Hypoxia, defined as dissolved oxygen (DO) in water < 2 mg L-1, has occurred worldwide in estuarine and coastal environments during the past five decades. Estuarine and coastal hypoxia not only alters regional biogeochemical processes and also affects biodiversity and fisheries. It is well known that climate warming and eutrophication are increasingly important to hypoxia occurrence in terrestrial aquatic environments, the mechanisms underlying estuarine and coastal hypoxia, however, are still poorly constrained, mostly due to the limited long-term observation and interpretation.

In a new study published in the journal JGR Biogeosciences, authors compared DO concentrations and the driving factors of hypoxia between northwestern and southern Hong Kong and Mirs Bay.

According to the study, deoxygenation was weak in the bottom layer in northwestern Hong Kong, although the DO was consistently undersaturated, whereas a rapid decrease in the annual minimum DO was observed in the bottom layer in southern Hong Kong and Mirs Bay. “The seasonal DO depletion and/or hypoxia in the bottom water was accompanied by supersaturated DO and high Chl-a in surface water in southern Hong Kong, indicating local excessive productivity and triggering oxygen depletion” comments Dr. Wwi Qian from the Key Laboratory for Humid Subtropical Eco-geographical Processes of the Ministry of Education, Fujian Normal University, China.

The predeoxygenation of bottom water and long water residence time have contributed to the deoxygenation in Mirs Bay. Water stratification could exacerbate hypoxia by preventing oxygen replenishment from the surface to the bottom layers. The upwelling water from the South China Sea and/or Kuroshio contributed inappreciably to the significant deoxygenation in southern Hong Kong and Mirs Bay.

“These results suggest that enhanced productivity and oxygen consumption, combined with stratification and currents, are increasingly driving hypoxia in the Pearl River Estuary and adjacent areas” concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona

Reference: Qian, W., Zhang, S., Tong, C., Sardans, J., Peñuelas, J., Li, X. 2022. Long-term Patterns of Dissolved Oxygen Dynamics in the Pearl River Estuary. JGR Biogeosciences 127(7), e2022JG006967, doi: 10.1029/2022JG006967.

Climatic warming has lengthened the photosynthetically active season in recent decades, thus affecting the functioning and biogeochemistry of ecosystems, the global carbon cycle, and climate. The temperature response of carbon uptake phenology varies spatially and temporally, even within species, and the daily total intensity of radiation may play a role.

In a new study, published in the journal Global Change Biology, authors empirically modelled the thresholds of temperature and radiation under which daily carbon uptake is constrained in the temperate and cold regions of the Northern Hemisphere, which include temperate forests, boreal forests, alpine, and tundra biomes.

According to the study, radiation will constrain the trend towards longer growing seasons with future warming, but differently during the start and end of season and depending on the biome type and region. The study revealed that radiation is a major factor limiting photosynthetic activity that constrains the phenology response to temperature during the end-of-season. The beginning of carbon uptake, on the other hand, is highly sensitive to temperature but not constrained by radiation at the hemispheric scale. Dr. Adrià Descals from CREAF-CSIC says “Our results show that the photosynthetically active season in evergreen needleleaved forests begins shortly after conditions for growth become favorable and ends when these conditions get worse.” He also says, “It is important to take into account radiation, temperature, and their covariance when modeling the photosynthetically active season in evergreen needleleaved forests and their responses to climatic warming.” 

The study shows that the senescence stage has a low temperature dependency due to the constraints of radiation, and this might be a reason for the lower magnitude in the end-of-season delay than the start-of-season advance.

“This study thus revealed that while at the end-of-season the phenology response to warming is constrained at the hemispheric scale, at the start-of-season the advance of spring onset may continue, even if it is at a slower pace”, concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona

Reference: Descals, A., Verger, A., Yin, G., Filella, I., Fu, Y.H., Piao, S., Janssens, I.A., Peñuelas, J. 2022. Radiation‐constrained boundaries cause nonuniform responses of the carbon uptake phenology to climatic warming in the Northern Hemisphere. Global Change Biology, doi: 10.1111/gcb.16502, in press.

As air temperature rises, the phenological cycle of Northern Hemisphere (NH) ecosystems is shifting progressively towards earlier leaf emergence and delayed leaf senescence, which leads to rapid lengthening of the active growing season.

Vegetation biophysics have long been recognized as a key regulator of seasonal air temperature climatology. For example, in early spring, the rate of air temperature increase rapidly decreases after leaf unfolding (typically for deciduous forests) due to increased transpiration after leaf-out that can effectively cool the leaf surface.

In a new study published in the journal Nature Communications, authors go into the critical role of plants in local temperature seasonality suggesting that greening will alter the seasonality of NH warming at annual to decadal timescales.

