Karst ecosystems are characterized by the dissolution of soluble rocks, displaying distinctive landscape features such as rugged peaks, steep slopes, and deep valleys. Afforestation is an effective approach for improving soil quality in rocky desertification areas because plants have evolved unique adaptations to thrive in such environments. However, the effects of tree species composition and cultivation patterns on the soil quality, microbial diversity, stability, and functions in rocky desertification areas remain unclear. In this work, four study plots including three types of forests—pure Pinus massoniana plantations, Toona sinensis plantations, mixed coniferous and broadleaf plantations (Pinus massoniana–Betula luminifera forests), and unforested area as the control—were established in a karst desertification area in the Hunan province of China. Soil properties including soil bulk density, soil organic carbon, total nitrogen, total phosphate, soil ammonium nitrogen, nitrate, available phosphate, soil pH, and soil microbial diversity were investigated in the study area. The results showed that the forests significantly increased the soil organic carbon, total nitrogen, and ammonium nitrogen compared to the unforested area. The microbial diversity indicators in mixed forests were significantly higher than those in the Pinus massoniana forests. The dominant bacteria phyla included Proteobacteria, Acidobacteria, and Actinobacteria, while fungi species such as Ascomycota and Basidiomycota were identified in all study plots. In addition, the AVD index evaluation revealed that the mixed forests enhanced the stability of the soil microbial communities compared to the monoculture plantations and unforested plots in rocky desertification areas. The research results indicated that, among the various forest types, the mixed forest was the most effective choice for afforestation in terms of improving the soil quality by changing the soil’s physiological properties in rocky desertification areas. Our study provided guidance and insights for afforestation technology and the optimal allocation of different tree species in the cultivation and management of plantation forests in rocky desertification regions.

湘西石漠化地区是我国生态系统脆弱而又敏感的区域,土壤微生物在维持石漠化区森林生态系统结构和功能稳定中发挥重要作用.选取石漠化地区立地条件相同的32年生的马尾松纯林、光皮桦纯林及马尾松-光皮桦混交林为研究对象,以立地条件相似的未造林荒地演变成的灌草群落作为对照,比较分析石漠化地区不同造林模式对土壤真菌群落结构和多样性的影响及其主要驱动因素.采用Illumina HiSeq第二代高通量测序技术,分析了 3种森林土壤真菌群落组成及多样性.结果表明,不同造林模式下土壤真菌优势类群不同,光皮桦、马尾松-光皮桦混交林以及石漠化灌草地土壤真菌优势门均为子囊菌门(Ascomycota),且在石漠化灌草地相对丰度最大,为64.0％;马尾松则以担子菌门(Basidiomycota)为优势类群,其相对丰度占57.9％.混交林土壤真菌物种总数和Shannon指数显著高于马尾松和光皮桦林地,整体上真菌群落多样性表现为:未造林灌草地＞混交林＞马尾松林＞光皮桦林.与未造林灌草地相比,马尾松-光皮桦混交林和光皮桦纯林显著提升了土壤有机碳(SOC)和全氮(TN)含量.Mantel test检验结果显示,真菌群落结构与全磷(TP)、有机碳(SOC)、铵态氮(NH4+-N)、硝态氮(NO3-N)、全氮(TN)、pH和含水量(SWC)具有显著相关性(P＜0.05),其中土壤SOC、TN、pH值对真菌群落结构影响最大.冗余分析(RDA)结果发现,子囊菌(Ascomycota)与pH、TP、SOC、TN、AP、NO3-N含量均呈正相关;担子菌门(Basidiomycota)和被孢霉门(Mortierellomycota)主要与 NH4+-N 成正相关,与 pH、TP、SOC、TN、AP、NO3-N 呈负相,而罗氏菌门(Rozellomycota)与 SWC 呈正相关(P＜0.05).综上,相比针叶纯林,石漠化地区针阔混交林能通过增加土壤SOC、TN而显著提高真菌群落多样性,促进土壤肥力状况的提升.此研究结果可以为石漠化区人工植被恢复以及土壤肥力管理提供依据.

Objective: To study the growth, accumulation and soil nutrient content of each overseeded species under different interharvesting intensity treatments of Eucalyptus, and to explore the best re-cultivation method suitable for mixed overseeded species after Eucalyptus interharvesting. Methods: In Guangxi state-owned Qipo forest, Eucalyptus tailorii with different planting densities (DH32-29) were mixed with Castanopsis hystrix, Mytilaria laosensis and Michelia macclurei, and four different treatments (CK, LT, MT and HT) were established for re-cultivation of Eucalyptus near-mature forests with different logging intensities, and the differences in growth conditions and soil physicochemical properties of each species were analyzed. Results: (1) As the proportion of Eucalyptus allocation decreased, the growth of Eucalyptus diameter at breast height, tree height and individual wood volume could be promoted; the growth of the three parameters of HT and MT Eucalyptus were significantly different from LT and CK. (2) The average wood volume per plant of the set species in the CK and LT treatments was Mytilaria laosensis > Michelia macclurei > Castanopsis hystrix, while in the MT and HT treatments it was Mytilaria laosensis > Castanopsis hystrix > Michelia macclurei. (3) The differences in soil aeration, total saturated water holding capacity, capillary water holding capacity, and field water holding capacity in soil layers of different depth varied. In the same soil layer, soil aeration, total porosity and capillary porosity were HT > CK > LT > MT; saturated water holding capacity and capillary water holding capacity were HT > CK > LT > MT, while field water holding capacity was CK > HT > LT > MT. (4) Organic matter, pH, total nitrogen, total phosphorus, total potassium, fast-acting nitrogen, fast-acting phosphorus, and fast-acting potassium changed with varying soil depth in each treatment.

