Understorey vegetation moderates climate in open forests: The role of the skirt-forming grass tree Xanthorrhoea semiplana F.Muell

Microsites are created by abiotic and biotic features of the landscape and may provide essential habitats for the persistence of biota. Forest canopies and understorey plants may moderate wind and solar radiation to create microclimatic conditions that differ considerably from regional climates. Skirt-forming plants, where senescent leaves create hut-like cavities around the stem, create microsites that are sheltered from ambient conditions and extreme weather events, constituting potential refuges for wildlife. We investigate day and night temperatures and humidity for four locations (grass tree cavities, soil, 20 cm above-ground, 1 m above-ground) in a South Australian forest with relatively open canopy of stringybark eucalypts (Eucalyptus baxteri, E. obliqua) and an understorey of skirt-forming grass trees (Xanthorrhoea semiplana) at 5, 10, 20, and 40 m from the forest edge. We also measured the percentage of canopy and understorey covers. Generally, temperature and humidity differed significantly between more sheltered (grass tree cavities, soil) and open-air microsites, with the former being cooler during the day and warmer and more humid during the night. Furthermore, our results suggest that canopy cover tends to decrease, and understorey cover tends to increase, the temperature of microsites. Distance to the edge was not significantly related to temperature for any microsite, suggesting that the edge effect did not extend beyond 10 m from the edge. Overall, grass trees influenced microclimatic conditions by forming a dense understorey and providing cavities that are relatively insulated. The capacity of grass tree cavities to buffer external conditions increased linearly with ambient temperatures, by 0.46°C per degree increase in maximum and 0.25°C per degree decrease in minimum temperatures, potentially offsetting climate warming and enabling persistence of fauna within their thermal limits. These climate moderation properties will make grass trees increasingly important refuges as extreme weather events become more common under anthropogenic climate change.     

Tropical forests are thermally buffered despite intensive selective logging

Tropical rainforests are subject to extensive degradation by commercial selective logging. Despite pervasive changes to forest structure, selectively logged forests represent vital refugia for global biodiversity. The ability of these forests to buffer temperature‐sensitive species from climate warming will be an important determinant of their future conservation value, although this topic remains largely unexplored. Thermal buffering potential is broadly determined by: (i) the difference between the “macroclimate” (climate at a local scale, m to ha) and the “microclimate” (climate at a fine‐scale, mm to m, that is distinct from the macroclimate); (ii) thermal stability of microclimates (e.g. variation in daily temperatures); and (iii) the availability of microclimates to organisms. We compared these metrics in undisturbed primary forest and intensively logged forest on Borneo, using thermal images to capture cool microclimates on the surface of the forest floor, and information from dataloggers placed inside deadwood, tree holes and leaf litter. Although major differences in forest structure remained 9–12 years after repeated selective logging, we found that logging activity had very little effect on thermal buffering, in terms of macroclimate and microclimate temperatures, and the overall availability of microclimates. For 1°C warming in the macroclimate, temperature inside deadwood, tree holes and leaf litter warmed slightly more in primary forest than in logged forest, but the effect amounted to <0.1°C difference between forest types. We therefore conclude that selectively logged forests are similar to primary forests in their potential for thermal buffering, and subsequent ability to retain temperature‐sensitive species under climate change. Selectively logged forests can play a crucial role in the long‐term maintenance of global biodiversity.     

The role of capacitance in the water balance of Andean giant rosette species

Abstract Pith water storage capacity and its role in plant-water relations were studied in seven giant rosette species of the genus Espeletia from the Venezuelan Andes. Readily available water from the pith was calculated to be capable of sustaining mean transpiration for up to 2.5 h. The relative importance of water stored in the pith, however, differed among species. The species that grow in the higher and colder environments tended to have a greater capacitance than the species that grow in the lower and less extreme environments. The pith volume per unit leaf area (PV/LA) was found to be a good indicator of the relative water storage capacity of the adult individuals of each species. Diurnal fluctuations in leaf water potential were not as pronounced in the species with higher PV/LA values. The species-specific PV/LA was highly correlated with the leaf turgor loss point and with the total resistance to water flow from soil to leaves. These results suggested that species-specific capacitance in the genus Espeletia is a response to temperature-limited soil water availability and that cold tropical environments with frequent subfreezing temperatures tend to select for high water storage capacity in giant rosette plants.     

