The Response of Soil Processes to Climate Change: Results from Manipulation Studies of Shrublands Across an Environmental Gradient

Predicted changes in climate may affect key soil processes such as respiration and net nitrogen (N) mineralization and thus key ecosystem functions such as carbon (C) storage and nutrient availability. To identify the sensitivity of shrubland soils to predicted climate changes, we have carried out experimental manipulations involving ecosystem warming and prolonged summer drought in ericaceous shrublands across a European climate gradient. We used retractable covers to create artificial nighttime warming and prolonged summer drought to 20-m² experimental plots. Combining the data from across the environmental gradient with the results from the manipulation experiments provides evidence for strong climate controls on soil respiration, net N mineralization and nitrification, and litter decomposition. Trends of 0%–19% increases of soil respiration in response to warming and decreases of 3%–29% in response to drought were observed. Across the environmental gradient and below soil temperatures of 20°C at a depth of 5–10 cm, a mean Q₁₀ of 4.1 in respiration rates was observed although this varied from 2.4 to 7.0 between sites. Highest Q₁₀ values were observed in Spain and the UK and were therefore not correlated with soil temperature. A trend of increased accumulated surface litter mass loss was observed with experimental warming (2%– 22%) but there was no consistent response to experimental drought. In contrast to soil respiration and decomposition, variability in net N mineralization was best explained by soil moisture rather than temperature. When water was neither limiting or in excess, a Q₁₀ of 1.5 was observed for net N mineralization rates. These data suggest that key soil processes will be differentially affected by predicted changes in rainfall pattern and temperature and the net effect on ecosystem functioning will be difficult to predict without a greater understanding of the controls underlying the sensitivity of soils to climate variables.     

Impact of Seasonality on Artificial Drainage Discharge under Temperate Climate Conditions

Artificial drainage systems affect all components of the water and matter balance. For the proper simulation of water and solute fluxes, information is needed about artificial drainage discharge rates and their response times. However, there is relatively little information available about the response of artificial drainage systems to precipitation. To address this need, we analysed 11 datasets from artificial drainage study sites (daily or hourly resolution), one daily dataset from an open ditch system, and three datasets from rainfall simulations on tile‐drained fields. When we considered all 11 artificial drainage study sites, we found that artificial drainage discharge responded to 70% of all rainfall events during the year, and that the response rate differed significantly between 56% summer and 84% in winter. A median of 23% of the yearly precipitation rate is discharged by artificial drainage systems, varying from 9% of the precipitation in summer to 54% of the precipitation in winter. The artificial drainage systems usually started to respond within the first hour under rain fed conditions, and the response time increased at lower rainfall intensities (< 1 mm h^–1). The peak outflow normally occurred within the first two days. The influence of soil texture and land use on artificial drainage discharge rates could not be reproduced properly, due to the spatial high variability caused by other site‐specific properties. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

不同播期对紫花苜蓿生长性状及越冬性的影响研究

采用随机试验设计方法,在宁南旱作农业区进行了不同播期对紫花苜蓿出苗率、生长发育、越冬率和产草量影响的研究。结果表明,在宁南地区人工种植紫花苜蓿的出苗率与播期温度存在极显著正相关关系,而不同播期土壤耕层含水量变化率较小,且基本能满足苜蓿萌发与生长的需要;播期越早,根颈越粗,入土越深,但4月份前播种,出苗率低,群体小且易形成“小老苗”;7月份以后播种。由于生长期短,植株根颈细嫩,越冬率很低或完全冻死。综合不同播期出苗率、产草量和越冬率等因素,认为在宁南地区紫花苜蓿的适宜播种期应在4月30日～6月30日。     

Effects of Climate Change Drivers on Nitrous Oxide Fluxes in an Upland Temperate Grassland

