• Energy Research

AbstractTropical soils contain huge carbon stocks, which climate warming is projected to reduce by stimulating organic matter decomposition, creating a positive feedback that will promote further warming. Models predict that the loss of carbon from warming soils will be mediated by microbial physiology, but no empirical data are available on the response of soil carbon and microbial physiology to warming in tropical forests, which dominate the terrestrial carbon cycle. Here we show that warming caused a considerable loss of soil carbon that was enhanced by associated changes in microbial physiology. By translocating soils across a 3000 m elevation gradient in tropical forest, equivalent to a temperature change of ± 15 °C, we found that soil carbon declined over 5 years by 4% in response to each 1 °C increase in temperature. The total loss of carbon was related to its original quantity and lability, and was enhanced by changes in microbial physiology including increased microbial carbon‐use‐efficiency, shifts in community composition towards microbial taxa associated with warmer temperatures, and increased activity of hydrolytic enzymes. These findings suggest that microbial feedbacks will cause considerable loss of carbon from tropical forest soils in response to predicted climatic warming this century.

AbstractTropical forests face increasing climate risk1,2, yet our ability to predict their response to climate change is limited by poor understanding of their resistance to water stress. Although xylem embolism resistance thresholds (for example, $$\varPsi $$ Ψ 50) and hydraulic safety margins (for example, HSM50) are important predictors of drought-induced mortality risk3–5, little is known about how these vary across Earth’s largest tropical forest. Here, we present a pan-Amazon, fully standardized hydraulic traits dataset and use it to assess regional variation in drought sensitivity and hydraulic trait ability to predict species distributions and long-term forest biomass accumulation. Parameters $$\varPsi $$ Ψ 50 and HSM50 vary markedly across the Amazon and are related to average long-term rainfall characteristics. Both $$\varPsi $$ Ψ 50 and HSM50 influence the biogeographical distribution of Amazon tree species. However, HSM50 was the only significant predictor of observed decadal-scale changes in forest biomass. Old-growth forests with wide HSM50 are gaining more biomass than are low HSM50 forests. We propose that this may be associated with a growth–mortality trade-off whereby trees in forests consisting of fast-growing species take greater hydraulic risks and face greater mortality risk. Moreover, in regions of more pronounced climatic change, we find evidence that forests are losing biomass, suggesting that species in these regions may be operating beyond their hydraulic limits. Continued climate change is likely to further reduce HSM50 in the Amazon6,7, with strong implications for the Amazon carbon sink.

Aim Climate change causes shifts in species distributions, or ‘migrations’. Despite the centrality of species distributions to biodiversity conservation, the demonstrated large migration of tropical plant species in response to climate change in the past, and the expected sensitivity of species distributions to modern climate change, no study has tested for modern species migrations in tropical plants. Here we conduct a first test of the hypothesis that increasing temperatures are causing tropical trees to migrate to cooler areas. Location Tropical Andes biodiversity hotspot, south-eastern Peru, South America. Methods We use data from repeated (2003/04–2007/08) censuses of 14 1-ha forest inventory plots spanning an elevational gradient from 950 to 3400 m in Manu National Park in south-eastern Peru, to characterize changes in the elevational distributions of 38 Andean tree genera. We also analyse changes in the genus-level composition of the inventory plots through time. Results We show that most tropical Andean tree genera shifted their mean distributions upslope over the study period and that the mean rate of migration is approximately 2.5–3.5 vertical metres upslope per year. Consistent with upward migrations we also find increasing abundances of tree genera previously distributed at lower elevations in the majority of study plots. Main conclusions These findings are in accord with the a priori hypothesis of upward shifts in species ranges due to elevated temperatures, and are potentially the first documented evidence of present-day climate-driven migrations in a tropical plant community. The observed mean rate of change is less than predicted from the temperature increases for the region, possibly due to the influence of changes in moisture or non-climatic factors such as substrate, species interactions, lags in tree community response and/or dispersal limitations. Whatever the cause(s), continued slower-than-expected migration of tropical Andean trees would indicate a limited ability to respond to increased temperatures, which may lead to increased extinction risks with further climate change.

