Session 10
Authors: Poorter Lourens , Joswig Julia , Lee Ming Yang , Warschefsky Emily , Lau Su-Ee , Goel Komal 
Published: July 2023

Functional recovery of secondary tropical forests

Tropical forests disappear rapidly through deforestation but also have the potential to regrow naturally through secondary succession. To advance successional theory, it is essential to understand how these secondary forests and their assembly vary across broad spatial scales. Here I present some of the main findings of the [2ndFOR research network on secondary forest succession](https://www.2ndFOR.org) that provides a long-term perspective on succession using >100 chronosequence sites across the tropics. We synthesize continental-scale patterns in succession using a functional trait approach and show that the start and pathway of succession varies with climatic water availability. In dry forests, species turnover is driven by drought tolerance traits that are important early in succession and in wet forests by shade tolerance traits that are important later in succession. Based on these successional principles, we propose ecologically sound strategies to improve forest restoration success.

Climatic and soil factors explain the two-dimensional spectrum of global plant trait variation

Plant functional traits can predict community assembly and ecosystem functioning and are widely used in global models of vegetation dynamics and land–climate feedbacks. Still, we lack a global understanding of how land and climate affect plant traits. A previous global analysis of six traits observed two main axes of variation: (1) size variation at the organ and plant level and (2) leaf economics balancing leaf persistence against plant growth potential. The orthogonality of these two principal components suggests they are differently influenced by environmental drivers. We find these axes persist in a global dataset of 17 in-situ traits across more than 20,000 species. We find with ridge regression models and hierarchical partitioning a dominant joint effect of climate and soil on trait variation. Additional independent climate effects are also observed across most traits, whereas independent soil effects are almost exclusively observed for economics traits. Variation in size traits correlates well with a latitudinal gradient related to water or energy limitation. In contrast, variation in economics traits is better explained by interactions of climate with soil fertility. These findings have the potential to improve our understanding of biodiversity patterns and our predictions of climate change impacts on biogeochemical cycles.

Synergies and trade-offs in P acquisition strategies underlying tropical dipterocarp forests in Southeast Asia

Phosphorus limitation is pervasive throughout many pantropical forest communities. However, P acquisition strategies have rarely been examined in Southeast Asian dipterocarp-dominated forests, constraining our understanding of how pantropical species adapt to P limitation. Our study seeks to uncover trade-offs between P acquisition strategies across evolutionarily diverse tropical forest species and how root traits contribute towards inorganic and organic P uptake in nutrient-limited soils. We examined the root morphology, architecture, phosphomonoesterase activity, nutrient content and mycorrhizal colonisation intensity of 33 species in Bukit Timah Nature Reserve and found three main dimensions of trait variation. These dimensions capture multiple aspects of plant P acquisition strategies, including fungal collaboration with mycorrhizal, resource conservatism and variations in phosphatase activity to access organic P. Unexpectedly, arbuscular mycorrhizal colonisation was uncorrelated with the fungal collaboration gradient but correlated negatively with root tissue density on the resource conservatism gradient. Dipterocarps were rarely colonised by ectomycorrhizal but exhibited significantly greater phosphomonoesterase activity. Ultimately, our study expands the known diversity of trait combinations species utilise for P uptake in nutrient-limited environments, while providing evidence that trait ordinations observed from temperate and neotropical ecosystems may not be generalisable to Southeast Asian dipterocarp-dominated forests, mainly due to differences in mycorrhizal associations.

Tree crop diversity, conservation, and domestication

Trees provide more than one third of the world’s most important crops and it is increasingly clear that tree crops will play a critical role in the future of sustainable agriculture. Nevertheless, crop research often focuses on annual species, leaving our understanding of the processes and implications of tree domestication poorly defined. Here, I discuss how the tempo and mode of tree domestication is fundamentally different from that of annual crops and propose that many tree species are poised for rapid improvement and introduction into our global food systems. I then provide examples of two projects focused on understanding and conserving tree crop diversity. The first project uses genomic tools to provide insight into the evolution and domestication of Mangifera, a tropical tree genus that includes one of the world’s most important fruits: mango. Next, I introduce a new project that aims to build connections between U.S. botanic gardens and public genebank communities to promote collaborative conservation of taxa in 10 genera of North American fruit and nut trees. Alongside a growing body of research on tree crop diversity, these projects advance our understanding of tree domestication and conservation and refine our visions for sustainable agricultural systems of the future.

When banana meets drought: How does drought influence the transcriptome of Musa acuminata cv. Berangan and specifically MaMYB-86-like gene

Banana is the fourth economically important crop worldwide. However, drought stress adversely affects its yield and productivity worldwide. To combat drought stress, bananas have developed complex resistance and adaptation mechanisms. However, there is still a lack of understanding regarding the molecular regulation of drought stress signalling in the Berangan cultivar. Hence, this study determined the drought responses of Berangan at the transcriptome level. This study hypothesized that drought stress could alter gene expression in Berangan and the MYB transcription factor could be activated. To test this hypothesis, RNA-sequencing analysis was performed on well-watered, drought-stressed for 7 days, or water-recovered leaf samples. In total, 767 and 542 differentially expressed genes (DEGs) were identified in drought-stressed and water-recovered samples, respectively, compared to their respective well-watered plants. Notably, 81 of these DEGs were transcription factors, with the highest in the MYB family. To validate the role of the MYB transcription factor, a highly differentially expressed gene, MaMYB86-like, was ectopically expressed in yeast, and analyzed for protein-protein interaction. The results showed that MaMYB86-like-expressing yeast enhanced drought, heat, and salt tolerance through its interaction with MaC4H. These findings suggest that the MaMYB86-like-MaC4H interaction may enhance the production of secondary metabolites to cope with drought stress.

Daytime and night-time heating triggers asymmetric effects on CO2 assimilation and evolution pathways in Chenopodium quinoa

Please note this talk will not be available to watch after the live stream.

The growing human population and rising global temperatures exacerbate food insecurity and jeopardize crop production. Global climate change trends predict asymmetrical temperature shifts in daytime and night-time temperatures, hampering crop yield dramatically. This necessitates the diversification of agriculture with alternative crops exhibiting climate resilience and superior nutrition profiles. Chenopodium quinoa is a stress-resilient crop with high nutritional value. However, how asymmetrical temperature trends during the day and night affect quinoa growth and yield is unknown. We grew quinoa at control (22/20⁰C, day/night) and exposed it to asymmetrical day (38/22⁰C) and night heating (22/32⁰C) during vegetative and reproductive stages. A multi-level (physiological, biochemical, transcriptional, and metabolic) analysis was performed. The analysis of growth (biomass and yield) and gas exchange (An, gs, E, Ci, ETR, Fv/Fm, NPQ) parameters revealed that heat induces developmental stage-specific effects, wherein the reproductive stage is more heat sensitive, and night heating worsens the impact. The mechanistic basis of these observations is that daytime and night-time heating triggers asymmetric effects on CO2 assimilation and evolution pathways. Furthermore, transcriptome and metabolome data corroborated these results. Overall, we unravel the regulatory networks underlying heat responses in Chenopodium quinoa, which is crucial to expand the cultivation of this future food crop.