Our new article “Vegetation restoration in Northern China: A contrasted picture“ was just published in Land Degradation and Development. Lead author Feng Wang was a visiting professor in the Caylor Lab at Princeton for a year back in 2014 and we have been collaborating since then. See the abstract below for a quick overview of the study and results or head over to Land Degradation and Development’s website to read the full paper.
China started a long-term effort to mitigate desertification and ensure the sustainability of its environment by implementing multiple large-scale national ecological restoration projects since 1978, but their success has been highly debated for a long time. Here, we estimated the change of vegetation fraction cover (VFC) in the Three‐North Shelterbelt Programme (TNSP) region over the past three decades on the basis of the Normalized Difference Vegetation Index dataset from the Global Inventory Monitoring and Modeling System. We evaluate the national strategy of vegetation restoration in North China by comparing rainfall patterns, vegetation change, and national ecological restoration programs on the basis of the Global Meteorological Forcing Dataset and the China Forestry Statistical Yearbooks. We find that the western, central, and eastern parts of the TNSP region exhibited a distinct increase in vegetation coverage. The western region had the highest increase in annual precipitation, but this did not result in the highest VFC increase. We infer that ecological restoration activities are the factor leading to the observed increase in VFC in the eastern and central region compared with the western region. The low survival rate of planted trees in the forest of the TNSP region indicates that it is necessary to improve the mode of vegetation restoration to obtain optimal returns and avoid excessive investment. The success of new strategies, for example, natural restoration and quasi-natural afforestation are promising as an alternative method. China’s experiences in reforestation will be very beneficial for other countries to promote land degradation mitigation and vegetation improvement in the arid and semiarid areas.
Our new article “Dew‑induced transpiration suppression impacts the water and isotope balances of Colocasia leaves“ was just published in a special issue of Oecologia honoring the career of Jim Ehleringer. In collaboration with Paul Gauthier and my PhD advisor Kelly Caylor, this paper looks at the effects of dew deposition on the isotope composition of Colocasia esculenta leaf water. See the abstract below for a quick overview of the study and results or head over to Oecologia’s website to read the full paper.Abstract
Foliar uptake of water from the surface of leaves is common when rainfall is scarce and non-meteoric water such as dew or fog is more abundant. However, many species in more mesic environments have hydrophobic leaves that do not allow the plant to uptake water. Unlike foliar uptake, all species can benefit from dew- or fog-induced transpiration suppression, but despite its ubiquity, transpiration suppression has so far never been quantified. Here, we investigate the effect of dew-induced transpiration suppression on the water balance and the isotope composition of leaves via a series of experiments. Characteristically, hydrophobic leaves of a tropical plant, Colocasia esculenta, are misted with isotopically enriched water to reproduce dew deposition. This species does not uptake water from the surface of its leaves. We measure leaf water isotopes and water potential and find that misted leaves exhibit a higher water potential and a more depleted water isotope composition than dry leaves, suggesting a ∼30% decrease in transpiration rate compared to control leaves. We propose three possible mechanisms governing the interaction of water droplets with leaf energy balance: increase in albedo from the presence of dew droplets, decrease in leaf temperature from the evaporation of dew, and local decrease in vapor pressure deficit. Comparing previous studies on foliar uptake to our results, we conclude that transpiration suppression has an effect of similar amplitude, yet opposite sign to foliar uptake on leaf water isotopes.
Our new article, “Dew deposition suppresses transpiration and carbon uptake in leaves” was just published in Agricultural and Forest Meteorology. The work was a collaboration with Kelly Caylor, Sally Thompson’s lab at UC Berkeley, and Tony Rockwell at Harvard University. For this work, we built a leaf energy balance model to test the effects of dew and fog on the leaf water, carbon, and energy balances. We compared our model to data from UC Berkeley’s Blue Oak Ranch Reserve in CA. See the abstract below for a quick overview of the study and results or head to the A&FM website to read the full paper.
Dew deposition occurs in ecosystems worldwide, even in the driest deserts and in times of drought. Although some species absorb dew water directly via foliar uptake, a ubiquitous effect of dew on plant water balance is the interference of dew droplets with the leaf energy balance, which increases leaf albedo and emissivity and decreases leaf temperature through dew evaporation. Dew deposition frequency and amount are expected to be affected by changing environmental conditions, with unknown consequences for plant water stress and ecosystem carbon, water and energy fluxes. Here we present a simple leaf energy balance that characterizes the effect of deposition and the evaporation of dew on leaf energy balance, transpiration, and carbon uptake. The model is driven by five common meteorological variables and shows very good agreement with leaf wetness sensor data from the Blue Oak Ranch Reserve in California. We explore the tradeoffs between energy, water, and carbon balances for leaves of different sizes across a range of relative humidity, wind speed, and air temperature conditions. Our results show significant water savings from transpiration suppression up to 25% for leaf characteristic lengths of 50 cm. CO2 assimilation is decreased by up to 12% by the presence of dew, except for bigger leaves in windspeed conditions below 1 m s−1 when an increase in assimilation is expected.
A new paper entitled ‘Advancing ecohydrology in the changing tropics: Perspectives from early career scientists‘ just appeared in Ecohydrology today. The article is a student-lead paper focusing on current and future threats faced by tropical ecosystems, and what the potential research gaps that would help the scientific community better understand and mitigate some of these threats.
The article stemmed out of the AGU Chapman conference on tropical ecohydrology that I attended in June 2016. All the co-authors of the article are graduate students and early-career scientists from institutions around the world, and it was both a lot a fun and a great learning experience to write this together! You can see the article on the Ecohydrology website HERE.