Andean tropical montane forests (TMF) are hotspots of biodiversity that provide fundamental hydrological services as well as carbon sequestration and storage. Agroforestry systems occupy large areas in the Andes but climatic pressures, market volatility and diseases may result inagroforest abandonment, promoting secondary succession. Secondary forests are well-adapted and efficient carbon sinks whose conservation is vital to mitigate and adapt to climate change and to support biodiversity. Little is known, however, about how secondary TMF recover their aboveground biomass (AGB) and composition after abandonment. We established a 1.5 ha plot at 1780 masl on a 30-year old abandoned agroforest and compared it against two control forest plots at similar elevations. Agroforestry legacies influenced AGB leading to far lower stocks (42.3 ± 5.4–59.6 ± 7.9 Mg ha−1 using allometric equations) than those expected after 30 years (106 ± 33 Mg ha−1) based on IPCC standard growth rates for secondary montane forests. This suggests a regional overestimation of mitigation potentials when using IPCC standards. Satellite-derived AGB largely overestimated our plot values (179 ± 27.3 Mg ha−1). Secondary growth rates (1.41–2.0 Mg ha−1 yr−1 for DBH ≥ 10 cm) indicate recovery times of ca. 69 to 97 years to reach average control AGB values (137 ± 12.3 Mg ha−1). This is 26 years above the average residence time of montane forests at our elevation (71 ± 1.91 years) suggesting a non-recovery or far slower recovery to control AGB values. Three variables appear to define this outcome compared to the control plots: lower DBH (15.8 ± 5.9 cm vs 19.8 ± 11.0 cm), lower basal area (12.67 ± 0.7 vs 28.03 ± 1.5 m2 ha−1) and higher abundance of lighter-wood tree genera (0.46 ± 0.10 vs 0.57 ± 0.11 gr cm3) such as Inga, a common shade-tree in Andean agroforests. With 3.2 million hectares committed to restoration, Peru needs to target currently neglected TMF recovery schemes to support biodiversity, water and carbon storage and fulfill its international commitments.

