Flowering phenology in a species-rich temperate grassland is sensitive to warming but not elevated CO2

* Flowering is a critical stage in plant life cycles, and changes might alter processes at the species, community and ecosystem levels. Therefore, likely flowering-time responses to global change drivers are needed for predictions of global change impacts on natural and managed ecosystems. * Here, the impact of elevated atmospheric CO2 concentration ([CO2]) (550 micromol mol(-1)) and warming (+2 masculineC) is reported on flowering times in a native, species-rich, temperate grassland in Tasmania, Australia in both 2004 and 2005. * Elevated [CO2] did not affect average time of first flowering in either year, only affecting three out of 23 species. Warming reduced time to first flowering by an average of 19.1 d in 2004, acting on most species, but did not significantly alter flowering time in 2005, which might be related to the timing of rainfall. Elevated [CO2] and warming treatments did not interact on flowering time. * These results show elevated [CO2] did not alter average flowering time or duration in this grassland; neither did it alter the response to warming. Therefore, flowering phenology appears insensitive to increasing [CO2] in this ecosystem, although the response to warming varies between years but can be strong.     

Plant functional traits mediate reproductive phenology and success in response to experimental warming and snow addition in Tibet

Global climate change is predicted to have large impacts on the phenology and reproduction of alpine plants, which will have important implications for plant demography and community interactions, trophic dynamics, ecosystem energy balance, and human livelihoods. In this article we report results of a 3‐year, fully factorial experimental study exploring how warming, snow addition, and their combination affect reproductive phenology, effort, and success of four alpine plant species belonging to three different life forms in a semiarid, alpine meadow ecosystem on the central Tibetan Plateau. Our results indicate that warming and snow addition change reproductive phenology and success, but responses are not uniform across species. Moreover, traits associated with resource acquisition, such as rooting depth and life history (early vs. late flowering), mediate plant phenology, and reproductive responses to changing climatic conditions. Specifically, we found that warming delayed the reproductive phenology and decreased number of inflorescences of Kobresia pygmaea C. B. Clarke, a shallow‐rooted, early‐flowering plant, which may be mainly constrained by upper‐soil moisture availability. Because K. pygmaea is the dominant species in the alpine meadow ecosystem, these results may have important implications for ecosystem dynamics and for pastoralists and wildlife in the region.     

Foraging for nutrients, responses to changes in light, and competition in tropical deciduous tree seedlings

We evaluated (1) the responses of two co-occurring tropical tree species, Heliocarpuspallidus and Caesalpiniaeriostachys, to changes in light, (2) the ability of these species to search for and exploit a fertilized soil patch, (3) the relationship between the capacity to forage for a fertilized patch and the capacity to respond to changes in light availability and (4) how the relationship between light and nutrient acquisition influenced the competitive interactions between these species. Plants of the two species were exposed to a factorial combination of high (H) and low (L) light intensity and fertilized (+Fp) and unfertilized (−Fp) nutrient patches for 50 days. Half of the plants from H were then transferred to L (HL treatment), and half of the plants from L were transferred to H (LH). The remaining plants were kept in their original light condition and grown for another 50 days. Plants were grown in these light and patch treatments alone (one plant per pot) and in interspecific competition (one plant per species resulting in two plants per pot). Both species exploited fertilized patches by increasing root biomass and length in the patch. This enhanced plant productivity and growth rate mainly under LH and HH conditions for Heliocarpus and the HH condition for Caesalpinia). When plants in the HH light environment were grown with an unfertilized patch, plant biomass and relative growth rates (RGRs) were even lower than␣under the LL light environment [(HH–Fp)<LL]. However, the combined activity of shoot and roots when above- and below-ground resources were temporally and spatially heterogeneous influenced plant productivity and growth rate. The benefit from light increase (LH) was reduced when grown with an unfertilized patch. Larger reductions in root biomass, length and density in the patch, and in plant biomass and RGR, were exhibited by Heliocarpus than by Caesalpinia. These results suggest a close relationship between root foraging and light capture, where the benefit of the exploitation of the patch will be reflected in whole-plant benefit, if enough light is captured above-ground. In addition, the results suggest a change in the expected plant responses to light due to heterogeneity in soil nutrients, even though the fertilized patch was only a small proportion of the total soil volume. Leaf characteristics such as specific leaf area responded only to light conditions and not to patchily distributed nutrients. Root characteristics responded more strongly to nutrient heterogeneity. Competition modified the pattern of foraging under both high- and low-light conditions in Heliocarpus by 50 days, and the ability to forage for a fertilized patch under LL after 100 days of growth for Caesalpinia. Even though plant growth and productivity are greatly reduced under low-light conditions (HL and LL), competition modifies the ability of species to forage for a rich patch (especially for the fast-growing species Heliocarpus). Received: 24 November 1997 / Accepted: 15 June 1998     

