岩溶槽谷区植被恢复对土壤团聚体有机碳及碳库管理指数的影响

为揭示岩溶槽谷区植被恢复对土壤结构、土壤有机碳积累和碳库管理水平的影响,该研究选取了弃耕地、林地和草地三种土地利用方式,测定0～20 cm土层土壤团聚体组成、土壤有机碳(SOC)、团聚体有机碳以及土壤易氧化有机碳(EOC)含量。结果表明:(1)与弃耕地相比,林地和草地土壤团聚体平均重量直径(MWD)、几何平均重量直径(MGD)和2～5 mm团聚体含量显著增加,林地和草地土壤团聚体组成以2～5 mm为主,弃耕地以0.5～1 mm和0.25 mm为主,表明退耕还林还草能够促进土壤团聚体形成和稳定。(2)土壤团聚体有机碳含量呈现出林地草地弃耕地,随团聚体粒级增加而增加的趋势;林地和草地以2～5 mm团聚体有机碳贡献率最大,弃耕地则以0.25 mm团聚体贡献为主,表明弃耕地转变为林地和草地后,土壤SOC积累主要归功于2～5 mm有机碳含量的增加,以及团聚体由小粒径向大粒径转变。(3)与弃耕地比较,林地和草地土壤SOC、EOC含量和碳库管理指数(CPMI)均显著提高,其中土壤EOC含量和CPMI变化较为明显;土壤EOC可作为土壤碳库早期变化的有效指标,CPMI能够良好地表征植被恢复对土壤SOC和EOC的影响。     

线粒体全基因组揭示嫩江流域史前人群遗传结构的动态变化

嫩江流域是中国东北地区古代先民的重要栖息地之一。自新石器时代开始这里的先民一直以渔猎经济为主要生活方式,直到新石器时代晚期至早期青铜时代才开始兼营畜牧业和少量的种植业。嫩江流域青铜时代的生业模式的转变是否伴随着外来人群的融合与替代一直是考古研究的热点。为了探讨嫩江流域新石器时代与青铜铁器时代人群的构成是否改变,我们对嫩江流域新石器时代至青铜铁器时代的24个个体进行了线粒体全基因组分析。分析结果表明：嫩江流域青铜铁器时代人群与新石器时代人群具有一定遗传连续性的同时,晚期人群与西辽河地区古代人群有着更近的遗传联系,表明西辽河地区古代居民对嫩江流域青铜铁器时代人群具有部分遗传贡献。结合考古学文化、古气候学数据以及语言学证据,我们推测距今4000-3000年间,西辽河地区古代居民曾迁入到嫩江流域,并留下遗传印记。     

干热河谷主要造林树种气体交换特性的坡位效应

植物光合与水分生理特征是植物逆境适应能力评价的重要参考指标.极端生境下,坡位的选择有时成为造林成败的关键.探讨了元谋金沙江干热河谷9个主要造林树种光合与蒸腾作用在不同坡位间的空间差异及干热季向湿润季转换的时序差异.结果表明,低的坡位有助于树种维持相对高的净光合速率,且树种不同,由坡位引起的光合增益效应亦具有较大差别;低坡位的光合增益效应在干热季更为明显,而在湿润季,干热胁迫解除,低坡位的光合增益效应具有较大程度的降低;在不同坡位间发生的光合限制主要受非气孔因素主导.无论在干热季或湿润季,与净光合速率的变化情形一致,低的坡位均促进了树种的蒸腾速率.水分利用效率受坡位的影响较为复杂,因树种、季节而异.     

Landscapes and their relation to hominin habitats: case studies from Australopithecus sites in eastern and southern Africa