According to the study, vegetation greening also affects climate by interacting with other land-surface (e.g., snow or soil moisture) and atmospheric (e.g., water vapor, cloud, and circulation) processes the effects of which vary both geographically and seasonally. Thus, seasonal greening of Northern Hemisphere (NH) ecosystems, due to extended growing periods and enhanced photosynthetic activity, could modify near-surface warming by perturbing land-atmosphere energy exchanges, yet this biophysical control on warming seasonality is underexplored.

“We show that summer greening effectively dampens NH warming by −0.15 ± 0.03 °C for 1982–2014 due to enhanced evapotranspiration. However, greening generates weak temperature changes in spring (+0.02 ± 0.06 °C) and autumn (−0.05 ± 0.05 °C), because the evaporative cooling is counterbalanced by radiative warming from albedo and water vapor feedbacks. Moreover, greening-triggered energy imbalance is propagated forward by atmospheric circulation to subsequent seasons and causes sizable time-lagged climate effects. Overall, greening makes winter warmer and summer cooler, attenuating the seasonal amplitude of NH temperature” explains Dr. Xu Lian from the Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing, China.

Thus, the study highlights the need to better understand these biophysical processes operating both within and across seasons so that their potential time-lagged climate benefits and/or counterproductive consequences will not be overlooked.

“These findings demonstrate complex tradeoffs and linkages of vegetation-climate feedbacks among seasons and highlights the need to better understand these biophysical processes operating both within and across seasons so that their potential time-lagged climate benefits and/or counterproductive consequences will not be overlooked”, concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona, who adds: “The regulatory role of greening on seasonal climate also has implications for adaptation planning and decision-making, as greening is now increasingly shaped by human land-use practices such as afforestation and reforestation”.

Reference: Lian, X., Jeong, S., Park, C-E., Xu, H., Li, L.Z.X., Wang, T., Gentine, P., Peñuelas, J., Piao, S. 2022. Biophysical impacts of northern vegetation changes on seasonal warming patterns. Nature Communications (2022) 13:3925.  Doi: 10.1038/s41467-022-31671-z.

Trees play a vital role in the biosphere. As key agents in the flow of energy and matter, they protect catchments and stabilize drainage areas, sequester carbon, and regulate climate on local to global scale. Trees also provide habitat for a large proportion of the diversity of the world’s vertebrates, invertebrates, and fungi. The magnitude of many of these functions and services increases as tree diversity increases, and greater functional diversity of tree assemblages enhances ecosystem productivity and stability. However, continued global forest loss and degradation has decimated biodiversity among tree and tree-dependent organisms.

In a new study published in the journal Proceedings of the National Academy of Sciences, authors analyze a recently developed global database of 46,752 tree species’ ranges to:

1. assess range protection and anthropogenic pressures for tree species
2. identify priority areas for conservation of tree diversity considering multiple diversity dimensions
3. assess the geographic distribution of current protected areas and different potential conservation prioritization scenarios and their respective coverage of global tree species diversity.

According to this research study, globally, 83.8% of the 46,752 tree species evaluated in this analysis are subject to moderate to very high human pressure, with protected areas (PA) grid cells covering only ≤25% of the ranges for 23.5% of tree species. Further, a total of 6,377 small-range tree species remain completely unprotected, according to the study. At the same time, a total of 14.8% tree species experience high to very high human pressure even within existing PAs.

Further analysis carried out by the authors found existing PA grid cells are estimated to cover only about half of the critical areas for tree diversity, as quantified by taxonomic, phylogenetic and functional diversity dimensions. These results highlight the pressing need for stronger protection of Earth’s tree diversity. “Our results also show that expanding PAs according to the top 17% and especially the 50% priority areas, would yield strong improvements in PA coverage of trees, as would implementing some of the major proposals for increased general biodiversity protection, notably the Global 200 Ecoregions framework”, explains Dr. Guo from the Aarhus University (Denmark) and the East China Normal University (China).

The priority areas identified for trees match well to the Global 200 Ecoregions framework, revealing that priority areas for trees would in large part also optimize protection for terrestrial biodiversity overall.

“Based on range estimates for an unprecedented number of tree species, our findings show that a large proportion of tree species receive limited protection by current PAs and are under substantial human pressure. Improved protection of biodiversity overall would robustly benefit global tree diversity”, concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona.