Plasticity in laying dates of Canada Geese in response to spring phenology

Observed phenological changes can be explained either by individual phenotypic plasticity or by evolutionary changes, but there is more evidence pointing towards phenotypic plasticity to explain the mechanism behind changes in bird phenology. However, most studies on phenology have been conducted on insectivorous bird species for which breeding is closely tied to temperature and insect emergence. In this study, we examined the consequences of climatic conditions on the nesting phenology of temperate breeding Canada Geese Branta canadensis maxima, which rely on a continuous food supply, during a 14‐year period (2003–16). We determined whether laying dates were plastically adjusted to spring environmental conditions, and whether this adjustment resulted in a laying date advancement. We further estimated the strength and shape of selection acting on breeding timing, by looking at the effect of laying date on the relative number of young successfully hatched in a nest. We found that Geese plastically adjusted their laying date to spring maximum temperature (and not to precipitation or ice break‐up), resulting in a 9‐day advancement of laying date in the population for that period. Laying date was also moderately repeatable (r = 0.23) and subject to directional selection, but stabilizing selection was negligible. We thus demonstrate how Canada Geese plastically adjust laying dates to temperature, which may further be beneficial to nesting success. Evolutionary change of laying date to selection related to climate change, however, is still possible.     

Season,but not experimental warming,affects the activity and temperature sensitivity of extracellular enzymes

Climate change may affect the microbial production and temperature sensitivity of extracellular enzymes that release carbon (C) and nutrients from soil organic matter. We measured the response of six hydrolytic enzymes involved in C, nitrogen (N), and phosphorus (P) degradation to experimental warming in a mixed-deciduous forest persisting on highly-weathered Ultisols (Whitehall Forest, Georgia, US). We found that warming produced no consistent enzyme response. However, we observed significant seasonal variation in enzyme activities, temperature sensitivities and elemental enzyme ratios (C:N and C:P). Seasonal differences in enzyme activity and temperature sensitivity were best explained by soil moisture and temperature. Our results suggest that seasonal dynamics in soil microclimate, organic matter supply, and microbial demand exert more control on enzyme dynamics than does a uniform increase in soil temperature.     

Acclimation of photosynthetic temperature optima of temperate and boreal tree species in response to experimental forest warming

Rising temperatures caused by climate change could negatively alter plant ecosystems if temperatures exceed optimal temperatures for carbon gain. Such changes may threaten temperature‐sensitive species, causing local extinctions and range migrations. This study examined the optimal temperature of net photosynthesis (T_opt) of two boreal and four temperate deciduous tree species grown in the field in northern Minnesota, United States under two contrasting temperature regimes. We hypothesized that T_opt would be higher in temperate than co‐occurring boreal species, with temperate species exhibiting greater plasticity in T_opt, resulting in better acclimation to elevated temperatures. The chamberless experiment, located at two sites in both open and understory conditions, continuously warmed plants and soils during three growing seasons. Results show a modest, but significant shift in T_opt of 1.1 ± 0.21 °C on average for plants subjected to a mean 2.9 ± 0.01 °C warming during midday hours in summer, and shifts with warming were unrelated to species native ranges. The 1.1 °C shift in T_opt with 2.9 °C warming might be interpreted as suggesting limited capacity to shift temperature response functions to better match changes in temperature. However, T_opt of warmed plants was as well‐matched with prior midday temperatures as T_opt of plants in the ambient treatment, and T_opt in both treatments was at a level where realized photosynthesis was within 90–95% of maximum. These results suggest that seedlings of all species were close to optimizing photosynthetic temperature responses, and equally so in both temperature treatments. Our study suggests that temperate and boreal species have considerable capacity to match their photosynthetic temperature response functions to prevailing growing season temperatures that occur today and to those that will likely occur in the coming decades under climate change.     

Copepod life cycle adaptations and success in response to phytoplankton spring bloom phenology

In a seasonal environment, the timing of reproduction is usually scheduled to maximize the survival of offspring. Within deep water bodies, the phytoplankton spring bloom provides a short time window of high food quantity and quality for herbivores. The onset of algal bloom development, however, varies strongly from year to year due to interannual variability in meteorological conditions. Furthermore, the onset is predicted to change with global warming. Here, we use a long-term dataset to study (a) how a cyclopoid copepod, Cyclops vicinus , is dealing with the large variability in phytoplankton bloom phenology, and (b) if bloom phenology has an influence on offspring numbers. C. vicinus performed a two-phase dormancy, that is, the actual diapause of fourth copepodid stages at the lake bottom is followed by a delay in maturation, that is, a quiescence, within the fifth copepodid stage until the start of the spring bloom. This strategy seems to guarantee a high temporal match of the food requirements for successful offspring development, especially through the highly vulnerable naupliar stages, with the phytoplankton spring bloom. However, despite this match with food availability in all study years, offspring numbers, that is, offspring survival rates were higher in years with an early start of the phytoplankton bloom. In addition, the phenology of copepod development suggested that also within study years, early offspring seems to have lower mortality rates than late produced offspring. We suggest that this is due to a longer predator-free time period and/or reduced time stress for development. Hence, within the present climate variability, the copepod benefited from warmer spring temperatures resulting in an earlier phytoplankton spring bloom. Time will show if the copepod's strategy is flexible enough to cope with future warming.     