Water balance in Hemizonia luzulifolia: the role of extracellular polysaccharides

Abstract. The role of extracellular water in ameliorating drought stress was examined in Hemizonia luzulifola , an annual composite that comprises two subspecies differing significantly in the amount of extracellular polysaccharide within basal leaves. Rosette leaves of the high polysaccharide (HP) ssp were more than 30% pectin on a dry weight basis in contrast to only 4% in the low polysaccharide (LP) ssp. Concomitant with this difference in polysaccharide content was a significant difference in the dehydration response of leaves. Near full hydration, relative capacitances of HP leaves (0.7 MPa^-1) were an order of magnitude greater than the LP leaves (0.08 MPa^-1). Relative capacitance of the polysaccharide alone was 1.5 MPa^-1. The weight of water per unit leaf area was not significantly different in the two taxa. Nevertheless, the pectin-like polysaccharides significantly altered the distribution of metabolically available water from primarily cell-stored water in the LP ssp to apoplasmic and symplasmic capacitors in leaves of the HP ssp. The consequence of this apoplasmic water store with colloidal properties is that the Ψ-dependence of leaf capacitance ceases to be linked directly to cell water relations. Transfer resistances for water movement between capacitors and the xylem near full hydration (0 to -0.5 MPa) were significantly larger in the HP leaf. This difference in transfer resistance was interpreted to be the result of a large resistance to water movement between the polysaccharide and the xylem. Because of these large transfer resistances, the apoplasmic capacitor probably buffers cells at lower water potentials under transient water fluxes than expected from laboratory measurements made during slow desiccation. Field measurements support this conclusions; HP leaves were better buffered than LP leaves at midday water potentials.     

Hydraulic conductance and the maintenance of water balance in flowers

Flowers face desiccating conditions, yet little is known about their ability to transport water. We quantified variability in floral hydraulic conductance (K_flower) for 20 species from 10 families and related it to traits hypothesized to be associated with liquid and vapour phase water transport. Basal angiosperm flowers had trait values associated with higher water and carbon costs than monocot and eudicot flowers. K_flower was coordinated with water supply (vein length per area, VLA) and loss (minimum epidermal conductance, g_min) traits among the magnoliids, but was insensitive to variation in these traits among the monocots and eudicots. Phylogenetic independent contrast (PIC) correlations revealed that few traits had undergone coordinated evolution. However, VLA and the desiccation time (T_des), the quotient of water content and g_min, had significant trait and PIC correlations. The near absence of stomata from monocot and eudicot flowers may have been critical in minimizing water loss rates among these clades. Early divergent, basal angiosperm flowers maintain higher K_flower because of traits associated with high rates water loss and water supply, while monocot and eudicot flowers employ a more conservative strategy of limiting water loss and may rely on stored water to maintain turgor and delay desiccation.     

Topographic and vegetation drivers of thermal heterogeneity along the boreal–grassland transition zone in western Canada: Implications for climate change refugia

Climate change refugia are areas that are relatively buffered from contemporary climate change and may be important safe havens for wildlife and plants under anthropogenic climate change. Topographic variation is an important driver of thermal heterogeneity, but it is limited in relatively flat landscapes, such as the boreal plain and prairie regions of western Canada. Topographic variation within this region is mostly restricted to river valleys and hill systems, and their effects on local climates are not well documented. We sought to quantify thermal heterogeneity as a function of topography and vegetation cover within major valleys and hill systems across the boreal–grassland transition zone.Using iButton data loggers, we monitored local temperature at four hills and 12 river valley systems that comprised a wide range of habitats and ecosystems in Alberta, Canada (N = 240), between 2014 and 2020. We then modeled monthly temperature by season as a function of topography and different vegetation cover types using general linear mixed effect models.Summer maximum temperatures (T _max) varied nearly 6°C across the elevation gradient sampled. Local summer mean (T _mean) and maximum (T _max) temperatures on steep, north‐facing slopes (i.e., low levels of potential solar radiation) were up to 0.70°C and 2.90°C cooler than highly exposed areas, respectively. T _max in incised valleys was between 0.26 and 0.28°C cooler than other landforms, whereas areas with greater terrain roughness experienced maximum temperatures that were up to 1.62°C cooler. We also found that forest cover buffered temperatures locally, with coniferous and mixedwood forests decreasing summer T _mean from 0.23 to 0.72°C and increasing winter T _min by up to 2°C, relative to non‐forested areas.Spatial predictions of temperatures from iButton data loggers were similar to a gridded climate product (ClimateNA), but the difference between them increased with potential solar radiation, vegetation cover, and terrain roughness.Species that can track their climate niche may be able to compensate for regional climate warming through local migrations to cooler microsites. Topographic and vegetation characteristics that are related to cooler local climates should be considered in the evaluation of future climate change impacts and to identify potential refugia from climate change.     

