Landscape spatial patterns in freshwater snail assemblages across Northern Highland catchments

1. Limnologists and landscape ecologists have illustrated how the spatial position of a lake in a landscape influences many of its properties, from the physical to the social. Taking a community ecology perspective, we investigated whether freshwater gastropod assemblages respond to lake landscape position.
2. We determined: (a) whether there is any spatial pattern among lakes in either the species richness or composition of gastropod assemblages; (b) the form of any spatial pattern; and (c) if any explanatory variables (e.g. dispersal corridors and limiting local conditions) show a similar pattern.
3. In three different hydrological catchments, snail species richness increased from isolated highland lakes to stream-connected lowland lakes, probably reflecting increased colonization potential and less limiting local factors for lowland drainage lakes. Catchments appear to differ from one another with regard to relative species abundance, both in terms of macrophyte-associated snail fauna and snails from all habitats aggregated. One or more historical events, such as chance dispersal, may have produced this pattern. Taken together, these results suggest that within-catchment constraints produce repeated gradients in species richness, regardless of what species composition persists in the catchment.     

Fire regimes and forest changes in mid and upper montane forests of the southern Cascades, Lassen Volcanic National Park, California, U.S.A.

Aim Spatial and temporal variation in fire regime parameters and forest structure were assessed. Location A 2630‐ha area of mid‐ and upper montane forest in Lassen Volcanic National Park (LVNP). Methods Two hypotheses were tested concerned with fire‐vegetation relationships in southern Cascades forests: (1) fire regime parameters (return interval, season of burn, fire size, rotation period) vary by forest dominant, elevation and slope aspect; and (2) fire exclusion since 1905 has caused forest structural and compositional changes in both mid‐ and upper montane forests. The implications of the study for national park management are also discussed. Results Fire regime parameters varied by forest compositional group and elevation in LVNP. Median composite and point fire return intervals were shorter in low elevation Jeffrey pine (Pinus jeffreyi) (JP) (4–6 years, 16 years) and Jeffrey pine–white fir (Abies concolor) (JP‐WF) (5–10 years, 22 years) and longer in high elevation red fir (Abies magnifica)— western white pine (Pinus monticola) (RF‐WWP) forests (9–27 years, 70 years). Median fire return intervals were also shorter on east‐facing (6–9 years, 16.3 years) and longer on south‐ (11 years, 32.5 years) and west‐facing slopes (22–28 years, 54‐years) in all forests and in each forest composition group. Spatial patterns in fire rotation length were the same as those for fire return intervals. More growing season fires also occurred in JP (33.1%) and JP‐WF (17.5%) than in RF‐WWP (1.1%) forests. A dramatic decline in fire frequency occurred in all forests after 1905. Conclusions Changes in forest structure and composition occurred in both mid‐ and upper montane forests due to twentieth‐century fire exclusion. Forest density increased in JP and JP‐WF forests and white fir increased in JP‐WF forests and is now replacing Jeffrey pine. Forest density only increased in some RF‐WWP stands, but not others. Resource managers restoring fire to these now denser forests need to burn larger areas if fire is going to play its pre‐settlement role in montane forest dynamics.     

南亚热带季风常绿阔叶林水文功能及其养分动态的研究

 根据在鼎湖山季风常绿阔叶林集水区3年的观测结果,对这一南亚热带地带性植被的水文功能进行了较深入的探讨。由于林分结构复杂,季风常绿阔叶林对大气降水具有较高的林冠截留率,截留率的季节变化动态与降水量的季节分配有关。该森林土壤结构良好,其渗水速度快,加上有较厚的枯落物层,对于减缓地面径流,减少水土流失,功效甚大。但由于土层较薄,其蓄水功能有限。该森林的径流量占总降水量的比例特别是地表径流所占比例较小,分别为50.22％和14.19％。其季节分配有利于保持水土和植物生长。由于土壤蓄水量变化出现负值,用水量平衡法计算得出鼎湖山季风常绿阔叶林年蒸发散量为1323.98mm,占大气降水量的51.81％。该森林的降水中主要营养元素浓度较高,降水带来大量的养分,特别是氮素的年输入量高达35.29kg·hm-2。淋溶也给该森林带来较高的养分归还量,其中钾的淋溶量高达35.65kg·hm-2;镁的淋溶量高达8.9kg·hm-2,为林外雨输入的2.37倍。径流中的氮输出为28.35kg·hm-2,降水中的氮素净输入量为6.94kg·hm-2;但镁的净输入呈负值。     