未来气候变化对海南橡胶树春季物候期的影响

为研究未来气候变化对海南岛橡胶树春季物候期(第一蓬叶展叶期和春花期)的影响,以国内外关于橡胶树物候期量化研究和橡胶树观测试验数据为基础,结合作物生长钟模型,建立橡胶树春季物候期模型,开发成计算机软件RubberSP并进行适宜性评价。在此基础上,通过贝叶斯模型平均法(BMA)结合耦合模式比较计划第五阶段(CMIP5)多模式数据集中的5个大气环流模式(GCMs),分别在RCP2.6、RCP4.5和RCP8.5气候情景下,以1986—2017年为基准时段,预估2020—2099年气候变化对橡胶树春季物候期的可能影响。结果表明:RubberSP的模拟精度较高,模拟值与实测值的决定系数R²为0.73～0.87,均方根误差RMSE为3.26～4.15 d,归一化均方根误差NRMSE为3.4%～7.4%。BMA方法可以有效地处理单一GCMs带来的不确定性问题,较好地反映出气温变化趋势;预估RCP2.6、RCP4.5和RCP8.5情景下,海南岛至21世纪末较基准时段分别升温超过0.3、1.0和2.5 ℃。在未来气候情景下,春季物候期出现日序提前,产胶量提高的可能性变大。日序等值线均向西北方向移动,海南岛橡胶树种植最适宜区有向西北方向扩大的可能。第一蓬叶展叶期的空间差异性变大,春花期则略微变小。橡胶树春季物候期在未来3种情景下提前或推迟的变化幅度随RCP情景下升温的幅度而变化,RCP2.6最平缓,RCP8.5最剧烈。     

Variation in the phenology of photosynthesis among eastern white pine provenances in response to warming

In higher‐latitude trees, temperature and photoperiod control the beginning and end of the photosynthetically active season. Elevated temperature (ET) has advanced spring warming and delayed autumn cooling while photoperiod remains unchanged. We assessed the effects of warming on the length of the photosynthetically active season of three provenances of Pinus strobus L. seedlings from different latitudes, and evaluated the accuracy of the photochemical reflectance index (PRI) and the chlorophyll/carotenoid index (CCI) for tracking the predicted variation in spring and autumn phenology of photosynthesis among provenances. Seedlings from northern, local and southern P. strobus provenances were planted in a temperature‐free‐air‐controlled enhancement (T‐FACE) experiment and exposed to ET (+1.5/3°C; day/night). Over 18 months, we assessed photosynthetic phenology by measuring chlorophyll fluorescence, gas exchange, leaf spectral reflectance and pigment content. During autumn, all seedlings regardless of provenance followed the same sequence of phenological events with the initial downregulation of photosynthesis, followed by the modulation of non‐photochemical quenching and associated adjustments of zeaxanthin pool sizes. However, the timing of autumn downregulation differed between provenances, with delayed onset in the southern provenance (SP) and earlier onset in the northern relative to the local provenance, indicating that photoperiod at the provenance origin is a dominant factor controlling autumn phenology. Experimental warming further delayed the downregulation of photosynthesis during autumn in the SP. A provenance effect during spring was also observed but was generally not significant. The vegetation indices PRI and CCI were both effective at tracking the seasonal variations of energy partitioning in needles and the differences of carotenoid pigments indicative of the stress status of needles. These results demonstrate that PRI and CCI can be useful tools for monitoring conifer phenology and for the remote monitoring of the length of the photosynthetically active season of conifers in a changing climate.     

东北地区5种阔叶树苗木对火烧的生理响应

以3年生水曲柳、胡桃楸、蒙古栎、黄菠萝、白桦为研究对象,研究3种火烧处理(T1处理:对叶片火烧;T2处理:对枝火烧;T3处理:对茎火烧)对幼树丙二醛(MDA)含量、叶绿素含量和净光合速率的影响。结果显示:5种幼树火害叶(T1处理)丙二醛含量与对照相比都显著提高,说明幼树叶片细胞都受到了火的影响,发生了膜脂过氧化作用。水曲柳、胡桃楸、白桦火害叶(T1处理)叶绿素含量与对照相比显著提高;水曲柳、胡桃楸火害叶(T1处理)叶绿素a/b与对照相比显著降低。火烧处理后幼树新生叶丙二醛含量的变化因物种而异。5种幼树3种火烧处理后新生叶叶绿素含量除蒙古栎的茎处理和胡桃楸的枝处理显著降低外,大多表现为升高的趋势;新生叶叶绿素a/b的变化因物种而异。5种幼树3种火烧处理后新生叶净光合速率除蒙古栎的茎处理显著降低外,其他都有不同程度的提高。表明火烧提高了幼树的光合作用能力。     