Natural forests exhibit higher carbon sequestration and lower water consumption than planted forests in China

Large‐scale planted forests (PF) have been given a higher priority in China for improving the environment and mitigating climate change relative to natural forests (NF). However, the ecological consequences of these PF on water resource security have been less considered in the national scale. Moreover, a critically needed comparison on key ecological effects between PF and NF under climate change has rarely been conducted. Here, we compare carbon sequestration and water consumption in PF and NF across China using combination of remote sensing and field inventory. We found that, on average, NF consumed 6.8% (37.5 mm per growing season) less water but sequestered 1.1% (12.5 g C m^?2 growing season^?1) more carbon than PF in the period of 2000–2012. While there was no significant difference in water consumption (p = 0.6) between PF and NF in energy‐limited areas (dryness index [DI] < 1), water consumption was significantly (p < 0.001) higher in PF than that in NF in water‐limited regions (DI > 1). Moreover, a distinct and larger shift of water yield was identified in PF than in NF from the 1980s to the 2000s, indicating that PF were more sensitive to climate change, leading to a higher water consumption when compared with NF. Our results suggest NF should be properly valued in terms of maximizing the benefits of carbon sequestration and water yield. Future forest plantation projects should be planned with caution, particularly in water‐limited regions where they might have less positive effect on carbon sequestration but lead to significant water yield reduction.     

Hydrology and water balance of Lake Peipsi

Lake Peipsi is a large (3558 km²) but shallow (up to 15.3 m deep) tripartite waterbody hydrologically investigated already since the 19th century. Surface discharge by rivers accounts for more than 80% of its water balance. The residental time of water is about two years in the whole lake but several times less in its shallower southern parts receiving the biggest rivers. The annual water regime is characterized by the highest water in spring, the average amplitude of yearly level fluctuations being 1.15 m. There are known long-term hydrological cycles of 80–90, about 22, 9–11, and even fewer years. Several temporary wind-dependent circular currents exist in the subsurface layers. Alternating transitional currents occur in the narrowest part of the lake. Five different periods are distinguishable in the annual thermic cycle. The duration of the stable ice cover is up to five months (December-April) in the shallower parts but a shorter time in the centre of the lake. The maximum surface temperature in July usually reaches 21–22°C in the open regions but considerably higher (up to 27–28°C in some years) on shallows. The unstable summer stratification is often disturbed by waves and currents. Biological summer, with surface temperatures over 10°C, lasts on an average 134 days.     

不同补水方式对白星花金龟水分平衡的影响

为研究水分散失和水分补充对新疆新害虫白星花金龟Potosia brevitarsis Lewis的影响,在30℃恒温条件下,采用重量法测定白星花金龟脱水过程以及不同补水方式下(补蒸馏水;补盐水;补糖水)体内水分含量的变化,并与步甲、拟步甲的水分代谢进行比较。结果表明,白星花金龟的脱水与拟步甲科的网目拟地甲Opatrum subaratum Fald相似,在10h内脱水率均约为5%,而斑步甲Anisodactylus signatus 10h内脱水率约为20%。不同补水处理后,白星花金龟体内含水量迅速增加,随后继续脱水;脱水10d后,补蒸馏水、补盐水和补糖水处理的白星花金龟脱水率分别为28%,27%和21%,而未补水白星花金龟的脱水率为34%;未补水处理的甲虫脱水率和补蒸馏水和补盐水处理之间无显著性差异,而和补糖水处理之间存在显著性差异。未补水、补蒸馏水、补盐水和补糖水处理的LT50分别约为9,12,13和17d,补糖水能有效延长甲虫的存活时间。糖能有效地增加白星花金龟体内含水量,对维持其体内水分平衡起重要作用。     