Despite increasing interest in the patterns of trace gas emissions in terrestrial ecosystems, little is known about the impacts of climate change on nitrous oxide (N₂O) fluxes. The aim of this study was to determine the importance of the three main drivers of climate change (warming, summer drought, and elevated CO₂ concentrations) on N₂O fluxes from an extensively managed, upland grassland. Over a 2-year period, we monitored N₂O fluxes in an in situ ecosystem manipulation experiment simulating the climate predicted for the study area in 2080 (3.5°C temperature increase, 20% reduction in summer rainfall and atmospheric CO₂ levels of 600 ppm). N₂O fluxes showed significant seasonal and interannual variation irrespective of climate treatment, and were higher in summer and autumn compared with winter and spring. Overall, N₂O emissions showed a positive correlation with soil temperature and rainfall. Elevated temperature had a positive impact on mean annual N₂O fluxes but effects were only significant in 2007. Contrary to expectations, neither combined summer drought and warming nor the simultaneous application of elevated atmospheric CO₂ concentrations, summer drought and warming had any significant effect on annual N₂O fluxes. However, the maximum N₂O flux rates observed during the study occurred when elevated CO₂ was combined with warming and drought, suggesting the potential for important, short-term N₂O–N losses in enriched CO₂ environments. Taken together, our results suggest that the N₂O responses of temperate, extensively managed grasslands to future climate change scenarios may be primarily driven by temperature effects.     

Species-Independent Down-Regulation of Leaf Photosynthesis and Respiration in Response to Shading: Evidence from Six Temperate Tree Species

The ability to down-regulate leaf maximum net photosynthetic capacity (Amax) and dark respiration rate (Rdark) in response to shading is thought to be an important adaptation of trees to the wide range of light environments that they are exposed to across space and time. A simple, general rule that accurately described this down-regulation would improve carbon cycle models and enhance our understanding of how forest successional diversity is maintained. In this paper, we investigated the light response of Amax and Rdark for saplings of six temperate forest tree species in New Jersey, USA, and formulated a simple model of down-regulation that could be incorporated into carbon cycle models. We found that full-sun values of Amax and Rdark differed significantly among species, but the rate of down-regulation (proportional decrease in Amax or Rdark relative to the full-sun value) in response to shade was not significantly species- or taxon-specific. Shade leaves of sun-grown plants appear to follow the same pattern of down-regulation in response to shade as leaves of shade-grown plants. Given the light level above a leaf and one species-specific number (either the full-sun Amax or full-sun Rdark), we provide a formula that can accurately predict the leaf''s Amax and Rdark. We further show that most of the down regulation of per unit area Rdark and Amax is caused by reductions in leaf mass per unit area (LMA): as light decreases, leaves get thinner, while per unit mass Amax and Rdark remain approximately constant.     

成熟度与烘干温度对结球甘蓝种子质量的影响

以结球甘蓝品种冬升种子为材料,研究了不同成熟度和烘干温度下种子秕粒率、千粒重、发芽率、生理活性情况以及不同烘干温度下种子的含水量.结果表明,结球甘蓝冬升开花后45～55 d采收的种子,发芽率均达到了95%以上;随着种子成熟度提高,其种子质量、发芽活力及其超氧化物歧化酶(SOD)、过氧化物酶(POD)、脱氢酶活性显著上升,而相对电导率显著下降.与对照(自然风干)相比,30～50℃的烘干温度对种子千粒重和秕粒率无显著性影响,也仅在50℃下可使种子的发芽活力显著降低;随着烘干温度的升高,种子的SOD、POD和脱氢酶活性逐渐显著下降,相对电导率则逐渐显著上升;30～50℃烘干6 h种子的含水量由13.3%降至5.4%左右.研究发现,结球甘蓝冬升开花授粉后45 d种子已达到了采收程度,30～50℃烘干6 h种子含水量已达到储藏要求,并且愈接近自然干燥温度(30～40℃)的处理,种子发芽能力愈好;甘蓝种子活力与其SOD、POD和脱氢酶活性呈正相关,而与其相对电导率呈负相关.     

暗绿绣眼鸟春季和冬季取食生态位初步研究

2014年10—12月和2015年3—5月在广西壮族自治区宜州市对暗绿绣眼鸟Zosterops japonicus春季和冬季的取食空间生态位进行了研究,主要记录暗绿绣眼鸟的数量、取食时段、食物种类以及包括取食高度、水平取食位置、取食方向等相关取食行为数据。结果表明,暗绿绣眼鸟为杂食性鸟类,主要采食植物嫩叶、果实,偶尔采食昆虫或花瓣。春季取食的植物有31种,食物生态位宽度为13.86;冬季取食的植物有21种,食物生态位宽度为11.75;春季和冬季的食物生态位重叠度为0.903。春季暗绿绣眼鸟在06∶00—09∶00取食频次最高(占42.93%),而冬季则是在09∶00—12∶00取食频次最高(占38.04%)。卡方独立性检验表明:春季和冬季暗绿绣眼鸟在取食时间和取食高度上的差异均有统计学意义(P0.05),在水平取食位置和取食方向上的差异无统计学意义(P0.05)。     

Ecosystem Processes Show Uniform Sensitivity to Winter Soil Temperature Change Across a Gradient from Central to Cold Marginal Stands of a Major Temperate Forest Tree

Ecosystems - The magnitude and frequency of soil frost events might increase in northern temperate regions in response to climate warming due to reduced insulation caused by declining snow cover....     