Reference: Guo, W-Y., Serra-Diaz, J.M., Schrodt, F., Eiserhardt, W.L., Maitner, B.S., Merow, C., Violle, C., Anand, M., Belluau, M., Bruun, H.H., Byun, C., Catford, J.A., Cerabolini, B.E.L., Chacón-Madrigal, E., Ciccarelli, D., Cornelissen, J.H.C., Dang-Le, A.T., de Frutos, A., Dias, A.S., Giroldo, A.B., Guo, K., Gutiérrez, A.G., Hattingh, W., He, T., Hietz, P., Hough-Snee, N., Jansen, S., Kattge, J., Klein, T., Komac, B., Kraft, N., Kramer, K., Lavorel, S., Lusk, C.H., Martin, A.R., Mencuccini, M., Michaletz, S.T., Minden, V., Mori, A.S., Niinemets, U., Onoda, Y., Peñuelas, J., Pillar, V.D., Pisek, J., Robroek, B.J.M., Schamp, B., Slot, M., Egon Sosinski Jr., E., Soudzilovskaia, N.A., Thiffault, N., van Bodegom, P., van der Plas, F., Wright, J.J., Bing Xu, W., Zheng, J., Enquist, B.J., Svenning, J.C.. 2022. High exposure of global tree diversity to human pressure. Proceedings of the National Academy of Sciences 119 (25), e2026733119. Doi: 10.1073/pnas.2026733119 1.

Trees may benefit from advanced springs in cold humid areas but not in dry areas

Under accelerating global change, large changes are happening in the onset, duration and cessation of the vegetative season in extratropical ecosystems. These changes directly influence vegetation phenology. Numerous studies have shown a tight link between thermal conditions and leaf phenology, but there is still a lack of knowledge on the impacts of phenological changes on tree growth since the beneficial effects of spring warmth on growing season productivity can be dramatically offset by increasing carbon losses due to summer droughts or autumn warming. Tree stem wood is the primary long-term carbon storage pool in forests. A wood-oriented view on phenological impacts is thus essential for predicting changes in growth and productivity.

In a new study published in the journal Nature Ecology and Evolution, authors assessed the relationships between the start of the thermal growing season and tree growth across the extratropical Northern Hemisphere using 3,451 tree-ring chronologies and daily climatic data for 1948–2014. According to the study an earlier start of the thermal growing season promoted growth in regions with high ratios of precipitation to temperature but limited growth in cold–dry regions. “Path analyses carried out indicated that an earlier start of the thermal growing season enhanced growth primarily by alleviating thermal limitations on wood formation in boreal forests and by lengthening the period of growth in temperate and Mediterranean forests” comments Prof Eryuan Liang, from the State Key Laboratory of Tibetan Plateau Earth System, Resources and Environment (TPESRE), Chinese Academy of Sciences, China.

“Semi-arid and dry subalpine forests, however, did not benefit from an earlier onset of growth and a longer growing season, presumably due to associated water loss and/or more frequent early spring frosts. These emergent patterns of how climatic impacts on wood phenology affect tree growth at regional to hemispheric scales hint at how future phenological changes may affect the carbon sequestration capacity of extratropical forest ecosystems”, explains Dr. Gao from the same research institute.

Authors addressed these questions by investigating the relationships between the thermal start of season (TSOS) and tree radial growth across the extratropical Northern Hemisphere with correlation analyses and by identifying the dominant mechanisms controlling the relationships in path analyses for several regions with contrasting climates. A total of 3451 tree-ring width chronologies and daily climatic data for 1948-2014 were used to conduct these analyses.

Areas where tree growth benefit from an advanced TSOS are generally located at the higher latitudes (above 60°N), in central Europe, as well as in eastern and western coastal North America. These cool and humid regions are not strongly limited by water availability during the growing season. The regions with negative effects of advanced TSOS on growth were mainly located on the Colorado Plateau and the Tibetan Plateau, which correspond to cold and dry conditions, where forests are typically limited by a number of factors including low temperatures, drought events, and poor soil fertility.

The study further asked why a changing TSOS affects tree growth and tested a series of hypotheses: (1) an advanced TSOS will extend the vegetative season, so that trees have more time to grow; (2) an advanced TSOS will result in higher heat accumulation, so that trees can grow faster; (3) an advanced TSOS will alter the soil moisture conditions and thereby affect tree growth. Based on these hypotheses, authors proposed a path model and decomposed the effect of advanced TSOS on growth. The study found distinct latitudinal responses:

• In boreal forests of northern Asia and Europe, advanced TSOS enhanced tree growth primarily due to the alleviation of cold stress.
• In the temperate forests of central Europe and the eastern US coast, as well as in forests of the Mediterranean region and along the western US coast, advanced TSOS also enhanced growth, but primarily due to the extension of the growing season.
• In semi-arid forests of the Colorado Plateau and dry subalpine forests of the Tibetan Plateau, advanced TSOS did not benefit growth, as a longer growing season induces both atmospheric and soil drought there and increases the risk of tree exposure to spring frost

“This study reveals how climate affects tree growth through wood phenology and contributes to improving our ability to predict trends in the capacity of forests to sequester carbon at regional to global scales, especially in extratropical forest ecosystems” concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona.