The role of insect water balance in pollination ecology: Xylocopa and Calotropis

Summary Two carpenter bees (Xylocopa spp.) in southern Israel both use the asclepiad Calotropis procera as a primary nectar source. This plant genus is coevolved with carpenter bees, and aspects of the insect-flower interaction in Israel suggest that the smaller bee, X. sulcatipes, is the natural co-adapted pollinator, a view borne out by the geographical distributions of the species concerned. There are significant mismatches between the plant and the larger X. pubescens, involving physical fit and behaviour. These mismatches are particularly evident when the physiologies of the bees and the plant are considered. The different sizes and colours of the two bees lead to different daily activity patterns, only X. sulcatipes being thermally suited to, and thus abundant at, times of maximum nectar production by Calotropis. Similarly the water requirements of X. sulcatipes are finely balanced with the water production in the floral nectar; this bee gains just enough water when foraging to restore its blood concentration and production in the floral nectar; for deposition in the nest. X. pubescens does not incur net water loss in flight and gains too much water from Calotropis flowers, necessitating copious urination and tonguelashing. Hence physiological information can be of use in deciphering insect-plant coevolutionary patterns, and the water component of nectar is confirmed as a potentially major determinant of foraging activities. The circumstances where this will be particularly true, and cases where it may not apply, are discussed.     

Vocal buffering of the stress response: exposure to conspecific vocalizations moderates urinary cortisol excretion in isolated marmosets

For many species, the presence of a significant social partner can lessen the behavioral and physiological responses to stressful stimuli. This study examined whether a single, individually specific, signature vocalization (phee call) could attenuate the physiological stress response that is induced in marmosets by housing them in short-term social isolation. Utilizing a repeated-measures design, adult marmosets (n=10) were temporarily isolated from their long-term pair mate and exposed to three conditions: signature vocalizations from the pair mate, phee calls from an unfamiliar opposite sex individual, or no auditory stimuli. Levels of urinary cortisol were monitored as a physiological indicator of the stress response. Urinary cortisol levels were also monitored, while subjects remained undisturbed in their home cages to provide baseline levels. Temporarily isolated marmosets showed significantly higher levels of urinary cortisol than undisturbed marmosets. However, the nature of the acoustic stimulus experienced during isolation led to differences in the excretion of urinary cortisol. Isolated marmosets exposed to a familiar pair mate's vocalization showed significantly lower levels of urinary cortisol than when exposed to unfamiliar marmoset vocalizations (P <0.04) or to no auditory stimuli (P <0.03). Neither the duration of pairing nor the quality of relationship in the pair (indexed by spatial proximity scores) predicted the magnitude of reduction in cortisol in the familiar vocalization condition. The results presented here provide the first evidence that a single, individually specific communication signal can decrease the magnitude of a physiological stress response in a manner analogous to the physical presence of a social partner, a process we term "vocal buffering."     

The European carbon balance. Part 3: forests

We present a new synthesis, based on a suite of complementary approaches, of the primary production and carbon sink in forests of the 25 member states of the European Union (EU‐25) during 1990–2005. Upscaled terrestrial observations and model‐based approaches agree within 25% on the mean net primary production (NPP) of forests, i.e. 520±75 g C m^?2 yr^?1 over a forest area of 1.32 × 10⁶ km² to 1.55 × 10⁶ km² (EU‐25). New estimates of the mean long‐term carbon forest sink (net biome production, NBP) of EU‐25 forests amounts 75±20 g C m^?2 yr^?1. The ratio of NBP to NPP is 0.15±0.05. Estimates of the fate of the carbon inputs via NPP in wood harvests, forest fires, losses to lakes and rivers and heterotrophic respiration remain uncertain, which explains the considerable uncertainty of NBP. Inventory‐based assessments and assumptions suggest that 29±15% of the NBP (i.e., 22 g C m^?2 yr^?1) is sequestered in the forest soil, but large uncertainty remains concerning the drivers and future of the soil organic carbon. The remaining 71±15% of the NBP (i.e., 53 g C m^?2 yr^?1) is realized as woody biomass increments. In the EU‐25, the relatively large forest NBP is thought to be the result of a sustained difference between NPP, which increased during the past decades, and carbon losses primarily by harvest and heterotrophic respiration, which increased less over the same period.     