Vernalisation of Winter Rye by Negative Temperatures and the Influence of Vernalisation upon the Lamina Length of the First and Second Leaf in Winter Rye, Spring Barley, and Winter Barley

The lowest effective temperature observed for vernalising PetkuaWinter Rye was –4.5° C., whereas –6° to–10° C. did not induce any hastening of flowering.Seedlings of 20–25 mm. length were as susceptible to –3°C. as seeds in the stage at which the radicle had just brokenthrough the pericarp. Vernalising temperatures alternating between7 days +1° C. and 3 days –3° C. were as effectiveas continuous treatment by +1° C. The lamina length of thefirst and second leaf is shortened by raising the vernalisingtemperatures from –3° C. to +3° C. and also isfurther shortened by prolonging the vernalisation period inwinter rye and winter barley. No progressive shortening of thelamina length, however, was observed in spring barley when treatedlike winter barley. This suggests a direct dependence of thelamina length of the first and second leaf on the degree ofvernalisation reached in the embryo.     

The Effect of Gibberellic Acid on the Flowering of Spring and Winter Rye

The effects of leaf applications of gibberellic acid on theflowering of unvernalised and partially vernalised winter ryeand on spring rye have been investigated. A small stimulationof the progress to flowering was obtained but it was subsequentlylost over a period of seven or eight weeks. The stimulationwas not due to a reduction in the vernalisation requirementof the winter variety since similareffects were obtained inspring rye. Treatment with gibberellic acid stimulated meristems of boththe vegetative and reproductive parts of the rye plant. Thehastening of development of floral primordia was consideredto be part of this overall stimulatory effect, which is concernedwith growth rather than with development. The relation between these results and the influence of gibberellicacid on the flowering of some other long- and short-day plantsis briefly discussed.     

Increased Drought Impacts on Temperate Rainforests from Southern South America: Results of a Process-Based,Dynamic Forest Model

Increased droughts due to regional shifts in temperature and rainfall regimes are likely to affect forests in temperate regions in the coming decades. To assess their consequences for forest dynamics, we need predictive tools that couple hydrologic processes, soil moisture dynamics and plant productivity. Here, we developed and tested a dynamic forest model that predicts the hydrologic balance of North Patagonian rainforests on Chiloé Island, in temperate South America (42°S). The model incorporates the dynamic linkages between changing rainfall regimes, soil moisture and individual tree growth. Declining rainfall, as predicted for the study area, should mean up to 50% less summer rain by year 2100. We analysed forest responses to increased drought using the model proposed focusing on changes in evapotranspiration, soil moisture and forest structure (above-ground biomass and basal area). We compared the responses of a young stand (YS, ca. 60 years-old) and an old-growth forest (OG, >500 years-old) in the same area. Based on detailed field measurements of water fluxes, the model provides a reliable account of the hydrologic balance of these evergreen, broad-leaved rainforests. We found higher evapotranspiration in OG than YS under current climate. Increasing drought predicted for this century can reduce evapotranspiration by 15% in the OG compared to current values. Drier climate will alter forest structure, leading to decreases in above ground biomass by 27% of the current value in OG. The model presented here can be used to assess the potential impacts of climate change on forest hydrology and other threats of global change on future forests such as fragmentation, introduction of exotic tree species, and changes in fire regimes. Our study expands the applicability of forest dynamics models in remote and hitherto overlooked regions of the world, such as southern temperate rainforests.     