Effect of calcium restriction on cardenolide accumulation in two cell lines of Digitalis thapsi grown under different light regimes

The effect of calcium-deprivation on growth and the production of cardenolides in two undifferentiated cell lines of Digitalis thapsi maintained under three different light regimes (16 h photoperiod, darkness, or continuous light) was investigated. Growth was stimulated by continuous light in both cell lines cultured in complete medium. The light regime did not affect cardenolide accumulation in the cells of the hypocotyl-derived line; by contrast, continuous light or darkness increased the production in the leaf-derived line. The elimination of calcium favoured cardenolide production independently of the origin of the suspensions and the light regime, this beneficial effect being predominantly manifested under continuous light.     

Predictability of the terrestrial carbon cycle

Terrestrial ecosystems sequester roughly 30% of anthropogenic carbon emission. However this estimate has not been directly deduced from studies of terrestrial ecosystems themselves, but inferred from atmospheric and oceanic data. This raises a question: to what extent is the terrestrial carbon cycle intrinsically predictable? In this paper, we investigated fundamental properties of the terrestrial carbon cycle, examined its intrinsic predictability, and proposed a suite of future research directions to improve empirical understanding and model predictive ability. Specifically, we isolated endogenous internal processes of the terrestrial carbon cycle from exogenous forcing variables. The internal processes share five fundamental properties (i.e., compartmentalization, carbon input through photosynthesis, partitioning among pools, donor pool‐dominant transfers, and the first‐order decay) among all types of ecosystems on the Earth. The five properties together result in an emergent constraint on predictability of various carbon cycle components in response to five classes of exogenous forcing. Future observational and experimental research should be focused on those less predictive components while modeling research needs to improve model predictive ability for those highly predictive components. We argue that an understanding of predictability should provide guidance on future observational, experimental and modeling research.     

鄱阳湖湿地灰化苔草种群生产力特征及其水文响应

淡水湖泊湿地中,水文条件是影响湿地植物分布和生长发育的关键因素,研究特定湿地植物种群与水文变化之间关系,对于认识湿地植被格局形成及进行湿地生态调控与恢复具有重要意义。选取鄱阳湖湿地洲滩优势植物——灰化苔草(Carex cinerascens)种群作为研究对象,基于野外实地观测数据,研究不同高程带灰化苔草春草种群生产力特征及其对水文变化的响应。结果表明:春草生长季内各高程带灰化苔草种群变化规律基本一致,但其生长发育过程对水文条件产生差异性反应,长期连续水淹和半水淹条件抑制灰化苔草的生长,而间歇性半水淹和未水淹条件则促进灰化苔草伸长生长和生物量积累;生长初期灰化苔草通过储水策略应对水分缺乏形成的干旱胁迫,而生长末期则通过增加干物质含量来应对淹水胁迫;灰化苔草定植与生长发育需要一定的水文条件,淹没期平均水深3.70—2.78 m、淹没频率42.08%—43.17%、平均距湖水面高度-0.23—0.77 m的水文环境更有利于灰化苔草的生长发育。研究结果可为未来鄱阳湖湿地植被保护和湖泊水位调控提供重要参考依据。     

基于SWAT的西北干旱区县域水文模拟——以临泽县为例

以西北干旱区的临泽县为例,利用1980—2012年的气象数据、土地利用数据、土壤数据、数字高程数据驱动SWAT模型,对县域水文过程进行了模拟并对行政区内的水资源状况进行了时空特征分析。研究表明临泽县1980—2012年均实际蒸发量、下渗量、壤中流补给量、地下水补给量、产流量、可用地表水资源量和产流系数分别为130.53、49.78、68.95、48.00、53.47 mm、(13.17±0.60)×108m3和0.16;生态用水量大(3.56±0.12)×1011m3),且呈现出增加趋势。由于黑河分水措施的影响,各水量要素的突变年份出现在2000年之后的5年内。从空间分布上看,地下水补给量和产流系数都呈现“南高北低”的趋势。研究结果也表明临泽县1980—2012年的产流量由地下水补给量控制,壤中流和地下径流的贡献分别为43%和57%;而可利用水资源量主要依赖上游的来水,上游来水量的贡献率达到83%。此外,我们的研究也发现临泽县2007—2012的实际蒸发持续增加,从而导致“蒸发悖论”现象的存在。