Reference: Gao, S., Liang, E., Liu, R., Babst, F., Camarero, J.J., Fu, Y.H., Piao, S., Rossi, S., Shen, M., Wang, T., Peñuelas, J. 2022. An earlier start of the thermal growing season enhances tree growth in cold humid areas but not in dry areas. Nature Ecology and Evolution. Doi: 10.1038/s41559-022-01668-4

Un avançament de la temporada de creixement dels arbres millora el seu creixement en àrees fredes i humides però no en àrees seques

Els efectes del canvi global inclouen grans canvis en l’inici, la durada i el final de la temporada vegetativa de les plantes. Nombrosos estudis han demostrat un vincle estret entre les condicions tèrmiques i la fenologia de les fulles, però encara manca informació sobre els impactes d’aquests canvis fenològics en el creixement dels arbres, ja que els efectes beneficiosos de la calor primaveral en la productivitat de la temporada de creixement poden ser dràsticament contrarestats per l’augment de les pèrdues de carboni a causa de les sequeres estivals o de l’escalfament de la tardor. La fusta del tronc dels arbres és el principal magatzem de carboni a llarg termini als boscos, de manera que estudiar  els impactes fenològics a la fusta és crucial per a predir els canvis en el creixement i la productivitat de les plantes.

En un nou estudi publicat a la revista Nature Ecology and Evolution, els autors van avaluar les relacions entre el canvi climàtic i el creixement dels arbres a l’hemisferi nord extratropical, tot utilitzant 3451 cronologies del creixement radial dels arbres i dades climàtiques diàries entre 1948 i 2014. Segons l’estudi, el progressiu escalfament climàtic va promoure el creixement en regions amb elevades precipitacions i temperatures, però un creixement limitat en regions fredes i seques. El Prof. Eryuan Liang, de l’Acadèmia de Ciències de la Xina, explica que les anàlisis realitzades van indicar que un avançament de la temporada de creixement generat per l’escalfament climàtic va millorar el creixement principalment a causa de la reducció de les limitacions tèrmiques en la formació de fusta als boscos boreals i també a l’allargar el període de creixement als boscos temperats i mediterranis.

• 

El Dr. Gao, del mateix institut de recerca, afegeix que els boscos subalpins secs i semiàrids, en canvi, no es van beneficiar d’aquest avançament i major durada de la temporada de creixement, presumiblement a causa de la pèrdua d’aigua associada i /o a una major freqüència de gelades primaverals. Aquests patrons emergents de com els impactes climàtics en la fenologia de la fusta afecten al creixement dels arbres a escales regionals i hemisfèriques, suggereixen la manera com els canvis fenològics futurs poden afectar a la capacitat de segrest de carboni dels ecosistemes forestals.

Les àrees on el creixement dels arbres es beneficia d’un avançament de la temporada de creixent generalment es trobaven en les latituds més altes (per sobre de 60 ° N), a l’Europa central, així com a les costes est i oest d’Amèrica del Nord. Aquestes regions fredes i humides no estan molt limitades per la disponibilitat d’aigua durant la temporada de creixement. Les regions amb efectes negatius de l’avançament de la temporada de creixent es van situar principalment a l’altiplà de Colorado i l’altiplà tibetà, que corresponen a regions fredes i seques, on els boscos solen estar limitats per una sèrie de factors que inclouen baixes temperatures, sequera i sòls pobres.

L’estudi es va preguntar també per què un avançament de la temporada de creixent afecta el creixement dels arbres i amb aquest objectiu va testar una sèrie d’hipòtesis: (1) un avançament de la temporada de creixent estendria la temporada vegetativa, de manera que els arbres tindrien més temps per créixer; (2) un avançament de la temporada de creixent donaria com a resultat una major acumulació de calor, de manera que els arbres podrien créixer més ràpid; (3) un avançament de la temporada de creixent alteraria les condicions d’humitat del terra i, per tant, afectaria al creixement dels arbres. En base a aquestes hipòtesis, els autors van realitzar diferents anàlisis estadístiques i van trobar diferents respostes en funció de la latitud:

• Als boscos boreals del nord d’Àsia i Europa, l’avançament de la temporada de creixent va millorar el creixement dels arbres, principalment a causa de la reducció de l’estrès per fred.
• Als boscos temperats de l’’Europa central i la costa est dels EUA, així com als boscos de la regió mediterrània i al llarg de la costa occidental dels EUA, l’avançament de la temporada de creixement també va millorar el creixement, però principalment a causa de l’extensió de la temporada.
• Als boscos semiàrids de l’altiplà de Colorado i als boscos subalpins secs de l’altiplà tibetà, l’avançament de la temporada de creixent no va beneficiar el creixement, ja que l’allargament de la temporada indueix allà sequera tant atmosfèrica com del sòl i augmenta el risc d’exposició dels arbres a les gelades primaverals.