We examine the links between geomorphological processes, specific landscape features, surface water drainage, and the creation of suitable habitats for hominins. The existence of mosaic (i.e., heterogeneous) habitats within hominin site landscape reconstructions is typically explained using models of the riverine and gallery forest settings, or the pan or lake setting. We propose a different model: the Tectonic Landscape Model (TLM), where tectonic faulting and volcanism disrupts existing pan or river settings at small-scales (∼10-25 km). Our model encompasses the interpretation of the landscape features, the role of tectonics in creating these landscapes, and the implications for hominins. In particular, the model explains the underlying mechanism for the creation and maintenance of heterogeneous habitats in regions of active tectonics. We illustrate how areas with faulting and disturbed drainage patterns would have been attractive habitats for hominins, such as Australopithecus, and other fauna. Wetland areas are an important characteristic of surface water disturbance by fault activity; therefore we examine the tectonically-controlled Okavango Delta (Botswana) and the Nylsvley wetland (South Africa) as modern examples of how tectonics in a riverine setting significantly enhance the faunal and floral biodiversity. While tectonic landscapes may not have been the only type of attractive habitats to hominins, we propose a suite of landscape, faunal, and floral indicators, which when recovered together suggest that site environments may have been influenced by tectonic and/or volcanic activity while hominins were present. For the fossil sites, we interpret the faulting and landscapes around australopithecine-bearing sites of the Middle Awash (Ethiopia) and Makapansgat, Taung, and Sterkfontein (South Africa) to illustrate these relationships between landscape features and surface water bodies. Exploitation of tectonically active landscapes may explain why the paleoenvironmental signals, anatomy, diets, as well as the fauna associated with Australopithecus appear largely heterogeneous through time and space. This hypothesis is discussed in light of potential preservation and time-averaging effects which may affect patterns visible in the fossil record. The model, however, offers insight into the landscape processes of how such habitats are formed. The landscape features and range of habitat conditions, specifically the wetter, down-dropped plains and drier, uplifted flanks persist in close proximity for as long as the fault motion continues. The Tectonic Landscape Model provides an alternative explanation of why mixed habitats may be represented at certain sites over longer timescales.     

岷江上游干旱河谷景观变化及驱动力分析

基于遥感和地理信息系统,应用景观格局分析软件,研究了岷江上游干旱河谷1974-2000年的景观变化,并对其驱动因子进行了分析.结果表明,岷江上游干旱河谷的面积在不断扩大,灌木林地面积占景观面积的60%以上,为景观基质.在景观类型面积比例的变化中,耕地的变幅最大.干旱河谷的整体形状较简单,1974-1995年破碎化程度和异质性程度持续增加,1995-2000年表现为降低趋势,而斑块内部的连通性先降低后增加,具体表现为斑块密度、多样性指数先增大后减小,蔓延度指数先减小后增大,而边界密度和分维数持续减小.人口增长和国家政策是导致岷江上游干旱河谷景观变化的主要驱动力.     

Dental indicators of health and stress in early Egyptian and Nubian agriculturalists: a difficult transition and gradual recovery

Although agriculture is now the globally predominant mode of food production, studies of the skeletal remains of early agriculturalists have indicated high levels of physiological stress and poor health relative to hunter-gatherers in similar environments. Previous studies identifying this trend in different regions prompt further research of the causes and effects of subsistence transitions in human societies. Here, 242 dentitions from five ancient Egyptian and Nubian populations are examined: 38 individuals from Jebel Sahaba (Upper Paleolithic), 56 from Badari (Predynastic), 54 from Naqada (Predynastic), 47 from Tarkhan (Dynastic), and 47 from Kerma (Dynastic). These populations span the early period of agricultural intensification along the Nile valley. Skeletal remains were scored for the presence of linear enamel hypoplasia (LEH) of the dentition, an established indicator of physiological stress and growth interruption. The prevalence of LEH was highest in the "proto-agricultural" (pastoralist) Badari population, with a gradual decline throughout the late Predynastic and early Dynastic periods of state formation. This suggests that the period surrounding the emergence of early agriculture in the Nile valley was associated with high stress and poor health, but that the health of agriculturalists improved substantially with the increasing urbanization and trade that accompanied the formation of the Egyptian state. This evidence for poor health among proto- and early agriculturalists in the Nile valley supports theories that agricultural intensification occurred as a response to ecological or demographic pressure rather than simply as an innovation over an existing stable subsistence strategy.     

金沙江干热河谷希蒙得木光合及叶绿素荧光特性

比较研究了4a生希蒙得木[Simmondsia chinensis(Link.)Schneider]两个种源(美国Hyder和以色列Vacaville)叶片的光合及叶绿素荧光特性。结果表明:在金沙江干热河谷地区两个种源的希蒙得木的净光合速率(Pn)、气孔导度日变化均呈单峰曲线,峰值出现在上午10:00。相同的试验条件下,Vacaville种源的净光合速率、气孔导度高于Hyder种源;经充分暗适应后,Vacaville种源的叶片叶绿素F0、Fm、Fv、Fv/F0、NPQ和ETR均高于Hyder种源。光强度在200 μmol m-2s-1以下,两个种源的PhiCO2和PhiPS2呈线性负相关;而光强度在200-2000 μmol m-2s-1间则呈线性正相关。空气中CO2浓度和荧光光合速率、PhiPS2、PhiCO2值存在着一定的正相关关系。Vacaville种源较Hyder种源更适应金沙江干热河谷气候。     