La jacinthe d'eau, Pontederia crassipes, est une plante très envahissante originaire d'Amérique du Sud et l'une des plantes aquatiques les plus envahissantes au monde. Pour son contrôle, la cicadelle Megamelus scutellaris Berg (Hemiptera : Delphacidae), un phloème nourricier également originaire d'Amérique du Sud, a été introduite aux États-Unis et en Afrique du Sud. Compte tenu des scénarios de changement climatique prévus, il est crucial de comprendre leurs impacts sur les agents de lutte biologique. Un sujet intrigant mais à peine exploré, est l'effet des changements climatiques sur les endosymbiotes obligés associés aux mangeoires suceuses de sève. Les planthoppers établissent une relation obligatoire avec les symbiotes de type levure (YLS), des micro-organismes fongiques unicellulaires qui jouent un rôle important dans leur développement, fournissant des nutriments manquants dans leur alimentation. Étant donné que l'augmentation du CO2 atmosphérique affecte la composition chimique des plantes, cela pourrait avoir un impact direct sur leur hôte insecte et sur leur nombre de YLS. Nous avons évalué l'effet de deux environnements CO2 différents : courant (cCO2 − 400 ppm) et élevé (eCO2 − 800 ppm) sur l'abondance de YLS (nombre de cellules YLS/insecte) de M. scutellaris, ainsi que la structure d'âge, le sexe et le poids des insectes. Les femelles plus lourdes hébergeaient plus de YLS sous eCO2, ce qui souligne l'importance de l'interaction des niveaux de CO2 et du poids des insectes dans la formation de l'abondance de YLS. De plus, il y a eu une augmentation significative de l'abondance totale des insectes pour les stades III à V et les adultes dans des conditions eCO2. Cependant, le nombre d'hommes dépassait considérablement celui des femmes dans les deux conditions de CO2. Nos résultats suggèrent un impact positif potentiel de l'eCO2 sur les populations de M. scutellaris, ce qui pourrait, à son tour, améliorer le contrôle de P. crassipes. El jacinto de agua, Pontederia crassipes, es una planta altamente invasiva originaria de América del Sur y una de las plantas acuáticas más invasivas del mundo. Para su control, se ha introducido en EEUU y Sudáfrica el saltamontes Megamelus scutellaris Berg (Hemiptera: Delphacidae), un alimentador de floemas también originario de Sudamérica. Teniendo en cuenta los escenarios de cambio climático previstos, es crucial comprender sus impactos en los agentes de control biológico. Un tema intrigante pero apenas explorado es el efecto de los cambios climáticos en los endosimbiontes obligados asociados con los alimentadores chupadores de savia. Los saltamontes establecen una relación obligada con los simbiontes similares a la levadura (YLS), microorganismos fúngicos unicelulares que desempeñan un papel importante en su desarrollo, proporcionando los nutrientes que faltan en su dieta. Teniendo en cuenta que el aumento del CO2 atmosférico afecta a la composición química de las plantas, esto podría tener un impacto directo en su insecto huésped y en su número de YLS. Evaluamos el efecto de dos entornos de CO2 diferentes: actual (cCO2 − 400 ppm) y elevado (eCO2 − 800 ppm) sobre la abundancia de YLS (número de células YLS/insecto) de M. scutellaris, así como la estructura de edad, sexo y peso de los insectos. Las hembras más pesadas albergaban más YLS bajo eCO2, lo que subraya la importancia de la interacción de los niveles de CO2 y el peso de los insectos para dar forma a la abundancia de YLS. Además, hubo un aumento significativo en la abundancia total de insectos para los estadios III a V y adultos en condiciones de eCO2. Sin embargo, el número de hombres superó significativamente al de mujeres en ambas condiciones de CO2. Nuestros resultados sugieren un posible impacto positivo de eCO2 en las poblaciones de M. scutellaris, lo que a su vez podría mejorar el control de P. crassipes. Water hyacinth, Pontederia crassipes, is a highly invasive plant native to South America and one of the most invasive aquatic plants in the world. For its control, the planthopper Megamelus scutellaris Berg (Hemiptera: Delphacidae), a phloem feeder also native to South America has been introduced to the USA and South Africa. Considering predicted climate change scenarios, understanding their impacts on biological control agents is crucial. An intriguing yet scarcely explored subject, is the effect of climatic changes on the obligate endosymbionts associated with sap-sucking feeders. Planthoppers establish an obligate relationship with yeast-like symbiotes (YLS), unicellular fungal microorganisms that play an important role in their development, providing missing nutrients in their diet. Considering that increased atmospheric CO2 affects plant chemical composition, this might have a direct impact on their insect host and on their number of YLS. We evaluated the effect of two different CO2 environments: current (cCO2 − 400 ppm) and elevated (eCO2 − 800 ppm) on the abundance of YLS (number of YLS cells/insect) of M. scutellaris, as well as the, age structure, sex, and weight of insects. Heavier females harbored more YLS under eCO2 which underscores the importance of the interaction of CO2 levels and insects' weight in shaping the abundance of YLS. Additionally, there was a significant increase in the total abundance of insects for instars III to V and adults under eCO2 conditions. However, male number significantly exceeded that of females under both CO2 conditions. Our results suggest a potential positive impact of eCO2 on M. scutellaris populations, which could, in turn, enhance the control of P. crassipes. صفير الماء، Pontederia crassipes، هو نبات شديد التوغل موطنه أمريكا الجنوبية وواحد من أكثر النباتات المائية توغلاً في العالم. من أجل السيطرة عليها، تم إدخال النطاط النباتي Megamelus scutellaris Berg (Hemiptera: Delphacidae)، وهو مغذي اللحاء الأصلي أيضًا في أمريكا الجنوبية إلى الولايات المتحدة الأمريكية وجنوب إفريقيا. بالنظر إلى سيناريوهات تغير المناخ المتوقعة، فإن فهم آثارها على عوامل المكافحة البيولوجية أمر بالغ الأهمية. من الموضوعات المثيرة للاهتمام التي لم يتم استكشافها إلا نادراً، تأثير التغيرات المناخية على التعايش الداخلي الإلزامي المرتبط بمغذيات امتصاص العصارة. ينشئ النطاطات علاقة ملزمة مع المتكافلات الشبيهة بالخميرة (YLS)، وهي كائنات دقيقة فطرية وحيدة الخلية تلعب دورًا مهمًا في نموها، وتوفر العناصر الغذائية المفقودة في نظامها الغذائي. بالنظر إلى أن زيادة ثاني أكسيد الكربون في الغلاف الجوي تؤثر على التركيب الكيميائي للنبات، فقد يكون لذلك تأثير مباشر على مضيف الحشرات وعلى عدد YLS. قمنا بتقييم تأثير بيئتين مختلفتين من ثاني أكسيد الكربون: التيار (cCO2 − 400 جزء في المليون) والمرتفع (eCO2 − 800 جزء في المليون) على وفرة YLS (عدد خلايا/حشرات YLS) من M. scutellaris، بالإضافة إلى البنية العمرية والجنس ووزن الحشرات. تحمل الإناث الأثقل وزنًا المزيد من YLS تحت eCO2 مما يؤكد على أهمية تفاعل مستويات ثاني أكسيد الكربون ووزن الحشرات في تشكيل وفرة YLS. بالإضافة إلى ذلك، كانت هناك زيادة كبيرة في الوفرة الإجمالية للحشرات للمراحل من الثالث إلى الخامس والبالغين في ظل ظروف ثاني أكسيد الكربون. ومع ذلك، تجاوز عدد الذكور بشكل كبير عدد الإناث في كلتا الحالتين من ثاني أكسيد الكربون. تشير نتائجنا إلى وجود تأثير إيجابي محتمل لثاني أكسيد الكربون eCO2 على مجموعات م. سكوتيلاريس، والذي بدوره يمكن أن يعزز السيطرة على P. crassipes.

AbstractAimGlobal‐scale studies are necessary to draw general conclusions on how trophic interactions vary with urbanization and to explore how the effects of urbanization change along latitudinal gradients. We predict that the intensity of trophic interactions decreases in response to urbanization (quantified by human population density). Since trophic interactions are more intense at lower latitudes, we also expect major impacts of urbanization at higher latitudes, where base levels are essentially lower.LocationGlobal (881 study sites).Time period2000–2021.Major taxa studiedBirds, arthropods and woody plants.MethodsWe compiled global data on insect herbivory and bird predation from studies that employed similar methods and fitted generalized linear mixed models to test how these trophic interactions vary with human population density, latitude and their interactions.ResultsThe intensity of herbivory and predation decreased with an increase in human population density at lower latitudes. Surprisingly, it remained unaffected at intermediate latitudes and even increased at higher latitudes.Main conclusionsThe observed patterns may be attributed to local climate changes in urban areas, such as the Urban Heat Island effect, which disrupts thermal stability in the tropics while increasing niche availability at polar latitudes.