A theoretical model of C- and N-acquiring exoenzyme activities,which balances microbial demands during decomposition

We developed an Extracellular EnZYme model (EEZY) of decomposition that produces two separate pools of C- and N-acquiring enzymes, that in turn hydrolyze two qualitatively different substrates, one containing only C (e.g., cellulose) and the other containing both C and N (e.g., chitin or protein). Hence, this model approximates the actions of commonly measured indicator enzymes ß-1,4-glucosidase and ß-1,4-N-acetylglucosaminidase (or leucine aminopeptidase) as they hydrolyze cellulose and chitin (or protein), respectively. EEZY provides an analytical solution to the allocation of these two enzymes, which in turn release C and N from the two substrates to maximize microbial growth. Model behaviors were both qualitatively and quantitatively consistent with patterns of litter decay generated by other decomposition models. However, EEZY demonstrated greater sensitivity to the C:N of individual substrate pools in addition to responding to factors directly affecting enzyme activity. Output approximated field observations of extracellular enzyme activities from studies of terrestrial soils, aquatic sediments, freshwater biofilm and plankton communities. Although EEZY is largely a theoretical model, simulated C- and N-acquiring enzyme activities approximated a 1:1 ratio, consistent with the bulk of these field observations, only when the N-containing substrate had a C:N ratio similar to commonly occurring substrates (e.g., proteins or chitin). This result supported the emerging view of the stoichiometry of extracellular enzyme activities from an environmental context, which suggests that a relatively narrow range of microbial C:N, carbon use efficiency and soil/sediment organic matter C:N across ecosystems explains the tendency towards this 1:1 ratio of enzyme activities associated with C- and N-acquisition. Sensitivity analyses indicated that simulated extracellular enzyme activity was most responsive to variations in carbon use efficiency of microorganisms, although kinetic characteristics of enzymes also had significant impacts. Thus EEZY provides a quantitative framework in which to interpret mechanisms underlying empirical patterns of extracellular enzyme activity.     

A positive relationship between the abundance of ammonia oxidizing archaea and natural abundance δ15N of ecosystems

We present a significant relationship between the natural abundance isotopic composition of ecosystem pools and the abundance of a microbial gene. Natural abundance ¹⁵N of soils and soil DNA were analysed and compared with archaeal ammonia oxidizer abundance along an elevation gradient in northern Arizona and along a substrate age gradient in Hawai'i. There was a significant positive correlation between the abundance of archaeal amoA genes and natural abundance δ¹⁵N of total soil or DNA suggesting that ammonia oxidizing archaea play an important role in ecosystem N release.     

分时段修正双源模型在西北干旱区玉米蒸散量模拟中的应用

蒸散发(ET)是陆地水循环过程的重要组成部分,同时也是区域能量平衡以及水量平衡的关键环节,精确估算ET,对于提高水分利用效率以及优化区域用水结构具有重要意义。本文利用黑河重大计划观测数据,对比了考虑CO_2浓度和不考虑CO_2浓度对玉米冠层影响的冠层阻力模型,分别将其耦合到双源的Shuttleworth-Wallace(S-W)模型中,并利用这两种模型分时段对玉米整个生育期内半小时尺度上的ET进行模拟,利用涡度相关实测数据对模型进行验证,最后分别对影响玉米冠层阻力的气象要素和影响ET的阻力参数进行敏感性分析,探寻大气CO_2浓度改变条件下黑河中游绿洲区玉米不同生长阶段的农田耗水规律。结果表明:本文所修正的考虑CO_2浓度对玉米冠层影响的冠层阻力模型耦合到S-W模型后,能够较精准地模拟玉米整个生育期不同生长阶段半小时尺度上农田耗水过程。敏感性分析表明:各生长阶段冠层阻力(r_s~c)和冠层面高度到参考面高度间的空气动力阻力(r_a~a)对ET的影响最为强烈,其他阻力参数对ET的影响不明显,ET的变化程度随着r_s~c和r_a~a的增大而减小。本文所修正的考虑CO_2浓度影响的分时段双源模型能够精准地模拟玉米整个生育期各生长阶段的ET,可为种植结构调整和土地利用方式改变以及CO_2浓度变化环境下的农田蒸散研究提供参考。     