El Prof. Josep Peñuelas del CREAF-CSIC Barcelona conclou que aquest estudi revela com el clima afecta el creixement dels arbres a través de la fenologia de la fusta i contribueix a millorar la nostra capacitat per predir tendències en la capacitat dels boscos per capturar carboni a escales regionals i globals, especialment en ecosistemes forestals extratropicals.

Referència: Gao, S., Liang, E., Liu, R., Babst, F., Camarero, J.J., Fu, Y.H., Piao, S., Rossi, S., Shen, M., Wang, T., Peñuelas, J. 2022. An earlier start of the thermal growing season enhances tree growth in cold humid areas but not in dry areas. Nature Ecology and Evolution. Doi: 10.1038/s41559-022-01668-4

Un inicio avanzado de la temporada de crecimiento mejora el crecimiento de los árboles en áreas frías y húmedas pero no en áreas secas

Los efectos del cambio global acelerado incluyen grandes cambios en el inicio, la duración y el final de la temporada vegetativa en los ecosistemas extratropicales. Numerosos estudios han demostrado un vínculo estrecho entre las condiciones térmicas y la fenología de las hojas, pero todavía falta información sobre los impactos de estos cambios fenológicos en el crecimiento de los árboles, ya que los efectos beneficiosos del calor primaveral en la productividad de la temporada de crecimiento pueden ser drásticamente contrarrestados por el aumento de las pérdidas de carbono debido a las sequías estivales o al calentamiento otoñal. La madera del tronco de los árboles es el principal almacén de carbono a largo plazo en los bosques, de forma que los estudios de los impactos del calentamiento climático sobre la fenología de la madera son, por lo tanto, esenciales para predecir los cambios en el crecimiento y la productividad y por tanto el almacenamiento de carbono.

En un nuevo estudio publicado en la revista Nature Ecology and Evolution, los autores evaluan las relaciones entre el calentamiento climático y el crecimiento de los árboles en el hemisferio norte extratropical, utilizando 3451 cronologías del crecimiento radial de los árboles y datos climáticos diarios entre 1948 y 2014. Según el estudio, un inicio avanzado de la temporada de crecimiento promovió el crecimiento en regiones con altas precipitaciones y temperaturas, pero un crecimiento limitado en regiones frías y secas. El Prof. Eryuan Liang, de la Academia de Ciencias de China, explica que los análisis realizados indican que un inicio avanzado de la temporada de crecimiento mejora el crecimiento principalmente debido a la reducción de las limitaciones térmicas en la formación de madera en los bosques boreales y también a alargar el período de crecimiento en los bosques templados y mediterráneos.

El Dr. Gao, del mismo instituto de investigación, añade que los bosques subalpinos secos y semiáridos, sin embargo, no se benefician de este inicio avanzado y de esta mayor duración de la temporada de crecimiento, presumiblemente debido a la pérdida de agua asociada y/o a las mayor frecuencia de heladas primaverales. Estos patrones emergentes de cómo los impactos climáticos en la fenología de la madera afectan al crecimiento de los árboles a escalas regionales y hemisféricas, sugieren la forma cómo los cambios fenológicos futuros pueden afectar a la capacidad de secuestro de carbono de los ecosistemas forestales extratropicales.  

Las áreas en las que el crecimiento de los árboles se beneficia de un avance de la temporada de crecimiento generalmente se encuentran a  latitudes más altas (por encima de 60 ° N), en Europa central, así como en la costa este y oeste de América del Norte. Estas regiones frías y húmedas no están altamente limitadas por la disponibilidad de agua durante la temporada de crecimiento. Las regiones con efectos negativos del avance de la temporada de crecimiento se ubican principalmente en la meseta de Colorado y la meseta tibetana, que corresponden a regiones frías y secas, donde los bosques suelen estar limitados por una serie de factores que incluyen bajas temperaturas, eventos de sequía y suelos pobres.

El estudio se preguntó además por qué un avance de la temporada de crecimiento afecta al crecimiento de los árboles y para ello testó una serie de hipótesis: (1) un avance de la temporada de crecimiento extendería la temporada vegetativa, de modo que los árboles tendrían más tiempo para crecer; (2) un avance de la temporada de crecimiento daría como resultado una mayor acumulación de calor, de modo que los árboles podrían crecer más rápido; (3) un avance de la temporada de crecimiento alteraría las condiciones de humedad del suelo y, por lo tanto, afectaría al crecimiento de los árboles. Con base a estas hipótesis, los autores realizaron diferentes análisis estadísticos y encontraron respuestas distintas en función de la latitud:

• En los bosques boreales del norte de Asia y Europa, el avance de la temporada de crecimiento mejoró el crecimiento de los árboles, principalmente debido a la reducción del estrés por frío.
• En los bosques templados de Europa central y la costa este de los EE. UU., así como en los bosques de la región mediterránea y a lo largo de la costa occidental de los EE. UU., el avance de la temporada de crecimiento también mejoró el crecimiento, pero principalmente debido a la extensión de la temporada de crecimiento.
• En los bosques semiáridos de la meseta de Colorado y los bosques subalpinos secos de la meseta tibetana, el avance de la temporada de crecimiento no benefició el crecimiento, ya que una temporada más larga induce allí sequía tanto atmosférica como del suelo y aumenta el riesgo de exposición de los árboles a las heladas primaverales.