Spatial heterogeneity of tree diversity response to climate warming in montane forests

Many studies reported biotic change along a continental warming gradient. However, the temporal and spatial change of tree diversity and their sensitivity to climate warming might differ from region to region. Understanding of the variation among studies with regard to the magnitude of such biotic changes is minimal, especially in montane ecosystems. Our aim is to better understand changes in spatial heterogeneity and temporal dynamics of mountain tree communities under climate warming over the past four decades. In 2017, we resurveyed and recorded all tree species from 107 long‐term monitoring plots that were first studied between 1974 and 1976. These plots were located in montane forests in the Giant Panda National Park (GPNP), China. Our results showed that spatial differences were found in tree species diversity changes response to mean annual temperature change over the past four decades. Tree species richness increased significantly under climate warming in Minshan (MS) and Xiaoxiangling (XXL) with higher warming rate than Qionglai (QLS) and Liangshan (LS). The trees species diversity in MS and XXL were more sensitive to climatic warming. MS and XXL should receive priority protection in the next conservation plan of the GPNP. The GPNP should avoid taking a “one‐size‐fits‐all” approach for diversity conservation due to spatial heterogeneity in plant community dynamics.     

Earlier plant flowering in spring as a response to global warming in the Washington, DC, area

Evidence for global warming is inferred from spring advances in first-flowering in plants. The trend of average first-flowering times per year for the study group shows a significant advance of 2.4 days over a 30-year period. When 11 species that exhibit later first-flowering times are excluded from the data set, the remaining 89 show a significant advance of 4.5 days. Significant trends for earlier-flowering species range from -3.2 to -46 days, while those for later-flowering species range from +3.1 to +10.4 days. Advances of first-flowering in these 89 species are directly correlated with local increase in minimum temperature (T _min).     

秦岭山区植被春季物候的海拔敏感性

植被物候作为自然界规律性、周期性的现象,对自然环境尤其是气候变化有着重要的指示作用,研究其时空变化特征对陆地植被生态环境监测具有重要意义。本研究采用Savitzky-Golay滤波法重建秦岭山区2001—2018年MODIS增强植被指数时间序列影像,利用动态阈值法提取研究区春季物候信息(返青期),并对返青期多年平均值和年际变化与海拔、坡度进行相关分析。结果表明: 海拔每升高100 m,植被返青期推迟1.82 d;返青期的年际变化趋势主要集中在0~5 d·(10 a)^-1。其中,呈推迟趋势的像元主要分布在低海拔地区,呈提前趋势的像元主要分布在高海拔地区。高海拔地区返青期的年际变化比低海拔地区复杂;秦岭山区植被返青期存在南北差异。北坡植被返青期多年平均值较南坡早2.9 d,南坡植被返青期的推迟程度大于北坡。南北坡植被返青期的年际变化在低海拔地区呈推迟趋势,且南北坡相差不大,而提前趋势在中高海拔地区存在显著差异。     

Leaf and root phenology and biomass of Eriophorum vaginatum in response to warming in the Arctic

北极地区气候变暖对莎草地上和地下部分物候和生物量的影响 北极地区的土壤和植被中存储了大量的碳,在气候变化的大背景下,北极升温速度几乎是地球其他地区的2倍。由于缺乏同步测量,尚不清楚北极地区植被地上部分和地下部分的物候和生物 量对气候变化的反应。在2016和2017年的生长季节,我们在北极的Toolik Lake站点上建立了一个移植花园,并沿纬度变化从高到低依次从 Sagwon、Toolik Lake和Coolfoot这3个站点移植了3种不同生态类型的莎草(Eriophorum vaginatum)。一半莎草用作增温处理,另一半为控制处理。我们用物候相机、手持式光谱仪和微根窗分别观测3种生态型莎草的绿色度、归一化植被指数(NDVI)和根长动态,根据NDVI和根长计算了叶片和细根的生物量。研究发现,莎草的叶和根生长是异步的,叶片开始生长的时间比根系生长的时间早约28天。气温升高1°C会延迟叶片衰老的时间,从而延长生长期,但温度升高对根系物候没有显着影响,变暖在统计学上没有增加叶片和根的生物量。此外,叶片生长的季节动态受气温的影响,但根的生长与土壤融化深度有关。因此,我们建议在使用碳和养分循环模型时,应将叶和根成分分开考虑,因为地上和地下的以及功能属性可能对气候变暖有不同的反应。