession, but the secondary forest had significantly higher bacterial α-diversity than the shrubland and primary forest. Our non-metric multidimensional scaling (NMDS) analysis indicated that the soil bacterial community in the primary forest was close to the shrubland but diverged from the secondary forest, and that the fungal community could be discriminated along forest succession. Also, the microbial co-occurrence network indicated that soil fungi had less but more intense relationships than bacteria in the karst forests. Furthermore, the redundancy analysis (RDA) showed that soil properties, soil microbial biomass, and plant factors drove the dynamics of the soil bacterial community, while soil properties rather than plant factors explained the variation of the soil fungal community along karst forest succession. The different responses of soil bacteria and fungi to forest succession in a karst region informs ecological restoration along forest succession in the karst region.
We analyzed soil quality based on soil microbial characteristics of three different vegetation types in the wetlands of East Dongting Lake, including Carex tristachya wetland (CTW), Phragmites australis wetland (PAW), and Salix babylonica wetland (SBW). The soil microbial biomass carbon (MBC), nitrogen (MBN) and enzyme activities were measured and the key influen-cing factors were analyzed during the normal, flood, and dry periods. The results showed that: 1) The amounts of MBC, MBN, and the activities of invertase and cellulase (except cellulase of dry season) in 0-10 cm were higher than those in 10-20 cm for all wetlands, while the catalase activity showed an opposite pattern. 2) The amounts of MBC and MBN and the values of MBC/TOC and MBN/TN for the 0-20 cm soil layer of each vegetation type wetland were the lowest in flood period. 3) Soil invertase activity for each vegetation type wetland in the 0-20 cm soil layer peaked in the dry period, while soil cellulase activity peaked in the normal period. The seasonal fluctuation of soil catalase activities in all wetlands were small, with activities being slightly higher in flood period than the other two periods. 4) Among different vegetation types, soil invertase activity of PAW was significantly higher than that of other vegetation types, and cellulase activity of which was the lowest in both normal and flood periods. There was no difference in these two enzymes activities among wetlands during the dry period. The highest soil catalase activity was found in CTW during normal period and in SBW during dry period, respectively, while its lowest value was in PAW during flood period. 5) Soil MBC, MBN and invertase activity were correlated positively with soil TOC, TN and TP, and negatively correlated with soil pH. The activities of soil cellulase and catalase were significantly negatively correlated with TOC, TN, TP and positively correlated with pH. It suggested that the seasonal fluctuation of water level affected soil C, N, P contents and pH values, with consequences on soil MBC, MBN and enzyme activities.为从土壤微生物的角度分析东洞庭湖不同植被类型湿地土壤质量状况,本研究选取了苔草、芦苇和柳树3种典型植被类型为对象,在平水期、丰水期和枯水期对其土壤微生物生物量碳(MBC)、氮(MBN)和酶活性进行监测,并分析其主要影响因子。结果表明: 1)3个水位时期,各植被类型湿地土壤MBC、MBN、蔗糖酶和纤维素酶活性(枯水期纤维素酶除外)均表现为0～10 cm高于10～20 cm,而土壤过氧化氢酶活性则相反。2)各植被类型湿地0～20 cm土层土壤MBC、MBN和MBC/TOC(总有机碳)、MBN/TN(总氮)皆以丰水期最低。3)各植被类型湿地0～20 cm土层土壤蔗糖酶活性峰值均出现在枯水期,而纤维素酶活性峰值出现在平水期,过氧化氢酶活性季节性波动较小,以丰水期稍高。4)不同植被类型间比较:平水期和丰水期,芦苇湿地土壤蔗糖酶活性显著高于其他植被类型,而其土壤纤维素酶活性最低,枯水期不同湿地间两种酶活性差异不显著。土壤过氧化氢酶活性在平水期以苔草湿地最高,枯水期以柳树湿地最高,丰水期以芦苇湿地最低。5)相关性分析表明,土壤MBC、MBN和蔗糖酶与TOC、TN、总磷(TP)呈显著正相关,而与pH值呈显著负相关。土壤纤维素酶和过氧化氢酶与TOC、TN、TP呈显著负相关,与pH值呈显著正相关。表明季节性水位波动影响土壤C、N、P和pH值,并对土壤微生物生物量碳、氮和酶活性产生显著影响,使其呈现明显的季节性变化特征。.
In karst ecosystems, plants absorbing smaller amounts of nutrients, owing to shallow soil, show limited growth. In addition, fine roots (diameter < 2 mm) contribute to the regulation of nutrient cycles in terrestrial ecosystems. However, the spatial and temporal variations of fine root biomass in different vegetation types of the karst region remains poorly understood. In this study, we investigated the seasonal and vertical variation in biomass, necromass, and total mass of fine roots using sequential soil coring under different stages of vegetation restoration (grassland, shrubland, secondary forest, and primary forest) in Southwest China. The results showed that the fine root biomass and necromass ranged from 136.99 to 216.18 g m-2 and 47.34 to 86.94 g m-2, respectively. The total mass of fine roots and their production ranged from 187.00 to 303.11 g m-2 and 55.74 to 100.84 g m-2 year-1, respectively. They showed a single peak across the vegetation restoration gradient. The fine root biomass and total fine root mass also showed a single peak with seasonal change. In autumn, the fine root biomass was high, whereas the necromass was low. Most of the fine roots were concentrated in the surface soil layer (0-10 cm), which accounted more than 57% root biomass, and decreased with increasing soil depth. In addition, fine root production showed a similar vertical pattern of variation with biomass. Overall, our results suggested that fine roots show clear seasonal and vertical changes with vegetation succession. Moreover, there was a higher seasonal fluctuation and a greater vertical decreasing trend in late-successional stages than in the early-successional stages. The conversion of degraded land to forest could improve the productivity of underground ecosystems and vegetation restoration projects in the fragile karst region should, therefore, continue.
Based on the investigation and analysis of seven soil mineral substance variables, nine vegetation factors, four topographical factors, and ten soil physicochemical factors in the 200 m x 40 m dynamic monitoring plots in farmland, forest plantation, secondary forest, and primary forest in the depressions between hills in karst region, and by using traditional statistical analysis, principal component analysis (PCA), and canonical correlation analysis (CCA), this paper studied the compositional characteristics and roles of soil mineral substances as well as the coupling relationships between the mineral substances and the vegetation, topography, and other soil properties. In the depressions, soil mineral substances were mainly composed of SiO2, Al2O3, K2O, and Fe2O3, whose contents were obviously lower than the mean background values of the soils in the world and in the zonal red soils at the same latitudes. The soil CaO and MgO contents were at medium level, while the soil MnO content was very low. The composition of soil mineral substances and their variation degrees varied with the ecosystems, and the soil development degree also varied. There was a positive correlation between vegetation origin and soil origin, suggesting the potential risk of rock desertification. Due to the high landscape heterogeneity of the four ecosystems, PCA didn't show good effect in lowering dimension. In all of the four ecosystems, soil mineral substances were the main affecting factors, and had very close relationships with vegetation, topography, and other soil properties. Especially for SiO2, CaO, and MnO, they mainly affected the vegetation species diversity and the soil organic matter, total nitrogen, and total potassium. This study indicated that soil mineral substances were the one of the factors limiting the soil fertility and vegetation growth in the depressions between hills in karst region. To effectively use the soil mineral resources and rationally apply mineral nutrients would have significances in the restoration and reconstruction of karst degraded ecosystems.
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