El Prof. Josep Peñuelas del CREAF-CSIC. Barcelona concluye que este estudio revela cómo el clima afecta al crecimiento de los árboles a través de la fenología de la madera y contribuye a mejorar nuestra capacidad para predecir tendencias en la capacidad de los bosques para capturar carbono a escalas regionales y globales, especialmente en ecosistemas forestales extratropicales.

Referencia: Gao, S., Liang, E., Liu, R., Babst, F., Camarero, J.J., Fu, Y.H., Piao, S., Rossi, S., Shen, M., Wang, T., Peñuelas, J. 2022. An earlier start of the thermal growing season enhances tree growth in cold humid areas but not in dry areas. Nature Ecology and Evolution. Doi: 10.1038/s41559-022-01668-4

La ciència ja ha demostrat que el canvi climàtic està avançant la primavera fenològica. Fins ara, els hiverns suaus provocats per l’escalfament global se’n consideraven la causa principal. Tot i això, un estudi publicat avui a la revista Nature Climate Changeafegeix que la manca de pluja també provoca que les plantes brotin abans d’hora a l’hemisferi nord. En aquesta zona del planeta, les pluges han disminuït la seva freqüència els darrers trenta anys i ara es demostra que això afecta també el calendari natural de les plantes. La recerca, liderada per Jian Wang, de la Ohio State University dels EEUU, i per Josep Peñuelas, professor d’investigació del CSIC al CREAF, relaciona per primera vegada la manca de pluja i el despertar prematur de la natura, concretament preveu un avançament addicional de la primavera biològica d’entre 1’2 i 2’2 dies per dècada com a conseqüència només de la minva en la freqüència de les pluges prevista per aquest segle.  

Menys precipitació vol dir menys nuvolositat, el que dona més hores de sol,  temperatures més altes al migdia, i nits més fredes que avancen l’acumulació de fred requerida per a la brotada de les fulles. El còctel de condicions confon les plantes i les fa brotar abans. 

“Aquest hivern estem vivint una situació paradigmàtica per entendre els resultats d’aquest article. No plou i tenim gelades i contrastos forts que han fet avançar la primavera de forma evident. Tot i que aquest estudi parla de clima, i no hem de confondre la meteorologia d’aquest hivern amb la climatologia, sí que la situació que estem vivint ens ajuda a entendre com la manca de nuvolositat arriba a confondre les nostres plantes”, explica Josep Peñuelas. 

Per dur a terme la recerca l’equip ha mesurat el fluxos de carboni de la vegetació, ja que quan les plantes es desperten comencen a fer la fotosíntesi i canvien els fluxos de carboni, han registrat in situ la sortida de les fulles i han comprovat a gran escala amb imatges de satèl·lit els canvis en la verdor de la vegetació.

La manca de núvols les confon

El fet és comprensible. Si els hiverns cada cop tenen menys pluges això vol dir que hi a menys núvols. Els cels clars donen contrastos forts de temperatura entre el dia i la nit i la temperatura de dia també s’enfila molt més amunt. De la mateixa manera, sense el filtre de la nuvolositat les plantes reben radiació solar durant moltes més hores. De nit, a la inversa, l’ambient es refreda ràpidament i gela fàcilment. Tot plegat confon les plantes perquè ho perceben com les senyals típiques que la primavera ja ha arribat: acumulen abans les hores de fred i de radiació que necessiten i, juntament amb els contrastos de temperatura típics de la primavera, desperten de la dormició hivernal abans d’hora.

“Si les plantes broten abans, comencen abans a fer la fotosíntesi i això afecta els cicles de carboni d’arreu del món. Saber que els descens en la freqüència de pluges també afecta aquest ritme natural és un coneixement clau a tenir en compte en les prediccions de canvi climàtic”, conclou Josep Peñuelas.

El CREAF i el Meteocat complementen els seus estudis més científics amb iniciatives ciutadanes que acosten els efectes del canvi climàtic als calendaris naturals a la societat. Durant aquest any 2021 han llançat FenoTwin amb la col·laboració de la Fundació Espanyola per a la Ciència i la Tecnologia (FECYT). Aquesta iniciativa pretén elaborar mapes per veure com canvia la natura a cada estació però unint la feina de satèl·lits, que ho segueixen des de l’aire, i de voluntaris i voluntàries, que ho segueixen des del mateix territori. Els mapes resultants són el que s’anomena un digital twin o bessó digital. Per fer-ho possible, el projecte consta d’una vessant educativa per obtenir dades a la vegada que es fan tallers educatius on s’expliquen conceptes tan importants com els cicles dels éssers vius, l’observació de la terra, o el propi canvi climàtic i els incentiva a apropar-se a la natura per conèixer-la i estudiar-la.

