The role of cyanobacteria in crystallization of magnesium calcites

Laboratory experiments showed the effect of the cyanobacterium Microcoleus chthonoplastes on the formation of magnesium calcites, using model solutions (2.14M MgCl₂-0.05M CaCl₂-0.6M NaCl-0.18M NaHCO₃). The conditions of existence of cyanobacteria in such solutions in light or darkness significantly alter the structure of the sediment and the shape and size of the carbonate crystals. Cyanobacteria slow down crystallization due to the formation of exometabolites with a chelating effect, which leads to the precipitation of high-magnesium calcites. In the photosynthetic environment the presence of huntite (CaMg₃(CO₃)₄), possible forerunner of dolomite, is prominent.     

Rainfall and parasitic wasp (Hymenoptera: Ichneumonoidea) activity in successional forest stages at Barro Colorado Nature Monument, Panama, and La Selva Biological Station, Costa Rica

1 In 1997, we ran two Malaise insect traps in each of four stands of wet forest in Costa Rica (two old‐growth and two 20‐year‐old stands) and four stands of moist forest in Panama (old‐growth, 20, 40 and 120‐year‐old stands). 2 Wet forest traps caught 2.32 times as many ichneumonoids as moist forest traps. The average catch per old‐growth trap was 1.89 times greater than the average catch per second‐growth trap. 3 Parasitoids of lepidopteran larvae were caught in higher proportions in the wet forest, while pupal parasitoids were relatively more active in the moist forest. 4 We hypothesize that moisture availability is of key importance in determining parasitoid activity, community composition and trophic interactions.     

Climate controls on C3 vs. C4 productivity in North American grasslands from carbon isotope composition of soil organic matter

We analyzed the δ¹³C of soil organic matter (SOM) and fine roots from 55 native grassland sites widely distributed across the US and Canadian Great Plains to examine the relative production of C₃ vs. C₄ plants (hereafter %C₄) at the continental scale. Our climate vs. %C₄ results agreed well with North American field studies on %C₄, but showed bias with respect to %C₄ from a US vegetation database (statsgo ) and weak agreement with a physiologically based prediction that depends on crossover temperature. Although monthly average temperatures have been used in many studies to predict %C₄, our analysis shows that high temperatures are better predictors of %C₄. In particular, we found that July climate (average of daily high temperature and month's total rainfall) predicted %C₄ better than other months, seasons or annual averages, suggesting that the outcome of competition between C₃ and C₄ plants in North American grasslands was particularly sensitive to climate during this narrow window of time. Root δ¹³C increased about 1‰ between the A and B horizon, suggesting that C₄ roots become relatively more common than C₃ roots with depth. These differences in depth distribution likely contribute to the isotopic enrichment with depth in SOM where both C₃ and C₄ grasses are present.     

Apparent survival of tropical birds in a wet,premontane forest in Costa Rica

Despite the importance of tropical birds in the development of life history theory, we lack information about demographic rates and drivers of population dynamics for most species. We used a 7‐year (2007–2013) capture‐mark‐recapture dataset from an exceptionally wet premontane forest at mid‐elevation in Costa Rica to estimate apparent survival for seven species of tropical passerines. For four of these species, we provide the first published demographic parameters. Recapture probabilities ranged from 0.21 to 0.53, and annual estimates of apparent survival varied from 0.23 to 1.00. We also assessed the consequences of inter‐annual variation in rainfall on demographic rates. Our results are consistent with inter‐annual rainfall increasing estimates of apparent survival for two species and decreasing estimates for three species. For the three species where we could compare our estimates of apparent survival to estimates from drier regions, our estimates were not consistently higher or lower than those published previously. The temporal and spatial variability in demographic rates we document within and among species highlights the difficulties of generalizing life history characteristics across broad biogeographic gradients. Most importantly, this work emphasizes the context‐specific role of precipitation in shaping tropical avian demographic rates and underscores the need for mechanistic studies of environmental drivers of tropical life histories.     