Tropical ecosystems offer a unique setting for understanding ecohydrological processes, but to date, such investigations have been limited. The purpose of this paper is to highlight the importance of studying these processes—specifically, how they are being affected by the transformative changes taking place in the tropics—and to offer an agenda for future research. At present, the ongoing loss of native ecosystems is largely due to agricultural expansion, but parallel processes of afforestation are also taking place, leading to shifts in ecohydrological fluxes. Similarly, shifts in water availability due to climate change will affect both water and carbon fluxes in tropical ecosystems. A number of methods exist that can help us better understand how changes in land use and climate affect ecohydrological processes; these include stable isotopes, remote sensing, and process-based models. Still, our knowledge of the underlying physical mechanisms, especially those that determine the effects of scale on ecosystem processes, remains incomplete. We assert that development of a knowledge base concerning the effects of transformative change on ecological, hydrological, and biogeochemical processes at different spatio-temporal scales is an urgent need for tropical regions and should serve as a compass for emerging ecohydrologists. To reach this goal, we advocate a research agenda that expands the number and diversity of ecosystems targeted for ecohydrological investigations and connects researchers across the tropics. We believe that the use of big data and open source software—already an important integrative tool/skill for the young ecohydrologist — will be key in expanding research capabilities.
Photo credits: James Aldred
After thinking a lot about pre-print and how they fit in the world of plant research, I have decided to give it a try! My first pre-print entitled “Dew-induced transpiration suppression impacts the water and isotope balances of Colocasia leaves“ is now available on the bioRxiv: see the article!
The paper examines the effects of dew on transpiration suppression in Colocasia esculenta leaves using stable isotopes of water to track changes in the water status of the leaves. The article has been submitted to a peer-reviewed journal.
Abstract: Foliar uptake of water from the surface of leaves is common when rainfall is scarce and non-meteoric water such as dew or fog is more abundant. However, many species in more mesic environments have hydrophobic leaves that do not allow the plant to uptake water. Unlike foliar uptake, all species can benefit from dew- or fog-induced transpiration suppression, but despite its ubiquity, transpiration suppression has so far never been quantified. Here, we investigate the effect of dew-induced transpiration suppression on the water balance and the isotopic composition of leaves via a series of experiments. Characteristically hydrophobic leaves of a tropical plant, Colocasia esculenta, are misted with isotopically enriched water to reproduce dew deposition. We measure leaf water isotopes and water potential and find that misted leaves exhibit a higher water potential (p < 0.05) and a more depleted water isotopic composition than misted leaves (p < 0.001), suggesting a ∼30% decrease in transpiration rate (p < 0.001) compared to control leaves. We propose three possible mechanisms governing the interaction of water droplets with leaf energy balance. Comparing previous studies on foliar uptake to our results, we conclude that transpiration suppression has an effect of similar amplitude, yet opposite sign to foliar uptake on leaf water isotopes.
My new paper is finally available online on Plant, Cell & Environment. For this paper, entitled “Leaf water 18O and 2H maps show directional enrichment discrepancy in Colocasia esculenta“, we looked at spatial patterns of water isotopes in Colocasia esculenta leaves. See the abstract below for a quick overview of the study and results or head to the PCE website to read the full paper.
Spatial patterns of leaf water isotopes are challenging to predict because of the intricate link between vein and lamina water. Many models have attempted to predict these patterns, but to date most have focused on monocots with parallel veins. These provide a simple system to study, but do not represent the majority of plant species. Here, a new protocol is developed using a Picarro induction module coupled to a cavity ringdown spectrometer to obtain maps of the leaf water isotopes (18O and 2H). The technique is applied to Colocasia esculenta leaves. The results are compared to isotope ratio mass spectrometry. In C. esculenta, a large enrichment in the radial direction is observed, but not in the longitudinal direction. The string-of-lakes model fails to predict the observed patterns, while the Farquhar-Gan model is more successful, especially when enrichment is accounted for along the radial direction. Our results show that reticulate veined leaves experience a larger enrichment along the axis of the secondary veins than along the midrib. We hypothesize that this is due to the lower major/minor vein ratio that leads to longer pathways between major veins and sites of evaporation.
Two new articles I co-authored recently came out.
The influence of memory, sample size effects, and filter paper material on online laser-based plant and soil water isotope measurements, published in Rapid Communications in Mass Spectrometry looks at the performance of the Picarro Induction Module for rapid, in-situ analysis of water isotopes in plant and soil samples. The lead author, Jiangpeng Cui, is a PhD student from the Institute of Tibetan Plateau Research at the Chinese Academy of Sciences. Jiangpeng approached me at the AGU Fall Meeting 2014 where I presented work using the induction module, and we have collaborated ever since.
See the article.
Global sources, emissions, transport and deposition of dust
and sand and their effects on the climate and environment:
a review, published in Frontiers of Environmental Science & Engineering is a review paper on some of the positive aspects of dust and sand storms. Lead author Feng Wang was a visiting professor in the Caylor Lab at Princeton for almost a year back in 2014 and has kept in touch with the lab since then.
Elliot Chang, a senior at Princeton University who has been working in the Caylor Lab since his freshman year, just published his senior thesis in the journal Rapid Communications in Mass Spectrometry. The article focuses on the innovative use of solid-phase extraction (SPE) to remove organic compounds such as ethanol and methanol from water samples extracted from plants. Those organic compounds are known for causing interferences when using isotope ratio infrared spectroscopy to determine the isotopic composition of the extracted water. The article is co-authored by Kelly Caylor, Adam Wolf and myself.
Go to the article.