The rapid growth and expansion ofCryptomeria japonica (Thunb. ex L. f.) D. Don in karst area strongly affects plant composition of native deciduous broad-leaved forest, which seriously threat ecosystem function and service. Given the importance of soil microorganisms in regulating nutrients cycling and plant species coexistence, understanding soil microbial attributes and their relationships with soil and vegetation features in forests harboring different C. japonica abundance will help understanding the drivers of ecosystem function changes. Here we examined the diversity and composition of soil bacterial and fungal communities and their correlations with plant diversity as well as soil physicochemical properties in karst broad-leaved forests with different relative abundances of C. japonica (i.e., a high, moderate, low and no proportion level with a stem density of 1,487, 538, 156 and 0 plant/hm2, respectively) in Mid-Subtropical China. We found that soil pH decreased while soil water content (SWC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) tended to increase with the increase in C. japonica abundance. In contrast, soil available nitrogen (AN), available phosphorus (AP) and available potassium (AK) content declined by 26.1%∼49.3% under the high level of C. japonica abundance. A gradual decrease in relative abundance of Acidobacteria and Chloroflexi while a pronounced increase in relative abundance of Ascomycota and Basidiomycota were observed with increase of C. japonica abundance. Alternations in bacterial composition were closely related to changes in AP and AK, while the change of fungal structure was mainly related to SWC, soil organic carbon (SOC) and pH, indicating that bacterial community was sensitive to declines in soil available nutrients and fungal structure was sensitive to changes in soil physicochemical properties (i.e., pH and SWC) and organic carbon resource. Understory plants had the highest α-diversity in forest containing moderate abundance of C. japonica, which might be related to the high bacterial diversity. Our findings suggest conservation of soil bacterial and fungal taxa that are responsible for nutrients availability and carbon sequestration is of great significance for improving the resistance of natural deciduous broad-leaved forests to the rapid spread of C. japonica in karst areas. Moreover, Acidobacteria, Chloroflexi, Ascomycota and Basidiomycota are potential indicators for soil properties changes, which should be taken into consideration in karst forest managements.

本文以武陵山石漠化综合治理国家长期科研基地3.5 hm2人工混交林为研究对象,运用结构化森林经营技术指标评价了林分的稳定性以及石漠化与各项指标的相关性.结果表明:该区域人工混交林群落物种组成丰富,林分组成以樟科、杉科为代表的优势树种占主体地位;林分胸径分布范围较宽,以幼苗、幼树、中龄树居多;林木个体分布格局不尽相同,大部分为团状分布,林分混交度较好,隔离程度高;石漠化程度与大小比数、竞争指数呈显著正相关,与开敞度呈显著负相关,与胸径、树高呈极显著负相关;香樟、构树、喜树等生长指标较好,空间结构合理,在植被恢复过程中可优先考虑栽植.

在武陵山石漠化地区选择立地条件、造林时间均相同的鹅掌楸纯林(LC)、台湾杉纯林(TC)、鹅掌楸-台湾杉混交林(MF)为研究对象,以未造林灌草地为对照,研究武陵山石漠化地区不同人工林林下植物多样性与土壤理化性质.结果表明:不同类型人工林林下灌草重要值最高的植物种类不同,鹅掌楸-台湾杉混交林林下植物组成最丰富.未造林灌草地的植物多样性高于人工林的,草本植物的Shannon-Wiener多样性指数、优势度指数均表现为CK>MF>LC>TC,草本植物的均匀度指数在LC、TC、MF间均无显著性差异.不同类型林分林下植物组成相似度均较低.人工林土壤的含水率及土壤中的SOM、TN、AP含量均显著高于未造林灌草地的(P<0.05),不同林分土壤中的SOM、TN、TP、AP含量均表现为MF>LC>TC>CK;NH4-N、NO3-N含量在不同林分中均表现为CK>MF>LC>TC.林下植物Shannon-Wiener多样性指数、均匀度指数均与土壤NH4-N、NO3-N含量均呈正相关,优势度指数与土壤TN含量呈显著正相关;Shannon-Wiener多样性指数与林分平均树高呈极显著正相关,与林分平均胸径、林分密度、林分郁闭度均呈负相关.

石漠化地区人工林培育与经营技术是当今林业亟需解决的问题之一.以湖南省湘西自治州青坪国有林场的35年南酸枣、40年台湾杉及40年香椿3个树种的试验林为研究对象,分别设置标准地展开系统调查研究,对标准地标准木进行树干解析,分析其生长规律,推算林分生物量.结果 表明,南酸枣、台湾杉、香椿单木胸径、树高及材积的总生长量均随树龄的增加而增加;3个树种的林分生产量以乔木层占比最大,乔木层林分生产力从大到小排列为南酸枣(51.94 t/hm2)>香椿(49.48 t/hm2)>台湾杉(49.33 t/hm2),3个树种各器官的生产力均表现为树干>树根>树枝>树叶.通过对这3个树种生长过程的量化研究,对各树种生长的速生期及数量成熟期有所了解,可为提高林木生产力提供理论依据,同时也为湘西喀斯特地区南酸枣、台湾杉及香椿人工林的科学经营与管理提供一定的理论基础,从而推动喀斯特地区人工林的发展.