新疆陆生贝类区系及动物地理学分析

1974-1976年和2000年先后调查了新疆36个县、市和地区,采集了一批陆生贝类标本,经鉴定,共计有9科22属和亚属,52种和亚种。其中,粉上华蜗牛、滑槲果螺、双线中亚桥齿蜗牛、黑带巴蜗牛、同型巴蜗牛、野缨蛞蝓6种为牛、羊、骆驼等家畜双腔科吸虫第一中间宿主;粉上华蜗牛、双线中亚桥齿蜗牛为本地区优势种。从种类区系组成分析,新疆陆生贝类主要属于古北界中亚亚界蒙新区,仅有少数东洋界的种类渗入,南北疆虽有差异,但大致相同。     

猴樟、鹅掌楸对马尾松苗木生理活性的他感效应

用凋落物浸提液生物鉴定的方法,研究了猴樟Cinnamomum bodinieri和鹅掌楸Liriodendron chinense对马尾松Pinus massoniana幼苗生理活性的他感作用。结果表明,两供体植物对受抟光合色素质量分数和质膜相对透性的影响,总体表现为促进作用;对受体光合速率和蒸腾速率的影响,基本表现为抑制效应。对氮、磷吸收的影响两供体表现出低促高抑的作用趋势。而对受体钾元素的吸收,均表现出一定的促进效应。从对受体光合速率的影响看,鹅掌楸可初步作为马尾松伴生树种的选择。图1表3参18     

Organic carbon in the upper 100 m and downward flux in the banda sea; monsoonal differences

Organic carbon was measured in the upper 100 m and its downward flux from the euphotic zone recorded, as part of a multidisciplinary study in the Banda Sea on monsoonal differences in the upper water layers.All 35 stations occupied showed on average 1.5 times higher POC values in August 1984 (4.9 g·m⁻², SE monsoon, upwelling period) than in February/March 1985 (3.3 g·m⁻², NW monsoon, downwelling period) for the 0 to 100 m water column. Monsoonal variation in POC was confined to the surface layer and related to a variation in phytoplankton content; it can be explained by — local— upwelling during the SE monsoon. At 100 m no seasonal variation occurred.Contrary to POC, average figures for DOC in February/March were almost twice the average observed in August (66.5 against 37.5 g·m⁻² for the 0 to 100 m water column). In February/March spatial variation was more pronounced than in August with highest values occurring in the NE part (>100 g·m⁻², 0 to 100 m), with a subsurface maximum. In this period the NW monsoon causes a surface current to the east. This might cause a westward subsurface countercurrent of Arafura Sea water rich in riverine or benthic layer DOC, influencing the eastern Banda Sea.At 100 m depth daily sedimentation amounted to ∼50 mg C·m⁻². The limited number of data do not indicate a difference between the 2 periods. On average the daily downward flux at 100 m depth amounted to 1.2% of POC and 0.8% of chlorophyll present in the 0 to 100 m water column, and equalled 5% of the daily primary production.     

Soil pH drives the spatial distribution of bacterial communities along elevation on Changbai Mountain

The elevational patterns of diversity for plants and animals have been well established over the past century. However, it is unclear whether there is a general elevational distribution pattern for microbes. Changbai Mountain is one of few well conserved natural ecosystems, where the vertical distribution of vegetation is known to mirror the vegetation horizontal zonation from temperate to frigid zones on the Eurasian continent. Here, we present a comprehensive analysis of soil bacterial community composition and diversity along six elevations representing six typical vegetation types from forest to alpine tundra using a bar-coded pyrosequencing technique. The bacterial communities differed dramatically along elevations (vegetation types), and the community composition was significantly correlated with soil pH, carbon/nitrogen ratio (C/N), moisture or total organic carbon (TOC), respectively. Phylogenetic diversity was positively correlated with soil pH (P = 0.024), while phylotype richness was positively correlated with soil pH (P = 0.004), total nitrogen (TN) (P = 0.030), and negatively correlated with C/N ratio (P = 0.021). Our results emphasize that pH is a better predictor of soil bacterial elevational distribution and also suggest that vegetation types may indirectly affect soil bacterial elevational distribution through altering soil C and N status.     