L’observatori de ciència ciutadana RitmeNatura convida també a persones anònimes a trobar evidències de que la primavera s’està avançant a tot arreu, quines espècies desperten abans, si veuen floració prematura, l’arribada de les oronetes, etc. Són canvis en els cicles biològics que tothom pot detectar i que són molt útils després per fer avançar la ciència.

La gent pot participar-hi enviant fotografies a iNaturalist.org/projects/ritmenatura, una plataforma digital que els darrers dies s’ha omplert d’imatges d’ametllers, cirerers o mimoses en flor.

Article:

Jian Wang, Desheng Liu, Philippe Ciais, Josep Peñuelas. Decreasing rainfall frequency contributes to earlier leaf onset in northern ecosystems. Nature Climate Change. Doi: 10.1038/s41558-022-01285-w

Font: Blog CREAF

The journal Science publishes on Friday 21th a perspective article by CREAF researchersJosep Peñuelas and Jordi Sardans on the imbalance of nutrients on Earth, its effects on life and possible solutions.

Human action is altering the balance of nirogen and phosphorus, two elements essential for life on earth. Image: chemistryworld.com

The text ‘The global nitrogen-phosphorus imbalance‘ is based on recent research data from both specialists, and sets out the state of the issue and its scope for the international scientific community. They also propose alternatives and solutions aimed at political decision-makers.

According to Peñuelas and Sardans, ecosystems and species are at risk due to the global nutrient imbalance caused by the different ratio of nitrogen and phosphorus in land and water. These two elements are essential for life, and their ratio is being altered by human action. Both nitrogen and phosphorus affect the growth rate of micro-organisms, plants and animals. Plant species need CO2 for photosynthesis and nutrients to build their structures, of which the ratio of nitrogen to phosphorus is key. In addition, for optimal growth, adequate amounts and ratios of nitrogen and phosphorus are required. In recent decades, however, humans have enriched the biosphere with nitrogen through over-fertilisation and thus changed its relationship with phosphorus.

“International environmental bodies should address the risk to the biosphere posed by the nitrogen-phosphorus imbalance in a coordinated global policy.”

JOSEP PEÑUELAS, researcher at CREAF & CSIC.

Alternatives to imbalance

Among the possible alternatives, experts recommend increasing the efficiency of nitrogen and phosphorus use and cycling through precision farming, which avoids disproportionate fertiliser application. They also advocate applying methods, both management and innovative biotechnology, that enhance the efficiency of plants in capturing nutrients and benefiting from phosphorus sources. Other necessary policies that Peñuelas and Sardans point to include stimulating phosphorus recycling through national and regional regulations, subsidies or legislation, as well as reducing livestock production. Such solutions are in the early stages of implementation.

Too much nitrogen

Humans are over-fertilising the biosphere with nitrogen through nitrogen oxides emitted from burning fossil fuels, planting nitrogen-fixing crops, and using enriched fertilisers that leach into waterways. Although human activities have also increased the amount of phosphorus in soils and waters – for example, applying phosphorus-rich fertilisers and detergents – the overall increase in phosphorus in the soil is still less than that of nitrogen.

In fact, these are two synergistic problems. On the one hand, the presence of nutrients in the soil has increased disproportionately, and on the other hand, the balance between nitrogen and phosphorus has been disturbed. When there are too many nutrients in the environment, it becomes eutrophic: the increase of nutrients in freshwater causes algae and phytoplankton to grow out of control, until the ecosystem collapses. As a result, some countries have developed water treatment strategies to reduce the concentration of both chemicals. However, the technology used by water treatment plants retains more phosphorus than nitrogen, which encourages even more imbalance between the two nutrients.

Stability in doubtThe global imbalance between nitrogen and phosphorus may be even greater at the local and regional level, as nitrogen and phosphorus inputs are not evenly distributed around the world.

The global imbalance between nitrogen and phosphorus may be even greater at local and regional scales, as the inputs of both compounds are not evenly distributed around the world. Phosphorus, for example, is less soluble in water and does not volatilise, often adsorbs and precipitates in soil in mineral form, and remains buried in sediments. It therefore tends to remain close to its source of emission. In contrast, nitrogen is much more water-soluble and much more volatile, which makes it easier for it to disperse over a larger radius from its emission source.

The biological impacts of the increasing imbalance between the two nutrients have been observed in inland water bodies, on the structure and function of soil living communities, as well as on the species composition of plant communities. The lack of stability will have an increasing impact as the imbalance continues to shift in the same direction.