The Impact of Invasive Earthworms on Soil Respiration and Soil Carbon Within Temperate Hardwood Forests

Improving current understanding of the factors that control soil carbon (C) dynamics in forest ecosystems remains an important topic of research as it plays an integral role in the fertility of forest soils and the global C cycle. Invasive earthworms have the potential to alter soil C dynamics, though mechanisms and effects remain poorly understood. To investigate potential effects of invasive earthworms on forest C, the forest floor, mineral soil, fine root biomass, litterfall and microbial litter decay rates, and total soil respiration (TSR) over a full year were measured at an invaded and uninvaded deciduous forest site in southern Ontario. The uninvaded site was approximately 300 m from the invaded site and a distinct invasion front between sites was present. Along the invasion front, the biomass of the forest floor was negatively correlated with earthworm abundance and biomass. There was no significant difference between litterfall, microbial litter decay, and TSR between the invaded and uninvaded sites, but fine root biomass was approximately 30% lower at the invaded site. There was no significant difference in total soil C pools (0–30 cm) between the invaded and uninvaded sites. Despite profound impacts on forest floor soil C pools, earthworm invasion does not significantly increase TSR, most likely because increased heterotrophic respiration associated with earthworms is largely offset by a decrease in autotrophic respiration caused by lower fine root biomass.     

Cold Hardening of Spring and Winter Wheat and Rape Results in Differential Effects on Growth,Carbon Metabolism,and Carbohydrate Content

The effect of long-term (months) exposure to low temperature (5[deg]C) on growth, photosynthesis, and carbon metabolism was studied in spring and winter cultivars of wheat (Triticum aestivum) and rape (Brassica napus). Cold-grown winter rape and winter wheat maintained higher net assimilation rates and higher in situ CO2 exchange rates than the respective cold-grown spring cultivars. In particular, the relative growth rate of spring rape declined over time at low temperature, and this was associated with a 92% loss in in situ CO2 exchange rates. Associated with the high photosynthetic rates of cold-grown winter cultivars was a 2-fold increase per unit of protein in both stromal and cytosolic fructose-1,6-bisphosphatase activity and a 1.5- to 2-fold increase in sucrose-phosphate synthase activity. Neither spring cultivar increased enzyme activity on a per unit of protein basis. We suggest that the recovery of photosynthetic capacity at low temperature and the regulation of enzymatic activity represent acclimation in winter cultivars. This allow these overwintering herbaceous annuals to maximize the production of sugars with possible cryoprotective function and to accumulate sufficient carbohydrate storage reserve to support basal metabolism and regrowth in the spring.     

Barking Up The Wrong Treelength: The Impact of Gap Penalty on Alignment and Tree Accuracy

Several methods have been developed for simultaneous estimation of alignment and tree, of which POY is the most popular. In a 2007 paper published in Systematic Biology, Ogden and Rosenberg reported on a simulation study in which they compared POY to estimating the alignment using ClustalW and then analyzing the resultant alignment using maximum parsimony. They found that ClustalW+MP outperformed POY with respect to alignment and phylogenetic tree accuracy, and they concluded that simultaneous estimation techniques are not competitive with two-phase techniques. Our paper presents a simulation study in which we focus on the NP-hard optimization problem that POY addresses: minimizing treelength. Our study considers the impact of the gap penalty and suggests that the poor performance observed for POY by Ogden and Rosenberg is due to the simple gap penalties they used to score alignment/tree pairs. Our study suggests that optimizing under an affine gap penalty might produce alignments that are better than ClustalW alignments, and competitive with those produced by the best current alignment methods. We also show that optimizing under this affine gap penalty produces trees whose topological accuracy is better than ClustalW+MP, and competitive with the current best two-phase methods.     

Disentangling the Legacies of Climate and Management on Tree Growth

Ecosystems - Legacies of past climate conditions and historical management govern forest productivity and tree growth. Understanding how these processes interact and the timescales over which they...     

The Impact of Winter Heating on Air Pollution in China

Fossil-fuel combustion related winter heating has become a major air quality and public health concern in northern China recently. We analyzed the impact of winter heating on aerosol loadings over China using the MODIS-Aqua Collection 6 aerosol product from 2004–2012. Absolute humidity (AH) and planetary boundary layer height (PBL) -adjusted aerosol optical depth (AOD^*) was constructed to reflect ground-level PM_2.5 concentrations. GIS analysis, standard statistical tests, and statistical modeling indicate that winter heating is an important factor causing increased PM_2.5 levels in more than three-quarters of central and eastern China. The heating season AOD^* was more than five times higher as the non-heating season AOD^*, and the increase in AOD^* in the heating areas was greater than in the non-heating areas. Finally, central heating tend to contribute less to air pollution relative to other means of household heating.