岷江上游干旱河谷岷江柏的光合与水分生理特征干湿季对比研究

岷江柏（Cupressus chengiana）是干旱河谷地区的重要生态恢复物种,为探讨岷江柏对干旱河谷环境的适应策略,以生长于岷江上游干旱河谷自然生境中的岷江柏为研究对象,研究分析了其在湿季（7月）和干季（11月）的水分生理特征和光合生理特征。结果表明：（1）水分生理方面,相较于湿季,干季岷江柏的脯氨酸（Pro）、可溶性糖（SS）、过氧化物酶（POD）显著增加（P<0.05）,比叶重（LMA）、黎明水势（Ψ_pl）、正午水势（Ψ_ml）则显著下降（P<0.05）;（2）光合生理方面,相较于湿季,岷江柏在干季的气孔导度（G_s）、蒸腾速率（T_r）、饱和光下最大净光合速率（P_nmax）、初始羧化效率（CE）、光合能力（A_max）、CO₂补偿点（Γ）、光呼吸速率（R_p）、最大羧化速率（V_cmax）、最大电子传递速率（J_max）、磷酸丙糖利用率（TPU）、J_max/V_cmax、光能捕获效率（F_v''/F_m''）、PSII实际光化学效率（Ф_PSII）、光化学猝灭系数（qP）、电子传递效率（ETR）均显著下降（P<0.05）,而暗呼吸速率（R_d）、水分利用效率（WUE）、非光化学猝灭系数（NPQ）则显著上升（P<0.05）。干季,岷江柏采取增加水分获取能力并降低水分散失的水分利用策略、增加光合产物消耗策略、增加热耗散的光合器官保护策略等,以适应干季干旱、低温等环境胁迫,进而表现出较强的环境适应性。     

干热河谷失稳性坡面植物碳氮磷化学计量特征对土壤性质的响应

以干热河谷阴坡和阳坡典型失稳性坡面不同区段(稳定区、失稳区和堆积区)的草本植物为研究对象,分析植物地上和地下碳(C)、氮(N)、磷(P)含量及其化学计量特征对土壤性质的响应机制。结果表明:失稳性坡面植物地上C含量(320.59 g·kg^-1)、N含量(12.15 g·kg^-1)和C/P(25.37)均显著高于地下(分别为254.01 g·kg^-1、6.12 g·kg^-1、13.43),C/N则表现为地下(43.09)显著高于地上(31.90)。阳坡植物地上和地下C含量、N/P均表现为稳定区和失稳区显著高于堆积区,N含量则表现为失稳区显著高于堆积区;阴坡植物地上N、P含量及地下P含量均表现为堆积区显著高于稳定区和失稳区,地下C含量则反之。植物地上生长主要受P限制,根系生长主要受N限制并随区段向下呈逐渐增加趋势;阴坡植物生长受P的限制程度高于阳坡,N限制弱于阳坡。土壤含水量(SWC)是影响植物地上C、N、P含量变化的重要因子,影响值分别为28.8%、20.8%、19.9%,土壤有机碳(SOC)则显著影响植物地下C、N含量,影响值分别为49.5%、22.1%,植物地下N含量的变化主要受土壤pH值的影响(24.3%)。坡向、区段及土壤因子均显著影响植物养分的分配,SWC和SOC是主要影响因子,同时还受土壤pH值的影响。     

干旱死亡叶片与自然凋落叶化学性质对比研究

为了解干旱死亡叶片与自然凋落叶化学性质的差异性,对云南元江干热河谷5种植物(鞍叶羊蹄甲、白皮乌口树、灰毛浆果楝、细基丸和九里香)干旱死亡叶片和自然凋落叶化学性质进行比较分析。结果表明,干旱死亡叶片和自然凋落叶在碳和养分化学特性上表现出较大变异,且不同树种间存在极显著差异(P<0.001)。与自然凋落叶相比,干旱死亡叶片具有较高的可溶性碳、C/N比和Mg含量,而木质素、半纤维素和N含量则较低。干旱死亡叶片与自然凋落叶间的碳(R²=0.56,P<0.01)、纤维素(R²=0.52,P<0.01)、半纤维素(R²=0.85,P<0.001)、单宁(R²=0.99,P<0.001)、木质素/N(R²=0.60,P<0.01)、C/N(R²=0.64,P<0.001)和氮含量(R²=0.85,P<0.001)呈显著正相关。因此,可根据自然凋落叶化学性质预测未来极端干旱条件下干旱死亡叶片的化学性质。