Effects of grazing intensity and grazing exclusion on litter decomposition in the temperate steppe of Nei Mongol,China

Aims Grazing intensity and grazing exclusion affect ecosystem carbon cycling by changing the plant community and soil micro-environment in grassland ecosystems. The aims of this study were: 1) to determine the effects of grazing intensity and grazing exclusion on litter decomposition in the temperate grasslands of Nei Mongol; 2) to compare the difference between above-ground and below-ground litter decomposition; 3) to identify the effects of precipitation on litter production and decomposition. Methods We measured litter production, quality, decomposition rates and soil nutrient contents during the growing season in 2011 and 2012 in four plots, i.e. light grazing, heavy grazing, light grazing exclusion and heavy grazing exclusion. Quadrate surveys and litter bags were used to measure litter production and decomposition rates. All data were analyzed with ANOVA and Pearson’s correlation procedures in SPSS. Important findings Litter production and decomposition rates differed greatly among four plots. During the two years of our study, above-ground litter production and decomposition in heavy-grazing plots were faster than those in light-grazing plots. In the dry year, below-ground litter production and decomposition in light-grazing plots were faster than those in heavy-grazing plots, which is opposite to the findings in the wet year. Short-term grazing exclusion could promote litter production, and the exclusion of light-grazing could increase litter decomposition and nutrient cycling. In contrast, heavy-grazing exclusion decreased litter decomposition. Thus, grazing exclusion is beneficial to the restoration of the light-grazing grasslands, and more human management measures are needed during the restoration of heavy-grazing grasslands. Precipitation increased litter production and decomposition, and below-ground litter was more vulnerable to the inter-annual change of precipitation than above-ground litter. Compared to the light-grazing grasslands, heavy-grazing grasslands had higher sensitivity to precipitation. The above-ground litter decomposition was strongly positively correlated with the litter N content (R² = 0.489, p < 0.01) and strongly negatively correlated with the soil total N content (R² = 0.450, p < 0.01), but it was not significantly correlated with C:N and lignin:N. Below-ground litter decomposition was negatively correlated with the litter C (R² = 0.263, p < 0.01), C:N (R² = 0.349, p < 0.01) and cellulose content (R² = 0.460, p < 0.01). Our results will provide a theoretical basis for ecosystem restoration and the research of carbon cycling.     

恢复状态下羊草（Leymus chinensis）草原植被根冠比动态及影响因子

利用内蒙古羊草草原围栏样地连续两年的地上、地下生物量数据和当地同时期的降水、气温资料，分析了退化羊草草原，在恢复过程中植被根冠比动态及与水热因子之间的关系。研究结果表明：（1）羊草草原植被地上、地下生物量季节变化均呈单峰型曲线，峰值出现在8月。（2）羊草草原植被根冠比具有明显的季节变化，生长季初和生长季末根冠比值较大，最低值出现在地上生物量最高的8月中下旬。（3）羊草草原植被月根冠比与上上月月降水量相关关系极显著，与七月平均气温相关关系显著；以根冠比为因变量，上上月月降水量、上月平均气温为自变量可分别建立线性回归方程。该方程可以较好地模拟羊草草原植被生长季内月根冠比的动态变化，这样在草地恢复过程中，可由上月的水热因子来指导下月的草地管理，并为更准确地估算草原生态系统生产力及碳储存动态提供重要参数。     

下辽河平原降雨中氮素的动态变化

为了了解降雨中氮对农田生态系统的影响,分析了2004-2006年下辽河平原连续3年定位收集的降雨观测资料与历史资料.结果表明:降雨中氮输入量季节变化显著,夏季最高,这主要与降雨量及空气中NH4 -N浓度变化有关;降雨中DON量与NO3--N含量相当,均接近24%,是雨水中氮的重要组分;与1985年相比,近3年降雨输入到该地区农田生态系统的年氮通量已有较大提高,降雨较多的2005年输入的无机氮量更是20年前的2倍以上;2004-2006年随降雨输入农田生态系统的氮平均占可利用肥料氮的28.3%,对农田生态系统有着重要影响.