Phosphorus human crisis

Food security and agricultural production are the main victims of this imbalance, which has a direct impact on natural ecosystems and people. Nitrogen-containing fertilisers have an unlimited source – the atmosphere – from which this nutrient can be extracted through the Haber-Bösh reaction. This innovation has allowed its production to increase steadily, as well as its use as a fertiliser since the 1950s. However, sources of phosphorus have been largely limited to mines and are concentrated in very few countries, such as Morocco.Phosphorus may become economically inaccessible to low-income and food-deficit countries as it becomes depleted or unavailable for geopolitical and economic reasons.

In this sense, phosphorus could become economically inaccessible to low-income and food-deficit countries as these sources are depleted or become unavailable due to geopolitical and economic issues. In the future, phosphorus-producing countries are likely to manage their reserves to maximise the profits of their domestic mining and agricultural industries, making phosphorus-based fertilisers increasingly unaffordable for farmers in poorer countries and further exacerbating the imbalance between the two nutrients in regions where the problem is most acute. It would be a crisis that would further aggravate the economic gap between rich and poor countries.

Phosphorus and nitrogen lack

The lack of balance between these two elements in the soil changes the chemical composition of crops and can affect the health of people who consume products grown on these soils, thus creating a public health problem. For example, in regions where there is excessive use of inorganic and organic phosphorus fertilisers, phosphorus accumulates in soils and water bodies. Food produced in these environments can cause the local population to consume excess phosphorus, which can have negative implications for their health. Nutrient imbalance is also known to affect infectious and non-infectious human diseases that are strongly associated with diet, such as coeliac disease. CREAF researchers already warned in 2021 that excessive nitrogen fertilisation of wheat crops could explain the high prevalence of coeliac disease.

As if that were not enough, CREAF researchers point out that when the relationship between nitrogen and phosphorus is destabilised, human activities also generate imbalances between other elements. For example, changes have been observed in the relationship between carbon and nitrogen, in relation to iron, zinc, calcium and potassium, among others, in plant tissues. This indirectly leads to the fact that organisms, communities and ecosystems on planet earth are having their entire elementome, their elemental composition, modified.

Source: Blog CREAF

Nitrogen enrichment buffers phosphorus limitation by mobilizing mineral-bound soil phosphorus in grasslands. Phosphorus (P) limitation is expected to increase due to nitrogen (N)-induced terrestrial eutrophication, although most soils contain large P pools immobilized in minerals (Pi) and organic matter (Po).

In a new study published in the journal Ecology authors assessed whether transformations of these P pools can increase plant available pools alleviating P limitation under enhanced N availability.

The mechanisms underlying these possible transformations were explored by combining results from a 10-year field N-addition experiment and a 3700-km transect covering wide ranges in soil pH, soil N, aridity, leaching, and weathering that can affect soil P status in grasslands.

“Nitrogen addition promoted dissolution of immobile Pi (mainly Ca-bound recalcitrant P) to more available forms of Pi (including Al- and Fe-bound P fractions and Olsen P) by decreasing soil pH from 7.6 to 4.7, but did not affect Po”, explain Dr. Wang from State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China.

According to this study, soil total P declined by 10% from 385±6.8 to 346±9.5 mg kg-1, while available-P increased by 546% from 3.5±0.3 to 22.6±2.4 mg kg-1 after 10-year N addition experiment, associated with an increase in Pi mobilization, plant uptake, and leaching. Similar to the N-addition experiment, the drop in soil pH from 7.5 to 5.6 and increase in soil N concentration along the grassland transect were associated with an increased ratio between relatively mobile Pi and immobile Pi.

These results provide a new mechanistic understanding of the important role of soil Pi mobilization in maintaining plant P supply and accelerating biogeochemical P cycles under anthropogenic N enrichment. This mobilization process temporarily buffers ecosystem P-limitation or even causes P eutrophication but will extensively deplete soil P pools in the long run

“Our results also suggest that ecosystem P cycling model predictions should incorporate the interactions of N and P cycles by considering N enrichment effects on accelerating soil P cycling rates, that models can be further refined via delineating the dependence of Pi transformation on precipitation, and the ubiquitous role of soil pH in driving the biogeochemical pathways of Pi transformation”, concludes Prof. Josep Penuelas from CREAF-CSIC Barcelona.

Reference: Wang, R., Yang, J., Liu, H., Sardans, J., Zhang, Y., Wang, X., Wei, C., Lü, X., Dijkstra, F.A., Jiang, Y., Han, X., Peñuelas, J. 2021. Nitrogen enrichment buffers phosphorus limitation by mobilizing mineral-bound soil phosphorus in grasslands. Ecology, doi: 10.1002/ecy.3616