Environmental change and the carbon balance of Amazonian forests

Extreme climatic events and land‐use change are known to influence strongly the current carbon cycle of Amazonia, and have the potential to cause significant global climate impacts. This review intends to evaluate the effects of both climate and anthropogenic perturbations on the carbon balance of the Brazilian Amazon and to understand how they interact with each other. By analysing the outputs of the Intergovernmental Panel for Climate Change (IPCC) Assessment Report 4 (AR4) model ensemble, we demonstrate that Amazonian temperatures and water stress are both likely to increase over the 21st Century. Curbing deforestation in the Brazilian Amazon by 62% in 2010 relative to the 1990s mean decreased the Brazilian Amazon's deforestation contribution to global land use carbon emissions from 17% in the 1990s and early 2000s to 9% by 2010. Carbon sources in Amazonia are likely to be dominated by climatic impacts allied with forest fires (48.3% relative contribution) during extreme droughts. The current net carbon sink (net biome productivity, NBP) of +0.16 (ranging from +0.11 to +0.21) Pg C year^?1 in the Brazilian Amazon, equivalent to 13.3% of global carbon emissions from land‐use change for 2008, can be negated or reversed during drought years [NBP = ?0.06 (?0.31 to +0.01) Pg C year^?1]. Therefore, reducing forest fires, in addition to reducing deforestation, would be an important measure for minimizing future emissions. Conversely, doubling the current area of secondary forests and avoiding additional removal of primary forests would help the Amazonian gross forest sink to offset approximately 42% of global land‐use change emissions. We conclude that a few strategic environmental policy measures are likely to strengthen the Amazonian net carbon sink with global implications. Moreover, these actions could increase the resilience of the net carbon sink to future increases in drought frequency.     

Social modulation of fear: Facilitation vs buffering

Social behaviors largely constitute mutual exchanges of social cues and the responses to them. The adaptive response also requires proper interpretation of the current context. In fear behaviors, social signals have bidirectional effects—some cues elicit or enhance fear whereas other suppress or buffer it. Studies on the social facilitation and social buffering of fear provide evidence of competition between social cues of opposing meanings. Co‐expression of opposing cues by the same animal may explain the contradicting outcomes from the interaction between naive and frightened conspecifics, which reflect the fine balance between fear facilitation and buffering. The neuronal mechanisms that determine that balance provide an exciting target for future studies to probe the brain circuits underlying social modulation of emotional behaviors.     

橡胶与砂仁间作小气候特点初探

橡胶与砂仁间作小气候特点初探周再知,郑海水,杨曾奖,尹光天（中国林业科学院热带林业研究所,广州５１０５２０）ＲｅｓｅａｒｃｈｏｎＭｉｃｒｏｃｌｉｍａｔｉｃＣｈａｒａｃｔｅｒｉｓｔｉｃｉｎＰｌａｎｔａｔｉｏｎｏｆＲｕｂｂｅｒＩｎｔｅｒｃｒｏｐｐｅｄｗｉ...     

Behavioural plasticity under a changing climate; how an experimental local climate affects the nest construction of the zebra finch Taeniopygia guttata

Successful reproduction in most avian species is dependent on the construction of a nest that provides protection and a suitable microclimate for the eggs and developing nestlings. Observational studies suggest that climatic variation may affect the structure of the nest, but to date there have been no attempts to experimentally determine the role that local climate plays in the construction of a suitable nest. Using a within‐individual counter balanced design we investigated how nest composition and construction differ in zebra finches breeding in ambient conditions of 18°C and 30°C. We found that at 18°C birds built nests that were over 20% heavier, and with significantly more thread and less grass than those built at 30°C. Our results highlight the degree of plasticity in nest building behaviour in relation to local ambient conditions. These results suggest that nest building behaviour is one route through which birds can respond to a changing climate and modify the microclimate of their nest in line with projected changes in ambient conditions.