Modeling the optimal ecological security pattern for guiding the urban constructed land expansions

Rapid urbanization has induced numerous ecological and environmental issues seriously threatening the ecological security. The ecological security pattern (ESP), an effective way for protecting the ecological security, is becoming increasingly important in reconciling the rapid urbanization and ecology protection in urban planning practices. Based on the cost-distance analysis method, we constructed a three-rank (basic, moderate and strict-rank) composite ESP of Gaoming (Guangdong, China) aiming at protecting the survivals and habitat securities of rare vegetations, wild animals and human beings. The proposed composite ESP is established on five equal-weighted individual ESPs (namely Geology-ESP, Hydrology-ESP, Atmosphere-ESP, Biodiversity-ESP and Farmland-ESP) for geologic disasters prevention, flood prevention and drinking water protection, air pollution prevention, biodiversity conservation and farmland protection, respectively. Our results show that under the basic, moderate, and strict- rank ESPs, the integration and connectivity of the ecological components are constantly improved, but the connectivity between neighboring urban patches decline gradually. The moderate-rank ESP proves to be the optimal spatial pattern for balancing the conflicts between urban development and ecological protection. Notably, the ESP that considers the security of atmosphere and farmland securities, which protects the regional farmlands better and well balance the expansions of industrial and residual lands, proves to be much more reasonable.     

Impacts and adaptation of the cropping systems to climate change in the Northeast Farming Region of China

The Northeast Farming Region of China (NFR) is a very important crop growing area, comprising seven sub-regions: Xing’anling (XA), Sanjiang (SJ), Northwest Songliao (NSL), Central Songliao (CSL), Southwest Songliao (SSL), Changbaishan (CB) and Liaodong (LD), which has been severely affected by extreme climate events and climatic change. Therefore, a set of expert survey has been done to identify current and project future climate limitations to crop production and explore appropriate adaptation measures in NFR. Droughts have been the largest limitation for maize (Zea mays L.) in NSL and SSL, and for soybean (Glycine max L. Merr.) in SSL. Chilling damage has been the largest limitation for rice (Oryza sativa L.) production in XA, SJ and CB. Projected climate change is expected to be beneficial for expanding the crop growing season, and to provide more suitable conditions for sowing and harvest. Autumn frost will occur later in most parts of NFR, and chilling damage will also decrease, particularly for rice production in XA and SJ. Drought and heat stress are expected to become more severe for maize and soybean production in most parts of NFR. Also, plant diseases, pests and weeds are considered to become more severe for crop production under climate change. Adaptation measures that have already been implemented in recent decades to cope with current climatic limitations include changes in timing of cultivation, variety choice, soil tillage practices, crop protection, irrigation and use of plastic film for soil cover. With the projected climate change and increasing risk of climatic extremes, additional adaptation measures will become relevant for sustaining and improving productivity of crops in NFR to ensure food security in China.     

Accounting for both parameter and model structure uncertainty in crop model predictions of phenology: A case study on rice

We consider predictions of the impact of climate warming on rice development times in Sri Lanka. The major emphasis is on the uncertainty of the predictions, and in particular on the estimation of mean squared error of prediction. Three contributions to mean squared error are considered. The first is parameter uncertainty that results from model calibration. To take proper account of the complex data structure, generalized least squares is used to estimate the parameters and the variance-covariance matrix of the parameter estimators. The second contribution is model structure uncertainty, which we estimate using two different models. An ANOVA analysis is used to separate the contributions of parameter and model uncertainty to mean squared error. The third contribution is model error, which is estimated using hindcasts. Mean squared error of prediction of time from emergence to maturity, for baseline +2 °C, is estimated as 108 days², with model error contributing 86 days², followed by model structure uncertainty which contributes 15 days² and parameter uncertainty which contributes 7 days². We also show how prediction uncertainty is reduced if prediction concerns development time averaged over years, or the difference in development time between baseline and warmer temperatures.