Research overview
My collaborative group is broadly interested in understanding how climate and vegetation interact with each other, in terms of carbon, water and energy fluxes. In particular, we strive to develop a more integrative, quantitative and predictive framework for global change ecology and earth system science. Three core areas of our research are (I) developing novel approaches to enable accurate monitoring of plant chemistry, phenology, physiology and diversity, (II) understanding fundamental mechanisms that link climate, species compositions and ecosystem processes over various spatial and temporal scales, and (III) integrating advanced research tools (point I) and improved scientific understanding (point II) to enable trait-based earth system modeling, which provides benefits for both real-time monitoring of earth surface, and also for future projection of terrestrial ecosystems under global change.
Selected research topics:
1. Cryptic phenology in Amazon |
Tropical forest leaf phenology has long been interested by the science community but remains controversial. By using tower-mounted phenocams in several central Amazonian forests spanning in various rainfall gradients, we for the first time showed a quite unique phenology pattern in the rainforests: the whole system remains evergreen all year around (as shown by the above figures, left panel; example data of a rainforest near Manaus, Brazil from Dr. Bruce Nelson, INPA), with significant dynamics of leaf phenology at the individual scale (as shown by the above figures, right panel). This cryptic phenology further results in a modest seasonality in ecosystem-scale leaf quantity (i.e. canopy leaf area) but much stronger seasonal variation in leaf age demography.
Find out more in Lopes, Nelson, Wu et al. [2016, Remote Sensing of Environment], Wu et al. [2016, Science], and Saleska, Wu et al. [2016, Nature].
Find out more in Lopes, Nelson, Wu et al. [2016, Remote Sensing of Environment], Wu et al. [2016, Science], and Saleska, Wu et al. [2016, Nature].
2. Partitioning abiotic and biotic controls on tropical physiology
We hypothesized that both abiotic (i.e. meteorological variables) and biotic (i.e. leaf biochemistry, canopy leaf area) factors control tropical forest photosynthesis (which is abbreviated as GPP in the above figures), and developed a new approach to partition the two controls across different timescales. Our results show that there is a timescale-dependent mechanism in regulating tropical forest photosynthesis, with environmental variability dominating at shorter timescales (hourly to daily) and biotic factors dominating over longer timescales (monthly and yearly). By collaborating with Dr. Matthew Hayek from Harvard, we found a similar mechanism also exerts a role in regulating the tropical forest net ecosystem exchange of carbon fluxes.
Find out more in Wu et al. [2017a, Global Change Biology] and Hayek, Longo, Wu et al. [2018, Biogeosciences].
Find out more in Wu et al. [2017a, Global Change Biology] and Hayek, Longo, Wu et al. [2018, Biogeosciences].
3. The phenology of leaf quality matters for important ecosystem processes
We proposed and tested the two hypotheses—leaf quantity (i.e. canopy leaf area) and leaf quality (i.e. leaf age demography and age-dependent leaf photosynthetic capacity and albedo)—to understand what determines biotic factors and thus controls tropical forest photosynthetic seasonality and satellite-detected landscape greenness seasonality. Combining tower-camera observations of tropical leaf phenology and field-observed age-dependent leaf function with eddy flux measurements across the Amazon basin, we showed that the phenology of leaf quality is the primary cause of high photosynthetic seasonality in these tropical forests, as the newly mature leaves have much higher photosynthetic capacity than the old leaves being replaced. This finding was featured as the cover story of science in the issue of February 2016 (as shown by the above figures; left panel). Furthermore, we found that such leaf quality effect also largely regulates landscape greenness seasonality (as shown by the right panel; the background figure courtesy by Drs. Jian Bi and Ranga Myneni).
Find out more in Wu et al. [2016, Science], Wu et al. [2017b, Global Change Biology], Albert, Wu et al. [2018, New Phytologist], and Wu et al. [2018, New Phytologist].
Find out more in Wu et al. [2016, Science], Wu et al. [2017b, Global Change Biology], Albert, Wu et al. [2018, New Phytologist], and Wu et al. [2018, New Phytologist].
4. Vegetation spectroscopy of plant functional traits
Vegetation spectroscopy, which tightly connects leaf/plant optical properties with their chemical composition, cell structure, and physiological properties, has become an increasingly important tool in plant ecophysiology and ecology. Here, we demonstrated that novel vegetation spectroscopy enables an efficient, consistent means of monitoring leaf age (as shown by the above figures), traits, and trait-age relationships within and across diverse tree species. This finding highlights that the spectroscopy technique not only captures the spatial variability in plant functional traits, but also enables the capturing of temporal variability.
Find out more in Wu et al. [2017, New Phytologist], Chavana-Bryant, Malhi, Wu et al. [2017, New Phytologist], and Yang, Tang, Mustard, Wu et al. [2016, Remote Sensing of Environment].
Find out more in Wu et al. [2017, New Phytologist], Chavana-Bryant, Malhi, Wu et al. [2017, New Phytologist], and Yang, Tang, Mustard, Wu et al. [2016, Remote Sensing of Environment].